低温级以CO2为工质的复叠式制冷循环热力学分析

传统的复叠式制冷循环通常采用的几种工质破坏臭氧层且温室效应较强，为此，对低温级以CO2为工质的复叠式制冷系统进行热力学理论分析，计算了不同蒸发温度下最佳COP及其对应的低温循环冷凝温度和流量比．通过对几种工质组合(R22-R12，R134a-CO2，NH3-CO2，R290-CO2，CO2-CO2，CO2-CO2加膨胀机)的比较，可发现自然工质的COP与传统工质的相当．综合考虑环境因素及设备的选择，自然工质系统值得推荐．

Thermodynamic Analysis on Cascade Refrigeration System with CO2 Working in Low Temperature Stage

Some refrigerants used in traditional cascade refigerating system can destruct the ozonesphere and cause strong greenhouse effect,so the cascade refrigeration systems with CO_2 working in the low temperature stage are analysed theoretically in this paper. The variation of optimum coefficient of performance (COP) was calculated with the change of the evaporation temperature.The condensation temperature for the low temperature stage and mass flow ratio for the high temperature stage to that of the low temperature corresponding to the optimum COP of different evaporation temperature was also calculated . Comparisons between several groups of refrigerant combinations (R22-R12, R134a-CO_2, NH_3-CO_2, R290-CO_2, CO_2-CO_2, and CO_2-CO_2 with expander), show that the COPs of natural working fluids are quite the same as those of conventional ones. Therefore, the natural working fluids systems are promising if the environmental factors and the selection of equipment are taken into account comprehensively.