Assuming laminar, in compressible flow with negligible friction, head, or thermal losses ,
From the Bernoulli equation
V = ( 2P/d )^0.5
[ or sq rt ( 2P/d ) or
sq rt ( 2*g*h) .....(P= d*g*h) ]
V = velocity
P = differential pressure
d = density
Area = A = pi(r^2)
Flowrate = Q = VA
If you have a section of pipe and know only the diameter and just the gage pressure, you cannot determine the flow rate.
If you have a short piece of pipe discharging to the atmosphere and you know what the fluid is, the diameter and the pressure entering the pipe, then the flow rate can be determined from the velocity formula. V =(2g H)^1/2 where H is the pressure converted to the equivalent height of the fluid. For water it is 2.31 Ft per psi. Multiply the velocity by the area to get the volumetric rate Q=AV in cubic ft per min. The actual flow will be dimnished a little depending on the smoothness contour at the pipe entrance.
For a long piece of pipe discharging to the atmosphere the available head at the entrance will be diminished by the dynamic friction losses of the flow. These losses depend on the velocity, friction factor and equivalent length of the piping.
If the only pressure for the pipe is that of a pitometer, that value will be the velocity pressure of the fluid. Use that value for H in the velocity formula, but reduce it 20% because the velocity profile will be maximun in the center of flow where the pitot tube is located and minimum along the walls.
The above works for liquid turbulant snf lsminsr flows, but for laminar flows the velocity pressure canl be quite low.
For compressible flows like gasses, the formulas are a bit more involved.
You haven't given enough information to get a flowrate from.
Need an allowable pressure drop per foot, or per 100 ft as a minimum, and the pipe material would help also.
The procedure and equations are not simple and there are 3 or 4 different methods to use.
To do a pipe flow calculation you need at a minimum pipe diameter, a pipe length and the pressure drop over that length.
If you are referring to a stub with circular opening of given diameter
and negligible length, say so.
Approximations are available.
http://www.engineeringtoolbox.com/bernou...
are there imperical formulas? thanks
