2ND-LAW ANALYSIS OF ADSORPTIVE REFRIGERATION CYCLES - THE ROLE OF THERMAL COUPLING ENTROPY PRODUCTION

The reason why the performance of adsorptive refrigeration cycles is a lways less than that of the Carnot cycle corresponding to the same hea t reservoir temperatures is analysed. This analysis is performed using the entropy production concept and introducing numbers of entropy pro duction which are a direct measure for the efficiency degradation. The thermal entropy production due to the external thermal coupling of th e isothermal heat reservoirs to the temperature varying adsorbers is i mportant in all cases considered. It prevails for the basic uniform te mperature cycle (about 95% of the total entropy production). For n-ads orber uniform temperature cycles, internal thermal entropy production (due to heat recovery between adsorbers) may reach 50% of the external thermal entropy production. The entropy production due to the refrige rant flow inside the unit does not depend on the process and is small (less than about 10%) in all cases. For thermal wave cycles, the origi n of the entropy production depends highly on the cycle time. For very short cycle times, the external thermal entropy production is very sm all but an important internal thermal entropy production is observed i n the adsorbers. For long cycle times, it is the opposite, the externa l thermal entropy production becomes very large while the internal the rmal entropy production in the adsorbers does not increase. Copyright (C) 1996 Published by Elsevier Science Ltd.