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
vii
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
viii
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
