Energy Systems and Nanotechnology (Advances in Sustainability Science and Technology) 9811612552, 9789811612558

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Advances in Sustainability Science and Technology

Dharmendra Tripathi R. K. Sharma   Editors

Energy Systems and Nanotechnology

Advances in Sustainability Science and Technology Series Editors Robert J. Howlett, Bournemouth University & KES International, Shoreham-by-sea, UK John Littlewood, School of Art & Design, Cardiff Metropolitan University, Cardiff, UK Lakhmi C. Jain, University of Technology Sydney, Broadway, NSW, Australia

The book series aims at bringing together valuable and novel scientific contributions that address the critical issues of renewable energy, sustainable building, sustainable manufacturing, and other sustainability science and technology topics that have an impact in this diverse and fast-changing research community in academia and industry. The areas to be covered are • • • • • • • • • • • • • • • • • • • • •

Climate change and mitigation, atmospheric carbon reduction, global warming Sustainability science, sustainability technologies Sustainable building technologies Intelligent buildings Sustainable energy generation Combined heat and power and district heating systems Control and optimization of renewable energy systems Smart grids and micro grids, local energy markets Smart cities, smart buildings, smart districts, smart countryside Energy and environmental assessment in buildings and cities Sustainable design, innovation and services Sustainable manufacturing processes and technology Sustainable manufacturing systems and enterprises Decision support for sustainability Micro/nanomachining, microelectromechanical machines (MEMS) Sustainable transport, smart vehicles and smart roads Information technology and artificial intelligence applied to sustainability Big data and data analytics applied to sustainability Sustainable food production, sustainable horticulture and agriculture Sustainability of air, water and other natural resources Sustainability policy, shaping the future, the triple bottom line, the circular economy

High quality content is an essential feature for all book proposals accepted for the series. It is expected that editors of all accepted volumes will ensure that contributions are subjected to an appropriate level of reviewing process and adhere to KES quality principles. The series will include monographs, edited volumes, and selected proceedings.

More information about this series at http://www.springer.com/series/16477

Dharmendra Tripathi R. K. Sharma •

Editors

Energy Systems and Nanotechnology

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Editors Dharmendra Tripathi Department of Mathematics National Institute of Technology Srinagar, Uttarakhand, India

R. K. Sharma Department of Mechanical Engineering Manipal University Jaipur, Rajasthan, India

ISSN 2662-6829 ISSN 2662-6837 (electronic) Advances in Sustainability Science and Technology ISBN 978-981-16-1255-8 ISBN 978-981-16-1256-5 (eBook) https://doi.org/10.1007/978-981-16-1256-5 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

Energy demand, storage and its supply gap have consistently been increasing due to continuous depletion of natural and fossil fuels. A study shows that by 2050, the energy requirement will get doubled, and by 2100, it will be tripled of what is being currently used. In order to bridge this gap, scientists and researchers across the globe are developing new and renewable resources of energy. Globally, researchers are also working on the enhancement of the performance of such systems. Apart from developing alternate energy resources, its storage is also equally important and challenging. The solar energy is abundantly available and if stored appropriately can contribute largely in minimizing the energy demand and supply gap. This will also reduce the CO2 emission drastically which is one of the greatest prevailing environmental threats. There have been numerous attempts in addressing these challenging issues, and many books related to energy have frequently been reported in the literature across the World to introduce the needs of the energy, recycling of the energy, new resource of the energy, revolution in energy, etc. Following to that, the role of nanotechnology in the energy systems was addressed in a book published by Springer in 2013. This book provided an overview of the development in nanotechnology for the energy systems of Brazil. The present book is aimed to provide a review analysis of the emerging developments in energy systems and nanotechnology as well as new mathematical and experimental works on relevant topics. The present book is organized with nineteen chapters related to renewable energy, sensible and latent heat energy storage systems and use of nanotechnology in such systems and submitted by the renowned authors across the globe. The first chapter of this book gives an insight into the different generation of solar cells for energy harvesting. It presents an extensive review on the secondgeneration binary and ternary compounds for their doping and thin film forming properties. The next two chapters (second and third) deal with the phase change materials (PCMs) for latent heat storage. The latent heat energy storage devices play a vital role in energy saving and to bridge the energy demand and supply gap. These chapters deal majorly with the organic phase change materials which possess many favourable characteristics including long durability, non-toxicity, and come without v

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supercooling. Following that the fourth chapter deals with the solar air heater, wherein the effect of ribs on the heater’s performance is discussed. The computational fluid dynamics technique has been adopted for investigating its performance. The next two chapters (fifth and sixth) are based on the use of renewable energy in electric vehicle and photovoltaics. The electric vehicles are the future, and these chapters deal with the charging hurdles in these vehicles. The seventh, eighth and ninth chapters deal with the nanotechnology in renewable energy. The seventh chapter provides an insight into the use of nanomaterials in lipase immobilization. It shows that lipase immobilization and lipid extraction from microalgae is non-economical process. It also depicts that the use nanotechnology in algae production is increasing due to its high performance. It also describes the interaction between nanomaterial and bioanalysis of microalgae for enhanced biodiesel production as well as different methods for enzyme immobilizations for lipase on industrial scale. The eighth chapter investigates the effect of nanoparticles on the combustion properties of fuel. The results indicated that for in-cylinder pressure, minimum variation of about 0.82% lies between D94W5S1-Si50 test fuel and diesel. The ninth chapter talks about the role of nanotechnology in the solar photovoltaic. The nanomaterials have been a key aspect for enhancing their performance. The tenth chapter also follows the same principle and shows how important alcohols are for enhancing the performance of diesel engines. The eleventh chapter provides a comprehensive review of pyrolysis process of tyre. The tyres become waste after they worn out, and doing a pyrolysis of them gives a clean fuel which can be used as a blend with diesel for enhancing the engine properties. The residue of this pyrolysis process is char which is a pure carbonous material and can be used as binder in many industries. The twelfth chapter presented a numerical analysis for laminar forced convection through a phase change material embedded pipe where hybrid (Ag-MgO) nanofluids and CNT nanofluids are used for heat transfer fluids. It was reported that Reynolds number plays a key role in dynamic features of heat transfer fluid and phase change material temperatures. A comparative analysis for hybrid (Ag-MgO) nanofluids and CNT nanofluids was also made to examine the better thermal performance. The next two chapters (thirteenth and fourteenth) investigate the role of electric and magnetic fields in the thermal transport of nanofluids. The thirteenth chapter considered the cal2o3/H2O and cal2o3/C2H6O2 elastico-viscous nanofluid; however, the fourteenth chapter considered the couple stress nanofluids to see the rheological effects on thermal analysis. The applications of the findings can be seen in various energy systems nanotechnology including micro-/nano-pumping devices, electromagnetic nano-energy harvesting, thermal control of biomimetic microfluidics, nanomedicine, etc. The next three chapters (fifteen, sixteen and seventeen) present the mathematical models for nanofluids flow over the stretching sheets. The fifteen chapter discussed the nonlinear radiation and curvature effects on boundary layer flow. The sixteen chapter analysed the permeability effects; however, the seventeen chapter analysed

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the Cattaneo–Christov heat flux on Al2O3-Cu/H2O–(CH2OH)2 hybrid nanofluid. The findings of the numerical simulations will be useful for the thermal process of the nanomaterial coating in nano-technological systems. This book covers novel analysis, experimental findings, mathematical models and numerical simulations on recent developments on energy systems and future challenges of energy generation, storage, demands and supply as well as development in nanotechnologies. Editors are enough confident that this book will be helpful for the readers and provide a benchmark for future developments and research scopes. Srinagar, India Jaipur, India

Dharmendra Tripathi R. K. Sharma

Contents

Investigation of Bulk, Doped and Thin Film Solar Cells: A Review Article . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aditi Gaur, Karina Khan, Jagrati Sahariya, Alpa Dashora, and Amit Soni

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Study of Thermal Properties of Eutectic Phase Change Materials for Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. K. Ansu, Pooja Singh, and R. K. Sharma

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A Review on Thermal Conductivity Enhancement of Organic Phase Change Material-Based Form-Stable Phase Change Materials . . . . . . . . Pooja Singh, A. K. Ansu, and R. K. Sharma

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Performance Evaluation of a Solar Air Heater with Transverse Ribs on the Absorber Surface Using CFD Technique . . . . . . . . . . . . . . . . . . Amit Kumar, Apurba Layek, A. K. Ansu, and Atwari Rawani

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Renewable Energy-Driven Charging Station for Electric Vehicles . . . . . Rudraksh S. Gupta, Arjun Tyagi, V. V. Tyagi, Y. Anand, A. Sawhney, and S. Anand Review on Optoelectronic Response of Emerging Solar Photovoltaic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Karina Khan, Aditi Gaur, Kamal Nayan Sharma, Amit Soni, and Jagrati Sahariya Nanotechnology in Production of Microalgal Biofuel: Application of Nanomaterials and Lipase Immobilization . . . . . . . . . . . Himanshi Singh, Kunwar Paritosh, and Vivekanand Vivekanand

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Effects of Silicon Dioxide Nanoparticles on the Combustion Features of Diesel Engine Using Water Diesel Emulsified Fuel . . . . . . . . . . . . . . . 119 Deepti Khatri, Rahul Goyal, and Abhishek Sharma

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Hybrid Solar PVT Systems for Thermal Energy Storage: Role of Nanomaterials, Challenges, and Opportunities . . . . . . . . . . . . . . 131 W. Rashmi, V. Mahesh, S. Anirban, P. Sharnil, and M. Khalid Use of Alcohols and Biofuels as Automotive Engine Fuel . . . . . . . . . . . . 161 Sumit Taneja, Perminderjit Singh, Abhishek Sharma, and Gurjeet Singh Environmentally Friendly Fuel Obtained from Pyrolysis of Waste Tyres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Abhishek Sharma, Deepti Khatri, Rahul Goyal, Alok Agrawal, Vivek Mishra, and Dulari Hansdah Comparison of Hybrid and CNT-Nanofluids Used as Heat Transfer Fluid for Forced Convection Through a Phase Change Material (PCM) Filled Vertical Cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 Fatih Selimefendigil and Hakan F. Oztop Thermal Analysis of cAl2O3/H2O and cAl2O3/C2H6O2 Elastico-Viscous Nanofluid Flow Driven by Peristaltic Wave Propagation with Electroosmotic and Magnetohydrodynamic Effects: Applications in Nanotechnological Energy Systems . . . . . . . . . . . . . . . . 223 Dharmendra Tripathi, J. Prakash, O. Anwar Bég, and Rakesh Kumar Thermal Transport of MHD Electroosmotic Couple Stress Nanofluid Flow in Microchannels in the Presence of Various Zeta Potentials . . . . 261 V. Sridhar and K. Ramesh Modelling the Impact of Melting and Nonlinear Radiation on Reactive Buongiorno Nanofluid Boundary Layer Flow from an Inclined Stretching Cylinder with Cross-diffusion and Curvature Effects . . . . . . 279 Mahesh Garvandha, V. K. Narla, Dharmendra Tripathi, and O. Anwar Bég Heat Transfer in a Nanoliquid Flow Due to a Permeable Quadratically Stretching Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 Mahesha Narayana and Ramone R. Jackson Impact of Cattaneo–Christov Heat Flux On Al2O3–Cu/H2O– (CH2OH)2 Hybrid Nanofluid Flow Between Two Stretchable Rotating Disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 Sachin Shaw MHD Flow in a Rotating Channel Surrounded in a Porous Medium with an Inclined Magnetic Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 Ram Prakash Sharma, S. K. Ghosh, and S. Das

Editors and Contributors

About the Editors Dr. Dharmendra Tripathi has been working as Associate Professor in Department of Mathematics, National Institute of Technology, Uttarakhand. Prior to joining NIT Uttarakhand, he has worked more than 10 years as faculty member (Associate Professor, Assistant Professor) in various reputed institutions like Manipal University Jaipur, NIT Delhi, IIT Ropar and BITS Pilani Hyderabad. He completed his Ph.D. in Applied Mathematics (Mathematical Modelling of Physiological flows) in 2009 from Indian Institute of Technology BHU and M.Sc. in Mathematics from Banaras Hindu University. He has supervised four Ph.D. students and four are working under his supervision. He has also guided 20 B.Tech. projects. He has published more than 130 papers in reputed international journals, five book chapters and presented more than 30 papers in International and National Conferences. His research h-index is 39 and i-10 index is 111 and his papers have more than 4000 citations. He has recently achieved World rank 375 and Indian Rank 6 in top 2% researchers/scientist across the World as per Updated science-wide author databases of standardized citation indicators in field of Mechanical Engineering and Transport published on October 16, 2020. He has been recognized by the Head of Institution for excellent work and contribution for the NIT Uttarakhand. He was awarded some prestigious fellowships INAE fellowship in 2015 & 2016, 2017 and 2018, postdoctoral fellowships (NBHM, Dr. D. S. Kothari and Indo-EU) in 2010 etc. He has delivered more than 40 invited talks in National and International conferences, STC/STTP/FDP/Workshop. He has also organized various events like National and International conferences/STC/STTP/FDP/ Workshops/Winter School.

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He is lifetime member of various professional bodies, member of editorial board of two journals, and reviewer of more than 50 International Journals and reviewed more than 100 articles. His research work is focused on the mathematical modelling and simulation of biological flows in deformable domains, Peristaltic flow of Newtonian and non-Newtonian fluids, microfluidics; CFD, Biomechanics; Numerical methods and biomechanics. Dr. R. K. Sharma has been working with Manipal University Jaipur as Associate Professor in the Department of Mechanical Engineering. He has total of 15 years of teaching and research experience in various reputed Indian and foreign universities. He earned his Ph.D. in Thermal Engineering from the University of Malaya, Malaysia, in 2016, and masters from BITS Pilani, India. He has published 25 research papers in international journals of repute and presented his research work in many international conferences in India and abroad. He has also written four book chapters and been a reviewer of many international journals. He has also delivered many invited/keynote speeches in FDP/STTP/Workshop and conferences. His current area of research is renewable energy and thermal energy storage, in particular solar energy. His primary research is focused on the development of phase change materials or rapid heat transfer by enhancing their thermal conductivity. He is also working on the development of carbon-based materials. His research is being cited globally, and one of his papers has been in the top downloaded articles and most cited in the journal for more than a year.

Contributors Alok Agrawal Department of Mechanical Engineering, Sagar Institute of Research and Technology-Excellence, Bhopal, Madhya Pradesh, India S. Anand School of Energy Management, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India Y. Anand School of Energy Management, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India S. Anirban Symbiosis Institute of Technology, Symbiosis International (Deemed) University, Pune, Maharashtra, India A. K. Ansu Mechanical Engineering Department, Manipal University Jaipur, Jaipur, India O. Anwar Bég Multi-Physical Engineering Sciences Group, Department of Mechanical and Aeronautical Engineering, SEE, Salford University, Salford, England, UK

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S. Das Department of Mathematics, University of Gour Banga, Malda, West Bengal, India Alpa Dashora Department of Physics, Faculty of Science, The M.S. University of Baroda, Vadodra, India Mahesh Garvandha Department of Mathematics, GITAM (Deemed to be University), Hyderabad, India Aditi Gaur Department of Electrical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India S. K. Ghosh Department of Mathematics, Narajole Raj College, Narajole, West Bengal, India Rahul Goyal Department of Mechanical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India Rudraksh S. Gupta School of Energy Management, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India Dulari Hansdah Department of Mechanical Engineering, National Institute of Technology Jamshedpur, Jharkhand, India Ramone R. Jackson Department of Mathematics, The University of the West Indies, Mona Campus, Kingston, Jamaica M. Khalid Graphene and Advanced 2D Materials Research Group, School of Science and Technology, Petaling Jaya, Selangor, Malaysia Karina Khan Department of Physics, Manipal University Jaipur, Jaipur, Rajasthan, India Deepti Khatri Department of Mechanical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India Amit Kumar Department of Mechanical Engineering, NIT Durgapur, Durgapur, West Bengal, India Rakesh Kumar Department of Mechanical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India Apurba Layek Department of Mechanical Engineering, NIT Durgapur, Durgapur, West Bengal, India V. Mahesh School of Engineering and Computer Science, Taylor’s University, Subang Jaya, Selangor, Malaysia Vivek Mishra Department of Mechanical Engineering, Indore Institute of Science and Technology, Indore, Madhya Pradesh, India Mahesha Narayana Department of Mathematics, The University of the West Indies, Mona Campus, Kingston, Jamaica

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V. K. Narla Department of Mathematics, GITAM (Deemed to be University), Hyderabad, India Hakan F. Oztop Department of Mechanical Engineering, Technology Faculty, Fırat University, Elazıg, Turkey Kunwar Paritosh Centre for Energy and Environment, Malaviya National Institute of Technology, Jaipur, Rajasthan, India J. Prakash Department of Mathematics, Avvaiyar Government College for Women, Karaikal, U. T of Puducherry, India K. Ramesh Department of Mathematics, Symbiosis Institute of Technology, Symbiosis International (Deemed University), Pune, India W. Rashmi School of New Energy and Chemical Engineering, Sepang, Selangor, Malaysia Atwari Rawani Department of Mechanical Engineering, Bengal College of Engineering and Technology, Durgapur, India Jagrati Sahariya Department of Physics, National Institute of Technology, Srinagar (Garhwal), Uttarakhand, India A. Sawhney Department of Physics, GGM Science College, Jammu, Jammu and Kashmir, India Fatih Selimefendigil Department of Mechanical Engineering, Celal Bayar University, Manisa, Turkey Abhishek Sharma Department of Mechanical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India Kamal Nayan Sharma Amity School of Applied Sciences, Amity University, Gurugram, Haryana, India R. K. Sharma Mechanical Engineering Department, Manipal University Jaipur, Jaipur, India Ram Prakash Sharma Department of Mechanical Engineering, National Institute of Technology Arunachal Pradesh, Yupia, Arunachal Pradesh, India P. Sharnil Symbiosis Centre for Applied Artificial Intelligence, Symbiosis International (Deemed) University, Pune, India Sachin Shaw Botswana International University of Science and Technology, Palapye, Botswana Gurjeet Singh Mechanical Chandigarh, India

Engineering,

Punjab

Engineering

College,

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Himanshi Singh Centre for Converging Technology, University of Rajasthan, Jaipur, Rajasthan, India Perminderjit Singh Mechanical Engineering, Punjab Engineering College, Chandigarh, India Pooja Singh Department of Mechanical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India Amit Soni Department of Electrical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India V. Sridhar Department of Mathematics, Symbiosis Institute of Technology, Symbiosis International (Deemed University), Pune, India Sumit Taneja Mechanical Engineering, Manipal University Jaipur, Jaipur, India Dharmendra Tripathi Department of Mathematics, National Institute of Technology Uttarakhand, Srinagar, India Arjun Tyagi School of Electrical Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India V. V. Tyagi School of Energy Management, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India Vivekanand Vivekanand Centre for Energy and Environment, Malaviya National Institute of Technology, Jaipur, Rajasthan, India

Investigation of Bulk, Doped and Thin Film Solar Cells: A Review Article Aditi Gaur, Karina Khan, Jagrati Sahariya, Alpa Dashora, and Amit Soni

Abstract In this chapter, we have presented detailed review of different generations of solar cells including newer inventions of harvesting solar energy. Solar energy is one of the most reliable and inexhaustible renewable energy sources. In this context, hierarchical generations of solar cells, thin film solar cells (a-Si, CdTe and CIGS) form the second generation which offers an apt conversion efficiency in comparison to the first generation. We have presented a specific review related to second-generation binary and ternary compounds like ZnSnAs2, ZnGeAs2, ZnSiAs2, ZnS, ZnGa2S4, CuGaS2, CuAlS2, CuInS2 materials with respect to its bulk, doped and thin film form. All these samples have been divided into pure, doped or thin film materials based on their theoretical investigations or experimental examinations to attain their optoelectronic analysis which helps in determining their utility as solar cell materials. Optical characteristics like absorption, reflection, refraction and dielectric tensor help in presenting an idea about the utility of sample in a particular optoelectronic field. This review helps in presenting newly discovered possibilities of solar cell materials through bandgap engineering. Thus, this review based on bulk, doped and thin film materials helps in giving an overview on different experimental and theoretical approaches followed to attain an analysis of various characteristic properties. Keywords Chalcopyrites


DFT
Optical properties
Thin film
Solar cells

A. Gaur
A. Soni (&) Department of Electrical Engineering, Manipal University Jaipur, Jaipur, Rajasthan 303007, India K. Khan Department of Physics, Manipal University Jaipur, Jaipur, Rajasthan 303007, India J. Sahariya (&) Department of Physics, National Institute of Technology, Srinagar (Garhwal), Uttarakhand 246174, India A. Dashora Department of Physics, Faculty of Science, The M.S. University of Baroda, Vadodra 390002, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_1

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1 Introduction In current technological era, solar cells are the most promising feature of energy generation. Solar energy has an advantage over conventional energy due to a continuous supply of energy through Sun and direct conversion of solar energy through solar cells into electrical energy. This has a benefit of effective cost and generation of non-toxic materials, thus named it as green energy, and hence, solar cells have achieved exclusive growth in the field of sustainable energy. The principle followed for modern photovoltaic technology comprises the involvement of p-type and n-type semiconducting material layers. The photon on striking the material layers of this combination excites an electron from one to another layer consequently, generating electrical energy through the acquired energy of photon in electron. The usage of this phenomenon for production of solar cells in modern technologies is done, but they are limited by major setbacks like less efficiency and high cost [1]. Initially over a period of several years, the wide usage of crystalline silicon solar cells was done but more cost-effective and efficient cells have now been developed. The efficiency is depicted in the Table 1. Thus, for a convenient depiction, the solar cell types are classified as silicon-based, compound semiconductor-based, dye-sensitized and polymer/organic solar cells along with some new technological concepts. Based on types of generation [2], another kind of solar cell classification is done as: first-, second- and third-generation solar cells. The first-generation solar cells include conventional, traditional or wafer-based cells which are made of crystalline silicon. Though they have high manufacturing cost, they offer better efficiency. Solar cells belonging to the second generation include thin film solar cells in their classification. This generation being cost-effective than first-generation silicon solar cells which offers lesser efficiency. Flexibility of this generation, i.e. being lightweighted, results in the usage of such materials in solar panels. Various materials

Table 1 Reported solar cell efficiencies [1]

Type of solar cell

Efficiency

Crystalline silicon solar cell Multi-crystalline silicon solar cell Amorphous silicon solar cell HIT solar cell GaAs solar cell InP solar cell Multi-junction solar cell CdTe solar cell CIGS solar cell CuInS2 solar cell DSSC (dye-sensitized solar cell) Organic solar cell

24.7 20.3 10.1 23 26.1 21.9 40.8 16.5 19.9 12.5 11.1 6.1

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used for second-generation solar cells are: cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon (a-Si) and microamorphous silicon (la-Si) materials. Non-semiconducting technologies are the ones included in third-generation solar cells, e.g. quantum dot technology tandem/multi-junction solar cells, technologies having up and down conversion, solar thermal technologies and hot carrier cells. Solar cells also find a place in the space applications as quantum well devices like quantum dots, ropes, etc. and devices incorporating carbon nanotubes. Fourth-generation solar cells are assumed to be a hypothetical one with a prediction of composite photovoltaic technology involvement. Polymers with nanoparticles hold a place in this technology that can be blended together to create a single multi-spectrum layer. Thin multi-spectrum layers are assembled to create multi-spectrum solar cells which are more efficient and cost-effective in nature. The basis of its making concept is polymer solar cell, and this kind of multi-junction technology has found its presence in the MARS mission by NASA.

2 Renewable Energy Resources of the renewable energy provide an effective solution to the current environmental problems, and proper enhancement in this leads to an appropriate sustainable growth. Technology has a key currency in terms of energy, and it provides support to the growth and development of society whether in terms of energy supplies, technological advancements, etc. The problems faced w.r.t energy supply use do not only revolve around global warming, but also environmental issues like ozone depletion, air pollution, acid precipitation, emission of radioactive substances and deforestation, etc. These concerns need to be considered for a brighter future in energy causing least environmental impacts. The oil crises of 1970s led to the active research and development in renewable energy resources worldwide. Energy conversion systems based on technologies utilizing renewable energy gained a space in the field due to estimated high oil cost and offer convenient implementation of renewable energy systems. In present times, a beneficial effect on the environmental, essential technical, political and economic issues of the renewable energy sources can be observed. The major environmental problems are acid rain, greenhouse effect, stratospheric ozone depletion, environmental degradation, non-renewable energy source’s depletion, increased energy usage, etc. [3]. A renewable energy, i.e. obtained from sun, is the solar energy which is considered as reliable, non-polluting and clean energy source. There is no release of harmful gases unlike other sources of energy. The potential of Sun’s energy is incomparable, and theoretically, solar power is abundantly obtained thus fulfilling the electrical energy demands. Recent years has seen a great increase in the efficiency of solar power technologies and has recorded a steady decrement in the cost of it which are assumed to fall even more. Solar power systems operate at a very low cost despite of a little investment in its instalment. Due to immobile parts of the

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solar cells, there is no noise pollution observed and it is durable in nature with least maintenance. One of the best ways to deal with the future needs of energy is the solar energy due to its commendable features like availability, accessibility, cost-effectiveness, capacity and efficiency as compared to other renewable sources of energy [4].

3 Types of Solar Cells 3.1

Chalcopyrite Solar Cells

For the thin film photovoltaics, the highest efficiency is offered by chalcopyrite solar cells most particularly Cu(In, Ga)Se2 they help in forming active layers both in the form of small cells or modules. The role of materials depicting feature of active absorber is played by chalcopyrite compounds as highest performing thin film photovoltaics. Chalcopyrite’s basic crystal lattice structure and its schematic layer arrangement make up a fundamental chalcopyrite solar cell as shown in Fig. 1. The chalcopyrite layer which accounts to be active and depicts the role of light absorbance is comprised to be one or two microns thick. Their preparation involves any basic method of thin film deposition [5]. The modules based on chalcopyrite thin film photovoltaics when enfolded offer a durable existence in terms of stability. The chalcopyrite compound family accounted for the applications of solar cell belongs to the I-III-VI2 stoichiometry and composition, wherein group I has Cu or Ag, group III has Al, In or Ga, and the group VI has S, Se or Te. Group I element shows lesser optimal devices in their category and materials with more number of group I element cannot operate in devices. Mutual solubility is observed in this

Fig. 1 Crystal lattice structure of chalcopyrite [5]

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category semiconductor so that alloys with little or no miscibility gaps are observed. But we can observe a broader range of ordered stable point defects. The compounds belonging to II-IV-VI2 group are also useful but have not been discovered more. To reduce the use of group III elements which are rare and expensive the use of kesterite compound like Cu2ZnSnS4 has been done. When provided with a wide range of compounds, it becomes easier to choose from a basic set via a proper selection criteria. Copper chalcopyrite offers the production of best devices. These offer high optical absorption coefficient and carrier mobility probably, and such compounds are originated from Cu- or Ag-based compounds. The 3d atomic orbitals of the low-lying copper element puts in a strong affect over the electronic structure of a compound’s valence band. Due to the repetitive folding of the band structure in the complex chalcopyrite, lattice high density states originate. These states are present in the typical range of energy particularly for the solar photon’s absorption. Conclusively, the crystal lattice of chalcopyrite provides advantage of intrinsic nature in comparison to the parent diamond and zinc blende structures (e.g. Ge or ZnSe). The increasing amount of complexity leads to the origination of point defects. These can thus lead to have a benefit over the extended defects’ passivation. This can, however, cause degradation in the device performance due to uncontrollable stoichiometry. The most typical but acceptable crystal structure is represented by chalcopyrite. Also due to the introduction of extra defects, the kesterite compounds will eventually be unacceptable. For illustrative description, highly concentrated IIII and IIII antisite defects along with all the common vacancies are exhibited by the chalcopyrites. Group III, II-V, III, III-V, IV-I and IV-II defects are assumed to be depicted by the kesterites, and the vacancies probably on every sub-lattice have multiple valence band states present in the energy gap. These complex materials with the multiplicity of defects will further prove unacceptable.

3.2

Perovskite Solar Cells

In the field of commercial solar cell, the Si solar cells play a superior role as per their high power conversion efficiency (PCE) and high stability feature. But the high melting point of Si leads to its expensive device fabrication, and thus, an alternative type of commercial solar cells has been found as perovskite solar cells [6]. A new kind of solar cell, promising in nature, meeting the energy demands of the world with its better efficiency range is the perovskite solar cell. It has shown a tremendous improvement in the efficiency ranging from 3.8 to 24.2%. The combination of organic–inorganic hybrid perovskite materials has proved to be the most efficient PSCs. These are composed of PQX3 compound, where P stands for organic cation [methyl-ammonium (MA+), formamidinium (FA+) or their mixture], Q stands for Pb2+ and X stands for Br−, I− or mixture of the two. But these organic perovskites lack in terms of stability when exposed to air or any such external factor like oxygen, heat, moisture or even illumination. This is caused due to the organic compound’s volatile nature. This can be illustrated with the example of MAPbI3

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where its decomposition into MA and PbI3 occurs. MAI further can decompose to any of the compound at higher range of temperature depending on type of material and its different kind of alteration technique. We can thus attain intrinsic stability at a higher degree by the replacement of organic cations with inorganic ions of caesium (Cs+) [7]. Easy decomposition of inorganic perovskites does not take place in the presence of atmospheric factors. Hence, efficient fabrication and stability have been recorded for inorganic perovskite compounds. The general formula for a halide perovskite is depicted by PQX3, in which P is the site that refers to a monovalent cation, i.e. Cs+, MA+, Q is the site that refers to a bivalent cation (Pb2+/Sn2+) and X is the site that refers to halide (I−, Br− or Cl−). Based on the semiconductor photovoltaics, the electrons present in the valence band gets excited by the photons and jump to the conduction band across the bandgap. In the form of carriers, extraction task is caused by both electrons and holes with the effect of built-in electric fields or diffusion. Low bandgap semiconductors are capable of absorbing more light and generating higher current. But the output voltage is also affected, limited by the quasi-Fermi levels’ difference between the electrons and holes. Light absorption and the output current are limited by the high bandgap. The range of 1.1–1.4 eV optimal bandgap for single junction is achieved by high efficiency of around 33%. Higher efficiency and improved stability are offered by lead-based inorganic perovskites than the lead-free perovskites. But caesium being the most common element at the P site of perovskites is used as high-efficiency inorganic PSCs. Pure Halide Perovskite (a) CsPbBr3—Direct bandgap in the range 2.25–2.37 eV is observed in case of caesium lead bromide perovskite; this may vary with the involvement of different fabrication techniques. The emission of green light in CsPbBr3 leads to its usage in the application of lasers and light-emitting diodes. Whereas the wide energy gap of CsPbBr3 nominates a good candidature for construction of semitransparent or tandem solar cell. Further, the enhancement of stability and cost reduction of inorganic PSCs, the study of HTL-free and carbon-based PSCs was done. (b) CsPbI3—The cubic phase of CsPbI3 offers a bandgap of about 1.73 eV along with 720 nm absorption edge. As the black CsPbI3 behaves as non-perovskite orthorhombic phase (Pnma), it turns out to be unstable thermodynamically at room temperature due to the lower tolerance factor s of CsPbI3 (0.807) as compared to CsPbBr3 (0.824). And many more such examples are there depicting the inorganic perovskite materials. Replacement of lead by tin at Q-site cation brings a large change in the properties such as stability and energy bandgap of CsSnX3 perovskite. The ideal bandgap for photovoltaic devices as per Shockley–Queisser limit is 1.34 eV closer to respective bandgaps of CsSnI3, CsSnI2Br, CsSnIBr2 and CsSnBr3 which are about 1.30, 1.40, 1.65 and 1.75 eV as compared to lead-based perovskites. The promising materials

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7

for the construction of PSCs are theoretical tin-based perovskites. CsSnI3 offers high optical absorption coefficient (around 104 cm−1 for visible range), low exciton binding energy (about 18 meV) and at different temperatures exhibits a total of four phases. Presently, not enough work has been done on large-area and flexible inorganic PSCs. With the improvement in device efficiency and stability increased research activities for upcoming future are expected. For large-scale production of perovskite films, the technology that is currently being used is vacuum deposition and solution-processing methods. For the improvement of the efficiency and stability of inorganic PSCs, a novel robust charge transport materials, functional additives and interface modifiers are developed. Due to increased power conversion efficiency, the stability of solar cells with or without encapsulation is anticipated to be tested for long term under the presence of harsh conditions.

4 Bulk Solar Cell Materials The first-generation solar cells comprise of what is known as the bulk solar cell materials. These solar cells are the conventional, traditional or based on wafer cells which are made up of crystalline silicon. Crystalline silicon (c-Si) is thus termed as the most ubiquitous type of bulk material which is otherwise known as solar grade silicon. According to the crystallinity and crystal size in the resultant ingot, multiple categories of bulk silicon in the form of ribbon or wafer are found. The basic principle of p-n based junction is applied in these solar cells entirely. The dimension of wafers lies in the range of 160–240-lm-thick solar cells constituted of c-Si [8].

5 Thin Film Solar Cell Materials The benefit of knowing thin film technologies is to reduce the usage of active material in a cell. The design of these active materials takes place between two panes of glass. Although only one glass pane is used in silicon solar, the crystalline panels of silicon are less heavy than the thin film panels. Also they have a smaller ecological impact. The domination of inorganic photovoltaic technologies such as silicon, cadmium telluride (CdTe), III-V group semiconductors and copper indium gallium selenide (CIGS) [9] in the PV market is seen. The thin film solar cell materials also introduce the concept of intermediate band in photovoltaics. In terms of the efficiency of solar cell, different methods are provided by the intermediate band photovoltaics in solar cell research for exceeding the Shockley–Queisser limit. This band is introduced as an intermediate band (IB) between the energy levels of valence and conduction bands. Theoretically, the concept involves excitation of electron by two photons with a lesser energy than the bandgap from the valence to conduction band. Thus, the increment in induced photo current and the cell efficiency is observed.

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(a) Mono

(b) Poly

(c) Thin film

Fig. 2 Different types of solar panels [10]

With the usage of detailed balance and one mid-gap energy level, Luque and Marti derived a theoretical limit for an IB device. The assumption they made was that under full concentration the device had no carriers collected at IB. They recorded maximum efficiency as 63.2%, with the IB being 0.71 eV and bandgap being 1.95 eV either from the valence band or conduction band. The limiting efficiency was known to be 47% (Fig. 2).

6 Doping in Solar Cell Materials The introduction of impurities into the crystal is termed as doping which is helpful in order to modify conductivity. The semiconductor crystal is integrated with dopant into its lattice structure. Type of doping is defined by the number of outer electrons. P-type doping is the one which involves elements with 3-valence electrons and n-doping involves 5-valued elements. The pentavalent dopant contains outermost electrons more than the silicon atoms. Every silicon atom combines with four outer electrons of dopants with free movement of fifth electron, serving as charge carrier. Electron donor is the dopant which emits an electron. Very less energy is required by the free electron to move from the valence into conduction band as compared to electrons causing intrinsic conductivity in silicon. By the reduction of negative charge carriers, the dopants tend to be positively charged and are present in the lattice. The movement of only the negative electrons is observed. N-type or n-doped elements are the doped semimetals with their conductivity based on free (negative) electrons. The number of free electrons if higher is known as majority charge carriers, and free mobility holes are known as minority charge carriers. The 3-valent dopants include the involvement of extra outer electron leaving a hole in the silicon atoms’ valence band. This causes the electron to be mobile in the valence band. The movement of holes and electrons is in opposite direction. With only 1% energy requirement from a dopant, a valence electron of silicon can be lifted into the conduction band.

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When an electron is included, the dopant known as acceptor turns out to be negatively charged. With the dopant being fixed in the crystal lattice, only positive charge movement is observed. Due to these positive holes, semiconductor is also known as p-doped. Here holes are termed as majority charge carriers and the free electrons as minority charge carriers [11]. Electrical neutrality is observed in doped semiconductors. The n- and p-type doped term refers only to the majority charge carriers. Doping in wide-gap materials when examined theoretically suggests several generalized and practical principles of doping which guide us in providing experimental strategies for overcoming disadvantages of doping [12].

7 Theoretical Investigation Tools The theoretical investigation of bulk, doped and thin film solar cells was done based on DFT-based tool known as Wien2k. Several other theoretical tools are present in the research field like CASTEP, VASP, Quantum Espresso, etc. Theoretical approach is beneficial for the knowledge of predictive power. Through the following years, a remarkable change has been reported in condensed matter theory. Earlier the main basis was to regenerate the results of experiment that too performed on similar set of systems. But presently, the theoretical approach is applied regardless of any experimental basis, i.e. to anticipate new solid properties and to revive new experimental knowledge [13, 14]. The investigation of the material paradigm is done through computational approach. It involves studying the structure of materials and relating them to their properties. The structure–property correlation mentions the performance of materials in a certain application can then be studied. Therefore, to attain the discovery and design of new materials in computer, it needs to accurately predict the structure of materials and calculate its properties. The structure of materials includes many of the electrical, magnetic and chemical properties of materials which arise from their atomic structures. The features involved in structure calculation are unit cell, lattice, space group, etc. The two major steps in crystal structure prediction are the energy of structure and efficient minimization algorithm.

7.1 7.1.1

Solar Cell Compounds Taken Under Investigation ZnSnAs2

ZnSnAs2 turns out to be ternary semiconductor with a structure of chalcopyrite, and the value of direct bandgap is 0.7 eV. The future of opt-spintronics is expected to be met by ZnSnAs2 as the promising solar material [15]. It is the member of II-IV-V2 semiconductor group which offers the application of thermo-photovoltaic,

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infrared detectors and nonlinear optics [16]. A comparison has been placed between the reported values in chalcopyrite phase (CP) of bulk ZnSnAs2’s lattice constant, i.e. 5.8520 Å and 5.8537 Å in the sphalerite phase (SP). In one work, the investigation ZnSnAs2 electronic structure along with its optical properties has been done to prove the usefulness of material in photonic devices. The various properties have been investigated using generalized gradient approximation (GGA) exchange correlation imbibed in full potential linearized augmented plane wave method. Our computations revealed a direct bandgap of about 0.42 eV [17]. The thermal and elastic properties are investigated by the first-principles calculations for ZnSnY2 (Y = P, As, Sb), employing ultra-soft pseudo-potentials and generalized gradient approximation (GGA) under the density functional theory concept [18]. Formation energies of Mn-doped ZnSnAs2 have been studied with the creation of *1 eV semiconducting gap created in the minority channel due to the splitting of large bonding—antibonding of the p-d hybridization [19, 20]. The properties including structural, electronic and magnetic characteristics of chalcopyrite (Zn, X)SnAs2 and Zn(Sn, X)As2 where X is the transition metal have been studied by the Korringa–Kohn–Rostoker method which is combined with coherent potential approximation present within local spin density approximation; here ‘X’ depicts 3d transition metal. The structural determination of ZnSnAs2 thin films has been done [21]. The structural, magnetic and electrical properties of Cr-doped ZnSnAs2 thin films have been investigated using the MBE growth experimental technique [22]. Magnetic phase change of Mn-doped ZnSnAs2 thin film has been studied using the 3D atom probe tomography [23] The comparative study for the three categories of the compound has been showcased in Table 2.

7.1.2

ZnGeAs2

The examination of various properties of ZnGeAs2 is done using first-principles band structure method based on density functional theory. The binary compound GaAs has a ternary analog named ZnGeAs2. With the help of band structure calculation, ZnGeAs2 present in chalcopyrite structure shows a direct bandgap with a value of 0.31 eV smaller than bandgap of GaAs. The valence band offset between ZnGeAs2 and GaAs is calculated as 0.18 eV; thus, the alignment of the band of ZnGeAs2/GaAs system belongs to type I having holes and electrons localized on ZnGeAs2 [24]. The experimental bandgap for ZnGeAs2 is 1.37 eV. The bandgap Table 2 Comparison table for bulk, doped and thin film ZnSnAs2

Author

Sample

Bandgap (eV)

Choi et al. Soni et al. Bouhani-Benziane et al.

ZnSnAs2 ZnSnAs2 Mn-doped ZnSnAs2

0.65 0.42 *1

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dielectric-function spectra of single-crystal ZnGeAs2 grown epitaxially on (001) GaAs and studied theoretically [25]. The elastic, optoelectronic and structural properties of ZnGeAs2 semiconductor have been explored using pseudo-potential plane wave method within the concept of density functional theory (DFT). The value of C point-bandgap belonging to Brillouin zone is found to be 0.536 eV. From the absorption spectrum curve, we can easily observe that the absorption edge starts from 0.498 eV for ZnGeAs2 semiconductor. The calculated reflectivity has the maximum value at 14.08 eV. This shows ZnGeAs2 semiconductor is transparent in IR [26]. The doping of Mn in ZnGeAs2 is used to identify the application of spintronics. At higher temperature, a spontaneous magnetization occurs [27]. The Mn substitution at Zn and in other case at Ge yields a bandgap larger than undoped ZnGeAs2 [28]. Thin films based on ZnGeAs2 were studied as per optical properties to investigate its usage as photovoltaic material [29]. The comparative study for the three categories of the compound has been showcased in Table 3.

7.1.3

ZnSiAs2

ZnSiAs2 represents pnictide-type II-IV-V2 compound that crystallizes in tetragonal space group D21 2d with four units in each cell and has chalcopyrite structure similar to zinc blende structure. LDA-based electronic and optical properties for ZnSiAs2 were studied with a pseudo-direct bandgap [30] FP-LAPW-based PBE-GGA correlation for calculation of optoelectronic properties was done [31]. The experimental value of the compound is found to be 2.19 eV [32]. Synthesizing Mn-doped ZnSiAs2 in order to study effects like magnetization, magneto-resistivity, electrical resistivity, etc. [33] ZnSiAs2’s effect with Mn doping is studied for analysing electric and magnetic characteristics [34]. The comparative study for the three categories of the compound has been showcased in Table 4. Table 3 Comparison table for bulk, doped and thin film ZnGeAs2

Author

Sample

Bandgap (eV)

Janotti et al. Choi et al. Tripathy and Kumar T. Peshek et al.

ZnGeAs2 ZnGeAs2 ZnGeAs2 ZnGeAs2 thin film

0.31 1.15 0.536 1.5 ± 0.5

Table 4 Comparison table for bulk, doped and thin film ZnSiAs2

Author

Sample

Bandgap (eV)

F. Boukabrine et al. Xu et al. L. Koroleva et al. Poplavnoi et al.

ZnSiAs2 ZnSiAs2 ZnSiAs2 ZnSiAs2

1.74 1.152 2.1 2.19

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ZnS

A II-VI semiconductor group with a bandgap wide about 3.7 eV is zinc sulphide which stands suitable for solar cell applications, solar selective decorative coatings, LED, electroluminescence, UV light-emitting diode, the phosphors in flat panel displays, photo catalysts and nonlinear optical devices [35]. Diluted magnetic semiconductors containing different consistency ratio ranging from 0 to 0.07 were processed using ethylene-di-amine as a modifier by hydrothermal method. Using various methods like high-resolution-based transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), etc. bulk and Ni-doped nanocrystals were investigated to verify the effect caused by the concentration of Ni doping on the magnetic, microstructure, morphology and optical properties [36]. Using wet chemical synthesis, the copper-doped zinc sulphide nanoparticles were investigated. The nanoparticles’ physical properties are obtained using UV absorption, X-ray diffraction and photoluminescence spectroscopy analysis [37]. Tin-doped ZnS powders with tin percentages to be 0.00, 0.02, 0.05 and 0.08 were processed by solid-state reaction and characterized by scanning electron microscope (SEM), etc. The bandgap of Zn1−xSnxS powders lies in the range 3.51–3.58 eV. Higher optical absorption for pure ZnS particles was observed in case of nanoparticles of Sn-doped ZnS belonging to visible region [38]. Another work depicts a doped wide bandgap semiconductor ZnS by Sn at Zn site in order to form the supercell of Zn0.94Sn0.06S. Two kinds of behaviours w.r.t structural and optoelectronic for Zn0.94Sn0.06S have been obtained through DFT in the framework of Wien2k code. The 6.25% Sn doping at Zn site has decremented the bandgap to 1.70 eV from 2.15 eV [39]. Using the technique of thermal evaporation for stating the photovoltaic usage, the film has found to be having a large transmittance lying in the visible range along with an optical energy gap of about 3.5 eV [40]. The ZnS thin film grown using chemical route process and in the polyvinyl alcohol solution leads to an increased bandgap due to the decrement in crystallite size [41]. The comparative study for the three categories of the compound has been showcased in Table 5. Table 5 Comparison table for bulk, doped and thin film ZnS Author

Sample

Bandgap (eV)

W. Yen and S. Shionoya Chaitanyakumar et al. Kurnia and Hart [42]

ZnS Sn-doped ZnS Cd-doped ZnS Ni-doped ZnS Sn-doped ZnS ZnS thin film ZnS nanocrystalline thin films

3.7 3.51–3.58 0.24 2.3 1.7 3.5–3.76 3.88

A. Gaur et al. Agbo et al. [43] J. Borah and K. Sharma

Investigation of Bulk, Doped and Thin Film …

7.1.5

13

ZnGa2S4

ZnGa2S4 offers a bandgap reported higher than 3 eV and belongs to wideband VI XIIYIII 2 Z4 semiconducting compound. The utility in optoelectronic applications including infrared materials, LED, solar applications, etc. of this compound is found [44]. ZnGa2S4 after the thiourea reduction has reported a reduced bandgap of about 2.27 eV using the HSE06 methodology [45]. Co2+ doping is done in ZnGa2S4 through the method of optical absorption in polycrystalline powders [46]. Mn and Ni doping in ZnGa2S4 provides a single crystal explored by the process of chemical vapour deposition technique as presented in a work by Park et al. [47]. In a work by Sahariya et al. [44] a comprehensive investigation of Si doping on the wide bandgap ternary semiconductor ZnGa2S4 has been depicted. Effect of Cu(I) and Ga (III) showed photocatalytic activity along with defect chalcopyrite structure which has yielded a bandgap in the range 2.50–3.40 eV [48]. Eu-doped ZnGa2S4 records the synthesis by solid-state reaction and investigation of its luminescent properties [49]. The comparative study for the three categories of the compound has been showcased in Table 6.

7.1.6

CuInS2

Using CASTEP, a theoretical approach in the optoelectronic properties of CuInS2 was done with the reported experimental bandgap being 1.55 eV [51], and practically, the theoretical value yielded was 0 eV due to the underestimation of bandgap in theoretical procedures [52]. The investigation based on structure, electronic and optical characteristics has yielded a bandgap of 1.24 eV [53]. Rapid thermal process (RTP) has been used to create a CuInS2 absorber layer [54]. Discussion on the nanocrystals of CuInS2 has been done based on structural, chemical and optical properties [55]. The integrated outcomes of optical fluorescence and magnetic resonance imaging for Gd3+-doped CuInS2 can be seen. Due to this doping, this doping provides strong electronic paramagnetic resonance signals [56]. Gallium-doped CuInS2 has yielded 1.50–1.51 eV ranged energy gap with the process of chemical bath deposition [57]. The involvement of Ti as the doping element in CuInS2 has

Table 6 Comparison table for bulk, doped and thin film ZnGa2S4 Author

Sample

Bandgap (eV)

Georgobianai et al. [50] D. Peng et al. J. Sahariya et al. W. Kim H. Park et al.

ZnGa2S4 ZnGa2S4 ZnGa2S4 Co2+-doped ZnGa2S4 Mn2+-doped ZnGa2S4 Ni2+ ZnGa2S4

3 2.27 3.75 2.60 3.21 3.15

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Table 7 Comparison table for bulk, doped and thin film CuInS2

Author

Sample

Bandgap (eV)

C. Guillen et al. Belarbi et al. [63] Alonso et al. [64] G. T. Pan et al. A. Kotbi et al. M. Krunks et al. J. Zhu et al.

CuInS2 CuInS2

1.55 0.8 and 1.35

CuInS2

1.53

Ga-doped CuInS2 CuInS2 thin films CuInS2 thin films Ce-doped CuInS2 thin film

1.50–1.51 1.46 1.45–2 1.38–1.21

given traces of no effect on the chalcopyrite crystal structure, and an increment in the efficiency as solar cell has been found [58]. Electrical properties along with growth characteristics have been described in CuInS2 thin film processing [59]. Spray pyrolysis method has been used in the creation of CuInS2 thin films, and theoretically, also it was studied for investigating optical and structural properties [60]. Using the powdered metallurgy method, the Ce-doped CuInS2 thin film was synthesized and has observed an optical tunable bandgap in the range 1.38–1.21 eV [61]. The oriented CuInS2 films with varying Cu and In ratios through spraying solution [62] have been prepared for analysing characteristics like surface roughness and optical transmittance. The comparative study for the three categories of the compound has been showcased in Table 7.

7.1.7

CuGaS2

Using the LCAO method, CuGaS2 has been investigated in terms of electronic structure. The reported bandgap of the compound is 1.96 eV, 2.15 eV, 3.79 eV and 0.86 eV by DFT-LDA, DFT-GGA, B3LYP and GGA (as per FP-LAPW), respectively [58]. Crystal growth of CuGaS2 has been promoted by the method of chemical vapour transport. The structure of this crystal is looked by XRD method [65]. The theoretical investigation of various properties has been done under the framework of DFT indicating the formation of direct bandgap of about 2.071 eV in CuGaS2 [66]. The incorporation of Al in CuGaS2 has given a bandgap of about 2.32 eV by the use of chemical vapour transport using iodine [67]. Sn-doped CuGaS2 was used for investigating intermediate bandgaps; there has been decrement in bandgap from 2.32 to 1.98 eV [68]. Crystals of CuGaS2 were recombined at different temperatures to investigate the electrical properties [69]. The multi-band electronic structure formation for Cr-doped CuGaS2 thin films was prepared by chemical spray pyrolysis method [70]. Doping of Yb in CuGaS2 thin films has been done in order to analyse the effect on structural and optical properties. The decrement of bandgap from 2.40 eV in bulk to 2.20 and 2.10 eV for 1 and 2% Yb and increment of

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Table 8 Comparison table for bulk, doped and thin film CuGaS2 Author

Sample

Bandgap (eV)

A. Soni et al. P. Kumar et al. He et al. Qin et al. Kalainathan et al.

CuGaS2 CuGaS2 Al-doped CuGaS2 Sn-doped CuGaS2 Yb-doped CuGaS2 thin film

Kalainathan et al.

Cr-doped CuGaS2 thin film

1.96 2.071 2.32 2.32–1.98 2.20–2.10 (1–2%) 2.47–2.61 (3–4%) 2.25

bandgap from 2.40 to 2.47 eV and 2.61 eV for 3 and 4% Yb [71]. Cr-doped CuGaS2 thin films were observed to have shown a decrement in bandgap of the film with 2.25 eV and 2.15 eV at 1 and 2% of Cr [72]. The comparative study for the three categories of the compound has been showcased in Table 8.

7.1.8

CuAlS2

CuAlS2 is the compound that comes under the category of wideband semiconductor with a bandgap offering of 3.5 eV [73]. The electronic and excitonic structures of CuAlS2 are analysed experimentally by temperature-dependent measurements at two different temperatures [74]. Theoretical investigation using two kinds of correlation function, i.e. PBE (GGA) and TB-mBJ, has been done in two of the research works mentioning the analysis of different optoelectronic and structural properties [75, 76]. The application of LEDs emitting blue and green light can be obtained by the incorporation of Zn in CuAlS2 and thus creating their hetero-junction [77]. With the incorporation of Tm or Er in CuAlS2 the infrared luminescence spectra are investigated. Due to doping, the material is found to be offering a sharp luminescence spectra in between 1.33 and 3.54 eV range [78]. Substitution of Be in the wideband compound CuAlS2 the observation turns out to be that the insertion of Be at Al proves to be a good p-type dopant [79]. Optical and structural investigation of CuAlS2 thin film has been done based on the chemical bath deposition methodology. The optical transitions take place in the bandgap energy ranges of 2.81–2.4 eV [80]. The CuAlS2 film deposited by the method of spray pyrolysis to investigate morphological, structural and optical properties has been taken. Optical energy gap reported for CuAlS2 film is valued as 3.45 eV [81]. High-quality CuAlS2 crystals have been grown with the use of CVT. Thin films of CuAlS2 were created by the technique of dip coating and the effect of different illuminations on CuAlS2 thin film depicted its usage as absorption material [82]. The two-stage thermal vacuum evaporation technique for the creation of CuAlS2 thin films was done. On the increment of substrate, the optical energy gap seems to transit from 1.95 to 1.77 eV [83]. CuAlS2 owns a promising place in the

16 Table 9 Comparison table for bulk, doped and thin film CuAlS2

A. Gaur et al. Author

Sample

Bandgap (eV)

Ho et al. A. Soni et al. A. Ghosh et al. Caglar et al. Guo et al.

CuAlS2 CuAlS2 CuAlS2 CuAlS2 film Sn-doped CuAlS2 thin film

3.5 1.77 2.665 3.45 1.91 and 1.31

Theoretical Analysis eV

Fig. 3 Theoretical analysis on various approaches for the optoelectronic compounds

4 3 2 1 0

3.75 0.536

2.15 1.152

1.35

0.65

2.665 2.071

Compounds Bandgap (eV)

Experimental analysis eV

Fig. 4 Experimental analysis on various approaches for the optoelectronic compounds

4 3 2 1 0

3.7

3

3.5 2.53

2.19

0.7

1.55

1.37

Compounds Bandgap (eV)

intermediate bandgap solar cells (IBSCs) group. The value sub-bands are calculated by both experimental and theoretical processes which are 1.91 and 1.31 eV [84]. Zn doping in CuAlS2 thin films which is created by the deposition of pulse plasma methodology forms the p-type conductive material. Structural, electrical, surface morphological along with the compound’s optical properties have been studied. The XRD analysis of the compound film is also done [85]. The comparative study for the three categories of the compound has been showcased in Table 9. The comparative analysis depending on the review of the various compounds presented above can be divided into two parts based on the theoretical and experimental approach (Figs. 3 and 4).

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8 Summary The concluding part of this review presents a brief overview of the different chalcopyrite ternary and binary or other compounds which can be utilized as the different optoelectronic applicants. We have discussed a varied number of compounds which either has narrow or wide bandgap whose alteration can yield a particular application oriented material. For illustration, we can say that ZnGeAs2 is a narrow band compound or ZnS a wideband compound which can be utilized as solar cell applications on proper measures of bandgap engineering. Moreover, experimental and theoretical analysis of the materials has been reviewed giving an idea about the recent trends followed in both the approaches. The chapter covers a wide range of bulk, doped and thin film approaches followed on a particular sample and presents a different perspective to utilize the material.

