NEW PERFORMANCE BOUNDS FOR A FINITE-TIME CARNOT REFRIGERATOR

An upper bound for the coefficient of performance (COP) of endoreversi ble refrigerators which depends only on the ratio tau = T-c/T-h betwee n the cold and hot reservoir temperatures has been elusive to date. We address here this long standing problem by analyzing an endoreversibl e Carnot refrigerator that operates in conditions of maximum per-unit- time COP. Two novel results are obtained: (1) A long sought tau-depend ent upper bound for the COP of refrigerators. (2) A tau-dependent opti mum distribution of the heat conductances associated with the coupling between the refrigerant and the heat reservoirs. Moreover, when the m ethod is applied to heat engines, the resulting optimum efficiency is even closer to real efficiencies than the well-known Curzon-Ahlborn re sult.