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How It Works
This calculator covers two essential pipe flow equations. The Reynolds number (Re = ρVD/μ) predicts whether flow is laminar (Re < 2,300), transitional, or turbulent (Re > 4,000). The flow rate equation (Q = πD²V/4) relates volumetric discharge to pipe diameter and velocity.
Example Problem
Water (ρ = 998 kg/m³, μ = 0.001 Pa·s) flows at 1.5 m/s through a 25 mm pipe. Is the flow laminar or turbulent?
- Re = 998 × 1.5 × 0.025 / 0.001
- Re = 37,425 — well above 4,000, so the flow is turbulent
Frequently Asked Questions
What is the Reynolds number?
A dimensionless ratio of inertial to viscous forces. Below 2,300 the flow is laminar (smooth layers); above 4,000 it is turbulent (chaotic mixing). Most engineering pipe flows are turbulent.
Why does flow regime matter?
Laminar and turbulent flows have very different friction factors, heat transfer rates, and mixing behavior. The Darcy friction factor for laminar flow is f = 64/Re; for turbulent flow you must use the Colebrook equation.
How do I convert flow rate to velocity?
V = 4Q / (πD²). For a 50 mm pipe carrying 0.002 m³/s: V = 4(0.002)/(π×0.0025) = 1.02 m/s.
Related Calculators
- Colebrook Equation Calculator — find the friction factor for turbulent pipe flow.
- Darcy-Weisbach Calculator — calculate head loss using the friction factor from pipe flow analysis.
- Continuity Equation Calculator — relate flow rate, area, and velocity with unit conversions.
- Reynolds Number Calculator — determine laminar vs. turbulent flow regime in the pipe.
- Hazen-Williams Calculator — an alternative pipe flow formula for water distribution systems.
- Pressure Unit Converter — convert between psi, kPa, and bar for pipe pressure drop.