质子交换膜燃料电池动态特性实验研究

质子交换膜燃料电池动态特性的研究对于实际应用来说非常重要,实验研究了质子交换膜单体燃料电池在负载动态变化及启动过程中性能的响应.基于计算机控制的负载变化,得到了在不同进气加湿程度下电池性能在负载突变时的响应和在启动工况中的变化,结果表明电池电流对电压动态变换的响应很迅速,突变工况下电流密度出现了过增现象,高加湿程度的电池在设计启动过程中获得了更好的性能.     

不同进气湿度PEMFC动态响应分析

质子交换膜燃料电池(PEMFC)工作参数的影响最终要体现在对电池内传质过程的影响上。实验得到了在不同进气加湿程度下电池性能在启动工况中的变化,基于非稳态数学模型计算了不同阴极入口湿度下电池在负载渐变工况下膜内含水量和电流密度的瞬态响应,并与相应的实验工况进行了对比。     

质子交换膜燃料电池电流分布的动态响应

动态特性是理解质子交换膜燃料电池性能的重要参数之一.运用燃料电池测试系统、恒电流/恒电压多通道测试仪和燃料电池电流密度分布测试装置,试验测量了质子交换膜燃料电池在不同加湿温度、电池温度和压力下的电流分布动态响应和动态特性.研究发现:不同区域的局部电流达到新的平衡所需的时间不同;加湿温度变化时,不同区域的局部电流的变化趋...     

采用阴/阳极通流的热再生氨电池性能

构建采用阴/阳极通流的穿透电极型热再生氨电池(Thermally Regenerative Ammonia-based Battery,TRAB),并研究了电解液/氨流量比、氨浓度、电极孔隙和支持电解质浓度对电池性能的影响.结果 表明,电解液/氨流量比过低会导致氨渗透,恶化阴极性能,进而降低电池性能;通过增大流量比,可加强传质提升电池功率.一定流量比下,随氨浓度增加,电池性能逐渐提升,但过高浓度会引起氨渗透,恶化电池性能.电极孔隙密度越大,电极反应表面积越大,电池性能提升.随硫酸铵浓度增大,电解质电导率不断增大,电池性能逐渐提升,在高浓度(＞2 mol.L-1)下,浓度增大对电池性能提升不明显.     

燃气轮机合成气燃烧室中燃烧噪声的现场测试与分析

燃气轮机的燃烧噪声是反映燃烧室燃烧稳定性的主要参数.本文对国内某座煤基IGCC示范电站的40 MW级燃气轮机在诸多运行条件下的燃烧噪声进行了现场测试,分析了气液双燃料喷嘴在燃烧轻柴油、燃烧合成气以及油气切换过程中燃烧室的燃烧噪声,另外分析了合成气掺烧驰放气与合成气加湿对燃烧稳定性的影响.结果表明:合成气燃烧室在油气切换过程中燃烧噪声会增加,但距离振荡燃烧的阈值仍有很大的裕度;烧合成气时随着燃气轮机功率增加燃烧噪声降低;合成气加湿时随着蒸汽流量增加污染物NOx排放显著降低,并且燃烧噪声也有降低的趋势.     

封闭式喷雾冷却系统启动时间

 以蒸馏水为冷却工质,对冷凝器内置的封闭式光滑表面喷雾冷却系统进行了启动时间变化规律的实验研究,结果表明喷雾系统不同模块最优启动顺序为冷凝器、泵和加热器。采取6种不同的启动顺序,启动后加热表面的温度不均匀度均小于0.25 ℃。在最优启动顺序下,研究了冷却水流量、泵高度、加热功率和喷雾流量对启动时间的影响。随冷却水流量和喷雾流量增加启动时间缩短,随泵高度增加启动时间略微增大,随加热功率增大启动时间先增大后减小。启动时间影响程度由大到小的因素依次为喷雾流量、冷却水流量、加热功率及泵相对于加热表面的高度。喷雾工质流量由10 mL/min增大到35 mL/min时,封闭式喷雾系统的启动时间缩短了5 000 s。同样操作条件下,封闭式系统的启动时间比开放式系统延长15%~20%。     

