# Hydraulic Diameter

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Hydraulic diameter, abbreviated as $$d_h$$, is normally used when the flow is in non-circular pipe or tubes and channels.  Circular pipe has the same pressure drop of a rectangular channel but a greater average velocity.  Square or rectangular pipes have a greater weight and a greater pressure drop compared with a circular pipe with the same section.  For established shapes, various calculations are linked below.

 $$\large{ d_h = \frac { 4 \;A } { P } }$$ Where: $$\large{ d_h }$$ = hydraulic diameter $$\large{ A }$$ = cross-section area $$\large{ P }$$ = cross-section wetting perimeter