Research on temperature measurement model of loose coal considering humidity using acoustic wave method.

• Sound waves travel mainly through voids in the loose coal. • Influence of humidity on acoustic coal temperature measurement can not be ignored. • Acoustic temperature measurement technology can be applied to loose coal. Spontaneous coal bunker combustion disasters not only cause a waste of resources, but also cause huge economic losses and heavy casualties. The existing coal spontaneous combustion detection technology has obvious limitations, and there is an urgent need for new coal spontaneous combustion high temperature point detection technology. This paper constructs a model for measuring the temperature of loose coal using acoustic wave method that takes humidity into account. By measuring the mechanical properties of coal, it is found that when sound waves propagate in loose coal, they mainly propagate through the air in the gaps of loose coal. By analyzing the relationship between sound speed and temperature in free atmospheric pressure, a loose coal acoustic temperature measurement model considering humidity was constructed, and a correction factor was introduced to modify the temperature measurement model. Using the frequency sweep signal as the sound source signal, the temperatures of loose coal with three different degrees of metamorphism were measured. The results show that the temperature measurement of loose coal considering gas environment relative humidity is more accurate. The measured long flame coal temperature is closest to the real temperature, with a maximum absolute error of 1.68 °C and a maximum relative error of 5.44 %. Error analysis shows that the temperature measurement error is mainly caused by changes in the gas composition of the voids in the loose coal, the functional relationship between the characteristic factor and temperature, and errors in sound wave flight time measurement. This study can provide certain theoretical support for the acoustic method to measure the temperature of high temperature points in coal bunkers, and provide a new temperature detection method for coal fire disaster prevention and control. [ABSTRACT FROM AUTHOR]