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Study of Thermal Properties of Eutectic Phase Change Materials for Energy Storage A. K. Ansu, Pooja Singh, and R. K. Sharma

Abstract The current study gives out the preparation and development of novel ternary eutectic mixture comprises of polyethylene glycol (PEG) molecular weight of 2000, 6000 and 10,000. The mixture was developed in various weight fraction ratios. Differential scanning calorimetry (DSC) result suggests that the fusion latent heat and melting temperature of the eutectic lies in the desired range. The fusion latent heat varies from 220 to 154.39 kJ/kg, and melting temperature ranges between 59.1 and 47.8 °C. The maximum value of fusion latent heat of ternary mixture is 172.74 kJ/kg, whereas the melting temperature is 52 °C when the ratio PEG 2000:PEG 6000:PEG 1000 is 60:10:30. Fourier-transform infrared spectroscopy (FT-IR) analysis was carried out to determine the chemical functional group changes, and the result shows that material is chemically stable irrespective of change in weight percentage ratio of PEGs. Results revealed that the ternary mixture can be suitable material which can be used for thermal energy storage applications. Keywords Polyethylene glycol Thermal energy storage


Phase change materials
DSC
FT-IR


Nomenclature PEG DSC FT-IR PCM TES LHTES S

Polyethylene glycol Differential scanning calorimetry Fourier-transform infrared radiation Phase change materials Thermal energy storage Latent heat thermal energy storage system Sample name

A. K. Ansu
P. Singh
R. K. Sharma (&) Department of Mechanical Engineering, Manipal University Jaipur, Jaipur, Rajasthan 303007, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_2

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1 Introduction Energy is considered to be the backbone and most important element for human beings after air, water and food. Energy is divided into two types, renewable and non-renewable resources. The non-renewable energy resources like petroleum and coal take millions of years for their formation and are being used much faster than new ones are being made. The decrease in availability increases the cost of non-renewable energy source. It is very harmful for environment because carbon dioxide and other climate gases are released in large quantities. Renewable energy is pollution-free resource of energy, and it includes solar, tidal, wind, hydropower and biogas. These energy sources are not being used properly because of lack of awareness and their availabilities and constant supply. Solar energy is the best example for the above statement as it is available only in daytime, available in abundant, but they are intermittent in nature. Thus, some heat storage system is needed to save the thermal energy. Sensible energy storage and latent energy storage are the two methods used widely in order to store thermal energy [1, 2]. For storing the energy, phase change materials (PCMs) have been used for many years, and it has been found that it can absorb and reject ample amount of energy at required temperature [3, 4]. Phase change materials provide the realistic and sustainable solution to increase the efficiency of energy storage system. When a PCM melts, it absorbs a large amount of energy and when it freezes, high amount of latent heat is released at a relatively constant temperature. The stored energy is the materials released during nighttime resulting in the solidification of the PCM. These PCMs can be implied in various active or passive systems such as, water heater, cold storage, building comfort and solar water purifier. [5–9]. PCMs are basically divided into three groups, i.e. organic, inorganic and eutectic mixtures. Out of the three, organic phase change materials (OPCMs) are been mostly preferred by most of the researchers [10–13] because of its unique properties such as uniform melting, chemically stable, thermally durable, high latent heat and relatively low or negligible change in volume during phase change. Organic PCMs involve paraffin, fatty acids and sugar alcohols whereas salt hydrates, salt solutions and metals comprise inorganic PCMs. To achieve a desired melting temperature, eutectics and mixtures are often formulated. Inorganic PCMs has high thermal conductivity then OPCMs and also has suitable latent heat and melting temperature range which makes it a suitable candidate to be used in the passive thermal energy storage applications (TES). A common example is that of indoor solar cooking which uses magnesium chloride hexahydrate as phase change materials. On the other hand inorganic PCMs has some disadvantages like subcooling, corrosion and phase segregation issue, i.e. incongruent melting which is an undesirable property. Eutectic PCMs are mainly the combination of two or three materials which are mixed in varying weight fraction in the liquid state. Eutectic PCMs has advantage over OPCMs and inorganic PCMs that any desired latent heat or melting point can be achieved or can be tailored as per the need of application purpose. The selection of PCMs is very necessary in the form of thermal efficiency, feasibility economically and utility life of thermal heat storage systems [3]. Preparation of eutectic PCMs as a new PCM

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has gained a significant interest among the researcher for heating and cooling TES applications in the recent year [14–18]. Sari [18] experimentally prepared fatty acid-based eutectic mixtures. Result revealed fair thermal properties. The reliability of the prepared eutectics was confirmed by the doing thermal accelerated cycling test which shows only a slight deviation in results. Tunçbilek et al. [19] prepared a fatty acid eutectic binary mixture of lauric acid and palmitic acid in weight % of 69 and 31, respectively. Results show 35.2 °C melting temperature and melting latent heat of 166.3 J/g. Similarly, many fatty acid-based eutectic mixture and their thermal properties have been studied in the past by researcher [20–26]. Among the estimated PCMs, polyethylene glycols (PEGs) are favourable ones due to its suitable temperature, good latent heat capacity, no volume change during change of phase and good chemical stability. The thermal properties of different PEGs were first analyse by Pielichowski and Flejtuch [27], and they found that it is potential PCMs for latent heat energy storage. Also, PEGs come with different molecular weights ranging from 400 to 30,000 which make it unique material as compare to other fatty acids. The latent heat and melting temperature vary with different molecular weights, and accordingly, it can be used for the appropriate TES applications as per the temperature requirement. The current work deals with the preparation of ternary eutectic PCMs comprising of PEG 2000, PEG 6000 and PEG 10,000. The materials were prepared in the varying weight fraction of all the three materials. DSC technique was done to evaluate the latent heat of fusion and melting temperature of the prepared eutectic mixture. To check the chemical stability, Fourier infrared radiation technique was carried out in wavenumber range between 4000 and 400 cm−1. Overall results shows that the prepared ternary eutectic mixture can be potential PCMs which can be used in a TES application like building walls, solar water heater and dryer, industry applications, etc.

2 Material Preparation and Characterization Commercial grade polyethylene glycols (PEGs) of various molecular weights PEG 2000, PEG 6000 and PEG 10,000 with purity of more than 98% were used to prepare the ternary eutectic mixture. The materials were procured from Sigma Aldrich Company and used for examining as received without any further modifications. The melting temperature of PEG 2000, PEG 6000 and PEG 10,000 ranges between 49 and 52 °C, 58–63 °C and 62–65 °C, respectively. Ternary mixture of PEGs was prepared using one-step method by mixing PEGs in the weight fraction of 10% in the mass fraction range of 10–80%. The temperature of hot plate was set 15°C above the melting point temperature of PEG having highest melting point temperature, i.e. PEG 10,000. PEG 2000 was added in glass beaker and was kept at hot plate having temperature 80°C. When PEG 2000 was completely melted, then PEG 6000 and PEG 10,000 were added slowly in small quantities to form the mixture. The approximate weight of each sample was around 40–50 gm. The

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mixture is then stirred continuously at 500 RPM for 35 min so that the homogeneous mixture can be obtained, and then, the mixture was cooled at the room temperature; thereafter, it was send for the testing. Latent heat and melting point was determined by using DSC technique. The analysis was done at the heating rate of 10°C/min within the temperature of 30–90 °C. The measured data was taken for three times per sample for getting the accuracy in results, and the average of three was taken into consideration. FT-IR analysis was done between wavenumber 4000–500 cm−1 to determine the chemical stability of materials with spectral resolution of 2 cm−1.

3 Results and Discussions 3.1

Thermal Properties

Thermal properties of PEG 2000, PEG 6000 and PEG 10,000 and the eutectic mixture of PEGs in different weight fractions were determined by DSC technique and shown in Figs. 1 and 2 between temperature of 30 and 90 °C. The thermal

Fig. 1 DSC analysis curve of a PEG 2000, b PEG 6000 and c PEG 10,000

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Fig. 2 DSC analysis curve of eutectic mixture PEG 2000, PEG 6000 and PEG 10,000 in the various mass fraction ratios

history was removed by keeping the machine idle at both the extreme temperature for 3 min. Table 1 represents the value of latent heat and melting point temperature obtained by DSC analysis. The fusion latent heat of PEG 2000, PEG 6000 and PEG 10,000 is 173.47 kJ/kg, 220 kJ/kg and 168.19 kJ/kg, whereas the melting point is 48 °C, 58 °C and 59.1 °C, respectively. The calculated value of melting temperature measured from DSC varies slightly as compare to the value given by supplier company. It can be observed from the table that when the ratio of ternary eutectic mixture PEG2 K:PEG6 K:PEG10 K is 50:30:20, the melting temperature is 51 °C,

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Table 1 Thermal properties of PEG 2000, PEG 6000 and PEG 10,000 mixture Sample name

Composition of PEG 2 K:6 K:10 K weight %

Melting point (°C)

Latent heat of fusion (kJ/kg)

S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8

100:0:0 0:100:0 0:0:100 50:30:20 60:30:10 60:10:30 70:20:10 80:10:10

48 58 59.1 51 47.8 52 49.4 50

173.47 220.0 168.19 171.25 171.48 172.74 154.39 156.49

and when the ratio changes to 60:30:10, the melting temperature of the eutectic reduces to 47.8 °C. There is a small increase and decrease in melting temperature when the weight % of PEG 2000 is 60% and 70%, respectively. Finally, the temperature reaches to 50 °C when the ratio of mixture is 80:10:10. The overall change in temperature ranges between 52 and 47.8 °C which is in the good agreement in the entire mixture as there is not much variation in the temperature. The latent heat of polyethylene glycol 6000 has the maximum value among the three PEGs which is due to its linear polymer chain with hydroxyl groups on two ends. The fusion latent heat of a mixture is 171.25 kJ/kg when the ratio is 50:30:20. The fusion latent heat is almost constant when the ratio of mixture is 60:30:10 and 60:10:30. Finally, the latent heat decreases to 154.39 and 156.69 kJ/kg when the weight % of PEG 2000 is 70 and 80% which may be because of the inadequate movement of chains of PEGs and the difference in specific heat of materials. The latent heat of samples S-4, S-5 and S-6 is in a desirable range and can be used for latent energy storage system. The above data shows that the mixture bears a desirable thermal property and prepared samples can also be used for the material ranging between 47 and 52 °C.

3.2

Chemical Properties

FT-IR is a technique which is mainly used to determine the chemical (functional group) changes of the prepared sample. This method measures the adsorption of infra-red radiation by the sample compound versus wavelength in the range of 4000–500 cm−1. Figure 3 shows the FT-IR analysis of different PEGs with varying mass fraction ratio. The sharp and intense band is due to symmetrical stretching vibrations, whereas the medium band occurs due to vibrations of hydroxyl group. The small peaks are because of the presence of C–H vibrations. As it is clearly seen from FT-IR spectra that peaks of all the samples lie in the same frequency band, but the FT-IR transmittance spectrum of all the samples are

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Fig. 3 FT-IR spectrum of different mass ratios of eutectic mixture PEG 2000, PEG 6000 and PEG 10,000

different from each other, transmittance of some samples are high comparatively to others. The greater transmittance is primarily due to the shorter chain length of material that absorbs the lesser fraction of the infra-red. It can be concluded that there is minute variation in peaks, and the material is still very much chemically stable.

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4 Conclusions The objective was to develop a ternary eutectic phase change material (PCM) mixtures of PEG 2000, PEG 6000 and PEG 10,000. Ternary mixture was developed by using one-step melt blending method in varying weight fraction of PEG 2000, PEG 6000 and PEG 10,000. Differential scanning calorimetry (DSC) was used to measure the melting temperature and fusion latent heat of the prepared sample. Results shows that the melting temperature of the eutectics lies in the range of 47.8–52 °C and latent heat of fusion varies from 171 to 154 kJ/kg. The variation in the melting temperature is very small which proves that the material is thermally stable and can be used for LHTES. FT-IR analysis suggests that there is not much alteration in functional group of prepared eutectics by changing the weight percentage of PEGs which proves that the materials are chemically stable. Based on the above findings, the changes in melting temperature and latent heat are in acceptable level and thus the prepared eutectic mixture can be used for latent heat storage applications. Acknowledgements The financial support for this work is provided by the Manipal University, Jaipur (grant no: EF/2017-18/QE04-04). The author would also like to thank Central Analytical Facility (Manipal University, Jaipur) and Central Instrumentation Facility (Jiwaji University, Gwalior), India.

References 1. Reddy KS, Mudgal V, Mallick TK (2018) Review of latent heat thermal energy storage for improved material stability and effective load management. J Energy Storage 15:205–227 2. Pielichowska K, Pielichowski K (2014) Phase change materials for thermal energy storage. Prog Mater Sci 65:67–123 3. Yuan Y, Zhang N, Tao W, Cao X, He Y (2014) Fatty acids as phase change materials: a review. Renew Sustain Energy Rev 29:482–498 4. Zalba B, Marın JM, Cabeza LF, Mehling H (2003) Review on thermal energy storage with phase change: materials, heat transfer analysis and applications. Appl Therm Eng 23(3):251– 283 5. Farid MM, Khudhair AM, Razack SAK, Al-Hallaj S (2004) A review on phase change energy storage: materials and applications. Energy Convers Manag 45(9–10):1597–1615 6. Khudhair AM, Farid MM (2004) A review on energy conservation in building applications with thermal storage by latent heat using phase change materials. Energy Convers Manag 45 (2):263–275 7. Zhou D, Zhao CY, Tian Y (2012) Review on thermal energy storage with phase change materials (PCMs) in building applications. Appl Energy 92:593–605 8. Oró E, De Gracia A, Castell A, Farid MM, Cabeza LF (2012) Review on phase change materials (PCMs) for cold thermal energy storage applications. Appl Energy 99:513–533 9. Sarier N, Onder E (2012) Organic phase change materials and their textile applications: an overview. Thermochim Acta 540:7–60 10. Kenisarin MM (2014) Thermophysical properties of some organic phase change materials for latent heat storage: a review. Sol Energy 107:553–575

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11. Sharma RK, Ganesan P, Tyagi VV, Metselaar HSC, Sandaran SC (2015) Developments in organic solid–liquid phase change materials and their applications in thermal energy storage. Energy Convers Manag 95:193–228 12. Aydın AA (2013) High-chain fatty acid esters of 1-octadecanol as novel organic phase change materials and mathematical correlations for estimating the thermal properties of higher fatty acid esters’ homologous series. Sol Energy Mater Sol Cells 113:44–51 13. Ansu AK, Sharma RK, Tyagi VV, Tripathi D (2020) Prediction of thermal properties and reliability testing of binary eutectic mixture of polyethylene glycol 2000 and 10000 as phase change materials. Chem Select 5(31):9745–9757 14. Deka PP, Ansu AK, Sharma RK, Tyagi VV, Sarı A Development and characterization of form‐stable porous TiO2/tetradecanoic acid based composite PCM with long‐term stability as solar thermal energy storage material. Int J Energy Res 15. Nazir H, Batool M, Ali M, Kannan AM (2018) Fatty acids based eutectic phase change system for thermal energy storage applications. Appl Thermal Eng 142:466–475 16. Ke H (2017) Phase diagrams, eutectic mass ratios and thermal energy storage properties of multiple fatty acid eutectics as novel solid-liquid phase change materials for storage and retrieval of thermal energy. Appl Therm Eng 113:1319–1331 17. Sharma RK, Sarı A, Hekimoğlu G, Zahir MH, Tyagi VV (2020) Effects of thermal cycling operation on solar thermal energy storage, morphology, chemical/crystalline structure, and thermal degradation properties of some fatty alcohols as organic PCMs. Energy Fuels 34 (7):9011–9019 18. Sarı A, Sarı H, Önal A (2004) Thermal properties and thermal reliability of eutectic mixtures of some fatty acids as latent heat storage materials. Energy Convers Manag 45(3):365–376 19. Tuncbilek K, Sari A, Tarhan S, Ergüneş G, Kaygusuz K (2005) Lauric and palmitic acids eutectic mixture as latent heat storage material for low temperature heating applications. Energy 30(5):677–692 20. Sari A, Kaygusuz K (2002) Thermal performance of a eutectic mixture of lauric and stearic acids as PCM encapsulated in the annulus of two concentric pipes. Sol Energy 72(6):493–504 21. Roxas-Dimaano MN, Watanabe T (2002) The capric and lauric acid mixture with chemical additives as latent heat storage materials for cooling application. Energy 27(9):869–888 22. Feldman D, Banu D, Hawes DW (1995) Development and application of organic phase change mixtures in thermal storage gypsum wallboard. Sol Energy Mater Sol Cells 36 (2):147–157 23. Nazir H, Batool M, Osorio FJB, Isaza-Ruiz M, Xu X, Vignarooban K, … Kannan AM (2019) Recent developments in phase change materials for energy storage applications: a review. Int J Heat Mass Transf 129:491–523 24. Lin Y, Jia Y, Alva G, Fang G (2018) Review on thermal conductivity enhancement, thermal properties and applications of phase change materials in thermal energy storage. Renew Sustain Energy Rev 82:2730–2742 25. Faraj K, Khaled M, Faraj J, Hachem F, Castelain C (2020) A review on phase change materials for thermal energy storage in buildings: heating and hybrid applications. J Energy Storage, 101913 26. Da Cunha JP, Eames P (2016) Thermal energy storage for low and medium temperature applications using phase change materials–a review. Appl Energy 177:227–238 27. Pielichowski K, Flejtuch K (2003) Differential scanning calorimetry study of blends of poly (ethylene glycol) with selected fatty acids. Macromol Mater Eng 288(3):259–264 28. Dimaano MNR, Watanabe T (2002) Performance investigation of the capric and lauric acid mixture as latent heat energy storage for a cooling system. Sol Energy 72(3):205–215

A Review on Thermal Conductivity Enhancement of Organic Phase Change Material-Based Form-Stable Phase Change Materials Pooja Singh, A. K. Ansu, and R. K. Sharma

Abstract In the present day, manufacturing of energy from renewable energy origins is one of our top major concerns; to address this, researchers are putting efforts to solve this energy crisis. Organic phase change materials (PCMs) are extensively used for storing thermal energy to strengthen and control this renewable energy. During the phase transition process, phase transition materials are prone to leak out, which limits their application. The form stabilization process is being used to overcome this problem by adding some percentage of supporting material in the organic phase change materials which not only prevent the leakage and increases stability but also helps in increasing thermal conductivity as contrast to the original material. But some supporting materials also suffer with the low thermal conductivity issue. Hence, some additional materials with high thermal conductive characteristic are required in that case. So, this paper delivers an overall detail on change in thermal conductivity of form-stable phase change materials (FSPCMs) by the addition of supporting materials as well the additional high thermal conductive materials. Lastly, the multifaceted application of FSPCMs has been discussed in thermal management and thermal energy storage (TES) systems. Keywords PCMs


TES
Organic PCMs
FSPCMs

1 Introduction Thermal heat storage structures are used for renewable energy, reuse processes, and solar thermal systems. Due to their large storing capacity as well as moderate temperature fluctuations from storage to recovery, latent heat energy storage is most desirable in various heat storage systems. In an open-ended thermostat, energy is reserved at the time of melting and restored for the period of cooling of PCM.

P. Singh
A. K. Ansu
R. K. Sharma (&) Mechanical Engineering Department, Manipal University Jaipur, Jaipur 303007, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_3

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Under this context, TES offers solutions in specific areas: • Time period and time and energy used between the production or distribution of energy and its use in the acceptance of systems (solar power, fusion, etc.) • Security of power supply (hospitals, data centers, etc.) • Thermal safety. In 1940, Telkes [1] pioneered the study of organic PCMs. However, it received little courtesy till the energy emergency of late 1970s and initial 1980s when broadly investigated for its usage in various applications, specifically for systems in solar heating. Even though when investigation on latent energy storage for the solar heating structures carried on, considerable efforts have been done to discover the consumption of PCMs in different applications, such as air acclimatizing building, underfloor heating, building envelope cooling system, electronics refrigeration, waste energy recovery, textiles, food preservation, milk to name a few. Integrating a material with greater value of thermal conductivity with the organic PCM can be categorized into two types. First method is to make a form-stable PCM compound in which the PCMs are immersed into the holes of the supportive material to fully prevent leakage when the PCM has been phased out from solid to liquid. Another is related to the addition of a minor sum of substance of greater thermal conductivity to the PCMs to boost the thermal conductivity of composite formed; the available blend may be called a composite PCM project, as the leakage of liquid-form PCM cannot be averted.

2 Synthesis of Organic PCM-Based FSPCM Sari and Karaipekli [2] synthesized CA/PA (capric acid/palmitic acid) double blends by blending the bottom-up atomic weight constituent in 10% mass proportions from 0 to 100%. The strong components measured inside ±0.1 mg exactness were blended in fluid state homogeneously and after that cool down to room temperature. DSC thermic investigation strategy was used to measure the liquefaction temperatures of the corrosive constituents, and their blends arranged at distinctive mass combinations are shown in Fig. 1. Within the case of Jeong et al. [3], natural PCMs were n-hexadecane, n-octadecane, and paraffin wax. The PCM/diatomite form-stable composite was synthesized by utilizing vacuum impregnation technique. To discover the greatest PCM sum in diatomite, 80 g PCM was impregnated into 50 g diatomite. Excess PCM remained within the container and was evacuated through sifting. The microstructure of the PCM and their composites are shown in Fig. 2. Tang et al. [4] mixed PA with CA (weight proportion of 12–88) in a measuring utensil. Fatty acids were blended consistently by mixing at 75 °C with the help of a magnetic stirrer for 1 h. At that point, diatomite was included whereas a stirrer kept mixing. When the diatomite is fairly utilized as a supporting precursor, its mass

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Fig. 1 Melting temperature of CA/PA blends versus combination of elements [2]

Fig. 2 Microstructure of a diatomite, b composite of n-hexadecane/diatomite, c composite of n-octadecane/diatomite, d composite of paraffin wax/diatomite [3]

division within the CPCMs was kept little to extend the specific heat of the CPCM. Wang et al. [5] arranged the PCM by a self-assembled graphene/organic cross-breed polymerization strategy. Yang et al. [6] utilized the altered Hummers’ strategy to get (graphene oxide) GO from extended graphite powder gotten by thermal development of expandable graphite. The combined PCMs were

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arranged by employing a vacuum impregnation strategy. Starting with, a 5.0 mg/ mL GO solution was arranged, and after that distinctive volumes of GNP (5, 10, 20, 50) mg/mL were included to plan a blend of GO/GNP arrangement through ultrasonic shower treatment and solenoid mixing as shown in Fig. 3. In Yu et al. [7] resurvey organic PCMs with a phase transition temperature 28.13 ° C and latent energy content 149.20 J/g were utilized straightforwardly as phase change materials. Two sorts of carbon nanomaterials, carbon nanotubes (CNT) and exfoliated graphene platelets (xGnP) were arranged. The tests were arranged by including CNT and xGnP at diverse concentrations into bio-based PCMs, employing a sonication procedure. Sample preparation process is manifested in Fig. 4. Sheng et al. [8] research utilized commercially accessible retentive cotton cuts as the crude material for the manufacture of carbon absorbent. Paraffin wax (PW) was utilized as the phase change material, which was liquefied around 100.00 °C and then soaked into the above-mentioned carbon wipes beneath a vacuum. After cooling and hardening of PCM, the PW/carbon wipe compound tests were secured. Preparation of carbon sponge and its composite is shown in Fig. 5. In Gao et al. [9] research, the nano-SiO2-EG-PW(expanded graphite—paraffin wax) FSPCM was arranged through retaining PW with nano-SiO2 and expanded graphite (EG). The development process of composite is represented in Fig. 6. Great thermal effectiveness, such as good latent heat, and requisite stage transition temperatures are the foremost alluring properties of PCMs for conceivable utilization in thermal vitality storage. PCM ought to be thermally steady over its

Fig. 3 Photographs of a GO aerogel, b PEG/GO, c HGA2, d PEG/HGA2 [6]

Fig. 4 Sample preparation route scheme [7]

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Fig. 5 Representation for making carbon sponge and PCM/carbon sponge compound [8]

Fig. 6 Representation of nano-SiO2-EG-PW PCM and nano-SiO2-EG-PW/PW/HTPB/compounds development process [9]

range of working temperatures. Subsequently, thermic solidness is also considered as a basic parameter for a PCM to be utilized in thermal energy storage applications. The foremost broadly utilized approach to look at the warm steadiness of PCMs is TG analysis.

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3 Thermal Conductivity Enhancement of Organic PCM-Based FSPCM The performance of stored energy and output of integrated phase transition material depends largely on thermal performance. Hence, the thermal conductivity of PCM compounds is a major factor for application of thermal energy storage. The thermal conductivity of FSPCMs has been studied broadly by researchers as exhibited in Table 1. As Khedache et al. [43] mentioned, mixing a part of PCM into structured red brick and by adding expanded graphite into mass to increase the paraffin thermal conductivity. Pure paraffin thermal conductivity is 0.1716 W/m-K, whereas the thermal conductivity of the FSPCM in addition to 10% expanded graphite is 0.520 W/m-K−1, which is around three times greater than pure PCM. The deviation in thermal conductivity with mass constituent of expanded graphite (EG) additive is shown in Fig. 7. According to Wen et al. [33], stearic acid mixed (SA) with carbonized sunflower straw (CSS) 16.3% (w/w) to make form-stable SA/CSS, and this results in increase of thermal conductivity from 0.16 W/m-K of SA to 0.33 W/m-K of SA/CSS, which is around 106% higher than the SA. This means the CSS acting as the supporting material is potential for boosting the thermal conductivity of SA/CSS. Sarı et al. [39] mentioned that along with melting temperature and latent energy, the most important parameter in TES is thermal conductivity of organic PCMs. The FSPCM prepared in his paper is the composite of lauric acid and expanded perlite (LA/EP). However, thermal conductivity of both materials is low, and it is 0.07 W/m-K. To increase these lower thermal conductivities of FSPCMs, the expanded graphite (EG) has been added in the fraction of 10% in the composite. Prepared composite (LA/EP/EG) final thermal conductivity was recorded as 0.13 W/m-K. 86% of increase in thermal conductivity occurs in prepared FSPCM due to the EG additive. According to Karaipekli and Sarı [20], the thermal conductivity of FSPCM capric–myristic acid/vermiculite (VMT) composite is low (0.065 W/m-K) because of VMT low conductivity. So to increase the thermal conductivity, some additives are introduced like graphite powder and metal particles. In this case, expanded graphite (EG) of (2% weight) is added to form CA–MA/VMT/EG composite with a thermal conductivity of 0.22 W/m-K. This results the boost in thermal conductivity up to 85% from CA-MA/VMT. Zeng et al. [30] mentioned that thermal conductivity of tetradecanol (TD)/EG is enhanced majorly by increasing the loading of EG in form-stable phase change material. The thermal conductivity of pure EG is 0.433 W/m K which is increased to 5.37 times of previously mentioned by adding 7% EG to attain thermal conductivity of 2.76 W/m K. It is further enhanced to 5.71 W/m K when 40 wt% of EG was added.

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Table 1 Thermal conductivity of FSPCMs containing organic PCMs PCM

Supporting material

Additional material

% Change in thermal conductivity

References

Bio-based PCM

Exfoliated graphite nanoplatelets Carbon nanotube Expanded graphite Expanded graphite Pitch-based graphite foam Diatomite

–

336

[7]

– – – –

248 1200 500 85

[10] [11] [12]

Expanded graphene

53.7

[4]

Graphite powder Expanded graphite Halloysite nanotube Poly-methyl methacrylate

– – Graphite Modified graphite

338.71 67.74 180 195.9

[13] [14] [15]

Expanded perlite

Expanded graphite –

64

[16]

75

[17]

94.7

[18]

84

[19]

58

[20]

30

[21]

361

[6]

67 250

[22] [23]

237.5

[24]

463 95

[25] [26]

o-Mannitol Acetamide Polyurethane Palmitic acid and capric acid eutectic mixture High-density polyethylene Capric acid Capric acid(CA)myristic acid(MA) eutectic Capric acid Bio-based PCM

Paraffin

Capric acid and myristic acid Polyaniline Polyethylene glycol Ethyl cinnamate Palmitic acid

Polyethylene glycol Lauric-palmitic-stearic acid ternary eutectic mixture

Exfoliated graphite nanoplatelets (xGnP) Silica gel Carbon black nanopowder Vermiculite 1-Tetradecanol Hybrid graphene aerogels Silver nanoparticles High-density polyethylene Polyaniline

Cellulose Expanded perlite

Expanded graphite – Expanded graphite Carbon nanotube Graphite nanoplatelets – Graphite nanoplatelets Exfoliated graphite nanoplatelets (xGnP) GNP –

(continued)

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Table 1 (continued) PCM

Supporting material

Additional material

% Change in thermal conductivity

References

Palmitic acid Polyethylene glycol Capric–myristic acid

Expanded graphite Diatomite Vermiculite composite Expanded perlite Halloysite nanotube Expanded perlite

– EG EG

252.9 131 85

[27] [28] [20]

EG Graphite EG

58 58 95

[29] [14] [26]

– –

537.3 78.8

[30] [31]

– –

96.9 106.3

[32] [33]

–

144.6

[34]

–

170.5

Carbon

31.6

[35]

Titanium dioxide SiO2 (20.8%) –

20.3%

[36]

94.7 30

[18] [37]

Carbon nanotubes (5.27%) EG (10%)

382

[38]

86

[39]

17.7

[40]

30

[37]

150 110

[41]

Capric acid Lauric-palmitic-stearic acid (LA-PA-SA) Tetradecanol (TD) Lauric acid Palmitic acid (PA) Stearic acid

Tetradecylamine (TDA) Octadecylamine (ODA) Capric–myristic– stearic acid (CA-MA-SA) Stearic acid (SA) Paraffin Polyethylene glycol Paraffin

Lauric acid (LA) Micro-encapsulated paraffin Polyethylene glycol (PEG) Capric acid–lauric acid Capric acid–palmitic acid Capric acid–stearic acid

EG Modified sepiolite (40%) Diatomite (45%) Carbonized sunflower straw (16.3%) Porous 3D graphene sponge (GS) Modified expanded vermiculite composite Modified expanded vermiculite EG (7.2%) Silica hydroxyl (SHC) Expanded perlite

Expanded perlite (EP) High-density polyethylene/wood flour composite Silica hydroxyl (SHC) Expanded vermiculite (VNT)

Micro-mist graphite MMG (8.8 wt%)

Expanded graphite (10%)

104 (continued)

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Table 1 (continued) PCM

Supporting material

Additional material

% Change in thermal conductivity

References

Myristic acid

High-density polyethylene (HDPE)

Nano–Al2O3 (NAO) Nano-graphite (NG) EG (10%)

95

[42]

Paraffin (PA) Myristic acid

Red brick (Br) Graphite nanoplatelets (2%)

121 203 38

[43] [44]

Fig. 7 Thermal conductivity of PCM/Br composite containing EG [43]

4 Applications of FSPCM With the fast growth of society, fossil fuel consumption is gradually infuriated, making the energy scarcity even more consequential. In addition, the security of the ecosystem is absolutely imminent. Phase change material is a type of modern technology that can solve energy crises and decrease waste in the environment. Because of high latent heat power and limited temperature fluctuations in phase change operation, PCM has major advantages in thermal energy storage. In Sun et al. [37] study, the PEG/SHC (polyethyl glycol/silica hydroxyl compound) FSPCMs have been favorably synthesized using simple sol–gel process, in which silica gel industrial waste has been reutilized to acquire the SHC network for PEG support. PEG was established to be binded to SHC by tough physical

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interactivity, which can encapsulate approximately 80% of weight component of polyethylene glycol in SHC with well-shaped stable properties. It has been shown that the simple sol–gel technique prepared in this research work has not only been able to obtain organic PCM-based FSPCMs with excellent performance for latent energy storage and also to suggest an efficient way of generating economic advantages through the reuse of industrial waste. Wu et al.’s [45] work has shown that a novel versatile MF/RGO/PW PCM composite with high latent heat, strong encapsulation strength, solar thermal energy storage capacity, and thermal-light-actuated memory properties can be used to maintain house temperature constancy. Super-elastic MF/RGO foam-assisted PCM composites have tremendous potential for innovative applications such as solar energy harvesting and energysaving buildings. Yu et al. [46] developed and prepared an energy harvesting system composed of robust N- and P-type PCM composites. It was anticipated that this research will provide insight into thermo-electric energy transfer and lead to the design of energy harvesting devices for various applications, such as wireless sensors and medical devices. Fang et al.’s [47] work has shown the preparation and classification of the form-stable LA/SiO2 composite PCMs. Form-stable LA/SiO2 composite PCMs have better thermal stability and can be used frequently in a thermal energy storage device. It has been described in the sense of a severe energy scarcity, and FSPCMs can provide significant support for energy efficiency and environmental security. With the special advantages, in the future, clay mineral-based FSPCM can occupy an irreplaceable role in thermal energy storage. Maintaining an indoor climate at an acceptable temperature contributes to a high degree of energy consumption. Construct energy efficiency is of the highest importance. Passive solar heating is an efficient way to reduce indoor temperature spike and conserve electricity. PCM has a big influence on energy-saving construction. Clay mineral-based FSPCM has excellent compatibility with construction materials and important properties in building envelope. Additionally, clay mineral-based FSPCMs are appropriate for building energy preservation and passive solar heating.

5 Conclusion This paper reviews the synthesis of organic PCM-based FSPCMs with the addition of some high thermal conductivity materials. With the addition of metal- and carbon-based supporting materials in organic PCMs, they not only prevent the leakage but also increase the thermal conductivity property of overall composite. The number of supporting materials which are mixed with organic PCMs to form FSPCMs composite is being analyzed on the basis of their thermal conductivity property and their results are also discussed. It has been concluded that the thermal

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conductivity of organic PCM can be enhanced to a great amount when metal- and carbon-based supporting materials are added. But some supporting materials like clay-based materials are having low thermal conductivity. Hence in order to increase the thermal conductivity of clay-based FSPCMs, some additional materials are integrated to them. The change in thermal conductivity varies with the loading capacity of supporting or additional material. FSPCM has been found to be most suitable in the field of thermal energy storage devices. And after analyzing all this, we came across the versatile application of organic FSPCM in different sectors and industries which can help us to store one kind of renewable energy and can be used of further purpose.

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35. Wei H, Xie X, Li X, Lin X (2016) Preparation and characterization of capric-myristic-stearic acid eutectic mixture/modified expanded vermiculite composite as a form-stable phase change material. Appl Energy 178:616–623 36. Li X, Wei H, Lin X, Xie X (2016) Preparation of stearic acid/modified expanded vermiculite composite phase change material with simultaneously enhanced thermal conductivity and latent heat. Sol Energy Mater Sol Cells 155:9–13 37. Sun K, Kou Y, Zheng H, Liu X, Tan Z, Shi Q (2018) Using silicagel industrial wastes to synthesize polyethylene glycol/silica-hydroxyl form-stable phase change materials for thermal energy storage applications. Sol Energy Mater Sol Cells 178:139–145 38. Zhang X et al (2017) Enhancement of thermal conductivity by the introduction of carbon nanotubes as a filler in paraffin/expanded perlite form-stable phase-change materials. Energy Build 149:463–470 39. Sarı A, Karaipekli A, Alkan C (2009) Preparation, characterization and thermal properties of lauric acid/expanded perlite as novel form-stable composite phase change material. Chem Eng J 155(3):899–904 40. Li J, Xue P, Ding W, Han J, Sun G (2009) Micro-encapsulated paraffin/high-density polyethylene/wood flour composite as form-stable phase change material for thermal energy storage. Sol Energy Mater Sol Cells 93(10):1761–1767 41. Karaipekli A, Sarı A (2010) Preparation, thermal properties and thermal reliability of eutectic mixtures of fatty acids/expanded vermiculite as novel form-stable composites for energy storage. J Ind Eng Chem 16(5):767–773 42. Tang Y, Su D, Huang X, Alva G, Liu L, Fang G (2016) Synthesis and thermal properties of the MA/HDPE composites with nano-additives as form-stable PCM with improved thermal conductivity. Appl Energy 180:116–129 43. Khedache S, Makhlouf S, Djefel D, Lefebvre G, Royon L (2015) Preparation and thermal characterization of composite ‘Paraffin/Red Brick’ as a novel form-stable of phase change material for thermal energy storage. Int J Hydrogen Energy 40(39):13771–13776 44. İnce Ş, Seki Y, Ezan MA, Turgut A, Erek A (2015) Thermal properties of myristic acid/ graphite nanoplates composite phase change materials. Renew Energy 75:243–248 45. Wu H et al (2020) Melamine foam/reduced graphene oxide supported form-stable phase change materials with simultaneous shape memory property and light-to-thermal energy storage capability. Chem Eng J 379: 46. Yu C, Yang SH, Pak SY, Youn JR, Song YS (2018) Graphene embedded form stable phase change materials for drawing the thermo-electric energy harvesting. Energy Convers Manag 169:88–96 47. Fang G, Li H, Liu X (2010) Preparation and properties of lauric acid/silicon dioxide composites as form-stable phase change materials for thermal energy storage. Mater Chem Phys 122(2–3):533–536

Performance Evaluation of a Solar Air Heater with Transverse Ribs on the Absorber Surface Using CFD Technique Amit Kumar, Apurba Layek, A. K. Ansu, and Atwari Rawani

Abstract The paper attempts to present the study of an experimental and two-dimensional (CFD)fluent numerical simulation of a solar air heater system to get the enhanced effect on heat transfer propagation of the flowing fluid. An artificial roughness of circular-shaped transversely placed on the absorber surface has been used, and its effect on heat transfer phenomenon and flowing fluid behavior have been investigated. The non-dimensional form of relative roughness pitch (P/e) and relative roughness height (e/Dh) are taken as design variables. The possible effect of roughness and its geometrical parameters on Nusselt number and friction factor has been investigated having Reynolds number (Re) ranges between 8000 and 11,500 keeping value of heat flux constant. Two distinct values of relative roughness pitch (P/e) of 10 and 20 have been considered keeping relative roughness height, i.e., e/ Dh = 0.0174. The commercially used package of ANSYS FLUENT 16.0 is used in order to anticipate the characteristics of the flowing stream. On the basis of different turbulence models, their results are compared with the experimentally observed data. The turbulence model of RNG, k–e and realizable, k–e was chosen from the sets of different turbulence models. The results are predicted by (CFD)fluent simulation technique, and it is observed that (RNG) k–e model results were in good accuracy and accordingly to get the best possible effect on heat transfer rate. Keywords (CFD)fluent


Solar air heater
Heat transfer
Artificial roughness

A. Kumar (&)
A. Layek Department of Mechanical Engineering, NIT Durgapur, Durgapur, West Bengal, India A. K. Ansu Department of Mechanical Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India A. Rawani Department of Mechanical Engineering, Bengal College of Engineering and Technology, Durgapur, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_4

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Nomenclature h D Cp k Nu Re Qu m V q

Convective heat-transfer coefficient for fluid, W/m2 K Hydraulic diameter, m Specific heat of fluid, J/kg K Thermal conductivity of air, W/m K Nusselt number Reynolds number (dimensionless) Useful heat gain, W Air mass flow-rate of, kg/s Fluid velocity duct, m/s Density, Kg/m3

1 Introduction The fast reduction of fossil fuels emerged as an urgent look for alternative sources of energy. Researchers are focused to improve the performance of the solar energy usage structures. The solar air heater is one in every solar thermal system generally used for area heating, drying of vegetation and many more sectors. In the solar air heater channel, heat is transferred from the absorber plate and the alternative walls are stored insulated. Between the heated absorber plate and the fluid medium, the heat transfer coefficient is generally low causing low thermal efficiency of the device, which may be improved by the use of proficient conversion and utilization technique. Various investigators have considered to improvise the heat transfer characteristics of a solar air heater by the use of the extended floor, packed bed and different types of roughness element on the absorber plate. In the present analysis, the (CFD)fluent (ANSYS FLUENT v 16.0) is used to predict the heat transfer. To a few extents, experimental and theoretical work on solar air heater has been done in the last decades. Gandhi et al. [1] conducted (CFD)fluent work to examine the effect of artificial roughness on the flowing fluid which flows across a channel having backside wall roughened with repeated transverse ribs of wedge-shaped. 2-D numerical modeling of the rectangular duct has been done using ANSYS FLUENT software which shows fairly correct settlement with the experimental observations. Yadav and Bhagoria [2] investigated the usage of (CFD)fluent analysis of roughened solar air heater having round transverse rib roughness connected at the absorber plate, and the simulation outcomes show that RNG, k–e turbulence model anticipate being a great flow characteristic. The results that are received via the turbulence model, i.e., (RNG, k–e version), were discovered to be accurate in accord with the Dittus–Boelter equation and Blasius empirical equation. Researchers have focused on the number of experiments on solar air heater duct design for distinct roughness parameters based on unique shapes, sizes, and orientations and found that it is a good way to get the best results on the basis of roughness geometry [3–5]. Kumar

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et al. [5] additionally investigated that the turbulence version considering the RNG, k–e turbulence version suggests having settlement properly with empirical correlation, i.e., Dittus–Boelter relation for smooth duct. Bolemtafes and Benzaoui [6] conducted (CFD)fluent analysis on the roughened surface on the basis of the different turbulence models. Kumar and Layek [7] did the comparison analysis using (CFD)fluent and LCT approach on solar air heater having transverse circular rib for attaining its optimal condition for Nusselt number and friction characteristics. In this study, performance analysis on heat transfer augmentation supposes to achieve because of artificial roughness on the absorber plate of solar air heater. Renormalization group (RNG) k–e and (realizable) k–e turbulence model are selected. An extensive study of the heat transfer in the system between the inter rib region has been done using the sets of turbulence model. In order to recognize the mechanism of heat transfer inside the inter-rib space, it is far required to examine the fluid flow pattern and turbulence depth. Hence, it is targeted to get the distribution along a point of separation, reattachment point among the ribs, wake zones formation behind and infront of the ribs, and diffusion of turbulence inside the domain is favored. After the validation with empirical correlation using RNG, k–e and realizable, k–e turbulence model, a detailed pattern of fluid flow and heat transfer evaluation has been done based on the use of rib shapes in order to optimize the roughness parameter. The outcome on the basis of its shapes that gives the overall performance of the system, without being conducted any experimentation decreases both time and cost.

2 Experimental Procedure Figure 1 shows experimental installation, and arrows indicate the direction of air flow via the structures (air blower). Thermometers had been positioned at ten locations of kind factors within the rectangular duct, i.e., at entry, test and at the exit of the duct to measure the air temperature as represented in Fig. 1. In order to

Fig. 1 Experimental setup schematic diagram

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measure the mass flow rate, an orifice meter has been used and a virtual pyrometer is used to measure the sun radiation. The experimental setup includes an entry section, exit section and test section which go with the orifice meter and a three-phase centrifugal blower. The duct is of size 1680 mm  280 mm  60 mm and is produced from wooden panels. The surface plate is of 1-mm-thick aluminum plate which forms the top large wall of the duct. A calibrated orifice meter is used for measuring the flow rate, and the flow is regulated by using the control valves installed within the lines. The suction of air has been done using a centrifugal blower which must be switched on initially ensuring that there is no leakage in the joints of the channel. The heater must be switched on at the required condition to become set. Generally, the system took 2– 3 h to acquire steady-state circumstances. The effects obtained for Nusselt number and friction factor are in comparison with Dittus–Boelter and Blasius correlations, respectively, for validation.

3 (CFD)Fluent Flow Simulation This segment describes the procedure of modeling of domain structure, generation of grid, mathematical basis, boundary situations and turbulence version choice/ validation and answer system. The ANSYS 16.0 is used as a design modeler on the basis of design variables considered. The absorber plate with different positions of circular transverse wire ribs has been used as depicted in Fig. 2. Grids of non-uniform shapes have been taken into consideration for the evaluation of the 2-D governing equations for mass, momentum and energy. Non-uniform grids generated the use of ANSYS ICEM (CFD)fluent v 16.0 software. Investigation of the solar air heater is executed having Reynolds number variation of 8000–11,500 and at constant heat flux of 900 W/m2 is given on the absorber surface. In (CFD)fluent, velocity (2.10–2.74 m/s) calculated using Reynolds number was specified at the inlet of the duct. The inlet condition of air temperature is maintained at 305 K. Aluminum plate is used as a selected material for absorber plate. At exit,

Fig. 2 Absorber surface with different configurations of circular transverse ribs

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boundary situation is unique within the form of constant atmospheric pressure. A set of turbulence model has been used as a computational procedure to previse the effect of turbulence.

4 Data Reduction Data amassed during experimental and numerical observations are used to calculate Nusselt number and friction factor. The equations generally used to evaluate the required value of mass flow rate ‘m’, heat gain by air ‘Qs’ and heat transfer coefficient ‘h’ are written as: 
0:5 m ¼ Cd Ao 2qDP= 1  b4

ð1Þ

The required value of heat gain by the flowing fluid is given by Qs ¼ mCp ðTo  Ti Þ

ð2Þ

where Ti and To measured the usage of thermocouples placed at inlet section and outlet section. The Nusselt range (Nu) and friction component (fr) in experimental research calculated the usage of the following relation hDh k
DP

ð3Þ

Nu ¼ fr ¼

l

2qV 2

ð4Þ

D

where Dh is known as hydraulic diameter and the air temperature corresponds to bulk mean temperature. The heat transfer enhancement of a solar air heater using artificial rib roughness causes considerable enhancement of friction losses. The method that taken by Webb and Eckert [8] in the form of thermo-hydraulic performance parameter (THPP) is given by Eq. (7) Thermo - hydraulic Performance ParameterðTHPPÞ ¼

Nur =Nus ðfr =fs Þ1=3

ð5Þ

Nusselt number for smooth duct (Nus) can be obtained using the Dittus–Boelter equation [9]

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Nus ¼ 0:023Re0:8 Pr0:4

ð6Þ

Similarly, friction factor for smooth duct (fs) can be calculated using Blasius equation [10] fs ¼ 0:0791Re0:25

ð7Þ

5 Result and Discussion Experimental and (CFD)fluent analysis of two-dimensional solar air heater duct are to be taken out in order to get the effect of heat transfer coefficient and friction aspect on the basis of varying Reynolds number. The two equation models have been optimized for a particular class of flow. The approach to turbulence modeling looks completely at the solution to those generated by others and to experimental data. The results hence obtained are in comparison and verified with the outcomes of smooth absorber plate under the same states of flow.

5.1

Effect of Heat Transfer and Friction Characteristics

According to the manner of logical concept, the foremost outcomes meet the experimental data satisfactory with that of the considered turbulence model. As the Reynolds number increases, the effect of kinetic energy increases because of turbulence impact and its dissipation rate, which leads to the greater effect of turbulent depth consequently increases the Nusselt number due to increase in heat transfer coefficient between the flowing stream and absorber surface. The contour image of turbulence kinetic energy shows the phenomenon of heat transfer. Figure 3 visualizes the contour image of turbulence intensity having Reynolds number of 11,149. The turbulence intensity of low level leads to a low level of heat transfer. Figure 4 depicts the contour plot velocity on the basis of RNG, k–e turbulence model at a fixed Reynolds number of 11,149. At the centerline of the duct, the magnitude of velocity is maximum and minimum near the wall. It can be observed from the simulation results that the velocity at the inlet is assumed to be somewhat lower than the outlet of the rectangular channel, mainly due to its flow acceleration in the stream-wise direction. Figure 5 depicts the variation of Nusselt number as function of Reynolds number for two different values of relative roughness pitch. The increase in Reynolds number increases the Nusselt number mainly due to increase in turbulence intensity and its dissipation rate. At P/e of 10, the number of reattachment of free shear layer at different locations is assumed to be high which increases the heat transfer rate of the flowing stream. Similarly, it is observed that at P/e of 20 there is non-reattachment of free shear layer decreasing the heat transfer

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Fig. 3 Contour image of turbulent intensity for Re = 11,149

Fig. 4 Contour image of velocity for Re = 11,149

rate. The value of Nusselt number obtained at any Reynolds number by RNG, k–e model is approximately close to experimental value. Figure 6 depicts the variation of friction factor with Reynolds number for two different values of relative roughness pitch. The values of friction factor are observed to decrease with increase in Reynolds number due to suppression of viscous sub-layer. The rib roughness effect is reported from Fig. 6 that it contributes the higher friction factor than those of smooth plate. At P/e of 10, the number of ribs per unit length is more, i.e., more obstruction along the flowing stream which is observed to be higher friction factor, and at P/e of 20 the number of ribs decreases in a unit length causing less obstruction along the fluid stream, thus decreasing the friction factor. The value of friction factor obtained at any Reynolds number by RNG, k–e model is approximately similar to experimental value.

54

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e/Dh=0.0174

60

Nu

50 40 30

Smooth CFD at P/e=10 CFD at P/e=20 Experimental at P/e=10 Experimental at P/e=20

20 10 0 8200

8700

9200

9700

10200

10700

11200

Re

Fig. 5 Nusselt number variation as function of Reynolds number

5.2

Thermo-hydraulic Performance Parameter

The enhancement in heat transfer which is predicted by present (CFD)fluent investigation with the previous experimental results for distinct Reynolds number at a constant value of relative roughness height is depicted in Fig. 5. Webb and Eckert [8] formulated the thermo-hydraulic performance parameter (THPP) which correlates the overall performance of the solar air heater system. Figure 7 shows the changes that occurred in thermo-hydraulic performance parameter due to variation of Reynolds number. It is targeted that the thermo-hydraulic performance parameter (THPP) must be above unity for all the cases. It is reported from Fig. 7 that THPP

0.035

Friction factor,fr

0.03

Smooth Duct Experimental at p/e=10 Experimental at p/e=20 CFD result at p/e=10 CFD result at p/e=20

e/Dh=0.0174

0.025 0.02 0.015 0.01 0.005 0 8000

8500

9000

9500

10000

10500

Re

Fig. 6 Friction factor variation as function of Reynolds number

11000

11500

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55

1.19 e/Dh=0.0174

1.18

THPP

1.17 1.16 1.15 1.14 Experimental,P/e=10,

1.13

CFD, P/e=10 ,RNG K-ξ model

1.12 8200

8700

9200

9700 Re

10200

10700

11200

Fig. 7 THPP variation as function of Reynolds number

attains its highest value of about 1.18 at its higher Reynolds number of approximately 11,000 for the investigated parameters. In order to validate the available experimental results, the results are compared with present numerical model. On the basis of the analysis, it is seen that the present computational results are found to fall in between the experimental results. Therefore, it is a sign of good agreement between numerical and experimental values. Hence, it is suggested that circular transverse wire rib-roughened absorber plate with e = 1.2 mm and P = 10 mm ensures the accuracy.

6 Conclusions Two-dimensional (CFD)fluent analysis of solar air heater has been performed on different turbulent models having six different sets of Reynolds number ranging from 8551 to 11,149. The following broad conclusions can be drawn from the observations: • Experimental- and (CFD)fluent-based analysis using ANSYS FLUENT 16.0 in order to evaluate the heat transfer characteristics of solar air heater duct. Combined effect of turbulence and its dissipation rate of fluid, which was considered to be responsible in the increase in heat transfer rate. • It is clear from result and discussion that turbulence intensity increases average Nusselt number but simultaneously it will also increase friction factor. • The maximum value of Nusselt number obtained at P/e of 10 for constant e/Dh at a higher Reynolds number of 11,149.

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• The friction factor attains its optimum value at P/e of 10 for constant e/Dh at a lower Reynolds number, 8551. • For the given rib roughness, the THPP value is observed to be 1.18 which is maximum at P/e = 10 with rib height e = 1.2 mm for the studied Reynolds number and hence can be enlisted for heat transfer augmentation.

