Darcy Friction Factor (Swamee-Jain / Colebrook)
The Darcy friction factor for pipe/duct head loss.
Example
You enter
- Reynolds number Re 100000
- Relative roughness eps/D 0.0003
You get
- Darcy friction factor f 0.0195
Checked against published worked examples from: CED Engineering (H. Bengtson).
Details, formula, and sources
ScopeLaminar 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 or tablef = 64/Re (Re < 2300); else f = 0.25 / [log10(eps/D / 3.7 + 5.74 / Re^0.9)]^2 (Swamee-Jain).
Source and editionThe laminar Darcy factor 64/Re and the Swamee-Jain (1976) explicit approximation to the Colebrook-White equation, by name.
Free accessThe 64/Re laminar relation and the Swamee-Jain explicit friction-factor fit are published free in any fluid-mechanics reference.
What governsEstimate. AHJ and licensed professional govern.
API field namesreynolds, rel_roughness, f
- Laminar f = 64/Re for Re < 2300, roughness-independentDarcy-Weisbach
- Turbulent Swamee-Jain f = 0.25 / [log10(eps/D/3.7 + 5.74/Re^0.9)]^2Swamee & Jain 1976
- Transition band 2300-4000 is indeterminate; estimate flaggedscope of this tile