Study On Mass Transfer Characteristics Of Ultrasonic Atomization Feed DMFC

With the superiority of high theoretical energy density and easy to operate,direct methanol fuel cell(DMFC)is regarded as the best candidate to replace traditional lithium fuel cell.However,the problem of methanol crossover restricts its promotion and application.A new method based on ultrasonic atomization supply to mitigate methanol crossover is put forward in this research and the validity of the method is verified in the earlier stage research.Based on this background,the simulation modeling method is used to study the mass transfer process of methanol in ultrasonic atomized DMFC,and the measures to optimize methanol mass transfer and alleviate methanol crossover are proposed.The main research in this paper are as followings:Firstly,In this paper,the mass transfer of methanol in ultrasonic atomization DMFC is divided into three parts: Cotton Core Mass Transfer,Atomizer Mass Transfer and Fuel cell Membrane Mass Transfer,and establish a simulation model of each part of mass transfer.The model of the mass transfer part of the cotton core is to simplify the cotton core into a certain amount of capillary tube,and analyze the force,the influence factors of flow process and flow rate of methanol in a single capillary.The effects of the diameter of the cotton core capillary,the working environment of the mass transfer and the placement of the cotton core on the mass transfer rate of the cotton core were studied by simulation.The results turn out that the mass transfer rate of methanol in the cotton core decreases with the increase of the capillary radius of the cotton core.As the ambient temperature ranges from 20 to 50,the rate of methanol transport in the cotton core is increasing,but the stable height of methanol in the cotton core decreases with increasing temperature.Secondly,In the mass transfer part of the atomizer,ANSYS software is used to analyze the modal and harmonic response of the atomizer model.The modal analysis determines the natural frequency and vibration mode of the atomization piece,and determines the best mode for the actual working condition.The harmonic response analysis was carried out,and the influence of the structure of the atomized sheet on the vibration of the atomized sheet structure was analyzed,and compare with the experimental results.The result show that,the simulation shows that the optimal driving frequency of the atomizing sheet is 111.47 KHZ.The best driving frequency of the atomizing sheet is 110.58 KHZ through the vibration measurement experiment and the atomization amount experiment.Finally,the mass transfer part of the fuel cell membrane analyzes the transport process of each substance in each layer of the fuel cell membrane and sequentially establishes the mathematical model of each material in the membrane.Then through simulation,the distribution of various physical quantities including methanol,oxygen partial pressure,ion potential and anode proton current density in the thickness direction of the fuel cell is obtained.Using fuel cell performance and methanol permeation as criteria for judging methanol mass transfer,The fuel cell operating conditions including the operating temperature of the fuel cell,the methanol concentration,and the fuel cell structure including the thickness of the diffusion layer,the porosity of the diffusion layer,the thickness of the catalytic layer,the porosity of the catalytic layer,and the thickness of the electrolyte membrane on the fuel cell performance are investigated.Simulation results shows that: the mass transfer resistance of methanol and oxygen is concentrated in the diffusion layer;the higher the working environment temperature of the fuel cell,the better the fuel cell performance;Compared with methanol feed concentration,diffusion layer structure and electrolyte membrane structure,the structure parameters of catalytic layer have a greater impact on the mass transfer of methanol.Through the simulation results of this paper,the mass transfer law of methanol in the inner core,atomizer and fuel cell film of ultrasonic atomized methanol fuel cell system is obtained,which provides a theoretical basis for the selection of cotton core and nebulizer in the ultrasonic nebulization methanol fuel cell system and the improvement of the cell membrane structure.