Analysis of GDL flooding effects on PEMFC performance

One of the major concerns of the gas diffusion layer (GDL) inside a proton exchange membrane fuel cell (PEMFC) is water management. Treatment of the pores of the GDL can affect the PEMFC performance due to the degree of water flooding inside the GDL. In this work, GDL flooding was investigated using a simplified approach in an established numerical model. The predictions are compared with experimental data of GDLs with different treatments. Local distributions inside the cell are given and the effect of homogenous GDL flooding on these is discussed.     

Combustion synthesis and electrochemical characterisation of Pt–Ru–Ni anode electrocatalyst for PEMFC

The present work studies the synthesis by the combustion method of an anode catalyst for protonic exchange membrane fuel cell (PEMFC) employing two different fuels, that is, urea and sucrose. The unsupported pure solid solution Pt_0.6Ru_0.3Ni_0.1 was selected from a calculated and empirical ternary phase diagram, which was previously studied. Theoretically, this particular composition exhibited single-phase features without the presence of secondary phases as RuO₃ and NiO, regarding the oxygen partial pressure conditions generated during the combustion synthesis. In the X-ray diffraction (XRD) analysis of the nanoparticles synthesized by using two different fuels, a single-phase Pt_0.6Ru_0.3Ni_0.1 alloy was detected. However, the X-ray photoelectron spectroscopy (XPS) studies showed that the nanoparticles prepared could present an onion-shell structure, in the case of the sample synthesized with sucrose as fuel, the external layers are partially constituted by Ni hydroxides, which can exhibit an active role in the hydrogen oxidation reaction. The electrochemical behaviour of this unsupported catalyst was performed by preparing MEAs, which were evaluated using a I–V polarisation curve test. The results obtained indicated that the nanoparticles prepared by sucrose have better performance, 260 mW/cm², than those prepared using urea, 170 mW/cm². These results are discussed in relation with the hydrogen oxidation mechanism. The results obtained reveal combustion synthesis as an appropriate method for preparing PEMFC electrocatalysts, due to its versatility, simplicity and fastness.     

阴、阳极加湿程度对PEMFC内部传质的影响

为了研究常规流场下阴、阳极增湿程度对电池内部水分布、传递、膜性能及水拖曳系数等的影响,对PEMFC进行二维建模,应用控制容积法对控制方程进行离散,然后求解,得到了电池内部水和反应气浓度、速度分布、膜中电流密度、电势分布及膜中水分布,考察了气体不同增湿程度对质子交换膜电导率及电池内部传质的影响.结果表明,PEMFC中水综合拖曳系数随着阳极加湿程度的增加而增大,随阴极增湿程度的增加而减小,但阳极增湿对水综合拖曳系数的影响比同增湿程度下阴极增湿对水综合拖曳系数的影响大得多.同时,随着阳极加湿程度的升高,质子交换膜（PEM）电导率急剧升高,而阴极加湿程度对PEM电导率的影响只是停留在较小的电流范围之内.故PEMFC在小电流密度工作时,应该使阳极气体充分增湿;而在大电流密度工作时,应该适当降低阳极的增湿程度以降低阴极两相流的机会,从而改善阴极的传质状况.     

基于直流内阻和交流阻抗特性的PEMFC水管理状态分析

基于Randles等效电路,研究质子交换膜燃料电池(PEMFC)操作温度和湿度耦合关系,建立电堆直流内阻和交流阻抗特性模型。通过两种方法相结合,研究不同操作条件下的电化学阻抗谱图和U-I输出特性曲线的变化规律,以及不同水管理状态在直流内阻和交流阻抗变化规律中体现出的对应关系,进而分析水管理状态对电堆输出性能的影响作用。仿真和实验结果表明,温湿度耦合关系下的不同水管理状态,在电化学阻抗谱图和U-I特性曲线中具有一致的变化规律和对应的量化关系;电堆输出性能中的膜干、水淹等现象,在直流内阻值和交流阻抗图的变化中具有明显的表现特征;通过研究水管理状态对两者的影响,能够实现操作条件的优化和电堆输出性能的优化控制。     

