微型直接甲醇燃料电池三维性能数值仿真

采用CFD软件对微型甲醇燃料电池(Micro Direct Methnol Fuel Cells,μDMFC)进行模型的建立和性能仿真,并比较了不同的流场结构设计对电池性能的影响.结果表明,蛇形流场结构比较点型和平行流场结构具有更好的电池性能,且由于甲醇的渗透,甲醇浓度增加时,会引起电流密度的有所下降.     

基于Fluent的微型直接甲醇燃料电池阳极流场结构分析

微型直接甲醇燃料电池中阳极流场结构对电池的性能有着重要的影响。为了合理设计阳极流场结构,改善甲醇燃料在阳极流场中的分布,采用计算流体动力学(CFD)软件Fluent对微型直接甲醇燃料电池进行建模并仿真分析。分析比较了点型、平行和蛇形3种不同流场图案下得到的压降与流速分布,得出蛇形流场能够更有利于甲醇燃料的均匀分配。在此基础上分别建立不同流道宽度(800,400,200,100μm)的蛇形流场模型,通过仿真计算甲醇燃料的分布情况来分析其对燃料电池性能的影响,并结合实验结果进行对比得出流道宽度为200～400μm之间为优化值。     

微型自吸氧直接甲醇燃料电池的阳极极板设计研究

在体积微型化条件下,极板流场图形的设计对燃料电池的性能优化,尤其是提高面积比功率,具有极其重要的意义.本文设计了不同沟道和沟脊宽度的阳极极板,测试了相应微型自吸氧燃料电池的性能变化.实验结果表明,在沟脊宽度小于沟道宽度的条件下,增加沟道或沟脊宽度都能改善微型燃料电池的性能,但改善幅度随宽度增加而趋缓.当沟道和沟脊宽度等比例变化时,性能随宽度的增加的最优值为600μm,其性能达到了2.87 mW/cm2,优于沟道和沟脊均为400μm和800μm的燃料电池的性能.     

微型直接甲醇燃料电池CO2气泡排除问题研究

利用CFD方法模拟了微型直接甲醇燃料电池阳极二氧化碳气体在沟道中的流动与分布.结合两相流理论,研究了不同流场布局、沟道尺寸和燃料入口流速对两相流压力降及气体分布的影响,得到了最大残余体积含气率与流道宽度及入口速度的关系.结果表明蛇形流场排泡效果要优于平行流场,尤以流道宽度为600μm时最佳.根据计算结果,分别对蛇型流场、平行流场和三通道蛇型流场中气体聚集的位置进行了预测.研究结果为流场的参数设计和结构优化提供了参考.     

采用硅和PDMS的堆栈式微型直接甲醇燃料电池的设计和制作

在堆栈式微型直接甲醇燃料电池μ-DMFC(Micro-Direct Methanol Fuel Cell)中,为了避免硅基流场板因为封装压力过大而破裂,采用了硅和PDMS(Polydimethylsiloxane,聚二甲基硅氧烷)材料分别制作阳极和阴极流场板。首先,采用微机电系统MEMS(Micro-Electro-Mechanical Systems)技术制作硅基阳极流场板。其次,通过铜箔与阴极流场板一体成型、有机清洗和PDMS表面活化等改进措施显著提升了PDMS阴极流场板金属化的能力。最后,比较和分析阳极流场板上3种不同结构的流道形式的堆栈式μ-DMFC的输出性能。实验结果表明,活化后的PDMS阴极流场板与Cr/Au的粘附性能和粘接强度显著提高,同时阳极流场板的流道一半开设为凸台,一半开设为通孔时,其堆栈式μ-DMFC的输出性能最优。最大输出电流密度为81.25 mA/cm2,最大输出功率为7.73 mW/cm2。采用硅和PDMS材料分别制作流场板,不仅简化了堆栈式μ-DMFC的结构,而且能够缓冲锁紧力,有效保护硅基阳极流场板。同时优化阳极流场板上的流道结构,能够有效提升堆栈式μ-DMFC的输出性能。     

