# flow

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

## Knudsen Number

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

$$Knudsen \; number \;=\; \frac{ mean \; free \; path } { length }$$

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

Where:

$$Kn$$ = Knudsen number

$$\lambda$$ (Greek symbol lambda) = mean free path

$$l$$ = length

Solve for:

$$\lambda = Knl$$

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