Determination of the Relative Permittivity and Density within the Gas Phase and Liquid Volume Fraction Formed within the Two-Phase Region for (0.4026 CH4 + 0.5974 C3H8) with a Radio Frequency Re-entrant Cavity

The gas-phase relative electric permittivities, densities, and liquid drop out volumes within the two-phase envelope have been determined from measurements of the resonance frequency of the lowest order inductive-capacitance mode of a re-entrant cavity for (0.4026 CH4 + 0.5974 C3H8); the dew temperatures between (315.5 and 340.4) K that correspond to dew pressures of (2.87 to 6.83) MPa for this mixture along with a description of the apparatus were reported by Kandil et al. (J. Chem. Thermodyn. 2005, 37, 684-691). The relative permittivity of the gas was determined with an uncertainty of 0.01 %. These results differed by between -(0.02 and 0.4) % from estimates obtained from the correlation reported by Harvey and Lemmon (Int. J. Thermophys. 2005, 26, 31-46) and the precise measurements of Schmidt and Moldover (Int. J. Thermophys. 2003, 24, 375- 403) for the pure components when the Oster (J. Am. Chem. Soc. 1946, 68, 2036-2041) mixing rule for total molar polarizabilities was applied. Gas densities were obtained from the relative electric permittivity with an estimated uncertainty of +/- 0.8 %, and the results lie within +/- 1.5 % of the density estimated from a cubic equation of state including crossover. The relationship between the volume of liquid in the cavity and the measured resonance frequency was established by calibration with octane. This calibration was then used to determine the liquid volume fractions, in the two-phase region, from the resonance frequency, over the range of (0.5 to 7) cm(3) in a total system volume of about 54 cm(3). The liquid volume fractions have an estimated expanded uncertainty of 0.01. The measured liquid volume fractions agree within the expanded uncertainty with estimates obtained from the Peng-Robinson cubic equation of state with volume translation.