# Knudsen number ( related to mean free path)

## Description

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. This length scale could be, for example, the radius of the body in a fluid. (The mean free path is the average distance travelled by a moving particle (such as an atom, a molecule, a photon) between successive impacts (collisions), which modify its direction or energy or other particle properties.)

Related formulas## Variables

K_{n} | The Knudsen number (dimensionless) |

λ | The molecular mean free path length (m) |

L | The representative physical length scale (m) |