基于格子Boltzmann方法的燃料电池多相传输现象研究

发布时间：2018-06-28 12:49

本文选题：质子交换膜燃料电池 + 水管理　；参考：《浙江大学》2014年博士论文

【摘要】：燃料电池是直接将化学能转化为电能的能源动力装置,具有效率高、环境友好等优点,被认为是极具发展潜力和应用前景的可持续利用清洁能源装置。以质子交换膜燃料电池为代表的燃料电池技术表现出巨大的商业应用价值,吸引了众多研究人员的关注和兴趣。从最新的研究情况看,虽然质子交换膜燃料电池技术正在趋于成熟,但仍有许多关键问题急需解决,成为制约其大规模商业化的重要因素。本论文着眼于质子交换膜燃料电池的水管理问题,针对目前实验技术无法达到的区域,基于格子Boltzmann数值计算方法,开发了一套可以实时动态分析和模拟质子交换膜燃料电池内部多相多组分流动的计算程序,系统分析了质子交换膜燃料电池中液态水的传输现象。具体研究内容包括以下几个部分：第一,充分认识液态水在气体扩散层和微孔层内部的传输过程对质子交换膜燃料电池的水平衡管理,避免水淹引起的性能下降至关重要。本文通过数值重构GDL-MPL多孔介质模型,采用格子Boltzmann方法两相流动模型研究了液态水在GDL-MPL模型中的传输机理、微观孔隙结构对水传输的影响,详细分析了气体扩散层内部水传输现象,微孔层存在对水管理的作用,以及气体扩散层、微孔层以及两者交界面中存在不同裂缝时对水传输的影响。研究结果表明：多孔介质内部水传输主要受毛细力控制；微孔层可以有效控制液态水回流,缓解水淹电极的情况；GDL-MPL模型内部存在裂缝对水饱和度有显著影响。第二,质子交换膜燃料电池电化学反应所产生的液态水经毛细力作用通过多孔气体扩散层后,最终会以液滴的形式出现在扩散层表面。研究与气体扩散层界面相关的气液两相传输现象是分析质子交换膜燃料电池内部反应物输送和水管理的重要内容。本文采用格子Boltzmann方法两相流动模型,对气体扩散层与气道交界面上的气液两相传输问题进行了研究,详细探讨了不同孔隙间距、微通道气体速度大小不同孔隙直径以及扩散层表面润湿特性对液滴形成和动态特性的影响。研究结果表明：增大孔隙间距和气体流速,采用疏水性表面可以减少液滴之间的相互作用,提高液态水排出效率。模拟结果为深入理解气体扩散层界面水传递机制提供了参考。第三,液态水经气体扩散层表面脱落后进入气体流道。针对液态水在气道中的有效排出虽然已开展了大量的研究工作,但仍有许多问题有待深入理解,特别是水在流道内的具体传递过程。本文采用格子Boltzmann方法两相流动模型模拟了不同形状气体流道内水滴的传递现象。研究结果表明：对于直角型气道,水滴最终都附着在气道壁面上,很难从气道内排出；而对于U-型气道,水滴的传输特性有很大改善,气体流道内的水滴较容易排出,特别是当提高气体流速以及表面接触角时效果更明显。最后,由于质子交换膜燃料电池催化层内部传输特性复杂,目前对其孔隙尺度传输现象的研究报道较少。本文将二维多相多组分格子Boltzmann模型成功拓展到三维,参考催化层真实微观结构,并对其进行了一定的简化处理,数值重构了催化层三维多孔结构；采用三维格子Boltzmann多相多组分模型对催化层传输特性进行了初步模拟分析。研究结果表明：多孔介质微观结构对催化层传输特性有显著影响。本文针对质子交换膜燃料电池水管理问题,从孔隙尺度上系统研究了气体扩散层、微孔层、气体扩散层表面、气体流道、催化层内部流动过程,揭示了其传输机理,研究结果为改善质子交换膜燃料电池水管理技术提供了有力的分析手段和理论基础。
[Abstract]:Fuel cell is an energy power device that directly converts chemical energy into electrical energy. It has the advantages of high efficiency and friendly environment. It is considered to be a sustainable and clean energy device with great potential and application prospects. The fuel cell technology represented by proton exchange membrane fuel cell has shown great commercial application value and attracted many people. According to the latest research situation, although proton exchange membrane fuel cell technology is becoming mature, there are still many key problems to be solved and become an important factor restricting its large-scale commercialization. This paper focuses on the water management of proton exchange membrane fuel cells, aiming at the current experimental technology. Based on the lattice Boltzmann numerical calculation method, a set of computational program for real-time dynamic analysis and Simulation of multiphase multicomponent flow in proton exchange membrane fuel cells is developed. The transmission of liquid water in proton exchange membrane fuel cells is analyzed systematically. The specific contents include the following parts:
First, we fully understand the water balance management of the liquid water in the gas diffusion layer and the microporous layer and the water balance management of the proton exchange membrane fuel cell, so as to avoid the performance decline caused by water flooding. In this paper, the GDL-MPL porous medium model is reconstructed by numerical method and the lattice Boltzmann square flow model is used to study the liquid water in the GDL-MPL The transmission mechanism in the model and the effect of micro pore structure on the water transport are analyzed in detail. The effects of the microporous layer on water management, the effect of the gas diffusion layer, the microporous layer and the different cracks on the water transport are analyzed. The results show that the water transmission inside the porous medium is water transmission. The transmission is mainly controlled by the capillary force, and the microporous layer can effectively control the reflux of liquid water and alleviate the condition of water flooded electrode. The internal cracks in the GDL-MPL model have a significant influence on water saturation.
