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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:

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 d h = 0.01 (m) and Reynolds number Re = 10 7 - the relative rougness can be calculated as

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 .

An 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. Involving velocity, pressure, density and temperature as functions of space and time.

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