Solar Water Heating: Fundamentals and Applications 1536193208, 9781536193206

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WATER RESOURCE PLANNING, DEVELOPMENT AND MANAGEMENT

SOLAR WATER HEATING FUNDAMENTALS AND APPLICATIONS

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WATER RESOURCE PLANNING, DEVELOPMENT AND MANAGEMENT

SOLAR WATER HEATING FUNDAMENTALS AND APPLICATIONS

KHALIL KASSMI EDITOR

Copyright © 2021 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. We have partnered with Copyright Clearance Center to make it easy for you to obtain permissions to reuse content from this publication. Simply navigate to this publication’s page on Nova’s website and locate the “Get Permission” button below the title description. This button is linked directly to the title’s permission page on copyright.com. Alternatively, you can visit copyright.com and search by title, ISBN, or ISSN. For further questions about using the service on copyright.com, please contact: Copyright Clearance Center Phone: +1-(978) 750-8400 Fax: +1-(978) 750-4470 E-mail: [email protected].

NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the Publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

Library of Congress Cataloging-in-Publication Data ISBN: H%RRN

Published by Nova Science Publishers, Inc. † New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

ix Water Heating with a Multi-Stage Hybrid Solar System MSDH N. El Moussaoui, K. Kassmi, S. Alexoupolos, K. Schwarzer and H. Chayeb Adoption Potential, Thermal Engineering and Economic Viability of Solar Water Heating Systems Abhishek Saxena and Brian Norton Daily Comparison Energy and Exergy Analysis and Thermal Energy Storage Performance of Solar Collectors Ayhan Atiz, Hatice Karakilcik, Abhishek Saxena and Mehmet Karakilcik Steam Generation for Process Applications Using Solar Water Heating Enabled by Nanofluids Y. Raja Sekhar, E. Porpatham, Abel Rouboa, Khalid Bouziane, K. V. Sharma, I.M. Mahbubul and Anil Singh

1

21

59

85

vi Chapter 5

Chapter 6

Chapter 7

Chapter 8

Contents Influence of Nano-Enhanced Phase Change Material (NEPCM) on the Performance of Solar Water Heater P. Manoj Kumar, K. Mylsamy, P. Michael Joseph Stalin, Alagar Karthick and P. T. Saravanakumar

113

Thermal Model and Simulations of Solar Water Heating F. Bagui and K. Kassmi

137

Thermal Performance Evaluation of a Modified Solar Water Heater Integrated with Parabolic Trough Concentrator V. Rastogi, A. Saxena, A. K. Singh and M. Karakilcik

151

Hydrogen Production and Space Heating Using Water Heated by Solar Radiation Ayhan Atiz, Hatice Karakilcik and Mehmet Karakilcik

177

Chapter 9

Photovoltaic Solar Water Heating System I. Atmane, N. El Moussaoui, K. Kassmi, O. Deblecker and N. Bachiri

Chapter 10

Potential Techniques for Thermal Performance Enhancement for Solar Water Heaters A. Saxena and P. Verma

227

Humidification-Dehumidification Desalination Through Solar Water Heating System T. Srinivas

265

Chapter 11

203

Contents Chapter 12

Influence of Various Nanofluids on the Performance of Solar Water Heaters P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran, P. Manoj Kumar and N. Sadanandam

vii

285

About the Editor

315

Index

317

PREFACE The sharp increase in the price of oil in 1973 led man to turn his attention to renewable sources of energy for the first time, foremost among them solar energy. The main characteristics of this solar energy are its free availability, its availability over a large part of the earth and the absence of the risk of exhaustion, known by fossil energy sources. Solar energy has reduced operating costs and offers cost-effective alternatives to conventional energy sources. The development of the use of solar energy will be linked not only to its economic advantages (which will grow as fossil energy reserves decrease) but above all to considerations related to environmental protection: no polluting discharges (fumes containing CO2 and NOx by thermal power plants), no radioactive danger and bulky waste (nuclear power plants), possibility of limiting the use of CFCs (production of solar cooling by adsorption). In solar energy applications, there are two types of energy: 



THERMAL SOLAR ENERGY, used in the form of heat. It is about taking full advantage of the sun's radiation for the production of hot water, for domestic or industrial consumption, air conditioning of swimming pools, heating of homes, hotels, schools, factories, etc. PHOTOVOLTAIC SOLAR ENERGY which transforms the sun's radiation into electricity by means of photovoltaic cells or

x

Khalil Kassmi photovoltaic panels. This electricity is used for domestic and industrial use, to drive pumps to heat sanitary water and in solar still systems for the production of drinking water.

Currently, a lot of research work is being done on solar water heating systems and their optimizations for each application, that interests man and industry. This is largely justified by the advantages of mature technology offering an efficiency of over 80% in summer. In this context, in this book "Solar Water Heating: Fundamentals and Applications" we present current research on the development of solar water heating systems. More specifically, we present the solar techniques used (Thermal and Photovoltaic), thermal operation, thermal and electrical modeling, performance in terms of heating temperature and efficiency. The 12 proposed chapters are: Chapter 1 - In this chapter, we present a multi-stage hybrid solar desalination system (MSDH). In this system, the basis of operation is the heating of the water by the 8.4 m2 thermal collectors during the day, and at night by the batteries, charged by the photovoltaic panels with a maximum power of 3 kW. Simulations are carried out at a daytime irradiance intensity and ambient temperature of 824 W/m2 and 23°C respectively. The results obtained show, the maximum water temperatures of the stages, the maximum flow rates and the cumulative quantity of production of the order of 99.8°C, 14.06 kg/h and 134 liters respectively. All of the results obtained show the proper functioning of the solar water heating system, and the production of distilled water by the MSDH multi-source solar energy system. Chapter 2 -The present chapter focus on real global market potential, thermal engineering and economic viability of solar water heaters. In which analysis of heat transfer in water heaters helps to identify thermal performance indicators. Achieving this at a life-cycle cost comparable with competing options is a key to significant market penetration. Apart this, a highly efficient water heater with a high cost is unlikely to be in high demand in market. Therefore, to determine the best design of water heater for a specific location it is necessary to take into account both the heat transfer

Preface

xi

and economics. Present work focuses on these parameters to provide a gateway to the new scholars, researchers and industrialists at one platform. Chapter 3 - In recent years, energy systems using clean and renewable energy sources that do not pollute the environment are attracted attention. The most important of these are solar energy systems that generate thermal energy and electricity. For this purpose, a new study was carried out to determine the energy and exergy efficiency of FPSCs, ETSCs and PTSCs on a sunny day for January in Adana of Turkey, where hot water is the most needed. It was determined how the energy and exergy yields of three collectors on a sunny day in the winter varies according to the increasing area. As a result, it was found that while the energy efficiency of FPSC and ETSC decreased with the increase of the surface area, the exergy efficiency did not change significantly, On the contrary, the energy efficiency of PTSC did not change and the exergy efficiency increased. Chapter 4 - The chapter “STEAM GENERATION FOR PROCESS APPLICATIONS USING SOLAR WATER HEATING ENABLED BY NANOFLUIDS” describe the use of nanotechnology for steam generation by solar energy using volumetric heating concept. This chapter introduce readers about the possible sustainable solutions reported by various authors in literature on nanofluids for steam generation. Steam generation capability with TiO2 nanofluid prepared at different concentrations as working fluid were studied using fabricated test setup. Use of nanofluid has shown five times better steam generation capability compared to water and observed to be effective in terms of economic as well as carbon emissions. Still there is lot of scope for research to explore with reference to use of nanotechnology for standalone applications in developing countries and transition economies. Chapter 5 -This chapter elucidates the variation in the performance of an evacuated tube solar water heater under the influence of a new kind of nano-enhanced phase change material (NEPCM). The NEPCMs were prepared by disseminating different mass concentrations of SiO2 nanoparticles within the paraffin matrix and assimilated with the storage tank of the solar water heater. The experiments revealed that the NEPCM consist of 1.0% mass of SiO2 nanoparticles improved the energy efficiency

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Khalil Kassmi

of the solar water heater by 18.57% and delivered the hot water at 41.1°C on the next morning, even after the withdrawal of water on the previous evening. Chapter 6 – This chapter is devoted to the functioning analyse of domestic solar water heating. For this propos a mathematical model of heat transfer in tank and in the collector is developed. Simulations using this model allows us the study of the impact of different input parameters of the process. Obtained results using different configurations shows that a SWH installation can be very profitable. The system can operate despite nonoptimal radiation conditions. For better efficiency, the system must include a control system and can be coupled to a photovoltaic system to make it autonomous. The study we conducted constitutes a first approach of process analyse. Mathematical model can be a useful for design or sizing of the system. Chapter 7 - In the present work efforts are made to approach a technique to minimize the demand of hot water supply in buildings. For this, a parabolic trough concentrator is developed which is further integrated into a new designed close and open loop based water heating system. It is observed that the rate of rise and fall in temperature for open loop system is higher than the close loop system. In March 2019, the maximum value of thermal efficiency obtained for open loop and close loop circulation is 39% and 26%, respectively, while for January the values are 37% and 22%, respectively. It is found that present design is not only compact, low cost and user friendly but also efficient that can save the electricity consumed for water heating in homes and buildings. Chapter 8 - In this study, the various renewable energy conversions such as heat, electricity and hydrogen were carried out using an integrated system consisting of evacuated tube solar collectors (ETSCs), organic Rankine cycle (ORC) and proton exchanger membrane (PEM) operating with renewable resources (e.g., solar and geothermal energy). In order to improve the heat, electricity and hydrogen production performance of this system, the performance analyzes of geothermal source assisted solar collectors were performed on a sunny day in January from 9 am to 15 pm in Nevşehir of Turkey. As a result, the energy and exergy efficiencies of overall system

Preface

xiii

were found. In addition, the energy and exergy analyzes of the system were performed using ORC's n-butane and isobutane fluids. Chapter 9 -The aim of the work presented in this chapter is to develop solar photovoltaic salt water heating systems in order to produce condensation of heated water vapor, and consequently pure water droplets. The proposed system is formed by 600 W/peak panels, two DC/DC converters, two heating resistors and a remote control, regulation and supervision block. The first typical results obtained show that heating a liter of saline water for an illumination of 650 W/m², an ambient temperature of 34°C and an overall output power of the converters of 350 W, the heating of the heating resistors of 600°C after 10 seconds, water 90°C after 15 min and producing 500 ml of distilled water per day. Chapter 10 - The role of convection heat transfer is much important to improve thermal efficiency of water heater. Present chapter focuses on different potential techniques like; collector design, extended geometries, integrated thermal storage, selective coating for better heat transfer and thermal insulation for thermal performance augmentation of water heaters. Chapter also discussed water flow inside a solar heater for a better understanding of thermal response that would result in the enhancement of water heating performance of a simple design. Overall, it’s a gateway to the new UG and PG scholars, researchers, and industrialists. Chapter 11 - The water can be heated using solar energy with flat plate collector and evacuated tube solar collector at the low temperature. Solar desalination based on water heating also works at the same temperature range. Therefore, solar stills and other thermal desalination systems can be developed with the solar water heating process. Out of many thermal desalination methods, humidification-dehumidification (HDH) is a simple, cost effective and works at temperature of solar water heating. In this chapter, humidification-dehumidification has been studied and analysed with the solar water heating and sensible storage unit. No need to maintain vacuum in HDH desalination and works at the atmospheric pressure. HDH desalination with solar water heating has been focused to find the instantaneous and cumulative production through the dynamic simulation

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using finite difference method. The developed desalination works on offgrid mode with the source of solar photo voltaic and thermal (PV/T) energies Chapter 12 - This chapter deals with developing of the mathematical model based on the fundamental energy balance equations for analyzing the influences of various nanofluids on the thermal performance of solar water heater. During the study, six different nanofluids are analyzed by varying the volume concentration and concluded that CeO2/water nanofluids enhanced the thermal efficiency by 15.21%, reduced the collector size by 27.86% and effectively reduced the payback period when compared with conventional fluid.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 1

WATER HEATING WITH A MULTI-STAGE HYBRID SOLAR SYSTEM MSDH N. El Moussaoui1, K. Kassmi1,, S. Alexoupolos2, K. Schwarzer2,3 and H. Chayeb2 1

Mohamed First University, Department of Physics, Oujda, Morocco 2 Solar-Institut Jülich (SIJ), FH Aachen, Germany 3 Engineering Office of Energy and Environmental Technology (IBEU), Jülich, Germany

ABSTRACT In this chapter, we present the structure and simulation of the operation of a multi-stage hybrid solar desalination system (MSDH). In this system, the basis of operation is the heating of the water by the 8.4 m2 thermal collectors during the day, and at night by the batteries, charged by the photovoltaic panels with a maximum power of 3 kW during the day. We established the thermal/electrical operating models for each stage, then simulated the water temperature and the production of distilled water during the day and at night. In the case of heating by photovoltaic energy, the water is heated by thermal resistors, integrated in the MSDH 

Corresponding Author’s E-mail: [email protected].

2

N. El Moussaoui, K. Kassmi, S. Alexoupolos et al. system. Simulations are carried out, taking into account the weather conditions of one day in the winter month (January 2020), where the irradiance intensity and the ambient temperature reach 824 W/m2 and 23°C respectively. The results obtained show, during the day, maximum water temperatures of the stages, flow rates and cumulative production quantity of about 80°C, 4.6 kg/h and 30 liters respectively. During the night, the maximum water temperatures of the stages, the maximum flow rates and the maximum cumulative production quantity are 99.8°C, 14.06 kg/h and 104 liters respectively. From these results, we deduce a quantity of water produced by the heating of the water by a solar thermal and photovoltaic energy of 134 liters during 18 H. Also, from these results we deduce that the PV energy improves the water production by a factor of 3.46 and ensures, by storing energy in the batteries, the heating of water day and night, without using and relying on the energy of the electrical network.

Keywords: MSDH, solar radiation, heating water, solar thermal and photovoltaic energy, solar battery, heating temperature, flow rate, distilled water production

1. INTRODUCTION The need for more efficient, sustainable, without pollution and renewable solar-powered water heating systems is current (JOUHARA Hussam et al. 2017). The use of solar thermal systems is known as an efficient method to cope with the high energy demand and related challenges, and has great potential for development. More particularly, solar water heating by solar energy (Shukla Ruch et al. 2013), in solar desalination systems (Zhang Ying et al. 2018), is the subject of much research in order to make the system more reliable and to produce drinking water at low prices (Zhang Ying et al. 2018). The work published in (Shukla Ruch et al. 2013, Al-Badi A. H. and Albadi 2012, Yan Chengchu et al. 2015) has shown that solar water heating technologies offer simple, reliable, user-friendly and cost-effective techniques and methods. These technologies have been widely used in many countries and regions around the world (Cassard Hannah et al. 2011, Wu Wei et al. 2018) to harness solar energy to meet the needs of homes and buildings and businesses for sanitary water and drinking

Water Heating with a Multi-Stage Hybrid Solar System MSDH

3

water production (Al-Badi A. H. and Albadi 2012, Yan Chengchu et al. 2015, Deniz Emrah and Çinar Serkan 2016). Solar water heating systems generally consist of solar thermal collectors (DAGHIGH Roonak and SHAFIEIAN Abdellah 2016, Krishnavel et al. 2014) and a thermal fluid system to transfer heat from the collector to its point of use, or to a tank to store the heated water for later use (Al-Badi A. H. and Albadi 2012). In the particular case of distilled water production applications, the water is heated by thermal energy using flat plate thermal collectors (Krishnavel et al. 2014, Sint, Nang Khin Chaw et al. 2017) evacuated tube collectors (Hamanda Lia and Nugroho Gunawan 2020, Alqdah Khaled et al. 2020), parabolic concentrators (Rajamohan et al. 2017) or parabolic cylindrical concentrators (Hadjiat et al. 2018). These classic techniques are highly dependent on solar irradiance and therefore suffer from the sporadic nature of solar energy over a given time interval, and especially during the night when there is no sunlight. Usually, the continuous and efficient operation of conventional heating systems requires additional electric heating to compensate for thermal energy, which will increase energy consumption and greenhouse gas emissions (Deniz Emrah and Çinar Serkan 2016, Daghigh Roonak and Shafieian Abdellah 2016). In this context, within the framework of the projects undertaken with national and international partners, we carry out research on the improvement of functioning of the production systems of distilled water, by heating the water by solar thermal and photovoltaic energy. The proposed hybrid system is therefore autonomous and operates on solar energy day and night. In this chapter we propose to model and simulate water heating in a hybrid multistage solar desalination system. This system is heated by solar thermal energy, produced by solar collectors with an area of 8.4 m2 during the day, and electrical energy stored in solar batteries at night. Electrical energy is produced by PV panels with a maximum power of 3 kW, then stored in solar batteries. A special intention is attached to the heating of water on each stage, cumulative flow and quantity of distilled water during the day and at night.

4

N. El Moussaoui, K. Kassmi, S. Alexoupolos et al.

2. STRUCTURE AND FUNCTIONING OF SYSTEM MSD The multistage water heating system (MSDH), which is the subject of our study, is shown in Figure 1. The different blocks of this system are:  



A salt water storage tank (A), produced by a photovoltaic (PV) pumping system A field of four thermal solar collectors with a surface area of 8.4 m2, whose role is to heat distilled water, using thermal solar energy. This water circulates between these collectors and the lower basin of the MSDH system. Thermal resistors supplied by means of a regulation and remote control unit by photovoltaic solar energy. The energy is produced by a field of photovoltaic panels (of power 3 kW) during the day and stored in the solar batteries during the day, then used during the night when there is no sunlight.

1. Structure of the solar thermaland and photovoltaic heating system in a in a FigureFigure 1. Structure of the solar thermal photovoltaicwater water heating system hybrid solar desalination system (MSDH). hybrid solar desalination system (MSDH).

Water Heating with a Multi-Stage Hybrid Solar System MSDH 





5

A desalination unit formed by a frame containing eight stages and a lower basin. The unit is supplied with water from reservoir A, from the highest stage (eighth stage). After filling the latter, the excess salt water is continuously injected through an overflow pipe to fill and compensate for the lack of water in the lower stages. The same principle is repeated until the first stage is filled. The lower basin is powered by distilled water heated by the four sensors during the day, and the thermal heating resistor, powered by electrical energy stored in the batteries. This results in the heating of each stage by the phase conversion energy released, also called the enthalpy of evaporation. Then the saline water, containing in these eight stages, evaporates and condenses at the bottom surface of each conical stage. As a result of this condensation, droplets of pure water form and flow to the basin through the drainage gutter, welded to the two side walls of the frame. The excess distilled water in the basin is then drained to the storage tank. A distilled water storage tank (B).

3. NUMERICAL MODEL FOR THE MULTI-STAGE DESALINATION PLANT In this paragraph, we have established the thermal/electrical models governing the heating of water with solar/photovoltaic energy at each stage of the system in Figure 1. In our study we took into consideration the following assumptions and conditions (Reddy et al. 2012): 



Due to the low temperature difference between adjacent stages, heat transfer by radiation and natural convection is negligible. The heat transfer between the hot surface of the saline water and the condensing surface, in each stage, is mainly carried by the processes of evaporation and condensation The system operates at atmospheric pressure

6

N. El Moussaoui, K. Kassmi, S. Alexoupolos et al.      



Condensation on the walls of the trays occurs only in the form of a homogeneous and continuous film Steam losses (leaks) between the stage and the frame inside the still are negligible The stages are well placed while ensuring a better seal between each stages Fresh water exits at a temperature equal to the condensing surface temperature at each stage of the system During the day the water is heated by solar thermal energy, supplied by flat plate solar thermal collectors During the night the water is heated by the electrical energy stored in the batteries. This energy is produced by the photovoltaic panels during the day The desalination system works without the addition of salt water, day and night.

Assuming the above assumptions and basic relations of thermodynamics (Reddy et al. 2012, Adhikari et al. 1995, Feilizadeh Mansoor et al. 2015, Schwarzer Klemens et al. 2011) and the diagram shown in Figure 2, the energy balance at each stage (basin up to the 8th stage) is:

3.1. Energy Balance of the Basin At this stage the model of heat exchange on the water of temperature 𝑇𝑠𝑏 , written as function of ambient temperatures and freshwate (𝑇𝑎𝑚𝑏 ,𝑇𝑐𝑏 ), electric heating power (P) during the night, the useful energy of the supply thermal collector during the day 𝑄̇𝑐𝑜𝑙 , the evacuation energy of the fresh water produced on the stage i (𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 ), heat flow lost by evaporation (𝑚̇𝑏 .ℎ∗𝑓𝑔𝑏 ), the overall heat losses 𝛥𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑏 and heat loss on stage i (𝑚̇𝑠𝑖 . 𝑐𝑝𝑏 . 𝑇𝑐𝑏 ) due to fresh water draining into the tank. Taking into account these different exchanges, the exchange model is written in the basin:

Water Heating with a Multi-Stage Hybrid Solar System MSDH 

7

During the day:

𝑀𝑠𝑏 . 𝑐𝑝𝑏 .

𝑑𝑇𝑠𝑏 𝑑𝑡

= 𝑸̇𝒄𝒐𝒍 + ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑏 . 𝑇𝑐𝑏 −

𝑚̇𝑠𝑏 .ℎ∗𝑓𝑔𝑏 − 𝛥𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑏 = 𝐴𝑐𝑜𝑙 𝐸̇ (𝑡) 𝜂0 − 𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠−𝑐𝑜𝑙 + ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑏 . 𝑇𝑐𝑏 − 𝑚̇𝑠𝑏 .ℎ∗𝑓𝑔𝑏 − 𝑈𝑏 𝐴𝑏 (𝑇𝑠𝑏 − 𝑇𝑎𝑚𝑏 ) 

(1)

During the night:

𝑀𝑠𝑏 . 𝑐𝑝𝑏 .

𝑑𝑇𝑠𝑏 𝑑𝑡

= 𝐏 + 𝑄̇𝑐𝑜𝑙 + ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑏 . 𝑇𝑐𝑏 −

𝑚̇𝑠𝑏 .ℎ∗𝑓𝑔𝑏 − 𝛥𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑏 = 𝐴𝑐𝑜𝑙 𝐸̇ (𝑡) 𝜂0 − 𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠−𝑐𝑜𝑙 + ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑏 . 𝑇𝑐𝑏 − 𝑚̇𝑠𝑏 .ℎ∗𝑓𝑔𝑏 − 𝑈𝑏 𝐴𝑏 (𝑇𝑠𝑏 − 𝑇𝑎𝑚𝑏 )

(2)

where: i: Stage number (1 to 8), b : basin, 𝑀𝑠𝑏 : Distilled water mass in the basin (kg), 𝑐𝑝𝑏 : Heat capacity of water in the basin (J/kg.°C), 𝑇𝑠𝑏 : Basin water temperature (°C), 𝐴𝑐𝑜𝑙 : Solar collector area (m2), 𝜂0 : Optical collector efficiency, 𝑚̇𝑠𝑖 : The distillate output rate (kg/s) in stages equal to the evaporation rate of the brackish water, it is calculated by the following relation: 𝑚̇𝑠𝑖 =

(𝑇𝑠𝑖 −𝑇𝑐𝑖 ) ℎ𝑒𝑣𝑖 𝐴𝑠𝑖 ℎ𝑓𝑔𝑖

With: 𝑇𝑠𝑖 : Water temperature in the ith stage (°C), 𝑇𝑐𝑖 : Water condensation temperature of ith stage (°C), 𝐴𝑠𝑖 : Surface area of the water in the ith stage (m2),

(3)

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N. El Moussaoui, K. Kassmi, S. Alexoupolos et al.

ℎ𝑒𝑣𝑖 : Evaporative heat transfer coefficient (W/m2.K), It is calculated by the following relation (Kalidasa Murugavel and Srithar 2011): 𝑃 −𝑃

ℎ𝑒𝑣𝑖 = 16.273 × 10−3 ℎ𝑐𝑖 (𝑇𝑠𝑖−𝑇𝑐𝑖) 𝑠𝑖

(4)

𝑐𝑖

where: ℎ𝑐𝑖 ∶ Convective heat transfer coefficient (W/m2.K),), It is calculated by the following relation (Kalidasa Murugavel and Srithar 2011): ℎ𝑐𝑖 = 0.884 × ((𝑇𝑠𝑖 − 𝑇𝑐𝑖 ) +

(𝑃𝑠𝑖 −𝑃𝑐𝑖 )(𝑇𝑠𝑖 +273) 1 268.9×103 −𝑃𝑠𝑖

)3

(5)

With: 𝑃𝑠𝑖 ∶ Partial pressure (Pa) at temperature 𝑇𝑠𝑖 calculated by the following relation (Chen Zhili et al. 2011, El Moussaoui and Kassmi 2019): 𝑃𝑠𝑖 = 𝑒

5144 ) 𝑇𝑠𝑖 +273

(25.317−

(6)

𝑃𝑐𝑖 ∶ Partial pressure (Pa) at temperature 𝑇𝑐𝑖 . calculated by the following relation (Chen Zhili et al. 2011, El Moussaoui and Kassmi 2019): 𝑃𝑐𝑖 = 𝑒

(25.317−

5144 ) 𝑇𝑐𝑖 +273

(7)

ℎ∗𝑓𝑔𝑖 : Modified latent heat of vaporization of water (J/kg). It is given by the following relation proposed by (El Moussaoui Noureddine et al. 2019): ℎ∗𝑓𝑔𝑖 = ℎ𝑓𝑔𝑖 + 0.68 × 𝑐𝑝𝑖 (𝑇𝑠𝑖 − 𝑇𝑐𝑖 ) where:

(8)

Water Heating with a Multi-Stage Hybrid Solar System MSDH

9

ℎ𝑓𝑔𝑖 : Latent heat of vaporization of water (J/kg). It is given by the following relation (Feilizadeh Mansoor et al. 2015, El Moussaoui and Kassmi 2019): ℎ𝑓𝑔𝑖 =1000 × (3161.5 − 2.4074(𝑇𝑠𝑖 + 273))

(9)

𝑐𝑝𝑖 : Thermal capacity of water (J/kg.°C). It is defined as a function of water temperature by the following relation (El Moussaoui and Kassmi 2019): 𝑐𝑝𝑖 = 1000 × (4.2101 − 0.0022 × 𝑇𝑠𝑖 + 5 × 10−5 × 𝑇𝑠𝑖2 − 3 × 10−7×𝑇𝑠𝑖3 ) (10) 𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠−𝑐𝑜𝑙 : Thermal losses from the collector. They are written according to solar irradiation 𝐸̇ (𝑡) and ambient temperature 𝑇𝑎𝑚𝑏 by following relation (Schwarzer Klemens et al. 2011): 𝑈 𝐴 𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠−𝑐𝑜𝑙 = 𝐿 ̇ (𝑡)𝑐𝑜𝑙 (𝑇𝑐𝑜𝑙 − 𝑇𝑎𝑚𝑏 ) 𝐸

(11)

With: 𝑈𝐿 : Collector overall losses coefficient (W/m2. K).

3.2. Energy Balance from 1st to 8th Stage At stage i (1 < i < 8), the model of heat exchange on the water of temperature 𝑇𝑠𝑖 , written as function of ambient and freshwater temperatures (𝑇𝑎𝑚𝑏 , 𝑇𝑐𝑖 ), heat flow lost by evaporation at lower stage (for I = 1 is 𝑚̇𝑏 ℎ∗ 𝑏 , for i≠1 is 𝑚̇𝑠𝑖−1 .ℎ∗𝑓𝑔𝑖−1), due to the condensation of water vapor on the condensation surface, the heat flux lost by evaporation (𝑚̇𝑠𝑖 .ℎ∗𝑓𝑔𝑖 ), overall losses 𝛥𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑖 and heat loss (𝑚̇𝑠𝑖 .𝑐𝑝𝑖 . 𝑇𝑐𝑖 ), due to the evacuation of fresh water flowing to the basin, by the expression:

10

N. El Moussaoui, K. Kassmi, S. Alexoupolos et al. 𝑑𝑇𝑠𝑖 = 𝑚̇𝑖−1 ℎ∗ 𝑖−1 − 𝑚̇𝑠𝑖 .ℎ∗𝑓𝑔𝑖 − 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 𝑑𝑡 𝑚̇𝑠𝑖−1 ℎ∗𝑓𝑔𝑖−1 − 𝑚̇𝑠𝑖 ℎ∗𝑓𝑔𝑖 − 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − 𝑈𝑖 𝐴𝑖 (𝑇𝑠𝑖

𝑀𝑠𝑖 . 𝑐𝑝𝑖 .

− 𝛥𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑖

=

− 𝑇𝑎𝑚𝑏 )

(12)

With: 𝑀𝑠𝑖 (kg): Water mass in each stage (1st to 8th stage). It is determined from the following conservation relation: 𝑑𝑀𝑠𝑖 𝑑𝑡

= −𝑚̇𝑠𝑖

(13)

Δ𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑖 : Heat losses (W) by stage i. They are calculated by the following relation: Δ𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑖 = 𝑈𝑖 𝐴𝑖 (𝑇𝑠𝑖 − 𝑇𝑎𝑚𝑏 )

(14)

where: 𝐴𝑖 : Surface area of the water in the ith stage (m2), 𝑈𝑖 : Heat loss coefficient (W/m2.°C), defined by: 1

𝜆

𝑈𝑖 = 1/(ℎ + 𝛿𝑖 + ℎ 𝑐𝑖

𝑖

1 𝑎𝑚𝑏

)

(15)

With: 𝜆𝑖 : Coefficient of thermal conductivity of the insulating material (W/m. K), δ𝑖 : Insulating thickness (m) ℎ𝑎𝑚𝑏 : Heat transfer convection coefficient with ambient (W/m2.K)

Water Heating with a Multi-Stage Hybrid Solar System MSDH

11

𝑚𝑖 .ℎ∗𝑓𝑔𝑖

Figure 2. Diagram of the energy balances of an MSDH single-tank, 8-stage solar Figure 2. Diagram of the energy balances of an MSDH single-tank, 8-stage solar still system. still system.

4. NUMERICAL RESOLUTION We determined the temperature of the basin (𝑇𝑠𝑏 ) and that of the stages (𝑇𝑠𝑖 ), as well as their quantities of distilled water produced (𝑚𝑠𝑖 ), numerically solving equations 16, 17 and 18 by the order 4 Runge-kutta method (RK4) (El Moussaoui and Kassmi 2019; Talbi et al. 2019). This numerical resolution consists in writing the system of system equations MSDH (Equations 1, 2 and 12), in the form of a first order differential equation, in the following form: For the basin water, during the day:

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N. El Moussaoui, K. Kassmi, S. Alexoupolos et al.

𝑑𝑇𝑠𝑏 1 = 𝑀 .𝑐𝑝 (𝑄̇𝑐𝑜𝑙 + 𝑑𝑡 𝑠𝑏 𝑏 ∗ ̇ 𝑚̇𝑠𝑏 .ℎ 𝑓𝑔𝑏 − 𝛥𝑄𝑙𝑜𝑠𝑠𝑒𝑠𝑏 )

∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑏 . 𝑇𝑐𝑏 − (16)

For the basin water, during the night: 𝑑𝑇𝑠𝑏 1 = 𝑀 .𝑐𝑝 (𝑃 + 𝑄̇𝑐𝑜𝑙 𝑑𝑡 𝑠𝑏 𝑏 ∗ ̇ 𝑚̇𝑠𝑏 .ℎ 𝑓𝑔𝑏 − 𝛥𝑄𝑙𝑜𝑠𝑠𝑒𝑠𝑏 )

+ ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − ∑8𝑖=1 𝑚̇𝑠𝑖 . 𝑐𝑝𝑏 . 𝑇𝑐𝑏 − (17)

Water in the 8 stages: 𝑑𝑇𝑠𝑖 𝑑𝑡

=𝑀

1 (𝑚̇𝑖−1 ℎ∗ 𝑖−1 𝑠𝑖 .𝑐𝑝𝑖

− 𝑚̇𝑠𝑖 .ℎ∗𝑓𝑔𝑖 − 𝑚̇𝑠𝑖 . 𝑐𝑝𝑖 . 𝑇𝑐𝑖 − 𝛥𝑄̇𝑙𝑜𝑠𝑠𝑒𝑠𝑖 ) (18)

where: i: Stage number (1 to 8), b : basin, 𝑇𝑠𝑏 : Unknown (basin water temperature) Tsi : Unknown (i stage water temperature) 𝑚̇𝑠𝑖 : Unknown (hourly flow rate mass of produced water) The program, developed under the Matlab language, consists in solving numerically the system of first order differential equations (16, 17 and 18), and deducing the temperatures 𝑇𝑠𝑏 and Tsi and the quantity of fresh water produced by the MSDH system, following the steps in Figure 3:  

 

Initialization of the temperatures and the water mass of the stages and the basin: Tsb, Ts1, Ts2, Ts3,Msb, Ms1, Ms2 Ms3 . Data entry:  Thermophysical properties of the system Cp, λi,δi, Aei, Acap …  Ambient temperature and solar irradiation Tamb, 𝐸̇ (𝑡).P Calculate of Tcb, Cpb, Tci and Cpi, Calculation of partial pressures Psi, Pci, Psb, Pcb water vapor for each stage,

Water Heating with a Multi-Stage Hybrid Solar System MSDH

13



Calculation of the different heat exchange coefficients in order hfgi, ℎ∗𝑓𝑔𝑖 , hsci, hevi, hfgb, ℎ∗𝑓𝑔𝑏 , hscb, hevb,

 

Determination of the water temperature of each stage Tsi and Tsb, Determination of the body of water Msi and Msb in different stages at all times,

Figure 3. Flowchart of resolution by the Runge-kutta method of order 4.

14

N. El Moussaoui, K. Kassmi, S. Alexoupolos et al.

5. RESULTS AND SIMULATION We simulated the operation of the hybrid solar desalination system MSDH in Figure (1) taking into account the weather conditions of a day and night Figure (4), typical of the month of a winter month (January 2020), and electrical energy stored in 1000Ah batteries. This electrical energy is supplied by the 3 kW PV panels during the day. The typical results obtained, concerning the temperatures, the flow rates and the cumulative quantities of the distilled water produced, for the basin and the eight stages, are shown in Figure 4.

100 90

Temperature (°C)

80 70 60 50 40 30 20 09:00

12:00

15:00

18:00

21:00

Time(hr:min)

Figure 4. (Continued)

00:00 24:00

27:00 03:00

06:00 30:00

Water Heating with a Multi-Stage Hybrid Solar System MSDH

15

Figure 4. Variation of solar irradiance, ambient temperature, water temperatures, hourly flow rate and production of the hybrid still for electric heating power (Batteries) of 3 kW.

From these results we can deduce:   



 



The maximum irradiance intensity of 825 W/m2 is around 12 h, The average ambient temperature during the day is 22°C-23°C, and 20°C at night., During the day, at 3 p.m., the water temperatures of the stages, the maximum flow rates and the cumulative production quantity are of the order of 80°C, 4.6 kg/h and 30 liters of distilled water, respectively, During the night, the maximum water temperatures of the stages, the maximum flow rates and cumulative production quantity are of the order of 99.8°C, 14.06 kg/h and 104 liters respectively, The maximum production in 18 hours is around 134 kg of distilled water, From 6 p.m., the electric heating system comes into operation. The temperatures in the basin and on the eight stages rise remarkably. The temperature of the basin rises from 68°C to 99.8°C (or 46%). The 8 stages undergo an increase of between 64% and 46%. From 8:00 am when the electric heating is switched off, the temperatures on the stages are significantly reduced. The

16

N. El Moussaoui, K. Kassmi, S. Alexoupolos et al.



temperature of the basin and the 8 stages are reduced. This is due to the switching of the thermal energy to the solar desalination system. In other words, from the electrical energy, supplied by the batteries, to the thermal energy supplied by the thermal collectors. The latter is very low in the morning, At night, the production of distilled water and the operation of the desalination system is completed around 3:00 am. This is due to the evaporation of the water content of the 1st stage for a heating capacity of 3 kW.

These first simulation results clearly show the correct operation of the hybrid system in Figure 4, and the possibility to heat by solar thermal energy during the day, and photovoltaic electrical energy, produced during the day, stored in the batteries during the night. Also, the availability of electrical energy in the solar batteries, during the night, favours the continuous operation of the MSDH system and the production of a significant amount of distilled water compared to the day. Almost 77.6% of distilled water is produced by photovoltaic energy during the night. In perspective, this work will be validated in the field by heating the water of the hybrid desalination system by photovoltaic solar energy, during the day and at night. Depending on the results obtained, an economic study and yield analyses will be carried out according to the seasons of the year.

CONCLUSION In this chapter, we have presented the design, operation, modelling as well as the first simulation results of the multiple stage solar desalination system (MSDH). System operation is based on heating and evaporating salt water using solar thermal energy during the day, and solar photovoltaic energy stored in solar batteries at night. Photovoltaic solar energy is produced during the day. The first simulation results obtained, data for one day in January 2020, show:

Water Heating with a Multi-Stage Hybrid Solar System MSDH 







17

Under a maximum illumination of 824 W/m2, and an ambient temperature of 23°C, the maximum temperature value of the basin and the eight stages vary from 51°C to 100°C. These values are largely sufficient to evaporate the saline water, its condensation and the formation of droplets from the distilled water, During the day, the maximum hourly flow rates and cumulative production quantity reach 80°C, 4.6 kg/h and 30 liters of distilled water, respectively, During the night, the maximum water temperatures of the stages, the maximum hourly flow rates and cumulative production quantity reach respectively 99.8°C, 14.06 kg/h and 104 liters, The maximum total production obtained is around 134 kg of distilled water

The analysis of these results and their comparisons with the literature, allowed us to conclude the feasibility of this type of this hybrid desalination system of eight stages, in terms of heating of the stages by solar thermal and photovoltaic energy. This work is continued, in order to validate the operation and production of drinking water from the hybrid MSDH system throughout the year.

ACKNOWLEDGMENTS This work falls within the framework of the Program of Cooperation Morocco-Allemand of Scientific Research PMARS III, Project PMARS III 2015-64 (2016-2019), in collaboration with:   

Mohamed First University Oujda, Morocco Solar-Institut Jülich (SIJ), FH Aachen, Germany Engineering Office of Energy and Environmental Technology (IBEU), Jülich, Germany.

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REFERENCES Adhikari, R. S., Ashvini Kumar, and G. D. Sootha. “Simulation Studies on a Multi-Stage Stacked Tray Solar Still.” Solar Energy 54, no. 5 (May 1995): 317–325. doi:10.1016/0038-092x(95)00001-8. Al-Badi, A. H. et Albadi, M. H. Domestic solar water heating system in Oman: Current status and future prospects. Renewable and Sustainable Energy Reviews, 2012, vol. 16, no 8, p. 5727-5731. Alqdah, Khaled S., Alfredi, Abdullah, Alnuman, Nasser, et al. Design, Fabrication and Testing of Shell and Tube Heat Exchanger Integrated with Vacuum Tubes Solar Water Heater. Journal of Energy Research and Reviews, 2020, p. 1-16. Cassard, H., P. Denholm, S. Ong, Technical and economic performance of residential solar water heating in the United States, Renew. Sust. Energ. Rev. 15 (8) (2011) 3789–3800. Chen, Zhili, Jingtang Peng, Guanyi Chen, Lian Hou, Tao Yu, Yang Yao, and Hongfei Zheng. “Analysis of Heat and Mass Transferring Mechanism of Multi-Stage Stacked-Tray Solar Seawater Desalination Still and Experimental Research on Its Performance.” Solar Energy 142 (January 2017): 278–287. doi:10.1016/j.solener.2016.12.028. Daghigh, R., A. Shafieian, Energy and exergy evaluation of an integrated solar heat pipe wall system for space heating, Sādhanā 41 (2016) 877– 886. Deniz, Emrah et Çinar, Serkan. Energy, exergy, economic and environmental (4E) analysis of a solar desalination system with humidification-dehumidification. Energy Conversion and Management, 2016, vol. 126, p. 12-19. El Moussaoui, Noureddine, and Khalil Kassmi. “Modeling and Simulation Studies on a Multi-Stage Solar Water Desalination System.” 2019 International Conference of Computer Science and Renewable Energies (ICCSRE) (July 2019). doi:10.1109/iccsre.2019.8807623. Feilizadeh, Mansoor, M. R. Karimi Estahbanati, Khosrow Jafarpur, Reza Roostaazad, Mehrzad Feilizadeh, and Hamed Taghvaei. “Year-Round Outdoor Experiments on a Multi-Stage Active Solar Still with Different

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Numbers of Solar Collectors.” Applied Energy 152 (August 2015): 39– 46. doi:10.1016/j.apenergy.2015.04.084. Hadjiat, M. M., Hazmoune, M., Ouali, S., et al. Design and analysis of a novel ICS solar water heater with CPC reflectors. Journal of Energy Storage, 2018, vol. 16, p. 203-210. Hamanda, Lia et Nugroho, Gunawan. Mathematics Modelling and Performance Analysis of the Heat Transfer on Vacuum Tube Collector of Water Heater Application. In: E3S Web of Conferences. EDP Sciences, 2020. p. 00022. Jouhara, H., A. Chauhan, T. Nannou, S. Almahmoud, B. Delpech, L. Wrobel, Heat pipe based systems - Advances and applications, Energy 128 (2017) 729–754. Kalidasa Murugavel, K., and K. Srithar. “Performance Study on Basin Type Double Slope Solar Still with Different Wick Materials and Minimum Mass of Water.” Renewable Energy 36, no. 2 (February 2011): 612–620. doi:10.1016/j.renene.2010.08.009. Krishnavel, V., A. Karthick, K. K. Murugavel, Experimental analysis of concrete absorber solar water heating systems, Energy Build. 84 (2014) 501–505. Rajamohan, G., Kumar, P., Anwar, M., et al. Analysis of solar water heater with parabolic dish concentrator and conical absorber. In: IOP conference series: materials science and engineering. 2017. Reddy, K. S., K. Ravi Kumar, Tadhg S. O’Donovan, and T. K. Mallick. “Performance Analysis of an Evacuated Multi-Stage Solar Water Desalination System.” Desalination 288 (March 2012): 80–92. doi:10.1016/j.desal.2011.12.016. Schwarzer, K., M. Eugênia Vieira da Silva, and T. Schwarzer. “Field Results in Namibia and Brazil of the New Solar Desalination System for Decentralised Drinking Water Production.” Desalination and Water Treatment 31, no. 1–3 (July 2011): 379–386. doi:10.5004/dwt. 2011.2339. Shukla, Ruchi, Sumathy, K., Erickson, Phillip, et al. Recent advances in the solar water heating systems: A review. Renewable and Sustainable Energy Reviews, 2013, vol. 19, p. 173-190.

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Sint, Nang Khin Chaw, Choudhury, I. A., Masjuki, Haji Hassan, et al. Theoretical analysis to determine the efficiency of a CuO-water nanofluid based-flat plate solar collector for domestic solar water heating system in Myanmar. Solar Energy, 2017, vol. 155, p. 608-619. Talbi, S., K. Kassmi, O. Deblecker, and N. Bachiri. “Thermal Heating by Photovoltaic Solar Energy.” Materials Today: Proceedings 13 (2019): 1125–1133. doi:10.1016/j.matpr.2019.04.080. Wu, Wei, Dai, Suzhou, Liu, Zundi, et al. Experimental study on the performance of a novel solar water heating system with and without PCM. Solar Energy, 2018, vol. 171, p. 604-612. Yan, Chengchu, Wang, Shengwei, MA, Zhenjun, et al. A simplified method for optimal design of solar water heating systems based on life-cycle energy analysis. Renewable Energy, 2015, vol. 74, p. 271-278. Zhang, Ying, Sivakumar, Muttucumaru, Yang, Shuqing, et al. Application of solar energy in water treatment processes: A review. Desalination, 2018, vol. 428, p. 116-145.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 2

ADOPTION POTENTIAL, THERMAL ENGINEERING AND ECONOMIC VIABILITY OF SOLAR WATER HEATING SYSTEMS Abhishek Saxena1, and Brian Norton2,3,4 1

Department of Mechanical Engineering, Moradabad Institute of Technology, Moradabad, India 2 Dublin Energy Lab, Technological University Dublin, Ireland 3 IERC, Tyndall National Institute, University College Cork, Ireland 4 MaREI; the SFI Centre for Energy, Climate and Marine, Ireland

ABSTRACT The global market potential, thermal engineering and economic viability of solar water heaters (SWH) is discussed. Globally there are opportunities for further adoption of SWH to supply hot water in residential and commercial sectors. In many countries, realizing these opportunities requires improved economic viability. This entails a combination of lower installed cost, improved system efficiency, durability and ease of maintenance. High solar energy to heat system conversion 

Corresponding Author’s E-mail: [email protected].

22

Abhishek Saxena and Brian Norton efficiency is usually a prerequisite to a SWH providing a high solar fraction of a total hot water load. Achieving this at a life-cycle cost comparable with competing options is key to significant market penetration. In locations with sufficient solar radiation to enable an appropriately designed SWH to satisfy year-round hot water demands, life-cycle cost optimized design is a key enabler to raising market demand.

Keywords: solar water heating, market potential, heat transfer, performance, life cycle, payback

NOMENCLATURE I

m  Tamb Asc , Patm Tm Tw Qu Cp Ut

 

solar radiation mass flow rate efficiency ambient temperature Ac solar collector area atmospheric pressure mean temperature water temperature heat gain specific heat top heat loss coefficient absorptivity transmissivity

ABBREVIATIONS SWH SWHS FPC CPC

solar water heater solar water heating systems flat plate collector concentrating parabolic collector

Adoption Potential, Thermal Engineering … ETC OLS CLS CLSDB LCC NPW PBP PCM TES

23

evacuated tube collector open loop system close loop system close loop system with drain back life cycle cost net present worth payback period phase change material thermal energy storage

1. INTRODUCTION On an average 60 x l013 MWh of solar radiant energy is received per annum on earth (Saxena and Agarwal 2018). The viable potential uses of that solar radiation depend on the specific geographical location (Garg 1986). In India, for example, incident solar energy; ranges from 4 to 7 KWh per square meter/day. In such conditions solar energy can be converted into thermal, mechanical, electrical, or chemical energy for a; solar cooking (Saxena et al., 2012), solar water heating (Saxena and Srivasatva 2012) space heating (Saxena et al., 2015), drying (Saxena and Goel 2013), power generation (Saxena and Goel 2013, Browne et, al 2015) purification of brackish water (Norton 2014) and refrigeration (Norton 1992). Solar water heater systems (SWHS) have been one of the earliest engineered applications of solar energy with designs ranging from the complex to quite simple configurations with low cost ((Garg, 1977, Norton, 2011). As well as domestic water heating, other applications included the heating of swimming pools and industrial water heating (Norton, 2014). Nowadays SWHS has a wide market round the world as shown in Figure 1.

24

Abhishek Saxena and Brian Norton

Figure 1. Potential of Solar water Heaters (Global SWH market 2017).

Figure 2. Climax solar water heater by CM. Kemp (Kemp 1891).

The first commercial SWH designed by Kemp in Baltimore, USA in 1886 was the ‘Climax’ SWH that comprised a water tank in an insulated wooden box with single glazing as shown in Figure 2. In 1909 Bailey patented a thermosyphon water heating system which separated the storage

Adoption Potential, Thermal Engineering …

25

tank from the solar collector. This design of SWH became popular in California and Florida. In 1930’s solar energy was relatively widely adopted to provide hot water services in south Florida. There also continued to be novel, though not widely adopted, design innovations. For example in 1940 Freeman (Freeman 1942) patented a novel water solar heater using a tracking lens to concentrate solar energy on a storage tank. Considerable experience has gained during 1950’s in Australia when a design guide on the working and construction of SWH was released by CSIRO. From the 1980s SWH has become well established in many countries to supply the system for desirable design at a reasonable cost (McVeigh, 1983). A wide variety of design software is now available for SWH design. At the system-level artificial neural network approaches have been applied for estimating the performance of SWHS (Kalogirou 2000). At the detailed component-level CFD has been used for analysis of heat transfer and fluid flow characteristics (Garnier et al., 2018).

1.2. Types of Solar Water Heating Systems A solar water heating system (SWHS) usually comprises solar collectors, heat exchangers, storage tanks, control valves and pumps (if not using natural circulation). These are connected by pipes for fluid flow, hot water withdrawal and cold-water replenishment. A pumped system also requires control sensors (Saxena et al., 2013). As shown in Figure 3, a basic SWH can comprise a blackened-tin flat plate solar collector, PVC pipes, and a PVC-walled storage tank. Most flat plate solar collectors include solar selective absorber coatings, are well-sealed to ensure a trapped air-layer insulates the absorber from the aperture and are thermally insulated at the back and edges (Norton, 2014). In evacuated tube collectors, heat loss is inhibited by a vacuum between the absorber and the tubular aperture. Figure 4 shows the close view of storage tank with insulated sockets for inserting an ETC.

26

Abhishek Saxena and Brian Norton

Figure 3. Solar water heater installed on the roof top of MIT, Moradabad. Moradabad

a a

b Figure 4. (a) View of the insulated sockets for ETC (b) evacuated tube structure Figure 4. (a) View of the insulated sockets for ETC (b) evacuated tube structure (Norton, 2011). (Norton, 2011)

The solar collector collects and converts solar energy into heat. A heat transfer fluid (HTF) passing through the solar collector conveys heat, usually via a heat exchanger, to a hot water tank. This stored heat energy can be utilized directly (Norton and Probert 1986). SWHS fall into two broad categories; (i) active systems that use a pump to circulate the fluid inside the SWHS and (ii) passive systems where buoyancy-driven circulation is employed (Kalogirou, 2014). Each of these categories includes a range of systems and components as indicated in Table 1 and Figure 5.

Adoption Potential, Thermal Engineering …

27

Table 1. Types of water heaters (Kalogirou 2014) Active systems Indirect pumped circulation system with external or internal heat exchangers Direct pumped circulation systems Heat pump systems Pool heating systems Air-to-water heat exchange systems

Passive systems Direct and indirect thermosyphon systems Integral collector storage systems

Figure 5. Different types used in {(a) 80’s- natural {(a) -circulation natural circulation Figure 5. Different typesofof SWHs SWHs used in 80’s type SWH, (b) type SWH, (b) singlesystem, tank system, double tank systems} (Duffie,(Duffie, 1980) - single -tank (c)(c)- -double tank systems} 1980).

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Abhishek Saxena and Brian Norton

In SWHS the basic elements can be organized in different configurations. The sizes of SWHS vary considerably depending on user requirements for hot water and whether the system is used to provide space heating. For solely water heating applications, small SWHS generally fulfill domestic hot water needs. Large SWHS are used to meet hot water demands in commercial buildings, hostels, hospitals, hotels as well as being found in industrial process heat applications (Saxena et al., 2018).

1.2.1. Natural Circulation Passive SWHS As these types of SWHS are quite simple in design, they generally incur low costs to both purchase and maintain. A natural circulation (or thermosyphon) SWH is shown in Figure 6.

Figure 6. Schematic of thermosyphon SWH with external storage tank (Laughton 2010).

