PEMFCs的膜及阴极催化层数值模拟

本文提出了一个质子交换膜燃料电池的膜和阴极催化层的一维非稳态数学模型,模型考虑了电化学反应及反应中的传质过程。本文结合算例分析了燃料电池膜及阴极催化层的性能,结果能验证燃料电池内阻理论。论文结果表明:(1)随着输出电流密度的增大,氧浓度分布不均匀性增大; (2)阴极催化层厚度减小,可提高电池输出电压; (3)电池进口处氧气摩尔浓度增大,可增加电池的输出电压。     

基于扩展单粒子模型的锂离子电池参数识别策略

为了精确识别电动汽车锂离子动力电池的关键状态参数,基于多孔电极理论和浓度理论,建立了一种考虑液相动力学行为的锂离子电池扩展单粒子模型.相较于传统单粒子模型,该模型增加了对负电极表面固体电解质界面膜参数的描述,并考虑了温度和液相浓度变化对锂离子电池关键参数的耦合影响.基于所建立的扩展单粒子模型,提出一种简化的参数灵敏度分析方法和有效的锂电池参数识别策略,用以确定特定工况下的高灵敏度待识别参数,进而利用遗传算法实现参数的优化求解.最后,通过对比分析本文模型和传统单粒子模型的仿真输出电压和相同工况下电池的实验输出电压验证了提出模型和参数识别方法的有效性和可行性,为电池管理系统的健康状态估计提供了理论基础.     

1维亚微米弹道二极管在不同外加电压脉冲下的数值模拟

 以适合亚微米器件的流体动力学模型为基础，建立了1维数值模拟程序，程序中采用耦合牛顿法求解非线性方程组。应用该程序对亚微米1维弹道二极管进行了瞬态数值模拟，分析了外加低电压和高电压脉冲情况下的电场强度、载流子浓度、载流子温度等参数的变化情况。低电压脉冲下的结果与文献一致；对于文献中并未开展的高电压脉冲下的模拟，得到了器件处于非正常工作状态的各参数分布曲线，并尝试用二次击穿理论对结果进行分析。结果显示:随着外电压的升高，载流子的碰撞电离将导致少子空穴浓度急剧增大，并达到与电子浓度相同的量级，这时在器件分析中空穴方程已不能省略，并且载流子浓度将取代掺杂浓度控制电势分布，并进而影响电场及电流密度，涌极附近电场将增强，电流密度也将迅速增加。结论可为研究瞬态电磁脉冲对2维器件的损伤效应提供参考。     

PEMFC气体扩散层内各向异性传递过程数值模拟

质子交换膜燃料电池(PEMFC)气体扩散层(GDL)具有各向异性属性,常规数值模拟对GDL采取均匀模型,忽略了各向异性传递过程对PEMFC性能的影响。本文发展了一个三维非等温单相模型,在GDL平面内和GDL厚度方向采用不同的传递系数,模拟了各向异性传递系数对PEMFC整体和局部性能的影响。在本文计算条件下,GDL各向异性和均匀模型模拟得到的电池极化曲线几乎完全相同,但电池电流密度分布和温度分布等局部特性存在很大差异。该结果进一步证明了不能单独用极化曲线来验证电池数学模型的正确性。     

平板式阳极支撑SOFC多场耦合数值模拟

建立了平板式固体氧化物燃料电池多场耦合数学模型,利用商业CFD软件FLUENT对包括阳极和阴极多孔介质、致密固体氧化物电解质、燃料流道、氧化剂流道、电流收集双极板、外壳的单电池三维整体计算区域进行了数值模拟,得到了流场、温度场、组分浓度场、电流密度场、Nernst电动势、活化过电势和欧姆过电势等重要物理量的详细分布,并分析了影响电池性能的主要因素。模拟结果与SOFC研制单位提供的实验数据基本符合。     

基于遗传算法的锂离子电池等效电路参数识别

结合锂离子电池双极性等效电路模型提出了一种基于遗传算法的参数识别方法,该方法通过指数函数对电路模型中的电阻、电容、恒压源等元件进行有理逼近,根据电池在不同充放电速率下的输出电压特性数据,通过实数编码遗传算法得到最优的函数参数,从而得到最优的电阻、电容,开路电压等电路参数值,针对电池在不同的工作状态,不同的工作参数下的运行数据,系列仿真和实验结果表明该算法原理简明,收敛较快,辨识得到的最优模型其电压输出特性与电池的实际电压输出特性基本吻合,能较精确的反映电池的实际特性,具有较高的辨识精度。     

