PEMFC 全功率变流量喷射器流场特性研究

针对质子交换膜燃料电池全功率氢循环对喷射器变流量的需求,提出并设计了不同嵌套方式的四喷嘴喷射器,以实现不同工况下变流量性能。为研究不同嵌套方式喷射器的流场特性及其循环性能,采用计算流体力学方法对喷射器进行建模和分析。结果表明,部分嵌套喷射器的内部流场比全嵌套喷射器的内部流场稳定;当二次流压力和背压不变时,一次流压力从6 bar(1 bar=100 kPa)增加到10 bar,部分嵌套喷射器引射比先上升后下降,在压力为7 bar时存在最大值;而全嵌套喷射器引射比是下降的趋势,通过与实验数据的比较,部分嵌套喷射器具有更优的性能;最后通过多喷嘴PWM逻辑控制,实现了170 kW燃料电池全功率变流量拟线性调控性能,满足燃料电池在变功率运行下的氢循环需求。     

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。     

低温制冷系统两级喷射器设计与性能分析

本文提出了一种用于渔船低温制冷系统的两级喷射器,并对其进行了优化设计和性能分析。为达到最大引射性能,提出了基于流场参数匹配的两级喷射器优化设计方法,使用计算流体力学仿真软件对两级喷射器进行了建模和参数优化。此外,采用了水冷式冷凝器来减小冷凝器与蒸发器之间的压差,从而获得了更高的引射比。研究结果表明,所设计的两级喷射器可使蒸发温度低至248.15 K,第一级和第二级喷射器最优面积比分别为11.8和6.5。中间压力在253～324 kPa之间,引射比先增加后减小,在中间压力为304 kPa时达到最大值0.096,此时系统能效比达到0.074。可以认为,采用优化设计的两级喷射器和水冷式冷凝器,利用渔船余热驱动的低温制冷系统具有较好的节能效果。     

喷射器设计与使用管理中的一种特殊现象研究

基于大量试验发现了喷射器扩压管喉径与喷嘴喉径匹配过程中存在的中间迟钝现象,并对它进行了较深入的研究。结果表明,这一现象的出现时机主要取决于喷嘴喉径、出入口流体的压力及压差;在对大量试验数据按数值方法进行处理后,得出了中间迟钝现象出现时机的简易判据。应用这一研究,可以有效减少喷射器设计的工作量,提高设计效率;可以形象地说明喷射器实际工况偏离设计点时效率下降的原因;还可用于指导喷射器变工况下的使用管理,减小变工况下工作调节的盲目性。     

超音速喷射器内部流场及变工况CFD分析

针对超音速空气喷射器的性能进行了数值研究,得到了喷射器内部的压力场和流动特性,并计算了喷射器的变工况特性。分析表明,当喷射器工作背压小于临界背压时,混合室中的压力基本为定值,喷射系数不变,在混合室中或出口处出现激波链;当工作背压达到临界背压时,激波链收缩到混合室入口,混合室中的定压混合过程消失;当工作背压大于临界背压,在混合室的入口处产生强激波链,出现阻塞,喷射器系数减小。此外,随着工作流体压力的升高,对应的临界背压增大,当工作压力比较低时,激波链从混合室出口向混合室入口收缩的速度更快。     

机车用350 kW燃料电池热管理系统设计

针对机车平台整体功率高、工作温度跨度大、运用环境恶劣等特点,设计了匹配350 kW燃料电池系统的热管理系统。根据机车空间布局与燃料电池系统功能划分进行热管理系统结构搭建,并针对电堆冷却循环、电力电子冷却循环、低温冷启动循环等3个主要功能循环的换热需求进行了分析计算,最终根据换热需求和匹配的部件特性给出不同工况的运行模式与控制策略。通过集成化、模块设计、策略优化的系统设计,满足了有限车体空间内大功率散热需求,并能够实现零度以下低温冷启动,拓宽了既有轨道交通车辆燃料电池热管系统的功率等级和工作温度范围。     

高温喷射器的近似计算及其应用

本文研究高温喷射器的近似理论计算问题;建立了常温气流及高温气流的两股流体的动量方程和能量方程。根据优化条件决定最佳面积比和混合室的压力值以及采用渐近法得到混合室的温度及引射系数。并讨论了喷射器端口阻力特性对喷射器性能的影响     

基于多物理场耦合的高温掺合阀温度场数值模拟研究

为了研究柱塞式高温掺合阀在实际生产中流体域内温度场、速度场、压力场及阀耦合温度场的分布规律,分别采用理论计算方法和基于ANSYS的有限元方法对实际生产工况条件下该阀的流场、温度场进行耦合计算.给出了理论计算过程,为模拟分析提供依据,给出了流体域内温度场、速度场、压力场及阀耦合温度场的计算过程和结果.结果表明:阀内流体域...     

