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Li Xing, X.J. Feng, Ming-Hao Si, Jintao Zhang, Hong Lin, Keith Gillis, Michael Moldover
Abstract
We review recent determinations of the Boltzmann constant kB and the differences T-T90 that used cylindrical acoustic gas thermometry (c-AGT). These determinations measured the acoustic resonances frequencies of argon gas enclosed by metal-walled, cylindrical cavities. (Here, T is the thermodynamic temperature and T90 is the temperature measured on the International Temperature Scale ITS-90.) In the range 234 K to 303 K, the standard uncertainty of c-AGT ranges from 1.9×10^(-6) T to 2.6×10^(-6) T. This uncertainty is much smaller than the errors in ITS-90; therefore, c-AGT can help improve ITS-90. Moreover, we are extending c-AGT up to 1358 K. With increasing temperatures, c-AGT becomes advantageous relative to AGT based quasi-spherical cavities because long cylindrical cavities: (1) naturally fit into cylindrical heat pipes or multi-shelled thermostats, (2) provide the immersion required by transfer temperature standards such as long-stemmed platinum resistance thermometers, and (3) have more useful, low-frequency acoustic resonances. In preparation for high-temperature c-AGT, we identified suitable materials for fabricating cylindrical cavities and we developed techniques for measuring acoustic resonance frequencies using sources and detectors outside the high-temperature thermostat. We also considered alternative test gases and optimal dimensions of cavities.
Xing, L.
, Feng, X.
, Si, M.
, Zhang, J.
, Lin, H.
, Gillis, K.
and Moldover, M.
(2023),
Cylindrical Acoustic Gas Thermometry, Journal of Physical and Chemical Reference Data, [online], https://doi.org/10.1063/5.0139385, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=936070
(Accessed October 13, 2025)