AVS 49th International Symposium
    Vacuum Technology Thursday Sessions
       Session VT-ThM

Paper VT-ThM7
Two-Dimensional and Three-Dimensional Monte Carlo Simulation on the Pumping Performance of a Turbomolecular Pump with Rough-Surface Blades

Thursday, November 7, 2002, 10:20 am, Room C-104

Session: Gas Dynamics and Flow
Presenter: T. Sawada, Akita University, Japan
Authors: M. Yabuki, Akita University, Japan
T. Sawada, Akita University, Japan
W. Sugiyama, Akita University, Japan
M. Watanabe, Osaka Vacuum Ltd., Japan
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The elements of a turbomolecular pump (TMP) are sometimes coated with ceramic (SiO@sub 2@) film for the purpose of preventing corrosion on the TMP. The blades coated with SiO@sub 2@ have relatively rough surfaces, and it has been confirmed by previous experiments that the SiO@sub 2@-coated TMP gives a higher maximum-compression ratio than the non-coated TMP. This paper describes the Monte Carlo simulation on the effects of the surface roughness of blades on the pumping performance of a TMP. The surface roughness was measured by SEM, and then the distribution of roughness slope angles was obtained from the surface roughness data. The surface roughness was modeled by statistically located circular-conic peaks and dimples of the same base radius and various base angles. The base angles were sampled in a statistical manner so as to accord with the measured slope angle distribution. Both the 2D and 3D Monte Carlo simulations were done in the free molecule flow regime and the simulated maximum-compression ratios were compared with the previously measured values. The 3D simulation naturally showed a better agreement with the measured values than the 2D simulation. However, it was proved that the 2D simulation gave reasonable results with much less computation time than the 3D simulation when the ratio of blade height to pitch was larger than the unity.