Knudsen layer

 ( Fluid Dynamics ) 

The Knudsen layer, also known as evaporation layer, is the thin layer of vapor near a liquid or solid. It is named after Denmark physicist Martin Knudsen (1871–1949).

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Definition At the interface of a vapor and a liquid/solid, the gas interaction with the liquid/solid dominates the gas behavior, and the gas is, very locally, not in equilibrium. This region, several mean free path lengths thick, is called the Knudsen layer.

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Knudsen layer thickness The Knudsen layer thickness can be approximated by $l\_c$, given by

$l\_c\; =\backslash frac\{k\; T\_s\}\{\backslash pi\; d^2\; p\_s\}$,

where $k$ is the Boltzmann constant, $T\_s$ is the temperature, $d$ is the molecular diameter and $p\_s$ is the pressure.

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Applications One of the applications of Knudsen layer is in the coma of comets. It has been used specially in the coma chemistry model (ComChem model).

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