Knudsen layer

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


This region, several mean free path lengths thick, is called the Knudsen layer.[1]

Knudsen layer thickness[edit]

The knudsen layer thickness can be approximated by l_c, given by[2]

l_c =\frac{k T_s}{\pi d^2 p_s},

where k is Boltzmann's 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).[3]


  1. ^ Aoki, K. (2003). "Knudsen Layer for Gas Mixtures". Journal of Statistical Physics 112 (3/4): 629–655. doi:10.1023/A:1023876025363.  edit
  2. ^ Gusarov, A. V.; Smurov, I. (2002). "Gas-dynamic boundary conditions of evaporation and condensation: Numerical analysis of the Knudsen layer". Physics of Fluids 14 (12): 4242. Bibcode:2002PhFl...14.4242G. doi:10.1063/1.1516211.  edit
  3. ^ Huebner, W. F. (1987). "First Polymer in Space Identified in Comet Halley". Science 237 (4815): 628–630. doi:10.1126/science.237.4815.628. PMID 17758563.  edit