In this SWH type the hot water storage tank is located above the solar collector. Fluid inside the collector flows through natural convection driven by the heating induced by incident solar radiation. If necessary, auxiliary heat energy is introduced near the top to the storage tank to sustain hot-water temperature. The hot water stored into storage tank is thermally stratified, with hotter less dense water above comparative denser cooler water (Goswami et al., 2000). The temperature of water withdrawn from the top

Adoption Potential, Thermal Engineering …

29

of the hot water tank is thus higher than the mean temperature of the water in the tank. This often obviates the need for auxiliary heating to meet the required demand temperature. In most thermosyphon SWH the location of the tank higher than the solar collector prevents nocturnal back-circulation of cold water from the collector reducing the temperature of the stored hot water (Norton and Probert, 1983). This enables nightime and early morning hot water demands to be met, Direct thermosyphon water heating systems without heat exchangers are generally limited to locations with non-freezing weather conditions unless evacuated tube collectors are used. Indirect thermosyphon SWH, in which an aqueous propylene glycol solution in conveyed in closed circuit integrated with a heat exchanger, are used in mild freezing climates (Norton and Edmonds, 1991). 1.2.1.1. Research on Natural Circulation Systems Many models have been developed for solar water heating by using natural convection. Close (Close 1962) developed a natural circulation SWH model to analyze relationships between heat transfer and water flow characteristics. Similarity theory has been applied to predict the SWH performance (Huang 1980). Thermosyphon single and multi-pass SWH have been tested for different ambient conditions and vertical heights (Norton and Probert 1984). It has been concluded that single and multi-pass SWH gave comparable heat gain efficiencies under peak irradiance but for lower insolation a single pass water heater performed better. Heat transfer and fluid flow correlations in SWH have been analyzed experimentally (Siddqui 1997) as has the dynamic response under variation of solar insolation (Riahi and Taherian 2011). Correlations for natural circulation in an evacuated tube collector (ETC) water heater have been determined through experimental and numerical study (Budihardjo et al., 2007). An experimentally tested thermosyphon SWH (Nahar 2003) that consisted of a flat plate collector (FPC) and storage tank with a capacity of 100l achieved a water temperature about 61oC with an overall system efficiency of about 57%. For eight solar water heaters linked in series to meet a high hot water demand in Taiwan (Liu et al., 2012), thermal

30

Abhishek Saxena and Brian Norton

stratification and flow rate were examined with (i) no a hot water load, (ii) an intermittent load and (iii) with a continuous load. Overall thermal efficiency for the intermittent load was higher by 7%. A glass FPC with selective surface absorber developed for a thermosyphon water heater (Zelzouli et al., 2014) achieved an annual system efficiency of about 39% with the yearly performance rising by 5% when the storage heat loss coefficient decreased by about 1 W/m2K. Low cost thermosyphon SWHs has been developed in many countries including Cyprus (Kalogirou 2014), Australia, Israel (Norton, 2011) and Brazil (Barbosa et. al., 2019). In a novel application, natural circulation water heaters with compound parabolic concentrating (CPC) and flat plate (FPC) collectors have been developed to constrain bacterial growth in soil by placing it in hot water (Yamfang et al., 2018).

1.2.2. Forced Circulation Active SWHS Forced circulation active systems require a pump that can be powered from mains electricity or, for system autonomy and reliability, by a photovoltaic module. In thermosyphon SWH the tank generally needs to be located above the store; as low fluid flow resistance pipework is required, long pipe lengths are avoided. As neither of these constraints apply to forced circulation SWH, greater design flexibility is available to adapt forced circulation system layouts to particular circumstances, especially in commercial buildings (Kalogirou 2014). Forced circulation SWHS can be used as open-loop systems (OLS), closed-loop systems (CLS) or closed-loop systems with a drain-back mode (CLSDB). Figure 7 shows a forced circulated SWHS. Pump control is by a differential thermostat that determines if the temperature at the top header is greater by an appropriate margin than the water temperature in the tank base (Joudi and Abd-Alzahra 1984). A check valve is included to stop nocturnal natural circulation reverse flow that would result in nighttime heat losses through the collector. These SWHS are generally indirect systems, so can be used in freezing weather conditions.

Adoption Potential, Thermal Engineering …

31

Figure 7. Schematic of typical pumped collector with storage on ground (Laughton 2010).

In OLS, solar collectors are empty if not providing heat (because the solar loop is held at atmospheric pressure). High pumping power is necessary to pump water to the solar collector. To overcome of this, in a pressurized CLS the solar loop is left full with fluid under pressure. To allow for thermal expansion of water, a low capacity expansion tank along with a pressure relief valve is provided in solar loop. Stagnation with no fluid flow through the collector can (in a hot climate) cause the temperature inside solar collector to rise sufficiently to cause high pressure leakage so air enters the circulation loop causing dry running of the pump. To overcome of this, in a CLSDB when the pump shuts off, water from solar collectors drains back into separate dedicated holding tank (Goswami et al., 2014, Kalogirou 2014). In all the above configurations, a differential controller measures the temperature variance between the collector and tank, turning on or off the water circulation pump if the temperature difference is more than a set limit.

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Abhishek Saxena and Brian Norton

1.2.2.1. Research on Forced Circulation Systems When comparing forced circulation SWHs using packed-bed collectors incorporating stones, iron chips and gravels, iron chips were found to be the best packing material, giving s payback period was estimated to be slightly over 3 years (Mishra and Bhatt 1981). Using a 0.05% volumetric fraction of Cu in H2O nano-fluid as the heat transfer fluid has been found improve the performance of SWH by 6.3% under the climatic conditions of India (Micheal and Iniyan 2015). Forced circulation SWHS have been integrated with a large-aperture heat pipe ETC under the climatic conditions of Mediterranean (Maraj et. al., 2019). A transient performance analysis of a forced circulation SWH integrated with heat pipe FPC under the climatic conditions of Morocco (Allouhi et al., 2019) revealed the tested system had the energy efficiency and exergy efficiency about 33% and 4%, respectively. SWH have been combined with heat pumps (Sutthivirode et al., 2009; Sterling and Collins, 2011). Luo et al., (2005) showed that an electric heat pump combined with a SWH can save around 38% power consumption compared with conventional electric water heating. Approaches have been developed for the optimum control of heat pump based SWHs (Wanjiru et al., 2017).

1.3. Advanced Designs of Water Heaters A hybrid water heater in South Africa comprised a PV module, wind generator and a heat pump water heater that supplied excess electricity to grid showed a payback period of about of 3.9 years (Sichilalu et al., 2017). A novel tabular daylight device (Marmoush et al., 2018) integrated with a thermosyphon SWH shown in Figure 8 tested in Cairo, Egypt successfully achieved a water temperature of about 62oC with an efficiency about 21.17%. It also provided typical illuminance of about 6.5 W/m2.

Adoption Potential, Thermal Engineering …

33

Figure 8. A novel hybrid solar water heater (www-irena.org).

Figure 9. A new ICS type water heater with a CPC (Hadjait et al., 2018).

SWHs developed in Cyprus for domestic and commercial building like hotels, showed payback periods for FPC and parabolic trough collector PTC of 8.3 years and 7.3 years, respectively (Kalogirou and Lloyd, 1992). Hybrid photovoltaic-thermal PV/T system performance simulations have concluded that PV/T systems can economically viability produce both water heating and electricity (Kalogirou and Tripanagnostopoulos, 2006). A parametric study of a SWH in India with a minimum-tracking CPC with an acceptance angle of about 64o showed that the system successfully attained a water temperature of 53oC with an efficiency of 38% (Varghese et al., 2017). An ICS type water heater with a CPC with single storage tank shown in in Figure

34

Abhishek Saxena and Brian Norton

9 tested in Algeria was found to maintain water temperatures from 48oC to 52oC (Hadjait et al., 2018). The effect of different gases between the cover and absorber on the thermal performance evaluation of a cylindrical SWH in climatic conditions of Iran was examined by Sadeghi et al., (2019). Maximum thermal efficiencies were about 52.14% and 48.17% respectively for argon and air at an optimum mass flow rate about 3.5 kg/h. SWHs have been modified to include a glass-to-glass PV modules (Tiwari and Dev, 2019), A performance comparison between an ICS water heater and a hybrid PV/T module (Smyth et al., 2019) showed that an ICS-SWH performs better thermally than an unglazed hybrid PV/T system though additional electrical power produced by the hybrid system made the overall collection efficiency about equal. The heat retention efficiency of hybrid system has been found moreover than ICS system. A SWH has also been combined with a planar thermoelectric generator (Faddouli et al., 2020). A techno-economic analysis of a PV assisted heat pump SWH shown in Figure 10 with a storage capacity of 190 l was carried out in Spain (Aguilar et al., 2019). The pump could be grid-operated or PV-operated without any battery storage The complete annualized cost of the system for 25 years was estimated to be about 337€/year while the CO2 emissions were reduced by 82%.

Figure 10. A photovoltaic assisted heat pump solar water heater for hot water supply.

Adoption Potential, Thermal Engineering …

35

Aluminum twisted tape inside the tubes of heat exchanger promote turbulence results in increased convective heat transfer (Isravel et al., 2020). Mirror reflectors project more solar radiation to a collector aperture. An experimental study has shown that a double pass SWH with a high reflectivity reflector had a system efficiency of about 50.26% at 0.0044 kg/s (Mandal and Ghosh, 2020).

2. POTENTIAL OF SOLAR WATER HEATERS In many countries, though there have been many national schemes to promote solar thermal systems there often remains needs for a variety of regulatory interventions that ensure that SWHS are ecofriendly, reliable, economic and user-friendly. Even with these in place, market take-up can be impeded by a lack of public awareness of these attributes (Saxena et al., 2013). The global SWH market as shown in Figure 11, has potential to grow. The implementation of policies mandating use of SWH in various nations will be likely to grow the SWHS market as shown in Figure 12.

Figure 11. SWHS market size for USA up to 2025 (Global market outlook on SWH 2018).

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Abhishek Saxena and Brian Norton

Figure 12. SWHS market size for different regions in 2018 (SWH market size by collector 2018).

Source: www.statista.com. Figure 13. Cumulative SWHS capacity nationwide in 2017 (in Giga-Watts).

Adoption Potential, Thermal Engineering …

37

Table 2. Different promotion policies about SWHS in the different countries (ENERDATA 2018) Country

Measures Types

Target

Morocco

Subsidies

Tunisia South Africa

Subsidies Tax rebates

1.7 million m2 by 2020 2.5 million m2 by 2020 4 million homes equipped by 2020 1.05 million m2 by 2020

Lebanon Israel

United States Brazil Mexico India China Taiwan South Korea Australia

SWH is mandatory on new building Tax credit Subsidies Subsidies, Investment grant Subsidies Subsidies Subsidies, Tax credit, Program certificate

Expected CO2 emission reduction (ktCO2)3 450 670

290

15 million m2 by 2020 1.8 million m2 by 2020 20 million m2 by 2020

3700 500 5500

300 million m2 by 2020 6 million m2 by 2020 342 ktoe by 2020 12% of homes equipped by 2020

54500 1100 1100

The market for SWH is worth over $1 billion in 2018 while the annual installation capacity is expected to grow to more than three million units by 2025. Asia-Pacific is expected to be the largest SWH markets because of increasing number of SWH installations in India and China. SWH markets have continued strong growth in Germany and South Africa. Flat plate collectors (FPC) in 2018 account for 70% of global SWH market, with thermosyphon SWH installations growing in India, Japan, Australia and Israel. Commercial installations are on target to have one million systems installed yearly by 2025. Appropriateness across will fuel SWH growth. The cumulative SWH system round the globe are shown in Figure 13 while Table

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Abhishek Saxena and Brian Norton

2 indicates support policies for water heaters adopted in specific nations. The total installed capacity of SWH is estimated to be about 688.50 million m2 in the world in 2018 which is subdivided in FPC (around 160.30 million m2), ETC (around 485.70 million m2) and unglazed water collectors (around 42.50 million m2) as shown in Figure 14. Figure 15 shows the recent installation capacity of both the glazed and unglazed type water collector/heaters for the top ten leading markets worldwide in 2018.

Figure 14. Total capacity of solar collectors in operation in the world in 2018 (Solar heat worldwide, 2020).

Figure 15. Top 10 markets in the world for SWH collectors in 2018 (absolute figures in MWth) (IEA, 2020).

Adoption Potential, Thermal Engineering …

39

Figure 16. Development of the glazed SWH collectors market in different regions from 2000 to 2018 (IEA).

Figure 16 shows the market declined and grown at different times in different regions. Declined in markets in Japan and South Korea recovered within a year. From 2009 the market in India, Japan, South Korea, Taiwan and Thailand have improved however Latin America showed the most steady increase to 2014.

3. THERMAL ANALYSES OF SOLAR WATER HEATERS Figure 17 shows the schematic of a natural convection SWH. The following assumptions have been made to develop a thermal model (Garg 2008): 1. For each different element of a SWH that contains water (i.e., storage tank, tubes, absorber), their mean temperatures are equal. 2. The temperature difference in the different elements of SWH (inlet and outlet flow section, connecting tubes etc.) is assumed negligible. 3. There is a linear temperature distribution in pipes connecting the collector and storage tank.

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Abhishek Saxena and Brian Norton

Figure 17. Thermosyphon SWH (Kalogirou 2014).

Assuming a fixed water flow rate through THE storage tank then the energy balance for entire SWH throughout the sunshine hours can be expressed as (Sodha and Tiwari 1981);

W

dTm  U (Tm  ta )  M (t )C (Tm  Tamb )  I . Asc .Fp .( ) dt

(1)

Equation (1) is used to estimate the mean unit temperature throughout the solar hours. The water storage energy balance can be expressed as;

dTm  U t (Tm  ta )  M (t ).C.(Tm  Tamb ) (2) dt Equation (2) is used to estimate m under natural circulation flow. The Qu  mc.(T3  T5 )  Wt '

energy balance during off-solar hours can be expressed as;

Wt '

dTm  U t (Tm  ta )  M (t ).C.(Tm  Tamb )  0 dt

(3)

Adoption Potential, Thermal Engineering …

41

where U  Fc Asc (Uc  Ut )  Ui Ai , and Wt '  Wt  Wwt ,

W  thermal capacities of various components Equation (3) is used to estimate the mean unit temperature throughout the non-solar hours. Solving eq. (1) and (3) with the initial conditions;

Tm  Tm0 at t  0 and Tm '  Tm' 0 at t  t '



t

 Tm  exp  f (t )dt 0

  g(t) exp   f (t)dt  dt  T t

t

0

0

m0



t

exp  f (t )dt 0



(4)

and



t

 Tm'  exp  ' F (t )dt

where, f (t ) 

g (t ) 

t

  G(t) exp   F (t)dt  dt  T t

t

'

'

t

t

' m0



t



exp  ' F (t )dt (5) t

U  M (t )C , W

 .Fc Ac W

U  U  M (t )C M (t )C I   ta  Tamb  , F (t )  t Wt ' W W 

and

U  M (t )C G (t )   t ta  Tamb  Wt  Wt 

Assuming climatic conditions where I, Tamb and ta are in general periodic, G(t) and g(t) can be expressed as;

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Abhishek Saxena and Brian Norton

g (t )  g o   g n cos(nwt   n ) n

G (t )  Go   Gn cos(nwt   n' ) n

Thus equations (4) and (5) can be presented as; g  e ft (e ft  1) g n   nw Tm  e ft  o (e ft  1)  Tm 0     cos(nwt   n )  sin(nwt   n )  2 2 f  f  f 1  n w     2  f   '  G  e T 'm  e F (t t )  o (e Ft  e Ft ' )  Tm' 0    F 

 F ( t t ' )

(e F (t t )  1)Gn  nw    cos(nwt   ' n )  sin(nwt   n' )  F  n 2 w2    F 1  2  F  

(6)

'

(7)

Withdrawal rate of hot water inside the storage tank when there is solar heat gain can be estimated by dTm/dt = 0

(8)

in equation 1 so

( M )const . 

1  Fc Asc I  U (Tamb  ta ) (Tm  Tamb )C

(9)

The efficiency of solar energy utilization can be determined from; t'

 MC (T

m



 Tamb )dt  Wt ' (Tm (t ' )  Tm 0 )

0



t'

0

(10)

Asc .I .dt

with natural circulation flow rate m given by;

Adoption Potential, Thermal Engineering …

m(t )

3



43

f ( s )(2 ATm  B)  dTm  x Wt  U t (Tm  ta )  M (t )C (Tm  Tamb )  DC dt   (11)

Increasing m increases efficiency ( ) however if the mean temperature (Tm) is increased than efficiency decreases due to higher heat losses Sodha and Tiwari (1981). Forced circulation water heaters comprise a heat exchanger, solar collector, hot water storage tank and a pump. Figure 18 shows a schematic diagram of a closed-loop forced circulation SWH. The energy balance equation for entire solar water heating unit is given by (Sodha et al., 1982);

dTm  UT (Tm  Tamb )  Qout dt

(12)

where, Qin  Ac FR [ .I  hL (Tm  Tamb )]

(13)

Qin  WT

and

 Ac hL F '   MC p  FR    1  exp  Ac hL   MC p  

(14)

The energy demand ‘Edw’ for hot water can be determined from the mains water temperature (Tm) and desired hot water temperature (Tw) (Kalogirou, 2000);

Edw  V ..c p .(Tw  Tm ) where, V  N days .N persons .Vperon

(15) (16)

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Abhishek Saxena and Brian Norton

4. ECONOMICS OF SOLAR WATER HEATERS Solar energy applications normally have relatively high initial cost and lower running costs. Their economic viability therefore needs to be considered in longer-term perspectives. The different types of cost associated with an SWH are shown in Table 3. Table 3. Different types of cost and items Capital cost items Solar collector Distribution system Air-conditioning components Heat storage Pump Hot water system Mechanical controls and electrical systems Other energy components (in hybrid systems) Installation

Other considerable costs Operation Maintenance Acquisition Repair and replacement Space used Taxes Credit for roofing replaced Insurance Advancement in design or other modification Siting Salvage value

4.1. Life Cycle Cost (LCC) Life cycle cost is the total cost associated with energy supply over its lifecycle considering the time worth of money. It can be assessed over a fixed period. The complete LCC of SWH can be estimated by summing all the present worth values (Kalogirou 2014, Sharma et al., 2011);

Adoption Potential, Thermal Engineering … LCC = initial investment + PW of annual mortgage payments + PW of annual energy and maintenance cost + PW of capital replacement cost + PWof salvage value emmision reduction valuation

45

(17)

where, PW = present worth The complete cost of a solar system (Tcs) is specified by summing areadependent costs (Ccad) and area-independent costs (Ccaid); expressed by:

Tcs  Ccad  Ccaid

(18)

where, Ccad includes the cost of every element of SWH including a portion of heat storage, pump etc. Actual fuel savings can be estimated through deducting yearly cost of fuel in a comparable fuel-only system. t

Caux  C fa  Laux .dt 0

(19)

Similarly, the cost of complete load for 1st year can be obtained by; t

CL  CFL  L.dt 0

(20)

where, Cfa and CFL are the cost ($/GJ) of secondary energy and conserved fuel respectively. The annual cost of the heat load can be expressed as; Annual cos t  mortgage payment +fuel cost + maintenace cost + property taxes + parasitic enrgy cost +insuarace cost -income tax savings

(21)

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Abhishek Saxena and Brian Norton

In many countries (such as the USA), tax refunds depended on whether the activity is non-revenue generating (e.g., a household) or revenue generating e.g., a business). For a non-revenue generating unit; Income tax savings (ITs ) = effective tax rate (ETr )  interest payment (Ip )  property tax (PTax )

(22) For a revenue generating unit; interest payment (I p )  PTax    Income tax savings (ITs ) = effective tax rate (E Tr )   + fuel expenses + M +   I + parasitic energy - d   

(23)

where M is the maintenance cost, d is the depreciation cost, I is the insurance cost . Many countries have national and local tax rates. In the USA for example the effective tax rate is given by;

ETr = (FTR) + (STR) - (FTR x STR)

(24)

where FTR and STR are federal and state tax rates.

4.2. Present Worth Factor Net present worth (NPW) is the total variation of future costs with present costs. For a SWH this is between the LCC of fuel displaced by a SWH and the LCC of the SWH plus any secondary energy unit (Kalogirou 2014). The present worth of 1$ over N periods (typically years) in the future offering a discount rate ‘d’ from the market, is

PW 

1 (1  d ) N

(25)

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47

For a 1st expense in a sequence being X, the 2nd being Y and the Nth being Z. then at the Nth time the cost becomes X(1+i)N-1. The present worth (PW) over that period cost is;

PWN 

X (1  i) N 1 (1  d ) N

(26)

4.3. Payback Period Payback period can be defined as the total time to get back the total cash expended on a solar energy system from the net energy savings from using that system Kalogirou 2014).. Payback time can be estimated; 

without discounting fuel savings

 Ci  In  s F  1 FLCF 1  PBP   In(1  iF ) 

(27)

with discounting fuel savings

if iF  d ,  C (i  d )  In  s F  1 FLCF 1   PBP  1  i  F  In    1 d 

(28)

if iF  d ,  C (i  1)  PBP   s F   FLCF 1 

(29)

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Abhishek Saxena and Brian Norton

where F is the solar fraction, L is the load (GJ), CF1 is the 1st year unit energy cost and iF is the inflation rate.

5. BENEFITS OF SWHS SWHS displace the use of conventional fuels such as; coal, woodpellets, cow dung cakes, kerosene and solid waste to heat water avoiding their adverse environmental pollution. These are considerable larger than the environmental pollution incurred in the manufacture of SWH (Hepsali 2008, Ibrahim et al., 2014). By displacing fossil fuels, the use of SWHS reduces the amount of CO2 produced (Jerneck 2013, Saxena et al., 2013). The benefits of using solar water heaters include; 1. 2. 3. 4. 5. 6. 7. 8. 9.

Use a clean and “free” fuel Reduce environmental pollution and greenhouse emissions. Silent operation Available in different designs with installation flexibility Low operating and maintenance costs Viable payback periods and long life span Built in hot water storage Appropriate for remote locations Operate without continuous attention

CONCLUSION In non-domestic settings, solar water heating is generally less commonplace. Large non-domestic solar hot water systems are usually custom-designed for each application. This presents barriers to achieving economies of scale. This is particularly so in their supply and installation, leading to limited uneven, market uptake. To remove such barriers to achieving market uptake of non-domestic solar water heating requires larger scale bespoke solar water heating systems that are;

Adoption Potential, Thermal Engineering …      

49

Designed for installation and commissioning in most buildings Readily installed causing limited disruption Adaptable to diverse building aesthetics Includable in design tools already used by architects, User-centric with flexible control via real-time interfaces Readily compliant with relevant certifications and regulations

Many innovative solutions now provide solar water heating systems that successfully meet consumer demands in different climatic, operational and market contexts. Compact modular systems ubiquitously provide domestic hot water in many parts of the world. They take a variety of forms largely informed by local manufacturing approaches and incumbent supply chains. In China, for example, evacuated tube collector systems would be commonplace whereas, for example in Cyprus, flat plate collector closecoupled thermosyphon system are in widespread use.

REFERENCES Aguilar, F., Crespí-Llorens, D., Quiles, P. V. (2019). Environmental benefits and economic feasibility of a photovoltaic assisted heat pump water heater. Solar Energy, 193: 20-30. Allouhi, A., Amine, M. B., Buker, MS., Kousksou, T. and Jamil, A. (2019). Forced-circulation solar water heating system using heat pipe-flat plate collectors: energy and exergy analysis. Energy, 180: 429-443. Barbosa, E. G., de-Araujo, M. E. V., de-Moraes, M. J. and Martins, M. A. (2019). Influence of the absorber tubes configuration on the performance of low cost solar water heating systems. Journal of Cleaner Production, 222: 22-28. Browne, M. C., Norton, B. and McCormack, S. J. (2015). Phase change materials for Photovoltaic thermal management. Renewable and Sustainable Energy Reviews, 47: 762-782.

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Close, D. J. (1962). The performance of solar water heaters with natural circulation. Solar Energy, (6): 33-40. Duffie, J. A. (1980). Active solar systems, in Solar energy conversion-II. Pergamon press, Canada ENERDATA, from REN21 and the IEA report, 2018. Faddouli, A., Fadili, S., Labrim, H., Hartiti, B., Ertugrul, M., Belouaggadia, N. and Stitou, M. (2020). Comparative study of a normal solar water heater and smart thermal/thermoelectric hybrid systems. Materials Today: Proceedings [Article in Press], (doi.org/10.1016/ j.matpr.2020.04.499). Freeman, C. M. (1942). Sun water heater. USA patent-2277311, USA. Garg, H. P. (1986). Solar water heating systems. D. Reidel Publishing Company, USA. Global Solar Water Heater Market 2017-2021. Report published in 2017. Goswami, D. Y., Kreith, F. and Kreider, J. F. (2000). Principles of solar engineering. 2nd Ed., CRC press, UK. Hadjiat, M. M., Hazmoune, M., Ouali, S., Gama, A. and Yaiche, M. R. (2018). Design and analysis of a novel ICS solar water heater with CPC reflectors. Journal of Energy Storage, 16: 203-210. Hepbasli, A., Giresunlu, U. (2008). Environmental Impacts from the solar energy systems. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 31(2): 131-138. Hobson, P. A., Norton, B. (1988). Verified accurate performance simulation model of direct thermosyphon solar water heater. ASME Journal of Solar Energy Engineering, 110: 282-292. Huang, B. J. (1980). Similarity theory of solar water heater with natural circulation. Solar Energy, 25: 105-116. Budihardjo, I., Morrison, G. L. and Behnia, M. (2007). Natural circulation flow through water-in-glass evacuated tube solar collectors. Solar Energy, 81: 1460-1472. Ibrahim, O., Fardoun, F. and Younes, R. (2014). Hasna Louahlia-Gualou, Review of water-heating systems: General selection approach based on energy and environmental aspects. Building and Environment, 72: 259286.

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Isravel, R. S., Raja, M., Saravanan, S. and Vijayan, V. (2020). Thermal augmentation in parabolic trough collector solar water heater using rings attached twisted tapes. Materials Today: Proceedings, 21: 127-129. Jerneck, A. and Olsson, L. (2013). A smoke-free kitchen: initiating community based coproduction for cleaner cooking and cuts in carbon emissions. Journal of Cleaner Production, 60: 208-18. Joudi, K. A. and Abd-Alzahra, H. A. A. (1984). An experimental investigation into the performance of a domestic forced circulation solar water heater under varying operating conditions. Energy Conversion Management, 24 (4): 377- 384. Kalogirou, S. A. (2000). Long-term performance prediction of forced circulation solar domestic water heating systems using artificial neural networks. Applied Energy, 66: 63-74. Kalogirou, S. A. (2014) Solar energy engineering. Elsevier publications, USA Kalogirou, S. A. and Llyod, S. (1992). Use of solar parabolic trough collectors for hot water production in Cyprus- a feasibility study. Renewable Energy, 2: 117-124. Kalogirou, S. A. and Tripanagnostopoulos, Y. (2006). Hybrid PV/T solar systems for domestic hot water and electricity production. Energy Conversion and Management, 47: 3368–3382. Laughton, C. (2010). Solar domestic water heating, the Earthscan expert handbook for planning, design and installation. Earthscan ltd., London Liu, Y., Chung, K., Chang, K. and Lee, T. (2012). Performance of thermosyphon solar water heaters in series. Energies, 5: 3266-3278. Luo, Q., Tang, G., Liu, Z. and Wang, J. (2005). A novel water heater integrating thermoelectric heat pump with separating thermosiphon. Applied Thermal Engineering, 25: 2193–2203. Mandal, S. and Ghosh, S. K. (2020). Experimental investigation of the performance of a double pass solar water heater with reflector. Renewable Energy, 149: 631-640. Maraj, A., Londo, A., Gebremedhin, A. and Firat, C. (2019). Energy performance analysis of a forced circulation solar water heating system

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equipped with a heat pipe evacuated tube collector under the Mediterranean climate conditions. Renewable Energy, 140: 874-883. Marmoush, M. M., Rezk, H., Shehata, N., Henry, J. and Gomaa, M. R. (2018). A novel merging tubular daylight device with solar water heater -experimental study. Renewable Energy, 125: 947-961. McVeigh, J. C. (1983). Sun Power, an introduction to the applications of solar energy. Second Ed., Pergamon Press, Great Britain. Michael, J. J. and Iniyan, S. (2015). Performance of copper oxide/water nanofluid in a flat plate solar water heater under natural and forced circulations. Energy Conversion and Management, 95: 160-169. Mishra, C. B. and Bhatt, A. K. (1981). Performance study of forced circulation solar water heaters using packed bed collectors. Energy Conversion Management, 21: 121-123. Nahar, N. M. (2003). Year round performance and potential of a natural circulation type of solar water heater in India. Energy and Buildings 35: 239-247. Norton, B. and Probert, S. D. (1983). Achieving thermal rectification in natural-circulation solar-energy water heaters. Applied Energy, 14: 211225. Norton B. and Probert, S. D. (1984). Measured performances of naturalcirculation solar energy water-heaters. Applied Energy 16: 1-26. Norton, B. and Probert, S. D. (1986). Thermosyphon solar energy water heaters, in Advances in Solar Energy, Kluwer Pub, 125-170. Norton, B. and Edmonds, J. E. J. (1991) Aqueous propylene-glycol concentrations for the freeze protection of thermosyphon solar energy water heaters. Solar Energy, 47: 375-382. Norton, B. (1992). Solar energy thermal technology. Springer-Verlag, London. Norton, B. (2011). Solar water heaters: a review of systems research and design innovation, Green, 1: 189-207. Norton, B. (2014). Harnessing solar heat. Springer-Verlag, USA Riahi A. and Taherian, H. (2011). Experimental investigation on the performance of thermosyphon solar water heater in the south Caspian sea, Thermal Science, 15 (2): 447-456.

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Sadeghi, G., Safarzadeh, H., Bahiraei, M., Ameri, M. and Raziani, M. (2019). Comparative study of air and argon gases between cover and absorber coil in a cylindrical solar water heater: an experimental study. Renewable Energy, 135: 426-436. Saxena, A., Agarwal, N. and Lath, S. (2013). Impacts of biomass burning on living areas. Teri Information Digest on Energy and Environment (TIDEE), 12: 1-6. Saxena, A. and Agarwal, N. (2018). Performance characteristics of a new hybrid solar cooker with air duct. Solar Energy, 159: 628-637. Saxena, A., Srivastava, G. and Goel, V. (2012). A technical note- on performance testing of a solar box cooker provided with sensible storage material on the surface of absorbing plate. International Journal Renewable of Energy Technology, 3: 165-173. Saxena, A. and Srivasatva, G. (2012). Potential and economics of solar water heater, MIT International Journal of Mechanical Engineering, 2: 97104. Saxena, A. and Srivastava, G. (2013). Performance studies of a multipurpose solar energy system for remote areas. MIT International Journal of Mechanical Engineering, 3: 21–33. Saxena, A. and Goel, V. (2013). A technical note on- fabrication and thermal performance studies of a solar pond model. Journal of Renewable Energy, Article ID 475282: 1-5. Saxena, A. and Goel, V. (2013). Solar air heaters with thermal heat storages. Chinese Journal of Engineering, Article ID 190279: 1-11 Saxena, A., Goel, V. and El-Sebaii, A. A. (2015). A thermodynamic review of solar air heaters. Renewable and Sustainable Energy Reviews, 43: 863-890. Saxena, A., Goel, V. and Karakilcik, M. (2018). Solar food processing and cooking methodologies. Applications of Solar Energy, Springer-Nature Series: 251-294. Saxena, A., Verma, P., Srivasatva, G. and Nandkishore. (2020). Design and thermal performance evaluation of an air heater with low cost thermal energy storage. Applied Thermal Engineering, 167: 114768.

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Sharma, A., Saxena, A., Sethi, M., Shree, V. and Goel, V. (2011). Life cycle assessment of buildings: a review. Renewable and Sustainable Energy Reviews, 15: 871–875. Sichilalu, S., Mathaba, T. and Xia, X. (2017). Optimal control of a wind– PV-hybrid powered heat pump water heater. Applied Energy, 185: 11731184. Siddiqui, M. A. (1997). Heat transfer and fluid flow studies in the collector tubes of a closed-loop natural circulation solar water heater, Energy Conversion Management, 38 (8): 799-812. Smyth, M., Pugsley, A., Hanna, G., Zacharopoulos, A., Mondol, J., Besheer, A. and Savvides, A. (2019). Experimental performance characterization of a hybrid Photovoltaic/solar thermal façade module compared to a flat integrated collector storage solar water heater module. Renewable Energy 137: 137-143. Sodha, M. S. and Tiwari, G. N. (1981). Analysis of natural circulation solar water heating systems. Energy Conversion Management, 21: 283-288. Sodha, M. S., Shukla, S. N. and Tiwari, G. N. (1982). Transient analysis of forced circulation solar water heating system. Energy Conversion Management, 22: 55-62. Solar heat worldwide, detailed market data 2018 (2020 Edition) Global Market Development and Trends in 2019, IEA Solar Heating & Cooling Programme, May 2020. Solar Water Heater - Global Market Outlook (2017-2026), published 2018. Solar Water Heater Market Size By Collector (Evacuated Tube, Flat Plate and Unglazed Water), By System (Thermosiphon, Pumped), By Application {Residential, Commercial (Educational Institutes, Offices, Government Buildings, Others), Industrial} Industry Analysis Report, Regional Outlook, Competitive Market Share & Forecast, 2019 – 2025, published 2018. Sterling, S. J. and Collins, M. R. (2012). Feasibility analysis of an indirect heat pump assisted solar domestic hot water system. Applied Energy, 93: 11–17.

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Sutthivirode, K., Namprakai, P. and Roonprasang, N. (2009). A new version of a solar water heating system coupled with a solar water pump. Applied Energy, 86: 1423–1430. Tewari, K. and Dev, R. (2019). Exergy, environmental and economic analysis of modified domestic solar water heater with glass-to-glass PV module. Energy, 170: 1130-1150. Varghese, J. S. and Manjunath, K. (2017). A parametric study of a concentrating integral storage solar water heater for domestic uses. Applied Thermal Engineering, 111: 734–744. Wanjiru, E. M., Sichilalu, S. M. and Xia, X. (2017). Optimal operation of integrated heat pump-instant water heaters with renewable energy, Energy Procedia, 105: 2151–2156. Open-sourcehttps://www.statista.com/statistics/260697/global-solarwater-heating-capacity/. Open source- https://solarwaterheaters02.weebly.com/the-history-of-solarwater-heaters.html. Open-sourcehttps://www.irena.org/remap/IRENA_REmap_UAE_ report_2015.pdf. Yamfang, M., Thepa, S. and Kongkiattikajorn, J. (2018). Development of a solar hot water system and investigation of the effects of soil density to inhibit microbial performance in soil with hot water dropping. Renewable Energy, 117: 28-36. Zelzouli, K., Guizani, A. and Kerkeni, C. (2014). Numerical and experimental investigation of thermosyphon solar water heater. Energy Conversion and Management, 78: 913–922.

APPENDIX 1 Important terms and cofficients: 1. Heat transfer coefficient (h) –It is proportionality constant between heat flux and the thermodynamic driving force for the flow of heat and unit is W/(m2°C). It is a quantifiable characteristic.

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Abhishek Saxena and Brian Norton 2. Overall heat transfer coefficient (U) -It refers to how well the heat is conducted over a sequence of resistant modes and unit is W/(m2°C). 3. Mass flow rate (m) - It is the mass of a substance that passes through a specific area with fixed velocity per unit of time and unit is kg/s. 4. Plate efficiency factor (Fp) - This can be estimated by considering the temperature distribution between 02 channels of the plate absorber and pretentious that the temperature gradient in the direction of flow is insignificant. 5. Friction factor (f) - It is the ratio of the shear stress on the bounding walls of the channel or pipes to dynamic pressure of coolant. It is a dimensionless number. 6. Thermal capacity (W) - It is the property of a substance or material to captivate heat when it is heated and to discharge heat when it is cooled. 7. Rate of heat flow (Q) – It is the amount of heat which is transferred per unit of time in some materials and it is measured in Watt. 8. Heat removal Factor (Fr) - It is defined as the quantity which relates the net useful energy gain of a absorber plate to the useful energy gain if the whole absorber surface are at the fluid inlet temperature 9. Initial Investment – It is the capital money over a business owner needs to purchase something for long term benefit or to start up a firm which include owners money, money borrowed by different sources. 10. Mortgage payment – It is a long-term loan intended to aid you purchase a costly product. 11. Maintenance cost – It is the cost associated with a product to keep it in in good condition through a regularly checkup and providing essential repairing 12. Replacement cost - It is the amount obligatory to replace an existing asset with a likewise valued or alike asset at the existing market price.

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13. Salvage value - It is the book value of an asset subsequently all depreciation is fully expensed. 14. Parasitic energy- It is a term used with respect to electrical appliances generally. It characterizes the power (energy) consumed by the system even it is shut off, that is standby power.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 3

DAILY COMPARISON ENERGY AND EXERGY ANALYSIS AND THERMAL ENERGY STORAGE PERFORMANCE OF SOLAR COLLECTORS Ayhan Atiz1, Hatice Karakilcik2, Abhishek Saxena3 and Mehmet Karakilcik4, 1

Department of Mathematics and Science Education, Alanya Alaaddin Keykubat University, Antalya, Turkey 2 Department of Geology Engineering, Cukurova University, Adana, Turkey 3 Moradabad Inst Technol, Dept Mech Engn, Moradabad, India 4 Department of Physics, Cukurova University, Adana, Turkey

ABSTRACT In this chapter, energy and exergy analyses of flat plate solar collectors (FPSCs), parabolic trough solar collectors (PTSCs) and evacuated tube 

Corresponding Author’s E-mail: [email protected].

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Ayhan Atiz, Hatice Karakilcik, Abhishek Saxena et al. solar collectors (ETSCs) were investigated for a day selected in January under daily solar radiation. For three different configurations, the surface area of each collector is considered as 50 m2, 100 m2, and 150 m2 separately. The analyses of the solar thermal system were carried out by using Engineering Equation Solver (EES) software under solar radiation from 8 a.m. to 17 p.m. The water at 9.5℃ is upgraded to higher degree by the solar collectors (SCs) and pumped to a storage tank. The energy and exergy efficiencies were found depending on the three different surface areas of each solar collector. The maximum energy efficiencies of FPSCs, ETSCs and PTSCs for the surface area of 50 m2 were found as 49.54%, 66.22% and 68.95%, and the maximum exergy efficiency were found as 5.30%, 9.05% and 7.14%, respectively. The maximum energy efficiencies of FPSCs, ETSCs and PTSCs for the surface area of 100 m2 were found as 38.43%, 55.09% and 68.96%, and the maximum exergy efficiency were found as 5.93%, 10.79% and 12.79%, respectively. The maximum energy efficiencies of FPSCs, ETSCs and PTSCs for the surface area of 150 m2 were found as 31.39%, 46.84% and 68.95%, and the maximum exergy efficiency were found as 5.69%, 10.63% and 17.10%, respectively. It was found that the energy efficiency of FPSCs and ETSCs decreased with the increase in surface area and their low exergy efficiency did not change significantly. However, it was found that the energy efficiency of PTSCs did not change, but the exergy efficiency was increased. Therefore, PTSCs have higher exergetic performance compared to other two solar collectors and can be preferred in high power generation.

NOMENCLATURE A C Ė Ėx ex h İ ṁ T

aperture area (m2) specific heat energy (W or kW) exergy (W or kW) specific exergy (kW/kg) enthalpy (kW/kg) solar radiation (W/m2) mass flow rate (kg/s) temperature (℃ or K)

Daily Comparison Energy and Exergy Analysis …

Greek Symbols η ψ Δ

efficiency exergy efficiency difference

Subscripts ETSCs dest destcol dr df FPSCs in loss m out PTSCs SCs s tot re U w 0

evacuated tube solar collectors destruction destruction collector direct diffuse flat plate solar collectors input losing mean output parabolic trough solar collectors solar collectors sun total reflected useful water reference

ABBREVIATIONS EES ETSC FPSC

engineering equation solver evacuated tube solar collector flat plate solar collector

61

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Ayhan Atiz, Hatice Karakilcik, Abhishek Saxena et al. PTSC SC

parabolic trough solar collector solar collector

1. INTRODUCTION In today’s world, environmental pollution and global warming are increasing due to the use of fossil fuels. In order to reduce these effects, intense studies have been done in the world. One of these studies is to obtain energy from renewable and clean sources. Solar energy is the most important clean and renewable energy source. Electrical and thermal energy can be produced by using solar energy. The produced energy is used in many places in the world (in industry, houses, factories, greenhouses, water treatment, etc.). The systems that convert solar energy into thermal energy are solar collectors. They have attracted a lot of attention for years due to their low costs and advantages (Ozturk 2012). Solar collectors are used for many years to supply hot water in buildings. Solar energy passes through the glass of the collector and transfers its energy to the water in the collector and it is obtaining hot water at a higher temperature than its initially temperature. Thus, the stored hot water in a tank can be used at any time whenever needed (Kalogirou 2004). The three most important solar collectors are given as follows: FPSCs, ETSCs and PTSCs. Studies about three collectors have been done on improving their efficiency. For example, the performance of the FPSCs was calculated for different absorbent surface layers (Bahadır et al. 2017). Parameters such as kind of material, thickness and area of the absorber plate of the FPSC have a great influence on their performance. (Jafarkazemi and Ahmadifard 2013). If the energy efficiency of the FPSCs is improved it can increase the temperature of liquids to higher temperature. Therefore, increasing the energy efficiency of the FPSCs is extremely important (Ziyadanogullari et al. 2018). In addition, the most researched collector in the world to produce domestic hot water is FPSCs (Yogi Goswami 2015). Another technology of solar collectors is ETSCs, which have good thermal performance and advantage in producing hot water (Chow et al.

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2011). ETSCs can be upgraded the temperature of the input water from lowgrade to high-grade by utilizing solar radiation in a short time (MartínezRodríguez et al. 2018). The hot water obtained by using ETSCs can be used for many different purposes. For example, it can meet significant amount of heat demand of a family (Kroll and Ziegler 2011). Also, ETSCs can be used for electricity generation by integrating with a geothermal source (Atiz, et al. 2019). The other solar collector is the PTSCs. It can increase the temperature of the fluid up to 300-400 degrees by using solar energy. PTSCs have been researched with incredible interest in recent years due to its good performance that can produce thermal energy at high temperatures (Yılmaz and Söylemez 2014). For example, PTSCs generates thermal energy through solar energy to operate different technologies for generating electrical energy (AlZahrani and Dincer 2018). Also, PTSCs can be used in a great range of applications such as, chemical processes, solar cooling, desalination, industrial heat, besides electrical energy generation (Kumar et al. 2020). Therefore, a lot of research is being done on PTSCs (Bellos et al. 2018). It is extremely important to understand how these collectors perform in the same conditions. Therefore, thermal efficiency, hydrogen and electricity production performances of ETSCs and FPSCs were examined in Adana. As a result, it was found that ETSCs performed better than FPSCs (Atiz and Karakilcik 2020). Also, ETSCs was found to be economically better than FPSCs by 41% (Sokhansefat et al. 2018). ETSCs and PTSCs were investigated in terms of power generation and cost for three different zone (Qin et al. 2017). In this study, the energetic and exergetic efficiencies of FPSCs, ETSCs and PTSCs were investigated for climatic conditions in Adana. The performance of these collectors was evaluated in January. In the studies carried out so far, energy and exergy efficiencies of FPSCs, ETSCs and PTSCs have not been compared for Adana. Therefore, the aim of this study is to determine how the performances of these collectors change according to the aperture area of the collectors for a sunny day in the winter. Thus, it can be found which collector performs better than others. This study will

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contribute to the literature in terms of evaluating the thermodynamic performances of these collectors under same conditions. All these analyze were performed by using Engineering Equation Solver (EES) software. As a result, these collectors produce thermal energy from solar radiation without any harm the environment.

2. SYSTEM DESCRIPTION Figure 1 shows the integrated system that consists of SCs, a hot water storage tank and a house. By using the SCs one by one, studies were carried out on the energy and exergy efficiency of each. SCs have been used efficiently in the fields such as obtaining hot water, heating building, air conditioning applications, industrial processes and the production of electricity. The aim of this study is to produce high amount of thermal energy for space heating and hot water for domestic usage. For this purpose, temperature of the water that coming from city water network entering the collector from the point 2 is raised by SCs harvesting solar radiation and sent to the storage tank. Thus, hot water requirement of a house can be provided by this system.

Figure 1. Solar thermal integrated system.

Daily Comparison Energy and Exergy Analysis …

65

3. ANALYSES OF THE SYSTEM Thermodynamic analyses were performed to evaluate the all system energetically and exergetically. Thus, energy and exergy balance equations for all the components in the system were formulated. For this aim, mass, energy and exergy balance equations are given for each component and afterwards the energy and exergy distributions energetic and exergetic performance and exergy destruction in the SCs are found. Most of energy entering the system is supplied by the SCs from solar radiation and little is entered by pump and city water. The mass balance equation for the SCs can be given as follows: ṁ2 = ṁ3

(1)

where ṁ2 and ṁ3 are the input and output mass flow rates of the SCs. The energy balance equation for the SCs is given as follows: Ėin = Ėout

(2)

Ėin = ṁ2 h2 + ĖSCs

(3)

Ėout = ṁ3 h3 + Ėloss,SCs

(4)

When the equation 3 and 4 is substituted in the equation 2 yields the equation 5. ṁ2 h2 + ĖSCs = ṁ3 h3 + Ėloss,SCs

(5)

where h2 and h3 are the enthalpies at point 2 and 3, ĖSCs is the total solar energy reaching the SCs and Ėloss,SCs is the loss energy in the SCs. The exergy balance equation for the SCs can be found as follows: Ėxin = Ėxout

(6)

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Ayhan Atiz, Hatice Karakilcik, Abhishek Saxena et al. Ėxin = ṁ2 ex2 + ĖxSCs

(7)

Ėxout = ṁ3 ex3 + Ėxloss,SCs + Ėxdest,SCs

(8)

When the equation 7 and 8 is substituted in the equation 6 yields the equation 9. ṁ2 ex2 + ĖxSCs = ṁ3 ex3 + Ėxloss,SCs + Ėxdest,SCs

(9)

where ex2 and ex3 are the specific exergy at point 2 and 3, Ė𝑥SCs is the total solar exergy reaching the SCs, Ė𝑥loss,SCs is the loss exergy in the SCs and Ėxdest,SCs is the exergy destruction in the SCs.

3.1. Energy and Exergy Analyses of the SCs The temperature of city water, daily solar radiation and air temperature affect the energetic and exergetic performances of SCs and also exergy destruction. Some part of the thermal energy produced by SCs transfers to the environment and other remaining part transfers to the water as useful energy. Balance equation for the SCs is written as: ĖSCs = ĖU + Ėloss,SCs

(10)

ĖSCs = İSCs ASCs

(11)

where İSCs is the incident solar radiation, ASCs is the total aperture area of the SCs. ĖU is the useful energy of the SCs and given as (Duffie and Beckman 2013): ĖU = ṁw Cw (T3 − T2 )

(12)

Daily Comparison Energy and Exergy Analysis …

67

where ṁw is the input mass flow rate of the SCs, Cw is the specific heat of water. T2 and T3 are the inlet and outlet temperatures for the SCs, respectively. Energy efficiency for the SCs is given as: 𝜂SCs =

ĖU ĖSCs

(13)

𝜂SCs =

ṁw Cw (T3 −T2 ) İSC ASCs

(14)

where 𝜂SCs is the energy efficiency of the SCs. Since PTSCs, ETSCs and FPSCs are used in this system one by one, energy efficiency equation for each collector should be written separately. For this purpose, firstly solar radiation reaching the SCs should be found. Total incident solar radiation for inclined surface (İSC ) for FPSCs and ETSCs can be given as follows (Duffie and Beckman 2013): İSC = İdr + İdf + İre

(15)

İdr = İb R b

(16)

cos θ cos θz

(17)

Rb =

where θ is the angle of incidence for the FPSCs and θz is the zenith angle for the ETSCs. These angles can be written for the northern hemisphere as follows: cos θ = sin δ sin(∅ − β) + cos δ cos(∅ − β) cos w

(18)

cos θz = sin δ sin ∅ + cos δ cos ∅ cos w

(19)

1 İdf = 2 İd (1 + cos β)

(20)

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Ayhan Atiz, Hatice Karakilcik, Abhishek Saxena et al. 1 İre = 2 ρİ(1 − cos β)

(21)

where İdr is the direct solar radiation on the SCs, İdf is the diffuse solar radiation on the SC, İre is the reflected radiation from the environment to the surface of the SC, İb is the direct solar radiation, İd is the diffuse solar radiation, Rb is the direct radiation coefficient, β is the slope angle of the collector, δ is the declination angle, ∅ is the latitude of the city, w is the hour angle, ρ is the surface reflection rate and İ is the sum of the beam and diffuse solar radiation, respectively. The energetic performance of the SCs depends on the solar radiation that reaches the SCs and it can be found from eqs.15. However, solar radiation on the surface of the PTSCs is different than solar radiation on the FPSCs and ETSCs due to it follows the sun from east to west. Energetic performance of the PTSCs can be obtained as follows (Arasu and Sornakumar 2007): 𝜂PTSCs = 0.69 − 0.39(Tin − T0 )⁄İbm

(22)

İbm = İb R bm

(23)

R bm =

cos θwe cos θz

(24)

Angel of incident can be found from east to west from [18]: cos θwe = √1 − cos2 δ sin2 w

(25)

where Tin is the inlet temperature of the PTSCs that equals to T2 and T0 is the environment temperature. In addition, energy efficiencies of the ETSCs and FPSCs depend on the mean and environment temperatures and total incident solar radiation for inclined surface (İSCs ). Thus, energy efficiencies of the ETSCs and FPSCs can be found as follows (Ucar and Inalli 2008):

Daily Comparison Energy and Exergy Analysis … 𝜂ETSCs = 0.84 −

2.02(Tm −T0 ) − İSC

𝜂FPSCs = 0.70 − 3.4

(T −T ) 0.0046İSCs [ mİ 0 ]

69

2

SC

(Tm −T0 ) İSC

(26)

(27)

where Tm is the mean temperature of the FPSCs and ESCs. Tm =

T2 +T3 2

(28)

Exergy balance equation for the SCs can be written as given: Ėxin = ĖxU + Ėxloss + Ėxdestcol

(29)

Also, exergy destruction in the SCs can be found as follows: Ėx

𝜓SCs = Ėx U = 1 − in

Ėxloss +ĖxdestSCs Ėxin

(30)

where Ė𝑥in is the total solar exergy reaching the SCs, ĖxU is the useful exergy of the SCs, Ėxloss is the exergy loss in the SCs and Ė𝑥destSCs is the exergy destruction in the collectors. The total exergy of the selected surface should be found for a better understanding of the system. Thus, the system can be better evaluated in terms of thermodynamics. The total exergy (Ėxsolar ) for the selected surface that depends on solar radiation can be given as follows (Petela 2003): 4

4 T +273 1 T +273 Ėxsolar = Ėtot [1 − 3 ( 0 T ) + 3 ( 0 T ) ] s

s

(31)

where Ėtot is the total solar radiation for the selected surface area of the SCs.

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4. RESULTS In this chapter, energy and exergy analysis of FPSCs, ETSCs and PTSCs were carried out for the same environment condition. Since these collectors can increase the temperature of water by solar energy, solar energy reaching the horizontal surface and the average temperature of each month should be known. Thus, it can be found how the performance of these collectors was affected in January. Figure 2 shows solar energy and temperature distribution on a horizontal surface for each month for a year. The monthly solar energy and temperature distributions for the Adana were taken from Adana Regional Meteorology Station.

Figure 2. Solar energy, exergy and temperature distributions.

