Temperature Profiles in Microwave Heating of Solids: a Systematic Study

Time-temperature profiles in microwave heating depend qualitatively on several additional parameters (dielectric properties, size, shape) in contrast with conventional heating where only thermal properties are needed. These additional parameters can give rise to qualitatively different transient and spatial temperature profiles. Using an analytical solution to the heat equation, three characteristic temperature profiles were identified in microwave heating of a solid in the absence of evaporation and microwave concentrations due to shape. As a first approximation, thermal diffusion can be ignored compared to heat generation during the initial heating period and temperature profiles were similar to those obtained in conventional heating. Intermediate heating period was characterized by a temperature peak that developed near the surface and propagated inward as heating continued. After sufficient duration of heating, the profiles developed a concave down shape, characteristic of the steady state with internal heat generation. Effects of penetration depth, applied microwave power, and surface convection was also studied.