Investigation On Performance Of Dual-throat Nozzle Ejector And Transcritial CO₂ Two-phase Ejector Refrigeration System

The ejector has got more and more attention of people because of its simple structure, no moving parts as well as the advantage of recycling expansion work. Research group show that using the dual-throat nozzle ejector comparing with the Laval nozzle ejector can improve system performance. Thus in this paper, the internal flow characteristics of the two phase flow ejector were simulated numerically, and the performances of the two phase flow ejector and the transcritical CO2 refrigeration system with the ejector were measured under different working conditions for different geometry of the ejector nozzles. The effects of the outlet pressure and temperature of the gas cooler on the ejector performance and system COP were analyzed for the fixed ejector nozzle sizes, the effects on the performance of the ejector and system of the nozzle size, including the equivalent diameter of the first-throat,he equivalent diameter of the nozzle connection as well as the equivalent diameter of the second-throat, were analyzed under a fixed experimental condition. The experiments and numerical simulation results were summarized and compared.The conclusions as follows:(1)The simulation and experimental results show that under the condition of a fixed ejector geometry sizes,the entrainment ratio rises with the increase of the gas cooler outlet pressure.Under the fixed condition of the gas cooler outlet pressure of 8.5 MPa, outlet temperature of 40℃and evaporation temperature of 6℃,both of the experimental entrainment ratios and numerical simulation one reduce with the decrease of the equivalent diameter of the connection nozzle.(2)The Experiment results indicate that as the equivalent diameter of the first throat increases, the cooling capacity of the system is increased, and the power consumption of the compressor increase firstly, and then decrease. When the diameter is 2.0 mm, the power consumption of the compressor reaches the maximum. The COP of the system rises with the increase of the equivalent diameter of the first throat. Both the COP of the system and the entrainment ratios reduce with the increase of the equivalent diameter of the connection nozzle.(3) The simulation results show that under a fixed working condition, the entrainment ratio increases firstly, then decreases with the increase of the equivalent diameter of the first throat, and when the throat diameter is 2 mm, the entrainment ratio of the ejector reaches the maximum value. The entrainment ratio decreases nearly linearly with the increase of the equivalent diameter of the connection nozzle.(4)Comparing the performance of the ejector refrigeration system and the conventional system, it is indicated that the experimental and simulated results of the system COP reduce with the increase of the gas cooler outlet temperature, and the COP rises with the increase of the gas cooler outlet pressure. The COP of the ejector system are higher than that of the traditional system, and the maximum is about 15.3%.