Abstract:

In order to improve the performance of R404A／CO2 cascade refrigeration system, a theoretical study was carried out. According to the thermal physical properties of R404A／CO2 and the efficiencies of compressors, thermodynamic analysis and mathematical simulation were adopted to get the influence of the important factors such as the evaporating temperature Te, the condensing temperature Tk and the temperature difference ΔT in the cascadecondenser. The optimum condensing temperature in the CO2 lowtemperature cycle, the optimum mass flow ratio of the high／low temperature cycle and the optimum coefficient of performance under different conditions were  obtained by simulation. There exists an optimum coefficient of performance when Te, Tk and  ΔT are definite in this cascade refrigeration system. The coefficient of performance can be improved by increasing Te, decreasing  ΔT in the cascadecondenser and Tk. Under the same conditions, the optimum coefficient of performance of the R404A／CO2 cascade refrigeration system is slightly higher than that of NH3／CO2 refrigeration system.

Key words: CO2, cascade refrigeration, coefficient of performance, the optimum mass flow ratio