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The speed of sound in ethanol and benzene was measured over the temperature range of (253.2 to 353.2) K with pressures up to 30 MPa utilizing the double-path length pulse-echo technique. The speed of sound system was calibrated with pure water at temperatures between T = (274.15 and 353.15) K and ambient pressure. The reference equation of state for ordinary water represents the calibration data within the uncertainty of the equation of 0.005 %. The relative combined expanded uncertainty (k = 2) in speed of sound was 0.025 % for ethanol and 0.036 % for benzene. Comparisons of the measured speed of sound data for ethanol and benzene with values calculated from the equations of state as implemented as substance specific reference in the NIST REFPROP database are presented. Both equations do not represent the experimental data within their uncertainties. However, relative deviations of the experimental data from values calculated with the equations of state are within the uncertainties reported for the equations, which were 1.0 % for ethanol and 0.5 % for benzene. For ethanol relative deviations were between (−0.53 and 0.19) %, and for benzene relative deviations of (−0.43 to 0.37) % were observed.

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The CO 2 Mix CO 2 -rich mix effect on the accurate mod operation of University o measurement physical prop © 2 Selection and

The speed of sound of two (argon + carbon dioxide) mixtures was measured over the temperature range from (275 to 500) K with pressures up to 8 MPa utilizing a spherical acoustic resonator. The compositions of the gravimetrically prepared mixtures were (0.50104 and 0.74981) mole fraction carbon dioxide. The vibrational relaxation of pure carbon dioxide led to high sound absorption, which significantly impeded the sound-speed measurements on carbon dioxide and its mixtures; pre-condensation may have also affected the results for some measurements near the dew line. Thus, in contrast to the standard operating procedure for speed-of-sound measurements with a spherical resonator, non-radial resonances at lower frequencies were taken into account. Still, the data show a comparatively large scatter, and the usual repeatability of this general type of instrument could not be realized with the present measurements. Nonetheless, the average relative combined expanded uncertainty (k = 2) in speed of sound ranged from (0.042 to 0.056)% for both mixtures, with individual state-point uncertainties increasing to 0.1%. These uncertainties are adequate for our intended purpose of evaluating thermodynamic models. The results are compared to a Helmholtz energy equation of state for carbon capture and storage applications; relative deviations of (−0.64 to 0.08)% for the (0.49896 argon + 0.50104 carbon dioxide) mixture, and of (−1.52 to 0.77)% for the (0.25019 argon + 0.74981 carbon dioxide) mixture were observed.