The 'Darcy-Weisbach' equation for head loss hf in a pipe is:
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hf = V²/2g only (velocity head)
hf = f×(L/D)×V²/(2g) — Darcy-Weisbach with Moody chart friction factor f; fundamental for all pipe flow
hf = 10.67×L×Q^1.85/(C^1.85×D^4.87) (Hazen-Williams, not Darcy-Weisbach)
hf = f×L (no velocity or diameter term)
Correct Answer
B. hf = f×(L/D)×V²/(2g) — Darcy-Weisbach with Moody chart friction factor f; fundamental for all pipe flow
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Darcy-Weisbach: hf = f×(L/D)×V²/(2g) = f×L×Q²/(12.1×D⁵) (practical form). Friction factor f: Moody chart — laminar: f = 64/Re; turbulent smooth: Blasius f = 0.316/Re^0.25; turbulent rough: Colebrook-White (implicit) or Swamee-Jain (explicit). L = pipe length (m), D = diameter (m). Fundamental equation, unlike Hazen-Williams which is empirical. HW: V = 0.849×C×R^0.63×S^0.54 (C = HW coefficient, empirical for water).
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