A Solar Powered Aqua-ammonia Absorption Refrigerator

Abstract

An experimental intermittent solar refrigerator using ammonia-water as the refrigerant-absorbent combination and powered by two flat-plate collectors has been designed, fabricated and tested under outdoor conditions in Nairobi, Kenya. The research was conducted in order to study the performance of the system in the Kenyan climate and to determine the prospects of the system in the climatic region. It was also carried out with a view of investigating how variations in the initial solution mass, the initial ammonia concentration in the solution and the final generator temperature affect the system performance. The generator-absorber consisted of two copper flat-plate collectors, each having eight 12.7 mm diameter steel furniture tubes soldered onto it at 100 mm intervals and glazed by two glass covers. The total effective collecting surface area of the two collectors was 1.463 m2. The condenser-evaporator was a one shell pass, one tube pass, multi-tube vertical heat exchanger, with condensation-inside the tubes .and refrigerant storage in the-condenser tubes. The condenser was water cooled. Tests were performed with different concentrations in the range 0.35 to 0.58 kg NH / 9 kg solution with different solution masses. System parameters during regeneration and refrigeration proceses were measured, and the cooling effect and the system coefficient of performance computed. The maximum generator temperature attained was 100°C with an initial solution mass of 10.65 kg and an initial concentration of 0.37 kg NH9/kg solution. Cooling ratios in the range of 0.24 to 0.49 were obtained and the overall coefficient of performance was found to be in the range of 0.07 to 0.17. The effective cooling per unit area of collector surface per day for the experimental refrigerator was in the 2 range of 825.4 kJ/m , for an initial solution concentration of 0.37 kg NH /kg solution and initial ;) solution mass of 10.65 kg, to 2463.4 kJ/m2 for an initial solution concentration of 0.58 kg NH /kg 1) solution and initial solution mass of 13.8 kg, for clear sunny days. The results obtained herein compare favourably with those obtained by El-Shaarawi and Ramadan (1986) from their investigation carried out in Egypt, which is an example of a tropical climatic region. Hence the good performance of the system demonstrates the applicability of the system in the Nairobi climatic conditions. Although the performance is limited by the characteristics of the intermittent cycle as compared to the continuous cycles, the simplicity of the unit makes it adequate for use in small household and other food chillers in the rural areas where there is no electricity