PEM燃料电池中的两相传质及其影响

建立了一个新的二维、两相流模型来研究质子交换膜(PEM)燃料电池中的两相传质及其对质子膜阻抗和阴极性能的影响。模型不仅将催化剂层(CL)包含在电极中,还考虑了电池中相变及其对传质的影响。模型可同时使用在电池的阴极和阳极。主要模拟了电池阴极中两相传质、质子膜阻抗、阴极有效孔隙率和电流密度。模拟结果显示,提高加湿温度可以降低质子膜的阻抗,但过高的加湿温度会降低阴极气体扩散层(GDL)的有效孔隙率,降低阴极的性能。     

PEMFC尾气冷凝的自增湿运行

为增强质子交换膜的导电特性,在燃料电池,特别是大功率长时间运行的电堆中,需要有大量的加湿水。本文提出用冷凝器来冷却出口尾气,以收集大量的液态水并实现电池自增湿的方法。结果表明:尾气经冷凝降到一定温度分离出的液态水能有效满足反应气体的加湿要求,实现电堆的自增湿运行。     

质子交换膜燃料电池动态响应性能实验研究

本文实验研究了质子交换膜燃料电池负载变化时的动态性能,分析了氧气计量比流量和流场板结构的影响。结果表明,在本文的操作条件下,燃料电池动态响应能力的控制因素为质子交换膜水含量及液态水传递过程。随着氧气计量比流量的增加,电池性能及动态响应能力提高。采用不同流场板结构时,在输出电流较小的运行区间,平行流场板电池性能较好,随着平行流道数目减少,电池性能逐渐变差。     

密度锁反向启动特性实验研究

实验研究了密度锁反向启动特性,结果表明：启动流量是影响密度锁反向启动过程的关键因素,启动流量偏离平衡流量较小时,余热排出回路反向流量较小,依靠系统本身具有的自稳定性,将很快建立密度锁内水力平衡关系;而启动流量偏离平衡流量较大时,由于余热排出回路流量较大,较多冷却水进入主回路,导致加热水箱入口温度降低,入口温度的降低对密...     

Regression of solid polymer fuel strands in opposed-flow combustion with gaseous oxidizer

The combustion of solid fuels is a complex feedback loop, coupling the decomposition of the solid fuel into volatile gases with the gas-phase combustion which is responsible for the heat flux that drives decomposition. This study aims to explore the combustion of a solid fuel, hydroxyl-terminated polybutadiene (HTPB), with different mixtures of oxygen and nitrogen in an opposed-flow burner (OFB) configuration to better understand these coupled processes. An experimental OFB setup is described, which utilizes a nichrome wire and linear variable differential transformer (LVDT) to capture regression rate and shadowgraph imaging to measure flame thickness. Experimental measurements are compared with results from a complimentary one-dimensional opposed-flow combustion model with a pyrolyzing solid fuel boundary condition that conserves mass, species, and energy at the solid-gas interface. The oxidizer mass flux, ratio of oxygen to nitrogen, and separation distance of the fuel and oxidizer are varied to understand their influence on the combustion process and subsequently their effect on the regression rate. In numerical results, fuel regression rate increases when oxygen mole fraction or mass flux increase, or when separation distance decreases. Experimental regression rates and flame thicknesses are compared to simulated results. Though the actual values do not agree exactly, numerical and experimental results are reasonably close and present similar trends. These results demonstrate the utility of simple optical diagnostics in measuring OFB flames and provide a starting point for future opposed-flow combustion model improvements.     

Polymer electrolyte membrane fuel cell as a hydrogen flow rate monitoring device

There is a substantial demand for hydrogen flow rate monitoring devices in applications where hydrogen is utilised or produced and which include oil refineries, ammonia production, food and chemical industries, coal gasification, methane steam reforming and water electrolysis. In this paper, a polymer electrolyte membrane (PEM) fuel cell has been demonstrated for measuring accurate flow rates of hydrogen or hydrogen-containing gases. The concept involves applying a constant voltage to a PEM fuel cell to oxidise the entire hydrogen supplied to the anode compartment of the fuel cell and observing limiting current values attained and relating these to the hydrogen flow rates. PEM fuel cells with an active area of 50 cm² were constructed and used to accurately measure the flow rates of hydrogen up to 170 mL/min. A device with a capability to monitor significantly higher hydrogen flow rates can be constructed by using several cells in a stacking arrangement or by using electrically isolated cells in a single device. The paper discusses advantages and limitations of the technique and the flow rate-measuring response for gases containing 5–100 % hydrogen. The response time for hydrogen gas was of the order of 1–2 min. However, the fuel cell flow field design can be optimised for faster response times.     

