Three-dimensional numerical simulations of water droplet dynamics in a PEMFC gas channel
Three-dimensional numerical simulations of water droplet dynamics in a PEMFC gas channel
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DOI：
10.1016/j.jpowsour.2008.03.005
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发表时间：
2008-06
影响因子：
9.2
通讯作者：
Xun Zhu;P. Sui;N. Djilali
中科院分区：
文献类型：
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作者：
Xun Zhu;P. Sui;N. Djilali
以一个长1000μm、截面积为250 μm×250μm的空气微通道为模型，模拟了液态水从气体扩散层（GDL）进入PEMFC气体流道的动力学行为。瞬态三维两相流是用计算流体动力学结合流体体积法求解的。水滴的出现，生长，变形和脱离的过程进行模拟，明确跟踪的液-气界面的演变，并表征的动态水滴进行空气流在大部分的气体通道中的离开直径，流动阻力系数，水饱和度，和水覆盖率。参数模拟包括空气流速、水注入速度和孔尺寸的影响，特别关注GDL表面的疏水性的影响，同时将其他通道壁的静态接触角设定为45°。微通道表面的润湿性被示出对水滴的动态具有重大影响，液滴更容易分裂并且在疏水表面上迅速对流，而对于亲水表面，存在扩散和膜流形成的趋势。微通道的亲水性侧壁似乎通过从GDL表面提升附着的水而提供一些益处，从而释放GDL-流动通道界面以改善反应物的传质。更高的空气入口速度被示出以减少GDL表面的水覆盖。较低的注水速度以及较小的孔径导致更早的水滴离开和更低的微通道中水的体积分数。
The dynamic behavior of liquid water emerging from the gas diffusion layer (GDL) into the gas flow channel of a polymer electrolyte membrane fuel cell (PEMFC) is modeled by considering a 1000μm long air flow microchannel with a 250μm×250μm square cross section and having a pore on the GDL surface through which water emerges with prescribed flow rates. The transient three-dimensional two-phase flow is solved using Computational fluid dynamics in conjunction with a volume of fluid method. Simulations of the processes of water droplet emergence, growth, deformation and detachment are performed to explicitly track the evolution of the liquid–gas interface, and to characterize the dynamics of a water droplet subjected to air flow in the bulk of the gas channel in terms of departure diameter, flow resistance coefficient, water saturation, and water coverage ratio. Parametric simulations including the effects of air flow velocity, water injection velocity, and dimensions of the pore are performed with a particular focus on the effect of the hydrophobicity of the GDL surface while the static contact angles of the other channel walls are set to 45°. The wettability of the microchannel surface is shown to have a major impact on the dynamics of the water droplet, with a droplet splitting more readily and convecting rapidly on a hydrophobic surface, while for a hydrophilic surface there is a tendency for spreading and film flow formation. The hydrophilic side walls of the microchannel appear to provide some benefit by lifting the attached water from the GDL surface, thus freeing the GDL-flow channel interface for improved mass transfer of the reactant. Higher air inlet velocities are shown to reduce water coverage of the GDL surface. Lower water injection velocities as well as smaller pore sizes result in earlier departure of water droplets and lower water volume fraction in the microchannel.