Knudsen layer

The Knudsen layer, also known as evaporation layer, is the thin layer between liquid and vapour. It is named after Danish physicist Martin Knudsen (1871–1949).

Contents

Definition

On molecular level, the state of matter can be hard to define. From kinetic theory, it can be derived that if liquid is in contact with vapour, there is a small layer where the phase is between liquid and vapour. This region, several mean free path lengths thick, is called the Knudsen layer.[1]

Knudsen layer thickness

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.

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)[3].

References

  1. ^ Aoki, K. (2003). 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. 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