Moody Diagram

Moody Diagram 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:

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 = 0.1 (m) and Reynolds number Re = 107 - the relative rougness can be calculated as 

k/Rh = (0.0015 10-3 m) / (0.02 m) 

       = 0.000075

From the diagram above, with the relative rougness and the Reynolds number - the friction factor can be estimated to aprox. 0.011

Alternative Moody Diagram

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

moody diagram

Related Topics

  • Fluid Mechanics - The study of fluids - liquids and gases. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time.

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