title: Acoustic and microwave tests in a cylindrical cavity for acoustic gas thermometry at high temperature.
abstract: Relative primary acoustic gas thermometry (AGT) determines the ratios of thermodynamic temperatures from measured ratios of acoustic and microwave resonance frequencies in a gas-filled metal cavity on isotherms of interest. When measured in a cavity with known dimensions, the frequencies of acoustic resonances in a gas determine the speed of sound, which is a known function of the thermodynamic temperature T. Changes in the dimensions of the cavity are measured using the frequencies of the cavity's microwave resonances. We explored techniques and materials for AGT at high temperatures using a cylindrical cavity with remote acoustic transducers. We used gas-filled ducts as acoustic waveguides to transmit sound between the cavity at high temperatures and the acoustic transducers at room temperature. We measured non-degenerate acoustic modes in a cylindrical cavity in the range 295 K<T<797 K. The fractional uncertainty of the measured acoustic frequencies increased from 2×10(-6) at 295 K to 5×10(-6) at 797 K. In addition, we measured the frequencies of several transverse magnetic (TM) microwave resonances up to 1000 K in order to track changes in the cavity's length L and radius R. The fractional standard deviation of the values of L deduced from three TM modes increased from 3×10(-6) for T<600 K to 57 × 10(-6) at 1000 K. We observed similar inconsistencies in a previous study.
authors.affiliation: Department of Thermal Engineering, Tsinghua University, Beijing 100084, People's Republic of China Division of Thermophysics and Process Measurements, National Institute of Metrology, Beijing 100029, People's Republic of China.
authors.forename: K
authors.initials: K
authors.lastname: Zhang
authors.affiliation: Division of Thermophysics and Process Measurements, National Institute of Metrology, Beijing 100029, People's Republic of China.
authors.forename: X J
authors.initials: XJ
authors.lastname: Feng
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors.forename: K
authors.initials: K
authors.lastname: Gillis
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors.forename: M
authors.initials: M
authors.lastname: Moldover
authors.affiliation: Division of Thermophysics and Process Measurements, National Institute of Metrology, Beijing 100029, People's Republic of China zhangjint@nim.ac.cn.
authors.forename: J T
authors.initials: JT
authors.lastname: Zhang
authors.affiliation: Division of Thermophysics and Process Measurements, National Institute of Metrology, Beijing 100029, People's Republic of China.
authors.forename: H
authors.initials: H
authors.lastname: Lin
authors.affiliation: Division of Thermophysics and Process Measurements, National Institute of Metrology, Beijing 100029, People's Republic of China.
authors.forename: J F
authors.initials: JF
authors.lastname: Qu
authors.affiliation: Division of Thermophysics and Process Measurements, National Institute of Metrology, Beijing 100029, People's Republic of China.
authors.forename: Y N
authors.initials: YN
authors.lastname: Duan
keywords: acoustic resonator; cylindrical acoustic gas thermometer; microwave resonator; thermodynamic temperature; waveguide