Knudsen Number Calculator
Calculate Kn = λ / L and interpret flow regime for micro/nano-scale and rarefied gas dynamics.
How to Use This Calculator
Choose a unit scale
Work in meters, micrometers, or nanometers for convenience.
Enter mean free path λ
Use appropriate value for the gas, temperature, and pressure.
Enter characteristic length L
Typical L is channel height, diameter, or feature size relevant to flow.
Calculate and interpret
Press Calculate to get Kn and identify the corresponding flow regime.
Formula
Kn = λ / L
Where: λ is mean free path of molecules; L is characteristic length scale of the system.
Example: λ = 65 nm, L = 1 µm ⇒ Kn = 0.065 (Slip regime).
About Knudsen Number Calculator
The Knudsen number determines whether continuum assumptions hold. It is critical in microfluidics, vacuum technology, and high-altitude aerothermodynamics.
When to Use This Calculator
- MEMS and microchannels: Assess slip effects.
- Vacuum systems: Identify free-molecular conditions.
- High-altitude flow: Evaluate rarefaction impacts.
Why Use Our Calculator?
- ✅ Straightforward: Minimal inputs, immediate interpretation.
- ✅ Flexible units: Work directly in m, µm, or nm.
- ✅ Educational: Clear guidance on regime thresholds.
Frequently Asked Questions
How do I estimate mean free path?
For ideal gases, λ depends on temperature, pressure, and molecular diameter. Data tables or kinetic theory formulas can be used for estimates.
Which L should I pick?
Choose the dimension most relevant to flow gradients (e.g., channel height, pipe diameter, or narrowest feature size).
What if Kn ~ 0.1?
This is the transition between slip and transition regimes; specialized models (e.g., Boltzmann-based) may be required for accuracy.