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Mechanical EngineeringP0

Reynolds Number Calculator

Calculate Reynolds number to determine flow regime (laminar, transitional, turbulent) in pipes.

Inputs
Enter your values below

Water at 20°C ≈ 0.001 Pa·s

Result
Reynolds Number (Re)
—
Enter values and click Calculate
Formula
density × velocity × diameter ÷ viscosity
Result unit: dimensionless

Re = ρ × v × D / μ. Density (kg/m³), velocity (m/s), diameter (m), dynamic viscosity (Pa·s). Re < 2300 laminar, 2300-4000 transitional, >4000 turbulent.

Introduction

Reynolds number is the dimensionless ratio of inertial to viscous forces in a fluid. It determines whether flow is laminar (Re < 2300), transitional (2300-4000), or turbulent (Re > 4000). Essential for friction factor selection and pressure drop calculations.

Calculation Example

Water at 2 m/s in 100mm pipe: Re = 200,000 → turbulent flow

Inputs: density=1000, velocity=2, diameter=100, viscosity=0.001
Result: 200000

Engineering Applications

  • •Flow regime determination
  • •Friction factor calculation
  • •Pressure drop estimation
  • •Heat transfer design

Frequently Asked Questions

What is a good Reynolds number for pipe flow?

For most industrial applications, turbulent flow with Re > 10,000 is desirable for good mixing and heat transfer. Laminar flow (Re < 2300) is common in very viscous fluids or small pipes.

Why does Reynolds number matter?

Re determines which pressure drop equation to use and is required to find the friction factor in the Darcy-Weisbach equation.

Related Calculators

Pressure Drop Calculator (Darcy-Weisbach)Pipe Flow CalculatorFriction Loss Calculator

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Disclaimer: Calculations are for reference and educational purposes only. Always verify results independently for engineering design. See full disclaimer.