Knudsen number

The Knudsen number ( after the Danish scientist Martin Knudsen ) measures the ratio of the mean free path of the gas molecules to a geometric reference length ( eg diameter of the tube through which flow ).

It is a measure of the density of the gas flow. For the laws of gas dynamics are continuous media, while valid for the kinetic theory of gases, laws of highly diluted media.

It is defined as:

With

  • = Mean free path length in m
  • = Characteristic length for the flow / flow in m
  • = Temperature in K
  • = Boltzmann's constant ( 1.38 x 10-23 J · K-1)
  • = Total pressure in Pa
  • = Diameter of the molecules in m
  • Statistical Physics
  • Code ( chemistry)
481398
de