Abstract:

Understanding the ice melting process in the porous electrode structure during cold start is helpful to improve the cold start capability of fuel cells. In order to reveal the effect of gas diffusion layer (GDL) pore distribution on ice melting during cold start-up, this paper adopts a numerical random reconstruction method. By adjusting the porosity of each layer, the GDL structure with different porosity distribution along the thickness direction (linear gradient, polyline distribution and different commercial type distribution) is obtained. A 3D pore scale model based on the total enthalpy model is developed to investigate the effect of porosity distributions on the ice melting process. The results show that the pore distribution with increasing porosity along thickness direction helps to accelerate the ice melting and temperature rise during the melting process. For the polygonal distribution, the lower pore fluctuation range (e.g. 0.85—0.65) is more likely to melt ice than the higher pore fluctuation range (0.95—0.55). For commercial GDL, the existence of high porosity stratification at the bottom caused by actual manufacturing is not conducive to ice melting, and the porosity distribution is the most uneven in TGH060 structure, giving the worst cold start performance. This work advances the understanding of the effect of GDL pore distribution on cold start performance and helps to optimize the design of GDL and batteries.

Key words: porous media, mesoscale, numerical simulation, fuel cell, cold start

摘要：

了解冷启动过程中多孔电极结构内的冰融化过程有助于提高燃料电池的冷启动能力。为了揭示气体扩散层（gas diffusion layer，GDL）孔隙分布对于冷启动过程中冰融化的影响，基于数值随机重构的方法，通过调控各分层的孔隙率获得具有沿厚度方向上不同孔隙率分布（线性梯度、折线分布及不同商业类型分布）的GDL结构。发展基于总焓模型的三维孔隙尺度模型数值探究了不同孔隙率分布对于冰融化过程的影响。结果显示：在融化过程中，采用孔隙率沿厚度递增的孔隙分布有助于加快内部冰融化及温度上升；对于折线分布，采用较低的孔隙波动范围（如0.85~0.65）比更高的孔隙范围（0.95~0.55）更易使冰融化；对于商业所使用的GDL，其在实际加工制造中所造成的底端高孔隙率分层的存在不利于冰融化，在TGH060结构内孔隙率分布最不均匀，冷启动性能最差。这项工作促进了对GDL孔隙分布影响冷启动性能的理解，有助于优化GDL及电池的设计。

关键词: 多孔介质, 介尺度, 数值模拟, 燃料电池, 冷启动