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The Reynolds number (Re) predicts whether fluid flow is laminar (smooth, Re < 2,300) or turbulent (chaotic, Re > 4,000). It is dimensionless and fundamental to fluid dynamics.

Formula

Re = ρvL/μ = vL/ν | where ρ = density, v = velocity, L = characteristic length, μ = dynamic viscosity, ν = kinematic viscosity

Re: Reynolds number (dimensionless)
ρ: Fluid density (kg/m³)
v: Flow velocity (m/s)
L: Characteristic length (m)
μ: Dynamic viscosity (Pa·s)
ν: Kinematic viscosity (m²/s)

Guida passo passo

1Re = ρ × v × d / μ
2ρ = density (kg/m³); v = velocity (m/s); d = diameter (m); μ = dynamic viscosity (Pa·s)
3Water at 20°C: μ ≈ 0.001 Pa·s
4Air at 20°C: μ ≈ 1.81×10⁻⁵ Pa·s

Esempi risolti

Ingresso

Water at 0.5m/s in 5cm pipe

Risultato

Re = 998 × 0.5 × 0.05 / 0.001 = 24,950 — Turbulent

Domande frequenti

What is Reynolds Number?

The Reynolds number (Re) predicts whether fluid flow is laminar (smooth, Re < 2,300) or turbulent (chaotic, Re > 4,000). It is dimensionless and fundamental to fluid dynamics

How accurate is the Reynolds Number calculator?

The calculator uses the standard published formula for reynolds number. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

What units does the Reynolds Number calculator use?

This calculator works with kilograms, inches, Celsius, watts. You can enter values in the units shown — the calculator handles all conversions internally.

What formula does the Reynolds Number calculator use?

The core formula is: Re = ρ × v × d / μ. Each step in the calculation is shown so you can verify the result manually.

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