89833718 Solar Pond Report

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<p>PERFORMANCE STUDY OF A SOLAR POND USING SELECTIVE COATING</p> <p>PREPARED BY Muhammad Ashraful Kabir Roll No. 0405023</p> <p>DEPARTMENT OF MECHANICAL ENGINEERING KHULNA UNIVERSITY OF ENGINEERING &amp; TECHNOLOGY March, 2009</p> <p>PERFORMANCE STUDY OF A SOLAR POND USING SELECTIVE COATING</p> <p>A project report submitted to the Department of Mechanical Engineering of Khulna University of Engineering &amp; Technology, in partial fulfillment of the requirements for the degree of Bachelor of Science in Mechanical Engineering.</p> <p>Supervisor: Dr. A.N.M. Mizanur Rahman Professor Department of Mechanical Engineering KUET.</p> <p>Submitted By: Muhammad Ashraful Kabir Roll No. 0405023</p> <p>DEPARTMENT OF MECHANICAL ENGINEERING KHULNA UNIVERSITY OF ENGINEERING &amp; TECHNOLOGY March, 2009</p> <p>ACKNOWLEDGEMENT</p> <p>First of all, thanks to Almighty Allah for his immense blessing and mercy and also for enabling me to complete this project work. I am grateful to my supervisor Professor Dr. A.N.M. Mizanur Rahman, Department of Mechanical Engineering, Khulna University of Engineering &amp; Technology, for his close guidance, valuable suggestions and kind cooperation towards completing this project work successfully and preparing this report. I am also grateful to Professor Dr. Tarapada Bhowmick, Head, Department of Mechanical Engineering, Khulna University of Engineering &amp; Technology, for his kind permission to use the workshop and laboratory facilities of Mechanical Engineering Department. Thanks are extended to the Vice-Chancellor, Khulna University of Engineering &amp; Technology for providing the financial assistance to my project. Special thanks to the staffs of Chemistry Lab, for their co-operation for testing the density of saline water. Gratitude is extended to the Engineering Section for their support during the project work. Finally, I would to like to offer heartiest thanks to the staffs of Heat Engine Lab and Wood Shop for their co-operation towards the completion of this work.</p> <p>Muhammad Ashraful Kabir</p> <p>ABSTRACT</p> <p>Solar pond is an articially constructed pond in which signicant temperature rise occurs in the lower region by preventing convection. To prevent convection, salt water is used in the pond. Those ponds are called salt gradient solar pond. In the last 15 years, many salt gradient solar ponds varying in size from a few hundred to a few thousand square meters of surface area have been built in a number of countries. Nowa-days, mini solar ponds are also being constructed for various thermal applications. In this project work, a solar pond system was constructed with better insulation, transparent cover on the upper surface and improved absorber coating. The temperatures within the pond was measured at various levels and compared with other works.</p> <p>In this work, performance of the solar pond was observed with varying salinity. It is seen that maximum temperature developed in the storage zone increases with increasing salinity. The pond also works as storage. Because with varying solar intensity temperature developed in the storage zone reaches to maximum at the end of the day. Thus, the solar pond also works with diffuse radiation.</p> <p>The present system shows better output than the previous work. Maximum temperature developed in the storage zone is higher than that developed in the previous work. This shows better heat transfer characteristics of the system.</p> <p>LIST OF FIGURES</p> <p>Figure No. 2.1</p> <p>Caption Schematic Diagram of a typical Salt Gradient Solar Pond</p> <p>Page No.</p> <p>5 6 6 6 14 17</p> <p>2.2 2.3 2.4 2.5 3.1 5.1</p> <p>Schematic Diagram of the UCZ Layer Schematic Diagram of the NCZ Layer Schematic Diagram of the LCZ Layer Effect of Shading Area Experimental Setup of the Solar Pond System Effect of Varying Salinity in the Pond on Lower Convective Zone Temperature</p> <p>27 28</p> <p>5.2 5.3</p> <p>Variation of Solar Radiation Intensity with Time of Day Variation of Temperature with Time at Lower Convective Zone</p> <p>28</p> <p>5.4</p> <p>Variation of Temperature with Time at Upper Convective Zone 29</p> <p>LIST OF TABLES</p> <p>Table No. 4.1</p> <p>Title Temperature Distribution at Various Levels after Mixing 70 kg Salt</p> <p>Page No.</p> <p>21</p> <p>4.2</p> <p>Temperature Distribution at Various Levels after Mixing 80 kg Salt 23</p> <p>4.3</p> <p>Temperature Distribution at Various Levels after Mixing 90 kg Salt 25 26</p> <p>4.4</p> <p>Density of Water after Mixing Salt</p> <p>CONTENTSPage No.