The Knudsen layer, also known as
evaporation
Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...
layer, is the thin layer of vapor near a liquid or solid. It is named after
Danish
Danish may refer to:
* Something of, from, or related to the country of Denmark
People
* A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark
* Culture of Denmark
* Danish people or Danes, people with a Danish a ...
physicist
Martin Knudsen
Martin Hans Christian Knudsen (February 15, 1871 in Hasmark on Funen – May 27, 1949 in Copenhagen) was a Danish physicist who taught and conducted research at the Technical University of Denmark.
He is primarily known for his study of molec ...
(1871–1949).
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
In physics, mean free path is the average distance over which a moving particle (such as an atom, a molecule, or a photon) travels before substantially changing its direction or energy (or, in a specific context, other properties), typically as a ...
lengths thick, is called the Knudsen layer.
Knudsen layer thickness
The Knudsen layer thickness can be approximated by
, given by
,
where
is
Boltzmann's constant
The Boltzmann constant ( or ) is the proportionality factor that relates the average relative kinetic energy of particles in a gas with the thermodynamic temperature of the gas. It occurs in the definitions of the kelvin and the gas constant, ...
,
is the temperature,
is the molecular diameter and
is the pressure.
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).
References
Fluid dynamics
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