Knudsen layer

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.{{Cite journal | last1 = Dongari | first1 = Nishanth | first2 = Yonghao | last2 = Zhang | first3 = Jason M. | last3 = Reese | author-link3 = Jason Reese | title = The 'Knudsen Layer' Effect on Thermal Transiporation of Rarefied Gases | year = 2008 | journal = GASMEMS Report | url = http://www.gasmems.eu/site/www/fichiers/GASMEMS11_QR_12-11_ESR1.pdf | url-status = dead | archive-url = https://web.archive.org/web/20160603141550/http://www.gasmems.eu/site/www/fichiers/GASMEMS11_QR_12-11_ESR1.pdf | archive-date = 2016-06-03 }} This region, several mean free path lengths thick, is called the Knudsen layer.{{Cite journal | last1 = Aoki | first1 = K. |title=Knudsen Layer for Gas Mixtures| journal = Journal of Statistical Physics | volume = 112 | issue = 3/4 | pages = 629–655 | doi = 10.1023/A:1023876025363 | year = 2003 | bibcode = 2003JSP...112..629A | s2cid = 116416271 }}

The Knudsen layer thickness can be approximated by $l\_c$, given by{{Cite journal | last1 = Gusarov | first1 = A. V. | last2 = Smurov | first2 = I. | doi = 10.1063/1.1516211 | title = Gas-dynamic boundary conditions of evaporation and condensation: Numerical analysis of the Knudsen layer | journal = Physics of Fluids | volume = 14 | issue = 12 | pages = 4242 | year = 2002 |bibcode = 2002PhFl...14.4242G }}

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

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

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).{{Cite journal | last1 = Huebner | first1 = W. F. | title = First Polymer in Space Identified in Comet Halley | doi = 10.1126/science.237.4815.628 | journal = Science | volume = 237 | issue = 4815 | pages = 628–630 | year = 1987 | pmid = 17758563|bibcode = 1987Sci...237..628H | s2cid = 22850190 }}

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Category:Fluid dynamics

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