A New Free Volume Model for Dynamic Viscosity and Density of Dense Fluids Versus Pressure and Temperature

Abstract This article presents a model based on the free volume concept, which describes the variations of dynamic viscosity and density versus temperature and pressure for the dense fluids (density > 200 kg · m−3). This model involves 6 constants for each pure compound: 3 for viscosity and 4 for density (1 constant is common to both quantities). Moreover if the viscosity and the density are known at a pressure and temperature of reference, it is sufficient to use 4 constants per pure compound. If the density is assumed to be known the model fits the viscosity data with an average absolute deviation of 3.8% for 3297 data corresponding to 41 very different pure compounds (alkanes, alkylbenzenes, cycloalkanes, alcohols, carbon dioxide, refrigerants). If the pressure is lower than 110MPa the average absolute deviation is 2.8% for viscosity (2977 points). The model gives also good results for water (3.6%). If the density is unknown, for pressures lower than 110MPa the model represents viscosity with an average absolute deviation of 3.5% and for the density the average absolute deviation is 1.5%.