CRYOPUMPING IN THE NEAR FREE-MOLECULE FLOW REGION

Results are presented of an experimental study on the cryopumping of CO2 at liquid N2 temperature at pressures where the mean free path is comparable to the cryosurfac dimensions. In this range, it is shown that the pumping speed is no longer constant as it is in the low pressure ranges (free-molecu...

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Bibliographic Details
Main Authors: WANG,E.S.J, COLLINS,J.A. JR, HAYGOOD,J.D
Format: Report
Language:English
Subjects:
ANALYSIS
CARBON DIOXIDE
CRYOGENICS
LIQUEFIED GASES
LOW TEMPERATURE RESEARCH
NITROGEN
PRESSURE
RAREFIED GAS DYNAMICS
TESTS
THEORY
VACUUM APPARATUS
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Summary:Results are presented of an experimental study on the cryopumping of CO2 at liquid N2 temperature at pressures where the mean free path is comparable to the cryosurfac dimensions. In this range, it is shown that the pumping speed is no longer constant as it is in the low pressure ranges (free-molecule flow), but increases with increasing pressure through what is termed the tr nsitio region and approaches a constant value in the higher pressure ranges (continuum flow). The pumping speed in the continuum region is shown to be as much as three times that in the free-molecule region. Theoretical analyses of experimental results are presented, including an explanation of the threefold increase in pumping speed. (Author)