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 dif ferent transient and spatial temperature profiles. Using an analytical solution to the heat equation, three characteristic temperature profi les were identified in microwave heating of a solid in the absence of evaporation and microwave concentrations due to shape. As a first appr oximation, thermal diffusion can be ignored compared to heat generatio n during the initial heating period and temperature profiles were simi lar to those obtained in conventional heating. Intermediate heating pe riod was characterized by a temperature peak that developed near the s urface and propagated inward as heating continued. After sufficient du ration of heating, the profiles developed a concave down shape, charac teristic of the steady state with internal heat generation. Effects of penetration depth, applied microwave power, and surface convection wa s also studied.