</p> <p>CHAPTER I</p> <p>INTRODUCTION 1.1 Overview 1.2 Objectives</p> <p>1-2 1 2 3-15 3 4 5 7 7 8 8 9 9 9 10 10 10</p> <p>CHAPTER II</p> <p>LITERATURE REVIEW 2.1 Solar Energy 2.2 Solar Pond 2.3 Working Principle of Solar Pond 2.4 Types of Solar Ponds 2.4.1 Nonconvecting Pond 2.4.2 Convecting Pond 2.5 Application of Solar Pond 2.5.1 Greenhouse Heating 2.5.2 Process Heat in Dairy Industries 2.5.3 Desalination 2.5.4 Power Production 2.5.5 Hot Water Applications in Agriculture 2.5.6 Economics of Solar Ponds for Heating</p> <p>2.5.7 Industries with Potential Applications for Solar Ponds 11</p> <p>2.6 Advantages and Disadvantages of Solar Pond 2.7 Theoretical Analysis of the LCZ Temperature 2.8 Factors Affecting Pond Performance 2.8.1. Water Turbidity and Bottom Reflectivity 2.8.2 Wall Shading Effect 2.8.3 Effect of Energy Extraction</p> <p>12 12 13 14 14 15</p> <p>CHAPTER III</p> <p>DESIGN CONSIDERATION AND ANALYSIS 3.1 Transparent Cover Design 3.1.1 Size of Cover Frame 3.2 Selection of Materials 3.2.1 Glazing Materials 3.2.2 Absorber Surface Coating 3.2.3 Insulating Material</p> <p>16-19 16 16 17 17 18 18</p> <p>CHAPTER IV</p> <p>CONSTRUCTION AND EXPERIMENTAL PROCEDURE 4.1 Construction of Solar Pond 4.2 Method of Making Salinity Gradient 4.3 Maintenance and Working Procedure 4.4 Experimental Data 20-26 20 20 20 21</p> <p>CHAPTER V</p> <p>RESULT AND DISCUSSION 5.1 Result of the Work 5.2 Discussion ` 5.3 Conclusion</p> <p>27-30 27 29 30 31</p> <p>REFERENCES</p> <p>CHAPTER I INTRODUCTION1.1 Overview: As technology develops, the energy needs of communities increases. This energy need is provided from different energy sources known as traditional energy sources, such as coal, fuel oils, geothermal energy, hydraulic energy, and nuclear energy. These energy sources have some disadvantages. The first three of these energy sources have limited life time. Hydraulic energy is an insufficient energy source and nuclear energy has some unsolved environmental and safety problems. Therefore, the researchers have condensed their studies on new alternative energy sources known as renewable energy sources [1]. Solar energy is a form of renewable energy sources. Solar Energy is the radiation produced by nuclear fusion reactions deep in the Suns core. The Sun provides almost all the heat and light which earth receives and therefore sustains every living being. People can make indirect use of solar energy that has been naturally collected. Earth's atmosphere, oceans, and plant life, for example, collect solar energy that people later extract to power technology. Now-a-days, salinity-gradient solar technology is a useful form of utilizing solar energy. It is a generic name given to the application of a salinity gradient in a body of water for the purpose of collecting and storing solar energy. One type of salinity-gradient technology is called the salinity-gradient solar pond. A solar pond is a shallow body of saline water several meters deep, set up in such a way that there is increasing salinity with depth. Solar radiation entering the pond is stored as heat in the lower layer. This heat (up to 80C) is then available on a 24 hour basis [2]. Solar pond is used for various thermal applications like green house heating, process heat in dairy industries, desalination and power production. The solar pond provides a unique opportunity to do research in such areas as double diffusive convection, wind/wave interaction, flow in stratified fluids, and computer modeling. In addition, the state of the art equipment on site provides an excellent opportunity for energy efficiency studies, cost analysis, system studies, heat exchanger [3].</p> <p>Some years back an undergraduate project work was done on solar pond system which was constructed by using ferrocement and tested. But it had some limitations such as inadequate insulation of the side walls, no attempt to prevent convection and radiation heat loss to air from upper surface, absorber surface coating having limited life etc. The main objective of the present work is to improve the solar pond performance by removing above limitations and comparing it with the previous one. For this some steps were taken considering the various factors affecting solar pond performance such as water turbidity, bottom reflectivity, heat insulation etc. In order to increase the thermal capacity of absorber surface special type coating was applied which was supposed to have more durability than the coating used in previous work. Two types of coatings are available in market: Epoxy coating and Synthetic Enamel paint (matt finish). The first one is better but costs too high. The later is a type of cement paint with superior adhesion qualities. It is available in two types of finishes glossy and matt and can stick to all primers [4]. To prevent water turbidity and convection and radiation heat loss to air from upper surface, transparent cover over the pond surface was used to improve pond efficiency.</p> <p>1.2 Objectives: 1. To identify the limitations and problems of the solar pond constructed earlier. 2. To modify the solar pond system thus avoiding previous limitations. 3. To monitor the performance of the solar pond.</p> <p>CHAPTER II LITERATURE REVIEW2.1 Solar Energy: Solar energy is the utilization of the radiant energy from the Sun. