Swamee-Jain equation

The Swamee-Jain equation is used to solve directly for the Darcy-Weisbach friction factor f for a full-flowing circular pipe. It is an approximation of the implicit Colebrook-White equation.

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Where f is a function of:

• roughness height, ε (m, ft)
• pipe diameter, D (m, ft)
• Reynolds number, Re (unitless).

The equation was found to match the Colebrook-White equation within 1.0% for 10^-6 < ε/D < 10^-2 and 5000 < Re < 10⁸.

References

• Swamee, P.K.; Jain, A.K. (1976). "Explicit equations for pipe-flow problems". Journal of the Hydraulics Division, ASCE 102 (5): 657–664.