ABSTRACT

This work investigated the variation of top loss heat transfer coefficient with the emittance of the absorber plate, the collector tilt angle and air gap spacing between the absorber plate and the cover plate. The effects of the emittance of the absorber plate, the collector tilt angle and air gap spacing between the plate and the cover on the collector performance were also considered. Data collected from the thermosyphon solar water heater constructed by the National Centre for Energy Research and Development (NCERD), UNN was used in the analysis. Evaluations of thermal losses by radiative and convective heat transfer coefficient were performed. It was observed that increase in the emittance of the absorber plate resulted in dissipation of more heat to the atmosphere and consequent increase in top loss heat transfer coefficient which led to reduced system performance. The collector tilt angle had little effect on the top loss heat transfer coefficient and consequently had insignificant effect on the performance of the collector. Increase in the air gap spacing between the absorber plate and the cover plate resulted in decrease in the top loss heat transfer coefficient. It was also observed that passive flatplate solar collector had a better performance at a low mean absorber plate temperature. In addition, a correlation that relates the efficiency of the collector with the absorber plate emittance, collector tilt angle and the air gap spacing between the absorber plate and the cover plate was developed for the NCERD thermosyphon water heater. 

TABLE OF CONTENTS

Title Page i

Approval ii

Dedication iii

Acknowledgement iv

Abstract v

Table of content vi

List of Table ix

List of Figure x

Nomenclature xi

CHAPTER ONE

INTRODUCTION

1.1 Need for Solar Energy 1

1.2 The Structure of the Sun 1

1.3 The Energy of the Sum 2

1.4 Solar Energy Utilization 3

1.4.1 Photochemcial Processes 3

1.4.2 Photovoltaic Processes 3

1.4.3 Photothermal Processes 4

1.5 Need for Solar Plate Collector 4

1.6 Solution Method 4

1.7 The Objective of the Thesis 5

CHAPTER TWO

LITERATURE REVIEW

2.1 Flat Plate Collector 6

2.2 Consideration of Some Flat Plate Collector Models 6

2.3 Conclusion 12

CHAPTER THREE

THEORETICAL CONSIDERATION

3.1 The Solar Constant 13

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3.2 Electromagnetic Spectrum 14

3.3 Thermal Radiation 14

3.4 Solar Radiation at Earth’s Surface 14

3.5 Radiation Heat Transfer for Solar Energy Utilization 15

3.6 General Description of Flat-Plate Collector 16

3.7 The Principle of Flat-Plate Collectors 17

3.8 Energy Absorbed by the Flat-Plate Collector 18

3.9 Thermal Losses in Flat-Plate Collector 18

3.10 Radiation Transmission through Covers 19

3.11 Collector Overall Heat Transfer Coefficient 20

3.12 Evaluation of Top-loss Coefficient 22

3.13 Thermal Losses and Efficiency of Flat-Plate Collector 23

3.14 Heat Transfer Analysis of the Solar Collector 24

3.15 Collector Efficiency Factor 25

3.16 Temperature Distribution in Flow Direction 26

3.17 Collector Heat Removal Factor 27

3.18 Collector Efficiency 27

3.19 Multiple Linear Regressions 29

3.20 LU Decomposition 30

CHAPTER FOUR

ANALYSIS OF RESULTS AND DISCUSSION

4.1 Source of Data 31

4.2 Determination of Heat Transfer Coefficients 33

4.3 Determination of Cover Plate Temperature, Tg 34

4.4 Determination of the Mean Plate Temperature, T 35

4.5 Determination of the Collector Efficiency,  36

4.6 Evaluation of Parameters for Day 1 to Day 5 36

4.7 Summary of the computed results 37

4.8 Variation of top loss coefficient and efficiency

with plate emittance 43

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4.9 Variation of top loss coefficient and

efficiency with collector tilt angle 46

4.10 Variation of top loss coefficient and efficiency with air gap

spacing between the absorber plate and the cover plate 48

4.11 Correlation of the collector efficiency with the absorber

plate emittance, collector tilt angle and the air gap spacing 49

4.12 Coefficient of Determination 51

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION 53

REFERENCES 54

Appendix I Computed Values for the Parameters 57

Appendix I1: Visual Basic Solution Source Codes 122

Appendix III: Some Important parameters of the

Solar Plate Collector 137

Appendix IV: Some Important Physical Constant 138

Appendix V: Metallic Properties for Absorber Plates 139

Appendix VI: Thermal insulating Properties for Solar

Collectors 140

Appendix VII: Thermal and Optical Properties of

Cover Plate Material 141

Appendix VIII: Variation of Some Properties of

Air with Temperature at atmospheric

Pressure 142

Appendix IX: Latitude and Longitude of some

Cities in Nigeria 143