Fluid mechanicsMVP
Reynolds number
Check whether flow in a channel is laminar or turbulent.
Inputs
Result
Enter values and calculate to see the result.
Interpretation
Enter your fluid and channel values and calculate to see the flow regime. Below ~2000 the flow is laminar; above ~4000 it is turbulent.
Formula
Re = ρ · v · Dₕ / μ
Dimensionless ratio of inertial to viscous forces.
Variables
| Symbol | Variable | Unit |
|---|---|---|
| Re | Reynolds number | — |
| ρ | Fluid density | kg/m³ |
| v | Mean velocity | m/s |
| Dₕ | Hydraulic diameter | m |
| μ | Dynamic viscosity | Pa·s |
Assumptions & validity
This tool assumes:
- Newtonian, incompressible fluid.
- Hydraulic diameter Dₕ is appropriate for the channel cross-section.
- Transition thresholds use conventional pipe-flow values (laminar < 2000, transitional 2000–4000, turbulent > 4000); the true transition in microchannels can differ.
Worked example
Water (ρ = 1000 kg/m³, μ = 1.0 mPa·s) flows at v = 0.01 m/s through a channel with Dₕ = 100 µm.
Re = (1000 × 0.01 × 100×10⁻⁶) / 1.0×10⁻³ = 1.0
Re ≈ 1 → firmly laminar.