Thermal analysis of a vapour absorption refrigeration unit

Abstract

Absorption refrigeration systems are an alternative to vapour compression systems by being thermally activated. Such heat energy may come from the sun or even from hot exhaust gases from a particular engineering process. Vapour absorption systems utilize four major heat exchangers: an evaporator, condenser, absorber and generator. The operating temperatures of these units affect dramatically the performance of the system. Various mathematical models have been created in the past. Much of the focus of these studies was put on systems using water-Lithium Bromide refrigerant-absorbent pair. Analysis of these systems has also been extended to multi effect units. Nowadays, the investigation of ammonia-water systems is becoming more and more important especially with the introduction of efficient Generator-Absorber Heat Exchange absorption units. By means of carefully devised assumptions a simple linear model was created for an absorption system employing either water-lithium bromide or ammonia-water refrigerant-absorbent pairs. A thorough investigation of the optimal operating temperatures is necessary to ensure effective operation of the system. In this paper, the system response to varying absorber, generator, and condenser temperatures is analyzed. Particular attention is given to the effects of rates of change of temperature on system performance. The simulation also incorporates a simplified model of solar cooling and interesting results are presented such as solar panel area versus absorber temperature which provides extensive guidance in the design of solar cooling units. This work will serve as a foundation for an experimental system which will be built in the coming future.