【作者】 李文凯；

【导师】 章俊良；

【作者基本信息】 上海交通大学 ， 动力工程及工程热物理， 2017， 硕士

【摘要】 在过去几十年里,对绿色能源的渴望促使人类不断探索新能源技术,其中,由于较高的能量转换效率和真正的零排放,燃料电池技术受到人们更多的关注。质子交换膜燃料电池（PEMFC）可以直接将氢气中的化学能转化为电能,能量转换效率高达60%,使其成为最有前途的绿色能源转换技术。然而,PEMFC的商业化一直被一些技术问题所阻碍,其中水管理是很关键的一个问题。阴极水淹将导致反应气体传质受限,会迅速恶化燃料电池堆的性能。在过去几十年中,学术界已经做出了很多努力来解决这一问题,其主要的方法为优化双极板上的流场设计,就该问题,本文提出一种新型实用的波状蛇形流场并通过CFD模拟和实验相结合的方法进行了深入分析。首先,本文就传统蛇形流场的缺陷有针对性的提出引入波浪特性和加深传统蛇形流场弯曲区域的设计方向,并分别设计了具有0°,15°,30°和45°波浪特征的四个不同流场,使用CFD建模仿真需找最优值。研究结果发现随着工作电压的降低,四个模型的电流密度差异逐渐增加,30°Cell模型显示出性能最佳,15°Cell模型性能最差。GDL和流道界面处的氧气质量分数在15°,30°,45°的流场中有明显的周期波动特征。在阴极GDL中间层上的H₂O质量分数分布具有由波浪特征引起的周期性水含量波动,其中15°流场是最明显的。阴极流道中的速度矢量图表明强制对流在15°,30°和45°的流场中分布广泛。从仿真结果分析看出波浪特征确实可以引起周期性局部强制对流,这增强了GDL中的反应气体传质和电池的排水效果,进而提高了电池性能,其中15°是一个较优的波浪特征设计。为了使设计思路得到进一步验证,本文就50cm²的PEMFC,设计了可以实验验证的波浪蛇形流动（WSFF）,并首先基于FLUENT PEM燃料电池模块建立了三维,多相,稳定,等温,层流模拟模型,进行模拟预测,仿真结果显示WSFF在促进气体扩散层（GDL）氧气传质和排出多孔介质层中聚集的液态水方面总体上优于CSFF,其周期性波浪特征结构引起反应气体局部流动方向,局部流速和局部压力的周期性变化,使得流道中出现较广泛的局部强制对流。最后,WSFF的优越性能得到了实验验证,实验结果显示WSFF不仅能够在整个电流密度范围内拥有更低的压降,而且与在高电流密度区域相比CSFF,拥有更高的电池性能。从实验测得的数据来看,使用WSFF的电池最大净功率密度比CSFF提高了17.8%,使得WSFF成为一种有希望广泛实际应用的PEMFC新型流场。更多还原

【Abstract】 In the past few decades,the desire for green energy has driven mankind to constantly explore new energy technologies.Due to their high efficiencies and zero emissions,fuel cell technologies always get much attention.Proton exchange membrane fuel cell（PEMFC） can directly convert chemical energy that from hydrogen to electrical energy with up to 60% energy conversion efficiency,making it the most promising green energy conversion technologies for various fields such as vehicles,stationary power generation and portable power sources.However,the commercialization of the PEMFC has been postponed by several technical issues,among which water flooding is one of the most critical ones.Flooding would cause mass transport limitation and thus seriously deteriorate the performance of a fuel cell stack.In the past decades years,great efforts have been done to tackle this critical problem,and the best way of them is to develop a great design of flow field on the bipolar plate,in this regard,a new practical waved serpentine flow field were designed and analyzed by CFD simulation and experiment in this paper.At first,a design scheme is proposed to introduce the wave characteristics and deepen the curved area on the traditional serpentine flow field.Four different flow fields with wave features of 0°,15°,30° and 45°,respectively,were designed and modeled using CFD simulation.Then,the simulation results of the battery performance and characteristics under 0.5V voltage are discussed.With the decrease of working voltage,the difference of current density of four models gradually increased,and the 30° Cell model showed the best performance and the 15° Cell model had the worst performance.The oxygen mass fraction at the interface of GDL-channel showed that there were obvious periodic wave fluctuations in the flow field of 15°,30°,45°,and the periodic fluctuation of 15° Cell was the longest and 45°Cell is the shortest.The distribution of H₂O mass fraction on the cathode GDL interlayer has the periodic water content fluctuation caused by the wave feature,among which the 15° Cell is the most obvious.The velocity vectors of the cathode flow channel in the four models show that the forced convection is distributed widely in the 15°,30° and 45° flow fields,and it can be confirmed that the wave features cause periodic local forced convection,which enhances the effect of GDL In the mass transfer and battery drain effect,thereby improving the battery performance,among them,15° is a preferred wave feature design.In order to further validate the design idea,this paper designs a wave-serpentine flow（WSFF）that can be experimentally verified on a 50cm² PEMFC.A three-dimensional,multi-phase,steady,isothermal,laminar simulation model is firstly established based on FLUENT PEM fuel cell module,and this model reveals that WSFF is overall better than CSFF in promoting oxygen transport though the diffusion layer and removing liquid water accumulated in microstructure.Its periodic waved structure introduces cyclical variation of local flow direction,local flow velocity and local pressure,leading to enhanced forced-convection.At last,the superior performance of WSFF has also been experimental verified,which proves that WSFF not only enables a lower pressure drop over the entire current density range,but also improves the cell performance in comparison to CSFF at high current density region.Specifically,there is a 17.8% increment in peak power density with the use of WSFF,which making WSFF a promising new PEMFC flow field.更多还原