Ecological optimization of an endoreversible Brayton cycle

In this paper, finite-time thermodynamics has been applied to ecologically optimize the power output of closed Brayton cycles for infinite thermal capacitance rates of the heat reservoirs. The optimum values of power, thermal efficiency and second-law efficiency of Brayton cycles are presented. The ratio of ecologically optimum power to maximum power is independent of the numbers of transfer units of the hot-side and the cold-side heat exchangers, and this ratio is much higher than the ratio of the entropy generation rate at maximum ecological function to that at maximum power. With the introduction of the ecological function, the improvement in second-law efficiency and in thermal efficiency is evident, especially for low hot-cold temperature ratios. Moreover, the thermal efficiency at maximum ecological function is about the average of the maximum-power efficiency and the reversible Carnot efficiency. (C) 1997 Elsevier Science Ltd.