physics - Knudsen number

The Knudsen number (Kn) is a dimensionless number defined as the ratio of the molecular mean free path length to a representative physical length scale.

It is defined as:

$\mathit{Kn} = \frac {\lambda}{L} = \frac {k_B T}{\sqrt{2}\pi\sigma^2 P L}$

where

T, temperature (K)
k_B, Boltzmann's constant
P, total pressure (Pa)
$σ$ , diameter (m)

Knudsen number

See also