Viscosity measurements of (CH4 + C3H8 + CO2) mixtures at temperatures between (203 and 420) K and pressures between (3 and 31) MPa

Abstract In this work, viscosity measurements of the ternary mixture [0.6511CH 4  + 0.0808C 3 H 8  + 0.2681CO 2 ] were made over the temperature range (203–420) K and at pressures up to 31 MPa, with a combined overall standard uncertainty of 2.5%. The presence of CO 2 or propane in the ternary mixture was found to always increase the viscosity relative to the constituent binary mixtures with larger differences observed at the highest density conditions: adding 26.8% mole fraction of CO 2 to the binary mixture [ x CH 4  + (1− x )C 3 H 8 ] with x  = 0.8888, increased the viscosity by up to 45%. Similarly, adding 8.1% mole fraction of propane to the binary mixture [ x CH 4  + (1− x )CO 2 ] with x  = 0.7084, increased the viscosity by up to 23%; in this case, while the effect was apparent at lower temperatures, it was negligible at 370 K and above. The ternary mixture data were compared with the predictions of five models: corresponding states based approaches (ECS, SuperTRAPP and PFCT), the LBC model used widely by petroleum engineers, and a model (LJ) based on molecular dynamics simulations of Lennard Jones fluids. The relative deviations of the measured viscosities from those calculated by the five models exhibited a similar, systematic dependence on density, with stronger and larger systematic relative deviations observed at the lowest temperatures. The average absolute deviations from the measured viscosities were 2.5%, 6.4%, 8.0%, 4.2% and 3.9% for the ECS, ST, PFCT, LBC and LJ models respectively, with the ECS model providing a better representation of the data over the entire range. The present study reveals how well various engineering models can describe the viscosity of a multi-component mixture under supercritical conditions, which are of increasing interest in the energy industrial sector.