气体扩散层厚度对PEMFC性能的影响

质子交换膜燃料电池(PEMFC)的气体扩散层(GDL)厚度对燃料电池的输出性能有重要影响。文章利用多物理场直接耦合分析软件(COMSOL Multiphysics 5.0),在电池温度为70℃的条件下,对4种不同厚度的GDL进行模拟分析,并在相同的操作条件下,得到了4组极化曲线、阴极氧气浓度、阴极水浓度、阳极氢气浓度以及电流密度的变化趋势图。对比分析4组变化趋势图后发现:GDL的厚度越小,燃料电池的性能越好;GDL的厚度对阳极氢气的浓度分布影响不大;当GDL的厚度增大时,产生的液态水会堵塞GDL的孔隙,降低GDL的孔隙率。     

不同衰退机理对PEMFC怠速工况性能衰退影响的模拟研究

分析质子交换膜燃料电池(PEMFC)怠速工况衰退机理,确定怠速工况不同衰退机理对燃料电池模型参数的影响,采用所建立的PEMFC二维等温多物理场模型,仿真研究燃料电池在怠速工况衰退前后的性能及各种衰退因素对电压衰减量的贡献和内部反应气体分布变化.研究结果表明,阴极活化损失增大是怠速工况下最重要的衰退因素,其次是开路电压衰...     

扩散层孔隙率对PEMFC性能影响的模拟研究

为了研究扩散层孔隙率对质子交换膜燃料电池(PEMFC)性能的影响,采用COMSOL软件,通过数值模拟得出气体扩散层不同孔隙率(0.2,0.4,0.6和0.8)时,单直通道和具有楔形肋片(长1 mm,高1.5 mm,宽2 mm)的PEMFC性能曲线、阴极氧气质量分数分布和水质量分数分布。结果表明:扩散层孔隙率对燃料电池性能具有较大影响,随着扩散层孔隙率从0.2增大到0.8,PEMFC的电流密度逐渐增加,最大可达847 mA/cm~2;相对于单直通道,增加孔隙率比添加楔形肋片更利于提升电池性能;在孔隙率为0.6和0.8时,氧气更易扩散到反应区,排水效果更好。     

PEMFC翅脉流道传质及输出性能分析

为研究流道结构对质子交换膜燃料电池（PEMFC）反应气体质量传输及输出性能的影响,建立翅脉流道、叶脉流道及蛇形流道的三维PEMFC几何模型,并对比3种流道的反应气体浓度分布、压力分布及电流密度分布,最后对翅脉流道结构参数进行优化。结果表明,与蛇形流道、叶脉流道相比,翅脉流道能明显改善流道和扩散层内反应气体浓度分布的均匀性,有利于强化反应气体向催化层的质量传递;翅脉流道能减小气体压力分布梯度,使反应气体扩散更加充分;翅脉流道的平均膜电流密度更大,有利于促进电化学反应稳定进行;翅脉流道能改善PEMFC的输出性能,翅脉流道峰值功率密度比蛇形流道、叶脉流道分别提高7.72%和6.25%;减小翅脉流道的直流道长度或圆弧流道圆心角,可提升翅脉流道输出性能。     

进气加湿与富氧对船用柴油机NOx-Soot排放的影响

通过一台满足TierⅡ排放标准的四冲程增压中冷船用柴油机,模拟研究了富氧燃烧结合进气加湿改善NOx-soot折衷关系的潜力,并探讨了实现TierⅢ排放标准的技术路线.本研究使用AVLFire软件建立仿真模型.结果表明:单独使用富氧燃烧时,缸内温度较高,燃烧持续期较短,soot排放减少,NOx排放恶化,而单独使用进气加湿时呈相反的趋势.当发动机运行在转速为1350 r/min、75%负荷工况下,进气氧体积分数为21%~23%、加湿率为0~100%时,可实现NOx-soot排放同时降低且低于原机.氧体积分数为21%和加湿率为100%匹配,可以实现TierⅢ排放法规.两种措施的优化组合可以获得NOx-soot排放的最佳优化区域.     

