Reynolds Number
Compute Reynolds number Re from density ρ, velocity v, characteristic D and dynamic viscosity μ.
Inputs
Formula
Re = ρ·v·D/μ
Re<2300 laminar, Re>4000 turbulent, between is transitional.
Fundamentals
Compute Reynolds number Re from density ρ, velocity v, characteristic D and dynamic viscosity μ.
This tool computes Reynolds Number from the formula: Re = ρ·v·D/μ
History
Fluid mechanics and heat transfer were established in the 18th–19th centuries with steam engines and thermodynamics.
Engineering applications
Used for piping, heat-exchange and hydraulic system estimates.
Glossary
| Density ρ | Input parameter |
| Velocity v | Input parameter |
| Char. length D | Input parameter |
| Reynolds Re | Output result |
How to use
- Fill in Density ρ, Velocity v, Char. length D, Dyn. viscosity μ in the Inputs section (watch the unit on each field).
- Click Calculate; the tool evaluates the formula shown above.
- Read Reynolds Re in the results area.
Formula · Worked Example · Knowledge
Formula
核心计算关系：Re = ρ·v·D/μ
输入变量：
- Density ρ
rho— kg/m³ - Velocity v
v— m/s - Char. length D
D— m - Dyn. viscosity μ
mu— Pa·s
输出结果：
- Reynolds Re
Re
假设/适用：Flow formulas assume steady, incompressible, continuous flow; correct for compressible/high-speed.
Worked Example
根据公式 Re = ρ·v·D/μ，取 Density ρ = 1,000 kg/m³；Velocity v = 2 m/s；Char. length D = 0.05 m；Dyn. viscosity μ = 0.001 Pa·s。
代入计算得：Reynolds Re = 100,000。
Key Points
- Flow formulas assume steady, incompressible, continuous flow; correct for compressible/high-speed.
- Reynolds Re sets laminar/turbulent; friction f depends on regime & roughness.
- Energy eqn includes elevation, pressure and velocity heads; keep units as length.
Parameters
Inputs
| Parameter | Symbol | Unit | Default |
|---|---|---|---|
| Density ρ (kg/m³) | rho | kg/m³ | 1000 |
| Velocity v (m/s) | v | m/s | 2 |
| Char. length D (m) | D | m | 0.05 |
| Dyn. viscosity μ (Pa·s) | mu | Pa·s | 0.001 |
Outputs
| Result | Symbol | Unit |
|---|---|---|
| Reynolds Re | Re |
Applications
- Pipe flow rate and pressure drop
- Hydraulic cylinder force/speed design
- Flow-meter selection and calibration
FAQ
What formula does this tool use?
This tool computes per ISO / AGMA / ASME standard formulas: Re = ρ·v·D/μ
How accurate are the results?
Results match input precision, based on SI units and common engineering approximations; for critical duty re-check with a safety factor.
Where is it used?
Pipe flow rate and pressure drop