References 1. Gandhi K, Singh K (2010) Experimental and numerical investigations on flow through wedge shape rib roughened duct. J Inst Eng (India)-MC 90:8–13 2. Yadav AS, Bhagoria JL (2013) Heat transfer and fluid flow analysis of solar air heater: a review of CFD approach. Renew Sustain Energy Rev 23:60–79 3. Hans VS, Saini RP, Saini JS (2009) Performance of artificially roughened solar air heaters a review. Renew Sustain Energy Rev 13:1854–1869 4. Bhushan B, Singh R (2010) A review on methodology of artificial roughness used in duct of solar air heaters. Energy 35:202–212 5. Kumar A, Saini RP, Saini JS (2012) Heat and fluid flow characteristics of roughened solar air heater ducts, a review. Renew Energy 47:77–94 6. Boulemtafes A, Benzaoui A (2014) CFD based analysis of heat transfer enhancement of solar air heater provided with transverse rectangular rib. Energy 7. Kumar A, Layek A (2019) Nusseltt number and fluid flow analysis of solar air heater having transverse circular rib roughness on absorber plate using LCT and computational technique. Therm Sci Eng Prog 14:100398 8. Webb RL, Eckert ERG (1972) Application of rough surfaces to heat exchanger design. Int J Heat Mass Transf 15(9):1647–1658 9. McAdams WH (1942) Heat transmission. McGraw-Hill, New York, NY, UK 10. Fox W, Pritchard P, McDonald A (2010) Introduction to fluid mechanics. John Wiley & Sons, New York, NY, USA

Renewable Energy-Driven Charging Station for Electric Vehicles Rudraksh S. Gupta, Arjun Tyagi, V. V. Tyagi, Y. Anand, A. Sawhney, and S. Anand

Abstract With the depletion of the conventional sources of energy, the transportation sector has been one of the major affected domains. To reduce this effect on transportation sector, electric vehicles (EV) came up but which in turn augmented the load on the prevailing power grid. Therefore, a new domain has to be explored to reduce the transporting dependency on fossil fuel by reducing the encumbrance on the power grid. Renewable energy penetration in the grid system was considered as a sustainable option which can be used as a standalone source to charge EVs and can also be used as an on-grid system to support the grid during peak load time thus working as ancillary service for grid network. Renewable energy can be from any energy source such as solar photovoltaic, wind, etc. depending on its availability. Charging station can be constructed in workplaces with long working hours. The charging station will have features of fast charging and can also use the property of vehicle-to-grid technology (V2G) so as to use power from vehicles when idle to get a more economic benefit tariff-based charging system. The integration renewable energy will be improving the voltage stabilization and power loss in the grid therefore, reducing the overall economic losses. Keywords Charging standards placement Renewable energy





Charging station
Electric vehicle
Optimal

R. S. Gupta
V. V. Tyagi
Y. Anand
S. Anand (&) School of Energy Management, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India A. Tyagi School of Electrical Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India A. Sawhney Department of Physics, GGM Science College, Jammu, Jammu and Kashmir, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_5

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1 Introduction For a long time, civilization has been reliant on the consumption of fossil fuels such as oil, coal for the generation of energy which is required in multiple sectors such as industrial, transportation, household, etc. In the above-stated sectors, the transportation sector is utilizing around 20–25% of fossil fuel for smooth working. With an increase in pollution levels and drastic changes in climate, it became an obligation to pave out ways to counter the problem [1]. It is not surprising that the invention of the electric vehicle was dated long back to the invention of the internal combustion (IC) engines. The IC engines dated back to 1860 which is around 33 years after the invention of electric vehicles (EVs). But the IC engine became more popular due to its lesser cost and easy availability of fuel for consumers as compared to EVs. But today due to the depletion of the conventional sources of energy, the transportation sector is one of the major affected domains. To abbreviate this effect on the transportation sector, electric vehicles (EVs) came up as a resolution but it increased the load on the prevailing power grid. The impact of EVs on the power grid is diverse. Besides, with the uncertainty of the changing patterns of the consumers, it becomes challenging to meet the demand without constant power cuts being observed. The rapid expansion of the use of electric vehicles has led to the development of advanced charging and power delivery stations. Therefore, using EVs, a new domain has to be explored to reduce the transporting dependency on fossil fuel and reducing the encumbrance on the power grid. Moreover, renewable energy penetration in the power grid system is considered as a sustainable option for the future. The reason for the consideration of this is it was part of the green energy initiative, helps in the reduction of greenhouse gas emission, and helps in achieving 17 United Nations Sustainable Development Goals. Renewable energy can be used as a standalone source to charge EVs and can also be used as an on-grid system to support the grid during the peak load time, thus working as an ancillary service for the grid network. The use of renewable energy-based charging station can also improve the voltage stabilization and reduce power loss in the grid. Therefore, reducing the overall economic loss of the system and increasing the stability of the system along with the environmental benefits. Depending on the availability of capital, land, and other technical factors, the charging station can have features of fast charging. It can also be used as vehicle-to-grid technology (V2G) to support the power from vehicles to the grid when EVs are in idle state. To get a more economic benefit tariff-based charging systems are considered. Consideration for EV user preference can also be provided. Electric vehicles charging stations can be built on various construction methods. They usually depend on numerous parameters such as power requirement, multidirectional charging station, the time required for charging, location with the support of renewable energy.

Renewable Energy-Driven Charging Station for Electric …

1.1

59

Electric Vehicle and It’s Working

Electric vehicle as the name suggests works on electric propulsion drives. The main storage unit of an EV is a battery that is used to store the energy required to run an EV. The EV that solely employs the battery as its powering unit is called as battery electric vehicles (BEVs), whereas the EV that employs two or more sources of energy is called plug-in hybrid electric vehicles (PHEVs). This can be applied to any combination, but the main powering unit should be battery supplied. Some of the features of different EVs are discussed in Table 1. The components of EV are different from the conventional ICE vehicles. These components include the battery, electric traction motor, charging port, transmission (electric), DC/DC converter, and on-board charger [2]. The electric vehicle has three main subparts. First is the energy propulsion system, which includes an electronic controller, power converter, electric motor, and a mechanical transmission drive. Another subpart is the energy source system which includes the energy management unit and energy source. The third subpart consists of an auxiliary subsystem which is incorporated with power string and auxiliary power supply for an internal electric utility. For the smooth propulsion of electric vehicles, the accelerator paddle signals the controller for the supply of electric power which is stored in the battery. The battery acts accordingly and supplies the power to the converter which is installed according to the type of electric motor mounted in the EV. This converter further sends the power signal to the electric drives which are connected to the wheels and thus produces a torque that helps in the movement of the vehicle. The drive is usually subdivided into four categories, i.e. series hybrid, parallel hybrid, series–parallel hybrid, and complex hybrid to provide the desired output which can be speed or torque. For the better working of any EV, battery specifications are very important. The battery check is very important because the range travelled by an EV depends on the battery and being one of the costliest installations on an EV needs to be protected and taken care of. Some of the factors have for the optimal working of battery are • • • • • • • •

High specific energy (kWh/kg) and energy density (kWh/L); High specific power (kWh/kg) and power density (kW/L); Fast charging and deep-discharging capabilities; Long cycle and service lives; Self-discharging rate and high-charging efficiency; Maintenance-free; Safety and cost-effectiveness; Environmentally sound and recyclable.

Energy source • Battery • Ultracapacitor

• Battery • Ultracapacitor • ICE

Propulsion type

• Electric motor

• Electric motor • ICE

EV type

BEV

PHEV

Table 1 Characteristics of different types of EV

• • • • Little emission Large range Complex structure Power requirement fulfilled by both oil and battery system

• Zero emission • Zero dependence on oil • Battery dependent range

Features

• Less range • Charging time • Availability of charging stations • Battery and engine optimization • Complex system

Problems

60 R. S. Gupta et al.

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1.2

61

Typical Charging Station

There are different types of charging stations based on the area to be installed and the requirements. (a) The municipality or privately owned parking areas These categories’ structures are fundamentally a parking area with inbuilt charging availability. These stations are fitted with the chargers which can be either be wall-mounted or may be installed on a pillar in front of every parked vehicle. This type of structure is usually found in the workplace or parking lots which can be multi-storey parking also. Such charging stations are installed with slow and medium charging stations. There are multiple variations for the designing of such parking structures which are shown in Figs. 1 and 2. (b) Fast charging stations Fast charging stations are usually seen as a refuelling station on state highways, national highways, and in some cases parking spaces adjacent to pedestrian zone for quick charging as shown in Fig. 3. These charging stations are used for quick refuelling for long travel or emergency charging in some cases. Such types of charging stations are installed with three phases of AC supply or a DC supply. (c) Public vehicle charging stations Such types of charging stations are utilized by public vehicles because the travel time and distance by such vehicles are far greater than that of regular vehicles. Therefore, they need rapid chargers to charge them fast and should be available frequently. These types of charges are made on the bus stops so that they are easily available (Fig. 4).

Fig. 1 Public charging station. Source [3]

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Fig. 2 Private charging station. Source [4]

Fig. 3 Fast charging stations near walkways. Source [5]

2 Components in Charging Stations A new and advanced EVCS consists of a large number of passive and active components that help in charging, fault analysis, and protection purpose. The different types of components used in the EVCS are disused here.

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63

Fig. 4 Public vehicle charging structure. Source [6]

2.1

Smart Transformers

In a traditional system, power is transmitted to long distance via a transmission line and appropriate use of step-up and step-down transformers. The transformer should be able to provide adequate active and reactive power to the system. Generally, all the consumer-side load operates at low voltage and due to the introduction of EVs, the system load will be increased. This low voltage and high-power consumption may overload the system causing huge resistive loss, thus reducing the efficiency of the system. Therefore, additional AC/DC converters are used to supply the charging station, which are capable to supply both AC and DC loads. It is also capable to accept reverse power flow from renewable energy sources. The use of such systems leads to increased efficiency and reduced losses [7].

2.2

Power Socket

A power socket is used for the on-board charging of EVs. There are different types of power sockets based on location, level, and type of charging. The common voltage range in India is 220–240 V with a frequency of 50 Hz. These power sockets are also fitted with technology which helps to communicate between the grid and EVs. This communication system helps in fault detection, state of charge identification, and charging levels. The Indian government has issued a notice for the use of combined charging system (CCS) and CHArge de Move (CHAdeMO) type of charges for fast charging and Bharat AC, Bharat DC chargers for slow and moderate charging.

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Table 2 Types of charging sockets S. No.

Power type

1.

AC supply

Type 1

IEC 62196-2 2.

Type 2

GB/T Part 2

Combined AC and DC supply

CHAdeMO CCS

CCS—J1772 charging inlet is used for the CCS charging port with an addition of two more high-speed charging pins at the bottom. This combination forms CCS charging port. It was developed by the society of automotive engineers (SAE) and is accepted by most automotive manufactures. CHAdeMO: CHAdeMo was developed by the Japanese utility TEPCO. It is the official standard in Japan, and all DC fast chargers in Japan use a CHAdeMO connector. Table 2 shows the different types of power sockets used for the charging of EV [8].

2.3

Charging Techniques

Another component in our inventory is the charging technique. Charging can be done either with wired infrastructure generally referred to as direct contact and wirelessly. With the direct method technology, we have two subsets of power available AC and DC power supply, where AC can be in the form of a single- or three-phase system and DC with a single-phase system. Both these systems are used with a voltage control system to maintain the available voltage at a constant level, and current can be varied accordingly. Mostly, direct contact charging is preferred due to certain factors as low cost, less maintenance, and high-power transfer capability. Like we have different plug types socket in direct contact charging in wireless charging, we have different modes of power transfer wirelessly such as capacitive power transfer, electromagnet field-based transfer, inductive power

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Fig. 5 Closed-loop wireless charging system

Fig. 6 AC-DC converter

transfer, and permanent magnet-based power transfer, whereas in Fig. 5, this a closed-loop wireless charging station that has been explained [7]. In Fig. 6, a simplified rectifier is shown which is utilized for the grid to vehicle charging. This contains a bridge rectifier, filter, and a MOSFET for constant voltage and frequency output [9].

2.4

Charging Pillar

The charging pillar can also be stated as the heart of the charging station. The charging pillar has three major roles which are protection, control, and sense.

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The charging pillar consists of a user interface, electrical distribution, communication system, charging plug, and charging module. The electrical distribution has multiple functions and different components to protect the charging pillar from the output side. The few are as protection from overcurrent and overvoltage, earth protection relay, and current transformer leakage current [10]. Similarly, the charging module is used to protect the output side which is the link between the output of the charging pillar and the input of electric vehicles. The charging module is a device that consists of IGBT power conversion, MOSFETS driver control, rectifiers, GATE driver controls, and thermistor temperature sensor. In another subarray, we have a communication and user interface which is used to communicate with the consumer and cloud storage to provide information to users and service provider for the seamless working of charging station. Figure 7 shows that the charging array is divided into four segments considering the power flow in the system. At the first stage, we have an AC grid input whose function is to protect from overcurrent and voltage or any fault occurring in the AC system. In the second and third stages, we have rectifiers, MOSFET which is used to convert AC to DC. This is also helpful to reduce the ripples in DC and check for any over current or over voltages. All this is done with the help of controllers which are used to transmit data also. In the final stage, we have DC output where the system is checked for any faults if any before delivering power to the EV.

Fig. 7 Charging panel array

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3 Design Aspects/Consideration of Proposed Charging Stations 3.1

Optimal Placement of Charging Station

With the consideration of the installation of an EV charging station, it should have an ability to serve the mass with minimum loss and maximum profit. Therefore, certain aspects need to be considered while installing the EV charging station [11, 12] as, 1. 2. 3. 4. 5.

Power availability Constructability Environmental issues Type of equipment used Accessibility.

3.1.1

Power Availability

While designing a charging station one of the important parameters is power availability. The power source has to be available 24  7 throughout the year to provide uninterrupted service to the customers. Even if we consider the solar energy powered charging station, we still need the availability of power at night to provide the charging facility.

3.1.2

Constructability

The constructability parameters mainly focus on the reduction of power loss, capital investment, and natural hazards. Usually, when installing a charging station, the prime focus is to locate it near the distribution grid, to save the cost of trenching for the cable running in the conduits. This also helps to reduce the power loss in the system and relax the stressed power grid. Another important factor is to minimize the natural hazards, and the charging station should not be in a frequent flooded or high-wind-speed flow region/zone. That may destroy the whole construction too often that it has to be reinstalled again and again. Moreover, the installation should be in a place which should not be near to any high rise building so that solar panels work properly without any hindrance caused due to the shadow of skyscrapers.

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3.1.3

Environmental Issues

The EV charging stations require land which can vary from a small portion to large size depending on the type of charging station. While placing a charging station it has to be kept in attention that none in the environmental regulation is being disrupted.

3.1.4

Type of Equipment Used

As we have mentioned earlier that we have different modes of charging based on the power supply as slow, medium, and fast charging. Slow charging equipment can be installed in the houses or the night/long-hours parking space in a community, whereas if we use a medium charging speed such types of charging stations are installed in the workplace, commercial places, or housing communities where the time spent is more than 30 min. And finally, fast charging stations that are mostly installed on the highways for long travel ranges, a public charging station in the vicinity of a city, or in the industries where large carriers are charged with huge battery capacity.

3.1.5

Accessibility

One of the key parameters is the accessibility of the charging station by a consumer. The charging station should not be in the remote area where a consumer has to specially go outside his route to charge. The installation should not be causing any hindrance to the regular vehicular movement.

3.2

Design Aspects of Charging Station

In designing an EV charging station with support of renewable energy generation, numerous aspects to be kept in mind for the appropriate operation of charging stations. There are many possible arrangements and designs for EV charging stations depending on the layout, land availability, power availability, sunlight availability, etc. The general site plan requirements for EV charging stations are as under. 1. 2. 3. 4. 5. 6.

Type of charging stations; Modes of charging stations; Paved way and barriers; Networks and communications; Presence of sunlight; Access to disabled.

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Types of Charging

(a) Normal power or slow charging stations—these types of charging stations are installed with charger connectors rated between 3 and 7 kW. These are mostly installed in domestic areas and takes a very long time for charging a battery. (b) Medium power or quick charge stations—these types of charging stations are installed with connectors ranging from 7 to 22 kW. They can be used for both private and public EVs. (c) High-power or fast charging stations—these types of charging stations are installed with connector power ranging above 22 kW and takes a very short time to charge a battery. (d) Battery swapping charging stations—this type of service station has a pre-charged battery and just needs to be swapped with the new one [13]. The different type of charging and their comparison is shown in Table 3.

3.2.2

Modes of Charging

There are different modes in which electric vehicle is charged which as labelled as follows [13], (a) Mode 1—This mode depicts the slow charging connection from the household sockets. There needs to be a separate installation of the circuit breaker and earthing system to protect it from overload and fault current, respectively. (b) Mode 2—This mode represents the slow charging but with inbuilt safety features within the cable. This solution is more expensive than the Mode-1. (c) Mode 3—This depicts an overall system with all safety features and a dedicated circuit in the charging installation. This mode also has a load shedding technique to help operate household appliances perfectly.

Table 3 Types of charging S. No.

Charging method

Connection

Rated power

Max. current

Connection type

1

Normal power Medium power High power High power Battery swapping

1-phase AC connection 1- or 3-phase AC connection 3-phase AC connection DC connection

3–7 KW

10–16

Domestic

7–22 KW

16–32

Greater than 22 KW Greater than 22 KW –

Greater than 32 Greater than 32 –

Domestic and public Public

2 3 4 5

–

Public Public

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(d) Mode 4—This mode is installed with AC-to-DC converter in the charging installation to help in the fast charging of the EV with all inbuilt safety functions.

3.2.3

Paved Way and Barrier Protection

The paved way is essential in large charging stations to help the EV consumer to park their vehicles in the designated slots depending on their requirements. Whereas barrier protection is necessary for EV chargers to protect it from unwanted damages caused due to over running of cars in the charging pillar in the slots.

3.2.4

Networks and Communications

Networks and communication are essential parameters for any EV charging station. In most EVCS, we can find an installation of an advanced metering system that is linked with an online network that tracks the usage of customer, slot availability, usage pattern which in turn helps in the management of electric load. This type of technology is useful in location any vacant charging station nearby by regulating the information available in the cloud storage. Any consumer can connect to it using Wi-Fi, Ethernet, or cellular networks. This helps consumers to charge their vehicles according to their convenience [11].

3.2.5

Presence of Sunlight

While designing renewable solar energy powered EVCS, sunlight should be available in abundance for the maximum time during the day time. The panels should be connected and face south in the northern hemisphere and vice versa. The latitude of the location should be set as an optimal tilt angle for the solar panel. The output can be utilized as both AC and DC depending on the type of charging station and modes of charging in it. Any kind of nearby shadow should be avoided.

3.2.6

Access to Disable

This parameter is usually considered to provide the charging facility for people with disabilities. It is essential to construct spaces and paths that are safe and accessible to drivers of all physical abilities. Accessibility strategies should seek to limit tripping threats and minimize liability trepidations.

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4 Integration of Renewable Energy Source with an EV Charging Station The power generated from large power plants needs to travel a long distance through transmission lines which require quality infrastructure and extended maintenance. Moreover, chances of power disruption are quite frequent in such cases due to any reason such as a fault in the transmission line, internal damage, overloading, etc. Furthermore, the increasing load increased the burden on the transmission system. But in addition to the conventional power supply, there is a range of small-scale renewable energy sources such as solar energy, wind energy, flywheel, geothermal, biomass, etc. These small-scale renewable energy sources can be used near to end-user terminals as alternatives for conventional power supply. Among all renewable energy sources solar and wind energy are preferred due to their availability and advancement in generation technology. Both of the above-stated sources are discussed in detail below.

4.1

Solar Energy

The solar photovoltaic panel is a flat surface structure embedded with solar cell arrays which are used to convert light energy into electrical energy. Solar energy is widely used due to its ease of availability. The total amount of solar radiation on the outer periphery of the earth’s surface is around 1300 W/m2. But due to diffusion and reflection from the clouds, we receive around 1000 W/m2. This condition is called a standard testing condition. The conversion efficiency of these panels is ranged from 9 to 24% depending on the type of solar panel used. When installing a solar plant on the roof of a charging station a few considerations have to be taken into account. The tilt angle of the panel should be equal to the latitude of the location. The azimuth angle should be south-facing for the northern hemisphere and vice versa. A minimum amount of shadow should be present there and for this a shadow test on 21 December needs to be performed [14]. An inverter can be integrated on the site depending on the charging station output, and it could be installed with a net metering system for the consumption of electricity. The total power generated from a solar panel can be calculated with the formula presented in Eq. 1. PPV

  
 GT  1  c  Tj  25 ¼ PPV;STC   NPVs  NPVp 1000 Tj ¼ Tamb þ

GT  ðNOct  20Þ 800

ð1Þ ð2Þ

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where PPV = Solar PV array output. Tj = Temperature of solar panel. Tamb = Ambient temperature. GT = Solar irradiance at STC in W/m2. PPV,STC = Rated power output of single array at MPP. c = Temperature parameter at MPP. NPVs = Series PV string. NPVp = Parallel PV array. Considering the present technology in a 200 m2 area and 375 W panel, a 20–26 kW system can be installed. Some advantages of considering solar energy are the availability of energy even when grid supply is off, less carbon emission, and support green energy initiative. This comes up with few challenges also such as it requires frequent cleaning in polluted areas, regular maintenance, low conversion efficiency, and high initial cost.

4.2

Wind Energy

Wind energy is another source of renewable energy that extracts electrical energy with the help of wind turbines and generators. We have two types of wind turbines to extract the power from wind, namely horizontal axis wind turbine (HAWT) and vertical axis wind turbine (VAWT). For public areas, VWAT turbines are much more suitable because of their less area requirement. Wind turbines need to be installed on a high rooftop to have access to high wind speed because the wind speed is quite constant at heights. Savonius turbines are mostly used for the residential area because in HWAT risk is very high in terms of any damage caused. The maximum power generated by VWAT is given by Eq. 3 [15]. 16 1 q:d:h:v3 ð3Þ 27 2 where Pmax is the maximum power, q is the density of air (kg/m3), d is the diameter of rotor (m), h is the height of rotor (m), and v is wind velocity (m/s). The output received in this is only AC so a rectifier is needed if it is used in DC charging station. Pmax ¼

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5 Significance of Use of EVs with Renewable Energy The initiative of any research and study is to provide improved technology and ease of living while keeping the environmental impacts in check. The use of EV has multiple significance in terms of environment, cost benefits, health impacts, economic development of the nation. These parameters are discussed below [16].

5.1

Conventional Fuel Saving

One of the main aims to shift to EV from ICE vehicles was the depletion of fossil fuel. With the rapid increase in power demand and vehicles on roads the consumption of fossil fuel reached its alarming stage. Considering all the options transport sector was considered to have a technology advancement and shift to EVs to reduce the dependency on fossil fuel to cater the transportation needs. However, EVs are powered by electricity that is again generated by conventional methods that used again fossil fuel. Therefore, it is required to shift the electricity generation to renewable energy resources and to construct renewable energy-based EV charging stations.

5.2

Environmental Protection and Reduction of Carbon Emissions

With the use of ICE vehicles, it has seen that a large chunk of CO2 gas is released which leads to multiple environmental issues such as climate change and global warming. This climate change brings many disasters with it such as an increase in water level, a rise in atmospheric temperature, and extinction of flora and fauna. Therefore, with the shift of the transportation sector to EVs, which constitutes about 25% of total fossil fuel consumption saw an opportunity to reduce these effects at a considerable level. This shifts with the integration of renewable energy charging station, further reduces carbon emissions around the globe and protects the environment. Taking an example of driving a Nissan Leaf (EV) instead of a similar-powered Honda Civic on gasoline will reduce carbon emissions by 4096 lb per year [17].

5.3

Health Impacts

According to the environmental protection agency burring of fuel in ICE, vehicles produce very fine particles that are very harmful to the human body. Some of the fine particles are SOx, NOx. They can cause early death, causes cardiovascular

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problem, respiratory problems (asthma, inflammation). With the use of EV and renewable energy, the problem of emission of fine particles is ruled out, whereas with the use of renewable the particles producing in powerplants are also reduced to a much greater extent.

5.4

EV as Ancillary Service to Grid

It has been seen with an increase in power demand and its irregular demand and supply cause power outages in the grid. The EVs can work as an external energy storage device when not in use. EVs can store energy during off-peak hours and provide backup during peak load hours. This technology is called V2G technology. This technique not only helps to maintain the grid stability but also help users to generate passive income when EV is not in use.

5.5

Economic Development

Indian being a developing nation needs lots of economic support for progress. India is not considered an oil-rich country and has to import most of the fuel from Arabic nations for transportation and other industrial purposes. With the shift to EVs, this import cost will be reduced to a much greater extent and can be used within the country to develop infrastructure for the betterment of the nation.

6 Tariff-Based Charging and Discharging of EVs With a transference to newer technology, there was seen unwillingness among the masses due to the high initial cost and maintenance of the vehicles. To intensify the adoption of EVs, people were provided with some economic benefits. They were able to charge the vehicles based on tariff-based charging mechanism where they can charge their vehicles at low-cost tariff during the off-peak hours as compared to higher rated at peak load hours. This not only helped to maintain a constant load in the grid at all times but also reduces the transmission losses during peak hours [18]. Extending the benefits, people are permitted to use the V2G technology of their electric vehicles. This technology involves parked vehicles to provide generation service to the grid. In simple words, they could provide the surplus power in there EVs battery to the grid during peak hours by connecting them to the live charging system. This technique helps them to get paid according to the tariff system. It has been studied in [19] that most of the EVs are idle 95% times. V2G technology not only helps an individual but also the grid system in terms of voltage stability, frequency stability, and loss reduction. Economic benefits can be seen as an attraction for both the individual and power Distributor.

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7 EV Charging Standards Whenever operating an electrical or mechanical appliance, there is a certain organization that incorporates the standardization to make them adapt to the prevailing system with ease and there is no problem in working on that equipment. Some important safety standards by various organizations all around the world are given in Table 4 [20, 21].

Table 4 Safety standards S. No.

Organization

Standard code

Standard description

1

International Electro-mechanical Commission (IEC)

1. 2. 3. 4. 5. 6. 7. 8. 9.

2

National Electric Codes (NEC)

1. 625 2. 626

3

Institute of Electrical and Electronic Engineers (IEEE)

1. P1809 2. P2100 3. P2100.1

4

International Organization for Standardization Society for Automobile Engineers (SAE)

1. ISO 6469-2

1. Electrical installation and protection 2. Electrical and electronic equipment 3. Plugs and socket-outlets 4. Safety protection against overcurrent 5. Low-voltage installation earthing arrangement 6. The integration of renewable energy in the grid 7. Different modes of charging 8. Vehicle connectors and cable assemblies 9. Part-1 General requirements of WPT 10. System for EV 1. EV charging system and safety 2. EV parking space characteristics 1. Electric transport infrastructure 2. Wireless power and charging setup 3. Wireless power and charging systems 1. EV safety specifications

5

TC 64 TC 22 60309-1 60364-4 60364-5 61850-7 61851-1 62196-1 TC69

1. J2847/6 2. UL2750 3. J2954

1. Wireless charging communication 2. Between PHEV and the utility grid 3. Wireless charging safety 4. Wireless charging frequencies

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8 EV Adoption Challenges in India Although EVs have various benefits. It also has few issues which work as a hindrance for its adoption with ease in a new era in the transportation sector. Those factors are explained below in detail.

8.1

Limited Range

For electric vehicles, the battery is the main source of power on which it runs. Being rechargeable, the battery gets depleted with time. At present, though the battery has high storage capacity, they are very expensive also and cannot be used extensively, whereas the low-cost battery is not capable to provide a long-range for travel thus causing range anxiety in individuals. The range of EV also depends on the speed with which it travels, the terrain it is travelling in, and energy consumption during working on EV (air conditioner, lighting). Thus, the battery discharge is also different thus causing the problem in its adoption.

8.2

Long Charging Period

EV uses electric energy as a power source to run. For this, the battery requires frequent charging which depends on different factors such as different modes and different levels of charging. These methods constitute one factor that is the time taken by EV. With present technology and charging infrastructure, not all the charging stations have fast charging capability. Moreover, some of the charging stations are not large enough to cater to the requirement of EV, thus have a long wait time problem also. This wait time leads to customer inconvenience. At present, internal combustion engine (ICE) vehicles are having lesser refilling times, whereas EV takes around 15–20 min with the fastest technology that may further lead to the waiting time.

8.3

Social Acceptance

With the upcoming technology and new trends in the transportation sector, there has been no doubt that resistance has been seen in its adoption. The main reason constituting it is the change in basic hobbit regarding the travel pattern and refilling which are not easy to adopt if one is using ICE vehicles for a long time.

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Insufficient Charging Infrastructure

It has been seen that there has been a steady increase in the charging infrastructure, but it is not sufficient to cater to the rapidly increased demand for EV vehicles. Moreover, with new technology, it has been seen that more capital is required to construct or renovate existing refilling stations to an EV charging station.

8.5

High Initial Cost

Considering the initial cost of ICE vehicles, EVs are far more expensive than ICE vehicles. The main reason for that is the battery which is being used. Mostly, lithium-ion or nickel-metal batteries are used which are very expensive. This battery system constitutes a major investment cost in a vehicle, thus making EV expensive. Though the government has taken initiative in the research area of battery cost reduction, range extension, and some incentives are also provided to bring more interest in the adoption of EVs. Such as EVs in India are exempted from any road tax charges.

9 Conclusion The electric power system is experiencing an intense change, driven by the amassed penetration of modern transportation systems and renewable energy resources. This is due to several factors such as reducing carbon emissions and having a sustainable life. The electrical vehicles are a vital solution to reduce the significant amount of dependency on fossil fuels. They also use two-way flows of electricity and information to create a broadly distributed automated energy distribution network. Though today, there has been a very slow and steady penetration of EV in the grid system. But, as per the policies and environmental effects are growing too fast, in the near future the use of EVs will be huge. Therefore, this increased load required careful attention. This chapter discusses various types of charging stations being implemented in the prevailing system.

References 1. Global EV Outlook 2020. In: Global EV Outlook 2020. https://doi.org/10.1787/d394399e-en 2. Chan CC (2002) The state of the art of electric and hybrid vehicles. Proc IEEE 90(2):247– 275. https://doi.org/10.1109/5.989873

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3. MERCOM, Charging Station. [Online]. Available https://mercomindia.com/noida-metrofloats-tender-ev-charging-stations/ 4. Fraunhofer-Gesellschaft, Solar vehicle charging at home. [Online]. Available https://phys.org/ news/2015-11-solar-vehicle-home.html 5. Duran-Ortiz M, Nissan Leaf, Ford C-Max Energi and Honda Fit EV at a public charging station in front of San Francisco City Hall. [Online]. Available https://www.flickr.com/ photos/30998987@N03/17267948315 6. Rédaction L, Bus électriques : deux stations de charge ultra-rapide ABB pour Göteborg. [Online]. Available https://www.breezcar.com/actualites/article/commande-goteborg-stationscharge-450-kw-bus-electriques-1217 7. Lu J, Hossain J (2015) Vehicle-to-grid: linking electric vehicles to the smart grid. Scopus 8. Enel X, The different EV charging connector types. [Online]. Available https://evcharging. enelx.com/eu/about/news/blog/552-ev-charging-connector-types 9. Larminie J, Lowry J (2003) Electric vehicle technology explained 10. Karner D, Garetson T, Francfort J (2016) EV charging infrastructure roadmap, pp 1–19. [Online]. Available http://avt.inl.gov 11. WXY Architecture + Urban Design (2012) Siting and design guidelines for electric vehicle supply equipment. Nov, pp 1–34. [Online]. Available http://www.transportationandclimate. org/sites/default/files/EV_Siting_and_Design_Guidelines.pdf 12. U.S. Department of Energy (2015) Electric vehicle charging station locations. Altern Fuel Data Cent 105(June):1–5. [Online]. Available http://www.afdc.energy.gov/fuels/electricity_ locations.html 13. Falvo MC, Sbordone D, Bayram IS, Devetsikiotis M (2014) EV charging stations and modes: international standards. In: 2014 International symposium on power electronics, electrical drives, automation and motion, SPEEDAM 2014, pp 1134–1139. https://doi.org/10.1109/ speedam.2014.6872107 14. Wakter S (2014) A novel shade analysis technique for solar photovoltaic systems, p 32. [Online]. Available https://www.diva-portal.org/smash/get/diva2:735243/FULLTEXT01.pdf 15. Menet J-LJ, Bourabaa N, Bouraba N (2004) Increase in the Savonius rotors efficiency via a parametric investigation. EWEA—2004 Eur Wind Energy Conf April. [Online]. Available http://www.wrapwind.com/download/vawt/23_1400_jeanlucmenet_01.pdf 16. Malmgren I (2016) Quantifying the societal benefits of electric vehicles. World Electr Veh J 8 (4):986–997. https://doi.org/10.3390/wevj8040996 17. [email protected]. [Online]. Available https://nyserda.wattplan.com/ 18. Turton H, Moura F (2008) Vehicle-to-grid systems for sustainable development: an integrated energy analysis. Technol Forecast Soc Change 75(8):1091–1108. https://doi.org/10.1016/j. techfore.2007.11.013 19. Ehsani M, Falahi M, Lotfifard S (2012) Vehicle to grid services: potential and applications. Energies 5(10):4076–4090. https://doi.org/10.3390/en5104076 20. Automotive Industry Standards Committee AISC (2016) AIS 138-1: electric vehicle conductive AC charging system. 138(Feb) 21. Automotive Industry Standards Committee (AISC) (2018) Electric vehicle conductive DC charging system (AIS-138). 138(Jan):1–142

Review on Optoelectronic Response of Emerging Solar Photovoltaic Materials Karina Khan, Aditi Gaur, Kamal Nayan Sharma, Amit Soni, and Jagrati Sahariya

Abstract Solar photovoltaic (SPV) technology is established as the most reliable, eco-friendly, and inexhaustible leading renewable which is adopted to harvest solar energy into electrical energy. Among all hierarchical generations of solar cells, wide band gap chalcopyrite semiconductors are reported with good conversion efficiencies and hence are reasonably preferred. Present chapter reveals the detailed investigation on structural, electronic, and optical response for promising chalcopyrites semiconducting materials ABX2 (A = Mg, Zn; B = Si, Ge, Sn; X = P, N, As) and inorganic lead-free perovskite ASnX3 (A = Cs, Rb, K; X = Cl, Br) compounds. These materials are reported as cheap, non-toxic, thermally stable, and reported to have nonlinear optical behavior. Promising optoelectronic response for computed series affirms their effective utilization in photovoltaic and other leading optoelectronic applications. Keywords Photovoltaic material


Solar energy
Chlcopyrites
Perovskite

1 Introduction The rapid growth of the human population has become a major concern of the world as natural resources are being consumed at a very intense rate. Also, the requisition of the energy is increasing with the expansion of the population. The K. Khan Department of Physics, Manipal University Jaipur, Jaipur, Rajasthan 303007, India A. Gaur
A. Soni (&) Department of Electrical Engineering, Manipal University Jaipur, Jaipur, Rajasthan 303007, India K. N. Sharma Amity School of Applied Sciences, Amity University, Gurugram, Haryana 122413, India J. Sahariya (&) Department of Physics, National Institute of Technology, Srinagar (Garhwal), Uttarakhand 246174, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_6

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classification of the energy is done broadly into two groups one is renewable energy sources and another one is non-renewable energy resources. But currently, world’s nation demand of energy is met mostly through non-renewable energy resources, i.e., fossil fuels which are the hydrocarbons present in the earth’s crust such as natural gases, coal, petroleum, tar sands, bitumen, heavy oil, and oil shales. All these substitutes of the fossil fuels contain mainly carbon as they were produced by the long-term geological process inside the earth’s crust. Their combustion is possible in the presence of oxygen only and this produces a huge amount of energy which are being utilized for many practical applications such as generating electricity, heating, transportation, and many more. But these fossil fuels are exhaustible in nature, i.e., it will take 1000 of years to reform and with the excess use they are depleting rapidly. Further, the combustion of fossil fuels in the environment emits harmful gases including the oxides of nitrogen, sulfur, and carbon which produces harmful residues along with them. These substances are detrimental for health of living beings and for environmental resources like air, land, and water. The excessive use of fossil fuels increases the greenhouse gases that cause global warming which results in the depletion of ozone layer [1–4]. a. Renewable Energy The energy becomes the most serious issue for society because the energy plays vital role in the development for every nation [1, 5]. The well-known limitations and drawbacks of conventional energy sources have forced the society to search for the alternative energy sources. In this context, there is a need of energy source which are capable of completing the need of the present era as well as will remain for the coming generations, and this kind of growth is termed as the sustainable development. Although it will take long time to achieve the sustainable development to palm off with the hazardous situation by which environment is suffering [6], the energy which is replenished by the nature itself and unlimited is known as the renewable energy. The renewable energy is clean source of energy and has the capability to regenerate again and again in a very less interval of time. This energy can be produced directly and indirectly from the sun as well as through the natural movement also. The energy which is renewed directly from the sun includes photoelectrical, photochemical, and heat energy while the wind energy, hydro-power energy, and biomass energy are renewed indirectly via sun. The geothermal and tidal energy are the result of natural movements. The different form of renewable energy and their application are presented in Fig. 1. The renewable energy is the benison for the earth as the innovation in these resources are narrow down the costliness as it leads toward the clean future for the environment because its minimize the carbon emission in the environment. For the betterment of global community, the renewable energy plays the crucial role, as it does not produce any harmful gases and residues and hence have no direct or indirect negative impact on environment [7, 8].

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Some Applications

Fig. 1 Different energies sources and some of their applications [7]

b. Solar Energy and Solar Cells As we all know that the sun is most important for the existence of the universe. All the planets remain in their orbit due to the immense power gravity of the sun. The interaction of earth with the sun is responsible for various seasons, current produced in oceans, climate, etc. That is why, among all the available renewable energy resources, the solar energy is considered as the most preferable source for energy. The renewable sources can produce 3000 times more energy than the conventional resources, and out of all the renewable energy, the major part is covered by the solar energy. A schematic diagram, showing the capacity of various renewable sources to generate the energy, is presented in Fig. 2 for clear understanding. The sunlight is treated as the cleanest and safest fuel for generating power. The sunlight is evenly disseminated over the surface of the earth. The energy received through the sunlight is known as the solar energy. This energy is free and abundant in nature which produces least harm to environment and ecological system. The energy received by the sun in 60 min is more than the energy utilized by the people of all over the world in the whole year [9–12]. Hence, the solar energy has vast potential to meet the world energy demand for future. Since the solar energy is

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Solar Energy 2850 Ɵmes to the convenƟonal energy Wind Energy 200 times to the conventional energy Biomass 15 times to the conventional energy Geothermal 5 times to the conventional energy Marine 2 times to the conventional energy Hydro 2 times to the conventional energy

Fig. 2 Resources of energy of all over the world [8]

received in dispersed and discontinuous form, it cannot be used as it is for the generation of energy. Therefore, the conversion and storage of solar power are essential to replace the conventional fuels by solar energy [1]. To convert the solar energy into the electrical energy, solar cells are used. Solar cell works on the principle of photovoltaic effect, according to which the light in the form of photon falls on the material to excite its electrons. Some part of light gets reflected and some part of it gets absorbed by the electron which leads to the generation of electron hole pair. These generated electron hole pairs are separated in the presence of an electric field. This results in the flow of photocurrent in the external circuit, if an electric load is connected with circuit as shown in Fig. 3. The major concern in the conversion of solar to electrical energy is the efficiency and cost of material. This has initiated the investigations of the cost-effective, eco-friendly materials which can provide maximum conversion efficiency even at the high temperature. As the temperature on the earth varies in a vast range; therefore, the researchers are also focused to investigate the solar cell materials that can have capability to sustain in large temperature ranges [13–15]. On the basis of efficiency, cost, toxicity, and materials, solar cells are divided in a different generation. Monocrystalline silicon, polycrystalline silicon, amorphous silicon, CdTe, Cu(InGa)Se2, dye synthesized, organic and inorganic perovskites are the common materials used in various generation of solar cells [16]. Recently, a lot of research is

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Fig. 3 Systematic for solar cell when it is connected with an electrical load

going on to improve the efficiency of the solar cells already commercially and to get the less expensive solar cells. In this chapter, we focus on the density functional theory (DFT)-based investigations of structural, electronic, and optical properties of some inorganic tin halide perovskites and chalcopyrites solar cells. c. Density Functional Theory To determine the structural, electronic, optical, and other properties of any system, it is required to solve the Schrodinger equation to obtain the energy as well as position of the electron with respect to space and time [17]. Schrodinger equation can be easily solved for the one electron system, but it is difficult to solve this equation for many particle systems. For the real problems of solids, Schrodinger equation had been reformulated by the Hohenburg and Kohn using the well-known density functional theory (DFT). The DFT is used to calculate the approximate solution of the behavior of the electrons of materials. In this theory, all the ground state properties of a system are obtained by minimizing the energy. This is done by using the different exchange correlation functional which is to be approximated for obtaining the accuracy in the DFT calculations [18]. The DFT is useful in the field of chemistry, solid-state physics, and material science as the Hartee–Fock approximation is bit hassle for solving the Schrodinger equation for the materials possess zero band gap. Therefore, by adopting DFT, it can become easy to sort out the material’s properties with one parameter exchange correlational functional. The DFT is a technique in which there is low computational cost as well as yield accuracy in the results. The DFT becomes a precedent in the field of computational materials science with the help of which a material scientist is able to compute all

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the ground state properties of any material along with this it offers the researchers to predicting new materials for their further investigation purposes [19, 20].

2 Perovskite Solar Cell The perovskite solar cells are now globally accepted low-cost solar cells with their eco-friendly nature. The perovskite materials are efficient to convert the sunlight into the electrical form. These solar cells are treated as a better option over the conventional solar cells as they generate better output in the diverse climatic condition [11]. The organic and inorganic halide perovskite with general crystal structure formula ABX3 (where A = monovalent cation; B = divalent metal, and X = halides anion) have been reported with the excellent performance in optoelectronic devices. Several theoretical and experimental studies have been reported on these perovskites to show their potential utilization in photovoltaic applications [11, 21–25]. The power conversion efficiency (PCE) up to 23.6% has been achieved with the lead-based perovskites and hence are frequently used in many optoelectronic applications such as light emitting diodes (LED), photovoltaic materials, photosensors, lasers, and radiation detector. But the major drawbacks with these perovskites are the toxic nature of lead which has negative impact on the mental and physical development of human being. In addition, the toxic nature of lead makes it hazardous for the environment also. This has demanded the replacement of Pb with an environmental-friendly material such as Sn. The organic lead-free halide perovskite ASnX3 where A belongs to organic group like phenylethylammonium/ formamidinium has been also explored at a good level, as they have better efficiency and are frequently used in the dye-sensitize solar cell, photo-luminescence devices, photovoltaic devices, and infrared detection applications. The ASnX3 perovskite, with rare earth and alkaline earth metal at A-site, is also well explored because of their potential applications in sustainable energy development. The solar cells with these compounds are preferable due to good efficiency and low cost [26–29]. The lead-free cesium tin halide perovskite, CsSnX3 (X = Cl, Br, I), have attracted the researchers due to their striking properties like adjustable bandgap, high absorption coefficient, high charge carrier mobility, and great dielectric properties. All the candidates of this group also exhibit the extraordinary physical and chemical combination which includes fast ionic transport and high quantum efficiency. The synthesis root of CsSnX3 (X = Cl, Br, I) is quite simple as it follows the low temperature route, unlike to the other organic perovskite and lead-based CsPbX3 which are converted into the non-perovskite shortly due to their instability. Because of extreme potential of CsSnX3 (X = Cl, Br, I) in the optoelectronic applications, these compounds have been studied thoroughly using various theoretical methods and are also synthesized using different synthesis route [28, 30–35]. Further, lead-free tin halide perovskite, ASnX3 (A = Rb and K), are still not explored so much except some theoretical analysis. The available theoretical data reveals these compounds are also promising candidates for photovoltaic application

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as their band gaps lie in the range of solar absorber material. The metal tin halide perovskite, ASnX3 (A = Cs, Rb, K; X = Cl, Br), are also reported as the thermodynamically stable compounds [22–24]. a. Structural Properties The CsSnX3 (X = Cl, Br, I) compounds exits in the cubic, tetragonal, monoclinic, and orthorhombic structures at different temperatures. All these structure of the CsSnX3 (X = Cl, Br, I) have been experimentally synthesized by different techniques. Theoretical investigations for these structures have also been reported using DFT. At room temperature, CsSnBr3 crystallizes in cubic structure, whereas CsSnCl3 is found to be stable in monoclinic phase at room temperature. Although the cubic structures of the cesium, tin halide perovskite (CsSnX3) have been explored more as comparative to the other structure. The lattice constant of the CsSnX3 completely depends upon the atomic size of halide ions. The lattice constant of CsSnX3 decreases when Br subrogated the Cl. This happens due to the larger atomic size of Br in comparison with Cl [28, 30–35]. The structural properties of metal tin halide perovskite ASnX3 (A = Rb, K; X = Cl, Br) have been investigated theoretically using various exchange and correlation potential within the framework of density functional theory. ASnX3 compounds crystallizes in various structures, but orthorhombic and cubic phases are most stable at ambient temperature and pressure. The properties and applications of these perovskite are diverse for different phase. The cubic ASnX3 compounds, having the space group 221 (Pm3m), remain undistorted at ambient conditions [23–25, 36]. The crystal structure for cubic perovskite, ASnX3 (A = Cs, Rb, K; X = Cl, Br, I), is depicted in Fig. 4. The orthorhombic RbSnX3 (X = Br, I) compounds with space group 62 (Pnma) have been reported as the ferromagnetic and photovoltaic in nature [24, 25]. The lattice parameters for orthorhombic and cubic phase of RbSnCl3 and RbSnBr3 have been calculated by different computational codes and are collated in Table 1 [37–39].

Cs/Rb/K Sn Cl/Br

Fig. 4 Crystal structure for cubic ASnX3 (A = Cs, Rb, K; X = Cl, Br)

86 Table 1 Reported lattice constant of metal tin halide perovskite ASnX3 (A = Cs, Rb, K; X = Cl, Br) in Å

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Structure

Lattice constant a b

Orthorhombic 10.328a 17.677a CsSnCl3 CsSnBr3 Orthorhombic 8.2149a 11.6321a RbSnCl3 Orthorhombic 3.32c 3.34c b RbSnBr3 Orthorhombic 8.38 11.55b a CsSnCl3 Cubic 5.56 5.56a a CsSnBr3 Cubic 5.795 5.795a d RbSnCl3 Cubic 5.596 5.596d RbSnBr3 Cubic 5.863d 5.863d b c d a Ref. [34], Ref. [37], Ref. [38], Ref. [39]

c 4.765a 8.1844a 14.65c 7.98b 5.56a 5.795a 5.596d 5.863d

b. Electronic and Optical Properties All the metal tin halide perovskite ASnX3 (A = Cs, Rb, K; X = Cl, Br) compounds are the best alternative to the lead halide perovskite compounds as their band gaps are suitable for the solar cell material and also these are non-toxic unlike lead halide perovskite compounds [24]. It is worth mentioning that the electronic properties of any material, which generally includes the energy band gap, band structure, and density of states, play a very important role in determining the nature of the materials and their utilizations in various applications. The electronic structure for CsSnX3 (X = Cl, Br) has been calculated experimentally and theoretically and it has been observed that all the phases of CsSnX3 (X = Cl, Br) have direct band gap nature as their valence band maximum and conduction band minimum both lies at same momentum points. The band gaps of CsSnX3 (X = Cl, Br) lie in the visible range of electromagnetic spectrum and hence are suitable for the photovoltaic applications [28, 30–35]. The electronic properties of the ASnX3 (A = Rb, K; X = Cl, Br) have been examined for both orthorhombic and cubic crystal structure in terms of energy bands and density of states within framework of DFT by various workers using the various theoretical methodologies [23–25, 36, 37, 40]. In all the metal tin halide perovskite, ASnX3 (A = Cs, Rb, K; X = Cl, Br) reduction in band gap of compound is observed when Cl is replaced by Br. This is due to the fact that as the atomic number of halides increase it causes the increment in the number of charge carriers in valence and conduction band which shift the band toward the Fermi energy level [28, 30–35]. The reported energy band gaps of ASnX3 (A = Cs, Rb, K; X = Cl, Br) compounds are presented in Fig. 5. The reported optical properties of ASnX3 (A = Rb, K; X = Cl, Br) have shown the potential of these compounds in photovoltaic applications. The absorption coefficient explains the optical activity of materials when the photon of energy greater than the band gap of material is incident in it [41, 42]. The ABX3 perovskites are reported as high absorbance coefficient materials [25]. The optical properties of tetragonal and orthorhombic CsSnX3 (X = Cl, Br) show the anisotropic behavior while their cubic structure show the isotropic behavior [34]. The absorption of the orthorhombic RbSnCl3 posses the anisotropic nature and shows

Band Gap (eV)

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3.99

2.9 1.92

1.33 1.26

CsSnCl3

2.01 1.43

1.37

1.1

CsSnBr3 RbSnCl3 Samples

RbSnBr3

Orthorhombic

Cubic

0 KSnCl3

Fig. 5 Earlier reported band gap for cubic and orthorhombic ASnX3 (A = Cs, Rb, K; X = Cl, Br) [5]

the good absorbance for the wide range of electromagnetic spectrum, i.e., visible to UV range [38]. It is quoted that RbSnBr3 with 0.57 eV has a better photonic absorbance [43]. The study performed on the ASnX3 (A = Cs, Rb, K; X = Cl, Br) till now proved that these compounds have good potential in photovoltaic applications [6].

3 Chalcopyrites The chalcopyrites are the most copious resource of the copper globally as it can vastly found in the solid waste. CuFeS2, which is the structural analog of the sphalerite (ZnS), is considered as the conventional chalcopyrite. There are so many minerals exist in the chalcopyrite such as iron, sulfur, and zinc. The chalcopyrite having the semiconducting nature belongs to the I-III-VI2 and II-IV-V2 groups of the periodic table. Most of these chalcopyrites crystallizes in tetragonal structure with the space group I42d. Among all copper sulfides, the chalcopyrites have the maximum stability due to its structural configuration. It provides the cost evenness between the photovoltaic technology and convention energy supplements. Till now, only copper indium gallium selenide solar cells (CIGS) and CdTe have been arisen in the market for providing solar energy conversion module [44–46]. It has been reported that I-III-VI2 and II-IV-V2 chalcopyrite compounds exhibit all the essential requirements to become a promising candidate for the solar materials. The compounds of these groups are utilized in many electrical and optical applications such as light emitting diode and photovoltaic devices. Further, properties like non-toxicity, hardness, nonlinear optical parameters, mechanical and optical thermal stability of II-IV-V2 group compound make these more promising for optoelectronic in comparison with I-III-V2 compounds. All these features of compounds

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of II-IV-V2 make them attractive for the researchers in photovoltaic applications. The chalcopyrites of II-IV-V2 have similar structure to that of III-V group’s semiconductors [47–49]. Herein, we report the structural, electronic, and optical properties of some II-IV-V2 (II—Zn, Mg, IV—Si, Ge, Sn; V = P, N, As) chalcopyrites compounds. a. Structural Properties The ternary chalcopyrites of the group II-IV-V2 are the stable compounds and most of them crystallizes in the body centered tetragonal structure. Although, in case of different cationic arrangement, these compounds can also exist in simple orthorhombic structure [50]. There are several experimental and theoretical investigations available on the structural properties of these compounds which shows that II-IV-V2 chalcopyrite compounds are the crystal analogous of GaAs and silicon substrate. The tetragonal crystal structure of II-IV-V2 compounds is formed by combining the two cubic zinc blende structures. The crystal structure for II-IV-V2 chalcopyrites is shown in Fig. 6. Thus, their crystal structure is like the superlattice of zinc blende compound [51]. Due to the resemblance in crystal structure of the ternary II-IV-V2 with binary zinc blende compound, their physical properties are also similar. The reported experimental and theoretical structural parameters of the II-IV-V2 (II—Zn, Mg, IV—Si, Ge, Sn; V = P, N, As) are listed in Tables 2 and 3. Further from Tables 2 and 3, it is observed that the ratio of c and a is approximately equals to 2. The lattice constant increases as we move toward the P to As but decreases when Mg is replaced by Zn [52].

