Research On The Multiphysics Mechanism In Microwave Reactor With A Microwave Mode Stirrer

Due to the depletion of fossil fuels and environmental degradation,the development of a sustainable green economy is crucial.Biodiesel has attracted much attention because of its renewable,non-toxic and non-polluting properties.Microwave reactors are widely used in the preparation of biodiesel because they can effectively improve the chemical reactions conversion rate.However,microwave uneven heating and the small preparation scale of microwave reactors are problems that need to be solved urgently.Therefore,this paper introduced the mode stirring technology into the design of a pilot-scale microwave reactor.The microwave electromagnetic field is stirred by a mode stirrer to control the spatial distribution characteristics of the electromagnetic field in the reactor and improves the microwave heating effect.In order to obtain the multiphysics characteristics and its influencing factors in the microwave reactor with a mode stirrer,and to optimize this design.In this paper,the Maxwell and heat transfer equations were coupled,and the dynamic grid technology was used to deal with the mode stirring,and the electric and temperature field in the reactor were numerically calculated by the method of multi-physics simulation.By studying the influence of the mode stirrer structure,material properties and other factors on the microwave heating characteristics,the reactor optimization method was proposed.Finally,the multi-physical properties and the key factors of design in the microwave reactor with a mode stirrer were obtained.The main research contents and conclusions are as follows:(1)Design optimization of the mode stirrer structure.Multiphysics simulation was carried out on the microwave heating process under mode stirring,and the effect of the mode stirrer’s height,length and speed on microwave heating were discussed.It was found that compared with the model without mode stirrer,mode stirrer improves the microwave heating efficiency and uniformity.Through the response surface analysis,the order of primary and secondary effect on average temperature and coefficient of variation(COV)was found to be:stirrer height>stirring speed>stirrer length,and there is an interactive relationship between different factors.Considering the average temperature and COV,the optimal stirring conditions for response surface optimization are stirrer height λ_H of 0.164,length λ_B of 0.31,and stirring speed N of30 r/min.(2)Analysis of the influence of reactor material properties on microwave heating.Taking the optimized microwave reactor as the simulation model,the influence of the mode stirrer and interlayer different material properties on the microwave heating was explored.It was found that compared with the single-material mode stirrer,the composite material mode stirrer improves the microwave heating efficiency and heating uniformity,and reduces the hot spot temperature.Under the rotation of the mode stirrer,the corundum interlayer improves the microwave heating efficiency.The combination of aluminum mode stirrer and corundum interlayer significantly improves the microwave heating efficiency.(3)Optimization of microwave reactor based on mode stirrer and waveguide structure.The microwave heating effect was explored from the mode stirrer shape and the waveguide structure.It was found that the number of mode paddles has little effect on the microwave heating uniformity,and the microwave heating efficiency decreases with the increase of the mode paddles number.Under the same microwave power condition,compared with the microwave reactor with single waveguide structure,the reactor with double waveguide structure under the rotation of the composite material mode stirrer improves the microwave heating efficiency.Under the rotation of the composite material mode stirrer,the microwave heating efficiency tends to increase with the decrease of the add waveguide height,and the waveguide height has little effect on the heating uniformity.Therefore,when the height of add waveguide is 164 mm,the microwave heating efficiency is significantly improved.