Second-law analysis of adsorptive refrigeration cycles: The role of thermal coupling entropy production

Abstract

Abstract The reason why the performance of adsorptive refrigeration cycles is always less than that of the Carnot cycle corresponding to the same heat reservoir temperatures is analysed. This analysis is performed using the entropy production concept and introducing numbers of entropy production which are a direct measure for the efficiency degradation. The thermal entropy production due to the external thermal coupling of the isothermal heat reservoirs to the temperature varying adsorbers is important in all cases considered. It prevails for the basic uniform temperature cycle (about 95% of the total entropy production). For n-adsorber 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 refrigerant 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 origin of the entropy production depends highly on the cycle time. For very short cycle times, the external thermal entropy production is very small but an important internal thermal entropy production is observed in the adsorbers. For long cycle times, it is the opposite, the external thermal entropy production becomes very large while the internal thermal entropy production in the adsorbers does not increase.