Darcy Friction Factor

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Darcy friction factor, abbreviated as \(f_d\), a dimensionless number, also called Darcy-Weisbach friction factor, formulas are equations that help calculate the friction losses in pipe flow and open channel flow.  This coefficient is used in the Darcy-Weisbach equation.

Fanning friction factor is not the same as the Darcy friction factor.  It is equal to 1/4 the Darcy friction factor.  Since they are basically the same, you need to note which one is being used when doing calculations.  Use \(f_f\) or \(f_d\) for the Fanning or Darcy friction factor, respectively.


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Darcy friction factor formula

\(\large{ f_d = \frac { 2 \; h_l \; d \; g } { l_p \; v^2 } }\)   


\(\large{ f_d }\) = Darcy friction factor

\(\large{ g }\) = gravitational acceleration

\(\large{ h_l }\) = head loss

\(\large{ l_p }\) = lenght of pipe

\(\large{ v }\) = mean flow velocity

\(\large{ d }\) = pipe inside diameter


Tags: Equations for Friction Equations for Flow