Visualization Study Of Products Management With The Use Of Special-shaped Flow Field In The Direct Methanol Fuel Cell

The development of human beings and society can not be separated from energy.However,the current way of energy utilization based on fossil fuel has caused many problems,such as wasting resources,producing a large number of poisonous gases and polluting environment severely.The direct methanol fuel cell?DMFC?is regarded as one of the most promising candidates to be the next-generation power source for portable or vehicular applications due to its advantages,namely abundant fuel,low working temperature,high energy density,environmental friendliness,etc.Nevertheless,there are still many critical issues impeding its large-scale commercialization,such as methanol management including methanol delivery and methanol crossover?MCO?control,CO₂ management and water management.To this end,this thesis focused on the visualization study of products management by optimizing the structure of flow field plate in an active DMFC and passive DMFC.On the basis of a traditional right-angle serpentine flow field,rounded-corner serpentine pattern and step-wise broadening serpentine pattern are used to investigate the cell performance,bubble behaviors,pressure drop characteristics and water behaviors of an active liquid-feed DMFC.Based on above research,the influence rules and action mechanisms related to better products management caused by optimized flow fields are analyzed in particular.Compared to the right-angle pattern,the rounded-corner pattern removes gas bubbles rapidly and steadily and the step-wise broadening pattern has a lower amplitude and average value of pressure drop.By using optimized flow fields,the cell performance is improved by 18.9%and the amplitude and mean value of pressure drop are reduced by 25%and 5.6%at most,respectively.On the basis of a common expanded metal mesh,a 3D porous fish scale flow field is designed and manufactured to investigate the cell performance,bubble behaviors and water behaviors of a passive liquid-feed DMFC under the condition of different structural parameters and assembly modes.Particularly,the action mechanisms of two-phase flow are studied by using different assembly modes of the novel flow field.At a lower methanol concentration,the novel pattern increases the cell performance by 21.5%than the traditional perforated pattern.In addition,the BU assembly mode at the anode and BL mode at the cathode are conducive to remove gas bubbles and water droplets,respectively.Therefore,the best cell performance of15.4mW·cm^-2 is yielded and is 17.1%higher than that with the use of the worst assembly mode.Based on the investigation of water behaviors in the expanded mesh flow field,a transparent simulated half-cell without the electrode is designed and manufactured to better visually observe the whole evolvement process of water passage underneath the expanded mesh.Furthermore,the pattern of water passage is improved by using absorbent cottons,suitable feed rates and an upright texture direction of the mesh.By these ways,the area of water passage is reduced by 50%and the number of blocked meshes is reduced from 13 to 2,which provides new ideas and strategies for the water management at the cathode in a passive DMFC.