Study On Performance Of Variable Working Conditions In Ejector-Expansion CO₂ Refrigeration System

The application of Freon has damaged the atmosphere of the earth severely.The study of environment-friendly refrigerants to replace it has got popularity,among which,CO₂ is the most promising one.Due to its low critical temperature,most of the CO₂ refrigeration systems work in transcritical region.As a result,applying conventional throttle valve into this kind of system,a higher work loss will come out.The ejector can handle this issue effectively.The ejector is a simple,non-moving component fluid machine that can be driven by discharge heat.These features enable it to achieve energy-saving and environmental-friendly effects.Therefore,people apply it to various fields such as aerospace,chemical,refrigeration,etc.A large number of studies have focused on the influence of the size of ejectors,operating parameters,on the efficiency of ejector,the study of fixed-size ejectors.In this case,the flow rate of ejector is fixed.In actual practice,a refrigeration system is required to adjust the supply of its refrigerant at any time according to changes in the environment so as to satisfy different refrigeration requirements.This requires the study of a variable-flow ejector.In order to solve this problem,a multi-ejector model is proposed in this paper.The specific research contents are as follows:?1?With the ej ector released by the previous people being basic model,the size of its each part is enlarged and reduced according to a certain proportion relationship to obtain the four groups of sizes required for establishing the multi-ejector in this paper;?2?The CREO and the MESH is used to model and mesh the multi-ejector proposed in this paper respectively;?3?Arrange and combine the meshed models to obtain 15 different configurations of ejector;?4?Select the appropriate calculation model and simulate the 15th cases by means of FLUENT.Analyze the calculated results and get the characteristics of mass flow inside the multi-ejector.?5?By modelling and analysing the ejector-expansion system,we draw a conclusion that,with evaporation temperature being 0?,-5? and-10?,an optimum working condition will be obtained when the entrained ratio of ejector falls on about 0.48-0.49.?6?Not only can a multi-ejector model adjust the mass flowrate flexibly,but also,maintain a higher COP.