Acoustic and microwave tests in a cylindrical cavity for acoustic gas thermometry at high temperature

Published: February 22, 2016

Author(s)

K. Zhang, X.J. Feng, Keith A. Gillis, Michael R. Moldover, Jintao Zhang, Hong Lin, Jifeng Qu

Abstract

Relative primary acoustic gas thermometry 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. To measure accurate temperature ratios, the same monatomic gas must be used at the reference temperature and at the unknown temperature, and the cavity's dimensions must not change during the short time interval required to measure the acoustic and microwave frequencies. We explored acoustic gas thermometry 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.
Citation: Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences
Volume: A374
Pub Type: Journals

Keywords

cylindrical acoustic gas thermometer, waveguide, acoustic resonator, microwave resonator, thermodynamic temperature
Created February 22, 2016, Updated November 10, 2018