Ecological optimization of an irreversible Brayton heat engine

Finite-time thermodynamics is used to determine the maximum ecological function, its corresponding thermal efficiency and power output of an irreversible Brayton heat engine. The ecological function of a heat engine is defined as the power output minus the loss power, which is equal to the product of the environmental temperature and the entropy production rate. The ecological function is optimized with respect to the thermal conductance ratio and the adiabatic temperature ratio. The optimum values of adiabatic temperature ratios and thermal conductance ratios of irreversible Brayton heat engines are presented. To obtain a higher ecological function, the thermal conductance of the cold-side heat exchanger should be larger than that of the hot-side heat exchanger. The effects of the total number of transfer units of heat exchangers, turbine and compressor isentropic efficiencies, thermal reservoir temperature ratios and heat leaks on the maximum ecological function and its corresponding parameters are studied and discussed. Results can be used as important criteria in the design of Brayton heat engines.