进气畸变对回流燃烧室性能的影响研究

针对燃气轮机实际运行过程中不同火焰筒之间的空气流量畸变问题,以回流燃烧室为研究对象,开展三维数值模拟,分析进气流量改变对燃烧室多物理场分布特征和燃烧室性能的影响。结果表明：进气流量偏离理想设计对燃烧室回流区结构、温度场、总压恢复系数和燃烧效率等参数产生不利影响,而对燃烧室空气流量分配比例、主燃孔和掺混孔射流深度等参数的影响不明显;随着进气流量的减小,燃烧火焰拉长,燃烧室出口温度均匀性变差,燃烧效率急剧降低。     

出口形式对防浪级阻力性能影响的研究

燃气轮机进气系统的结构和气动性能是燃气轮机装舰技术研究的重要组成部分。针对这方面的要求，进行了燃气轮机进气防浪级的设计及数值模拟计算，为设计制造高性能的船用燃气轮机进气系统提供可靠的依据。对进气防浪级作的数值计算和实验研究，其结果是相当令人满意的，研究方法对燃气轮机进气系统的研究有一定的参考价值和指导意义。     

进气参数及燃烧室结构对LNG发动机排放性能的影响

以L23/30A发动机为研究对象,研究了不同进气参数及不同燃烧室几何形状对缸内燃烧特性对柴油机性能及排放的影响。研究结果表明:随着进气压力的增大和燃烧室过渡圆深度的加深,缸内挤流作用加强,油气混合均匀,缸内燃烧充分,降低了soot及NO_x的生成;减小燃烧室的缩口直径及提高进气温度,缸内湍流分层严重,滞缓了缸内涡团的破碎与聚合,局部油气分布过浓燃烧不完全,导致局部温度、压力过高,诱发燃烧过程中soot及NO_x的生成。因此,在加深燃烧室过渡圆深度的前提下,通过提高低温燃烧的进气压力,可以改善发动机的燃烧特性。     

可控进气涡流对柴油机低负荷性能影响的研究

就双进气道可控进气涡流系统改善大功率增压中冷柴油机低负荷性能的作用机理进行了理论分析与试验研究。研究结果表明：在低负荷工况下，双气道进气时的涡流强度小于螺旋气道，大于直流气道；螺旋气道进气流量较之双气道虽有所减少，但其涡流比仍保持较高水平，致使缸内爆压、预混合燃烧量和最大放热速率均较大。理论计算与试验结果证明，采用双进气道可控进气涡流系统是改善大功率柴油机低负荷性能的一个有效途径。     

Effects of anode and cathode perforated flow field plates on proton exchange membrane fuel cell performance

The effects of both anode and cathode perforated flow field configurations on proton exchange membrane fuel cell performance are studied herein through electrochemical polarization techniques, electrochemical impedance spectroscopy, and cyclic voltammetry. The results demonstrate that serpentine flow field configuration in both anodes and cathodes is the best arrangement for cell performance (serpentine/serpentine, perforated/perforated, and serpentine/perforated). An electrochemical impedance spectroscopy examination shows that the serpentine/serpentine flow plate configuration results in a significant reduction in charge transfer resistance in a high current density (low voltage) regime. It further indicates that in a serpentine/serpentine flow pattern, a maximum electrochemical area is obtained with a higher Pt utilization of about 70% and is secured with full hydration at a cell temperature of 80°C. Finally, energy and exergy efficiencies analyses were also made. Data have been extracted and presented. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of the membrane thickness and ionomer volume fraction on the performance of PEMFC with U-shaped serpentine channel

