Water Management in PEM Fuel Cells

PEM 燃料电池中的水管理

• 批准号: 0405965
• 负责人: Keith Promislow
• 金额: $ 11万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0405965&HistoricalAwards=false
• 关键词: Water; Management; PEM; Fuel; Cells

The goal of this project is the first mathematical analysis of the structure and scaling of the multiphase flow in the gas di_usion layer of PEM fuel cells. The weak flux regime identified from the scaling suggests a reduction of the coupled degenerate parabolic system of conservation laws for heat and mass transport with phase change to a sharp interface model, with a linear problem on either side of a slowly moving free interface. A rigorous analysis of this problem, based upon the renormalization group, will yield analytical expressions for vapor and liquid fluxes in terms of prescribed boundary conditions and material parameters. Based upon this reduction, a suite of fast, robust numerical schemes in 1+2 and 1+3D will be developed to investigate control strategies for water management. We estimate a speed up in computational time of 3-4 orders of magnitude over resolution of the full problem. A key application is the development of drying purge cycles, these minimize damage from ice formation after shut-downby dehydrating the gas di_usion layer and flow fields, while maintaining humidification levels in the membrane. Numerical simulation of drying purges requires fast and accurate capturing of the multiphase fronts, a feature unavailable in existing codes. In addition, a simplified model of the coupled parabolic-elliptic problem for water management in the ionomer membrane will be developed and analyzed. Recent experimental work has shown multiple steady states, hysteresis, and long-time oscillations in membrane hydration levels. At low inlet humidity levels associated with autohumidification the membrane hydration couples strongly to the electric potential through the membrane conductivity, leading to "dry-cell" bifurcations and slow moving fronts. Autohumidification criteria which avoid the dry-cell bifurcation will be developed, the inverse problem detecting the dry-cell bifurcation from external voltage measurements will be investigated. A model of the cathode catalyst layer including oxygen and hydronium transport, the overpotential, the electric potential, and build-up of liquid water layers will be developed. The connection between averaged reaction rates and catalyst layer micro-structure will be rigorously established through homogenization theory by solving key cell-problems which elucidate the role of triple junction points and catalyst layer geometry on over-all performance. A connection between micro-structure geometry and the experimental technique of AC impedance spectroscopy will be pursued.Proton electrolyte membrane (PEM) fuel cells are unique energy conversion devices with a broad range of applications. Powered by hydrogen gas or directly from methanol, they hold promise to revolutionize the automotive industry while at the same time yielding e_cient power generation for cell phones, laptop computers, camcorders, digital cameras, PDAs, and other applications in the 10-100 Watt range. However, optimization is required to achieve targets of cost reduction, unit power density, operational lifetime, and to improve performance for autohumidification regimes. Water management is key not only to e_cient cell operation but also to prolonging cell operational lifetime. The development of the proposed models and high-performance computational tools for water management in PEM fuel cells represent a significant breakthrough in the computational resolution of the delicate free-surface motion required tounderstand water management. These novel computational tools will improve resolution while reducing computation time from from weeks to minutes. This dramatic enhancement of computational performance will have substantial impact on the development of new materials and manufacturing processes for the fuel cell industry, including the PI's industrial partners, Ballard Power Systems andW.L. Gore. Moreover, the development of lightweight, durable, low thermal and acoustic signature power sources has been identified by the Intelligence Community as an important ingredient of homeland security.

本计画的目标是首次对质子交换膜燃料电池气体扩散层中多相流的结构与尺度进行数学分析。弱通量制度确定的缩放表明减少耦合退化抛物型系统的守恒定律的热量和质量的运输与相变的尖锐的接口模型，与线性问题的任何一方的缓慢移动的自由界面。这个问题的严格分析，重整化群的基础上，将产生蒸汽和液体通量的解析表达式在规定的边界条件和材料参数。在此基础上，一套快速，强大的数值方案在1+2和1+ 3维将开发研究控制策略的水管理。我们估计在整个问题的分辨率的计算时间的3-4个数量级的速度。一个关键的应用是干燥清洗循环的开发，这些通过使气体扩散层和流场脱水，同时保持膜中的加湿水平，最大限度地减少了关闭后结冰造成的损害。干燥吹扫的数值模拟需要快速准确地捕获多相前沿，这是现有代码中不可用的功能。此外，一个简化的模型的耦合抛物椭圆问题的水管理的离聚物膜将开发和分析。最近的实验工作表明，多个稳态，滞后，和长时间的振荡膜水合水平。在与自增湿相关的低入口湿度水平下，膜水合通过膜电导率强烈耦合到电势，导致“干电池”分叉和缓慢移动的前沿。提出了避免干电池分岔的自增湿判据，并研究了从外部电压测量值检测干电池分岔的反问题。阴极催化剂层的模型，包括氧气和水合氢的运输，超电势，电势，和液体水层的建立将被开发。平均反应速率和催化剂层微观结构之间的联系将通过均质化理论通过解决关键单元问题来严格建立，这些问题阐明了三重连接点和催化剂层几何形状对整体性能的作用。质子电解质膜（PEM）燃料电池是一种独特的能量转换器件，具有广泛的应用前景。它们由氢气或直接由甲醇提供动力，有望彻底改变汽车工业，同时为手机、笔记本电脑、摄像机、数码相机、PDA和10-100瓦范围内的其他应用提供高效的发电。然而，需要优化以实现降低成本、单位功率密度、操作寿命的目标，并提高自动增湿制度的性能。水管理不仅是电池高效运行的关键，也是延长电池使用寿命的关键。所提出的模型和高性能计算工具的发展，在PEM燃料电池的水管理代表了一个显着的突破，在计算分辨率的微妙的自由表面运动所需的理解水管理。这些新的计算工具将提高分辨率，同时将计算时间从数周减少到数分钟。这种计算性能的显著增强将对燃料电池行业的新材料和制造工艺的开发产生重大影响，包括PI的工业合作伙伴巴拉德动力系统公司和W.L.戈尔。此外，情报界已将轻质、耐用、低热和声学特征电源的开发确定为国土安全的重要组成部分。