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Hem Vs. Hne For Two Phase Flow Psv Design / Rating

hem hne two phase flow design rating psv prode

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#1 frpe

frpe

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Posted 26 September 2014 - 11:27 AM

I have some doubts about the selection of HEM (Homogeneous Equilibrium Model)

vs. HNE (Homogeneous Non-equilibrium Model)  model in PRODE

with ISPF() macro in Excel for PSV design / rating.
I have read that HNE should give more accurate results (compared with HEM)

when liquid fraction is close to 1.0
while in general HEM is more conservative...
is that true ?
Can you comment ?
Thanks.



#2 marchem

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Posted 26 September 2014 - 01:09 PM

yes,

according many tests HNE  is more accurate (than HEM)

when liquid fraction is close to 1.0,

HEM near bubble point (liquid fraction 1.0)

predicts a very low speed of sound (and critical mass flux)

while HNE introduces a correction for non-equilibrium,

there are many papers discussing this but

you can easily compare the two models from the Excel page

distributed with Prode Properties.

with Prode you can also evaluate the speed of sound

(in liquid and two phase flow) predicted by HEM at different fractions,

 

for a mixture of C3 0.3 C7 0.7 P 10 bar.a

liquid fraction 0.98 T 366.7 K , model Peng Robinson

the macro =StrMSS(1) returns 62.82 m/s

 

while at liquid fraction 0.5 T 432.7 K

the macro =StrMSS(1) returns 117.29 m/s

 

as reference the speed of sound predicted

by Peng Robinson at 10 Bar.a 364 K

for liquid phase is 543.79 m/s

 

hoping this helps.



#3 bponcet

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Posted 06 October 2014 - 07:11 AM

usually I prefer HEM which I expect to be more conservative

as shows in marchen examples...






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