摘 要

如今，随着社会的快速发展，人类生活水平的提高，环境与能源危机已经成为人类无法避免的问题。燃料电池技术的发展可以很好的缓解这一问题。燃料电池是一种高效率，无污染的能量转换装置，它通过电化学反应，将燃料中的化学能直接转化为电能。然而，燃料电池在发展过程中，仍然需要解决一些关键问题，才能实现其商业化。水管理问题是燃料电池最重要的问题之一，其对PEMFC的性能影响较大。如果没有进行恰当的水管理，会造成膜脱水、电极水泛滥等问题，从而严重影响燃料电池的耐久性、性能及寿命。

本文主要研究的是燃料电池气体扩散层（GDL）的水传递的研究，利用格子Boltzmann法，基于扩散表面理论，并使用反弹边界以及无滑移边界条件，建立MRTLBM（Multiple-Relaxation-Time Lattice Boltzmann）模型，来模拟气体扩散层中多相流（气液）及多粘度比的流体流动特性。对GDL孔隙结构的数值重构，利用已开发的格子玻尔兹曼计算程序，计算并分析通过数值重构的多孔介质，并且在服务器上运算及后处理，对结果进行分析和归纳，得出影响质子交换膜燃料电池扩散层中水传递的主要因素。

本文主要讨论了接触角、表面张力、压差、粘度比等因素对GDL内水传递的影响。

研究结果表明：

(1)在其它条件相同时，随着压差的增大，水在GDL内的流动趋势没有发生明显的变化（流动趋势主要由润湿性质及材料的憎水性决定）。但是，压差的增大促进了水在GDL内的传递，使得水的饱和度增大。

(2)粘度比的变化对水的流动趋势没有产生明显的影响。粘度比从M=54变为M=18时，加快了水在GDL内的传递，也提高了在各个接触角下水在GDL内的饱和度。

(3)表面张力的减小并不会明显地改变水的流动趋势。减小表面张力会导致水在计算区域中的渗透轻微减小，从而饱和度略有降低。并且在稳定的位移状态下，表面张力主要提供抵抗外部压力的变化和粘性阻力。

(4)同时增大压差和粘度比时，减缓了水的流动，水的饱和度降低。说明在这种情况下粘度比对水传递的影响占主导作用。

(5)水的饱和度随接触角的增大而逐渐减小。流动趋势并未发生明显变化。

关键词：格子Boltzmann法；气体扩散层；多相流；孔隙介质；水传递

Abstract

Nowadays, with the rapid development of society and the improvement of human living standard, environmental and energy crisis has become an unavoidable problem. The development of fuel cell technology can alleviate this problem very well. Fuel cell is a kind of energy conversion device with high efficiency and no pollution. It converts the chemical energy of fuel directly into electric energy by electrochemical reaction. However, in the development of fuel cells, there are still some key problems to be solved before they can be commercialized. Water management is one of the most important problems in fuel cells, which has a great impact on the performance of PEMFC. Some situations, such as membrane dehydration, electrode flooding and so on will seriously affect on the performance of fuel cells without proper water management.

This paper mainly deals with the study of the water transfer in the gas diffusion layer (GDL) of fuel cells. Using the lattice Boltzmann method, based on the diffusion surface theory, and using the bounce-back boundary and the non-slip boundary conditions, the MRTLBM (multiple-relaxation-time lattice Boltzmann) model is established to simulate the multiphase (gas and liquid) and multi-viscosity ratio flow in the gas diffusion layer. In this paper, I reconstructed the GDL pore numerical structure, calculate and analyze the porous media by developed lattice Boltzmann calculation program. And then I analyzed and summed up the results.The main factors affecting the water transfer in the diffuser layer of the proton exchange membrane fuel cell are obtained.

In this paper, effects on water transportation in GDL of four factors are discussed, including contact angle, surface tension, pressure difference and viscosity ratio.

The results show that:

(1) When other conditions are the same, with the increase of pressure difference, the flow trend of water in GDL does not change obviously (the flow trend is mainly determined by the wettability and the hydrophobicity of the material. However, the increase of pressure difference promotes the transfer of water in GDL and increases the saturation of water.

(2) The change of viscosity ratio has no obvious effect on the flow trend of water. The viscosity ratio changed from M=54 to M=18, which accelerated the water transfer in GDL and increased the saturation of water in GDL at various contact angles.

(3) The decrease of surface tension does not obviously change the flow trend of water. The decrease of surface tension will result in a slight decrease of water permeability in the calculated area and a slight decrease in saturation. And in stable displacement state, surface tension mainly provides resistance to external pressure and viscous resistance.

(4) When the pressure difference and viscosity ratio increase simultaneously, the flow of water is slowed down, and the saturation of water decreases. In this case, the effect of viscosity ratio on water transport is dominant.

(5) The saturation of water decreases with the increase of contact angle. The current trend has not changed significantly.

Key Words: Lattice Boltzmann method; Gas diffusion layer; multi-phase flow; porous media; water transport

目录

摘 要 I

Abstract II

目录 IV

第1章 绪论 1

1.1课题研究背景 1

1.2本文的研究内容和意义 1

1.3本章小结 2

第2章 燃料电池概述 3

2.1燃料电池基本概念及分类 3

2.2燃料电池的发展和基本原理 5

2.3燃料电池的应用 8

2.4目前燃料电池存在的问题 9

2.5影响质子交换膜燃料电池性能的因素^[8] 12

2.6 PEMFC的水管理概述 13

2.7问题的提出 14

2.8本章小结 15

第3章 数值模型 16

3.1研究多孔介质中两相流的理论方法 16

3.2国内外研究现状 17

3.3玻尔兹曼方程 19

3.4格子玻尔兹曼方程 20

3.5边界条件 21

3.5.1周期性边界条件 21

3.5.2反弹边界条件 22

3.6多重松弛时间（MRT）格子玻尔兹曼法 23

3.6.1碰撞模型的选择 23

3.6.2 MRT模型 24

3.7 FVM-PSM 25

3.8格子单元与物理单元的转化 27

3.9本章小结 28

第4章 结果与讨论 29

4.1 PEMFC气体扩散层孔隙结构 29

4.2 结果讨论 32

4.3本章小结 51

第5章 总结与展望 52

5.1全文总结 52

5.2进一步研究展望 53

参考文献 54

致谢 56

第1章 绪论

1.1课题研究背景

如今，随着社会的快速进步和发展，日益突出的环境问题与传统能源的危机越来越被人们所重视，成为了人类的可持续发展目标的核心问题。过去传统的能源系统已经渐渐地无法满足人类可持续发展的要求，寻找清洁、高效率、且经济安全的能源成为未来几十年的主要议题。世界各国开始了对燃料电池的研究热潮，燃料电池以其高效率、环境友好、以及稳定的性能，能够很好地解决环境污染问题以及能源危机^[1]。燃料电池的优势使其可以在很多应用领域替代传统的能源，如固定电站、分散式电站、交通运输方面、军事应用等等^[2]。近几十年来，随着科学技术的进步，燃料电池相关的技术也有了巨大的突破，并且在世界各国政府与企业的合作下，正在逐步实现其商业化进程。但是，在燃料电池的发展中，仍然有许多关键性的问题急需解决，如提高其耐久性和使用寿命、关键材料的选择、降低催化剂成本、结构设计的优化、水管理等。其中水管理问题是影响燃料电池使用寿命和性能稳定的关键性问题^[3]。

1.2本文的研究内容和意义