Help with Thermodynamics equations

[Ángel Martin]

at last some progress - I've figured out the method used to calculate the discrepancies, which it really is nothing more than applying the definitions in a form that is compatible with the equation of state available:

Dis(F) = R.T.Ln(Z) + ITG{(P – R.T/V).dV} at constant T ; and
Dis(S) = - d[Dis(F)]/dT ; at constant V

The first equation involves a couple of integrals of the type ITG {dx/(ax+b)} and ITG { dx/(ax+b)^2}. Integration limits are the quid, as they define the origins used for the different properties. The final expression is very close to the reversed-engineered formula, except a term of the equation where an error was coded.

The second equation is a bear to handle, laborious but conceptually not complicated - all you need is your theory of derivatives and pay close attention to the details. There seems to be at least a couple of ways to write the final expression (that I have come up with) but neither can be reconciled with the formula I reversed-engineered from the code... so I'm assuming there were errors in the original program.

I also got rid of the "forced" origins for enthalpy and entropy. In summary, the results are now very close to the substance charts within the range of applicability - next step is to figure out the valid ranges!

I removed the MOD files from this thread, will post an update in the software section when ready.

If only I had documented all this when i wrote the program 30 years ago...

Cheers,
ÁM