Darcy–Weisbach Pipe Head Loss
Darcy–Weisbach Head Loss in a Pipe
Friction between a moving fluid and the pipe wall dissipates energy, expressed as a head loss that the pump must overcome. This worksheet computes the friction head loss along a straight pipe run.
The Darcy–Weisbach equation is h_f = f·(L/D)·v²/(2g), where f is the Darcy friction factor (read from a Moody chart or Colebrook equation), L the length, D the diameter and v the mean velocity.
Inputs
f := 0.02=0.02
L := 100 m=100 m
D := 100 mm=100 mm
v := 2.5 m/s=2.5 m/s
g := 9.81 m/s^2=9.81 m/s^2
Friction head loss
h_f := f·(L/D)·v^2/(2·g)=6.37 m
Results
The head loss is expressed as an equivalent height of fluid column. Multiply by ρg to get a pressure drop. Minor (fitting) losses from bends, valves and entries are additional and are often added as equivalent lengths or K-factors.
Assumptions & limitations
- Fully developed, steady, incompressible flow.
- Single constant-diameter pipe; friction factor assumed known.
- Minor losses excluded — add them separately.