Moody chart

In engineering, the Moody chart or Moody diagram (also Stanton diagram) is a graph in non-dimensional form that relates the Darcy–Weisbach friction factor fD, Reynolds number Re, and surface roughness for fully developed flow in a circular pipe.

It can be used to predict pressure drop or flow rate down such a pipe.

It adapts the work of Hunter Rouse[2] but uses the more practical choice of coordinates employed by R. J. S. Pigott,[3] whose work was based upon an analysis of some 10,000 experiments from various sources.

[4] Measurements of fluid flow in artificially roughened pipes by J. Nikuradse[5] were at the time too recent to include in Pigott's chart.

The chart's purpose was to provide a graphical representation of the function of C. F. Colebrook in collaboration with C. M. White,[6] which provided a practical form of transition curve to bridge the transition zone between smooth and rough pipes, the region of incomplete turbulence.

Moody's team used the available data (including that of Nikuradse) to show that fluid flow in rough pipes could be described by four dimensionless quantities: Reynolds number, pressure loss coefficient, diameter ratio of the pipe and the relative roughness of the pipe.

They then produced a single plot which showed that all of these collapsed onto a series of lines, now known as the Moody chart.

This dimensionless chart is used to work out pressure drop,

Head loss can be calculated using the Darcy–Weisbach equation in which the Darcy friction factor

The Moody chart can be divided into two regimes of flow: laminar and turbulent.

< ~3000), roughness has no discernible effect, and the Darcy–Weisbach friction factor

was determined analytically by Poiseuille: For the turbulent flow regime, the relationship between the friction factor

, equal to one fourth the Darcy-Weisbach friction factor