Moody Diagram
A Moody diagram that can be used to estimate friction coefficients
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 Darcy-Weisbach 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 dh = 0.01 (m) and Reynolds number Re = 107 - the relative rougness can be calculated as
r = k / dh
= (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.
Alternative Moody Diagram
A very nice Moody diagram in pdf-format from Glasgow College of Nautical Studies can be found here:
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