Moody Diagram
Calculate fluid flow friction coefficients from a Moody diagram.
There are two definitions of the friction factor
 SI based
 Imperial based
The SI based friction factor is four times larger than the Imperial based friction factor.
SI based Moody Diagram
The Moody friction factor  λ (or f)  is used in the DarcyWeisbach major loss equation. The coefficient can be estimated with the diagram below:
If the flow is transient  2300 < Re < 4000  the flow varies between laminar and turbulent flow and the friction coefiicient is not possible to determine. The friction factor can usually be interpolated between the laminar value at Re = 2300 and the turbulent value at Re = 4000 .
Example  SI based Friction Factor
For a PVC pipe with absolute roughness k = 0.0015 10^{3} (m) , hydraulic diameter d _{ h } = 0.01 (m) and Reynolds number Re = 10 ^{ 7 }  the relative rougness can be calculated as
r = k / d _{ h }
= (0.0015 10^{3} m) / (0.01 m)
= 0.00015
From the diagram above, with the relative rougness and the Reynolds number  the friction factor can be estimated to aprox. 0.013 .
An Alternative Moody Diagram
A very nice Moody diagram in pdfformat from Glasgow College of Nautical Studies can be found here:
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Fluid Mechanics
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