The friction theory (FT) approach relates the viscosity of a fluid to its equation of state (EoS), and it is known to give good results for a large number of compounds over wide ranges of temperature and pressure. Previous FT versions were restricted to use EoS of the van der Waals type, i.e., EoS explicitly consisting of a repulsive and an attractive term, which limited the number of usable EoS as well as the accuracy of the viscosity predictions. In this work, the restriction is removed by means of a pragmatic generalized definition of repulsive and attractive terms based on the internal pressure concept. As a result, the FT theory can be extended to practically all types of EoS, from theoretical ones (e.g., EoS based on thermostatistical or renormalization theories) to the highly accurate empirical reference EoS. In combination with the later, the FT is shown to represent experimental viscosity data for several fluids, including water, with an accuracy as high as that required for reference models. Additionally, some relevant phenomena, such as the critical anomaly, appear to follow naturally from the physics already built into the EoS.

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Abstract

The original Redlich-Kwong equation, together with the usual quadratic mixing rules, has been used to calculate phase diagrams for binary fluid mixtures and to classify them according to the system of van Konynenburg and Scott. Global phase diagrams (maps) showing the extent of the various phase diagram classes in the space of the Redlich-Kwong parameters are presented. While for molecules of equal size the results are very similar to those known for the van der Waals equation, the maps become topologically different for molecules of unequal sizes; some complicated phase diagram classes, which otherwise cover small domains on the maps or cannot be found at all, become quite important.

Brown's characteristic curves (also known as ideal curves) describe states at which one thermodynamic property of a real pure fluid matches that of an ideal gas; these curves can be used for testing the extrapolation behavior of equations of state. In this work, some characteristic curves are computed directlywithout recourse to an equation of statefor some pair potentials by Monte Carlo computer simulation. The potentials used are an ab initio potential for argon, the 1-center Lennard-Jones potential, and a softer pair potential whose short-range part is in accordance with quantum mechanical predictions. The influence of the short-distance repulsion on the characteristic curves is found to be significant even in the 10−100 MPa pressure range.

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