Cp/Cv correction in Hysys
Cp/Cv correction in Hysys
(OP)
In Hysys simulator application, the Specific Heat Ratio shown for streams is incorrect. There is a formuala for calculating the correct Cp/Cv values. Would anybody out there know what this correct formula be. Thanks very much.





RE: Cp/Cv correction in Hysys
Is it incorrect every time, for every gas and every gas mixture?
Have you called Hyprotech to discuss this with them?
Thanks!
Pete
RE: Cp/Cv correction in Hysys
Worth checking...
Regards,
Bob
RE: Cp/Cv correction in Hysys
You can calculate the 'ideal' value by the following formula:
Cp/Cv (ideal) = Cp / (Cp - R)
where Cp = molar heat capacity of gas stream (kJ/kmolK)
R = universal gas constant = 8.314 kJ/kmolK
I suggest (although cannot confirm) that you use the ideal value in most formulae (e.g. PSV sizing) since these formulae are often derived with some 'ideal' assumptions.
If in doubt, use the value which gives the most conservative result.
RE: Cp/Cv correction in Hysys
We are finding that less experienced engineers are using the 'real' Cp/Cv data in datasheets sent to vendors for purchase. For RV's this is less conservative but not necessarily unsafe - it depends on the vendor sizing calculations, margins, whether they use HYSYS and are aware of this change.
Quoting both values to the vendor could cause confusion so I'd support Will48's suggestion to use the Cp/(Cp-R) on datasheets.