Transport Phenomena in Micro/Miniature Passive Vapor Feed Direct Alcohol Fuel Cells

直接酒精燃料电池(DAFC)是许多便携式应用的理想候选者，因为与传统电池相比，它的每次加油寿命更长，重量更轻。在这种类型的燃料电池中，无论是直接甲醇燃料电池(DMFC)还是直接乙醇燃料电池(DEFC)，酒精不会转化为氢气，而是以非常简单的方式直接使用。其30-100℃的低工作温度是微型到微型尺寸的理想选择。DAFC的主要好处之一是燃料可以储存在液体状态，并有可能通过被动方式提供，使产生的所有电力可供外部工作使用。设计DAFC的主要问题之一是控制酒精交叉量。醇交叉是通过膜扩散并在阴极催化层上反应的醇。智能优点：拟议工作的主要目标是发展基本的基础知识，这些知识对于设计和开发具有高效热流体管理系统的无源微型DAFC来说是缺乏的，并且是必不可少的。目前，有效的无源DAFC设计受到缺乏对这些装置内多相、多组分传输现象的物理过程的详细了解的限制，无论是在燃料输送系统中还是在燃料电池中。目标是开发一个详细的物理非等温模型，包括2D-3D数值模拟，并将其与建议的详细实验结果进行比较。瞬变模型解决了：跨界、燃料输送、水和热管理问题。在我们看来，这项研究代表了便携式被动燃料电池令人兴奋的未来的前沿。所提出的分析方法通过多流体模型方法分别模拟了液体和气相中的运移。需要一个适当的统计分布函数来创建局部孔洞属性以及与孔洞的连通性直接相关的连续相限制。模型还应该使用能量方程，这在被动运行的燃料电池中很重要，因为没有强迫对流效应来保持电池在几乎恒定的温度下运行。现有的多相模型都没有考虑气液两相中孔隙性质的局部变异性或不可约的饱和极限，包括连续/不连续相极限的影响。最重要的是，目前还没有一个非等温多相物理模型来预测进气被动DAFC系统中的各种过程。更广泛的影响：本提案中对微型DAFC中传输现象的基础研究有助于推动用于交通应用和一些固定应用的大型DAFC系统的发展。这项工作将通过研究生和本科生的教育以及燃料电池领域的持续讲习班进行传播。

The Direct Alcohol Fuel Cell (DAFC) is an ideal candidate for many portable applications because of its extended-life per refueling and its low weight as compared to a conventional battery. In this type of fuel cell, either direct methanol fuel cell (DMFC) or direct ethanol fuel cell (DEFC), alcohol is not reformed into hydrogen gas but is used directly in a very simple manner. Its low operating temperature of 30-100C is ideal for micro to miniature sizes. One of the leading benefits of a DAFC is that the fuel can be stored in its liquid state, and has the potential to be delivered by passive means, making all the power produced available for external work. One of the major issues with designing a DAFC is controlling the amount of alcohol crossover. Alcohol crossover is alcohol that diffuses through the membrane and reacts at the cathode catalyst layer. Intellectual Merit: The primary goal of the proposed work is to develop basic fundamental knowledge which is lacking and essential for design and development of passive miniature DAFC with an efficient thermal-fluids management system to replace existing batteries At present, effective passive DAFC design is restricted by the lack of detailed knowledge of the physical processes of multiphase, multi-component transport phenomena within these devices, both in the fuel delivery system and the fuel cell. The goal is to develop a detailed physical non-isothermal model including a 2D-3D numerical simulation, and compare it to the proposed detailed experimental results. The transient model addresses: crossover, fuel delivery, water and thermal management issues. In our view, this research represents the leading edge in the exciting future of portable passive fuel cells. The proposed analysis simulates transport in the liquid and gas phases separately through a multi-fluid model approach. An appropriate statistical distribution function is needed to create the local pore properties, as well as the continuous phase limitation, which directly relates to connectivity of the pores. The model should also employ the energy equation, which is important in passively operated fuel cells, since no forced convection effects are available to keep the cell operating at a nearly constant temperature. None of the existing multiphase models take into account the local variability of porous properties or the irreducible saturation limits, including the effect of continuous/discontinuous phase limitation, in the liquid and vapor phases. Most importantly, presently there is no non isothermal multiphase physical model for the prediction of various processes in vapor feed passive DAFC systems. Broader Impacts: The fundamental research on transport phenomena in mico/minature DAFCs in this proposal can benefit the advancement of larger DAFC systems used for transportation applications and some stationary applications. The work will be disseminated to through education of both graduate and undergraduate students and continued workshops in the fuel cell area.