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
r = k / d h
= (0.0015 10 -3 m) / (0.01 m)
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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