As seen in Figure 2, the maximum solar energy reaching the horizontal surface for Adana is 756 MJ/m2, 792 MJ/m2 and 735 MJ/m2 for June, July and August, respectively. The maximum solar exergy reaching the horizontal surface is 706 MJ/m2, 739 MJ/m2 and 686 MJ/m2 for June, July and August, respectively. The minimum solar energy reaching the horizontal surface for Adana is 269 MJ/m2, 240 MJ/m2and 226 MJ/m2 for November,

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December and January, respectively. The minimum solar exergy reaching the horizontal surface for Adana is 251 MJ/m2, 225 MJ/m2 and 212 MJ/m2 for November, December and January, respectively. The minimum average temperature of the air is 9.50℃, 10.50℃ and 11.2℃ for January, February and December, respectively. It is seen that the amount of solar energy reaching the surface and the average air temperature drops significantly in winter. Therefore, it is understood that the highest thermal energy requirement is in January. As the solar energy coming to the horizontal surface increases in the summer, the average air temperature reaches up higher degree than in the winter months. Thus, the need for thermal energy decreases in the summertime. However, a great amount of thermal energy is needed during the winter months, especially in January. Therefore, analysis of this system was done in January. In this work, the temperature of the water coming from the city water network was upgraded by using SCs that have 50 m2, 100 m2 and 150 m2 aperture areas for three different configurations. For this purpose, solar radiation and exergy distributions on the surface of the SCs was found in order to make thermodynamic evaluation. Thus, the total solar energy and exergy on the surface of the SCs should be found under daily reaching solar radiation. Figure 3 shows average solar energy and exergy distributions on the surface of the FPSCs and ETSCs between the hours of 0800 - 1700. Solar energy and exergy reaching the surface varies due to shape of collectors and sun position. Since FPSCs and ETSCs are inclined solar collectors, the same amount of solar energy and exergy reach their surfaces. However, since PTSCs follow the sun, the solar energy and exergy reaching its surface is different than FPSCs and ETSCs. The minimum and maximum solar energy on the FPSCs and ETSCs were found as 1.92 kW and 27.01 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 50 m2. The minimum and maximum solar energy on the FPSCs and ETSCs were found as 3.84 kW and 54.02 kW between the hours of 1100 1300 and 1600 - 1700 for aperture area of 100 m2. The minimum and maximum solar energy on the FPSCs and ETSCs were found as 5.76 kW and 81.03 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 150 m2.

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Solar exergy reaching the surface of FPSCs and ETSCs is calculated with equation 31.The minimum and maximum solar exergy on the FPSCs and ETSCs were found as 1.79 kW and 25.25 kW between the hours of 1100 1300 and 1600 - 1700 for aperture area of 50 m2. The minimum and maximum solar exergy on the FPSCs and ETSCs were found as 3.59 kW and 50.49 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 100 m2. The minimum and maximum solar exergy on the FPSCs and ETSCs were found as 5.38 kW and 75.74 kW between the hours of 1100 - 1300 and 1600 1700 for aperture area of 150 m2. Solar energy and exergy on the PTSCs depends on the direct beam radiation. Therefore, energy and exergy on the PTSCs are found in different way than the FPSCs and ETSCs. Figure 4 shows solar energy and exergy distributions on the surface of the PTSCs for the aperture area of 50 m2, 100 m2 and 150 m2 between the hours of 0800 - 1700. The minimum and maximum solar energy on the PTSCs were found as 2.37 kW and 18.69 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 50 m2. The minimum and maximum solar energy on the PTSCs were found as 4.75 kW and 37.38 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 100 m2. The minimum and maximum solar energy on the PTSCs were found as 7.12 kW and 56.07 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 150 m2. The minimum and maximum solar exergy on the PTSCs were found as 2.22 kW and 17.47 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 50 m2. The minimum and maximum solar exergy on the PTSCs were found as 4.44 kW and 34.94 kW between the hours of 1100 1300 and 1600 - 1700 for aperture area of 100 m2. The minimum and maximum solar exergy on the PTSCs were found as 6.66 kW and 52.41 kW between the hours of 1100 - 1300 and 1600 - 1700 for aperture area of 150 m2. The maximum value of solar energy and exergy on the SCs were measured between the hours of 1100 - 1300. The minimum value of solar radiation and exergy on the SCs were measured between the hours of 1600 - 1700.

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Figure 3. Solar energy and exergy on the FPSCs and ETSCs from 8 a.m. to 17 p.m.

Figure 4. Solar energy and exergy on the PTSCs from 8 a.m. to 17 p.m.

Output temperatures of the SCs are affected by input water temperature, solar radiation and air temperature. So, these output temperatures also affect the storage temperature. Therefore, the output temperatures of the SCs were found.

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Figure 5. Output temperature of the FPSCs, ETSCs and PTSCs from 8 a.m. to 17 p.m.

Figure 5 shows the output temperature of FPSCs, ETSCs and PTSCs for the aperture area of 50 m2, 100 m2 and 150 m2 between 8 a.m. and 17 p.m. The maximum and minimum output temperatures of FPSCs are 74.02℃ and 14.28℃ between the hours of 1100 - 1300 and 1600 - 1700 for the surface area of 50 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of FPSCs are 109.3℃ and 16.65℃ between the hours of 1100 - 1300 and 1600 - 1700 for the surface area of 100 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of FPSCs are 131.7℃ and 18.14℃ between the hours of 1100 - 1300 and 1600 - 1700 for the surface area of 150 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of ETSCs are 95.58℃ and 16.01℃ between the hours of 1100 - 1300 and 1600 - 1700 for the surface area of 50 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of ETSCs are 148.8℃ and 20.04℃ between the hours of 1100 - 1300 and 1600 - 1700 for the surface area of 100 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of ETSCs are 183.8℃ and 22.91℃ between the hours of 1100

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- 1300 and 1600 - 1700 for the surface area of 150 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of PTSCs are 71.65℃ and 17.08℃ between the hours of 1100 - 1300 and 1600 - 1700 for the surface area of 50 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of PTSCs are 133.3℃ and 25.59℃ between the hours of 1100 - 1300 and 1600 - 1700 for the surface area of 100 m2 when the input water temperature is 10℃. The maximum and minimum output temperatures of PTSCs are 195℃ and 33.39℃ between the hours of 1100 1300 and 1600 - 1700 for the surface area of 150 m2 when the input water temperature is 10℃. While the aperture area of the collectors is 50 m2, ETSCs show the best performance among the three collectors. However, when the aperture area of the SCs is 150 m2, PTSCs perform better than the other two collectors. Table 1 shows hourly energy efficiencies of the SCs for the aperture area of 50 m2, 100 m2 and 150 m2 from 8 a.m. to 17 p.m. The maximum and minimum energy efficiencies of the SCs were found between the hours of 1100 - 1300 and 1600 - 1700, respectively. It was found that the energy efficiencies of FPSCs and ETSCs decreased with the increase of aperture area but energy efficiency of the PTSCs did not change. In addition, increasing the aperture area significantly reduced the energy efficiency of the FPSCs and ETSCs. PTSCs showed the highest energetic performance among three collectors. Figure 6 shows hourly exergetic performance of the SCs. One of the important thermodynamic data of the system is exergetic performance of the SCs. This parameter is also known as the second law of thermodynamics. This parameter provides an important thermodynamic data about the SCs. The maximum and minimum exergetic performances of the FPSCs were found as 5.30% and 0.46% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 50 m2. The maximum and minimum exergetic performances of the FPSCs were found as 5.93% and 0.51% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 100 m2. The maximum and minimum exergetic performances of the FPSCs were

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found as 5.69% and 0.50% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 150 m2. Table 1. Energy efficiencies of the SCs (%)

Hour 8-9 9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-17

FPSCs (m2) 50 100 49.22 38.18 49.44 38.35 49.51 38.41 49.54 38.43 49.54 38.43 49.51 38.41 49.44 38.35 49.22 38.18 46.62 36.16

150 31.19 31.33 31.37 31.39 31.39 31.37 31.33 31.19 29.54

ETSCs (m2) 50 100 66.73 55.08 66.52 54.43 66.33 53.95 66.22 53.70 66.22 53.70 66.33 53.95 66.52 54.43 66.73 55.08 65.42 54.61

150 46.71 45.79 45.14 44.82 44.82 45.14 45.79 46.71 46.84

PTSCs (m2) 50 100 68.88 68.88 68.93 68.93 68.94 68.94 68.95 68.95 68.95 68.95 68.94 68.94 68.93 68.93 68.88 68.88 68.59 68.59

150 68.88 68.93 68.94 68.95 68.95 68.94 68.93 68.88 68.59

Figure 6. Exergetic performance of the FPSCs, ETSCs and PTSCs from 8 a.m. to 17 p.m.

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The maximum and minimum exergetic performances of the ETSCs were found as 9.05% and 0.85% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 50 m2. The maximum and minimum exergetic performances of the ETSCs were found as 10.79% and 1.11% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 100 m2. The maximum and minimum exergetic performances of the ETSCs were found as 10.69% and 1.19% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 150 m2. The maximum and minimum exergetic performances of the PTSCs were found as 7.14% and 1.12% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 50 m2. The maximum and minimum exergetic performances of the PTSCs were found as 12.64% and 2.07% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 100 m2. The maximum and minimum exergetic performances of the PTSCs were found as 17.10% and 3% between the hours of 1100 – 1300 and 1600 – 1700 for the aperture area of 150 m2.

Figure 7. Exergy destruction of the FPSCs, ETSCs and PTSCs from 8 a.m. to 17 p.m.

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When the aperture area of the SCs is changed, it is seen that they exhibit different exergetic performance. For example, when the aperture area of FPSCs is increased from 100 m2 to the 150 m2, exergetic performance decreases slightly. ETSCs have a maximum exergetic performance while having aperture area of 100 m2 between the hours of 1100 - 1300. When the exergetic performances of the SCs are examined, the highest performance was showed by the PTSCs that have aperture area of 150 m2. Figure 7 shows hourly exergy destruction in the SCs. The main reason of SCs have different exergetic performance is the exergy destruction. When the exergy destruction in the SCs increases, the exergetic performance decreases. The maximum and minimum exergy destructions in the FPSCs were found as 22.50 kW and 1.778 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 50 m2. The maximum and minimum exergy destructions of the FPSCs were found as 42.48 kW and 3.539 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 100 m2. The maximum and minimum exergy destructions of the FPSCs were found as 61.51 kW and 5.294 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 150 m2. The maximum and minimum exergy destructions of the ETSCs were found as 21.75 kW and 1.772 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 50 m2. The maximum and minimum exergy destructions of the ETSCs were found as 40.09 kW and 3.517 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 100 m2. The maximum and minimum exergy destructions of the ETSCs were found as 57.12 kW and 5.248 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 150 m2. The maximum and minimum exergy destructions of the PTSCs were found as 15.64 kW and 2.184 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 50 m2. The maximum and minimum exergy destructions of the PTSCs were found as 28.43 kW and 4.306 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 100 m2. The maximum and minimum exergy destructions of the PTSCs were

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found as 39.13 kW and 6.369 kW between the hours of 1100 - 1300 and 1600 - 1700 for the aperture area of 150 m2. Increasing the aperture area of the SCs caused to different exergy destructions in the collectors. As the aperture area increased, exergy destruction also increased in the SCs. While the highest exergy destruction was occurred in the FPSCs, the least exergy destruction was occurred in the PTSCs. One of the most important parameters that affect the energetic and exergetic performance is the air temperature. So far, the air temperature was taken as 9.5℃ at this study. Finding how the air temperature affects the performance of the collectors allows us to obtain important data about thermodynamics of the collectors. To accomplish this aim, the air temperature was varied from 0℃ to 20℃ between the hours of 1200 - 1300. Thus, both energy and exergy performances of the SCs were obtained. Table 2 shows energetic performance of the solar collectors between the hours of 1200 - 1300. The increase in the air temperature did not affect the energy efficiency of the SCs under constant solar radiation. Figure 8 shows the exergetic performance of the SCs when the air temperature changes from 0℃ to 20℃. There is an important relationship between the air temperature and exergetic performance. The maximum and minimum exergetic performances of the FPSCs were found as 5.45% and 5.15% at 0℃ and 20℃ for the aperture area of 50 m2. The maximum and minimum exergetic performances of the FPSCs were found as 6.09% and 5.77% at 0℃ and 20℃ for the aperture area of 100 m2. The maximum and minimum exergetic performances of the FPSCs were found as 5.84% and 5.55% at 0℃ and 20℃ for the aperture area of 150 m2. The maximum and minimum exergetic performances of the ETSCs were found as 9.29% and 8.80% at 0℃ and 20℃ for the aperture area of 50 m2. The maximum and minimum exergetic performances of the ETSCs were found as 11.05% and 10.52% at 0℃ and 20℃ for the aperture area of 100 m2. The maximum and minimum exergetic performances of the ETSCs were found as 10.87% and 10.38% at 0℃ and 20℃ for the aperture area of 150 m2.

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Ayhan Atiz, Hatice Karakilcik, Abhishek Saxena et al. Table 2. Energy efficiencies of the SCs from 0℃ to 20℃ Air Temp.(℃) 0 2.5 5 7.5 10 12.5 15 17.5 20

FPSCs (m2) 50 100 49.54 38.43 49.54 38.43 49.54 38.43 49.54 38.43 49.54 38.43 49.54 38.43 49.54 38.43 49.54 38.43 49.54 38.43

150 31.39 31.39 31.39 31.39 31.39 31.39 31.39 31.39 31.39

ETSCs (m2) 50 100 66.22 53.7 66.22 53.7 66.22 53.7 66.22 53.7 66.22 53.7 66.22 53.7 66.22 53.7 66.22 53.7 66.22 53.7

150 44.82 44.82 44.82 44.82 44.82 44.82 44.82 44.82 44.82

PTSCs (m2) 50 100 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95

150 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95 68.95

Figure 8. Exergetic performance of the FPSCs, ETSCs and PTSCs from 0℃ to 20℃.

The maximum and minimum exergetic performances of the PTSCs were found as 7.34% and 6.94% at 0℃ and 20℃ for the aperture area of 50 m2. The maximum and minimum exergetic performances of the PTSCs were found as 12.96% and 12.32% at 0℃ and 20℃ for the aperture area of 100 m2.

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The maximum and minimum exergetic performances of the PTSCs were found as 17.48% and 16.70% at 0℃ and 20℃ for the aperture area of 150 m2. As the air temperature increases, exergetic performance of the SCs decreases slightly. PTSCs for the aperture area of 150 m2 have the highest performance among three collectors. FPSCs for all aperture areas have the lowest performance among three collectors.

CONCLUSION In this paper, energetic and exergetic performance of FPSCs, ETSCs and PTSCs were investigated and compared for energy and exergy analyses for the aperture areas of 50 m2, 100 m2 and 150 m2 between the hours of 0800 1700. PTSCs have the best energetic performance among three collectors for all aperture areas and at all hours of the day. FPSCs have the worst energetic performance among three collectors. The energetic performance of FPSCs and ETSCs decreases while the aperture area increases. However, this increase not cause any change on the energetic performance of PTSCs. When the SCs are examined in terms of exergy, it is seen that PTSCs have the best performance; FPSCs have the worst performance as in energy comparison. In terms of outlet water temperature, PTSCs have the best performance and FPSCs have the worst performance as in the energy and exergy comparison. Increasing air temperature did not affect the energetic efficiency of all collectors, but it decreased the exergetic efficiency. As a result, it was found that the significant amounts of thermal energy can be produced by the SCs. Nowadays the use of such a system can be very convenient in terms of thermal energy production besides other energy systems. If the performance of the collectors can be improved much more, thermal energy can be produced more efficiently and it can be used whenever needs.

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REFERENCES AlZahrani, A. A., Dincer, I. (2018). Energy and exergy analyses of a parabolic trough solar power plant using carbon dioxide power cycle. Energy Conversion and Management, 158, 476–488. Arasu, A. V., Sornakumar, T. (2007). Design, manufacture and testing of fiberglass reinforced parabola trough for parabolic trough solar collectors. Solar Energy, 81, 1273–1279. Atiz, A., Karakilcik, H., Erden, M., Karakilcik, M. (2019). Investigation energy, exergy and electricity production performance of an integrated system based on a low-temperature geothermal resource and solar energy. Energy Conversion and Management, 195, 798–809. Atiz, A., Karakilcik, M. (2020). Comparison of heat efficiencies of flat-plate and vacuum tube collectors integrated with Organic Rankine Cycle in Adana climate conditions. Pamukkale University Journal of Engineering Sciences, 26(1), 106-112. Bahadır, M., Özdemir, M., Yatarkalkmaz, M., Dağli, G. (2017). Experimental analysis of flat plate collectors with different absorber surface types. Journal of Polytechnic, 20(2), 441-449, 2017. Bellos, E., Tzivanidis, C., Tsimpoukis, D. (2018). Enhancing the performance of parabolic trough collectors using nanofluids and turbulators. Renewable and Sustainable Energy Reviews, 91, 358–375. Chow, T. T., Dong, Z., Chan, L. S., Fong, K. F., Bai, Y. (2011). Performance evaluation of evacuated tube solar domestic hot water systems in Hong Kong. Energy and Buildings, 43, 3467–3474. Duffie, J. A., Beckman, W. A. (2013). Solar engineering of thermal process. Fourth Edition, Wiley Interscience, New York. Jafarkazemi, F., Ahmadifard, E. (2013). Energetic and exergetic evaluation of flat plate solar collectors. Renewable Energy, 56, 55-63. Kalogirou S. A. 2004. Solar thermal collectors and applications. Progress in Energy and Combustion Science, 30, 231–295. Kroll, J. A, Ziegler, F. (2011). The use of ground heat storages and evacuated tube solar collectors for meeting the annual heating demand of familysized houses. Solar Energy, 85, 2611–2621.

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Kumar, A., Sharma, M., Thakurd, P., Thakur, K. V., Rahatekar, S. S., Kumar, R. (2020). A review on exergy analysis of solar parabolic collectors. Solar Energy, 197, 411–432. Martínez-Rodríguez, G., Fuentes-Silva, A. L., Picon-Núnez, M. (2018). Solar thermal networks operating with evacuated-tube collectors. Energy, 146, 26-33. Ozturk, H. (2012). Solar energy and applications. Birsen Publisher. Petela, R. (2003). Exergy of undiluted thermal radiations. Solar Energy, 74, 469-488. Qin, J., Hu, E., Nathan, J. G., Chen, L. (2017). Concentrating or nonconcentrating solar collectors for solar Aided Power Generation? Energy Conversion and Management, 152, 281–290. Sokhansefat, T., Kasaeian, A., Rahmani, K., Haji Heidari A. H., Aghakhani F., Mahian O. (2018). Thermoeconomic and environmental analysis of solar flat plate and evacuated tube collectors in cold climatic conditions. Renewable Energy, 115, 501-508. Ucar, A., Inalli, M. (2008). Thermal and economic comparisons of solar heating systems with seasonal storage used in building heating. Renewable Energy, 33, 2532– 2539. Yılmaz, H. I., Söylemez, M. S. (2014). Thermo-mathematical modeling of parabolic trough collector. Energy Conversion and Management, 88, 768–784. Yogi Goswami, D. (2015). Principles of solar engineering, third ed. CRC Press Taylor & Francis Group. Ziyadanogullari, N. B., Yucel, H. L., Yildiz, C. (2018). Thermal performance enhancement of flat-plate solar collectors by means of three different nanofluids. Thermal Science and Engineering Progress, 8, 55-65.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 4

STEAM GENERATION FOR PROCESS APPLICATIONS USING SOLAR WATER HEATING ENABLED BY NANOFLUIDS Y. Raja Sekhar1,2,*, E. Porpatham1, Abel Rouboa3, Khalid Bouziane4, K. V. Sharma5, I.M. Mahbubul6 and Anil Singh1 1

School of Mechanical Engineering, Vellore Institute of Technology, Vellore, India 2 Center for Disaster Management and Mitigation (CDMM), Vellore Institute of Technology, Vellore, India 3 Escola de Ciencias e Tecnologias, Departamento de Engenharias, Universidade de Trás-os-Montes e Alto Douro – UTAD, Quinta de Prados, Vila Real, Portugal 4 School of Renewable Energies & Petroleum Studies, Université Internationale de Rabat, Morocco 5 Centre for Energy studies, JNTUH College of Engineering, Hyderabad, India 6 Institute of Energy Engineering, Dhaka University of Engineering & Technology, Dhaka, Bangladesh *

Corresponding Author’s E-mail: [email protected].

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ABSTRACT Global challenges such as climate change and depleting conventional sources are threatening human existence. In most industries, steam is a basic form of an energy source used in multiple processes. Steam generation is used in various processes, including water purification, distillation, and power plants. Conventional methods of steam generation cause energy losses. Thus, employing advanced scientific methods in industrial processes is essential to balance economy and ecology. A recent development is that steam generation at the industrial scale possible with energy from solar concentrator by using nanofluids as an absorption medium. This chapter deals with the feasibility to use titanium dioxide nanofluid as an absorbing medium to generate steam. Steam generation efficiency was inferred through lab-scale experiments carried out under different operating conditions. The experiment setup was initially validated using water, and the results are in agreement with the literature. The efficiency of the system was 32.23% at an irradiance of 683 W/m2. Further, the economics of the proposed process was determined to estimate commercial feasibility in industries. Finally, suggestions regarding how nanofluids can be incorporated into various industries for steam generation systems either as a complementary system during excess load or as a standalone application were discussed.

1. INTRODUCTION 1.1. Background Currently, scientific advances, along with innovations, have made human life comfortable. Contrary to these advances, the adverse effects on humans in the long term such as climate change and polar ice cap melting, have often been ignored by engineering practitioners. Thus, it is time that the scientific community adopts sustainable development practices reflected in the sustainable development goals (SDG) of UNDP. Sustainability refers to utilizing resources and scientific evidence to develop new ventures that maintain ecological balance and construct more established undertakings. Renewable energy can provide sustainable solutions for challenges encountered in the modern world. The development of products based on

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photovoltaic cells and Scheffler dishes have proven that Sun energy can produce energy for various industries. Because of its latent heat of vaporization, steam can be an essential form of energy storage useful in multiple processes for most industries, including power and pharmaceuticals. In common practice, specific processes require different steam quality and quantity for desalination plants hospitals, power plants, etc. Usually, a power plant has a boiler operated on conventional energy sources, such as coal, to achieve a higher steam volume. However, an eco-friendly steam generation technique is the future need using solar concentrator technologies to obtain either low or high volumes. Nanofluids with favourable stability and light absorption capability can demonstrate high efficiency in volumetric solar steam generation, which is a new domain. According to Taylor (2012), a significant benefit of using nanofluids in the proposed steam generation process is that vapour occurs quickly even before the entire fluid volume reach corresponding boiling temperature.

1.2. The Literature on Nanotechnology for Steam Generation Energy from the Sun has various applications, ranging from the modular to macro scale, including power generation. However, while using solar energy, there exist challenges related to low capacity (in the kW range) energy applications, especially in domestic and process industries (Liu et al. 2017). Liu et al. (2018) described two strategies for using solar energy: photoelectric conversion and photo-thermal conversion. In addition to steam generation, photo-thermal conversion has numerous applications, such as in water heating, refrigeration, space cooling and heating, thermal power generation, and industrial process heating. Recently, nanofluids have been used to generate vapor or steam by concentrating solar energy directly, named direct absorption solar collectors. Nanoparticles that absorb light across the solar spectrum can instantaneously produce steam when diffused in base fluids, such as water, and can reach steam temperatures over 100°C in compact geometries (Neumann et al. 2015; Neumann et al. 2013).

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Many studies in literature examined different nanoparticles possessing the direct absorption capability to understand their photo-thermal performance including Ag (Chen et al. 2015), Au (Amjad et al. 2017; Guo et al. 2017; Zhang et al. 2014), carbon nanotubes (CNTs) (Zhang et al. 2014; Wenjing Chen et al. 2019), Al2O3 (Hu et al. 2017), graphite (KMML, 2018), rBm nanoparticles (Liu et al. 2017), and titanium dioxide (TiO2) (Yang and Liu 2017; Cong Qi et al. 2016). A study by Haichuan Jin et al. 2016, reported that the specific absorption rate of gold nanoparticles was higher than that of other nanoparticles. It is because gold nanoparticles can absorb optical radiation due to delocalized conduction electron resonance activity. Nonradiative (Landau) damping occurs when the surface plasmons, delocalized conduction electrons, are in an excited state; hence optical energy dissipates (Gao et al. 2011). The preparation of recoverable nanofluids using brine could enhance the evaporation efficiency from 24.91% to 76.65%. The concentration of multiwalled CNTs ranged from 0 wt.% to 0.04 wt.% (Wenjing Chen et al. 2019; Kasaeian et al. 2015). Other studies have mainly reviewed nanoparticles uses suspended in fluids in various solar-powered energy systems such as solar collectors, photovoltaic thermal systems, energy storage systems, thermoelectric solar devices, and solar cells. A significant environmental benefit of using nanofluids is a reduction in CO2 emissions resulting from increased efficiency. Besides, nanofluid-based collectors manufacturing processes produce lower emissions (Kasaeian et al. 2015; Ashish K. Sharma et al. 2016), indicate the possibility of solar industrial process heating competency. The present study aimed to employ nanofluids for solar steam generation, especially in process industries. A two-step method was employed to synthesize TiO2 nanofluid in various concentrations using cetyl trimethyl ammonium bromide (CTAB) as a surfactant. Furthermore, the prepared nanofluids performed characterization studies using a transmission electron microscope (TEM) and a UV–Vis spectrophotometer.

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An indigenous set up was built to determine the amount of steam generated under steady-state conditions using a stable nanofluid at various concentrations. The results showed that steam formation was more efficient when using the nanofluid than a reference fluid (i.e., water). Furthermore, case studies of steam generation for three process applications: sterilization, desalination plants, and textile industry were reported. As an alternate for various conventional fuels, careful cost analysis evaluation confirm the viability of using nanofluids at the commercial scale for steam generation.

2. METHODOLOGY AND EXPERIMENTAL PROCEDURE 2.1. Materials Considering economic factors, we used distilled water as the base fluid. We selected TiO2 as the nanopowder because it forms a highly efficient nanofluid when combined with water and is economically viable. TiO2 was purchased from M/s. Sigma-Aldrich (Merck), India and Table 1 lists the properties of TiO2 nanopowder. However, TiO2 nanopowder tends to agglomerate because of high surface tension and Van der Waals force when mixed with base fluid. To avoid agglomeration, surfactant CTAB was used whose properties are shown in Table 2. CTAB forms a colloidal solution with water and has an aggregation number ranging from 75 to 120.

2.1.1. Reasons for Using TiO2 Nanopowder TiO2 has high dispersity and chemical stability and is nontoxic. TiO2 nanopowder is chemically stable and resistant to acids, alkalis, and erosion by most organic solutions. After synthesizing TiO2 nanofluid from TiO2 nanopowder, the fluid can be treated as a single-phase fluid since it forms a stable nanofluid. In both polar and nonpolar base fluids, TiO2 nanoparticles exhibit relatively satisfactory dispensability, particularly when a dispersant is added.

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Product name Molecular weight Appearance Particle size Purity Pure density

Titanium(IV) Dioxide (a mixture of rutile and anatase) 79.87 g/mol White powder < 100 nm (BET), < 50 nm (XRD) 99.5% based on trace metal analysis 4.23 g/cm³

Table 2. Properties of surfactant Product name Chemical formula Molecular weight Appearance

Cetyl Trimethyl Ammonium Bromide (CTAB) C19H42NBr 364.46 g/mol White powder

2.2. Preparation of Nanofluids 2.2.1. Experimental Procedure (Two-Step Method) For the preparation of TiO2 nanofluid, the base fluid distilled water was initially subjected to ultrasonication for 30 min. Subsequently, the surfactant was added to ultrasonicated distilled water. CTAB was used at 0.01 wt.% of the TiO2 nanoparticle concentration. By using a magnetic stirrer, the surfactant was dispersed into the base fluid for 30 min. The nanofluid was prepared at the concentrations of 0.2 wt.%, 0.5 wt.% and 0.7 wt.%, as shown in Figure 1(a) and (b). The weight of TiO2 nanopowder was calculated based on the equation, as shown in Table 3. Subsequently, after nanoparticle addition, the solution was again subjected to the mixing at high RPM using a magnetic stirrer and then subjected to ultrasonication at 25 kHz for 30 min and 3 hours. The prepared solution was not disturbed for a week to examine the stability of the nanofluid.

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Figure 1. (a) 0.5 wt.% TiO2 nanofluid and (b) 0.7 wt.% TiO2 nanofluid.

Table 3. Calculations for the nanofluid volume concentration Volume concentration,  (%)

0.2

0.5

0.7

% 𝐕𝐨𝐥𝐮𝐦𝐞 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐓𝐢𝐭𝐚𝐧𝐢𝐮𝐦 𝐃𝐢𝐨𝐱𝐢𝐝𝐞 𝐃𝐞𝐧𝐬𝐢𝐭𝐲 𝐨𝐟 𝐓𝐢𝐭𝐚𝐧𝐢𝐮𝐦 𝐃𝐢𝐨𝐱𝐢𝐝𝐞 = 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐓𝐢𝐭𝐚𝐧𝐢𝐮𝐦 𝐃𝐢𝐨𝐱𝐢𝐝𝐞 𝐖𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐛𝐚𝐬𝐞 𝐟𝐥𝐮𝐢𝐝 ( )+( ) 𝐃𝐞𝐧𝐬𝐢𝐭𝐲 𝐨𝐟 𝐓𝐢𝐭𝐚𝐧𝐢𝐮𝐦 𝐃𝐢𝐨𝐱𝐢𝐝𝐞 𝐃𝐞𝐧𝐬𝐢𝐭𝐲 𝐨𝐟 𝐛𝐚𝐬𝐞 𝐟𝐥𝐮𝐢𝐝 x 0.2 4230 = 100 ( x ) + ( 0.1 ) 4230 1000 𝑥 0.5 4230 = 100 ( 𝑥 ) + ( 0.1 ) 4230 1000 𝑥 0.7 4230 = 100 ( 𝑥 ) + ( 0.1 ) 4230 1000

Weight of nanoparticle, x (Grams)

0.848

2.126

2.982

2.2.2. Characterization TEM images were taken on the FEI-Tecnai G220 Twin microscope to determine the morphology of nanoparticles. Nanofluid sample optical properties were measured and examined using a UV–Vis spectrophotometer (Company JASCO, Model V-670) at wavelengths ranging from 200 and 800 nm.

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2.2.3. Steam Generation Experiments An indigenous experiment setup was built to evaluate direct solar vapor generation using water and nanofluid. The setup comprises high-precision electronic scale, glass beakers, acrylic tubes, Fresnel lens and measurement instruments for temperature and solar radiation. Fluid containers were kept inside an acrylic cylindrical tube, and the gap between container and the tube was filled with glass wool for insulation. The top of the fluid container was left open to allow vapor generation. T-type thermocouples were inserted into containers at heights of 10, 20, and 30 mm to measure temperature distribution across the liquid section. Besides, another thermocouple was used to measure ambient temperature. The thermocouples measurement accuracy was calibrated within ± 0.5°C and two-fluid cylinders, one filled with 30 ml of 0.5 wt.% TiO2 nanofluid, and another with 30 ml water were kept as the reference sample. Under natural solar irradiation condition, evaporation experiments were conducted on sunny days from 12:30 to 2:30 pm on an open terrace at VIT, Vellore, India (12.9721°N, 79.1596°E). Fresnel lenses were used to concentrate the sunlight onto the container, as shown in Fig. 2. Digital Electronic scale, with an accuracy of 0.001 g, was used to measure the mass loss in the liquid sample due to evaporation during each experiment. The mass change that occurred due to external factors, such as wind, was minimal and neglected. During the experiment, pyranometer and pyrheliometer instruments were used to measure global and beam radiation. The experiment set was performed three times under similar weather conditions to obtain statistically significant satisfactory results.

2.3. Models for Thermal Conductivity As per literature, different factors that can affect nanofluids heat transfer enhancement were the Brownian motion of nanoparticles, clustering of nanoparticles, nanolayering of the liquid at the liquid–nanoparticle interface, ballistic transport and nonlocal effect, thermophoretic effect, and near-field radiation. To date, most studies have focused on the Brownian motion of

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nanoparticles, molecular-level layering of the liquid at the liquid–particle interface (nanolayer), nanoparticle clustering, and a combination of these factors together with other conditional parameters such as temperature, nanoparticle size, and volume fraction. Hence, a perfect theoretical understanding to model the nanoparticle thermal conductivity behaviour under steady-state and transient conditions are limited.

3. RESULTS AND DISCUSSION This chapter discusses the use of nanoparticles for steam generation using concentrated solar energy. TiO2 nanoparticles are used to generate steam in small quantity by lab-scale apparatus. In this section, analysis of the results from the carried out experiments under different operating conditions is discussed.

Figure 2. Schematic illustration of the experimental setup for solar steam generation.

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3.1. Characterization Figure 3 shows the TEM image of TiO2 nanopowder considered for the present analysis obtained by FEI-Tecnai G220 Twin microscope. The average size of the nanoparticles was 50 nm. Despite the careful preparation of samples, particles tend to agglomerate due to their small size. Hence, a surfactant is necessary to reduce and prevent attraction between small particles. Figure 4(a) shows the UV–Vis spectrum of nanofluids and water measured using a UV–Vis spectrophotometer. The stability of 0.5 wt.% TiO2 nanofluid samples that were examined for 45 days before and after the vapor generation experiment.

Figure 3. TEM image of TiO2 nanopowder.

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As shown in Figure 4(a), water absorbs light between 200 and 400 nm in the near-ultraviolet range. Nanofluids have a broad absorption band in the visible range, ranging from 380 to 750 nm. Figure 4(a) depicts that nanoparticles addition extends the solar energy absorption band of water. The absorption of 0.5 wt.% TiO2 nanofluid solution that was kept stable for 45 days tended to be similar to that of water, particularly in the range of 500 to 800 nm, possibly due to low stability and agglomeration. The nanofluids absorption capacity was found to be slightly higher after the vapor generation experiment than before it. To analyze results, the plot for the transmittance of TiO2 nanofluid and water, as shown in Figure 4(b). The nanofluid transmittance was lower than that of water; even the transmittance of 0.5 wt.% TiO2 nanofluid solution kept stable for 45 days was lower than that of water until the wavelength of 650 nm. This finding indicated that even low concentrations of nanofluids could capture a higher amount of solar light than water. 4.0

Absorption

3.5

0.5% TiO2 Before Experiment

3.0

0.5% TiO2 After Experiment

2.5

Water [C Qi et al., 2017]

0.5% TiO2 After 45 Days

2.0 1.5 1.0 0.5 0.0 200

300

400

500

600

Wavelength (nm) Figure 4. (a) UV-Vis spectrum for nanofluids and water samples.

700

800

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3.2. Stability of Nanofluids For determination of nanofluid stability through physical examination, long-term sedimentation test was performed at different nanofluid samples concentrations by arranging them in different cuvettes with a cap to prevent evaporation. The absorption intensity of the stable 0.5 wt.% TiO2 nanofluid sample reduces with time, as shown in Figure 4(a), indicate that it was losing its stability due to agglomeration. Therefore, surfactant was added to the samples to improve stability. Also, it was observed that the 0.5 wt.% TiO2 nanofluid sample showed higher stability than 0.2 wt.% and 0.7 wt.% TiO2 nanofluid samples. Hence, in the present analysis 0.5 wt.% TiO2 nanofluid sample were used in subsequent experiments. 100 90 80

Transmittance (%)

70 60 50 40 30 20

0.5% TiO2 Before Experiment

10

0.5% TiO2 After Experiment 0.5% TiO2 After 45 Days Water [C Qi et al., 2017]

0 200

300

400

500

600

Wavelength (nm) Figure 4. (b) Transmittance of the TiO2 Nanofluid and water.

700

800

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3.3. Evaporation of Nanofluids The solar steam generation experiments were performed to analyze the applicability of the TiO2 nanofluids. A simple custom-built setup was used to perform experiments under various operating conditions, as shown in Figure 2. Parametric measurements include the mass loss of the vaporized nanofluid under direct solar illumination as a function of time, solar radiation, ambient temperature, and vapor and fluid temperature. Figure 5a depicts rate of mass change of water and nanofluid working fluid with time. The sample water readings were validated with Chen et al. [2019] to confirm the test setup working. It was observed that the rate of change of mass of water was slightly lower in the present study with the trend of mass loss remain the same. One explanation for this observation can be attributed to a difference in solar illumination levels and ambient conditions between the two studies. Comparing the rate of mass loss of water and TiO2 nanofluids within a 120 min interval indicates better evaporation rate for TiO2 nanofluid. The rate of mass loss of water steadily increased and became constant after a certain amount of time. The mass loss in nanofluids exhibited a decreasing trend but was higher than that in water. The highest loss of mass occurred for TiO2 nanofluids (0.5 wt.%) within 120 min, and it was approximately 4.8 times higher than that of water. Furthermore, the vapor generation efficiency (η) to evaluate the effectiveness of the TiO2 nanofluid was calculated using Eqn. (1). Solar steam generation efficiency is calculated as the ratio of energy required for steam generation to the net solar irradiation incident on the surface (Wenjing Chen et al. 2019). η=

ṁ ℎ𝑣𝑎𝑝 𝑄𝑠 𝐴

(1)

where, ṁ is the steady-state vapor mass flux, hvap is the latent heat of vaporization at 1 atm pressure (2257 kJ/kg), 𝑄𝑠 is the total incoming heat flux, and A is the area exposed to incoming solar radiation (3.419 × 10−3 m2).

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0

-2

Mass change (g)

-4

-6

-8

Water 0.5% TiO2

-10

Water [Chen et al., 2019] -12

-14 0

20

40

60

80

100

120

140

Time (min)

Figure 5. (a) Rate of mass change of working fluid. 1000

30

950

25

Solar Radiation, W/m

2

Solar radiation, W/m TiO2

850

2

20

Water

800

15

750

10

700 5

650 600

0

20

40

60

80

100

120

Time, mins

Figure 5. (b) Evaporation efficiency concerning time and solar radiation.

0 140

Evaporation Efficiency, %

900

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The vapor generation efficiency was calculated for the corresponding mass loss during experimentation (120 min). As shown in Figure 5(b), the efficiency increased over time for the TiO2 nanofluid. Initially, the vapor generation was low because the nanofluid required some time to absorb the latent heat of vaporization. Until 40 min, surface boiling occurred due to resonant heating which is explained in section 3.4. Subsequently, bulk boiling occurred, resulting in an increase in efficiency with time. The highest vapor generation efficiency of 27.21% was observed during the last 20 min. Between 60 and 80 min of the experiment, it was observed that a slight momentary decrease in efficiency because of the sudden movement in clouds causing shade. However, the efficiency increased immediately afterwards as the ambient temperature and beam radiation remained high. The generation efficiency gradually increased for water, remained stable for some time, and then decreased. During experiments with water, the vapor generation efficiency of 3.8% was highest between 60 and 80 min. It was observed that the efficiency of the nanofluid was nearly seven times higher than that of water. The value of ṁ (dm/dt) had a determination coefficient of R2 > 0.99 (Ni et al. 2015). The experiment was conducted on bright days to prevent radical fluctuations in solar irradiation. Besides, the average value of the total incoming heat flux (Qs) in equation (1) for an illumination time of 120 min was considered.

3.4. Vapor Generation Mechanisms The presence of surface plasmons enables metallic nanoparticles to absorb optical radiation. When sunlight is incident on these plasmons, they are excited, and waves are scattered through Landau damping, causing a considerable increase in temperature within nanoparticles vicinity. This energy can be utilized to trap the latent heat of vaporization of water in the TiO2 nanofluid, resulting in the resonant heating of water molecules surrounding the nanoparticle. This particle’s vapor volume continuously increases, making it move toward the air-water interface, thus releasing steam.

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Figure 6. Mechanism of vapor generation by using nanofluids.

Many researchers have reported that vapor generation occurs due to an increase in the nanofluid bulk temperature. Keblinski et al. (2002) reported two-time scales for heating the nanofluid. They explained that heating on the microsecond scale was due to the nanofluid global heating. On the other hand, heating on the nanosecond scale was due to the bulk heating mechanism described in Figure 6. To better understand the vapor generation mechanism, during the experiment, the change in bulk temperature and water was observed, and inferences from the calculations were recorded in Figure 7. As working fluid absorbed energy, their bulk temperature gradually increases because of the sensible heat leading to vapor generation. However, as both water and nanofluid temperatures began to increase, heat loss caused due to convection and radiation started to dominate the heat transfer mechanism. The water reached the steady-state condition after approximately 80 min, whereas the nanofluid reached the steady-state condition within 65 min duration as confirmed by Chen et al. (2019). The increase in bulk temperature under the steady-state condition was higher for the nanofluid (12°C) than for water (6.8°C). Because of this difference in the increase in bulk temperature, evaporation and steam generation efficiency increased at higher nanofluid concentrations.

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16

12

0

Bulk Temperature Rise ( C)

14

10 8 6 4

Water 0.5% TiO2

2

Water [Chen et al., 2019] 0 0

20

40

60

80

100

120

140

Time (min) Figure 7. Temperature profile for the increase in bulk temperature for water and 0.5 wt.% nanofluid.

3.5. Case Studies of Industrial Applications In the current economic scenario, capital costs incurred for a particular heat capacity steam generator operating on conventional energy resources, are lower than systems operating on renewable energy. Thus, these conventional resources should be replaced with renewable energy sources, even if it incurs high initial or running costs to achieve sustainability. In remote areas where adequate solar irradiation is available throughout the year and where the cost of fossil fuel is considerably high, solar energy can be a viable alternative. Thus, as a cost-effective option, the application of solar steam generation by using the TiO2 nanofluid can be realized in preexisting thermal applications. The following are some of the factors that affect the production capacity of an industrial-scale plant in practical applications for solar steam generation by using the TiO2 nanofluid:

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Whether to replace fossil fuel completely or to implement it as a hybrid system to fulfil the excessive demand Changing prices of electricity (buying and selling) Solar radiation availability on a daily and seasonal basis Cost-effectiveness

3.5.1. Soil Sterilization Although most Indian farmers still follow traditional practices, they require technical upgradation, which must be economically viable to the average farmer. Pathogens and parasites may survive deep in the soil for several years before they infect plantations. Their existence might reduce the crop yield, leading to substantial losses for the farmer. Soil sterilization equipment usually contains a two-step system: a boiler to increase water temperature and a tool to break the soil for ensuring that the entire volume is sterilized, as shown in Figure 8. Most farmers use fertilizers and pesticides, unaware of the chain reaction they cause because many pests survive and become genetically immune to pesticides. Besides, these methods cause soil erosion and groundwater contamination. Sterilizing the soil with steam is a cost-effective solution for this problem. This method is a viable option that can be implemented even at remote parts of the country with low-income tags which generate high crop yields. Moreover, a maximum temperature of only 80°C–90°C is required for steam sterilization. To ensure whether the steam sterilization of soil is economically viable and ecologically beneficial, a comparison of an existing system operating costs with the proposed method. The existing generator was a portable Sioux Steam Flo Generator (Sioux, 2018). The generator requires approximately 11 L of petrol per hour during regular operation, i.e., 17.6 L of diesel per hour, and 12.1 m3 of compressed natural gas per hour. The net cost of operation is approximately INR 12,000, with 100 kg of CO2 being generated for the total fuel consumed. However, the existing system was not ecofriendly and harmed the farm by adversely affecting air quality by releasing greenhouse gases into the atmosphere.

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Figure 8. Schematic showing the concept of a steam generator used for Soil sterilization.

Table 4. Net cost for operating a system using conventional fuel Volume (L)

Price /L

Net price (INR)

Equivalent units of CO2 produced (kg/L)

Petrol Diesel

11.5 17.6

869.63 1456.421

2.31 2.68

Natural Gas (m3) Net cost for operation Net CO2 produced

12.1

75.6 82.75 12 781.7

CO2 produ ced per hour (kg) 26.565 47.168

9486.57

2.26

27.346

11784.62 101.07 9

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Table 5. Net cost for operating a system using the TiO2 nanofluid Basic Rate of TiO2 nanopowder (INR/MT) TiO2 required for 208 L of water (kg) Net Cost TiO2 (INR) Petrol Required (L) Cost of Petrol (INR) Net Cost (INR)

750000 4.421306 3337.85 11.5 869.63 4207.48

Furthermore, this can prove counterproductive for an average Indian farmer who is already struggling to allocate funds for better quality inputs to achieve better yields. In case the conceptualized method is adopted and put into practice, calculations reveal that there may be nill CO2 emissions possible, as shown in Table 4. Moreover, the residue left after using the nanofluid can be reused to prepare another nanofluid batch for further use. In this scenario, CO2 is only produced by the petrol-operated engine, which can also be negated if the farmer opts for a portable system driven by cattle. However, a minor drawback would be the ultrasonication cost, which would add to the system capital cost as revealed in Table 5. However, this can also be negated by the nanofluid mass production by the supplier of these generators, which can be sold separately to generate extra revenue.

3.5.2. Desalination of Seawater 3.5.2.1. Solar Stills Solar stills utilize direct sunlight to produce freshwater, as shown in Figure 9. Although most solar stills have a conversion efficiency of < 50%, they are considered ideal for supplying fresh water to remote locations. Solar stills can produce approximately 3–4 L of freshwater per unit area. Based on this study experience, dispersing nanoparticles increase water productivity from solar stills can be envisaged from seawater desalination. This concept can be applied as an efficient process to domestic and commercial scale by considering design parameters for using low-cost construction materials. Though the initial capital cost presumed to be high for procuring nanoparticles for such a system, it would be convincing that system maintenance cost is less and nanoparticle can be recycled multiple times.

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Figure 9. A conceptual diagram of a solar still.

3.5.2.2. Low-Temperature Multi-Effect Desalination and Multi-Stage Flash Process Further, steam utilization happens in multi-effect distillation (MED) process, in which multiple shell and tube heat exchangers are used for seawater desalination. In this process, steam pre-heat the input feed water in each stage and seawater absorbs energy to release vapor in multiple stages. The steam required by the MED process can be generated by the proposed process discussed in this study using the TiO2 nanofluid with an inbuilt suntracking system. 3.5.3. Solar Autoclaves for Hospitals Autoclaves are commonly used equipment for the sterilization of surgical utilities in hospitals, which also require steam. Currently, steambased autoclave systems are prevalent only in developed and developing countries. In underdeveloped countries, inadequate electricity makes these systems an economic burden on the hospital industry. Thus, the use of the TiO2 nanofluid for steam generation can help employ autoclave systems for sterilization at a lower cost. Solar autoclaves can use the high-temperature steam generated by nanofluids as solar photo-thermal heaters to sanitize medical instruments. Concentred solar energy can be directed to the system

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having TiO2 nanofluid to produce steam up to a temperature of 130°C. The condensate return water can be collected in a fluid vessel in a closed-loop cycle for reuse. High concentrations of the TiO2 nanofluid can be used because they generate the required steam and nanoparticles can be reused and economical. This method is mostly favourable for remote areas where there is a lack of sterilization processes in hospitals or clinics. Figure 10 shows a sterilization system designed by Neumann et al. (2013). This system comprises three modules. Module I is the steam generation module. A Fresnel lens concentrator (k) helps sunlight concentrate on a solar collector (g) equipped with nanofluid. Module II connects the first and third modules and transfers generated steam to Module III, the sterilization valve. Neumann et al. (2013) experimented with Au nanoshells and can deliver steam within a temperature range of 115°C – 135°C at a 14-L volume for sterilization. Thus, Au nanoshells can be replaced with the TiO2 nanofluid because of their comparable generation efficiency. Also, TiO2 nanofluid is more economical than Au nanoshells. Hence, using the proposed system can reduce autoclaves overall cost, making them more viable in developing countries.

Figure 10. Schematic of a solar autoclave (Neumann et al. 2013).

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3.5.4. Paper and Pulp Industry The paper and pulp industry requires a large amount of water. Approximately 80% of the net energy utilized in this industry is consumed as steam. Standard steam generators such as boilers and waste recovery systems are widely used in these industries. Nanofluids application as a hybrid system can reduce the excessive load in bleaching, pulp drying, washing, and refining processes. These processes require steam at atmospheric pressure with the maximum temperature up to 100°C. 3.5.5. Textile Industry The textile industry includes numerous processes such as washing the yarns and fabric, steam ironing the fabric, colouring and dyeing, finishing treatment, and polymer treatment. During bleaching, the fabric produced is brought to a reaction temperature by a set of rollers through a set of horizontal and vertical steamers. Steam consumption in these individual processes averages approximately 8 kg/h, ranging from 15 to 30 seconds depending on the dye or discharge process. Such steam requirements may apply nanofluid-based solar steam generation ideal for the textile industry, especially for small-scale plants.

3.6. Limitations Several problems were encountered during the implementation of TiO2 nanofluid in field conditions to simulate industrial results. In this study, the concentration of solar energy to the fluid container based on sun movement was the first significant issue since tracking was not adopted. Sun tracking must have enhanced efficiency, which is considered for future scope. The other limitation was to tackle the intermittent wind and clouding effect, which lead to a momentary drop in irradiation values. As the system was provided with proper insulation, it helped prevent the disturbance due to change in ambient conditions. However, the natural phenomenon of cloud movements over the region altered the evaporation rates. In this study, commercially available Fresnal lens was used wherein it is not designed for

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specific purpose and capacity of steam generation. Design of Fresnel lens or implication of any other solar concentration method that exactly matches the input requirements must have enhanced the steam generation rate. Moreover, steam quality generated through this method can further be enhanced to saturated or supersaturated condition using a boiler operated on a hybrid system, thereby addressing reduced carbon emissions. Another aspect of this study is that it did not consider the actual steam quality requirements required for the industry. Hence, further detailed future studies have been considered to deal with all the limitations mentioned in this section.

CONCLUSION Solar energy, a prominent source of renewable energy, can provide a sustainable solution for the current and future challenges of reducing global warming. The advantages of using concentrated solar energy for steam generation are carbon-free process, rapid energy conversion and freely available source. However, some disadvantages include inconsistent energy resource, limited energy conversion efficiency and restricted operation only during the day. This study focused on using nanofluids for steam generation through volumetric fluid heating by using concentrated solar energy. By following a two-step method, 0.5 wt.% stable TiO2 nanofluids were prepared by using CTAB as a surfactant. UV–Vis spectrophotometry results indicated that the TiO2 nanofluid possess energy absorption characteristics in the solar spectrum wavelength range. Experiments were carried out on an indigenous test setup using the Fresnel lens to provide concentrated energy and the TiO2 nanofluid. The efficiency of the system was observed to be 32.23% at an irradiance of 683 W/m2. The efficiency rate was directly dependent on the intensity of solar irradiation. The vapor generation rate for 0.5 wt.% TiO2 nanofluid was calculated to be five times higher than that of water under identical experimental conditions. A significant advantage of using this steam generation method is that steam could be generated even at a low bulk temperature of the fluid because

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of the volumetric heating process. Economic and carbon emission analyses revealed that the nanofluid-based solar steam generation process could have a faster breakeven period and reduce emissions when used for large-scale industrial applications. Some potential applications that can adopt the steam generation technique were also discussed.

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Taylor, R. A., Phelan, P. E., Adrian, R. J., Gunawan, A. & Otanicar, T. P. (2012). Characterization of light-induced, volumetric steam generation in nanofluids. International Journal of Thermal Sciences, 56, pp. 1-11. The Kerala minerals and metal limited (KMML). (2018). Product Price list Accessed during March 2018. http://www.kmml.com/php/ show Content.php?linkid=69&partid=2 (KMML, 2018). Wenjing, Chen, Changjun Zou, Xiaoke Li. & Hao Liang. “Application of Recoverable Carbon Nanotube Nanofluids in Solar Desalination System: An Experimental Investigation.” Desalination, 451, (February 1, 2019), 92–101. Yang, Liu. & Yuhan Hu. (2017). “Toward TiO2 Nanofluids-Part 1: Preparation and Properties.” Nanoscale Research Letters, 12 (1), 417. Zhang, Hui, Hui-Jiuan Chen, Xiaoze Du. & Dongsheng Wen. (2014). “Photo-thermal Conversion Characteristics of Gold Nanoparticle Dispersions.” Solar Energy, 100, (February), 141–47.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 5

INFLUENCE OF NANO-ENHANCED PHASE CHANGE MATERIAL (NEPCM) ON THE PERFORMANCE OF SOLAR WATER HEATER P. Manoj Kumar1,, K. Mylsamy2, P. Michael Joseph Stalin3, Alagar Karthick4 and P. T. Saravanakumar5 1



Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamilnadu, India 2 Department of Mechanical Engineering, Adithya Institute of Technology, Coimbatore, Tamilnadu, India 3 Department of Mechanical Engineering, Audisankara College of Engineering and Technology, Gudur, Andhra Pradesh, India 4 Department of Electrical and Electronics Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamilnadu, India 5 Department of Automobile Engineering, Hindusthan Institute of Technology, Coimbatore, Tamilnadu, India

Corresponding Author’s E-mail: [email protected].

