PEM燃料电池变径流道设计与仿真

优化质子交换膜燃料电池(Proton Exchange Membrane Fuel Cell, PEMFC)流场是强化电池物质传递、分布和提升输出性能的有效途径。通过建立新型流道模型,研究变径结构对阴极气体传质和电流密度的影响。结构表明,该变径流道能够明显提高流道出口附近区域的气体流速;流道内入口于出口间压差增大,有利于提高反应气体传递;强化了反应气体在流道于扩散层中的传质,能够提高O₂在扩散层中的质量分数及O₂的分布均匀性;改善了流道的排水性,降低催化界面水的质量分数;提升了反应界面整体电流密度,电流密度分布更加均匀。     

液滴撞击疏水/超疏水表面运动特性的数值模拟

采用计算流体动力学对液滴撞击疏水/超疏水表面的过程进行数值模拟,分析液滴滴落高度、表面润湿性和表面倾斜角度3个因素对液滴运动的影响。结果表明,随着液滴滴落高度的增大,液滴铺展系数增大,回弹系数减小,滴落高度对液滴铺展系数和回弹系数的影响随表面静态接触角的增大而增大;表面疏水性增强,液滴铺展系数减小,回弹系数增大,滴落高度的增大会减弱表面润湿性对液滴铺展系数和回弹系数的影响;表面倾斜角度增大,液滴铺展系数和回弹系数减小,液滴内部最大速度增大。     

内置周期挡板的T-型微混合器

设计了一种流道内布置周期挡板结构的高效T-型微混合器来提高微流控系统的混合效率。该微混合器结构简单,周期布置的挡板可以有效地缩短流体混合所需的流道长度和时间,混合效率高。安排了正交实验组,利用计算流体力学软件ANSYS CFX研究了流道结构参数对混合效果的影响。采用静态田口分析法对数值模拟结果进行分析。结果表明:流道结构参数对混合效果的相对影响程度排列如下:挡板攻角(θ)流道高度(H)挡板宽度(L)相邻混合单元之间距离(D)。根据结构参数对混合效果的影响程度,得出研究参数范围内的最优组合为:θ=75°,H=0.4 Wm,L=0.7 Wm,D=0.6 Wm(这里Wm为流道宽度,等于200μm)。实验显示,结构参数符合最优参数组合的微混合器的混合效果提升显著,雷诺数Re=54时即可实现完全混合(混合指标M95%)。文中研究了流道结构对进出口压降的影响,结果显示,攻角θ对进出口压降的影响趋势在不同雷诺数下相同,参数H,D亦如此。     

二维倾斜方腔水自然对流分离过程模拟分析

以水为传热介质,对温差驱动的二维方腔内自然对流换热过程进行了模拟分析。利用流体流动与热量传递的无因次控制方程,采用热线及流线可视化方法,取相同Ra=5×107值,倾斜角为控制参数,讨论分析了方腔中的温度、流动及对流换热传输结构。给出了倾斜角对于流型、分离点、对流换热传输结构及高低温壁面的传热性能的影响。分析结果表明:当Ra=5×107时,随着的θ增大,双涡结构越来越明显,倾斜角度对于方腔的流动的流型,具有较大的影响;分离点从低温壁面下部开始形成,随着倾斜角的增大分离点沿着低温壁面向上流动,接着到达绝热壁面,最终到达高温壁面;温度梯度受θ变化的影响较大,不同θ时,产生温度梯度最大值的地点不同;高低温壁面的平均Nu在60°最大,180°时最小。     

叶顶间隙对低比转速混流泵性能及内部流场影响的数值研究

为了解叶顶间隙对低比转速混流泵性能及内部流场的影响,选取无叶顶间隙和叶顶间隙δ分别为0.25 mm、0.75 mm和1 mm共四种方案,基于ANSYS-CFX对一比转速为149的混流泵进行了全流道数值模拟。计算域采用ICEM-CFD和TurboGrid进行结构化网格划分。利用Tecplot对计算结果进行处理,得到叶顶间隙对外特性参数、轮缘泄漏、流道中心S2流面流场等的影响。结果显示,叶顶间隙对大流量工况（1.25Q_d和1.5Q_d）下性能参数的影响大于小流量工况（0.5Q_d和0.75Q_d）,且效率减小量与叶顶间隙变化量的比值（Δη/Δδ）和相对流量m之间近似呈二次抛物线关系;当间隙为0.75 mm时,随着流量的增加,在叶轮流道进口附近形成的旋涡逐渐向出口方向移动,且旋涡强度及其对主流的影响范围均增大;当间隙进一步增大到1 mm时,泄漏流和主流之间发生了更为严重的卷吸效应。     

