| Microwave heating,because of its different mechanism of conventional heating methods,has the characteristics of uniform heating,strong selectivity,environmental protection and energy saving,and has a non-thermal effect during heating.It has a special catalytic effect on the reaction process,thus in the field of microwave chemistry How to use this feature has become the focus of scholars and researchers.At the same time,since the distribution of the electromagnetic field in the microwave chemical reactor is closely related to the type of the cavity and the structural parameters,it becomes difficult to design a chemical reactor that can efficiently use microwave energy.Based on the commercial project "Microwave Ground Distillation of Oily Mixtures such as Oil Shale",a high-efficiency microwave heating system is designed with the coaxial cavity as the reactor,and the design of the cylindrical resonant cavity for parameter measurement is completed.We also design a high-power waveguide coaxial converter for microwave energy supply.This article starts with the dielectric characteristics of non-magnetic dielectric materials,and uses Debye's equation to briefly introduce the relationship between the complex dielectric constant of the dielectric,frequency and temperature,the relationship between microwave thermal effects and dielectric loss,and then we derive the theory and proof the existence of the microwave non-thermal effect from different standpoints;the cylindrical resonator theory used in the test and the coaxial resonator theory used for microwave heating are introduced in this paper,and the field distributions of various resonant modes are given.At the last,we derive Perturbation theory of resonators.Next,according to the requirements of the test frequency of 915 MHz and the resonance mode,a cylindrical cavity is designed using HFSS and CAD.Combined with the software simulation results of the eigenmode,a ring coupling structure is selected as the excitation source of the cavity,and the location and dimension of the sample placement hole are reasonably designed,and the simulation result of shielding effectiveness reach 39.9dB.Then we derive the related theory of dielectric constant measurement.Subsequently,a variety of coaxial impedance compensation methods are introduced,and conical compensation is selected to design the coaxial heating cavity.By analyzing the complex dielectric constant of the material,we reduce the influence of the structural parameters on the standing wave ratio of the cavity;to improve the heating uniformity of the cavity,the cavity structure was optimized;we design a high-power waveguide coaxial converter,using a door knob coaxial converter with a gradually changing inner conductor,and the power capacity fully meets the project requirements.Finally,the processed cylindrical resonant cavity is first tested for the coupling strength and the excitation mode of the resonant mode,which are consistent with the theoretical simulation.We also mearsure the complex permittivity of the oily mixture.We build a complete microwave heating system for the oily mixture.A portable vector network analyzer is used to test the standing wave ratio of the cavity,which is in good agreement with the software simulation results,and finally we analyze the source of the error. |