双螺杆转子结构特性流固耦合数值模拟

以双螺杆转子为研究对象,依据流固耦合理论,通过求解捏合机内部流体和双螺杆转子固体耦合方程,研究不同工况下的流体压力和扭矩对双螺杆转子应力和变形的影响规律。分析计算结果表明:螺杆转子的变形和应力主要是不同工况下的扭矩、流体压力载荷及耦合场作用引起的;螺杆间隙对捏合机的生产效率和质量有很大影响,阴阳螺杆转子最大变形量是设计最佳螺杆间隙的关键因素;一定功率下,转子的最大变形量和最大应力值分别与转子扭矩、流体压力的大小正相关;一定转速下,转子的最大变形量和最大应力值与捏合机功率正相关。研究结果为新型双螺杆捏合机的合理设计与性能预测提供了理论依据。     

混流式水轮机转轮流场单向、双向流固耦合数值的分析比较研究

针对水轮机转轮单向流固耦合和双向流固耦合计算结果的比较问题,建立了精确的水轮机流场及结构场模型,分别对低水头、低转速和高水头、高转速两种工况下转轮单向、双向流固耦合进行了数值模拟。对比了两种工况在单向、双向耦合时转轮表面流体域的最大压力、最大速度及转轮结构域的最大应力、最大应变、最大总位移,最后结合流固耦合公式对计算结果作了进一步的分析。研究结果表明,在使用单向流固耦合进行数值计算时,流固耦合作用越强,则计算偏差越大;通过同一流场和结构场的单向流固耦合和双向流固耦合计算值对比可知,无论是流体域还是结构域的计算值,相同节点的单向耦合计算值均小于理论上更为精确的双向耦合计算值。     

舱外服大循环量引射器优化设计与实验研究

为进一步提高舱外航天服供氧通风能力,对其引射器进行优化设计。采用一维气体动力学模型建立喷嘴控制方程;根据实验结果确定喷嘴等熵效率,设计缩放喷嘴;采用3D打印技术加工不同结构的引射器;利用氮气进行常压引射实验,研究挡板位置、喷嘴类型与喷嘴出口位置(Nozzle Exit Position,NXP)等结构参数对混合流量的影响,寻找最优的引射器结构。研究表明:挡板位置对引射器混合流量的影响与喷嘴类型相耦合。前移挡板,亚音速引射器混合流量可提高56.90%以上,而超音速引射器则降低12.08%以上。将渐缩喷嘴换为缩放喷嘴,混合流量可以提高1.81倍以上;对于挡板前移的亚音速引射器,则可提高36.90%以上。所有亚音速引射器均无法满足当前性能要求。然而,对于超音速引射器,对于所有的NXP,在典型工况下引射器循环量均可满足要求;存在最优的NXP使得混合流量最大。NXP为6 mm时,超音速引射器混合流量最大,为144.83 L/min(工作流绝对压力为0.503 MPa);在全工况下(工作流表压为0.30～0.55 MPa),混合流量可至少提高1.59倍。设计的最优引射器测试结果均满足性能要求。     

特定条件下气-液喷射器结构合理性分析

为找出喷射器气液混合效果不理想的原因,创建了喷射器流场模型,采用CFX软件对喷射器流场进行了稳态和瞬态的数值模拟计算。得到了模型在不同工况下的气液混合效果、两进口的压差和两进口流量和压力的波动情况。计算结果表明此喷射器气-液混合效果受两进口压差的影响较大,只有在两进口压差较小的情况下才能完成气液混合。     

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.     

MSF海水淡化装置喷射器性能分析

结合蒸汽动力函数和热力学分析方法,建立蒸汽喷射器的数学模型,分析最佳引射系数的影响因素,引射系数随混合蒸汽出口压力的关系及引射压力随工作蒸汽压力和混合蒸汽出口压力的关系。分析指出,工作条件一定时,最佳引射系数是固定值;在达到极限值前,引射系数随混合蒸汽出口压力的增大而降低,达到极限值时,引射系数不随出口蒸汽压力的变化而变化;引射压力在设计范围内随工作蒸汽压力的升高而降低,随混合蒸汽出口压力的升高而升高。     

Effects of key operating parameters on the efficiency of two types of pem fuel cell systems (High-Pressure and Low-Pressure operating) for Automotive Applications

The proton exchange membrane (PEM) fuel cell system consisting of stack and balance of plant (BOP) was modeled in a MATLAB/Simulink environment. High-pressure operating (compressor type) and low-pressure operating (air blower type) fuel cell systems were considered, The effects of two main operating parameters (humidity and the pressure of the supplied gas) on the power distribution characteristics of BOP and the net system efficiency of the two systems mentioned above were compared and discussed. The simulation determines an optimum condition regarding parameters such as the cathode air pressure and the relative humidity for maximum net system efficiency for the operating fuel cell systems. This study contributes to get a basic insight into the fuel cell stack and BOP component sizing. Further research using multiobject variable optimization packages and the approach developed by this study can effectively contribute to an operating strategy for the practical use of fuel cell systems for vehicles.     

