Selective microwave heating can significantly impact the performance of multiphase reactors, such as slurry reactors, where the dispersed (solid particles) and continuum (liquid) phases have different dielectric properties. Lack of tools to measure and predict the temperature difference between the dispersed and continuum phases hinders the understanding and optimization of microwave-heated slurry reactors. We utilize experiments, theory, and multiscale simulations to investigate microwave heating of slurries consisting of microwave absorbing solid particles dispersed in a non-polar liquid. Using controlled experiments and mathematical modeling, we propose an ideal slurry reactor and develop analytical expressions to predict the temperature evolution of the solid and liquid phases during microwave heating. Our experiments show a strong impact of the solid material and concentration on the heating rate of slurries, whereas no difference is observed in conventionally heated slurries. We also perform multiscale simulations of microwave-heated slurries employing a coarse-graining methodology to handle the large separation of length scales in slurries and compare them against experiments. © 2020 Elsevier B.V.