无人机燃料电池氢循环引射器设计及流动性能研究

氢燃料电池无人机发展迅速,但无人机结构紧凑气源容量有限,如何提高氢气利用率,进一步增强续航能力是一个亟待解决的问题。针对该问题,本文设计了引射循环系统,将排空的氢气进行回收利用,以提高氢气利用率。以典型的1.7 kW无人机燃料电池为例,采用计算流体力学方法设计了氢循环引射器,并进行性能分析,揭示了不同工况下内部流场特性。结果表明在二次流压力与出口压力压差为10 kPa时,一次流压力在300～700 kPa的范围内具有良好的引射性能。同时研究了关键结构参数喉嘴面积比(AR)和不同工况对引射性能的影响,研究表明,最佳AR随一次流压力变化而变化,统筹考虑本文选择AR=16,满足了不同工况下的全局最优引射性能,氢气利用率最高提升了30.3%,进一步延长了无人机的续航能力。     

金属极板燃料电池电堆接触压力的分布规律

燃料电池电堆装配质量影响反应气体密封、电堆内阻和流道侵入,从而影响整个电堆系统的性能。基于商用有限元软件ANSYS,研究了包括端板、密封垫圈在内的金属极板质子交换膜燃料电池(PEMFC)电堆三维装配模型的仿真建模方法,分析了层叠式电堆组件间接触压力分布及其传递规律。组装了金属极板燃料电池实验电堆,并进行了电堆装配实验,验证了本文建模方法的准确性。     

基于系统辨识的PEMFC温度非线性建模与预测

针对质子交换膜燃料电池(PEMFC)等一类具有严重非线性的复杂被控对象，提出一种基于模糊模型的模糊预测算法，并对PEMFC系统进行建模。在建模过程中，采用离线学习和在线修正辨识出对象的模糊模型。其中，模型的参数通过模糊聚类初始化和离线反向传播算法进行学习，必要时可通过在线调整后件参数，以使得模型的预测精度能满足实时控制的需要。仿真和实验结果表明了该模糊辨识建模方法具有建模简单、模型精度高等优点，亦证明了该算法的有效性和优越性。     

燃料电池氢循环喷射器性能分析与结构优化

喷射器以其体积小、无运动部件、不产生寄生能耗等一系列优点,正成为氢燃料电池氢气再循环的理想解决方案.但电堆变工况下喷射器的循环流体与供给流体的高度耦合特性致使其与电堆的匹配和优化难度较大.本文针对燃料电池变负载工况下喷射器引射流体压力与背压耦合变化的情况,采用计算流体力学(CFD)流体力学计算和实验相结合的方法,获取多...     

质子交换膜燃料电池电化学阻抗谱弛豫时间分布研究

电化学阻抗谱技术能够获取燃料电池不同频率阻抗,但对阻抗的构成缺乏进一步解析,难以直接构建精准的等效电路模型进行阻抗拟合分析,而弛豫时间分布(Distribution of relaxation time, DRT)方法不需要定义特定的等效电路模型,即可解析燃料电池不同时间常数的极化过程。针对实验室用质子交换膜燃料电池,在不同运行条件下对其进行阻抗谱测量,并通过Kramers-Kronig关系验证所记录阻抗数据的质量。基于DRT分析方法,系统地解释阻抗谱中各频段阻抗对应的物理或化学意义。研究表明,该电池的电化学阻抗谱主要由3个不同时间常数频段的极化阻抗构成,通过与运行条件相关性的系统分析,确定低频段阻抗为氧气在多孔介质中的传输阻碍,中频段阻抗为与氧还原反应有关的电荷传递阻碍,中高频段阻抗为阴极催化剂层中的质子传输阻碍。为进一步确定DRT分析结果的合理性,采用等效电路模型拟合测量的阻抗数据,辨识的电阻元件参数变化趋势与DRT分析结果一致。     

Mechanisms of accelerated degradation in the front cells of PEMFC stacks and some mitigation strategies

