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| Application of microwave resonance method in high temperature acoustic gas thermometer |
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Abstract The difference between the thermodynamic temperature T and the international temperature scale ITS 90 T90 at temperatures higher than 335 K is important for the temperature community in the world. Acoustic gas thermometry, based on the determination of thermodynamic temperature from the speed of sound in gases, is one of the promising methods for this temperature range. The speed of sound in gases could be measured from acoustic resonant frequency and the inner dimension of the cavity. Microwave resonance method is a technical route for real-time and in-situ measurement of cavity size and thermal expansion at high-temperature. We optimized the high-temperature acoustic gas thermometry system to improve the temperature and pressure stability. Homemade high-temperature microwave cable and sensor were used for the measurement of microwave resonant frequencies in a cylindrical cavity from 335 K to 493 K with a relative standard deviation of (2~13)×10-8. The variation of the cavity size with temperature was obtained through microwave resonance frequencies. The stability of geometric of the cylindrical cavity was acceptable. Then the refractive index and pressure of the gas inside the cylindrical cavity were determined for analyzing the pressure difference from flowing gas. These results are helpful for future determination of T-T90 above 335 K with low uncertainties.
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Received: 23 April 2024
Published: 26 September 2024
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2024, Vol. 45 
