1 reply to this topic

[apeli]

Dear Experts,

I would like to know some basic rule of thumb in selecting Fluid package or property package.
Currently I am following this

• Peng rob for light hydrocarbons upto C8 (Naptha),
• SRK for higher hydro carbon
• NRTL for polar
• NRTL-RK for mixture of polar +non polar
• Elect NRTL for electrolyte

I would like to confirm is these assumptions are right and also I need to know the other assumptions one should take care while selecting packages
All your expert comments are highly appreciated.

Thanks
Eli

[PaoloPemi]

that depends from the thermodynamic models available in your software,
for each model there are variants which may extend the area of application,
as example consider alpha functions in PR or SRK models,
it has been verified that standard alpha function in SRK fits better (than PR) fluids with low acentric factor (for example CH4) while PR (standard alpha) works better for fluids with higher acentric factors,
however for both PR and SRK different alpha correlations have been proposed and the above rule is no longer true (both EOS can work well with a large number of fluids).
Now consider another problem, the large errors in liquid densities calculated with SRK and PR,
corrections as that proposed by Peneloux or methods as Corresponding State Liquid Density (COSTALD) can reduce these errors,
a different approach is that of Prode Properties where SRK and PR parameters are calculated by fitting vapor pressures, enthalpies and liquid densities, as result you get relatively small errors also with fluids as water, this gives in my opinion much more flexibility (compared with traditional approach).
Another important point to consider is the operating condition (pressure, temperature) , you may prefer a EOS with complex mixing rules (Huron Vidal, Wong Sandler etc.) for polar fluids at high t, p.
Finally there are models as CPA and SAFT which may provide advantages (over standard models) in many areas of application.

Edited by PaoloPemi, 03 June 2012 - 10:51 AM.