Cryopumping in the Near Free-Molecule Flow Region
Fluid mechanics can be analytically separated into the three flow regions—continuum, transition and free-molecular--by use of the Knudsen number Kn (the ratio of the mean free path to a characteristic body dimension). The ratio expresses the degree of molecule-surface interaction. In spite of the fact that the Knudsen number can only be calculated from system dimensions within an order of magnitude, it is customary to arbitrarily separate the three regions according to the Knudsen number as follows: for Kn less than 0.01, the flow is in the continuum region; for Kn between 0.01 and 10, the flow is said to be in the transition region; and for Kn greater than 10, free-molecular flow conditions prevail.
Unable to display preview. Download preview PDF.
- 1.L. H. Sentman, “Free-Molecule Flow Theory and Its Application to the Determination of Aerodynamic Forces,” LMSC 448514 (October 1961).Google Scholar
- 2.J. A. Collins, Jr., J. D. Haygood, and E. S. J. Wang, “Initial Study of the Effect of Cryosurface Geometry on Cryopumping,” AEDC-TDR-62–46 (April 1962).Google Scholar
- 3.D. D. Carlson and R. H. Underwood, “Design of an Aerospace Systems Environmental Chamber,” AEDC-TR-61–10 (July 1961).Google Scholar
- 4.D. Alpert, J. App. Phys., Vol. 24, No. 7 (1953).Google Scholar
- 5.R. D. Present, Kinetic Theory of Gases, McGraw-Hill Book Company, Inc., New York (1958).Google Scholar
- 7.J. Jeans, An Introduction to the Kinetic Theory of Gases, Cambridge University Press (1952).Google Scholar