Viscosity of a [xCH4 + (1 − x)C3H8] mixture with x = 0.8888 at temperatures between (203 and 424) K and pressures between (2 and 31) MPa

Abstract Viscosity measurements of [ x CH 4  + (1 −  x )C 3 H 8 ] with x  = 0.8888 are reported for temperatures between (203 and 424) K and pressures between (2 and 31) MPa using a vibrating wire viscometer clamped at both ends and operating in a steady-state mode. Reliable operation over this range of conditions required a detailed set of calibration and validation measurements using pure reference fluids. Most previous viscosity determinations with vibrating wire instruments have determined the important vacuum damping parameter Δ 0 from a single measurement and assumed it was temperature independent. Here we extended the calibration procedure beyond measurements in vacuum and helium (to determine the wire radius) to include low density methane ( ρ  ≤ 1.2 kg·m −3 ) from (223 to 420) K. Using viscosity values for these reference fluids linked to ab initio calculations revealed Δ 0 had a temperature dependence below about 350 K, increasing from 2.04 × 10 −5 at 372 K to 5.79 × 10 −5 at 223 K. Subsequent validation measurements with pure N 2, He and CH 4 at pressures to 30 MPa confirmed the estimated standard relative uncertainty in viscosity of less 2.5%. The binary mixture measurements were compared with literature data and the predictions of four models including two corresponding states based approaches (ECS and ST), a semi-theoretical model (VW) based on an extended hard-sphere scheme derived from the Enskog equation, and a model (LJ) based on molecular dynamics simulations of Lennard Jones fluids. The ECS and ST models exhibited systematic relative deviations from the data of up to −5% at 150 kg·m −3 and –10% at 300 kg·m −3 , respectively. The LJ and VW models provided far better (