Second, the liquid water produced by the electrochemical reaction of the proton exchange membrane fuel cell passes through the porous gas diffusion layer through the capillary force action through the porous gas diffusion layer and eventually appears on the surface of the diffusion layer in the form of droplets. The gas and liquid two phase transport phenomena related to the interface of the gas diffusion layer are the analysis of the transport and water of the internal reactant in the proton exchange membrane fuel cell. In this paper, the two phase flow model of the lattice Boltzmann method is used to study the gas and liquid two phase transport in the gas diffusion layer and the airway interface. The formation and dynamic characteristics of the droplet formation and the wetting characteristics of the microchannel gas velocity, as well as the wetting characteristics of the diffusion layer surface, are discussed in detail. The results show that the increase of pore space and gas flow velocity, the use of hydrophobic surface can reduce the interaction between droplets and improve the efficiency of liquid water discharge. The simulation results provide a reference for understanding the mechanism of water transfer at the interface of gas diffusion layer.
Third, liquid water goes into the gas channel after the surface of the gas diffusion layer falls off. Although a lot of research work has been carried out on the effective discharge of liquid water in the airways, there are still many problems to be deeply understood, especially the concrete transfer process of water in the flow channel. This paper uses the lattice Boltzmann method to simulate the two phase flow model. The transfer of water droplets in the same shape gas channel shows that the drop of water droplets is difficult to discharge from the airway for the right angle airway, and it is difficult to discharge from the airways. For the U- type airways, the transmission characteristics of the droplets are greatly improved, and the water droplets in the gas channel are easily discharged, especially when the gas flow velocity and surface connection are raised. The effect of the antennae is more obvious.
At last, due to the complex transmission characteristics in the catalytic layer of proton exchange membrane fuel cell (PEMFC), there are few reports on the pore size transmission at present. In this paper, the two-dimensional multiphase multi component lattice Boltzmann model has been successfully expanded to three-dimensional, and the real microstructure of the catalytic layer is referred to, and a certain simplified treatment is carried out. The three-dimensional porous structure of the layer is transformed, and the transmission characteristics of the catalytic layer are simulated by the three-dimensional lattice Boltzmann multiphase multicomponent model. The results show that the microstructure of the porous medium has a significant influence on the transmission characteristics of the catalytic layer.
Aiming at the water management of proton exchange membrane fuel cell, this paper systematically studies the gas diffusion layer, microporous layer, the surface of the gas diffusion layer, the gas flow channel, the internal flow process of the catalytic layer from the pore scale, and reveals its transmission mechanism. The results provide a powerful analysis method for improving the water management technology of the proton exchange membrane fuel cell. Theoretical basis.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM911.4

【共引文献】