Karthik R
Administrator

he Knudsen Number represent the ratio between the mean-free-path of the molecules (lambda) and the problem characteristic length (L):

Kn = lambda/L

This number is used in fluid dynamics to define the limits of the continuum approximation. For Kn<<1 a fluid can be assume to be a continuum, while at Kn close to 1 or larger we have free molecular flow. Also, in the range of values 0.01