The friction theory (f-theory) for viscosity modeling

In this work, a new theory for viscosity modeling based on friction concept s of classical mechanics and the Van der Waals theory of fluids is presente d. The fundamental difference between this theory and other available theor ies is the fact that the viscosity of dense fluids, which characterizes pur e shear flow, is approached as a mechanical, rather than as a transport, pr operty. Thus, separating the total viscosity into a dilute gas term and a f riction term, a connection between the Van der Waals repulsive and attracti ve pressure terms and the Amontons-Coulomb friction law can be established. Then, using only two or three temperature-dependent friction coefficients, this theory links the residual friction term to the Van der Waals repulsiv e and attractive pressure terms. As a result, a rather simple cubic equatio n of state (EOS) can be used as a basis for obtaining highly accurate model ing of the viscosity of fluids from low to extreme high pressures. Since th e cubic equations of state are well tuned for accurate pressure-temperature performance, and pressure is the main mechanical property linked to fricti on, the obtained accuracy does not depend on the density performance of the equation. To illustrate the capabilities of the theory, two well-known cub ic equations of state are used to model the viscosity of n-alkanes from met hane to n-decane, as well as some of their binary mixtures and, in most cas es, absolute average deviations within experimental uncertainty are obtaine d. (C) 2000 Elsevier Science B.V. All rights reserved.