Knudsen Number Calculator

Your details

Direct mode uses a known mean free path. Kinetic-theory mode derives the mean free path from temperature, pressure, and molecular diameter.
Average distance a molecule travels between successive collisions.
The relevant physical dimension: pipe diameter, gap width, MEMS channel size, etc.
Knudsen Number (Kn)Slip flow
0.0068

Dimensionless ratio of mean free path to characteristic length

Flow regimeSlip flow
Mean free path (λ)68.00 nm
Characteristic length (L)10.0000 μm
λ (m)0
0.0068
Continuum<0.001Slip0.001-0.1Transition0.1-10Free-molecular10+

Kn = 0.0068, Slip flow.

  • Mean free path: 68.00 nm. Characteristic length: 10.0000 μm.
  • You are in the slip-flow regime. The Navier-Stokes equations remain useful but must be paired with velocity-slip and temperature-jump boundary conditions at surfaces.

Next stepApply Maxwell slip and Smoluchowski temperature-jump boundary conditions in your CFD solver.

 = Powered by OnlyCalculators