Research On Calculation Of Turbo-molecular Pump Of Pumping Performance In Transition Flow Range

In recent years,with the rapid development of semiconductor,medicine chemical industry,aerospace and other industries,there is an important application for turbo-molecular pump to achieve high vacuum.Turbo-molecular pump,with the advantage of high pumping speed,starting and stopping quickly,can continue to get clean high vacuum environment.Taken into account the superior performance of turbo molecular pumps,the development of molecular pumps has gradually entered the trend of precision and miniaturization,and its application widely.Especially in analytical instruments,the application range of molecular pumps has entered the transition Range.In the process of developing molecular pump,it is necessary to accurately calculate pumping performance of turbo-molecular pump in transition range.In order to promote the development of turbo-molecular pump in the transition range,this paper mainly focuses on the calculation of the pumping performance of the turbo molecular pump in the transition range.The method is established to calculate the pumping performance of the turbo-molecular pump in the transition range,and analyze the change of pumping performance of turbo molecular pump in transition range.Based on the continuum flow equation and the characteristic coefficient method,the pumping performance of the turbo-molecular pump in the transition range was calculated in different speed ratio,pitch ratio and angle.Considering the shortcomings and advantages of the two methods,a hybrid segmentation method is established to improve the accuracy of calculation method.Besides,based on DSMC,the flow field of turbine blades in the transition range is calculated and analyzed.It is found that the pressure ratio and pumping efficient change in different blade structure,gas temperature and flow range.The results show that the pumping performance of the turbo-molecular pump decreases with the decrease of Kn in the transition range.Moreover,the influence of speed ratio,pitch ratio and angle on the pumping performance of the molecular pump in the transitional range is similar to that of the molecular pump in the molecular range,but its influence is small.With the decline of Kn,the collision between the molecules are more intense,so the probability of collision with the wall is relatively reduced,and the pumping performance decrease.In addition,the increase of gas temperature affect the pumping performance of the turbo molecular pump.When the gas temperature is higher,the thermal motion of the molecule is more intense,the speed of the molecule through the channel is larger,so the pumping speed is higher,But because the more molecules at outlet and more speed,the molecules are more likely to move from the outlet to the inlet,so pressure ratio is smaller.It shows that pressure ratio increase when the blade cross-section decrease in a variable channel.According to the theoretical calculation of the pressure ratio of the turbine blade,and compared with the experimental data,it is concluded that the theoretical calculation curve agrees well with the experimental curve,and it is proved that the method of calculating the pumping performance of the turbo molecular pump is effective.It is an important theoretical basis and means of calculation to design and develop molecular pump.