Study On Novel Completely Smooth Cross-sectional Profiles And Rotor Performance For Twin-Screw Vacuum Pumps

Twin-screw vacuum pump is a positive-displacement pump.The screw rotor plays a key role in determining the performance of the twin-screw vacuum pump.The design process of the existing screw rotor profile is complicated,and the large area of blowhole leads to serious leakage between stages.In order to solve the problems above,two new meshing models were established based on conjugate meshing principle,meshing relation of spiral curve with variable speed and meshing relation of elliptic arc.According to these two meshing models,a novel type of completely smooth screw rotor was proposed.The design program of the rotor profile was developed and the equations was deduced.Its design method,geometric parameters and meshing performance were studied.The three-dimensional structure of variable pitch screw rotor and twin-screw vacuum pump were designed,and the influences of the main structural parameters to screw rotor were analyzed.The pressure distribution and velocity vector in the internal flow field of the new type of twin-screw vacuum pump were revealed by numerical simulation of the gas flow process in the working process.Through the analysis of the stress and deformation of the screw rotor,the differences between the new type of screw rotor and the existing screw rotor were compared.The meshing model of spiral curve with variable speed was established to solve the problem of smooth connection between two concentric arcs on the cross-sectional profile of rotary fluid machinery.The meshing model of elliptic arc was established to effectively reduce the area of leakage triangle caused by correction of tooth tip.Compared with the existing screw rotors,the composition curve of the proposed screw rotor is simpler.The proposed screw rotor has advantages of small area of leakage triangle,smooth and short space contact lines,and better sealing performance between stages.In the simulation of flow field,gas pressurization in twin screw vacuum pump is a common result of internal compression,leakage between stages and gas mixing at discharge side.In the analysis of the mechanical properties,the stress distribution of the proposed screw rotor is better than that of the existing rotor.Compared with the existing rotor,there is no stress concentration at the dedendum of the proposed rotor,and the radial deformation of the proposed rotor is less.Therefore,the reserved assembly clearance can be reduced to improve sealing performance.The research of this paper enriches the types of screw rotors,and has great theoretical and engineering significance for the design and optimization of twin-screw vacuum pumps.