Microwave Heating Stability Analysis Based On Cusp Catastrophe Theory

Microwave energy is a clean and efficient energy source,and it has been widely used in chemical metallurgy,food processing,material preparation and other fields for its characteristics of short heating duration,high efficiency,high energy utilization and easy control in the heating process.In contrast to traditional heating method,microwave heating has the advantages such as selective heating,internal heating and integral heating.On the one hand,the efficient heating method allows users to achieve the heating effect as quickly as possible,on the other hand,the heated material will be locally overheated during the heating process for the unique heating method,and local "hot spots" will appear,resulting in uneven material temperature and even produce "thermal runaway" phenomenon,which will bring many detrimental effects on heating operation.Thus,there are two important research directions in the field of microwave heating:(1)The stability analysis of heating process.The factors that affect the temperature uniformity of materials have been studied by adopting qualitative or quantitative methods,so as to obtain the stability of system in the heating process;(2)The improvement of temperature uniformity.By adopting different optimization methods to change the rising trend of the material temperature,the occurrence of thermal runaway during the heating process can be suppressed.Therefore,the thesis is based on the National Natural Science Foundation of China project "Modeling and Optimal Control of Microwave and Polymetallic Mineral Interaction Process"(61863020),taking solid medium silicon carbide ceramics as the research object.The thermal runaway phenomenon in microwave heating is quantitatively analyzed by studying the physical characteristics and temperature changes of the heated materials in the process of microwave heating,and combining with the cusp catastrophe theory and finite element numerical calculation method.The research contents can be summarized as follows:(1)The cusp catastrophic model of thermal runaway during microwave heating of silicon carbide solid medium was established.Based on the principle of microwave heating,considering the electromagnetic characteristics of the materials during the heating process,and combining the catastrophe theory,the cusp catastrophic model can be constructed.Moreover,through further analysis,the necessary and sufficient criteria and the critical temperature expression for judging the stability of heating process can be obtained.(2)The simulation and quantitative analysis of microwave heating silicon carbide ceramics were carried out.Firstly,the change of material temperature was obtained through the simulation of heating process of Si C ceramic by finite element method based on COMSOL Multiphysics software platform.The simulation results show that the temperature rise rate of the upper and lower surfaces of the ceramic is faster,which means that thermal runaway is more likely to occur.In the middle part,the temperature rise is relatively stable,and the possibility of thermal runaway is relatively small.Then,the cross section of the ceramic is cut off and some points are selected,and the corresponding experimental data are substituted into the thermal runaway charge criterion.The critical temperature value of the selected point and the calculated value of the steady state criterion are obtained by calculation,and compared with the finite element analysis results.The quantitative analysis results show that the calculation results of the cusp catastrophic model are basically consistent with the finite element analysis results,which verifies the effectiveness and feasibility of the cusp catastrophic model proposed in this study.