Kr
Kr provides ideal gas thermodynamic properties for krypton valid over the temperature range from 200 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 146.323 kJ/kmol-K at 298.15 K and 101.3 kPa.
Thermal conductivity data are from:
"Reference Handbook of Thermal Conductivity of Liquids and Gases, Vargaftik et al., 1994, CRC Press
These data are provided in the range from 25 K to 5000 K.
Viscosity data are from:
"A Reference Correlation for the Viscosity of Krypton From Entropy Scaling",
Sofia Polychroniadou, Konstantinos D. Antoniadis, Marc J. Assael and Ian H. Bell
International Journal of Thermophysics (2022) 43:6
https://doi.org/10.1007/s10765-021-02927-5
These data are provided in the range from 70 K to 5000 K
Note that Ne provides thermodynamic properties assuming ideal gas behavior. Use Krypton to provide real fluid properties in the subcooled, saturated mixture, and superheated regimes.