【作者】 杨云珍；

【导师】 张海鸥；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2008， 博士

【摘要】 固体氧化物燃料电池(Solid Oxide Fuel Cell,SOFC)作为一种新型发电方式,因为其能源供应的零污染、全固态结构、高能量转换效率、对燃料的广泛适应性、供电规模多元化和安装地点灵活等一系列优点,已成为新能源开发的研究热点。由于SOFCs在能量转换过程中需要经历复杂的传热、传质、电化学反应等过程,因此,SOFCs输出功率密度和力学性能直接影响其能量转换效率和使役寿命。然而,能量转换效率和力学性能受SOFCs部件材料离子导电率、阳极/电解质/阴极界面电阻的影响和化学反应活性面积的相互依赖的影响,难以用实验手段测定各个影响参数对SOFCs性能的影响。为此,利用模拟计算技术来选择和优化SOFCs结构设计、材料设计和电池运行条件是改善和提高其综合性能的行之有效的方法之一。基于SOFC工作原理,对其系统内固—气共存多相传热传质建立热流模型,采用“尘气模型”(Dust Gas Model)研究了多组分气体在流道和多孔介质内的传输,率先采用改进的BFD(Brinkman-Forschheimer-Darcy)模型,描述气体在多孔介质内的渗流,考虑了混相多组分气体在传输过程中的质量、动量和能量源项,然后提出采用有限元软件和外部子程序的方法对此模型进行求解。首次建立了针对复杂结构和材料的SOFCs的智能化电化学模型,定量描述SOFCs系统内能量转换过程中伴随的化学反应与热流电化学模型的耦合关系,研究了瓦楞和多面体SOFCs复杂结构电极内和电解质内的电子三维不定向迁移、电流、电压和输出功率与系统内化学反应程度和速度的关系,并介绍软件的系统设计、实现了无须重新前处理的智能化、面向对象程序设计和FLUENT二次开发。为避免电极和电解质间界面接触状态影响电池输出功率和由于热膨胀系数差异引起高温循环操作后的剥离或“串气”,率先在SOFC电极和电解质之间引入了功能梯度层,保证了在热膨胀系数差异较大的阴极、阳极和电解质之间的梯度层物性参数和孔隙连续渐变,寻求兼高能密度和较好力学性能的SOFCs最佳结构设计。为了扩大燃料气适应性,研究了碳氢化合物混合气体作为燃料气的SOFCs的综合性能,考虑了甲烷气体的重整反应、可逆的水交换反应以及电化学反应过程中多种化学反应机制对输出功率密度的影响。率先发现碳氢化合物作为燃料气在小型SOFCs能量转换过程中氢气逐渐增多的趋势,据此提出了采用碳氢化合物和其尾气循环供应燃料气的方法,并从理论上阐明了碳氢化合物作为燃料气的对工业尾气回收利用的可行性。首次基于SOFCs实际工作运行过程中的温度分布,对复杂结构包括瓦楞和多面体SOFCs的热应力进行分析,结合不同结构SOFCs的电化学性能特点,提出了采用多面体结构SOFCs可以达到兼顾力学性能和提高电池能量密度的预期效果。采用复阻抗技术测试功能梯度SOFCs复合电极的电导率,实验验证了功能梯度层可以改善阴/阳极和电解质界面接触状态从而减小SOFCs界面电阻,并分析了各自离子导电性能与工作温度,结构设计和材料的关系。更多还原

【Abstract】 SOFC has been a priority research focus in the new power area due to its advantage of zero pollution,solid structure,high energy transfer efficiency,widely suitable to fuels, multiple scales of power supply and flexible installation,etc.During the transferring process of the energy in the SOFC system,the heat and mass transfer and electrochemical reactions are complex.Therefore,the output power and mechanical performance of SOFCs influence its energy transfer efficiency and service life. The energy transfer efficiency and mechanical performance are influenced by the ionic conductivity of the components,the resistance of the interface between the anode/cathode and electrolyte and the activate areas of the reactions.It is difficult to validate the influence of each parameter on the SOFC performance due to the relating influence. Hence,the geometry,material design and working conditions of SOFCs are choose and optimized to improve the comprehensive performance of SOFCs based on the numerical simulation.On the basis of the SOFC principle,the thermo-fluid model was constructed to describe the multiphase and heat and mass transfer in the system.The dust-gas model was selected to describe the transfer of multi-component gas in the porous media and channel. The BFD(Brinkman-Forschheimer-Darcy) was used to describe the seep of gas in the porous electrodes and research the mass sources,momentum sources and energy sources in the process of the transfer of multi-phase and multi-component gas.Then the finite software and external routine were coupled to solve these models.The intelligent electrochemical model was constructed to simulate the couple relation of the reaction and thermo-fluid model during the process of the energy transfer in the SOFC system.The ionic transfer,current,voltage and the output power in the corrugated and multi-plane SOFCs were studied.The software design,intelligent pre-processing and secondary exploitation of FLUENT software were presented.To avoid the stripping and gas leakage caused by the thermal expansion coefficients difference or circle operating under the high temperature and improve the contact of the interface between the electrodes and electrolyte influenced the output power of SOFC,the functionally graded layers were designed between the electrodes and electrolyte to make the physical parameters and porosity of the graded layers change continuously.By this means,the best geometry design was expected to improve the high power density and mechanical performance of SOFC. SOFC operates in the high temperature conditions,so the contact of interface between the cathode/anode and the electrolyte influence severely on the output power of SOFC.In particular,the stripping and gas leakage was caused by the difference of the components material of SOFC and the cyclical high temperature operating conditions.In order to release the deformation and crack induced by the difference of the components material of SOFC,in the thesis,the idea of the functionally graded material(FGM) is introduced into the design of SOFC.Between the electrodes,including cathode and anode,and electrolyte, the FGM layers with continuously graded physical prosperity and porosity are prepared. With the same volume of SOFC unit,the comprehensive performances of functionally graded SOFC were compared with those of SOFC without graded layers to seek the optimal design of SOFC with high power density and ideal mechanical performance.In order to enlarge the adaptability of SOFC to fuels,the multi-specious mixture generated by decomposing universal hydrocarbon was used as the fuel gas.The influences of reforming reaction of methane,water shift reaction and electrochemical reaction on the output power of SOFC were researched.The results show that the hydrogen mass fraction is increase along the fuel flow direction in the small type SOFC using the hydrocarbon fuel,hence,the hydrogen and hydrocarbon fuels can be supplied circularly.The industrial exhaust gas can be used as the fuel of SOFC,which is validated in the theory.Based on the temperature distribution calculated from the actual operation process, thermal stress of complex structure SOFCs(corrugated and octagon type) were first analyzed.A novel octagon typed SOFC was presented after the comparisons of the electrochemical performance of different structures,which could obtain the desired effect of both the mechanics performance and the improvement of cell energy density.The complex impedance method was employed to test the electrical conductivity of functionally graded SOFCs.It was experimentally validated that functionally graded layers can effectively improve the interface contact condition between cathode or anode and electrolyte,thus the decrease of the interface resistance.Moreover,the relationships were also investigated among ionic conducting properties,operation temperature,structure design and materials.更多还原