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ABSTRACT In recent days, solar energy is considered to be the predominant source of energy, which extended the hope of satisfying ever-growing energy demand. Among the different applications of solar energy, solar water heaters are playing a key role in satisfying the hot water demands in households, commercial sectors, and industries. However, the performance of the solar water heaters is not at the expected level as they are chastely affected with the fluctuating solar radiation, limited availability of the sun, and local weather. In this chapter, the opportunities for augmenting the performance of a natural circulation all-glass evacuated tube solar water heater by assimilating it with a paraffin-based phase change material (PCM) and with the nano-enhanced phase change materials (NEPCM) containing different mass of SiO2 nanoparticles (0.5%, 1.0%, 2.0%) in paraffin are presented. Initially, the experimental investigations on the NEPCMs proved that the melting and freezing temperature of the paraffin had appropriately adjusted by the SiO2 nanoparticles until the mass fraction of 1.0% in paraffin, and the thermal conductivity of the paraffin was amplified up to 33.34%. Further, the daily energy efficiency of the solar water heater was enriched by 18.57%, while using paraffin with 1.0% mass of SiO2 nanoparticles. The results revealed that the integration of NEPCM containing paraffin with 1.0% mass of SiO2 nanoparticles relatively tapped-out the better performance of solar water heater.

Keywords: solar water heater, PCM, NEPCM, SiO2 nanoparticles, thermal energy storage

1. INTRODUCTION Rapid expansion in the global population, economy, and industrial growth, coupled with rapid urbanization, has led to a dramatic increase in energy demand every year. In this present global scenario, energy demand is estimated to rise rapidly to two times in 2040 compared to the current situation (Karthick et al. 2020). Conversely, the World Health Organization (WHO) reported that around seven million people around the world had lost their lives solely due to air pollution in 2012. The reason for this terrible occurrence is ascribed to the burning of fossil fuels to meet energy needs, primarily for power generation, transport, domestic and industrial heat

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 115 requirements. Moreover, the burning of fossil fuels also ended up in producing greenhouse gases, which in turn gradually increasedthe global temperatures. In 2018 alone, coal-fired power plants released 10 Gigatonnes of CO2 globally to the atmosphere, accounting for one-third of total emissions in the corresponding year (Kumar et al. 2019a). The nations are facing a challenge to meet the ever-increasing demand for energy in the future without further damaging the ecosphere. In light of these factors, countries are consistently thriving to shape their energy policies in such a way that it will encouragethe generation of energy through renewable sources. Heat energy is reported to be predominant among all the types of energy end-use, and it plays a vital role in the domestic, commercial, and industrial sectors. It is calculated that about half of the global energy generation has been used for heating applications such as industrial heating, drying, space heating, domestic hot water, etc.Further, around 46 percent of the heat energy is used to heat the water for various domestic, commercial, and industrial requirements such as cooking, bathing, washing, cleaning, preheating of water in power plants, leather and textile processing, and food processing industries (Kumar et al. 2019b; Kumar et al. 2020a; Manoj Kumar et al. 2021a). It can be revealed that a significant part of the electrical energy produced from a large variety of fuels, primarily fossil fuels, has been converted into heat, which is essentially a low-grade energy. Therefore, the heat from direct sources can reduce a lot of conversion losses, and, in particular, the heat from renewable sources will result in the least emission levels in the biosphere. Solar energy is one of the auspicious renewable sources of energy. It is essentially sunlight and heat that can be harnessed using two different types of conversion methods, such as solar thermal and solar photovoltaic. The heating of water to a desirable temperature with a solar water heater is purely depending on the available solar radiation on a particular day, and it is weather dependent. Also, the heat losses (day losses and night losses) through the system are inevitable, which in turn diminishes the energy efficiency of the system. Hence, it will become necessary to stabilize the system with a suitable mechanism to reduce the losses, improve the system

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efficiency, and supply hot water at the required temperature irrespective of the weather conditions. Nonetheless, the integration of thermal energy storage materials with solar water heaters can positively address the drawbacks associated with the solar thermal system (Magendran et al. 2019; Manoj Kumar and Mylsamy 2020). Thermal energy storage is attaining greater considerationin recent years due to its importance in renewable energy systems, specifically in solar thermal energy applications. Amid the different types of thermal energy storage materials, latent heat storage (LHS) materials are mostly recommended by the scholars for solar thermal applications seeing their loftier properties such as high energy density, easy accessibility, wide temperature usability, low expansion, and compact size (Yang et al. 2016; Manoj Kumar et al. 2020). LHS materials are otherwise called phase change materials (PCM), which can store a vast volume of heat energy during their phase transition in the form of latent heat and give back the same during their reverse phase transition. Solid to liquid phase change materials are always preferred over liquid to gaseous phase change materials because the latter requires a huge amount of storage volume during their phase transition (Kumar et al. 2020b; Manoj Kumar et al. 2021b). The examples for the solid to liquid PCMs include paraffin, esters, fatty acids, and inorganic salt hydrates. The recent studies have proved that the organic paraffin-based phase change materials exhibit the maximum desirable qualities than other PCMs, specifically for the low and medium temperature solar thermal storage applications. Paraffin waxes are safe, odorless, chemically inert, non-corrosive, less cost, good in latent heat capacity, and plenty availability. However, their common issue is their low thermal conductivity that lessens the rate of heat transfer during charging and discharging periods (Kee et al. 2018). Because of this setback, the full potential of the paraffin cannot be able to reaped-out effectively. The problem with the low thermal conductivity of the PCMs was dealt with in different ways in previous studies, such as an increased surface area with modified encapsulation or with an increased number of containers, introducing fins in the containment, introducing highly conductive porous medium in the PCM, and dispersing high conductivity nano-sized particles

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 117 in the PCM (Kumar et al. 2020c; Kumar et al. 2020d; Manoj Kumar et al. 2021c). However, the studies suggested adding highly conductive nanoengineered particles for refining the thermal conductivity of the PCM, and this method is claimed to be an economical and feasible technique (Lin et al. 2018; Pasupathi et al. 2020). From the extensive literature review, the research papers have been found, which either reporting the study on the influence of highly conductive nanoparticles on thermo-physical properties of PCMs or discussing the investigation on the performance of solar water heaters with PCM. The combination of these studies has nowhere been reported. Hence, the present chapter focuses on the following research objectives, 





To design, fabricate, and commission a thermosyphonic flow allglass evacuated tube solar water heater and investigate its performance (without any PCM) in the real-time solar environment with the help of energy analysis. To synthesize the nano-enhanced PCMs (NEPCMs) by dispersing nano-SiO2 particles at three progressive mass percentages (0.5%, 1.0%, and 2.0%) in paraffin and characterize them experimentally to determine the impact of nanoparticles and their mass percentages on thermo-physical properties of paraffin. To conduct the experimental investigations on the fabricated solar water by assimilating it with PCM (paraffin) and nano-enhanced PCMs to assess the influence of PCM and nano-enhanced PCMs on the performance of a solar water heater.

2. EXPERIMENTAL SETUP OF SOLAR WATER HEATER The experiments were piloted using the solar water heater combined with a longitudinal water storage tank of more than 100 liters storage capacity (even after including PCM/NEPCM), which had been fabricated inhouse as per the MNRE (Ministry of New and Renewable Energy, India) standard. The collector tubes were erected on the support with an inclination

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of 26° with the ground and the solar water heater was placed in such a way that the collector tubes had to face south for reaping out the maximum possible solar energy (Kabeel et al. 2015; Tang et al. 2011). Figure 2.1 shows the tank of the solar water heater.

Figure 2.1. Position of water storage tank in ETC solar water heater.

Figure 2.2. Photograph of (a) PCM/NEPCM encapsulating cylindrical container (b) Position of container inside the storage tank.

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 119

Figure 2.3. Experimental setup with measuring instruments.

It was decided to use 14 kg of PCM/NEPCM for experimentation based on the calculated energy storage requirement as conceived from previous studies (Nallusamy et al. 2007; Al-Kayiem and Lin 2014; Murali et al. 2015), as shown in Figure 2.2. The temperature from different points of the system such as, water temperature, PCM temperature, and ambient temperature was measured with K-type thermocouples (accuracy of ±0.1°C) using a multi-channel digital temperature indicator. The solar irradiation was observed with a solar power meter with an inherent accuracy of ±5.0 W/m2. The experimental setup after connecting it with all the data gathering instruments is shown in Figure 2.3.

3. PREPARATION AND CHARACTERIZATION OF PCM AND NANO-ENHANCED PCM As discussed, SiO2 nanoparticles were used as the nano-enhancers for improving the thermal conductivity of the paraffin. It was decided to use

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three progressive mass percentages for each type of nanoparticle with paraffin such as 0.5%, 1.0%, and 2.0% of nanoparticles in paraffin, based on the previous literature (Wang et al. 2014; Luo et al. 2015; Mohamed et al. 2017). The experimentation was planned in five cases. The first case was without any PCM, the next case with paraffin as PCM, and the remaining nine cases with nano-enhanced PCMs containing SiO2 nanoparticles in the aforementioned compositions. The commercial-grade paraffin with a melting range of 56°C - 64°C was used in this work. SiO2 nanoparticles with an average particle diameter of 20 nm was used during the experimentation. The thermo-physical properties of the PCM and nanoparticles are presented in Table 1. The NEPCMs were prepared using the two-step method (Manoj Kumar, Mylsamy and Saravanakumar 2020). In this method, the commercially procured nanoparticles of predetermined mass fractions were dispersed in the paraffin to obtain the required composition of nano-enhanced PCM. Utterly, three compositions of nano-enhanced PCMs were prepared by dispersing nano-SiO2 particles at 0.5, 1.0, and 2.0 mass concentrations in paraffin, respectively. The chemical composition of the different PCMs is given in Table 2. Table 1. Thermo-physical properties of paraffin and nanoparticles Properties Colour Physical form Melting point (°C) Solidification point (°C) Density (kg/m3) Specific heat (kJ/kgK) Latent Heat of fusion (kJ/kg) Thermal Conductivity (W/mK)

Materials Paraffin wax White Pellets 64 57 890 2.1 140.2 0.180

SiO2 nanoparticles White Powder 1713 2200 0.745 1.5

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 121 Table 2. Chemical composition of nano-enhanced PCMs prepared for the experimental investigation S.No. 1. 2. 3. 4.

Designated name of NEPCM Paraffin 0.5 SiO2-NEPCM 1.0 SiO2-NEPCM 2.0 SiO2-NEPCM

Chemical composition in mass percentage (%) 0 nano-SiO2 + 100 paraffin 0.5 nano-SiO2 + 99.5 paraffin 1.0 nano-SiO2 + 99.0 paraffin 2.0 nano-SiO2 + 98.0 paraffin

During the preparation of NEPCMs, a sample of each composition was taken out and solidified into a cylindrical form to assess their thermophysical properties using Differential Scanning Calorimetry (DSC) and thermal properties analyzer.

4. EXPERIMENTAL PROCEDURE The experimental work with the solar water heaterwas piloted in Coimbatore, Tamil Nadu, India, which is 410 m above sea level and located at 10.98° Northern latitude, 6.96° Eastern longitude. The effect of incorporating PCM and NEPCMs on the performance of the solar water heater was examined in terms of energy analysis. The first case was without integrating any PCM with storage tank, the second case with pure paraffin as PCM inside the storage tank, and the remaining nine cases were conducted with NEPCMs namely, 0.5 SiO2-NEPCM, 1.0 SiO2-NEPCM, and 2.0 SiO2-NEPCM containing SiO2 nanoparticles, with three different compositions as mentioned in Table 2. The experimental setup was used to run continuously for twenty-four hours for every case of the investigation. The experiment for each case was commenced by filling freshwater in the water storage tank by 6.00 a.m. in the morning and ended by 6.00 a.m. on the next day morning. To replicate the real-time demand in the experimentation, the entire quantity of water was withdrawnfrom the tank by recharging with the freshwater of the same

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quantity at 6.00 p.m. in the evening during all the cases of experiments (Singh and Turkiya 2013).

4.1. Thermodynamic Analysis The following are the assumptions proposed in the thermodynamic analysis of this investigation.    

The glass tube temperature is assumed to be uniform. It is negligible to conduct axial heat along the length of the tube. Thermo-physical properties of the water and PCM remain unchanged with variation in temperature. Ambient conditions are considered to be the dead state.

A portion of solar irradiation striking the absorber is transferred to the water present inside the tubes, and the remaining part is lost to the surrounding. The detailed thermal network model of the evacuated tube solar water heater is presented in Figure 1. Where, ‘Tamb’ is the ambient temperature, ‘R’ terms are the corresponding thermal resistances. Further, the suffixes ‘g,o,’ ‘g,i,’ ‘amb,’ and ‘ab’ are meant for outer glass tube, inner glass tube, ambient, and absorber, respectively. The energy balance equation can be written as follows for the solar water heater with built-in storage (Ceylan 2012), Qi = Qs + Qb + QL

(1)

where, Q i is the energy collected by the collector, Q s is the energy stored in the storing medium inside the storage tank, Q b is the absorbed heat of the system body, and Q L is the loss of heat to the atmosphere during a time interval between Ti and Tf. The energy stored within the water storage tank becomes the sum of energy stored by storage mediums such as the energy stored by water (Qw)

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 123 alone in the first case, water as well as phase change material (Qpcm) in the remaining cases (Chen et al. 2009; Mahfuz et al. 2014), Q s = Q w + Q pcm

(2)

Q s = [mw × Cp,w (Tw,f − Tw,i )] + {mpcm [Cp,pcm (Tpcm,f − Tpcm,i ) + am ∆hpcm ]}

(3)

where, mw is mass of water, mpcm is mass of PCM/NEPCM, Cp,w and Cp,pcm are the specific heat of water and PCM, respectively. Further, am is the melting fraction, ∆hpcm is the latent heat of PCM/NEPCM, Tw,i, Tpcm,i, Tw,f, and Tpcm,f are the initial and final temperature of the water and PCM/NEPCM, respectively. Energy engrossed by the collector can be premeditated from the following equation if we know the area of the collector (Ac) and hourly radiation (Ht) (Al-Kayiem and Lin 2014), Q i = Ac × Ht

(4)

Hence, the efficiency of the collector can be calculated from Equations (2), (3) and (4) as, ηc =

Qs Qi

× 100

Figure 1. Thermal network model of the evacuated tube solar water heater.

(5)

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4.2. Uncertainty Analysis In this work, the system efficiencies are found to be depending on the specific heat of water (Cp,w), the specific heat of phase change material (Cp,pcm), tank water temperature (Tw), PCM temperature (Tpcm), and obtained solar insolation (Ht). In this study, the experimental uncertainties associated with the measuring equipment were examined from the following mathematical expression, which was given by Kumar and Mylsamy (2019), δx

2

δx

2

δx

2

σ = √[∑ni=1 ( x i) ] = √[( x 1 ) + ( x 2 ) + ⋯ ] i

1

2

(6)

where, ‘δx’ is the probable inaccuracy of the ‘x’ quantity and ‘1,2,…i’ meant for the number of such quantities involved in the calculation of the required parameter. Using Equation (6), the value of uncertainty concerning with energy efficiency of the system was determined as 1.222%. These small inaccuracies of the final outcomes are inevitable, and it lies within the acceptable range. Hence, they may not affect the final findings.

5. RESULTS AND DISCUSSION 5.1. Characterization Studies on NEPCMs The DSC analysis was carried out to experimentally determine the melting point, solidification point, latent heat of fusion, and the latent heat of solidification of the PCM and NEPCMs. The obtained results are plotted as shown in Figure 2. It is observed from Figure 2 that all the PCM/NEPCM samples have commonly found with two distinguished peaks during their heating and cooling, irrespective of their composition. In the heating curve, the small peak can be acknowledged with the solid to the solid phase transition of the material. The breaking-up of the crystalline structure due to the increase in temperature would have become the reason for this small peak.

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 125

Figure 2. DSC results of paraffin and SiO2-NEPCMs.

Table 3. Thermal properties of PCM and NEPCMs measured by DSC NEPCMs

Paraffin 0.5 SiO2-NEPCM 1.0 SiO2-NEPCM 2.0 SiO2-NEPCM

Thermal properties Melting Latent Heat point during (°C) melting(kJ/kg) 63.74 140.2 63.1 137.2 62.72 135.0 62.08 106.3

Solidification Latent Heat during Point (°C) solidification(kJ/kg) 57.01 57.15 57.54 59.41

134.6 130.3 128.2 97.4

The thermal properties of the PCM and NEPCM samples have been experimentally measured with DSC and presented in Table 3. Among the different tested NEPCMs, the samples with 1.0% SiO2 nanoparticles have relatively served better with paraffin, when prioritizing in terms of latent heat capacity. Thermal conductivity is the prime constituent, which determines the rate of heat transfer in/out of an elemental mass. The PCM and NEPCM’s thermal conductivity were noted down with the thermal properties analyzer and presented in Figure 3.

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It could be noticed that the thermal conductivity of the paraffin was enhanced with the augmented mass percentage of nanoparticles in paraffin. However, the slope of the curve seems to be non-linear as obtained by Choi et al. (2014), and Mohamed et al. (2017). 0.25

Thermal Conductivity (W/mK)

0.24

0.23

0.22

0.21

0.20

0.19

0.18 0.0

0.5

1.0

1.5

2.0

2.5

Mass fraction of SiO2 nanoparticles in paraffin (%)

Figure 3. Thermal conductivity of SiO2-NEPCMs at different mass fraction.

Table 4. Thermal conductivity of PCM and NEPCMs NEPCMs Paraffin 0.5 SiO2-NEPCM 1.0 SiO2-NEPCM 2.0 SiO2-NEPCM

Thermal conductivity (W/mK) 0.18 0.203 0.221 0.24

Percentage improvement (%) 0 12.78 22.78 33.34

The maximum augmentation in thermal conductivity was achieved with a 2.0% mass of SiO2 nanoparticles in paraffin, which is 33.34% higher than the thermal conductivity of pure paraffin, followed by 1.0 SiO2-NEPCM and 0.5 SiO2-NEPCM showed better results as given in Table 4.

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 127 In the view of thermal conductivity improvement, 2.0 SiO2-NEPCM observed to be impressive in improving the heat transfer rate of the paraffin. However, the DSC results evidenced that this particular NEPCM attributed to the poor thermal storage capacity in terms of their latent heat capacity. Altogether, SiO2 nanoparticles in 1.0% mass fraction (1.0 SiO2-NEPCM) appear to be superior in improving the overall thermal properties of the paraffin in all the aspects, comparing to the other two compositions.

5.2. Experimental investigations on solar water heater with PCM and NEPCM 40

Atmospheric Temperature (°C)

38 36 34 32 30 28 26 24 22 20

Without PCM With Paraffin as PCM With 0.5 SiO2-NEPCM With 1.0 SiO2-NEPCM With 2.0 SiO2-NEPCM

6 a 7 .m. a 8 .m. a 9 .m. 10 a.m . 11 a.m . 12 a.m p . 1 .m. p 2 .m. p 3 .m. p 4 .m. p 5 .m. p 6 .m. p 7 .m. p 8 .m. p 9 .m. 10 p.m . 11 p.m . 12 p.m a . 1 .m. a 2 .m. a 3 .m. a 4 .m. a 5 .m. a 6 .m. a. m .

18

Time (Hours)

Figure 4. Atmospheric temperature on the experimental days.

The solar water heater was fabricated and investigated in five different cases as deliberated in the earlier sections, and the acquired results are discussed in detail as follows. Each case of the investigation was steered-up for a minimum of five days to confirm the reliability of the results, and the days having the similar solar radiation pattern were considered for further analysis from each case. Figure 4 and Figure 5 shows the pattern of received

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1000

800

600

400 Without PCM With Paraffin as PCM With 0.5 SiO2-NEPCM With 1.0 SiO2-NEPCM With 2.0 SiO2-NEPCM

200

. p. m . 2 p. m . 3 p. m . 4 p. m . 5 p. m . 6 p. m . 7 p. m .

.

m

1

p. 12

11

a.

m

.

.

m a.

10

.

a. m 9

.

a. m 8

a. m 6

7

.

0

a. m

Instantaneous Solar Radiation (W/m2)

solar energy and atmospheric temperature during five cases of experiments, respectively.

Time (Hour)

Figure 5. Solar radiation on the experimental days.

5.2.1. Energy Efficiency of the Solar Water Heater in Different Cases The energy efficiency of the solar water heater is the quantitative measure of effective utilization of energy received by the solar collector from the sun. Based on the equations elucidated in the earlier sections, the hourly energy efficiency of the solar water heater was calculated for the cases such as without PCM, with paraffin, and with SiO2-NEPCMs and illustrated in the Figure 6.

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 129 100

Hourly energy efficiency (%)

90 80 70 60 50 40

Without PCM With Paraffin as PCM With 0.5 SiO2-NEPCM With 1.0 SiO2-NEPCM With 2.0 SiO2-NEPCM

30 20 10

.

.

p. m 6

.

p. m 5

. 4

p. m

.

p. m 3

.

p. m 2

. m

p. m 1

. m

p. 12

a. 11

m

.

.

a. 10

.

a. m 9

a. m 8

7

a. m

.

0

Time (Hour)

Figure 6. Hourly energy efficiency of solar water heater.

Figure 7. Peak hourly energy efficiency of solar water heater.

It could be visibly noticed that the hourly energy efficiencies followed the same trend for all the cases of the experiment. The efficiency happened to increase from minimum to maximum value during the morning hours along with the increase in solar radiation and curved down into the lowest

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value after the noon hours, as in the case of solar radiation pattern observed in Figure 6. It is evident that the energy efficiency of the solar water heater is predominantly influenced by the intensity of solar flux falling on the collector. The peak value of hourly energy efficiency was observed between 12 p.m. and 2 p.m. during the five cases of the experiment, which is due to the availability highly intense solar flux at this time period. The peak value of hourly energy efficiency for the five cases of the experiment is separately presented in Figure 7. The hourly peak value in the energy efficiency of the solar water heater (SWH) without any PCM was observed as 76.18%, which is around 10% lesser than other cases of the experiment. The case of solar water heater with paraffin as PCM was acknowledged with the maximum hourly energy efficiency of 84.87%, which is 8.69% more than that of the case without PCM. It is yet again a piece of strong evidence for the improved performance of the solar water heater while integrating it with paraffin.

Figure 8. Daily energy efficiency of solar water heater.

Figure 8 gives the daily energy efficiency of the SWH for the five experimented cases. The daily efficiency of the SWH without any PCM was perceived to be 58.75%, which is approximately 10% to 20% lesser than all the other cases. The same for the case with paraffin as PCM was calculated as 69.64%, which is again 5% to 9% lesser than the cases with NEPCMs.

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 131 These results are sufficiently substantiating that the dispersion of nanoparticles in paraffin improved the heat transfer characteristics of the paraffin, which in turn enhanced the energy efficiency of the solar water heating system. The maximum daily energy efficiency was achieved with the solar water heater using 1.0 SiO2-NEPCM, which was reported as 77.32%. Critically analyzing all the cases, the SiO2-NEPCM cases have shown the appreciable improvements in energy efficiency until the mass fraction of 1.0% in paraffin.

CONCLUSION The all-glass evacuated tube solar water heater with an integrated storage tank was fabricated and exposed for experimentation in five different cases i.e., without PCM, with paraffin as PCM, and with three compositions of SiO2-NEPCMs (0.5 SiO2-NEPCM, 1.0 SiO2-NEPCM, and 2.0 SiO2NEPCM), under the real-time sunshine condition. The experiments were accomplished with the following conclusions. 



The DSC results proved that the SiO2 nanoparticles had excellently reduced the temperature gap between the melting and crystallization point of paraffin, without affecting latent heat of paraffin. In the same way, the thermal conductivity was improved by 12.78%, 22.78%, and 33.34%, respectively with 0.5 SiO2-NEPCM, 1.0 SiO2NEPCM, and 2.0 SiO2-NEPCM. The daily energy efficiency of the solar water heater was enriched by 10.9%, 16.04%, 18.57%, and 16.18%, with PCM, 0.5 SiO2NEPCM, 1.0 SiO2-NEPCM, and 2.0 SiO2-NEPCM, respectively. Chiefly, 1.0 SiO2-NEPCM assisted to improve the energy efficiency of the solar water heater significantly.

On the whole, the SiO2 nanoparticles can be recommended as the potential agent to enhance the thermo-physical properties of the paraffin.

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Further, the integration of NEPCM containing nano-SiO2 particles with the thermosyphonic flow-based solar water heaters is highly suggested to attain the enhanced performance. Specifically, the SiO2 nanoparticles have been recommended at the mass fraction of 1.0% in paraffin to get the maximum benefit.

REFERENCES Al-Kayiem, H. H. and Lin, S. C. (2014). Performance evaluation of a solar water heater integrated with a PCM nanocomposite TES at various inclinations. Solar Energy, 109, 82-92. Ceylan, I. (2012). Energy and exergy analyses of a temperature controlled solar water heater. Energy and Buildings, 47, 630-635. Chen, B. R., Chang, Y. W., Lee, W.S. and Chen, S.L. (2009). Long-term thermal performance of a two-phase thermosyphon solar water heater. Solar Energy, 83(7), 1048-1055. Choi, D. H., Lee, J., Hong, H. and Kang, Y. T. (2014). Thermal conductivity and heat transfer performance enhancement of phase change materials (PCM) containing carbon additives for heat storage application. International Journal of Refrigeration, 42, 112-120. Kabeel, A. E., Khalil, A., Elsayed, S. S., and Alatyar, A. M. (2015). Modified mathematical model for evaluating the performance of waterin-glass evacuated tube solar collector considering tube shading effect. Energy, 89, 24-34. Karthick, A., Manokar Athikesavan, M., Pasupathi, M. K., Manoj Kumar, N., Chopra, S.S. and Ghosh, A. (2020). Investigation of Inorganic Phase Change Material for a Semi-Transparent Photovoltaic (STPV) Module. Energies, 13(14), 3582. Kumar, P. M., Anandkumar, R., Sudarvizhi, D., Prakash, K. B. and Mylsamy, K. (2019a). Experimental investigations on thermal management and performance improvement of solar PV panel using a phase change material. AIP Conference Proceedings, 2128(1), 020023.

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 133 Kumar, P. M. and Mylsamy, K. (2019). Experimental investigation of solar water heater integrated with a nanocomposite phase change material. Journal of Thermal Analysis and Calorimetry, 136(1), 121-132. Kumar, P. M., Anandkumar, R., Mylsamy, K. and Prakash, K.B. (2020a). Experimental investigation on thermal conductivity of nanoparticle dispersed paraffin (NDP). Materials Today: Proceedings. Kumar, P. M., Anandkumar, R., Sudarvizhi, D., Mylsamy, K. and Nithish, M. (2020b). Experimental and Theoretical Investigations on Thermal Conductivity of the Paraffin Wax using CuO Nanoparticles. Materials Today: Proceedings, 22, 1987-1993. Kumar, P. M., Mylsamy, K., Prakash, K. B., Nithish, M. and Anandkumar, R. (2020c). Investigating thermal properties of Nanoparticle Dispersed Paraffin (NDP) as phase change material for thermal energy storage. Materials Today: Proceedings. Kumar, P. M., Mylsamy, K., Saravanakumar, P. T., Anandkumar, R. and Pranav, A. (2020d). Experimental Study on Thermal Properties of NanoTiO2 Embedded Paraffin (NEP) for Thermal Energy Storage Applications. Materials Today: Proceedings, 22, 2153-2159. Kumar, P. M., Saravanakumar, P. T., Mylsamy, K., Kishore, P. and Prakash, K. B. (2019b). Study on thermal conductivity of the candle making wax (CMW) using nano-TiO2 particles for thermal energy storage applications. AIP Conference Proceedings,2128(1),020027. Lin, Y., Jia, Y., Alva, G. and Fang, G. (2018). Review on thermal conductivity enhancement, thermal properties and applications of phase change materials in thermal energy storage. Renewable and Sustainable Energy Reviews, 82, 2730-2742. Luo, R., Wang, S., Wang, T., Zhu, C., Nomura, T. and Akiyama, T. (2015). Fabrication of paraffin@ SiO2 shape-stabilized composite phase change material via chemical precipitation method for building energy conservation. Energy and Buildings, 108, 373-380. Magendran, S. S., Khan, F. S. A., Mubarak, N. M., Vaka, M., Walvekar, R., Khalid, M. and Karri, R. R. (2019). Synthesis of organic phase change materials (PCM) for energy storage applications: A review. NanoStructures & Nano-Objects, 20, 100399.

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Mahfuz, M. H., Kamyar, A., Afshar, O., Sarraf, M., Anisur, M. R., Kibria, M. A. and Metselaar, I. H. S. C. (2014). Exergetic analysis of a solar thermal power system with PCM storage. Energy Conversion and Management, 78, 486-492. Manoj Kumar, P. and Mylsamy, K. (2020). A comprehensive study on thermal storage characteristics of nano-CeO2 embedded phase change material and its influence on the performance of evacuated tube solar water heater. Renewable Energy, 162, 662-676. Manoj Kumar, P., Mylsamy, K. and Saravanakumar, P. T. (2020). Experimental investigations on thermal properties of nano-SiO2/paraffin phase change material (PCM) for solar thermal energy storage applications. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 42(19), 2420-2433. Manoj Kumar, P., Mylsamy, K., Karthick Alagar and Sudhakar, K. (2020). Investigations on an evacuated tube solar water heater using hybridnano based organic Phase Change Material. International Journal of Green Energy, 17(13), 872-883. Manoj Kumar, P., Arunthathi, S., Jeevan Prasanth, S., Aswin, T., Anish Antony, A., Deepak Daniel, Mohankumar, D., Nikhil Babu, P. (2021a). Investigation on a Desiccant based Solar Water Recuperator for Generating Water from Atmospheric Air. Materials Today: Proceedings. Manoj Kumar, P., Sudarvizhi, D., Michael Joseph Stalin, P., Aarif, A., Abhinandhana, R., Renuprasanth, A., Sathya, V., Thirukkural Ezhilan, N. (2021b). Thermal characteristics analysis of a phase change material under the influence of nanoparticles. Materials Today: Proceedings. Manoj Kumar, P., Sudarvizhi, D., Prakash, K.B., Anupradeepa, A. M., Boomiha Raj, S., Shanmathi, S., Sumithra, K., Surya, S. (2021c). Investigating the Performance of a Single Slope Solar Still with a NanoPhase Change Material. Materials Today: Proceedings. Mohamed, N. H., Soliman, F. S., El Maghraby, H. and Moustfa, Y. M. (2017). Thermal conductivity enhancement of treated petroleum waxes, as phase change material, by α nano alumina: Energy storage. Renewable and Sustainable Energy Reviews, 70, 1052-1058.

Influence of Nano-Enhanced Phase Change Material (NEPCM) … 135 Murali, G., Mayilsamy, K. and Arjunan, T. V. (2015). An experimental study of PCM-incorporated thermosyphon solar water heating system. International Journal of Green Energy, 12(9), 978-986. Nallusamy, N., Sampath, S. and Velraj, R. (2007). Experimental investigation on a combined sensible and latent heat storage system integrated with constant/varying (solar) heat sources. Renewable Energy, 32(7), 1206-1227. Pasupathi, M.K., Alagar, K., Mm, M. and Aritra, G. (2020). Characterization of Hybrid-nano/Paraffin Organic Phase Change Material for Thermal Energy Storage Applications in Solar Thermal Systems. Energies, 13(19), 5079. Sharma, R. K., Ganesan, P., Tyagi, V. V., Metselaar, H. S. C. and Sandaran, S. C. (2015). Developments in organic solid–liquid phase change materials and their applications in thermal energy storage. Energy Conversion and Management, 95, 193-228. Singh, O. and Turkiya, S. (2013). A survey of household domestic water consumption patterns in rural semi-arid village, India. GeoJournal, 78(5), 777-790. Tang, R., Yang, Y. and Gao, W. (2011). Comparative studies on thermal performance of water-in-glass evacuated tube solar water heaters with different collector tilt-angles. Solar Energy, 85(7), 1381-1389. Wang, J., Xie, H., Guo, Z., Guan, L. and Li, Y. (2014). Improved thermal properties of paraffin wax by the addition of TiO2 nanoparticles. Applied Thermal Engineering, 73(2), 1541-1547. Yang, J., Yang, L., Xu, C. and Du, X. (2016). Experimental study on enhancement of thermal energy storage with phase-change material. Applied Energy, 169, 164-176.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 6

THERMAL MODEL AND SIMULATIONS OF SOLAR WATER HEATING F. Bagui1, and K. Kassmi2 1

CESI School of Engineering, Campus CESI Rouen, France 2 Mohamed First University, Faculty of Science, Department of Physics, Oujda, Morocco

ABSTRACT Solar energy is the most important renewable energy within environmentally-friendly electricity production. Solar energy is transferred for storage or immediate use. This chapter is devoted to the description and modelling of the solar hot water (SWH) process. The main components of SWH are solar collectors, storage tank units and pumps. SWH is based on the absorption of sun energy by collectors and its transfer for storage into tanks. Collectors are devices converting the radiant energy of the sun into heat, which is then transferred by using a heat-transfer fluid. Temperature sensors supervise the process and allow performance control. In this chapter, we propose a mathematical model, which simulates the temperatures of the heat transfer fluid and the tank water. This model allows us to analyse temperature variations under different conditions. 

Corresponding Author’s E-mail: [email protected].

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Keywords: solar energy, heat transfer, solar water heating

NOMENCLATURE T Temperature Q Mass flow rate Cp Specific heat capacity V Volume h Heat transfer coefficient S Surface t Time A Overall heat transfer coefficient Φ Incident thermal solar flux 𝜌 Density τ Time constant Indices c Collector f Fluid i Input

(K) (m³sˉ ¹) (JKgˉ ¹Kˉ ¹) (m³) (Wmˉ ²Kˉ ¹) (m²) (s) (Wmˉ ²Kˉ ¹) (Wmˉ ²) (kg mˉ ³) (s) o t w

Output Tank Water.

1. INTRODUCTION Solar water heating is the simplest and cheapest process among environmental processes. It has the advantage of functioning even with a weak radiative flux. There have been several research works in recent years concerning the design, the optimization of the system or the improvement of its functioning (Amiche El Hassar, Larabi, Khan Khand, Aguilar and Quiles, 2020; Tagliafico, Scarpa, and De Rosa, 2014; Ma, Li, and Kazemian, 2020). A large majority of the articles are devoted to coupling with photovoltaic panels or phase change materials (Moghadam, Farshchi, Ashkan and Sharak, 2011; Dhinakaran, Muraliraja, Elansezhian, Baskar, Satish and

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Shaisundaram, 2020; Young, Kim, Chang-Hyo Sonc, Yoon and Choi, 2020). The present study limits itself to for exclusively solar energy powered installations domestic hot water production. However, the study includes domestic electricity as auxiliary source in case of absent sunlight. The installation consists of a flat solar collector with liquid circulation. The collector converts the sun emitted radiation energy into heat energy. The energy captured is transferred to the water storage tank by forced convection. A regulation device controls the system by measuring the tank water and heat transfer fluid temperatures. The heat transfer in bulk has a slow dynamic and is not sensitive to fluctuations, so a simple control device is sufficient. The first part of this chapter is devoted to the technological description of the process. The second part deals with modelling and simulation aspects concerning the main components of a SHW system. Our mathematical model describes the thermal behaviour and energy balance of different solar collectors and hot water storage tanks. This model will be used to evaluate the performances of the system and simulates the impact of different parameters such as thermal efficiency of collectors, solar radiation and fluid characteristics on process efficiency. Simulation results using this model allow a better choice of appropriate components and help to evaluate the best design configurations under any operative condition, as they take into account occasional use as well as the seasonal and monthly domestic hot water demand.

2. MATHEMATICAL MODEL Water heating using domestic solar water heaters is the most feasible, economical and popular means of solar energy utilization in many countries of the world. In recent years the world market for their utilization has expanded significantly. There are many experimental and theoretical– numerical studies made on the performance evaluation of solar heating systems and storage tanks used on them under different operation or design

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parameters in the literature (Ucar And Inalli, 2007; Kharchi, Imessad, Sami, Hakem, Bouchaib, Chenak, Hamidat, Larbi-Youcef and Sahnoune, 2019). The thermal performance of the SHW system depends essentially of the collector efficiency and the pertinent choice of the heat fluid. Indeed, in this reference (Moghadam, Farshchi, Ashkan and Sharak, 2011), authors present how a MATLAB-based code is used to calculate the daily optimum tilt angle. For more efficiency, system can be also equipped with a controlled sun tracker photovoltaic system to maximize the collected solar irradiation. Different studies also show that maximum heat gain is obtained at highest heat convection, which can be obtained at highest air mass flow rate. On the other hand, at higher solar radiation value, the heat gain is relatively higher. In this section, a simple description of a SWH will be discussed. Figure 1 presents the different constituent elements of solar water heating system. For a typical installation with a storage tank having 0.2 m3 of capacity, the surface of the collector panel must be over 2 m2.

Figure 1. Schematic diagram of the SHW process.

The next section emphasizes the energy balance equations, which represent a system of thermal solar collectors. This model allow to demonstrate the effects of chosen parameters on the performance of the collector system.

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The model describing the behaviour of the solar thermal system is obtained using the global approach of each subset. Only the physical input and output parameters are taken into account. Pressure and thermal losses in the pipes are considered negligible and the tank temperature is uniform.

2.1. Heat Transfer within a Collector By Appling energy balance, we obtain governing equations of the heat transfer within solar collector: 𝑑𝑇𝑐𝑜 (𝑡) 𝑑𝑡

=

𝑄𝑓 𝑉𝑓𝑐 𝐶𝑝𝑓

𝑆𝑐 𝜂0 ∅(𝑡) 𝑉 𝑓 𝑓𝑐 𝐶𝑝𝑓

(𝑇𝑐𝑖 (𝑡) − 𝑇𝑐𝑜 (𝑡)) + 𝜌

+

𝐴𝑙𝑜𝑠𝑠 𝑆𝑐 𝑇 (𝑡)+𝑇𝑐𝑖 (𝑡) (𝑡) − 𝑐𝑜 (𝑇 ) 𝑒𝑥𝑡 𝜌𝑓 𝑉𝑓𝑐 𝐶𝑝𝑓 2 𝑑𝑇𝑐𝑖 (𝑡) 𝑑𝑡

=𝑉

𝑄𝑓 𝑓𝑡 𝐶𝑝𝑓

(1)

(𝑇𝑐𝑜 (𝑡) − 𝑇𝑐𝑖 (𝑡)) + 𝜌

ℎ𝑓𝑡 𝑆𝑡 𝑓 𝑉𝑓𝑡 𝐶𝑝𝑓

(𝑇𝑤 (𝑡) − 𝑇𝑐𝑖 (𝑡))

(2)

𝑇𝑖𝑛𝑠𝑖𝑑𝑒 (𝑡) is relative to the temperature indoor the house and could be assumed constant. 𝑇𝑐𝑜𝑙𝑑𝑓 (𝑡) is the temperature of cold water. For simulations, the parameter corresponding to the energy losses 𝐴𝑙𝑜𝑠𝑠 𝑆𝑐 𝑇 (𝑡)+𝑇𝑐𝑖 (𝑡) (𝑇𝑒𝑥𝑡 (𝑡) − 𝑐𝑜 ) 𝜌𝑓 𝑉𝑓𝑐 𝐶𝑝𝑓 2

can be neglected.

In this equation, 𝜂0 is the ratio between useful heat absorption by the fluid and the incident energy over the collector surface. By applying the Laplace transform to the equation (1) we obtain the following relationship:

𝑇𝑐𝑜 (𝑝) = where:

∝ ( 1⁄𝜏1 ) ∅(𝑝) 1+𝑝⁄ ( 𝜏1 )

+

−𝛽 𝛽 ( 1⁄2𝜏 ) ( 1⁄𝜏1 ) 1 (𝑝) 𝑇 + 𝑇𝑐𝑖 (𝑝) 𝑒𝑥𝑡 1+𝑝⁄ 1+𝑝⁄ ( ( 𝜏1 ) 𝜏1 )

(3)

142

F. Bagui and K. Kassmi 𝜏1 = 𝑉

𝑄𝑓

𝐴

𝑓𝑐 𝐶𝑝𝑓

𝑆

𝑆𝑐 𝜇0 𝑉 𝑓 𝑓𝑐 𝐶𝑝𝑓

𝑐 + 2𝜌 𝑙𝑜𝑠𝑠 , ∝1 = 𝜌 𝑉 𝐶𝑝 𝑓 𝑓𝑐

𝑓

𝐴𝑙𝑜𝑠𝑠 𝑆𝑐 𝑓 𝑉𝑓𝑐 𝐶𝑝𝑓

and 𝛽1 = 𝜌

(4)

This equation shows that the relationship between output temperature, solar flux, and temperatures of ambient air and input fluid is a sum of first order functions with τ as a time constant. Input temperature for the heat transfer fluid within the tank, the application of Laplace transformation to the equation (2), the transfer function can be written as follows:

𝑇𝑐𝑖 (𝑝) =

∝ ( 2⁄𝜏2 ) 𝑇𝑐𝑜 (𝑝) 1+𝑝⁄ ( 𝜏2 )

+

𝛽 ( 2⁄𝜏2 ) 𝑇𝑤 (𝑝) 1+𝑝⁄ ( 𝜏2 )

(5)

where: 𝜏2 = 𝑉 ∝2 =

𝑄𝑓 𝑓𝑐 𝐶𝑝𝑓

𝑄𝑓 𝑉𝑓𝑐 𝐶𝑝𝑓

+𝜌

ℎ𝑓𝑡 𝑆𝑡

(6)

𝑓 𝑉𝑓𝑡 𝐶𝑝𝑓

and 𝛽2 =

ℎ𝑓𝑡 𝑆𝑡 𝜌𝑓 𝑉𝑓𝑡 𝐶𝑝𝑓

(7)

2.2. Heat Transfer within the Storage Tank In reference (Comakl, Cakır, Kaya, Bakirci, 2012), transient thermal performance behaviour of a vertical domestic solar water heating system storage tank with a mantle heat exchanger has been investigated numerically in discharge/consumption mode. In our case, we consider that thermal stratification in the storage tank is negligible. In these conditions, temperature of water in the tank is given by:

Thermal Model and Simulations of Solar Water Heating 𝑑𝑇𝑤 (𝑡) 𝑑𝑡

=

143

ℎ 𝑆 𝑄𝑤 (𝑇𝑐𝑜𝑙𝑑𝑓 (𝑡) − 𝑇𝑤 (𝑡)) + 𝑓𝑡 𝑡 (𝑇𝑤 (𝑡) + 𝑉𝑓𝑡 𝐶𝑝𝑤 𝜌𝑤 𝑉𝑡 𝐶𝑝𝑤

𝑇𝑐𝑜 (𝑡)+𝑇𝑐𝑖 (𝑡) 𝐴 𝑆 ) + 𝑡 𝑐 (𝑇𝑖𝑛𝑠𝑖𝑑𝑒 (𝑡) − 𝑇𝑤 (𝑡)) 2 𝜌𝑤 𝑉𝑡 𝐶𝑝𝑤

(7)

In this study, we consider a closed-circuit cycle. In order to transfer heat between collector fluid and water inside the tank, a heat exchanger is used. The outlet of the collector and the inlet of the storage meet in a common space. This is where the transfer of the energy occurs; therefore, the temperatures of the storage outlet and the collector inlet are the same. Within the tank, the heat exchange takes place between the working fluid and the sanitary water. The collector fluid within a heat exchanger pipe passes through the storage fluid. There is no physical contact between the two fluids, but there is less useful surface for the heat transfer in contrast to the mixed heat storage. It is therefore necessary to make an energy balance to characterize the heat transfer fluid and the fluid contained within the tank. Water temperature inside the storage tank can be written as follows: 𝑇𝑤 (𝑝) =

∝ 𝛽 ( 3⁄𝜏3 ) ( 3⁄𝜏3 ) (𝑝) 𝑇 + 𝑇𝑐𝑜 (𝑝) 𝑐𝑜𝑙𝑑 1+𝑝⁄ 1+𝑝⁄ ( ( 𝜏3 ) 𝜏3 )

+

𝛾 ( 3⁄𝜏3 ) 𝑇𝑖𝑛𝑠𝑖𝑑𝑒 (𝑝) 1+𝑝⁄ ( 𝜏3 )

𝛽 ( 3⁄𝜏3 ) 𝑇𝑐𝑖 (𝑝) + 1+𝑝⁄ ( 𝜏3 )

(9)

where: 𝑄𝑤 𝑓𝑡 𝐶𝑝𝑤

+𝜌

𝑄𝑤 𝑓𝑡 𝐶𝑝𝑤

; 𝛽2 = 2𝜌

𝜏3 = 𝑉 ∝3 = 𝑉

𝐴𝑡 𝑆𝑐 𝑤 𝑉𝑡 𝐶𝑝𝑤

−𝜌

ℎ𝑓𝑡 𝑆𝑡

(10)

𝑤 𝑉𝑡 𝐶𝑝𝑤

ℎ𝑓𝑡 𝑆𝑡 𝑤 𝑉𝑡 𝐶𝑝𝑤

𝐴𝑡 𝑆𝑐 𝑤 𝑉𝑡 𝐶𝑝𝑤

and 𝛾3 = 𝜌

(11)

The model obtained allows the simulation of temperature evolution within the storage tank. In the case of non use of hot water, the sanitary water flow takes a zero value: Qw = 0.

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3. SIMULATIONS The system has three input parameters: solar irradiation, ambient temperature and the required mass flow of the loaded hot water. The mathematical model is used to evaluate the temperature evolution within the storage tank as function of solar irradiation. For a typical installation, the simulation of technical and physical parameters are given in the Table below. The mathematical model presented in the previous section, allows the simulation of different temperature evolutions as a function of solar flux radiation. In the present stage of the work, the simulation was carried out by means of measured data including global radiation, inlet and ambient temperature. Figure 2 presents an example of day radiation without any abrupt variation of solar flux. Simulations of fluid at the collector output and water fluid within the tank under these conditions are given in Figure 3. This simulation shows that after 5 pm the working fluid temperature at the panel inlets becomes lower than that of the water in tank. It is therefore necessary to stop the circulation of the working fluid to improve the thermal efficiency. Table 1. Simulation of Parameter values Parameter 𝐶𝑝𝑓

Value 6000

J/Kg.K

𝐶𝑝𝑤

4200

J/Kg.K

𝜌𝑓

1200

Kg/m³

𝜌𝑤 𝑆𝑡 𝑆𝑐 ℎ𝑓𝑡

1000 0,8 4 100

Kg/m³ m² m² W/m².K

𝐴𝑙𝑜𝑠𝑠 𝐴𝑡 𝜂0

0,4 4 85%

W/m².K W/m².K ------

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Figure 2. Solar radiation on a typical day.

Figure 3. Temperatures of Tco and Tw as a function of time.

This result shows that the numerical model offers a methodology to predict thermal behaviour of the system under different conditions in typical summer and winter days by using real data of solar flux.

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Figure 4. Temperature Tw as a function of flux.

Figure 6 presents temperatures of water in the tank and working fluid at the output of solar collector when the presence of clouds degraded the radiation.

Figure 5. Example of Solar flux with presence of clouds.

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Figure 6. Temperatures of Tco and Tw as a function of time.

These simulations show that the presence of a cloud has an immediate effect on the temperature fluid leaving the solar collector. It is therefore important to provide the system with a regulation that prevents the cooling of the water temperature within the tank.

CONCLUSION Integration of the solar process as a major improvement for the environment and energy saving. Using solar energy with solar water heating (SWH) technology has been greatly improved during the past century. In this chapter, physical process and mathematics of solar water heating are both carefully introduced. This model can constitute a basis for optimizing the dimensioning of a hot water heating installation by solar energy. Different simulations were carried out to estimate water temperature evolution within the storage tank. Results show that the application of active solar systems is very efficient. In many studies and publications, it is advised

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that the temperature of the usable water should be between 45 and 60 °C. In reference (Dehghan, and Barzegar, 2011) authors shows that in this case, the ratio of storage tank volume to collector area can be between 50 and 70 L/m2. Based on the above analysis, the system can improve its efficiency by being coupled to photovoltaic panels. For better efficiency, phase change materials can maintain operation overnight.

REFERENCES Amiche, A. El Hassar, S. M. K. Larabi, A., Khan, Z. A. Khand, Z. Aguilar, F. J. and Quiles, P. V. Innovative overheating solution for solar thermal collector using a reflective surface included in the air gap. Renewable Energy. Volume 151, May 2020, Pages 355-365. Buzas, J. Farkas, I. biro, A. and Németh, R. Modelling and Simulation of a Solar Thermal System. Mathematics and Computers in Simulations vol 48 (1998) pp 33-46. Comakl, K. Cakır, U. Kaya, M. Bakirci, K. The relation of collector and storage tank size in solar heating systems. Energy Conversion and Management 63 (2012) 112–117. Dehghan, A. A. and Barzegar, A. Thermal performance behavior of a domestic hot water solar storage tank during consumption operation. Energy Conversion and Management 52(1):468-476 (2011). Dhinakaran, R. Muraliraja, R. Elansezhian, R., Baskar, S. Satish, S. and Shaisundaram, V. S. Utilization of solar resource using phase change material assisted solar water Materials Today: Proceedings. Available online 21 July 2020. Kharchi, K. Imessad, K. Sami, S. Hakem, S. Bouchaib, S. Chenak, A. Hamidat, A. Larbi-Youcef, S. and Sahnoune, F. Solar energy for heating a building used for offices AIP Conference Proceedings 2190, (2019) https://doi.org/10.1063/1.5138491. Ma, T. Li, M. and Kazemian, A. Photovoltaic thermal module and solar thermal collector connected in series to produce electricity and highgrade heat simultaneously. Applied Energy. Volume 261, 1 March 2020.

