Analysis and control of the thermal runaway of ceramic slab under microwave heating

Thermal runaway is a special macroscopic phenomenon of the dielectrics during microwave heating, in which there is a big jump of the steady state temperature while the applied microwave power varies slightly. It hinders the applications of microwave heating technique in industry. A simulation based on the finite difference time domain (FDTD) method to solve Maxwell's equations coupled with the finite difference (FD) method to solve a heat transfer equation (HTE) is presented, and the temperature variation in a ceramic slab during microwave heating is obtained. The temperature variation in the ceramic slab during microwave heating is simulated with various ceramic parameters and applied microwave powers so as to analyze the condition under which thermal runaway is introduced. Moreover, a microwave power control method, based on a single temperature threshold and dual applied microwave powers, is presented, which improves microwave heating efficiency and controls thermal runaway. The relation between the final applied microwave power and the monitored temperature threshold is presented as well. This method can be applied in many fields related with microwave heating techniques.