KEVOS® MAKEOS · Hydraulics
Pipe Friction Factor and Pressure Drop
What friction factor and pressure drop does this flow have in this pipe?
Reynolds number, Darcy friction factor (laminar 64/Re or Colebrook–White for turbulent flow), pressure drop and head loss for a straight pipe plus fittings.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Flow | L/min | Volume flow through the pipe. |
| Pipe inside diameter | mm | Inside diameter (not nominal size). |
| Pipe length | m | Length of straight pipe. |
| Kinematic viscosity | cSt | Kinematic viscosity at the operating temperature (1 cSt = 1 mm²/s; ISO VG 32 oil is 32 cSt at 40 °C, water about 1 cSt). |
| Density | kg/m³ | Density of the fluid at the working temperature (mineral hydraulic oil about 870 kg/m³, water about 998 kg/m³). |
| Pipe roughness | mm | Absolute roughness: about 0.0015 mm for drawn tube, 0.045 mm for commercial steel. |
| Sum of fitting loss coefficients | Sum of loss coefficients for bends, tees and valves from fittings data. |
Method and formulas
- v = Q ÷ A; Re = v d ÷ ν.
- Laminar (Re < 2300): f = 64 ÷ Re. Turbulent: 1/√f = −2 log₁₀(ε/3.7d + 2.51/(Re√f)) solved iteratively.
- Δp = (f L ÷ d + ΣK) × ρ v² ÷ 2.
- Example: 100 L/min of 15 cSt oil in a 25 mm pipe gives Re = 5,658.8, f = 0.03816 and 1.6814 bar.
Limitations
- Fully developed, incompressible flow; the transition region (Re about 2300–4000) is uncertain.
- Viscosity of oil changes strongly with temperature; use the operating value.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size hydraulic, coolant and water lines
- Find the pressure drop to a remote user
- Compare pipe sizes and materials
Who it is for
- Hydraulic and process engineers
- Maintenance engineers
- Design engineers
What you get
- Velocity and Reynolds number
- Flow regime and friction factor
- Pressure drop and head loss
Interpreting the result
- If the drop is too high, a larger diameter is far more effective than any other change (Δp ∝ 1/d⁵ in turbulent flow).
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027. Topic reference; no source tables or recommended settings are reproduced.
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