Accurate Density Measurements on Ternary Mixtures (Carbon Dioxide + Nitrogen + Argon) at Temperatures from (323.15 to 423.15) K with Pressures from (3 to 31) MPa using a Single-Sinker Densimeter

The densities of two ternary mixtures (0.900 carbon dioxide + 0.050 nitrogen + 0.050 argon and 0.950 carbon dioxide + 0.040 nitrogen + 0.010 argon in mole fraction) were measured at temperatures from (323.15 to 423.15) K with pressures from (3 to 31) MPa using a single-sinker magnetic suspension densimeter. The expanded measurement uncertainties (k = 2) were 35 mK for temperature, 3.4 kPa for pressure, and 0.033 % for density. Mixture samples were prepared gravimetrically with the expanded uncertainty (k = 2) in composition 0.001 mole fraction. With all of the measurement and composition effects considered, the expanded combined uncertainty (k = 2) in the density determination was generally within 0.2 % except at thermal states at the vicinity of the critical point near the Widom line. Relative deviations of the experimental data from the GERG-2008 equation of state (EOS), a Helmholtz energy model for natural gas mixtures, and from the EOS-CG, another new Helmholtz energy model for humid gases and fluid m...