The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell（PEMFC） stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and configuration of the gas intake manifold, which may lead to the maldistribution of flow and pressure. In order to find out the mechanisms of the accelerated degradation in the front cells, an extensive program of experimental and simulation work is initiated and the results are reported. It is found that after long-term lifetime tests the accelerated degradation in the front cells occurs in all three fuel cell stacks with different flow-fields under the U-type feed configuration. Compared with the rear cells of the stack, the voltage of the front cells is much lower at the same current densities and the membrane electrode assembly（MEA） has smaller active area, more catalyst particle agglomeration and higher ohmic impedance. For further investigation, a series of three dimensional isothermal numerical models are built to investigate the degradation mechanisms based on the experimental data. The simulation results reveal that the dry working condition of the membrane and the effect of high-speed gas scouting the MEA are the main causes of the accelerated degradation in the front cells of a PEM fuel cell stack under the U-type feed configuration. Several mitigation strategies that would mitigate these phenomena are presented： removing cells that have failed and replacing them with those of the same aging condition as the average of the stack; choosing a Z-type feed pattern instead of a U-type one; putting several air flow-field plates without MEA in the front of the stack; or exchanging the gas inlet and outlet alternately at a certain interval. This paper specifies the causes of the accelerated degradation in the front cells and provides the mitigation strategies.     

车用质子交换膜燃料电池仿真技术路线

质子交换膜燃料电池作为燃料电池中重要的一种类型,可应用于汽车及小规模的发电站与便携式移动能源,是当前新能源领域的研究热点。主要针对车用质子交换膜燃料电池的三种仿真参数模型就当前国内外研究进展进行论述。     

Influence of weave structures on the tribological properties of hybrid Kevlar/PTFE fabric composites

The existing research of the woven fabric self-lubricating liner mainly focus on the tribological performance improvements and the service life raised by changing different fiber type combinations, adding additive modification, and performing fiber surface modification. As fabric composites, the weave structures play an important role in the mechanical and tribological performances of the liners. However, hardly any literature is available on the friction and wear behavior of such composites with different weave structures. In this paper, three weave structures (plain, twill 1/3 and satin 8/5) of hybrid Kevlar/PTFE fabric composites are selected and pin-on-flat linear reciprocating wear studies are done on a CETR tester under different pressures and different frequencies. The relationship between the tensile strength and the wear performance are studied. The morphologies of the worn surfaces under the typical test conditions are analyzed by means of scanning electron microscopy (SEM). The analysis results show that at 10 MPa, satin 8/5 performs the best in friction-reduction and antiwear performance, and plain is the worst. At 30 MPa, however, the antiwear performance is reversed and satin 8/5 does not even complete the 2 h wear test at 16 Hz. There is no clear evidence proving that the tensile strength has an influence on the wear performance. So the different tribological performance of the three weave structures of fabric composites may be attributed to the different PTFE proportions in the fabric surface and the different wear mechanisms. The fabric composites are divided into three regions: the lubrication region, the reinforced region and the bonding region. The major mechanisms are fatigue wear and the shear effects of the friction force in the lubrication region. In the reinforced region fiber-matrix de-bonding and fiber breakage are involved. The proposed research proposes a regional wear model and further indicates the wear process and the wear mechanism of fabric composites.     

车用质子交换膜燃料电池动态建模与仿真分析

基于质子交换膜燃料电池（PEMFC）工作机理的分析,考察工作过程中影响其输出特性的5个主要因素（包括理想电动势、欧姆极化电压、活化极化电压、浓度差极化电压和辅助系统电压）,建立了PEMFC的动态数学模型,利用Matlab/Simulink仿真平台对该模型进行了仿真,结果表明,模型输出能有效反映PEMFC的电压输出特性,为PEMFC控制系统的开发奠定了基础。     

燃料电池发动机水热管理仿真分析综述

质子交换膜燃料电池作为燃料电池中重要的一种类型,可应用于汽车及小规模的发电站与便携式移动能源,是当前新能源领域的研究热点。主要针对质子交换膜燃料电池不同维度的水热管理仿真模型的研究现状进行了论述。     

Corrosion of Mild Steel by Urban River Water

The corrosion processes of mild steel immersed in river water were investigated. The reaction of the Bahlui River on common steel used in domestic and industrial installations was studied. The corrosion of mild steel is an extensive topic approached in different media, yet little information about river water as a corrosive has been reported. The experimental determinations were performed for short term immersion of four alloys in the laboratory. By using Tafel extrapolation and electrochemical impedance spectroscopy, the corrosion of the alloys was investigated. Scanning electron microscopy coupled with energy dispersive X-ray analysis and Fourier-transform infrared spectroscopy were employed to characterize the morphology of corrosion products and identify their phases. The corrosive activity of river water leads to the formation of inner compact and outer porous layers. The differences between corrosion products formed in the presence of underground and surface waters are described.     

