CO2/NH3 cascade refrigeration system, CO2 charge, fault diagnosis
This paper analyzes a CO2/NH3 cascade refrigeration system of two temperature range applied in the cold storage. A mathematical model is presented to determine the optimal middle temperatures of the cascade-condenser for obtaining the maximum coefficient of performance (COP) under different operation conditions. Three main parameters including the evaporation temperature in the cold storage, the evaporation temperature in the refrigerated storage and the condensation temperature in the high temperature stage are used to study the optimal middle temperature of CO2 in the cascade-condenser. The results show that the optimal middle temperature increases with the increment of three main parameters. Moreover, under specific conditions, the optimal temperature is equal to the evaporation temperature of refrigerated storage. The results shown in this paper is helpful to the control strategy of CO2/NH3 cascade refrigeration systems for two temperature ranges.