Updated determination of the molar gas constantRby acoustic measurements in argon at UVa-CEM

Abstract

A new determination of the molar gas constant was performed from measurements of the speed of sound in argon at the triple point of water and extrapolation to zero pressure. A new resonant cavity was used. This is a triaxial ellipsoid whose walls are gold-coated steel and which is divided into two identical halves that are bolted and sealed with an O-ring. Microwave and electroacoustic traducers are located in the northern and southern parts of the cavity, respectively, so that measurements of microwave and acoustic frequencies are carried out in the same experiment. Measurements were taken at pressures from 600 kPa to 60 kPa and at 273.16 K. The internal equivalent radius of the cavity was accurately determined by microwave measurements and the first four radial symmetric acoustic modes were simultaneously measured and used to calculate the speed of sound. The improvements made using the new cavity have reduced by half the main contributions to the uncertainty due to the radius determination using microwave measurements which amounts to 4.7 parts in 10 6 and the acoustic measurements, 4.4 parts in 10 6 , where the main contribution (3.7 parts in 10 6) is the relative excess half-widths associated with the limit of our acoustic model, compared with our previous measurements. As a result of all the improvements with the new cavity and the measurements performed, we determined the molar gas constant R = (8.314449  0.000056) J•K-1 •mol-1 which corresponds to a relative standard uncertainty of 6.7 parts in 10 6. The value reported in this paper lies-1.3 parts 2 in 10 6 below the recommended value of CODATA 2014, although still within the range consistent with it.

The Boltzmann project

“…In addition, the recent low-uncertainty determinations INRiM-15 [25], PTB-17 [52], NIM/NIST-17 [85], NPL-17 [46], LNE-17 [26], NIM-17 [27], UVa/CEM-17 [29] and NIST-17 [87] are listed in table 3 with uncertainty values in italics. With the DCGT result PTB-17 [52] and the noise result NIM/NIST-17 [85], the second CCT condition [2], demanding an independent method with a relative standard uncertainty below 3 × 10 −6 , is fulfilled.…”

“…The 2017 measurement by Universidad de Valladolid (UVa) in collaboration with CEM used argon gas in a gold-coated stainless steel, quasi-spherical resonator with a radius of 40 mm [29]. Several features of the measurement were unique within the project [10].…”

Wide-Ranging Reference Correlations for Dilute Gas Transport Properties Based onAb InitioCalculations and Viscosity Ratio Measurements

“…Dilute gas transport properties serve as a basis for predicting transport properties at high pressures and are important for calibrating scientific apparatus and other measurement devices. 1, 2 For example, accurate viscosities are crucial for the calibration of certain low-flow meters for mass spectrometers, 3,4 and precise thermal conductivities at low densities are required for acoustic thermometry, determination of the universal gas constant, 5,6 and were important to recent (and final) measurements of the Boltzmann constant prior to its redefinition. 7 Several experimental methods are available for measuring viscosities accurately under low density conditions, including rotating-body viscometers, [8][9][10] oscillating-disk viscometers [11][12][13][14] and capillary viscometers.…”

Speed of sound for three binary (CH4 + H2) mixtures from p = (0.5 up to 20) MPa at T = (273.16 to 375) K

“…Both the acoustic cavity and the transducer designs are based on those used by Trusler, Wakeham and Zarari [19][20][21] to measure pure methane and related mixtures. Further details concerning the setup may be found in [22][23][24], while only a brief description is given here. spring of electrical contact, 6. screw, 7. cover plate.…”