Performance of three-heat-reservoir absorption cycles with external and internal irreversibilities

Abstract

The ideal three-heat-reservoir (THR) model for absorption refrigeration cycles is extended to include external and internal ireversibilities. The operating point of the cycle is determined by equating the internal entropy generation to the net entropy transfer from the working fluid. The main features of the entropy transfer function are presented. Three empirical functions are used to model the internal entropy generation of the cycle. The parameters of the these functions are estimated by fitting data obtained by simulation to the predictions of the THR model. The THR model using a linear function or a logarithmic function for the internal entropy generation is able to reproduce performance data for single-stage and double-stage absorption systems with good accuracy. The THR model provides a convenient means for representing performance characteristics of absorption cooling systems over a wide range operating temperatures. It can be used in preliminary design studies and in larger simulation programmes in which the absorption machine is a sub-component.