Reduced Friction Factor = Φ

Quantitative dimensionless measure  $//<![CDATA[ \begin{array}{l}\Phi\end{array} //]]>$ of the friction forces between fluid pipe flow and inner pipe walls based on Darcy–Weisbach equation.

where 

Unlike Darcy friction factor  $//<![CDATA[ \begin{array}{l}f({\rm Re})\end{array} //]]>$ the Reduced Friction Factor  $//<![CDATA[ \begin{array}{l}\Phi({\rm Re})\end{array} //]]>$ does not have a singularity at  $//<![CDATA[ \begin{array}{l}{\rm Re} \rightarrow 0\end{array} //]]>$ and finds wider use in computations.

Reduced Friction Factor  $//<![CDATA[ \begin{array}{l}\Phi({\rm Re})\end{array} //]]>$ is always positive  $//<![CDATA[ \begin{array}{l}\Phi({\rm Re}) > 0\end{array} //]]>$ .
It takes unit value for laminar flow $//<![CDATA[ \begin{array}{l}{\rm Re} \leq 2,100 \ \Rightarrow \Phi = 1\end{array} //]]>$ and then starts building up towards developing a linear growth for high turbulent flow:  $//<![CDATA[ \begin{array}{l}{\rm Re} \rightarrow \infty \ \Rightarrow \Phi \sim {\rm Re}\end{array} //]]>$

See also

Physics / Fluid Dynamics / Pipe Flow Dynamics / Darcy–Weisbach equation 

[ Darcy friction factor (f) ]