Dynamics and Control of Liquid Water Movement in PEM Fuel Cells

采用benzigermodel聚合物电解质膜（PEM）燃料电池反应器来阐明水传输的关键物理特性，以建立改进的动力学模型和控制系统。以前的PEM燃料电池模型缺少驱动水通过气体扩散层（GDL）所必需的液压的基本物理特性，这导致水塞阻塞了气体流动通道和排气歧管。简化的质子交换膜燃料电池模型有助于确定控制质子交换膜燃料电池中水传输动力学的基本物理。新的实验计划采用简化的模型反应器来量化表面张力、重力和粘度对GDL中水输送、气体流动通道和排气歧管的影响。流动可视化与局部电流密度测量相结合，以确定更好的控制系统，以最小的燃料循环来提高燃料利用率。使用简化模型反应堆可以极大地提高我们对燃料电池中的反应和传输的理解，有助于改进燃料电池的设计、操作和控制。知识价值：一种新的方法来分析燃料电池的运行，重点是燃料电池作为一个化学反应器将被使用。PI之前对一维搅拌槽反应器（STR） PEM燃料电池的动力学研究揭示了燃料电池运行中以前未认识到的复杂行为。STR - PEM燃料电池的动态响应表明，膜中产生的水与质子电导率之间的正反馈导致了电流的点火/熄灭和稳态多重性。过去的研究使用了一个模型二维分段阳极平行通道燃料电池，证明了电流点火与聚合物膜中扩散的水流耦合导致电流密度沿流道传播。SAPC燃料电池的研究结果表明，PEM燃料电池的泛水是由于气体流动通道中形成的水塞阻塞了反应物的供应。这项工作显示了气体流动通道中的段塞运动如何与局部电流密度波动相关。通过提高对燃料电池基本物理知识的了解，有可能开发出无通道自排水PEM燃料电池，该电池可以在130ºC的干燥进料下工作，电流密度为1 A/cm2。自排水燃料电池的设计也导致了一种可变面积燃料电池的发展，它可以满足100%燃料利用率的电力需求，并且对温度不敏感。该项目旨在展示GDL孔径、重力和气体速度对燃料电池运行中液滴运动的重要性，以及它们如何改变电流和功率输出。采用模型微流控系统进行实验，阐明两相微流控系统中液体运动的动力学特性，从而确定PEM燃料电池所需的进料控制以匹配可变功率负载。采用模型反应堆系统来确定PEM燃料电池运行的基本物理特性的方法是独特的。燃料电池开发和研究中使用的复杂反应堆结构提供了综合响应，而关键物理是模糊的。只有通过精心设计实验系统，才能在系统规模上隔离反应和传输的基本物理，才能设计出性能最佳的PEM燃料电池。更广泛的影响：燃料电池已被确定为氢经济的重要组成部分，以减少对化石燃料的需求并改善环境。PEM燃料电池的水管理是实现稳健和简化操作的主要障碍，而这对消费者的接受度至关重要。本文所讨论的燃料电池动力学和控制的基本原理对高效燃料电池的工程设计至关重要。从这项工作中开发的数据和模型将作为PEM燃料电池系统工程的基础，使其成为经济上可行的技术。这些基础研究也为教育推广提供了一个杰出的论坛。过去的研究工作有十多名本科生和三名高中教师参与。当地三所高中的9-12年级已经实施了实验和教学模块，这些实验和教学模块将扩展到向新生介绍能源技术

CBET-0754715BenzigerModel Polymer Electrolyte Membrane (PEM) fuel cell reactors are employed to elucidate the key physics of water transport to develop improved dynamic models and control systems. Previous models of PEM fuel cells have missed essential physics of the necessary hydraulic pressure to drive water transport through the gas diffusion layer (GDL), which results in water slugs blocking the gas flow channels and exhaust manifolds. Simplified model PEM fuel cells have helped identify the essential physics that govern the water transport dynamics in PEM fuel cells. New experiments are planned employing simplified model reactors to quantify the effects of surface tension, gravity, and viscosity for water transport in the GDL, the gas flow channels and the exhaust manifold. Flow visualization coupled with local current density measurements to identify better control systems to improve fuel utilization with minimal fuel recycle. The use of simplified model reactors can vastly improve our understanding of reaction and transport in fuel cells, assisting in their improved design, operation and control. Intellectual Merit: A new methodology for analyzing fuel cell operation, focusing on the fuel cell as a chemical reactor will be used. The PI's previous studies of the dynamics of a one-dimensional Stirred Tank Reactor (STR) PEM fuel cell unearthed complex behavior not previously recognized in fuel cell operation. The dynamic response of the STR PEM fuel cell showed that the positive feedback between water produced and proton conductivity in the membrane resulted in current ignition/extinction and steady state multiplicity. Past studies were with a model 2-dimensional segmented anode parallel channel fuel cell that demonstrated current ignition coupled with diffusive water flow in the polymer membrane resulted in current density fronts propagating along the flow channel. The results with the SAPC fuel cell demonstrate flooding in PEM fuel cells occurs due to water slug formation in the gas flow channels which blocks reactant supplies. This work shows how slug motion in the gas flow channels is correlated with local current density fluctuations. By improving knowledge of the basic physics in fuel cells it is possible to develop the channel-less self-draining PEM fuel cell that operates with dry feeds to temperatures of 130ºC with current densities 1 A/cm2. The self-draining fuel cell design has also led to the development of a variable area fuel cell that follows power demands with 100% fuel utilization and is insensitive to temperature. This project is to show the importance that GDL pore size, gravity, and gas velocity have in liquid droplet motion in fuel cell operation, and how that alters the current and power output. Experiments with model micro-fluidic systems to elucidate the dynamics of liquid motion in 2-phase micro-fluidic systems that can identify the necessary feed control to match variable power loads for PEM fuel cells will be done. The approach of employing model reactor systems to identify the essential physics of PEM fuel cell operation is unique. The complex reactor configurations employed in fuel cell development and research has provided integrated responses where the key physics is obscured. Only by the careful design of experimental systems to can isolate the essential physics of reaction and transport on a system scale will it be possible to design PEM fuel cells that optimize performance. Broader Impact: Fuel cells have been identified as an essential element of the hydrogen economy to reduce demand for fossil fuels and improve the environment. Water management in PEM fuel cells is a major stumbling block to robust and simplified operation that is essential for consumer acceptance. The fundamentals of fuel cell dynamics and control addressed here are critical to the engineering design of efficient fuel cells. The data and models developed from this work will serve as a basis for systems engineering of PEM fuel cell systems to make them an economically viable technology. These fundamental studies have also provided an outstanding forum for educational outreach. Past work engaged more than ten undergraduates and three high school teachers in this research. Experiments and teaching modules have been put in place for grades 9-12 in three local high schools and these will be expanded to introduce energy technology to new students