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

Paper VT-WeA8
Conic Peak/Dimple Roughness Model for Explaining the Reduction of Flow Rate through Passages with Rough Walls

Wednesday, October 4, 2000, 4:20 pm, Room 201

Session: Vacuum Gas Dynamics
Presenter: T. Sawada, Akita University, Japan
Authors: T. Sawada, Akita University, Japan
W. Sugiyama, Akita University, Japan
M. Yabuki, Akita University, Japan
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Passages with rough walls allow for smaller conductance for rarefied gas flow than passages with smooth walls. For the purpose of clarifying the effects of surface roughness on rarefied gas flow through passages, surface roughness is modeled by circular-conical peaks and dimples with the same base radius. Cones (peaks and dimples) are located in a statistical manner. Cone height and depth are also determined in a statistical manner from the measured angle distributions of actual surface roughness. The following are assumed in the model: (1). Cones are optional in contact with one another. (2). Cones higher than 1.2r(r: radius of base circle) are cut at the height of 1.2r and the upper parts are removed, but the top flat faces are not open for molecules to fly into. (3) The distance traveled by molecules between collisions with cone surfaces on the same macroscopic surface does not affect the macroscopic transfer of molecules. (4) Molecules do not collide with one another during their travel on a macroscopic surface. (5) Molecules are regarded as hard spheres and they scatter on cone surfaces according to cosine law. (6) The height of cone roughness is much smaller than the height of the passage. The calculated results predict well the measured reduction of free molecule and near free molecule flow conductance through channels composed of two flat plates.