【作者】 张宇；

【导师】 魏炜；

【作者基本信息】 大连理工大学 ， 安全科学与工程， 2021， 硕士

【摘要】 固体氧化物燃料电池（SOFC）作为一种能量转换装置,能将化学能转化成电能。当燃料气选用碳氢燃料时,SOFC的发展潜力很大。由于SOFC工作时,操作温度过高,电池尺寸过小,采用实验方法难以测量其内部的关键物理量,而电池的操作参数和微结构特性直接影响了电池的电化学性能。获得电池工作状态下的关键物理量参数,是提高电池性能的关键,所以,需要借助数值模拟的方法来确定物理量参数。首先,搭建了阳极支撑板式SOFC单电池实验测试装置,建立了以H₂-CO为燃料的板式SOFC的三维数值模型,对模型进行质量传递、动量传递、热量传递、组分传递、电荷传递及电化学反应耦合求解,考察了电池内部的组分浓度、温度、速度、电流密度等物理参数的分布规律,研究气体流向、操作温度、燃料流量、空气流量、燃料气比例等操作参数和孔隙率、曲折度、粒径、孔径等微结构参数对电池的电化学性能影响,以期对SOFC的设计和运行提供帮助。结果表明,沿着气体流动方向,燃料在阳极气体通道中的摩尔分数比在功能层中的摩尔分数更大,在阳极气体通道中摩尔分数下降得较快,氧气在阴极气体通道中的摩尔分数远大于在流道两侧电极连接体下方的摩尔分数,电池的温度升高,阳极温度高于阴极温度,阳极气体通道中出口处气体流速高于入口处气体流速,阴极气体通道中出口处气体流速低于入口处气体流速,电极连接体的电流密度低于中心流道处的电流密度,流道壁面处的电流密度大于流道中心处的电流密度,电解质层平均电流密度从出口到入口逐渐下降。当工作电压恒定在0.7 V、燃料流量为200 sccm、空气流量为500 sccm时,随着操作温度升高,SOFC的最大功率密度提高,电池性能不断提升,浓差超电势增大,活化超电势和欧姆超电势降低。当电流密度较低时,顺流、逆流两种操作条件下的SOFC性能曲线基本重合;当电流密度增大到0.4 A/cm²以后,顺流时的电压下降趋势高于逆流时的下降趋势,逆流相比于顺流具有优势,但采用逆流方式时在燃料出口处的温度梯度最大,使电池组件产生较大热应力,电池的使用寿命减少。当操作温度为800℃、工作电压恒定在0.7 V、空气流量为1000 sccm时,随着燃料流量增加,电池温度、功率密度、阴极浓差超电势均是先增大再减小;H₂和CO的燃料利用率、阳极浓差超电势、进出口处阳极和阴极的组分改变量均为下降趋势;活化超电势、欧姆超电势、出口处电解质层平均电流密度均增大。电流密度>0.8 A/cm²,燃料比例中H₂占比越大,电池性能越好。燃料流量为100 sccm时,起初随着空气流量增加,功率密度增大;当空气流量增至800 sccm以后,继续增加空气流量,电池性能保持不变,空气流量利用率逐渐下降。当操作温度为800℃、工作电压恒定在0.7 V、燃料流量为100 sccm、空气流量为1000 sccm时,随着孔隙率增加,电池性能提高;当孔隙率增加至0.5以后,H₂的燃料利用率提高,CO的燃料利用率下降。曲折度从3.5下降至1.5,粒径从1μm下降至0.2μm,孔径从0.1μm增加至0.9μm,电池性能、最大功率密度、出口处电极温度、进出口阳极和阴极的组分改变量、燃料利用率和出口处电解质层平均电流密度提高,进出口处电池的浓差超电势、活化超电势和欧姆超电势的变化量均升高。更多还原

