Physics

Knudsen Number Calculator

Find the Knudsen number to classify a flow regime.

Mean free path

Characteristic length

Calculated Output

Knudsen number 0.0001

Formula: Kn = λ ÷ L

Step-by-Step Breakdown

1. Values used:

2. Mean free path = 0

3. Characteristic length = 0.001

5. Knudsen number = Mean free path / Characteristic length = 0 / 0.001 = 0.0001

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The math behind it

Kn = λ ÷ L. Kn < 0.01 is continuum flow; Kn > 10 is free molecular flow.

λ 70 nm, L 1 mm → Kn ≈ 7 × 10⁻⁵ (continuum).

When does continuum break down?

At low pressure or tiny scales (MEMS, vacuum), where Kn becomes large.