Zn/Mg Si/ Ge/ Sn P/ N/ As

Fig. 6 Body centered tetragonal crystal structure of chalcopyrite

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Table 2 Experimental and theoretical lattice constant of ZnBX2 (B = Si, Ge, Sn; X = P, N, As) in Å Samples

Theoretical a b

Experimental a b

c

c

5.30– 5.30– 10.40– 5.39– 5.39– 10.40– ZnSiP2 (tetragonal) 5.45a−e 5.45a−e 10.5a−e 5.40a−e 5.40a−e 10.43a−e 5.46– ZnGeP2 5.46– 10.70– 5.465– 5.465– 10.70– (tetragonal) 5.51d−h 5.51d−h 10.87d−h 5.463f−g 5.463f−g 10.71f−g k k 5.64– ZnSnP2 5.64– 11.30– 5.651 5.651 11.302k (tetragonal) 5.76d, i−k 5.76d, i−k 11.35d, i−k 6.22– ZnSiN2 5.28– 5.07–5.27l 6.280l 5.246l 5.022l l l (orthorhombic) 6.311 5.58 6.51– ZnGeN2 5.53– 5.26–5.27l 6.446l 5.467l 5.191l (orthorhombic) 6.52l 5.52l 6.815l ZnSnN2 5.917l 5.543l 6.753l 5.848l 5.464l (orthorhombic) 5.60b, m ZnSiAs2 5.60b, m 10.93– 5.60o 5.60o 10.87o (tetragonal) 10.88b, m 5.671m ZnGeAs2 5.671m 11.153m 5.671n 5.671n 11.20n (tetragonal) 5.851m ZnSnAs2 5.851m 11.703m 5.908o 5.908o 11.670o (tetragonal) a Ref. [53], bRef. [54], cRef. [55], dRef. [56], eRef. [57], fRef. [58], gRef. [59], hRef. [60], iRef. [61], j Ref. [62], kRef. [63], lRef. [64], mRef. [65], nRef. [66], oRef. [67]

Table 3 Reported experimental and theoretical lattice constant of MgBX2 (B = Si, Ge, Sn; X = P, N, As) in Å Samples

Theoretical a

MgSiP2 (tetragonal) MgGeP2 (tetragonal)

a

5.44–5.78a, b, c

5.64–5.78b, c

MgSnP2 (tetragonal) MgSiN2 (tetragonal) MgGeN2 (tetragonal) MgSnN2 (würtzite structure) MgSnN2 (cubic) MgSiAs2 (tetragonal)

5.9–6.1b 4.44c 4.69c 6.71d

MgGeAs2 (tetragonal) MgSnAs2 (tetragonal)

5.8–6.0b 5.9–6.1b

Ref [69],

b

4.48e 5.6–6.0a,

Ref [70], c Ref [71],

d

b

c

Experimental a b

c

5.68– 5.78a 5.64– 5.78b, c 5.9–6.1b 4.44c 4.69c 5.74d

10.0–10.3a

5.718a,

5.718a

10.109a

–

–

–

– – – –

– – – –

– – – –

– –

– –

– –

– –

– –

– –

10.7– 11.02b, c 11.58–12.0b 8.72c 9.89c 5.31d

4.48e 10.53– b 10.89a, b 5.8–6.0b 11.2–11.5b b 5.9–6.1 12.05– 12.06b e Ref [72], Ref [73]

b

4.48e 5.6–6.0a,

b

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b. Electronic Properties The ABX2 (A = Mg, Zn; B = Si, Ge, Sn; X = P, N, As) compounds belong to the II-IV-V2 group. These compounds are the similar in structure to III-V group, therefore, along with their structural properties their electronic properties also resemble with each other [69]. Most of the compounds of this group crystallize in tetragonal geometry and possess semiconducting nature with direct band gap. It may also be noted that in heavier elements the magnetic character also appeared in chalcopyrites due to some geometry distortion which affect the electronic properties of the chalcopyrite compounds. The electronic properties of these compounds are well explored experimentally and theoretically by various researchers. Further, electronic properties of these compounds are investigated in terms of energy bands DOS. The measured band gaps of these compounds are reported to lie in the energy range of 0.75–3.0 eV [50]. Due to this wide range band gap, these compounds have shown their potential in many optoelectronic applications. The comparative graphical representation of theoretical and experimental band gaps of ABX2 (A = Mg, Zn; B = Si, Ge, Sn; X = P, N, As) is presented in Figs. 7 and 8. (i) ZnXP2 (X = Si, Ge, Sn)

Band Gap (eV)

The electronic properties of ZnXP2 (X = Si, Ge, Sn) compounds are discussed by computing the energy band structure along the high symmetry direction of first Brillouin zone. For the tetragonal ZnXP2 (X = Si, Ge, Sn), valence band maximum and conduction band minimum both lie at the same momentum points revealing the direct band gap nature of these semiconductors [53]. The energy band gap gradually decreases by replacing the Si from Ge. This means that in the body centered tetragonal chalcopyrite compounds, the entry of heavier element causes the 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

4.46 3.84 2.1

2.06 2.05

2.1 2.06

3.99 3.4

2.64 2.12 2

Samples Theoretical

1.85

1.15 1.1

0.74 0.71

Experimental

Fig. 7 Reported theoretical and experimental energy band gap (eV) of ZnBX2 (B = Si, Ge, Sn; X = P, N, As) [42, 44–58]

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Band Gap (eV)

6 5 4

4.87 3.5

3 2

2.08

3 2.1

3.33

2.48

3.43 2.43

2.15

2.67

1.65 2.28

1 0

0

Samples Theoretical

3

0

2.05 0

Experimental

Fig. 8 Reported theoretical and experimental energy band gap (eV) of MgBX2 (B = Si, Ge, Sn; X = P, N, As) [60–63, 67]

reduction in the band gap [70]. It is reported that the energy bands of tetragonal compounds are mainly divided in three subatomic bands. The upper most region of the valance bands are dominated by the p states of P and X atoms. Similarly, the conduction band minimum is mainly clouded by the sp states of P and X atoms. This reveals that the electronic properties of ZnXP2 (X = Si, Ge, Sn) compounds are mainly controlled by Si, Ge, and Sn atoms [49, 53, 70]. (ii) ZnXN2 (X = Si, Ge, Sn) The orthorhombic crystal structure is the most stable phase for zinc nitride-based chalcopyrites compounds ZnXN2 (X = Si, Ge, Sn). It is reported that unlike ZnXP2, the valence band maximum and conduction band minimum for orthorhombic ZnXN2 (X = Si, Ge) exist at the different momentum point, and hence these compounds are indirect band gap semiconductors. Although orthorhombic ZnSnN2 shows the direct band gap nature, this happens due to the more energy of p state of Sn then Si and Ge. From the reported DOS, it is observed that energy bands in the valence band and conduction bands are mainly dominated by the p state of N with the small contribution of d and p states of Zn and X, respectively. The effect of the p state, in the formation of bands, increases when X is changed from Si to Sn. This is the major reason for the drastic reduction in band gap of ZnXN2 compounds when X moves from Si to Sn [64]. (iii) ZnXAs2 (X = Si, Ge, Sn) The contribution of different energy states in the formation of the energy bands, and hence in electronic properties of ZnXAs2 (X = Si, Ge, Sn) compounds are explained in terms of their energy bands and DOS. The energy gap and

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semiconducting nature of the arsenide decrease when X is changed from Si to Sn. The ZnSiAs2 shows the pseudo-direct band gap while ZnGeAs2 and ZnSnAs2 exhibit the direct band gap nature. It is reported that due to the larger size of Sn in comparison with Si and Ge, energy gap of ZnSnAs2 is very much lower than ZnSiAs2 and ZnGeAs2 compounds. Further, it is also observed that the energy band gaps of the ZnXAs2 compounds are lower than the ZnXP2 and ZnXN2 due to the larger size of As. The strong hybridization of d state of Zn with the p state of As and X (X = Si, Ge, Sn) give rise to the covalent character in the ZnXAs2 [54, 55, 63, 66–68]. (iv) MgXP2 (X = Si, Ge, Sn) The ternary chalcopyrite compounds MgXP2 (X = Si, Ge, Sn) are found to be stable in tetragonal structure at ambient conditions. The reported band structure and DOS of the MgXP2 (X = Si, Ge, Sn) reveal that these compounds have direct band gap nature. Reported band gap for these compounds shows the potential of these compounds in various optoelectronic devices. MgSiP2 and MgGeP2 are quoted as pseudo-direct band gap materials also by some researchers. Further, it is also reported that all these compounds have almost equal value of energy gap. The band gap of all three compounds is nearly equals to 2 eV and hence except the shifting of energy bands toward the Fermi level, there is no major change visible in the energy bands and DOS of these compounds. The bonding character in MgXP2 is reported to be partial covalent [70–72]. (v) MgXN2 (X = Si, Ge, Sn) MgXN2 (X = Si, Ge, Sn) chalcopyrite compounds are not explored much, only few theoretical studies are reported for these compounds. These compounds are the wide band gap semiconductors with the band gap approximately equals to the 2– 4 eV. Due to the wide band gap range, these compounds are emerged as potential candidate for photovoltaic applications. The width of the valence band of MgXN2 is smaller than the MgXP2 compounds due to larger atomic size of P in comparison with N. At room temperature, würtzite and cubic phases of MgXN2 (X = Si, Ge, Sn) compounds are also stable. The cubic and würtzite compounds are also used in various electronic appliances [70–73]. (vi) MgXAs2 (X = Si, Ge, Sn) The electronic properties of MgXAs2 (X = Si, Ge, Sn) are also explained through the energy band structure and DOS of these compounds. The band gap of MgSiAs2 and MgGeAs2 are almost similar, although the significant difference in band gap of MgSnAs2 is observed. Band structure of MgXAs2 (X = Si, Ge, Sn) reveals the direct band gap nature of these compounds, which makes them suitable for photonic devices. Further, from the reported DOS, it is observed that the valance bands of these compounds are the result of hybridization between sp states of Mg with p states of X and As. The mixing of sp states of Mg and X with p state of As gives rise to the conduction bands. MgXAs2 (X = Si, Ge, Sn) compounds are reported to

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exhibit the mixed covalent-ionic bond character as As shows the ionic and covalent bonding character with Mg and X (Si, Ge, Sn), respectively [71, 72]. c. Optical Properties The detailed investigation of optical properties of any compound is very important to explain the utility of material in optoelectronic applications. The optical properties of a material are generally described through the complex dielectric tensor, absorption spectra, loss function, reflectivity and refractivity spectra. For the photovoltaic applications, the sum of the reflection and absorption should fall in the visible region of electromagnetic spectrum. It is found that most of the compounds of the group ABX2 (A = Mg, Zn; B = Si, Ge, Sn; X = P, N, As) show the isotropic nature for the optical response. The compounds, having the band gap greater than 1.2 eV, show the more absorption and less reflection. Further, the compounds having the wide band gap, i.e., higher than the 1.7 eV, show more reflection than the absorption. These compounds show the comparable reflection with III-V compounds, as these compounds are the crystal analogous to III-V compounds. The MgBX2 (B = Si, Ge, Sn; X = P, N, As) compounds show the lower absorbance as compared to the ZnBX2. Among ZnBX2 (B = Si, Ge, Sn; X = P, N, As) compounds, ZnSiP2 has the least absorbance. The band gaps of all these compounds are approximately equal to 1.5 eV which is the optimum band gap for the solar cell devices; therefore, these compounds can be used as the solar cell material [53–75].

4 Conclusion The present chapter is based on describing the structural, electronic, and optical property of the two different classes of photovoltaic materials, namely inorganic metal lead-free tin halide perovskite materials ASnX3 (A = Cs, Rb, K; X = Cl, Br) and ternary chalcopyrite ABX2 (A = Mg, Zn; B = Si, Ge, Sn; X = P, N, As). All these materials crystallize in different structural phases, and according to their structure, applications of these compounds are also distinguished. It is also observed that arsenic compounds are easier to fabricate in comparison with P-based ternaries, and hence their installation cost is also less. All the materials reported here are abundant in nature, less toxic, and provide better efficiency for the clean future environment. The electronic properties of these compounds reveal that the band gaps of these compounds vary from the narrow to wide energy range. Most of the compounds possess the direct band gap nature and a few exhibits the pseudo-direct band gap. In this study, we observe that Rb and K-based tin halide perovskites are not explored much even their band gaps are optimum for the solar cell devices. Evenly, some of ABX2 (A = Mg, Zn; B = Si, Ge, Sn; X = P, N, As) is still not investigated either theoretically or experimentally. The optical properties of these compounds affirm their utility in the photovoltaic devices.

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5 Future Scope The photovoltaic technology is most emerging technology for future world. The lead-free perovskite materials are considered as the good absorber for solar radiations. In this context, some more low-cost, environmental-friendly lead-free perovskite with the good efficiency can be explored. The most of compounds of II-IV-V2 group are not well explored, hence, there is a need to explored the optoelectronic properties of these compounds to ensure their possible utilization in many electrical and optical applications. Presently, copper-based chalcopyrite is the commercially utilized in photovoltaic industries, and more compounds of II-IV-V2 group should also be introduced well to open the photovoltaic market for all class of society.

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Nanotechnology in Production of Microalgal Biofuel: Application of Nanomaterials and Lipase Immobilization Himanshi Singh, Kunwar Paritosh, and Vivekanand Vivekanand

Abstract Biodiesel is a promising replacement of fossil-based diesel as biofuel for sustainable development. Various feedstocks have been exploited for the biodiesel production. Feedstock like jatropha has gained serious attention in past decades. Among exploited feedstock, microalgae have emerged as promising feedstock for biofuel production. The high lipid content, ability to sequestrate atmospheric carbon and ability to be grown and harvested on both land and water make it desirable candidate for biofuel production. However, lipase immobilization and lipid extraction from microalgae are non-economical process. Recently, nanotechnology is gaining attention in production of microalgal-based biofuels. Nanomaterials may have desired ability to enhance the microalgae cultivation, lipid extraction, transesterification and may act as a nano-biocatalyst. This chapter describes the interaction between nanomaterial and bioanalysis of microalgae for enhanced biodiesel production as well as different methods for enzyme immobilizations for lipase on industrial scale.




Keywords Microalgae Nanomaterials Enzyme Immobilized lipase





Nanotechnology
Nanobiocatalysts


1 Introduction Biofuels play crucial role in sustainable fuel and as emerging energy production solution for the future generation. The world is facing increased demand for fuels which cannot be satisfied by only using fossils or other power resources and with traditional crops as well as they are not environment-friendly options. They are H. Singh Centre for Converging Technology, University of Rajasthan, Jaipur, Rajasthan, India K. Paritosh
V. Vivekanand (&) Centre for Energy and Environment, Malaviya National Institute of Technology, Jaipur, Rajasthan, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_7

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classified as primary and secondary biofuels. The primary biofuels can be directly produced from plants, forest residues, animal wastes, etc. Meanwhile, production of secondary biofuels performed using microorganisms and biomass feedstock which is later categorized into (i) first-generation, (ii) second-generation and (iii) third-generation biofuels [1, 2]. First-generation biofuels are produced from abundant amount of edible crops such as rapeseed, corn, tall grass, wheat, rapeseed, sugarcane, soybean, barley but this method arises disputes as certain limitation-related food security, deforestation and shortage of freshwater can directly increase the price of biofuel [3]. Second-generation biofuels are generated from non-food feedstock plant biomass or woody residues such as wheat grass, grass, jatropha, miscanthas, cassava, corn cob, (Jatropacurcus, Pongamia pinnata, Simarouba glauca, etc.) which can cut down the food security crisis but lead to the finite production and not yet developed [4–6]. Based on abovementioned drawbacks associated with first- and second-generation biofuels, third generation seems to be viable alternative source of energy to replace fossil fuels. Third-generation biofuels are synthesized from different oleaginous microalgae biomass as a raw material that can thrive in fresh or saline water, artificial reactors and non-arable land, etc. Biofuels (biohydrogen, bioethanol, biogas, biodiesel) are receiving increased attention among researchers because they are alternate or clean and green renewable fuel, low greenhouse gases emissions, use diverse feedstocks that are accessible, non-edible and cheap and considered waste [7, 8]. Nanotechnology can play crucial role here by minimizing production costs and higher yield, and process-related enzymes show good catalytic activity, thermal stability, reusability, large surface area to volume ratio, energy efficient and high adsorption capacity which introduces new innovative alternatives in the field of biofuels production [9]. They could either be metallic, polymeric, semiconductor in nature. The biodiesels in standard automotive engines induce low emissions of carbon dioxide as well as carbon monoxide which act as major air pollutant. Biodiesel advantageously characterized by excess presence of hydrogen and oxygen, also higher lubricant capacity, can improve the fuel injection system and life of sliding metallic components of the engine [10]. Biofuels hold more opportunities in the case of minimizing the dependency on fossil fuels and act as an alternative fully or partially. It is one of the trending and developing eco-friendly business or research themes needed for the sustainable future. This chapter enlightens the application of different nanomaterials (NMs) and use of nanotechnology in the different processes of microalgal fuel production as well as various enzyme immobilization methods for lipase.

2 Importance of Nanotechnology Nanotechnology is science or technology of building extremely small devices or materials at a nanoscale of 1–100 nm (Fig. 1). This field is an advanced and future technique which has different implementations in various fields such as

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Fig. 1 Illustration of nanoscale

pharmaceuticals, drug delivery, cosmaceuticals, photonic crystals, bioremediation, agriculture, material science and bio-energy as well. It can be named as a new tool for the production of biofuels via producing different nano-carriers.

2.1 2.1.1

Different Nanocarriers in Biofuel Polymer-based NPS

Polymeric NPs have high stability, simple synthesis, number of functional groups, uniform size distribution etc. Nanogels structures are hydrophilic nonporous which facilitate enzyme immobilization via encapsulation method that is most commonly used technique [11]. Using in situ polymerization, a-chymotrypsin was immobilized on mesoporous magnetic nanogels. Meanwhile, more than two enzymes also have been co-immobilized on surface of nanogels. Covalent linking led to formation of covalent bond between functional groups of nanogels and enzymes. Nanogels can behave as a shield for the enzyme itself.

2.1.2

Carbon-based NPS

All nanostructures having carbon in their configuration are considered as carbon-based nanostructures are carbon nanotubes (NTs), carbon nanodots, carbon nanofibers, carbon nanosheets of graphene, fullerenes, and nano-diamonds are more significant nanocarriers in various industrial applications and producing nano-biocatalysts NBC (Fig. 2). They have attracted bulk attention due to their extraordinary characteristics such as heat resistant, radiation hard, thermal stability and biocompatibility.

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Fig. 2 Carbon-based different nanoparticles

CNTs possess 1D tubular hydrophobic structure and contain high thermal and electrical conductivity. They can be categorized on the basis of number of graphene sheets rolled up into cylindrical shape: (i) consist of single graphene layer single-walled carbon nanotubes (SWCNTs) (ii) consist of two or more graphene layers with van der Waals forces between them, multi-walled carbon nanotubes (MWCNTs). By using physical adsorption method, enzyme can be immobilized onto single-walled carbon nanotubes (SWCNTs) without chemical modification through sequential steps [12]. Likewise, lipase adsorption onto multi-walled CNTs ensures stability and reusability [13]. The ionic strength of the medium determines the time required by CNTs for complete enzyme adsorption. It was concluded that medium ionic strength can enhance hydrophobic interactions which led to successful enzyme immobilization. CNTs can be synthesized by following methods such as laser ablation, discharge, gas phase catalytic growth and chemical vapor deposition (CVD). Graphene or nanosheets (-SOH)—one of the amorphous carbons has drawn attention for biodiesel production because of noteworthy features like good mechanical properties, high electrical conductivity, high catalytic activity, large surface area, high rates of charge mobility and many more. Graphene is made from reduction in graphene oxide (GO), usually called as reduced graphene. Compared to graphene, reduced graphene oxide is much more hydrophilic due to the presence of partially reduced O2, and this property helps in immobilized enzymes [14]. Thus, carbon-based NPs used need to be investigated for further improvement and in order to increase their efficiency in biodiesel production, medical, biofuel cells and other applications.

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Metal-based NPs

Metal-based NPs are widely used for fabricating NBCs due to their high recyclability of biocatalysts. Several types of catalysts included silver, silver oxide, nickel oxide, magnesium oxide, Fe2O3, ZnO, copper oxide, bimetallic and many more. Metal oxide predominately is practiced in view of certain characteristics such as antimicrobial, antifungal, non-toxicity, large surface to volume ratio and semiconducting properties. In order to increase enzyme immobilization, they have high activity toward creating strong interaction with enzyme molecules, in that case functional groups such as amino carboxylate and thiolate phosphate bonds can be attached onto metals surfaces of NPs. The enzyme immobilization on non-porous gold biocomposite induces high biocatalytic activity as well as enzyme stability [15]. ZnO nanorods having positive (anions) and negative ions (cations) were used to produce biodiesel from olive oil. A thin layer of polymers is essential for coating onto metal surface for the reaction taking place between functional group and enzymes. Chitosan, PEG, poly vinyl alcohol, polyacrylates and polyethyleneimine (PEI) can be considered for the coating purpose [16, 17]. Several processes have been investigated to synthesize metal and metal oxide NPs as follows: • Physical methods include ball milling, spray pyrolysis, layer-by-layer growth, plasma arcing, thermal evaporation, pulsed layer desorption, sputter deposition, e-beam lithographic techniques, etc. • Chemical methods: sol–gel synthesis, electrodeposition, chemical solution and chemical vapor deposition, supercritical fluid method, co-precipitation, wet chemical methods, Langmuir–Blodgett method. • Biological method: using plant-based and microbes-based mechanism such as bacteria, fungi and algae.

3 General Perspective of Microalgae They are unicellular or multicellular photoautotrophic microorganisms which can trap sunlight CO2 in the presence of solar energy 50 times way more better than plants during photosynthesis [18, 19]. Numerous species of microalgae studied using nanoparticles such as Chlorella sp., Crypthecodiniumcohnii, Nanochloropsis sp., Botryococcusbraunii, Dunaliellaprimolecta produce large quantities of lipid and hydrocarbons (Tables 1 and 2). They require larger quantities of lipid content, and higher growth rate emerges as a desirable or innovative alternative source of energy. Algae biomass mainly comprises carbohydrates, lipids and proteins. The arrangement of lipids occurs in microalgae in the configuration of triacyl glycerides (TAGs) which provides reliant and promisingrole in the production of biodiesel (Fig. 3) [20].

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Table 1 Characteristics of different types of nanocarriers Polymer

Silica

Carbon

Metal

Source

Synthetic and natural polymer

Silica

CNTs, graphene, diamond

Configuration

NFs, nanogels, NPs and nano-containers Functional groups accessible from polymers covalent binding, entrapment, cross-linking Attached to microporous arrangement or magnetic particles

NPs, mesoporous structure and containers Highly porous complex, including external functional groups, physical adsorption, entrapment, cross-linking Attached to magnetic particles

Weak

Strong

Single wall and multi wall NTs and nanofilms Hydrophobic surfaces, including external functional groups physical adsorption, covalent binding Attached to magnetic particles or detached by density differences Strong

Mg, Cu, Zn, gold, Ca and metal oxides NPs

Contributor of nanocarriers for NBCs NBC fabrication

Recycle

Mechanical strength

Functional groups and thin layer of polymer established onto metal surfaces covalent binding

Centrifugal or magnetic separation

Strong

Table 2 Applications of nano-additives for biodiesel yield during microalgae to biodiesel conversion with suitable conversion processes and efficiencies Nano-additives

Conversion processes

Conversion efficiency

Ref.

Calcium oxide NPs blends (CaO– NPs) Mesoporous silica nano-catalyst, Ti-loaded SBA-15

Catalytic transesterification Transesterification

91%

[60] [61, 62]

Niobia (N2O5) incorporated with SBA-15 PAN nanofiber, ferric oxide and non-porous gold incorporation, silica NPs, Fe2SiO4 and magnetic NPs incorporation, polyacrylonitrile nanofiber KF/CaO–Fe3SO4, Li (Lithium)-doped CaO–Fe3SO4, sulfate (SO4) incorporated Zi (zirconium), sodium titanate and carbon-based nanotubes NTs and NPs

Esterification

10 times above yield than other catalysts 3 times much more other than effective catalysts TiO2–S and TS-1 Significant increase in biodiesel yield High increase in biodiesel productivity

More than 95%

[57, 43]

Transesterification

Transesterification

[63, 57]

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Harvesting of cells

2

Drying of cells

3

Microalgae biomass Lipid extraction

4

Functionalized NPs used as carrier of chemicals which perform as organic solvent

Lipid 5

Transesterification

NMs used as carrier of enzyme catalyst (lipase)& catalyst as alkaline metaloxide

Bio-diesel + Glycerol as byproduct Fig. 3 Nanotechnology application in biodiesel production from heterotrophic microalgae

Compared to fossil fuels, microalgae-based biofuels have many advantages which are as follows: • Higher growth rate. • Contain oil level of normally 50% but production can reache upto 80% of its dry cell weight. • Higher photosynthetic efficiency, meanwhile absorbs carbon dioxide from atmosphere be instrumental into greenhouse gases (GHG) mitigation. • Utilization of wasteland unsuitable for agriculture. • Removal of nitrogen, phosphorous and heavy metals from municipality, agricultural and industrial wastewater. • Synthesis of other value-added products has applications in nutraceuticals and pharmaceuticals and also can be used as fertilizer and in bioethanol production, etc. • Capacity to thrive and expand under stress conditions such as nitrogen deficiency; they can be produced all over the year. • Lack of competition with food crops.

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Nanotechnology for Algal Biofuel Nanomaterials in Lipid Extraction from Microalgae

In biodiesel production, lipid extraction process directly affects the production cost and responsible for 70% share of it. The reason behind this is that the cell wall constitutes of complex carbohydrates and glycoprotein compounds which provide high resistance toward chemical as well as mechanical strength [21, 22]. Commonly used method for lipid extraction is solvents extraction that is using different solvents such as hexane, methanol and chloroform individually and in combination. They were practiced in washing of dry and wet algal biomass repeatedly to obtain lipids. The lipid extraction is aided by ultrasonication, homogenization, solvent-lipid separation (distillation) and irradiation [23–26]. The disadvantages of current methods are as follows: (i) Energy-intensive techniques. (ii) Observe toxicity of solvents on microalgal cells. (iii) Increased extraction cost with low yield. Nanomaterial application in microalgae cultivation showed no toxic release and increased lipid content. Lin [27] studied that the application of spherical nanoparticle for lipid accumulation showed less or no effect on the microalgae cellular growth which can be operated continuously, and hence, the process avoids re-cultivation. With the use of amino clay, NPs for Chlorella sp. KR-1 in lipid extraction resulted in higher oil extraction efficiency with increase in microalgal harvesting efficiency [28]. It was displayed that Fe amino clay NPs in addition to hydrogen peroxide (H2O2) generated OH free radicals helped in oil extraction [29, 30] founded application of aminoclay-TiO2 nanocomposites in the presence of UV radiations on harvesting and algal cell disruption. Razack [31] reported the benefit of upsurge accumulation of silver (Ag) NPs from 50 to 150 Ug/g resulted in enhancement of Chlorella vulgaris sp. oil content from 8.44 to 17.68%. Applications and synthesis of different functionalized nanomaterials appeared to be more potential in lipid accumulation and cell disruption which should be investigated.

3.1.2

Transesterification by Nanomaterials Application

Transesterification is the mostly applied oil conversion process into biodiesel production. The oils derived from plants, animals or oleaginous microorganisms’ sources react with alcohol (mainly methanol) for synthesizing fatty acid methyl esters-FAME or biodiesel. Currently, synthesis of biodiesel carried out using four categories of catalysts which are heterogenous, acid, base and enzymes catalysts. During event of biodiesel production, the acid catalysts HCl and H2SO4 are needed in laboratory scale studies [24, 32] whereas NaOH and KOH acting as bases

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were frequently utilized in industrial level. There are concerns related to every type of catalysts. In case of acid-catalyzed method, they need proper care and maintenance due to their aggressive performance in reactor, and besides this, it consumes more methanol [24]. While, in base catalyzed, it consumes base due to soap formation [33]. According to studies, application of enzyme biocatalyst such as lipase can substitute acid and base catalysts, and it is also environmental friendly and efficient [34, 35]. The reason behind the lipase-catalyzed biodiesel production is costly because raw material usage for lipase production was high. Lipase-facilitated process is high priced due to the fact such as costly raw material uses for lipase production. The production cost can be minimizing in the following ways: (a) lowering lipase production cost using innovative cost-effective and efficient methods, (b) introducing lipase reusability in process for reduction in biodiesel production cost and (c) increasing lipase catalytic activity and stability. All these can be resolved by immobilization of enzymes onto surface of nanomaterials (NMs) which have positive economic impact and recyclability (Table 3) [32, 36, 37].

3.1.3

Transesterification in Microreactor

The size of microreactor is smaller than thick credit card. It has been equipped with small microchannels having width of human hair stacked parallel in series. From one side of each microchannel, they are infused with alcohol catalyst and oil mixture which is converted into biodiesel at small-scale level. This minute design has the capacity for biodiesel production faster than other reactors used in large industrial level. This design can be engineered in size of suitcase, where small

Table 3 Different nanoparticles (NPs) used for microalgal oil transesterification Nanoparticles

Algal species

Size

Yield %

Gold (magnetic NP) Cadmium sulfide Gold (magnetic NP) Silver (magnetic NP) Palladium (immobilized NP) Palladium (immobilized NP) Nickel (immobilized NP) Gold (magnetic NP) Silver (magnetic NP) Silver (magnetic NP) Silver (magnetic NP) Silver (magnetic NP) Silver (magnetic NP)

Chlorella vulgaris Scenedesmus Eolimna minima Botryococcusbraunii Plectonemmaboryanum C.vulgaris Nostocmuscorum Anabaena oryzae Nostochumifusum Wollea sp. Oscillatoria willei S. platensis Janiarubens

40–60 – 5–100 15.67 95% at high water content and methanol to oil ratio [56]. The authors suggested two ways with regard to transesterification process and analyzed their yield. According to the first approach, using sonification the microalgal oil was extracted, and for transesterification organic solvents were used; while as per the second approach, transesterification was carried out precisely on disrupted microalgal biomass in the absence of oil extraction and dewatering. As a result of the second method, lipase immobilization gave increased biodiesel yield followed by raised water level (71% by weight for algal biomass) and high methanol to oil ratio (up to 68%). The recovered immobilized lipase enzymes from the process show efficient activity in the next six cycles, without any significant loss. The preparation procedure of alkyl grafted Fe3O4–SiO2 should be checked due to its high price and to maintain similar consistency for enzyme immobilization. The advantages of following method are reusability, operational stability, higher yield of biodiesel without applying solvent extraction technique and application in industrial scale. • Using microalgal species C. vulgaris, immobilized Burkholderia lipase produced high FAME conversion efficiency by 97%. The experimental study of [57] presented that enzyme extracted from Pseudomonas cepacia integrated upon NPs such as PAN nanofiber, nanoporous gold and Fe3O4; ferric silica and magnetic NPs with lipase Burkholederia sp., moreover lipase enzyme from Rhizopus miehei with silica NPs; polyacrylonitrile PAN nanofiber absorbed with lipase from Thermomyces lanuginosas presented higher biodiesel production from diverse bio-oils during transesterification process. • Wang et al. developed four-bed reactor (Fig. 5) for repetition and increased efficiency of lipase, utilizing lipase immobilized on Fe2O3 NPs for production of biodiesel. The four-bed reactor conversion rate and also stability were higher when compared to single-bed reactor. It showed the conversion time of biodiesel preserved at two time intervals for both reactors in case of four-bed reactor, rate was more than 88% in 194 h.; (ii) then dropped at 75% afterward 240 h., whereas for single-bed reactor, the rate after 192 h. was found to be 45% only [58]. The advantages of four-bed reactor over single bed are low inhibition of catalyst by-products, low biodiesel cost due to efficient reusability of enzymes catalysts (change only words not line). It proved to have great potential in biodiesel prod at large-scale nano BCs systems. • Using impregnation method, the nanomagnetic solid catalyst was developed in which Fe2O3 magnetic core and mixture of MgO, CaO and SrO are thoroughly

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Fig. 5 Four-bed reactor system for bio-diesel production

mixed and dipped into aqueous solution of KF with different mass range. They [58] demonstrated the methods for characterizing these NMs catalysts by means of X-ray diffraction as well as TEM techniques. The catalyst had porous arrangement with diameter of 50 nm and a characteristic of ferromagnetism. The KF and water mass ratio in reaction, calcinations temperature during synthesis of catalysts, etc., were investigated for efficient biodiesel production. Under suitable conditions, it yielded more than 95% in 3 h., and the immobilized lipase catalyst can be reutilized for about 14 times without compromising its enzyme activity. • The biodiesel production from methanol and oleic acid, a novel solid acid catalyst named sulfonated multi-walled carbon nanotubes (s-MWCNTs) has been used in the process with the transformation rate of 95% [59]. The procedure for the preparation of s-MWCNTs was carried out using fluidized bed reactor dipped in solution of H2SO4. The catalyst had stability in structure, and there were no changes in the structure of s-MWCNTs after sulfonation, as characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. Such discoveries and experiments help the easy transportation of enzymes or their immobilization via different techniques for more and effective production of biodiesel with excellent or increased catalytic activity of enzymes with low cost.

6 Conclusions The scarcity of hydrocarbon-based fuels increases the urgency of environmental friendliness, clean and green energy alternative which leads to bio-energy option. The biofuels derived from microalgae are most desirable because of their

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extraordinary features. The application of nanomaterials plays advantageous role in different phases of microalgae cultivation, lipid extraction, harvesting and transesterification which in result lowers the method price as well as enhances yield. The contemporary and novel advancements have been done and are in the progress in the field of the enzyme immobilized onto surface of nanomaterials such as carbon nanotubes (CNTs), magnetic NPs, metal oxide NPs and polymer NPs. They showed promising results in biofuel production with higher yields, when compared to free enzymes and can be separated for further use which makes them cost effective but still in infant stage. Nanotechnology can play pivotal role in the production of biofuels, but some issues need to be addressed such as synthesis of NPs which are non-toxic to microorganisms, less expensive also environmentally friendly. The role of nanotechnology in biofuels is still not fully explored and understood. It can also affect negatively human health and environment. Furthermore, the following recommendations are proposed for future studies: screening of NPs with wide variety of concentration to understand their effects on microbial activity and establish optimum process conditions. The effort should be made in case of identification of suitable microalgae species and improvement in their latest conversion technologies or processes used, application of different size and shape of NPs, in order to understand their behavior on the performance of biocatalysts and need to conduct experimental and computational studies as to provide fundamental understanding of mechanism involved in biofuel production. In near future, biofuels from using nanomaterials have capability to occupy the market place for clean and green energy solutions in a sustainable way. Acknowledgements Authors thank the editor for providing the opportunity to share the knowledge through this book chapter.

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Effects of Silicon Dioxide Nanoparticles on the Combustion Features of Diesel Engine Using Water Diesel Emulsified Fuel Deepti Khatri, Rahul Goyal, and Abhishek Sharma

Abstract In this work, the consequences of silicon dioxide nanoparticles were explored for the combustion features of diesel engine using water diesel emulsified fuel. For this study, four-stroke, single-cylinder diesel engine was used at an invariable 1500 RPM (speed) with 18 (compression ratio), and the results were correlated with diesel. The diesel was taken as 94%, water as 5%, and SPAN 80 as 1% (all by vol.). For preparing four samples of test fuels, the amount of silicon dioxide nanoparticles was varied from 25 to 100 ppm (varied in the gap of 25 ppm). The ultrasonication technique was employed for maximum dispersion of test fuels. All the test fuels exhibits the fuel properties as per EN 590 standard. The results indicated that for in-cylinder pressure, minimum variation of about 0.82% lies between D94W5S1–Si50 test fuel and diesel. The peak value of heat release rate was hiked by 1.07% with the addition of nanoparticles (50 ppm). There exists marginal difference between the mass fraction of fuel burned and mean gas temperature of diesel fuel and other fuels. The inclusion of silicon dioxide nanoparticles resulted into enhanced fuel–air mixing with superior atomization and hence accelerated the process of combustion. Keywords Silicon dioxide nanoparticles diesel emulsified fuel


Diesel engine
Combustion
Water

1 Introduction Due to the fast and continual usage of energy, the reservoir of fossil fuels is deteriorating at a speedy rate. Also, to solve the issues of harmful emissions from diesel engines various approaches are utilized by the investigators, which involves the application of distinct alternative fuels [4, 10]. In the recent times, water diesel emulsified fuel appears to be an originating alternative fuel for the diesel engines D. Khatri
R. Goyal (&)
A. Sharma Department of Mechanical Engineering, Manipal University Jaipur, Rajasthan 303007, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_8

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[12]. This fuel can be straight away used in the diesel engines without any adjustments [7]. The emulsified fuel displays “secondary-atomization” emerging through “micro-explosion” of water molecules and is crucial due to the combustion of the fuel [14]. Few explorations confirmed that when nanoparticle are used as additives to water emulsified fuel, acquires beneficial qualities to increase the engine attributes, as they possess better surface–volume ratio which enhances the fuel air mixing [16, 17]. Only some investigational works have been regulated by different researchers which indicated the potential use of nanoparticles to emulsified fuel. Basha and Anand [2] demonstrated the use of carbon nanotubes to emulsified diesel fuel, and they observed enhancement in the combustion levels. Vellaiyan and Amirthagadeswaran [18] utilized zinc oxide nanoparticles, and they reported improvement in combustion, emission, and performance. They recognized the curbing of ignition delay by the utilization of nanoparticles to the emulsified fuel. Annamalai et al. [1] worked with 30 ppm of ceria nanoparticle in addition to the emulsified biofuel. They observed rise in performance features and fall in combustion attributes of heat release rate and peak pressure of the cylinder considering the ignition delay condition. Dhinesh and Annamalai [5] added cerium-oxide nanoparticles to the biofuel for the assessment of combustion in addition to the performance behavior of the diesel engine. They revealed that the absolute combustion occurred considering the ample amount of oxygen present in the nanoparticle. Also, performance and emission features were upgraded. Recently, Khatri and Goyal [13] incorporated silicon dioxide nanoparticle to the emulsified diesel fuel and analyzed emission along with performance aspects. They noted maximum emission reduction and performance enhancement with ppm dosing of nanoparticle. However, the combustion analysis was not reported in their study. So, through this work, an effort has been made to be acquainted with the repercussions of silicon dioxide nanoparticles for the combustion attributes, when the water diesel emulsified fuel was utilized. So, in this experimental work, silicon dioxide nanoparticles were utilized in the range of 25–100 ppm (gap of 25 ppm) to the emulsified diesel fuel. The percentage of water was fixed as 5% (by vol.%) for all the test fuels due to the observations made by different researchers previously that the water percentage less than 10% would yield improved chemical features, successfully qualifies the corrosion examination, and accomplishes the mandatory conditions required by any automobile diesel [11, 14].

2 Materials and Methods 2.1

Materials

For performing the experiments, silicon dioxide nanoparticles (particle size: 30–50 nm; purity: 99.9% with specific area: 120–150 m2/g) were purchased from Ultrananotech–Bangalore, India. For the formulation of different test fuels, SPAN

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80 (procured from Scientific Chemical, Jaipur, India) with hydrophilic–lipophilic balance (HLB): 4.3 was used up as a surfactant. The diesel was obtained from the local market.

2.2

Method for Formulation of Different Samples

For preparing samples of test fuels; Diesel, water, and silicon dioxide nanoparticles were measured in desired quantity. The diesel was taken as 94% (by vol.), water as 5% (by vol.), and SPAN 80 as 1% (by vol.). For preparing four different samples of test fuels, the quantity of silicon dioxide nanoparticles was varied from 25 to 100 ppm (varied in the gap of 25 ppm). For better mixing of the samples, the magnetic stirrer was used and operated at 1000 revolutions per minute (RPM) for the duration of 25 min. After that, for maximum diffusion and improved stability, ultrasonication was carried out (for 30 min) by using Ultrasonicator of 500 W power, frequency level of 20 kHz with sound proof encloser, and titanium alloy probe as shown in Fig. 1. So, for experimental investigations four samples of test fuels were formulated and labeled as: D94W5S1–Si25, D94W5S1–Si50, D94W5S1–Si75, and D94W5S1–Si100, respectively. The different fuel properties were found out, the basis of which was EN 590 standard and are shown in Table 1 [13]. The appearances of test fuels were milky white in color as shown in Fig. 2.

Fig. 1 Ultrasonicator with sound proof encloser

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Table 1 Properties of test fuels [13] Test—fuels

Density @ 15 °C (kg/m3)

Viscosity (40 °C) mm2/sec

Flash point (°C)

Cetane index

Method Desired range D94W5S1–Si25 D94W5S1–Si50 D94W5S1–Si75 D94W5S1–Si100

EN ISO 3675 820–860 842.1 846.2 851.1 854.3

EN ISO 3104 2–4.5 2.5 2.8 3.1 3.3

EN ISO 2719 Minimum 55 73 76 78 80

EN ISO 4264 Minimum 46 51.5 50.2 48.2 50.1

Fig. 2 Photograph of prepared sample

2.3

Experimental Approach

For experimental purpose, a single-cylinder, 4-stroke computerized diesel engine with 87.5 mm bore and 3.5 kW was utilized. The compression ratio can be transformed from 12 to 18. For combustion analysis, the test rig was provided with “Engine Soft” software. Figure 3 shows the test rig with analysis software. The experiments were conducted with an unchanging compression ratio: 18; preset 23°bTDC injection timing, and engine speed was set as 1500 RPM. The load of the engine was changed from 2 kg till 12 kg for all the test fuels (advancement of 2 kg each). The combustion analysis software provided the quantitative values related to combustion attributes such as in-cylinder pressure (in bar), hear release

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Fig. 3 Research engine test rig with combustion analysis software

rate (in J/deg), mass fraction of fuel burnt (in %), and mean gas temperature (in K). These readings were noted, and graphical analysis was done with respect to crank angle in degrees. The base readings were taken by using diesel fuel only. Afterward, each of the test fuel with varying dosing levels of silicon dioxide nanoparticles was investigated for combustion attributes. The values were correlated to the diesel.

3 Results and Discussions 3.1

In-Cylinder Pressure (ICP)

The in-cylinder pressure (ICP) is that pressure which is produced within the combustion chamber all thorough the four strokes of the engine [3]. The interaction between ICP and crank angle (in degrees) is recorded for diesel fuel as well as all

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Fig. 4 Interaction between ICP and crank angle at full load

the test fuels at full engine load with 1500 RPM engine speed. Figure 4 depicts that the diesel shows maximum ICP of 61 bars, D94W5S1–Si25: 59.5 bar, D94W5S1– Si50: 60.5 bar, D94W5S1–Si75: 59 bar, and D94W5S1–Si100: 58.5 bar, respectively. The ICP of diesel fuel was more or less close to the ICP of test fuels with water diesel emulsified fuel incorporated with silicon dioxide nanoparticles. Among all the test fuels, D94W5S1–Si50 displays maximum ICP, which is almost close to that of ICP of neat diesel fuel. There exists a marginal difference of about 0.82% among D94W5S1–Si50 test fuel and diesel fuel values. This little difference occurred due to the lessening of flame temperature of cylinder generally, through addition of water to the diesel, resulting in lower ICP [20]. Also, shorter ignition delay was responsible for lower ICP of test fuels [15]. However, it was also discovered that for all the test fuels, there remained the value of ICP close to each other. These reported values showed not much difference with respect to that of diesel fuel readings. This could be attributed to the fact that by adding nanoparticles to water diesel emulsified fuel might have assisted the test fuels for accelerating the combustion process [6]. Also, the higher surface–volume ratio of nanoparticles improves the transport of heat among the particles and the droplets of fuel, thereby upgrades the atomization of fuel droplets as well as process of combustion [13]. The similar observations were revealed by other researchers also [2, 19].

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Heat Release Rate (HRR)

Figure 5 displays the interaction between heat release rate (HRR) and crank angle for diesel and other test fuels at 1500 RPM speed and maximum load condition. The process of combustion inside the cylinder of the engine is defined by heat release rate. Improved combustion represents superior HRR, whereas inferior combustion shows lower HRR. From Fig. 5, it is represented that the peak value of HRR for diesel fuel is 46.5 J/deg, whereas for D94W5S1–Si25, D94W5S1–Si50, D94W5S1–Si75, and D94W5S1–Si100 test fuel it shows 45.5, 47, 46, and 45.5 (all in J/deg), respectively. The HRR for D94W5S1–Si50 test fuel is higher than all other test fuels. This might be due to the improved surface to volume proportion, which has increased the combustion attributes, and also due to shortest ignition delay [6]. Accordingly, the process of combustion becomes advanced and as a result peak value of HRR is increased as compared to other test fuels.

3.3

Mass Fraction of Fuel Burnt (MFFB)

The percentage of MFFB is an indication to the fraction of fuel burned all through the combustion process inside the combustion chamber [8]. During initial

Fig. 5 Interaction between heat release rate versus crank angle

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Fig. 6 Interaction between mass fractions of fuel burned versus crank angle

combustion process, the zone of combustion is separated by two regions namely: burned zone and unburned zone. As the process of combustion advances further, the burned region increases with simultaneous reduction of unburned region. The variation of MFFB with crank angle for diesel and other test fuels at 1500 RPM speed and maximum load (12 kg) condition is depicted through Fig. 6. It is marked from the Fig. 6 that 50%, 90%, and 100% of the diesel fuel burns quicker than any other test fuels at fixed engine speed. This tendency might be due to the advanced viscosity of test fuels, which in turn leads to the late commencement of combustion process. Almost all the test fuels with different quantities of silicon dioxide nanoparticles showed equivalent percentages of MFFB, and there was marginal difference between MFFB of diesel fuel and other fuels. The inclusion of silicon dioxide nanoparticles to water emulsified diesel fuel increases the pace of evaporation and results into enhanced fuel–air mixing as well as declination in the ignition delay [13]. Figure 7 shows the respective crank angle (In degrees) for 10%, 50%, and 90% of the fuel burned at maximum load condition. It can be visualized form this figure that 10% of MFFB happens at 0°, 2°, 1.5°, 1.5°, and 1° for diesel, test fuel with 25 ppm of nanoparticle, 50, 75, and 100 ppm of nanoparticle, respectively. Similarly, 50% of MFFB occurs at 16.8°, 18°, 17°, 17.5°, and 17° for diesel and other four test fuels, respectively. 90% of MFFB happens at 35°, 37°, 36°, 37.5°, and 37° respectively, for diesel and other test fuels with increasing amount of silicon dioxide nanoparticles, respectively. It can be observed that emulsified test

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Fig. 7 Mass fraction of fuel burned 10%, 50%, and 90% with respect to crank angle

fuels with silicon dioxide nanoparticles burns at a little faster rate that diesel fuel. This could be due to the reason of affirmative effect of nanoparticles, which enhanced the pace of evaporation and thereby hikes the rate of mixing of fuel with air, thereby ignition delay reduces [13].

3.4

Mean Gas Temperature (MGT)

The mean gas temperature (MGT) is the mean value of temperature of the cylinder of burned and unburned gases present within the combustion chamber. Inside the cylinder, there exists mix of burnt and unburnt air–fuel mixture. MGT demonstrates the pace of reaction from the combustion of fuel and it is preferable to have the value quite near to the adiabatic flame temperature (AFT). The flame, which is generated inside the combustion chamber reach out the wall of combustion chamber away from the injector by about 15° after top dead center [9]. The condition of highest pressure is reached at this point, but the combustion process still continues for additional few crank angle degrees. As a result, the highest temperature was attained at about 15° ahead of maximum pressure. The interaction between MGT and crank angle is shown here through Fig. 8. It is observed that the MGT of the diesel fuel was little higher than test fuels at engine speed of 1500 RPM and full

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Fig. 8 Interaction between mean gas temperature versus crank angle

load. The highest value of MGT for diesel fuel (1387.15 K) is about 2.73% more as compared to the test fuel with 25 ppm dosing of silicon dioxide nanoparticle (1349.15 K). Figure 8 shows the maximum value of MGT; 1352.15 K for test fuel with 50 ppm of nanoparticle, 1382.15 K both for 75 ppm test fuel, and 100 ppm test fuel. It may be due to the increment in in-cylinder pressure of diesel as correlated to other test fuels. The MGT also increases with the addition of silicon dioxide nanoparticle due to the affirmative effects of nanoparticles which enhances the process of combustion.

4 Conclusions In this work, various experiments were conducted to analyze the effects of silicon dioxide nanoparticles for the combustion features of diesel engine fueled with water diesel emulsified fuel. The dosing of nanoparticles varied from 25 to 100 ppm. The experimental work was carried out with an unchanging 1500 RPM speed and 18 as compression ratio. The load of the engine was changed from 2 to 12 kg, and the various combustion attributes were explored. The following are the conclusions from this study:

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• There exists a marginal difference for the peak in-cylinder pressure (ICP) values of diesel and other fuels of water diesel emulsified fuel incorporated with silicon dioxide nanoparticles. Among all the test fuels D94W5S1–Si50 demonstrated the greatest ICP, which was almost close to that of ICP of diesel. There exists a variation of about 0.82% between D94W5S1–Si50 test fuel and diesel fuel value. • The higher surface–volume fraction of nanoparticles improved the transport of heat among the particles and the droplets of fuel, thereby upgraded the atomization of fuel droplets as well as accelerated the process of combustion. • The peak value of heat release rate (HRR) was increased, and the process of combustion becomes advanced. • There was minor disparity between mass fraction of fuel burned of diesel fuel and other fuels. The inclusion of silicon dioxide nanoparticles intensified the pace of evaporation and resulted into enhanced fuel–air mixing as well as declination in the ignition delay. • The mean gas temperature (MGT) of the diesel fuel was little higher than test fuels. The MGT also increases with the addition of silicon dioxide nanoparticle which enhanced the process of combustion due to the affirmative effects of nanoparticles. • Mostly, the superlative combustion features of the engine were attained at a silicon dioxide nanoparticle quantity of 50 ppm to the water diesel emulsified fuel. • Furthermore, there exists a need to explore the effects of nanoparticles on various engine mechanisms, when the engine is operated for the long hours.

References 1. Annamalai M, Dhinesh B, Nanthagopal K, SivaramaKrishnan P, Lalvani JIJ, Parthasarathy M, Annamalai K (2016) An assessment on performance, combustion and emission behavior of a diesel engine powered by ceria nanoparticle blended emulsified biofuel. Energy Convers Manag 123:372–380 2. Basha JS, Anand RB (2014) Performance, emission and combustion characteristics of a diesel engine using carbon nano tube blended Jatropha methyl ester emulsion. Alex Eng J 53:259– 273 3. Behera P, Murugan S, Nagarajan G (2014) Dual fuel operation of used transformer oil with acetylene in a DI diesel engine. Energy Convers Manag 87:840–847 4. Caligiuri C, Renzi M, Bietresato M, Baratieri M (2019) Experimental investigation on the effects of bioethanol addition in diesel-biodiesel blends on emissions and performances of a micro-cogeneration system. Energy Convers Manag 185:55–65 5. Dhinesh B, Annamalai M (2018) A study on performance, combustion and emission behaviour of diesel engine powered by novel nano nerium oleander biofuel. J Clean Prod 196:74–83 6. El-Seesy AI, Abdel-Rahman AK, Bady M, Ookawara S (2017) Performance, combustion, and emission characteristics of a diesel engine fueled by biodiesel-diesel mixtures with multi-walled carbon nanotubes additives. Energy Convers Manag 135:373–393

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7. Ghojel J, Honnery D (2005) Heat release model for the combustion of diesel oil emulsions in DI diesel engines. Appl Therm Eng 25:2072–2085 8. Ghojel JI (2010) Review of the development and applications of the Wiebe function: a tribute to the contribution of Ivan Wiebe to engine research. Int J Engine Res 11:297–312 9. Gupta HN (2009) Fundamentals of internal combustion engines, 2nd edn. PHL Learning Private Limited, New Delhi 10. Huang H, Huang R, Guo X, Pan M, Teng W, Chen Y, Li Z (2019) Effects of pine oil additive and pilot injection strategies on energy distribution, combustion and emissions in a diesel engine at low-load condition. Appl Energy 250:185–197 11. Jiaqiang E, Zhang Z, Chen J, Pham MH, Zhao X, Peng Q, Zhanga B, Yin Z (2018) Performance and emission evaluation of a marine diesel engine fueled by water biodiesel-diesel emulsion blends with a fuel additive of a cerium oxide nanoparticle. Energy Convers Manag 169:194–205 12. Khatri D, Goyal R (2020) Performance, emission and combustion characteristics of water diesel emulsified fuel for diesel engine: a review. Mater Today Proc 28:2275–2278 13. Khatri D, Goyal R (2020) Effects of silicon dioxide nanoparticles on the performance and emission features at different injection timings using water diesel emulsified fuel. Energy Convers Manag 205: 14. Mondal PK, Mandal BK (2019) A comprehensive review on the feasibility of using water emulsified diesel as a CI engine fuel. Fuel 237:937–960 15. Ozener O, Yuksek L, Ergenc AP, Ozkan M (2014) Effects of soybean biodiesel on a DI diesel engine performance, emission and combustion characteristics. Fuel 115:875–883 16. Sekoai PT, Ouma CN, Du Preez SP, Modisha P, Engelbrecht N, Bessarabov DG, Ghimire A (2019) Application of nanoparticles in biofuels: an overview. Fuel 237:380–397 17. Srinidhi C, Madhusudhan A, Channapattana SV (2019) Effect of NiO nanoparticles on performance and emission characteristics at various injection timings using biodiesel–diesel blends. Fuel 235:185–193 18. Vellaiyan S, Amirthagadeswaran KS (2016) Zinc oxide incorporated water-in-diesel emulsion fuel—formulation, particle size measurement and emission characteristics assessment. Pet Sci Technol 34(2):114–122 19. Vellaiyan S, Subbiah A, Chockalingam P (2018) Combustion, performance, and emission analysis of diesel engine fueled with water-biodiesel emulsion fuel and nanoadditive. Environ Sci Pollut Res 25:33478–33489 20. Vigneswaran R, Annamalai K, Dhinesh B, Krishnamoorthy R (2018) Experimental investigation of unmodified diesel engine performance, combustion and emission with multipurpose additive along with water-in-diesel emulsion fuel. Energy Convers Manag 172:370–380

Hybrid Solar PVT Systems for Thermal Energy Storage: Role of Nanomaterials, Challenges, and Opportunities W. Rashmi, V. Mahesh, S. Anirban, P. Sharnil, and M. Khalid

Abstract Spectral splitting of CPV/T (concentrated/photovoltaic thermal) system utilizes the full range of solar radiation to obtain useful energy by coupling solar cells and other thermal absorbers. The PCM coupled with PV/T systems can absorb the heat from solar cells and allowed the PV/T systems to operate at low temperatures. Furthermore, the potential use of PCM and nanofluids with PV/T systems to improve the thermal and electrical efficiency was investigated. The integration of PCM with PV/T systems for building heating, HVAC, desalination and drying applications has been highlighted. The heating COP (coefficient of performance) of build-in PCM with PV/T system can be 70% higher than the conventional air-conditioning systems, and the overall efficiency was about 75.49%, 17.77% of electrical and 55.76% of thermal efficiency. The heat storage capacity of hybrid nanomaterial-based eutectic salts acts as a storage medium for energy storage applications are compared and reviewed. The role of the nanomaterials in terms of optical properties, thermal properties, long-term stability and cost will be discussed, which will guide future research and innovation. Utilizing the full solar spectrum is desirable to enhance the conversion efficiency of solar cells in combination with solar thermal collectors and photovoltaic collectors (PV) for electricity generation W. Rashmi (&) School of New Energy and Chemical Engineering, Jalan Sunsuria, Bandar Sunsuria, 43900 Sepang, Selangor, Malaysia V. Mahesh School of Engineering and Computer Science, Taylor’s University, No 1 Jalan Taylor’s, Subang Jaya, Selangor, Malaysia S. Anirban Symbiosis Institute of Technology, Symbiosis International (Deemed) University, Pune, Maharashtra, India P. Sharnil Symbiosis Centre for Applied Artificial Intelligence, Symbiosis International (Deemed) University, Pune, India M. Khalid Graphene and Advanced 2D Materials Research Group, School of Science and Technology, 5, Jalan Universiti, Bandar Sunway, 47500 Petaling Jaya, Selangor, Malaysia © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_9

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as a hybrid system despite their advantages and disadvantages. The spectral splitting plays a key role in any hybrid or coupled systems, as PV works under spectrum rays and thermal collectors work under infra rays. Thus, optical and thermal design of PV and thermal collectors is required to improve the efficiency of the system. Hence, the hybrid PV thermal (PV-T) collectors can generate electricity and heat energy simultaneously. Finally, the basics of PV-T collectors and the feasibility studies of two novel applications of PV-T collectors (solar cooling and solar still) have been analysed.










