Moody chart

[martin ruben]

Dear Friends,
Could anybody tell me why the Moody chart from TP 410 ed. 2009 is different from 1999 ed.?
Thank You

[Marty Thompson]

Go here for a discussion

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Perry's pipe friction loss equation has a 4 coefficient, and the chart is 4 time less than Crane # 410. Now Crane #410's chart is 400% larger, but their friction loss equation drops the 4 coefficient. Therefore, both ways produce the same numbers in the end.


The graphs in Crane #410 (A-24 and A-25) are for Moody Friction factor, which is 4 times Fanning friction factor. That is, f = 64/Re is Moody and f = 16/Re is Fanning.

Be careful. It is easy to mix the two and calculate 400% greater (or 25% less) head loss. The calculation for head loss in feet is:

using Moody Friction factor -
h(friction) = f(M) * (L/D) * v^2 / (2 * g)

using Fanning Friction factor -
h(friction) = 4*f(F) * (L/D) * v^2 / (2 * g)

where,
f(M) = Moody Friction factor
f(F) = Fanning Friction factor
L = length in feet
D = pipe inside diameter in feet
v = velocity in ft/s
g = 32.174 ft/s^2, acceleration due to gravity

The Colebrook-White equation is an iterative method that calculates Fanning friction factor.
f(F)^2 = 1 / ( -4 * Log(eps / (3.7 * D) + 1.256 / (Re * √f(F) )

where,
eps = pipe roughness in feet
Re = Reynold's number

[martin ruben]

Thank You.