Active Optimizations And Managements Of Thermal And Liquid Water In PEMFC With 3D Flow Fields

Proton exchange membrane fuel cells(PEMFCs)are promising power devices that can convert chemical energy into electrical energy without the need for hydrogen combustion.They offer advantages such as high energy conversion efficiency,low pollutant emissions,and fast startup.Currently,the focus of research is on how to further improve their power generation performance.PEMFCs consist of bipolar plates,gas diffusion layers,catalyst layers,and proton exchange membranes.The gas flow channels are typically etched on the bipolar plates to facilitate the transport of reactant gases into the PEMFC and the removal of liquid water generated by electrochemical reactions timely.The layout of high-performance gas flow channels can enhance gaseous reactants’transport and the liquid water removal inside the pores of the porous electrode,these mentioned above make the gas flow channel plays a crucial role in the performance of PEMFCs.Investigating the influence of different factors on the gaseous reactants’transportation characteristics of PEMFCs,seeking efficient optimization designs for gas flow channels,and improving the material transport capacity within PEMFCs are key technologies to enhance the stability and performance of PEMFCs.As the core component of the PEMFC,gas flow channels play an important role in the transport of gaseous reactants and the removal of liquid water.Therefore,this study focuses on the enhancement in the gas transportation of PEMFCs and explores the impact of gas flow channel designs on the reactants and generation transport in the PEMFC,as well as the effects of operating parameters on the performance of PEMFC.The research work in this paper mainly consists of three parts.The first part provides a theoretical basis for the mass transfer enhancement strategy of the 3D flow field by constructing gas channels with forced convection effects.The second part investigates the relationship between the operational parameters and the performance of the fuel cell.The third part examines the variation of irreversibility and entropy generation within the PEMFC and proposes an evaluation index to assess the relationship between the flow field mass transfer performance and flow losses based on the major processes causing entropy generation changes.The specific research contents of each part are as follows:Firstly,based on previous research on wave-shaped gas channels,PEMFCs with parallel,interdigitated,and serpentine flow fields with wave-like gas flow channels were constructed.By comparing the mass transfer enhancement of wave-like gas channels in flow fields with three different convective intensities,the performance improvement of wave-like gas channels in parallel,interdigitated,and serpentine flow fields was analyzed.According to the principle of achieving the highest current density improvement,the flow field configuration most suitable for wave-like gas channels was determined.It was revealed that the fundamental reason for the performance enhancement caused by the wave-like structure lies in the increase in convective intensity within the flow field,thus obtaining the flow field structure most suitable for wave-like gas channels.Secondly,the impact of operating pressure and cathode inlet pump power on the performance of the cell was analyzed.Regarding the operating pressure,a geometric model was developed by analyzing the mechanical characteristics of the membrane electrode to depict the micro-deformation of the membrane electrode caused by different operating pressures of the anode and cathode.The influence of the pressure difference of reactants on the cell performance was explained from the perspective of microscopic deformation.As for the cathode pump power,the relationship between the cathode pump power and the oxygen transport flux in the fuel cell was established.The optimal operating range of pumping power for flow fields with different convective intensities and the optimal output performance of the cell was determined.Additionally,a novel flow field with localized pressure enhancement,known as the bamboo-shaped flow field,was proposed,filling the gap between the optimal power generation ranges of parallel and serpentine flow fields.Finally,a comparison was made regarding the entropy generation resulting from various physicochemical processes occurring in the fuel cell.The influence mechanisms of mass transfer and flow processes on the internal entropy generation of the fuel cell were revealed.A relationship was established between the maximum variation in mass transfer entropy generation and flow entropy generation in the optimization design of the flow field.An evaluation index was proposed to reflect the interrelationship between mass transfer entropy generation and flow entropy generation.Furthermore,the impact of flow fields with enhanced convective intensity on the entropy generation mechanism was further analyzed.This enables the evaluation and selection of flow field priorities without the need to calculate the pumping power consumed by the fuel cell.