采用硅和PDMS的堆栈式微型直接甲醇燃料的设计和制作

在堆栈式微型直接甲醇燃料电池（Micro-direct methanol fuel cell，简称μ-DMFC）中，为了避免硅基流场板因为封装压力过大而破裂，采用了硅和PDMS（Polydimethylsiloxane，聚二甲基硅氧烷）材料分别制作阳极和阴极流场板。首先，采用MEMS（Micro-Electro-Mechanical Systems，微机电系统）技术制作硅基阳极流场板。其次，通过铜箔与阴极流场板一体成型、有机清洗和PDMS 表面活化等改进措施显著提升了PDMS阴极流场板金属化的能力。最后，比较和分析阳极流场板上三种不同结构的流道形式的堆栈式μ-DMFC 的输出性能。实验结果表明，活化后的PDMS 阴极流场板与Cr/Au 的粘附性能和粘接强度显著提高，同时阳极流场板的流道一半开设为凸台，一半开设为通孔时，其堆栈式μ-DMFC 的输出性能最优。最大输出电流密度为81.25mA/cm2，最大输出功率为7.73mW/cm2。采用硅和PDMS 材料分别制作流场板，不仅简化了堆栈式μ-DMFC 的结构，而且能够缓冲锁紧力，有效保护硅基阳极流场板。同时优化阳极流场板上的流道结构，能够有效提升堆栈式μ-DMFC 的输出性能。     

MEMS微型质子交换膜燃料电池的阴极极板模型研究与优化设计

针对一种基于MEMS技术制造的H2/air自呼吸式微型质子交换膜燃料电池,建立了二维等温的阴极数学模型,计算了电池的平均电流密度及功率密度.由于阴极采用空气自呼吸式,阴极流场板结构的空占比就成为影响电池性能的重要因素.通过优化,确定空占比为0.7左右时,燃料电池的性能最佳.制作器件的测试结果表明采用该优化设计的燃料电池的峰值功率密度高达135 mW/cm2.     

基于遗传算法的直接甲醇燃料电池的数学模型及优化设计

微型直接甲醇燃料电池由于具有系统结构简单、体积小、环境友好、燃料比能量高及便于携带与储存等优点,在便携式电源,如手机、笔记本电脑等上展示出良好的应用前景。研究DMFC的数学模型可以深入了解DMFC中物质的传递过程和电化学机理,为寻找DMFC性能的最优化工作条件提供理论依据。主要依据微型直接甲醇燃料电池中物质传递的基本原理及电化学动力学机理,建立微型直接甲醇燃料电池的一维数学模型,利用遗传算法对其进行优化设计。仿真结果显示当阳极甲醇浓度为2.32mol/L,阴极氧气浓度为0.06mol/L,电流密度为545.67mA/cm2,DMFC的功率密度达到最大值为71.5mW/cm2。     

微型直接甲醇燃料电池的三维数值模拟研究

运用计算流体力学软件COMSOLTM建立了微型直接甲醇燃料电池(μDMFC)三维数值模型,并用MEMS工艺制作电池进行实验验证.模型耦合了连续性方程、电化学反应方程和动量方程等.通过对模型求解,输出了平均电流密度和电压等参数.分析了扩散层和催化层结构参数对电池性能的影响,结果表明:过厚的催化层对电池性能提升并无太大帮助,在增大电催化剂Pt担量前提下应尽量减小催化层厚度.     

