Viscosity Correlation of CO₂, HFCs, HFOs, and Their Mixtures: Review of Experimental Data and Modeling Techniques

This work proposes reference viscosity corrections that combine the Peng−Robinson (PR), Volume−Translated PR (VTPR), and Cubic−Plus−Association (CPA) Equation of State (EoS) with the friction theory (FT) model for carbon dioxide (CO₂), hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), and their binary and ternary mixtures. The viscosity value is divided into the diluent gas term and residual friction term consisting of van der Waals repulsion and attraction forces. The established FT model employs the temperature−dependent coefficients connecting the friction forces to the Amontons-Coulomb equation. Additionally, correlations between these FT coefficients and existing experimental viscosity data were established, and the binary interaction parameters (BIPs) employed in deriving vdW mixing rules were also computed for the binary blends consisting of HFOs. The PR + FT, VTPR + FT, and CPA + FT models can reasonably reproduce the viscosity for unary compounds and match the experiment viscosities with the measurement uncertainties. However, PR and CPA EoS will substantially deviate from the reference experimental densities at high temperatures and pressures. At the same time, the VTPR + VdW + FT model has a good predictive ability by comparing the experimental viscosity data of the binary and ternary potential refrigerant mixtures. These findings are expected to provide a satisfactory and appropriate theory for investigating the properties of heat and mass transfer in refrigeration systems.