Flow Field Design Of Bipolar Plate For Fuel Cell To Strengthen Mass Transfer

Since the 21st century,environmental problems and energy shortage are becoming more and more serious.As a result,many countries are committed to the development of renewable energy.Among them,proton exchange membrane fuel cell(PEMFC)has been widely used in various fields because of its advantages such as environment friendly,high power density,long working life and so on.Bipolar plate is one of the core components of proton exchange fuel cell,which has the functions of gas distribution,heat transfer,drainage and current separation.The layout of flow field structure will affect the output performance of fuel cell.Reasonable flow field structure can improve the output power density of PEMFC,improve the uniformity of gas distribution,and reduce or even avoid flooding.The traditional parallel flow field fuel cell has some problems,such as uneven gas distribution and serious water flooding.In order to improve these problems,flow structures are proposed to enhance the mass transfer capacity of PEMFC.Firstly,a type of parallel flow field with stepped bipolar plate is proposed.The gas diffusion rate is increased by reducing the cross-sectional area in the stepped channel.The influence of the quantity of steps on the polarization curve,oxygen mass fraction distribution,current density distribution and liquid water saturation in PEMFC are studied.The results suggest that the fuel cells with stepped flow field are superior than the traditional fuel cell with parallel flow field.The stepped flow field improves the uniformity of gas concentration and current density distribution,accelerates the discharge of liquid water,and alleviates the flooding phenomenon.Compared with the traditional parallel flow field,the power density of the fuel cell with stepped flow field increases by 22.4%.Secondly,a kind of serrated bipolar parallel flow field is proposed.The effects of wavelength and amplitude on the the polarization curve,oxygen mass fraction distribution,current density distribution and liquid water saturation in PEMFC are studied.The results indicate that the output performance of fuel cell with serrated flow field is higher than that of fuel cell with parallel flow field.The serrated structure will cause periodic disturbance to the gas in the channel,increase the gas velocity,improve the phenomenon of uneven gas distribution,and improve the drainage performance.In several typical flow field structures,the design with Case6 shows the best output performance.Compared with the traditional parallel flow field,the output power density is increased by 34.9%.Finally,a bipolar plate parallel flow field with gradual wave structure is proposed.The oxygen mass fraction distribution,current density distribution and liquid water saturation in different gradual size wave parallel flow field are studied.The results indicate that the output performance of the fuel cell with gradual wave-shaped parallel flow field is higher than that of the traditional parallel flow field.The gradual wave structure can effectively strengthen the gas transmission in the flow field and improve the flooding problem.The reason is that the gradual wave structure will cause the gas to flow longitudinally,increasing the gas velocity in the channel,strengthening the gas mass transfer under the ribs,and improving the overall performance.Compared with a fuel cell with a traditional parallel flow field,the output power density of a fuel cell with a gradual wave-shaped parallel flow field is increased by 28.9%.