# 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 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 d

*and Reynolds number*

_{h}= 0.01 (m)*Re = 10*- the relative rougness can be calculated as

^{7}*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*.

### Alternative Moody Diagram

A very nice Moody diagram in pdf-format from Glasgow College of Nautical Studies can be found here: