Wetted Perimeter

Wetting perimeter, abbreviated as P_w, is the portion of the channel or pipe that is in contact with the fluid flowing.

 

 

 

 

 

 

 

 

 

Wetting perimeter of a circular pipe formula
\(\large{ P_w =  cos^{-1} \left( 1 - \frac{h}{r} \right) \; d }\)
Symbol	English	Metric
\(\large{ P_w }\) = wetting perimeter	\(\large{ in }\)	\(\large{ mm }\)
\(\large{ d }\) = outside diameter	\(\large{ in }\)	\(\large{ mm }\)
\(\large{ h }\) = fluid depth	\(\large{ in }\)	\(\large{ mm }\)
\(\large{ r }\) = radius	\(\large{ in }\)	\(\large{ mm }\)

 

 

 

 

 

 

 

 

 

 

 

Wetting perimeter of a Rectangular Channel formula
\(\large{ P_w =  b + 2 \; h  }\)
Symbol	English	Metric
\(\large{ P_w }\) = wetting perimeter	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ b }\) = bottom width	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ h }\) = fluid depth	\(\large{ ft }\)	\(\large{ m }\)

 

Wetting perimeter of a Trapezoidal Channel formula
\(\large{ P_w =  b + 2 \; \left(  \left(  \frac{t \;-\;b}{2}  \right)^2  + h^2  \right)^\frac{1}{2}   }\)
Symbol	English	Metric
\(\large{ P_w }\) = wetting perimeter	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ b }\) = bottom width of liquid	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ t }\) = top width of liquid	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ h }\) = fluid depth	\(\large{ ft }\)	\(\large{ m }\)

 

Wetting perimeter of a Triangle Channel formula
\(\large{ P_w =  2 \; h \; \left( 1 + z^2 \right)^\frac{1}{2}   }\)
Symbol	English	Metric
\(\large{ P_w }\) = wetting perimeter	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ h }\) = fluid depth	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ z }\) = horiz. side slope	\(\large{ ft }\)	\(\large{ m }\)