Darcy Friction Factor (Swamee-Jain / Colebrook)
The Darcy friction factor for pipe/duct head loss: laminar f = 64/Re (Re < 2300), turbulent via the Swamee-Jain fit to Colebrook, f = 0.25/[log10(eps/D/3.7 + 5.74/Re^0.9)]^2. Re 100,000, eps/D 0.0003 -> f 0.0195 (the Moody value for commercial steel); Re 1500 -> 64/1500 = 0.0427. Feeds h = f (L/D) V^2/2g. A design aid.
Formula and source
f = 64/Re (Re < 2300); else f = 0.25 / [log10(eps/D / 3.7 + 5.74 / Re^0.9)]^2 (Swamee-Jain).
The laminar Darcy factor 64/Re and the Swamee-Jain (1976) explicit approximation to the Colebrook-White equation, by name.
Audience
This tile is built for hvac and the adjacent professions in the HVAC group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.