基于MEMS技术的微型直接甲醇燃料电池的制作

为了进一步简化微型直接甲醇燃料电池(μDMFC)系统,便于电池批量生产,采用MEMS技术制作μDMFC.电池的制作包括传统的MEMS工艺,如,氧化、光刻、湿法刻蚀、硅-玻璃键合等方法,还包括一种新的催化电极制备方法,即采用硅片阳极氧化的方法.首先,制得多孔硅(PS)作为催化电极的基底,然后,采用化学镀法分别在PS上沉积出Pt阴极催化电极和Pt-Ru阳极催化电极.PS具有巨大的比表面积,使化学镀的催化剂层拥有不连续的三维结构,能显著增加催化剂的活性面积,同时,化学镀液中贵金属的利用率高达95%,可以有效地节约贵金属用量.研究中采用扫描电镜(SEM),能量色散X射线分析(EDX)对催化剂层的形貌和成分等物理性能进行了分析.     

Capillary-driven pumping for passive degassing and fuel supply in direct methanol fuel cells

In this paper we present a new concept of creating and using capillary pressure gradients for passive degassing and passive methanol supply in direct methanol fuel cells (DMFCs). An anode flow field consisting of parallel tapered channels structures is applied to achieve the passive supply mechanism. The flow is propelled by the surface forces of deformed CO₂ bubbles, generated as a reaction product during DMFC operation. This work focuses on studying the influence of channel geometry and surface properties on the capillary-induced liquid flow rates at various bubbly gas flow rates. Besides the aspect ratios and opening angles of the tapered channels, the static contact angle as well as the effect of contact angle hysteresis has been identified to significantly influence the liquid flow rates induced by capillary forces at the bubble menisci. Applying the novel concept, we show that the liquid flow rates are up to thirteen times higher than the methanol oxidation reaction on the anode requires. Experimental results are presented that demonstrate the continuous passive operation of a DMFC for more than 15 h.     

A Methanol-Tolerant Gas-Venting Microchannel for a Microdirect Methanol Fuel Cell

As a byproduct, gas is constantly generated from the electrochemical reactions of direct methanol fuel cells (DMFCs). In the anodic channel of a DMFC, the gas forms bubbles, which leads to bubble clogging and pressure buildup if the device is miniaturized. Bubble clogging increases the flow resistance in microchannels, calling for excessive power consumption for fuel delivery. Pressure buildup aggravates the undesired crossover of methanol. In order to solve those problems, this paper introduces a gas-venting microchannel that directly removes gas bubbles from the two-phase flows of gas and methanol solution without leakage. By employing a hydrophobic nanoporous membrane, successful venting is achieved for both water and methanol fuel with a concentration of as high as 10 M. The fuel is contained without leakage under overpressures of as high as 200 kPa for both water and 10-M methanol, fulfilling the requirement of the current- as well as next-generation microdirect methanol fuel cells. A 1-D venting rate model is developed and experimentally verified for elongated bubbles. The reported bubble removal approach is also useful for other microfluidic devices, in which the accidental introduction of gas bubbles is prevalent.     

Capillary driven movement of gas bubbles in tapered structures

This article presents a study on the capillary driven movement of gas bubbles confined in tapered channel configurations. These configurations can be used to transport growing gas bubbles in micro fluidic systems in a passive way, i.e. without external actuation. A typical application is the passive degassing of CO₂ in micro direct methanol fuel cells (μDMFC). Here, a one-dimensional model for the bubble movement in wide tapered channels is derived and calibrated by experimental observations. The movement of gas bubbles is modelled on straight trajectories based on a balance of forces. The bubble geometry is considered as three dimensional. In the development of the model, the effects of surface tension, inertia, viscosity, dynamic contact angle and thin film deposition are considered. It is found that in addition to viscous dissipation, the dynamics related to the contact line—dynamic contact angle and thin film deposition—are essential to describe the gas bubble’s movement. Nevertheless, it was also found that both of these effects, as modelled within this work, have similar impact and are hard to distinguish. The model was calibrated against experiments in a parameter range relevant for the application of travelling gas bubbles in passive degassing structures for μDMFCs.     