燃料电池新型流道对气体扩散层表面水去除的影响

质子交换膜燃料电池(Proton exchange membrane fuel cell,PEMFC)中气体扩散层(Gas diffusion layer,GDL)表面液态水的有效去除和输送对PEMFC的水管理非常重要。为了有效去除GDL表面液态水,提出一种新型流道结构,采用流体体积法对流道内液态水的传输过程进行三维数值研究,研究进气速度、表面润湿性和液滴尺寸对流道内液态水的传输过程和GDL表面液态水去除的影响。研究结果表明,新型流道结构可以有效去除GDL表面液态水。随着进气速度的增大,沿流动方向的空气剪切力增大,流道内水去除速率和压降增大,GDL表面水覆盖率降低。表面润湿性对液态水传输影响显著,GDL表面润湿性增强会减缓液滴运输,流道内阻力降低,压降减小,GDL表面水覆盖率增大。管表面润湿性增强,流道内压降和GDL表面水覆盖率降低。新型流道适用于流道内大液滴的去除。当θ_GDL=150°和θ_pipe=30°时,新型流道结构有较好的GDL表面除水性能。本研究工作为流道结构提供了一种新的选择,对GDL表面液态水的去除具有一定的指导意义。     

A new method of scanning tunneling spectroscopy for study of the energy structure of semiconductors and free electron gas in metals

In this study, anew method for the scanning tunneling spectroscopy (STS) of direct and indirect gap semiconductors and free electron gas in metals is proposed. Band structures of Si, porous Si, and Ge were studied. The tunneling current-voltage characteristics of Si and porous Si surfaces were measured over different voltage intervals from tens of mV to 20 V under incident light from an Xe lamp and those of a Ge surface in the dark. The correlation between the shapes of the I-V curves and band structure of the materials was calculated. It was found that the curves are linear if measured in the voltage range V₀ E_g/(2e) and nonlinear when V₀ α E_g/(2e) (in the measurements the applied voltage was changed from -V₀ to V₀). The method was used for the observation of a new effect of tunneling of free electron gas having thermal energies from a metal tip to a band gap state of the semiconductor. The energy spectrum of free electron gas was measured.     

扫描电化学池显微镜阿基米德螺旋快速扫描方法的研究

针对现有扫描电化学池显微镜(scanning electrochemical cell microscopy, SECCM)的扫描方法在扫描成像快速性上的不足,提出一种基于阿基米德螺旋线的新型SECCM快速扫描方法。传统跳跃扫描模式的跳跃高度是在没有先验知识的情况下靠人工经验设定的,为了避免碰撞其取值往往偏大,因此设置的扫描行程越长,消耗时间越久,速度慢、效率低。利用螺旋线轨迹预扫描快速获得待测平面的最高点,进而有效地降低了传统跳跃模式的跳跃行程,大幅提高了SECCM的扫描成像速度。此外,以螺旋线轨迹高速运动来检测最高点时,轨迹具有无冲击、因此样本运动过程无偏移,该扫描方法具有成像稳定性高的优点。通过带状金属表面成像实验表明,相对于传统跳跃扫描模式,阿基米德螺旋扫描方法在保证成像质量的同时扫描速度提高了约110%。可见提出的方法对提升SECCM扫描速度和成像质量有着重要的意义。     

Peculiarities of diamonds formed in alkaline carbonate-carbon melts at pressures of 8–10 GPA: Scanning electron microscopy and cathodoluminescence data

Diamond crystallization with both spontaneous and seeded nucleation was realized in the system Na₂Mg(CO₃)₂-K₂Mg(CO₃)₂-C (graphite) at 8–10 GPa and 1700–1800°C. The crystallization products were transparent colorless diamond single crystals of octahedral habit up to 100–150 μm in size. Scanning electron microscopy (SEM) showed that the growing diamond material was precipitated on both octahedral {111} and cubic { 100 } faces of synthetic and natural diamond seed crystals by layers of octahedral orientation, much like the growth of the natural diamond. The physicochemical conditions for diamond crystallization are interpreted as a crystal growth from carbon solutions in alkaline-carbonate melts. Color cathodoluminescence scanning electron microscopy (CCL-SEM) and cathodoluminescence (CL) spectroscopy studies suggested specific peculiarities of the synthetic “carbonate-carbon”(CC) diamonds resembling natural crystals in comparison with diamonds produced by metal-carbon (MC) synthesis. The main feature of the CC product is the lack, for both spontaneous and seed stimulated diamonds, of surface color cathodoluminescence as in the case for natural diamonds with lower concentrations of nitrogen impurity (type II). The CL spectra of the CC diamonds showed the simultaneous luminescent three-band system - H3, 575 nm, and a weak blue A-band - the H3 band structure of which resembles that of natural diamonds of type IIa.     

