Numerical Simulation Study Of Gas Flow In Dry Scroll Vacuum Pump

Dry scroll vacuum pumps(DSVPs)are gradually prevailing in semiconductor industry,chemical engineering,pharmacy,scientific instrument and other industries and fields due to their advantages of oil-freeness,dependable performance,wide working range,small variation of torque,toughness against severe operating conditions,low noisy,low vibration and so on.As DSVP might work under complicated and harsh conditions,such as the variation of temperature and pressure,corrosive gas,dust particle and so on,it is quite necessary to further study the fluid mechanics and thermodynamics properties of the pump.The application of computational fluid dynamics(CFD)simulation technology in dry scroll vacuum pump was the main project concern.A three-dimensional(3-D)model of the fluid region was proposed,basing on the internal structure of dry scroll vacuum pump.The grid-mesh of fluid region(computational domain)was generated,with ICEM software.Then the elastic smooth dynamic grid technique was employed to update the grid.Combined with CFX(14.0)software,the transient simulation of flow field and temperature field inside the dry scroll vacuum pump was conducted.Indicators including speed distribution,temperature and pressure were obtained to study the transfer phenomenon of internal gas flow.Firstly,based on CFD method and dynamics mesh method,the transient flow simulation model of dry scroll vacuum pump was established.Numerical calculation was carried out under three kinds of typical working conditions of viscous flow state including under-compression,slightly over-compression and over-compression.Simulation results are in line with the results of experiment or theoretical calculation on the whole.The maximum error of pumping speed between the simulation and the experiment is about 30%,and the minimum is close to 10%.The predicted compression power accords with the theoretical prediction of approximate polytropic process.The simulation pressure inside the pump also has a consistent change process with experimental results.The contrast and analysis of the simulation model and the physical experiments suggest that the further correctly modified geometric parameters and boundary conditions according to practical situations can significantly improve the accuracy of the numerical calculation.Further analysis of the main flow phenomena and characteristics of scroll compression chamber at the discharge side during the discharge process confirms that under-compression and over-compression lead to the large variation of gas pressure and dramatic fluctuation of compression torque.Then according to VARIAN TriScroll 300 bilateral dry scroll vacuum pump,its flowing region geometry model was proposed.And based on the technology platform of ANSYS-CFX and dynamic grid technology,transient flow numerical simulation model of bilateral dry scroll vacuum pump was established.Through numerical simulation,the working process,flow phenomenon and flow characteristics,temperature and pressure distribution in the pump chamber were analyzed.Hope to provide theoretical foundation to the further study of theory and design of dry scroll vacuum pump.In the work,the phenomena in the flow process such as clearance leakage,expansion flow of the gas in the clearance volume,the turbulent eddy distribution were also studied.Although there are some aspects need to be improved and modified,the current study has practical significance for the improving of the researches and the performance of dry scroll vacuum pump.