Study On The Performance Of Ejector In Multi-evaporator Refrigeration System With Three-dimensional Simulation

In this paper,an ejector-based multi-evaporator refrigeration system with two different operating modes is proposed.By switching different valves,two working modes of single ejector under refrigeration-freezing condition and two-stage ejector under air-condition-（refrigeration-freezing）conditions are achieved.Three-dimensional numerical simulation can reflect the flow characteristics of ejectors more accurately than two-dimensional numerical simulation,and can solve some problems that two-dimensional numerical simulation cannot study.Three-dimensional CFD simulation is used to study the influence of geometric parameters and auxiliary entrainment on ejector performance in this paper.The specific work and key conclusions are as follows:Firstly,the influence of relative position,cross-sectional area and angle of the secondary flow inlet on the performance of single-stage ejector is analyzed.Next,auxiliary entrainment is proposed and the influence of relative position,cross-sectional area and angle of the auxiliary entrainment inlet on the ejector performance is accordingly identified.The results show that:（1）the performance of the ejector with the secondary flow in vertical direction of the primary flow is slightly better than that in parallel direction of the primary flow,and the optimal angle of the secondary flow inlet is 30°;（2）the effect of the cross-sectional area of the secondary flow has a relatively evident influence on ER,but its effect becomes ignored when the inlet area increases to a certain value;（3）both optimum relative position and axial width of auxiliary entrainment inlet ring are 15 mm;（4）relative position and axial width of auxiliary entrainment inlet ring are important factors influencing ejector performance,after optimizing these two geometries,the ejector ER can be increased by 97.7%.Secondly,the influence of the radius of the first and second constant area mixing section of the two-stage ejector on the minimum pressure of the constant area mixing section and diffuser section of the two-stage ejector is studied,and then the influence of the minimum pressure on the auxiliary entrainment is verified.The results show that:（1）as the radius of the second-stage constant-area mixing section increases,the P_min1decreases and the P_min2increases.R_am2has a great influence on both P_min1and P_min2;（2）The decreasing effect of P_min1and increasing effect of P_min2are weakened with the increase of the radius of the first mixing stage;（3）The minimum pressure of constant area mixing section and diffuser section of the first and second ejector has great influence on the effect of auxiliary entrainment.When P_min1is no more than 29.7k Pa,the first-stage auxiliary entrainment effect is relatively good,while when P_min2is no more than 50k Pa,it has a good second-stage auxiliary entrainment effect.