6. Recommendations for estimating the viscosity of pressurized liquids

A set of five models was presented for calculating the viscosity of liquids under pressure: the Lucas model, the model derived from the Tait equation, the model derived from the theory of hard spheres, the free volume model and the friction model. The Lucas model calculates viscosity as a function of reduced pressure and reduced temperature, with an accuracy of around 10% when tested on a set of fluids. The model derived from Tait's equation is more of an interpolation model for experimental data. In its extension proposed by Kanti et al. which only requires knowledge of a viscosity point, accuracy remains low, at around 10%. The theory of smooth hard spheres provides the best results, but it should be pointed out that in this model, nine parameters are required to determine the viscosity of each pure body. The use of this model requires precise knowledge of density, as small differences...