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为了提高R404A/CO2复叠式制冷系统的性能,对该系统开展了理论分析和优化研究。根据R404A和CO2的热物性及压缩机效率,采用热力学方法分析蒸发温度Te、冷凝温度Tk、冷凝蒸发器的传热温差ΔT等因素对系统性能的影响。通过模拟获得不同工况下低温端最佳冷凝温度、高低温端最佳质量流量比和最佳性能系数。结果表明:在一定Te、Tk和ΔT条件下,系统性能系数ε存在一个最佳值。为了提高系统性能系数ε,应尽量升高Te,减小ΔT和降低Tk。在同样工况下,R404A/CO2系统的最佳性能系数比NH3/CO2系统的稍高。
In order to improve the performance of the R404A / CO2 cascade refrigeration system, theoretical analysis and optimization of the system were carried out. According to the thermophysical properties and compressor efficiency of R404A and CO2, the influence of factors such as evaporating temperature Te, condensing temperature Tk, heat transfer temperature difference ΔT of the condensing evaporator on the system performance was analyzed by thermodynamic method. The optimum condensing temperature, optimal mass flow rate ratio and optimal performance coefficient at the low temperature end under different conditions were obtained through simulation. The results show that there is an optimum value of system performance coefficient ε under some Te, Tk and ΔT conditions. In order to improve the system performance coefficient ε, try to increase Te, decrease ΔT and decrease Tk. Under the same conditions, the best coefficient of performance for the R404A / CO2 system is slightly higher than for the NH3 / CO2 system.