Choke P2 Calculation
Choke P2 Calculation
(OP)
I am trying to solve a choke problem. I would like to solve for the downstream pressure if all other variables are known. I am collecting data from flow meters and pressure transmitters and want to compare the measured downstream pressure to the calculated downstream pressure to determine if the choke has eroded. I am trying to accomplish for both sonic and sub-sonic conditions.
The best equation I have located for the sub-sonic condition is attached. Does anyone know how to solve this equation for P2?
Or any other equation to accomplish the same?
Thanks for your help.
The best equation I have located for the sub-sonic condition is attached. Does anyone know how to solve this equation for P2?
Or any other equation to accomplish the same?
Thanks for your help.





RE: Choke P2 Calculation
Before a different equation could be recommended, I'd like more details on the process. Having a flow coefficient in the equation, implies there is a constriction of some kind, but what type?
If you have the measured downstream pressure as stated, why not solve for Qsc and compare that to the measured flow? I suspect you'd need to change the actual flow rate to the flow rate at standard conditions. or vice versa, but that seems much easier that solving for pdn.
Good luck,
Latexman
RE: Choke P2 Calculation
I am measureing the pressure upstream/downsteram of a choke. I am trying to determine how much the choke has erroded by comparing the measured downstream pressure to the calculated downstream pressure.
The problem with trying to do this with using the flow rate, is the pressure cut is across a choke, not an AGA orifice plate - so I think using the pressure is the way to go.
Can you point me in the right direction no the excel solver.
Thanks again.
RE: Choke P2 Calculation
Good luck,
Latexman
RE: Choke P2 Calculation
RE: Choke P2 Calculation
Tt / T = (1 + M^2(k - 1)/2)
pt / p = (1 + M^2(k - 1)/2)^(k/(k-1))
ht = (h + v^2/2)
Tt = (T + v^2/(2cp))
In my opinion, for known inlet condition such as stagnation temperature and pressure and knowing that that flow gets choked (M = 1), it should not be difficult to find out outlet conditions such as static temperature and pressure.
One can always reverse the problem and start with static temperature and pressure for the choked flow and try to find out inlet conditions such as stagnation temperature and pressure.
For outlet conditions, one can always use the ideal gas state equation pv = RT and density = 1/v to determine the mass flow rate at choked conditions -- m = density * v * A.
In my opinion, A needs to be known.
The above is valid for choked/sonic conditions. Similar approach can be taken for subsonic conditions.
Here is a URL for an online nozzle calculator that can speed up isentropic compressible flow calculations:
http://www.engineering-4e.com/calc5.htm
I do hope that my input will be of some help to you.
http://www.engineering-4e.com
RE: Choke P2 Calculation
Note: The nozzle performance plot should be a general plot even though it makes a reference to the inlet stagnation conditions of 1,500 [K] and 10 [atm] when the working fluid is air!
http://www.engineering-4e.com