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Moghadam, H. Farshchi, F. Ashkan, T. and Sharak, Z. Optimization of solar flat collector inclination. Desalination. Volume 265, Issues 1–3, 15 January 2011, Pages 107-111. Tagliafico, L. A. Scarpa, F. and De Rosa, M. Dynamic thermal models and CFD analysis for flat-plate thermal solar collectors – A review. Renewable and Sustainable Energy Reviews. Volume 30, February 2014, Pages 526-537. Ucar, A. and Inalli, M. A thermo-economical optimization of a domestic solar heating plant with seasonal storage. Applied Thermal Engineering; Volume 27, Issues 2–3, February 2007, Pages 450-456. Young, H. U. C. Kim, B. Chang-Hyo Sonc, C. H. Yoon, J. I. and Choi, K. H. Experimental study on the performance of heat pump water heating system coupled with air type PV/T collector. Applied Thermal Engineering. Volume 178, September 2020, 115427.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 7

THERMAL PERFORMANCE EVALUATION OF A MODIFIED SOLAR WATER HEATER INTEGRATED WITH PARABOLIC TROUGH CONCENTRATOR V. Rastogi1, A. Saxena1,*, A. K. Singh1 and M. Karakilcik2 1

Department of Mechanical Engineering, Moradabad Institute of Technology, Moradabad, India 2 Department of Physics, Cukurova University, Adana, Turkey

ABSTRACT Parabolic trough concentrators (PTC) are one of the best techniques to utilize the available solar energy for different heating process like thermal power generation etc. Therefore, in the present work efforts have been made to approach this technique for minimizing the demand of hot water supply in residential and commercial sectors. For this, a PTC has been developed for a specific geographic location i.e., Moradabad city, India. Further, it has been integrated into a new designed close and open loop based solar water heating system. Attention has been given to develop the water heating system and experimentally comparison of thermal performance of close loop circulation (by using mineral oil) and open loop

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V. Rastogi, A. Saxena, A. K. Singh et al. circulation system. The experimental study investigates the thermal performance of proposed solar water heating system. Thermal efficiency is taken as a performance parameter to show feasibility of the present system to perform round the year at any region which is full of sunshine. The aim of the experimental study is not only to design a user friendly water heater but also to develop a compact water heating system that can save the fossil fuels and electricity consumed for water heating in buildings like, simple households, hospital and hostels at zero pollution during operation.

Keywords: parabolic trough, water heater, thermal performance, testing

NOMENCLATURE Symbol X Y p f a h ɸ D CRo Ar Ir Ia ή ES EC m ρW VW Cp Ti+1 Ti Tamb Twat A I Ih

Parameter length of abscissa from origin length of corresponding ordinate distance from vertex to focus focal length of the parabola aperture width of parabola height of parabola rim angle of parabola diameter of receiver tube optical concentration ratio surface area of receiver solar radiations reflected by the reflecting surface of collector solar radiations fall on the aperture area of collector thermal efficiency energy stored in the tank energy received by the collector mass of water accumulated in the tank density of water volume of water in the tank specific heat of water average temperature of tank water at (i+1)th time average temperature of tank water at ith time ambient temperature water temperature aperture area of trough collector Solar intensity falling on trough collector hourly direct beam solar irradiations

Unit cm cm cm m m m degree m m2 W/m2 W/m2 % J J kg Kg/m3 m3 J/kg℃ ℃ ℃ ℃ ℃ m2 W/m2 J/m2h

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1. INTRODUCTION Increasing consumption of energy and its effect on nature in the form of extreme weather conditions, global climate change, acid rain, global warming etc., encourage government to adopt and researchers to work for clean energy resources. One of a best option to satisfy energy demand is to use solar energy as a gift of nature (Saxena and Agarwal, 2018). Solar energy is a high temperature and radiant energy source with none of any problem like atmospheric emissions. India is blessed with an average of over 1500 sunshine hours and 300 sunny days a year. Theoretically, India has a reception of five trillion KWh (Saxena et al., 2020). It has ability to satisfy demand at commercial and domestic level but the only problem is the unavailability of practical systems which can collect and store the energy in effective manner (Saxena and Karakilcik, 2017). Solar energy systems are non-polluted systems through which the risk of various accidents is negligible (Saxena et al., 2013) therefore our life is completely risk free while utilizing the solar energy systems. Number of the applications has been operated on this clean and free source of energy such as;       

Solar cooking systems (Saxena et al, 2012) Solar air heating systems (Saxena et al, 2020) Solar drying systems (Saxena and Goel, 2013) Solar space heating (Saxena et al., 2015) Solar water heating systems (Saxena aand Srisatava, 2012) Solar distillation systems (Saxena and Deval, 2016) Solar electricity generating systems (Saxena and Goel, 2013)

Noticeably, Flat plate solar collectors (FPC) are the one of a most popular conventional technology to produce power by using sunlight (Saxena et al., 2013). The major drawback behind FPC panels is static position which leads to its limited effective exposure to the sunlight. While its large space occupied and bulky nature makes it unfit for domestic purpose. These problems can be easily solved by solar concentrators which

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are considered to be most effective to work as a solar hot water system (Saxena et al., 2013). Solar concentrators have the speciality of high concentration ratio due to the embedded reflecting surfaces which concentrates the incident solar energy falling on collector, onto the absorber surface. The only limitation of CSP systems is that only direct beam radiations can contribute to produce energy while flat solar panels can take benefit from direct as well as diffuse radiations (Saxena et al., 2020). Among all concentrated solar power technologies (CSP) such as parabolic dish collector, parabolic trough collector (PTC) and Fresnel towers, the PTC technology is grooving up all over the world and proved to be highly effective for commercial water heating applications (Mendelshon, 2012). The parabola is an intriguing geometry with useful practical applications including solar concentration. The curve of the parabolic collector is such that the light travelling parallel to the axis of a high reflecting parabolic sheet will reflect from it and concentrate on a single point that is the focal point of parabolic curve. A parabolic trough is the extension of the parabolic curve to 3D geometry, along with the focal point into focal line. Physically, a pipe with a flowing liquid is located on this focal line. The incident sun rays falling on the parabolic trough, concentrates it on this pipe which act as an absorber of heat and use to transfer the heat to the liquid flowing through it. The liquid use here is carrier of enthalpy which can be move in open or close loop to heat the water. Therefore, a PTC solar water heater consists of (1) a collector, (2) an absorber and (3) working fluid and (4) a storage tank (5) PTC. A large number of researches are going on PTC technology due to its large number of applications. Most of the work is available for the design improvement of PTC to increase the overall efficiency of the system operating at high temperature. The PTC technology can also be useful for domestic water heating (Vinuesa et al., 2016). In this work, a most practical design of low cost, compact and user friendly domestic water heating system integrated with parabolic trough has been experimentally studied. Along with this, the model of SWH has fabricated and experiments have performed to analyse the performance of open and close loop system to determine the best fit for domestic use.

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2. SYSTEM DESIGN The collector is of 3D parabolic geometry which consists of the number of focal points of the parabolic cross-sections. The incident sun rays falling on the collector get concentrate on the focus. This phenomenon creates an opportunity of heat concentration at these focal points. The main characteristics which define the effectiveness of the PTC are its: length, focus, aperture, rim angle and reflecting surface. The large length and aperture width of the trough increase the exposure to the sunlight which results in more heating but the material as well as space constraints these parameters in limit. The position of the focal point of parabola completes its geometry by defining the ideal location of receiver tube and the distance from it up to the vertex of parabola is called focal length. The parabola can be described by the drawing the following curve in Cartesian coordinates:

2  4 p.Y

(1)

X = length of abscissa from origin Y = length of corresponding ordinate p = distance from vertex to focus The above equation can be rewrite in terms of height (h), aperture width (a) and focal length (f) of the parabola:

a2  16 f .h

(2)

From the above equation, it can be concluded that on keeping the aperture width constant, the focal length increases with increase in flatness (Figure 1). This flatness of the collector also characterizes another important constructive trait of the parabola called rim angle (Ф). The less value of rim angle means the curvier parabola. The rim angle may be finding in terms of the parabola dimensions (Mohammad, 2012):

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 a 2h  tan   1/     8h a 

(3)

Figure 1. Half cross section curve of cylindrical parabolic trough collector.

The receiver is one of the most complex elements of the PTC system which plays a vital role in overall performance (Vinuesa, 2016). Therefore, selecting its design parameters carefully is an important task. The receiver diameter (D) can be theoretically calculated using aperture width and rim angle as follows (Mohammad, 2012):

D

a.sin(0.267) sin( )

(4)

The diameter of receiver decides the intercept factor for the system which can define as the ratio of light intercepted on the receiver tube to the energy reflected. Many experiments had been performed to increase the value of intercept factor by using different methods like use of evacuated glass envelope, black coatings for high absorptivity and polish to decrease emissivity for the tube surface (Yaghoubi and Ahmadi, 2013; Sagde and Aher, 2013; Ladgoankar et al., 2014; Ali et al., 2017; Daviran et al., 2016). The most appropriate among all carried out treatments consists in using

Thermal Performance Evaluation of a Modified Solar Water Heater … 157 black high paint which is simple, economic and effective for systems having working temperature less than 200oC (Mohammad, 2012; Afsar et al., 2014). The evacuated glass envelope can be used to make the participation of diffuse solar radiations possible but as per the consideration of cost to efficiency ratio, it is suitable for systems operating at more than 110oC (Jarmillo and Borunda 2013). The absorbed radiation on the surface in the form of heat, is need to transfer to working fluid by conduction and convection. So, the high thermal conductivity also becomes an essential feature of the receiver tube. The materials generally used for receiver tube are copper, aluminium and stainless steel (Brooks and Mills, 2005; Valan, 2007; Jarmillio and Venegas, 2013; Coccia and Nicola, 2012). Reflecting surface is used to make the trough surface brighter in order to reflect as much as radiations to the receiver. To improve the efficiency of the system, provision is to use glass mirror, stainless steel sheets, aluminium sheets, stretched coated, or stretched membranes (Hamza and Mokhiamar, 2016). The selection of the reflecting surface greatly affects the Optical Concentration Ratio (CRO) of the system. It can be calculated using the following equations (Kumaresan et al., 2012):

CRo 

1/ Ar  Ir.dAr Ia

(5)

Where, Ar is the receiver’s surface area, Ir represents radiations reflected by the reflecting surface of collector and Ia is the radiations fall on the collector aperture area while the geometric concentration ratio (CRG) is the ratio of aperture area to the surface area of trough collector. Working fluid behaves as the thermal energy storage (TES) carrier which transfers the heat from receiver tube to storage system through the insulated pipes. The selection of appropriate thermal fluid for the PTC system is an important task and can be considered on the basis of some important factors like availability, toxicity, cost etc. Some available heat transfer fluids that are using currently for parabolic trough collectors are water, nanofluids, glycol, mineral oils, molten salts, molten metals and

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synthetic oils (Zarza et el., 2001; Geyer et al., 2001; Kerney and Herrmann, 2012; Mohammed, 2012). Table 1. Design parameters for the proposed parabolic trough solar water heating system Sr. No. 1

Components Collector

2 3

Reflecting surface Receiver

4

Coating

5 6

Insulation Working Fluid (close loop)

7

Tank

8

Pump

9

Thermostat

Item length Aperture width Focal length Rim angle Height Material Material Reflectance Length Internal Diameter Outer Diameter Material Material Absorptivity Material Material Supplier Operating temp. range Volume Material Supplier Power Voltage Head max Output Supplier Temperature control range Input power

Value 1m 0.6m 0.15m 90 0.15m Aluminium Miller film 75% 1m 0.010mm 0.012mm Copper Black paint 85% Glass-wool Mineral oil (Hydro treated heavy paraffinic distillate) ParathermTM HE 0oC-330℃ 1×0.5×0.5 m3 Mild Steel Sunpak 1 HP- 2HP 165-250V/50Hz 1.85m 1100L/H Generic SE121 -50-110 DC12V

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Figure 2. Open loop circulation system.

Figure 3. Close loop circulation system.

The main aspect behind the selection of working fluid is the system’s application of the work. Water as the cheapest fluid can be suitable for low temperature applications (Mohammed, 2012) while for high temperature and close loop systems nanofluids, mineral oils and molten salts can be a good choice.

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The design parameters for the proposed design have been decided on the basis of our demand of size, material availability, maximum temperature and economic cost of the desired system (Table 1). In close loop circulating system (Figure 3), the mineral oil (caloria) circulates through the pipe in the closed loop with the help of a positive displacement pump. When the pump is ON, the fluid starts circulating, increases its temperature during the passage through the hot absorber tube and transfers the large amount of heat to the reservoir water while in open loop circulation (Figure 2), normal water pumps from the reservoir tank, passes through the hot absorber tube, get heated and return back to the reservoir. In each cycle the water temperature rises and cycle repeats again and again until the desired temperature is achieved. The user has to just install the system on the roof. Then the only need is to switch it ON, during high solar intensity period and save the reading of desired water temperature on the thermostat keypad that should be less than 100oC. When the water attains the temperature saved on the thermostat, then the supply to the pump automatically cut down and consequently water circulation stops. The hot water stored in the insulated tank can be supplied via pipeline to the tap as per demand. The collector is faced towards East-West direction so that the solar beam radiations directly reflects to the black painted copper tube during best working hours. It avoids the complexity; cost as well as power spends for the tracking of the system which is desirable in our case. In the Solidworks™ software, a complete three-dimension model of both the proposed parabolic trough water heating systems is established.

3. EXPERIMENTAL METHODOLOGY The experimental work has been performed at the rooftop of Moradabad Institute of Technology campus, Moradabad, India (latitude- 28.8467N, longitude- 80.9462E). First of all, experiments are carried out to plot the hourly irradiance vs time behaviour for two extreme climatic conditions i.e., during the month January (winter) and March (summer). Two days, having

Thermal Performance Evaluation of a Modified Solar Water Heater … 161 almost the same weather conditions has been selected from January and March 2020 to analyse the performance of open loop and close loop circulation system, respectively. Then performance of open loop system measured on 02.01.2020 and 13.03.2020 while for close loop system, on 03.01.2020 and 14.03.2020.

(a)

(b)

(c)

Figure 4. Various components of parabolic trough solar water heating system at MIT, Moradabad {(a) wooden PTC cabinet (b) PTC with GI pipes and (c) complete PTC}.

About the measuring instruments, a 10 wire k-type thermocouple meter with 0.1 of accuracy is used for temperature variations, an anemometer with 0.2 accuracy is used for wind velocity measurement, a commonly used apparatus ‘solarimeter’ with accuracy of 1 W/m2 is used for irradiance measurement. The performance of both the proposed heating systems has assessed by calculating thermal efficiency for both the system in summer and winter season. The thermal efficiency of the proposed system (Figure 4) is defined as the solar energy stored in storage tank per hour to solar energy received by the collector per hour (Kumaresan et al., 2012). ή = Energy stored in the tank/Energy received by the collector

 

Es Ec

(6)

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The energy stored in the water storage tank is the energy collected in the tank throughout an hour interval which can be calculated as (Bhakta and Pandey, 2018):

Es  mC p (Ti 1  Ti )

(7)

While hourly solar energy received is the total amount of direct beam solar irradiations fall on the aperture area of the trough collector. EC = A.Ih (8) Now,



mC P (Ti 1  Ti ) AI

(9)

where, m = mass of water accumulated in the tank (kg) = ρWVW = 1000 × 0.2 = 200 kg CP = Specific heat of water = 4180J/kg℃ Ti = Average temperature of tank water at ith time (℃), Ti+1 = Average temperature of tank water at (i+1)th time (℃) A = Aperture area of trough collector= 0.6 m2 Ih = Hourly direct beam solar irradiations (W/m2)

4. THERMAL PERFORMANCE ANALYSIS At the geographical zone, the experiments have been performed to determine the behaviour of direct beam solar irradiation with time. The variations of solar beam irradiation with respect to time have been measured on 2nd January, 3rd January, 13th March and 14th March. All the readings are taken from 11 am to 4 pm with a time gap of one hour using pyrheliometer (CHP1-L).

Thermal Performance Evaluation of a Modified Solar Water Heater … 163 From the above graph, it can be observe that for both summer and winter, the maximum value of solar beam irradiation is nearly found at 1 pm and then starts to decrease. For March, the value of maximum solar beam irradiation on the surface is about 760 W/m2 while for January; it is only 670 W/m2. As a part of experiment, four tests have been conducted to analyse the performance of two proposed systems. The performance of open loop system is measured on 02.012020 and 13.03.2020 while for close loop system, on 03.01.2020 and 14.03.2020. All the tests have been conducted from 11am to 4:30 pm with a time interval of 30 minutes to control the variation of Tamb and average Twat inside the tank with time. The tank temperature measured using digital thermostat (Generic SE121) which is a part of proposed system while ambient temperature of the environment measured using LM35D analog temperature sensor module. Figure 5, 6, 7, 8, 9, 10 and 11 shows the thermodynamic performance of the new design on open and closed loop configuration under the climatic condition of Moradabad city.

Figure 5. Variation of beam irradiation with respect to time.

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Figure 6. Variation of Storage tank Twat and Tamb with time for open loop circulation solar heating system on 13th March.

From the above graphs plotted to analyse the performance in summer, it can be clear that for open system the peak temperature achieved by the tank water is 86oC while for close loop circulation system it is only 73oC. It can also be found that the rate of rise and fall in temperature for open loop system is higher than the close loop system where the maximum temperature of tank water can be maintain for longer period due to high thermal capacity of the mineral oil (hydro treated heavy paraffinic distillate).

Figure 7. Variation of Storage tank Twat and Tamb with time for close loop circulation solar heating system, on 14th March.

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Figure 8. Variation of storage tank Twat and Tamb with time for open loop circulation solar heating system, on 2nd January.

From the above graphs plotted to analyse the performance in winter, it can be observe that for open system the peak temperature achieved by the tank water is 63℃ while for close loop circulation system it is only 52℃. Again like summer, the increasing and decreasing rate in tank temperature of open loop circulation system is higher than the close loop system. Moreover for both the seasons, the time taken to attain the maximum value of stored Twat by the open system is almost one hour prior than the close loop system.

Figure 9. Variation of storage tank Twat and Tamb with time for close loop circulation solar heating system, on 3rd January.

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Figure 10. Variation of Thermal efficiency with time in March.

From the temperature curves drawn for the proposed open and close loop circulation system in both seasons, the thermal efficiency has been calculated to determine the performance. It can be observed from the above plot, showing variation of thermal efficiency with time that in March the maximum value of thermal efficiency obtained for open loop and close loop circulation is 34% and 22% respectively while for January the values are 26% and 17% respectively. It is also interesting to note that the value of thermal efficiency for open loop circulation system is much higher than the close loop circulation during the early span of day when the intensity of solar irradiation is high while after 2 pm the close loop system becomes more efficient than the open loop. This is due to the large heat absorbing capacity of mineral oil than water which makes it capable to keep heat transfer process continuous even at low solar intensity.

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Figure 11. Variation of Thermal efficiency with time in January.

Table 2. Results comparison with conventional systems Sr. No. 1

Component Category Reflecting surface Solar tracking system

Kumaresan et al., (2012) Parabolic glass Mirror Semi atomatic tacking System

Santosh et al., (2012) Rectangular mirror strips Automatic tracking system

3

Sunlight receptor

evacuated glass tube

4

Working fluid

Borosilicate glass cover envelope Therminol 55

5

Max. thermal efficiency

2

35%

Thermic fluid 20%

Current System Miller Sheet Manual tracking with a facility to move freely the whole system by providing wheels on the base of reservoir to trace sunlight _____

Water and Mineral oil 34%

The result of the proposed system has been compared to two previously developed thermal hot water systems by Santosh et al., (2012) and Kumaresan et al., (2012) as follows (Table 2). Kumaresan et al., (2012) developed a PTC system, integrated with thermal energy storage tank containing 230 L of Therminol-55 as heat transfer fluid and positive displacement pump. The system was incorporated

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with absorber tube surrounded by borosilicate glass envelope to reduce heat loss and a single axis tracking system consists of timer control, AC motor and reduction gear box. On a clear sunny day, the maximum thermal efficiency of overall system was evaluated to be around 35%. Santosh et al., (2012) design and fabricate a parabolic trough solar water heater for hot water generation. The efficiency of the PTSC was measured for two absorber tubes of copper and aluminum. A composite 1.5 mm thick glass mirror having reflectivity of about 92% was used as a reflecting material on a support having manual tracking system. The experiment was conducted on 15th April (Ia = 705 W/m2, Tamb = 31.9C), the maximum efficiency were found to be 20.25%. The maximum thermal efficiency is 34% for open loop circulation system while it is 22% for close loop circulation system. These figures are much more optimistic with respect to conservative economic inputs (low increase of energy on high investment) and show the proposed water heater as a viable concept.

5. ECONOMIC ANALYSIS The proposed system has been designed kept in mind the overall cost effectiveness of the system. Various expensive components which previously were the essential part for the large scale system and whose cost/efficiency ratio is not found to be good for domestic and low temperature application system, have been removed or replaced with some other alternatives to reduce the cost and simplify the whole water heating process. Different kinds of cost associated with the current system, after cutting down the various expensive components are as follows:

5.1. Raw Material Cost All the raw material for the system has been arranged from local market of Moradabad city (Table 3).

Thermal Performance Evaluation of a Modified Solar Water Heater … 169 Table 3. Raw Material Price for the proposed heating system Sr. No. Raw material 1 Aluminum sheet 2 Miller film 3 Copper tube 4 Mild steel sheet 5 Galvanized steel pipes 6 Pump 7 Thermostat 8 Glass wool 9 Overhead Total raw material cost

Quantity 4.05 kg 1 m2 700 g 25 kg 6 kg 1 1 6 kg --------

Price (INR) 580 240 300 1125 360 350 320 240 500 4015 = $61.11

5.2. Manufacturing Cost The system designed to simplify the overall manufacturing process. The removal of tedious tasks like evacuating and cutting the glass tube, manufacturing the parabolic glass mirror and complex tracking system intensely decrease the total manufacturing cost.

5.3. Transportation Cost The system is free to assemble and disassemble into multiple components which make it portable as well as compact in nature. Moreover, the sensitive components like evacuated glass tube and glass mirror are also removed to make the transportation process easy.

5.4. Maintenance and Replacement Cost Due to absence of any sensitive component in the system, there is negligible or very low maintenance and replacement cost. The easy

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disassembling property of the system allows to easy replacement of damaged part only.

5.5. Operating Cost The system is designed to minimize the human intervention or supervision to the system operation. A thermostat and auto-cut positive displacement pump is provided to set the desired temperature and automatic turning off the fluid circulation process on acquiring the set temperature. Moreover, the tracking system is not present which reduces the cost of using auxiliary power sources. The proposed system can saves about 30MJ of energy per day in heating 500 litres of water per day. This is to taking up the tank water temperature from ambient temperature to about 80°C. There are 300 sunny days in a year therefore the heating system can be used for 300 days per year. The economic evaluation and payback period have been computed by considering the following: Raw material cost = Rs. 4015 Manufacturing cost = Rs. 4000 Other overhead costs = Rs. 2000 Energy saving = 30MJ/day Electricity price = Rs. 6/unit Total working days = 300 Payback Period = (Total cost/ Total saving per year) × 365 days = (1015/ 14400) ×365 days = 253.5 days The payback period for the proposed solar water heating system has been worked out by considering total 300 working days per year, comes out to be around 253 days.

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CONCLUSION In the present work efforts have been made to approach a technique for minimizing the demand of hot water supply in residential and commercial sectors. For this, a PTC has been developed for a specific geographic location i.e., Moradabad city of India. Further, it has been integrated into a new designed close and open loop based solar water heating system. Attention has been given to develop the water heating system and then experimentally comparison of thermal performance of close loop circulation (by using mineral oil) and open loop circulation system using the plots of direct solar beam irradiation, ambient temperature, tank water temperature curves. It has been observed that the rate of rise and fall in temperature for open loop system is higher than the close loop system where the maximum temperature of tank water can be maintained for longer period due to high thermal capacity of the mineral oil (caloria). The thermal efficiency taken as a performance parameter for the propose water heating system. In March the maximum value of thermal efficiency obtained for open loop and close loop circulation is 39% and 26% respectively while for January the values are 37% and 22% respectively which shows the present system is feasible to perform round the year at any region which is full of sunshine. It has been found from the experimental study that both the proposed water heating systems are not only compact, low cost and user friendly but also efficient that can save the electricity consumed for water heating in homes and buildings like hospital and hostels.

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Saxena, A. and Srivastava, G. (2013). Performance studies of a multipurpose solar energy system for remote areas. MIT International Journal of Mechanical Engineering, 3: 21–33. Saxena, A. and Goel, V. (2013). A technical note on- fabrication and thermal performance studies of a solar pond model. Journal of Renewable Energy, Article ID 475282: 1-5. Saxena, A. Goel, V. (2013). Solar air heaters with thermal heat storages, Chinese Journal of Engineering, Article ID 190279: 1-11. Saxena, A., Goel, V. and El-Sebaii, AA. (2015). A thermodynamic review of solar air heaters. Renewable and Sustainable Energy Reviews, 43: 863-890. Saxena, A., Goel, V. and Karakilcik, M. (2018). Solar food processing and cooking methodologies. Applications of Solar Energy, Springer-Nature Series, 251-294. Saxena, A. and Karakilcik, M. (2017). Performance evaluation of a solar cooker with low cost heat storage material. International Journal of Sustainable and Green Energy, 6 (4): 57-63. Saxena, A., Verma, P., Srivasatva, G. and Nandkishore. (2020). Design and thermal performance evaluation of an air heater with low cost thermal energy storage. Applied Thermal Engineering, 167: 114768. Saxena, A., Agarwal, N. and Cuce, E. (2020). Thermal performance evaluation of a solar air heater integrated with helical tubes carrying phase change material. Journal of Energy Storage, 30: 101406. Saxena, A. and Deval, N. (2016). A high rated solar water distillation unit for solar homes. Journal of Engineering, Article ID 7937696: 1-8. Saxena, A., Agarwal, N. and Srivastava, G. (2013). Design and performance of a solar air heater with long term heat storage. International Journal of Heat and Mass Transfer, 60: 8-16. Vinuesa, R., de Arevalo, L. F., Luna, M. and Cachafeiro. H. (2016). Simulations and experiment of heat loss from a parabolic trough absorber tube over a range of pressures and gas compositions in vacuum chamber. Journal of Renewable and Sustainable Energy, 8: 023701711.

Thermal Performance Evaluation of a Modified Solar Water Heater … 175 Yaghoubi, M., Ahmadi, F. and Bandehee, M. (2013). Analysis of heat losses of absorber of parabolic trough collector of Shiraz solar power plant. Journal of Clean Energy Technologies, 1: 33-37. Zarza, E., Valenzuela, L., Leon, J., Weyers, H. D., Eickhoff, M., Eck, M. and Hennecke, K. (2001). The DISS project: direct steam generation in parabolic trough systems operation and maintenance experience: update on project status. ASME Journal of Solar Energy Engineering, 124: 126133.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 8

HYDROGEN PRODUCTION AND SPACE HEATING USING WATER HEATED BY SOLAR RADIATION Ayhan Atiz1, Hatice Karakilcik2 and Mehmet Karakilcik3, 1

Department of Mathematics and Science Education, Alanya Alaaddin Keykubat University, Antalya, Turkey 2 Department of Geology Eng, Cukurova University, Adana, Turkey 3 Department of Physics, Cukurova University, Adana, Turkey

ABSTRACT In this chapter, water heating performance of evacuated tube solar collectors (ETSCs) which harvesting solar radiation is investigated. It is aimed to produce electricity and hydrogen with the hot water obtained. For this purpose, water from the geothermal source is pumped to the ETSCs to obtain water at sufficient temperature faster. Thus, a considerable amount of electrical energy is generated by the organic Rankine cycle (ORC) that



Corresponding Author’s E-mail: [email protected].

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Ayhan Atiz, Hatice Karakilcik and Mehmet Karakilcik is operated using water heated by solar radiation. N-butane and isobutane are considered as a working fluid in the ORC and it is found that the performance of n-butane is higher than isobutane. While hydrogen was produced with the electrical energy produced by the ORC, space heating was performed for mushroom production by using the waste heat in the system. Energy and exergy analyses of the system were carried out by utilizing the Engineering Equation Solver (EES) software. As a result, it is observed that under solar radiation, ETSCs can produce hot water at a temperature that will operate ORC and a significant amount of hydrogen can be produced.

NOMENCLATURE A C con Ė EES ETSC Ėx Eva Fung h ṁ ORC PEM S T Tur U Q̇ W

surface area (m2) specific heat capacity (J/kg °C) condenser energy (W/m2) engineering equation solver evacuated tube solar collector exergy evaporator fungus enthalpy (kJ/kg) mass flow (kg/s) organic Rankine cycle proton exchange membrane entropy (kJ/kg K) temperature (℃ or K) turbine heat loss coefficient heat (W or kW) power (kW)

Hydrogen Production and Space Heating Using Water …

Greek Symbols η ψ Δ

efficiency exergy efficiency difference

Subscripts con el ETSC eva fung G geo in m net ORC out pump r R s solar sys T th tot U w 0

condenser electricity evacuated solar collectors evaporator fungus generator geothermal inlet mean net power organic Rankine cycle outlet pumping reference removal sun solar radiation system turbine thermal total useful water reference

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1. INTRODUCTION In recent times, the energy demand of the world has reached different dimensions with the gradual decline of available energy resources and changes in world politics. Nowadays, industrialization, population growth and rapid urbanization cause to demand more energy than the past. Therefore, humanity has been tried to utilize different forms of energy. Solar energy and geothermal resources are important resources that can be used to provide the energy needs of societies around the world. Solar energy is a vast resource. It is important to produce usable energy by employing solar energy. Systems that produce thermal energy or electrical energy by utilizing solar energy are solar technologies. One of the solar technologies is the solar collector that converts solar energy into thermal energy to transfer to the flowing water in it. The thermal energy that store in a tank can be utilized whenever needed (Kalogirou 2004). Thus, solar energy can be used to produce thermal energy for different purposes. For example, solar collectors are clean, economical, applicable and environmentally friendly. Therefore, they can be used as an alternative to fossil fuels in industry, which is an important part of real life (Kumar et al. 2019). Also, the thermal energy is produced by the solar collectors can be stored in a tank to provide heat demand, cooling and feed water at cloudy days or night (Tian and Zhao 2013). One of the solar collector technologies is the evacuated tube solar collectors (ETSCs) that have advantageous thermal performance and hot water than flat plate solar collectors (FPCs) (Chow et al. 2011). Besides, ETSCs were found to be more economical than FPC up to 41% and was obtained more useful thermal energy than FPC by 30% in the simulation TRNSYS16 for cold climate (Sokhansefat et al. 2018). ETSCs can increase the temperature of the water from low-grade to high-grade in a short time. The different inlet temperatures of the water were increased to a higher temperature by using varied numbers of the ETSCs. For example, the temperature of 4 L/min mass flow rate water can be increased from 17℃ to 80℃ by employing 25 pieces ETSC under solar radiation 800 W/m2 (Martínez-Rodríguez et al. 2018). ETSCs can be used for different purposes. One of them is that solar energy can be converted to thermal energy by the

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ETSCs to provide a large portion of the heat demand of normal family-size. (Kroll and Ziegler 2018). Geothermal sources are important thermal energy sources. The energy sources can be used for electricity generation, heating (regional, residential, thermal facility, greenhouse, etc.), chemical production, drying, plant and aquaculture, thermal tourism etc. (General Directorate of Electrical Works Survey Administration (EIE) Ankara. The temperature of most of the geothermal resources in the world is below 150℃ (Li et al. 2020). Therefore, higher temperature fluid can be obtained by integrating the geothermal source with solar collectors. For example, a room was heated by using ETSCs integrated a heat pump and a rather low temperature geothermal source. Solar collectors provided 48% of the heat requirement of the room (Kim et al. 2013). To produce electrical energy, organic Rankine cycle (ORC) is very important system that produces electrical energy by using the thermal energy that produces from solar radiation or geothermal source. For this purpose, (ORC) can produce electricity by using thermal energy that is obtained by solar technologies and geothermal source. Also, ORC is one of the key technologies that generate electricity from low temperatures source (Saleh et al. 2007). For example, three different geothermal sources with a temperature of 63℃, 74℃, and 86℃ were integrated with the ETSCs that increased the temperature of the geothermal fluid higher degrees than initial source temperature. In this system, the electricity generation performance of the integrated system was examined using n-butane, n-pentane and n-hexane in the ORC as a working fluid and it was found that the best option is the combination of n-butane and geothermal source at 86℃. In addition, the average ambient temperature in this system is 16.7℃ (Atiz, et al. 2019). The electrical energy generated from any system can be converted to other energy forms for later use. One of the important forms is the hydrogen production via electrolysis system by utilizing electrical energy. Hydrogen is a suitable energy form for storing and using whenever needed (Bicer and Dincer 2016). The electricity produced in many systems that ETSCs are integrated or not integrated can be converted to hydrogen. For example, in a study, monthly hydrogen production performances of the system integrated with ETSCs and FPCs were compared to for total 10 m2 area of the collectors

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and it was found that the system with ETSCs produced more hydrogen than the system with the FPSCs. Hydrogen was produced in all other months except for some winter months when solar energy was low (Atiz and Karakilcik 2020). Another solar thermal integrated system that consisted of the ETSCs with a solar pond is used for generation electricity and hydrogen daily. The total area of the ETSCs and solar pond were 300 m2 and 217 m2 in the integrated system. ORC produced 377 MJ of electrical energy for using in the electrolysis system that generated 3204 g of hydrogen for a day (Atiz et al. 2019). Another integrated system was designed with 2.4 m2 photovoltaic (PV), 34.8 m2 ETSCs and Proton Exchange Membrane (PEM) electrolysis system to investigate electricity and hydrogen production under 400-1000 W/m2 solar radiation. The electricity and hydrogen production increased from 130.6 kW to 154.8 kW and 0.0007 kg/s to 0.0013 kg/s when solar radiation increased from 400 to 1000 W/m2 (Corumlu, et al. 2018). If any system operates with solar energy and geothermal source for producing electricity and hydrogen, the efficiency of the system must be found for thermodynamics analyses. Energy and exergy efficiencies of the system were determined to evaluate the system thermodynamically. Thus, extremely important data can be obtained for a system thermodynamically (Arabhosseini et al. 2019). The thermal energy, electricity and hydrogen production performance of the ETSCs integrated or non-integrated has been researched in some studies. The aim of this study is to investigate the energy and exergy analyses and electricity and hydrogen production of the ETSCs integrated with a geothermal source. When the literature is examined, there is almost no study about ETSCs integrated with geothermal resource to produce thermal energy for converting hydrogen. Thus, this study aims to contribute to the literature for integrated systems in future studies about the solar collectors integrated with geothermal source to generate thermal energy, electricity and hydrogen. In this study, ETSCs integrated with geothermal source produced thermal energy under daily solar radiation for the ORC that is operated n-butane and isobutane to generate electrical energy. Finally, electrical energy was used for hydrogen production in the electrolysis system. As a result, electricity and hydrogen production of the two configurations were compared to

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evaluate their performance. It was seen that electricity and hydrogen can be produced in both systems but the performance of the n-butane was found higher than isobutane. This study proposes to store thermal energy produced by using solar radiation and geothermal source by converting to hydrogen. Thus, this study contributes to the literature in that for storing the produced thermal energy as hydrogen.

2. SYSTEM DESCRIPTION The system in the Figure 1 consists of a geothermal source, ETSCs, a fungus production room, an ORC that is operated n-butane and isobutane and an electrolysis system. In brief, the ETSCs increase the temperature of the geothermal fluid under daily solar radiation to operate the ORC for generating electricity. So, the electrolysis system uses that electricity for hydrogen production as a final product. In detail, geothermal water from the production well is pumped to the ETSCs by pump1 to obtain high temperature fluid under daily solar radiance. So, the upgraded fluid enters the evaporator from point 3. Significant amount of heat energy is absorbed by the working fluid in the ORC and the evaporated fluid expands throughout the turbine to generate electricity. The circulation of the working fluid in the ORC is ensured by the pump 2. The geothermal fluid leaving the evaporator is injected underground. The waste heat extracted from the condenser is used to heat the fungus production room. For this purpose, water is circulated between the condenser and the radiators by the pump 3. The electricity produced by the ORC is converted from AC to DC by a rectifier for the electrolysis of water. As a result, oxygen and hydrogen is obtained from point 14 and 15.

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Figure 1. Hydrogen production and space heating using water heated by solar radiation.

3. ANALYSES OF THE SYSTEM 3.1. Energy and Exergy Analyses of ETSCs ETSCs system has many cylindrical glass tubes that have well light transmittance. The surface of the interior tube is covered with a good light absorbent matter. The water is displaced in the ETSCs by natural convection. The solar radiance is absorbed by water in the tubes to convert into thermal energy and then warm water rises to the storage area (Budihardjo and Morrison 2009). Thus, the ETSCs produce hot water for use whenever needed for any purpose. Energy balance equation for the ETSCs can be written as follows:

Hydrogen Production and Space Heating Using Water … Ėin = ĖU + Ėloss

185 (1)

Some of the energy entering ETSCs is lost and the other part is used as useful energy. The useful thermal energy of the ETSCs can be expressed as given (Ucar and Inalli 2008): ĖU = 𝜂ETSC AETSC Ė 𝜂ETSC = 0.84 −

(2)

2.02(Tm −T0 ) − Ė

2

(T −T ) 0.0046Ė [ mĖ 0 ]

(3)

where 𝜂ETSC is the energy efficiency of ETSCs, AETSC=300 m2 is the aperture area of the each ETSC and Tm is the mean temperature of the ETSC is found as follows: Tm =

T2 +T3 2

(4)

where T2 and T3 are the inlet and outlet temperatures of the ETSCs, respectively. Also, the useful thermal energy of the ETSC can be obtained depending on the inlet and outlet temperatures as follows: ĖU = ṁw Cw (T3 − T2 )

(5)

Exergy balance equation of the ETSCs can be written as given: Ė𝑥in = Ė𝑥U + Ė𝑥loss + Ė𝑥destcol

(6)

Also, exergy destruction and exergy loss of the ETSCs can be found as follows: Ė𝑥

𝜓ETSC = Ė𝑥 𝑈 = 1 − in

Ė𝑥loss +Ė𝑥destcol Ė𝑥in

(7)

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where Ė𝑥in is the total solar exergy reaching the ETSCs, Ė𝑥𝑈 is the useful exergy of the ETSCs, Ė𝑥loss is the exergy loss in the ETSCs and Ė𝑥destcol is the exergy destruction in the collectors. The total exergy of the selected surface should be found for a better understanding of the system. Thus, the system can be evaluated better way with respect to thermodynamics. The total exergy Ėxsolar for the selected surface that depends on the solar radiation can be given as follows (Petela 2003): 4

4 T +273 1 T +273 Ė𝑥solar = Ėtot [1 − 3 ( 0 T ) + 3 ( 0 T ) ] s

s

(8)

where Ėtot is the total solar radiation reaching the aperture area of the ETSCs.

3.2. Energy and Exergy Analyses of ORC An ORC operates by thermal energy and it generates electricity at low temperature. It produces mechanical power by expanding organic fluid vapor throughout a turbine that turns a shaft. This shaft is connected to a generator for producing electricity (Quoilin et al. 2013). The following equations are arranged for the system in Fig 1. The ORC is the most important parameters in the system for generating electricity. The net electricity in the system is found as given: Ẇnet = ẆG − (Ẇpump1 + Ẇpump2 + Ẇpump3 )

(9)

where ẆG is the turbine generator power. ẆG = 𝜂T 𝜂G ṁ5 (h5 − h6 )

(10)

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where 𝜂T 𝜂G =0.35 is the efficiency of the turbine generator, ṁ5 , h5 and h6 are the mass flow rate and enthalpies in points 5 and 6. Moreover, Ẇpump1 Ẇpump2 and Ẇpump3 are pumping powers. ẇpump1 = ṁ1 (h2 − h1 )

(11)

ẇpump2 = ṁ8 (h8 − h7 )

(12)

ẇpump3 = ṁ10 (h11 − h10 )

(13)

Thus, the energetic performance of the ORC (𝜂ORC ) can be found as given: 𝜂ORC =

Ẇnet Q̇ev

(14)

where Q̇ ev is the thermal energy entering the evaporator and it can be found as follows: Q̇ ev = ṁ5 (h5 − h8 )

(15)

In order to find exergy analysis of the ORC, each component should be examined separately. The exergy balance equation for the evaporator is written as follows: Ėx3 + Ėx8 = Ėx5 + Ėx4 + Ėxdest,eva

(16)

where Ėx3 and Ėx8 are the inlet exergies of the evaporator, Ėx4 and Ėx5 are the outlet exergies of the evaporator, Ėxdest,eva is the exergy destruction in the evaporator, respectively. The exergy balance equation of the turbine generator can be found as follows:

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Ayhan Atiz, Hatice Karakilcik and Mehmet Karakilcik Ėx5 = Ėx6 + ẆG + Ėxdest,T

(17)

where Ėx5 is the inlet exergy of the turbine, Ėx6 is the outlet exergy of the turbine and Ėxdest,tur is the exergy destruction in the turbine, respectively. The exergy balance equation of the condenser can be found as follows: Ėx6 + Ėx11 = Ėx7 + Ėx9 + Ėxdest,con

(18)

where Ėx6 and Ėx11 are the inlet exergies of the condenser, Ėx7 and Ėx9 are the outlet exergies of the condenser, Ėxdest,con is the exergy destruction in the condenser, respectively. The exergy balance equation for the pump2 can be found as follows: Ėx7 + Ẇpump2 = Ėx8 + Ėxdest,pump2

(19)

In addition, total exergy destruction in the ORC can be written as follows: Ėxdest,ORC = Ėxdest,eva + Ėxdest,tur + Ėxdest,con + Ėxdest,pump2

(20)

Moreover, another important parameter of the system is the overall exergetic performance of the ORC that gives us better knowledge about thermodynamics aspect of the ORC and it is found as follows (Long et al. 2014): Ẇnet

𝜓𝑂𝑅𝐶 = Ėx

in,ORC

(21)

where Ėxin,ORC inlet exergy to the ORC is given as: Ėxin,ORC = ṁ3 [(h3 − h0 ) − T0 (s3 − s0 )]

(22)

where h0 , s3 and s0 are the enthalpy and entropies at the point 0 and 3.

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3.3. Overall Energy and Exergy Efficiencies of Solar Thermal System The most important factor affecting the performance of the system is the total exergy destruction. If the exergy destruction is found in each components of the system it can be understood where the performance of the system decreases. Therefore, total exergy destruction in the integrated system is obtained as follows: Ėxdest,tot = Ėxdest,ETSCs + Ėxdest,eva + Ėxdest,tur + Ėxdest,con + Ėxdest,pumps + Ėxdest,fung (23) where Ėxdest,pumps is the exergy destruction in the all pumps and Ėxdest,fungis the exergy destruction in the fungus production and they can be found as follows: Ėxdest,pumps = Ėxdest,pump1 + Ėxdest,pump2 + Ėxdest,pump3

(24)

Ėxdest,fung = Ėx9 − Ėx10

(25)

In order to evaluate a system as a whole, it must be found both of energy and exergy efficiency of the system. Thus, the overall energy efficiency of the solar thermal system can be found as given: 𝜂𝑠𝑦𝑠 = Ė

Ẇnet geo +Ėtot

(26)

where Ėgeo is the energy of geothermal water. Also, the overall exergy efficiency of the solar thermal system can be found as given: 𝜓𝑠𝑦𝑠 = Eẋ

Ẇnet geo +Ėxsolar

where Ėxgeo is the exergy of geothermal water.

(27)

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3.4. PEM Electrolysis PEM electrolysis unit is combined with the integrated system that consists of the ETSCs with a geothermal source. Water is split into hydrogen and oxygen by electricity that was produced by the ORC. The chemical reaction of the PEM unit for hydrogen production is given as follows (Saeed and Warkozek 2015): H2 O → H2 + 1⁄2O2 ∆h = 285.84 kJ/mol

(28)

Table 1. The parameters of the ETSC integrated with PV-T Num.

Fluid

0 0’ 0’’ 1 2 3 4 5 6 7 8 5’ 6’ 7’ 8’ 9 10 11

H2O n-butane Isobut. H2O H2O H2O H2O n-butane n-butane n-butane n-butane Isobut. Isobut. Isobut. Isobut. H2O H2O H2O

Temp. (℃) -0,3 -0.3 -0.3 93 93.2 50 T3-10 60 55 T7+0.2 T3-10 60 55 T7+0.2 55 45 45.2

Press. (kPa) 101.3 101.3 101.3 75 75 300 50 2000 1750 1750 2000 2000 1750 1750 2000 200 200 200

Mass flow rate (kg/s) 0.0500 0.0500 0.0500 0.0500 0.0375 0.0375 0.0375 0.0375 0.0375 0.0375 0.0375 0.0375 0.0025 0.0025 0.0025

Enthalpy (kJ/kg) -333.4 584.2 557.4 2665 2665 209.4 322.6 297.2 298.6 349.6 336.3 336.8 230.3 188.4 189.3

Entropy (kJ/kgK) -1.223 2.409 2.368 7.462 7.463 0.703 1.402 1.322 1325 1.484 1.444 1.444 0.769 0.638 0.641

Exergy (kW) 630 630.1 17.43 84.30 86.38 85.87 33.20 30.86 20.83 20.83 14.30 14.43

While some parameters were kept as constant under the varying solar radiation in the simulation, some other parameters were changed. Table 1 shows some important parameters related with the ETSCs supported by a geothermal source that was operated under daily solar radiance. The parameters 0, 1, 2, 4, 6, 7, 8, 9, 10, 11 in Table 1 were kept as a constant.

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But the parameters 3 and 5 were changed depending on the solar radiance, geothermal source temperature and pumping power.

4. RESULTS ETSCs were integrated with a geothermal source at 93℃ for producing hot water and steam mixture. The temperature of the water in the collectors is upgraded by solar energy. So, the obtained thermal energy is used to operate the ORC. Finally, water is split into hydrogen and oxygen by using electricity that is transferred from the ORC to electrolysis system and mushroom production building is heated by the excess thermal energy of the system from morning to evening. Two different organic fluids n-butane and isobutene were tested to improve the performance of the system. In this integrated system, it is aimed to obtain the maximum amount of electricity and hydrogen production by integrating the ETSCs with a geothermal source. Thus, the integrated system was operated during the hours when the sun was effective and the system was examined for these hours. Therefore, it is essential to find the amount of solar radiation that reaches the aperture area of the ETSCs that was taken as 300 m2 for this study. In addition, to make the thermodynamic analysis of the integrated system, solar energy and exergy reaching that area must be calculated. Figure 2 shows solar energy and exergy distributions reaching the ETSCs with outlet temperature of ETSCs. Thus, the minimum solar energy and exergy for the ETSCs were found as 115.2 kW and 107.9 kW between the hours of 0900-1000 and 1400-1500, respectively. The maximum solar energy and exergy for the ETSCs were found as 165.2 kW and 154.8 kW between the hours of 1100-1300, respectively. It is normal for the exergy values to be smaller than the energy values due to exergy destruction. The outlet water temperature of the ETSCs depends on the solar radiation. Thus, the minimum outlet water temperature of the ETSCs was obtained as 135.9℃ between the hours of 0900-1000 and 1400-1500. The maximum outlet temperature of the ETSCs was found as 196.7℃ between the hours of 11001300. It was found that as the solar energy reaching the ETSCs increases, the

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outlet temperature also increases considerably. Therefore, ETSCs have a great importance for electricity and hydrogen generation and space heating. To evaluate the ETSCs integrated with geothermal source, firstly the thermodynamic efficiencies of the ETSCs must be found. The solar radiation reaching the ETSCs, environment temperature and geothermal source temperature affect the energy and exergy efficiencies of the ETSCs.

Figure 2. Solar energy and exergy distributions reaching the ETSCs with outlet temperature of ETSCs.

Figure 3 shows the energy and exergy efficiencies of the ETSCs. The minimum exergy and energy efficiencies of the ETSCs were found as 2.44% and 7.75% between the hours of 0900-1000 and 1400-1500, respectively. The maximum exergy and energy efficiencies of the ETSCs were found as 13.09% and 4.81% between the hours of 1100-1300. The energy and exergy efficiency of the ETSCs have positively affected with the increasing solar radiation up to noon. In parallel with the low level of solar radiation in the morning and afternoon, the energy and exergy efficiencies of the ETSCs have also decreased.

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Figure 3. Energy and exergy efficiencies of the ETSCs.

Since ORC is an important component of the system, energy and exergy efficiencies of the ORC were found first to make a better evaluation on the system thermodynamically. Figure 4 shows the thermal energy efficiency of the ORC for the working fluids n-butane and isobutane. The minimum thermal energy efficiencies of the ORC were found as 33.71% and 33.63% for n-butane and isobutane between the hours of 0900-1000 and 1400-1500, respectively. The maximum thermal energy efficiencies of the ORC were found as 34.05% and 34.00% for n-butane and isobutane between the hours of 1100-1300, respectively. The thermal energy efficiency of the ORC was increased for both working fluids by the solar radiation up to noon. While solar radiation decreased in day time, energy efficiency of the ORC was also decreased. The thermal energy efficiency of ORC when working with n-butane was found to be slightly higher than isobutane. Figure 5 shows the overall exergy efficiency of the ORC for the working fluids n-butane and isobutane. The minimum overall exergy efficiencies of the ORC were found as 13.33% and 12.62% for n-butane and isobutane between the hours of 0900-1000 and 1400-1500, respectively. The maximum

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overall exergy efficiencies of the ORC were found as 17.41% and 16.58% for n-butane and isobutane between the hours of 1100-1300, respectively. The thermal overall exergy of the ORC was increased for both working fluids by the solar radiation up to noon like thermal energy efficiency of the ORC. While solar exergy decreased in day time, overall exergy efficiency of the ORC was also decreased. The overall exergy of the ORC when working with n-butane was found to be slightly higher than isobutane.

Figure 4. The thermal energy efficiency of the ORC.

Figure 6 shows the hourly average net electricity generation of the system for the working fluids n-butane and isobutane. The minimum average net electricity generation of the system was found as 5.47 kW and 5.17 kW for n-butane and isobutane between the hours of 0900-1000 and 1400-1500, respectively. The maximum average net electricity generation of the system was found as 7.56 kW and 7.20 kW for n-butane and isobutane between the hours of 1100-1300, respectively. The net electricity generation of the system increases through the noon. Electricity generation decreases in the morning and afternoon due to low solar radiation. The produced net electricity in the system when the ORC operates with n-butane was found to be slightly higher than isobutane.

Hydrogen Production and Space Heating Using Water …

Figure 5. The overall exergy efficiency of the ORC.

Figure 6. The hourly average net electricity generation of the system.

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Tables 2-3 show the exergy destruction in the all components of the integrated system for the working fluids n-butane and isobutane. Thus, exergy destruction distribution of two working fluids was found for two configurations. Since the inlet and outlet temperature of the ETSCs and the solar radiation are kept constant, exergy destruction in the ETSCs is the same as shown in Table 2-3. When these tables are analyzed, the highest exergy destruction was found in the collectors and evaporator. Exergy destruction in the turbine, condenser, pumps and fungus production was found quite low compared to the ETSCs and evaporator. It is clear that the lower exergy destruction is found at morning and afternoon. In addition, the exergy destruction in the system is slightly greater when the ORC operates with isobutane. Therefore, it is understood that the system with working n-butane produces more electricity than the system with working isobutane. Table 2. Exergy destruction in the system by using n-butane

Hour 9-10 10-11 11-12 12-13 13-14 14-15

ETSCs (kW) 73.79 89.77 97.45 97.45 89.77 73.79

n-butane Eva. (kW) 35.69 35.86 35.93 35.93 35.86 35.69

Tur. (kW) 1.478 2.636 3.357 3.357 2.636 1.478

Con. (kW) 0.070 0.070 0.070 0.070 0.070 0.070

Fung. (kW) 0.0163 0.0163 0.0163 0.0163 0.0163 0.0163

Pumps (kW) 0.0214 0.0214 0.0214 0.0214 0.0214 0.0214

Total (kW) 111.1 128.4 136.9 136.9 128.4 111.1

Table 3. Exergy destruction in the system by using isobutene

Hour 9-10 10-11 11-12 12-13 13-14 14-15

ETSCs (kW) 73.79 89.77 97.45 97.45 89.77 73.79

Isobutene Eva. (kW) 36.15 36.38 36.46 36.46 36.38 36.15

Tur. (kW) 1.169 2.278 2.979 2.979 2.278 1.169

Con. (kW) 0.0716 0.0716 0.0716 0.0716 0.0716 0.0716

Fung. (kW) 0.0163 0.0163 0.0163 0.0163 0.0163 0.0163

Pumps (kW) 0.0189 0.0189 0.0189 0.0189 0.0189 0.0189

Total (kW) 111.2 128.5 137.0 137.0 128.5 111.2

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The thermal energy produced in the system is used to generate electricity by the ORC that was operated n-butane and isobutane. The energy and exergy efficiencies of the system were found according to the electricity generation by two working fluids. In order to evaluate a system as a whole, energy and exergy efficiencies of the system must be obtained. Figure 7 shows the overall energy efficiency of the system for two working fluids. The minimum overall energy efficiency of the system was found as 2.20% and 2.08% for n-butane and isobutane between the hours of 0900-1000 and 1400-1500, respectively. The maximum overall energy efficiency of the systems was found as 2.53% and 2.41% for n-butane and isobutane between the hours of 1100-1300, respectively. The overall energy efficiency of the system that consists of the n-butane was found higher than the system that consists of isobutene.

