The latest version of the equivalent length method given
in Crane Technical Paper 410 (Crane Co. 1991) requires the use of two friction
factors. The first is the actual friction factor for flow in the straight pipe
(f ), and the second is a standard friction factor for the particular fitting(fT)
hL = Kfv2/2g
where
Kf = 4f(Leq/D)
The value of f is determined from the Colebrook equation
f =0.0625/[log(3.7D/E)]2
where
E is the pipe roughness (0.0018 in., 0.045mm) for
commercial steel pipe.
The Crane paper gives fT for a
wide variety of fittings, valves, etc. This method gives satisfactory results
for high turbulence levels (e.g., high Reynolds number) but is
less accurate at low Reynolds number. This method
provides a better estimate for the effect of geometry, but does not reflect any
Reynolds number dependence.
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