The Design and Development of a Solar Powered Refrigerator

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The Design and Development of a Solar Powered Refrigerator

R.H.B. Exell, Sommai Kornsakoo, D.G.D.C Wijeratna. Bangkok, Thailand: Asian Institute of Technology, 1976.

Preface

This research report describes work on the development of a solar powered refrigeration system which will eventually lead to the production of a village size ice maker or to a cold storage unit for food preservation.

This subject was examined by Mr. D.G.D.C. Wijeratna in his Individual Studies Project Report (No. 34), and the experimental unit was designed by Dr. R.H.B. Exell. The construction and testing of the unit was by Mr. Sommai Kornsakoo for his Master Degree Thesis.

The Asian Institute of Technology (AIT) is indebted to the John F. Kennedy Foundation, Thailand, for financial support in the form of a grant for solar energy research made in response to a proposal made in 1973 by Professor H.E. Hoelscher, President of AIT, to Dr. Tbanat Khoman, Chairman of the Foundation.

Summary

A small ammonia-water intermittent absorption refrigerator with a 1.44 m² flat plate solar collector has been tested as a first step towards the development of a village ice maker. No oil or electricity is used. Regeneration takes place during the day and refrigeration at night. Rapid absorption is obtained by means of a new feature, first proposed by Swartman, in which the heat of absorption is dissipated from the flat plate.

In the generator 15 kg of solution containing 46% ammonia in water are used. On a clear day the solution temperature rises from 30^oC, to 88^oC and 0.9 kg of pure ammonia is condensed at 32^oC. During refrigeration the temperature of the ammonia drops to -7^oC. The estimated overall solar coefficient of performance (cooling effect divided by solar heat absorbed) is 0.09, which though small is comparable with previously published work. Developments in the design are discussed.

Contents

I INTRODUCTION

• The Basis for Considering Solar Energy

There are several important reasons for considering solar energy as an energy resource to meet the needs of developing countries. First, most the countries called developing are in or adjacent to the tropics and have good solar radiation available. Secondly, energy is a critical need of these countries but they do not have widely distributed, readily available supplies of conventional energy resources. Thirdly, most of the developing countries are characterised by arid climates, dispersed and inaccessible populations and a lack of investment capital and are thus faced with practically insuperable obstacles to the provision of energy by conventional means, for example, by electrification. In contrast to this solar energy is readily available and is already distributed to the potential users. Fourthly, because of the diffuse nature of solar energy the developments all over the world have been in smaller units which fits well into the pattern of rural economics.

• Objectives of the Study

• Possibilities for Research and Development

• The Rationale for Selecting Solar Refrigeration

II SOLAR REFRIGERATION

• Indices of Performance
• Operation of the Intermittent Ammonia-Water System
• Analysis of the Ideal Cycle
• Rigorous Analysis of the Ammonia-Water Cycle
• Historical Development

Page 21 by Simon:

${\displaystyle Q_{c}=W'_{6}L_{m}}$

where

${\displaystyle L_{m}}$ = mean latent heat of the refrigerant during the process 6-1.

${\displaystyle W'_{6}}$ = weight on the refrigerant at point 6.

The heat supplied during the regeneration process 1-3-4 is given by

${\displaystyle Q_{g}=W_{4}H_{4}-W_{1}H_{1}+\int _{W_{4}}^{W_{1}}H_{v}\mathrm {d} W,}$

where

${\displaystyle w}$ = weight of the solution, suffix indicating the point of the cycle,

${\displaystyle H}$ = specific enthalpy of the solution, suffix indicating the point of the cycle,

${\displaystyle H_{v}}$ = specific enthalpy of the vapor boiling out of the liquid,

${\displaystyle \mathrm {d} W}$ = differential mass of the vapor boiling out of the liquid.

Thus the expression for the C.O.P. becomes

${\displaystyle {\frac {W'_{6}L_{m}}{W_{4}H_{4}-W_{1}H_{1}+\int _{W_{4}}^{W_{1}}H_{v}\mathrm {d} W}}}$

III DESIGN OF THE EXPERIMENTAL UNIT

• Choice of Configuration
• Operation of the System
• Concentration of Aqua-Ammonia
• Regeneration Phase of the Cycle
• Refrigeration Phase of the Cycle
• Collector-Generator Specifications
• The Volume of the Generator
• The Size of the Receiver for Ammonia
• Heat of Generation
• Heat of Condensation
• Further Details of the Design

IV EXPERIMENTAL TESTS

• Relationship between Plate Temperature and Solution
• Temperature
• Experimental Results
• Amount of Ammonia Distilled
• Cooling Ratio
• Heat Absorbed by Solution During Regeneration
• Solar Coefficient of Performance
• Discussion

V CONCLUSIONS AND PLANS FOR CONTINUING RESEARCH

• Conclusions
• Economic Considerations
• Modifications
• The Development of a Village Ice-Maker
• Alternatives

References

Appendix A

• Charging - Equipment - Procedure

Appendix B

• Estimation of Incident Solar Radiation