【Abstract】 As an energy conversion device,solid oxide fuel cell（SOFC）can convert chemical energy into electrical energy.When hydrocarbon fuel is used as fuel gas,SOFC has great development potential.Because the operating temperature of SOFC is too high and the size of SOFC is too small,it is difficult to measure the key physical parameters of SOFC by experimental methods,and the operating parameters and microstructure characteristics of SOFC directly affect the electrochemical performance of SOFC.It is the key to improve the performance of the battery to obtain the key physical parameters under the working state of the battery.Therefore,it is necessary to use the numerical simulation method to determine the physical parameters.Firstly,the experimental test device of anode supported SOFC single cell was built.The three-dimensional numerical model of the plate SOFC with H₂-CO as fuel was established.The model was solved by mass transfer,momentum transfer,heat transfer,component transfer,charge transfer and electrochemical reaction coupling.The distribution of physical parameters such as component concentration,temperature,velocity and current density were investigated.The effects of operating parameters such as gas flow direction,operating temperature,fuel flow rate,air flow rate,fuel gas ratio and microstructure parameters such as porosity,tortuosity,particle size and pore size on the electrochemical performance of SOFC were studied in order to provide help for the design and operation of SOFC.The results show that the mole fraction of fuel in the anode gas channel is larger than that in the functional layer along the gas flow direction,and the mole fraction decreases rapidly in the anode gas channel.The mole fraction of oxygen in the cathode gas channel is much larger than that under the electrode connectors on both sides of the channel,and the temperature of the cell increases,The results show that the anode temperature is higher than the cathode temperature,the gas velocity at the outlet of the anode gas channel is higher than that at the inlet,the gas velocity at the outlet of the cathode gas channel is lower than that at the inlet,the current density of the electrode connector is lower than that at the center of the channel,and the current density at the wall of the channel is higher than that at the center of the channel,The average current density of electrolyte layer decreases gradually from outlet to inlet.When the operating voltage is constant at 0.7 V,the fuel flow rate is 200 sccm and the air flow rate is 500 sccm,the maximum power density of SOFC increases with the increase of operating temperature,the performance of SOFC increases,the concentration overpotential increases,and the activation overpotential and ohmic overpotential decrease.When the current density is low,the performance curves of SOFC under forward current and reverse current are basically coincident;When the current density increases to 0.4 A/cm²,the downward trend of the voltage in the forward flow is higher than that in the reverse flow,and the reverse flow has advantages over the forward flow.However,the temperature gradient at the fuel outlet is the largest when the reverse flow mode is adopted,resulting in greater thermal stress on the battery module and reduced service life of the battery.When the operating temperature is 800℃,the operating voltage is constant at 0.7 V,and the air flow rate is 1000 sccm,the cell temperature,power density and cathode concentration overpotential first increase and then decrease with the increase of fuel flow rate;The fuel utilization rate of H₂ and CO,the overpotential of anode concentration difference,and the composition change of anode and cathode at the inlet and outlet all show a downward trend;The activation overpotential,ohmic overpotential and the average current density of the electrolyte layer at the outlet increase.When the current density is more than 0.8 A/cm²,the larger the proportion of H₂ in the fuel,the better the performance of the cell.When the fuel flow is 100 sccm,the power density increases with the increase of air flow;When the air flow rate increases to 800 sccm,the battery performance remains unchanged,while the air flow utilization rate decreases gradually.When the operating temperature is 800℃,the operating voltage is 0.7 V,the fuel flow rate is 100 sccm,and the air flow rate is 1000 sccm,the performance of the cell is improved with the increase of porosity.However,when the porosity rises to 0.5,the fuel utilization of H₂ increases and the fuel utilization of CO decreases.When the tortuous degree decreases from 3.5 to 1.5,the particle size decreases from 1μm to 0.2μm,the pore size increases from0.1μm to 0.9μm,the battery performance,maximum power density,electrode temperature at the outlet,composition changes of anode and cathode at the inlet and outlet,fuel utilization ratio and average current density of electrolyte layer at the outlet increase,and changes of three kinds of overpotential at the inlet and outlet increase,the concentration overpotential,activation overpotential and ohmic overpotential of the battery at the inlet and outlet increase.更多还原