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Darcy-Weisbach formula

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Darcy-Weisbach formula diagram
The equation states that the pressure loss ΔP=fLρV²/2D (where L and D are th pipe length and diameter, ρ is the fluid density, V is the average velocity through the pipe, and f is the Darcy friction factor).
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Pipe diameter:
Pipe length:
Discharge rate:
Darcy friction factor:

Pressure drop:
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Only either the velocity or the discharge rate needs to be entered. The Darcy friction factor f is also known as the "flow coefficient" λ or the Moody friction factor, and is 4x the Fanning friction factor. It is dependant on many factors such as the pipe material, shape, and fluid velocity. Therefore, it must be known or calculated for each specific use. For laminar flow in a circular pipe, it is 64/Re.
Other calcs designed for specific conditions are available, which do not have the need for a known value of f.