Research On The Thermal-electromagnetic Coupling Characteristics Of Microwave Heating Debye Medium

Microwave heating,as a new type of green heating method,has been widely used in metallurgy,chemical industry,food processing and other fields.Compared with the traditional heating method,microwave can be coupled with the dielectric medium to directly volume heat.In addition,microwave heating has the advantages of selective heating,rapidly heating rate,energy saving and so on.With the increasing attention to energy conservation and emission reduction,microwave heating has brought technological and equipment innovation to many industries involving heat treatment.Because the researches on the interaction between microwave heating and medium have not understanding enough,it often leads to the uneven heating of medium under the unmatched microwave radiation.If we can not effectively understand the thermalelectromagnetic coupling characteristics of medium,it will not only lead to the low utilization rate of microwave energy,but also cause the thermal runaway phenomena,such as combustion and explosion.The simulation can not only visualize the coupling process of electromagnetic wave and medium,but also guide the design of experiment with accurate and effective numerical simulation,so as to minimize the number of experiments and reduce the cost.In this paper,the relationship between ‘microwave –time-medium' and it is analyzed from the point of view of simulation.Aiming at the time-varying dielectric Debye medium with different polarity,the relationship between the evolution and coupling of the electromagnetic field and the thermal field in its interior is revealed in order to restrain the thermal runaway,improve the local overheating phenomenon and the microwave heating efficiency.It is found that the dielectric property of the medium is the bridge between the electromagnetic field and the thermal field.In the thermo electromagnetic coupling model of microwave multi physical field,the time-varying dielectric simulation results are closer to the experimental values than the electromagnetic field model of constant dielectric.The polarity,position and microwave power of Debye medium have an effect on its internal global heat transfer characteristics.The strong polar Debye medium has a greater effect on the standing wave of electromagnetic field,while the weak polar medium has a smaller effect.It is found that the higher the microwave heating power is,the faster the heating rate is.Taking the energy consumption ratio of 1000 W and 500 W as an example,the ratio in the early stage of microwave heating is more than 1,showing a positive correlation;but with the temperature rising,the ratio is less than 1,showing a negative correlation.According to the industrial application,the power level is selected.Low power is suitable for microwave heating which requires uniform heat and energy saving,while heigh power is suitable for differential heat or rapid heating.The susceptor can be used to assist the microwave heating of the weak absorbing materials,and the susceptor structure will affect the global thermal electromagnetic coupling efficiency.Compared with the periodic and ‘defective' array structures,five Y-TZP spheres are evenly and symmetrically distributed in the cylindrical cavity,and the triangular array without two Y-TZP are more efficient than the circular array;the duty cycle of the hollow hole in the Si C susceptor is better between 14-18mm(duty ratio 0.56?0.73);the asynchronous air hole changes,when the outer air hole diameter are 18 mm and the inner are 16 mm better,the phenomenon of experimental calcination is consistent with the simulation results;the lack of air holes in the circular array plays a guiding role in heat diffusion.Microwave heating silicon carbide susceptor after 60 s,the global temperature of the transparent aluminum oxide insulating board increased by 32 ? and the maximum temperature reached 68.8 ?.In addition,the ‘defect' position of some air holes in the susceptor has a guiding effect on heat diffusion.To sum up,the paper reveals the relationship between the global heat transfer characteristics of the medium and the multiple physical parameters such as power input,time-varying dielectric,location,array structure and duty cycle,and further describes the mechanism process of the space-time transformation of microwave heated Debye medium,which provides some new ideas for broadening the application scope of microwave heating and high-efficiency microwave heated Debye medium in the future.