Compressible Flow Basic Question
Compressible Flow Basic Question
(OP)
Is there any way that I can calculate the properties of flow(in a pipe) after choke?
Let's assume I have a long horizontal pipe and the flow could be Adiabatic or Isothermal. Because of huge flowrate I have a choke somewhere at the middle of the pipe(and I can calculate that). But what would be the pressure, temperature, and density at the end of pipe which is atmospheric pressure?
The answer to this question can also help me to visualize the phenomenon of double choke which is not rare in discharge side of PSV's.
Thanks
Let's assume I have a long horizontal pipe and the flow could be Adiabatic or Isothermal. Because of huge flowrate I have a choke somewhere at the middle of the pipe(and I can calculate that). But what would be the pressure, temperature, and density at the end of pipe which is atmospheric pressure?
The answer to this question can also help me to visualize the phenomenon of double choke which is not rare in discharge side of PSV's.
Thanks





RE: Compressible Flow Basic Question
if you model as isothermal tout=tin and pout (as you write) = patm
for adiabatic Hout = Hin,
you may consider (or not) the contribute of kinetic energy,
see the other posts discussing this topic in Safety Relief Valve forum,
or am I misunderstanding the question ?
RE: Compressible Flow Basic Question
If you're speaking about a vent line, gas velocity inside should be sufficiently high to approximate the thermal behaviour to adiabatic ... in this way you can estimate the outlet temperature by means of an isenthalpic. However, be aware of the gas velocity: if it's very high (e.g. 0.3 Mach or higher) the cooling effect could be higher than pure isenthalpic ... in this case you can have an estimation with the Fanno Flow.
In both cases, above suggestions only work for a first estimation, but it could be enough for a first conceptual design.
Good luck.
Matt17
Process Engineer
RE: Compressible Flow Basic Question
Good luck,
Latexman
RE: Compressible Flow Basic Question
Matt17
Process Engineer
RE: Compressible Flow Basic Question
Obviously my understanding is conventional. I am very anxious to hear more.
best wishes,
sshep
RE: Compressible Flow Basic Question
I found a portion of my answer in the below link:
http://www.eng-tips.com/viewthread.cfm?qid=100632
As zdas04 (Mechanical)says:
"One point that is missing is that sonic flow is not sustainable in straight pipe. Period. If you enter a pipe at sonic velocity (downstream of a choke for example), friction effects will begin to reduce the velocity immediately and the duration of M=1.0 is meters, not kilometers or even tens of meters."
So, it means after a choke, within a certain distance(how can we calculate this distance?)the flow drops to subsonic again, and again opportunity for another choke if situations is suitable.
RE: Compressible Flow Basic Question
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Compressible Flow Basic Question