Keywords PV-T collectors Spectral filter/splitting Energy storage Nanofluids

1 Hybrid PVT Systems Due to the limited availability of fossil fuels, the global increase in the demand for conventional energy and environmental concerns (greenhouse the effect, carbon dioxide emissions, etc.) have raised the concerns, and solar energy is prevalent renewable energy which is a clean, green, sustainable and inexhaustible source of energy which has potentially replace conventional use of fossil fuels. Researchers have found that utilization of solar energy for multiple applications has enormous potential for opening new opportunities in commercial and development sectors. The driving force for development, economic growth, automation and modernization is sustainable energy [1]. The negative impacts of fossil fuels have triggered many countries that have forced them to use alternative energy source such as solar energy. This paves the road towards reducing the environmental impact with zero-waste by-products, thus providing security to the future energy needs [2–5]. Utilization of solar energy using photovoltaic (PV) cells has been very popular worldwide. The installed capacity of PV has increases from 5.1 to 320 GW [6]. PV technology was stimulated by the government of different countries initially, and within 10–12 years it became very popular and cost-effective with minimum maintenance cost. It is simple in design with the stand-alone system providing an energy source for power generation, water pumping, in solar home systems, communications, satellites, for reverse osmosis in plants and many more [1]. As a result, the utilization of solar energy in the grid using PV technology is very common for many countries and it is going to be the cheapest available energy source very soon. Based on the estimation worlds, total final consumption of various energy sources from the year 2002 to 2030 will increase by 1.6% [8]. A photovoltaic cell is a type of semiconductor that converts visible light (spectrum) into direct current and without any harmful emissions. The generation of photovoltage occurs when light shines on the solar cells. The voltage generated across the solar cell can drive the current in an external circuit and therefore can deliver power. The power output of the cell depends on the condition like temperature, radiations [9]. The average overall efficiency of the PV solar panels has

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Table 1 Development and installation projections in various countries [7] Year

USA (MW)

Europe (MW)

Japan (MW)

Worldwide (MW)

2000 2010 2020 2030

140 3000 15,000 25,000

150 3000 1500 30,000

250 5000 30,000 72,000

1000 14,000 70,000 140,000

recently found out to be 15% and the electric output is around 3%–4%. Table 1 shows the projection of development and installation of solar photovoltaic electricity in the USA, Europe, Japan and worldwide by 2030. To increase the efficiency of the PV system, various studies have been carried out. However, in PV technology, the following challenges have been encountered by various researchers: (i) PV cells can transform 10–15% of the total solar light to electricity leading rest portion being reflected or thermalized. (ii) The cost of batteries (used for storing electricity) has increased energy storage cost particularly for industrial use of solar energy. (iii) Solar energy is not continuous and it varies with the presence of cloud, wind velocity on the atmosphere. So, to make it continuous thermal energy storage is required [6]. (iv) For the PV module, the installation cost is higher than the production cost [7]. (v) Finding a suitable place for PV system installations is a challenge for urban areas. To overcome these problems, scientist has developed solar thermal technology. Compared to PV technology, solar thermal collectors have advantages such as 80% high solar energy collection efficiency and solar thermal collectors manufacturing cost are lower compared to PV cells. Solar collectors are commonly used for solar water heating but also can be used for large power generation using parabolic trough collectors (PTC) and solar towers. Solar thermal collectors are classified as low, mid and high-temperature collectors using flat plates for low and mid-temperature and mirrors/lenses for high-temperature application [10]. Solar heating is commonly used for passive heating; hence, residential and commercial building architectures are very much interested to utilize solar heat for different heating applications to reduce the electricity cost and make the building green. Utilization of solar thermal energy for various application is domestic water heating and cooking food especially the area where grid electricity is very scared, desalinating or demineralized of water for domestic and industrial purpose, industrial process heat especially the surface finish industries, producing steam, electricity generation and industrial use. The temperature ranges for various applications in shown in Table 2.

134 Table 2 Various applications of hot water temperatures obtained from solar thermal collectors [11]

W. Rashmi et al. Temperature range (oC)

Applications

60–90 35–90 40–90 35–60 20–50 70–200 150–350

Desalination District heating (space heating) Industrial process heat Domestic hot water Pool heating Solar cooling Electricity generation

Due to the versatile applications of solar heat as shown in Table 2, researchers are working on developing novel technologies for capturing, storing solar heat at different temperatures. Solar thermal collectors like a flat plate, evacuated or parabolic troughs can capture solar energy under clear sunlight and that can be used for different applications at minimal cost compared to other technology used for electrical energy generations [12]. Researchers observed that under high concentration ratio, PV systems electric generation efficiency reduces. Due to the uneven distribution of spectrum and poor heat dissipating technology from PV cells, the temperature gradient inside the PV cells increases. To reduce the temperature gradient and maintain low thermal resistance inside the PV cell, active cooling requires [12–14]. The four main research areas as identified by BINE [15] are PTC technology, Fresnel system, tower power plants and tests and quality assurance. Based on the BINE The men info brochure, 95% of the commercially operated solar thermal power plants are PTC, while Fresnel systems provide world capacity of 45.5 MW as of the year 2013 which are generally used for high temperature/high-pressure application. It is proved that solar thermal power plants can store thermal energy more efficiently and cheaply compared to PV cells [16]. It has been observed that maximum energy produced in the world from steam generation using coal, oil, gas, biomass or other sources [17]. Distributed solar thermal collectors with thermal storage is a good option for generating heat (steam) for power generation and also, it can solve the problem of intermittency of solar energy. Heat-carrying and storing water is the most suitable and popular thermal fluid for solar thermal collectors. As solar thermal collectors and PV, both are useful for electricity generation and they have their own advantages and disadvantages, thus coupling these two systems could be a solution to overcome the disadvantages. The most challenging task for coupling these two is the operating temperature of each. PV is efficient under low temperature while thermal collectors work more efficiently under high temperatures. So for hybrid or coupled system first splitting of the solar spectrum is required, as PV works under spectrum rays and thermal collectors work under infra ray. Thus, proper optical and thermal design of PV and thermal collectors is required. Hence, the concept of hybrid PV thermal (PVT) collector’s originated which can generate simultaneously electricity and heat [18]. Two different types of PV-T modules; Type A and Type B integrated with tube- and sheet-type and

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parallel plate-type thermal collectors were used. The hybrid PV-T collectors increased the average thermal efficiency by 40.7% for Type A and 39.4% for Type B at 0.03 kg/s flow rate under tropical climatic conditions. Zhu et al. [19] conducted experiments by immersing the PV cells in water for high concentration system. The module temperature was cooled to 45 °C, at an irradiance of 940 W/ m2. It was also noted that the long immersion in water degraded electrical performance. The various advantages of the hybrid PV-T collectors include: (i) Hybrid PV-T solar collectors can keep PV cells more relaxed and increase dispatchable electricity generation efficiency, with lower cost [20]. (ii) It produces electrical energy and thermal energy simultaneously at day time so thermal energy can be stored in the thermal storage system and can utilize during high demand such as solar desalination, industrial processing, food processing, sterilization, domestic water heating, etc. [21]. Alternatively, if the thermal fluid temperature can exceed above 300 °C, it can be utilized for steam power generation [22]. (iii) Hybrid PV-T collectors allow the PV cell to operate at low temperatures. (iv) Literature reviews show that most commonly approach for hybrid PV-T collectors is the utilization of spectral splitting [12, 23, 24]. Spectral splitting enables hybrid PV-T collectors to absorbed heat energy from the sun rays and directly satisfy the residential and industrial heat demand and simultaneously produce the electricity as per onsite demand or distribute electricity through the grid [25]. Over the years, researchers have developed different types of PV-T collectors and analysed their performance. The different configuration such as heat transfer fluid as air/liquid, forced or free convection, with/without concentrators, glazed/ unglazed PV cells, different materials for solar cells like monocrystalline, polycrystalline, amorphous silicon, thin film, etc. Figure 1 shows the cross section of a PV-T collector. In this system cell for circulation of cold water and keep the PV cell temperature low, heat exchanger pipes have installed in between the PV cells. Air, water with or without antifreeze (glycerine) liquid, nanofluids have been used as thermal fluid, and heat has been used for space heating, hot water heating, process heating, sorption cooling also. High-performance selective coating (black chrome or titanium oxide over a nickel or copper base) has been used on the upper surface of pipes for maximizing the heat absorption capacity and keep the PV cell temperatures low [27]. PV-T collectors are installed horizontally in parallel rows on the roof of buildings and maintained a distance between each row for avoiding shading. Literature proves that due to high overall efficiencies, PV-T collectors are promising and very useful for densely populated urban areas where available spaces are limited. Combined thermal and electrical efficiency can be achieved by 70%, 15– 20% for PV and 50–55% for thermal collectors. In urban areas, PV-T collectors can handle 60% of heating demand (residential/industrial) including direct heating and also fulfil electricity demand [12].

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Fig. 1 Cross-sectional view of hybrid PV-T collectors [26]

2 Nanofluids as Heat Transfer Fluids Heat transfer fluids (HTF) generally is a gas or liquid that transfers the heat as a medium in cooling on one end of the system, transporting the heat and storing the thermal heat energy on the other side of the system. Conventional fluids such as water, ethylene glycol, oil, and ethylene glycol + water are mostly used HTF. These conventional fluids play a crucial role in industrial processes such as chemical, heating, cooling processes, thermal energy and microelectronics [28]. However, the main disadvantage with these base fluids is low thermal conductivity, which restricts them to reach to high exchange rates or heat transfer capability in thermal or heat transfer applications [8, 9, 27]. Recently, new techniques are available to improve the heat transfer of nanofluids. Nanofluids proved to be an efficient way to increase the heat transfer rate of base fluids. One of such techniques is the addition of highly thermal conductive nano-sized nanoparticles in base fluids, which can be termed as “nanofluids” [28–30]. Choi first coined the term “nanofluids” in 1995 [30]. Moreover, the increase in heat transfer in conventional fluids might be due to the Brownian motion of nanoparticles, and decrease in the thermal boundary layer is one of the possible reasons as stated by Ali et al. [31]. Most commonly used nanoparticles in base fluids to enhance the thermal conductivity and heat transfer properties are such as metals, metal oxides, metal nitrides, metal carbide, and carbon nanomaterials. Many researchers conducted different studies related to the impact of nanofluids to improve the efficiency of the system. Ziyadanogullari et al. [32] study the influence of three different nanofluids such as Al2O3, CuO, and TiO2 at 0.2, 0.4, and 0.8 vol.% dispersed in water to increase the thermal efficiency of the solar flat plate collector. The results showed that CuO/water-based nanofluid displayed the highest efficiency, while the lowest was reported for TiO2/water. This might be due to the changes in terms of conductivity values of nanoparticles. Sadeghi et al. [33] observed the increase in the thermal efficiency of a solar water heating system with the addition of CuO/water-based nanofluid. Different vol.% of CuO from 0.01 to 0.08 was investigated both numerically and experimentally to enhance the thermal

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performance of evacuated tube collector. The results exhibited that the nanofluid with 0.08 vol.% showed increased energy and exergy efficiency by 10% and 12.7%. Al-Waeli et al. [34] demonstrated the use of SiC nanofluid without surfactant which was analysed for a PV/T system. The nanofluid with 3 wt% of SiC was tested within the temperature range of 25–60 °C and found an increase in thermal conductivity up to 8.2%. Furthermore, the results showed the 3 wt% of SiC nanofluids exhibit 24.1% increased electrical efficiency and 88.9% improved overall efficiency compared to the standard PV system. However, the main problem associated with these nanofluids is poor stability, high cost, and the viscosity increase of nanoparticles followed by the increase in frictional pressure drop and pumping power. To overcome these issues, researchers come up with an alternative solution by using hybrid nanofluids as an effective replacement to single nanoparticles. However, the use of hybrid nanoparticles as hybrid nanofluid is still at an early stage and the synergistic effect of these hybrid nanoparticles an added advantage to improve the efficiency and performance of the system in solar applications. For instance, traditional fluids such as water and the air were used as a circulating fluid underneath the solar panel to improve the effectiveness by cooling the solar cells [35, 36]. Besides, the cooling effect can be further enhanced with hybrid nanofluids by substituting the existing nanofluids due to their synergistic effect and improved thermophysical properties. The application of nanofluids in various solar collectors is discussed in the later section.

3 Thermal Energy Storage Medium Thermal energy storage (TES) is nothing but the change in internal energy of a material due to sensible heat, latent heat, or a combination of these [37]. TES process can be explained clearly in Fig. 2.

Fig. 2 TES process during energy storage and release [38]

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The Function of TES Systems

In the current scenario, there is a huge demand for thermal energy to satisfy the present needs. However, there is an availability of thermal energy still few gaps between thermal energy supply and demand exists. (i) Price variation in thermal energy during peak and off-peak time. (ii) The time difference in thermal energy throughout the generation and consumption process. (iii) The space between the energy source and the location of consumption. Thermal energy is stored for a longer duration or not consumed results in the dissipation of energy in the form of wastage. The most convenient way to generate thermal energy generation based on the requirement is by burning fuels that lead to environmental pollution, greenhouse effect, and global warming. The increase in usage of fossil fuels increases the overall cost, which allows in search of new technology to harvest free thermal energy from renewable sources such as the sun [39]. TES systems provide socio-economic and environmental benefits by decreasing the consumption of fossil fuels. The role of TES is to store the excess of heat by preventing thermal energy loss until further use.

3.2

Sensible Thermal Energy Storage

In the case of sensible thermal energy storage (STES), the energy is stored by increasing the temperature of material either solid or liquid. STES system uses specific heat capacity (Cp) to store the amount of heat energy in a material; there is no significant phase change with the change in temperature during charging and discharging phase. The thermal energy stored in STES systems is given by: Q ¼ m
Cp
dT

ð1Þ

For example, water has the highest specific heat and tends to best STES liquid due to its low cost. However, molten salts, oils, and liquid metal were used as perfect materials above 100 °C.

3.2.1

Sensible Thermal Energy Storage Materials

Sensible thermal energy storage materials are categorized into two based on their nature as shown in Table 3 below. (i) Liquid storage medium; (ii) Solid storage medium.

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Table 3 Different types of sensible thermal energy storage materials commonly available

Sensible thermal energy storage materials

Water

Liquid storage medium

Mineral Oil Molten salts Liquid metals and alloys Rock

Solid storage medium

Concrete Sand Bricks

3.3

Latent Thermal Energy Storage

Latent thermal energy storage (LTES) is defined as when the material undergoes phase/state transition from solid–solid, solid–liquid, and liquid–gas or vice versa during absorption or releasing heat. The storage capacity of the LTES system with phase change materials (PCMs) is termed as latent thermal energy storage materials [40].

3.3.1

Latent Thermal Energy Storage Materials

Phase change materials (PCMs) play a crucial role in energy interchange process, where the material melts with the rise of temperature and changes its phase from solid to liquid by releasing the heat. In the case of temperature drop, the material turns to solid state by absorbing the heat, which is demonstrated in Fig. 3. LTES materials must have high thermal conductivity and high latent heat [41]. These materials should have melting point at the operational temperature range of TES and melts accordingly with minimal subcooling, which is chemically stable,

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Fig. 3 Phase transition process of PCM during melting and solidification cycles [38]

cost-effective, non-toxic, and less corrosive [42]. Moreover, these materials should have a smaller temperature difference between storing and evolving heat [41]. Besides, these materials should possess some of the properties such as thermophysical, chemical, and kinetic properties, while designing the thermal energy storage systems based on their availability and economic aspects [43]. Thermal properties (i) High latent heat of fusion; (ii) Phase transition temperature; (iii) Excellent HTF. Selection of desire material for a particular application requires high latent heat to reduce the size of the heat store physically. High thermal conductivity to minimize the losses during charging and discharging and the working temperature of the material during the heating and cooling process must match to the transition temperature. (a) Physical properties; (i) (ii) (iii) (iv)

Good phase equilibrium; High density; Low vapour pressure; Small volume change.

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The material should be stable during freezing and melting to maintain proper thermal energy storage, and high density is acquired to strict the size of the container to a smaller one. (b) Chemical properties; (i) (ii) (iii) (iv)

Chemically stable for a long duration; Material compatibility; Not harmful; No fire hazard.

These materials sometimes undergo degradation due to moisture loss, chemical decomposition. Materials tend to incompatible during the fabrication or assembly process. Importantly, these should not be toxic, flammable, and explosive for safety purposes. (c) Kinetic properties; (i) No super cooling; (ii) Adequate crystallization rate. In the case of salt hydrate, supercooling is the most worrying part and more than a few degrees will restrict with proper heat extraction from the store, and 5–10 °C of supercooling will stop it completely. (d) Economics; (i) Easily available; (ii) Ample; (iii) Profitable. Low price, abundant availability of the materials are also given high priority. The latent thermal energy storage materials are classified as organic and inorganic materials. The various materials and their advantages and disadvantages are listed in Table 4. Out of different types of thermal energy storage materials, only molten salts and phase change materials play a prominent role in solar thermal plants.

3.3.2

Molten Salts

Currently, molten salts have become a promising candidate to serve the purpose of both heat transfer fluid (HTF) and thermal energy storage (TES) medium. The following criteria make them as a potential material such as wide temperature range, low cost, environmentally friendly [48]. The addition of nanoparticles plays a crucial role in increasing the specific heat capacity and by reducing the overall cost of storage on solar thermal plants [49]. Still, scientists continue to find the best combination of salts and nanoparticle that can be potential to be used in large-scale applications [50].

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Table 4 Classification of latent thermal energy storage materials [44–47] Type

Storage materials

Advantages

Disadvantages

Organic

Paraffin wax

– Pure paraffin waxes are very expensive – Commercial waxes are cheap – Melting temp range from 5 to 127 °C – Moderate thermal storage densities – Safe to use, reliable, non-corrosive, cost-effective – The high heat of fusion – No effect of super cooling – Chemical stability – Excellent melting temperature range – Low supercooling during phase transition – The high heat of fusion – Melting temp range from 14 to 102 °C – Melting temp range from 29 to 69 °C – Low super cooling – Chemically stable – Chemically, thermally stable, – Non-toxic, non-flammable, low cost, non-corrosive – Melting temp range from 50 to 260 °C – High latent heat – Non-toxic, low cost – Salt hydrate working temp around 30–50 °C – High temp salts working range from 250 to 600 °C – Small volume change on melting – High latent heat of fusion – High thermal conductivity, thermal stability, reliability

– Low thermal conductivity – Non-compatible with a plastic container – Flammable – Large volume change

Fatty acids

Esters

Glycols

Alcohols

Inorganic

Salts

Metals and alloys Eutectic

– Melting temp range from 13 to 767 °C

– Low phase transition, low enthalpy of phase change – Low thermal conductivity, density, large volume change – More expensive than Paraffin – Expensive – Low density, thermal conductivity – Highest super cooling – Low thermal conductivity – Poor chemical stability and cycling stability

– Low thermal conductivity – Poor nucleating properties – Supercooling

– Low vapour pressure – Low specific heat – Low specific heat capacity

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Phase Change Materials (PCMs)

PCMs are designed to absorb heat from solar collector and transfer to another medium for steam or electricity generation. These materials are commonly integrated with solar collector systems for the building sector to decrease the temperature change and increase the collector performance [51]. The integration of PCM with flat plate collector (FPC) to increase the performance was not a new technique and well known since 1987 [52]. Several researchers reported the usage of PCMs with FPC to improve the overall performance, thermal and electrical efficiencies. Poole et al. studied the transpired solar collector (TSC) integrated with PCM (80 kgs of salt hydrate) and evaluated the performance of TSC using one-stage and two-stage configurations [53]. The results indicated that the TSC combined with PCM can store 34% of total useful heat energy during night times over seven days in April. Furthermore, one-stage TSC showed 8% increased efficiency and produced 2 °C rise in temperature than two-stage TSC at a suction velocity of 0.023 m/ s. The effect of PCM in flat plate solar collectors (FPSC) was analysed by Enibe [54] and Ali et al. [55] and found an increase in the thermal efficiency of 22% and 96%. However, the efficiencies of FPSC were not compared with other kinds of collectors with water as a medium. This might be due to the low convective coefficients in case of air compared to water. Indartono et al. investigated the use of yellow petroleum jelly as PCM for passive cooling of the PV system [56]. The results highlighted that the application of PCM on PV displayed an increased efficiency of 21.2%, higher power and decrease in temperature. Preet et al. experimentally investigated three different systems consists of conventional PV, water-based PV/T, and PCM integrated PV/T [57]. The results showed an increase in electrical efficiency of 10.66 with water-based PV/T, and about 12.6 was found for PCM-based PV/T panel. During the day time, the average electrical efficiency was observed around 230% for water-based and 300% for PCM-based PV/T compared to conventional PV. Yang et al. conducted experimental studies on PV and PV/T systems [58]. The results reported that PV/T and PV/T-PCM achieved thermal efficiencies of 58.35% and 69.84%. Moreover, the solar electrical efficiency of PV/T and PV/T-PCM was observed as 6.98% and 8.16%. Andasol-type power plants are constructed in Spain with 50 MW capacity integrated with thermal storage tanks that run for 8 h cycle as shown in Fig. 4. In the Andasol plant, heat from the thermal oil (HTF) is transferred to the salt tank shown in green for storage while in the molten salt tank, the salt itself is used as a heat transfer medium. In conclusion, PCM usage is very crucial for enhancing the thermal, electrical efficiencies and overall performance of PV/T systems.

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Fig. 4 Comparison of Andasol and molten salt plants. Source DLR

4 Spectral Filter Technology The idea of maximum utilization of solar energy by the solar ray splitting approach was suggested by Jackson [59] in 1955. Then in 1978, Moon et al. [60] successfully experimented spectral beam splitting methods. Even today, scientists are still using their experimental approach. Immense and Mills [61] had reviewed extensively on spectral beam splitting the technology and its application on harvesting solar energy. Scientists proved that spectral beam splitting methods contain high

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solar energy conversion efficiencies and huge scope of design flexibility; hence, scientist is still working and exploring these technologies and developing novel designs. Four spectral splitting approaches are applicable for the PV-T collector’s system, which are based on absorption, refraction, reflection, and diffraction. Spectral beam splitting methods can be considered as PV cell’s heat absorption management system. These heat management systems remove the wavelength of infrared from solar ray, which is not useful for PV cells and responsible for generating heat. Solar spectrum beam splitting process consists of two basic processes: (i) photothermal process and (ii) photovoltaic process. Conversion of heat from spectrum beam is dependent on optical properties of PV cells, selective coatings or thermal absorbing materials. The photovoltaic process depends on spectrum wavelength, and it possesses maximum efficiency when converting photons very close to the PV cell bandgap energy. Photons larger than PV cell bandgap energy are partially used for the photovoltaic process, and remains are converted into electric energy. Photons smaller than PV cell bandgap energy easily pass through the PV cell and generate heat energy. Hence, spectral beam splitting approach has been introduced where higher energy conversion efficiency can be achieved using photothermal and photovoltaic processes simultaneously. In solar beam spectral methods, the solar beam is splinted into two parts and optimum solar energy is utilized by PV cell and solar thermal collectors which is commonly called PV-T collectors. In common PV-T collectors, the PV cells produce electricity as well as absorbed heat. Figure 5a shows a traditional PV-T collector working, where sunlight directly strikes on the PV cell. Parts of sunlight get converted into electricity and the rest part are absorbed by PV cell material. Heat produced by the PV cell is absorbed by the thermal fluid, which flows at the bottom part of the PV cell [62]. Scientists observed that the heat transfer between the PV cell and its surroundings can be limited by the contact thermal resistance. To reduce this contract thermal resistance, researchers used different cooling techniques such as microchannel cooling, heat tube cooling, liquid immersion cooling. Scientists have noticed that liquid immersion cooling gave better performance compared to other cooling methods as this technology effectively reduces the thermal contact resistance of the PV cells. Moreover, non-uniform temperature distribution on the PV cell was observed after the long-term exposure of the PV cells to deionized water, which can reduce the IV performance of PV cells. The main disadvantage of this system is a thermal coupling between PV cell and thermal fluid that diminishes the PV cell performance. The continuous heat drawn by the thermal fluid from the PV cells turns down the PV cell efficiency rapidly which is another biggest concern. To overcome this problem, spectral beam splitting has been introduced [63–65] where researchers have decoupled PV cell and thermal fluid. With the help of spectral beam splitting technology, the sunlight beam has been decomposed into different spectral bands. Then each band is directed towards suitable receivers like PV cell, thermal absorber, etc. (Fig. 5b). As PV cell and thermal absorber are in a decoupled state, temperature increases inside the thermal absorber higher than the PV cell temperature.

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Fig. 5 PV-T collectors with a thermal fluid b decoupled with thermal fluid

Ruhle et al. [66] developed a selective absorbing material of varying (along with the thickness) refractive index structure which consists of high mechanical strength and toughness and highly stable under thermal loading (Fig. 6a). They used dichroic material for selective absorber, and it absorbed infrared rays and reduced wavelength to 675 nm, which is an effective spectrum for PV cell. From this configuration, they observed the overall efficiency of the cell reached 17% which is higher than pure PV cell (12.3%). Further, Mitchell et al. [67] developed double-stage spectral splitting medium integrating with three PV cells, and Eisler et al. [68] applied multi-stage spectral splitting for seven different solar cells. Figure 6b shows a liquid-based spectral splitting PV-T system. It is observed that the liquid filter acts as an optical filter as well as thermal fluid. Part of the solar rays, i.e. infrared rays absorbed by the liquid filter and rest spectrum rays, passes to PV cell. Due to this phenomenon, enthalpy of liquid filter increased. An additional cooling system has been used for recovering waste heat from the PV cell, which also increased overall efficiency [13].

Fig. 6 a Spectral splitting methods based on absorptive filters, b absorption-based spectral splitting PV-T system

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Nanofluids Application in PV/T with Spectral Splitting

Different types of spectral splitting methods have been discussed above, out of that absorption-based approached is very popular in PV-T collectors due to its thermal characteristics. Thus, here nanofluids which have been used for absorptive-based filters have been discussed. Researchers have already worked on heat transfer and spectral splitting properties of nanofluids and nanoparticles for the PV-T system [69, 70]. They have developed nanoparticles which can filter solar energy (absorb the infrared remaining transparent to PV cell) [71]. The literature reviewed shows [72–75] that by the help of the above-discussed nanofluids, PV-T collectors have been developed and their performance has been observed. Table 5 shows different nanofluids and its performance on the PV-T collector. Thermophysical properties, glass cover transmissivity, nanoparticles volume fraction and absorption properties of nanofluids make them most significant for increasing in collector’s efficiency and thermal storage applications. Nanofluids are used in direct absorption solar collectors for low-temperature application across the world. The absorption properties of working fluid play a significant role in deciding the efficiency of the collectors. Literature review shows that infused nanofluid within solar collector has increased efficiency and performance of solar collector and thermal storage system [76]. For volume fraction range of 0.8–1.6%, the efficiency increased by 8% for [77]. The above table shows that nanofluid possesses better thermal conductivity and a higher heat transfer coefficient. Therefore, employing nanofluid in the solar collector is always advantageous as the size of the collector can reduce with increases in thermal conductivity and heat capacity of thermofluid. Recent developments in nanotechnology have led to the fabrication of nanoparticles that can selectively filter solar energy. Scientists have noted the following advantages after using nanofluids in PV-T collectors. (i) As nanoparticles have high thermal conductivity, so heat transfer performances of nanofluid increase. (ii) Due to the very tiny size of nanoparticles, it mixed up uniformly with base fluid and can move faster inside the solid blocks or porous medium and gives very good results for heat transfer. (iii) Nanofluids have a large surface area (more than 100 m2/g) compared to traditional fluid, so it gives a high heat transfer rate. (iv) The nanofluid reduces the scaling and fouling problem in conventional collectors. (v) Thermal conductivity, heat capacity, viscosity, the density of nanofluids can be varied with its particle concentration which makes it suitable for different industrial applications. Due to high heat capacity, it can store a large amount of heat compare to pure liquid.

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Table 5 Various nanofluids and their application Types of nanofluid

Application

Remarks

Graphite/Therminol VP-I [78]

Tower collectors 10–100 MW Flat plate collector

Improvement in efficiency with a variety of concentration Increase in collector’s efficiency and effectiveness for various weight fractions and pH ranges 3.5, 6.5 and 9.5 Weight concentration varies 0.2% to 0.4% (Nanoparticle size 15 nm) 28.3% increase in collector efficiency compared to the pure water of different mass flow rate Using surfactant maximum collector efficiency 15% for volume fraction 0.005% Collector efficiency increase 8.1% for 1.5 LPM and 4.2% for 2 LPM compared to pure water 5–10% increase in thermal efficiency

MWCNT/Water [79]

Al2O3/Water ZnO/Water MgO/Water [80]

Tubular collector Flat plate collector

Al2O3/Water [81]

Direct absorption solar collector

Aluminium particle base fluid (Thermal VP-1) 0.05% volume concentration [82] Nanoparticle-enhanced ionic liquid [83]

Concentrating parabolic solar collector Flat plate collector

Copper oxide [84]

Flat plate collector

Highly selective dichroic coating [85]

Concentrating collector, PV cell and mirror

Silica-coated nanoparticle and water as a base fluid [86, 87]

PV cell

5% increase in thermal conductivity on the variation of ionic concentration 23% increase in heat capacity for alumina-based nanofluid 26% increase in heat capacity for silica-based nanofluids Reduction in entropy and pressure drop and increased in heat transfer capacity Infrared absorbed by the thermal receiver and narrowband spectrum absorbed by the PV cell Diffuse solar spectrum also absorbed High efficiency Used for absorbing high-energy photons

(vi) For equivalent heat transfer, nanofluids require less pumping power compared to the conventional thermal fluid. (vii) Due to the very less fouling and clogging effect, nanofluids are very useful for microchannel heat exchanger applications. (viii) The heat transfer increases as a result of an increase in the heat transfer surface area between the particles and fluids.

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(ix) Due to good optical and thermal properties, nanofluids can easily absorb solar heat and scatter solar spectrum. (x) Due to Brownian motion phenomena, liquid nanofluid can sustain and possess stable properties under high-temperature conditions. (xi) Nanofluids have less friction and wears when it flows inside the pipe because nanoparticles dispersed fast in base fluids. (xii) Turbulence can generate easily inside the nanofluids due to the presence of nanofluids, and it increases heat transfer performance. For selecting solar beam splitting fluid, its optimal and thermal properties, the stability of fluid, and cost are very important concerns. Most of the researchers have used single nanoparticle, but as per Mie scattering theory if multi-material-based nanofluids can increase optical properties and its stability under high temperature. Literature shows that effective absorption properties are varied for different nanoparticles. Multiple nanoparticle-based nanofluids can be a novel filter with very good performance close to the ideal filter if different nanoparticles can mix in such a way that nanofluids should transmit 100% filter wavelength range to PV cell and should possess high spectrum transmissivity and absorbance of infrared. These nanofluids should split solar spectrum beam into two parts (100% filter wavelength range and 0% spectral passing outside the PV Cell) and optical losses become zero. Nanofluids should obtain high transparency inside the wavelength range and low transparency for the rest of the solar beam spectrum and should able to convert useful heat by absorbing infrared rays. For that, it should have high heat capacity, high thermal conductivity, and a big range of operating temperatures depending on the PV-T application. Looser et al. [66] inspected 18 different liquid-based adsorptive filters like Duratherm 600, Duratherm G, industrial propylene glycol (PG), pink-dyed PG, and Royco 782. They suggested industrial propylene glycol and Duratherm G for PV-T collector’s application due to low-cost, good optical properties, and high-temperature stability. Solar infrared spectral comprises in the nanoparticle doped thermofluid. Duratherm S [88] selects as the base fluid of filter. It is a polydimethylsiloxane-based oil and obtains very good optical properties. It possesses thermal stability at high temperature (204 °C and can extend up to 315 ° C at inert gas atmosphere region) [89]. For increasing thermal conductivity and heat capacity of the base fluid, gold nanospheres and indium tin oxide [(ITO) nanocrystals (nominally hexagonal crystals) for controlling optical properties in the infrared spectral region] can be mixed. Silica-coated nanospheres can also be provided by nanocomposite nominally 50 nm gold diameter with a 25 nm silica shell [90].

4.2

Application of PV/T

After the above discussion on PV-T, two main applications have been proposed using PV-T collectors as a key source. Aim of these examples such as solar cooling

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and solar stills is to explore the PV-T collector’s knowledge beyond the aforementioned studies. The proposed applications are the integration of PV-T collectors, solar cooling technology, thermal energy storage materials, and heat transfer fluids to satisfy the requirements such as cooling systems for cold storages and water distillation plant for buildings.

4.2.1

Solar Cooling

Due to the diminishing stock of fossil fuel and environmental issues regarding CFC/ HCFC refrigerant, using of solar cooling technology is getting more attention in recent years. Vapour compression cycle which is very popular for cooling is facing difficulties to run refrigeration/air condition system in rural areas due to unavailability or scarcity of grid electricity. Due to the poor storage facility near the cultivation field, every year large quantities of agriculture products perish annually. Also, it has been noticed that due to the time gap between milking and storage milk in rural areas, spoilage is more. Therefore, to develop a cold storing facility in rural areas and overcome the above difficulties, low-grade energy (solar heat) driven by a cooling system is a good option. Cooling systems utilizing low-grade thermal energy sources have the advantages of not having the harmful effects of traditional vapour compression refrigeration systems to a great extent. In other words, these alternative systems can cater to the rising demand for sustainable technology. Utilization of solar and waste energy is the key solution to reduce electricity requirements without compromising on the advancement of technology and the level of comforts [91–94]. Cooling can be attained by two basic methods. The first one is a PV (photovoltaic)-based solar energy system, where solar energy can convert into electrical energy and use it to run conventional vapour compression system for refrigeration. Solar energy can be transformed into electricity with the help of photovoltaic cells, and then, compressor of the refrigeration system can run by that electricity. The second one utilizes a solar thermal refrigeration system, where a solar collector directly heats the refrigerant through collector tubes instead of using solar electric power. Heat energy receiving from PVT collectors can be a good option for this system. Heat absorbed by heat transfer fluid (HTF) from PV cell can use for solar thermal refrigeration. Figure 7 represents a solar refrigeration system which can run by PV-T system. For solar thermal cooling, adsorption refrigeration technology has been proposed here. In an adsorption refrigeration system, the conventional mechanical compressor of the vapour compression cycle has been replaced by the thermal compressor (adsorber/desorber bed). The main components of an adsorption refrigeration system are the adsorber/desorber bed, condenser, evaporator, and throttling valve. Thermal compressor, which is a combination of adsorber/desorber, is operated by stored heat from thermal storage (Fig. 6). This adsorption system integrates with two loops (cooling and heating). Through heating loop, HTF (nanofluid) carries the heat from PCM material of thermal storage and deliver it to desorber bed. Desorber

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Fig. 7 Hybrid solar cooling system using PV-T collectors

bed is a closed heat exchanger in which porous adsorbent (filled with refrigerant in its micro/mesopores) presents. Due to heating up by HTF, refrigerant adsorbed inside the adsorbent is vaporized and comes out from adsorbent pores. Hence, the refrigerant vapour pressure, inside the desorber bed, increases. After achieving the condenser pressure valve between desorber and condenser opens and vaporize refrigerants goes to the evaporator through the expansion valve and desire cooling effect generates in the evaporator (Fig. 6). To ensure the seamless operation of the refrigeration process, the solar load intermittency issue, a thermal energy storage system (TES) has been proposed. It can be capable of storing and supplying heat at a medium temperature range (120– 200 °C), where PCM material has been used as a storage material. It is coupled with PV-T collectors from where heat transfer fluid carries the heat and stores inside the PCM material. Phase change materials (PCMs) have proven to be an effective solution in this context by acting as isothermal heat reservoirs with high energy storage density. The excess heat available during the high sunshine hours will be directed to a PCM-based heat exchanger through a heat transfer fluid (HTF). The heat stored in PCM will be later released to the heating zone for the refrigeration process by another HTF (nanofluid). Although adsorption refrigeration is technically successful, it is not commercially competitive with the conventional vapour compression or absorption refrigerators. Hence, further research is required either to improve the existing designs for more efficient performance or to reduce system unit cost or to achieve both [95].

4.2.2

Solar Desalination/Distillation

Solar desalination/distillation is a water purification process for concerting distilled water from hard water or brackish (water contains salt, impurities) to meet the demand for economically drinking purpose [96]. Recently, solar distillation/

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Fig. 8 Solar still using PV-T collectors

desalination has attracted several scientists’ attention to providing clean and reliable water supply to the customers. Several researchers have studied different types of techniques such as solar stills, wicked, inclined and stepped solar stills to achieve the desired range of distillation rate [97]. In this process, unpurified water kept in a closed basin cover by the glass (Fig. 8). Heat energy absorbs by PV-T collectors, carries by heat transfer fluid (HTF), and circulates surrounding the store water lower part of the basin. Due to the transfer of thermal energy inside the stored water, water evaporates in the closed basin. Outside temperature of the closed basin is very less compared to the inside water vapour temperature. Due to this temperature difference, water vapour becomes condensed to store lower part of the basin (Fig. 8). From there, pure water will be collected [98, 99]. This process removes salts and other impurities. Ammous and Chaabene [100] designed a PV/T-based desalination system for tomato irrigation, where the coolant was used to heat the brackish water through a heat exchanger. Kumar et al. [101] used hybrid active and passive solar stills integrated with PV flat plate collector to preheat the water. The active solar still showed higher thermal performance and 20% more efficient than the passive solar still. The results showed that the annual yield of active solar still is 3.5 times higher than the passive solar still.

5 Solar PV/T for Building Applications The power consumption in buildings has been increased gradually to 7% from the past few decades [102, 103]. Besides, electricity generation, there is a need to develop and design a wide range of PV/T-based building applications including use of PCMs to potentially reduce the heating or cooling loads in buildings [104–106]. Building-integrated and roof-integrated PV/T systems are the most commonly used approaches in buildings. Lin et al. [107] developed a ceiling ventilation system integrated with PV/T and PCM to evaluate the performance of the system (Fig. 9).

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Fig. 9 Hybrid PV/T-PCM for HVAC in buildings [107]

The system provides low grading heating using winter daylight radiation and cooling energy for buildings using summer night-time sky radiative cooling besides electricity generation. The results showed that the hybrid system can increase the thermal comfort of the buildings with an increase in temperature to 23.1 °C in the air during the winter without using any air-conditioning systems. Feng et al. [108] proposed a novel CPC (compound parabolic concentrator) combined with the solar PV/T/D (photovoltaic/thermal/daylighting) as a transparent roof with green building design. The hybrid system can achieve high efficiency using solar energy, which can improve the visual comfort of the building by controlling the daylighting and overheating of the building during the noon. Yao et al. [109] designed a hybrid solar PV/T heat pump combined with build-in PCM for underfloor heating for building applications. The results indicated that the heating COP (coefficient of performance) of build-in PCM can be 70% higher than the conventional air-conditioning systems and the overall efficiency was about 75.49% including 17.77% of electrical and 55.76% of thermal efficiency.

6 Challenges and Opportunities Solar thermal collectors face several challenges such as complicated design, transportation energy losses, cost of the system is high due to complicated design, manual operation and maintenance. However, the existing challenges can be solved by improving the design and automating the operation. The use of thermal oil in the system for heat transfer poses another challenge due to seepage of the toxic oil underground during system leakage. Hence, more advanced and effective heat transfer fluids have to be designed. Improving the economic efficiency of the

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Fig. 10 Flow patterns in the horizontal tube during evaporation. Source DLR

Fresnel system and solar towers especially the receivers improves the overall efficiency of the system. PTC being the most effective system operating at high process temperature and greater efficiency poses a technological challenge indirect steam generation. So, the entire tube system has to be designed to operate at high pressure up to 100 bar due to existence of the two-phase system, particularly controllability and mechanical loads due to formation of water slugs as shown in Fig. 10. Furthermore, due to poor heat transfer between the tube wall and steam phase, there exists a dry out point, which adds additional thermal stress [15]. Thus, the absorber tube is the key component in the PTC system. Among the various heating fluids used, nanofluids are the most recent and advanced. However, the use of nanofluids also has the following challenges in an application such as: (i) Stability of nanofluid at transient condition (optical and thermal properties); (ii) Reducing of sedimentation of nanoparticles by maintaining a steady mass flow rate of nanofluids; (iii) The behaviour of nanofluids (optical and thermal properties) at medium and high temperatures; (iv) Nanoparticles behaviour (extinction coefficient variation with time) under infrared and visible spectrums; (v) Stability of nanofluids (Brownian motion) at different pressure and temperature condition; (vi) The viscosity of nanofluids variation concerning temperatures (an increase of nanofluids viscosity also increase pumping energy of the plant, thus it increases operating cost); (vii) Nanofluids economic, entropy, energy analysis for high and medium temperature solar thermal application (PV/T solar collector); (viii) Design of collector for achieving efficient and cost-effective solar thermal system; (ix) Longevity and durability of PV/T collector is under daily thermal cycles. Thus, molten salts are more successful as an energy storage medium at a commercial scale. The use of molten salts as heat transfer medium is proven to be more technology saving, operating at high-temperature range compared to thermal oils or nanofluids thus increasing process efficiency and storage capacity.

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7 Conclusion This chapter highlights the role of nanofluids, PCMs, and spectral splitting for efficient thermal management and increasing the overall system performance. Liquid-based PV/T systems offer a wide range of applications using nanofluids and optical filters by utilizing the maximum amount of solar radiation, whereas PCM-based PV/T systems are still at trails and testing stage to be used for commercial purpose. The PCM coupled with PV/T systems can absorb the heat from solar cells and allowed the PV/T systems to operate at low temperatures. Also, the use of PCM with PV/T can significantly improve the overall performance of the system in terms of thermal and electrical efficiency. However, the increased thickness of the PCM in the system can further absorb more heat has to be considered. More studies have to be conducted on PV/T-PCM hybrid systems under real-time conditions. Finally, BIPV/T, PV/T with PCM and heat pipe for building heating, HVAC, desalination and drying applications have been reviewed but still, further investigation is required to improve the economic aspects and in achieving higher efficiencies. Based on the past studies, it can be concluded that reduction in electrical efficiency of PV panels has dependent on inevitable heating and high-temperature rise of PV panels. PV-T collectors have been developed to absorb the thermal energy from solar radiation and keep PV collectors at optimum temperatures. Among the various approaches, nanofluids have proven to be the most efficient coolant and also spectral splitting agents. Furthermore, the thermal energy acquired by the nanofluids can be successfully stored using energy storage materials comprising of various phase change materials. However, there are still loopholes that need to be considered in future research such as corrosion, waste minimization, cost or sustainability, leakage, improved design of PV-T/PTC systems and optimize the operating parameters and conditions.

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Use of Alcohols and Biofuels as Automotive Engine Fuel Sumit Taneja, Perminderjit Singh, Abhishek Sharma, and Gurjeet Singh

Abstract Ever-depleting reserves of fossil fuel have propelled researchers across the globe to look for alternative fuels. Also, ever-increasing pollution forces the engineers to develop cleaner technology and more efficient engines to meet the stringent demand of the modern automobile emission norms. To address both the above-said issues, the present-day researches focus on fossil fuel compensation with biofuel additives like alcohols for gasoline engine. The combined effect of alcohol blending and exhaust gas recirculation (EGR) can significantly improve the performance and emission of an SI engine. Recently, the use of ethanol for automotive engines has gained more importance, as it can be used in both SI and CI engines and reduces the engine emissions. Even the bioethanol derived from bio-wastes, known as second-generation ethanol, can be used as an alternative fuel for SI engines. It also helps in the proper disposal of tonnes of bio-waste which otherwise lies unused and pollutes the environment. Effect of ethanol blending on engine performance parameters like BSFC, BTE, EGT and engine emissions like CO, HC, NOx and CO2 is discussed in detail. Ethanol–gasoline blends result in reduced CO and HC emissions, whereas NOx emissions are sometimes reported higher. In this context, this article presents detailed information about the ethanol fuel, its synthesis, its utilization in SI engine and its influence on engine performance parameters. Keywords Automotive fuels SI engine performance


Ethanol–gasoline blends
Exhaust emissions


S. Taneja (&)
A. Sharma Mechanical Engineering, Manipal University Jaipur, Jaipur 303007, India P. Singh
G. Singh Mechanical Engineering, Punjab Engineering College, Chandigarh 160012, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_10

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1 Introduction: Need for Alternative Fuels It is a well-known fact that the fossil fuels like coal and crude oil reserves are depleting very fast and will not last for too long. Thus, there is a pressing need to find newer alternative fuels that can be used for various day-to-day activities like cooking food, running our vehicles, generating electricity and providing energy security to our future generations, driven by numerous factors like cost, availability, performance, exhaust emissions, etc. Also, new suitable ways are needed to be developed for using these alternative fuels. Another serious problem of present age is the continually increasing environmental pollution which leads to various respiratory diseases and badly affects the human health. This environmental pollution is primarily due to the burning of fuel like wood, etc., for cooking purpose, industrial applications and burning of petroleum products in automobiles. Rapidly increasing vehicles on the roads hugely contribute to this menace called air pollution. Globally, many big cities are already struggling with this problem as the elevated level of pollution is posing serious health concerns and making them unlivable [1, 2]. This forthcoming energy crisis coupled with the continually rising environmental pollution caused by the fossil fuels becomes the most serious problems of the present time and necessitates the development and use of clean alternative fuels particularly for vehicular engines. These two issues are deeply interlinked and can be jointly addressed to a great extent by adopting a single solution. Using cleaner alternative fuels in vehicles will on the one hand reduce the dependency on fossil fuels and on the other hand will help in minimizing the environmental pollution too. In developing countries like India, the foreign exchange expenditure incurred on import of the crude oil, fluctuation in its prices and its perilous exhaust emissions all combine together to make it an even bigger critical issue required to be judiciously addressed. Thus nowadays, researchers are putting huge focus to develop cleaner fuels for future automobiles that can help solving these twin problems of energy security and environmental pollution [3].

2 Major Alternative Automotive Fuels Developing an altogether newer alternative fuel takes long time and requires lot of research; thus, engineers have been experimenting with a simple idea of using suitable additives which can be added to the petroleum-based fuels in smaller quantities without drastically effecting its properties and combustion behaviour. The major additive fuels presently under consideration are ethanol, methanol, propane and natural gas. Alcohols like methanol and ethanol are termed as renewable fuels which can be derived from natural bioproducts, whereas natural gas is a non-renewable fossil fuel in gaseous form but present in ample quantity [4].

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Renewable fuel includes both gaseous and liquid fuels as well as the electricity derived from renewable biomass energy sources. Compared to the fossil fuels, most renewable fuels are capable of achieving significant life cycle greenhouse gas emission reduction. In the USA, increased usage of renewable fuels has reduced its dependence on imported crude oil and fostered the development of domestic energy resources, while simultaneously providing reductions in greenhouse gas emissions which influence climate change [5]. The following are the main alternative or additive fuels: • Natural Gas Natural gas is undisputedly one of the best alternative fuels currently available and has considerable benefits when compared to diesel or gasoline in terms of the cleaner exhaust, lower price, higher octane number and reduced maintenance. But because of the lower density of compressed natural gas (CNG), its volumetric efficiency is low. CNG as an automotive fuel possesses low flame speed, thus taking more time for complete combustion. This can be nullified by advancing the ignition timing, but this results in lower pressure rise in the engine cylinder. Hence, it is mandatory to optimize the spark timing so that ignition occurs properly. Also for lean air–fuel mixtures, CNG exhibits poor combustion characteristics [4]. • Methanol Methanol can be produced from charcoal or natural gas, while ethanol is produced from corn, cane sugar, molasses, starch, potato and wheat. Methanol is an aggressive material which causes the corrosion and degradation of metallic components of fuel supply system, thus the addition of methanol as an oxygenate to gasoline to increase octane rating is not permitted however methanol blends in gasoline produce less toxic engine emissions [3]. • Ethanol Ethanol or ethyl alcohol is one of the most prominent alternative fuels which can be used in spark-ignition engine particularly as an additive into the gasoline. Use of ethanol in the engine is marked by lower emission along with improved efficiency, power output and fuel economy [5, 6]. • ETBE ETBE stands for ethyl tertiary butyl ether. This is a chemical compound produced by the chemical reaction of ethanol and isobutylene (a by-product of petroleum refining). ETBE possesses superior combustion characteristics as compared to other ethers like high octane value, low volatility, lower hydrocarbon and carbon monoxide emissions and superior drivability. ETBE and ethanol are the oxygenate used in the ‘reformulated gasoline’ mandated in ozone non-attainment zones in USA [7]. • Propane Propane is obtained as a by-product of petroleum refining or natural gas processing. Propane is a low energy fuel often used for central residential heating,

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portable stoves, barbecues and oxy-gas torches. Propane with excessive propene is not suitable for use as automotive engine fuels. Some of the prominent alternative fuels being used in gasoline engine in India are: • • • •

LPG. CNG. Ethanol–gasoline blends. LNG and enriched biogas.

Liquefied petroleum gas was the pioneer alternative fuel that India had adopted in its quest to have clean air in metro cities. Gasoline engine of commercial vehicles was retrofitted with LPG conversion kits or dual-fuel engine kits, thereby reducing pollution. LPG is generated as a by-product during the processing of crude oil or natural gas. LPG is primarily a mixture of propane (57%) and butane (41%). Due to its higher octane rating, lower carbon-to-hydrogen ratio and its ability to form homogeneous mixture, it burns much cleaner and produces lower emissions than gasoline. Moreover, minimal carbon deposit on spark plug and other parts increase their service life [4]. It proves more economical than gasoline but at the cost of slightly reduced power. Safety is an issue with LPG, and its storage also occupies a lot of boot space. Compressed natural gas is established as a very successful alternative automotive fuel across the world. Natural gas has very low energy density; thus, it is compressed to 1/200 of its volume to form CNG and can be easily obtained from gas and oil wells. It is primarily composed of methane gas (85%). Some attractive features of CNG as an automotive fuel are low noise, less maintenance, low exhaust emissions and drivers’ comfort, and it is not prone to adulteration. It is very lighter, thus mixing with air easily. Supreme Court of India in 2002 mandated all heavy commercial vehicles operating in NCR Delhi to be converted to CNG. That was the turning moment for CNG adoption in India, and it significantly reduced pollution. Many car manufacturers are selling CNG versions of their famous cars in India. In spite of the higher refilling time, CNG offers many benefits like: • Reduced CO, NOx and particulate emissions. • No visible tail pipe emissions. • Higher octane value of CNG reduces engine knocking problems. Ethanol–gasoline blends use an alcohol called ethyl alcohol or ethanol produced by the fermentation of the starch present in crops or cellulosic biomass materials. It is a renewable fuel having properties very closely resembling gasoline. It can be easily mixed in gasoline and gives very low emissions. National Biofuel Policy dated 29 November 2011 proposed 5% ethanol blending in gasoline because of its numerous benefits like: • It is renewable, burns clean and reduces import of fossil fuels. • Lower blends do not need any physical modifications in engine. • It gives decent engine performance with minimal power loss [8, 9].

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National Biofuel Policy 2016 mandated 10% ethanol blending in gasoline; however due to limited availability of bioethanol, it is still not achieved and being pursued. Liquefied natural gas is obtained when natural gas is compressed to 1/600 of its original volume. It exists as liquid and is an even better fuel than CNG in terms of energy density. India is currently aiming to become a gas-based economy with main focus on LNG. LNG-fired power plants are replacing coal fired ones due to lower cost, clean burning and reduced pollution. Long-term purchase agreements of LNG are signed with gulf countries for feeding power plants and for supply as piped cooking gas to households due to its higher heating value, safe usage and lower storage space requirements. Research on its use as automotive fuel is in early stages but has huge potential. India is currently aggressively pushing towards a LNG-based economy [10]. Ethanol is emerging strongly as the most suitable additive to gasoline. Sustained efforts for gradual phasing out of the leaded gasoline led to ethanol becoming popular as a high-quality octane booster fuel additive. Ethanol has higher oxygen content; thus, it burns more completely and pollutes less [11]. USA has been successfully using E10 (10% ethanol by volume in gasoline or petrol) since 2001, to reduce its imports. No physical changes in the gasoline engine are needed for using E10 fuel. Brazil also has been using 15% of ethanol with petrol since 2003. Automobile manufacturers recommend ethanol blends in gasoline for their vehicles due to its benefits like: enhanced gas mileage, reduced knocking, improved starting qualities and better acceleration [12]. Ethanol blends even produce lesser toxic engine emissions on combustion. E-10 Unleaded is approved for warranties by all the automobile manufacturers marketing their cars in USA. In fact, Daimler-Chrysler, USA, highly recommends the usage of oxygenated fuels like ethanol blends due to their improved performance qualities and clean air benefits [5]. Additional benefits of using ethanol are: • Ethanol is an excellent cleaning agent and keeps the engine cleaner in new vehicles. For older vehicles, sometimes it loosens up the residues deposited in the car’s fuel supply system. These loosened particles occasionally get collected in the fuel filter from where they may be removed by simply replacing the fuel filter. • All the alcohols have a natural ability of absorbing water. Thus, the condensation of water is arrested in the fuel supply systems so it gets no chance to collect and freeze. E10 thus eliminates the need of using ‘gas-line antifreeze’ in winters. • Ethanol is an excellent fuel for both the newer and the old technology engines. Automobile engine older than 1970 having non-hardened valve seats might require a lead substitute to be added to the ethanol–gasoline blends for preventing the premature wear of the valve seat. Valve burning is significantly reduced in engines where ethanol blends are used as the ethanol burns cooler

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than the normal petrol. That is the reason why many racing cars use alcohol as fuel. • Use of ethanol in the engine is characterized by lower exhaust emission along with improved efficiency, power output and fuel economy [13, 14].

3 Ethanol—The Fuel Ethanol is a flammable, volatile, colourless liquid which is the intoxicating agent in liquors and is also used as a transportation fuel or solvent in syrups. It is often referred as grain alcohol or ethyl alcohol. It is a colourless clear liquid having a very mild characteristic smell that boils at 78 °C and freezes at −112 °C. On burning, ethanol produces a pale blue flame with considerably high energy and no residue, thus proving it an ideal fuel. It is an alcohol formed by the fermentation of corn or sugarcane. Ethanol is used for a wide range of purpose, right from producing medicine, synthesizing chemical products to fuelling our vehicles, lamps and heaters. It is exactly the same alcohol which is used in the beverage alcohol, but it meets the fuel-grade standards. Ethanol meant for use as a fuel is first denatured by mixing little bit of gasoline into it; thus, it becomes unfit for drinking by humans.

4 History—Transition from Alcohol to Fuel Ethanol is famous as an intoxicating drink since ancient times. In USA around the late 1800s, ethanol was often used as a spirit or lamp fuel with annual sales exceeding 25 million gallons. The US government imposed taxes on ethanol during the civil war, which devastated the ethanol industry. Ethanol fuel flourished nicely after the lifting of taxes in 1906 until the crude oil came. The first use of ethanol as an automotive fuel happened in the early 1900s when petrol supplies were short in Europe. Henry Ford’s Model T along with other early 1920s vehicles in USA was designed originally to run on alcohol fuel. Both Germany and US armies used to rely on ethanol for powering their vehicles in world war. Post-Second World War, the crude oil prices crashed that reduced the use of ethanol. After this, a limited usage of ethanol went on till the oil crisis came in the early 1970s [5]. In 1973, the OPEC countries blocked shipments of crude oil to USA causing gasoline shortage by raising crude prices. This action warranted attention as USA depended hugely on imported oil. This shifted the focus once again towards additive fuels like ethanol. Gasoline containing ethanol at that time was named ‘gasohol’. Afterwards, as gasoline got plentiful, the ethanol-blended gasoline was introduced for increasing the octane ratings with the name ‘gasohol’ being dropped in favour of names like ‘E-10 Unleaded’ [5].

