【作者】 林鹏；

【导师】 吴承伟；

【作者基本信息】 大连理工大学 ， 工程力学， 2011， 博士

【摘要】 燃料电池是将氢气与氧气的化学能直接转化为电能的电化学发电装置,最终主要反应产物只有水。随着能源危机和环境污染问题不断加重,燃料电池作为一种高效、清洁、环境友好的能源设备得到了广泛关注。其中,质子交换膜燃料电池(Proton Exchange Membrane Fuel Cell, PEMFC)由于可在室温快速启动、无电解液流失以及寿命长等优点,成为目前研究最多、应用最广的燃料电池类型之一,在航空、航天、航海、移动电源和分散电站等领域都有着良好的应用前景。特别是在汽车工业中,PEMFC被认为是新型环保汽车的最佳动力源。实际应用中的PEMFC产品多为大型电堆结构,研究和解决PEMFC电堆在封装载荷作用下的力学问题,对推动PEMFC技术的发展,提高PEMFC的效率、可靠性及寿命等综合性能具有重要意义。其中分析温度影响、选取封装载荷以及优化设计端板结构等封装力学问题尤为关键。本文以PEMFC电堆为研究对象,以数值仿真为主要研究方法,针对上述力学问题展开一系列研究。本论文共分为五章,主要研究工作如下：第一章介绍了燃料电池的种类和研究进展,随后重点介绍了PEMFC的工作原理、结构特点和组件功能,并详细论述了PEMFC电堆封装过程中温度的影响、封装载荷的选取以及端板的优化设计等关键力学问题。第二章结合计算流体动力学(Computational Fluid Dynamics, CFD)与有限单元法(Finite Element Method, FEM),基于典型结构分别建立了PEMFC单电池和多级电堆的热力耦合仿真模型,依次分析和对比了两种结构在不同工作状态时温度、应力、应变及膜电极(Membrane Electrolyte Assembly, ME A)表面接触压力的分布形式和变化规律,研究了多级电堆整体及内部各级双极板的变形规律,最后讨论了工作环境散热、冷却介质流速以及冷却介质类型等散热因素对结构温度和应力分布的影响。第三章针对目前对大型PEMFC电堆进行整体力学性能计算耗时巨大的难题,基于等效刚度的基本思想,提出了大型PEMFC电堆整体封装的等效刚度力学模型,利用此模型可快速求得电堆系统在封装载荷作用下的力学响应,进而可以研究封装载荷、外界环境和工作温度对PEMFC电堆主要结构承载和变形规律的影响。通过将等效刚度模型与FEM进行典型PEMFC单电池结构整体刚度的对比计算,发现前者将节省至少一个量级的计算时间,同时还可给予良好的精度,为电堆封装载荷设计提供了新的设计手段。第四章以典型PEMFC电堆结构为研究对象,从结构强度、产品性能和温度影响等因素出发,详细论述了系统使用等效刚度模型进行封装载荷选取的完整设计过程,并将等效刚度模型的应用扩展到燃料电池结构可靠性设计领域,利用等效刚度模型分析了典型PEMFC电堆的结构可靠性。研究进一步表明,等效刚度模型的提出为电堆封装研究提供了全新的设计思路和高效的设计工具。第五章基于典型PEMFC电堆结构,结合FEM建立了用于端板优化设计的多目标拓扑优化模型。利用加权系数法将问题转化成单目标优化问题进行分析,并引入等效刚度模型进行了适当的简化以减少不必要的计算工作。经过拓扑优化设计后,可使端板结构达到质量轻、刚度高的相关设计要求,既节省材料成本,还可提高电堆的性能和寿命。最后讨论了封装螺栓个数、电堆设计级数以及多目标优化加权函数等设计参数对电堆优化设计的影响。更多还原

【Abstract】 Fuel cells are electrochemical devices which directly convert the chemical energy of hydrogen and oxygen into the electrical energy, and the final reaction product is water. Since the energy crisis and the pollution situation are deteriorated at present, fuel cells have received considerable attentions as a kind of effective, clean and environmentally friendly energy equipment. As one of the most interested and useful fuel cells, proton exchange membrane fuel cell (PEMFC) has a good potential in the applications of aviation, space, navigation, mobile power sources and distributed power plants owing to the advantages of quick-start at room temperature, no loss of electrolyte, long operating lifespan and so on. Especially in the automobile industry, PEMFC has been regarded as the optimal power source in a modern car for environmental protection.Most PEMFC products in practice are assembled as large cell stacks, therefore it is necessary to study and solve the mechanics problems existing in the assembled PEMFC stack, and this has significant importance to the development of PEMFC technology and the improvement of PEMFC’s performance, reliability and lifespan. Among those problems, the thermal influence, the assembly load determination and the optimal end plate design are especially critical. Taking PEMFC stack as the study object and numerical simulation as the study method, a series of researches on the above structure dependent mechanics problems of the PEMFC stack assembly are carried out in this dissertation.There are five chapters in this dissertation, and the research work mainly covers the following aspects:In chapter 1, types and current research status of the fuel cells are introduced, especially the operating principle, structure features and component functions of the PEMFC. Moreover, some key mechanics problems during the assembly mechanics research, such as the thermal management, the assembly load determination and the optimal end plate design, are separately discussed in detail.In chapter 2, combining the computational fluid dynamics (CFD) and the finite element method (FEM), three-dimensional thermal-mechanical coupled numerical models for a PEMFC single cell and a multi-cell stack are respectively established on the basis of typical fuel cell structures. The corresponding distribution and variation regularity of temperature, stress, strain and the membrane electrolyte assembly (MEA) surface contact pressure under different working conditions are analyzed and compared in turn. Also the deformation roles of the whole multi-cell stack and the bipolar plates are studied. Finally, effects of several heat dissipation factors, such as heat dissipation of the working environment, velocity and selection of the coolant fluid, on the temperature and stress distributions are discussed.In chapter 3, a mechanical equivalent stiffness model is proposed for large PEMFC stack assembly according to the basic idea of equivalent stiffness, for the purpose of dealing with the difficulty of analyzing mechanical performance for the whole large PEMFC stacks. Using this model, mechanical responses of the stack system under the assembly load can be quickly obtained, and then influences on the main structural bearing and deformation regularity of the PEMFC stack, which are caused by the assembly load, external environment and operating temperature can be studied. Verified with FEM, it shows that the equivalent stiffness model not only saves at least one order of time but also gives good calculation accuracy when calculating the whole structual stiffness of a typical PEMFC single cell, which may provide a new methodology for designing the assembly load.In chapter 4, the complete assembly load design for a typical PEMFC stack using the equivalent stiffness model is introduced considering factors as structural strength, product performance and temperature effect. In addition, application field of the equivalent stiffness model is expanded into the fuel cell structural reliability design, and the structural reliability of a typical PEMFC stack is studied based on the equivalent stiffness model. It also proceeds to show that the equivalent stiffness model offers a new design solution and an efficient and convenient tool for the large PEMFC stack assembly research.In chapter 5, based on a typical PEMFC stack, a multi-objective topology optimization model for designing the optimal end plate is established combining with FEM. The proposed optimization model is converted into a single-objective optimization problem by means of the weighting coefficient method. Also the equivalent stiffness model is used for proper simplifications to reduce the unnecessary calculation. After topology optimization of the end plate, the corresponding design requirements such as light weight and high stiffness can be well satisfied. Therefore, not only material cost can be reduced, but also the product performance can be promoted simultaneously. In the end of this chapter, influences of several design parameters, such as the number of clamping bolts, the number of design cells, and the different weighting coefficients, on the stack optimization design are discussed.更多还原