# Knudsen Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

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

### Knudsen Number FORMULA

:(Kn

$$\large{ Kn = \frac{ \lambda }{ l } }$$

Where:

$$\large{ Kn }$$ = Knudsen number

$$\large{ l }$$ = length

$$\large{ \lambda }$$  (Greek symbol lambda) = mean free path

Solve for:

$$\large{ \lambda = Knl }$$

$$\large{ l = \frac{ \lambda }{ Kn } }$$