AVS 51st International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeM

Paper VT-WeM11
Slip Fluid Model of a Holweck Vacuum Pump in the Viscous and Transition Regime

Wednesday, November 17, 2004, 11:40 am, Room 303D

Session: Contamination Control, Outgassing and Modeling
Presenter: S. Giors, Varian S.p.A., Italy
Authors: S. Giors, Varian S.p.A., Italy
F. Subba, Dipartimento di Energetica, Italy
R. Zanino, Dipartimento di Energetica, Italy
Correspondent: Click to Email
Computational Fluid Dynamics (CFD) is playing an increasingly important role in the study of rarefied internal flows in vacuum pumps. Holweck pumps are used as high pressure stages in modern hybrid turbomolecular vacuum pumps, to extend the maximum compression ratio up to outlet pressures in the 1-10 mbar range, corresponding to the transition and the viscous laminar regime, for the typical pump's dimensions. The study of Holweck pump stages in the viscous regime has been carried out by Boulon et. al.@footnote 1@, using a no-slip fluid model. They show a good level of agreement with experimental data, but the accuracy of their model decreased for pressures corresponding to Knudsen number Kn>0.01. They suggest the need of slip boundary conditions to improve the accuracy of the model. In this work a three-dimensional model for the Holweck pump, based on the Navier-Stokes equations, with viscous slip and thermal jump boundary conditions is developed and a commercial CFD code is used to solve it in an outlet pressure range corresponding to the viscous laminar regime and transition to molecular flow for an experimental pump. The validation against the experimental data shows a good level of accuracy in terms of both compression ratio and dissipated mechanical power, up to Knudsen number Kn=0.1. @FootnoteText@ @footnote 1@ O. Boulon, R. Mathes, "Flow modeling of a Holweck pump stage in the viscous regime", Vacuum 60, 73-83 (2001).