基于一种FGA–ANFIS技术的DMFC温度建模和控制

为了提高直接甲醇燃料电池(DMFC)的发电性能,采用自适应神经模糊推理技术(FGA-ANFIS)对电池的工作温度进行建模与控制.首先,基于实验的输入输出数据建立了DMFC电堆温度的自适应神经模糊辨识模型,避开了DMFC电堆的内部复杂性.然后,将训练好的网络模型作为DMFC控制系统的参考模型,采用一种改进的模糊遗传算法对神经模糊控制器的参数和模糊规则进行自适应调整.最后,通过仿真.将所提出的算法与非线性PID和传统模糊算法进行比较,结果表明所设计的神经模糊控制器具有较好的性能.     

Modeling of multi-connected porous passageway for mould cooling

Cooling channel design in the plastic injection moulding process is of paramount importance to the performance of the mould, influencing the quality of the parts being produced and productivity of the process. However, cooling channel design is usually limited to relatively simple configurations as well as conventional machining processes, such as straight-line drilling, and milling, etc. The cooling performance may not meet the expectations of the mould engineers.This paper proposes an alternative design method for a conformal cooling passageway with multi-connected porous characteristics based on the duality principle. The proposed method can provide a more uniform cooling performance between the mould plate and the conformal cooling passageway than the existing conformal cooling channel design. Injection mould defects like warpage or hot spots can be avoided.In this study, a 3D mould plate model was offset negatively and the location of the proposed multi-connected porous cooling passageway was identified. The negatively offset model was decomposed into a finite number of cubical cells via the sub-boundary spatial enumerated cell decomposition. Then a duality relationship between the primal and the dual graphs was developed. This provided the preliminary layout of the multi-connected porous passageway for the coolant flow in multiple directions. The cooling channel axis design of the multi-connected porous passageway, illustrated by the skeleton from the dual graph, was created. Following a Boolean difference operation, the proposed multi-connected porous cooling passageway inside the mould plate was able to be generated and fabricated with the aid of rapid tooling technologies. A real-life case study for the design of a multi-connected porous cooling passageway was implemented and examined. The effects of coolant flow and cooling performances, analyzed by computational fluid dynamics simulation, were validated.     

基于神经网络辨识的DMFC电压模型研究

介绍并分析了直接甲醇燃料电池(DMYC)的工作原理及理论电压模型,并针对直接甲醇燃料电池系统过于复杂,理论电压模型存在明显不足的特点,试图绕开DMYC的内部复杂性,基于实验数据,利用神经网络逼近任意复杂非线性函数的能力,将神经网络辨识方法应用到DMYC这种高度非线性系统的建模中去,以1000组电池电压、电流密度实验数据作为训练样本,采用基于LM算法的改进BP神经网络,建立了不同温度下电池电压一电流密度的神经网络辨识模型。仿真结果表明这种方法是可行的,建立的模型精度较高。     

基于改进BP神经网络辨识的DMFC建模研究

针对直接甲醇燃料电池（DMFC）系统过于复杂，难以建模的特点，该文试图绕开DMFC的内部复杂性，基于实验数据。利用神经网络逼近任意复杂非线性函数的能力，将神经网络辨识方法应用到DMFC这种高度非线性系统的建模。以1000组电池电压、电流密度实验数据作为训练样本，采用基于LM算法的改进BP神经网络，建立了不同温度下电池电压-电流密度动态响应模型。仿真结果表明这种方法是可行的，建立的模型精度较高，它使得设计DMFC的实时控制器成为可能。     

燃料电池的模糊辨识建模与变结构控制研究

该文从DMFC实际应用的角度出发,首先利用模糊聚类和线性辨识方法基于实验的输入(甲醇、空气、冷却水的流速)输出(温度)数据建立DMFC的T-S模糊预测模型,然后基于该辨识的温度模型,设计了一个DMFC电堆工作温度的在线系统。最后,用辨识的温度模型代替实际的DMFC电堆进行控制仿真,仿真结果证明对DMFC电堆采用辨识建模的方法是有效的,建立的模型精度较高,以及所设计的变结构控制器性能优越,它对不同的系统状态都能调节控制量将电堆温度较平滑地过渡到试验的理想值。