Moody Diagram

A Moody diagram that can be used 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:

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:

Related Topics

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

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