Reference Correlation of the Viscosity of Argon.

This paper presents a new wide-ranging reference correlation for the viscosity of argon, incorporating recent ab initio dilute-gas calculations and critically evaluated experimental data. The correlation is designed to be used with a high-accuracy Helmholtz equation of state that extends from the triple point (83.8058 K) to 700 K, and at pressures up to 1000 MPa. The estimated uncertainty of the correlation based on comparisons with the best experimental data indicate that the uncertainty for the gas at pressures from zero to 0.1 MPa for temperatures from 202 K to 394 K is 0.076% (at k = 2), the uncertainty of the best experimental data, offering a significant improvement over the current reference equation that has an uncertainty in this region of 0.5%. A zero-density correlation based on ab-initio values is incorporated that is valid over a temperature range between 84 K and 10 000 K and has an uncertainty of 0.12% (at the 95% confidence level). The estimated uncertainty for moderate pressures from 1 MPa to 100 MPa is 1% for temperatures from roughly 195 K to 300 K, rising to 2% at 175 K. For the high-pressure region, the estimated uncertainty of the correlation is about 2% for temperatures between 175 K and 308 K at pressures from 100 MPa to 606 MPa. For temperatures from 308 K to 700 K at pressures to 5.2 GPa, the equation has an estimated uncertainty of 10%. The estimated uncertainty in the liquid phase at pressures up to 34 MPa is 3%. The correlation behaves in a physically reasonable manner over the full range of applicability of the EOS, although uncertainties may be higher in regions where data were not available for full validation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10765-025-03603-8.