A three-dimensional, multi-component, single-phase model is applied for analyzing the electrochemical performance of the proton exchange membrane fuel cell (PEMFC) with U-shaped channel using COMSOL Multiphysics software. To validate the numerical model, the results are compared with the experimental data available in the literature. This work numerically investigates the effects of convection and diffusion under the rib, membrane thickness, ionomer content, and current density distribution at an interface between the gas diffusion layer and the catalyst layer. These effects were not studied for a U-shaped single serpentine channel despite having several benefits such as uniform reactant distribution through convection and diffusion under the rib and the resulting uniform current generation. A total of three membranes with 2, 3.5, and 5 mil thicknesses are analyzed, and an improvement of 17% in PEMFC performance with 2 mil thickness is observed owing to a decrease in internal resistance compared to 3.5 and 5 mil. Furthermore, an ionomer volume fraction in the catalyst layer is varied from 0.3 to 0.6, and the performance enhancement of 7% is reported at 0.5 volume fraction.     

The impact of flow field pattern on concentration and performance in PEMFC

In this study, we present a rigorous mathematical model, to treat prediction and analysis of proton exchange membrane fuel cells gas concentration and current density distribution in mass transfer area and chemical reaction area performed in 3‐D geometry. The model is based on the solution of the conservation equations of mass, momentum, species, and electric current in a fully integrated finite‐volume solver using the CFDRC commercial code. The influences of fuel cell performance with two kinds of flow channel pattern design are studied. The gas concentration of the straight flow pattern appears excessively non‐uniform, resulting in a local concentration polarization. On the other hand, the gas concentration is well distributed for the serpentine flow pattern, creating a better mass transfer phenomena. The performance curves (polarization curves) are also well correlated with experimental data. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of operational parameters on the performance of PEMFC assembled with Au-coated Ni-foam

An innovative proton exchange membrane fuel cell was assembled using Au-coated nickel foam instead of the conventional flow field (carbon plate). The effect of operational parameters on the performance of this cell was investigated by DC polarization and electrochemical impedance spectroscopy techniques. Parameters such as cell operating temperature, cathode humidification temperature, and cathode-gas stoichiometry were of concern.     

CFD investigating the effects of different operating conditions on the performance and the characteristics of a high-temperature PEMFC

The effects of different operating conditions on the performance and the characteristics of a high-temperature proton exchange membrane fuel cell (PEMFC) are investigated using a three-dimensional (3-D) computational fluid dynamics (CFD) fuel-cell model. This model consists of the thermal-hydraulic equations and the electrochemical equations. Different operating conditions studied in this paper include the inlet gas temperature, system pressure, and inlet gas flow rate, respectively. Corresponding experiments are also carried out to assess the accuracy of this CFD model. Under the different operating conditions, the PEMFC performance curves predicted by the model correspond well with the experimentally measured ones. The performance of PEMFC is improved as the increase in the inlet temperature, system pressure or flow rate, which is precisely captured by the CFD fuel cell model. In addition, the concentration polarization caused by the insufficient supply of fuel gas can be also simulated as the high-temperature PEMFC is operated at the higher current density. Based on the calculation results, the localized thermal-hydraulic characteristics within a PEMFC can be reasonably captured. These characteristics include the fuel gas distribution, temperature variation, liquid water saturation distribution, and membrane conductivity, etc.     

蛇形流场结构质子交换膜燃料电池的性能研究

建立包括催化层、扩散层、质子膜在内的三维质子交换膜燃料电池模型,通过Fluent软件模拟4种不同结构的蛇形流场,通过对速度、膜中水含量以及功率密度等分析得出蛇形流场的最优结构,并对最优结构进行参数优化。研究表明,4种不同蛇形流场结构中,Multi-serpentine II为最优,随着温度、压强的增加,这种流场结构的燃料电池呈现出良好的性能,从而为质子交换膜燃料电池双极板的设计提供依据。     

Mechanism analysis of starvation in PEMFC based on external characteristics

As an energy conversion device that converts hydrogen energy into electrical energy, the fuel cell is one of the most promising. Starvation is the main reasons that shortens the lifetime of Proton Exchange Membrane Fuel Cell (PEMFC) for vehicle usage. Therefore, combining the experimental and simulation results, as well as previous studies, based on the external characteristics of PEMFCs, the mechanism of judging the starvation in PEMFCs is explored. It provides a theoretical basis for judging the starvation using external characteristics. In addition, the starvation index is proposed to solve the problem that the starvation in the process of fuel cell loading, which could not be evaluated in the past. This factor can provide guidance for matching and controlling the fuel cell supply system, as well as optimizing the internal structural parameters of the fuel cell.     

