The constant-frequency double-stage compression refrigeration system fails to run in the best state at the working or load changing conditions. To improve its performance

maintain the maximum performance coefficient

and achieve rapid and accurate cooling

a variable-flow double-stage compression experimental bench was set up. The proposed method was able to control the refrigerant gas flow rate of the low-pressure compressor and change the refrigerant mass flow rate. Therefore

the experimental study of two-stage compression cooling was conducted. Results showed that the refrigeration capacity of the system decreased with an increase in the ratio of input gas of low- and high-pressure compressors (in the range of 1.25 to 3.33) at the condensation temperature of 30 ℃

evaporation temperature of ?35–?20 ℃. The cooling capacity of the system gradually decreased with the increase of the ratio of input gas of low- and high-pressure compressors and the maximum coefficient of performance (COP) is2.37. The ratio of input gas of low- and high-pressure compressor under the optimum COP increased with the decrease of evaporation temperature. Considerably

as the evaporation temperature decreased by 5 ℃ when the evaporation temperature was in ?35–?20 ℃

the ratio of the inputgas of the low- and high-pressure compressors under the optimal COP increased by 22.10%

12.52%

and 14.29%

respectively. Therefore

for the actual system design

the experimental data can be used to adjust the ratio of input gas of low- and high-pressure compressors according to the different evaporation temperatures and refrigeration demands.