Figure 7. The overall energy efficiency of the system.

Figure 8 shows the overall exergy efficiency of the system for both working fluids. The minimum overall exergy efficiency of the system was obtained as 3.92% and 3.71% for n-butane and isobutane between the hours

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of 0900-1000 and 1400-1500, respectively. The maximum overall exergy efficiency of the ORC was found as 4.06% and 3.86% for n-butane and isobutane between the hours of 1100-1300, respectively. The overall exergy of the system that consists of the n-butane was found higher than the system that consists of isobutane. It is also seen that the exergy efficiency of the system was found higher than the energy efficiency.

Figure 8. The overall exergy efficiency of the system.

Figure 9 shows the hourly generated hydrogen of the system for both working fluids. The efficiency of the PEM electrolysis system and rectifier were taken as 75% and 95% in the two configurations. Thus, the minimum hourly hydrogen generation of the system was found as 98.15 g and 92.86 g for n-butane and isobutane between the hours of 0900-1000 and 1400-1500, respectively. The maximum hourly hydrogen generation of the system was found as 135.7 g and 129.2 g for n-butane and isobutane between the hours of 1100-1300, respectively. As a result, total hydrogen generation is 714.1 g and 678.12 g for n-butane and isobutane, respectively for a day. The produced hydrogen can be stored for later use. Thus, the thermal energy

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produced in the system can be converted into hydrogen, which is another form that it can be easily use later.

Figure 9. The hourly hydrogen production for two configurations.

CONCLUSION In this chapter, hot water production performance of the ETSCs under solar radiation is researched. It is aimed to produce electricity mainly and hydrogen as a final product by operating ORC with the thermal energy produced in this way. It is seen that the performance of the ORC is higher when operates with n-butane than isobutane. Therefore the selection of the working fluid in the ORC is so important. Therefore the selection of the working fluid in the ORC is so important. All the calculations are made using EES for hot water, electricity and hydrogen production under daily solar radiance between the hours of 0900 - 1500 according to the meteorological data for the 5th of January at the city Nevşehir in Turkey. It

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is calculated that the ETSCs can increase the temperature of thermal water from 93℃ to 196.7℃. Thus, the proposed system can reach up to 714.1 g hydrogen production for a day. With the waste heat in ORC, space heating is also performed for mushroom production. These kinds of systems contribute to the generation of thermal energy, electricity and hydrogen via solar energy. These kinds of systems contribute to the generation of thermal energy, electricity and hydrogen via solar energy. Therefore, the world will have much more clean energy thanks to advances in these systems.

REFERENCES Arabhosseini, A., Samimi-Akhijahani, H., Motahayyer, M. (2019). Increasing the energy and exergy efficiencies of a collector using porous and recycling system. Renewable Energy, 132, 308–325. Atiz, A., Karakilcik, H., Erden, M., Karakilcik, M. (2019). Investigation energy, exergy and electricity production performance of an integrated system based on a low-temperature geothermal resource and solar energy. Energy Conversion and Management, 1951, 798–809. Atiz, A., Karakilcik, M. (2020). Comparison of heat efficiencies of flat-plate and vacuum tube collectors integrated with Organic Rankine Cycle in Adana climate conditions. Pamukkale University Journal of Engineering Sciences, 26 (1), 106–112. Atiz, A., Karakilcik, H., Erden, M., Karakilcik, M. (2019). Assessment of electricity and hydrogen production performance of evacuated tube solar collectors. International Journal of Hydrogen Energy, 44 (27), 14137– 14144. Bicer, Y., Dincer, I. (2016). Development of a new solar and geothermal based combined system for hydrogen production. Solar Energy, 127, 269-284. Budihardjo, I., Morrison, G. L. (2009). Performance of water-in-glass evacuated tube solar water heaters. Solar Energy, 83, 49–56.

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Chow, T. T., Dong, Z., Chan, L. S., Fong, K. F., Bai, Y. (2011). Performance evaluation of evacuated tube solar domestic hot water systems in Hong Kong. Energy and Buildings, 43, 3467–3474. Corumlu, V., Ozsoy, A., Ozturk, M. (2018). Thermodynamic studies of a novel heat pipe evacuated tube solar collectors based integrated process for hydrogen production. International Journal of Hydrogen Energy, 43 (2), 1060–1070. Evaluation of geothermal energy and electricity generation. General Directorate of Electrical Works Survey Administration (EIE) Ankara. Kalogirou, S. A. (2004). Solar thermal collectors and applications. Progress in Energy and Combustion Science, 30, 231–295. Kim, W., Choi, J., Cho, H. (2013). Performance analysis of hybrid solargeothermal CO2 heat pump system for residential heating. Renewable Energy, 50, 596–604. Kroll, J. A., Ziegler, F. (2018). The use of ground heat storages and evacuated tube solar collectors for meeting the annual heating demand of family-sized houses. Solar Energy, 85, 2611–2621. Kumar, L., Hasanuzzaman, M., Rahim, N. A. (2019). Global advancement of solar thermal energy technologies for industrial process heat and its future prospects: A review. Energy Conversion and Management, 1951, 885–908. Li, K., Liu, C., Jiang, S., Chen, Y. (2020). Review on hybrid geothermal and solar power systems. Journal of Cleaner Production, 25020, 119481. Long, R., Bao, Y. J., Huang, X., Liu, W. (2014). Exergy analysis and working fluid selection of organic Rankine cycle for low grade waste heat recovery. Energy, 73, 475–483. Martínez-Rodríguez, G., Fuentes-Silva, A. L., Picón-Núñez, M. (2018). Solar thermal networks operating with evacuated-tube collectors. Energy, 146, 26–33. Petela, R. (2003). Exergy of undiluted thermal radiations. Solar Energy, 74, 469–488. Saeed, W., Warkozek, G. (2015). Modeling and analysis of renewable PEM fuel cell system. Energy Procedia, 74, 87–101.

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Saleh, B., Koglbauer, G., Wendland, M., Fischer, J. (2007). Working fluids for low-temperature organic Rankine cycles. Energy, 32, 1210–1221. Sokhansefat, T., Kasaeian, A., Rahmani, K., Heidari, A. H., Aghakhani, F., Mahian, O. (2018). Thermoeconomic and environmental analysis of solar flat plate and evacuated tube collectors in cold climatic conditions. Renewable Energy, 115, 501–508. Tian, Y. and Zhao, C. Y. (2013). A review of solar collectors and thermal energy storage in solar thermal applications. Appl. Energy, 104, 538– 553. Quoilin, S., Den Broek, M. V., Declaye, S., Dewallef, P., Lemort, V. 2013. Techno-economic survey of organic Rankine cycle (ORC) systems. Renewable and Sust. Energy Reviews, 22, 168–186. Ucar, A., Inalli, M. (2008). Thermal and economic comparisons of solar heating systems with seasonal storage used in building heating. Renewable Energy, 33, 2532–2539.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 9

PHOTOVOLTAIC SOLAR WATER HEATING SYSTEM I. Atmane1, N. El Moussaoui1, K. Kassmi1,3,*, O. Deblecker2 and N. Bachiri3 1

Mohamed First University, Department of Physics, Oujda, Morocco 2 University of Mons, Polytechnic Faculty, Belgium 3 Man and Environment Association of Berkane (AHEB), Morocco

ABSTRACT In this chapter, we propose to develop solar photovoltaic salt water heating systems. This is exploited in order to produce condensation of the vapor of the heated water and consequently of the droplets of pure water. More specifically, we present the proposed system which is formed of 600 W/peak panels, two DC/DC converters, two heating resistors and a remote control, regulation and supervision block. The first typical results obtained show that heating one liter of saline water for an illumination of 650W/m², an ambient temperature of 34°C and an overall output power of the converters of 350 W, the heating of the heating resistors of 600°C after 10 seconds (i.e., a speed of 60°C/s), water of 90°C after 15 min (i.e., a speed *

Corresponding Author’s E-mail: [email protected].

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I. Atmane, N. El Moussaoui, K. Kassmi et al. of 4°C/min), and the production of 0.5 liter of distilled water from one liter of saline water per day. The electrical, thermal and distillation yields obtained are estimated at 87.5%, 80% and 25% respectively. The comparison of the results obtained with those of the literature on conventional thermal systems shows satisfactory distillation yields by photovoltaic solar energy. Consequently, the feasibility of heating water by photovoltaic solar energy and the production of distilled water.

Keywords: PV panels, MPPT control, DC/DC converters, thermal resistance, thermal efficiency, conversion efficiency, distilled water, control and supervision system

1. INTRODUCTION Providing fresh water has become one of the daily challenges of more than two billion people around the world (Mekonnen & Hoekstra 2016). More than four billion suffer from water scarcity for at least a month every year (UNESCO World Water Assessment Programme 2019). To remedy this shortage, in the literature (Elimelech & Phillip 2011), adequate, lowcost techniques are developed to purify brackish water from the sea, rivers, lakes and wells (Chandrashekara & Yadav 2017). Most of the techniques consist of heating the saline water using available energy sources: 

Electrical network: most of the techniques used for the desalination of saline water use the electrical network to supply the various boilers and pumps. Among the techniques, the most used, we find that of multi-stage flash evaporation (MFE) which is based on the vaporization of saline water and the condensed thereafter for it to be recovered in the form of pure water (El-Ghonemy 2018). The basic working principle of this FME process is to heat seawater to around 90-120°C, using the condensation of the produced steam and supplementing it with an external source of steam. The heated seawater is then flashed in successive stages maintained at decreasing pressure levels. The vapor produced is condensed and recovered in the form of pure water. The FME technique can accept

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a higher load of contaminants (suspended solids, heavy metals, oil, grease, etc.) in seawater. It is capable of producing good quality distilled water for: power plants electrical, process industries and many other high purity applications (El-Ghonemy 2018). Solar thermal: Techniques using this energy rely on the heat of the sun to heat water by solar collectors (Xue & al 2018, Sadeghi, Safarzadeh & Ameri 2019). Water heated to temperatures 50- 90°C is used directly in homes (sanitary facilities, kitchens, etc.), or evaporated and condensed to form droplets of distilled water. In reference (Xue & al 2018), it is shown that, by this technique, we can produce 8.1 liters of distilled water daily and an improvement in yields of 24% compared to conventional systems (Eggenkamp & Louvat 2018). Photovoltaic solar: this technique harnesses the electrical energy produced by photovoltaic (PV) panels under the sun to heat water through thermal resistances. Due to a lack of optimization and reliability, PV panels do not produce sufficient electrical energy to heat the thermal resistances and therefore the water. In (Pandya, Yadav & Patel 2019), solar batteries are used to store the energy produced by the PV panels, then heat the resistors and water. The low efficiency of the system proposed in these latest works (Joshi & Jani 2015, Pandya, Yadav, & Patel 2019) does not allow water to be heated by photovoltaic solar energy, and therefore its use in households and distillation of saline water.

The techniques discussed above allow water to be heated, for various applications, on both small and large scales. On the other hand, the systems deployed and the cost of heating are very expensive. In sunny countries, heating by solar thermal energy is increasingly favored, given the abundance of this energy. In order to reduce the cost of installations and increase the efficiency of installations, we are moving towards the use of heating by photovoltaic solar energy. This technology is promising, since it is not too bulky and uses equipment that does not require a lot of maintenance (PV

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panels, control system and heating resistors) (Ilias, Khalil, Sofian & Olivier 2020, Talbi & al 2019). In this context, and within the framework of the projects ``National Initiative for Human Development NIHD (n°2017/29) and Wallonie Bruxelles Internationale WBI (n°4.2)”, we propose to develop a saline water heating system by photovoltaic solar energy. This system is autonomous, equipped with blocks of powers, controls, regulations and remote supervision. It will provide optimized electrical energy, by PV panels, to heat water, by thermal resistances, and produce distilled (fresh) water at low cost. This new technique is sized according to the application: industrial, domestic (households in rural and urban areas)… In this chapter, we present the structure, the operation of the water heating system, by photovoltaic solar energy, for a domestic or industrial application, requiring 5 to 10 liters of pure water per day. We show the feasibility of the system with a power of 400 W, monitoring the heating temperatures of thermal resistances and 1 liter of saline water, and the production of pure water. Particular attention will be paid to the estimation of distillation and overall system yields.

2. STRUCTURE AND OPERATION OF THE PHOTOVOLTAIC HEATING SYSTEM 2.1. Synoptic Diagram Figure 1 shows the block diagram of the different blocks of the solar photovoltaic heating system, which was the subject of our work. This system is formed by:  

Block A: Photovoltaic generator, formed by PV panels that generate an overall electrical power of 600 W/peak, Block B: Power unit composed of:

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Two DC/DC boost type converters to power two thermal resistors according to the user’s needs. These converters are controlled by two PWM signals of frequency f = 10 kHz and of variable duty cycle α1 and α2. This topology is used to make the overall system more reliable and improve the efficiency of each converter (Baghaz & al 2013). o Two power switches (Swith 1 and Swith 2) to supply the Thermal resistors with electrical energy (Resistor 1 only, or Resistor 2 only, or both resistance at the same time). Block C: Heating plate made up of two thermal resistances, supporting a temperature above 1000°C. Depending on the application (Sanitary, distillations, etc.) and the power of the PV panels, the water is heated to boiling. Block D: Control and supervision circuit of the entire electronic system. It consists of a microcontroller which performs the following tasks: o Acquire the electrical quantities (input and output voltage, input and output current and power of the two converters), meteorological (lighting and ambient temperature) and thermal (temperature of the heating resistors and of the water to be heated). o Transmit the acquired data, from the entire system, to a user interface, installed in a PC, via a USB link. Block E: Management and supervision interface. It allows to: o Present the real-time animation of the operation of the entire system, by displaying the different electrical quantities (Voltage, Current, Power, Duty cycles) of each block, the energy yield, the intensity of the illumination and the temperatures heating resistors and water. o Graphically represent the data acquired in real time, o Store the various data acquired on a database that can be consulted remotely via the Internet.

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Store the various data acquired on a database that can be consulted remotely via the

Switch 1

Figure 1. Block diagram of the solar photovoltaic water heating system.

3. BLOCK OPERATION 3.1. Power Block The use of an adaptation stage between the PV generators (block A) and the heating resistors (Block C) is essential in order to guarantee optimal operation of the system. We therefore used two discretized Boost-type DC/DC converters, with efficiencies greater than 80% (Figure 2). DC/DC converters are designed and sized (Czarkowski 2011, Roberts 2015) for:     

operate continuously, generate two PWM signals, controlling the power switches of converters, frequency of 10 kHz and variables duty cycle α1, α2, input and output currents less than 12 A and 5 A, and input and output voltage less than 80 V and 100 V, the input and output voltage ripples are less than 200 mV, The current ripple in the inductor is less than 0.2 A.

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Figure 2. Boost type DC/DC converter.

3.2. Command and Control Block The control of the operation of the heating system proposed in this work is carried out by two electronic cards, designed and developed in our laboratory. They consist of a PIC18f4550 (Atmane & al 2019) microcontroller, in order to perform the tasks of acquiring electrical quantities, executing the MPPT algorithm, and creating and sending the frame to the computer, via a serial communication for processing. These tasks are performed by a program, in C language, developed and injected into the microcontroller, following the steps of the algorithm in Figure 3. The execution of this algorithm is carried out as follows:  

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The program begins by acquiring the electrical input quantities of the two floors, Once the acquisitions of all the quantities are made, the PIC generates the PWM signals, of variable duty cycle α1 and α2, at each power stage separately. The regulation of the operation of the DC/DC converters is based on the treatment of the powers of each stage and of the Hill Climbing method to converge towards the point of maximum power (PPM) (MPPT control) (Baghaz & al 2013), Then, the PIC acquires the other electrical quantities (output voltage and current of the two stages), thermal (temperatures of the two heating resistors) and meteorological (illumination and ambient temperature),

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Figure 3. Heating system control, acquisition and supervision program algorithm.



Finally, the program builds and sends a frame after a time ΔT, containing all the measurements carried out, to a supervision computer via a USB link. These functions run in an infinite loop in order to measure electrical and thermal quantities in real time.

Figure 4. Main page of the control and supervision interface of our heating system.

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3.3. Supervision Interface The data acquired by the electronic card is sent, in the form of a frame, every second, in order to ensure visualization and processing in real time by the graphical interface. This control and supervision interface, created and developed in our laboratory, is developed via LabVIEW and MySql (Atmane & al 2019) for database management. As shown in Figures 4 and 5, the interface allows: 

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Manage and supervise the heating system in real time and have a strong interaction between the various windows, the microcontroller and the heating system, Present on its main window (Figure 4), the detailed synoptic diagram of the heating system of Figure 1. By launching the data acquisition, they are received by the interface in the form of continuous flows, then their visualizations in real time. In addition to the digital display of the various data acquired, we have added a functionality to view all the graders in real time in the form of a graph (Figure 5), Store, record and view previous heating system operating data by directly accessing MySQL databases, or by exporting data directly from the interface as text or Excel depending on the user’s need.

Figure 5. Graphic and digital visualization of the various quantities acquired by the control and supervision interface.

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3.4. Hotplate The heating plate used in our heating system, shown in Figure 6, is composed by: 

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Two 13 Ω and 16 Ω heating resistors, housed in two temperatureresistant ceramics, 16 cm and 20 cm in diameter. On these ceramics are placed the receptions or distillation systems, containing water to be heated, Two contactors, equipped with indicator light, to connect or disconnect the two resistors independently, Two inputs connected directly to the two outputs of the DC / DC converters to supply the two heating resistors.

4. RESULTS AND DISCUSSIONS 4.1. Experimental Procedure The PV energy heating system, which is the subject of our work, designed and produced in our laboratory is shown in Figure 7. This system is composed of:

Figure 6. Heating plate designed and produced during this work.

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PV generators (A) formed by PV panels generating 600 W/peak power. This block also has a weather station formed by a CTN thermistor sensor to measure the ambient temperature, and a 50 W PV panel to charge the battery, which powers the system board, and to measure direct illumination. This station is connected to an acquisition card which transfers all data to the acquisition interface. Power block (B) formed by: o Two DC/DC boosters type. Each converter is designed to operate at a chopping frequency of 10 kHz, a power of 500 W and a maximum current of 12 A. o Two acquisition and control boards using a microcontroller (PIC 18F) which performs the following tasks:  The acquisition of electrical quantities of PV panels, meteorological (illumination and ambient temperature) and thermal (temperature of thermal and cooking resistances).  The display of acquired data on the LCD display,  transfer of acquired data to the graphical interface,  The automatic generation of two PWM signals, with a frequency of 10 kHz and duty cycles α1 and α2, by executing the MPPT algorithm to extract the maximum electrical power from the PV panels, and therefore supply the thermal resistors under optimal conditions. o A power supply board that generates the voltages (+ 12V, -12V, + 5V, GND) necessary for the proper functioning of the system. This card is powered by a small battery (50 Ah) which is charged by the 50 W panel, via a charge/discharge regulator. This card makes our system autonomous and functioning only on photovoltaic solar energy. Heating plate formed by two heating resistors (C), with a value of 13 and 16 Ω. They are chosen to withstand currents of 10 A and temperature greater than 1000°C. It produces heat to heat water with photovoltaic solar energy. Distillation system to produce distilled water from saline water, heated by the hot plate (C).

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A computer (E) connected to the control and data acquisition card, via a USB link. It runs a LabVIEW language application for acquiring and storing data in an SQL database. Also, it makes it possible to monitor, locally and remotely (Atmane & al 2019, Atmane & al 2020), the operation and efficiency of the heating system. Mobile trolley (D) used as a support to facilitate transport and operation of the heating system.

4.2. Operation of Photovoltaic Panels Optimal operation of the proposed heating system requires the sizing of thermal resistors and DC/DC converters, and knowledge of the electrical characteristics of the PV panels used. We therefore noted the current-voltage and power-voltage characteristics of PV panels used during a sunny day. The typical electrical characteristics obtained on a PV panel, for illuminances varying from 300 W/m2 to 900 W/m2, are represented in Figures 8. From these characteristics, we have determined and represented on Table 1 the optimal electrical quantities. We can therefore deduce:  

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The optimum characteristics of the panels used are in accordance with those provided by the supplier, When the illuminance varies from 300 W/m2 to 900 W/m2, the voltage, current, power and optimum resistance vary respectively from 22.4 to 25.4 (increase of 13.4%), 2.87 A to 8.61 (increase of one factor 3), 64 W to 218 W (increase by a factor of 3.4) and from 2.95 Ω to 7.8 Ω. (increase by a factor of 2.65). To ensure the operation of the two DC/DC Boost converters in continuous mode (Czarkowski 2011, Roberts 2015), the thermal resistance values must be greater than 8 Ω. In our case, we used thermal resistors with values of 13 Ω and 16 Ω.

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Figure 7. Solar photovoltaic water heating system, carried out in the laboratory during this work.

Figure 8. Current-voltage power-voltage characteristics of the photovoltaic panels used, for three illuminances (300 W/m², 500W/m², 900 W/m2). Ambient temperature = 30°C.

Table 1. The optimum electrical quantities of the PV panels used Le (W/m2) 300 500 900

Vopt (V) 22.4 23.9 25.4

Iopt (A) 2.87 4.78 8.61

Ropt (Ω) 7.8 5 2.95

Popt (W) 64.3 114.32 218.7

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4.3. Operation of DC/DC Converters For an illumination of 650 W/m2 and an ambient temperature of 40°C, we analyzed the operation of the two converters of the heating system in Figure 7. To do this, we noted, for each converter, the PWM signal which controls l. ‘switch, the voltages at the output of the switch (vQ) and of the diode (vD), the input (vpv) and output (vs) voltages, the coil current (iL). The typical results obtained, shown in Figure 9, show in the case of the two converters:  

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    

The duty cycles of the first and second converter are practically the same. They are of the order of α1 = α2 = 0.62, When the switches are closed (PWM signals amplitude = +12 V), the switches are closed (vQ = 0V), the diodes are blocked (vD = 77 V) and the inductors are charged, When the switches are open (Amplitude of the PWM signals = 0 V), the switches are open (vQ = 77 V), the diodes are conducting (vD = 0 V) and the inductors discharge. The current ripples of the coils are of the order of 1.5 A. The average input voltage of the two converters is 26 V. Their ripples are less than 100mV. The average values and the ripple of the output voltage of the two converters is vs = 77V and 20 mV. From the values of the output voltage vs and of the thermal resistance RTherm = 16 Ω, the overall output current is 4.6 A, From the power values at the input (400 W) and output (348 W), the efficiency of DC/DC converters are practically identical 1 = 2 = 87%.

The different waveforms and values of electrical quantities are in accordance with the relationships which govern the operation of DC/DC converters in continuous mode (Czarkowski 2011, Roberts 2015). These results and the good yields obtained testify to the good operation of the two

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converters, and consequently of the PV system dedicated to our application (heating with solar PV).

Output Input

Figure 9.Figure Experimentation of the waveforms DC/ DC / DC converters an illumination 9. Experimentation of the waveforms of of DC converters for anfor illumination of 800 W/m². of 800 W/m². A: PWM signals controlling the MOSFETs of the converters, B: Voltage at the output of the power switches, C: Voltage at the the output of the diodes, A: PWM signals controlling MOSFETs of the converters, D: Current in the coils, B: Voltage at the output of the power switches, E: Input and output voltages. C: Voltage at the output of the diodes, D: Current in the coils, E: Input and output voltages.

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4.4. Solar Photovoltaic Water Heating We experimented with the solar heating system in Figure 7, over a full sunny day, heating 1 liter of water. We recorded the light intensity, the ambient temperature, the duty cycles, the electrical power supplied by the PV panels and output, and the temperatures of the thermal resistance and water. The results obtained, represented in Figure 10, show:   

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During the day of the measurements, around 2 p.m., the intensity of the lighting reaches 650 W/m2 and the ambient temperature is 34°C, The best performances are obtained around 2 p.m. when the power of the PV panels reaches the value of 400 W, The PWM duty cycles of the first and second DC/DC converters (α1 and α2) vary from 0.05 to 0.62, respectively. The frequency of these PWM signals is f = 10 kHz, For an input power of 400 W, the power transmitted by the DC/ DC converters to the heating resistor is of the order of 350 W which means a conversion efficiency of 87.5%, Around 10 a.m., when the lighting intensity is 300 W/m² and the power supplied by the PV panels is around 200 W, the temperature of the resistor is around 800°C, At 2 p.m., the output power supplied by the heating system reaches 350 W for a maximum illumination of 650 W/m². For this power, the temperature of the resistance of the heating system reaches the value 1 400°C. The water temperature goes from 33°C to 73°C after 10 min of heating, i.e., a heating rate of 4°C/min and a thermal efficiency of 80% (Joshi & Jani 2013, Atmane 2020). The water temperature reaches 100°C after 18 min of heating, Heating 1 liter of saline water shows the appearance of the first droplets of distilled water after 12 min of boiling water. After 9 hours of heating, the cumulative quantity of water produced attains 500 ml.

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Figure 10. Illuminance and temperature intensity, Duty cycle, Input and output electrical power, Output power, converter efficiency, heating resistor temperature, Water temperature, amount of distilled water produced.

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By comparing these results with those obtained on classical thermal heating techniques by the sun (Herez Ramdan & Khaled 2018, Guidara, Suiddi, Morgenstern & Maalej 2017), we can deduce from the better heating performances by photovoltaic solar energy, developed during this work: improvements in the temperature reached, speed and heating time by a factor of 9, 4 and 2,77 respectively. These performances allow us to confirm the efficiency of our system (Figure 8) to produce distilled water with solar energy.

5. DISTILLATION AND OVERALL SYSTEM YIELDS The methods used to estimate the efficiency of a system are based on the knowledge of solar energy radiation 𝐸̇ (𝑡) received and the energy related to the heat of vaporization of the water (El Moussaoui & Kassmi 2019). In our case, the latter is related to the heat produced by the thermal resistance, fed to the photovoltaic power panels 𝑃𝑝𝑣 , by latent heat of vaporization (ℎ𝑓𝑔 ). Taking these considerations into account, the distillation yields (𝜂𝑑 ) and global (𝜂𝑔 ) of solar photovoltaic system (Figure 7), which produces a flow of distilled water (𝑚 ), are written according to the following relationships: 𝜼𝒅 =

𝜼𝒈 =

𝒎 .𝒉𝒇𝒈 𝑷.𝒑𝒗 𝒎 .𝒉𝒇𝒈 𝑨𝒑𝒗 𝑬̇(𝒕)

(1)

(2)

With: 𝐴𝑝𝑣 : Panels area PV, ℎ𝑓𝑔 : Latent heat of vaporization of water (J/kg), given as a function of the temperature of the water (𝑇𝑤𝑎𝑡𝑒𝑟 ) by the following relation (El Moussaoui & Kassmi 2019, Feilizadeh & al 2015):

Photovoltaic Solar Water Heating System

400

150

Ppv (W) Rate of Flow

120

PV Power (W)

350 300

90

250 200

60

150 100

30

Rate of Flow (ml/h)

450

221

50 0 08:00

10:00

12:00

14:00

16:00

18:00

0 20:00

Time [h] 30

Efficiency (%)

Global Efficiency (%) Distillation Efficiency (%)

20

10

0 08:00

10:00

12:00

14:00

16:00

18:00

20:00

Time [h]

Figure 11. Distilled water flow rate (m), power 𝑷𝒑𝒗 , distillation efficiency (d) global efficiency (g) of system in Figure 1.

𝒉𝒇𝒈 = 𝟏𝟎𝟎𝟎 × (𝟑𝟏𝟔𝟏. 𝟓 − 𝟐. 𝟒𝟎𝟕𝟒(𝑻𝒘𝒂𝒕𝒆𝒓 + 𝟐𝟕𝟑))

(3)

From the results of Figure 10, we deduced and plotted in Figure 11, during one day, the flow rate of distilled water (𝑚) as a function of the power 𝑃𝑝𝑣 , and on the same figure the overall yields and distillation. The results obtained show that the maximum flow rate of distilled water is obtained around 4 p.m. for an electric power of 400 W. Also, and the overall and distillation yields are obtained around 5 p.m. and they are respectively of the

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order of 6% and 25%. In the literature, in conventional solar desalination systems, saline water is heated by solar thermal energy. In these systems, energy losses are optimized and distillation yields can reach 65% (El-Sebaii & al 2011, Kumar & Bai 2008). In our case, the heating system (Figure 7) present energy losses when heating by the thermal resistances, and the distillation yields cannot exceed 25%. Our primary objective is to show the feasibility of the proposed system. In a work in progress, we propose the minimization of these losses and the improvement of these distillation yields, by heating the water by photovoltaic solar energy.

CONCLUSION In this chapter, we have shown the feasibility of heating salt water and producing distilled water using photovoltaic (PV) solar energy. In particular, we have presented the structure of the proposed system and its operation, during one day, by heating one liter of water with a power of 600 W/peak. The results obtained show:       

The intensity of the solar radiation attains 650 W/m2 and the ambient temperature 34°C, The temperature of the heating resistor reaches 1400°C for a power of 350 W. The heating resistor temperature reaches 600°C after 10 seconds of heating, The rapid rise in water temperature of 4°C/min, For a Ppv power of 400 W, after 18 minutes of heating, the water reaches 100°C, The thermal and distillation yields can reach 80% and 25% respectively. The production of 500 ml of distilled water with a power ranging from 200 W to 400 W.

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The comparison of the solar heating temperatures of our system by photovoltaic energy with those of the literature by conventional solar thermal energy (box oven, concentration oven, ...), show an improvement of the maximum temperature reached and of the heating speed, respectively by a factor of 9 and 4. All the results and performances obtained in this work clearly show the good functioning of the PV heating system and consequently its use to produce distilled water from solar photovoltaic energy.

ACKNOWLEDGMENTS This research is supported between the Mohamed First University of Oujda (Morocco), Polytechnic Faculty of Mons (Belgium) and the Association Man and Environment of Berkane AHEB (Morocco), within the framework of the following projects:  

Morocco-Wallonie Cooperation Program Brussels (2018-2022), Wallonie-Bruxelles-International WBI, project 4, n°2, National Initiative for Human Development INDH, Berkane Province, Morocco, project n°2017//29

REFERENCES Atmane, I., Melhaoui, M., Kassmi, K., Mahdi, Z., Alexopoulos, S., Schwarzer, K. & Bachiri, N. (2019). System of control and supervision of the solar distiller to install in Douar Al Hamri of the rural district of Boughriba (Province of Berkane). Materials Today: Proceedings, 13, 587-596. http://www.solardesigntool.com/components/module-panelsolar/JA-Solar/5126/JAM60S03-305-PR/specification-data-sheet.html. Baghaz, E., Melhaoui, M., Yaden, F., Hirech, K. & Kassmi, K. (2013). Design, realization and optimization of the photovoltaic systems

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equipped with analog and digital MPPT commands. Energy Procedia, 42, 270-279. Chandrashekara, M. & Yadav, A. (2017). Water desalination system using solar heat: a review. Renewable and Sustainable Energy Reviews, 67, 1308-1330. Cosgrove, C. E. & Cosgrove, W. J. (2012). The United Nations World Water Development Report–N° 4–The Dynamics of Global Water Futures: Driving Forces 2011–2050, (Vol. 2). UNESCO. Czarkowski, D. (2011). DC–DC Converters. In Power electronics handbook, (pp. 249-263). Butterworth-Heinemann. Dernane, C. (2018). Réduction des Irréversibilités Lors de la Séparation par Distillation (Doctoral dissertation). [Reduction of Irreversibilities During Separation by Distillation] Eggenkamp, H. G. M. & Louvat, P. (2018). A simple distillation method to extract bromine from natural water and salt samples for isotope analysis by multi‐collector inductively coupled plasma mass spectrometry. Rapid Communications in Mass Spectrometry, 32(8), 612-618. El Moussaoui, N. & Kassmi, K. (2019, July). Modeling and Simulation studies on a multi-stage solar water desalination system. In 2019 International Conference of Computer Science and Renewable Energies (ICCSRE), (pp. 1-7). IEEE. El-Ghonemy, A. M. K. (2018). Performance test of a sea water multi-stage flash distillation plant: Case study. Alexandria engineering journal, 57(4), 2401-2413. Elimelech, M. & Phillip, W. A. (2011). The future of seawater desalination: energy, technology, and the environment. Science, 333(6043), 712-717. El-Sebaii, A. A., Aboul-Enein, S., Ramadan, M. R. I. & Khallaf, A. M. (2011). Thermal performance of an active single basin solar still (ASBS) coupled to shallow solar pond (SSP). Desalination, 280(1-3), 183-190. Feilizadeh, M., Estahbanati, M. K., Jafarpur, K., Roostaazad, R., Feilizadeh, M. & Taghvaei, H. (2015). Year-round outdoor experiments on a multistage active solar still with different numbers of solar collectors. Applied energy, 152, 39-46.

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Guidara, Z., Souissi, M., Morgenstern, A. & Maalej, A. (2017). Thermal performance of a solar box cooker with outer reflectors: Numerical study and experimental investigation. Solar Energy, 158, 347-359. Herez, A., Ramadan, M. & Khaled, M. (2018). Review on solar cooker systems: Economic and environmental study for different Lebanese scenarios. Renewable and Sustainable Energy Reviews, 81, 421-432. Ilias, A., Khalil, K., Sofian, T. & Olivier, D. (2020, April). Feasibility of a Solar Heating Plate With Photovoltaic Energy. In 2020 1st International Conference on Innovative Research in Applied Science, Engineering and Technology (IRASET), (pp. 1-6). IEEE. Issaadi-Hamitouche, T., Besombes, C. & Allaf, K. (2017). Instant autovaporization as intensification way of classic distillation processes: fundamental and industrial applications. Energy Procedia, 139, 651657. Joshi, S. B. & Jani, A. R. (2013, November). Certain analysis of a solar cooker with dual axis sun tracker. In 2013 Nirma University International Conference on Engineering (NUiCONE), (pp. 1-5). IEEE. Joshi, S. B. & Jani, A. R. (2015). Design, development and testing of a small scale hybrid solar cooker. Solar Energy, 122, 148-155. Kumar, K. V. & Bai, R. K. (2008). Performance study on solar still with enhanced condensation. Desalination, 230(1-3), 51-61. Mekonnen, M. M. & Hoekstra, A. Y. (2016). Four billion people facing severe water scarcity. Science advances, 2(2), e1500323. Nafaa, H., Farhat, M. & Lassaad, S. (2017, March). A pv water desalination system using backstepping approach. In 2017 International Conference on Green Energy Conversion Systems (GECS), (pp. 1-5). IEEE. Pandya, V., Yadav, M. & Patel, R (2019). Design, Development and Analysis of an Automatic Hybrid Solar cooker with battery operated coils Cooking. Roberts, S. (2015). DC/DC book of knowledge: Practical tips for the User. Recom. Sadeghi, G., Safarzadeh, H. & Ameri, M. (2019). Experimental and numerical investigations on performance of evacuated tube solar collectors with parabolic concentrator, applying synthesized Cu2O/

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distilled water nanofluid. Energy for sustainable development, 48, 88106. Talbi, S., Kassmi, K., Atmane, I., Deblecker, O. & Elmoussaoui, N. (2019, November). Feasibility of a Box-type Solar Cooker Powered by Photovoltaic Energy. In 2019 7th International Renewable and Sustainable Energy Conference (IRSEC), (pp. 1-4). IEEE. Xue, G., Chen, Q., Lin, S., Duan, J., Yang, P., Liu, K. & Zhou, J. (2018). Highly efficient water harvesting with optimized solar thermal membrane distillation device. Global Challenges, 2(5-6), 1800001.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 10

POTENTIAL TECHNIQUES FOR THERMAL PERFORMANCE ENHANCEMENT FOR SOLAR WATER HEATERS A. Saxena1,* and P. Verma2 1

Department of Mechanical Engineering, Moradabad Institute of Technology, Moradabad, India 2 Department of Mechanical Engineering, GBPUAT, Pantnagar, India

ABSTRACT Solar energy is one of the promising resources of renewable energy for operating thermal applications like solar air heater, solar cooker, solar water heater and solar still. Several modifications have been made to the conventional design of water heater in which usage of thermal energy storage materials and selective coating is a common method to boost up the performance of water heater. The role of convection heat transfer is much important for improved thermal efficiency of water heater. The *

Corresponding Author’s E-mail: [email protected].

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A. Saxena and P. Verma present chapter focuses on the different potential techniques and its uses to enhance thermal performance of water heater like; collector design, extended geometries, integrated thermal storage, selective coating for better heat transfer and thermal insulation. This chapter also discussed water flow solar inside a water heater for a better understanding of

thermal response that would result in the enhancement of water heating performance of a simple design. Keywords: solar energy, water heater, thermal performance, energy storage, heat transfer

1. INTRODUCTION Energy is an important factor for the socio-economic development of any society. The increased demand of energy consumption in the current scenario of daily life poses a major challenge for the availability of fossil fuels in future. These conventional energy resources are being harnessed at rapid rate and with this ongoing consumption rate, the total fossil fuel available will be exhausted in near future (Hussein, 2015). The large utilization of these fossil fuels poses a threat to environment and leads to carbon emission and global warming. The use of solar energy and its efficient conversion is a potential alternative to reduce the adverse impact caused by excessive utilization of fossil fuels. The solar energy being pollution free and available in abundance has an upper edge over the fossil fuels. This free source of solar energy is used for cooking (Saxena et al., 2015), air heating (Saxena et al., 2020, Verma and Varshney, 2015), water heating (Saxena and Srivasatva, 2012), distillation (Saxena and Deval, 2016), agriculture products drying (Saxena et al., 2015), and power generation (Saxena and Goel 2013) etc. The hot water is an essential requirement for domestic purposes such as washing of clothes and utensils, taking baths etc., which indicates that out of total domestic energy consumption nearly 15-20% of it is utilized in heating of water, but nowadays demand of hot water has increased tremendously in other sectors also like hospitals, hotels, hostels, electricity

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generation etc., (Wu et al., 2011). Since a lot of energy is utilized in heating of water through traditional fuel so the load on this energy consumption can be minimized through the installation of flat plate collectors (FPC) for water heating. Water heater is one of the effective solar energy conversion techniques to heat water by means of FPC. A SWHS is classified as a low temperature device as the water is raised to a temperature lower than the boiling point of water.

Figure 1. The schematic of thermosyphon solar water heater system.

SWHS is a complete and simple unit consisting of various components like; water tank, solar collector, interconnecting pipelines and the water which flows in system. The irradiance incident on the FPC is trapped and absorbed through the blackened copper plate which heats and circulates the water due to difference in the density termed as thermosyphon effect (Figure 1). Thermal performance of SWHS largely depends on irradiance, transmittance, absorption and conduction of solar energy, surrounding temperature, fluid flow rate, and inclination of the FPC, position of water tank, wind velocity, relative humidity and the conductivity of working fluid. However, a number of methods can be used to enhance the thermal performance of these SWHS like; using phase change materials (PCM), improvement in collector design, integrated collector storage (ICS), coating of pipes, thermal insulation, collector tilt, fluid flow rate and insertion of twisted tapes (Sadishkumar and Balusamy, 2014).

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1.1. Types of Solar Water Heaters SWHS are grouped into two broad categories as passive and active heating systems as shown in Figure 2. The passive SWHS generally transfer heat energy by natural circulation. Due to the buoyancy effect there is difference of temperature between two regions; so the pumps are not needed to operate such systems. They are commonly used SWHS for domestic purpose. Active SWHS comprises of electric driven pumps, valves, and controlling mechanism for circulation of water or other heat transfer fluids through these collectors (Kalogirou, 2009)

Figure 2. The schematic of passive SWHS (Sodha and Tiwari, 1981).

The active SWHS heating the water directly is termed as a direct (open loop) system. However when a heat transfer fluid is circulated in a heat exchanger it is called an indirect or closed loop arrangement. The passive SWHS comprises of thermosyphon and ICS, Figure 3 depicts the complete classification of various types of SWHS available.

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Figure 3. Classification of SWHS.

1.1.1. Active Solar Water Heating Systems The active or a forced circulation system employs electrical pumps and controlling mechanism for circulation of water or the desired heat transfer fluids through the SWHS (Wang et al., 2015). This type of system employs a pump to circulate a non-freezing liquid in a solar collector and heat exchanger. Active SWHS employ the collectors to heat the flowing fluid and storage cells to accumulate solar energy. The dispensation devices are provided to make available the solar energy to the heated region in a controlled phase (Chan et al., 2010). This type of SWHS is costly and complex as compared to the thermosyphon system. Active SWHS are of two types i.e., the direct or indirect circulation system (Duffie and Beckman, 2013). In the direct circulation type of system the water is circulated by the pump in the collector and is supplied to the desired place, such systems do not use a heat exchanger. They perform better in climate where water rarely freezes (Hossain et al., 2011). Open loop SWHS heats the domestic water in the collectors and after heating the hot water is sent to storage tank through a pump to discharge for use. Such designs should only be used in those regions where the temperature of water does not fall below the freezing point (Soo et al., 2009). A closed loop or indirect circulation system pumps circulate a nonfreezing fluid that is generally a water antifreeze mixture, through the collectors and a heat exchanger device (Soo et al., 2009). The freeze

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resistance fluid circulated through these systems is ethylene glycol and propylene glycol solutions, silicon oils, hydrocarbon etc. This heats the water which is fed to the home. Such SWHS are popular in climatic conditions which are prone to freezing temperatures {Figure 4 (webgreenspec.co.uk)}.

Figure 4. A closed loop indirect circulation System.

1.1.2. Thermosyphon Solar Water Heater A thermosyphon SWH (Figure 5) works on the buoyancy force to cause fluid movement through a set up (Close, 1962). Since a thermosyphon system does not require controlling equipment’s hence it requires less maintenance and is simple to conceptualize (De-Souza and Lamas, 2014). It is achieved as it undergoes the natural circulation of a lower dense fluid to rise above a fluid of higher density due to the absorption of solar radiation. The density difference is created within the solar collector where heat is added to the liquid, causing the hot water to rise through the collector header at the top of the storage tank (Islam et al., 2013). Solar heated water rises into the insulated tank as heat is transferred to the water, and cold water from the tank flows due to natural convection to the lowest level of FPC creating natural spontaneous flow circuit termed as a thermosyphon loop.

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Figure 5. Schematic of a thermosyphon SWHS (Goswami 2015).

The effective working of thermosyphon SWH demands that the storage tank must be positioned higher (about 30 cm) than the top of collector, else at night, or when the collector temperature is less than the water in the tank (Kalogirou 2004). As the thermosyphon system works on a low density difference, proper size of pipe should be used to minimize friction losses in the pipe (Jamar et al., 2016). To use a thermosyphon system under freezing condition, an adequate nonfreezing fluid should be used with a heat exchanger unit installed between the potable water storage unit and the solar collector (Goswami, 2015). Hence, it’s limits the use of conventional thermosyphon system primarily in a nonfreezing climate.

1.1.3. Integrated Collector Systems (ICS) The ICS-SWH is comparatively a simple system. ICS or batch systems have different design with one or more black coated tanks or tubes (Hossain et al., 2011) in an insulated box where the solar energy will be absorbed on its exposed surface which is covered with a transparent sheet to allow irradiance (Rai, 1987). The insulation of the box and provision of glazing sheets are to reduce thermal losses from the collector. The cost as well as the maintenance of ICS-SWHS is relatively lower than that of other SWHS being solar collector and water storage tank work as an integrated unit (Garg

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et al., 1997). Some of the limitations with these ICS systems is that they can only be used in mild freeze climates and are subjected to the thermal losses at night (Jamar et al., 2016).

2. HEAT TRANSFER ENHANCEMENT TECHNIQUES A typical solar thermal system needs a high heat storage capacity and excellent heat transfer capability so that the surrounding thermal losses by the system should be low as possible. For this various techniques has been applied to different designs of heating and cooling systems. These techniques are as; rigid surface roughness, extended geometries on the collector surface, incorporation of high heat storage capacity material {latent heat storage (LHS) or sensible heat storage (SHS)}, selective surface coatings and extra radiation gain through mirror boosters/reflectors on the collector (Saxena et al., 2013). There are only three common methods to increase or enhance the heat transfer between two bodies. First is active method, passive method, and the compound method (Saxena et al., 2020).

2.1. Collector Design Design of the solar collector has a great importance on the performance of SWH. Commonly three types of the collector are used according to the demand of hot water and specific geographic locations at the users end. These collectors have been designed in such a way so that the system or object can absorb maximum solar radiant energy. These collectors are as; 1. Flat plate collector 2. Compound parabolic collector 3. Evacuated tube collector.

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2.1.1. Flat Plate Collector The basic principle of a FPC (Figure 6) is quite simple i.e., if a piece of metal is exposed to solar radiant energy the temperature of absorber continued to be increased until the rate at which heat is lost to the surrounding from absorber and this temperature is characterized as ‘equilibrium temperature’. A FPC is main element of solar application for an ambient operating range from 60oC to 100oC (Garg, 2008). The backside of FPC can be acted as a heat collector through adding a natural or forced water circulation system through soldering the water carrying pipes to the back surface. For designing of a specific FPC following design elements are mandatory to consider (Howell, 1979);

Figure 6. Schematic of a FPC (Kalogirou, 2009).

i. ii. iii. iv. v. vi. vii.

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Above are the basic design parameters of FPC-SWH an improvement in function of these elements results in improved efficiency of system such as the use of double glazing or transparent insulation materials (TIM) or selective absorber (Figure 7) will definitely enhance the performance (Saxena et al., 2013). However, ambient conditions will play a significant role in the thermal performance of any solar system.

(a)

(b)

(c) Figure 7. Different type of absorbers (a), (b), and (c) for solar water heating (Kalogirou, 2009).

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2.1.2. Compound Parabolic Collector Concentrators can be refractors or reflectors, cylindrical or planes of revolt, and can also be incessant or segmented. CPCs are concentrators of non-imaging. These concentrators (Figure 8) have the potential of reflecting to collector all of the incident irradiance in extensive limits. A solar trough can be used to set the orientation. CPCs can receive arriving irradiance for a comparatively wide span of orientation angles. Due to multiple interior reflections, the irradiance fallen on the aperture in the range of solar collector acceptance angle directs its path to the absorbing surface which can be flat, cylindrical, bifacial, and wedge. To attain a higher temperature through irradiance these CPC have been used.

[1]

(b)

(c)

(d)

Figure 8. different type of CPC absorbers; (a) flat absorber, (b) Bifacial absorber (c) Wedge absorber (d) Tube absorber (Kalogirou, 2009).

For designing of a specific CPC following design parameters are mandatory to consider (Rabl et al., 1978); i. The gap between absorber and the reflector ii. The glass tube surrounding receiver iii. Collector height iv. Mirror error and absorber alignment v. Fin efficiency vi. Flow factor for a CPC vii. Second stage concentrators viii. V- trough configuration

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2.1.3. Evacuated Tube Collector SWHS have been designed on the basis of site location, ambient conditions and size selection of system for fulfilling the demand of hot water supply. Technical survey somewhere necessary if the size is of large capacity of SWH due to safety point of view.

Figure 9. First ETC designed and developed by Speyer in 1965.

About the evacuated tube collectors (ETC), a senior physicist E. Speyer has designed and developed the ETC in 1965 (Figure 9). Although, FPC functions well but due to high heat losses the collector temperature does not rise above 90oC without any auxiliary support which is achieved by reducing the convective heat losses from collectors through the completely replacement of insulation by providing evacuated space between solar absorber and the cover. Each collector is in the form of a long transparent outside glass tube and selective blackened inside steel conduit while there is evacuated space between these two (Figure 10). The conduit through which the fluid flow remains suspended within evacuated tube. A detailed classification of ETC systems has been shown in Figure 10. For designing of a specific ETC following design parameters are mandatory to consider (Speyer, 1965); i. ii. iii. iv. v. vi.

Length and diameter of the tube Average gap width between the conduit and glass tube Conduit configurations Grazing angles Silvering Reflection losses

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Figure 10. Evacuated tube type solar water heater installed at Moradabad Institute of Technology, India.

Figure 11. Classification of evacuated tube solar collectors (Tiwari et al., 2016).

Above section presents the different design of SWHS. Previous research work explored that; in order to minimize the storage tank volume (Zeng at

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al., 2010) a novel mechanism has been developed and integrated with a stabilized shaped PCM to enhance the performance of building integrated SWH. Results shown that the energy storage ratio of the PCM based floor is better about 50% than the without PCB. Kumar and Rosen 2010 has been reported thermal response of SWH with a corrugated rectangular collector surface. Results have shown that the modified SWH found better. A scheffler reflector based SWH (Patil et al., 2011) has been developed and tested in India. The average power has been estimated about 1.3 kW while efficiency of the system has been noted about 21.61%. A SWH has been integrated with CPC collector (Gang et al., 2012) and a U-shaped pipe (test rig) to be tested for performance evaluation in eastern China. The minimum overall ƞtherm has been obtained about 43%. By keeping the space problem of building integrated SWH (Kong et al., 2014) a SWH integrated with a U-tube collector (ETC type) has been experimentally tested in Malaysia. The system performance in inclined position has been found better over than vertical position operating system. A PV/T type SWH with jet collision (Hasan et al., 2018) of water has been designed, fabricated and tested in Iraq, another PV/T SWH (Figure 12) assisted with heat pump (Dannemand et al., 2019) and a cold buffer storage has been designed and experimentally tested in Denmark.

Figure 12. A PV/T solar water heaterassisted with heat pump (Tiwari, 2014).

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2.2. Selective Coatings The diversity of raw materials and the numerous techniques applied in manufacturing or fabrication of a solar collector as well as the surface treatment either by a non-selective coating or selective surface coatings results in variations in thermal response of SWHS (Khullar et al., 2018). Fact about the solar application is that if solar system is economic viable than its conversion (ƞconv) and storage capacity is highly efficient. The ƞconv of a collector limited to thermal losses due to radiation, conduction and convection heat transfer from solar absorber (Lizama-Tzeca et al., 2019). Material properties like; specific heat, thermal conductivity etc., are major characteristics in thermal behavior of a solar system. Equation (1) shows the significance of a solar selective surface on the performance of a FPC (Abbas, 2000).



  1  

1 Cs

 EBB (T )     Es 

(1)

Where, C is the concentration ratio, ϕs is solar selctivity, Es is the irradaince per unit area, EBB is power emitted by black body at temperature. For an efficient thermal performance a solar water heater must have the following characteristics; 1. 2. 3. 4. 5. 6. 7. 8. 9.

Absorptivity should be more than 0.90 Thermal emittance should be less than 0.20 Wide angle recognition Extended performance in standard conditions of environment and operation High temperature stability High moisture conditions stability Long life cycle Reproducibility Economic life cycle

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2.3. Extended Surfaces Heat transfer is a major characteristic for thermal systems. If the heat transfer from a surface to contacting fluid is of high order the systems perform better. High rate of heat transfer can be achieved by attaching some good thermal conductive metal pieces as extended surfaces (fins) to the heat transferring surface (Razelos, 2003). Fins are attached adjunct to the principal heat transfer surface to enhance the rate of heat transfer. There are various types of profile available for the fins (Mokheimer, 2003) for increasing heat transfer rate. Figure 13 shows some commonly used extended surfaces for increasing heat transfer rate.

