基于框架设计的液流电池流场优化模拟研究

液流电池通常采用对角平推流流场,会形成电解液滞留区,造成电池局部浓差极化大,影响综合性能。鉴于此,提出了一种基于框架设计的流场优化方法,通过设计电极框架,可以得到"蛇形流道"和"平行流道"两类流场。以全钒液流电池为例,通过数学建模,研究了不同流场结构和参数对于多孔电极内电解液流动特性、电化学反应和温度变化特性的影响规律。计算结果与实验结果一致性良好,结果表明:电解液在"平行流场"内的流动均匀性比在"蛇形流场"内好,且不存在滞留区,同时在"平行流场"内浓差极化也较"蛇形流场"低;此外,对于同样的电极面积,在电极内部的"平行流道"越多,电解液的流速分布越均匀,反应特性越好。     

液流电池流场结构设计与优化研究进展

液流电池结构设计与优化研究是改善电池内部电解液流动性能、提高电堆功率密度和可靠性的重要途径之一。在石墨板上设计并行、交指和蛇形等流道是液流电池使用的传统流道结构,其缺点为流道种类单一、石墨板成本高及机械性能差。为了克服上述缺点,波纹状并行、分离式蛇形、螺旋形等新型流道,在电极上构建流道、引入独立的流道部件、环形与梯形等异形结构等先后被提出。本文从双极板、电极上的结构设计和异形结构设计与优化三方面系统综述了近年来液流电池结构设计与优化研究进展,阐释流场结构等对电池性能的影响机制及其与电池运行、装配间的适配规律,并提出进一步改善电池性能并适合普及应用的流场结构形式。     

全钒液流电池电解液流场结构优化设计

全钒液流电池电解液流场结构合理可使电流密度、钒电解液分布均匀,降低极化,提高电池性能。设计3种不同的电解液流场,研究流场结构对电池极化、充放电电流电压、功率密度和能量效率的影响。结果表明蛇形流场结构简单且易于加工,可使钒电解液均匀分布,增强电解液对流传质能力,能较充分利用钒电解液储能容量,电池的输出功率密度最高可达31.6 mW/cm2,与传统平行流场相比,电池电流效率提高13.9%,电压效率提高6.3%,能量效率提高14.8%,放电容量提高了35.3%。     

全钒液流电池电解液分布的数值模拟

为了提高全钒液流电池双极板流道电解液分布均匀性,考察流体流动行为,本文基于计算流体力学,在传统平直并联流道基础上通过增加倾斜挡板和入口流堰,改进流道结构;同时探究钒电池用电解液在分段式多通道蛇形流道内流体水力学特征。数值模拟结果表明：分段式多通道蛇形流道既可以保持传统蛇形流道流体均匀分配的性能,又能有效降低流阻,减少泵耗;合适的电解液流速及其均匀分布可以优化电解液活性物质浓度分布,提高电解液稳定性,增大钒电池能量效率。     

质子交换膜燃料电池流场板研究进展

流场板是质子交换膜燃料电池的核心部件之一,其结构直接影响着反应气体的利用效率以及燃料电池的排水及散热性能。综述了近十余年来质子交换膜燃料电池流场板的设计与研究进展。研究者们基于平行流场、蛇形流场、交指流场、点状流场,从流道尺寸、流道截面、进口分配段、流道布置等方面开展结构设计和优化,不同程度提高了燃料电池水热管理以及电性能。此外,各种形式的组合流场可综合不同流场优点,多级分形仿生流场优化了反应物、压力与电流密度分布,三维精细化流场通过改善供气方式降低了浓差极化。     

丙三醇对钒液流电池电解液影响的交流阻抗研究

采用交流阻抗法研究了添加剂丙三醇对全钒氧化还原液流电池阳极电解液电极反应影响的内部作用机理。通过RS(Cd(RpW))形式的等效电路对其阻抗谱进行了较好的模拟解析，研究结果发现，随着丙三醇含量的依次增加，溶液电阻、双电层电容和极化电阻均出现最小值，浓差极化电阻出现最大值，此时添加量均为1%，说明含有一定量供电子基团结构的丙三醇能够有效结合钒离子，均匀分散于溶液中，使得溶液电阻降低，当钒离子结合丙三醇后体积增大，双电层电容距离增加，从而双电层电容降低，当钒离子结合丙三醇后更利于向电极表面吸附，提高阳极电解液的催化效率，加大了电极表面反应物浓度与本体溶液中的差值，使得浓差极化电阻增强，电极反应效率提高。     

