基于多物理场模拟的低水甲烷燃料固体氧化物燃料电池的抗积碳阳极设计（英文）

本文采用与实验I-V曲线高度吻合的多物理场全耦合数值模型来模拟低水甲烷燃料SOFC的运行过程.基于抗积碳电流密度实验数据推导出的动力学积碳活性判据,利用多场耦合数值模型系统研究了电池工作参数和阳极扩散阻碍层厚度对阳极积碳倾向的影响.仿真模拟揭示了燃料利用率、电流密度、扩散阻碍层厚度和电池工作电压的相互关系.结果表明,在阳极添加400 um厚的扩散阻碍层是实现SOFC高功率密度和不积碳运行的最优设计.这种阳极结构设计对实现高效率低成本的SOFC技术具有重要意义.     

甲烷固体氧化物燃料电池多物理场模拟及积碳分析

建立了相关实验电池多物理场模型,该模型包括了电化学反应的电化学势平衡方程、甲烷水汽重整的通用速率方程和描述阳极复杂组分气体输运的菲克定律形式尘气模型. 该理论模型的电流～电压 曲线与实验数据很好地吻合,验证了理论模型的有效性. 理论分析发现,低水汽含量甲烷重整反应中水汽的反应级数为1. 理论模型的数值仿真计算还给出多个物理量的详细信息. 据此对碳沉积机制进行深入分析,清楚地描述了工作电流对抑制焦炭生成的机制. 分析比较了积碳活性的两个表达式,发现它们都可以正确地定性反映积碳活性变化趋势,但定量数值并不确切;阳极扩散层降低积碳临界电流的机制也获得了解释. 值得指出的是,虽然积碳活性模型只是定性正确,但分析表明积碳临界电流的降低却可以通过积碳活性模型进行定量解释.     

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。     

直接甲醇燃料电池气、液相流动数值模拟

本文建立了直接甲醇燃料电池(DMFC)的二维两相模型,并重点研究阳极的两相流动和质量传递.模型考虑甲醇串流现象,定量计算了在不同电流密度下甲醇串流量的大小及其对电池工作性能的影响;模型中提出求解气、液单相流速的方法,并分别研究气、液流速对物质传递和电池性能的影响.定量分析发现:由甲醇串流产生的寄生电势导致实际开路电压值远低于理论值;在大电流密度下扩散层和催化层内的气相体积分数非常大,阻碍了液相燃料向催化层扩散,成为制约电池性能的关键因素;扩散层和催化层内存在气、液两相的反向流动,且气、液相速度分别有利于排出生成气体并推动液体燃料到达催化层;减小多孔介质的扩散率将削弱对流,恶化电池性能.     

平板式固体氧化物燃料电池多物理场耦合建模

固体氧化物燃料电池(Solid oxide fuel cell,SOFC)在高温下工作,影响电池性能和结构完整性的因素众多,如何能够综合考虑这些因素并准确地预测和优化电池结构与工作性能是亟待解决的问题。使用COMSOL软件建立了单个平板式固体氧化物燃料电池多场耦合有限元三维模型,考虑电化学反应、物质浓度、流体流动、传热和固体力学多物理因素共同作用下,探明了电池在工作阶段的气体摩尔分数、电流密度、温度和热应力的分布规律。结果表明,氢气和氧气的摩尔分数随着气体流动的方向逐渐降低;在电池空气入口处,电解质电流密度较大;电池温度分布不均匀并产生了较大的热应力。本文建立的SOFC多场耦合模型可为后续SOFC的研究提供分析方法和理论支持。     

质子交换膜燃料电池及其发电系统模拟

本文通过质子交换膜燃料电池单电池子模型、布气管子模型、流场子模型相互耦合,对电池堆传热传质过程加以数值模拟,得到单电池及电池堆的流场、温场、当地电流密度分布、过电位分布;给定平均电流密度下单电池及电池堆输出电压等参数;并比较了平均电流密度、布气管尺寸对电池输出电压、堆内反应物分配的影响;在此基础上,对整个ＰＥＭＦＣ发电系统进行流程模拟和参数分析,得到平均电流密度、重整器Ｓ／Ｃ等主要参数对系统性能影响．     

被动式直接甲醇燃料电池阳极混合对流模拟

本文根据被动式微小型直接甲醇燃料电池的运行特性,建立了其阳极膜电极二维、非等温、稳态数学模型。模拟结果表明:阳极膜电极内部温度的分布是不均匀的,最高温度出现在阳极催化层,且质子交换膜的温度要高于阳极气体扩散层。由于被动式直接甲醇燃料电池燃料的供给与消耗所引起的强制对流的存在,使得混合对流温度场和速度矢量场与自然对流情况下的不尽相同,利用模型对此进行了数值分析。     

双钨极耦合电弧数值模拟

基于流体力学方程组和麦克斯韦方程组, 在合理的边界条件下, 建立了双钨极耦合电弧三维准静态数学模型. 通过对方程组的迭代求解, 获得了不同钨极间距和电弧长度下耦合电弧的温度场、流场、电弧压力和电流密度分布等重要结果, 与已有的实验研究符合良好. 模拟结果表明: 与相同条件下的钨极惰性气体保护焊电弧相比, 双钨极耦合电弧的最高温度和最大等离子流速较低, 阳极表面电弧压力和电流密度峰值明显减小; 钨极间距和弧长对耦合电弧的温度场、流场、电流密度和电弧压力等都具有显著的影响, 且耦合电弧阳极的电弧压力和电流密度分布不能用高斯近似进行描述. 关键词： 耦合电弧 三维模型 数值模拟     

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采用简化阴极的一维边界层模型,将同轴磁旋转电弧等离子体发生器的阴极与弧柱耦合求解,使用FLUENT软件,数值模拟了不同锥角阴极的形状对磁分散电弧等离子体、阴极弧根和阳极弧根位形的影响.结果表明:阴极弧根具有扩散特征,其电流密度为107A·m-2量级;阴极形状的改变引起阴极弧根位形和电流密度分布变化,从而影响等离子体参数分布;随着阴极锥角的增大,阴极弧根从阴极前端移动到阴极侧面,等离子体区域向下游偏移,等离子体轴向厚度减小.     

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。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.