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Microwave reheating process dynamic simulation and optimization design

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Tutor: PengJinHui
School: Kunming University of Science and Technology
Course: Non-ferrous metallurgy
Keywords: microwave heating,heterogeneous materials,dynamic simulation,optimization design
Type: PhD thesis
Year:  2013
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As an emerging green metallurgical method, microwave heating is widely used in many areas of metallurgical processes; due to it has specific advantages which traditional heating methods do not have. However, the interaction mechanism.between microwave and metallurgical materials is not clear enough; especially the lack of dynamic simulation for microwave heating process and the study of optimization design limit the applications of microwave metallurgical technology in a wide range.Combining with Maxwell’s equations, heat transfer equation, continuity equation and the equation of motion, this thesis suggests the simulation of multi-physics coupling for the dynamic process of the microwave heating, researches the effective electromagnetic properties of heterogeneous materials that closely associates with the process, and proposes the optimized design method of microwave reaction cavity that is helpful to improve energy efficiency. Simultaneously, the metamaterial sensor based on whispering gallery mode is designed and its potential applications in metallurgical processes is also discussed in this thesis.(1) Because previous research on effective permittivity of heterogeneous materials cannot reveal the interaction mechanism between materials microstructure and microwave under quasi-static conditions, this thesis establishes a simulation model in which microwave field interacts with lossless two-phase heterogeneous materials. The effective permittivity that varies with frequency is obtained by the finite element method and the scattering parameters inversion algorithm. The results show that the microstructure of materials will affect its macroscopic electromagnetic properties and it is theoretically discovered that lossless heterogeneous materials exhibit macroscopic dielectric loss properties.(2) Three dimensional R-C network model that is used to describe effective permittivity of two-phase heterogeneous materials composed by metal-insulator exists issues of intensive computation and time-consuming. So a parallel algorithm is proposed to solve them. The results show that the speedup and parallel efficiency of the algorithm increase with the network size as well as the number of components. For the convenience of users, the simulation software based on the algorithm is developed.(3) From a dynamic perspective, the microwave heating is the interaction between material and the material as well as material and microwave. The interaction is a complex non-linear and multi-disciplinary issue,which changes with lots of factors, such as material microscopic characteristics, microwave frequency, temperature, heating time and microwave field strength etc. Therefor, this thesis thoroughly simulates dynamic heating process of microwave for different materials by multi-physics coupling. It is proved that the difference in heterogeneous microstructure will present the huge difference in macroscopic electromagnetic properties.(4) Microwave reaction cavity is a place that electromagnetic interacts with material, thus the rational approach of design directly relates to the heating effect and energy efficiency. The focuses and difficulties for the optimization of microwave reaction cavity are that how to reduce the reflection power of the port and how to increase the energy absorption by the load. By the analysis.of eigenmode for empty cavity, this thesis points out that it is irrational for the design of microwave reaction cavity to use empty cavity model. Furthermore, the optimization method for the reflection power of the port is proposed based on genetic algorithm. This method minimizes the coupling between ports and feeds more than96%energy to the heating load. It is advantageous to the energy efficiency, the reduction of the design cost for microwave reaction cavity and the prolongation of service life of the microwave source.(5) The whispering gallery mode resonant sensor has many advantages, such as high Q factor, small effective mode volume, fast response speed and strongly anti-interfere ability etc. Metamaterial is a kind of composite materials with artificial structures and it exhibits extraordinary physical properties that normal materials do not have. Based on the merits of both, this thesis designs a new sensor with external whispering gallery mode that enhances the interaction between electromagnetic wave and matter. It has higher sensitivity and resolution compared with the conventional resonator sensor, which can be used for precise detection and sensing areas, for example, detecting whether biological tissue is cancerous, whether the food is bad, chemical reaction process, the moisture content of metallurgical materials and temperature-dependent material properties etc.The study in this thesis is significant in guiding the preparation of metallurgical materials and the optimal design of microwave reactor.
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