Mean Free Path
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Mean Free Path
(symbol l, Missing Image:img src="SP7_m_files/lambdasm.gif", L)
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1. Of any particle, the
average distance that a particle travels between successive collisions with
the other particles of an ensemble.
In vacuum technology, the ensemble
of particles of interest comprises only the molecules in the gas phase.
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2. Specifically, the average distance traveled by the molecules of
a perfect
gas between consecutive collisions with one another. It may be determined
roughly from either of the formulas
Mu) is the dynamic viscosity; v is the kinematic viscosity; p
(lower case Rho) is the density; c is the molecular speed (a function
of the gas temperature); n is the number of molecules per unit volume;
and d is the molecule diameter.
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Given the mean free path l0 at a level where the pressure is
p0 , the temperature is T0 (�K), and the acceleration of
gravity is g0, then its value at any other level is
gravity, respectively, at the new level. See mixing
length.
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3. For any process the reciprocal of the cross
section per unit volume for that process.
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References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
