AVS 45th International Symposium
    Vacuum Technology Division Tuesday Sessions
       Session VT-TuA

Paper VT-TuA5
Direct Simulation Monte-Carlo Method for Molecular and Transitional Flow Regimes in Vacuum Components

Tuesday, November 3, 1998, 3:20 pm, Room 329

Session: Drag Pumping and Transition Flow Phenomena
Presenter: O. Boulon, Alcatel High Vacuum, France
Authors: O. Boulon, Alcatel High Vacuum, France
R. Mathes, Alcatel High Vacuum, France
J.-P. Thibault, LEGI-IMG, France
Correspondent: Click to Email
With the active development of semiconductor fabrication technology, dilute gas flow phenomena are recently attracting attention. The gas flow through a vacuum component can be continuous, transitional or molecular depending on the pressure range and geometries involved. The present work proposes a method for simulating molecular and transitional flows using the direct simulation Monte-Carlo method (DSMC), first developed by Bird.@footnote 1@ DSMC codes directly simulate nature by moving computational particles through space. The computational model takes as data combinations of pressures, temperature of gas, type of gas and geometry of the vacuum components. The results of the computations are gasflow, local velocities, and molecular density distribution. The model was first tested and validated for several simples geometries such as circular and rectangular finite length tubes with static and moving walls, for different flow conditions. The molecular flow "aspect" is checked by comparing results with existing analytical values in the literature. The model was found to agree well with other published results in this field. From molecular to transitional flow, velocity profiles show the importance of viscosity effect for the different Knudsen numbers varying from 40 to 0.04 (pressure range from 5.e-03 to 5 Pa). The flow rate obtained for the smallest Knudsen number is close to the viscous value corresponding to Poiseuille's law. The aim of the study is to develop a model that we can adapt to more complicated geometries of vacuum components such as stage of turbomolecular or molecular pump and to predict the flow rate from molecular to transition flow regimes. @FootnoteText@ @footnote 1@G.A. Bird "Molecular gas dynamics and the direct simulation of gas flows". Oxford Science Publications, Clarendon Press, 1994.