体硅、SOI及DSOI MOSFET器件级电、热分析

利用简化的半导体电学方程,数值模拟获得了各种电学参数的分布,并结合简化电阻模型,模拟了体硅、SOI及DSOI的MOSFET器件的温度场。结果表明MOSFET器件的沟道,特别是靠近漏的区域电场强度及电流密度等各项电、热特性参数在该区域变化剧烈,是最主要的热源区。     

S波段分离腔振荡器的数值模拟与设计

通过粒子模拟的方法设计了分离腔振荡器(SCO),并建立了基于爆炸发射的阴极模型,对带有真实二极管结构的SCO进行了整体的粒子模拟研究。典型的数值模拟结果为:在二极管电压为495 kV,电流为3.93 kA时,输出高功率微波的功率为640 MW,微波频率为2.85 GHz,功率效率为33.0%。同时,还研究了二极管输入电压幅度及波形、阴-阳极间距、阴极半径等参数对SCO输出高功率微波特性的影响,初步研究结果表明:除了栅网的通过率,SCO对二极管阻抗、阴极半径等参数也比较敏感,对应一定的二极管阻抗,需有一个最佳的电压值与之匹配;三角波电压波形会明显降低SCO的功率效率。     

质子交换膜燃料电池阴极气场设计优化

通过建立质子交换膜燃料电池阴极气场的三维简化模型,研究了不同进气方式、不同进出气总管尺寸对电池堆流量分布的影响,并提出从单电池流道深度的角度优化气场分布的改进方案。结果表明,与单入口进气方式相比,双入口进气方式效果更优;采用2-2型进气方案时流量分布最为均匀,进气功耗最小;增大进气总管的宽度可以使电堆流量分布更加均匀;各单电池合理采用非均匀深度流道可以有效提高电池堆流量分布均匀性。     

PTS装置分层真空轴向绝缘堆设计

对PTS装置分层真空轴向绝缘堆的设计和分析方法进行了研究。利用全电路模拟方法得到了绝缘堆各层的电压波形。利用静电场数值模拟方法,对每层堆中的绝缘环、电极环、均压环、场调整环以及两端接口部分的形状都进行了设计和优化。2维和3维静电场模拟结果表明,绝缘堆的设计能够满足静电场设计要求。采用2维PIC程序初步计算了绝缘堆金属均压环真空侧电子发射对电压分配不均压度的影响,计算结果表明,真空侧的电子发射会较大地影响绝缘堆电压分配的均匀度,进而对绝缘堆的全堆闪络概率造成较大的影响。     

Design of 1 kW high temperature PEM fuel cell system and performance analysis under different operating conditions

This paper demonstrates the mathematical and MATLAB simulation model of 1 KW (28.8V_dc) PEM fuel cell system with boost convertor and RL load to analyze the yield behavior in accordance to control the hydrogen fuel utilization. Two cases have been designed to evaluate the performance of this model. In the first case, fuel cell parameters are examined with and without a fuel regulator that controls the hydrogen fuel rate while in the second case, the operating temperature of a fuel cell stack is varied to observe the impact on the system. PEM fuel cell based power systems can become an alternate choice in the transportation sector to overcome contamination concerns, especially in South Asia where the environmental issues are at peak. The purpose of this work is to introduce such environmentally friendly system of transportation in South Asia, especially in Pakistan and this stack model can be used as a prototype for developing FC based motorbike as currently no practical models have been tested in this region. Therefore, this model has unique advantages over the existing in the literature.     

质子交换膜燃料电池内传递现象的数值模拟

本文发展了一个质子交换膜燃料电池的三维数学模型,用于研究整个电池内的传递现象,模型全面考虑了流体 流动、热量传递、电化学动力学和多组分传递等物理化学过程。数值求解数学模型获得了电池内详细的温度、反应物浓度 和电流等的空间分布情况。为验证模型的正确性,将估算的电池性能与文献中的实验数据进行了比较。     

DMFC两相流及其对传质影响的研究

采用自制的实验系统对液态进料直接甲醇燃料电池(DMFC)阳极交叉指状流道内的两相况功特性进行了可视化实验研究.自制的DMFC单电池带有透明窗口,采用镀金的不锈钢阴极极板和透明的聚碳酸脂阳极流场板,电解质为Nafion117膜.实验过程中燃料电池的进口总管和出口总管是水平的,进口流道和出口流道是竖直的.实验发现,出口流道中典型的两相流流型是泡状流、而出口总管中的典型流型是弹状流.进口流道中的气弹和气柱导致了阳极传质恶化.     

