The Design And Optimization Of Falling Film Evaporator Inside Microwave Cavity

In recent years,as people come to understand more about the characteristics of microwave,microwave inductive heating has been more popular used in various industrial applications.In the processes of chemical production and separation,microwave inductive heating could be applied in microwave-assisted distillation,microwave-assisted extraction,microwave drying,organic synthesis,crystallization,membrane separation and so on.Microwave induced evaporation and separation of azeotropes have been studied in our research group.However,few people have studied how different heating conditions and cavity structures match with different microwave heating processes.Coupling the electromagnetism and heat transfer physical processes,this paper aims to study the influences of operating conditions and design parameters on microwave heating effect by simulating calculation thereby optimizing cavity and evaporator structure.A coupled model of microwave heating is numerically implemented firstly in this paper.Here a dual concentric cylinder shells made by glass is set as an evaporator.The smaller shell is inserted into the bigger one to leave a 1 mm thick layer filled with still water and glycol.Then the sample could be more sensitive to temperature.The dimensions of cavity and waveguide correspond to our actual experimental device dimension.To simplify the model,some assumptions are proposed to neglect complex conditions which are all within the scope of acceptable including mass transfer and heat transfer in the domains of air and glass.Coupling of two physical phenomena(electromagnetism and heat transfer)is accomplished by solving Maxwell equations and Fourier’s law.And the model is verified to be reliable by applying the experimental data in previous study.Basing on this model,per unit mass microwave absorption efficiency and coefficient of temperature variation are proposed to denote the energy utilization and temperature uniformity,respectively,to evaluate the heating effect.Firstly,some operating conditions such as microwave power,initial temperature of sample,variety of sample and the dielectric properties are changed respectively.Then the structure of cavity and evaporator is adjusted to optimize.The load is water and glycol.Input port height,input port direction,sample location,cavity shape,radius of glass shell and thickness of load layer are discussed.In a word,a model coupled with electromagnetism and heat transfer is built and the microwave heating process is studied by changing operating and design parameters in this article.As the microwave heating application is becoming more and more popular,microwave cavity will surely be used widely.The results can provide theoretical foundations for the related studies.