New Method Of Ejectors Structural Optimization Design And Shock Characteristics Analysis

The ejector is a pressure boosting device for coiling and mixing low pressure fluid with high pressure fluid,which has many advantages such as simple structure,no moving parts and can use low grade energy.It is widely used in petrochemical,aerospace,refrigeration,heating and other fields.At present,the axial dimensions of ejector are mainly calculated by the empirical formula summarized in the experimental data,but there are some problems and defects in the empirical formula.The supersonic flow in the ejector can lead to irreversible processes such as shock waves,which affect the performance of the ejector.On the basis of these,this paper proposes some new design methods of the ejector structure,and studies the shock characteristics.According to the theory of gas dynamics,a modified 1-D mixed model and a model with Fanno flow of calculating the mixing chamber length are presented by considering the properties of real fluid and the frictional loss in the fluid mixing process of the ejector.The entrainment ratios,the exit pressure and exit temperature of the ejector,the aspect ratio of the mixing chamber are calculated by these models,and calculated values can better match the experimental data,the feasibility of the calculation models are proved.Meanwhile,the relationships between different working parameters and structural parameters of ejector are analyzed.Based on the real fluid,a model of calculating the diffuser structure is presented by considering the frictional loss in the mixed fluid flow process of the diffuser and the change of the cross-sectional area.The exit pressure and exit temperature of the ejector,and the diffuser structure are calculated by this model,and the errors between the calculated values and the experimental values are within a reasonable range,the reliability of the calculation model is confirmed.At the same time,the relationships between the diffuser structure and expansion ratios,other structural parameters are analyzed.Because shock wave caused by supersonic flow in the ejector,a mathematical model of calculating the maximum length of the mixing chamber and mathematical model of the shock wave calculation are proposed according to the causes and characteristics of shock waves.The effects of the working parameters,structural parameters and working fluids of the ejector on the shock characteristics,the maximum length and aspect ratio of the mixing chamber are discussed.It provides some help for determining the position,strength and elimination and control of shock wave in the ejector under different conditions.In order to improve the performance of the ejector,a two-stage ejector is built by installing the second stage ejector after the single stage ejector,and a 1-D mixed model of the two-stage ejector is presented.The influence of the working parameters,structural parameters and working fluids of the ejector on the entrainment ratios and coefficient of performance of the two-stage stage are studied,provides some references for optimal performance of ejector refrigeration systems.In addition,it is pointed out that the working fluids should be chosen rationally according to the specific requirements of ejector.