A novel design and micro-fabrication for copper (Cu) electroforming bipolar plates

A novel design and micro-fabrication were developed for micro-proton exchange membrane (PEM) fuel cell stack bipolar plates with cross section of 5 cm² and thickness of about 650 μm. Copper metals were used to make bipolar plates (BPs) by using a LIGA-like micro-fabrication process of deep UV lithography in order to obtain SU-8 resist patterns/and SU-8 mould. Through two-sided exposure and development, copper metal bipolar plates with serpentine (meandering) flow field configurations for a micro PEM fuel cell stack, were fabricated and performance tests through polarization characteristics were conducted; this made it possible for the first time to consider copper sheets as suitable for BPs in micro PEM fuel cell stacks.     

Effects of flow field design on water management and reactant distribution in PEMFC: a review

The performance of a proton exchange membrane fuel cell (PEMFC) stack is affected by many factors, including the operating conditions, flow field and manifold design, and membrane performance. To achieve the desired PEMFC performance, the reactant must be uniformly distributed and effectively diffused into the catalyst layer for the electrochemical reaction. Water management and reactant distribution in fuel cells are crucial because they affect the distribution and diffusion rate of the reactant. This paper reviews the important research results reported in recent years related to the effects of water and reactant distribution on the performance and life span of PEMFC stacks.     

质子交换膜燃料电池低化学计量比的性能研究

以质子交换膜燃料电池实际应用为背景,研究了在反应物低化学计量比下,质子交换膜燃料电池不同温度、压力下的性能。得到了电池温度,压力对反应物化学计量比的影响。实验结果表明,反应物化学计量比1.0的电池性能低于足量反应气体工况下的电池性能;化学计量比为1.3时,电池能够在预期电流强度下稳定运行;反应气体的传质过程影响反应所需的化学计量比;当提升压力至0.13 MPa,化学计量比1.0的电池性能与足量反应气体工况下的性能相当。     

Relevance of the subgrid-scales for large eddy simulations of turbulence-radiation interactions in a turbulent plane jet

An a priori study based on direct numerical simulation (DNS) of a non-isothermal turbulent plane jet has been carried out in order to analyse the role of the small-scales of turbulence on thermal radiation. Filtered DNS and large eddy simulation (LES) without subgrid-scale (SGS) model have been estimated for the radiative heat transfer. The comparison of the results highlights the subgrid-scale influence over the filtered radiation quantities, such as the radiative intensity and the radiative emission. The influence of the optical thickness is also studied. It is shown that the subgrid-scales are not significant near the centerline of the jet, where the radiative heat transfer is more important, and therefore that the SGS can be neglected in this configuration. However, when the optical thickness increases, the SGS become relevant and SGS modeling may be needed.     

介质阻挡放电中的能量转换过程研究

研究了介质阻挡放电过程中的电流强度、电场强度以及电荷分布的演变规律，并对能量转换性质进行了分析.研究结果表明，在一个放电脉冲过程中，外加驱动电源所作的功、电场能量的增量均与起始时刻的壁电荷密度有关，而气体中放电电流所作的功即沉积于气体中的能量与起始时刻的壁电荷密度、放电电流的具体波形无关. 关键词： 介质阻挡放电 壁电荷 动力学过程 能量转换     

A simple new radiative transfer model for simulating the effect of cirrus clouds in the microwave spectral region

The upwelling atmospheric radiation in the millimeter wave spectral range is influenced by the presence of cirrus clouds. A plane parallel radiative transfer model which can take into account the effect of multiple scattering by ice particles in the cirrus has been developed and is used to simulate the brightness temperatures as they would be measured by a satellite instrument. The model uses an iterative procedure to solve the radiative transfer equation. The formulation of the model is such that it can easily be adapted to treat the full specific intensity vector instead of just the scalar total intensity. A convergence test for the model is explained and two cirrus cloud scenarios are simulated. The results illustrate the linearity of microwave radiative transfer for not too strong cirrus clouds in this frequency region.     

质子交换膜燃料电流道淹没与传质强化

在地面常重力环境下,采用透明电池可视化方法研究了质子交换膜燃料电池阳极和阴极的流道淹没现象。分别研究了阳极和阴极反应物流量对电池内部传质和电池性能的影响。结果表明,电池阴极的淹没区域比阳极大,由电极淹没引起的气体传质受限和电化学反应受限主要发生在阴极。提高反应物流量能够强化气体传质并提高电池性能,并且提高电池阴极侧反应物流量比提高阳极侧反应物流量对提高电池性能更有效。本文工作为进一步开展微重力环境中的燃料电池实验提供了比较依据。