Exploring Acoustic Wave Propagation and Equivalent Path in Quasi-Porous Medium of Loose Coal Mass

In acoustic temperature measurement, precise determination of sound propagation characteristics is critical for calculating sound propagation velocity. This study investigated the sound wave propagation path in loose coal by assessing the impact of average porosity and temperature on coal particles. Utilizing principles from acoustic temperature measurement and wave equation theory, we propose an equivalent path model for sound wave propagation in quasi-porous media of loose coal. We designed an experimental system and conducted acoustic propagation path tests on loose coal samples with three particle sizes: 0.6–1.5 cm, 1–3 cm and 3–5 cm. Through rigorous analysis, we identified key factors that influence the acoustic propagation path, such as particle size, temperature, and burial depth, which affect the average porosity of the quasi-porous medium. The measured sound velocities for coal samples of 0.6–1.5 cm, 1–3 cm, and 3–5 cm loose coal samples were 238.16 m/s, 252.11 m/s, and 277.36 m/s, respectively. We introduced the equivalent path conversion factor λ for sound wave propagation in loose coal, demonstrating its decrease with larger coal particle sizes. The research validated the accuracy of our equivalent path model, showing a minimal difference between measured and calibrated sound velocities (±4.47 m/s; 4.68% error rate). Our results have theoretical significance for acoustic temperature measurement in the field of loose coal body temperature assessment, offering valuable insights and methods for the advancement of acoustic coal temperature detection technology.