布雷顿和卡诺热机循环性能比较(Ⅰ)定常态流恒温热源循环

COMPARISON IN PERFORMANCES OF BRAYTON AND CARNOT THERMAL ENGINE CYCLES (Ⅰ) STEADY FLOW CYCLES WITH INFINITE RESERVOIRS

研究定常态恒温热源热机循环性能，导出内可逆卡诺热机和布雷顿热机的最佳功率、效率关系和最大功率及相应的效率界限，并对这两种热机循环的最优性能进行了比较。理论分析表明，只有当工质的热容率趋于无穷大时，布雷顿循环才能达到卡诺循环的性能。数值计算显示，当布雷顿循环的工质热容率为高、低温侧换热器的热导率总量的1．5倍时，布雷顿循环的功率已为卡诺循环功率的99％以上。

The performances of steady flow in Brayton and Carnot thermal engine cycles are studied for infinite thermal capacitance rates of heat reservoirs. The fundamental relations between power output and efficiency, the maximum power outputs and the corresponding efficiency bounds of the cycles are derived. A comparison of the characteristics of the two cycles under same boundary conditions (same heat source/sink temperatures and heat exchanger conductances) is presented.Theoritical analysis shows that the power output for Brayton cycle approaches as value as that for Carnot cycle when the factor (ratio of thermal capacitance rate of the working fluid to the total heat exchanger inventory) approaches infinity. Numerical calculation indicates that the power output for Brayton reaches higher than 99% of that for Carnot as the factor equals to 1. 5.