【作者】 赵英汝；

【导师】 陈金灿；

【作者基本信息】 厦门大学 ， 理论物理， 2008， 博士

【摘要】 20世纪以来,能量转换技术发展迅速。随着能源问题的日趋突显,寻求合适的新能源及清洁能源成为世界各国关注的焦点,而不断改进热力循环方式以提高能量转换装置的性能则一直是能源技术发展的主要趋势。在这种背景下,以揭示能量转换的内在机制、优化能量系统的工作特性为主要目的各种热力学分析方法应运而生,它对于开拓新型热力循环与系统、提高能源系统的整体性能都是十分有意义的。燃料电池是氢能利用的主要方式之一。它既适合于作分布式电源,又可组成大容量中心发电站,因此被认为是21世纪首选的高效、节能、环保的发电方式之一。而近一百年来,汽车产业的巨大进步,首先源于内燃机工业强劲发展的推动,同时又促进了内燃机自身的发展。内燃机发展至今,已广泛应用于工业、农业、电力、国防等各个领域,是当今用量最大、用途最广的最重要的热能动力机械。因此,对这两种典型的能量转换系统进行热力学研究,不仅有重要的理论意义,而且有极大的实用价值,对开发新能源、发展新技术、高效利用能源、改善生态环境、开拓交叉学科等都具有重要意义。基于以上原因,本论文围绕燃料电池系统和几种典型内燃机循环的性能优化问题展开,探索受各种不可逆因素影响的热力装置和系统的各种最优性能参数以及它们之间的关系。主要研究内容如下:在第一章中,简单介绍了能量转换系统的研究背景及发展。第二章对一类工作在稳定状态的燃料电池建立不可逆的理论模型,考虑来自电化学反应、电阻及与环境之间传热等多种不可逆性所造成的影响。从能量转换的角度出发,结合电化学、非平衡态热力学和有限时间热力学理论,研究了此类燃料电池的物理及电化学性能,具体讨论了各类设计及操作参数对燃料电池性能的影响。所得结果可为实际燃料电池的优化设计和运作提供一定的理论依据。第三章提出了一个新的理论模型用来描述在稳定状态下工作的燃料电池-热机混合系统的性能,对一些基本的设计特性以及潜在的关键问题进行了分析。在模型中综合考虑了多种不可逆损失,如电化学反应、电阻、燃料电池与热机之间的传热以及释放到环境中的热漏等。在研究中应用能量与熵分析的方法对多种不可逆损失进行阐明,并由此对整个混合系统的输出潜能加以评定。所得结果对燃料电池混合系统的优化设计和操作具有一定的实际指导意义。文中的新方法亦有助于为同类的能量转换装置及电化学体系的研究和发展提供更好的理论支持。第四章对Otto、Diesel、Atkinson、Miller和Dual 5种内燃机循环进行了有限时间热力学分析,建立不可逆热机的循环模型,对来自于非等熵压缩和膨胀过程、有限速率传热过程和透过气缸壁的热漏损失等多种不可逆性对循环性能的影响进行了研究。得到了一些重要参数的优化判据,由此确定出不可逆内燃机的最优工作区间。第五章集中探讨了绝热过程的内部摩擦损耗对Otto热机性能的影响。文中所建立的模型不仅摈弃了一般所采用的内可逆热机的假设,也避免了对不可逆热机活塞平均速率过于简化的描述。通过数值分析给出了一些性能参数的优化判据,并详细分析了一系列重要设计参数的影响,对实际热机的性能改善及优化设计具有一定的指导意义。第六章以Otto和Diesel两种内燃机循环为例,讨论了工质热容量随温度变化时,循环的参数影响及性能优化问题。通过严格推导得出热容量随温度变化时理想气体的绝热方程,并分析了Otto和Diesel热机的性能,给出了一些重要参数的优化判据。所得结果新颖而又具有普适性,相关参考文献中的一些重要结论可从中直接导出。最后一章概括了全文的主要结论,并对未来的研究提出设想与展望。本文的研究不仅有利于燃料电池和内燃机循环这两类能量转换装置的性能改进,所得结果对燃料电池-热机混合热力系统的研发也具有重要的理论价值和实际指导意义,可为相关能量转换系统的优化设计提供理论参考。更多还原

