<P> In fluid dynamics, the Darcy--Weisbach equation is a phenomenological equation, which relates the head loss, or pressure loss, due to friction along a given length of pipe to the average velocity of the fluid flow for an incompressible fluid . The equation is named after Henry Darcy and Julius Weisbach . </P> <P> The Darcy--Weisbach equation contains a dimensionless friction factor, known as the Darcy friction factor . This is also variously called the Darcy--Weisbach friction factor, friction factor, resistance coefficient, or flow coefficient . </P>

What is the head loss in pipe flow