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Low Flow in Pipes- posted in Ankur's blog


Compressible Flow Through A Short Pipe

compressible flow

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#1 akstapp


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Posted 13 July 2018 - 05:19 PM



I need to calculate the flow through a 2" piece of pipe containing gas phase benzene at 200F and 15psig.  At the end of the 2" pipe is a 16" flare header that runs at a pressure of 1 psig.  The pipe is SCH 40 carbon steel, new, and is about 30' long.  I am attempting to use the compressible flow formulas in Crane TP 410 to accomplish this.  I have tried the complete isothermal equation, simplified isothermal equation, Weymouth and Panhandle (which really don't apply), and modified Darcy equation, but I seem to be getting different answers depending on whether I am calculating a mass flow rate vs a volumetric flow rate, and I cannot find the error in my calculation anywhere.  I know that this flow is not really isothermal, but I need some sort of approximation, so that's where I am starting.  In particular Equations 1-28 and 1-29 should result in the same answer, but even those don't match up!  Any help appreciated.  Please see attached spreadsheet for calcs.

#2 Art Montemayor

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Posted 13 July 2018 - 05:34 PM

There are no spreadsheet calculations submitted.


You are either not entering the correct command in your thread submittal or something is wrong with the Forum's submittal instructions.


Please tell us if anything is going wrong on your end so that we can fix it.


Also: It looks like your attempts to calculate for a gaseous Benzene flow at 30 psia & 200 oF are based on wrong information.   The Benzene fluid is a liquid at the stated condition.  Read and study my spreadsheet submittal.


Attached File  Benzene Thermo Properties - 30psia.xlsx   17.85KB   11 downloads

#3 akstapp


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Posted 14 July 2018 - 09:26 AM



Thanks for the reply.  I went asking around about this, and it would appear that what is actually flowing through the pipe are various non-condensables off a benzene separation tower.  Should have checked the vapor pressure curve first thing, and I would have known to ask the question (and saved a lot of time).  I think I should be able to sort it out from here.


PS - I am not sure why the spreadsheet didn't attach, but I would almost guarantee an error on my part.


Best Regards,


#4 breizh


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Posted 14 July 2018 - 11:18 PM

Hi ,

Let us know if you find difficulties for your calculation, Art and I and probably others have published spreadsheets to perform such calculation , use the search engine in this forum to support your work.


Good luck

Breizh .

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