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Application of electroosmotic pumps to low temperature fuel cells.

机译：电渗泵在低温燃料电池中的应用。

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摘要

Proton exchange membrane fuel cells (PEMFCs) are attractive energy conversion devices due to their high efficiency and environmentally benign operation. PEMFCs are being developed for numerous applications ranging from transportation to portable electronics. PEMFCs encompass a general class of fuel cell architectures that employ a solid polymer, typically NafionRTM, as the electrolyte. PEMFCs can be further classified based on the fuel utilized. Hydrogen is the most popular fuel but PEMFCs also operate on various alcohols including ethanol and methanol. Direct methanol fuel cells (DMFCs) in particular oxidize aqueous methanol solutions at the cell anode to yield electrical energy, waste heat, and carbon dioxide. Liquid methanol has roughly half the volumetric energy density of gasoline, making DMFCs attractive for applications with size and weight constraints.;This study explores unique aspects of using electroosmotic (EO) pumping structures to remove water from PEMFC cathodes and to supply methanol and water mixtures to DMFCs. Electroosmotic flow is the bulk motion of an electrolyte caused by coulombic interaction of external electric fields and the charges of an electric double layer (EDL). Porous glass EO pumps offer large surface-to-volume ratio and relatively high zeta potential, &zgr;, defined as the potential drop across the diffuse charges of the EDL. EO pumps have no moving parts and can produce high flow rate per package volume. These properties make EO pumps highly suitable for fuel cell applications.;Recent experimental and numerical investigations on PEMFCs emphasize water management as a critical factor in the design of robust, high efficiency systems. Although various water management strategies have been proposed, water is still typically removed by pumping air into cathode channels at flow rates significantly higher than required by fuel cell stoichiometry. Such methods are thermodynamically unfavorable and constrain cathode flow channel design. We have developed proton exchange membrane fuel cells (PEMFCs) with integrated planar electroosmotic (EO) pumping structures which actively remove liquid water from cathode flow channels. EO pumps can relieve cathode design barriers and facilitate efficient water management in fuel cells. We demonstrate and quantify the efficacy of EO water pumping using controlled experiments in a single channel cathode flow structure. Our results show that, under certain operating conditions, removing water from the cathode using integrated EO pumping structures improves fuel cell performance and stability. The application of EO pumps for liquid water removal from PEMFC cathodes extends their operational range and reduces air flow rates.;With respect to fuel delivery for DMFCs we discuss several EO pump figures of merit pertinent to portable fuel cell applications including flow rate per power, thermodynamic efficiency, and the ratio of EO pump power to fuel cell power. Additionally, we discuss the complex coupling of DMFC and methanl fuel pumps caused by two phase flow in the DMFC anode. Gaseous CO2 in the anode, a byproduct of methanol oxidation, increases the pressure load by nearly one order of magnitude versus single phase flow. We present key considerations for methanol delivery through controlled parametric studies of the two phase pressure drop at the DMFC anode. Finally, we develop a semi-empirical model which predicts trends in DMFC performance and allows for design and analysis of optimal operating conditions. In particular we illuminate the delicate balance between increasing inlet methanol concentration (for reduced EO pump power) and mitigating methanol crossover (favoring lower concentration). Ultimately this work provides a basis for miniature DMFC system designs which aim to leverage EO pumping for fuel delivery.
机译：质子交换膜燃料电池（PEMFC）由于其高效率和对环境有益的操作而成为有吸引力的能量转换设备。 PEMFC正在为从运输到便携式电子的众多应用开发。 PEMFC涵盖了一般类型的燃料电池架构，这些架构采用固体聚合物（通常为NafionRTM）作为电解质。 PEMFC可根据使用的燃料进一步分类。氢是最受欢迎的燃料，但PEMFC还可使用多种醇（包括乙醇和甲醇）运行。直接甲醇燃料电池（DMFC）特别是在电池阳极处氧化甲醇水溶液，以产生电能，废热和二氧化碳。液态甲醇的能量密度约为汽油的一半，因此DMFC在尺寸和重量受限的应用中具有吸引力。;本研究探讨了使用电渗（EO）抽气结构从PEMFC阴极去除水以及供应甲醇和水混合物的独特方面DMFC。电渗流是由外部电场的库仑相互作用和双电层（EDL）的电荷引起的电解质的整体运动。多孔玻璃EO泵具有较大的表面体积比和相对较高的Zeta电势，它定义为EDL扩散电荷上的电势下降。 EO泵没有活动部件，每包装体积可产生高流量。这些特性使EO泵非常适合于燃料电池应用。；最近对PEMFC进行的实验和数值研究强调，水的管理是设计坚固，高效系统的关键因素。尽管已经提出了各种水管理策略，但是通常仍然通过以显着高于燃料电池化学计量要求的流速将空气泵送到阴极通道中来去除水。这样的方法在热力学上是不利的，并且限制了阴极流动通道的设计。我们已经开发出具有集成平面电渗（EO）泵浦结构的质子交换膜燃料电池（PEMFC），该结构可从阴极流道中主动去除液态水。 EO泵可以减轻阴极设计的障碍，并有助于燃料电池的高效水管理。我们演示和量化使用单通道阴极流结构中的受控实验的EO水泵的功效。我们的结果表明，在某些运行条件下，使用集成的EO泵浦结构从阴极除水可改善燃料电池的性能和稳定性。 EO泵用于从PEMFC阴极去除液态水的应用扩展了它们的工作范围并降低了空气流速。关于DMFC的燃料输送，我们讨论了与便携式燃料电池应用相关的几个EO泵性能指标，包括每功率流量，热力学效率以及EO泵功率与燃料电池功率之比。此外，我们讨论了DMFC阳极中的两相流引起的DMFC和甲烷燃料泵的复杂耦合。阳极中的气态CO2是甲醇氧化的副产物，相对于单相流，压力负荷将压力负荷提高了近一个数量级。通过对DMFC阳极两相压降的受控参数研究，我们提出了甲醇输送的关键考虑因素。最后，我们开发了一个半经验模型，该模型可以预测DMFC性能的趋势，并允许设计和分析最佳操作条件。特别是，我们阐明了增加入口甲醇浓度（降低EO泵功率）和减少甲醇交换（有利于降低浓度）之间的微妙平衡。最终，这项工作为微型DMFC系统设计奠定了基础，这些设计旨在利用EO泵进行燃料输送。

著录项

  • 作者

    Buie, Cullen Richard.;

  • 作者单位

    Stanford University.;

  • 授予单位 Stanford University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 140 p.
  • 总页数 140
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

  • 入库时间 2022-08-17 11:38:25

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