Thermo-Mechanical Response of Layered Rocks upon Single-Mode Microwave Treatments

ABSTRACT: Microwave heating is used in many applications including excavation of hard rocks and geo-energy recovery, where microcracks are induced at the boundary of mineral grains with different thermal and mechanical properties. To understand the multiphysics processes involved in microwave treatment of sedimentary rocks, impacts of varying the relative orientation of a single-mode microwave with respect to the major features of the rock fabric (bedding planes) and characteristics of microwave treatment (power level and exposure time) are investigated in this study. Series of two-dimensional models of dry layered rocks are developed and solved using finite element method. Then, the thermal and mechanical responses of the layered rock samples are analyzed and interpreted. Thinner interface layers with lower mechanical and thermal properties and higher dielectric properties absorb more energy and generate more heat. This concentrates stresses at the thin/thick layer interfaces because the thick layers conduct heat better, but do not deform easier. These temperature and deformation contrasts create microcracks. Treatment parallel to bedding planes may be least effective, but inclined and normal irradiation to the bedding planes would generate better results. High power level and low exposure time ensures the same outcome with less input energy than low power level and long exposure time.