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 h ...

layer, is the thin layer of vapor near a liquid or solid. It is named after Danish physicist Martin Knudsen (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 ...

lengths thick, is called the Knudsen layer.

Knudsen layer thickness

The Knudsen layer thickness can be approximated by

l_c

, given by

l_c =\frac

, 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).

References

Fluid dynamics {{fluiddynamics-stub