锌溴液流电池通道的计算流体力学模拟

针对不同类型的锌溴液流电池通道,利用流体力学计算软件 FLUENT对流体的流动状态进行了模拟。结果表明,在相同流速条件下,直角通道和弯角通道流体的局部流速最大值都出现边壁突变处;在液流电池反应区,流体的局部流速和湍流程度的分布存在不均匀现象。通过改变进出反应区的分流通道数量和结构,可以使电解液在反应区流动均匀,改进整个流动体系的传质性能,进而使锌溴液流电池电堆的充放电性能得到提高。     

钒离子浓度对全钒液流电池极化分布的影响

基于物质传递方程、电荷传递方程和电化学动力学方程提出了浓差极化系数的概念,建立了全钒液流电池二维模型,利用有限元法研究了钒电池极化过程,并对电极区域极化的分布进行了定量评估。研究表明:增加钒离子浓度,电极表面和溶液本体浓度趋同,活化极化和浓差极化减小,这种现象在高电流密度下尤为明显;浓度的增加也使得浓差极化系数减小,物质传递的影响减小,浓差极化相对于整个极化影响越来越弱;从进口到出口,浓差极化系数逐渐增加;电极与集流体接触面的浓差极化系数比电极中间区域高得多。     

固体氧化物电解池平行流道流动不均匀性优化模拟

氢能是一种具有高能量密度、无污染的可再生能源。当前,固体氧化物电解水制氢技术(SOEC)对于流场分布的关注较少,而平行流道的流动不均匀性会显著影响SOEC的反应效率和使用寿命。本研究结合燃料电池中对反应物流动情况的研究建立了电化学场、传热场、流场的多物理场耦合仿真模型研究反应物在电解中的分布情况,按照不同的流道宽度比改变平行流道的流道宽度,设计了一种新型Z型平行流场。结果表明：与传统Z型流场相比,8 000 A/m²电流密度下水蒸气摩尔分数不均匀系数由0.152 0下降至0.030 4,电解质局部电流密度差值由6 000 A/m²下降至2 000 A/m²,温差由105.9 K下降至97.2 K,均匀性有明显的提升。各个电流密度下,在出口处的产氢速率上升7%左右,在相同时间内可以产生更多的氢气,提高了制氢的效率。     

对称双阴极固体氧化物燃料电池阴极流道影响的数值模拟

基于热-电-力-化学多物理场耦合理论,针对对称双阴极固体氧化物燃料电池建立了一个三维数值模型,设计出一种具有强化传质能力的Ⅰ型流道,并与传统Z型阴极流道电池中流道的气体流动速率、氧气摩尔分数、压损、温度、应力分布以及电化学性能进行了对比研究。结果表明:在0.6 V工作电压下结构优化后的阴极Ⅰ型流道与传统Z型流道相比,传统Z型的氧气浓度分布差约为58.6%,优化Ⅰ型流道的氧气浓度分布差约为38%,氧气分布更加均匀,优化Ⅰ型流道相较于传统Z型流道压降损失减少约36%,随着工作电压的减少,电池的浓差极化损失越小,能够有效提升电池性能。     

Novel design of flow path spacers for reverse electrodialysis cell

Reverse electrodialysis (RED) is one of the technologies used to harness ‘Blue Energy’, which is generated from the controlled separation of ions between salt water and fresh water through cation and anion exchange membranes (CEM/AEM) stack with end electrodes. The spacers present in between CEM and AEM allows the flow of salt and fresh water significantly affecting the fouling and concentration polarization in the RED cell. The present work focuses on improvement in flow path design, which may be used in place of mesh spacers in order to reduce pressure drop and enhance shear stress on the surface of the membrane to reduce concentration polarization. A three-dimensional direct numerical simulation of the Navier–Stokes equation is conducted using Fluent 14.0 to analyze four different flow field designs, including serpentine, criss-cross, rhombus, diamond, and standard mesh spacers. The simulation predicted closely the experimental data on pressure drop for the mesh spacers available in the literature. The present study points out that the diamond type flow field design, which combines characteristics of mesh spacers and flow field plates, gives lesser pressure drop per unit length with the increase in velocity within the same range of shear stress generated in mesh spacers. In other words, net power density of RED would improve with the use of diamond type spacer flow field with the decrease in concentration polarization loss and pumping power density.     

