62,783 research outputs found
A direct reduction procedure for gas densities determination of R143a from acoustic measurements
No full text
Determination of a vapor phase Helmholtz equation for 1,1,1-trifluoroethane (HFC-143a) from speed-of-sound measurements
No full textAcoustic Measurements of the Thermodynamic Temperature between the Triple Point of Mercury and 380 K
No full textWe have measured the differences between the Kelvin thermodynamic
temperature and the temperature of the International Temperature Scale of
1990 on nine isotherms between the triple point of mercury and 380 K, by
means of a primary acoustic thermometer. For the present measurements the
standard uncertainty of (T − T90) ranges from 0.9mK at 234K to 1.7mK at
380 K. The experimental method is based on the measurement of the
acoustic resonance frequencies of an argon-filled spherical cavity and the
microwave resonance frequencies of the same cavity when evacuated. The
present results agree within the remarkably small combined uncertainties
with both NIST acoustic thermometry ([1] Moldover M R et al 1999 J. Res.
Natl Inst. Stand. Technol. 104 11–46; [2] Strouse G F et al 2002 Progress in
primary acoustic thermometry at NIST: 273K to 505K 8th Temperature
Symp. (Chicago, 21–24 October 2002)) and UCL acoustic thermometry
([3] Ewing M B and Trusler J P M 2000 J. Chem. Thermodyn. 32 1229–55)
in the overlapping temperature range
Vapor phase acoustic measurements for R125 and development of a Helmoltz free energy equation
No full textChamps acoustiques en melanges gaz-vapeurs saturees : diffusion moleculaire et precondensation aux parois
No full textUn nouveau mod`ele pour d ́ecrire le mouvement acoustique dans des m ́elanges gazeux est pr ́esent ́e ici en partant
des ́equations fondamentales de l’hydrodynamique et de la thermodynamique, et en y associant des conditions
aux fronti`eres adapt ́ees pour d ́ecrire les ph ́enom`enes d’ ́evaporation et de condensation sur les parois quand un des
composants du m ́elange se trouve au voisinage de son point de saturation. Les solutions analytiques g ́en ́erales
de ces ́equations orent `a pr ́esent une description unifi ́ee de la propagation acoustique en espaces infinis, semi
infinis et confin ́es, loin de et dans les couches limites. Ces solutions tiennent compte des couplages forts entre
le mouvement acoustique et les processus de diusion de chaleur et de concentration, incluant les ph ́enom`enes
de pr ́econdensation sur les parois. Les r ́esultats th ́eoriques ainsi obtenus sont compar ́es `a ceux issus de mod`eles
propos ́es et d’exp ́eriences eectu ́ees par le pass ́e, mais ne susent toujours pas `a expliquer tous les r ́esultats
exp ́erimentaux disponibles dans la litt ́erature. Des exp ́eriences sont en cours de pr ́eparation, qui ont pour but de
valider et compl ́eter cette approche analytique par une caract ́erisation empirique de certains param`etres li ́es aux
propri ́et ́es physiques des gaz utilis ́es et `a l’ ́etat de surface des parois
Correlations among acoustic measurements of the Boltzmann constant
No full textWe review correlated uncertainties among the accurate determinations of the Boltzmann
constant kB that used the techniques of primary acoustic gas thermometry (AGT). We find
correlated uncertainty contributions from four sources: (1) the uncertain chemical and isotopic
compositions of the test gases that lead to an uncertain average molar mass, (2) measurements
of the temperature, (3) measurements of the shape and dimensions of the cavity resonators,
and (4) fitting acoustic resonance frequencies as a function of the pressure. Molar-massdependent
uncertainties are correlated among those measurements that used argon with
isotopic abundances determined using an isotopic standard prepared at the Korea Research
Institute of Standards and Science in 2006. Correlated, cavity-dependent uncertainties result
from using the same cavity for more than one measurement. Small, correlated uncertainties
propagate into all the AGT determinations of kB when acoustic resonance frequencies
are fit for kB using uncertain literature data for the Avogadro constant and for the thermal
conductivity and the higher acoustic virial coefficients of helium or argon
Speed of sound in gaseous cis-1,3,3,3-tetrafluoropropene (R1234ze(Z)) between 307 K and 420 K
No full textMeasurements of the speed of sound in gaseous cis-1,3,3,3-tetrafluoroprop-1-ene, (R1234ze(Z)), are pre- sented. The measurements were performed using a quasi-spherical acoustic resonator at temperatures between 307 K and 420 K and pressures up to 1.8 MPa. Ideal-gas heat capacities and acoustic virial coeffi- cients over the same temperature range were directly calculated from the results. The relative accuracy of our determinations of the speed of sound w ( p,T ) of R1234ze(Z) was approximately ±0.02%. The accuracy of the determination of the ideal gas heat capacity ratio γ0 ( T ) was approximately ±0.25%. These data were found to be mostly consistent with the predictions of a fundamental equation of state of R1234ze(Z)
Toward the realization of a primary low-pressure standard using a superconducting microwave resonator
No full textWe describe a primary gas pressure standard based on the measurement of the refractive index of helium gas using a microwave resonant cavity in the range between 500 Pa and 20 kPa. To operate in this range, the sensitivity of the microwave refractive gas manometer (MRGM) to low-pressure variations is substantially enhanced by a niobium coating of the resonator surface, which becomes superconducting at temperatures below 9 K, allowing one to achieve a frequency resolution of about 0.3 Hz at 5.2 GHz, corresponding to a pressure resolution below 3 mPa at 20 Pa. The determination of helium pressure requires precise thermometry but is favored by the remarkable accuracy achieved by ab initio calculations of the thermodynamic and electromagnetic properties of the gas. The overall standard uncertainty of the MRGM is estimated to be of the order of 0.04%, corresponding to 0.2 Pa at 500 and 8.1 Pa at 20 kPa, with major contributions from thermometry and the repeatability of microwave frequency measurements. A direct comparison of the pressures realized by the MRGM with the reference provided by a traceable quartz transducer shows relative pressure differences between 0.025% at 20 kPa and -1.4% at 500 Pa. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
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