Experimental study on the performance of trans-critical CO₂ two-stage compression refrigeration system with and without an ejector at low temperatures

A trans-critical CO2 two-stage compression refrigeration system with and without an ejector at low temperatures was set up and the effects of gas cooler pressure, gas cooler outlet temperature, and electronic expansion valve opening on the performance of the gas cooler and the refrigeration system were investigated experimentally. At a gas cooler pressure of 91 bar, an outlet temperature of 33 degrees C, and an electronic expansion valve opening of 95%, the COP of a trans-critical CO2 ejection-expansion two-stage compression refrigeration system reaches a peak of 0.78, which is 2.28 times higher than that of a trans-critical CO2 two-stage compression refrigeration system under the same operating conditions. This experiment also obtained the optimal operating range of the ejector. The effect of gas cooler pressure on COP is the most obvious under the conditions studied in this paper, followed by the electronic expansion valve opening and finally the gas cooler outlet temperature. However, the higher COP can be obtained for the electronic expansion valve opening condition, and the corresponding triangle COP is higher. There exists both an optimal intermediate pressure and an optimal gas cooler pressure to maximize the COP.