Ecological optimization of an irreversible Brayton cycle with regeneration, inter-cooling and reheating

• The irreversible Brayton cycle is optimized twice using the criterion of ecological function.
• The advantages of adding regeneration, inter-cooling and reheating are presented.
• Results for ecological optimization are compared with those for power optimization.
• Ecological optimization brings benefits for thermal efficiency and entropy generation rate.

A mathematical model is developed for an irreversible Brayton cycle with regeneration, inter-cooling and reheating. The irreversibility are from the thermal resistance in the heat exchangers, the pressure drops in pipes, the non-isentropic behavior in the adiabatic expansions and compressions and the heat leakage to the cold source. The cycle is optimized by maximizing the ecological function, which is achieved by the search for optimal values for the temperatures of the cycle and for the pressure ratios of the first stage compression and the first stage expansion. The advantages of using the regenerator, intercooler and reheater are presented by comparison with cycles that do not incorporate one or more of these processes. Optimization results are compared with those obtained by maximizing the power output and it is concluded that the point of maximum ecological function has major advantages with respect to the entropy generation rate and the thermal efficiency, at the cost of a small loss in power.