增湿温度与气体流速对PEMFC阴极流道内液态水分布及排水影响

通过直条单流道可视化PEM单池研究了阴极流道内液态水的传递行为,给出了液态排水与流道进、出口压降间的直接关系。结合可视化与压降测量,开发一种评价流道内液态水积累及排出的新方法,考察了增湿温度与气体流速对流道内液态水分布及排水的影响。随着增湿温度提高,存水区域由流道下部向进口扩展。对于给定流道,存在一特定流速。在该流速下液滴临界直径与流道尺寸相当,流道内液态水积累最严重。在本实验条件下,该特定流速为2 m·s^-1。为了及时排出液态水,气体流速不能低于3 m·s^-1。     

Fundamental understanding of liquid water effects on the performance of a PEMFC with serpentine-parallel channels

A three-dimensional and unsteady proton exchange membrane fuel cell (PEMFC) model with serpentine-parallel channels has been incorporated to simulate not only the fluid flow, heat transfer, species transport, electrochemical reaction, and current density distribution but also the behaviors of liquid water in the gas-liquid flow of the channels and porous media. Using this general model, the behaviors of liquid water were investigated by performing the motion, deformation, coalescence and detachment of water droplets inside the channels and the penetration of liquid through the porous media at different time instants. The results showed that: tracking the interface of liquid water in a reacting gas-liquid flow in PEMFC can be fulfilled by using volume-of-fluid (VOF) algorithm combined with solving the conservation equations of continuity, momentum, energy, species transport and electrochemistry; the presence of liquid water in the channels has a significant impact on the flow fields, e.g., the gas flow became unevenly distributed due to the blockage of liquid water where the high pressure would be suddenly built up and the reactant gas transport in the channels and porous media would be hindered by liquid water occupation.     

Effect of ambient conditions on performance and current distribution of a polymer electrolyte membrane fuel cell

The performance and current distribution of a free-breathing polymer electrolyte membrane fuel cell (PEMFC) was studied experimentally in a climate chamber, in which temperature and relative humidity were controlled. The performance was studied by simulating ambient conditions in the temperature range 10 to 40 °C. The current distribution was measured with a segmented current collector. The results indicated that the operating conditions have a significant effect on the performance of the fuel cell. It was observed that a temperature gradient between the fuel cell and air is needed to achieve efficient oxygen transport to the electrode. Furthermore, varying the air humidity resulted in major changes in the mass diffusion overpotential at higher temperatures.     

热负荷分配比例对抽凝-背压供热机组能耗影响

抽凝-背压供热模式是实现能量梯级利用、降低火力发电煤耗的有效途径,研究不同室外温度下供热凝汽器与尖峰加热器热负荷分配比例对机组能耗的影响,确定最佳热负荷分配比例,是抽凝-背压供热机组节能降耗的核心问题之一。本文利用热网变工况模型及Ebsilon软件仿真,以某310MW抽凝-背压供热机组为研究对象,分析了供热期不同温度下供热凝汽器与尖峰加热器热负荷分配比例不同时机组的发电功率及煤耗。结果表明：对于抽凝-背压热电联产机组,并非供热凝汽器热负荷比例越高而发电功率越高,供热期不同阶段,机组发电功率随供热凝汽器热负荷变化呈现不同规律;相同室外温度下,供热凝汽器与尖峰加热器热负荷分配比例对机组能耗影响很大,凝汽器热负荷比例不同时,其极差最小值和最大值分别为2.02g/（kW·h）和5.50g/（kW·h）。     

Modelling effects of current distributions on performance of micro-tubular hollow fibre solid oxide fuel cells

