CO_2为低温循环工质的复叠式制冷系统的分析比较

Analysis and comparison of different cascade refrigeration systems using CO_2 as low-temperature working medium

通过对NH3/CO2、R290/CO2和R404A/CO2三种复叠式制冷系统的COP、最优低温循环冷凝温度和最佳质量流量比等进行理论分析及性能比较,得出在一定的蒸发温度、冷凝温度和冷凝蒸发器传热温差下,三种复叠式制冷系统的COP都随着低温循环冷凝温度的升高呈现出先增大后减少的趋势,其中NH3/CO2复叠式制冷系统的COP最大;三种复叠式制冷系统的最佳低温循环冷凝温度和最佳质量流量比都随着蒸发温度的升高而升高,其中R404A/CO2复叠式制冷系统的最佳低温循环冷凝温度最高,NH3/CO2复叠式制冷系统的最佳质量流量比最大。

Three kinds of cascade refrigeration systems, namely NH3/CO2 , R290/CO2 and R404A/CO2 ,were analyzed and compared theoretically in terms of coefficient of performance （COP）, optimum condensing temperature of CO2 and optimum mass flow rate ratio.The results show that,at definite evaporating,condensing temperatures and heat-transfer temperature difference of condensing evaporator,the COP of three kinds of cascade refrigeration systems firstly increases and then decreases with an increase in condensing temperature of CO2 ,and the COP of NH3/CO2 cascade refrigeration system is higher than that of the others.With an increase in evaporating temperature, the optimum condensing temperature of CO2 and optimum mass flow rate ratio of three kinds of cascade refrigeration systems increase, and the optimum condensing temperature of CO2 of R404A/CO2 cascade refrigeration system,the optimum mass flow rate ratio of NH3/CO2 cascade refrigeration system are the highest.