With the reasonable hypothesis on the cascade refrigeration system that uses carbon dioxide and ammonia as refrigerants, and applying the isentropic efficiency fitting formulas that are relative to compress rate of the compressor in calculating theoretical model, it is found that the results agreed closely with the reported experimental data. By the thermodynamic analysis of the cascade refrigeration system, it is discovered that the additional power caused by each of the main components of the refrigeration system have different effects on the system itself under different Tcas_c conditions. With the analysis of the data, a multilinear regression analysis is employed in term of evaporating, condensing and cascade heat exchanger temperature difference in order to develop mathematic expression for optimal condensing temperature of CO2 and the corresponding maximum COP.%对CO2/NH3复叠制冷系统进行合理的假设,并将与压比有关的压缩机等熵效率拟合公式引用到计算中,其结果与实验数据吻合的比较好.通过热力分析,可知系统各主要部件由不可逆而多消耗的附加功在不同的Tcas_c下对系统的影响程度是不同的.对数据进行分析并应用多元线性回归法拟合出以Te、Tc和ΔT为自变量的最优Tcas_c及相应COPmax数学表达式.
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