SUMMARYThe energy, exergy and entropy balance methods are used to analyse a double-stage LiBr-water absorption heat transformer cycle. An energy balance comparing component energy transfer is used to determine energy calculations. An exergy balance is employed to evaluate exergy destruction, and an entropy balance to verify entropy generation. A comparison of the results by the second law exergy and entropy balances indicates that they are consistent in identifying the location and relative significance of key non-idealities within the system. The results obtained clearly show the influence of irreversibilities of individual components on deterioration of the effectiveness and the coefficient of performance of the system. The second law analysis offers an alternative view of cycle performance and provides an insight that the first law analysis cannot. The differences between the first law analysis by energy balance method and second law analysis by exergy and entropy balance methods are illustrated quantitatively for the double-stage absorption heat transformer cycle, and the limitations and advantages of these methods are presented and discussed.
This study investigates the applicability of the second law of thermodynamics using an entropy balance method to analyse and design thermal systems. As examples, the entropy balance method is used to analyse a single stage chiller system and a single stage heat transformer, both with lithium‐bromide/water as the working fluid. The entropy method yields not only the same information as is conveyed by the methods of energy and exergy analysis, but it also predicts clearly the influence of irreversibilities of individual components on the coefficient of performance and its effectiveness, based on the process properties, rather than on ambient conditions. Furthermore, this method is capable of presenting the overall distribution of the heat input by displaying the additional heat required to overcome irreversibility of each component without ambiguity.
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