A three-dimensional model, considering mass, momentum, energy and charge conservation, was developed and the equations solved to describe the physico-chemical phenomena occurring within a single, micro-tubular hollow fibre solid oxide fuel cell (HF-SOFC). The model was used to investigate the spatial distributions of potential, current and reactants in a 10 mm long HF-SOFC. The predicted effects of location of current collectors, electrode conductivities, cathode thickness and porosity were analysed to minimise the ranges of current density distributions and maximise performance by judicious design. To decrease the computational load, azimuthal symmetry was assumed to model 50 and 100 mm long reactors in 2-D. With connectors at the same end of the HF-SOFC operating at a cell voltage of 0.5 V and a mean 5 kA m⁻², axial potential drops of ca. 0.14 V in the cathode were predicted, comparable to the cathode activation overpotential. Those potential drops caused average current densities to decrease from ca. 6.5 to ca.1 kA m⁻² as HF-SOFC length increased from 10 to 100 mm, at which much of the length was inactive. Peak power densities were predicted to vary from 3.8 to <2.5 kW m⁻², depending on the location of the current collectors; performance increased with increasing cathode thickness and decreasing porosity.     

Numerical study of the influence of the anode position and the electrolyte flow on the deposition of copper on a wire

The influence of the fluid flow and the cell geometry on the deposition of copper on wires was studied numerically. A numerical method based on the system residual distribution schemes and the finite element method was developed to calculate the fluid flow and the mass transfer including the effects of diffusion, migration, convection, homogeneous reactions, turbulence and multiple electrode reactions in arbitrary shaped geometries. The k-ω model was used to calculate the turbulent fluid flow, and the turbulent Schmidt number is assumed equal to one. It was demonstrated that a downstream position of the anode yields a much more uniform deposition compared with an upstream placement of the anode. From calculations with different imposed currents, it was established that mass transfer only plays an important role if the current is above 70% of the limiting current. Furthermore, simulations with different flow rates, indicated that turbulent flow reduces the effects of mass transfer on the current density distribution.     

高压水射流清洗机能量分布及清洗效率分析

目前我国高压水射流清洗机使用数量达数千台,但由于用户对清洗机的能量分布和如何更好地利用能量不熟悉,造成了极大的浪费,能耗大、效率低,该清掉的垢物清洗不下来.针对这一普遍现象做一些理论分析,以让这些机器发挥最大效率,让用户获得最大经济效益.     

整形和表面改性对人造石墨负极材料性能的影响

在对不同来源人造石墨原料进行理化性能分析的基础上,按照相同的工艺条件制成负极材料,比较了原料来源不同的人造石墨用作锂离子电池负极材料的性能。再以同一来源人造石墨为原料,采用不同设备、不同工艺、不同含量沥青进行整形、炭包覆及表面氧化改性处理,探讨了不同工艺处理对所制备的人造石墨负极材料的粒度分布、振实密度、比表面积和电化学性能的影响。结果表明,整形工艺与设备、炭包覆和表面氧化改性处理对提高负极材料的性能具有重要的作用。     

催化剂分布对可渗透阳极微流体燃料电池性能特性影响的研究

微流体燃料电池是一种新型微型电源装置。酸性体系下电池运行时产生的CO₂气泡会严重影响电池性能以及稳定性。研究电池运行过程中气泡动态行为对削弱气泡影响具有重要意义。本文构建具有可渗透阳极的自呼吸微流体燃料电池,实验研究了阳极催化剂分布对电池性能以及CO₂动态行为的影响。结果表明：催化剂分布在阳极两侧时电池性能最好,但电池波动性大。仅在一侧分布催化剂时,电池运行稳定,气泡主要在电解液流道形成。     

催化剂分布对可渗透阳极微流体燃料电池性能特性影响的研究

微流体燃料电池是一种新型微型电源装置。酸性体系下电池运行时产生的CO₂气泡会严重影响电池性能以及稳定性。研究电池运行过程中气泡动态行为对削弱气泡影响具有重要意义。本文构建具有可渗透阳极的自呼吸微流体燃料电池,实验研究了阳极催化剂分布对电池性能以及CO₂动态行为的影响。结果表明：催化剂分布在阳极两侧时电池性能最好,但电池波动性大。仅在一侧分布催化剂时,电池运行稳定,气泡主要在电解液流道形成。     

聚丙烯酸酯乳液粒度及其压敏胶粘性能的研究

采用预乳化半连续聚合工艺,制备了乳液型聚丙烯酸酯类压敏胶。讨论了乳化剂用量、引发剂用量、预乳液滴加时间和搅拌速率对乳胶粒粒度以及压敏胶粘接性能的影响。实验表明:在不同影响因素下,乳胶粒的粒度与压敏胶粘接性能之间呈现出不同的变化关系。     

