Analysis Of Mach Wave Characteristics And Structural Optimization Of The Ejector

With people’s increasing attention to the environment and energy problems,ejectors have been widely used in various fields due to their advantages of being able to be driven using low-grade heat sources.In the internal flow field of ejector,Mach waves can be generated at the nozzle outlet and the diffusion chamber.At different expansion ratios,the Mach waves at the nozzle outlet are shown as expansion waves,a oblique shock wave and a normal shock wave.The characteristics of Mach waves at the nozzle outlet of ejector with steam,ammonia,R22,R290,R134a and R600a as working fluids were studied by means of gas dynamics theory.The results show that at the low expansion ratio,the higher the adiabatic index is,the higher the Mach wave intensity is.The difference of the adiabatic index has a significant influence on the airflow turning angle of the working fluid through the Mach wave.At the same time,the intensity of the expansion wave and the intensity of the shock also decrease as the cone angle of the nozzle increases.Therefore,in order to achieve higher efficiency,the nozzle structure design should have an optimal parameter range.The mathematical model of shock wave inside the ejector is established,and the wave lengths of the shock and expansion waves at the nozzle exit are calculated.The distance between nozzle and mixing chamber is an important parameter which affects the performance of ejector.In this paper,Comsol is used for numerical simulation to obtain the law of influence of different nozzle distances on ejection coefficient and the change law of shock waves at the nozzle outlet under fixed working condition parameters.It is found in the simulation study that,with the gradual increase of NXP,the entrainment ratio of ejector in the first shock wave section first reaches a maximum value,then decreases and presents a certain volatility repeatedly in the following.Due to the unsteady working condition of the ejector,NXP does not have an optimal value,but the NXP should have an optimal interval.At the same time,the mathematical modeling and simulation of the optimal mixing chamber diameter were carried out,and the influence of the mixing chamber structure on the shock wave and the ejector’s performance was obtained.It is considered that the determination of the optimal nozzle distance is related to the diameter of the mixing chamber and the length of shock.