多孔层的孔隙特性和各向异性对燃料电池瞬态性能的影响

燃料电池(Fuelcell,FC)与外部环境之间的传热和多孔层的传质均会影响FC内的水热气电状态,进而影响到催化层的电化学反应速率,从而显著影响其瞬态性能(Transient performance,TSP)。多孔层的孔隙特性和各向异性是影响其传热传质能力的关键因素,充分认识其对FC-TSP的影响规律,对于优化车载FC动力源的负载响应有重要意义。为此,综合考虑FC与外部环境动态热交换,内部水热气电等各物理性质的空间动态分布以及气、液和溶解相等多相时变转化关系,建立FC多相三维瞬态传质传热数值模型,以分析多孔层非均质性质对动态过程的影响。进一步,以电流密度的阶跃变化模拟动态负载,分析FC的电压,膜的水含量和温度,微孔层|催化层界面的氧浓度。结果表明,多孔层的孔径大小和分布及各向异性对FC的TSP有明显影响。另外,不同热条件对FC的内部物理量分布的影响较对TSP的影响更为显著。     

An integrated PC-based image analysis system for microtomography and quantitative analysis of inner micro-object structure

A new type of image processing system, including microtomographic analysis, is presented. The great majority of existing approaches to image processing and analysis can be achieved by means of software, with a minimal amount of hardware. The addition of microtomographic methods to an image processing system allows quantitative parameters of inner object microstructure to be obtained non-destructively.     

基于模糊预测控制的燃料电池温度控制系统的研究

PEMFC的温度控制系统表现为多输入多输出、耦合、时滞、时变性、非线性、不确定性、信息量少等特点,采用传统的控制方法通常不能得到比较好的控制效果。因此,文章从控制和建模的角度出发,选择了一种基于模糊模型的预测控制算法对PEMFC的温度进行控制,并且通过仿真试验得出了比较满意的控制效果。     

Gross and microscopic observations on the lingual structure of the Franciscana (Pontoporia blainvillei--Gervais and d'Orbigny, 1844)

In most anatomical studies developed with mammals, the tongue is described as highly differentiated among different species. However, studies on the tongue of aquatic mammals are still limited as compared to those on terrestrial mammals. The aim of this study was to describe the tongue morphology of the Franciscana dolphin (Pontoporia blainvillei) using macroscopic observations, light, and scanning electron microscopy. Microscopically, the dorsal surface was covered by a keratinized stratified epithelium. Salivary gland acini were found on the middle and caudal third of the tongue. The dorsal surface was totally covered by filiform papillae with a connective tissue core and a connective tissue structure round in shape in the middle and caudal regions.     

Lifetime Evaluating and the Effects of Operation Conditions on Automotive Fuel Cells

Lifetime is one of the important indicators of automotive proton exchange membrane fuel cells. People used to evaluate the lifetime of vehicular fuel cells by laboratory tests or road tests that usually take thousands hours even years. In order to achieve a rapid evaluation technique and to seek lifetime extension methods, a lifetime calculation formation was drawn out in consideration of the vehicle driving cycle and the working condition factors. Bench experiments were individually carried out on two fuel-cell stacks same as ones applied on vehicle, and the performance decay rates of the two stacks were obtained under four operation conditions of changing load cycle, start-stop cycle, idling and heavy load. As a result, the predicted lifetimes rather conform to the actual running status in road test. And the research on the fuel cell performance decay rates under different load conditions was also done. Consequently, an unexpected finding was discovered that operating under micro-current has an effect on recovering fuel cell performance. The vehicle fuel cell rapid assessment method only requires four laboratory tests of driving cycle, load cycle, idle operating conditions and heavy load conditions, and the whole process merely lasts less than 250 h. These experimental results can be used to predict the vehicular fuel cell lifetimes on various utility models or driving cycles, therefore to optimize the application model to prolong the fuel cell lifetime. Actually in the experiment, it has already been proved successfully that the fuel cell lifetime could be extended from 1 100 h to 2 600 h by optimizing operating mode. The quick evaluation method is helpful to develop extended life fuel cell and to deplete fuel cell for a longer time.