A simple model for viscosity based on residual entropy scaling is proposed in this study. The thermodynamic model applied to calculate residual entropy is the Groupe Europeén de Recherches Gazieres (GERG) 2008 equation of state. Dimensionless pure-component viscosity as a function of residual entropy is correlated by a third-order polynomial. The component specific coefficients of the polynomial are adjusted to pure-component viscosity data. Averaged over all pure-component data points, deviation accounts to only 3.21%. Viscosity for mixtures is predicted by using the mole fraction weighted average of the purecomponent coefficients in the polynomial. Excellent results are obtained for natural gas mixtures. The averaged deviation for all 2021 evaluated natural gas data points is as low as 3.09%. Compared to alternative mixture viscosity models, this purely predictive approach is among the best performing models for most studied natural gas mixtures and sour gas samples. The proposed approach is not limited to natural gas viscosity, that is, methane-rich multi-component systems. Accurate predictions are also presented for binary and ternary mixtures over wide temperature and pressure ranges.

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Molecular dynamics simulations are reported for the thermodynamic properties of n-m Lennard-Jones fluids, where n = 10 and 12, and m = 5 and 6. Results are reported for the thermal expansion coefficient, isothermal and adiabatic compressibilities, isobaric and isochoric heat capacities, Joule-Thomson coefficient, and speed of sound at supercritical conditions covering a wide range of fluid densities. The thermodynamic criteria for maxima∕minima in the isochoric and isobaric heat capacities are identified and the simulation results are also compared with calculations from Lennard-Jones equations of state. The Johnson et al. [Mol. Phys. 78, 591 (1993)] equation of state can be used to reproduce all heat capacity phenomena reported [T. M. Yigzawe and R. J. Sadus, J. Chem. Phys. 138, 194502 (2013)] from molecular dynamics simulations for the 12-6 Lennard-Jones potential. Significantly, these calculations and molecular dynamics results for other n-m Lennard-Jones potentials support the existence of Cp minima at supercritical conditions. The values of n and m also have a significant influence on many other thermodynamic properties.