Power density analysis and optimization of an irreversible closed intercooled regenerated Brayton cycle

In this paper, power density, defined as the ratio of power output to the maximum specific volume in the cycle, is optimized for an irreversible closed intercooled regenerated Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of the theory of thermodynamic optimization. The analytical formulae for dimensionless power density and efficiency, as functions of the total pressure ratio, the intercooling pressure ratio, the components (the regenerator, the intercooler, the hot- and cold-side heat exchangers) effectiveness, the compressor and turbine efficiencies, the heat reservoir temperature ratio, and the temperature ratio of the cooling fluid in the intercooler and the cold-side heat reservoir, are derived. The optimum dimensionless power density is obtained by optimizing the intercooling pressure ratio. The maximum dimensionless power density is obtained by searching the optimum heat conductance distributions between the hot- and cold-side heat exchangers for a fixed total heat exchanger inventory and fixed heat conductance distributions of the regenerator and the intercooler, and by searching the optimum intercooling pressure ratio. When the optimization is performed with respect to the total pressure ratio of the cycle, the maximum dimensionless power density can be maximized again, and a double-maximum power density and the corresponding optimum total pressure ratios are obtained. The effects of the heat reservoir temperature ratio, the temperature ratio of the cooling fluid in the intercooler and the cold-side heat reservoir, the efficiencies of the compressors and the turbine, and the total heat exchanger inventory on the optimum power density, the maximum power density, and the double-maximum power density and the corresponding optimal total pressure ratio are analyzed by numerical examples. In the analysis, the heat resistance losses in the four heat exchangers, and the irreversible compression and expansion losses in the compressors and the turbine are taken into account.