Isochoric p-ρ-T and heat capacity Cv measurements on {xC3H8+(1-x)i-C4H10, x≈0.7, 0.3} from 200 to 400 K at pressures to 35 MPa

The p-rho-T relationships and constant volume heat capacity C-v were measured for binary hydrocarbon mixtures containing propane (C3H8) and isobutane (i-C4H10). Temperatures ranged from 200 K to 400 K for p-rho-T and from 203 K to 342 K for C-v with pressures up to 35 MPa for both measurements. Measurements of p-rho-T and C-v were conducted on liquid samples with the mole fraction compositions {xC(3)H(8) + (1 - x)i-C4H10} for x = 0.7006 and x: = 0.2979. Determinations of saturated-liquid densities were made by extrapolating each isochore to the saturated-liquid pressure and determining the temperature and density at the intersection. Published p-rho-T data are in good agreement with this study. For the p-rho-T apparatus, the uncertainty of the temperature is 0.03 K, and for pressure it is 0.01% at p > 3 MPa and 0.05% at p < 3 MPa. The principal source of uncertainty in density is the cell volume (similar to 28.5 cm(3)) with a standard uncertainty of 0.003 cm(3). When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor k = 2 and thus a two-standard-deviation estimate) of the density measurements is estimated to be 0.05%. For the C-v apparatus, the uncertainty is 0.002 K for the temperature rise and 0.2% for the change-of-volume work, which is the principal source of uncertainty. The expanded relative uncertainty of the heat capacity measurements is estimated to be 0.7%.