# Wetted Perimeter

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics  Wetting perimeter, abbreviated as P_w, is the portion of the channel or pipe that is in contact with the fluid flowing.

## Wetting perimeter formula

 $$\large{ P_w = \frac{ A_c }{ r_h } }$$

### Where:

 Units English Metric $$\large{ P_w }$$ = wetting perimeter $$\large{ ft }$$ $$\large{ m }$$ $$\large{ A_c }$$ = area cross-section of flow $$\large{ ft^2 }$$ $$\large{ m^2 }$$ $$\large{ r_h }$$ = hydraulic radius $$\large{ ft }$$ $$\large{ m }$$

## Related Wetted perimeter formulas

 $$\large{ P_w = 2 \; h \; \sqrt {1 + z^2 } }$$ (hydraulic radius) $$\large{ P_w = r \; \theta }$$ (Hydraulic Radius of a Partially Full Pipe (Less than Half Full)) $$\large{ P_w = 2 \; \pi \; r - r \; \theta }$$ (Hydraulic Radius of a Partially Full Pipe (More than Half Full))

### Where:

$$\large{ P_w }$$ = wetting perimeter

$$\large{ \theta }$$   (Greek symbol theta) = degree

$$\large{ h }$$ = depth of fluid

$$\large{ \pi }$$ = Pi

$$\large{ r }$$ = radius

$$\large{ z }$$ = width of channel slope Tags: Hydraulic Equations