Ar
Ar provides ideal gas thermodynamic properties for argon valid over the temperature range from 100 K to 6000 K based on the property information in McBride et al. (2002).
Bonnie J. McBride, Michael J. Zehe, and Sanford Gordon
"NASA Glenn Coefficients for Calculating Thermodynamic Properties of Individual Species"
NASA/TP-2002-211556, Sept. 2002
https://www.grc.nasa.gov/WWW/CEAWeb/
The reference state for specific enthalpy is 0 at 25 C. The reference state for specific entropy is 154.837 at 298.15 K and 101.3 kPa
Thermal conductivity data were fit from data in:
"Reference Handbook of Thermal Conductivity of Liquids and Gases, Vargaftik et al., 1994, CRC Press and applicable for temperatures between 100 K and 6000 K.
Viscosity is from the ideal gas contribution reported in:
E.W. Lemmon and R.T. Jacobsen
"Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air",
International Journal of Thermophysics, Vol. 25, No. 1, January 2004, pp. 21-69
Note that Ar provides thermodynamic properties assuming ideal gas behavior. Use Argon to provide real fluid properties in the subcooled, saturated mixture, and superheated regimes.