AVS 52nd International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeM

Paper VT-WeM4
Thermal Fluid Dynamic Model of a Holweck Vacuum Pump Operating in the Viscous and Transition Regimes

Wednesday, November 2, 2005, 9:20 am, Room 201

Session: Gas Flow and Pump Technology
Presenter: S. Giors, Varian Vacuum Technologies, Italy
Authors: S. Giors, Varian Vacuum Technologies, Italy
E. Colombo, Politecnico di Milano, Italy
F. Inzoli, Politecnico di Milano, Italy
F. Subba, Politecnico di Torino, Italy
R. Zanino, Politecnico di Torino, Italy
Correspondent: Click to Email
Holweck drag pumps are used as high-pressure stages in hybrid turbomolecular pumps, where they operate in the transition and the viscous regime. In these regimes, thermal problems related to the viscous heating of the rotor become a major issue in the design of the pump. The fluid dynamic study of the Holweck pump was carried out by Boulon et. al.,@footnote 1@ using a three-dimensional no-slip Navier-Stokes model. They show a good agreement with the experimental data in the viscous regime, and they suggest the need of slip-flow boundary conditions to improve the accuracy for Kn > 0.01. The benefits of slip-flow boundary conditions for Kn > 0.01 are also confirmed by Giors et. al.,@footnote 2@ for a Gaede drag pump. In this work the emphasis is on the application of slip-flow boundary conditions to a single-stage Holweck pump model, and on the heat exchange phenomena occurring between rotor and stator. A three-dimensional thermal fluid dynamic model of the pumping grooves is developed, based on the Navier-Stokes equations, with viscous slip and thermal jump boundary conditions. Taking advantage of the high Biot number, a lumped-parameter heat conduction model of the solid parts of the pump is justified and coupled to the three-dimensional fluid dynamic model. A commercial CFD code is used to solve the conjugate heat transfer problem in the viscous and transition regimes and to predict the pressure profile along the grooves, together with the friction power and the rotor temperature. The numerical results are compared with the available experimental data and critically analysed. @FootnoteText@ @footnote 1@ O. Boulon, R. Mathes, Flow modeling of a Holweck pump stage in the viscous regime, Vacuum 60, 73-83 (2001).@footnote 2@ S. Giors, F. Subba, R. Zanino, Navier-Stokes modelling of a Gaede pump stage in the viscous and transitional flow regimes using slip-flow boundary conditions, J. Vac. Sci. Technol. A, 23(2), 336-346 (2005).