An apparatus based on a microwave re-entrant cavity resonator, originally built for accurate measurements of the dielectric permittivity of natural gas mixtures, was refurbished and extensively characterized. This was done to enable the future investigation of phase equilibria and (p, ρ, T, x) behaviour of fluid mixtures utilizing the present experimental technique. Vacuum resonance frequencies and Q-factors of the resonator's modes were modelled using both analytic and finite element methods, and found to compare well with experimental values. The finite element models helped to identify two whispering gallery-type modes not previously reported for such cavity geometries. The models also predict distributions of the electric and magnetic fields in the re-entrant cavity resonator useful for identifying regions in the cavity more sensitive to the presence of a liquid. Following the resonator's characterisation, its ability to measure dew points was tested using a gravimetrically prepared (0.2501 argon +
A microwave
re-entrant cavity resonator was used for the determination
of dew points, dielectric permittivities, and molar densities of two
gravimetrically prepared (argon + carbon dioxide) mixtures, with carbon
dioxide mole fractions of 0.9495 and 0.7509. Isochoric dew-point measurements
of a (0.0505 argon + 0.9495 carbon dioxide) mixture were carried out
over the temperature range from (257 to 291) K at pressures between
(2.4 and 6.0) MPa. The measured dew-point pressures were consistent
with the predictions of the recently developed multiparameter equation
of state optimized for combustion gases (EOS-CG) within 0.35 %.
Measurements of each mixture’s dielectric permittivity in the
single-phase gas region over the temperature range from (273.2 to
313.3) K at pressures up to 6.5 MPa were used to determine the mixture
molar densities at the same conditions. The method used to determine
mixture molar densities from microwave-cavity measurements is based
on an inversion of the polarizability mixing rule developed by Harvey
and Prausnitz. The microwave-determined mixture densities had relative
deviations from values measured for the same mixture with a two-sinker
magnetic-suspension densimeter of 0.3 % or less. The new mixture density
data agree within 0.37 % of predictions made using the EOS-CG and
help identify literature data sets that should receive lower weighting
in future model development.
Accurate measurements of carbon monoxide's electrical properties were carried out at high pressure for the first time enabling stringent comparisons with theoretical values calculated ab initio. Dielectric permittivity measurements were conducted utilising a microwave re-entrant cavity resonator over the temperature range from (255 to 313) K and at pressures up to 8 MPa with a relative combined expanded uncertainty (k=2) less than or equal to 52 ppm. The new data enable carbon monoxide's molar polarizability to be correlated within 0.5 %, significantly improving upon existing literature data, which have a relative scatter of about 10 %. The measured molecular polarizability and electric dipole moment of carbon monoxide were determined to be 2.176×10 C m J and 0.107 D. Literature values from ab initio calculations for these properties are within 0.28 % and 3.9 %, respectively, of the measured quantities. Moreover, our measurement of the electric dipole moment at finite temperature agrees within 2.2 % with the value derived from accurate spectroscopic measurements for the ground rovibrational state. The second dielectric virial coefficient of carbon monoxide was determined experimentally for the first time to be b =(1.015±0.044) cm mol , which compares reasonably with ab initio estimates.
Accurate dew-point, dielectric permittivity, and density measurements of two binary (H 2 + CO 2 ) mixtures with CO 2 mole fractions of 0.94638 and 0.74576 were carried out utilizing an apparatus that employs a microwave re-entrant cavity resonator. Isochoric dew-point measurements were conducted at pressures up to 7.1 MPa and temperatures from T = (249.55 to 296.61) K for the (0.05362 H 2 + 0.94638 CO 2 ) mixture and between T = (251.63 and 280.44) K for the (0.25424 H 2 + 0.74576 CO 2 ) mixture. The combined expanded uncertainty with a level of confidence of approximately 95% (k = 2) in dew-point temperature and pressure ranged between (0.016 and 0.065) K and (0.0041 and 0.0177) MPa, respectively. Within 2.5%, the new data were consistent with the predictions of the GERG-2008 equation of state. Measurements of dielectric permittivity in the single-phase vapor region over the temperature range from (273.06 to 313.18) K at pressures up to 8.2 MPa and in the vicinity of the phase boundary were conducted to determine mixture molar densities by applying a method based on the polarizability mixing rule developed by Harvey and Prausnitz. The microwave-determined mixture densities near 5 MPa agree within 0.33% of reported values measured with a precision twosinker magnetic suspension densimeter; mixture densities near 8 MPa agree within 1.33% of values calculated with the GERG-2008 equation of state.
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