Moody chart

The Moody diagram is an important one for fluidic applications diagram was created empirically in 1944 by the American engineer Lewis F. Moody. It allows you to calculate the pressure drop in a straight pipe with fully developed laminar or turbulent flow.

It shows in logarithmic scale the connection between the unitless sizes of the friction coefficient λ, the Reynolds number and the relative roughness ( Rz = average surface roughness, and d the diameter of the tube ).

Constance border and border for hydraulically smooth behavior

The Moody diagram shows a clear difference between the flow behavior of laminar or turbulent flow. For turbulent flow, a constant limit is seen from which the coefficient of friction for a fixed relative roughness with increasing Reynolds number remains constant ( the coefficient of friction is independent of velocity and viscosity of the appropriate range of Reynolds number).

Similarly, a limit for hydraulically smooth behavior is noticeable: The coefficient of friction here for a certain Reynolds number has a minimum value that is not exceeded even for a very low average surface roughness. In this area ( the grooves of the pipe wall remain entirely within the strong frictional viscous sub- layer with the thickness).