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5 Why Ethanol Now? Ethanol production and use had grown appreciably in USA during the 1980s and 1990s. Increase in the use of ‘E-10 Unleaded’ gasoline occurred as this fuel performed very well in the automotive engine and was priced lower than the traditional gasoline. Major reasons for the elevated production and usage of ethanol globally include: 1. Ethanol is a renewable fuel and can be easily replenished using naturally occurring crops like corn, wheat, rice, sugarcane, etc. 2. Ethanol decreases the dependence of a nation on imported oil and thus lowers the trade deficit. It serves as a dependable source of energy if foreign supplies get interrupted. 3. Increased demand of grains for making the ethanol stabilizes the corn price. 4. Ethanol improves the air quality as the carbon monoxide emissions reduce due to its oxygenating nature. Also, lead and other carcinogens get removed from the gasoline. 5. Vehicle owners are benefitted by the elevated octane in fuel that lowers knock of engine. Also, ethanol fuel blends absorb moisture and thus keep the fuel system clean [5].

5.1

Means of Using Ethanol as Fuel

Ethanol is an excellent fuel and may be used as a transportation fuel in the following three primary ways: 1. As a blend, having 10 parts of ethanol in 90 parts of the unleaded gasoline, designated as ‘E-10 Unleaded’. 2. As a constituent of the reformulated gasoline, either directly or indirectly as ethyl tertiary butyl ether (ETBE). 3. As a primary fuel having 85% ethanol blended with 15% unleaded gasoline known as ‘E-85’. Ethanol when added to the gasoline enhances the octane level, reduces the exhaust emissions and prolongs the future availability of crude oil [6].

6 Ethanol—The Global Scenario Many countries have been using biofuels like ethanol as energy sources, including India. In 2011, USA and Brazil were the top ethanol producers globally producing 53 and 21 billion litres of ethanol, respectively, and amounting to 87% of global

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production of 85 billion litres. Strong government incentives to biofuels have helped ethanol industries grow in many countries like Brazil, France, Germany, Sweden, Spain, China, Canada, India, Thailand, Australia and few Central American countries. USA not only produces the maximum ethanol globally but also consumes the most. Ethanol’s use as a fuel goes back to 1896 when Henry Ford designed his first car, the ‘quadricycle’ to run on pure ethanol. Most cars in USA run on blend of up to 10% ethanol, and manufacturer designs them to even accommodate high ethanol blends. Portland, Oregon, in 2007 became the first city in USA to mandate 10% ethanol in all gasoline. In 2010, EPA granted the sale and use of E15 blend for cars manufactured in or after 2007 [15]. Brazil’s ethanol industry is more than 30 years old. It boasts of the world’s most successful biofuel programme, producing ethanol from sugarcane. Since 1977, Brazil made it mandatory to use E15, a blend of 15% ethanol in gasoline which requires just minor adjustments on normal gasoline engine. Now, the ethanol blends used nationwide are mandatorily instructed to possess 18% to 25% ethanol (E18 to E25) and these are used by all the regular gasoline cars as well as the flexible fuel vehicles [16]. Europe also has the largest bioethanol-consuming nations like Sweden, France and Spain. Sweden was pioneer in whole Europe in terms of using ethanol as a fuel, although Sweden mostly imports this ethanol. All the Swedish fuel stations are mandated to supply minimum one alternate fuel. Sweden’s every fifth car, at least partially, is driven on alternate fuel, mainly on ethanol. Sweden had the highest 1200 ethanol stations in Europe by 2008. France showed enthusiasm in using E30 fuel initially around 2001, but the conversion kits for enabling petrol engines to consume E30 or higher fuel efficiently could not be legalized. After the conversion kits were legalized around 2015, the use of E85 fuel grew rapidly in France and prompted governments to even ban diesel from cities. By 2018, E85 was easily available at all the gas stations in France, and presently in 2019, it is still cheaper (up to 50%) than petrol. Germany had built up a widespread biofuel infrastructure initially, but the E35 fuel disappeared completely from the fuel stations after the tax incentives for biofuels were withdrawn by the government in 2015. Biofuel is taxed equally as the regular fuel now. Thailand has been using E10 fuel since 2004 on a large scale. From 2008 beginning, Thailand initiated the sale of E20 and it introduced flexible fuel vehicles by late 2010. Thailand is presently converting its cassava stocks into ethanol fuel. India has also mandated 10% ethanol blending in all commercially sold gasoline, but due to lower production it has been able to achieve only 5% blending successfully till 2019. Australia derives its ethanol from feedstocks like wheat starch, molasses and grain sorghum. Australian legislations impose a 10% capping on the amount of ethanol in fuel blends. Biofuel contribution in the total transport fuel energy mix in Australia in 2016–17 was just 0.5%. Total commercial bioethanol production in 2018 was 250 million litres [14].

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USA and Brazil were the pioneering countries to experiment with ethanol as automotive fuel. Gradually, Canada, Sweden, France and India started taking clues from USA and Brazil to use ethanol as transportation fuel. Ethanol working knowledge primarily originated from USA and Brazil is worth many lessons.

7 USA’s Corn-Based Ethanol Ethanol is derived from the farm-grown raw products that are very abundant in USA. Sweetcorn is the grain primarily used for producing ethanol that supplies most of the raw material required. In 1994, ethanol production consumed around 500 million bushels of corn, thus creating a domestic market for corn which in turn adds around 5 cents a bushel for every 100 million bushel of corn consumed. Higher prices result in more income for farmers and less reliance on government subsidy programmes. Ethanol producers in USA use more than 700 million bushels of corn annually today. The growth of domestic ethanol industry has led to a rapid rise in the number of farmer-owned ethanol production facilities. US farmers have realized the additional benefits resulting through ownership of ethanol manufacturing plants. Around 10 billion gallon of top quality, high-performance ethanol fuel had been produced in the last two decades, using around 5 billion bushel of corn. Ethanol’s importance towards the agricultural sector in USA can be easily understood by the following data: • Ethanol making accounts for nearly 7% of the total corn usage in the USA and represents the third highest usage of corn, next only to domestic livestock feed consumption and exports. • Ethanol stimulates the rural economy by raising the corn prices and the rural income through the creation of value-added market for farmers. • Ethanol accounts for 14 cents of the value of every bushel of corn sold by US farmers. It varies as per global demand and supply scenario and the crop prospects. • Every 100 million bushel rise in the corn demand results into a hike of corn prices by 4–5 cents per bushel. • Every bushel of corn consumed for producing ethanol affects the prices of other commodities as well, adding around 2 cent to the wheat price and 10 cents to the soy bean price per bushel [5]. Production of ethanol from corn no way means that lesser corn is available as food. In fact, ethanol production leads to a number of protein-rich food and feed co-products. For instance, an acre of corn farming, yielding 125 bushels, produces around 300 gallons of ethanol, 189 lb of corn oil, 320 lb of sixty per cent gluten meal and 1350 lb of distiller’s grains. Distiller’s grain is extensively used as a premium animal feed ration and is considered a digestible, nutritional, cost-effective

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and palatable protein feed for sheep and cattle. Around 1.5 billion tonne of distiller’s grain is also produced in USA per year [5].

7.1

What’s in a Bushel of Corn: Food or Fuel?

Every bushel (8 gallons or 14 L) of the corn produces 2.4–2.6 gallons (3.8 L) of ethanol, depending on the type of milling process used. It is only the starch of the sweetcorn that is utilized for making ethanol. Rest all portion of the corn kernel remains as such, thus leaving behind the protein and valuable co-products for being utilized in the making of food for humans, livestock feed and numerous chemicals. This same bushel of corn used in making ethanol can also simultaneously generate co-products shown in the accompanying chart. Corn oil is used to produce food for humans. Also, the 21% protein feed is utilized for producing a high protein livestock feed [5]. The carbon dioxide produced can be used as a refrigerant and help crops grow rapidly in greenhouses. Only starch from the sweetcorn (oxygen, hydrogen and carbon) is utilized to derive ethanol effectively (Fig. 1).

8 Brazil’s Sugarcane-Based Ethanol Brazil’s ethanol is primarily derived from sugarcane which has the lowest rate of agrochemical use in agriculture across the world. Sugarcane exhibits the lowest soil erosion rates in agriculture which is significant considering that desertification and erosion are two of the world’s most serious problems, as 25% of the soil on the planet is decertified, as per the United Nations data. Sugarcane plantation and processing is an activity having minimal negative impact on water resources in Brazil that reflects another vital contribution considering that about 10% of the world’s water supply is hopelessly compromised by pollution and erosion, as per the United Nations [6]. Sugarcane agribusiness has become self-sustainable economic activity in Brazil accounting for 3.5 million direct jobs and 1.5% of GDP. No competition exists between food crop and energy crop. In fact, biofuels have given farmers a big opportunity to raise their productivity and income. Sugarcane farming area in Brazil was around 10% of the total area under cultivation, which represents a tiny percentage of Brazil’s total fertile landmass of 850 million hectares. Sugarcane cultivation over the years has mainly expanded in unused low fertile areas like the degraded pastures of the central Savannah area. Moreover, the use of vinasse, a sugarcane by-product rich in sulphur, calcium and potassium, as a fertilizer has hugely contributed in replacing nutrients in the soil. The cost of deriving ethanol from the sugarcane in Brazil is way lower than that of producing ethanol from wheat and sugar beet in Europe and from maize in USA.

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Fig. 1 Various co-products obtained from ethanol production [5]

The sugarcane plant requires a relatively dry climate for producing sucrose. In wet climate, sugarcane absorbs water like a sponge, thus lowering the sucrose formation. Brazil has demonstrated how the area planted with sugarcane can be doubled without using agricultural land. By using the degraded pastures and by substituting sugarcane for less profitable crops, producers have doubled the sugarcane area and hence their income.

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Huge plantation of sugarcane had many positive environmental impacts in Brazil. Sugarcane has the lowest soil erosion rates, and it needs very little amount of pesticide. All its waste like sugarcane bagasse, leaves, etc., are utilized for cogeneration. Because of ethanol’s use as fuel, the air quality has significantly improved in Brazil due to the removal of lead-based additives in gasoline and the reduction of greenhouse gases, contributing to a pollution reduction of about 20% for the whole energy sector [16].

9 Environmental Benefits of Using Sugarcane to Produce Ethanol There are numerous benefits to environment if ethanol is made from sugarcane. Prominent among these are: • Firstly, deriving ethanol from sugarcane is more energy efficient than from corn. Producing ethanol from sugarcane creates about 8 times the amount of energy consumed in producing it, while producing ethanol from corn only creates about 3 times the amount of energy consumed in producing it. • Second, sugarcane does not need to be irrigated unlike most of the corn currently grown in USA. Thus, there is no additional load on existing water resources for sugarcane crop. • Third, sugarcane needs relatively lesser amount of pesticides, chemical fertilizers and herbicide. It thus protects soil from contamination and leads to economies in sugarcane and ethanol production. • Fourth, while most ethanol refineries in USA are natural gas or coal powered, sugarcane-based ethanol refinery may be powered by sugarcane bagasse, a waste biomass left after the refining of sugar. In fact, bagasse-fuelled refineries can generate even more electricity than they require and can sell it back to grid, thus generating additional revenues. • Fifth, while corn is planted and harvested only once in a year, the sugarcane may be cut multiple times from the same stalk in a year in tropical climate. All of these points in favour of sugarcane-based ethanol are perfectly true for Brazil’s ethanol [17]. • Sixth, it provides energy security to the nation. Since Brazil is not self-sufficient in producing adequate gasoline to meet domestic demand, it is very important to complement the transportation energy mix with national sources. The bigger the share of a domestically sourced fuel (in this case ethanol) in the energy matrix, the less reliant the country is on fuel imports and the more resistant it is to external shocks. Figure 2 shows how Brazil reduced its external fuel dependence hugely by launching the second phase of ‘Proálcool’. Brazilian dependence on imported oil

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Fig. 2 Brazilian dependence on energy imports [16]

(yellow line in Fig. 2) decreased substantially as the hydrated ethanol production increases considerably. • Seventh, use of ethanol as fuel reduces greenhouse gas (GHG) emissions. Recently, the United States Environmental Protection Agency (EPA) declared sugarcane ethanol as an advanced biofuel as its use as a fuel results in a 61% reduction in CO2 emissions compared to gasoline. This is because the CO2 released from the burning of ethanol in vehicles is absorbed via photosynthesis by the sugarcane plants as they grew. Furthermore, when compared to ethanol produced from other feedstocks, sugarcane-based ethanol demonstrates a very favourable GHG emission balance. For instance, the use of ethanol as fuel in Brazil instead of gasoline avoided the release of 35 million tonnes of CO2 in 2012 alone (Fig. 3).

10

How to Make Ethanol: Commercial Production

Ethanol can be derived from any crop or biomass having sugar or starch present in it. Converting the starch present in the kernels of sweetcorn into sugar and then converting this sugar into ethanol is a complicated process that needs applying a combination of technologies like engineering, chemistry and microbiology. Ethanol can be produced by adopting any one of the given standard processes: dry milling or wet milling.

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Fig. 3 Emissions avoided in Brazil in 2012 (million tonnes) [16]

11

Dry Milling

Most of the ethanol plants in USA work on dry milling process. The main steps involved in the dry milling process are: i. Milling: After proper cleaning of the corn grains or any biomass, it is firstly passed through hammer mills, where it gets grinded into fine powder. ii. Liquefaction: Then, this finely milled powder is mixed with an enzyme called alpha amylase and water in the cookers to liquefy the starch. Heat is given to enable the liquefaction. Sulphuric acid is added in it for maintaining pH 7. Cookers having high temperature stage of 120–150 °C and lower temperature (95 °C) holding period are used. Higher temperature lowers the bacteria level in this mash. iii. Saccharification: This mash is then cooled down, and an enzyme called glucoamylase is mixed in it for converting the starch into fermentable sugar. iv. Fermentation: Now, ‘yeast’ is mixed in this mash for fermenting the sugar into ethanol plus carbon dioxide. In a batch fermentation process, this mash remains in one fermenter for around 2 days, while in continuous fermentation process, the fermenting mash passes through many fermenters until it gets completely fermented and then it exits the tank. v. Distillation: This fermented mash is known as ‘beer’ and possesses around 10% alcohol along with all the non-fermentable solids of the corn and the yeast cells. The alcohol is then separated from the solids and water by pumping this mash into a continuous flow, multi-column distillation system. Now, alcohol at 96% strength leaves from the top of the last column, whereas

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the residue mash known as ‘stillage’ is shifted from this column’s base to the co-product processing zone. vi. Dehydration: This hydrous alcohol is then passed from a dehydration system. All the remaining moisture also gets removed here. A molecular sieve is mostly used to trap the last traces of moisture present in the ethanol. Pure alcohol obtained at this point is referred as ‘anhydrous ethanol’. vii. Denaturing: The ethanol which is to be used as fuel can be denatured now, by adding very little amount (2–5%) of gasoline, thus making it unfit for human consumption [5].

12

Wet Milling

This operation is much more complex as the grain has to be separated into its components. Unlike dry milling where the entire mash is fermented, here only the starch is fermented in wet milling. The wet milling process is detailed in the flow chart as shown in Fig. 4. Similar process is used for deriving ethanol from other feedstocks.

13

Ethanol Nomenclature

On the basis of the feedstock utilized for deriving ethanol, it is classified as first-generation or second-generation ethanol. First-Generation Ethanol: When ethanol is produced from the grains of a particular crop or feedstock like corn or wheat or maize, it is referred as first-generation ethanol. It is essentially a feedstock-dependent ethanol. Although the yield is very high, diverting the food crop for energy raises a question mark which leads to ‘food vs. fuel’ debate. Second-Generation Ethanol: When ethanol is derived from available bio-wastes like rice husk, wheat husk, fruit pulp left after juice extraction, and rotten fruits and vegetables, it is referred as second-generation ethanol or 2G ethanol. Appreciable amount of starch is still present in these bio-wastes which can be utilized for deriving ethanol. Although this process is more expensive and the yield is also low, it is preferred as no food crop is being sacrificed here for producing energy. For instance, India is one of the largest producers and exporters of sugar which is produced from sugarcane. Sugarcane bagasse is left over as waste in this process, but it carries huge amount of starch which generally goes unutilized. Moreover, bagasse is finally burnt off to dispose it which further pollutes the surrounding air.

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Fig. 4 Dry milling versus wet milling process [5]

Now using this bagasse for 2G ethanol production helps in waste disposal, protects environment and generates revenue too. Sugar mills in India are now actively producing ethanol from sugarcane bagasse also.

14

Ethanol Economics

The production and use of ethanol lead to appreciable economic growth of a nation. Ethanol, a renewable fuel made from biomass and agricultural products, when produced and used in a country, increases its economic activity, creates jobs for its people, stabilizes farm commodity price, stimulates agriculture-based GDP and

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boosts farm income. The ethanol industry has contributed to the economy of USA in a very positive manner. US economy has expanded due to the creation of direct and indirect jobs and due to increase in corn prices and rural income. A report by a panel of economists at Kellogg’s School of Business, Northwestern University, on the economic prospects of the ethanol industry in USA over a period of seven years from 1996 to 2002 has concluded the following benefits: • Approximately, $51 billion will be added to the US economy by ethanol. The services and goods bought by the producers of ethanol result in an increased demand for other industries. This includes the purchase of feedstock, water, electricity, natural gas, grains, communications, accounting and legal services. • Ethanol production will lead to an increase in the farm income of corn producers by $4.5 billion annually. Higher demand for the crop grown by farmers shall provide market support for higher prices as well as income. • Nearly 55,000 jobs are supported by ethanol industry. Ethanol making accounts directly for about 6000 jobs in fuel or food processing industry in 20 provinces. Moreover, the money spent by the ethanol producers on purchasing goods and services supports indirectly another 49,000 jobs on average. • Gross household income shall enhance by $12.5 billion in the next seven years due to ethanol production alone. Wages of $277 million are paid directly to employees by the ethanol industry. This money earned is spent by the employees and their family, which further creates demand for other goods and services. Additional $1.8 billion is added annually to household income due to the indirect impact of ethanol production. • About $555 million of net tax revenue is generated annually by ethanol for US federal treasury by personal and corporate income tax collection. Additional revenues, generated by the taxes on the farm and household income provided by the ethanol industry, help in offsetting the cost of the excise tax exemptions provided to support ethanol-blended gasoline [15].

15

Utilization of Ethanol–Gasoline Blends in SI Engine

Hasan et al. [11] studied the effects of using unleaded gasoline–ethanol blends (0– 25% ethanol in the increments of 2.5%) on a Toyota four-cylinder SI engine emission and performance. Blending ethanol in unleaded gasoline resulted in an increase in volumetric efficiency, brake thermal efficiency and brake power by around 7, 9 and 8.5%, while brake-specific fuel consumption decreased by 2.4%. Ethanol as an additive to gasoline improves the performance of engine and lowers exhaust emissions. Author observed a 46.5 and 24.3% reduction for CO and HC emission, respectively, while CO2 emissions increased by 7.5%. Blend with 20% ethanol gave least exhaust emissions.

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Rex Weber and Nebraska Ethanol Board [15] have presented a complete case study of ethanol adoption in USA citing the various economic benefits US has reaped due to ethanol revolution. The discussion on ethanol production and gradual adoption illustrated how USA achieved energy security, reduced dependence on oil imports and how US economy was hugely stimulated improving the life of millions of its people involved in ethanol production financially. Ethanol industry also contributes huge tax revenue of US $555 million to the federal treasury annually. Schifter et al. [18] experimentally investigated the ways to reduce pollution in Mexico using various fuel formulation and their emission measurements. Authors tested the effect of the physical properties and composition of gasoline on vehicles representing the actual fleet of the Mexico. Fourteen fuel blends were made using commercial gasoline available in Mexico. Oxygenate molecule (ethanol or MTBE) and Reid vapour pressure were the considered fuel parameters. United States Federal Test Procedure, FTP-75, was used to measure total HC, CO, NOx and other toxic exhaust emissions. Substitution of MTBE by ethanol decreased CO emission in the whole fleet by 26% without catalytic converter. The effect of different compression ratios on SI engine performance and exhaust emissions for various ethanol–gasoline blends was investigated by Yucesu et al. [19]. Experiments were carried out at three engine speeds of 2000, 3500 and 5000 rpm and wide open throttle. On increasing the compression ratio from 8:1 to 11:1, an increment of 8% was observed in engine torque at 2000 rpm with E0 fuel. The highest increment of 40% was reported for E40 fuel at 13:1 compression ratio. On increasing the compression ratio from 8:1 to 11:1, the BSFC of E0 fuel decreased about 10% and was least. Durbin et al. [20] reported the effect of ethanol content on the regulated and unregulated exhaust emissions. Two variables, namely fuel volatility and oxygenate content, were found to be significant parameters affecting the vehicle exhaust emissions. For this study, twelve California certified LEV vehicles were tested on a matrix of twelve fuels with different levels of ethanol content (0, 5.7 and 10% by volume), T50 (195, 215 and 235 °F) and T90 (295, 330 and 355 °F). Graham et al. [21] performed statistical analysis of the variation in tailpipe emissions because of the use of ethanol and included the results of two reference studies. The first study evaluated the impact of two lower ethanol blends E10 and E20 on evaporative and tailpipe emissions from a direct injection petrol engine vehicle and three multi-port fuel injection petrol vehicles operating at two different temperatures. The results showed that E10 usage resulted in 16% decrease in CO emissions; 9% increase in NMHC; and 15% benzene emissions with no significant changes in CO2, NOx, N2O and CH4 emissions. The emission and performance behaviour of a one-cylinder AVL SI engine was analysed by Schifter et al. [22] experimentally to study the effects of burning ethanol–gasoline mid-level blends, carrying 0–20% ethanol. Blends having up to 10% ethanol showed marginal effect in combustion rate. The increase in the fuel consumption was observed to be lesser than predicted by the reduction in the energy content of the blended fuel, showcasing a positive influence of ethanol on the combustion efficiency which counteracts the net heating value reduction.

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Increasing the ethanol content in the fuel leads to a progressive reduction in HC and CO although NOx emissions increased. The maximum computed reductions in the emissions were 19 and 52% for HC and CO, respectively, for 20% blended fuel. The combustion behaviour of bioethanol in a direct injection gasoline engine was studied by Turner et al. [12]. Authors observed that bioethanol has a strong potential as an alternative to petroleum gasoline and investigated the combustion performance by fuelling engine with various blending ratios of bioethanol/gasoline (0–100% ethanol) with respect to a different spark timing (19–39 b TDC). It was concluded that advantages of adding ethanol to gasoline are increased efficiency and reduced engine-out emission which result from the improved evaporation behaviour of the blended fuel because of ethanol addition that in turn raises the vapour pressure in lower ethanol blends. It is further related to the availability of more oxygen in the ethanol molecule which raises flame speed, resulting in improved efficiency along with combustion stability. Effect of inlet air temperature on the emissions, combustion efficiency and thermal efficiency of HCCI engine was investigated by Maurya and Agarwal [23] who performed experimental study on a HCCI engine. HCCI engine has ultra-low emission and high efficiency. Authors investigated the emission and combustion behaviour of a HCCI engine, obtained by modifying a twin cylinder engine powered by ethanol. Tests were conducted by varying the inlet air temperature (120– 150 °C) and air–fuel ratios (ƛ = 2–5). Results indicated that air–fuel ratio and inlet air temperature significantly affect the peak in-cylinder pressure and its position, gas exchange efficiency, heat release rate and thermal efficiency. All stable HCCI operating conditions emitted very low NOx ( viscous force) in free convection, axial velocity is greater for (cAl2O3–C2H6O2) nanofluid as compared to (cAl2O3–H2O) nanofluid in the region (0  y  0.3686) and reverse flow patterns are computed in the region (0.3686  y  0.82). Figure 2c depicts the local wall shear stress distribution under the effects of Grashof number for both cAl2O3–H2O and cAl2O3–C2H6O2 nanofluids. It is evident that the magnitude of wall shear stress increases with greater Grashof number since the axial flow is boosted which manifests in higher shear rates at the microchannel boundaries. In the absence of buoyancy force (Gr = 0), shear stress is higher for (cAl2O3–H2O) nanofluid as compared to (cAl2O3–C2H6O2) nanofluid; however with relatively strong thermal buoyancy present, i.e. Gr = 1.2, shear stress for (cAl2O3–C2H6O2) nanofluid clearly exceeds that for (cAl2O3–H2O) nanofluid. The base fluid viscosity, i.e. ethylene glycol, is significantly more viscous than water, which inevitably contributes to the variation in shear stress.

Thermal Analysis of cAl2O3/H2O and cAl2O3/C2H6O2 … -0.2

Gr = 0 Gr = 0.25 Gr = 0.5

-0.4 -0.6

γ Al O - H O 2 3 2 γ Al O - C H O 2 3 2 6 2

dp/dx

-0.8 -1 -1.2 -1.4 -1.6 -1.8

(a) 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

x Gr = 0 Gr = 1 Gr = 2

0.2

y: 0.3686 u: 0.146

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0.05

γ Al O - H O 2 3

2

γ Al2O3 - C2H6O2 0 0

0.1

0.2

0.3

(b) 0.4

0.5

0.6

0.7

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Gr = 0 Gr = 0.5 Gr = 1

-0.2

γ Al O - H O 2 3

2

γ Al O - C H O 2 3

2 6 2

-0.25

-0.3

τ xy

Fig. 2 Influence of thermal Grashof number on a axial pressure gradient (dp/dx), b axial velocity (u) (at x = 0.5)  and  c axial shear stress sxy for a = 0.2; t = 0.4; UHS = 2; j = 0.2; H = 1; k1 = 0.2; v = 0.1; c = 0.1 and Q = 1

239

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-0.4

-0.45

(c) -0.5

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0.5

1

x

1.5

2

240 -0.6

γ Al O - H O

H=1 H = 1.5 H=2

-0.8 -1

2 3

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γ Al O - C H O 2 3

2 6 2

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-1.2 -1.4 -1.6 -1.8 -2 -2.2

(a) 0

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γ Al2O3 - C2H6O2

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γ Al O - H O 2 3

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γ Al O - C H O 2 3

2 6 2

-0.35

τxy

Fig. 3 Influence of Hartmann number on a axial pressure gradient (dp/dx), b axial velocity (u) (at x = 0.5)  and  c axial shear stress sxy for a = 0.2; t = 0.4; UHS = 2; j = 0.2; Gr = 0.1; k1 = 0.2; v = 0.1; c = 0.1 and Q = 1

D. Tripathi et al.

-0.4

-0.45

-0.5

(c) -0.55

0

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1

x

1.5

2

Thermal Analysis of cAl2O3/H2O and cAl2O3/C2H6O2 … -0.6

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Al2O3 - H2O Al O - C H O 2 3

2 6 2

-0.4

xy

Fig. 4 Influence of electroosmosis parameter on a axial pressure gradient (dp/ dx), b axial velocity (u) (at x = 0.5)  and  c axial shear stress sxy for a = 0.2; t = 0.4; UHS = 2; H = 1; Gr = 0.1; k1 = 0.2; v = 0.1; c = 0.1 and Q = 1

241

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γ Al O - C H O 2 3

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Fig. 5 Influence of Jeffery parameter on a axial pressure gradient (dp/dx), b axial velocity (u) (at x = 0.5)and c axial shear stress sxy for a = 0.2; t = 0.4; UHS = 2; H = 1; Gr = 0.1; j = 1; v = 0.1; c = 0.1 and Q = 1

D. Tripathi et al.

-0.45

-0.5

(c) -0.55

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2

Thermal Analysis of cAl2O3/H2O and cAl2O3/C2H6O2 … 0.6

=0 = 0.1 = 0.2

0.4 0.2

γ Al O - H O 2 3 2 γ Al O - C H O 2 3

2 6 2

dp/dx

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γ Al O - H O 2 3

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γ Al2O3 - C2H6O2

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2 6 2

-0.4

τxy

Fig. 6 Influence of solid fractional volume of nanofluid on a axial pressure gradient (dp/dx), b axial velocity (u) (at x = 0.5)  and  c axial shear stress sxy for a = 0.2; t = 0.4; UHS = 1; H = 1; Gr = 0.1; j = 1; k1 = 0.2; c = 0.1 and Q = 1

243

-0.45

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1

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γ Al2O3 - H2O

γ Al O - C H O

UHS = 0

2 3

2 6 2

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(a) 0

0.2

0.4

0.6

0.8

1

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1.4

1.6

1.8

2

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UHS = -2 UHS = 0 UHS = 2

0.2 y: 0.3276 u: 0.1545

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0.15

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0.05

γ Al2O3 - H2O γ Al2O3 - C2H6O2

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0.1

0.2

0.3

(b) 0.4

0.5

0.6

0.7

0.8

0.9

y -0.2

UHS = -1

γ Al2O3 - H2O γ Al2O3 - C2H6O2

UHS = 0

-0.25

UHS = 1 -0.3

τxy

Fig. 7 Influence of Helmholtz–Smoluchowski velocity on a axial pressure gradient (dp/dx), b axial velocity (u) (at x = 0.5)and c axial shear stress sxy for a = 0.2; t = 0.4; v = 0.1; H = 1; Gr = 0.1; j = 1; k1 = 0.2; c = 0.1 and Q = 1

D. Tripathi et al.

-0.35

-0.4

-0.45

(c) -0.5

0

0.5

1

x

1.5

2

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Figure 3a–c visualizes the magnetic field effect (Hartmann number)   on axial pressure gradient (dp/dx), axial velocity (u) and wall shear stress sxy profiles for (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids. Figure 3a reveals that by enhancing Hartmann number , the magnitude of pressure gradient (dp/dx) decreases. The Hartmann number (H) as noted earlier represents the ratio of electromagnetic (Lorentz) force to viscous force; higher H indicates stronger Lorentz force which suppresses pressure gradient, i.e. greater control is achieved of pressure distribution for H = 2 (magnetic force is double the viscous force) compared with H = 1 (both forces are equal). Figure 3b shows that with increment in Hartmann number, the axial velocity of (cAl2O3–water, cAl2O3–ethylene glycol) nanofluids, decreases for small y(0  y  0.3686), whereas for large y(0.3686  y  0.82), axial velocity increases. The switch in behaviour is characteristic of microchannel flows and is attributable to the re-distribution in linear momentum in the regime, as elaborated by Cramer and Pai [108]. However, it is pertinent to note, that flow reversal is not induced, i.e. negative velocities are not generated anywhere in the regime, and this is also a characteristic of peristaltic pumping which avoids the backflow associated with other pumping mechanisms in energy systems. Magnetic retarding force is clearly a potent regulatory mechanism for specific zones in the microchannel regime; i.e. it can mobilize both deceleration and acceleration where required and provides engineers with a useful and non-intrusive technique with minimal maintenance for optimizing microchannel performance, as noted by Rosa [35]. Figure 3c shows  that  an increase in the Hartmann number creates a decrement in wall shear stress sxy profile in the core section of the wavy channel. Strong axial flow deceleration is therefore generated again due to the inhibiting effect of transverse static magnetic field. At all axial locations, (cAl2O3–C2H6O2) nanofluids achieve noticeably higher shear stresses, however, than (cAl2O3–H2O) nanofluids. The non-magnetic case (H = 0) overall achieves the higher shear stresses compared to any magnetohydrodynamic case. Significant flow control is therefore achievable with imposition of transverse magnetic fields. At the entry zone (low values of x) and also exit zone (higher values of x) strongly negative shear stress is generated, whereas in the central axial zone consistently lower negative shear stresses are computed, for all values of Hartmann number, H. The effects of Debye–Hückel parameter  (j)  on axial pressure gradient (dp/dx), axial velocity (u) and wall shear stress sxy profiles for (cAl2O3–H2O, cAl2O3– C2H6O2) nanofluids have been displayed in Fig. 4a–c. The Debye–Hückel parameter j is the inverse of the Debye length (i.e. electric double layer (EDL) thickness). It is observed from Fig. 4a, axial pressure gradient increases at core part of the channel with the enhanced j-value for both (cAl2O3–H2O, cAl2O3– C2H6O2) nanofluids. The case j ! 0 corresponds to the non-electrical scenario (magnetohydrodynamic viscoelastic nanofluid peristaltic flow, since H is prescribed as 1). Figure 4b is perceived that an increasing trend is noticed in the right part region of single wave channel. Conversely, opposite behaviour is noted in the left part of the channel region. A decrease in wall shear stress profile is noticed when Debye–Hückel parameter j is enhanced for both (cAl2O3–water, cAl2O3–ethylene

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glycol) nanofluids, which is presented in Fig. 4c. It is noticed that the effect of cAl2O3–C2H6O2 nanofluid more strongly influences on wall shear stress profile as compared with the cAl2O3–H2O, cAl2O3–H2O nanofluid. The axial electric field effectively acts perpendicular to the decay of the EDL (or equivalently parallel with the surface). The surplus of either positive or negative ions results in a net body force on the electromagnetic viscoelastic nanofluid proportional to the local net charge density. The resulting velocity profile comprises a region of quite high shear rates near the surface where the velocity ascends from zero at the shear plane to its bulk phase velocity at the edge of the EDL. The proportionality between bulk phase velocity and the strength of the electric field, Ex, is quantified by the electroosmotic mobility which is dependent on both surface and solution phase properties. Contrary to conventional pressure-driven microchannel systems, uniform electroosmotic flow exhibits a flat or “plug flow” velocity profile outside the double layer region. Overall, it is abundantly evident that the electroosmotic effect imparts a significant modification in microchannel transport phenomena characteristics. The impact of Jeffery parameter (k1 , i.e. non-Newtonian parameter)   on axial pressure gradient (dp/dx), axial velocity (u) and wall shear stress sxy profiles for (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids, is illustrated in Fig. 5a–c. From Fig. 5a, it is noticed that elevation in the Jeffery parameter induces a significant delineation in the development of the axial pressure gradient for both (cAl2O3– H2O, cAl2O3–C2H6O2) nanofluids. It is specified that the axial pressure gradient increases as the base fluids behaviour changes from Newtonian ðk1 ¼ 0Þ to Jeffery nanofluids ðk1 [ 0Þ for both (cAl2O3–water, cAl2O3–ethylene glycol) nanofluids. In Fig. 5b, the axial velocity profile proportionately reduces in the left part of region y(0  y  0.3686) and the opposite trend is observed in the right part of region y (0.3686  y  0.82) for both (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids. Also, from Fig. 5c, it is observed that the wall shear stress profile distribution reduces with enhancing the value of Jeffery parameter; wall shear stress attains a maximum value for Newtonian nanofluids as compared to Jeffrey nanofluids. Jeffrey’s parameter, i.e. k1 , arises in the denominator of the augmented shear term in the ð123v2 þ 7:3v þ 1Þ @ 2 u transformed momentum equations, e.g. as the term, 1 þ k1 @y2 in Eq. (14). In certain zones of the microchannel, an increase in relaxation time relative to retardation time (k1 > 0) produces considerable deceleration (Fig. 5b) in the flow since elastic forces begin to dominate the viscous forces and the nanofluid takes longer to return to its relaxed state after deformation. There will also be an associated elevation in pressure difference as a result of this flow deceleration (as seen in Fig. 5a). Weakly viscoelastic nanofluid ðk1 ¼ 0:2Þ therefore generates higher axial velocity magnitudes compared with stronger viscoelastic nanofluid (k1 ¼ 0:2) but substantially lower magnitudes than Newtonian nanofluid (k1 ¼ 0 for which relaxation and retardation effects vanish). It is also of interest that even with high relaxation: retardation time ratio the flow is never reversed, i.e. back flow is not induced as testified to by the consistently positive values of axial velocity in Fig. 5b. The strongly laminar nature of the flow also ensures that flow separation or boundary layer detachment from the walls at the entry zone is also eliminated. Furthermore,

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there is an upper limit to physically realistic working fluids and therefore the case of k1 exceeding unity is not appropriate and ignored, as noted by Bird et al. [106]. Figure 6a–c illustrates the effects of solid fractional volume of nanofluid ðvÞ on dp, u and s profiles for both (cAl O –H O, cAl O –C H O ) nanofluids. xy 2 3 2 2 3 2 6 2 dx Figure 6a exposes that a significant drop in the axial pressure gradient of both nanofluids is identified when (cAl2O3–water, cAl2O3–ethylene glycol) nanofluids are prepared with large solid fractional volume of nanofluid, i.e. high percentage doping of the base fluids with nanoparticles. Clearly, this behaviour is generated by the enhanced viscosity of the homogenously dispersed cAl2O3–ethylene glycol nanoparticles. Figure 6b is drawn to explain the development in the axial velocity profile with an increment in the solid fractional volume of nanofluid; strong flow acceleration is computed in left region y(0  y  0.3686). It is also noticed that the wall shear stress is boosted with an increase in solid fractional volume of nanofluid ðvÞ as shown in Fig. 6c. The cAl2O3–ethylene glycol nanofluid is influenced more dramatically with solid fractional volume of nanofluid as compared with cAl2O3–water nanofluid. The variations in ddpx, u and sxy for cAl2O3–water, cAl2O3–ethylene glycol nanofluids with increment in Helmholtz–Smoluchowski velocity ðUHS Þ are examined through Fig. 7a–c. Helmholtz–Smoluchowski velocity (maximum electroosmotic velocity) represent the effects of external electric field and is defined as x eef 1 . A positive value of UHS [ 0 implies an opposing electrical field UHS ¼  Ecl bf orientation in the negative X-direction, UHS ¼ 0 corresponds to the absence of electric field and UHS \0 is associated with an assistive (supportive) electric field in the non-negative X-direction. It is apparent that for supporting electric field, axial pressure gradient is minimum, whereas it is a maximum for an opposing electric field, as visualized in Fig. 7a for both nanofluid cases (cAl2O3–H2O, cAl2O3– C2H6O2). From Fig. 7b, the impact of UHS on axial velocity reveals that axial flow acceleration is induced in right section of the region, whereas the converse effect arises in the left section of the region. An increase in UHS in the non-positive direction physically infers the presence of a strong assistive axial electric field which produces enhancement in the wall shear stress magnitudes (see Fig. 7c) for both (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids. The evolution in temperature distribution with Joule electrothermal parameter ðcÞ, solid fractional volume of nanofluid ðvÞ and dimensionless time (t) is visualized in Figs. 8, 9, 10. It is observed that the temperature of cAl2O3–water nanofluid is noticeably less than the temperature computed for cAl2O3–ethylene glycol nanofluid. These plots for temperature distribution are based on the no-slip boundary conditions enforced on the peristaltic microchannel walls. As a result of the shear-thinning nature of cAl2O3–water nanofluid ionic solution and a lower viscosity relative to that of cAl2O3–ethylene glycol nanofluid, the momentum diffusion rate of cAl2O3–water nanofluid exceeds that of the cAl2O3–ethylene glycol nanofluid (Prandtl number is fixed and expresses the ratio of momentum and thermal diffusivities). Due to enhanced cooling within the flow regime, cAl2O3–

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water nanofluid achieves lower temperature magnitudes than cAl2O3–ethylene glycol nanofluid. Figure 8 depicts the alteration in the temperature profile of (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids via higher values Joule heating parameter. The temperature distribution of the nanofluid is improved when more electric energy is changed into thermal energy due to Joule electrical dissipation, which is a very important effect in real electroosmotic fluid dynamics. A substantial elevation in the (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids temperature distribution for growing values of the solid fractional volume of nanofluid is also demonstrated in Fig. 9. As expected, due to the growth in the conductive heat transfer, there is a growth in the temperature distribution of the (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids for larger solid fractional volume of nanofluid. Figure 10 indicates that a considerable enhancement in temperature profile is induced with progress in time. The free movement of cAl2O3–water nanoparticles increases with interaction between molecules and the resulting ballistic collisions which is possible due to lower viscosity. However, the cAl2O3–ethylene glycol nanofluid possesses a higher viscosity and this inhibits ballistic nanoparticle collisions which results in a depression in nanoparticle temperature distribution since interaction between the molecules is inhibited. Figures 11, 12, and 13 illustrate the evolution in heat transfer coefficient (Z) with selected parameters for both (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids in the microchannel at t = 0.5. The heat transfer coefficient fundamentally evaluates the thermal gradient at the wall and also is a measure of the relative contribution of convection to conductive heat transfer. It is essentially a version of the Nusselt number. The heat transfer rate is strongly dependent on time for both (cAl2O3– H2O, cAl2O3–C2H6O2) nanofluids. The growth in the magnitude of the heat transfer coefficient for the various values of the Joule heating parameter is presented in Fig. 11. With increasing Joule heating parameter, the heat transfer coefficient for both cAl2O3–H2O, cAl2O3–C2H6O2 nanofluids increases at small axial locations along the microchannel, i.e. x 2 ½0; 0:5, whereas at larger axial locations, x 2 ½0:5; 1, Z decreases. Heat transfer rate is therefore simultaneously sensitive to axial location and time. The deviation of Z for distinct values of nanoparticle volume fraction,v is presented in Fig. 12. The graph shows that elevation in nanoparticle fraction v stimulates a sizeable enhancement in the absolute value of heat transfer coefficient for both cAl2O3–H2O, cAl2O3–C2H6O2 nanofluids. In Fig. 13, it is observed that the heat transfer coefficient exhibits an oscillatory nature, over time for both (cAl2O3–H2O, cAl2O3–C2H6O2) nanofluids, which is characteristic of peristaltic propulsion regimes. The maximum heat transfer coefficient corresponds to the cAl2O3–water nanofluid, and a highly frequently oscillatory behaviour is computed for cAl2O3–ethylene glycol nanofluid.

Thermal Analysis of cAl2O3/H2O and cAl2O3/C2H6O2 … Fig. 8 Influence of Joule heating parameter on temperature distribution (h) for a = 0.1; x = 0.6; t = 0.1 and v = 0.2

249

1

γ Al2O3 - H2O γ Al2O3 - C2H6O2

0.9 0.8 0.7

y

0.6 0.5 0.4 0.3

γ= 0 γ = 0.1 γ = 0.2

0.2 0.1 0

Fig. 9 Influence of solid fractional volume of nanofluid on temperature distribution (h) for a = 0.1; x = 0.6; t = 0.1 and c = 0.1

0

0.2

0.4

0.6

0.8

1

θ

1.2

1.4

1.6

1.8

2

1

γ Al2O3 - H2O γ Al2O3 - C2H6O2

0.9 0.8 0.7

y

0.6 0.5 0.4 0.3

=0 = 0.1 = 0.2

0.2 0.1 0

Fig. 10 Influence of dimensionless time on temperature distribution (h) for a = 0.1; x = 0.6; v = 0.2; c = 0.1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1

γ Al2O3 - H2O γ Al2O3 - C2H6O2

0.9 0.8 0.7

y

0.6 0.5 0.4 0.3

t = 0.1 t = 0.2 t = 0.3

0.2 0.1 0

0

0.2

0.4

0.6

0.8

1

1.2

1.4

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Fig. 11 Influence of Joule heating parameter on heat transfer coefficient (Z) for a = 0.3; t = 0.5 and v = 0.2

1.5

γ=0 γ = 0.1 γ = 0.2

1

0.5

Z

x: 0.5 Z: 0

0

-0.5

γ Al2O3 - H2O γ Al O - C H O 2 3 2 6 2

-1

-1.5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

x

Fig. 12 Influence of solid fractional volume of nanofluid on heat transfer coefficient (Z) for a = 0.3; t = 0.5 and c = 0.1

1

=0 = 0.1 = 0.2

0.5

x: 0.5 Z: 0

Z

0

-0.5

-1

-1.5

γ Al2O3 - H2O γ Al2O3 - C2H6O2 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

x

Fig. 13 Influence of dimensionless time on heat transfer coefficient (Z) for a = 0.3; v = 0.5 and c = 0.1

0.8

t=0 t = 0.1 t = 0.2

0.6 0.4 0.2

Z

0 -0.2 -0.4 -0.6

γ Al2O3 - H2O γ Al2O3 - C2H6O2

-0.8 -1

0

0.1

0.2

0.3

0.4

0.5

x

0.6

0.7

0.8

0.9

1

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6 Conclusions Motivated by new developments in bio-inspired electromagnetic nanofluid microchannel energy applications, a mathematical model has been developed for transient peristaltic electroosmotic hydromagnetic viscoelastic flow of water-based cAl2O3 nanofluids and ethylene glycol-based cAl2O3 nanofluids in a microchannel, under the action of mutually orthogonal electrical (axial) and magnetic (transverse) fields. Both magnetohydrodynamic and Joule electrical dissipation effects are included. The robust Jeffreys viscoelastic model is deployed to simulate rheological characteristics and a modified Tiwari-Das nanoscale model used for nanoparticle volume fraction effects. The conservation equations and associated boundary conditions are simplified via lubrication theory and rendered non-dimensionless. Analytic expressions for axial velocity, transverse velocity, stream function, axial pressure gradient and temperature are derived for both types of nanofluids. MATLAB symbolic software is implemented to evaluate the solutions for physically appropriate data of relevance to bio-inspired electromagnetic rheological nanofluid energy systems. Extensive visualization of the results is presented via graphs. The key finding of the present analysis may be crystallized as follows: • There is an enhancement in the axial pressure gradient with a reduction in solid fractional volume of nanofluid, i.e. nanoparticle percentage doping. • The axial velocity is suppressed with increasing the strength of the magnetic field and Jeffery rheological parameter, whereas it is enhanced with increasing axial electric field and EDL thickness. • Wall shear stress is strongly dependent on the magnetic field, electric field, Jeffery parameter and the Debye length electroosmotic parameter. • Wall heat transfer rates (heat transfer coefficient) for cAl2O3–ethylene glycol nanofluid are significantly lower than those computed for cAl2O3–water nanofluid. • Increasing nanoparticle fraction v produces a marked enhancement in the absolute value of heat transfer coefficient for both cAl2O3–H2O, cAl2O3– C2H6O2 nanofluids. • An increase in Helmholtz–Smoluchowski velocity in the negative axial direction physically generates a strong assistive axial electric field which produces enhancement in the wall shear stress magnitudes. • Wall shear stress increases with greater Grashof number since the axial flow is boosted which manifests in higher shear rates at the microchannel boundaries. In the absence of thermal buoyancy force (Gr = 0), i.e. for forced convection, shear stress is higher for (cAl2O3–H2O) nanofluid as compared to (cAl2O3–C2H6O2) nanofluid; however, with relatively strong thermal buoyancy present (Gr > 1) shear stress for (cAl2O3–C2H6O2) nanofluid clearly exceeds that for (cAl2O3– H2O) nanofluid. • cAl2O3–water nanofluid is more appropriate and efficient for deployment in heat transfer devices and microfluidic systems.

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The present study has revealed some interesting features of electromagnetic peristaltic non-Newtonian flows in microchannels for energy systems. However, the two-way, fully coupled interaction of the microchannel walls and the peristaltic propulsion regime has been ignored. Fluid–structure interaction (FSI) may be addressed more comprehensively with commercial computational fluid dynamics codes such as ANSYS FLUENT [109], COMSOL Multiphysics [110] and ADINA FSI [111]. Efforts in this direction are currently underway.

Appendix The constants as utilized in Eqs. (24)–(33) are as follows.  1  306v2  0:19v þ 1 ; k1 þ 1   H 2 ðk1 þ 1Þ 3vðr  1Þ þ1 ; a2 ¼ ð306v2  0:19v þ 1Þ r  vðr  1Þ þ 2   Grðk1 þ 1Þ ðqbÞs a3 ¼ v þ1  v ; ð306v2  0:19v þ 1Þ ðqbÞbf a1 ¼

a4 ¼

a6 ¼

UHS j2 ðk1 þ 1Þ cð254:3v2  3v þ 1Þ ; a ¼ 5 coshðjhÞð306v2  0:19v þ 1Þ ð28:905v2 þ 2:8273v þ 1Þ   3vðr  1Þ þ1 ; r  vð r  1Þ þ 2 @p @x

a1 a22 coshða2 hÞ 



a4 coshðjhÞ Pr a a a ah   þ 4 bf 3 5  2 4 7 a2 coshða2 hÞ a2 coshða2 hÞ coshða2 hÞ a22  j2

a8 sinhða2 hÞ Prbf a3 a5 h2 þ 2 ; coshða2 hÞ 2a2 coshða2 hÞ

2 þ Prbf a5 h2 a7 a4 ; a8 ¼  3 ; 2h a2  1  123v2 þ 7:3v þ 1 ; a9 ¼ k1 þ 1   H 2 ð k1 þ 1Þ 3vðr  1Þ þ1 ; a10 ¼ ð123v2 þ 7:3v þ 1Þ r  vðr  1Þ þ 2 a7 ¼

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a11 a12 a13

253

  ðqbÞs Grðk1 þ 1Þ v ¼ þ1  v ; ð123v2 þ 7:3v þ 1Þ ðqbÞbf   cð82:1v2 þ 3:9v þ 1Þ 3vðr  1Þ þ 1 ; ¼ ð4:97v2 þ 2:72v þ 1Þ r  vðr  1Þ þ 2 UHS j2 ðk1 þ 1Þ ; ¼ coshðjhÞð123v2 þ 7:3v þ 1Þ

a14 ¼

@p @x

a9 a210 coshða2 hÞ 

a15 ¼



a13 coshðjhÞ Pr a a a a h  2  þ 4 bf 11 12  2 13 15 2 a a cosh ð a h Þ coshða10 hÞ a10  j 2 10 10 coshða10 hÞ

a16 sinhða10 hÞ Prbf a11 a12 h2 þ 2 ; coshða10 hÞ 2a10 coshða2 hÞ

2 þ Prbf a12 h2 a15 a13 ; a16 ¼  3 : 2h a10

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Thermal Transport of MHD Electroosmotic Couple Stress Nanofluid Flow in Microchannels in the Presence of Various Zeta Potentials V. Sridhar and K. Ramesh

Abstract In the current chapter, the thermal transport of magnetohydrodynamic couple stress nanofluid under the impacts of electroosmosis and Hall currents in the microchannel is considered. The continuity, momentum, nanoparticle temperature, nanoparticle volume fraction and Poisson–Boltzmann equations have been considered to govern the nanofluid flow. The governing equations are simplified under the appropriate assumptions and non-dimensional quantities. The exact solutions are presented for the resulting dimensionless boundary value problems. The pictorial representations are presented for the nanoparticle temperature, nanoparticle volume fraction, velocity and Nusselt number. It is concluded from our results that the velocity of the fluid rises with enhancement of pressure gradient, Grashof number and electroosmosis parameter. The temperature enhances with rising values of Brownian motion, thermophoresis and heat generation parameters. The results of the present study can be utilized in electromagnetic and heat transfer pumping in the industry processes.







Keywords Magnetohydrodynamics Electroosmosis Couple stress nanofluids Slip boundary conditions Asymmetric zeta potentials







Nomenclature B0 cp g a1 p qf qp T C

Uniform magnetic field (T) Specific heat capacity (J kg K−1) Gravitational acceleration (m s−2) Thermal conductivity (W m−1 K−1) Pressure (kg m−1 s−1) Density of the fluid (kg m−3) Density of the nanoparticles (kg m−3) Nanoparticle temperature (K) Nanoparticle volume fraction (%)

V. Sridhar
K. Ramesh (&) Department of Mathematics, Symbiosis Institute of Technology, Symbiosis International (Deemed University), Pune 412115, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_14

261

262

lf r u DB DT Q0 M Rn a G Nu Gr Gc h Nt c Nb

V. Sridhar and K. Ramesh

Effective viscosity (kg m−1 s−1) Electrical conductivity (X1 m1 ) Velocity component (m s−1) Brownian diffusion coefficient (m s−1) Thermophoretic diffusion coefficient (m2 s−1) Heat generation parameter (m2 s−3) Hartmann number Radiation parameter Dimensionless velocity slip parameter Pressure gradient Nusselt number Thermal Grashof number Local nanoparticle Grashof number Dimensionless temperature Thermophoresis parameter Dimensionless heat generation parameter Brownian motion parameter

1 Introduction Nanofluids are created by adding dispersion of nanoparticles in the base fluids (preferably, with size P >

1 > : a M ðgi Þ ; ðgi gj ÞM ðgj Þ

i ¼ j; i 6¼ j;

i; j ¼ 1; 2; . . .; Ng :

Ng Y

M ðgi Þ ¼

 g gi  gj :

j¼1; i6¼j

ð29Þ The weighting coefficients of the higher-order derivative can be obtained as follows: h i h i

h ðr1Þ i ðr Þ ðr1Þ  Aij ¼ Aij Aij ¼ Aij Aij :

ð30Þ

It is pertinent to deploy Chebyshev–Gauss–Lobatto grid distribution:
 gi 1 i1 1  cos ¼ p ; 2 Ng  1 a

i ¼ 1; 2; . . .; Ng

ð31Þ

According to the GDQ, the discretized governing equations and the appropriate boundary conditions can then be generated, although for brevity we have omitted these lengthy algebraic expressions here. In the emerging formulations, parameters B and C arise, which represent the second- and third-order weighting coefficients, respectively. The values of the similarity flow variables, i.e. fi ; hi , i at each node in the solution domain, can be obtained. These may then in turn be utilized to compute the wall functions, i.e. skin friction, Nusselt number, Sherwood number and motile micro-organism wall mass flux. Comparisons of the Runge–Kutta method (RKM) solutions and the GDQ code (which is executed on an SGI Octane desk workstation and takes thirty seconds to converge) for skin friction coefficient, Nusselt number and Sherwood number are presented in Tables 1, 2 and 3, with all

Modelling the Impact of Melting and Nonlinear Radiation …

293

17 parameters given in the tables. After some numerical tests, 180 node points were used. Excellent correlation is achieved. Confidence in the present RKM solutions is therefore justifiably very high. Furthermore, Tables 1, 2 and 3 provide a solid benchmark for other researchers to extend the current model and to compare alternative numerical methods with the present RKM and GDQ techniques. Table 1 reveals that magnitude of skin friction coefficient increases with greater curvature parameter whereas the reverse trend prevails for higher values of melting parameter. Table 2 indicates that Nusselt number is an increasing function of Nt, Nb, Sr and Df and a decreasing function of Me, Rd and hw . Table 3 shows that Sherwood number is depleted with an elevation in Me, Nt, Sr and Df whereas it is increased by Nb.