流道结构和几何尺寸对燃料电池性能影响的实验研究

流场板是质子交换膜燃料电池重要部件之一。本文对以氢气和氧气作为反应气体的质子交换膜电池的极化曲线进行了实验测定,研究了不同流场板结构、流场板深度和宽度对电池性能的影响．研究发现采用组合流道的电池性能最佳．     

热物理参数对燃料电池内传质过程的影响

本文利用自行设计的实验系统,对自制的镀金不锈钢极板液态进料直接甲醇燃料电池的性能进行了测试。实验结果表明,较高的氧气压力和流量、较大的甲醇溶液流量、较高的电池温度均有助于强化燃料电池内部的传质过程。另外,在甲醇溶液浓度不超过2.0kmol/m~3的范围内,提高浓度有助于缓解催化层反应物不足的问题,从而改善燃料电池的性能。本文从机理上对这些实验结果进行了分析。     

不同流场下进气对质子交换膜燃料电池性能的影响

流场的结构对于质子交换膜燃料电池(PEMFC)的水管理和气体的传递具有十分重要的影响,相关研究一直是燃料电池的研究热点与重点。本文以纯氧气和空气作为阴极氧化剂,通过电池的性能测试、极化曲线和电化学阻抗分析等原位实验,分析了气体的流动与传输、不同流场下的电流密度、入口反应气体浓度等条件对电池性能的影响。实验结果表明,提高氧气浓度可以获得更好的质子交换膜燃料电池性能和最小化活化损失,纯氧气、波状流场的使用效果随进气量的变化而有明显的变化。     

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。     

Interrelation of anode and cathode processes in electrochemical carbon oxidation in a fuel cell with molten carbonate electrolyte

The object to be investigated is a fuel cell with a free molten carbonate electrolyte, which ensures direct electrochemical oxidation of solid hydrocarbons. The polarization characteristics of anode and cathode fuel cell assemblies, and also composition and gas release rate of gaseous products of anode reactions are studied. It is shown that the maximum voltages in the open cell circuit are obtained when the oxygen-carbon dioxide ratio in the cathode gas mixture corresponds to stoichiometric reaction coefficients that ensure replenishment of ions in electrolyte. However, the maximum current density values were obtained with a low carbon dioxide content. It is found that at high current values, anode potential fluctuations are observed. It is shown that carbon monoxide is the product of anode processes, along with carbon dioxide. The carbon monoxide content grows with temperature. The carbon dioxide content grows with increasing current in the fuel cell and with growing carbon dioxide content in cathode gases. The release rate of carbon oxidation products nonlinearly depends on the current value in the fuel cell. It is concluded that there is interrelation between the mass-exchange processes in the fuel cell, which is determined by the balance between cathode gas incoming into the reaction zone, the number of molecules generated during fuel oxidation, molecule dissolution and diffusion into the cathode region, and also the amount of gas released in the form of bubbles.     

平板型环路热管应用于LED的启动特性研究

本文将平板型环路热管应用于大功率LED的散热,通过实验研究了加热位置、放置方式和功率对启动特性的影响.蒸发器内的汽液分布影响着从蒸发器到补偿器的热泄漏,从而影响启动特性.如果非有效蒸发区内的液态工质量越多,则热泄漏越小,环路热管越容易启动.此外,补偿器内工质往液管流动,相当于补偿器对外做功,自身能量有减少的趋势,促使形成循环所需的更大压差.     

CO_2两相回路启动过程阶段蒸发和干烧现象分析

采用并联蒸发器作为传热元件,并联冷凝器作为散热部件,建立了包括热量收集、传递与排散的机械泵驱动两相回路集成试验系统,并对该系统的热启动进行实验研究.实验结果表明:(1)在冷工况、低热流密度的情况下,采用长程毛细管结构的蒸发器对分布式小热源进行集热时,会出现阶段性形核沸腾蒸发,并且上游过热液体形核沸腾后会导致下游出现干烧现象.(2)对于该系统,并联蒸发器相同热量同时启动是相对较好的启动方式.