| The design of flow channels and membrane electrode assembly(MEA)remains one of the primary strategies for effective water management in the Proton exchange membrane fuel cell(PEMFC).This is due to the strategic role they play in the effectiveness of reactant utilization and transport,water management,and overall cell output.The study on water transport models in PEMFCs provides a platform on which new channel designs demonstrate the inherently weak water management efficiency of existing traditional channels(its types or structures).Thus,a thorough knowledge of two-phase flow dynamics in channels and the gas diffusion layer(GDL)via the evaluation and optimization of alternative channel shapes is fundamental.In this work,the volume of fluid(VOF)model coupled with the level set(LS)function is used to investigate droplet behavior inside a sinusoidal flow channel.It is achieved by comparing three geometrically different channels that suit various nondimensional sinusoidal distances(pitch-amplitude ratio)and their water-expulsion trends.Emphasis is laid on vital design parameters such as the sinusoidal channel distance(pitch-amplitude ratio),the radius of curvature,and wall contact angle to understand their influence on liquid water removal.The performance of the sinusoidal,as opposed to the traditional channel,is examined based on the droplet expulsion rate and GDL surface water coverage.It is observed that the pitch-amplitude ratio and wall wettability significantly influence the droplet expulsion rate.As such,the optimized sinusoidal models also produced a very similar drop in pressure compared to the conventional design,in addition to improved fluid velocity and water removal capacity.A novel hybrid sinusoidal flow channel is also proposed.The two-phase flow is conducted using a three-dimensional(3D),transient computational fluid dynamics(CFD)simulation based on the VOF model.Hybrid and non-hybrid sinusoidal flow channel simulations,including a direct flow channel,are evaluated based on their water exhaust efficiency and pressure drops.The effects of inlet gas velocity,wall wettability,and droplet interaction in the flow channel on the dynamic tendencies of liquid water are also examined.Results show that the novel hybrid sinusoidal channel models are consistent with the rapid expulsion of water under various hydrophilic wall conditions.The interfacial water transport behavior was also conducted due to a lack of precise information on droplet motion on the GDL-channel interface.Employing the stochastic technique,uniform and non-uniform GDL microstructures are reconstructed for this purpose.The model is tested on an optimized sinusoidal flow channel under different wettability,droplet size,and inlet velocity conditions and implemented using the OpenFOAMCFD software.Droplet detachment speed and average speed is found to depend on fiber details,such as fiber diameter and structural arrangementFurthermore,a 3D compressed GDL microstructure is developed based on the finite volume method(FVM)and used to evaluate water transport behavior.The compressed GDL microstructure and two-phase flow VOF model is developed and validated on the OpenFOAMCFD platform.The models are compared to experimental data,with good agreement.Consequently,the reconstructed GDL microstructures are subjected to compressive stresses.The water uptake behavior in the three compressed samples with different(CR)compression ratios(10% CR,20% CR,and 40% CR),is compared to that in an uncompressed GDL microstructure.Also,the effects of GDL wettability,water pressure,and non-uniform fiber diameter arrangement in GDLs are investigated.It is found that excessive compression on GDLs constricts the pores,thereby restricting access of water through the pores.An empirical correlation is established between liquid water saturation and flow time.Thus care must be taken in the treatment of GDL carbon papers and clamping force during assembly since these significantly influences water patterns in them. |
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