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Viscosity of the binary mixture propane-isobutane in the gaseous state
Cornelia Küchenmeister, Eckhard Vogel, Jörg Baranski

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, hmix(0) and hmax(1), were deduced and used, including the coefficients of its pure components, hi(0) and hi(1), to derive values of the interaction viscosity in the limit of zero density, hij(0), 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 hij(0) were further used to calculate binary diffusion coefficients which were compared with data from the literature.

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