Two-phase flow instabilities in large arrays of microchannels in low temperature fuel cells

1133025 PI Litter拟议研究的目标是利用非线性分析来阐明低温燃料电池中大量并行微通道(10,000个)中的两相流动不稳定性，并将这些方法应用于设计新的高级诊断和控制程序。水管理仍然是低温燃料电池的重大技术挑战，例如聚合物电解质燃料电池(PEFCs)。防止严重液态水积聚的工程措施，即所谓的水淹，已经导致了几种性能和成本的折衷，包括高空气输送寄生负荷和对最小板厚的限制。大量平行微通道中的两相流不稳定性是导致电池效率低下的关键因素；然而，这些不稳定性并没有得到很好的理解或预测。此外，以前没有研究通道数(覆盖电极的通道数)对稳定性的影响。研究将分四个阶段进行。第一阶段：利用三个非现场实验平台研究两相不稳定性的动力学：i)以单通道流动显示和压降测量装置为对照。Ii)具有并行分流通道的单通道，其模拟没有两相流动扰动的通道间通信的并行通道。Iii)具有不同数目的平行通道的流场。这种三层方法将单通道动态与由两相干扰的通道间通信引起的动态区分开来。利用非线性时间序列分析技术来分析时间序列中信息丰富的结构。第二阶段：利用离散的一维流动方法和先进的两相流动关联式，建立大阵列平行微通道中两相流动的稳定性模拟框架。将进行广泛的参数空间模拟，以阐明动力学与设计和运行条件之间的关系。时空摄动将识别边际稳定性边界，从而构建广义流动稳定性图。第三阶段：研究通道多元化对PEFCs运行的原位动力学的影响。对电压和压降时间序列的非线性分析将阐明流型的转变和不稳定的开始。根据这些数据，将构建一族经验稳定性图。阶段4：建立基于非线性技术的混沌系统诊断和控制框架。其中一个组成部分是设计一种早期预警检测技术，这是工业界的一个关键兴趣。这项工作将建立混沌控制方法，以更有效地防止洪水泛滥。这项拟议的工作有几个新的研究途径。这项工作将是首次将非线性分析技术应用于燃料电池研究，将这些强大的技术引入该领域。PI将从实验和理论上研究多个通道对大阵列微通道中两相流动动力学的影响及其对燃料电池性能的影响。燃料电池开发者早就知道，通道多样性是PEFC设计中的一个重要因素，但还没有从根本上对其进行研究或量化。为了提供基本的见解，理论上的稳定性分析将被用来从边际稳定边界构建稳定图。PI还将研究利用非线性统计进行早期预警检测和混沌控制方法以缓解洪水的新方法。就更广泛的影响而言，PI旨在提高PEFC的性能和运行的健壮性。PEFC被广泛视为可持续能源基础设施的关键能源转换装置。这项工作充分利用了与业界的关系，产生了及时的、实际的影响。该研究也广泛适用于其他具有微通道内两相流的系统(如电解槽)。提出了一项有针对性的教育、推广和指导计划。这位PI将把这项研究纳入他的流体动力学和能源系统课程。对于外展，PI将通过利用大量已建立的活动来展示关于燃料电池和流体动力学的引人入胜的动手活动，从而最大限度地发挥影响。此外，卡内基梅隆大学的Gelfand中心将通过帮助向匹兹堡地区的学校传播材料和信息来支持这些努力，特别是服务不足的学校有高危学生群体。此外，PI将把这项研究与他为教师举办的能源系统研讨会结合在一起，作为什么是工程的一部分？卡内基梅隆大学的系列研讨会。

1133025 PI LitsterThe objectives of the proposed research are to elucidate the two-phase flow instabilities in the massive arrays of parallel micro-channels (10,000) in low temperature fuel cells using nonlinear analysis and to apply those approaches in devising new advanced diagnostics and control routines. Water management remains a significant technical challenge for low temperature fuel cells, such as polymer electrolyte fuel cells (PEFCs). Engineering measures to prevent severe liquid water accumulation, known as flooding, have resulted in several performance and cost compromises that include high air delivery parasitic loads and limitations on minimum plate thickness. Two-phase flow instabilities in the large arrays of parallel micro-channels are a key contributor to cell inefficiencies; however, these instabilities are not well understood or predictable. Furthermore, the influence of channel plurality (number of channels covering the electrode) on the stability has not been previously studied. The research will be performed in four phases. Phase 1: Investigate the dynamics of the two-phase instabilities using three ex situ experimental platforms: i) A single channel apparatus for flow visualization and pressure drop measurements serves as a control case. ii) A single channel with a parallel shunt channel that simulates parallel channels without inter-channel communication of two-phase flow disturbances. iii) A flow field with varying numbers of parallel channels. This three-tier approach distinguishes single-channel dynamics from those due to channel-to-channel communication of two-phase disturbances. Nonlinear time-series analysis techniques will be used to analyze the information-rich structure of the time-series. Phase 2: Establish a stability modeling framework for two-phase flow in large arrays of parallel micro-channels using a discretized, one-dimensional flow approach and advanced two-phase flow correlations. A broad parameter space will be simulated to elucidate relationships between the dynamics and the design and operating conditions. Spatio-temporal perturbations will identify marginal stability boundaries, allowing the construction of generalized flow stability maps. Phase 3: Investigate the effect of channel plurality on the in situ dynamics of operating PEFCs. Nonlinear analysis of voltage and pressure drop time-series will elucidate transitions in flow regime and onset of instability. From these data, a family of empirical stability maps will be constructed. Phase 4: Establish a diagnostic and control framework based on nonlinear techniques for chaotic systems. One component is devising an early warning detection technique, a key interest of industry. The work will establish chaos control methods to more efficiently prevent flooding. The proposed work has several avenues of new research. This work will be the first use of nonlinear analysis techniques in fuel-cell research, introducing these powerful techniques to the field. The PI will experimentally and theoretically investigate the influence of channel plurality on two-phase flow dynamics in large arrays of microchannels and its impact on fuel-cell performance. Fuel-cell developers have long known that channel plurality is an important factor in PEFC design, but it has not been fundamentally studied or quantified. To provide fundamental insight, a theoretical stability analysis will be used to construct a stability map from marginal stability boundaries. The PI will also investigate the novel approach of using nonlinear statistics for early warning detection and chaos control methods to mitigate flooding. In terms of the broader impacts, the PI aims to improve PEFC performance and robustness of operation. PEFCs are widely viewed as a key energy conversion device for a sustainable energy infrastructure. The work leverages relationships with industry for timely, practical impact. The research is also broadly applicable to other systems with two-phase flow in microchannels (e.g., electrolyzers). A targeted education, outreach, and mentoring plan is proposed. The PI will incorporate the research into his courses on fluid dynamics and energy systems. For outreach, the PI will maximize impact by leveraging a large number of established events to present engaging, hands-on activities on fuel cells and fluid dynamics. Furthermore, the Gelfand Center at Carnegie Mellon will support the efforts by helping to disseminate materials and information to Pittsburgh region schools, particularly underserved schools with at-risk student populations. In addition, the PI will integrate this research with his workshops on energy systems for teachers as part of the What is Engineering? workshop series at Carnegie Mellon.