Research On Composite Molecular Pump Performance Calculation And Optimization Of Pumping Performance

Composite molecular pump(CMP)combine the advantage of turbo molecular pump and molecular drag pump,it has a high pumping speed and a good compression ratio.CMP has superior performance over a wide pressure range,and it has become an important vacuum equipment in the field of semiconductor thin films production and other fields.Turbo molecular pump main works in molecular flow state,its pumping performance is decided by the turbine blade geometry,rotor line speed and turbine stages.This paper studies the effects of turbine blade geometry for the pumping performance.For the drag stage of CMP,we obtain new pumping speed and compression ratio formulas after considering the effect of rotor and stator gap reflux.Analysis how the drag stage helical groove depth,dip,rotor gap affect the pumping performance by a lot of calculation.The result shows,the compression ratio goes up firstly and then goes down with the groove depth increases,so the spiral groove depth should be chose based on actual drag molecular pump design parameters,and the minimum groove depth should not less than one millimeter.With the broadening of compound molecular pump applying field,the working condition of drug stage has already change from molecular flow regime to transition flow regime,even to viscous flow regime.There is a well-understood performance computing method of DMP in molecular and viscous flow regime,the computing method in transition flow regime is core problem in compound molecular design and computing.In this article,a method of transition flow regime will be introduce through basing on performance computing method of DMP in molecular and viscous flow regime and introducing a way of weighting coefficient,the weighting coefficient is related to Knudsen number.The theoretical and engineering design methods in this paper has reference value to composite molecular pump structural improvements and performance optimization.