Nist Refprop 9 ((full)) -

NIST REFPROP 9 (Reference Fluid Thermodynamic and Transport Properties Database) is a legacy version of the gold-standard software used by engineers and scientists to calculate the thermophysical properties of pure fluids and mixtures. While it has been largely superseded by Version 10.0, it remains a common citation in academic research and industrial simulations.  Key Functions & Capabilities 

It doesn't rely on simple, "back-of-the-napkin" calculations. Instead, it utilizes the most accurate physical models currently available, primarily the Helgerud-Mixon Equation of State (EOS) for pure fluids. This ensures that the data you pull—whether it's density, heat capacity, or surface tension—is as close to the experimental reality as physically possible. nist refprop 9

2. Custom Fluid Mixtures

To define a mixture, create a file with the .MIX extension specifying the mole fractions. For example: [Methane, 0.85; Ethane, 0.10; Propane, 0.05]. Then call REFPROP on that mixture name. NIST REFPROP 9 (Reference Fluid Thermodynamic and Transport

5. Working with Mixtures

Mixtures require GERG-2008 (or simpler mixing rules). Instead, it utilizes the most accurate physical models

Conclusion

Key Features of NIST REFPROP 9