镍基718材料表面润湿性对耐磨和耐腐蚀性能的影响

针对镍基高温合金Inconel 718材料,探究铣削加工参数与表面润湿特性的关系,研究不同液体介质(水、人工海水、32号润滑油)接触角变化对表面摩擦磨损及耐腐蚀性能的影响。利用正交试验法研究铣削参数(切削速度V_s、每齿进给量f_z以及切削深度a_p)与表面润湿性的关系,利用单因素试验研究接触角变化对摩擦系数f和腐蚀速率的影响。对于镍基高温合金Inconel 718材料表面,水的接触角θ、每齿进给量f_z对其影响最大,切削深度a_p次之,铣削速度V_s最小,且在V_s=60m/min、f_z=0.05mm/r、a_p=0.6mm时接触角最小;采用32号油润滑时,分别观察接触角θ为9°、12°、16°、19°、21°时摩擦系数的变化;随着θ的增大,摩擦系数f在0.08～0.20之间逐渐增加,增大趋势明显;对于水润滑,摩擦系数f随接触角θ增加,并在0.24～0.27之间变化,增大的趋势很微弱;对于长期工作于海水中的镍基高温合金Inconel 718材料表面,接触角θ从61°增大到79°时,相同时间内腐蚀量从0.65%下降为0.45%,耐腐蚀性变好。对于镍基高温合金Inconel 718材料表面的铣削加工,为获得较好的润湿性能,应重点关注每齿进给量f_z和切削深度a_p;为提高Inconel 718材料表面的摩擦性能,应尽量减小表面对润滑剂的接触角;提高对腐蚀性介质的疏水性则可以有效改善Inconel 718材料表面的耐腐蚀性能。     

板翅换热器流道结构改进与流体流动性能分析

研究超大型空分装备中板翅式换热器流道改进结构及其对换热器内流体流动影响,设计一种新型板翅换热器流道结构,该新型流道结构可以改变换热器流道内流体的流动方向,促使流体在板翅换热器内部呈M形流动,从而延长换热器中流体的流动距离,增大流体的湍流性能,强化换热器的换热效果。对板翅式换热器流道中转折位置流体的分布情况进行分析,着重分析换热器流道转折位置与流体流动速度、压力变化以及流体湍流性能之间的对应关系。采用Fluent分析流道结构改进前后板翅式换热器内流体的流动情况,可以看出改进后的流道结构可以显著增强换热器内流体的湍流性能,与结构改进之前的传统流道相比,新型流道结构的板翅式换热器通过增大内部流体的湍流性能的方式,提升换热器的换热效率。     

新型板式热交换器导流区数值模拟研究

建立了不同导流区结构的换热板片及其流道模型,并提出一种新型弧形导流区结构的换热板片及其流道,利用计算流体力学软件对流道内流体的流动和传热进行了数值模拟,分析了流道内的速度场、温度场和压力场。结果表明,新型导流区结构换热板片间的流体分布更均匀,在保持良好的传热性能情况下,压力损失明显降低。     

百叶窗翅片车辆散热器性能研究

通过数值模拟方法对百叶窗翅片散热器流道中流体的流动和传热性能进行研究,将数值模拟结果与文献实验关联式计算结果进行对比,验证了数值模拟方法的正确性。将百叶窗翅片散热器的翅片间距与百叶窗间距两者关联起来,分析了其比值Fp/Lp和百叶窗倾角对于百叶窗翅片流道传热和压降性能的影响。而后分析了百叶窗翅片结构参数对于百叶窗流道间流体流动效率的影响。研究表明,百叶窗翅片的传热系数和压降随着Re数的增大而增大,随着百叶窗翅片间距与百叶窗间距比值Fp/Lp的增大而减小,随着百叶窗倾角的增大而增大。流动效率随着Re数的增大而增大,随着百叶窗翅片间距与百叶窗间距比值的增大而减小,随着百叶窗倾角的增大而增大。     

