Design And Research On Reticular Radial Flow Field Structure Of Proton Exchange Membrane Fuel Cell

The emergence of hydrogen fuel cell technology has further promoted the speed of scientific research progress in fields such as physics,chemistry,and thermodynamics,and also helped us more conveniently obtain clean,safe,and efficient new energy.It is also in line with the country’s current focus on the "dual carbon" strategic goal.Proton exchange membrane fuel cell(PEMFC),as a new type of fuel cell,utilizes polymer membranes that can conduct ions as electrolytes to ensure efficient and stable operation,and has better energy-saving characteristics,such as smaller volume,wider temperature difference adaptation range,and better environmental friendliness.Therefore,PEMFC has been widely applied in various industries,such as automobiles,military,aviation,nuclear power plants,ocean detectors,ships,rockets,etc.The bipolar plate is a fundamental component of fuel cells,and its internal flow characteristics are of great significance for the transport and reuse of reactive gases.The network radial flow field proposed and studied in this article has multiple advantages compared to traditional structural flow fields,such as central intake,short intake path,and easy formation of electric stacks.Moreover,the optimization of flow channel structure has achieved better fluid distribution and heat and mass transfer effects,thereby improving the electrochemical performance of fuel cell cells,and has high research potential.This article conducts relevant research on the structural characteristics of radial flow field and the improvement of electrochemical performance of fuel cell monomers.Firstly,after collecting and comparing a large amount of natural and artificial materials,inspired by the shape of car wheels,a new type of mesh radial flow field structure was designed by cleverly integrating the structural characteristics of the wheels with the PEMFC radial flow field.This structure is mainly composed of multi-layer annular flow channels,with adjacent annular flow channels connected by branch flow channels extending from the inlet to the outlet.The branch flow channels adopt a wave like design,and there is a complete waveform between the two adjacent flow channels,and the peak directions of adjacent waveforms are opposite.Based on this structure,the order of the annular flow channel,the number of branch channels,and the amplitude of the branch channel wave structure are calculated α As a key variable,a complete three-dimensional steady state model of PEMFC monomer with the above different variables was established through COMSOL Multiphysics software.Through computational fluid dynamics,the electrochemical properties of PEMFC monomer in different aspects such as oxygen distribution,water distribution,voltage drop,battery output voltage and power were compared and analyzed.Research has shown that as the number of branches increases,the oxygen concentration in each layer of the annular flow channel improves,and the improvement effect on the inner annular flow channel is more obvious.The voltage and power output of the battery gradually increases at medium to high current densities,but this process cannot be sustained continuously.As the number of tributaries increases,the total area of the flow channel in the flow field area correspondingly increases,while the corresponding rib area gradually decreases.The two affect each other,and there is a most reasonable interval.Within the optimal range,the voltage and power output of the battery reach their peak.At the same time,a design scheme for the spacing between unequal flow channels was established and compared with the equidistant arrangement scheme.The results showed that the oxygen distribution,water distribution,current density,power density,and pressure drop at the interface between the cathode gas diffusion layer and the membrane did not significantly improve due to changes in channel spacing.Therefore,it can be determined that equidistant arrangement is still the optimal channel spacing setting method for radial flow fields.In the analysis of the impact of the amplitude of the branch channel wave shape on the cathode side flow field,it was found that in the outer annular channel,as the amplitude of the branch channel wave shape increased,the problem of low oxygen content in some areas of the channel increased,which also affected the removal of excess water in the channel.At medium to high current densities,the smaller the amplitude of the branch channel wave shape,the higher the output voltage at the same current density,and the higher the power density that can be achieved.The pressure drop in the cathode side channel also confirms the above inference.In addition,this study aimed to address the phenomenon of poor electrochemical performance of PEMFC monomers due to insufficient intake flow rate.By optimizing the channel width and depth dimensions,designing the variable diameter structure,and optimizing the cross-sectional shape,the electrochemical performance of PEMFC cells with insufficient intake flow rate was effectively improved.The research results indicate that the optimization of channel size has the most significant effect on improving the performance of PEMFC,followed by the design of cross-sectional shape,and then the variable diameter structure.After optimizing the channel size,the electrochemical performance of the single cell is significantly improved,which can effectively avoid the problem of increased mass transfer impedance and concentration impedance caused by insufficient intake flow rate,ultimately resulting in a certain increase in output voltage and power density.Finally,compare the mesh radial flow field scheme with good comprehensive performance with the direct current field and serpentine flow field under the same effective area.After comparison,it can be found that even though the output voltage and power of the mesh radial flow field are slightly inferior to the traditional serpentine flow field,it has better flow characteristics and pressure stability is significantly better than the traditional serpentine flow field.This indicates that the new flow field structure designed and studied in this thesis has played a certain role in improving the electrochemical characteristics of PEMFC.