Study on temperature measurement and experiment of loose coal based on acoustic thermometry

In order to enhance the accuracy of temperature measurement for loose coal using acoustic methods, this study constructed an experimental system based on the principle of acoustic thermometry. The system was designed to investigate the influence mechanisms of acoustic signal frequency, sensor spacing and temperature on the acoustic wave propagation characteristics. The acoustic wave transit time was measured under different frequency ranges, sensor spacings, and temperature conditions during the experiments. The results show that the acoustic transit time tends to stabilize in the range of 400-1000 Hz and 2000-3000 Hz, and the acoustic wave propagation effect is superior, which is more suitable for the preferred frequency range of the acoustic wave transit time test. The acoustic wave transit time increases with the sensor spacing, and the growth rate of the acoustic transit time in different frequency ranges shows a significant difference. As temperature rises, the acoustic wave transit time shows a decreasing trend, and the relative error between the inverted temperature and the reference temperature based on the acoustic temperature measurement model is 2.27%-7.13%, which verifies the reliability and accuracy of the model. This study provides important theoretical foundations and experimental basis for the accurate measurement of spontaneous combustion temperature in loose coal.