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# Colebrook-White equation

The Colebrook-White equation is used to iteratively solve for the Darcy-Weisbach friction factor f.

$\frac{1}{\sqrt{f}} = -2 \log (\frac{e}{12R} + \frac{2.51}{Re\sqrt{f}})$
For Full Flow (Closed Conduit):
$\frac{1}{\sqrt{f}} = -2 \log (\frac{e}{14.8R} + \frac{2.51}{Re\sqrt{f}})$

Where f is a function of:

• roughness height, e (m, ft)
• hydraulic radius, R (m, ft)
• Reynolds number Re (unitless)

Because the iterative search for the correct f value can be quite time-consuming, the Swamee-Jain equation can be used to solve directly for f.

## References

• 2002, Computer Applications In Hydraulic Engineering, 5th Ed., Haestad Press, pg. 16