Helmholtz Scaling: An Alternative Approach to Calculate Viscosity with the PCP-SAFT Equation of State

Abstract

We propose an alternative approach to calculate viscosity, based on the Rosenfeld scaling theory, which can be applied to pure components and their mixtures in a wide range of temperatures, pressures, and compositions. The Helmholtz scaling (A-scaling) applies the Chapman–Enskog relation, an Ansatz function, and the PCP-SAFT equation of state to predict the viscosity. Although it was implemented with the PCP-SAFT EoS, A-scaling has potential to be coupled with other EoS. Substances from n-alkanes, alcohols, aromatics, ethers, chlorofluorocarbons, carbon dioxide, and nitrogen were used to obtain five parameters to better correlate the experimental viscosity data. We tested the A-scaling performance of predicting the viscosity of 33 binary mixtures at different temperature and pressure conditions. For pure components, the minimum and maximum average absolute deviations (AADs) were 1.51 and 6.53%, respectively. Meanwhile, for mixtures, 0.70 and 23.95% were the lowest and highest values. By comparing this method with the successful and consolidated entropy scaling, it was found that AADs in most of the pure substances and mixtures were lower for A-scaling. Thus, since it is suitable for polar, nonpolar, and hydrogen-bonding substances, A-scaling covers many substances for industry applications, with no usage of adjustable parameters to predict viscosity for mixtures.