EFFECT OF RADIATION LOSSES ON HOTSPOT FORMATION AND PROPAGATION IN MICROWAVE-HEATING

The use of microwaves for the rapid heating of materials has found wid espread industrial use. However, a number of potential problems are in herent in this rapid heating, including the hotspot phenomenon. A hots pot is a type of thermal instability which arises because of the nonli near dependence of the electromagnetic and thermal properties of the m aterial on temperature. The evolution of a hotspot in a cylindrical ma terial is studied. The propagation of the microwaves is treated in the Wentzel-Kramers-Brillouin (WKB) limit (geometric optics), and the the rmal behaviour is studied in the limit of small thermal diffusivity. T he resulting temperature distributions are in excellent agreement with full numerical solutions of the governing equations, even outside the strict range of the asymptotic validity of the WKB approximation.