Experimental and numerical investigations of the effects of PBI loading and operating temperature on a high-temperature PEMFC

In this paper, experimental and numerical investigations of the effects of polybenzimidazole (PBI) loading and operating temperature on a high-temperature proton exchange membrane fuel cell (PEMFC) performance are carried out. Experiments related to a PBI-based PEMFC are performed and a two-dimensional (2-D) simulation model is developed to numerically predict the cell characteristics. Variations of 5–30 wt% in PBI amount in the catalyst layer (CL) and 160–200 °C in cell temperature are considered. On the basis of the experimental and numerical results, the negative effect of PBI content and positive effect of operating temperature on the cell performance can be precisely captured. These effects can also be shown by measurements of the impedance spectrum and predictions of O₂ concentration and current density distributions. In addition, non-uniform distributions in the O₂ concentration and the current density in the cathode compartment are also shown in the model simulation results. Cell performance curves predicted by the present model correspond well with those obtained from experimental measurements, showing the applicability of this model in a PBI-based PEMFC.     

Numerical investigation on the performance of PEMFC with rib-like flow channels

An innovative flow channel inspired by the physical structure of the human rib was developed in this paper. The performance of a proton exchange membrane fuel cell (PEMFC) with the proposed rib-like flow channels under different flow patterns and relative humidity of anode (RH_a) was investigated. Compared with the conventional interdigitated flow channel (CIFC) and cross-flow channel (CRFC), the maximum current density of the counter-flow channel (COFC) was 1.06 A/cm² at 0.4 V, with enhancements of 4.95% and 2.91%, respectively. In addition, the quantity referred to as non-uniformity N was introduced to quantify the concentration distribution of oxygen, the minimum non-uniformity N of 0.17 was obtained for CRFC, and the COFC exhibited a more uniform concentration distribution of temperature as compared with the CIFC and CRFC, indicating that the COFC would prevent the occurrence of local hot spots. The maximum net power density of COFC was 6.0% and 3.0% higher than that of the CIFC and CRFC. Finally, the maximum current density of RH_a = 30% was 1.06 A/cm², which was 3.9% and 7.1% higher than that of RH_a = 60% and RH_a = 100%. The temperature with RH_a = 100% was more uniform in comparison with RH_a = 30% and RH_a = 60%, and the mass fraction of H₂ decreased with the increase of values of RH_a. The proposed rib-like flow channel can further enrich PEMFC flow channel design and afford novel insights into the application of bionics in fuel cells.     

Experiment and simulation investigations for effects of flow channel patterns on the PEMFC performance

Experiments and simulations are presented in this paper to investigate the effects of flow channel patterns on the performance of proton exchange membrane fuel cell (PEMFC). The experiments are conducted in the Fuel Cell Center of Yuan Ze University and the simulations are performed by way of a three‐dimensional full‐cell computational fluid dynamics model. The flow channel patterns adopted in this study include the parallel and serpentine flow channels with the single path of uniform depth and four paths of step‐wise depth, respectively. Experimental measurements show that the performance (i.e. cell voltage) of PEMFC with the serpentine flow channel is superior to that with the parallel flow channel, which is precisely captured by the present simulation model. For the parallel flow channel, different depth patterns of flow channel have a strong influence on the PEMFC performance. However, this effect is insignificant for the serpentine flow channel. In addition, the calculated results obtained by the present model show satisfactory agreement with the experimental data for the PEMFC performance under different flow channel patterns. These validations reveal that this simulation model can supplement the useful and localized information for the PEMFC with confidence, which cannot be obtained from the experimental data. Copyright © 2007 John Wiley & Sons, Ltd.