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-   -   Help! Stagnation Pressure (http://www.cfd-online.com/Forums/fluent/34053-help-stagnation-pressure.html)

Leila June 27, 2004 10:10

Help! Stagnation Pressure
 
Hello

Dealing with a reasonably long pipe (about 7 km long) and a diameter of about 0.5m with a compressible fluid flowing through it and the pressures and, temperatures known at both head and tail end (about 1400 psia at the inlet and temperatures not too far from the STD condition) how should I estimate stagnation pressure needed for the inlet pressure boundary condition?

I have an idea. Please tell me whether I'm right or not.

I think I can guess a flow rate at the inlet, therefore knowing the diameter of the pipe I can find a velocity at the inlet. Up to here regarding to the inlet conditions I can find Mach number so stagnation pressure can be found. Am I right? I do not know much about fluid mechanics. Please help me. By the way I can't consider the flow adiabatic because of the long length of the pipe. Regards


ROOZBEH June 28, 2004 03:13

Re: Help! Stagnation Pressure
 
Hi; For a compressible flow, you can not use incompressible steady form of continuity equation, and consequently can not find the velocity from known area and flow rate!

You can refer to fluid mechanics 2, and find formulations to relate Mach number and flow rate.

Then, you can use M and P(static) and Cp/Cv to find inlet total pressure.

hope this help you

ROOZBEH

Hareesh K T June 28, 2004 07:32

Re: Help! Stagnation Pressure
 
Hi, Your calcualtion is still valid. with rho= pstatic/R.Tstatic now, v=flow rate/(rho* area)

and p total = pstatc + v**2/(2*g)

Since the above calculation is based just at your inlet condition, there is as such no assumption we are making about the non-adiabatic behaviour of long pipe. hope this will help.


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