Progress towards an acoustic determination of the Boltzmann constant at CEM-UVa

Abstract

An acoustic gas thermometer was used to achieve a determination of the Boltzmann constant, k B , using a misaligned stainless steel (316L) spherical cavity with an internal volume of approximately 268 cm 3 . Measurements of the speed of sound while the cavity is filled with argon at the temperature of the triple point of water, 273.16 K, and at different pressures between 78.2 kPa and 0.9 MPa, were used to extrapolate the value of the speed of sound in argon at zero pressure. The internal volume of the resonator was accurately determined by measuring microwave resonance frequencies at the same temperature and pressure conditions as for the acoustic measurements. The measurements were taken at pressures from 78.2 kPa up to 901.3 kPa, and at 273.16 K. As the results of the measurements, we determined k B = (1.380 644 1 ± 0.000 022 1) × 10 −23 J K −1 which means a relative standard uncertainty of 16 parts in 10 6 .

Heat capacities and acoustic virial coefficients for a synthetic coal mine methane mixture by speed of sound measurements at T = (273.16 and 250.00) K

“…Once the experimental data have been fitted to equation 3, heat capacities and, virial acoustic coefficients are calculated through equations (4) to (8). The standard uncertainties of these quantities have been evaluated according to the following equations: deviations are always lower than 0.11%, deviation which even decreases at lower pressures.…”

“…Details may be found in a previous work where this technique was used to determine the Boltzmann constant [8].…”

“…As stated at the beginning of this section, measurements of speed of sound may provide a great deal of useful thermodynamic information. Equations (1) to (8)…”

“…Comparison between calculated values of the isochoric and isobaric heat capacities (Cv pg and Cp pg ) and the adiabatic coefficient (γ pg ) at zero pressure and the acoustic virial coefficients (βa, γa) obtained from equations(7) and(8) and, those calculated using the GERG-2008 EoS for the synthetic CMM mixture at T = 250 K.…”

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

“…We have performed the geometrical characterization by means of the first three TM1n modes and the first three TE1n modes, getting three wellresolved components in all the cases thanks to the high electrical conductivity of the gold coating. This significantly reduces the resonance half-widths, compared with the broad microwave doublets previously measured with the misaligned cavity [2]. An Agilent Network…”