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for over 99.9% of the available flow of renewable energy on the Earth. The flows and stores of solar energy in the environment are vast in comparison to current human energy needs. The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850 Zettajoules (1021J) per year, while global wind energy within 80 m height, the minimum height of modern large wind turbines, is estimated as 2.25 ZJ per year. Photosynthesis captures approximately 3 ZJ per year in biomass. In contrast, worldwide electricity consumption was approximately 0.0567 ZJ in 2005, and total worldwide primary energy consumption was 0.487 ZJ in the same year [5]. Solar energy has been used since prehistoric times, but in a most primitive manner. Before 1970, some research and development was carried out in a few countries to exploit solar energy more efficiently, but most of this work remained mainly for academic purposes [5]. Solar power is often used interchangeably with solar energy but refers more specifically to the conversion of sunlight into electricity, either by photovoltaics and concentrating solar thermal devices, or by one of several experimental technologies such as thermoelectric converters, solar chimneys and solar ponds. Solar energy and shading are important considerations in building design. Thermal mass is used to conserve the heat that sunshine delivers to all buildings. Day lighting techniques optimize the use of light in buildings. Solar water heaters heat swimming pools and provide domestic hot water. In agriculture, greenhouses expand growing seasons and pumps powered by solar cells (also known as photovoltaics) provide water for grazing animals. Evaporation ponds are used to harvest salt and clean waste streams of contaminants. Solar energy is the fastest growing form of energy production. Solar distillation and disinfection techniques produce potable water for millions of people worldwide. Family-scale solar cookers and larger solar kitchens concentrate sunlight for cooking, drying and pasteurization. Clothes lines are a common</p> <p>application of solar energy. More sophisticated concentrating technologies magnify the rays of the Sun for high-temperature material testing, metal smelting and industrial chemical production. A range of prototype solar vehicles provide ground, air and sea transportation. Solar energy technologies use solar radiation for practical ends. Solar technologies such as photovoltaic and water or air heaters increase the supply of energy and may be characterized as supply side technologies. Technologies such as passive design and shading devices reduce the need for alternate resources and may be characterized as demand side. Optimizing the performance of solar technologies is often a matter of controlling the resource rather than simply maximizing its collection. A solar pond is large-scale solar energy collector with integral heat storage for supplying thermal energy. It is simply a pool of water which collects and stores solar energy. It contains layers of salt solutions with increasing concentration (and therefore density) to a certain depth, below which the solution has a uniform high salt concentration. 2.2 Solar Pond: A salinity gradient solar pond is an integral collection and storage device of solar energy. By virtue of having built-in thermal energy storage, it can be used irrespective of time and season. In an ordinary pond or lake, when the sun's rays heat up the water this heated water, being lighter, rises to the surface and loses its heat to the atmosphere. The net result is that the pond water remains at nearly atmospheric temperature. The solar pond technology inhibits these phenomena by dissolving salt into the bottom layer of this pond, making it too heavy to rise to the surface, even when hot. The salt concentration increases with depth, thereby forming a salinity gradient. The sunlight which reaches the bottom of the pond remains entrapped there. The useful thermal energy is then withdrawn from the solar pond in the form of hot brine. The heat trapped in the salty bottom layer can be used for many different purposes, such as heating of buildings or industrial hot water or to drive a turbine by using special working substance for generating electricity. The pre-requisites for establishing solar ponds are: a large tract of land (it could be barren), a lot of sun shine, and cheaply available salt (such as Sodium Chloride).</p> <p>2.3 Working Principle: Most people know that fluids such as water and air rise up when heated. The salinity gradient stops this process when large quantities of salt are dissolved in the hot bottom layer of the body of water, making it too dense to raise to the surface and cool [6].</p> <p>Fig. 2.1: Schematic Diagram of a typical Salt Gradient Solar Pond A typical salinity-gradient solar pond has three regions. The top region is called the surface zone, or upper convective zone (UCZ). The middle region is called the main gradient zone (MGZ), or nonconvective zone (NCZ). The lower region is called the storage zone, or lower convective zone (LCZ). The lower zone is a homogeneous, concentrated salt solution that can be either convecting or temperature stratified. Above it the NCZ constitutes a...</p>


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