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In free molecular flow, the pressure of the remaining gas can be considered as effectively zero. Thus, boiling points do not depend on the residual pressure. The flow can be considered to be individual particles moving in straight lines. Practically, the "vapor" cannot move around bends or into other
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For a gas passing through small holes in a thin wall in the
Knudsen-flow regime, the number of molecules that pass through a hole is proportional to the pressure of the gas and inversely proportional to its molecular mass. It is therefore possible to effect a partial separation of a mixture of gases
99:, the plasma is in a free molecular flow regime in scales less than 1 AU; thus, planets and moons are effectively under particle bombardment. However, on larger scales, fluid-like behavior is observed, because the probability of collisions between particles becomes significant.
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Yamamoto, K.; Pack, D. C.; Transient free molecular flow through a tube; Rarefied gas dynamics; Proceedings of the
Eleventh International Symposium, Cannes, France, July 3-8, 1978. Volume 1. (A80-34876 14-77) Paris, Commissariat a l'Energie Atomique, 1979, p.
119:. Depending on the source there is a range mentioned of 0.1>Kn>10 for which Knudsen flow occurs. Other names for this flow regime are intermediate, transitional, or slip flow, since it represents a transition state between free molecular flow and
50:(Kn). If Kn > 10, the system is in free molecular flow, also known as Knudsen flow. Knudsen flow has been defined as the transitional range between viscous flow and molecular flow, which is significant in the medium vacuum range where Ī» ā d.
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spaces behind obstacles, as they simply hit the tube wall. This implies conventional pumps cannot be used, as they rely on viscous flow and fluid pressure. Instead, special
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of the molecules is larger than the size of the chamber or of the object under test. For tubes/objects of the size of several cm, this means pressures well below 10
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are applicable, from 0.001<Kn<0.1, slip flow occurs, from 0.1ā¤Kn<10, transitional flow occurs and for Knā„10, free molecular flow occurs.
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Kogan, A. (1998). "Direct solar thermal splitting of water and on-site separation of the products - II. Experimental feasibility study".
148:, as a technique for separating hydrogen from the gaseous product mixture created when water is heated at high temperatures using
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123:. Thus the flow of fluids under Knudsen flow conditions is established both by molecular phenomena and by the viscosity.
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encountered at higher pressures. The presence of free molecular flow can be calculated, at least in estimation, with the
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The definition of a free molecular flow depends on the distance scale under consideration. For example, in the
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Gas flow can be grouped in four regimes: For Knā¤0.001, flow is continuous, and the
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through porous membranes. It has also been successfully demonstrated for use in
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if the components have different molecular masses. The technique is used to
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Statistical thermodynamics : fundamentals and applications
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in the flow space is of the same order of magnitude as the
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Gas flow with a relatively large mean free molecular path
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The
Knudsen number is a dimensionless number defined as:
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Free molecular flow occurs in various processes such as
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Vacuum
Technology - third, updated and enlarged edition
412:. 4.1.1 Velocity slip boundary in microscale gas flow.
235:{\displaystyle \mathrm {Kn} \ ={\frac {\lambda }{L}},}
164: ā Description of gas flow in free molecular flow
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Knudsen flow describes the movement of fluids with a
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458:. Hinsdale, Ill.: American Nuclear Society.
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34:. This is also called the regime of high
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256:{\displaystyle \lambda }
376:"What is Knudsen flow?"
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156:See also
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