Is there a way to infer isentropic temperature coefficient

[rotw]

Hello,

I have gas properties available from SRK or PR equation of state for mixtures such as
Entropy, enthalpy, Cp, Cv, isentropic volume exponent, density, compressibility.

Question: Is there a way to infer the 'isentropic temperature exponent' from combination of the above properties (by way of a direct formula)?

Objective is to not have to deal with derivatives and all the pain that comes along with them.


Other question:
In Prode properties is there direct access to these properties via DLL call from Fortran?

Thanks

Life is not about waiting for the storm to pass. It's about learning dance in the rain.

 

[pmover]

perhaps the attached will help you . . . notes from a long time ago

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1570392261/tips/Hand_Analysis_of_Isentropic_Temperature_Calc_fd6af7.pdf[/url]

 

[rotw]

pmover,

Thanks a lot for sharing your notes, I appreciate this very much. I had a look at the method, which I think is a method that would help finding the isentropic temperature of a compression process by proceeding iteratively. In my case, I do not have two end points (start and end point of compression path). It is more that I need to find gas properties (secondary) of a thermodynamic state based on pressure, temperature and gas composition.

Actually, I find a way to this.
There are directs formula that for a given (pressure, temperature and gas mixture) establish relashionship:

kv : isentropic volume exponent = F(Temperature, Molecular weight, Speed of sound, Compressibility)
kt : isentropic temperature expoment = G(Pressure, Temperature, Speed of Sound, Molecular weight, Isobaric Specific Heat, Isochoric Specific Heat, Density)

Out of lazyness, I wont write the complete formulas; if someone needs this, please let me know.

Life is not about waiting for the storm to pass. It's about learning dance in the rain.

 

[pmover]

rotw,

yes, you are correct in that the isentropic temp is found by interation using an EOS. the notes provided use BWR EOS. my initial search for the code written resulted in only my original notes. 2-hrs later i found the code.

not sure why the two values you seek are needed, but an internet search returned this link/posting

https://www.eng-tips.com/viewthread.cfm?qid=283850

good luck.

 

[rotw]

pmover,

I need the two values in order to calculate centrifugal compressor parameters (head, efficiency, etc.). I never use k ratio (=Cp/Cv) for this purpose because it is innacurate for real gases ; in this respect, ideal/perfect gas is just particular case of real gas case (k=Cp/Cv=kt=kv) so formulas work too.

Thanks for the link!

Life is not about waiting for the storm to pass. It's about learning dance in the rain.

 

[PaoloPemi]

yes, you can call Prode Properties from FORTRAN if you wish to verify your derivatives,
another software which comes to mind is, of course, Refprop,
also, you may find useful Bridgeman's tables (for unusual properties)

Paolo

 

[rotw]

Thanks Paolo. Will take a look at Bridgeman's tables which I did not know of.

Life is not about waiting for the storm to pass. It's about learning dance in the rain.