Research On Transmission Characteristics In Turbo Molecular Pump Vanes Considering Inlet Tube Influence

With the development of semiconductor,aerospace and thin film preparation industry,the demand for molecular pump greatly increased which can obtain clean and high vacuum environment.At home and abroad,the theoretical and experimental research on turbo molecular pump has been enriched and perfected.In this paper,TPMC method is used to simulate the pumping performance of turbine molecular pump under the influence of inlet beaming effect.The main contents include:(1)The molecular flow in the inlet tube of TMP is simulated by Molflow,a TPMC software.The results show an obvious beaming effect exist in the inlet tube,ie.,the incident density decrease along radius at the blade rows plane.Based on the simulate data the fitting formus is obtained.Connected with the former study,the TMP transmission probability that consider inet tube influence is obtained.(2)The Monte-Carlo mathematical model of the molecular flow in the inlet tube is established.Based on the theory,the simulation program is written by VB 6.0.With the program,the molecular incident density along the axial at inner wall and incident density along the rudius at blade rows plane are obtained.From the simulate data,the beaming effect is found in the inlet tube.The gas species,temperature and turbine speed have little effect on the result.(3)The incident molecular angle distribution at the blade rows plane is studied by two methold:TPMC and analytic method.The two mutual authentication.Angle beaming effect obviously exists in the inlet tube.The incident molecular angle distribution does not follow cosine law at the blade rows plane.The angle distribution for differernt tube length and different radius position is obtained.The resule shows the beaming effect figure is much thinner compared with the cosine law figure.And the figure is asymmetrical,slants to the direction far from the axial.(4)The 3D Monte-Carlo mathematical model of the molecular flow between blade rows is established.The plane that upper blade,lower blade,inner wall,turbine root,entrance,exit,equation of six plane is estabilished.Coordinate of intersection between the plane and the molecular fly route is given.The judgment method of whether the molecular arrive the plane or not is given.Based on the theory the program is written,and the pumping performance of the TMP is obtained.