Computational study of microwave heating for rock fragmentation; model development and validation

Microwave heating can be useful in mining, tunneling and mineral processing by reducing the strength of rocks and ores. Understanding the multiphysics interaction between electric and magnetic waves on rocks due to microwave irradiation is of utmost importance in optimizing energy absorption (heating) and maximizing micro-cracks generation. In this study, a coupled electromagnetic-thermal-flow-radiation model comprising of conservation of mass, momentum, energy and Maxwell equations is derived, developed and solved using the finite element method. The model is validated against an experimental benchmark in terms of the overall heat absorption as well as the local temperature distributions over a range of operating parameters, i.e. distance from the antenna, microwave power and exposure time. Results show that the real and imaginary part of the dielectric permittivity of the rocks significantly affect the temperature distribution and intensity of the energy absorption, respectively. The energy absorption is also affected by the distance of the rocks from the antenna. Furthermore, at higher microwave energy dosages, the natural convective flow starts to develop and the effect of thermal radiation becomes more prominent, which adversely affects the energy absorption in the rock sample by more than 20% in some cases.