Net Expansion Factor; K>100??
Net Expansion Factor; K>100??
(OP)
Hello All,
My brain's a little fuzzy this afternoon, but I'm running into a problem with Crane T.P. No. 410, pg. A-22 "Net Expansion factor Y for Compressible Flow..."
For my example:
P1 = 40 psig + 14.7 = 54.7 psia
P2 = 0.397 psig + 14.7 = 15.097 psia
DP = 39.603 psia
DP/P1 = 0.724
K = 752
Y = ???
The charts in Crane only go up to K = 100. Am I missing something?
Thanks again for your help.
My brain's a little fuzzy this afternoon, but I'm running into a problem with Crane T.P. No. 410, pg. A-22 "Net Expansion factor Y for Compressible Flow..."
For my example:
P1 = 40 psig + 14.7 = 54.7 psia
P2 = 0.397 psig + 14.7 = 15.097 psia
DP = 39.603 psia
DP/P1 = 0.724
K = 752
Y = ???
The charts in Crane only go up to K = 100. Am I missing something?
Thanks again for your help.





RE: Net Expansion Factor; K>100??
How did you come up with a K of 752?
Patricia Lougheed
******
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RE: Net Expansion Factor; K>100??
Largest diameter of pipe in system is 3.94 ID.
One section of pipe in the system is 330 ft of 2.067 ID pipe.
Beta = 2.067/3.94= 0.525
If Moody friction factor = 0.020, then:
K= 12*0.020*330/(2.067*0.525^4) = 497
Just this section alone has K greater than 100. Adding up the other sections similarly, K = 752.
Is there something I'm missing?
RE: Net Expansion Factor; K>100??
RE: Net Expansion Factor; K>100??
With compressible flow in a multiple diameter system it's always best to work in terms of the smallest diameter with these simple methods. That's where it will most likely choke anyway.
Good luck,
Latexman
RE: Net Expansion Factor; K>100??
I don't work much with compressible fluids, so I'm taking a swag here ... Based on the graphs on page A-22, it appears that for K>20, Y reaches a maximum value of 0.718 or 0.710. For a first round, try using that as your maximum.
Patricia Lougheed
******
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RE: Net Expansion Factor; K>100??
Thank you for your suggestion. Interestingly enough I did it the way you suggested, as well as breaking it up into nodes, and both results only differ by about 4% (though I could iterate further and get it a little closer).
Thanks for your help!
RE: Net Expansion Factor; K>100??
Good luck,
Latexman