Characteristics of Energy Conversion and Temperature Response of Coal Excited by a DC Electric Field

This study is aimed at investigating the characteristics of energy conversion and temperature response of coal excited by a direct current (DC) electric field (CEEDCEF). First, factors influencing energy conversion and temperature response of CEEDCEF were theoretically analyzed. Based on the analysis, the temperature distribution law of coal under different excitation conditions was simulated using the COMSOL software. The results of theoretical analysis and numerical simulation were verified through an experiment on the temperature distribution on the surface of CEEDCEF. Finally, the energy conversion mechanism and temperature response characteristics of CEEDCEF were revealed. The research results show that loading time and the loading voltage are the main factors influencing the temperature rise of CEEDCEF. Under the excitation of 6000 V constant DC voltage, the internal temperature at the lower end face of CEEDCEF increased from 29.4 to 92 °C within 20-90 min, the sections of the internal temperature increased from 36 to 94 °C under different voltage excitations of 3000-6000 V. Moreover, the temperature rise response process is divided into three stages, i.e., slow warming, fast warming, and slow cooling into stabilization. The coal shows a "capacitance effect" in the early stage of DC electric field excitation and a "resistance effect" after the charge reaches saturation. In addition, the temperature surges when the free radicals in the macromolecular structure of the coal turn into a current beam. With the increase in excitation time, the electrical parameters of the coal tend to be stable, and the surface temperature slowly decreases and stabilizes accordingly. The research results provide theoretical support for the gas production mechanism of the coal stimulated by the electric field and exploring methods for the monitoring and prewarning of these dynamic disasters.