Reynolds Number Calculator

Reynolds Number Equation:

\[ Re = \frac{\rho \times v \times D}{\mu} \]

Density (ρ):

kg/m³

Velocity (v):

m/s

Diameter (D):

Viscosity (μ):

Pa·s

Reynolds Number (Re):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Reynolds Number?

The Reynolds number (Re) is a dimensionless quantity used in fluid mechanics to predict flow patterns in different fluid flow situations. It compares inertial forces to viscous forces and helps determine whether flow will be laminar or turbulent.

2. How Does the Calculator Work?

The calculator uses the Reynolds number equation:

\[ Re = \frac{\rho \times v \times D}{\mu} \]

Where:

\( \rho \) — Density of the fluid (kg/m³)
\( v \) — Velocity of the fluid (m/s)
\( D \) — Characteristic diameter (m)
\( \mu \) — Dynamic viscosity of the fluid (Pa·s)

Explanation: The equation shows the ratio of inertial forces (ρvD) to viscous forces (μ) in the fluid flow.

3. Importance of Reynolds Number

Details: Reynolds number is crucial for predicting flow regimes:

Re < 2300: Laminar flow
2300 < Re < 4000: Transitional flow
Re > 4000: Turbulent flow

It's used in pipe flow analysis, aerodynamics, and many engineering applications.

4. Using the Calculator

Tips: Enter all values in consistent SI units. Density and viscosity values can be found in fluid property tables for common substances at different temperatures.

5. Frequently Asked Questions (FAQ)

Q1: What is the characteristic diameter?
A: For pipe flow, it's the pipe diameter. For other geometries, it's typically the hydraulic diameter (4 × cross-sectional area / wetted perimeter).

Q2: How does temperature affect Reynolds number?
A: Temperature affects viscosity and density. Higher temperatures generally decrease viscosity (increasing Re for liquids, decreasing for gases).

Q3: What's the difference between dynamic and kinematic viscosity?
A: Kinematic viscosity (ν) is dynamic viscosity (μ) divided by density (ρ). Reynolds number can also be expressed as Re = vD/ν.

Q4: Can Reynolds number be used for non-circular pipes?
A: Yes, by using hydraulic diameter instead of pipe diameter in the calculation.

Q5: What are typical Reynolds numbers in engineering applications?
A: Blood flow in arteries (~1000), water in pipes (~10,000-100,000), air over aircraft wings (~millions).