Isochoric Heat Capacities of Propane + Isobutane Mixtures at Temperatures from 280 to 420 K and at Pressures to 30 MPa

The isochoric heat capacity (cv ) and pressure–volume–temperature-composition (pvTx) properties were measured for propane+isobutane mixtures in the liquid phase and in the supercritical region. The expanded uncertainty (k =2) of temperature measurements is estimated to be ±13 mK, and that of pressure measurements is ±8 kPa. The expanded relative uncertainty for cv is ±3.2% for the liquid phase, increasing to ±4.8% for near-critical densities. The expanded uncertainty for density is estimated to be ±0.16%. The present measurements for {xC3H8 +(1−x)i-C4H10} with x =0.0, 0.498, 0.756, and 1.0, were obtained at 659 state points at temperatures from 270 to 420K and at pressures up to 30MPa. The experimental data were compared with a published equation of state.