Hello
I am encountering the following issue:
The capacity of a 12" pipe at 0.05 slope, is 3575 gpm, which means that 1500 gpm will not fill the pipe. In other words, the pipe will not be full at 1500 gpm. If that's the case, I wonder why does WaterCad calculates the velocity within the pipe by dividing 1500 gpm by the FULL AREA of the pipe as opposed to dividing 1500 gpm by the actual area that the fluid actually fills.
According to my calculations the partial area is 0.032015 m2 and the full area is 0.07258 m2. Therefore, the velocity should be 2.95 m/s. However WaterCad gives 1.35 m/s.
This calculation also affects the computation of the friction losses.
thanks
Vic.
WaterGEMS is a pressure pipe model which means that the calculations are based on a pipe flowing full.
If you want to calculate velocity in a partly full pipe, you need a model that solves the partial full pipe equations such as SewerCAD or SewerGEMS.
Answer Verified By: Sushma Choure