Knudsen Number

Assess continuum validity from mean free path to characteristic-length ratio.

visual calculatorDimensionless Numbers

Read the flow shape before trusting the number.

This page turns a CFD setup into regime, scale, and dominant-effect cues. Adjust the calculator below and compare the moving graphic with the computed result.

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Knudsenrarefactionmicrofluidics

formula

KaTeX rendered

\begin{aligned}\text{Kn = lambda / L}\end{aligned}

ASCII source

Kn = lambda / L

mean free path lambda (m)characteristic length L (m)

0.0007

regime

continuum

Once Kn moves into the slip or transitional range, continuum CFD usually needs wall slip, rarefaction corrections, or kinetic methods.

Knudsen rarefaction microfluidics