Experimental analysis of the refrigerant two-phase flow in an absorption chiller based on GAX cycle

The International Energy Agency reported the growing demand for cooling over the next three decades as one of the top drivers of global electricity consumption. To cut down the electricity demand and the carbon dioxide emissions, an encouraging alternative to the conventional chillers is the adoption of absorption machines operating with abundant and sustainable heat sources, like solar radiation or industrial waste heat. Within the framework of the European FriendSHIP project, a prototype of ammonia-water absorption chiller fed by solar heat has been developed to produce cold at -20∘^{\circ}C for industrial applications. Thanks to its innovative architecture based on a Generator-Absorber heat-exchange (GAX) cycle, a part of the heat rejected by the absorption process is recovered to generate the refrigerant vapor, thereby reducing the required heat from the external heat source supplied at the generator, and thus improving the performance of the cycle. The main goal of this research is to analyze the experimental data of a ammonia-water Generator-Absorber heat-exchange cooling cycle to evaluate the different operating conditions of the system. The analysis of experimental results enable to determine the thermodynamic conditions of the refrigerant flow and evaluate the performance of the evaporator, which is shown as the key component limiting the chiller performance. This study demonstrates that the refrigerant purity has a strong role in the two-phase flow conditions and the deviation between the bubble and dew lines of the ammonia-water couple can lead to limitation of the evaporation capacity.

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