Mechanism Research Of Supersonic Swirling Flow With Condensation

Supersonic separator is a new technology to condense and separate mixed gas with a tubular instrument.It combines the cooling properties of Laval nozzle with the principles of centrifugal separation.Due to simple structure without rotating parts,supersonic separator is not only easy to operate but also has high reliability.Involving high intensity swirling and supersonic flow with the condensation,the flow in the supersonic separator is very complicated.Therefore,it is necessary to carry out more studies on the complicated flow and reveal the working mechanism to provide technical references for the optimization of the device.In this paper,theoretical analysis and numerical simulation are combined to study the characteristics of supersonic swirling flow in the supersonic separator based on the gas dynamics,statistical thermodynamics and fluid dynamics.The main research work and conclusions are as follows:1)In the second chapter,the design method of overall structural for Laval modules in the supersonic separator was determined through theoretical analysis.The size of converging sections and throats of nozzles is calculated for specific operating conditions.The influence of expansion angle of divergent section on the flow in the Laval nozzle is analyzed by numerical calculation.It is found that the cooling characteristics of the nozzle improve with the increase of the expansion angle in the absence of shock wave.However,the larger the expansion angle,the more likely the shock wave is generated in the nozzle,which has an adverse impact on the condensation phase transition.Due to the above two factors,expansion angle is set at 10°.2)In the third chapter,the nucleation process in the condensation was explained by molecular dynamics,and the condensation in the nozzle was numerically calculated.The condensation phase change model was determined based on the molecular dynamics study,and the model was verified by experiments.3)In the fourth chapter,the condensing nucleation and the droplet growth theories are embedded into the Euler-Euler model in the form of UDF to establish a model predicting the supersonic flow accompanied by spontaneous condensation(Supersonic Swirl Condensation Flow Model).The model was used to calculate and analyze the flow of moist air in the Laval nozzle.The influence of inlet pressure,outlet pressure and other operating parameters on the condensation flow was studied.The results show that when the outlet pressure is large,the shock wave appears in the nozzle,which seriously damages the condensation of water vapor and is harmful to the separation of the mixed gas.The greater the inlet pressure,the higher the condensation rate of water vapor,but the change of the condensation rate is not obvious under a relatively small pressure change.The position where steam begins to condense moves forward along with the decrease of inlet temperature.Reducing the inlet temperature is beneficial to increase the condensation rate and further improve the removal efficiency of water vapor in the air.However,if the temperature is too low,the droplets will freeze on the wall,which will reduce the separation efficiency of the mixture.4)The influence of blade inclination angle on separation performance is studied in chapter 5.Four kinds of cyclones with blade inclination angles of 7.16°,20.65°,32.13° and41.32° were designed and the number of spiral blades was 6.Supersonic moist air flows with condensation in the four supersonic separators are simulated with the Supersonic Swirl Condensation Flow Model.It is found that the separation efficiency increases first and then decreases with the increase of the inclination angle,and the separation efficiency is the highest when the inclination angle is 32.13°.