Current distribution effects in AC impedance spectroscopy of electroceramic point contact and thin film model electrodes

The Finite-Element-Method (FEM) was used for the simulations of the effect of a changing current distribution during AC impedance spectrum recording on electroceramic point contact and thin film model electrodes. For pure electronic conducting point contact electrodes the transition from the primary current distribution to the DC current distribution restricted to the Three-Phase-Boundary (TPB) zone introduces an error in the determination of the reaction resistance, R_reac = Z(freq. → 0) − Z(freq. → ∞). The error is estimated for different width of the effective TPB zone and a rule of thumb regarding its significance is provided. The associated characteristic impedance spectrum shape change is simulated and its origin discussed. Furthermore, the characteristic shape of impedance spectra of thin electroceramic film electrodes with lateral ohmic resistance is studied as a function of an increasing lateral ohmic resistance. The characteristic change in the shape of the complex plane impedance plot with increasing lateral ohmic resistance is discussed in terms of extracting kinetic parameters such as electrolyte and reaction resistance.     

纯水静态闪蒸起始阶段气泡群时空分布规律的实验研究

设计搭建了静态闪蒸实验台,利用高速摄像对不同压降速率下纯水静态闪蒸起始阶段气泡群的时间和空间分布规律开展了实验研究。实验中液膜初始厚度为0.2 m,压降速率为0.27～0.64 MPa·s^-1。实验结果表明：气泡群主要出现在压力陡降段。在时间分布上,压降速率越大,气泡群出现的时间越早,气泡数目增长越快,且气泡群数目达到最大值所需要的时间越短。在空间分布上,气泡数量随深度呈现了“缓增-陡增-缓增”的增长趋势;压降速率越小,气泡分布越集中;相同深度范围内,压降速率越大,气泡数量越多;至压力陡降段结束时刻,气泡群相对数量随液膜深度的增大有峰值存在。最后,根据实验结果拟合了气泡群时间和空间分布规律的实验关系式,其计算值与实验值吻合良好。     

压力旋流喷嘴雾化滴径分布的模型预测和实验

利用激光片光荧光诱导技术（PLIF）测得不同液体流量下的压力旋流喷嘴雾化滴径分布,用平均粒径约束的三参数最大熵模型对雾化滴径分布进行预测。将理论预测分布与实验结果进行拟合,得到广义伽玛参数α随着液体流量变化的一般表达式。用拟合模型对粒径分布的特点和规律进行总结,结果表明：拟合模型能很好地预测粒径的数量分布,且不受小液滴的影响;随着液体流量的增加,液滴粒径分布范围逐渐变窄,峰值液滴粒径呈线性减小趋势,峰值液滴百分数呈线性增加趋势。     

传热模型对近临界工况CO2干气密封温压分布和稳态性能影响

干气密封流体膜与密封环间传热模型的合理选取对于准确求解密封温压分布和稳态性能至关重要。在CO₂近临界工况下,对比研究了密封环等温模型、绝热模型和共轭热传递模型对超临界CO₂干气密封端面温度、压力分布和开启力、泄漏率等稳态性能的影响,探讨了不同膜厚和转速条件下密封环等温模型和绝热模型的适用性,并基于共轭热传递模型研究了超临界CO₂和空气介质干气密封的温压分布和稳态性能差异。结果表明：以共轭热传递模型计算结果为基准,密封环等温模型假设适用于小膜厚低速流动工况,不过开启力偏低而泄漏率偏高,绝热模型假设适用于大膜厚高速流动工况;相较于空气介质干气密封,超临界CO₂干气密封在小膜厚下的温度分布和大膜厚下的压力分布基本接近,不过小膜厚下的温度更低,而在大膜厚下的压力更高。     

振动时间、比压等参数对炭阳极质量影响的研究

通过采用动态过程优化程序,对预焙阳极成型参数(振动时间、振动频率、振动比压、激振力和振幅)进行优化,探索出一套适宜多品种预焙阳极均质生产的方法。