How It Works
What is Reynolds Number?
The Reynolds number (Re) is a dimensionless quantity that predicts flow patterns. It represents the ratio of inertial forces to viscous forces in a fluid.
Reynolds Number Formula
Re = (V x D) / v = (V x D x rho) / mu
Where:
- V: Flow velocity (m/s or ft/s)
- D: Pipe inside diameter (m or ft)
- v: Kinematic viscosity (m2/s or cSt)
- rho: Density (kg/m3)
- mu: Dynamic viscosity (Pa.s)
Flow Regimes
- Laminar (Re < 2300): Smooth, orderly flow. Fluid moves in parallel layers. Low pressure loss. Typical in hydraulic systems.
- Transitional (2300 < Re < 4000): Unstable flow. Can switch between laminar and turbulent. Avoid designing in this range.
- Turbulent (Re > 4000): Chaotic, mixing flow. Higher pressure loss and heat generation. Common in water systems.
Hydraulic System Implications
- Most hydraulic oil systems operate in laminar flow due to high viscosity
- Laminar flow is preferred - lower pressure loss, less heat
- Water hydraulics often turbulent - different pressure loss formulas apply
- Cold starts may briefly see transitional flow as oil heats up
Pressure Loss Formulas
- Laminar: Hagen-Poiseuille equation (f = 64/Re)
- Turbulent: Colebrook-White or Blasius equations
Reynolds Number Calculator
Calculate Reynolds number and determine flow regime for hydraulic lines.
Flow Parameters
Fluid Properties
Typical: Oil 20-100 cSt, Water 1 cSt
Velocity Limits
Flow Regime
Enter parameters
Laminar
Re < 2300
Transitional
2300-4000
Turbulent
Re > 4000
Reynolds Number Analysis
Reynolds Number
--
Flow Regime
--
Flow Velocity
--
Velocity Limit
--
Friction Factor (f)
--
Pressure Loss Formula
--
Critical Re (laminar limit)
2300
Max Laminar Velocity
--
Recommended Velocities
| Line Type | Metric | Imperial |
|---|---|---|
| Pressure | 3-6 m/s | 10-20 ft/s |
| Return | 2-4 m/s | 6-13 ft/s |
| Suction | 0.6-1.2 m/s | 2-4 ft/s |