Study On Flow Field And Water-thermal Management Of PEMFC

With the rapid development of the social economy,energy consumption continues to rise,and the corresponding environmental problems are becoming increasingly serious.In order to meet these challenges,human beings must find clean and efficient ways of energy application in order to achieve transformation,upgrading and green development.As the fifth generation fuel cell,proton exchange membrane fuel cell(PEMFC)has the advantages of green and efficient.It has become a breakthrough point to solve the environmental and energy problems,and has attracted the attention of researchers in the field of energy all over the world.Although its performance and cost have achieved great development after many years of research,some bottlenecks have been hampering its commercialization,among which the level of cell hydrothermal management is one of the key items that need to be improved urgently.Due to the unique properties of PEMFC itself,the reaction product water and heat generation are related to each other during cell operation,while the bipolar plate plays an important role in the first level of distribution of each reaction component within the cell,that is,the flow field of bipolar plate also affects the distribution of water and heat inside the cell.Especially when applied to large-area fuel cell,the performance of the cell will be directly determined by the design rationality of bipolar flow field.At present,the research content of bipolar plate flow field mainly focuses on designs of the cross-sectional shape of the flow channel and the flow channel structure.while the former is mainly based on single geometric cross section,and the research content of composite cross section applied to flow channel is less.In order to investigate the effect of channel cross-section shape on the heat and mass transfer and output performance of the cell,a variety of composite cross-section schemes are proposed in this paper.Based on the semi-empirical model,the PEMFC module of FLUENT 16.0 is used to carry out the numerical simulation research.The cross-sectional shape of the gas flow channel has a more obvious influence on volt-ampere characteristics in the high current density region,and scheme d can obtain the best comprehensive performance.When the working voltage is 0.3V,the current density in scheme d can be increased by 5.23% compared with scheme a.It has positive engineering significance when proton exchange membrane fuel cell is applied to stack to improve power density.Although the internal pressure drop of the gas channel in scheme d is relatively high,it's acceptable for the system.The inclination angle of the side wall and the arc section at the top of the gas channel can make the cell have relatively good distribution of water mass fraction.At the same time,scheme d can obtain a relatively high velocity in the gas channel,which makes the temperature distribution of the MEA uniform,and the exchange membrane in a good wetting state,which is helpful to transfer proton.The working process of PEMFC is complex,and when the subject of the cell system is consistent,the operating conditions have an important effect on the performance and the internal temperature distribution of the cell.The effects of gas diffusion layer porosity,current density and operating temperature on cell performance were analyzed.The numerical simulation results show that the porosity of the diffusion layer decreases,which can improve the water distribution state and the performance of the cell to a certain extent.When the porosity of the gas diffusion layer is 0.5,the current density is maximum while maintaining a more uniform temperature distribution in the exchange membrane.The current density characterizes the electrochemical reaction rate,and the high current density operation leads to the increase of the internal temperature of the cell and the uniformity of the temperature distribution.Considering the uniformity of temperature distribution and the output performance of the cell,the working voltage of the battery should be between 0.45 and 0.65 V.Under the same working voltage,when the working temperature of the battery is lower than 353 K,the maximum temperature rise of the exchange membrane is lower than the increase of the working temperature,but when the working temperature is higher than 353 K,the increase of the working temperature basically brings the maximum temperature of the exchange membrane to rise equally.Therefore,in order to obtain better temperature distribution and output performance of the exchange membrane,the relative optimal operating temperature of the battery is 353 K.When the operating pressure is 0.25 Mpa,the output performance can be improved obviously while keeping the temperature distribution of the exchange membrane evenly.