Figure 13. Some commonly used extended fins (Karwa, 2017).

A lot of work has been carried out to enhance the thermal performance of SWH by applying different extended surface and among them, analysis of a corrugated steel sheet SWH (Shing-An 1979) has been carried in China. Collector efficiency has been estimated by a new modified equation and efficiency factor has been computed about 94%. In 1980, a SWH has been experimentally tested on forced circulation (Mishra and Bhat 1980) by using different packing materials for performance enhancement such as; iron chips, tiny stones and gravels. Among the three iron chips has been found better over the tiny stones and gravels by obtaining 54.80% ƞtherm. A cylindrical collector type SWH (Nahar and Malhotra, 1984) has been designed and experimentally studied in India. Results showed that the modified SWH has been found feasible to provide the hot water at 50oC60oC in the cold climates for a capacity of 50 liters/day. After that, some different designs collectors of SWHS (Fanney and Klien, 1988) has been experimentally tested at National Bureau of Standards for solar hot water

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test. Results revealed that the performance of a SWH can be enhanced by reducing the flow rate inside the tank by a specific return tube.

Figure 14. A novel type SWH for small scale hot water production (Khan et al., 2016).

Figure 15. Side view of model of thermosyphon SWH (open sourcewww.appropedia.org).

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Different authors have investigated small (Figure 14) and large scale type SWHS round the globe. To increase heat transfer between the internal surface water carrying tube and circulated water the concept of twisted tape has been applied (Kumar and Prasad, 2000). The extended surface increased heat transfer which results in improved performance of SWH. Again a model of themosyphon type SWH (Figure 15) has been designed (Tse and Chow, 2015) and experimentally studied for efficiency enhancement. The modification of the system is a circular tube ring heat exchanger which reduces friction losses of flowing fluid. Results showed that efficiency enhancement is possible through the said optimization.

2.4. Thermal Energy Storage The components which collect and store solar energy are responsible for thermal performance of TES systems (Ahmed et al., 2017). The solar energy is stored in the nature as plant matter in the form of biomass, ocean, heat energy, and hydropower. As solar radiation received is intermittent in nature so its availability changes by the time of the day and is seasonal, and also keep on varying during the day time owing to the clouds, so efficient thermal energy storage (TES) materials are required to store any excess thermal energy that is to be collected throughout the daytime for utilization at night (Pelaya et al., 2017). TES material transfers thermal energy to a storage medium when the charging occurs, and releases it while needed during the period of discharging mode. TES systems can be classified as; SHS (ii) LHS using phase change materials (PCMs) (iii) Thermochemical storage (TCS), which can also be classified as solid adsorption or liquid absorption systems. SHS is based on thermal energy storage for heating or cooling of liquid like water which is cheap and easily available or solid storage such as sand and rocks. LHS using PCMs, mainly employ solid to liquid phase transition to store thermal energy hence it enables a more compact, efficient and more cost effective system to run (Zhang et al., 2016). Use of PCMs in LHS systems significantly improves energy density but there are appreciable thermal energy losses.

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2.4.1. Classification of Thermal Energy Storage System TES systems can be categorized as SHS, LHS, or TCS systems i.e., the heat evolved with the chemical reaction process. 2.4.1.1. Sensible Heat Storage In a material of mass ‘m’ and specific heat ‘Cp’ the SHS is achieved by raising the temperature of the storage media from T1 to T2 and is given by Q = ρ.V.Cp.ΔT, where ρ is the density and ‘V’ is the volume of the TES material. Some general SHS materials are water, rocks, molten salts and ceramics. These TES materials with their thermopysical properties are listed in Table 1. The selection of material is done on the basis of physical properties like; i. ii. iii. iv.

The specific heat capacity of material (cp) Density of material (ρ) thermal conductivity of material (k) Ease of availability and price.

Depending on the application a lot of materials can be used as SHS materials. Among these materials water exhibits the highest value of specific heat. The low and medium temperature solar systems generally use water as a SHS mode as it has the following favorable properties; i. ii. iii. iv. v. vi.

It is cheap and abundant. Low cost and technology simplicity It has favorable thermal properties Simple usage. Design is simple as compared to other TES systems The system could be scaled easily

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Storage medium Temperature Average density Sand-rock mineral oil Reinforced concrete Nacl (solid) Water Rock Silica fire bricks Cast iron Liquid sodium Draw salt (50NaNO350KNO3)* Mineral oil Carbonate salts * Composition in % by weight.

Temperature range (°C) 200 -300 200 - 400 200 - 500 0-100 200-700 200 - 400 100-760 220-540

Average density (kg/m3) 1700 2200 2160 1000 1600 1820 7200 750 1733

Average heat conductivity (W/mK) 1 1.5 7 0.63 1.5 37 67.5 0.57

Average heat capacity (kJ/kg. K) 1.3 0.85 0.85 4.19 0.88 1 0.56 1.26 1.55

200-300 450-850

770 2100

0.12 2

2.6 1.8

2.4.1.2. Thermochemical Energy Storage TCS is stored by means of reversible chemical reactions as heat is involved in these reactions. The energy is stored in the chemical bonds. In this mode of energy storage when the breaking and formation of these chemical bond takes place then an appreciable amount of energy is absorbed and released. In this the reaction is endothermic when it occurs in the forward direction where as in the reverse direction it is exothermic i.e., the heat of reaction is released like, X+ΔH⇆Y+Z Where, Δ H is the heat of reaction / unit mass. TCS being a highly energetic process has many notable advantages such as; high energy density i.e., a large fraction of heat energy can be stored in a small quantity of TES material thus enabling a smaller storage per unit volume and hence lower thermal losses. The properties of few TCS materials are listed in Table 2.

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Table 2. Properties of TCS materials (Goswami, 2015) PCM

Temperature (˚C)

Calcium hydroxide Manganese oxide Calcium carbonate Magnesium hydride Ammonia Methane/water Magnesium oxide Sulphur trioxide

505 530 896 250-500 400-500 500-1000 250-400 520-960

Pressure (bar) 1 1 1 1

Chemical Reaction

Ca(OH)2 + Δ H ↔ CaO + H2O MnO2 + ΔH↔ 0.5Mn2O3 + 0.25O2 CaCO3 + Δ H ↔ CaO + CO2 MgH2 + Δ H ↔ Mg + H2 NH3 + Δ H ↔ 1/2N2 + 3/2H2 CH4 + H2O ↔ CO + 3H2 MgO + H2O ↔ Mg(OH)2 SO3 + Δ H ↔ SO2 +1/2 O2

ΔH (kJ/ mol) 112 42 167 75 67 206 81 99.6

ΔH (kWh/ m3) 364 336 113 111 675 280

2.4.1.3. Latent Heat Energy Storage The SHS requires a large container as compared to LHS and TCS for a particular requirement of thermal energy whereas TCS is related with high energy storage density. LHS is the most likely and attractive method due to its ability to store energy isothermally with respect to the phase change temperature of the material and has high energy storage density (Kumar and Verma, 2020). Thermal energy in a material can be stored as latent heat which undergoes phase change at a temperature based on the application desired, so if a PCM with phase change temperature of Tm is heated from T1 to T2 and if T1< Tm< T2, then the amount of thermal energy stored in PCM can be given as Q = m.L, where m is the mass and L is the latent heat of fusion. Phase change can be from: solid to solid, solid to liquid, solid to gas, liquid to gas and vice versa. The different types of PCMs can be categorized into three groups as; organic, inorganic and eutectics of both organic and inorganic PCM. The main advantages of organic PCMs are; i. ii. iii. iv. v. vi.

Low or no undercooling Non-corrosiveness, Ability of congruent melting without phase separation Possess chemical and thermal stability Self-nucleating properties Its compatibility with conventional materials.

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A number of organic and inorganic PCMs are investigated previously (Saxena et al., 2015). The major complications which are related with the salt hydrates are; i. ii. iii. iv.

Super cooling of material Resulting in phase segregation Corrosion effects Low thermal stability.

Eutectics are composition of two or more salts such as organic–organic, organic–inorganic and inorganic- inorganic which have fixed freezing and melting points (Garg et al., 1985). Apart from these TES materials, following factors should also be taken into account like; a. Selection of storage material which depends on the solar collection system, type of application b. Design of Storage or containment system c. Heat exchanger design

2.4.2. Solar Water Heaters with Energy Storage In the early phase of engineering applications it is a big challenge to store the solar energy for lateral use. With a metallic FPC there is no storage due to its low specific heat. Researchers have been found out the way through which this energy be stored at day time and can be utilized whenever required. This solution has become possible through the use of thermal energy storage (TES) materials. These TES materials have been identified as an attractive and potential material for solar energy storage (Figure 16). The energy stored during the solar hours can be utilized in the evening by withdrawn of heat from the system through the fluid. A system has been shown which is integrated with a parabolic cooker for cooking and water distillation (Figure 17). A simple SWH has been tested on three different PCM such as; Na2SO4.10H2O, Na2HPO4.12H2O and P116 wax in India (Bhargava, 1983). Mathematical model predicted that SWH is feasible to

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provide the hot water entire day. Another research in India (Tiwari et al., 1988), an analytical study has been carried out of PCM integrated SWH by combining the mass flow rate effect by a parallel plate employed at the solid liquid boundary. It has been found that by increasing the flow rate the ƞtherm is also increased up to 75%.

Figure 16. Schematic of energy storage water heater (Sun et al., 2013).

Figure 17. A novel distillation mechanism integrated with a SWH (Saxena and Deval 2016).

A building integrated solar energy storage system (Lin et al., 2003) that stored the solar heat through 2-phase closed loop to a water storage tank and released the stored energy in a TES material through 2-phase closed loop to a compact heat exchanger. Results showed that SWH has been given an

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optimum charge efficiency about 73% while discharge efficiency about 85%. An experimental study of a 2-phase SWH integrated with a LHS has been carried out in Taiwan (Lee at al., 2006). LHS such as; P116, water and NaCH3COO.3H2O has been studied experimentally for water heater. It has been concluded that SWH given optimum charge and discharge enactment under 40% alcohols fill ratio.

2.5. Extra Radiation Gain Solar radiation is one of the major characteristics which a direct significance on the performance of solar thermal systems. This is done with help of radiation boosters such as; mirror, reflector, trough and tilt angle. SWH with capacity of 90 liters with built in storage has been tested in Delhi with an extra radiation gain system of flat mirror (Dhiman and Tiwari, 1983). There has a significant effect of booster mirror (reflectance is 0.88) been found on the performance of SWH by 7oC excessive temperature. A comprehensive study on a FPC has been carried out for a year round performance (Garg and Hrishikesan, 1988). The system has augmented with two similar reflectors for extra thermal gain. About 6%, the performance of system has been improved. A thermosyphon SWH integrated with a plane mirror has been tested in Israel (Faiman and Zemel, 1988). The plane mirror has attached with the storage tank to enhance the energy collection for SWH. In India, a thermosymphon SWH has been tested to observe the significance of two additional booster reflectors (Kaushik et al., 1995) on the performance of SWH. Analysis has showed that improvement about 44% observed in winter while about 15% in summer. Solar radiation is major input for solar thermal systems and receiving solar energy for a maximum potential is completely depended upon its orientation. For this aspect, a SWH has been tested under different angles in Malaysia (Bari, 2001). Results revealed that un-accurate angles of collector gains less radiation about 10-35% while a good orientation angle received at least 50%. In the same aspect, two same ETC type SWH (model SWH-22 &

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SWH-46) has been constructed and tested in Bahrain (Tang et al., 2011). Results showed the model SWH-46 installed at 46o has the best performance. A novel ICSSWH has been designed and studied experimentally in Greece (Souliotis et al., 2011). The unit has integrated with two concentric cylinders inside an especially truncated CPC reflector trough. Comparative study with FP-SWH showed that the designed system is much better with much reduced thermal losses. A forced circulation SWH has been fabricated by integrating V-trough reflectors for performance improvement in Malaysia (Chong et. al., 2012). Results revealed that the optical efficiency of the system has been found about 70.54% and the Tw about 85.9oC. Table 3. Particulate matters through various heating sources Biomass heating device Open fireplace Simple log stove Modern log stove Wood Pellet Stove Wood Pellet Boiler Biomass boiler without emissions control Biomass boiler with emissions control {*g/GJ = grammes per gigajoule} (sources: iea.org)

PM (g/GJ)* 322 - 1610 140 - 225 46 – 90 3-43% 3-29% 28-57% 8-15%

%OC 40 - 75% 50% 20% 10% 5% 3% 2%

3. COMPARATIVE ANALYSIS Hot water demand is a daily need at various places like hospitals, hotels, domestic households and industries too. It is an imperative activity of disbursement and energy consumption. People who are unable to access the clean energy sources often used biomass for the same through which lot of pollution and high carbon emission is generated and also a reason of premature deaths around the globe. This biomass is available in the form of wood pellets, dung cakes, coal, solid waste etc. Tables 3 and 4 presents the biomass PM values and its effects

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while Figure 18 (WHO, 2015) and 19 (Saxena et al., 2013) shows emission of PM2.5 through residential heating and its effect on human beings. Table 4. Contribution of residential heating to outdoor MP2.5 and burden of disease for some specific regions up to 2010 (WHO 1999) Region

Central Europe Eastern Europe Western Europe North America Central Asia Global

PM2.5 from residential heating (%) 1990 2010 11.1 21.1

PM2.5 from residential heating (µg/m3) 990 2010 3.5 3.4

Premature deaths

1990 18000

2010 20000

Disability-adjustedlife-years (DALYs)/year 1990 2010 370000 340000

9.6

3.1

2.0

1.4

24000

21000

480000

410000

5.4

11.8

1.3

1.7

17000

20000

280000

290000

4.6

8.3

0.9

1.1

7500

9200

140000

160000

9.9

8.3

2.4

1.6

5500

4200

180000

110000

3.0

3.1

0.9

0.7

120000

110000

2800000

2200000

Figure 18. Projected score of residential heating emissions for MP2.5 upto 2030 (WHO 2015).

Present work focus on water heating and a comparison is much essential with the other sources of water heating. Different types of biomass products like; firewood, walnut etc., (Koyuncu and Pinar, 2007) have been burned for

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space and water heating in Turkey. Results showed that stove has efficiency about 46% but contains a lot of pollutants such as; NOx and SO2 flue gases. In India, (Saxena et al. 2013) has been assessed the burden of diseases and its impact on human structure (Figure 19) in remote areas of Uttar Pradesh state during biomass firing.

Figure 19. Impacts of biomass combustion on human structure (Saxena et al., 2013).

A review study has been shown (Chen et al., 2017) the effects of biomass burning on the atmosphere and human health. The study thoroughly carried out on various origins of biomass pollution in India, China and Australia. Sources of biomass, various pollutants from biomass burning and its physical properties, morphology and mixing state and health hazards has been studied for further research priorities. Experimental and review study by Chakarborty and Mondal, 2018, Niklitschek et al., 2020, Perrino et al.,

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2019 and Maxwell et el., 2020 has been shown the adverse effects of biomass heating on the human beings round the world. Therefore, solar energy (the clean fuel) is a viable option for domestic heating tasks such as water heating, cooking and agro drying. Through this heating process the problem of pollution and burden of diseases can be avoided for a maximum potential. If the one is talked about the choices of water heating system among various solar water heating systems than no doubt that all types of SWH are good from the economic and safety point of view but yet CPC based water heating is a good option for industrial water heating. The ETC type water heaters are good for residential areas to fulfill their hot water demand while the FPC based water system with a potential heat storage material is also a good option for hostels and religious places where the space availability is not an issue.

4. BENEFITS OF SWHS The benefits of using SWHS in domestic households or commercial sectors include (Saxena et al., 2013): 1. Operated on completely clean and free of cost fuel 2. Abridged environmental pollution as well as controlled greenhouse emissions 3. Silent operation 4. Different designs are available according to the need 5. Ease of installation on ground or on the roof 6. Quite low operating cost 7. Low maintenance cost 8. Short payback period 9. Long life cycle 10. Reduced electricity/gas/oil bills 11. Economic (fuel and money saver) 12. Built in hot water storage of different capacities

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User friendly Design is appropriate for villages and remote locations High year round performance without continuous attention Safety while operating is good

CONCLUSION Solar water heater is a common practice to produce hot water through sun energy. A lot of passive and active designs of small and large size of water heater fulfill the hot water demand in many geographic locations of the world either it is a simple household or a large commercial sector. Performance improvement of the SAH is an important task to increase the hot water supply especially in cold climates or regions. Design analysis shows that each element like; evacuated tube, flat plate collector, glazing, insulation, higher reflective surface of CPC, storage tank, water head, etc, has an important role to get the efficient performance of water heater round the year. The system has a significant effect of ambient conditions on thermal performance. Comparative study shows that the use of extended geometries, heat storage materials and selective coating has also a noteworthy role on the performance of water heaters. All these techniques for performance enhancement are good but it must be design and cost optimized for more economic results. A system is good if it is cost and design optimized and performs well round the year.

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Speyer, E. (1965). Solar energy collection with evacuated tubes. ASME Journal of Engineering for Power, 270-275. Sun, D., Xu, J. and Ding, P. (2013). Performance analysis and application of three different computational methods for solar heating system with seasonal water tank heat storage. Advances in Mechanical Engineering, Article ID 857941: 1-13. Tang, R., Yang, Y. and Gao, W. (2011). Comparative studies on thermal performance of water-in-glass evacuated tube solar water heaters with different collector tilt-angles, Solar Energy, 85:1381-1389. Tarhan, S., Sari, A. and Hakan, Y.M. (2006). Temperature distributions in trapezoidal built in storage solar water heating systems with/without phase change materials. Energy Conversion Management, 47: 2143-54. Tiwari, G.N., Rai, S.N., Ram, S. and Singh, M. (1988). Performance prediction of PCCM collection-cum-storage water heater: quasi-steady state solution. Energy Conversion and Management, 28: 219-223. Tiwari, G.N. (2014). Advances in renewable energy, QIP-course, IIT-Delhi. Tse, K. and Chow, T. (2015). Dynamic model and experimental validation of an indirect thermosyphon solar water heater coupled with a parallel circular tube rings type heat exchange coil. Solar Energy, 114: 114-133. Verma, P., Varun and Singal S.K. (2008). Review of mathematical modeling on latent heat thermal energy storage system using phase change materials, Renewable and Sustainable Energy Reviews, 12(4): 9991031. Verma, P. and Varshney, L. (2015). Parametric investigation on thermohydraulic performance of wire screen matrix packed solar air heater, Sustainable Energy Technologies and Assessments, 10: 40-52. Wang, Z., Yang, W., Qiu, F., Zhang, X. and Zhao, X. (2015). Solar water heating: from theory, application, marketing and research, Renewable and Sustainable Energy Reviews, 41: 68-84. Wu, S., Fang, G. and Liu, X. (2011). Dynamic discharging characteristics simulation on solar heat storage system with spherical capsules using paraffin as heat storage material. Renewable Energy, 36: 1190-5.

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Zeng, R., Wang, X., Xiao, W., Zhang, Y., Zhang, Q. and Di, H. (2010). Thermal performance of phase change material energy storage floor for active solar water-heating system. Frontiers Energy and Power Engineering in China, 4(2): 185-191. Zhang, H., Baeyens, J., Caceres, G., Degreve, J. and Yongqin, Lv. (2016). Thermal energy storage: Recent developments and practical aspects. Progress in Energy and Combustion Science, 53:1-40.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 11

HUMIDIFICATION-DEHUMIDIFICATION DESALINATION THROUGH SOLAR WATER HEATING SYSTEM T. Srinivas* Department of Mechanical Engineering, Dr B R Ambedkar National Institute of Technology, Jalandhar, Punjab, India

ABSTRACT Humidification-dehumidification (HDH) desalination is a simple water purification method operating on water cycle principle. Solar water heater (SWH) having flat plate collector (FPC) is coupled with sensible heat storage unit and HDH desalination. The SWH’s temperatures, instantaneous energy, FPC’s thermal efficiency and cumulative energy are simulated from sunrise to sunset using thermodynamic and heat transfer modeling. Transient analysis has been carried out to evaluate thermal storage and desalination performance. Finite difference method has been applied to sensible heat storage system with well mixed condition and

*

Corresponding Author’s E-mail: [email protected]; [email protected].

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stratification. The average hourly production rate of desalination is 2.0 liters at 1000 m3/h of the air. The accumulated desalination is 15 liters.

NOMENCLATURE A c C EPR G h m M Q SHF t T V U W y ε Ø ρ ω

area, m2 specific heat, kJ kg-1 K-1 velocity, m s-1 energy performance ratio solar radiation, W m-2 specific enthalpy, kJ kg-1 dry air mass flow rate, kg s-1 molecular weight, kg mole-1 heat, kW sensible heat factor time, s temperature, °C volume, m3 heat transfer coefficient, W m-2 K-1 work, kW weight factor effectiveness relative humidity density, k m-3 specific humidity, kg kg-1 dry air

Suffix APH da e

air preheater dry air equivalent

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267

hot water solar water heater

Acronyms APH ARH HDH

air preheater air reheater humidification-dehumidification

1. INTRODUCTION Flat plate collector (FPC) with thermal energy storage (TES) is suitable to humidification-dehumidification (HDH) desalination by removing the salts from the saline water with water cycle principle. Its performance is good compared to the conventional solar still as the air is subjected to humidification. HDH is a simple and cost effective solution for drinking water production. HDH is a safe technology as no chemicals are used and operates at atmospheric pressure. Low grade energy can be used to operate the plant. The literature on HDH desalination proves its merits compared to the existing solar stills. At water and air flow of 70 kg/h and 50 kg/h respectively, Farid and Al-Hajaj (1996) reported 12 L/m2/day drinking water with HDH and concluded that HDH’s production is triple compared to solar still. Nawayseh et al. (1997) conducted theoretical studies on HDH at Jordan to improve the water productivity and focused on surface area of humidifier and dehumidifier. They proved the strong connection between surface area and water yield. Summers et al. (2012) simulated the solar air heater in a HDH desalination with phase change material (PCM) storage unit. Using a two dimensional transient finite element model, it is found that a PCM layer of 8 cm below the absorber plate is sufficient to produce a consistent output temperature close to the PCM melting temperature with a time-averaged collector thermal efficiency of 35%. Rajaseenivasan et al. (2014) studied the performance of the single basin solar still by means of preheating the saline

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water using an integrated flat plate collector arrangement. Storage unit has been integrated to the solar still. The results showed a 60% improvement in desalination compared to the conventional still. Yu et al. (2019) proposed a new dynamic thermal model based on the response factor method. The daily heat transferred into room through walls has been studied with this model. Alsehli et al. (2019) studied the multi effect desalination (MED) with indirect heating sensible heat storage system. The system includes two tanks where one tank is used for solar charging while other tank is used for feeding MED. The dynamic simulation results quantified the desalination production with the size of the parabolic trough collector (PTC). Abbaspour et al. (2019) used a barometric water column to create the vacuum in a desalination connected to an evacuated tube solar water heating system and storage tank. Increasing vacuum level led to improved system performance and the highest hourly water production for the internal pressures of 23.4 kPa and 39.7 kPa was obtained as 1.134 kg/m2 h and 0.928 kg/m2 h respectively. Moreover, daily efficiency was calculated to be 47.6 and 33.1%, respectively. Dekhil et al. (2020) studied the arrangement of heat exchanger in a sensible heat storage system in the application of agro-food industry. The results stated that the use of a combination of fluid and solid zones inside the storage system is an interesting solution allowing an increase of the storage performance with a significant material reduction. Mohamed et al. (2020) studied the solar flat plate collector with storage tank and Nano fluid at Egypt. The results showed that, the storage tank temperature is attained to about 80°C in summer and 55°C in winter. Zinc Oxide nanoparticles with average diameter of 23 nm have been added to the tap water to produce the Nano fluid with volume fractions of 0.05% and 0.1%. Kalaiarasi et al. (2020) tested an integrated absorber plate cum storage unit for solar air heater. The integrated unit consists of a set of copper tubes with black painted copper foil, welded longitudinally on two main header tubes. A considerable increment in thermal efficiency has been proved with storage unit in solar air heater. Xu et al. (2020) studied the heat transfer aspects of air heater with PCM (paraffin) using theoretical and experimental method. The results indicated that heat-collecting efficiency increased continuously with larger air flow. Badiei et al. (2020) used a three

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dimensional transient CFD model to investigate a solar flat plate collector integrated with a layer of PCM. Results show that although the system with PCM has lower output temperatures in the morning, hot water can be supplied in a longer duration in the evening while discharging. Alptekin and Ezan (2020) considered a sensible heat thermal energy storage tank that is integrated with a flat plate solar collector to study the spatial and temporal temperature variations within the storage tank and the solar collector throughout a day under variable weather conditions. Ghorbani, et al. (2020) coupled a flat plate collector with a multi-stage desalination system the energy needed for water desalination. A thermal energy storage with stearic acid PCM along with natural gas-fired auxiliary boilers is added to this system to provide stable working conditions throughout the day. This process produces 4500 kg/h hot water at a temperature of 65.26°C, and 379.6 kg/h fresh water. The main focus of the current work is to formulate the sensible heat storage system integrated between solar FPC and HDH desalination and conduct the transient analysis to study the working of plant with the storage unit.

2. THEORETICAL PERSPECTIVES 2.1. Well Mixed Thermal Stratification with Direct Heat Transfer The methodology consists of evaluation of (1) storage system and (2) HDH desalination plant. Since the considered HDH desalination works below 100°C, a FPC with sensible heat storage system has been considered for this study. The analysis of storage with thermal stratification gives more realistic results compared to the total lumped analysis. In a thermally stratified situation, the temperature of the contained liquid varies from the bottom to the top, being less at the bottom and more at the top. Figure 1 is the particulars of well mixed sensible heat storage system with thermal stratification. The hot water from the FPC is communicated to

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storage unit. The high density fluid particles at low temperature are collected at the bottom of the tank. Similarly, low density fluid particles with high temperature are collected at the top of the tank. In fact, the temperature of the fluid increases continuously from bottom to top. The thermal model consists of two well mixed sections at two different temperatures, Tl1 and Tl2. The mass balance and energy balance equations are developed for transient simulation of temperature with respect to time. The energy balance equation of section 1, (𝜌𝑉𝑐𝑝 )𝑙1

𝑑𝑇𝑙1 = 𝑚̇𝑐𝑝 (𝑇𝑓𝑜 − 𝑇𝑙1 ) − 𝑚̇𝑙𝑜𝑎𝑑 𝑐𝑝 (𝑇𝑙1 − 𝑇𝑙2 ) 𝑑𝑡 −(𝑈𝐴)𝑡1 (𝑇𝑙1 − 𝑇𝑎 )

(1)

The ρVcp is the thermal capacity of the liquid in the storage tank. UA is the product of overall heat transfer coefficient and surface area of the tank.

 is the mass flow rate in solar collector and mload is the fluid flow in The m HDH desalination plant. Ta is the ambient temperature. Writing the equations in finite difference form, 𝑇𝑙1,𝑓 − 𝑇𝑙1,𝑖 𝑇𝑙1,𝑓 + 𝑇𝑙1,𝑖 (𝜌𝑉𝑐𝑝 )𝑙1 ( ) = 𝑚̇𝑐𝑝 (𝑇𝑓𝑜 − ) 𝛥𝑡 2 𝑇𝑙1,𝑓 +𝑇𝑙1,𝑖 𝑇𝑙2,𝑓 +𝑇𝑙2,𝑖 𝑇𝑙1,𝑓 +𝑇𝑙1,𝑖 −𝑚̇𝑙𝑜𝑎𝑑 𝑐𝑝 ( − ) − (𝑈𝐴)𝑡1 ( − 𝑇𝑎 ) 2

2

2

Figure 1. Well mixed and thermally stratified sensible heat liquid storage.

(2)

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In these equations, Tl1, f and Tl1, i represent the final and initial values of Tl1 over the time interval ∆t. After the simplification,   ( Vc p )l1       0.5m c p  m load c p  (UA)t1 Tl1, f  m load c pTl 2, f    t   T   ( Vc p )l1  l1,i   0.5m c p  m load c p  (UA)t1 Tl1,i  0.5m load c pT12,i  m c pT fo  (UA)t1Ta  t 

(3)

Similarly, the energy balance equation of section 2, T T   T  Tl1,i Tl 2, f  Tl 2,i   T  Tl 2,i    m load c p  l 2, f ( Vc p )l 2  l 2, f l 2,i   m c p  l1, f   Ti   t 2 2 2        T  Tl 2,i   (UA)t 2  l 2, f  Ta  2   (4)

The simplification results,   ( Vc p ) l 2     0.5m c p  m load c p  (UA) t 2 Tl 2, f  0.5m c pTl1, f      t   T    ( Vc p ) l 2  l 2,i   0.5m c p  m load c p  (UA) t 2 Tl 2,i  m load c pTi  0.5m c pTl1,i  (UA) t 2 Ta  t  

(5)

The simplified above two equations (Eq. 3 and Eq. 5) consist of two variables, Tl1 and Tl2. After assuming a suitable time interval, ∆t, the two temperatures of liquid, Tl1 and Tl2 are solved before and after the time interval. These two mathematical equations are developed using differentiation by assuming the collector exit temperature greater than the storage tank fluid temperature.

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2.2. HDH Desalination Figure 2 outlines the schematic flow of HDH plant associated with FPC and storage. The plant is designed to operate on off-grid mode and energy supply from solar PV and thermal (PV/T). The properties of this desalination plant are listed at in Table 1 after its evaluation. The atmospheric air forced into the plant by air circulating fan of condenser. Air preheater (APH) is used for sensible heating of air. It increases the humidification capacity in humidifier. The hot water from SWH is supplied to APH and humidifier. The supply of preheated air and hot saline water in the humidifier results heating and humidification. Humidifier consists of packing for wet contact surface to enhance the humidification. The brine solution is collected at the bottom and humid air flows to the top. After humidification, the air reaches to dehumidifier. Air is condensed after touching the cold body of dehumidifier. The circulating water in dehumidifier provides the cooling surface to condense the humid air by keeping its surface temperature below the dew point temperature. The droplet condensate from the dehumidifier forms the drinking water. The heat load in APH and humidifier is met by the solar FPC. The parasitic power required to operate pump and fan. Since the proposed plant is off-grid operation, solar PV is connected for parasitic load. In this plant, the dehumidifier consists of two parts: first part is the natural convective heat exchanger and the second is forced convective heat exchanger. The first part of dehumidifier uses metallic finned surface to reject the heat to surroundings. It also shares the cooling load in the subsequent dehumidification process. The condensate (soft water) is collected from the dehumidifier by gravity action. Thermodynamic model has been developed to simulate the HDH cycle using MATLAB environment. The properties of wet air in the plant are determined from the psychrometric formulation. The methodology to evaluate the HDH cycle has been detailed with the thermodynamic relations. Following sections are detailed about the assumptions and theoretical formulation of plant’s components used in numerical modelling and simulation. The formulae are resulted from mass balance and energy balance in the components (Anand and Srinivas, 2020).

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The air flow in the plant is assumed constant at 1000 m3/h with no air leakages for easy conversion of specific outputs into total values. The mass of the wet air is determined from its volume flow rate. Mass of wet air,

mair =

Vair M air 22.4

(6)

In the above equation, 22.4 is derived from Avogadro’s hypothesis. The wet air consists of dry and moisture content. All the psychrometric properties are formulated with the dry air reference.

Figure 2. HDH desalination with solar water heater and PV panel.

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Table 1. Thermodynamic properties of HDH cycle shown in Figure 1 State 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

P, bar 1.01 1.60 1.58 1.57 1.57 1.54 1.52 1.01 1.52 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.01

T,ºC 35.00 38.00 51.20 51.80 51.80 37.77 36.77 36.77 36.77 25.00 60.00 60.00 52.00 60.00 59.73 57.45 35.77 36.67

Ø 75.00 100.00 50.10 48.52 48.52 94.75 96.38 0.00 96.38 ----------

m, kg/h 1287.50 1287.50 1287.50 1287.76 1287.76 1286.58 1285.68 2.08 1285.68 0.26 1775.88 522.35 522.35 1253.53 1253.27 1775.88 971.09 971.09

h, kJ/kg 104.70 107.25 121.18 122.36 122.36 105.13 102.23 153.71 102.23 104.50 250.80 250.80 217.36 250.80 249.67 240.13 149.53 153.27

The dry air in the duct is determined from the wet air mass flow and its specific humidity,

mda =

mair 1+w

(7)

The specific humidity of air, ω is the mass of moisture in the air per kg of dry air. Air circulation fan is used to absorb the atmospheric air and force over APH coil. The inlet condition of air is at 28°C and 75% relative humidity (Ø). The velocity of air at inlet of fan is not accounted and the exit velocity is determined from the cross sectional area of duct and its air flow. The enthalpy and kinetic energy are functioned to determine electrical supply to fan. The power supply to fan from steady flow energy equation (SFEE),

Humidification-Dehumidification Desalination through Solar …

 C2  W fan  mda  hexit  hin  exit  2000  

275

(8)

In above SFEE, the energies considered are electrical supply to fan, enthalpies at inlet and outlet and the kinetic energy at outlet. The constant 2000 is used put all the terms in kW. APH is used to rise the temperature of air and decrease the relative humidity. The effectiveness, ε of APH is 0.6. The air exit temperature from the APH is determined from its effectiveness. Tair, exit = Tair, in + εAPH (Thw, in – Tair, in)

(9)

The saline water supply temperature to humidifier and ARH is 60°C. The liquid (water) to air mass ratio in the humidifier is 1. The effectiveness of humidifier heat transfer is 0.75. Humidifier’s sensible heat factor is 0.6. The liquid to air mass ratio,

mr =

mhot

water

(10)

mda

If humidifier is assumed as a heat exchanger, the air exit temperature is simulated from its effectiveness. Tair, exit = Tair, in + εhumidifier (Thot water, in – Tair, in)

(11)

Let h′ is the enthalpy of air at exit but at initial specific humidity. The enthalpy of air after the humidification

hair , exit  hair , in 

h  hair , in SHF

(12)

The above enthalpy and temperature of air at the exit of humidifier gives the relative humidity. The mass of hot water at the exit of humidifier is less

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than the inlet due to the evaporation of water particles in the humidifier. Sensible heat factor (SHF) is the ratio of sensible heat to total heat of the air. The hot water collected at the exit of humidifier, mhot water, exit = mho water, in – mda (ωexit – ωin)

(13)

Hot water exit temperature from the humidifier,

Thot ,

water exit

=

mhot water in c p ,hwThot water , in - mda (hair , mhot

exit

- hair , in )

c water ,exit pw

(14)

The above equation is the result of energy balance equation in humidifier. Dehumidifier is a heat exchanger where the humid air is cooled by circulating water in the cooling coil. The enthalpy of the exit air in the dehumidifier is determined from the inlet and outlet conditions. The enthalpy of exit air from the dehumidifier,

 Tair , in  Tair , exit )   hair , exit  hair , in  hair ,, in  hADP , air , in   Tair , in  T  ) ADP , air , in  





(15)

The exit temperature of air and enthalpy results the relative humidity of air. The average global radiation from sunrise to sunset is 480 W/m2. The solar PV panel to electricity efficiency is 15%. The thermal efficiency of SWH is function of fluid inlet temperature and solar radiation. The hot water inlet and exit temperatures in SWH are solved with the integration of HDH plant. The area of the SWH is evaluated with the standard method. The energy supply to the system is the sum of thermal energy and work. The parasitic power is the electrical energy supply to the HDH solar system. It consists of electricity supply to the air circulating fan and water pump. The parasitic power supply to the cycle is Wparasitic = Wfan + Wpump

(16)

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The performance of the desalination plant has been expressed as an energy performance ratio (EPR) as this energy efficiency consists of high grade energy and low grade energy. Since the value of high grade energy is more than the low grade energy, a weightage factor, 3 has been assigned. The cycle EPR,

EPR

cycle

=

mdesalination h fg QSWH + yeW parasitic

(17)

where ye is the factor assigned to high grade energy. The plant EPR,

EPR

plant

=

mdesalination h fg Gglobal APV + SWH

(18)

The difference between EPR of cycle and EPR of plant, is the exclusion of solar collector in the cycle.

3. RESULTS In this section the results of storage system and HDH desalination are furnished. Figure 3 analyzes the working of storage from sunrise to sunset with HDH. The studied collecting and storage temperatures are collector exit temperature, storage tank upper temperature and storage tank lower temperature (Figure 3a). During the operation, if the storage tank top temperature is more than the collector exit temperature, the storage tank should be isolated from the collector, otherwise, the temperature of the fluid in the storage tank decreases. A thermostatic valve controls the flow of hot water to the storage unit. Since the energy is storing from sunrise, the maximum collector’s exit temperature (72°C) is obtained after the solar noon. The instantaneous energies of solar radiation, collector and load are

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plotted in Figure 3b. The maximum solar radiation collected is 25 kW during the solar noon. The area under energy and time plot is equal to cumulative energy for the period of operation. The energy collected from the solar collector should be equal or greater than the energy required to load. The time period considered for the HDH desalination operation is 7 hours. The collector efficiency increases with increase in solar radiation, maximum at solar noon and falls later (Figure 3c). At peak, the collector’s thermal efficiency is approximately 50% at solar noon. Similar to the instantaneous energies, the cumulative energies are also plotted. The load from the HDH plant is less than the energy collected from collector (Figure 3d). More heat losses are observed from accumulated global solar energy to accumulated collected energy. The cumulative energy from the solar radiation is 8 × 105 kJ and the collected energy is 3 × 105 kJ. Figure 4 shows the instantaneous desalination and cumulative desalination of HDH plant with time. The time period shown is 7 hours. The start and end of the operation is designed as per the availability of thermal energy in the storage. The instantaneous desalination is increasing in diminishing rate with the thermal storage. The desalination rate is varied from 1.94 LPH to 2.06 LPH. The cumulative desalination is increasing linearly as shown in Figure 4b. The total desalination is 15 liters per day (LPD). The approximate desalination rate is 2 liters per hour (LPH). The HDH desalination results are reported in the literature and the air flow rate in each system is different. To compare the results with the literature, the specific desalination can be expressed in ml/m3 of air. At 1000 m3/h of air flow, the specific desalination resulted is from 1.94 ml/m3 to 2.06 ml/m3. Sharshir et al. (2016) showed the cumulative HDH desalination during the HDH operation. The accumulative productivity is increased nearly linear as shown. Ahmed et al. (2017) resulted 3 LPH of desalination from HDH desalination. The present results are showing approximately 2 LPH of desalination. Yamalı and Solmus (2008) reported 18 g/m3 of specific desalination from HDH experimental work and the current work is resulting 15 g/m3. Figure 5 presents the performance of HDH desalination plant with the use of thermal storage. The desalination increases with increase in hot water

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supply temperature. But EPR decreases with the added thermal energy to the plant. Chiranjeevi and Srinivas (2017) showed the cycle EPR at 0.18. The range of EPR during the operation of plant is 0.16 to 0.21. With the solar system’s losses, the plant efficiency is less than the cycle efficiency.

Figure 3. Analysis of solar water heater with storage tank.

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Figure 4. (a) Instantaneous desalination and (b) cumulative desalination of HDH plant with time.

Figure 5. EPR of HDH plant with time.

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Table 2. HDH plant specification operated by solar water heater with thermal storage at the air flow of 1000 m3/h S. No. 1. 2. 7. 8. 9. 12. 13. 14. 15. 16. 17. 18.

Description Specific desalination, ml/m3 air Total desalination, LPH Fan, kW Pump capacity for hot water, kW Pump capacity for circulating water Total parasitic power, kW Heat supplied to cycle, kW Area of solar PV plant, m2 Area of solar water heater, m2 Total solar collecting area, m2 Cycle EPR Plant EPR

Result 2.08 2.08 0.90 0.20 0.08 1.18 5.25 16.45 14.00 30.45 0.15 0.09

Table 2 presents the specific desalination and desalination rate at the air flow rate of 1000 m3/h. They are 2.08 ml/m3 and 2.08 LPH respectively. The electricity generated from 13 m2 solar PV plant can be used to meet the plant parasitic power of 1.18 kW. Nearly 30 m2 of solar FPC results hot water for the desalination for the operation of 7 hours. The resulted EPR is 0.15 and 0.09 respectively for cycle and plant.

CONCLUSION The dynamic analysis has been carried out to HDH desalination plant with the energy supply from solar FPC and thermal storage unit. Well mixed and thermal stratification unit of storage system is solved using finite difference method. The hot water is used for the HDH function of air preheating and humidification. The peak temperature in the storage tank is observed after solar noon. Nearly half of the solar radiation is converted to useful form for HDH desalination. The instantaneous desalination rate is increased from beginning to end of the operation. EPR is decreased from morning to evening. The desalination is 2 LPH and the cumulative

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desalination is 15 LPD. The cycle EPR and plant EPR are 0.15 and 0.09 respectively.

ACKNOWLEDGMENTS The author acknowledge the project grant of the Science and Engineering Research Board (SERB) under Impacting Research Innovation and Technology (IMPRINT-2), PAC Water Resources & River Systems, New Delhi, India (IMP/2019/000444).

REFERENCES Abbaspour, Mohammad Javad, Meysam Faegh, Mohammad Behshad Shafii. “Experimental examination of a natural vacuum desalination system integrated with evacuated tube collectors.” Desalination, 467, (2019), 79-85. Ahmed, Hossam A; Ismail, IM; Wael F. Saleh, Ahmed, M. “Experimental investigation of humidification-dehumidification desalination system with corrugated packing in the humidifier.” Desalination, 410, (2017), 19-29. Alptekin, Ersin, Mehmet Akif Ezan. “Performance investigations on a sensible heat thermal energy storage tank with a solar collector under variable climatic conditions.” Applied Thermal Engineering, 164, (2020), 114423. Alsehli, Mishal, Mussad Alzahrani, Jun-Ki Choi. “A novel design for solar integrated multi-effect distillation driven by sensible heat and alternate storage tanks.” Desalination, 468, (2019), 114061. Anand, B; Srinivas, T. “Cogeneration of Power and Desalination Using Concentrated Photovoltaic/Thermal Humidification and Dehumidification System.” In Advances in Energy Research, Vol. 1, pp. 125-137. Springer, Singapore, 2020.

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Badiei, Z; Eslami, M; Jafarpur. K. “Performance improvements in solar flat plate collectors by integrating with phase change materials and fins: A CFD modeling.” Energy, 192, (2020), 116719. Chiranjeevi, C; Srinivas, T. “Augmented desalination with cooling integration.” International Journal of Refrigeration, 80, (2017), 106119. Dekhil, Mohamed Amine, Jules Voguelin Simo Tala, Odin Bulliard-Sauret, Daniel Bougeard. “Development of an innovative heat exchanger for sensible heat storage in agro-food industry.” Applied Thermal Engineering, (2020), 115412. Farid, Mohammed, Abdul Wahid Al-Hajaj. “Solar desalination with a humidification-dehumidification cycle.” Desalination, 106, no. 1-3, (1996), 427-429. Ghorbani, Bahram, Mehdi Mehrpooya. “Thermo-economic analysis of a solar-driven multi-stage desalination unit equipped with a phase change material storage system to provide heating and fresh water for a residential complex.” Journal of Energy Storage, 30, (2020), 101555. Kalaiarasi, G; Velraj, R; Vanjeswaran, MN; Ganesh Pandian, N. “Experimental analysis and comparison of flat plate solar air heater with and without integrated sensible heat storage.” Renewable Energy, 150, (2020), 255-265. Mohamed, Mousa M; Nabil H. Mahmoud, Mohamed A. Farahat. “Energy storage system with flat plate solar collector and water-ZnO nanofluid.” Solar Energy, 202, (2020), 25-31. Nawayseh, Naser K; Mohammed Mehdi Farid, Abdul Aziz Omar, Said Mohd Al-Hallaj, Abdul Rahman Tamimi. “A simulation study to improve the performance of a solar humidification-dehumidification desalination unit constructed in Jordan.” Desalination, 109, no. 3, (1997), 277-284. Rajaseenivasan, T; Nelson Raja, P; Srithar, K. “An experimental investigation on a solar still with an integrated flat plate collector.” Desalination, 347, (2014), 131-137. Sharshir, SW; Guilong Peng, Nuo Yang, MOA; El-Samadony, Kabeel, AE. “A continuous desalination system using humidification–

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dehumidification and a solar still with an evacuated solar water heater.” Applied Thermal Engineering, 104, (2016), 734-742. Summers, Edward K; Mohammed A. Antar. “Design and optimization of an air heating solar collector with integrated phase change material energy storage for use in humidification–dehumidification desalination.” Solar Energy, 86, no. 11, (2012), 3417-3429. Xu, Bo, Jiaxin Xu, Zhenqian Chen. “Heat transfer study in solar collector with energy storage.” International Journal of Heat and Mass Transfer, 156, (2020), 119778. Yamalı, Cemil, İsmail Solmus. “A solar desalination system using humidification–dehumidification process: experimental study and comparison with the theoretical results.” Desalination, 220, no. 1-3, (2008), 538-551. Yu, Guoqing, Chengjun Du, Hengtao Chen, Le Xiong. “A dynamic model based on response factor method and seasonal performance analysis for integration of flat plate solar collector with building envelope.” Applied Thermal Engineering, 150, (2019), 316-328.

In: Solar Water Heating Editor: Khalil Kassmi

ISBN: 978-1-53619-320-6 © 2021 Nova Science Publishers, Inc.

Chapter 12

INFLUENCE OF VARIOUS NANOFLUIDS ON THE PERFORMANCE OF SOLAR WATER HEATERS P. Michael Joseph Stalin1,*, T. V. Arjunan2, M. M. Matheswaran3, P. Manoj Kumar4 and N. Sadanandam5 1

Audisankara College Engineering &Technology, Gudur, Andhra Pradesh, India 2 Guru Ghasidas Viswavidyalaya (Central University), Chhattisgarh, India 3 Jansons Institute of Technology, Coimbatore, Tanilnadu, India 4 KPR Institute of Engineering and Technology, Coimbatore, Tanilnadu, India 5 Coimbatore Institute of Engineering and Technology, Coimbatore, Tanilnadu, India

286 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al.

ABSTRACT The present theoretical work is performed to find out the performance enhancement of flat plate solar water heating systems using six different nanofluids namely CeO2/water, CuO/water, Al2O3/water, TiO2/water, Graphane/water and SiO2/water followed by the comparison with conventional fluid. Further exergy analysis has also been carried out in order to evaluate the theoretical performance working fluids for all the volume concentrations with respect to mass flow rates. It is evaluated that the efficiency of solar water heater using CeO2/water nanofluid having the particle volume concentration of 2.75% and the mass flow rate of 0.14 kg/s is 3.24% higher than that of Graphane/water nanofluid and about 9.20% more than that of other conventional working fluids. It is observed that the result of second law analysis using CeO2/water nanofluid operating with the mass flow rate of 0.01kg/s has shown maximum exergy enhancement of 15.21% higher than that of water as the working fluids and 6.52% higher efficiency than that of Graphane/water nanofluids. It is also observed that the maximum size reduction of 27.86% was attained using CeO2/water nanofluids when compared to water as working fluid at the mass flow rate of 0.03 kg/s.

Keywords: nanofluid, solar collector, exergy, water heater, CeO2

1. INTRODUCTION The usage of solar energy is receiving greater attention now a day because of the depletion of fossil fuels on one facet and environmental degradation. Many research works have been focused on the improvement in performance of flat plate solar collector in addition to the absorber plate performance. Different types of thermal losses and effectiveness of insulation materials, impact of tilt perspective have also been analyzed and elaborated with the help of many researcher studies. As a gift, the nanofluids have the outstanding potential in the heat transfer enhancement and many research works have been done on nanofluid properties and its overall heat transfer performances.

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287

At present, different types of Nanofluids are being prepared using the combinations of pure metals, metal oxides and carbide in many experimental investigations. Enhancement of the few thermal properties of working thermo-fluid was initially proposed by Choi (1995) with the incorporation of nanoparticles. From then onwards there has been much research in the development of nanofluids having thermo-physical properties such as thermal conductivity, thermal diffusivity and viscosity. Investigations have revealed that the thermo-physical properties of several fluids can be improved by the addition of small concentrations of nanoparticles. Nanofluids are prepared by mixing of nano-sized solid particles with the base fluid. Preparation of nanofluid is an important part in order to evaluate its effective thermal conductivity and viscosity. Nanofluids containing low volume fractions of nanoparticles can be used as a single phase fluid due to the treatment of it as single phase. Nanofluids can be prepared in the laboratories using single-step method and two-step method. In single-step method, nanoparticles are produced and dispersed into a base fluid in a single step. Common difficulty encountered in preparing the nanofluid is the agglomeration which was presented by Singh et al. (2008). To overcome this difficulty, researchers added the surfactant to the base fluids during preparation of nanofluids. In case of two-step process, ultrasonic agitation or mechanical stirring, the nanoparticles are slowly dispersed into base fluids by adjusting pH value of nanofluids. During ultrasonification and mechanical stirring, aggregates of nanoparticles are broken down so that stable nanofluid can be obtained. Even though there are so many methods available to prepare nanofluids in the laboratory, only twostep method is preferable by the researchers due to their more number of advantages than other methods. One of the main issues for the engineering applications (Liu et al. 2008) involving nanoparticles in the base fluid is its stability for long term. In theory, it is explained that there is existence of both attractive force in the form of Vander Waals force and repulsive forces in the form of electrostatic repulsion between particles (Ise et al.2005) when particles get too close together. It is also indicated that the repulsive force should be stronger than the attractive force in order to achieve the stability of nanoparticles in the base fluid; otherwise particles will aggregate which

288 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. leads to sedimentation. That is the reason the surfactants are added to the nanofluid to enhance the electrostatic repulsion of nanoparticles. New types of Nanofluids have been developed because of its superior thermophysical properties such as thermal conductivity, viscosity and specific heat. They affect the heat transfer rates when it is mixed with base fluids. It is seen that nanoparticles based on metals and metal oxides has shown superior thermal conductivity when compared to the thermal conductivity of pure liquids. The purity level, shape, size and concentration of nanoparticles are some of the important factors that alter the thermophysical properties. The term nanofluid was first coined by Choi (1995) at the Argonne National Laboratory, USA. The nanoparticles dispersed in the base fluid shown in Figure 5 show long-term stability and superior thermal conductivity as compared to micrometer sized particles in addition to little pressure drop. Many experimental and theoretical investigations have been carried out in order to study the change in thermal conductivity in the past. It is seen that the Brownian motion plays an important role in increasing the thermal conductivity with the addition of nanoparticles in a base fluid and it influences the thermal behavior of nanofluidas reported by Stalin et al.(2020). The another reason is the formation of interfacial layer, that is, the liquid molecules close to a solid particle form layered structures. These layered structures enhance the thermal conductivity of the nanofluid by acting as a thermal bridge between nanoparticles and a bulk liquid by Gupta et al. (2017). It is seen from several research works that the thermal efficiency of solar collector using nanofluids in base fluid depends on several thermo physical properties of nanoparticle. Wen and Ding (2005) reported in an experimental that there is a considerable enhancement of convective heat transfer while using the nanofluids. Tiwari et al. (2013) investigated the usage of nanofluids, which is basically liquid-nanoparticle colloidal dispersion as a working fluid and found to enhance solar flat plate collector thermal efficiency maximum by 30 percent. Gupta et al. (2015) carried out an experimental study to investigate the effect of 20 nm size of Al2O3–H2O nanofluid in direct absorption solar collector with 0.005% volume fraction at three different flow rates and found that enhancement in the efficiency of the collector

Influence of Various Nanofluids on the Performance …

289

reached up to 8.1% with the volume flow rate of 1.5 Lit/min. In another experimental investigation, Colangelo et al. (2015) used Al2O3/distilled water nanofluid at 3.0% volume concentration in a modified flat panel solar thermal collector and achieved an increase in thermal efficiency about 11.7%when compared to water as base fluid. Verma et al. (2016) have studied the impact of mass flow rate and particle volume fraction using MgO/water nanofluid on the efficiency of the collector experimentally and observed an efficiency enhancement of about 9.34% in comparison with water as working fluid, for 0.75% particle volume fraction at 1.5 Lit/min mass flow rate of nanofluid. Michael and Iniyan (2015) investigated the thermal performance of solar water heater using CuO/water nanofluid with 100 liters per day thermosyphon based indirect-type flat plate solar water heater by choosing 0.05%.volumetric fraction. Ham et al. (2016) studied the overall heat transfer coefficient of various nanofluids Al2O3, TiO2, Fe2O3, CuO, CNT, and SiO2, with the limitation of the dispersion stability. Menbari et al. (2016) investigated both analytically and experimentally, the effect of CuO/water nanofluid on the performance of a direct absorption parabolic collector. The results proved that by increasing volume fraction of nanoparticle from 0.002% to 0.008%, the thermal efficiency of the system could be improved from 18% to 52%. As per the literature review, an attractive amount of research has been done over the years in the field of domestic solar water heater technologies with thermosyphon or forced circulation modes. Most of the research works have concluded that the suspension of nanoparticles in the base fluid would enhance the performance of flat plate solar collector in the forced circulation. All the existing works mainly focused on the flat plate solar water heater using different nanofluids by considering volume concentration from 0.05% to 6%. Most of the researchers have concluded that optimum performance enhancement was obtained in the lower particle volume concentration for various reasons. It is seen that, no research was carried out focusing on the performance comparison of experimental and theoretical modeling of solar water heating system with various nanofluids over CeO2/water nanofluid. The objectives of the chapter are given below.

