Additional properties of a mixture about phasepy HOT 3 CLOSED

Hi, can you share your AGA8 Fortran code? Are you sure its giving you the residual properties?

from phasepy.

Hi!

Thanks for you interest in Phasepy.

The thermal derivatives properties (Entropy, Enthalpy, Cv, Cp and speed of sound) were just added recently to the package. After this enquiry I checked the functions and there is no bug in the functions (the relations are correctly coded). I used the following expressions:

There are several reasons that could explain the differences between the AGA8 package.

• In phasepy the thermal derivatives of the Helmholtz free energy are computed numerically (I tried different steps at your code and this didn't changed the results)
• Could you please confirm that the reported values from the Entropy and Enthalpy from AGA8 are computed in the (T,P,N) ensemble and that the reported value is the residual one.
• For the heat capacities it is my belief that the AGA8 package might be returning the total heat capacities (residual + ideal). Consider that the ideal contribution takes the values reported for methane (CpId = 35.315 # J / mol K and CvId = CpId - r # J / mol K, obtained from DIPPR 801), then the computed total isochoric and isobaric heat capacities are 27.01 and 35.46 J/mol K , respectively. Way closer to the reported values by AGA8. To complement this point, the reported isochoric and isobaric heat capacities on NIST for methane at 288K and 1 bar are 27.050 and 35.448 J / mol K.
• For the speed of sound calculation, the result can change considerably by means of the ideal gas contribution (CvId, CpId). Better results of this contribution can be obtained from the DIPPR 801 correlation. For example, as your mixture is mostly methane its reported value could be used (CpId = 35.315 # J / mol K and CvId = CpId - r # J / mol K). With those values the computed speed of sound is 387.097 m/s. This result is closer to the reported by AGA8.

It would be interesting to compare the source codes of both implementations!

I hope this help!

from phasepy.

Hi,

you are indeed correct and the AGA8 code is not reporting residual properties, I completely missed it from looking at the code.

the AGA8 implementation (at least for simple stuff) is public domain and you can find it here in 4 different languages:

https://github.com/usnistgov/AGA8

from phasepy.