Straight-run loss follows one chain: mean velocity, Reynolds number, friction factor, Darcy-Weisbach drop. Screening uses laminar f = 64/Re or Blasius f = 0.316/Re^0.25; rough or large-Re lines need Colebrook or Moody. Fittings join through K coefficients or equivalent length, and the total calibrates the system curve.
Formulas
Reynolds
Re = rho v D / mu
Below ~2300 laminar, above ~4000 turbulent.
Darcy-Weisbach
dP = f(L/D)(rho v^2/2)
f from 64/Re, Blasius, or Colebrook.
Worked example
DN100 x 100 m water
Inputs: Re 127000; L 100; D 100; v 1.27.
Calculation: f 0.0167; drop 0.135 bar.
Lesson:
Frequently asked questions
How do I know the regime?
Re below ~2300 laminar, above ~4000 turbulent; between is transitional.
Blasius or Colebrook?
Blasius suits smooth turbulent screening; rough or large Re needs Colebrook/Moody.
How do I add fittings?
Use sum-K for a few fittings or Le/D to metres of straight pipe.
Sources and further verification
- Darcy-Weisbach equation Wikipedia
- Moody chart Wikipedia
Next step