Higher load current of PEMFC

PEMFC的性能在很大程度上取决于其水管理。气体扩散层（GDL）和催化剂层是治理的主要目标，由于这些层属于微孔介质和碳基不透明材料，因此难以测量和观察。另一方面，PEMFC内气液两相流数值模拟是近年来发展起来的。在这一模拟进展中，MM模型作为处理GDL等多孔介质中两相现象的数学模型之一，似乎成功地模拟了电池运行过程中的泛水。但是对仿真结果的评价还不够充分。只是基于仿真和实验对IV特性的比较进行评价。模拟的两相现象，如GDL的含水饱和度，还没有用实验结果来评价。本文采用间接法测量了GDL含水饱和度，并与模拟结果进行了比较。我们制作了一个整个流体在GDL中强制流动的简单的交错槽，并通过GDL测量了压差，并通过压差估计了含水饱和度。在数值模拟中，我们建立了基于MM模型的全守恒方程，并考虑了交叉单元的边界条件。在仿真中，我们还进行了负载电流阶跃变化的暂态计算。在测量中，当负载电流超过0.5A/cm2时，电池电位显著下降。我们成功地解释了这种下降是由浓度过电位和估计的含水饱和度引起的。负载电流、加湿温度和气体利用率越高，水饱和率越高。这些操作条件被认为是控制GDL水淹的关键参数。模拟的IV特性成功地再现了测量值。但在大电流区未见浓度过电位的出现。模拟得到的压差与实测数据的定性吻合在15%以内。在瞬态计算中，电池电位变化复杂。我们可以用几个时间常数来解释这一现象，这些时间常数与细胞内正在进行的转运现象相对应。少

The performance of PEMFC largely depends on its water management. The flooding appeared in gas diffusion layer (GDL) and catalyst layer, which are main target to be managed, is difficult to measure and/or observe, because these layers are categorized as micro-porous media and opaque material based on carbon. On the other hand, the gas-liquid two-phase flow numerical simulation in PEMFC is developed recently. In this progress of simulation, the MM model, which is one of mathematical model to treat two-phase phenomena in porous media such as GDL, seems to successfully simulate the flooding during cell operation. However the evaluation of the simulation is not enough. Only the evaluation is based on the comparison of IV characteristic between simulation and experiment. The simulated two-phase phenomena, such as the water saturation ratio in GDL, have not been evaluated with experimental result.In this study, we measured the water saturation in GDL with indirect method and compared its res … More ult with that obtained from simulation. We fabricated a simple interdigitated cell where the whole fluid flows forcedly in GDL, and measured the differential pressure through GDL, and estimated the water saturation ratio from its differential pressure. In numerical simulation, we formulated the full conservation equations based on MM model, and executed with the boundary condition considering the interdigitated cell. In simulation we also executed the transient calculation in which the load current changed step-wisely.In measurement, the cell potential decreased significantly over 0.5A/cm2 load current. We successfully explained that this drop was caused by the concentration over potential accompanied with the water saturation estimated. The water saturation ratio increased with higher load current, humidification temperature, and gas utilization ratio. These operation conditions are noted as the key parameter to control the flooding in GDL. The simulated IV characteristics succeeded to reproduce the measured. But they could not show the concentration overpotential appeared in high current region. The differential pressure obtained from the simulation qualitatively agreed with the measured data within 15%. In transient calculation, the cell potential changed complexly. We could explain this with several time constant corresponding to the transport phenomena being progressed in cell. Less