【Abstract】 Since the 20^th century, the energy conversion technologies have been developed quite quickly. Along with the emergence of the serious energy issue, searching for new clean proper energy sources have became the focus of attention worldwide and enhancing the performance of the energy conversion devices through the improvement of thermodynamic cycles has been the main developing trend of the energy technologies. Under this background, the various thermodynamic analytical methods emerge as the times require to reveal the inherent mechanism of energy conversion and to optimize the performance of the energy systems, which is quite significant for the development of new thermodynamic cycles and the improvement of the system performance.As one of the most important applications of hydrogen energy, fuel cells may be used as distributed electric resources as well as the power plants with large capacities, and consequently, are considered to be one of the best choices for power generation with highly efficient, energy-saving and eco-friendly characteristics in the 21^th century. On the other hand, during the past hundred years, great advancement of the vehicle industry was, first of all, due to the development of the internal combustion engine, and accelerated this technology to a certain extent at the same time. So far the internal combustion engines have been widely used in the areas of industry, agriculture, electric power, national defense, and so on. Even today the internal combustion engine is still the most popular and important power mechanism with the largest range of applications. Therefore, the thermodynamic investigations about these two typical energy conversion systems are of great importance to the practical applications of new energy technologies, the efficient utilization of energy resources, the improvement of environment, and the exploitation of interdisciplinary research.Based on the above reasons, this dissertation is focused on the performance analysis and optimization of the fuel cell systems and several typical internal combustion engine cycles. The performance parameters of the systems under the influence of the various irreversibilities are optimized and the relations between the parameters are searched. The main research contents are organized as follows:In Chapter 1, the brief introduction of the research background and development of the energy conversion systems are given.In Chapter 2, an irreversible model of a class of fuel cells working at steady state is established, in which the irreversibilities resulting from electrochemical reaction, electrical resistance and heat transfer to the environment are taken into account. The physical and chemical performances of the fuel cell are investigated by using the theory of electrochemistry, non-equilibrium thermodynamics, and finite-time thermodynamics from an energetic point of view, and the influence of some design and operating parameters on the performance of the fuel cell is discussed in detail. The results obtained may provide a theoretical basis for both the optimal design and operation of real fuel cells.In Chapter 3, a theoretically modeling approach is presented which describes the behavior of a fuel cell-heat engine hybrid system in steady-state operating condition to provide useful fundamental design characteristics as well as potential critical problems. The different sources of irreversible losses, such as the electrochemical reaction, electric resistances, finite-rate heat transfer between the fuel cell and the heat engine, and heat leak from the fuel cell to the environment are specified and investigated. Energy and entropy analyses are used to indicate the multi-irreversible losses and to assess the work potentials of the hybrid system. The results obtained may give a practical guidance on both the optimal design and operation of real fuel cell-heat engine hybrid systems. This new approach can also provide some theoretical supports for the investigation and development of similar energy conversion settings and electrochemistry systems.In Chapter 4, the irreversible cycle models of five kinds of internal combustion engines such as the Otto, Diesel, Atkinson, Miller, and Dual cycles are established through finite-time thermodynamic analysis. By using these models the influence of multi-irreversibilities coming from the adiabatic compression and expansion processes, finite-rate heat transfer and heat leak loss through the cylinder wall on the performances of the heat engines are investigated. The optimum criteria of some important parameters are obtained, and consequently, the optimally operating regions of the engine cycles are determined.In Chapter 5, the effect of the internal friction dissipation in the adiabatic processes on the performance of an irreversible Otto heat engine is discussed in detail. The cycle model established here discards not only the usual hypotheses of endoreversible cycles but also the over simple description of the piston mean velocity for the irreversible heat engines. The optimum criteria of some main parameters are determined through numerical analyses, and the influence of the major design parameters is investigated. The results obtained may provide a significant guidance for the performance improvement and optimal design of real heat engines.In Chapter 6, the performance optimization and parameter selection issue of the Otto and Diesel engines are investigated with considering the temperature-dependent heat capacities of the working fluid. The adiabatic equation of ideal gases with the temperature-dependent heat capacity is strictly deduced and used to analyze the performances of the Otto and Diesel heat engines. The optimum criteria of some important parameters are given. The results obtained are novel and general, from which some relevant important conclusions in literature may be directly derived.In the last chapter, the conclusions obtained are summed up and the status and prospects of the present research are reviewed briefly.This research may provide a theoretical basis for both the optimal design and operation of real fuel cells and internal combustion engines, and it is also expected that this new method be used in the investigation and optimization of similar energy conversion settings and hybrid systems.更多还原