AVS 47th International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeA

Paper VT-WeA4
Power Dissipation in Gaede Stages of Turbomolecular-drag Pumps in Viscous High-pressure Regime

Wednesday, October 4, 2000, 3:00 pm, Room 201

Session: Vacuum Gas Dynamics
Presenter: R. Cerruti, Varian Vacuum Technologies, Italy
Authors: R. Cerruti, Varian Vacuum Technologies, Italy
S. Giors, Varian Vacuum Technologies, Italy
J.C. Helmer, Varian Vacuum Technologies, Italy
A. Netti, Varian Vacuum Technologies, Italy
Correspondent: Click to Email
Drag Gaede stages are used for extending the operating range of turbomolecular pumps to higher pressures. A practical limit to high pressure operation is set by the power dissipated by these stages, which comes mainly from the friction inside the gas boundary layer. The power has then a direct impact on the rotor temperature and the electrical consumption of the motor. In a previous paper we presented a transitional power consumption model, which allowed to predict the power consumption of a given drag stage up to about 10 mbar, correctly capturing the effect of the transition from molecular to viscous regime, but failing above a critical pressure. @footnote 1@ The present work is aimed to extend the model to higher pressures ranges, where turbulence and other instabilities can not be neglected: above a certain pressure the rotor and stator boundary layers get affected by the centrifugal force field, their structure becomes pressure dependent and eventually turbulent. The simple viscous model is extended in order to incorporate these effects through the definition of an "eddy viscosity", which is a pressure dependent parameter introduced by Prandtl turbulent mixing length theory. The model results, showing the power dissipation growing with pressure in the high pressure regime, are compared with experimental power consumption measurement up to 100 mbar, on single drag stages with different dimensions, different rotational speeds and different gases. The model is aimed to be used in the optimization of the multistage Gaede pumps at very high pressure. @FootnoteText@ @footnote 1@ R. Cerruti, M. Spagnol, J. C. Helmer, "Power dissipation in turbomolecular pumps at high pressure", J. Vac. Sci. Technol. A 17(5), 3096-3102, Sept/Oct 1999.