PSV two-phase HEM vs. API OMEGA vs HNE... 3

[mdepeche]

problem : PSV sizing for two phase (vapor+liquid) flow for HC mixtures

comment : I observe quite large differences 20/25% and more with different methods as HEM (API Omega) HEM (rigorous) HNE and HNE-DS, not sure which is the most accurate, In some cases HNE and HNE-DS return reduced areas (which seems in agreement with the description of these methods), API OMEGA (HEM with simplified parameters) shows large variations compared with rigorous HEM etc.
All calc's done with PRODE PROPERTIES , verified with proprietary software (Farris etc.)

question : in these cases (different methods giving different results) should I select the largest area ? (which is my rule)

 

[apetri]

I think the problem is about which method do apply,
I would not consider the differences in different variants, for example in API OMEGA (which is a HEM with simplified parameters) vs. the rigorous HEM included in PRODE PROPERTIES,
the point is that HNE models can give (in some cases) very different results and being included in standards (see the case of HNE-DS which is a HNE with simplified parameters and possibly included in ISO 4126) it is difficult to judge when adopt a reduced area or not,
that is not an easy question to answer,
personally I feel safe with HEM
(which in general is more conservativa than HNE)
but you may find different opinions.

 

[mdepeche]

thanks,
I suppose I should do that (i.e. choose the conservative approach)
altough costs are a important factor for final decision.

 

[Latexman]

IMO, there is a lot of uncertainty in two phase flow methods despite the amount of research done the past 50 years. I laugh when I see two significant digits from a two phase method. So go conservative; think along the lines of using 2-3X the calculated pressure drop to ensure your design will work every time.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.