Viscosity of the binary mixture propane - isobutane in the gaseous state

Abstract

Results of new relative high-precision viscosity measurements on the binary gaseous mixture propane-isobutane are reported. Eight series were carried out in an all-quartz oscillating-disk viscometer for an equimolar mixture from 297 K to 627 K and for densities between 0.009 and 0.042 mol l -1 . The uncertainty is estimated to be ±0.15% at ambient temperature increasing up to ±0.30% at the highest temperatures. Isothermal values were analysed with a density series for the viscosity in which only a linear contribution is included. The zero-density and initial-density viscosity coefficients for the equimolar mixture, η (0) mix and η (1) mix , were deduced and used, including the coefficients of its pure components, η (0) i and η (1) i , to derive values of the interaction viscosity in the limit of zero density, η (0) if , as a function of temperature. Then the Enskog-Thorne equations for hard-sphere systems were applied after a modification to describe the composition and density dependence of the viscosity of the real moderately dense gaseous mixture propane-isobutane. The values of η (0) if were further used to calculate binary diffusion coefficients which were compared with data from the literature.