What Is the Knudsen Number (Kn) Microfluidic Flow Regime Calculator?
The Knudsen number is a dimensionless number defined as the ratio of the molecular mean free path length to a representative physical length scale.
How Does the Knudsen Number (Kn) Microfluidic Flow Regime Calculator Work?
Calculates Kn = λ / Lc.
Identifies the flow regime: Continuum (Kn < 0.001), Slip flow (0.001 ≤ Kn < 0.1), Transition (0.1 ≤ Kn < 10), or Free molecular (Kn ≥ 10).
Knudsen Number (Kn) Microfluidic Flow Regime Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Kn = λ / Lc
Ratio of molecular mean free path to macroscopic characteristic physical length scale.
How to Use the Knudsen Number (Kn) Microfluidic Flow Regime Calculator
- Input molecular mean free path in nanometers.
- Specify channel dimension in microns.
Step-by-Step Example Calculation
MEMS Microchannel Gas Flow at STP
Input Values:
meanFreePath:68
dimension:1
Worked Steps: 68 nm mean free path in a 1.0 µm channel yielding Kn = 0.068 (Slip Flow regime).
Understanding Your Result
In the slip flow regime, standard Navier-Stokes equations remain valid if Maxwell velocity slip boundary conditions are applied at walls.
Factors That Affect the Result
- Gas pressure (mean free path is inversely proportional to pressure; high vacuum increases λ and Kn).
When Should You Use This Calculator?
- MEMS sensor design, micro-turbomachinery, vacuum chambers, and high-altitude flight.
Assumptions & Limitations
- Assumes hard-sphere molecular gas model.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard Knudsen classification per Karniadakis & Beskok.