Numerical Simulation of the Temperature Field of Coal Subjected to Microwave Directional Heating

Microwave directional heating can rapidly increase the temperature of coal and promote the desorption of coalbed methane. The temperature field of coal subjected to microwave directional heating was simulated by using COMSOL software. By coupling the energy conservation equation for an electromagnetic field with the heat conduction equation for solids, a heat conduction equation for the microwave directional heating of coal was established. The effects of the microwave heating time, power, frequency, incident distance and cross-sectional area of the waveguide on the temperature field of coal were studied via simulation. The results revealed that the increasing rate of temperature was high in the early stages of microwave heating. Moreover, higher microwave power corresponded to a higher coal sample temperature, a larger temperature gradient for the coal sample, and less energy being required to achieve the desired coal sample temperature. Additionally, it was found that there is an optimal microwave frequency that maximises the temperature of the coal sample. A larger microwave incident distance resulted in a lower average coal sample temperature. The waveguide was also found to have an optimal cross-sectional area that maximises the maximum temperature of the coal sample.