Research On Flow Field Structure And Water-gas Management Based On Enhanced Mass Transfer PEMFC

Proton exchange membrane fuel cell has many advantages such as high power density,high conversion efficiency,low noise,short start-up time,low operating temperature and zero emission,so it is a new power source technology with broad application prospects.The mass transfer performance of proton exchange membrane fuel cell is greatly affected by the increase of liquid water production under high current density.In order to improve the mass transfer capacity of fuel cell and enhance the performance of water and gas management,a new type of throttling flow channel is designed in this thesis.A new three-dimensional convex platform is set inside the cathode flow channel to form a throttling unit and make it produce throttling effect on air.In this thesis,the simulation and experiment are combined to study the performance of the throttling channel,and explore the design criteria for improving the mass transfer performance in the flow field.First of all,in order to explore the differences caused by different structure designs inside the flow channel,six different throttling flow channels and straight channel were designed for comparative study.Steady-state numerical simulation of their performance is carried out by using 3D simulation software.The polarization curve,water and gas distribution and uniformity index,pressure drop between inlet and outlet,local direction of oxygen flow,net power density and mass transfer coefficient were analyzed respectively.The results show that compared with the straight channel,the throttling channel can effectively improve the maximum current density and the maximum power density.The mass transfer effect of gas perpendicular to the membrane electrode can be improved and the land convection of gas can be increased.In addition,the convex can significantly reduce the water content and improve the water management performance of the battery.The presence of the throttling unit can lead to an increase in pressure drop,but the net power density is still greatly improved.Better mass transfer and water management performance can be achieved by locally encrypting the distribution of downstream interceptors without increasing the number of throttling units.In the design of several throttling flow channels,the ratio of the optimal length of the upstream and downstream non-intercepting is 2.The throttling channel can improve the mass transfer coefficient by about 58%-59% compared with the straight channel.Then,the overall flow field structure with double inlet and double outlet structure was designed,and the improvement of gas distribution uniformity and performance was verified in the flow field of straight channel.Based on the optimal ratio of upstream and downstream unthrottling lengths in a single flow channel,staggered arrangement and local encryption are used to throttling flow fields,and various performance indexes of different flow fields are analyzed.The results show that the dual-inlet and dual-outlet flow field structure can significantly improve the uniformity of gas distribution,and effectively improve the performance of the straight channel flow field battery at medium and high current density by about 6.1%.The mass transfer performance of the throttling flow field is about 4.5-5.5% higher than that of the straight channel flow field.The reaction gas tends to accumulate in the flow channel near the outlet,and the throttling flow field can reduce this trend and improve the gas distribution uniformity.Better mass transfer performance can be achieved by locally encrypting the distribution of throttling units downstream of the throttling flow field.Throttling flow field can improve the effect of land convection.Finally,on the basis of the whole battery field model has been established,the graphite flow field plate of the battery is designed and processed,and assembled into a single battery for experimental study.The difference of the polarization curves between the throttling flow field and the straight flow field was analyzed through the experimental data.The results show that the performance of the throttling flow field is slightly worse at low current density,but the concentration polarization of the throttling flow field is far less than that of the straight flow field at high current density.In addition,the dual-inlet design improves the performance of straight single cell only at high current density,with a maximum current density increase of about 5.1%.The performance of the dual-inlet design is better than that of the single-inlet design at the working condition below 1.6A/cm2,and the maximum improvement is about 3.5%.The throttling flow field has better operation stability and the voltage fluctuation is far less than the straight flow field.In the straight channel flow field,the voltage fluctuation can be significantly reduced by using the double inlet design.