Design And Numerical Simulation Of Ejector Based On Polytropic Efficiency

Using two-phase ejector to recover throttling loss in refrigeration system is one of the effective measures to improve the energy efficiency of HVAC and refrigeration units.It is of great significance to design an ejector with optimal performance for improving the efficiency of refrigeration system and speeding up the practical application in refrigeration system.Firstly,this paper studies the impacts of operating conditions on the performance of two-phase ejector and double evaporation compression/injection refrigeration system based on the designi of sentropic efficiency.Multi-stage efficiency is proposed to replace the isentropic efficiency according to the analysis of the experimental results,which advances the mathematical model of ejector and finally the impacts of various parameters on ejector performance is analyzed.Lastly,numerical simulation was carried out with FLUENT software to study the influence of structure size on the performance of ejector based on multi-stage efficiency design.The main research contents and conclusions are as follows:(1)The influence of operating conditions on ejector and refrigeration system based on isentropic efficiency design was studied experimentally.The results showed that the boost ratio of ejector increases with the increase of inlet temperature of hightemperature refrigerant water,inlet temperature of cooling water and compressor frequency.The entrainment ratio of ejector decreases with the increase of inlet temperature of high temperature refrigerant water,inlet temperature of cooling water and compressor frequency.The COP of the system increases with the increase of inlet temperature of high-temperature refrigerant water,inlet temperature of cooling water and compressor frequency.(2)The mathematical model of ejector is advanced by using multistage efficiency instead of isentropic efficiency.The size parameters of the ejector are obtained under the design conditions,and then the influence of each parameter on the performance of the ejector is analyzed.The following rules are obtained:(1)all diameters decrease with the increase of mainstream inlet pressure except the diameter of ejector outlet;The diameter of nozzle outlet and the diameter of equal area mixing section decrease with the increase of secondary flow inlet pressure;The length of equal area mixing section increases with the increase of back pressure;All diameters and lengths of injectors decrease with the increase of multistage efficiency(3)The simulation results of two injectors were comparetively analyzed by FLUENT software.The impacts of structure size on injector performance were studied.The results show that the designed ejector based on multistage efficiency is optimal in overall performance than the ejector designed based on isentropic efficiency.It is found that there is an optimal nozzle throat diameter of 2.0 mm by simulating injectors with different structural sizes;The performance of the ejector reaches the peak value when the mixing chamber length of the ejector is between 70-90 mm.The ejector has better boosting effect when the diffusion angle of the diffusion chamber is less than 16.