FREE-MOLECULE FLOW IN THE AXIAL-FLOW TURBOVACUUM PUMP
Final rept., Mar 1963
MASSACHUSETTS INST OF TECH CAMBRIDGE FLUID MECHANICS LAB
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The rarefied gas flow through a moving cascade of flat plates, as it applies to high-vacuum pumping, was investigated analytically and experimentally. The theory is based on the assumption of free-molecule flow, i. e., no collisions between molecules. The essential quantities determining the performance of a blade row are the net transmission probabilities from one side to the other. These transmission probabilities depend mainly on the blade angle and spacing-chord ratio and on the ratio of mechanical speed to mean molecular speed. The transmission coefficients are calculated by numerical solution of the governing integral equations, and are compared with the results of earlier Monte Carlo calculations. Experiments with a rotating test machine with either a single rotor or a rotor followed by a stator gave results in good agreement with the theory. A special means was developed for testing stationary cascades under conditions simulating the operation of a moving rotor. This apparatus was tested with several blade geometries. The results confirmed both the theory and the feasibility of the new rarefied gas wind-tunnel concept.
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