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

Paper VT-WeA2
Significance of Bulk Flow Velocity for Turbopump Design

Wednesday, October 4, 2000, 2:20 pm, Room 201

Session: Vacuum Gas Dynamics
Presenter: M.H. Hablanian, Varian Inc.
Authors: M.H. Hablanian, Varian Inc.
R. Cerruti, Varian Inc., Italy
Correspondent: Click to Email
Initially, studies of many aspects of the pumping mechanism of turbomolecular pumps were approached from the high-vacuum side rather than from atmospheric pressure. Therefore, some significant parameters, well known from the discipline of fluid mechanics, have been neglected. One such parameter is bulk fluid stream velocity, which can be a significant engineering consideration for creating an optimized design. Due to the enormous densification ratios achieved in modern turbomolecular pumps, especially of the hybrid or compound variety, the flow velocity at the exit end of the pump is often near zero. This induces a stagnant condition, particularly when backing pumps are very small, allowing, for example, increased back-diffusion of light gases (hydrogen and helium). In addition, the presence of the nearly stagnant gas produces adverse effects on power consumption, which is very significant in newer hybrid turbopumps that can reach 100 mbar exhaust pressure. Attempts to create a single algorithm for a design using one type of impeller do not produce a scheme for a viable pump. The selection of appropriate different types of impellers for the entire pump structure seems to be the best method for optimizing overall performance.