Numerical Simulation Study On Microwave Heating Active Coke

Electromagnetic-thermal coupling mechanism has been studied under the active coke heating condition by numerical simulation in this paper.First of all,simulation model in the same size of actual microwave heating experimental devices has been built by COMSOL Multiphysics software.The active coke heating has been simulated in the microware field.The temperature result is consistent with experimental data and the numerical reliability has been verified.The results show that the microwave spreads in the form of stationary ware in the cavity.The electric field intensity and electromagnetic energy are non-uniform.The maximum value of electric field intensity along the transversal line is 19.5 kV/m with no load.The active coke is graphite-like carbon structure,so radiated electrons of π bonds among carbon layers under VDM move along a specific direction and produce polarization characteristic.That can affect electromagnetic field distribution.And the maximum value of electric field intensity along the transversal line is 20.9 kV/m.In addition,important parameters,such as microwave frequency,microwave power,waveguide position and number,which can influence heating effect and electric field distribution have been studied.The maximum electric field intensity value |E|max is 14.2 kV/m under 2.45 GHz which is the resonant frequency magnitude of the cavity,and temperature range is from 200℃-250℃.When the frequency is not 2.45GHz,the electromagnetic energy absorption of the active coke decreases.The maximum temperature is less than 40℃ under the frequency of 2.4 GHz and 2.5 GHz.The temperature variation of active coke particles heated by microwave has been studied under the magnitude of input energy of 15 kJ、30 kJ、45 kJ and 60 kJ.The results show that the thermal heterogeneity inside the active coke increases with the power increasing and the heating is uniform under the condition of low power with same energy input.The position and quantity of the waveguide affect the temperature distribution of the electric field and the active coke in the cavity,the electric field in the cavity of the bottom-fed waveguide is mainly distributed in the vertical plane and |E|max is 30 kV/m.The high energy domain gathers at the bottom of the active coke and radiates upward,the maximum temperature reaches 245℃ after heating for 30s.Compared with bottom-fed waveguides,the distance between the side-fed waveguide and the insulator increases and the electric field in the cavity is mainly distributed in the horizontal plane.The maximum electric field value |E|max is 30 kV/m.With the increase of electric field intensity,the high energy domain is concentrated at the left side of the active coke,and the temperature value is twice that of the bottom-fed waveguide.The maximum electric field value |E|max is 60 kV/m.The vibration of polar molecules is accelerated and the temperature is about 4 times that of the bottom-fed waveguide.The microwave energy utilization rate is greatly increased.Finally,the electric field distribution and thermal effect factors under various load magnitude.The active coke distance has a significant effect on the microwave thermal effect.When the distance is 0.1mm,the electric field gathers at the gap to form a peak.The electric field value |E|max is 30.6 kV/m and the heating temperature is 450℃.Wen the distance is 5mm,the electric field value|E|max is 22.2 kV/m but the temperature of hot spots is only 260℃.The fading wave on the surface of the active coke tends to decrease with the increase of the distance,and the electric field intensity at the gap decreases continuously,so the microwave energy transferred by the "fading wave" decreases correspondingly.