Power optimization of a regenerated closed variable-temperature heat reservoir Brayton cycle

Abstract

In this paper, the power output of the cycle is taken as an objective for performance analysis and optimization of an irreversible regenerated closed Brayton cycle coupled to variable-temperature heat reservoirs in the viewpoint of finite time thermodynamics or entropy generation minimization. The analytical formulae about the relations between power output and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible compression and expansion losses in the compressor and turbine, the pressure drop losses at the heater, cooler and regenerator as well as in the piping and the effect of the finite thermal capacity rate of the heat reservoirs. The maximum power output optimization is performed in two aspects. The first is to search the optimum heat conductance distribution corresponding to the optimum power output among the hot- and cold-side of the heat exchangers and the regenerator for a fixed total heat exchanger inventory. The second is to search the optimum thermal capacitance rate matching corresponding to the optimum power output between the working fluid and the high-temperature heat source for a fixed ratio of the thermal capacitance rates of two heat reservoirs. The influences of some design parameters on the optimum heat conductance distribution, the optimum thermal capacitance rate matching and the maximum power output, which include the inlet temperature ratio of the heat reservoirs, the efficiencies of the compressor and the turbine, and the pressure recovery coefficient, are provided by numerical examples. The power plant design with optimization leads to a smaller size, including the compressor, turbine, and the hot- and cold-side heat exchangers and the regenerator. When the heat transfers between the working fluid and the heat reservoirs are carried out ideally, the pressure drop loss may be neglected, and the thermal capacity rates of the heat reservoirs become infinite. The results of this paper become those obtained in recent literature.