See Surface roughness for more data on typical values for various materials and processing conditions.

Interpolated full-range model

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The most popular full-range model of Darcy friction factor is:

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LaTeX Math Inline

body	--uriencoded--f_%7BCW%7D(\mbox%7BRe%7D, \epsilon)

LaTeX Math Inline

body	--uriencoded--\displaystyle k = \frac%7B f_%7BCW%7D( \mbox%7BRe%7D =4,000, \, \epsilon) -0.03048%7D%7B1,900%7D

interpolation multiplier between laminar and turbulent flow regimes

Churchill full-range model

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For many practical applications the Churchill correlation provides a fair (< 2 % accuracy and improving towards laminar flow) estimation of Darcy friction factor

LaTeX Math Inline

body	f

for all pipe flow regimes:

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