Table 1 Comparison of RKM and GDQ computations for numerical values of skin friction f 00 ð0Þ with a ¼ p=4; Grt ¼ 0:1; Grc ¼ 0:1; Q ¼ 0:1; Ec ¼ 0:1; Sc ¼ 0:5; Cr ¼ 0:3 c

Me

M

Nb

Nt

Sr

Df

Pr

Rd

hm

f 00 ð0Þ RKM

f 00 ð0Þ GDQ

0 0.5 1 1

0.5

1.5

0.2

0.2

0.2

0.2

1

2

1.2

0.5

0.2

0.2

0.2

0.2

1

1

1.2

0.5

0 0.5 1 0.5

1.5

0.2

0.2

0.2

0.2

1

1.2

0.1

0.5

0.5

0.3

0.2

0.2

1.5

1.2

0.5

0.5

0.5

0.1 0.3 0.5 0.2

0.7 1.0 1.3 1

0.2

0.2

1

1

1.2

0.5

0.5

1.5

0.2

0.1 0.3 0.5 0.2

0.3

1

1

1.2

0.5

0.5

1.5

0.2

0.2

0.5 1 1.5 0.5

1

1

1.2

0.5

0.5

0.5

0.2

0.2

0.2

0 0.3 0.6 0.2

1

1.2

0.5

0.5

0.5

0.2

0.2

0.2

0.2

1

0 1 2 1

1:7390 1:8874 2:0372 1:4601 1:3003 1:1780 1:8213 1:8572 1:8750 1:1441 1:1389 1:1361 1:1230 1:1207 1:1189 1:8547 1:8551 1:8556 1:1385 1:1342 1:1289 1:1202 1:1507 1:1594 1:1241 1:1457 1:1636

1:74010 1:8871 2:0369 1:4598 1:3004 1:1776 1:8209 1:8568 1:8749 1:1437 1:1384 1:1358 1:1227 1:1205 1:1186 1:8551 1:8553 1:8557 1:1383 1:1344 1:1287 1:1204 1:1504 1:1598 1:1238 1:1453 1:1634

1.1 1.3 1.5

294

M. Garvandha et al.

Table 2 Comparison of RKM and GDQ computations for numerical values of Nusselt number h0 ð0Þ, /0 ð0Þ with a ¼ p=4; Grt ¼ 0:1; Grc ¼ 0:1; Q ¼ 0:1; Ec ¼ 0:1; Sc ¼ 0:5; Cr ¼ 0:3; c

Me

M

Nb

Nt

Sr

Df

Pr

Rd

hm

h0 ð0Þ RKM

h0 ð0Þ GDQ

0 0.5 1 1

0.5

1.5

0.2

0.2

0.2

0.2

1

2

1.2

0.5

0.2

0.2

0.2

0.2

1

1

1.2

0.5

0 0.5 1 0.5

0.5

0.2

0.2

0.2

0.2

1

1.2

0.1

0.5

0.5

0.3

0.2

0.2

1.5

1.2

0.5

0.5

0.5

0.1 0.3 0.5 0.2

0.7 1.0 1.3 1

0.2

0.2

1

1

1.2

0.5

0.5

1.5

0.2

0.1 0.3 0.5 0.2

0.3

1

1

1.2

0.5

0.5

1.5

0.2

0.2

0.5 1 1.5 0.5

1

1

1.2

0.5

0.5

0.5

0.2

0.2

0.2

0 0.3 0.6 0.2

1

1.2

0.5

0.5

0.5

0.2

0.2

0.2

0.2

1

0 1 2 1

0:2247 0:4846 0:6954 0:8139 0:7409 0:6834 0:5473 0:6197 0:7015 0:5768 0:5841 0:5939 0:6350 0:6646 0:6995 0:6351 0:6377 0:6401 0:5698 0:5908 0:6164 0:6570 0:5105 0:4696 0:6374 0:5333 0:4487

0:2244 0:4842 0:6951 0:8136 0:7411 0:6837 0:5476 0:6198 0:7012 0:5766 0:5843 0:5937 0:6349 0:6643 0:6991 0:6347 0:6373 0:6404 0:5698 0:5905 0:6161 0:6572 0:5103 0:4693 0:6371 0:5335 0:4484

1.1 1.3 1.5

5 Results and Discussion Extensive computations have been performed with the RKM code for the impact of all pertinent parameters on velocity, temperature and concentration through graphs. In the computations, the following data is used: c ¼ 0:5ð0  c  1Þ; Me ¼ 0:5ð0  Me  1Þ, M ¼ 0:5ð0  M  1Þ, a ¼ p4 p6  a  p3 , Grt ¼ 0:1ð0:1  Grt  0:5Þ, Grc ¼ 0:1ð0:1  Grc  0:5Þ, Pr ¼ 1ð0:7  Pr  1:3Þ, Q ¼ 0:3ð0:1  Q  0:4Þ, Ec ¼ 0:1ð0:1  Ec  0:5Þ, Nt ¼ 0:2ð0:1  Nt  0:6Þ, Nb ¼ 0:2ð0:1  Nb  0:6Þ, Rd ¼ 1ð0  Rd  2Þ, hw ¼ 1:2ð1:1  hw  1:3Þ, Sr ¼ 0:2ð0:1  Sr  1:5Þ, Df ¼ 0:2ð0  Df  0:6Þ,

Modelling the Impact of Melting and Nonlinear Radiation …

295

Table 3 Comparison of RKM and GDQ computations for numerical values of Sherwood number /0 ð0Þ with a ¼ p=4; Grt ¼ 0:1; Grc ¼ 0:1; Q ¼ 0:1; Ec ¼ 0:1; Sc ¼ 0:5; Cr ¼ 0:3; c

Me

M

Nb

Nt

Sr

Df

Pr

Rd

hm

/0 ð0Þ RKM

/0 ð0Þ GDQ

0 0.5 1 1

0.5

1.5

0.2

0.2

0.2

0.2

1

2

1.2

0.5

0.2

0.2

0.2

0.2

1

1

1.2

0.5

0 0.5 1 0.5

1.5

0.2

0.2

0.2

0.2

1

1.2

0.1

0.5

0.5

0.3

0.2

0.2

1.5

1.2

0.5

0.5

0.5

0.1 0.3 0.5 0.2

0.7 1.0 1.3 1

0.2

0.2

1

1

1.2

0.5

0.5

1.5

0.2

0.1 0.3 0.5 0.2

0.3

1

1

1.2

0.5

0.5

1.5

0.2

0.2

0.5 1 1.5 0.5

1

1

1.2

0.5

0.5

0.5

0.2

0.2

0.2

0 0.3 0.6 0.2

1

1.2

0.5

0.5

0.5

0.2

0.2

0.2

0.2

1

0 1 2 1

0:0705 0:4162 0:6929 0:2506 0:2380 0:2272 0:2966 0:2540 0:1983 0:1841 0:2083 0:2111 0:3173 0:1961 0:0221 0:1992 0:1711 0:1449 0:3352 0:3180 0:2987 0:2554 0:3879 0:4244 0:2793 0:3755 0:4513

0:0702 0:4159 0:6927 0:2504 0:2377 0:2271 0:2963 0:2537 0:1985 0:1842 0:2084 0:2114 0:3175 0:1963 0:0223 0:1994 0:1714 0:1451 0:3354 0:3181 0:2989 0:2552 0:3882 0:4246 0:2794 0:3753 0:4512

1.1 1.3 1.5

Sc ¼ 0:5ð0  Sc  1Þ, Cr ¼ 0:3ð0:1  Cr  0:3Þ. These values correspond to aqueous magnetic nanocoatings and have been adopted from fundamental references including Epstein and Cho [36], Mondal et al. [59], Gebhart et al. [77], etc. Figures 2a–d depict the velocity profile for the influence of curvature, magnetic, melting and inclination parameters. Figure 2a indicates that greater curvature (c) results in an increase in the axial velocity. Momentum boundary layer thickness is therefore reduced considerably, and the stretching boundary layer flow is accelerated. The curvature parameter (c) arises multiple times in the momentum, energy and nanoparticle species conservation Eqs. (8–10), although it is absent in the boundary conditions. It features in 00 the shear terms ð1 þ 2gcÞf 000 and þ 2cf in the momentum Eq. (8), when c!0

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Fig. 2 Axial velocity for a curvature parameter, b magnetic parameter, c melting parameter and d inclination angle

curvature effects are negated. Clearly for this case, the flow is decelerated for the majority of the radial distance from the cylinder surface and momentum boundary layer thickness is increased. For c > 0, generally acceleration is prominent at intermediate distance from the cylinder surface (very close to the wall negligible difference is computed); however approaching the free stream, the curvature effect is reversed and a weak acceleration is observed for the vanishing curvature case. These trends concur with other studies including Ibrahim and Negera [73]. Figure 2b indicates that increasing magnetic parameter, M, significantly damps the axial velocity. This trend is sustained at all radial coordinates. The electrically non-conducting scenario (M = 0) therefore produces acceleration compared with the magnetic case. The radial magnetic field generates a transverse (axial) Lorentzian magnetohydrodynamic drag force, M 2 f 0 . This strongly retards the axial momentum development and regulates the coating flow. The effect is similar to conventional stationary wall magnetohydrodynamics. Effectively, momentum boundary layer thickness is therefore elevated along the cylinder periphery. The rB2 l

parameter M is distinct from the conventional Hartmann number, Ha. M 2 ¼ qU00 which expresses the relative contribution of Lorentzian magnetic force to inertial body force in the regime. When M = 1, both forces contribute equally. When M > 1, magnetic force exceeds inertial force, and this permits effective regulation of the boundary layer flow in nanocoating enrobing. Even at relatively weak magnetic field intensity (M = 2), the impact on velocity field is considerable.

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However, flow reversal, i.e. backflow, is never induced. Figure 2c reveals that a substantial elevation in axial velocity is induced with increasing melting parameter (Me). The melting parameter, Me, arises in the modified Stefan wall boundary condition (11), as Pr f ðgÞ þ Me h0 ðgÞ ¼ 0. This augmented condition modifies the velocity distribution via melting-induced temperature gradient. The intensification in melting effect imparts significant momentum to the nanofluid since warmer fluid penetrates into the boundary layer and this results in flow acceleration and thinning of the momentum boundary layer. In the absence of melting (no phase change, Me = 0), this boost in momentum is not present and results in a deceleration in the stretching boundary layer flow with a corresponding thicker momentum boundary layer. Figure 2d illustrates the evolution in velocity profiles with inclination of the cylinder to the vertical. This is simulated via the modified thermal and species (nanoparticle) buoyancy forces in the momentum boundary layer Eq. (8), namely þ ðGrt h þ Grc /Þcosa. For a = 0, cosa!1 and this corresponds to the vertical cylinder case. For a = p, the horizontal cylinder case is retrieved. As a is increased to p/6, p/4 and the maximum value of p/3, cosa is progressively reduced. This decreases the thermal and species buoyancy forces which results in a de-intensification in convection currents and a deceleration in the flow. This has been highlighted in many key studies in thermo-solutal convection boundary layer flows including Gebhart et al. [77]. Increasing tilt angle therefore consistently inhibits axial momentum development, increases hydrodynamic boundary layer thickness and provides thereby a useful mechanism for scaling gravity effects and regulating the coating stretching growth rate along the cylinder [78]. Figure 3a–d visualizes the temperature distributions (h) with radial coordinate (η) profiles for (a) curvature parameter, (b) magnetic parameter, (c) melting parameter and (d) Prandtl number. A significant boost in temperature is generated with increasing curvature parameter, as observed in Fig. 3a. The non-curvature case (c = 0) produces an approximately linear growth in temperature. However, a strongly parabolic response is computed in the temperature topology for (c > 0). Thermal boundary layer thickness is therefore enhanced in the magnetic nanocoating flow with greater curvature effect. This is understandable since the curvature parameter features in many terms in the thermal boundary layer (energy conservation) Eq. (9), including the thermal conduction terms, 0 ð1 þ 2gcÞh00 and 2ch . Figure 3b shows that an increase in magnetic parameter, M, markedly enhances temperature magnitudes in the regime. Magnetic parameter does not feature in the energy conservation Eq. (9). However via coupling terms with the momentum Eq. (8), e.g. Pr ðf h0  f 0 h þ QhÞ, and the thermal and solutal buoyancy forces, there is a strong interplay between heat and momentum transfer. The elevation in temperature is generated by the dissipation in supplementary work expended in dragging the nanofluid against the action of the magnetic as thermal energy. This manifests in an increase in thermal boundary layer thickness along the cylinder surface. The classical parabolic growth in temperature from the cylinder surface to the free stream is observed irrespective of whether magnetic effect is present or not. Figure 3c demonstrates that a strong reduction in temperature is

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induced with greater melting parameter, Me. This is connected to the boost in momentum with greater melting effect which is enhanced relative to the heat diffusion rate. Thermal boundary layer thickness is therefore decreased. Figure 3d illustrates that with elevation in Prandtl number Pr leads to a strong reduction in temperature distribution. Prandtl number is inversely proportional to effective thermal conductivity of the magnetic nanofluid. Pr = 1.3 corresponds to aqueous magnetic nanopolymers which combine the low Prandtl number ( > k nl < @y y¼0 ¼  L ðTw  T1 Þh ð0Þ for  qw ¼ > Prnl > : / q0 ½Uw ð X Þ 1 for PHF: Here, L ¼

pmffiffiffil a

PST; ð62Þ

is the characteristic length. The Nusselt number is given by Lqw knl ðTw  T1 Þ 8 h0 ð0Þ for PST > <
 ¼ kl > ½Hð0Þ1 for PHF : kgl s Prnl ¼ : /1

Nu ¼

ð63Þ

It should be noted that the Nusselt number for both PST and PHF cases turns out to be the same. Also, the Nusselt number is proportional to the parameter s and the nanoliquid Prandtl number Prnl , and inversely proportional to the parameter /1 . The following section throws light on the dynamics of the problem based on the analytical solutions obtained so far.

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6 Results and Discussion The flow of a nanoliquid due to a permeable quadratically stretching sheet is investigated with emphasis on heat transfer characteristics. Two types of nanoliquids, namely copper–water ðCu  H2 OÞ and alumina–water ðAl2 O3  H2 OÞ, are considered. The thermophysical properties of these liquids are listed in Table 1. The dynamic viscosity of water is taken to be ll ¼ 0:00089 kgm1 s1 at about 25 °C. We first begin with the discussion of flow characteristics. It should be recalled that the noticeable difference between the linear and quadratic stretching sheet problems is that the stretching rate appears explicitly in the solution of quadratic stretching sheet problem whereas it appears implicitly in the case of linear stretching sheet problem. As a result, it gives an opportunity to consider the stretching rate as a controlling parameter. This fact can be effectively used in achieving optimal cooling rate. Further, the quadratic stretching sheet problem forms a generalization of the linear stretching sheet problem by introduction of quadratic term in the stretching velocity as a mild perturbation. The solution of the flow problem is derived in line with the ones reported by Mahabaleshwar [33] and Narayana and Nerolu [29] with substantial rigor. The solution is obtained for all possible values of the transpiration parameter Vw , and the case of impermeable stretching sheet, i.e., Vw ¼ 0, forms a special case of the present study. The case of Vw [ 0 represents blowing (or injection) situation and that of Vw \ 0 represents the suction situation. Using the relation between s and s , one can write 0 Vw s ¼ @ þ 2

sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi11
2 Vw 1A þ : /1 2

The above relation clearly shows that s is defined for all possible real values of Vw as /1 always remains positive. The parameter s is plotted against the transpiration parameter Vw in the interval [−5, 5] for different values of nanoparticle volume fraction /, in Fig. 1a and b for the Cu  H2 O and Al2 O3  H2 O nanoliquids, respectively. From these figures, it is observed that s is an increasing function of Vw ; moreover, it increases steeply for positive values of Vw . Further, in the case of Cu  H2 O nanoliquid s decreases with the increasing values of nanoparticle volume fraction /, while the same trend is observed in the case of Al2 O3  H2 O nanoliquid but the changes are not appreciable. By setting wðX; Y Þ ¼ C, where C is a constant, and using Eq. (37), the equation for streamlines can be obtained in the following form: "  # s /1 1 1 X C s Y ¼   ln : s X þ b X 2

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Fig. 1 Variation of the parameter s with transpiration parameter Vw for different values of nanoparticle volume fraction /

This expression is used in plotting the streamlines for different values of the governing parameters. Figure 2a and b shows streamlines for different values of nanoparticle volume fraction for the cases of Cu  H2 O and Al2 O3  H2 O nanoliquids, respectively. It is clear from Fig. 2a and b that the streamlines are lifted for increasing values of nanoparticle volume fraction / in both the cases of Cu  H2 O and Al2 O3  H2 O nanoliquids but the lift is not so predominant in the case of Al2 O3  H2 O nanoliquid. Further, the lifting effect is evident for increasing values of quadratic stretching parameter b and the plots concerning the same are omitted for reasons of space (see Mahabaleshwar [33] for more details). From the streamline plots, it is difficult to judge what happens to velocity as the nanoparticle volume fraction is increased; as a result, the axial velocity distributions are plotted in Fig. 3a and b for different values of / in the case of Cu  H2 O and

Fig. 2 Streamlines wðX; Y Þ ¼ C for different values of nanoparticle volume fraction / for b ¼ 0:01 and Vw ¼ 1

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Al2 O3  H2 O nanoliquids, respectively. In the case of Cu  H2 O nanoliquid, the increase in the values of / results in decreasing the velocity as seen from Fig. 3a. This is quite usual as the introduction of suspended particles increases the viscosity of the liquid, thereby retarding the motion. Similar trend is observed in the case of Al2 O3  H2 O nanoliquid as seen from Fig. 3b, but the retardation is very small to be picked up from the plot. There was an abnormality noticed with respect to Al2 O3  H2 O nanoliquid by Narayana and Sibanda [41] in the case of a liquid film flow of a nanoliquid over a stretching sheet. They reported an opposite effect of increasing velocity with increasing the particle fraction. This was due to the fact that they considered volume fraction to be 0  /  0:2 but the volume fraction of 0  /  0:06 is needed for the validity of Brinkman law of viscosity. At this juncture, we divert our attention towards the heat transfer characteristics. It should be recalled that in a stretching sheet problem it is imperative that an optimum cooling of the sheet achieved so as to arrive at its desired mechanical properties. In this regard, the rate of stretching and the rate of cooling play vital roles. In what follows, the heat transfer aspects of nanoliquid which have direct impact on the cooling of the sheet in the considered problem will be discussed with the help of analytical solution. Two types of boundary heating, namely PST and PHF, are considered. The temperature profiles are shown in Fig. 4a and b for two different types of boundary heating. In the PST case, the temperature profiles increase with the nanoparticle volume fraction with respect to both nanoliquids. This shows that more heat is transferred from the sheet to the nanoliquid as the nanoparticle volume fraction is increased. Also, the temperature profile of the clear liquid ð/ ¼ 0Þ lies below those corresponding to the nanoliquid ð/ 6¼ 0Þ. These facts indicate that nanoliquids take more heat from the stretching sheet. Results of PST hold qualitatively in the PHF case as observed from Fig. 4b.

Fig. 3 Axial velocity distribution U ðX; Y Þ for different values of nanoparticle volume fraction / for b ¼ 0:01 and Vw ¼ 1

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Fig. 4 Temperature profile hðY Þ for different values of nanoparticle volume fraction / for different types of boundary heating with b ¼ 0:01 and Vw ¼ 1

Figure 5a and b shows temperature distributions T ðX; Y Þ in the case of two considered nanoliquids with a fixed nanoparticle volume fraction of / ¼ 0:05. These figures clearly indicate that in both the types of boundary heating considered the Al2 O3  H2 O nanoliquid has increased temperature distribution as compared to Cu  H2 O nanoliquid for sufficiently distant axial position X. Even though the temperature profiles hðY Þ and HðY Þ of Cu  H2 O nanoliquid lie above those of Prnl

Al2 O3  H2 O nanoliquid (see Fig. 4a and b), due to the factor ½Uw ð X Þ /1 the temperature distribution T ðX; Y Þ of Al2 O3  H2 O nanoliquid overtakes that Cu  H2 O nanoliquid, which means that Al2 O3  H2 O nanoliquid takes more heat from the stretching sheet aiding a faster cooling of the sheet. Hence, one can decide upon

Fig. 5 Temperature distribution T ðX; Y Þ for different nanoliquids with / ¼ 0:05; b ¼ 0:01 and Vw ¼ 1

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which nanoliquid to be used based on the desired cooling rate which will improve the mechanical properties for the final product. The overall impression of the discussion as it relates to heat transfer characteristics is that introduction of nanoparticle in the base liquids improves the heat carrying capacity and hence nanoliquids are better suited for industrial applications over the conventional coolants.

7 Conclusion Theoretical study of the flow of a nanoliquid due to a permeable quadratically stretching sheet with emphasis on heat transfer characteristics is presented in this chapter. The exact solutions obtained for velocity and temperature distributions are used in highlighting the heat transfer enhancement due to nanoliquids. The following are some of the salient outcomes of the present study: 1. The solution of the quadratic stretching sheet problem exists for all possible values of transpiration parameter Vw . 2. The velocity is a decreasing function of nanoparticle volume fraction in both the cases of Cu  H2 O and Al2 O3  H2 O nanoliquids. 3. Al2 O3  H2 O nanoliquid possesses increased temperature distribution as compared to Cu  H2 O nanoliquid. 4. Results of clear liquid and linear stretching sheet problems can be recovered from the present study by taking / ¼ 0 and b ¼ 0, respectively. 5. Results of shrinking sheet problem can be recovered by appropriate sign changes in the present analysis.

References 1. Tadmor Z, Klein I (1970) Engineering principles of plasticating extrusion. Van Norstrand Reinhold, New York 2. Fisher EG (1976) Extrusion of plastics. Wiley, New York 3. Tadmor Z, Gogos CG (2013) Principles of polymer processing. Wiley, New York 4. Sakiadis BC (1961) Boundary-layer behavior on continuous solid surfaces: I. Boundary-layer equations for two-dimensional and axisymmetric flow. AIChE J 7:26–28 5. Sakiadis BC (1961) Boundary-layer behavior on continuous solid surfaces: II. The boundary layer on a continuous flat surface. AIChE J 7:221–225 6. Sakiadis BC (1961) Boundary-layer behavior on continuous solid surfaces: III. The boundary layer on a continuous cylindrical surface. AIChE J 7:467–472 7. Crane LJ (1970) Flow past a stretching plate. ZAMP 21:645–647 8. Grubka LJ, Bobba KM (1985) Heat transfer characteristics of a continuous, stretching surface with variable temperature. J of Heat Trans 107:248–250 9. Gupta PS, Gupta AS (1977) Heat and mass transfer on a stretching sheet with suction or blowing. The Canadian J of Chem Eng 55:744–746

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10. Vleggaar J (1977) Laminar boundary-layer behaviour on continuous, accelerating surfaces. Chem Eng Sci 32:1517–1525 11. Pavlov KB (1974) Magnetohydrodynamic flow of an incompressible viscous fluid caused by deformation of a plane surface. Magnetohydrodynamics 10:507–510 12. Andersson HI (1995) An exact solution of Navier-Stokes equations for magnetohydrodynamic flow. Acta Mech 113:241–244 13. Liao SJ (2003) On the analytic solution of magnetohydrodynamic flows of non-Newtonian fluids over a stretching sheet. J Fluid Mech 488:189–212 14. Magyari E, Pop I, Keller B (2003) New analytical solutions of a well-known boundary value problem in fluid mechanics. Fluid Dyn Res 33:313–317 15. Siddheshwar PG, Mahabaleswar US (2005) Effects of radiation and heat source on MHD flow of a viscoelastic liquid and heat transfer over a stretching sheet. Int. J. of Non-Linear Mech. 40:807–820 16. Abel MS, Mahesha N (2008) Heat transfer in MHD viscoelastic fluid flow over a stretching sheet with variable thermal conductivity, non-uniform heat source and radiation. Appl Math Modell 32:1965–1983 17. Bataller RC (2010) Towards a numerical benchmark for MHD flows of upper-convected Maxwell UCM fluids over a porous stretching sheet. Fluid Dyn and Materials Processing 6:337–350 18. Hayat T, Qasim M, Abbas Z (2010) Homotopy solution for the unsteady three-dimensional MHD flow and mass transfer in a porous space. Comm in Nonlinear Sci and Numerical Simulation 15:2375–2387 19. Takhar HS, Raptis AA, Perdikis CP (1987) MHD asymmetric flow past a semi-infinite moving plate. Acta Mech 65:287–290 20. Kumaran V, Ramanaiah G (1996) A note on the flow over a stretching sheet. Acta Mech 116:229–233 21. Kumaran V, Kumar AV, Babu JSC (2011) Impulsive boundary layer flow past a permeable quadratically stretching sheet. In: Machado J, Luo A, Barbosa R, Silva M, Figueiredo L (eds) Nonlinear Science and Complexity. Nonlinear Sci. and Complexity, Springer, Dordrecht, pp 191–198 22. Weidman PD, Magyari E (2010) Generalized Crane flow induced by continuous surfaces stretching with arbitrary velocities. Acta Mech 209:353–362 23. Magyari E, Kumaran V (2010) Generalized Crane flows of micropolar fluids. Comm in Nonlinear Sci and Numerical Simulation 15:3237–3240 24. Raptis A, Perdikis C (2006) Viscous flow over a non-linearly stretching sheet in the presence of a chemical reaction and magnetic field. Int J Non-Linear Mech 41:527–529 25. Kelson NA (2011) Note on similarity solutions for viscous flow over an impermeable and nonlinearly (quadratic) stretching sheet. Int J Non-Linear Mech 46:1090–1091 26. Cortell R (2012) Further results on nonlinearly stretching permeable sheets: Analytic solution for MHD flow and mass transfer. Math Prob in Engng 2012: 27. Mukhopadhyay S (2013) Analysis of boundary layer flow over a porous nonlinearly stretching sheet with partial slip at the boundary. Alexandra Eng J 52:563–569 28. Nasir NAAM, Ishak A, Pop I (2017) Stagnation-point flow and heat transfer past a permeable quadratically stretching/shrinking sheet. Chinese J Phys 55:2081–2091 29. Narayana M, Nerolu M (2017) Exact solution of boundary layer flow due to quadratically shrinking sheet. RUAS-SASTECH J 17:21–24 30. Mahapatra TR, Sidui S (2016) An analytical solution of MHD flow of two visco-elastic fluids over a sheet shrinking with quadratic velocity. Alexandria Eng J 55:163–168 31. Khan SK, Sanjayanand E (2004) Viscoelastic boundary layer MHD flow through a porous medium over a porous quadratic stretching sheet. Arch Mech 56:191–204 32. Mahesha N (2010) Solutions of some boundary value problems arising in the flow, heat and mass transfer due to a linear/non-linear stretching surface. Ph.D. Thesis, Gulbarga University, India

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Impact of Cattaneo–Christov Heat Flux On Al2O3–Cu/H2O–(CH2OH)2 Hybrid Nanofluid Flow Between Two Stretchable Rotating Disks Sachin Shaw

Abstract An analysis is performed to studied the 3D MHD flow of Al2O3–Cu/ Water (H2O)–Ethylene glycol (C2H6O2) (50–50% volume) hybrid nanofluid between two rotating stretching disks. Thermal equation is constructed of Cattaneo– Christov heat flux model with the thermal radiation, heat generation, and viscous dissipation. Using the proper similarity transformation, the system of coupled partial differential equations is transformed into a system of coupled ordinary differential equations and then solves numerically using bvp4c MATLAB routine. Present results are compared with the existing literature under certain constraints. A significant difference is observed in comparison between the significant of hybrid nanofluid and general nanofluid in velocities, temperature, skin friction, Nusselt number, and entropy generation. A noteworthy nature is observed in the fluid flow and heat transfer due to effective parameters. Entropy generation and Bejan number are calculated and displayed the results through graphs and tables. Reynolds number and magnetic parameter observed to boost up the skin friction at the lower and upper rotating disks, while rotational ratio and suction/injection helps to slow down the skin friction at both surfaces of disks. Nusselt number accumulated with radiation while an opposite phenomena appears with increase of Brinkman number. Entropy generation improved with magnetic field and Brinkman number. Pressure distribution boost up with increase in velocity slip constants at the upper and lower surfaces of the disks and rotational ratio. Skin friction shows up increment with increase of suction/injection parameters. Brinkman number and magnetic parameter enhanced the entropy generation while an opposite phenomena observed for the Bejan number. This simulations may help in thermal energy generation system and computer storage devices.




Keywords Rotating disk Al2O3–Cu/H2O–(CH2OH)2 hybrid nanofluid Cattaneo–Christov heat flux Entropy generation Viscous dissipation










S. Shaw (&) Botswana International University of Science and Technology, Private Bag 16, Palapye, Botswana e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_17

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Nomenclature B0 Bi Cf cp Ec fw g hf K kf khnf k M Nux Pr QT Rd Re T W0 u; v; w x; y; z

Component of magnetic field Biot number Skin fraction coefficient Specific heat capacity Eckert number Suction/injection parameter Gravity Coefficient of convective heat transfer Permeability parameter Thermal conductivity of the base fluid Thermal conductivity of the hybrid nanofluid Mean absorption coefficient Magnetic parameter Nusselt number Prandtl number Heat source Radiation parameter Reynolds number Fluid temperature Suction velocity Velocity components Space coordinates

Greek letters a b C1 C2 f h lf lhnf mhnf qf qhnf r rnf rhnf /

Non-dimensional radial direction Relaxation time of heat flux Stretching parameter at lower disk Stretching parameter at lower disk Non-dimensional axial direction Dimensionless temperature Dynamic viscosity of base fluid Dynamic viscosity of hybrid nanofluid Kinematic viscosity of hybrid nanofluid Density of base fluid Density of hybrid nanofluid Stefan–Boltzmann constant Electrical conductivity of nanofluid Electrical conductivity of hybrid nanofluid Solid volume fraction parameter

Impact of Cattaneo–Christov Heat Flux on …

X X1 X2

331

Stretching ratio Rotation parameter for lower disk Rotation parameter for upper disk

Subscripts f s nf hnf

Fluid Solid Nanofluid Hybrid nanofluid

1 Introduction Nanomaterials have a tremendous application in industries, technology, and medical sciences. The concept of application of nanoparticles immersed in a base fluid is initially introduced by Choi [1], an idea to enhance of thermal conductivity of the fluid in the presence of nanoparticles. The nanoparticle materials include metals (e.g., silver copper, gold [2–4]), metal carbides (e.g., silicon carbide [5]), metal oxide (e.g., copper oxide, zinc oxide, ferric oxide, alumina, silicon oxide, titanium oxide, graphite oxide [6–12], metal nitrides (e.g., aluminum nitride, silicon nitride [13, 14]), various form of carbon (e.g., carbon nanotubes [15], graphite [16], diamond [17]) and multifunctional nanoparticles [18]. These nanoparticles are immersed in a base fluid, e.g., water, organic liquids (ethylene glycol, triethylene glycol [19, 20]), oil or lubricant [21], polymer solution [22], bio-fluids [23], and other common liquids. It is observed that in most of the work, water, and ethylene glycol considered as base fluid [24–27], very few reports have found on the oil-based nanofluid. It is found that the oil base nanofluids revealed better development of heat transfer appearances compare to the water-based nanofluids, and the viscosity of the oil could be crucial for the stability of nanofluids [28, 29]. Several theoretical and experimental studies have been taken on nanofluids for its better thermal conductivity property than ordinary fluid [30–38]. Recently, the technologist has observed that the simultaneously disperse of more than one nanoparticles (with their unique physical and thermal properties) in a base fluid carried a new streamline category of nanofluid which called hybrid nanofluid. Hybrid nanofluid can prepare by suspending (i) different types (more than one) of nanomaterials in the base fluid, and (ii) hybrid (composite) nanomaterials in base fluid. A hybrid material is a substance which combined of physical and chemical properties of different materials, and these properties are at a stable and homogeneous phase. In general, for an individual material does not able to process the all favorable characteristics required for a particular practical purpose; it may either good in thermal properties or may be other rheological properties. However, in

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many industrial or practical applications, it is essential to trade-off between several physical, chemical, and rheological properties at the same process and that is where the application of hybrid nanofluid comes. At the same time, the hybrid nanofluid supposed to yield better thermal conductivity with respect to individual nanofluids. The characteristics of hybrid nanofluid becomes an abundant topic of interest among the researchers due to its huge application in the field of medical sciences, propulsive, transportation, naval structure, defense, and other industries [39–43]. Many theoretical and experimental works are observed in this direction to understand the nature of the hybrid nanofluid and its behavior in different environments [44–49]. A comparison on heat transfer characteristics for the Al2O3–water nanofluid and Cu–Al2O3 hybrid nanofluid flow through a porous channel has been discussed by Das et al. [50]. An experimental study shows that the MWCNTs/ GNPs hybrid nanofluid shows a 58% enhancement in heat transfer rate than the base fluid [51]. Xie et al. [52] have studied a tribiological concert of the SiO2/ MoS2 hybrid nanoparticles for magnetism alloy steel contacts. They have observed that the SiO2/MoS2 hybrid nanoparticles display greater lubrication performances than their individual presence, i.e., SiO2—nanofluid or MoS2–nanofluid. Another experimental work on diamond–Fe3O4/water hybrid nanofluid in a minichannel shows that hybrid nanofluid is compatible better in hydrothermal characteristics than diamond/Fe3O4 nanofluid [53]. An enhancement of heat transfer rate in hybrid nanofluid that the general nanofluid has observed by Devi and Devi [54]. They have considered Cu and Al2O3 as nanoparticle which immersed in a base fluid water. Ijaz et al. [55] discussed the application of hybrid nanofluid in biomedical science. They have considered Cu–Cuo/blood hybrid nanofluid flow though the stenosed artery. They also made a comparison between the Cu–Cuo/blood hybrid nanofluid and Cu/ blood nanofluid and arise in a conclusion that the curve of temperature profile is higher when Cu/blood associate with the CuO/blood. A theoretical and experimental comparison of heat transfer rate for the mono and hybrid nanofluid have established by Yildiz et al. [56] for the Al2O3–SiO2/water hybrid nanofluid. They have observed that the heat transfer enhancement is not significant for lower particle volume fraction of nanoparticles. A review on entropy generation with a comparison of nanofluid and hybrid nanofluid flow in thermal system has been discussed by Huminic and Huminic [57]. Salman et al. [58] have discussed the flow and heat transfer phenomena for hybrid nanofluid flow over backward and forward steps. The hydrothermal characteristics of hybrid nanofluid will be more effective with the proper mixture ratio of the nanoparticles which immersed in base fluid. Charab et al. [59] observed that the thermal conductivity observed is better for the various mixing ratio of Al2O3–TiO2 such a way that the total volume should not exceed 1%. The thermal conductivity shows to increase up to 35.3% for the 2:3 ratio of volume fraction of Al2O3–TiO2. A maximum enhancement of thermal conductivity observed up to 16% for the ratio of two nanoparticles of 1:4 ratio (Hamid et al. [60]). Siddique et al. [61] discussed the thermophysical properties of Cu–Al2O3 hybrid nanofluid with different mixture of volume fraction of individual nanoparticles and observed a good stability and superior thermal conductivity for the mixing ratio 5:5. However, an experimentally studied by Bhattad et al. [62] shown

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that the hydrothermal characteristics of Al2O3–MWCNT/water hybrid nanofluid are not given any significant impact with varying the mixing ratio. Waini et al. [63] have discussed the transpiration effects for a hybrid nanofluid flow over a stretching/shrinking sheet. The hybrid nanofluid flow over/through different complex geometries have been discussed by many researchers (Tayebi and Oztop [64], Abbas et al. [65]) Recently, researchers shows an attention to study the heat transfer on the fluid flow over the surface of a rotating disk due to its various application in different field of science, engineering and industries, such as, e.g., gas turbine rotators, thermal energy generation system, power generation system, geothermal industry, medical equipment, aerodynamical system, and so on. Von Karman [66] first introduced the standard problem on rotating disk. He has used the integral method approach to simplify the Navier–Stokes equation for the steady flow. Later, researchers extended work for the unsteady flow (Cochran [67], Benton [68], Rogers and Lance [69]). Flow and thermal analysis of the copper–water nanofluid flow over a rotating disk was studied by Nayak et al. [70]. They have considered a Darcy–Forchheimer model and analyzed both the static and dynamical approach. Yin et al. [71] analyzed the flow characteristics and heat transfer for a Cu, CuO, and Al2O3 nanoparticles embedded in water based nanofluid flow over a rotating disk. Several researchers have studied that heat and mass transfer phenomena for a nanofluid flow over the rotating disk [72–74]. Heat and mass transfer characteristics for a hybrid nanofluid flow over a rotating disk have been discussed by Tassaddiq et al. [75]. They have used carbon nanotubes (CNTs) as nanoparticles. The influence of Hall current and thermal radiation for Cu–Al2O3 hybrid nanofluid flow over a rotating disk has been discussed by Khan et al. [76]. MHD flow of hybrid nanofluid through a rotating system among two surfaces has discussed by Chamkha et al. [77]. They considered the thermal radiation and Joule heating in the system which further enhanced the heat transfer rate at the surface. Their study based on the copper–graphene oxide/water-based hybrid nanofluid. Xu [78] considered a wide range of nanoparticles Al2O3, Cu and TiO2 immersed in water and analyzed a generalized hybrid nanofluid flow between two rotating disks. Hybrid nanofluid flow over a spinning disk has been discussed by Acharya et al. [79]. They considered the impact of Hall current and thermal radiation in the governing system. They observed that the hybrid nano-suspension advantages maximum temperature as compared to the usual nanofluid. Al2O3–Cu/Water base hybrid nanofluid flow over a stretchable rotating disk has studied by Ouyang et al. [80]. They considered velocity slip and convective condition at the surface of the disk. Ghadikolaei and Gholinia [81] have discussed the three-dimensional mixed convective hybrid nanofluid flow past a vertical stretched plate. They considered the effect of thermal radiation, viscous dissipation along with the momentum slip and convective boundary conditions at the surface. Impact of the convective boundary condition and momentum slip on a 3D hybrid nanofluid flow over a stretching sheet has been discussed by Khashi’ie et al. [82]. Izadi et al. [83] have discussed the hybrid nanofluid flow through a square porous enclosure in the presence of inclined periodic magnetic field. Hybrid nanofluid flow over a permeable shrinking cylinder

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has studied by Khashi’ie et al. [84]. They have considered the influence of Joule heating and magnetic field in the system. Thermal radiation in flow and heat transfer plays an important role, and it has a huge application in the design of many advanced energy conversion system operating at high temperature. Thermal radiation is more significant when the overall surface heat transfer is smaller than the convective heat transfer coefficient. By observing, it is important in different field, and many researchers are studied the impact of thermal radiation into different governing system [85–87]. In general, the radiative variable improved heat transfer rate at the surface. This phenomenon is significant for any size and any complex geometry (cavity) [88]. Gireesha et al. [89] have studied the hybrid nanofluid flow across a permeable longitudinal moving fan. Usman et al. [90] have studied the impact of nonlinearity in thermal radiation for Cu–Al2O3/water hybrid nanofluid flow through a permeable surface. MHD nanofluid flow over a rotating disk in the presence of linear and nonlinear thermal radiation and viscous dissipation has discussed by Abdel-Wahed and Akl [91]. Devi and Devi [92] have discussed the MHD fluid flow over a porous rotating infinite disk and study the impact of thermal radiation in the presence of Soret and Dofour effect. Heat transfer characteristics of a water-based nanofluid flow between two stretchable disks have been discussed by Imtiaz et al. [87]. They have observed that single-wall carbon nanotubes produce higher heat transfer rate that multi-wall carbon nanotubes. The impact of Hall current and thermal radiation for an unsteady MHD hybrid nanofluid flow on a rotating vertical channel has been discussed by Iqbal et al. [93]. Acahrya et al. [94] have discussed the thermal radiation impact on a magnetized TiO2-CoFe2O4/H2O hybrid nanofluid flow over a revolving disk. Zangooee et al. [95] have analyzed hydrothermal phenomena for MHD hybrid nanofluid flow between two rotating disk in the presence of thermal radiation. The impact of thermal radiation on entropy generation for a Darcy–Forchheimer flow under a rotating disk has been discussed by Nadeem et al. [96]. Viscous dissipation is an irreversible process where the viscosity of the fluid (for viscous fluid) takes energy from the motion of the fluid and transforms this kinetic energy to the internal energy of the fluid. As a result, it is heating up the fluid. Viscous dissipation has significant impact in the functioning of the machines operating in a high-speed aircraft and injection molding. The impact of the viscous dissipation for a MHD hybrid nanofluid flow over a stretching/shrinking sheet has discussed by Aly and Pop [97]. Further, they made a comparison between nanofluid and hybrid nanofluid. Impact of heat flux and viscous dissipation on the heat transfer analysis for Cu–Al2O3/H2O hybrid nanofluid flow in a permeable channel has been discussed by Ali et al. [98]. Roy et al. [99] have studied the viscous dissipation impact with the thermal radiation for a Cu–Al2O3/water hybrid nanofluid flow past a circular cylinder. Venkateswarlu and Narayan [100] have discussed Cu–Al2O3/water-based hybrid nanofluid flow past a permeable stretching sheet with viscous dissipation phenomena. Convective boundary condition is acted at the surface and based on the constant heat flux [101]. Impact of viscous dissipation on the mixed convective hybrid nanofluid flow due to a curve sheet is discussed by Muhammad et al. [102]. They

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made a comparative investigation between the hybrid nanofluid, nanofluid, and base fluid. They have observed efficient behaviors of hybrid nanofluid. Sadaf and Abdelsalam [103] have discussed adverse effect of a hybrid nanofluid flow in a wavy non-uniform annulus with convective boundary condition at the surface. Heat transfer is an important phenomenon in different industries, engineering and biomedical applications. Cattaneo–Christov heat flux model one of very important flux models which first introduced by Cattneo [104] with utilized the concept of the Fourier law with adding the thermal relaxation time which is capable to allowed heat flux. Christov [105] improved this heat flux model from Maxwell– Christov’s model. Properties of Cattaneo–Christov model have tested and discussed by Tibllo and Zampoli [106]. Influence of Cattaneo–Christov heat flux model has been discussed by Kundu et al. [107] with CNT-based Maxwell nanofluid flow over a stretching sheet. Makinde et al. [108] have studied the impact Cattaneo–Christov heat flux for a Casson nanofluid flow past a stretched cylinder. Gangadhar et al. [109] studied the MHD Carreau fluid flow past a stretching cylinder in the presence of Cattaneo–Christov heat flux. Tulu and Ibrahim [110] discussed the Cattaneo– Christov heat flux phenomena for a CNT-ethylene glycol nanofluid flow over a stretchable rotating disk. Entropy generation is a reversible process which measure of degenerate useful energy and deprivation of the performance of engineering systems. It is highly significant in industrial sectors where the fluid flow and heat transfer are elaborated. Khan et al. [111] have studied the entropy generation for hybrid nanofluid flow between two parallel plates. Hayat et al. [112] have studied the entropy generation for a MHD radiative fluid flow over a rotating disk in the presence of viscous dissipation and Joule heating. Khan et al. [113] analyzed the entropy generation for a Cu-TiO2/H2O hybrid nanofluid flow between two parallel rotating disks. They have observed that viscous dissipation has very weak influence on the flow fields while a significant impact observed for heat transfer rate. Entropy generation for a Cu–Al2O3/H2O hybrid nanofluid flow over a curved surface has been discussed by Afridi et al. [114]. Entropy generation significantly influenced by the viscous dissipation process. Farooq et al. [115] studied the entropy generation for a hybrid nanofluid flow over a nonlinear radially stretching sheet and shows the impact of viscous dissipation. Further, they observed that the entropy generation inside the boundary layer of a hybrid nanofluid is high compared to a nanofluid. Chamkha et al. [116] have studied a natural convective flow over a semicircular container with solid walls for Al2O3–Cu-water hybrid nanofluid. They have reported that an enhancement of only 5% of Al2O3–Cu nanoparticles shows a rise of average Nusselt number from 4.9 to 5.36 and magneto-hydrodynamic heat transfer and natural convection flow in a square porous enclosure. Gorla et al. [117] have observed that the mean Nusselt number diminishes appreciably for hybrid suspension when the position of the heat source changes. In addition, their results demonstrated that as compared to Cu and Al2O3, the hybrid suspension has a lower magnitude of the average Nusselt number. Tayebi and Chamkha [118] have examined natural convection in an annulus among two confocal elliptic cylinders full of a Cu–Al2O3/water hybrid nanofluid. It was proved that the heat transfer rate is

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more efficient if one employs a Cu–Al2O3/water hybrid as compared to the similar Al2O3/water nanofluid. Natural convection of hybrid nanofluid over an eccentric horizontal cylindrical annulus has been investigated by Tayebi and Chamkha [119]. From the above literature and discussion, it is very clear that the work on hybrid nanofluid is highly significant in the present time due to its huge application in different industrial sectors and medical sciences. But at the same time when two or more particles involve in the base fluid, it is always important to understand the physio-chemical properties and stability of the nanoparticles [120]. In the previous finding, it is observed that most of the works are based on the alumina (Al2O3) nanoparticle due its great deal with stability, chemical motionlessness, and further, it has lower thermal conductivity than other nanoparticles, namely zinc, silver, aluminum, and copper. So, in the mixture of metallic nanoparticles in the base fluid develop nanofluids with anticipated to augment the stability and thermophysical properties. To follow the previous literature, it is observed that the mixture of copper and alumina in the base fluid is more stable and properly fit with the thermophysical properties to develop a hybrid nanofluid with ethylene glycol–water mixtures as base fluid [121]. The aim of the present chapter is to show the impact of the Cattaneo–Christov heat flux on the Cu–Al2O3/water–ethylene glycol (50–50%) hybrid nanofluid flow between two parallel rotational stretching sheets. The magnetic field, thermal radiation, and viscous dissipation are taken into account. Further, imposed stretching slip condition, rotational velocity slip, and convective boundary condition are at the surface of the disks. The governing equations are highly coupled and nonlinear. Hence, simplified the governing equation by using similarity transformation and then solved numerically by using bvp4c MATLAB routine. The outcomes are displayed through graphs and table form. The outcomes are highly significant due to its application in industrial fields.

2 Mathematical Formulation The magneto radiative fluid flow is considered to be flow between two stretchable rotating disks. The fluid nature is considered as a hybrid nanofluid with base fluid as a mixture of ethylene glycol ðC2 H6 O2 Þ and water ðH2 OÞ with a 50–50 ratio. The space between two rotating disks is filled by the hybrid nanofluid which includes mixture of nanoparticles of alumina (Al2O3) and copper (Cu). The magnetic field acts parallel to the axis with magnetic field of strength B0 . The impact of viscous dissipation, thermal radiation, and heat generation on the hybrid nanofluid flow is investigated. The rotating disks are placed at a distance of h, and the lower and upper disks are rotated with rotational velocity X1 and X2 , respectively, (see Fig. 1). The lower and upper disks are stretched with a linear relation of radial direction and in the form of ra1 and ra2 , respectively, where a1 and a2 are the respective stretching rate of the lower and upper disk. Convective condition is applied at the

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337

Fig. 1 Schematic diagram of the problem

surface of the lower rotating disk. Considered the cylindrical coordinate system with ðr; h; zÞ and flow velocity components ðu; v; wÞ. With above consideration, the governing equations of the velocity and temperature field can be written as @u u @w þ þ ¼ 0; ð1Þ @r r @z
2  @u v2 @u 1 @p @ u 1 @u u @2u K u  þ ¼ mhnf  2 þ þw þ u  2 2 @r @z qhnf @r @r r @r r @z qhnf r rhnf B20 u;  qhnf ð2Þ
2  @v uv @v @ v 1 @v v @2v K rhnf B20  þw ¼ mhnf  þ þ v  v; u  @r r @z @r 2 r @r r2 @z2 qhnf qhnf ð3Þ

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S. Shaw



  @T @T @2T @2T @2T @u @w @T @w @u @T þv þ b u2 2 þ w2 2 þ 2uw þ u þw þ u þw @r @z @r @z @r@z @r @z @z @r @z @r !
  khnf 16r @2T 1 @T @2T QT rhnf B20  2 ¼ þ þ þ  þ ðT  T1 Þ þ u þ v2 @r2 r @r @z2 ðqcp Þhnf 3k ðqcp Þhnf ðqcp Þhnf ðqcp Þhnf "

2
2


 # 2lhnf @u 2 u2 @w @v @w @u 2 @ v 2 þ þ 2 þ þ þ þ r þ ; @r @z @z @r @z @r r ðqcp Þf r

u

ð4Þ with the corresponding boundary conditions   @T ¼ hf Tf  T ; @r u ¼ a2 r; v ¼ X2 r; w ¼ 0; T ¼ T2 ; at z ¼ h:

u ¼ a1 r; v ¼ X1 r; w ¼ W0 ; khnf

at z ¼ 0;

ð5Þ

The third term of the left side of the temperature equation (Eq. 14) represents the Cattaneo–Christov diffusion with the constant b, the relaxation time of heat flux. The following similarity transformation is using to transform the coupled nonlinear partial differential equations into coupled nonlinear ordinary differential equations. z ; u ¼ X1 rF 0 ðfÞ; v ¼ X1 rGðfÞ; w ¼ 2hX1 F ðfÞ; h

 T  T2 1 r2 ; p ¼ X1 qf mf PðfÞ þ # : hðfÞ ¼ 2 h2 T f  T2 f¼

ð6Þ

Equations (2–4) are written by using the similarity transformation (Eq. 6) as      0 e1 F 0000 þ 2Re GG0  F F 00  4Rea1 FF 00 þ F 02  Re e2 Kp þ Me3 F002 ¼ 0; ð7Þ

  e1 G00  Re e2 Kp þ e3 M G þ 2ReFG0 ¼ 0;

ð8Þ

e2 P0 þ 4ReFF 0 þ 2e1 F 00 ¼ 0;

ð9Þ


   1 4 e4 þ Rde5 h00  P F 2 h00 þ FF 0 h0 þ 2Fh0 Re Pr 3    2 þ e5 EcReMa2 F 02 þ G2 þ Qh þ e6 Ec 12F 02 þ 2a2 ðF 002 þ G0 Þ ¼ 0;

ð10Þ

and in the similar fashion, the boundary conditions are written as F 0 ¼ C1 ; G ¼ 1; F ¼ fw ; P ¼ 0; h0 ¼ Bi ð1  hð0ÞÞ; 0

F ¼ C2 ; G ¼ X; F ¼ 0; h ¼ 0;

at f ¼ 1:

at f ¼ 0;

ð11Þ

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339

The nanoparticle volume fraction-dependent constants are defined as qf mhnf e1 ¼ ; e2 ¼ ; e3 ¼ mf qhnf e5 ¼

rhnf rf qhnf qf

; e4 ¼

khnf kf ðqcp Þhnf ðqcp Þf

;

lhnf lf

1 ðqcp Þhnf ðqcp Þf

ð12Þ

; e6 ¼ ðqc Þ ; p hnf

ðqcp Þf

The non-dimensional parameters in Eqs.( 8–12)   are Reynolds number ðReÞ, radial parameter ðaÞ, permeability parameter Kp , magnetic parameter ðM Þ, Prandtl number ðPr Þ, radiation parameter ðRd Þ, thermal relaxation parameter ðPÞ, heat generation/absorption parameter ðQÞ, Eckert number ðEcÞ, stretching parameter at lower disk ðC1 Þ, stretching parameter at upper disk ðC2 Þ, suction/injection parameter ðfw Þ, rotational ratio parameter ðXÞ, and Biot number ðBi Þ at the lower disk and upper disk written as ðqcp Þf mf X1 h 2 r Kh rf B20 h ; a ¼ ; Kp ¼ ; M ¼ ; Pr ¼ ; h q f mf q f mf mf kf QT P ¼ 4b X1 ; Q ¼ ; ðqcp Þf X1

Re ¼

Ec ¼

lf X1 a a W0 X2 hhf   ; C1 ¼ 1 ; C2 ¼ 2 ; fw ¼ ; X ¼ ; Bi ¼ : X1 X1 2hX1 X1 kf ðqcp Þf Tf  T2

ð13Þ To find the pressure distribution, we integrating Eq. (9) with respect to f, we get  

e2 P ¼ 2 Re F 2  fw2 þ e1 ðF 0  C1 Þ ;

2.1

ð14Þ

Skin Friction, Nusselt Number

The shear stress at the surface of the lower rotating disk in the respective radial and tangential directions is szr1

 e1 lf rX1 00 @u F ð0Þ; ¼ lhnf  ¼ @z z¼0 e2 h

ð15Þ

szh1

 e1 lf rX1 0 @u G ð0Þ; ¼ lhnf  ¼ @z z¼0 e2 h

ð16Þ

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S. Shaw

So the total shear stress at the surface of the lower rotating disk is qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi s2zr1 þ s2zh1 ;

sw1 ¼

ð17Þ

By similar way, the shear stress of the upper rotating disk in the radial and tangential direction, and total shear stress are written as szr2

 e1 lf rX1 00 @u F ð1Þ; ¼ lhnf  ¼ @z z¼h e2 h

ð18Þ

szh2

 e1 lf rX1 0 @u G ð1Þ; ¼ lhnf  ¼ @z z¼h e2 h

ð19Þ

s w2 ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi s2zr2 þ s2zh2 :

ð20Þ

The skin friction coefficient at the respective lower and upper disk is written as Cf ð0Þ ¼ Cf ð1Þ ¼

sw1 qf ðrX1 Þ2 sw2 qf ðrX1 Þ2

¼

i e1 h 002 2 F ð0Þ þ G0 ð0Þ ; e2 Rer

ð21Þ

¼

i e1 h 002 2 F ð1Þ þ G0 ð1Þ ; e2 Rer

ð22Þ

where Rer ¼ rX1 h=mf is the local Reynolds number. The Nusselt number at the lower and upper rotating disks is written as Nuz ð0Þ ¼

    hqw hqw  ; Nuz ð1Þ ¼  ;  kf ðTf  T2 Þ z¼0 kf ðTf  T2 Þz¼h

ð23Þ

where wall heat flux qw at the lower rotating disk is qw jz¼0 ¼ khnf

@T Tf  T2 þ qr jz¼0 ¼  @z h


 16r T23 0 khnf þ h ð0Þ; 3k 

ð24Þ

and wall heat flux qw at the upper rotating disk is qw jz¼h ¼ khnf

@T Tf  T2 þ qr jz¼h ¼  @z h


 16r T23 0 khnf þ h ð1Þ: 3k 

ð25Þ

With the help of Eqs. (23), (24), and (25), the Nusselt number at the lower rotating disk surface and upper rotating disk surface is written as

Impact of Cattaneo–Christov Heat Flux on …



 khnf 4 khnf 4 0 Nuz ð0Þ ¼  þ Rd h ð0Þ; Nuz ð1Þ ¼  þ Rd h0 ð1Þ: 3 3 kf kf

2.2

341

ð26Þ

Entropy Generation

In thermodynamics, heat transfer in a system leads to thermodynamic irreversibilities due to entropy generation. The process of optimization of thermodynamic imperfections and fluid flow irreversibilities is known as the minimization of entropy. The entropy generation is written as SG

khnf ¼ 2 Tf

"

 #  lhnf @T 2 16r T23 @T 2 rhnf 2  2 þ Uþ B0 u þ v2 ; þ  @z @z 3k kf Tf Tf

ð27Þ

where the viscous dissipation ðUÞ is "

2 #
2
   @u 2 1 2 @w @v @w @u 2 @ v 2 þ U ¼ 2 þ 2u þ þ þ r : þ @r r @z @z @r @z @r r ð28Þ The entropy generation is combined of three terms, namely thermal irreversibility, fluid friction irreversibility and Joule dissipation and written from Eq. (27) with the help of Eq. (28) as 
#
 lhnf @v 2 @T 2 16r T23 @T 2 SG þ þ @z @z 3k  kf Tf @z "
 #
 lhnf @u 2 1 @w 2 þ2 þ 2 u2 þ @r r @z Tf
2    lhnf @w lhnf @u @ v 2 rhnf 2  2 þ þ þ r þ B0 u þ v2 : @r @z @r r Tf Tf Tf khnf ¼ 2 Tf

"


ð29Þ

Using the similarity transformation (Eq. 6), the entropy generation can be written in the non-dimensional form as NG ¼


  2 o  02 lhnf Br n 2 khnf 4 2 2 002 12F 0 þ 2a0 G0 þ F Re 1 þ Rd a1 h0 þ þ MBra2 F þ G2 ; 3 kf lf Re

ð30Þ

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S. Shaw

with the non-dimensional temperature difference a1 ¼ lf X21 h2 kf ðTf T2 Þ,

Tf T2 Tf ,

Brinkman number

Tf S G m f kf ðTf T2 ÞX1 ,

and entropy generation rate NG ¼ and mean temperature Br ¼ Tf . The Bejan number is a fraction of the heat transfer irreversibility and the total irreversibility. When heat transfer irreversibility dominates, the Bejan number is in the range Be  1/2. However, when Be  1/2, this implies that total irreversibility dominates. In the case where Be = 1, this means all irreversibility is due to heat transfer only. By using similarity transformation, the Bejan number is written as Be ¼

khnf kf

 Re 1 þ

4 3 Rd



khnf kf

a1 h0 þ 2

 Re 1 þ

lhnf Br 02 lf Re f12F

4 3 Rd



a1 h0

2

þ 2a2 ðG02 þ F 002 Þg þ MBra2 ðF 02 þ G2 Þ

:

ð31Þ

3 Numerical Scheme The system of governing Eqs. (7–10) is highly coupled and nonlinear. The analytical solution is not possible, and hence, the numerical simulations are required to solve the governing equations with the help of the given boundary condition (Eq. 11). The coupled and nonlinear governing equations are solved using shooting method of the symbolic computer algebraic software MATLAB by converting the boundary value problem into an initial value problem (IVP). At the initial stage, the higher-order term of the differential equation is written in the lower-order form as: F 0000 ¼ 

    1 2ReðGG0  F 0 F 00 Þ  4Rea1 FF 00 þ F 02  Re e2 Kp þ Me3 F 002 ; e1 ð32Þ P0 ¼  G00 ¼

4Re e1 y1 y2  2 y3 ; e2 e2

 1  Re e2 Kp þ e3 M G  2ReFG0 ; e1

ð33Þ ð34Þ

 2  Q 2 2 2Fh0 þ Qh þ e5 EcReMa2 F 0 þ G2 þ e6 Ec 12F 0 þ 2a2 ðF 002 þ G0 Þ þ FF 0 h0   Q 2 h00 ¼  ; 1 4 F Re Pr e4 þ 3 Rde5 þ

ð35Þ At the first, reduce the governing equations into a system of first-order differential equations and for that introducing the new variables as:

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343

y1 ¼ F; y2 ¼ F 0 ; y3 ¼ F 00 ; y4 ¼ F 000 ; y5 ¼ P; y6 ¼ G; y7 ¼ G0 ; y8 ¼ h; y9 ¼ h0 : ð36Þ Further, write the governing equations in a matrix form with y ¼ ½y1 ; y2 ; y3 ; y4 ; y5 ; y6 ; y7 ; y8 ; y9 T as 0 B B B B d B B B df B B B B @

y1 y2 y3 y4 y5 y6 y7 y8 y9

1

0

B B C B C B C B C B C B C C ¼ B B C B C B C B C B A B @

y2 y3 y4     e11 2Reðy6 y7  y2 y3 Þ  4Rea1 y1 y3 þ y22  Re e2 Kp þ Me3 y22  4Re y y  2 e1 y e2

1 2

e2 3

y7

Re e2 Kp þ e3 M y6  2Rey1 y6 y9 2y1 y9 þ Qy8 þ e5 EcReMa2 ðy22 þ y26 Þ þ e6 Ec ð12y22 þ 2a2 ðy23 þ y28 ÞÞ þ 4Py1 y2 y9 1 e þ 4Rde þ 4Py21 Re Prð 4 3 5 Þ



1 C C C C C C C C C C C C C C A

ð37Þ and the corresponding boundary conditions can be written as y1 ð0Þ þ fw ; y2 ð0Þ  C1 ; y1 ð1Þ; y2 ð1Þ  C2 ; y5 ð0Þ y6 ð0Þ  1; y6 ð1Þ  X; y9 ð0Þ þ Bi ð1  y8 ð0ÞÞ; y9 ð1Þ:

ð38Þ

Secondly, we transform the given BVP into an IVP and use an ODE solver in MATLAB to numerically integrate this system, with the initial conditions given by yð0Þ ¼ ½fw ; C1 ; S1 ; S2 ; 0; 1; S3 ; S4 ; Bi ð1  S4 Þ;

ð39Þ

where S1 ; S2 ; S3 and S4 are unknowns. Thirdly, consider a guess value for the unknowns and solve Eq. (37) using the MATLAB’s ODE solver. Shooting method is applied to find the initial guess which is based on the linear interpolation. Continue the process until get a convergence and for that we bound the convergence criteria as error jEi j \ tolerance ¼ 1010 where errors are defined as E1 ¼ y3 ð1; S1 Þ  F 00 ð1Þ; E2 ¼ y4 ð1; S2 Þ  F 000 ð1Þ; E3 ¼ y6 ð1; S3 Þ  G0 ð1Þ; E4 ¼ y7 ð1; S3 Þ  hð1Þ:

ð40Þ

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S. Shaw

After calculating the matrix y, we need to find the non-dimensional entropy generation number (Eq. 30) and Bejan number (Eq. 31) NG ¼ Re


    khnf 4 Br  2 12y2 þ 2a2 ðy26 þ y23 Þ þ MBra2 y22 þ y26 ; þ Rd a1 y29 þ 3 Re kf ð41Þ 



Be ¼ Re

khnf kf

khnf kf

þ

4 3 Rd



Rea1 y29  2   : Br þ 43 Rd a1 y29 þ Re 12y2 þ 2a2 ðy26 þ y23 Þ þ MBra2 y22 þ y26 ð42Þ

4 Validation A comparison made for the Newtonian fluid (in the absence of the hybrid nanoparticles, i.e., /1 ¼ /2 ¼ 0Þ, with the existing literature of Turkyilmazoglu et al. [122] and Hosseinzahed et al. [123] under certain constraints and shown in Tables 1 and 2. The comparison gives a confidence on the applied numerical scheme and further outcomes as a form of graphs and tables of the present work.