Hydrodynamic analysis of flow fields for redox flow battery applications

Electrolyte flow distribution is an important factor that contributes to the performance of the overall efficiency of a redox flow battery system. In the present paper, a comparative study of the hydrodynamics of the serpentine and interdigitated flow fields has been performed. Ex situ experiments were conducted using the two flow fields in conditions typical of flow battery applications. Limited in situ testing has also been conducted. These bring out the surprising result that the pressure drop in the interdigitated flow field is less than that in the serpentine for the same flow rate. Computational fluid dynamics studies show strong under-the-rib convection in the reaction zone exists in both flow fields but with a shorter residence time in case of the interdigitated. It is posited that this may explain the superior electrochemical performance of cells with interdigitated flow fields.     

Flow field design and optimization of high power density vanadium flow batteries: A novel trapezoid flow battery

Vanadium flow battery (VFB) is one of the preferred techniques for efficient large‐scale energy storage applications. The key issue for its commercialization is cost reduction, which can be achieved by developing high power density VFB stacks. One of the effective strategies for developing high power density stacks is to enhance the mass transport by performing flow field design. Based on the maldistribution characteristics of concentration polarization inside a conventional rectangular flow battery (RFB), a novel trapezoid flow battery (TFB) was first proposed. Furthermore, a practical and general strategy, consisting of a stepping optimization method and an arithmetic progression model, has been developed for the TFB's structure optimization. By combining numerical simulation with charge‐discharge test of the magnified stacks, it was verified that mass transport enhancement and performance improvement of the optimized TFB, with significant increments in voltage efficiency and electrolyte utilization, allowed it to possess great superiority over the RFB. © 2017 American Institute of Chemical Engineers AIChE J, 64: 782–795, 2018     

Effects of anode orientation and flow channel design on performance of refuelable zinc-air fuel cells

The effects of anode orientation (whether an anode is located above or under a cathode) and flow channel design (parallel or serpentine flow channel) on the performance of refuelable zinc-air fuel cells (RZAFC) continuously fed with KOH electrolyte were investigated. The performance test was conducted at different electrolyte flow rates of 2, 4, and 6 ml h^?1. A polarization test of the cell was conducted at the initial stage of operation, followed by a long-term current discharge test in potentiostatic mode. The spent zinc powders were characterized by a scanning electron microscope and X-ray diffraction. The experimental results revealed that the anode-bottom orientation in the cell performed much better than the anode-top orientation with 11.4 times higher zinc utilization. The performance reduction of the anode-top orientation cell was caused by the cathode overpotential, due to the flooding of the cathode by water crossover from the anode, which was induced by the gravity force. For the flow channel design effects, there was an optimum electrolyte flow rate, to yield a maximum current discharge capacity, of 4 ml h^?1 in this study. At this optimum flow rate, the total charge per gram of zinc delivered from the anode serpentine cell was 1.75 times higher than that from the anode-parallel one.     

采用泡沫铜电极的热再生氨电池性能数值模拟

以采用泡沫铜电极的热再生氨电池（thermally regenerative ammonia-based battery,TRAB）为研究对象,建立了多孔介质内物质传输与电化学反应耦合的稳态模型,计算获得了电池性能及多孔电极内物质传输特性,并研究了电解质浓度和电极孔隙率对电池性能的影响。研究结果表明,从主流区界面到多孔电极内部,阳极氨和阴极铜离子浓度逐渐降低,存在一定的浓度梯度,而且随着反应电流的增大,浓度梯度明显增大。在一定的范围内分别增大阳极氨浓度和阴极铜离子浓度,从主流区向多孔电极内物质传输增强,电池性能均能不断提升;随着硫酸铵浓度的增大,电解质电导率增大,电池性能逐渐提升,但增幅逐渐减小。此外,多孔电极孔隙率也会影响电池性能,本研究中TRAB在电极孔隙率为0.6时获得最高的最大功率(15.3 mW)。     

可溶铅酸液流电池模拟与仿真

可溶铅酸液流电池是一种使用单个容器存储电解液并且不需要微孔隔膜的氧化还原液流电池,这使得电池设计简单并降低了成本。建立二维暂态可溶铅酸液流电池模型,模型基于对质量、电荷以及能量的转移与守恒以及包含铅离子反应的宏观动力学模型为基础,研究了电极间隔、电极形状、电流密度、实验温度、入口电解液流速和电解质初始浓度对电池性能的影响。研究表明：与平板电极相比,弧形电极明显提高了充电时的电池电压。在影响铅酸液流电池性能的诸多条件中,电池温度和电流密度可能是优化电池性能的重要因素。