Parametric study of a high-performance ammonia-fed SOFC standalone system

Ammonia-fed solid oxide fuel cell (SOFC) power generation systems are very promising owing to their high efficiency and ease of fuel storage. However, understanding the complexity of fuel cell stacks and systems supplied by ammonia remains challenging. Therefore, it is proposed to investigate the standalone SOFC system to clearly elucidate the behavior of the stack and realize facile implementation. In this study, the stack was modeled and validated using experimental data to confirm its output characteristics. The system efficiency was then calculated under various operating conditions, such as current density, fuel utilization, and stack in/out temperature. The results show that the system efficiency is approximately 54 % and is highly dependent on fuel utilization and current density but not on temperature differences. However, the system can only operate at a temperature difference of 65 °C or higher owing to the effectiveness of the heat exchanger on the fuel side.

     

Efficiency measurement and uncertainty discussion of an electric engine powered by a "self-breathing" and "self-humidified" proton exchange membrane fuel cell

The efficiency of an automotive engine based on a "self-breathing" and "self-humidified" proton exchange membrane fuel cell stack (PEM FC) connected to a dc brushless electrical motor was measured under variable power load conditions. Experiments have been carried out on a small scale 150 W engine model. After determining the fuel cell static polarization curve and the time response to power steps, the system was driven to copy on the test bench a "standard urban load cycle" and its instantaneous efficiencies were measured at an acquisition rate of 5 Hz. The integral system efficiency over the entire urban load cycle, comprising the losses of the unavoidable auxiliary components of the engine, was then calculated. The fuel cell stack was operated mainly in "partial" dead-end mode, with a periodic anode flow channel purging, and one test was carried out in "pure" dead-end mode, with no anode channel purging. An uncertainty analysis of the efficiencies was carried out, taking into account either type A and type B evaluation methods, strengthening the discussion about the outcomes obtained for a system based on this novel simplified FC type. For our small scale engine we measured over the standard urban cycle, on the basis of the H(2) high heating value (HHV), a tank-to-wheel integral efficiency of (18.2+/-0.8)%, when the fuel cell was operated with periodic flow channel purging, and of (21.5+/-1.3)% in complete dead-end operation mode.     

新型可变可控三油楔轴承结构设计及静态特性分析

传统三油楔轴承结构形状固定,且运转工况单一,为适合变化的工况,提出一种可变可控三油楔轴承。将压电叠堆引入轴承结构中,压电叠堆在直流驱动电压作用下产生驱动力,使轴瓦内表面由圆形变为三油楔形状,且通过改变电压可以控制轴瓦变形大小。介绍该轴承的结构和工作原理,采用CREO软件建立不同驱动电压下油膜的几何模型并导入前处理软件ICEM中进行结构化网格划分,基于FLUENT软件中的两相流模型计算分析不同电压、偏心距和转速下轴承静态特性。结果表明：改变驱动电压可改变三油楔轴承油膜间隙,进而调控油膜压力分布和静态特性;在相同转速和偏心距下,随着驱动电压的升高,可变三油楔轴承变形加大,承载力和摩擦力逐渐减小,流量逐渐增大。     

变截面密封圈温度场及密封性能分析

为研究不同工况下变截面密封圈密封特性及润滑油膜温度场与黏温特性的关系，根据变截面密封圈密封机制，建立润滑油膜三维数值计算模型，考虑黏温特性和流体内摩擦效应，采用FLUENT和MATLAB软件，研究变截面密封圈润滑油膜在实际工况下的密封特性以及温度特性。结果表明：考虑黏温特性和在定黏度2种情况下所得结果差距明显，表明黏温特性对密封特性的影响不可忽略；油膜最高温度区域均处于外界环境侧，并随工况的改变而移动；油膜最高温度值随转速增加而升高，随密封压力增加而降低，但转速的影响大于其他工况参数；随润滑油温度升高，考虑黏温特性时油膜最高温度值随之增加，而定黏度时呈先减后增的趋势；泄漏量均随转速、密封压力和润滑油温度的增加而增大，但密封压力的影响最大。