290 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al.   



To compare the performance of solar water heating system using conventional fluids with six different nanofluids. To develop a theoretical model for the solar water heater in order to analyses the theoretical performance. To identify the influences of particle volume concentration and mass flow rate of the all nanofluids employed in solar water heating system based on theoretical performance. To compare the performance enhancement of flat plate solar water heating system with six different nanofluids by using energy, exergy and economic analysis.

2. EXPERIMENTALSETUP AND PROCEDURE The entire experimental setup required for this research work was installed at Solar Energy Research Centre situated in the campus of Coimbatore Institute of Engineering and Technology Coimbatore, India after fabricating in a mechanical workshop. Flat plate collector, absorber plate, storage tank with heat exchanger, nanofluid makeup tank, electrical pump, Rotometer, thermocouples, flow control valve, glazing, insulation and support structure are the main parts of the setup. The schematic diagram of the experimental setup is shown in Figure 1.The front and rear views of the experimental setup are shown in Figure 2. The solar collector is fixed at an inclination angle of 15° to the floor surface face to the south direction. The outer dimensions of the solar collector are 2m long, 1m wide and 0.15m high while the area of the collector is 2m2. To reduce the loss of radiation, a copper sheet of 0.45mm thickness has been used as the absorber plate. A toughened break and scratch resistant transparent glass of 4mm thick is used to cover the collector. The gap between the absorber plate and glass cover is maintained at 0.03m. The bottom portion and sides of the collector are insulated using glass wool with a thickness of 0.05m and 0.025m respectively for achieving minimum heat loss. The solar collector is fabricated with nine number of 0.01m diameter copper tubes in parallel, also called as risers, on the rear side of the absorber

Influence of Various Nanofluids on the Performance …

291

plate which again connected at the top and bottom by headers in order to provide homogeneous flow distribution. The ladder type heat exchanger is fabricated using copper tubes having the surface area of 0.12m2 placed inside the storage tank.

Figure 1. Schematic diagram of the experimental setup.

Figure 2. Front and Rear views of the experimental setup.

The prepared 8.5 liters capacity CeO2/water nanofluids are filled into heat exchanger circuit using a makeup tank before performing the experiments. The storage tank is filled with water and the flow rate of

292 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. working nanofluid is controlled by flow control value. The working fluid exchanges heat with the utility water in the storage tank and the cold working fluid is circulated back to the collector. The heat is exchanged continuously to water so that the water temperature is continuously increased. Once the water reaches the desired temperature of its intended end use, it will be taken out from the storage tank through the outlet pipe.

3. EXPERIMENTAL CALCULATION The energy gain (Qu) has been estimated based on the energy absorbed by the absorber plate and the lost energy from the absorber plate as in equations (1) given below. Qu= 𝑚̇Cp (T0- Ti)

(1)

where 𝒎̇ =mass flow rate of the working fluids Cp =Heat capacity of working fluid To and Ti are the outlet and inlet fluid temperatures respectively. The solar collector thermal efficiency (𝜂) can be get by dividing 𝑄𝑢 by the energy input of the collector (AC.GT) as in equation (2) is given by Stalin et al. (2017). Efficiency =

Qu AcGt

 100

(2)

Where Ac =Area of the collector and GT =Solar Radiation.

4. MATHEMATICAL MODELING The developed theoretical model clearly shows energy balance equations for all the climatic, design and operational parameters which affect

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293

the performance of solar water heater. The theoretical equations have been formed for hourly outlet water liner temperatures as a function of climatic and design parameters. These analytical expressions are based on energy balance equations for each and every component of solar water heater. A computer codes developed in MATLAB have been used to evaluate the hourly performance of the solar water heater. The values with respect to convective heat transfer coefficients used in this model have been derived in each case. The developed model can be used to predict the theoretical values of water outlet temperature as well as inlet and outlet temperature of working fluids at every hour including the comparison of the same with experimental results. The operating performance the solar water heater is determined at any time by using energy and mass balance relationships. The steady state behaviour of the solar water heater is described by the developed model and is provided by the energy balance on the glass cover, absorber plate and bottom plate. The following assumptions have been considered for developing the theoretical analysis.   

 

The system is in a quasi steady-state condition. The level of water in the storage tank is maintained at constant level. The loss of heat capacity due to the insulating material (placed at bottom and side of the collector), the glass cover and the absorbing material is negligible. All the risers in the collector are parallel to each other. The centerlines are lying in the same line of joining the absorber plate and risers as seen in the Figure 3.

294 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al.

Figure 3. Schematic layout of flat plate solar collector.

The thermal network diagram shown in Figure 4 describes the energy balance on each component of solar water heating system.

Figure 4. Thermal network diagram for flat plate collector.

4.1. Energy Balance Equation for the Glass Cover With reference to Figure 10, the heat balance equation for the glass cover is expressed by the equation (3)

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295

 G  h T  T  h T  T   A   h T  T  h T  T   A g T

cpc

p

g

rpc

p

g

c

cca

g

a

rca

g

a

c

(3) Where, αg is the radiation absorptivity of glass cover, hcpc, Convective heat transfer coefficient between plate and cover, Tp, absorber plate temperature, Tg, glass cover temperature, hrpc, radiative heat transfer coefficient between absorber plate and cover, hcca, Convective heat transfer coefficient between cover and air and hrca, radiative heat transfer coefficient between cover and air.

4.2. Energy Balance Equation for the Absorber Plate The energy balance equation for absorber plate is expressed by the following equation (4)

 g  p GT Ac  Qu  hcpc (Tp  Tg )  hrpc (Tp  Tg )  Ub (Tp  Tb )  Ue (Tp  Ta )Ac (4) Where, τg is the radiation transmittance of glass cover, αp, radiation absorptivity of absorber plate, Tb, bottom plate temperature, Ub, bottom heat loss coefficient, and Ue, edges heat loss coefficient of the collector.

4.3. Energy Balance Equation for the Bottom Plate The energy balance equation for the bottom plate is given by the following equation (5)

Ub Tp  Tb  Ac   hba Tb  Ta   Ac

(5)

296 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. Where, Ub is the heat loss coefficient between absorber plate and bottom plate of the collector hba is the convective heat transfer coefficient between bottom plate and ambient air. The equation (5) can be rewritten in the form the equation (6) given under:





Qu   g  p  AcGT  hcpc (Tp  Tg )  hrpc (Tp  Tg )  Ub (Tp  Tb )  U e (Tp  Ta ) Ac (6) By combining the equations (3), (4) and (6) based on overall loss coefficients, the following equation (7) is formed.





Qu  AC S  U t  U b  U e  T p  Ta



(7)

Ut =heat loss coefficient from the top of the glass cover and S= (τα)p GT. In the mathematical model, the performance of the solar collector is evaluated with different nanofluids. For evaluating the theoretical performance of the working nanofluid, the required thermo physical properties based on above theoretical model is described below. The following equations (8) and (9) for calculating the density of working fluids and heat capacity of the working fluids are given by Stalin et al. (2020).

 nf  np  1   bf

C p ,nf 

bf C pf 1      np Cnp , p  nf

(8)

(9)

Where Cp,np =Heat capacity of nanoparticle Cp,nf=Heat capacity of working fluids and Cp.bf = Heat capacity of base fluid. The viscosity of the working fluids is calculated from the following relations

Influence of Various Nanofluids on the Performance … 

 nf  bf 



1

 1

2 .5



297

  

(10)

where µ =viscosity. The subscripts of bf, nf, and np represents base fluid, nanofluid and nanoparticle respectively.

4.4. First Law Analysis The measure of energy (S) strikes on the top of the absorber plate is calculated by the equation S=(τα)pGT where τα is the effective transmittance absorptance product. The following equation (11) shows the link between absorbed heat and heat losses to the surroundings.





Qu  AC S  U L T p  Ta



(11)

Duffie et al. (2006) developed a equation to calculate the overall heat loss coefficient given in the equation (12), all the heat losses of the collector concentrates to a common sink temperature Ta:

U L  Ut  Ub  Ue

(12)

The main heat loss occurs from the top side of the collector. To calculate Ut, the following equation developed by Kalogirou (2013).



1 Ng

Ut  C Tp

 Tp  Ta     N g   

0.33







 Tp 2  Ta 2 Tp  Ta  2N g    1 1   Ng  p  0.05N g 1   p  g 1 hW (13)

298 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. whereNg σ ɛg ɛp

=Number of glass cover = Stefan–Boltzmann constant = Emissivity of the glass cover =Emissivity of the plate,

The parameter of hcca is the convective heat transfer coefficient between glass cover and ambient air and is calculated by the relation.

8.6 VW hcca  L0.4

0.6

(14)

where Vw and L denotes the wind velocity and length of collector respectively. The constants of τ and C are calculated by the following equations, where β is the collector slope

  1  0.04 hcca  0.0005 hcca 2



1  0.091N g 

(15)



(16)

C  365.9 1  0.00883  0.0001298  2

Heat loss coefficient from bottom side can be found using the equation (17) which is expressed below: Ub 

1 tb 1  kb hb , a

(17)

The equation (18) is used for calculating the heat loss coefficient from edges which is given below. Ue 

1 te 1  k e he,a

Ae Ac

(18)

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299

where tb = Insulation thickness in bottom area and, te = Thickness of insulation edge, kb = Thermal conductivity of the insulation in bottom surface, ke = Thermal conductivity of the insulation in edges and Ae = Surface area of the edges, The Tp value is taken up for calculating the UL and Qu. Then the value of Tp is calculated by the equation (19) and corrected by iterative method.

Tp  Tin 

Qu 1  FR  Ac FRU L

(19)

The condition used for the iterative process is expressed by the equation (20).

T 

p aume

 Tp  find

T  p

(20)

 10 5

find

Heat removal coefficient (FR) is developed by Kalogirou (2013) and it is expressed by the following equation (21) .

,   mCp   U L FAc FR  1  exp  . AcU L   mCp   .

    

(21)

The following equation (22) shows the efficiency factor F’ of collector which was developed by Kalogirou (2013)

F' 

1 UL

(22)

 1 1  W   U L D  (W  D ) F  Di h fi 

where Dand Di represents the outer and inner diameter of risers respectively. In the above equation W indicates tube spacing where as F is standard fin efficiency which can be evaluated by the equation (23):

300 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al.

F

tanh mW  D  / 2 mW  D  / 2

Where m=

(23)

Ul in which kc and bt are thermal conductivity and thickness kcbt

of absorber plate respectively. The internal heat transfer coefficient (hfi) for laminar flow conditions, the following equation (24) is used.

h fi 

48k nf

(24)

11Di

Reynolds and Prandtl numbers are given by the equations (25) and (26) respectively which are expressed below: .

4 mr Re  Di  nf Pr 

nf C p , nf knf

(25)

(26)

.

Where ( mr ) mass flow rate of riser. Outlet temperature of working fluids can be found out by the equation (27).

Tout  Tin 

Qu .

mCp

(27)

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301

4.5. Second law Analysis Exergy refers to transformation of accessible energy into useful work or energy thereby denotes the compactness of the thermal system. The major head loss is calculated by Mahian et al.(2014). hl. major = hl,riser 1 = hl,riser 2 = hl,riser 3 = …….. = hl,riser n

(28)

Total head loss (hL) can be expressed in terms of mass flow rate and is given as under. .

hL =hl, major +hl, minor =

8 mr2 2  g 2 Di4

n  Lr   f   K L  D i 1 i  

(29)

where ‘n’ represents the number of risers, KL is loss coefficient and Lr is the length of the riser. The value of KL is taken as 0.5 and 1 at the entrance and exit respectively as per Cengel YA, Cimbala JM (2010). The friction factor (f) is taken as to 64/Re due to which the Laminar flow condition. The pressure drop can be evaluated as under. P1

g

 z1 

P2

g

 z 2  hl

(30)

In the above relation, z2 and z1 is the datum distance between the outlet and inlet of riser, then (z2 - z1) = LrSin  . The pressure drop (ΔP) is calculated base on Mahian et al.(2014) P  P1  P2  g Lr sin   hl 

(31)

302 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al.

Figure 5. Flow chart for MATLAB program.

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303

Second law efficiency of the solar collector is calculated based on the equation (32) is developed by Mahian et al. (2014).

 Exergy

. m C p,nf   

  Tout  Tout Tin Ta ln  T   in   Ta Gt Ac   1 T s 

  P       nf

   

   

(32) Equations for mathematical modeling that have been developed above for analyzing the theoretical performance of solar water heating systems are solved with the help of MATLAB codes and its solving procedure is described in Figure 5.

5. RESULTS AND DISCUSSION The experimental results recorded for the flat plate solar water heater is operated with CeO2/water nanofluid is evaluated experimentally and theoretically based on the above developed model. The comparative results of both the experimental study and theoretical analysis of the solar collector at the mass flow rate of 2 Lit/min for CeO2/water nanofluid have been shown in Figure 6. It is clear from the Figure 6 that there is a good understanding among theoretical and experimental results for CeO2/water nanofluid under consideration. It is also seen that the maximum error percentage was observed to be 2.39%. Hence, it can be concluded that the theoretical model which was developed for the study is well suited for the working fluids under consideration within acceptable limits. Based on the developed theoretical model, the current theoretical work is performed to find out the performance enhancement of flat plate solar water heating systems using six different nanofluids CeO2/water, CuO/water, Al2O3/water, TiO2/water, Graphane/water and SiO2/water including conventional fluids. Further exergy analysis also carried out in

304 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. order to evaluate the theoretical performance of above all nanofluids compared with CeO2/water nanofluid for all the volume concentrations with respect to mass flow rates.

Figure 6. Theoretical and experimental of results of CeO2/water nanofluid.

6.1. Effects of Particle Volume Concentration on Thermal Efficiency Figure7 shows the influences of volume concentration on the thermal efficiency of solar water heating systems with various nanofluids under the constant solar radiation of 1000W/m2 and the inlet temperature of 302K. When the volume concentration of CeO2/water and CuO/water nanofluids is increased up to the volume concentration of 2.75%, the performance of the collector is also increased with the maximum thermal efficiency of 76%. Further increase of volume concentration of both the nanofluids, the thermal efficiency shows the reverse trend due to high density of the both nanofluids leads to the frictional dissipation and agglomeration of nanoparticles. These results in non-uniform temperature distribution within the nanofluid and hence excessive emissive losses occurs in the top layer temperature thereby drop in collector efficiency. In other five remaining nanofluids, when the

Influence of Various Nanofluids on the Performance …

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addition of particle volume concentration has also increased the thermal efficiency of the solar collector due the low density value of nanofluids.

Figure 7. Effects of volume concentration.

6.2. Effects of Reduced Temperature Parameter on Thermal Efficiency The theoretical performance of CeO2/water, CuO/water, Al2O3/water, TiO2/water, Graphane/water, SiO2/water nanofluids and conventional fluids are plotted between thermal efficiency and reduced temperature parameter (Ti–Ta)/GT are shown in Figure 8. Linear trend line equations for the theoretical data for all the nanofluids are fitted with describing characteristic parameters of flat plate solar water heater. It is observed that CeO2/water nanofluids has given maximum efficiency of 76% for the analysis while the thermal efficiency of Graphane/water nanofluid is 73% for the mass flow rate of 0.03kg/sec. It has been evaluated that the solar water heater efficiency of CeO2/water nanofluid with the mass flow rate of 0.03kg/sec is 6.57% higher than that of water for the same mass flow rate. It is predicted from equations that efficiency distribution is almost linear and slopes of the curve increases with a change in the character of the working nanofluid from

306 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. CeO2/water to Graphane/water nanofluids. This is due to solar water heater operated with CeO2/water nanofluid gives maximum performance enhancement even in lower volume concentration. Also because of higher thermal conductivity, lower specific heat and higher density CeO2/water nanofluid which leads to faster heat transfer and subsequently, it helps to increase the outlet temperature of solar collector when compared with other working fluids.

Figure 8. Collector Efficiency versus Reduced Temperature Parameter.

6.3. Effects of Mass Flow Rates on Thermal Efficiency Figure 9 shows the thermal performance of solar water heating systems working with CeO2/water, CuO/water, Al2O3/water, TiO2/water, Graphane/water and SiO2/water nanofluids with respect to various mass flow rates from 0.02 kg/s to 0.14 kg/s estimated with the particle volume concentration of 2.75%.The results shows that when the performance of the solar water heater is increased with increasing mass flow rates for all the nanofluids, the CeO2/water nanofluids shows the maximum thermal efficiency of 81.5% at the mass flow rates of 0.14 kg/s when compared to

Influence of Various Nanofluids on the Performance …

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other nanofluids. The performances of the solar collector using CeO2/water nanofluid is 9.20% higher than that of the water as the working fluids for the similar mass flow rates. It is also observed that all the nanofluids followed the similar pattern when rise the mass flow rates for the laminar flow conditions. This is due to increased mass flow rate of working nanofluids leads to increase the heat capacity and convective heat transfer coefficient nanofluids thereby enhances the thermal performance of the solar water heater at higher mass flow rates.

Figure 9. Thermal Efficiency versus Mass Flow Rates.

6.4. Effects of Solar Radiation on Thermal Efficiency The influence of solar radiation variation on solar water heater thermal performance is shown in Figure 10 with various working nanofluids at constant mass flow rate and particle volume concentration. It is found that solar collectors using CeO2/water nanofluids have shown more efficient than other working fluids, since it has a higher thermal conductivity than remaining nanofluids. All nanofluids have shown proportional rise in thermal efficiency when increasing radiation intensity up to the certain level.

308 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. After that, thermal efficiency remains constant and gets saturated because of proportionate increase in various losses incurred at higher temperature difference between the absorbing plate and the surrounding atmosphere. Solar collector efficiency rapidly increases for all working fluids up to 300 W/m2 of solar radiation. This is because heat transfer between the solar collector and working fluid is relatively low due to less heat flux under less solar radiation. In addition to this, the rate of increase for solar collector efficiency is negligible, beyond about 900 W/m2 of solar radiation. The reason is that the heat transfer performance of a solar collector reaches its limit and achieving a steady level of solar collector efficiency.

Figure 10. Analysis of solar water heater thermal efficiency according to solar radiation.

6.5. Exergy Efficiency Exergy refers to transformation of accessible energy into useful work or exergy thereby denotes the compactness of the thermal system. Figure 11 represents the difference of exergy efficiency with constant particle volume concentrations of 2.75% for various mass flow rates. It also exhibits the relationship between exergy efficiency, mass flow rate and particle volume concentration. It is seen from the Figure 11 that exergy efficiency decreases with increasing the mass flow rate with the constant particle volume

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concentration. Entropy generation increases as the mass flow rate increases, thus exergy efficiency decreases. It is also observed that the maximum exergy efficiency is attained at the lower mass flow rate of 0.01kg/s for 2.75% volume concentration when compared with higher mass flow rates. It is observed that CeO2/water nanofluid has the maximum exergy efficiency of 4. 6% for a mass flow rate of 0.01kg/s whereas Graphane/water nanofluids have attained the lowest exergy efficiency of 4.3% at the similar mass flow rates when compared to the other nanofluids. It is also evaluated that the exergy efficiency of solar water heater with CeO2/water nanofluid is 6.52% greater than that of Graphane/water nanofluid and 15.21% higher than that of water for the similar mass flow rate.

Figure 11. Analysis of exergy efficiency according to mass flow rates.

6.5. Economic Analysis of Solar Collector The main objective of the study is to evaluate how much material and cost can be saved in the design of solar collector with working different nanofluids. The working fluid constitutes an important part of the system in solar collector. To reduce the size of collector’s area, the equation developed

310 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. by Faizal et al.(2013) can be used after estimating the thermal efficiency of the flat plate solar collector. .

AC  m C p To  Ti 

GT 

(33)

Figure 12. Reduction in area of solar collector for different nanofluids.

Figure 12 shows the reduced size of solar water heating systems working with CeO2/water, CuO/water, Al2O3/water, TiO2/water, Graphane/water, SiO2/water nanofluids compared with conventional fluids with respect to the mass flow rates of 0.03 kg/s. The size reduction was designed based on a varaition of efficiencies of solar collector using differntnanofluids. The surface area of the collector acts as the input energy of the system in solar collector which can be modified to provide the same amount of outlet temperature using conventional working fluid. The reduction in collector area directly affects the total weight and embodied energy of the system. It is also observed that the maximum size reduction of 27.86% was attained using CeO2/water nanofluids when compared to water as working fluid at the mass flow rate of 0.03 kg/s. When compared with the water as working fluid, the collector areas of solar collectors using CuO/water, Al2O3/water, TiO2/water, Graphane/water, SiO2/water nanofluids reduced to 25.69%, 18.51%, 17.48%, 11.93% and 10.87%respectively for the same mass flow

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rates. This is due to the fact that the thermal properties of nanofluids are much higher when compared to thermal characteristics of conventional fluid. It was also evaluated that the payback period for the nanofluid based solar water heater is less than the payback period of conventional solar water heater mainly because of reduced size of the solar collector area coupled with the savings of material cost.

CONCLUSION The current experimental analysis concentrates on a comparative study of solar water heating systems with CeO2/water, CuO/water, Al2O3/water, TiO2/water, Graphane/water, SiO2/water nanofluids and conventional fluids. The theoretical work is performed for the mass flow rates of 0.02 and 0.14 kg/s with particle volume concentrations up to 6% and nanoparticle size of 25 nm. The findings of the study can be summarized as follows: 





The performance of the collector is enhanced by increasing the mass flow rate and volume concentration up to certain limit after which it exhibit reverse trend. Optimum mass flow rate and volume concentration depend on the thermal properties of the working fluids. Owing to the improved thermo physical properties of the nanofluid, the maximum thermal performance of solar water heater with CeO2/water nanofluids is 9.20% higher than water as the working fluid while it is 3.24% more than that of Graphane/water nanofluid for the system having the volume concentration of 2.75% and mass flow rate of 0.14 kg/s. It is also observed that CeO2/water and CuO/water performed better at lower particle volume concentration whereas Al2O3/water, TiO2/water, SiO2/water and Graphane/water nanofluids have given good performance at the higher particle volume concentration owing to the density similarity of the nanoparticles.

312 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. 



The CeO2/water nanofluid exergy efficiency is 15.21% higher than that of water as the working fluids and 6.52%% higher efficiency than that of Graphane/water nanofluid at the mass flow rate of 0.01kg/s. It is also observed that the maximum size reduction of 27.86% was attained using CeO2/water nanofluids when compared to water as working fluid at the mass flow rate of 0.03 kg/s.

REFERENCES Cengel, Y.A. and Cimbala,J.M(2010). Fluid Mechanics; Fundamentals and Applications. 2rd ed. NY: McGraw Hill Higher Education, 2010. Choi, S.U.S. (1995).Enhancing thermal conductivity of fluid with nanoparticles. In: Siginer, D.A., Wang, H.P. (Eds.), Developments and Applications of Non-Newtonian Flows, ASME, FED.231/MD.66. New York, 99–103. Colangelo, G., Favale, E., Miglietta, P., de Risi, A., Milanese, M. and Laforgia, D. (2015). Experimental test of an innovative high concentration nanofluid solar Collector. Applied Energy,154, 874–881. Duffie, J.A. and Beckman, W.A. (2006). Solar engineering of thermal processes, 3rd ed., New York, Wiley. Faizal, M., Saidur, R., Mekhilef, S. and Alim, M.A(2013). Energy, economic and environmental analysis of metal oxides nanofluid for flatplate solar collector. Energy Convervation Management, 76,162-168. Gupta, H.K., Agrawal, G.D. and Mathur, J. (2015). Investigations for effect of Al2O3–H2O nanofluid flow rate on the efficiency of direct absorption solar collector. Case Studies in Thermal Engineering,5, 70-78. Gupta, M., Singh, V., Kumar, R. and Said, Z. (2017). A review on thermophysical properties of nanofluids and heat transfer applications. Renewable and Sustainable Energy Reviews, 74, 638-670. Ham, J., Kim, J. and Cho, H. (2016). Theoretical analysis of thermal performance in a plate type liquid heat exchanger using various

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nanofluids based on Libr solution. Applied Thermal Engineering, 108, 1020-1032. Kalogirou, S.A. (2013). Solar energy engineering: processes and systems, 2nd ed. Oxford, Elsevier. Liu, Z.H. and Liao, L. (2008). Sorption and agglutination phenomena of nanofluids on a plain heating surface during pool boiling. International Journal of Heat and Mass Transfer, 51, 2593-2602. Mahian, O., Kianifar, A., Sahin, A.Z. and Wongwises, S. (2014) Performance analysis of a minichannel-based solar collector using different nanofluids. Energy Convervation Management, 88,129–38. Menbari, A., Alemrajabi, A. A. andRezaei, A. (2016). Heat transfer analysis and the effect of CuO/water nanofluid on direct absorption concentrating solar collector. Applied Thermal Engineering,104, 176183. Michael,J.J. andIniyan, S. (2015). Performance of copper oxide/water nanofluid in a flat plate solar water heater under natural and forced circulations. Energy Convervation Management, 95,160–169. Prakasam, M.J.S., Arjunan, T.V. and Nataraj, S. (2017). An experimental study of the mass flow rates effect on flat-plate solar water heater performance using Al2O3/water nanofluid. Thermal Science, 21(suppl. 2),379-388. Singh, A.K. and Raykar, V.S. (2008). Microwave synthesis of silver nanofluids with polyvinylpyrrolidone (PVP) and their transport properties. Colloid and Polymer Science, 286,1667-1673. Sogami, I. and Ise, N. (2005). Structure Formation in Solutions. Ionic Polymers and Colloidal Particles Publishers. Springer, Heidberg: Stalin, P.M.J., Arjunan, T.V., Matheswaran, M.M. Sadanandam, N. (2020). Effects of CeO2/Water Nanofluid on the Efficiency of Flat Plate Solar Collector. Journal of the Chinese Society of Mechanical Engineers, 41(1),75-83. Stalin, P.M.J., Arjunan, T.V., Matheswaran, M.M, Dolli, H. and Sadanandam, N. (2020). Energy, economic and environmental investigation of a flat plate solar collector with CeO2/water nanofluid. Journal of Thermal Analysis and Calorimetry,139(5),3219-3233.

314 P. Michael Joseph Stalin, T. V. Arjunan, M. M. Matheswaran et al. Sujit Kumar Verma, Arun Kumar Tiwari and Durg Singh Chauhan (2016). Performance augmentation in flat plate solar collector using MgO/water nanofluid. Energy Convervation Management,124, 607–617. Tiwari, A.K., Ghosh, P. andSarkar, J. (2013).Performance comparison of the plate heat exchanger using different nanofluids. Experimental Thermal and Fluid Science,49, 141-151. Wen, D. and Ding, Y. (2005). Experimental investigations into pool boiling heat transfer of aqueous based γ-Al2O3nanofluids’, Journal of Nanoparticle Research.7, 265 – 274.

ABOUT THE EDITOR

Khalil Kassmi, born in Casablanca (Morocco) in 1963, made all the higher education in the University Paul Sabatier (UPS) of Toulouse (France) from 1983 until 1991. In 1991, he obtained his PhD degree in Electronics from UPS in France. His different research was realized in the Laboratory of Automatic and Analysis of the Systems LAAS / CNRST (Toulouse) in MOS technology team. In 1992, he was recruited at SGS ThomsonCasablanca (Engineer), where he was responsible of the assembly chain of the powers electronic components (TO220, Thyristors). Then, in 1993, he integrated the Mohammed 1st University in Oujda, Morocco, as Professorresearcher, and he obtained his PhD degree (Doctorat d'état) in Electronics in 1996.

316

About the Editor

Since 2000, he is Professor at the Mohammed 1st University of Oujda. He is responsible of the research team ‘Materials Electronics and Renewable Energies MERE’ of Electromagnetism Signal Processing and Renewable Energies Laboratory LESPRE. He makes researches and manages PhD student thesis on materials and electronic components, cells and photovoltaic systems, solar energy system. He is a coauthor in more than 100 publications and international communications in the field of the photovoltaic renewable energies (materials, cells and photovoltaic systems). Since 2002, in the framework of the opening of the University to its socioeconomic environment: 

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He is responsible for cooperation’s national and international projects in the field of the Solar and Photovoltaic renewable energies (Formation and Research): Paul Sabatier University of Toulouse (France), Solar Institute of Julich, FH Aachen and Engineering Office of Energy and Environmental Technology (IBEU) (Germany), Polytechnic Faculty of Mons (Belgium), University Almanar of Tunis (Tunisia), Asamblea de Cooperación por la Paz ACPP (Spain), Man and Environment Association of Berkane (Morocco). He has Two patents of invention on photovoltaic control and regulation (heating by the photovoltaic energy, Power Regulator with RPSGE Energy Management System for Autonomous Photovoltaic Energy Installations. EXPERT-EVALUATOR at the National Center for Scientific and Technical Research CNRST, October 9, 2019 to October 9, 2023, Rabat, Morocco He a reviewer in Solar Energy, IEEE Eccess, Journal of Energy Storage, Electronics Letters, Journal of Enginnering Science and Technologie (JESTECH), International Journal of Hydrogen Energy. Co-Editor of the book Chapters ‘Sustainable Entrepreneurship, Renewable Energy Based Projects, and Digitalization’, Taylor & Francis Group, LLC, ISBN: 978-0-367-46837-8. To be published in December 2020

INDEX

A adverse effects, 86, 254 air quality, 102, 256 air temperature, 66, 71, 73, 79, 81 algorithm, 209, 210, 213 ambient air, 142, 296, 298 atmosphere, 102, 115, 122, 253, 308 atmospheric pressure, xiii, 5, 22, 31, 107, 267

B batteries, x, 1, 3, 4, 5, 6, 14, 16, 205 benefits, 48, 49, 254 biomass, 53, 173, 244, 251, 252, 253, 256, 258, 259, 260 biosphere, 115 boilers, 107, 204, 259, 269 Brownian motion, 92, 288

C carbon, xi, 51, 82, 88, 108, 109, 132, 228, 251 carbon dioxide, 82 carbon emissions, xi, 51, 108 carbon nanotubes, 88 CeO2, xiv, 134, 286, 289, 291, 303, 304, 305, 306, 307, 309, 310, 311, 312, 313 challenges, 2, 86, 87, 108, 204 chemical, 23, 63, 89, 109, 120, 133, 181, 190, 245, 246, 247, 256 chemical bonds, 246 chemical reactions, 246 chemical stability, 89 circulation, xii, 25, 26, 27, 28, 29, 30, 31, 32, 40, 42, 43, 49, 50, 51, 52, 54, 114, 139, 144, 151, 159, 160, 161, 164, 165, 166, 168, 170, 171, 183, 230, 231, 232, 235, 242, 251, 256, 257, 259, 261, 274, 289 classification, 230, 238 clean energy, 153, 200, 251

318

Index

coal, 48, 87, 115, 251, 260 coatings, 25, 156, 234, 241, 255, 259 commercial, 21, 24, 28, 30, 33, 86, 89, 104, 114, 115, 120, 151, 153, 154, 171, 254, 255 condensation, xiii, 5, 7, 9, 17, 203, 204, 225 conduction, 88, 157, 229, 241 conductivity, 10, 93, 114, 116, 119, 125, 126, 127, 131, 132, 133, 134, 157, 229, 241, 245, 287, 288, 299, 300, 306, 307, 312 configuration, 49, 163, 237, 258 consumption, ix, 32, 107, 135, 142, 148, 153, 228, 229 consumption patterns, 135 control and supervision system, 204 conversion efficiency, 22, 104, 108, 109, 204, 218 cooking, 23, 51, 53, 115, 153, 174, 213, 228, 248, 254, 261 cooling, ix, 63, 87, 124, 147, 180, 234, 244, 248, 256, 272, 276, 283 copper, 52, 157, 160, 168, 172, 229, 268, 290, 313 cost, ix, x, xii, xiii, 2, 21, 23, 25, 30, 34, 44, 45, 46, 47, 48, 49, 53, 56, 63, 89, 101, 102, 103, 104, 105, 106, 116, 154, 157, 160, 168, 169, 170, 171, 172, 173, 174, 204, 205, 206, 233, 244, 245, 254, 255, 261, 267, 309, 311 cycles, 202, 207, 213, 216, 218

D data gathering, 119 database, 207, 211, 214 database management, 211 DC/DC converters, xiii, 203, 204, 208, 209, 214, 216, 218 destruction, 61, 65, 66, 69, 77, 78, 79, 185, 186, 187, 188, 189, 191, 196

displacement, 160, 167, 170 distillation, 86, 105, 153, 174, 204, 205, 206, 212, 220, 221, 222, 224, 225, 226, 228, 248, 249, 260, 282 distillation processes, 225 distilled water, x, xiii, 1, 2, 3, 4, 5, 7, 11, 14, 15, 16, 17, 89, 90, 204, 205, 213, 218, 219, 220, 221, 222, 223, 226, 289 distilled water production, 2, 3 distribution, 39, 56, 70, 92, 196, 291, 304, 305 drinking water, x, 2, 17, 267, 272 drying, 23, 107, 115, 153, 181, 228, 254

E economic development, 228 economic evaluation, 170 economic performance, 18 economics, xi, 53, 86, 173, 261 economies of scale, 48 electricity, ix, xi, xii, 30, 32, 33, 51, 63, 64, 82, 102, 105, 137, 139, 148, 152, 153, 171, 177, 179, 181, 182, 183, 186, 190, 191, 192, 194, 195, 196, 197, 199, 200, 201, 228, 254, 276, 281 electrolysis, 181, 182, 183, 190, 191, 198 emission, 37, 109, 115, 228, 251, 252 encapsulation, 116 endothermic, 246 energy conservation, 133 energy consumption, 3, 228, 251 energy density, 116, 244, 246 energy efficiency, xi, 32, 60, 62, 67, 75, 79, 114, 115, 124, 128, 129, 130, 131, 185, 189, 193, 197, 198, 277 energy input, 292 energy storage, 19, 50, 87, 88, 116, 119, 133, 134, 174, 228, 240, 246, 247, 248, 249, 258, 259, 263, 269, 283, 284, 316 energy supply, 44, 272, 276, 281

Index engineering, x, 19, 21, 50, 51, 61, 82, 83, 86, 137, 178, 224, 248, 257, 258, 260, 287, 312, 313 environment, xi, 64, 66, 68, 70, 117, 147, 163, 192, 224, 228, 241, 272, 316 environmental aspects, 50 environmental degradation, 286 environmental protection, ix equipment, 102, 105, 124, 205, 232 evacuated tube collectors, 3, 25, 29, 83, 202, 238, 282 evaporation, 5, 6, 7, 9, 16, 88, 92, 96, 97, 100, 107, 204, 276 evolution, 143, 144, 147 exergy, v, xi, xii, 18, 32, 49, 55, 59, 60, 61, 63, 64, 65, 66, 69, 70, 71, 72, 73, 77, 78, 79, 81, 82, 83, 132, 178, 179, 182, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 195, 196, 197, 198, 200, 201, 286, 290, 301, 303, 308, 309, 312 exposure, 153, 155

F fabrication, 53, 174, 241, 258, 261 flow rate, x, 2, 12, 14, 15, 17, 22, 30, 34, 40, 42, 56, 60, 65, 67, 138, 140, 180, 187, 190, 221, 229, 243, 249, 257, 266, 270, 273, 278, 281, 286, 288, 290, 291, 292, 300, 301, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313 fluid, xi, xiv, 3, 25, 26, 29, 30, 31, 32, 54, 56, 63, 87, 89, 90, 92, 97, 98, 100, 106, 107, 108, 137, 139, 140, 141, 142, 143, 144, 146, 147, 154, 157, 159, 160, 167, 170, 172, 178, 181, 183, 186, 199, 201, 229, 230, 231, 232, 233, 238, 242, 244, 248, 268, 270, 271, 276, 277, 286, 287, 288, 289, 292, 296, 297, 308, 309, 310, 311, 312 food industry, 268, 283

319 formation, 17, 89, 246, 288 freezing, 29, 30, 114, 231, 232, 233, 248 freshwater, 9, 104, 121 friction, 233, 244, 258, 301 fungus, 178, 179, 183, 189, 196 fusion, 120, 124, 247

G geometry, 154, 155 global climate change, 153 global warming, 62, 108, 153, 228 glycol, 29, 52, 157, 232

H harvesting, 64, 177, 226 health, 253, 256, 260 heat capacity, 101, 116, 125, 127, 138, 246, 293, 296, 307 heat conductivity, 246 heat loss, 6, 9, 22, 25, 30, 43, 100, 115, 168, 174, 175, 178, 238, 278, 290, 295, 296, 297, 298 heat pumps, 32 heat transfer, x, xii, xiii, 5, 8, 10, 19, 22, 25, 26, 29, 32, 35, 54, 55, 56, 92, 100, 109, 116, 125, 127, 131, 132, 137, 138, 139, 141, 142, 143, 157, 166, 167, 172, 227, 228, 230, 231, 234, 241, 242, 244, 258, 259, 260, 265, 266, 268, 269, 270, 275, 284, 286, 288, 289, 293, 295, 296, 298, 300, 306, 307, 308, 312, 313, 314 heating rate, 218 heating temperature, x, 2, 206, 223 heating water, 2, 204 humidity, 229, 266, 274, 275, 276 hybrid, x, 1, 3, 4, 14, 15, 16, 17, 32, 33, 34, 44, 50, 53, 54, 102, 107, 108, 134, 173, 201, 225, 260

320

Index

hydrogen, xii, 63, 177, 181, 182, 183, 190, 191, 192, 198, 199, 200, 201

I illumination, xiii, 17, 97, 99, 203, 207, 209, 213, 216, 217, 218 improvements, 131, 220, 283 industrial sectors, 115 industrialization, 180 industries, 86, 87, 88, 107, 114, 115, 205, 251 insulation, xiii, 92, 107, 228, 229, 233, 236, 238, 255, 286, 290, 299 integrated collector-storage, 257 integration, 114, 116, 132, 276, 283, 284 interface, 92, 99, 207, 210, 211, 213 interfacial layer, 288 irradiation, 9, 12, 92, 97, 99, 101, 107, 108, 119, 122, 140, 144, 162, 163, 166, 171 isobutane, xiii, 178, 182, 183, 193, 194, 196, 197, 198, 199

melting, 86, 114, 120, 123, 124, 125, 131, 247, 248, 258, 267 metal oxides, 287, 288, 312 methodology, 145, 269, 272 MPPT control, 204, 209 MSDH, v, x, 1, 2, 4, 11, 12, 14, 16, 17

N nanofluid, xi, 20, 52, 86, 88, 89, 90, 91, 92, 94, 95, 96, 97, 99, 100, 101, 104, 105, 106, 107, 108, 109, 110, 226, 283, 286, 287, 288, 289, 290, 292, 296, 303, 304, 305, 307, 309, 311, 312, 313, 314 nanoparticles, xi, 88, 89, 91, 92, 93, 94, 95, 99, 104, 106, 110, 114, 117, 119, 120, 121, 125, 126, 127, 131, 134, 135, 268, 287, 288, 289, 304, 311, 312 nanotechnology, xi, 258 NEPCM, vi, xi, 113, 114, 117, 118, 119, 121, 123, 124, 125, 126, 127, 131, 132

O L life cycle, 22, 23, 44, 54, 241, 254 light, 87, 95, 110, 111, 115, 154, 156, 184, 212, 218 light transmittance, 184

M manufacturing, 49, 88, 169, 172, 241 market penetration, x, 22 market potential, x, 21, 22 materials, 19, 49, 56, 104, 114, 116, 132, 133, 135, 138, 148, 157, 227, 229, 236, 242, 244, 245, 246, 247, 248, 255, 262, 283, 286, 316

oil, ix, 151, 158, 160, 164, 166, 167, 171, 205, 246, 254 operating costs, ix, 102 operating data, 211 operating range, 235 operating system, 240 optimization, 138, 149, 171, 205, 223, 244, 284

P parabolic trough, vi, xii, 33, 51, 59, 61, 62, 82, 83, 151, 152, 154, 156, 157, 158, 160, 161, 168, 171, 172, 173, 174, 175, 268

Index payback, xiv, 22, 23, 32, 33, 47, 48, 170, 254, 311 performance, v, vi, vii, x, xi, xii, xiii, xiv, 18, 19, 20, 22, 25, 29, 30, 32, 33, 34, 49, 50, 51, 52, 53, 54, 55, 59, 60, 62, 63, 65, 68, 70, 75, 76, 78, 79, 80, 81, 82, 110, 113, 114, 117, 121, 130, 132, 134, 137, 139, 140, 149, 152, 154, 156, 161, 163, 164, 165, 166, 171, 172, 173, 174, 177, 181, 182, 187, 188, 189, 191, 199, 200, 201, 224, 225, 227, 229, 234, 236, 240, 241, 242, 243, 244, 250, 251, 255, 256, 257, 258, 259, 260, 261, 262, 265, 266, 267, 277, 278, 282, 283, 284, 285, 286, 289, 290, 293, 296, 303, 304, 305, 306, 308, 311, 313, 314 performance indicator, x photovoltaic cells, ix, 87 photovoltaic panels, x, 1, 4, 6, 138, 148, 215 physical properties, 117, 120, 121, 122, 131, 245, 253, 287, 288, 296, 311 pollution, 2, 48, 62, 114, 152, 228, 251, 253, 254, 256 power generation, 23, 60, 63, 87, 114, 151, 228 power plants, ix, 86, 87, 115, 205, 260 preparation, iv, 88, 90, 94, 121, 287 pumps, x, 25, 137, 160, 189, 196, 204, 230, 231 pure water, xiii, 5, 203, 204, 206 PV panels, 3, 14, 204, 205, 206, 207, 213, 214, 215, 218

R radiation, ix, xii, 2, 5, 22, 23, 28, 35, 59, 60, 63, 64, 65, 66, 67, 68, 69, 71, 72, 73, 79, 88, 92, 97, 98, 99, 100, 102, 114, 115, 123, 127, 128, 129, 139, 140, 144, 145, 146, 157, 177, 179, 180, 181, 182, 183, 184, 186, 190, 191, 192, 193, 194, 196,

321 199, 220, 222, 232, 234, 241, 244, 250, 266, 276, 277, 281, 290, 295, 304, 307, 308 reaction temperature, 107 renewable energy, xi, xii, 55, 62, 101, 108, 116, 137, 227, 262 researchers, xi, xiii, 100, 153, 287, 289 resistance, 30, 207, 214, 218, 232 resources, xii, 86, 101, 153, 180, 181, 227, 228 response, xiii, 29, 228, 240, 241, 268, 284

S saline water, xiii, 5, 17, 203, 204, 205, 206, 213, 218, 222, 267, 272, 275 salts, 157, 159, 245, 246, 248, 267 signals, 207, 208, 209, 213, 216, 217, 218 simulation, xiii, 1, 16, 50, 139, 143, 144, 180, 190, 262, 268, 270, 272, 283 SiO2 nanoparticles, xi, 114, 119, 120, 121, 125, 126, 127, 131 software, 25, 60, 64, 160, 178 solar battery, 2 solar collector, v, xii, xiii, 3, 4, 7, 19, 20, 22, 25, 26, 28, 29, 31, 38, 43, 44, 50, 59, 60, 61, 62, 63, 71, 79, 82, 83, 87, 88, 106, 128, 132, 137, 139, 140, 141, 146, 147, 149, 153, 172, 177, 178, 179, 180, 181, 182, 200, 201, 202, 205, 224, 225, 229, 231, 232, 233,234, 237, 239, 241, 256, 258, 260, 269, 270, 277, 278, 282, 283, 284, 286, 288, 289, 290, 292, 294, 296, 303, 305, 306, 307, 309, 310, 312, 313, 314 solar energy, ix, x, xi, xiii, 2, 3, 4, 16, 18, 20, 21, 23, 25, 26, 42, 44, 47, 49, 50, 51, 52, 53, 62, 63, 65, 70, 71, 72, 73, 82, 83, 87, 93, 95, 101, 105, 107, 108, 109, 110, 111, 114, 115, 118, 128, 132, 135, 137, 138, 139, 147, 148, 151, 153, 154, 161,

322 162, 172, 173, 174, 175, 180, 182, 191, 192, 200, 201, 204, 205, 206, 213, 220, 222, 225, 227, 228, 229, 231, 233, 244, 248, 249, 250, 254, 256, 257, 258, 259, 260, 261, 262, 278, 283, 284, 286, 290, 313, 316 solar radiation, vi, 2, 22, 23, 28, 35, 59, 60, 63, 64, 65, 66, 67, 68, 69, 71, 72, 73, 79, 92, 97, 98, 102, 114, 115, 127, 128, 129, 139, 140, 145, 152, 157, 177, 179, 180, 181, 182, 183, 184, 186, 190, 191, 192, 193, 194, 196, 199, 222, 232, 244, 250, 266, 276, 277, 281, 292, 304, 307, 308 solar system, 45, 50, 51, 147, 236, 241, 245, 276, 279 solar thermal and photovoltaic energy, 2, 3, 17 solar thermal energy, 3, 6, 16, 116, 134, 201, 205, 222, 223, 255, 258 solar water heater, vi, vii, x, xi, xiv, 18, 19, 21, 22, 23, 24, 26, 29, 33, 34, 35, 39, 44, 48, 50, 51, 52, 53, 54, 55, 113, 114, 115, 117, 118, 121, 122, 123, 127, 128, 129, 130, 131, 132, 133, 134, 135, 139, 151, 154, 168, 172, 173, 200, 227, 229, 230, 232, 239, 240, 241, 248, 255, 256, 257, 258, 259, 261, 262, 265, 267, 273, 279, 281, 284, 285, 286, 289, 290, 293, 303, 305, 306, 307, 308, 309, 311, 313 solar water heating, v, vi, x, xii, xiii, 2, 3, 18, 19, 20, 21, 22, 23, 25, 29, 43, 48, 49, 50, 51, 54, 55, 85, 131, 135, 137, 138, 140, 142, 147, 151, 153, 158, 161, 170, 171, 231, 236, 254, 257, 260, 261, 262, 265, 268, 286, 289, 290, 294, 303, 304, 306, 310, 311 solid phase, 124 solid waste, 48, 251 solution, 29, 89, 90, 95, 102, 108, 148, 248, 262, 267, 272, 313 specific heat, 22, 60, 67, 109, 123, 124, 152, 178, 241, 245, 248, 266, 288, 306

Index stability, 87, 90, 94, 95, 96, 241, 287, 288, 289 stratification, 30, 142, 266, 269, 281 structure, 1, 26, 124, 206, 222, 253, 290 supervision, xiii, 170, 203, 204, 206, 207, 210, 211, 223 surface area, xi, 4, 60, 69, 74, 75, 116, 152, 157, 178, 267, 270, 291, 310 surface layer, 62 surface tension, 89 surface treatment, 241 surfactant, 88, 89, 90, 94, 96, 108, 287 sustainable development, 86, 226, 258

T tanks, 25, 137, 139, 233, 256, 268, 282 techniques, x, xiii, 2, 3, 151, 204, 205, 220, 228, 229, 234, 241, 255 testing, 18, 53, 82, 152, 172, 173, 225, 260 textbook, 260 Thailand, 39 thermal efficiency, xii, xiii, xiv, 30, 63, 139, 144, 152, 161, 166, 167, 168, 171, 204, 218, 227, 265, 267, 276, 278, 288, 289, 292, 304, 305, 306, 307, 308, 310 thermal energy, xi, 3, 16, 23, 53, 62, 63, 64, 66, 71, 81, 114, 116, 133, 135, 157, 167, 172, 174, 180, 181, 182, 184, 185, 186, 187, 191, 193, 194, 197, 198, 199, 202, 227, 244, 247, 248, 257, 261, 262, 267, 276, 278, 279, 282 thermal energy storage, v, 23, 53, 59, 114, 116, 133, 134, 135, 157, 167, 172, 174, 202, 227, 244, 245, 248, 255, 257, 260, 261, 262, 263, 267, 282 thermal expansion, 31 thermal performance, vi, x, xiii, xiv, 34, 53, 62, 83, 88, 132, 135, 140, 142, 148, 151, 152, 162, 171, 174, 180, 224, 225, 227, 228, 229, 236, 241, 242, 244, 255, 257,

Index 258, 259, 261, 262, 263, 289, 306, 307, 311, 312 thermal properties, 121, 125, 127, 133, 134, 135, 245, 287, 311 thermal resistance, 122, 204, 205, 206, 207, 214, 216, 218, 220, 222 thermal stability, 247, 248 thermodynamics, 6, 69, 75, 79, 182, 186, 188 traditional practices, 102 transfer performance, 286, 308 transformation, 142, 301, 308 transmissivity, 22 transport, 92, 114, 214, 313 treatment, 20, 62, 107, 209, 287

V vacuum, xiii, 25, 82, 174, 200, 268, 282 valve, 30, 31, 106, 277, 290 vapor, 87, 92, 94, 95, 97, 99, 100, 105, 108, 110, 186, 203, 204

323 variations, 137, 161, 162, 241, 260, 269 velocity, 56, 161, 229, 266, 274, 298 viscosity, 287, 288, 296, 297

W water heater, x, xi, xiii, xiv, 19, 21, 22, 23, 24, 26, 27, 29, 30, 32, 33, 34, 38, 43, 48, 49, 50, 51, 52, 53, 54, 55, 114, 115, 117, 118, 121, 122, 123, 127, 128, 129, 130, 131, 132, 133, 134, 135, 139, 152, 154, 168, 172, 173, 200, 227, 228, 229, 239, 240, 241, 249, 250, 254, 255, 256, 257, 258, 259, 260, 261, 262, 265, 267, 273, 279, 281, 284, 286, 289, 290, 293, 303, 305, 306, 307, 308, 309, 311, 313 water purification, 86, 265 water vapor, xiii, 9, 12 wood, 48, 251, 259, 260 wool, 92, 158, 169, 290 working conditions, 269