Relative Roughness

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

relative roughness 1Relative roughness, abbreviated as k, is a dimensionless number of a pipe that is a ratio of the surface roughness to the diameter of the pipe.

Since the relative roughness is a dimensionless number, both the absolute roughness and diameter must carry the same units.  The relative roughness is used with the Moody Diagram when solving for the friction factor of a system. 

 

Formulas that use Relative Roughness

\(\large{ k = \frac {\epsilon} {d} }\)   

Where:

\(\large{ k }\) = relative roughness

\(\large{ \epsilon }\)  (Greek symbol epsilon) = absolute roughness

\(\large{ d }\) = pipe inside diameter

 

Relative Roughness CALCULATOR

 

Tags: Equations for Friction