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Moody Diagram

A Moody diagram that can be used to estimate friction coefficients

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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:

moody diagram

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:

moody diagram

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