The Design and Development of a Solar Powered Refrigerator: Difference between revisions

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Note for everyone in Group 17. When you upload the figures, please name them in the format of "G17fig.2.6 . jpg" Since everyone is going to upload figures in a common file, so it may be mixed up with the others. If you are wondering how to type math equation in HTML (this), you can take a look by my part below. I went to Wiki, found a page with a lot of formulas and learn from their script. Simon

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

Page 20 goes here Graham.

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

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

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

Historical Development

According to the Survey of Solar-Powered Refrigeration carried out by SWARTMAN, HA, and NEWTON ( 1972), the first study undertaken to explore the use of solar energy for refrigeration was probably in 1936 at the University of Florida by Green. The steam to power a steam jet refrigerator was produced by heating water flowing in a pipe placed at the focal line of a cylindro-parabolic reflector.

Oniga reported in 1937 that researchers in Brazil tried to adapt a parabolic reflector to an absorption refrigerator but the system never got beyond the experimental stage.

Kirpichev and Baum of Russia reported the successful operation of an assembly of solar refrigerators producing 250 kilograms of ice per day in 1954. The refrigerators were of the conventional vapor-compression type driven by a heat engine operating on the steam produced by a boiler placed at the focus of a large mirror. However, it has been generally conceded that the low efficiency of solar energy in a producing power, the very high cost of the equipment, and the complexity of this type of system, are unfavorable factors in the future development. Since this system was built, there has been little interest shown in this direction of the solar refrigeration.

The first major project on an all solar absorption refrigeration system was undertaken by TROMBE and FOEX (1964). Fig. 2.5 shows the general set-up of the system, which was these main features: ammonia-water solution is allowed to flow from a cold reservoir through a pipe placed at the focal line of a cylindro-parabolic reflector. Heated ammonia-water vaporized in the boiler is subsequently condensed in a cooling coil. The evaporator is a coil surrounding the container used as an ice box. The cylindro-parabolic reflector measured 1.5 ${\displaystyle m^{2}}$. In the prototype trials, the daily production of ice was about 6 kilograms or about 4 kilograms of ice per square meter of collecting area for four-four heating.

The design by Trombe and Foex is very promising and should be studied further although modifications may be necessary on the solar collector, boiler and condenser.

Williams and others at the University of Wasconsin built a small food cooler in 1957 intended for use in underdeveloped rural areas. The apparatus consisted of two vessels links together by a pipe as shown in Fig. 2.6. The energy was provided by a parabolic mirror of moulded 1.27 mm polystyrene with an aluminized mylar polyester film and stiffened at the rim by metal tubing. Ammonia-water and R-21-glycol ether were used as working solutions. This study showed that refrigeration can be achieved by the use of intermittent absorption refrigeration cycles. Although performance is limited by the characteristics of the intermittent cycle, the simplicity of the system accounts for the low temperature obtained in the evaporator. Finally, the study showed that ammonia-water has a superior performance over R-21-glycol ether in an intermittent refrigeration system.

• 

  Fig. 2.6 - The Basic Solar-Powered Intermittent Absorption Refrigerator.

• 

  Fig. 2.7 - Schematic Diagram of Solar Refrigerator Operated with Flat-Plate Collector by CHINNAPPA(1962)

CHINNAPPA (1962) built a simple intermittent refrigerator operated with a flat-plate collector at Columbo, Ceylon as shown in Fig. 2.7, The generator-absorber in this refrigerator was of welded pipe construction and incorporated with a flat-plate collector and a water cooled absorber. The solar collector was a copper sheet measuring 152.4 cm by 106.7 cm, 0.76 mm thick, and painted black. The plate was sodded to six 6.35 cm diameter steel pipes and the pipes were welded to headers. There were three glass covers on the collector which were supported by strips of cork board. An ammonia-water solution was used as working fluid.

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