Table 1 Comparison table for different value of X with Kp ¼ Rd ¼ C1 ¼ C2 ¼ Q ¼ Ec ¼ 0; Bi ! 1 X

F 00 ð0Þ Turkyilmazoglu [122]

Hosseinzadeh et al. [123]

Present

−1 −0.8 −0.3 0 0.5

0.06666313 0.08394206 0.10395088 0.09997221 0.06663419

0.06666265832 0.08394497836 0.1039497753 0.09996773288 0.06663026596

0.06666265672 0.08394497811 0.10394977482 0.09996773274 0.06663026575

Table 2 Comparison table for different value of X with Kp ¼ Rd ¼ C1 ¼ C2 ¼ Q ¼ Ec ¼ 0; Bi ! 1 X

G0 ð0Þ Turkyilmazoglu [122]

Hosseinzadeh et al. [123]

Present

−1 −0.8 −0.3 0 0.5

2.00095215 1.80258847 1.30442355 1.00427756 0.50261351

2.000952381 1.802594286 1.304432381 1.004285714 0.5026190476

2.000952292 1.802594279 1.304432380 1.004285716 0.5026190474

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5 Results and Discussions The governing Eqs. (7–10) are solved numerically by above-mentioned MATLAB bvp4c routine under the appropriate boundary condition given by Eq. (11). The significant impact of the different parameters such as non-dimensional radial parameter ðaÞ, magnetic parameter ðM Þ, Prandtl number ðPrÞ, radiation parameter ðRd Þ, thermal relaxation parameter ðP), Eckert number ðEcÞ, heat generation parameter ðQÞ, stretching parameter at the lower and upper rotation disk ðC1 ; C2 Þ, suction/injection parameter ðfw Þ, Biot number ðBi Þ, velocity ratio parameter ðXÞ, temperature parameter ða1 Þ and Brinkman number ðBr Þ on the velocity and temperature profile and on the other physical parameters such as skin friction, Nusselt number, entropy generation, and Bejan number are discussed in this section. The final results are displayed though graphs and tabular form. General value of the parameters are taken as Re ¼ 1; a ¼ Kp ¼ 0:1; M ¼ 2; Pr ¼ 7; Rd ¼ Q ¼ P ¼ 0:1; fw ¼ C1 ¼ C2 ¼ Bi ¼ 0:1; X ¼ 0:1; a1 ¼ 0:3; Br ¼ Pr  Ec. In the present problem, we have considered copper (Cu) and alumina (Al2O3) nanoparticles and a mixture of ethylene glycol and water in a ratio of 50–50%. The thermophysical properties of nanoparticle and base fluid are given in Table 3. The thermo-physical properties of hybrid nanofluid and general nanofluid are different. These thermo-physical properties such as viscosity, density, electric conductivity, coefficient of thermal expansion, heat capacity, and thermal conductivity are shown in Table 4. In each graph, a comparison between the nanofluid and hybrid nanofluid has shown by considering the volume fraction of the alumina (Al2O3) which is equal to zero. It only gives the volume fraction of Cu-nanoparticle in the base fluid water. It shows the importance of the hybrid nanofluid.

5.1

Axial Velocity

The significant influences of Re ; C2 ; fw and X on the axial velocity are shown in Figs. 2, 3, 4, and 5. The axial velocity calculated with the suction phenomena and so a back flow observed for the axial velocity. During suction, the fluid comes out from the system which enforces a back flow. Reynolds number is directly Table 3 Thermophysical properties of hybrid base fluid and nanoparticles Physical properties

C2 H6 O2  H2 Oð50  50Þ

Cu

Al2 O3

qðkg : m Þ

1063.8

8933

3970

cp ðJ:ðkg : K Þ1  k W:ðm : k Þ1

3630

385

765

0.387

401

40

3

bðK 1 Þ rðX:mÞ

5:8  104 1

9:75  104

Thermal conductivity

Coefficient of thermal expansion Heat Capacity

Electric conductivity rf

o

ðqc Þ

ðqbÞ / þ / ðqbÞs f

rf

knf kf

¼

ks þ ðm1Þkf ðm1Þ/ðkf ks Þ ks þ ðm1Þkf þ /ðkf ks Þ

f

ðqcp Þnf ¼ ðqcp Þf 1  / þ / ðqcpp Þs

n

ðqbÞnf ¼ ðqbÞf 1 

n o

1

k þ ðm1Þk ðm1Þ/ ðk k Þ

bf s2 2 bf ¼ s2 ks2 þ ðm1Þk bf þ /2 ðkbf ks2 Þ where kbf ks1 þ ðm1Þkf ðm1Þ/1 ðkf ks1 Þ ks1 þ ðm1Þkf þ / ðkf ks1 Þ kf ¼

khnf kbf

ðqcp Þhnf

f

ðqcp Þs1 ¼ ðqcp Þf ð1  /2 Þ 1  /1 þ /1 ðqcp Þf

(

) þ /2 ðqcp Þs2

n o ðqbÞ ðqbÞhnf ¼ ðqbÞf ð1  /2 Þ 1  /1 þ /1 ðqbÞs1 þ /2 ðqbÞs2

/ ¼ /1 þ /2

lnf ¼ lf ð1  /Þ2:5 n  o qnf ¼ qf 1  / þ / qqs f  9 8 r < 3 rs 1 / = f  rnf ¼ rf 1 þ : 2 þ rs  rs 1 /;

Viscosity

Density

Hybrid nanofluid lhnf ¼ lf ð1  /1 Þ2:5 ð1  /2 Þ2:5 n  o qhnf ¼ qf ð1  /2 Þ 1  /1 þ /1 qqs1 þ /2 qs2 f   3/ / r rhnf 1 1 þ /2 r2  rbf ð/1 þ /2 Þ  ; ¼ 1þ rf /1 r1 þ /2 r2 þ 2/rbf  /rbf /1 r1 þ /2 r2  rbf ð/1 þ /2 Þ

Nanofluid

Properties

Table 4 Thermophysical properties of hybrid nanofluid and a comparison with the nanofluid

346 S. Shaw

Impact of Cattaneo–Christov Heat Flux on … Fig. 2 Axial velocity along f axis for different Re

Fig. 3 Axial velocity along f axis for different C2

Fig. 4 Axial velocity along f axis for different fw

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Fig. 5 Axial velocity along f axis for different X

Fig. 6 Radial velocity along f axis for different a

proportional to the velocity of the fluid, and it obvious that with increase of the Reynolds number, the axial velocity of the fluid would be increasing (see Fig. 2). Hence, the momentum boundary layer thickness boosted with increase in the value of Re as mentioned by Hosseinzahed et al. [123]. Further, it observed that the fluid velocity is higher for the nanofluid than the hybrid nanofluid. It may be because of the presence of higher volume fraction of nanoparticles which restricted Brownian motion between two rotating disks which is an opposite phenomena as observed in the boundary layer flow (Sadiq [61]). It further observed that the velocity difference is more significant at f ¼ 0:5, mid-distance from the rotating disks. Comparability of the nanofluid and hybrid nanofluid is more significant for larger value of magnetic parameter. Radial velocity slip at the upper rotating disk plays a significant role in the axial velocity. It observed that with increase in the value of C2 , the axial velocity reduces (see Fig. 3). Impact of the suction/injection parameter is observed in Fig. 4. The suction/injection parameter fw [ 0 implies the suction, when the fluid

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349

Fig. 7 Radial velocity along f axis for different C1

Fig. 8 Radial velocity along f axis for different C2

goes out from the system, and fw \ 0 implies the injection, when the fluid comes into the system. fw ¼ 0 pointed out the neutral condition of the system. Fluid releases the system during suction, and hence, axial velocity is lower during suction. However, with increase in the value of fw , the axial velocity of fluid increases and it is higher during injection (see Fig. 4). Impact of the rotational ratio parameter X plays an important role in axial velocity. The rotational ratio parameter X [ 0 implies that both rotating disks are rotated in the same direction, while parameter X \ 0 implies that both rotating disks are rotated in the opposite direction. The upper disk assumed to be stationary for X ¼ 0. The axial velocity is observed larger when disks are rotating in the same direction and rotating in same direction increase the resultant force act on the fluid which enhanced the fluid velocity. When they rotating in opposite direction, then the resultant force becomes weak which further reduced the axial velocity (see Fig. 5).

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Radial Velocity

The radial velocity of the fluid for different value of a; C1 ; C2 and X is shown in Figs. 6, 7, 8, and 9. Radial velocity decreases with increase in the non-dimensional radial distance for the axis close to the lower rotating disk, while the radial velocity enhanced with the larger value of a when it close to upper rotating disk (see Fig. 6). In the present problem, we have considered the radial velocity at the lower and upper rotating disk as C1 and C2 . The general value of C1 and C2 is considered 0.1. Hence, the radial velocity profile starts with F'ð0Þ ¼ 0:1 and ends with F'ð0Þ ¼ 0:1 to follow the boundary condition. The radial velocity profile is initially decreasing with increase f and appeared a minimum value near f ¼ 0:6. Further, the radial velocity increases and attained the boundary condition. It is interested to note that the nature of the radial velocity near the lower rotating disk shows a completely opposite nature near to the upper rotating disk. With increase in the value of C1 , the radial velocity at the lower rotating disk increases to follow the boundary condition. Further, it attract the intersecting point close to the lower rotating disk. Usually, an opposite phenomena observed close to the upper rotating disk (see Fig. 7). The parameter C2 is related with the upper stretching rotating disk and measure the stretching of the upper disk. Hence, with increase in C2 , the radial velocity at the upper disk will increase to follow the condition at the surface. Though the nature is opposite near to the lower disk as shown in Fig. 8, interesting to note that, the interacting point is now close to the upper disk which is significantly different from C1 (as mentioned in Fig. 7). Rotating ratio ðXÞ represents the rotational motion of the upper disk with respect to the lower disk. With increase in X, the radial velocity of the fluid decreases near to the upper disk (see Fig. 9).

Fig. 9 Radial velocity along f axis for different X

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5.3

351

Tangential Velocity

Dependency of the magnetic parameter and rotational ratio on the tangential velocity is shown in Figs. 10 and 11. Due to the additional resistance force created by the magnetic field, the tangential velocity decreases with increase of magnetic parameter. In the absence of magnetic field, the tangential velocity linearly is related with the axial direction. However, it shows a nonlinear relation for nonzero magnetic parameter (see Fig. 10). Rotational ratio parameter is enhanced the tangential velocity at the surface of the upper disk while the tangential velocity at lower disk keep constant (see Fig. 11).

Fig. 10 Tangential velocity along f axis for different M

Fig. 11 Tangential velocity along f axis for different X

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Pressure Distribution

Pressure distribution in the system for different values of C1 ; C2 ; fw and X is shown in Figs. 12, 13, 14, and 15. Due to the stretching at the lower disk, the pressure increases in the system. Pressure distribution is more significant for the larger value of stretching parameter for lower disk (see Fig. 12). The pressure distribution is more interesting and significant due to the stretching of upper disk. The pressure graph slowly increases with f, and then there is a sharp fall near to upper disk surface. Larger value of C2 shows a sudden fall of pressure (see Fig. 13). Pressure distribution is larger for the injection when the fluid enters into the system and influences the fluid to go away from the surface, while it is decreasing for the suction phenomena (see Fig. 14). With increase in the rotational velocity ratio, it enhances the pressure distribution. However, the impact is not significant (see Fig. 15). Interested to that the pressure distribution is higher for the hybrid nanofluid than general nanofluid.

5.5

Temperature Distribution

Q Temperature profile for the different value of a; Rd; ; Ec; C1 ; C2 and Bi is displayed and discussed in Figs. 16, 17, 18, 19, 20, and 21. In general, the temperature profile starts with a higher value at lower rotating disk and ends at the upper rotating disk with a value 0 to follow the boundary condition. Figure 16 displays that the temperature at the lower disk increases with increase value of a. It enhanced the thermal boundary layer thickness. A similar phenomenon is observed by Dessie and Kishan [124] for the stretching surface. Radiation produces an external heat source which involves in the system through energy equation. Due to the additional heat Fig. 12 Pressure distribution along f axis for different C1

Impact of Cattaneo–Christov Heat Flux on … Fig. 13 Pressure distribution along f axis for different C2

Fig. 14 Pressure distribution along f axis for different fw

Fig. 15 Pressure distribution along f axis for different X

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Fig. 16 Temperature distribution along f axis for different a

Fig. 17 Temperature distribution along f axis for different Rd

source, the temperature of the fluid increases with increase of radiation parameter (see Fig. 17). In general, it is observed that the impact of the hybrid nanofluid is highly significant for the temperature profile. The thermal relaxation parameter ðPÞ represents the relaxation time taken by the fluid particle to transfer the heat energy to its adjacent particles. With increase in the value of P, it implies that the particle supposed to take more time to transfer the heat energy to his neighbor particle. The thermal boundary layer thickness observed decreases with increase in the value of P as shown in Fig. 18. This may be due to the closed boundaries. Eckert number is defined the ratio of the advective transport with respect to the heat dissipation. The parameter is attached with the viscous dissipation. With increase in the Eckert number, the temperature of the system increases as shown in Fig. 19. Due to stretching at the upper rotating disk, the nanoparticles are spread out from the

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355

Fig. 18 Temperature distribution along f axis for different P

Fig. 19 Temperature distribution along f axis for different Ec

surface with reduce the temperature at the surface as observed by Fig. 20. A sink temperature (negative) is observed for higher value of C2 . Biot number enhanced the convective heat transfer in the system which in general supports to increase the temperature at the system. However, in the present system the temperature at the lower rotating disk decreases with increase in Bi (see Fig. 21).

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Fig. 20 Temperature distribution along f axis for different Ec

Fig. 21 Temperature distribution along f axis for different Bi

5.6

Skin Friction and Nusselt Number

Impact of different governing parameters on the skin friction and the Nusselt number at lower and upper rotating disks are displayed in Figs. 22, 23, 24, and 25. Impact of the suction/injection parameter and rotational parameter ratio on skin friction shown in Figs. 22 and 23. The skin friction observed larger during injection ðfw ¼ 0:1Þ than the suction ðfw ¼ 0:1Þ phenomena for both the lower and upper rotating disks. It also observed that the skin friction decreases with increase of the rotational parameter. Skin friction is larger when the rotation of disks is opposite in direction. The Nusselt number at the lower and upper disks for different value of the Rd and Br is displayed in Figs. 24 and 25. It is evident that the radiation parameter

Impact of Cattaneo–Christov Heat Flux on …

357

enhanced the Nusselt number both at the lower and upper rotating disks. Heat transfer rate observed to be negative for lower value of Rd. Brinkman number which is a product of Prandtl number and Eckert number decreases the Nusselt number at both the rotating disks with increments in its values. Further, the impact of Re; a; Kp ; M; C1 ; C2 and fw on the skin friction at the lower and upper rotating disks is displayed in Table 5. Increase in Kp restricted the fluid flow and introduced an additional viscous force. As a result, the skin friction at both rotating disk increases with the increase in the value of Kp . Influence of Re; a; Pr; M; Ec; Bi and Rd on Nusselt number at both lower and upper rotating disks is displayed in Table 6.

5.7

Entropy Generation and Bejan Number

Entropy generation for different values of Rd; Br; M and Re are shown in Figs. 26 and 27. With increase in the value of Reynolds number, the entropy generation decreases which is obvious as shown in Eqs. (1 and 29) where non-dimensional entropy generation is inversely proportional to the Reynolds number (see Fig. 26). Magnetic parameter shows a similar phenomena as Re. Brinkman number enhanced the entropy. It shows an equal impact on nanofluid and hybrid nanofluid (see Fig. 27). The radiation parameter not significantly influences the entropy generation. Bejan number observed to be increased with increase of the radiation parameter as shown in Fig. 28. With increase of Br, the Bejan number decreases

Table 5 Skin friction at the lower parameters



Cf ð0Þ



and upper

Re

a

Kp

M

C1

C2

0.5 0.8 1

0.3

0.3

2

0.1

0.1



fw 0.1

0.1 0.5 0 0.5 0 5 0 0.5 0 0.5 -0.1 0

Cf ð1Þ



rotating disk for different

Cf ð0Þ

C f ð 1Þ

1.030514 1.538829 1.885829 1.028026 1.031098 0.924912 1.101999 0.321567 0.479095 1.027656 2.102256 1.032230 1.294342 1.363605 1.162367

0.973379 1.428920 1.734972 0.971036 0.973902 0.877657 1.037921 0.319010 0.467726 0.966775 2.057653 0.972992 1.237283 1.301111 1.088013

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Table 6 Nusselt number at the lower ðNux ð0ÞÞ and upper ðNux ð1ÞÞ rotating disk for different parameters Re

a

Pr

M

Ec

Q

Bi

Rd

Nuz ð0Þ

Nuz ð1Þ

0.5 0.8 1

0.3

7

2

0.1

0.1

0.1

0.5

0.068318 0.006854 -0.154546 0.077269 0.037991 0.074579 0.060505 0.074059 0.061454 0.082419 0.011916 0.068318 0.068318 0.214348 0.281112 0.057368 0.153344

0.079445 0.036797 -0.084609 0.084434 0.062544 0.083613 0.074056 0.085791 0.077707 0.086966 0.049358 0.079445 0.079445 0.232792 0.302901 0.068985 0.162948

0.1 0.5 6 8 0 5 0 0.5 0 0.5 1 1 0 1

Fig. 22 Skin friction at the lower disk vs. X for different fw

sharply and then converges to a finite value. Bejan number observed higher for the nanofluid than hybrid nanofluid. Impact of the entropy generation and Bejan numbers is tabulated for different values of Rd; Br; Re; M and a at Table 7.

Impact of Cattaneo–Christov Heat Flux on … Fig. 23 Skin friction at the upper disk vs. X for different fw

Fig. 24 Nusselt number at the lower disk vs. Br for different Rd

Fig. 25 Nusselt number at the upper disk vs. Br for different Rd

359

360 Fig. 26 Entropy generation at the lower disk vs. M for different Re

Fig. 27 Entropy generation at the lower disk vs. Br for different Rd

Fig. 28 Bejan number at the lower disk vs. Br for different Rd

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Table 7 Entropy generation ðNG ð0ÞÞ and Bejan number ðBeð0ÞÞ at the lower rotating disk Rd

Br

Re

M

a

NG ð0Þ

Beð0Þ

0.5 0 1

0.1

0.5

2

0.3

1.047467 1.046275 1.048625 0.450016 0.748741 0.947717 0.915069 0.300251 2.217303 0.437680 1.888206

0.001841 0.000704 0.002943 0.004284 0.002575 0.000971 0.000179 0.006994 0.000781 0.005030 0.000759

0.3 0.5 0.8 1 0 5 0.1 0.5

6 Conclusion The present problem is based on a three-dimensional MHD on Al2O3–Cu/H2O– (CH2OH)2 hybrid nanofluid flow between two stretching rotating disks. Cattaneo– Christov heat flux model is taken into the account. Further, thermal radiation, viscous dissipation, velocity slip condition, and convective condition imposed at the surface of the disks. The governing equations are solved numerically using bvp4c MATLAB routine. A comparison made with the existing literature under certain constraints. From this chapter, we can conclude that • rotational ratio significantly improved the tangential velocity and pressure distribution, while an opposite phenomena observed for radial velocity and temperature distribution. • suction/injection parameter reduces the axial velocity and pressure distribution, while it improve the radial velocity. • stretching parameter at lower and upper disk boost up the pressure distribution closure to the lower disk. • Cattaneo–Christov diffusion significantly reduced the temperature, and it is more significant for the hybrid nanofluid than the general nanofluid. • Hybrid nanofluid has a higher influence on augmenting Nusselt number and temperature profile compared to the general nanofluid. • Brinkman number decreases the Nusselt number at surface of the lower disk, while an opposite phenomena observed at the surface of the upper disk. • Entropy generation significantly improved by Reynolds number and magnetic parameter, while both suction/injection parameter and rotational ratio lead to an opposite phenomena.

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MHD Flow in a Rotating Channel Surrounded in a Porous Medium with an Inclined Magnetic Field Ram Prakash Sharma, S. K. Ghosh, and S. Das

Abstract MHD motion of a viscous incompressible electrically conducting liquid in a permeable media through a revolving channel with an inclined magnetic field is analyzed. The sheets of the channel are assumed perfectly conducting. The impact of the induced magnetic description on magnetohydrodynamic porous medium flow becomes significant by decisive importance to an inclined magnetic field. The explanation for the momentum and induced magnetic field distributions is attained in closed form. The frictional shearing stress and the rate of concentration of motion are obtained. An analysis has been made concerning a gradually revolving system once the conductivity of the liquid is small and the applied magnetic description is weak. Indeed, in a permeable medium flow, the MHD motion is generated by a Darcy number saturated by an inclined magnetic field. A literature survey reveals that none of the authors has studied such a fluid flow problem in the literature.







Keywords MHD porous medium flow Inclined magnetic field Darcy number Perfectly conducting plate




R. P. Sharma (&) Department of Mechanical Engineering, National Institute of Technology Arunachal Pradesh, Papum Pare District, Yupia 791112, Arunachal Pradesh, India e-mail: [email protected] S. K. Ghosh Department of Mathematics, Narajole Raj College, Narajole 721211, West Bengal, India S. Das Department of Mathematics, University of Gour Banga, Malda 732 103, West Bengal, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 D. Tripathi and R. K. Sharma (eds.), Energy Systems and Nanotechnology, Advances in Sustainability Science and Technology, https://doi.org/10.1007/978-981-16-1256-5_18

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1 Introduction The theory of a magnetohydrodynamic (MHD) revolving liquid is the theme stimulated by introducing numerous significant relevance of geophysics, astrophysics, and motion engineering. It finds wide applications in designing of the MHD power generator, turbine, centrifugal machine, and solar dynamo mechanism. MHD rotating flow takes place in different ordinary phenomena and for its existence of diverse technical conditions are required that are straight administrated by the exploit of Coriolis energy. Rotation of a fluid system produces two impacts, viz., Coriolis force and centrifugal force. A rigid body rotation of a fluid system (rotating as a whole) is close to which the returning outcome of Coriolis force controls the movement of liquid rudiments and depends on the virtual size of Coriolis force and other forces acting on the fluid. Rotating fluid has an essential constancy in the logic that if a liquid atom is evacuated from its steadiness position of an inflexible form revolution, the Coriolis force performances as a restoring force. The interplay of hydromagnetic energy to Coriolis energy is exposed to act arrives into this system to alter the mechanical behavior of the structure because of the occurrence of Lorentz force. Hydromagnetic motion in a revolving system was reported by many investigators. Mention can be much of the efforts of Cramer and Pai [1], Mazumder [2], Datta and Jana [3], Takenouchi [4], Linga Raju and Ramana Rao [5], Helmy [6], Naroua [7], Naroua et al. [8] and Helmy [9]. The exact solution for the hydromagnetic convective motion and energy transport over a continuous moving perpendicular sheet with a magnetic field and uniform suction was reported by Kumar et al. [10]. An extension of literature exerted by an inclined magnetic description in a revolving environment is to execute plasma fusion in a controllable tentative forced oscillation. This was examined by Ghosh [11, 12], Jaiswal and Soundalgekar [13], Chandran et al. [14]. Mishra and Sharma [15] have stated the temperature and concentration transport motion of magnetohydrodynamic in a revolving medium under the impact of hall current and an inclined magnetic field. The purpose of current investigation is to deal with the porous medium motion in a revolving system saturated over an inclined magnetic field. A literature survey reveals that none of the authors explored the impact of the induced magnetic field on hydromagnetic motion in a porous medium through the revolving situation under the influence of an inclined magnetic description. The simultaneous action of hydromagnetic force and Coriolis force play a significant part in describing the MHD motion behavior with a pivotal position to a Darcy number. MHD motion determines the trend of captivating positions of force in an MHD flow region as a result of the occurrence of Lorentz force by reference to the behavior of induced magnetic field saturated by an inclined magnetic field. The importance of a study of such behavior is an essential feature of magnetohydrodynamics. In relation to the permeable medium flow, the impact of the magnetic field exerted by the Darcy number to exhibit the behavior of magnetic lines of force concerning Lorentz force perturbing the original fluid motion.

MHD Flow in a Rotating Channel …

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The main goal of the current examination is to study MHD motion of a viscous incompressible electrically conducting liquid in a permeable media through a revolving channel saturated due to an inclined magnetic field. The surface of the medium is considered seamlessly conducting so that the magnetic field does not penetrate outside the sheet. In a permeable media flow, Darcy number acts a vital part in determining the MHD motion efforts with the influence of an inclined magnetic field. The impression of the induced magnetic field on the magnetohydrodynamic porous medium motion has an accurate feature of an MHD flow pattern with an inclined magnetic field. Exact solutions of momentum and induced magnetic field disseminations are obtained in a closed procedure. The frictional shearing stress and the rate of mass motion are obtained. It is important to note that in a perfectly conducting plate, and the rate of total magnetic flux inside the liquid region is zero. This situation reveals that the magnetic field does not penetrate outside the surface. It is noticed that in a gradually revolving structure once the conductivity of the liquid is small and the applied magnetics description is weedy, the main motion along with main induced magnetic description requires on magnetic field for h ¼ np wherever n is an even integer while the primary flow, as well as the primary induced magnetic description, are also in need of permeability of the medium while the secondary flow along with secondary induced magnetic description is independent of the magnetic field but depends on rotation. In relation to the physical condition of curiosity, the angle of inclination of a magnetic field h ¼ np maintains an even parity to restore the medium when n is an even integer.

2 Problem Formulation and Solution We study a horizontal layer of a soaked permeable medium followed by steady MHD motion of a viscous incompressible electrically conducting liquid limited between 2-infinite parallel sheets at a distance d separately, switch in agreement with a uniform angular velocity X about an axis perpendicular to the sheets with an oblique magnetic field by the optimistic direction of the axis of revolution. We take a Cartesian coordinate to z-axis is perpendicular to the channel sheets (z ¼ d). The x-axis is taken in the direction of the pressure gradient (Fig. 1). For effortlessness, the angular velocity is considered to be parallel to z-axis and the applied magnetic field B0 is inclined with the positive direction of the axis of revolution. The sheets are infinite along x and y-directions, the fields, set up for the steady state, will depend on z only. The hydromagnetic equation of flow and continuity in a revolving frame of reference for an incompressible viscous liquid are: @~ q 1 1 þ ð~ q
rÞ~ q þ 2X ^k  ~ q ¼  rp þ mr2~ ðr  ~ BÞ  ~ B qþ @t q le q

ð1Þ

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Fig. 1 Schematic diagram of the physical system

r
~ q ¼ 0;

ð2Þ

J ¼ r~ B; le~

ð3Þ

Maxwell equations are



!

@~ B ¼ r~ E @t

ð4Þ

r
~ B ¼ 0;

ð5Þ

r
~ J ¼ 0;

ð6Þ

! ! !

where p; le ; m; q; J ; E; B ; q are the liquid pressure, magnetic porosity, kinematic co-efficient of viscosity, the liquid density, the current density vector, the electric field vector, the magnetic field vector, velocity field vector, respectively. The Ohm’s law for a moving conductor is rð~ E þ~ q~ BÞ ¼ ~ J;

ð7Þ

where r is electrical conductivity of fluid. Equation (7) is equivalent to the magnetic induction equation @~ B 1 ¼ curlð~ q~ BÞ þ B r2~ @t r le

ð8Þ

Hence, Eqs. (7 and 8) are identical. The subsequent assumptions are in arrangement with the important equations of magnetohydrodynamics

MHD Flow in a Rotating Channel …

373

~ B ¼ ðBx þ B0 sin h; By ; B0 cos hÞ; ~ E ¼ ðEx ; Ey ; Ez Þ; ~ J q ¼ ðu0 ; v0 ; 0Þ; ~ ¼ ðJx ; Jy ; 0Þ 0

0

ð9Þ

The MHD equations of motion take the following form 2Xv0 ¼ 

1 @p @ 2 u0 1 @B0x m 0 þm 2 þ B0 cos h  u; q @x le q Kp1 @z @z

2Xu0 ¼ m

@B0y @ 2 v0 1 m 0 B0 cos h  þ v; 2 le q Kp1 @z @z

0 ¼ 

 1 @p 1 @
02 0  Bx þ By2 : q @z 2le q @z

ð10Þ ð11Þ ð12Þ

Equations (2 and 5) are identically satisfied. Combining Eqs. (3, 4, and 7), equations for magnetic flux density turn into @ 2 B0x @u0 ¼ 0; þ le rB0 cos h 2 @z @z

ð13Þ

@ 2 B0y @v0 ¼ 0: þ l rB cos h 0 e @z2 @z

ð14Þ

Equation (12) shows the reliability of magneto-liquid-dynamic compression along the axis of revolution. It is assumed that the liquid flows in the influence of a continuous pressure gradient ð q1 @p @x Þ in the direction of x-axis between 2-smoothly leading parallel sheets (z ¼  d). The velocity boundary conditions (no-slip) are given by u0 ¼ 0; v0 ¼ 0

at z ¼ d

ð15Þ

The magnetic boundary conditions for perfectly conducting plates become dB0y dB0x ¼ ¼ 0 at z ¼ d dz dz B0x ¼ B0y ¼ 0 at z ¼ 0

ð16Þ

We introduce dimensionless quantities as follows: g ¼

B0y z u0 d v0 d B0x ;u¼ ;v ¼ ; Bx ¼ ; By ¼ ; d m m r le mB0 r le mB0

Then, Eqs. (10), (11), (13) and (14) become

ð17Þ

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2K 2 v ¼ R þ 2K 2 u ¼

where M 2 ¼

rB20 d 2 qm

d2 u dBx  Kpu; þ M 2 cos h 2 dg dg

ð18Þ

d2 v dBy  Kpv; þ M 2 cos h 2 dg dg

ð19Þ

d 2 Bx du ¼ 0; þ 2 dg dg

ð20Þ

d 2 By dv ¼ 0; þ dg dg2

ð21Þ

is the square of Hartmann number, Kp ¼

d2 Kp1

¼

1 Da

the inverse

the Darcy number, K 2 ¼  dp Xd d3 m the revolution variable which is equal to Ekman number, and R ¼ q m2  dx the constant pressure gradient. The momentum and magnetic boundary conditions are: permeability parameter of the porous medium, Da ¼

Kp1 d2

2

at g ¼ 1;

u ¼ 0; v ¼ 0 dBy dBx ¼ ¼ 0; at g ¼ 1; dn dn at g ¼ 0; By ¼ Bx ¼ 0:

ð22Þ

pffiffiffiffiffiffiffi Introducing complex variables u þ iv ¼ F and Bx þ iBy ¼ h where i ¼ 1 the conditions (22) can be represented in the subsequent procedure as follows: F ¼ 0 dh ¼ 0 dg h ¼ 0

at g ¼ 1; at g ¼ 1;

ð23Þ

at g ¼ 0:

Equations (18) to (21) with the boundary conditions (23) can be explained simply and the explanation of momentum and induced magnetic fields can be stated as F ¼ u þ iv ¼ R

h ¼ Bx þ iBy ¼ R

ða  ibÞ2 ða2 þ b2 Þ2

ða  ibÞ2 ða2 þ b2 Þ2





 coshða þ ibÞg 1 ; coshða þ ibÞ

 sinhða þ ibÞg g ; ða þ ibÞ coshða þ ibÞ

ð24Þ

ð25Þ

MHD Flow in a Rotating Channel …

375

where i1=2 1 h a; b ¼ pffiffiffi fðM 2 cos h þ KpÞ2 þ 4K 4 g1=2  ðM 2 cos h þ KpÞ 2

ð26Þ

We shall now discuss a specific case of interest M 2 \\ 1; K 2 \\ 1 and Kp  Oð1Þ. When both M 2 and K 2 are small, we disregard square and complex powers of 2 M and K 2 to obtain u=R ¼

1 5 g2 g4 ð1  g2 Þ þ ðM 2 cos h þ KpÞ ð þ  Þ þ


; 2 24 4 24

5 g2 g4 þ  v=R ¼ K 2 þ


; 24 2 12

ð27Þ ð28Þ





  5 1 1 g3 g5 g Bx =R ¼  g 1  g2 þ M 2 cos h þ Kp þ þ


; 2 3 24 12 120 ð29Þ By =R ¼ K 2

5 g3 g5 g þ 12 6 60

þ




ð30Þ

Expressions (27–30) reveal that in a gradually revolving structure once the fluid conductivity is small and the applied magnetic field is weedy, and the magnetic field has no considerable effect on the secondary flow (28) as well as the secondary induced magnetic field given by (30), while the prime motion (27) and the prime-induced magnetic field become unaffected by rotation. It is manifested from (27) to (29) that the primary flow, as well as the primary induced magnetic description, is dependent on the magnetic field and permeability of the porous medium for h ¼ np where n is an even integer. In this state, h ¼ np sustains an even parity to restore the medium when n is an even integer.

3 Results and Discussion The closed-form systematic solution for the momentum, induced magnetic fields, frictional shearing stress, and mass motion is obtained in Sect. 2. To search out the astronomy of the work, the impact of the emerging flow constraints on the pertinent motion features is envisioned in Figs. 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15. Graphical study of the mathematical facts is obtainable by the support of Mathematica-7. To perform the mathematical recreations, the non-dimensional relevant variables are chosen as M 2 ¼ 5, K 2 ¼ 4, Kp ¼ 10 and h ¼ p=4. These

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(a) Primary velocity profiles

(b) Secondary velocity profiles

Fig. 2 Velocity profiles varying M 2

(a) Primary velocity profiles

(b) Secondary velocity profiles

Fig. 3 Velocity profiles varying K 2

(a) Primary velocity profiles

(b) Secondary velocity profiles

Fig. 4 Velocity profiles varying Kp

values are reserved as common for graphical exhibitions excluding for the diverse values as revealed in the individual graphs. Figure 2a, b is drawn to expose the impact of the M 2 on dimensionless momentum component descriptions. The primary momentum and the magnitude of

MHD Flow in a Rotating Channel …

(a) Primary velocity descriptions

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(b) Secondary velocity profiles

Fig. 5 Velocity descriptions varying h

(a) Primary induced magnetic field

(b) Secondary induced magnetic field

Fig. 6 Induced magnetic field component profiles varying M 2

(a) Primary induced magnetic field

(b) Secondary induced magnetic field

Fig. 7 Induced magnetic field component profiles varying K 2

the secondary momentum are both found to overcome because of augmentation in the M 2 across the channel. The primary momentum description is symmetric and upland across the vital region of the channel. Substantially, the enhancing values of the magnetic variable yield Lorentz energy which exploit the resisting energy on the flow motion, due to which the velocity components are diminished. The

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(a) Primary induced magnetic field

(b) Secondary induced magnetic field

Fig. 8 Induced magnetic field component profiles varying Kp

(a) Primary induced magnetic field

(b) Secondary induced magnetic field

Fig. 9 Induced magnetic field component profiles varying h

(a) Primary shear stress

(b) Secondary shear stress

Fig. 10 Shear stress components at the lower plate on varying K 2

submissions of this singularity can transfer electrically conducting fluid in the partying progressions as a dynamic micro-partying expertise technique. This is of excessive advantage in magnetic substantial dispensation structures. Figure 3a, b demonstrates the influence of revolution variable K 2 on momentum components.

MHD Flow in a Rotating Channel …

(a) Primary shear stress

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(b) Secondary shear stress

Fig. 11 Shear stress components at the lower plate on varying Kp

(a) Primary shear stress

(b) Secondary shear stress

Fig. 12 Shear stress components at the lower plate on varying h

(a) Primary shear stress

(b) Secondary shear stress

Fig. 13 Shear stress components at the upper plate on varying K 2

The prime momentum is lessened when K 2 is augmented (see Fig. 3a). In Fig. 3b, it is noted that the secondary momentum in magnitude is enhanced for growing values of K 2 . This fact has been conveyed by Ghosh [4]. Figure 4a, b reveals the effect of inverse Darcy number Kp on momentum unit descriptions. It is noticed that

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(a) Primary shear stress

(b) Secondary shear stress

Fig. 14 Shear stress components at the upper plate on varying Kp

(a) Primary shear stress

(b) Secondary shear stress

Fig. 15 Shear stress components at the upper plate on varying h

the prime momentum and the size of the secondary momentum are reduced when Kp increases. This is related to the fact that the Darcian permeable media confrontation is contrariwise comparative to the Darcy number. By enhancing Kp (i.e., decreasing Darcy number), the solid matrix fibers gradually reduce and the porosity is enhanced. As an outcome, the liquid finds further space for motion which augments the momentum inside the channel. The occurrence of a permeable media, hence, divulges a striking regulatory impact on the flow field and can be oppressed as a suitable controller device in magnetohydrodynamic power generating structures. The case when Kp ! 0, i.e., Da ! 1, the dense matrix threads almost disappear, and hence the regime converts virtuously viscous electrically conducting liquid. Figure 5a, b divulges the impact of the inclination of the magnetic field h on the momentum descriptions. Both the principal momentum and the size of the secondary momentum are boosted within the channel for the uprising values of h. The minimum primary momentum and secondary momentum in magnitude associate with h ¼ 0 (i.e., magnetic field is perpendicular to the motion direction or channel walls). It is worthy to note that all velocity component descriptions are symmetrical parabolas about the centerline of the channel (g ¼ 0), which is compatible with classical MHD channel flow.

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Figure 6a, b displays the impact of M 2 on dimensionless induced magnetic field units. It is demonstrated in graphs that the induced magnetic description strength deviations meaningfully in magnitude near the channel walls with increasing M 2 . The induced magnetic field strength is constructive in the lower partial space of the channel (1  g\0) and undesirable in the upper half space of the channel (0\g  1). Physically, higher values of the magnetic parameter strengthen the induced magnetic field due to which the magnetic lines of force are lifted near the channel walls although passing over the vital region, and these shapes vary with the magnetic parameter. The induced magnetic arena mechanisms are shrunk close to the lower sheet of the channel and amplified in the vicinity of the higher sheet of the channel when K 2 or Kp is increased (Figs. 7a, b and 8a, b). The impact of magnetic description inclination h on the induced magnetic field units is divulged in Fig. 9a, b. The prime-induced magnetic field component hx is bumped up close to the inferior sheet of the channel and diminished in the vicinity of the higher sheet of the channel when h is increased and the reverse trend is perceptible on the secondary induced magnetic description hy . The induced magnetic field strength becomes extinct in the vital area of the channel, i.e., the magnetic instability induction does not arise at the channel center (g ¼ 0), and it is very minute in the area of the channel focus line. It can be realized from Figs. 6, 7, 8, and 9 that a mirror symmetry nearby the focus line is noticeable for the description of the induced magnetic profile strength. The frictional shearing stresses in x and y-directions at the upper and lower plate (g ¼ 1) are given by  dF  a  ib ¼ R tanhða þ ibÞ; ð31Þ  dg g¼ 1 a 2 þ b2 where sx1 þ isy1 ¼



dF  dg g¼ 1 ,

sx2 þ isy2 ¼



dF  dg g¼ 1

and a, b are given by (26).

The mathematical values of dimensionless shear stress sx1 , sy1 , sx2 and sy2 for dissimilar values of M 2 , K 2 , Kp and h are portrayed in Figs. 10, 11, 12, 13, 14, and 15. The variation of the shear stresses sx1 and sy1 for dissimilar values of M 2 and K 2 at the lower plate (g ¼ 1) are presented in Fig. 10a, b. It is clear that the shear stress sx1 is observed to reduce when M 2 or K 2 is enhanced and the magnitude of the shear stress sy1 enhances for enhancing values of K 2 while it reduces when M 2 is increased. Magnetic Lorentz force has a propensity to restrain the motion, i.e., reduce the motion across the channel. Hence, the shear stresses are reduced by intensifying M 2 . Figure 11a, b is designed to reveal the influence of Kp on the shear stresses sx1 and sy1 . It can be noted that the shear stress sx1 and the magnitude of the shear stress sy1 are reduced by enlarging Kp. In Fig. 12a, b, h (the inclination of the magnetic field) is found to uplift both the shear stress sx1 and the magnitude of the shear stress sy1 . On the other hand, Fig. 13a, b is sketched to illustrate the impact of M 2 and K 2 on the shear stresses sx2 and sy2 . It is noticed that the shear stress sx2 is diminished

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when M 2 or K 2 is enhanced, and the magnitude of the shear stress sy2 enhances for enhancing values K 2 while it reduces when M 2 is increased. Figure 14a, b are analyze the influence of Kp on the shear stresses sx2 and sy2 . It is found that the magnitude of shear stress sx2 and the shear stress sy2 is found to be reduced by increasing Kp. This is because the Darcian drag force is enhanced by a rise in Kp or a decrease in Da. Figure 15a, b discloses that both the shear stress sx2 and the magnitude of the shear stress sy2 are enhanced by increasing the magnetic field inclination h. The shear stresses at the channel walls are unaffected when varying M 2 and h ¼ p=2 (i.e., the magnetic field is parallel to the motion direction) (Figs. 12 and 15). From Figs. 12 and 15, it is noticed that the wall shear stresses in magnitude are found to be minimized once the magnetic field is ? to the flow direction (h ¼ 0). It is divulged from figures that the secondary shear stresses at the channel walls are continuously adverse representing substantial back motion in the secondary flow. Also, motion separation does not arise as shear stresses are not once zero. Qx and Qy stand for the mass motion rates in x and y-directions and given by   Z1 ða  ibÞ2 tanhða þ ibÞ Qx þ iQy ¼ F dg ¼ 2R 1  ; ð32Þ a þ ib ða2 þ b2 Þ2 1

where a and b are given by (26). Table 1 is prepared to exhibit the distribution for the mass motion rates on account of the primary mass motion (Qx ) and secondary mass motion (Qy ) for diverse values of M 2 , K 2 , Kp and h. It is observed that the primary mass flow Qx reduces for rising values M 2 , K 2 and Kp, it is witnessed to enhance when h (the disposition of the magnetic description) starts to rise. Further, the secondary mass

Table 1 Rate of mass flow

M2

K2

Kp

h

Qx

 Qy

5 8 10 5 5 5 5 5 5 5 5 5

4 4 4 4 5 6 4 4 4 4 4 4

10 10 10 10 10 10 10 12 15 10 10 10

p=4 p=4 p=4 p=4 p=4 p=4 p=4 p=4 p=4 p=6 p=4 p=3

0.08710 0.08054 0.07678 0.08710 0.07866 0.07069 0.08710 0.08101 0.07280 0.08476 0.08710 0.09062

0.04173 0.03386 0.03032 0.04173 0.04705 0.05024 0.04173 0.034571 0.02642 0.03843 0.04173 0.04599

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motion rate Qy is exhibited with an enhancement in either M 2 or Kp and the reverse trend is seen for increasing values of h or K 2 . The total magnetic flux entrained by the channel can be represented by Z1

Z1 hðgÞ dg ¼  1

R 1

 g 2

ða  ibÞ2 ða2 þ b2 Þ

 sinhða þ ibÞg dg ¼ 0; ða þ ibÞ coshða þ ibÞ

ð33Þ

where a and b are given by (26). It is manifested from (33) that the total magnetic flux entrained by the channel behaves a coincident over the central section of the channel so that the magnetic lines of force cut from the central section on account of the occurrence of Lorentz force. These illustrations show that the magnetic field does not penetrate outside the plate because of the perfectly conducting plates.

4 Conclusion The hydromagnetic motion of a viscous incompressible electrically conducting liquid restricted between effortlessly showing perpendicular sheets followed by a horizontal layer of a soaked permeable media in a revolving channel saturated through an inclined magnetic field is studied. In a permeable medium flow, the magnetohydrodynamic flow exerts its influence of a Darcy number with pivotal importance to an inclined magnetic description. The effect of the induced magnetic field plays a significant role in MHD porous medium flow. In a perfectly conducting plates, the rate of total magnetic flux is zero. It shows that the magnetic field does not penetrate outside the plate. The analysis leads to a gradually revolving structure once the conductivity is small and the functional magnetic profile is weedy; the prime motion, as well as the prime-induced magnetic profile, is reliant on the magnetic field with the inclusion of porosity of the permeable media when h (the angle of inclination of the magnetic field) ¼ np where n is an even integer while the secondary flow, as well as the secondary induced magnetic field, is independent of the magnetic field but dependent on rotation. Eventually, the effect of Darcy number becomes significant over the entire MHD porous medium flow in a rotating environment.

References 1. Cramer KR, Pai SI (1973) Magnetofluid dynamics for engineers and applied physicists. McGraw-Hill, New York 2. Mazumder BS (1977) Effect of wall conductances on hydromagnetic flow and heat transfer in a rotating channel. Acta Mech 28:85–99

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3. Datta N, Jana RN (1977) Hall effects on hydromagnetic flow and heat transfer in a rotating channel. IMA J Appl Math 19(2):217–229 4. Takenouchi K (1985) Transient magnetohydrodynamic channel flow with axial symmetry at supersonic speed. J Phys Soc Jpn 54:1329–1338 5. Linga Raju T, Ramana Rao VV (1993) Hall effects on temperature distribution in a rotating ionized hydromagnetic flow between parallel wall. Int J Eng Sci 31(7):1073–1091 6. Helmy KA (1998) MHD unsteady free convection flow past a vertical porous plate. Z Angew Math Mech 98:255–270 7. Naroua H (2006) Computational solution of hydromagnetic free convective flow past a vertical plate in a rotating heat-generating fluid with Hall and ion slip currents. Int J Numer Methods Fluids 53(10):647–658 8. Naroua H, Takhar HS, Ram PC, Beg TA, Beg OA, Bhargava R (2007) Transient rotating hydromagnetic partially ionized heat-generating gas-dynamic flow with Hall/ionslip current effects: finite element analysis. Int J Fluid Mech Res 34(6):493–505 9. Helmy KA (2007) On the unsteady magnetohydrodynamic flow of viscous conducting fluid. Z Angew Math Mech 80:665–680 10. Kumar RB, Raghuraman DRS, Muthucumaraswamy R (2002) Hydromagnetic flow and heat transfer on a continuously moving vertical surface. Acta Mech 153:249–253 11. Ghosh SK (2001) A note on unsteady hydromagnetic flow in a rotating channel permeated by an inclined magnetic field in the presence of an oscillator. Czechoslovak J Phys 51(8):799– 804 12. Ghosh SK (2002) Effect of Hall current on MHD Couette flow in a rotating system with an arbitrary magnetic field. Czechoslovak J Phys 52(1):51–63 13. Jaiswal BS, Soundalgekar VM (2001) Unsteady free and forced convection MHD flow past an infinite vertical porous plate with variable suction and oscillating plate temperature. Bull Allahabad Math Soc 16:81–95 14. Chandran P, Sacheti NC, Singh AK (2002) On laminar boundary layer flow of electrically conducting liquids near an accelerated vertical plate. Phys Chem Liq 40(3):241–254 15. Mishra A, Sharma BK (2017) MHD mixed convection flow in a rotating channel in the presence of an inclined magnetic field with the hall effect. J Eng Phys Thermophys 90 (6):1488–1499