Reynolds Number Calculator
Calculate the Reynolds number for pipe flow to determine whether flow is laminar or turbulent.
Reynolds Number
200,000
Reynolds Number vs Flow Velocity (V)
Formula
## Reynolds Number The Reynolds number is a dimensionless quantity that predicts whether fluid flow will be laminar or turbulent. ### Formula **Re = V D / nu** where V is the mean velocity, D is the pipe inner diameter, and nu is the kinematic viscosity. For pipe flow: Re < 2300 is laminar, 2300 < Re < 4000 is transitional, and Re > 4000 is turbulent.
Exemplo Resolvido
Water at 20 deg C (nu = 1e-6 m^2/s) flowing at 2 m/s through a 100 mm pipe.
- 01Re = 2 x 0.1 / 1e-6 = 0.2 / 1e-6 = 200,000
- 02Since 200,000 >> 4000, flow is fully turbulent.
Perguntas Frequentes
What is kinematic viscosity for common fluids?
Water at 20 deg C: 1.0e-6 m^2/s. Air at 20 deg C: 1.5e-5 m^2/s. SAE 30 oil at 38 deg C: about 1.0e-4 m^2/s. Glycerin: about 1.2e-3 m^2/s.
Why does the Reynolds number matter?
It determines the flow regime, which affects friction losses, heat transfer rates, and mixing. Turbulent flow has higher friction but better heat transfer and mixing than laminar flow.
Can Reynolds number be used for non-circular ducts?
Yes, replace diameter D with the hydraulic diameter Dh = 4A/P, where A is the cross-sectional area and P is the wetted perimeter.
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