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Sonic Flow Pipe Exit

Question asked by Dave Frenk on Jul 23, 2011
Latest reply on Jul 25, 2011 by Rich Bayless

Perhaps someone has an answer to this problem I have. After running multiple flow simulations on a piping discharge from a relief valve the results show the gas velocity greater than mach 1, which cannot happen. See link below.

 

http://www.pipeflowcalculations.com/pipeflowtheory/maximum-flow-of-gases.php

 

 

Here are the conditions I'm using:

 

-methane

-pipe size 3", discharge from 3" pipe after an elbow

-inlet pressure (initial condition): 1670 psi

-inlet temp (initial condition): 135F

-outlet static pressure (boundary condition): 14.7 psi

 

The resulting mach number at the exit is 4.3, using the high mach flow option.

 

I'm not sure if I have the boundary conditions setup incorrectly or what else I can change.

 

Goal NameUnitValueAveraged ValueMinimum ValueMaximum Value
Static pressure inlet [lbf/in^2]1498.371497.491496.981498.37
Static pressure outlet [lbf/in^2]14.7014.7014.7014.70
Mass flow [lb/s]-28.63-28.64-28.65-28.63
Velocity outlet [ft/s]1791.141789.881788.921791.14
Velocity inlet [ft/s]637.21637.70637.21638.05
Mach number outlet [ ]4.344.344.344.34

 

I appreciate any feedback. I can send the solid models if anyone is interested.

 

Dave

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