Experimental Study on Performance of Double-throttling Device Transcritical CO2 Ejector Refrigeration System

Abstract

The double-throttling devices are adopted in the transcritical CO2 refrigeration system, and the devices are introduced in this paper. The first expansion valve is used to control the high-side pressure, and the second expansion valve is replaced by a two-phase flow ejector to recover the system expansion work. The performance of the double-throttling ejector refrigeration system is conducted experimentally, and the influence of the geometries and working conditions on the performance of the ejector and the COP is analyzed. The experimental results indicate that under a fixed working condition, with the increase in the first nozzle divergence angle, the entrainment ratio firstly increases and then decreases, but the COP has an opposite trend. As the equivalent diameter of the first throat is 2.00mm, the entrainment ratio and the COP reach the maximum value. With the increase in the outlet pressure and temperature of the gas cooler, the COP is a downward trend, and the entrainment ratio is on the rise. With the increase in the evaporation temperature, the entrainment ratio firstly increases and then decreases and the COP gradually increases, as the evaporation temperature is -1°C and -3°C, the COP and the entrainment ratio reach the maximum value respectively. And there is a certain relationship between the entrainment ratio of the ejector and the ability of the main ejection fluid entraining the suction fluid. Compared with the traditional system, the COP of the ejector refrigeration system with the double-throttling devices is higher and the maximum increase is up to 32.4%.