Research on performance of vehicle radiator with Iouvered fin

通过数值模拟方法对百叶窗翅片散热器流道中流体的流动和传热性能进行研究,将数值模拟结果与文献实验关联式计算结果进行对比,验证了数值模拟方法的正确性.将百叶窗翅片散热器的翅片间距与百叶窗间距两者关联起来,分析了其比值Fp/Lp和百叶窗倾角对于百叶窗翅片流道传热和压降性能的影响.而后分析了百叶窗翅片结构参数对于百叶窗流道间流体流动效率的影响.研究表明,百叶窗翅片的传热系数和压降随着Re数的增大而增大,随着百叶窗翅片间距与百叶窗间距比值Fp/Lp的增大而减小,随着百叶窗倾角的增大而增大.流动效率随着Re数的增大而增大,随着百叶窗翅片间距与百叶窗间距比值的增大而减小,随着百叶窗倾角的增大而增大.     

Pressure drop and flow distribution characteristics of single and parallel serpentine flow fields for polymer electrolyte membrane fuel cells

This study numerically investigates pressure drop and flow distribution characteristics of serpentine flow fields (SFFs) that are designed for polymer electrolyte membrane fuel cells, which consider the Poiseuille flow with secondary pressure drop in the gas channel (GC) and the Darcy flow in the porous gas diffusion layer (GDL). The numerical results for a conventional SFF agreed well with those obtained via computational fluid dynamics simulations, thus proving the validity of the present flow network model. This model is employed to characterize various single and parallel SFFs, including multi-pass serpentine flow fields (MPSFFs). Findings reveal that under-rib convection (convective flow through GDL under an interconnector rib) is an important transport process for conventional SFFs, with its intensity being significantly enhanced as GDL permeability increases. The results also indicate that under-rib convection can be significantly improved by employing MPSFFs as the reactant flow field, because of the closely interlaced structure of GC regions that have different path-lengths from the inlet. However, reactant flow rate through GCs proportionally decreases as under-rib convection intensity increases, suggesting that proper optimization is required between the flow velocity in GCs and the under-rib convection intensity in GDLs.     

Prediction of flow crossover in the GDL of PEFC using serpentine flow channel

A serpentine flow channel is one of the most common and practical channel layouts for Polymer electrolyte fuel cells (PEFCs) since it ensures the removal of water produced in the cell with an acceptable parasitic load. The operating parameters such as temperature, pressure and flow distribution in the flow channel and gas diffusion layer (GDL) has a great influence on the performance of PEFCs. It is desired to have an optimum pressure drop because a certain pressure drop helps to remove excess liquid water from the fuel cell, too much of pressure drop would increase parasitic power needed for the pumping air through the fuel cell. In order to accurately estimate the pressure drop precise calculation of mass conservation is necessary. Flow crossover in the serpentine channel and GDL of PEFC has been investigated by using a transient, non-isothermal and three-dimensional numerical model. Considerable amount of cross flow through GDL is found and its influence on the pressure variation in the channel is identified. The results obtained by numerical simulation are also compared with the experimental as well as theoretical solution.     

双流道泵输送固液介质的水力性能及磨损试验研究

为分析固液混合物对双流道输送泵性能的影响,采用平均粒径为10 mm和36 mm的固体颗粒对双流道泵在不同浓度和流量下开展输送固液两相介质的水力性能试验,并对泵的磨损进行分析。水力试验结果表明,在一定的流量下,随着输送混合物中固体颗粒浓度的增加,入口表压、出口表压、扬程及效率呈递减趋势。 与输送清水时比较,当输送固液两相介质时,随着流量的增大,轴功率上升较快,扬程的下降量在不同流量下几乎相同;效率曲线在不同流量下比输送清水时效率要低,差值随着流量的增大而增大。在同流量同浓度比工况下,泵的进出口压力、扬程和汽蚀性能在输送较大直径固体颗粒时,明显下降。通过对双流道泵磨损的分析表明,叶轮磨损部位主要在前盖板外缘、流道内偏前盖板的流道表面、压力面进口边,压力面的磨损区域呈三角形;泵体的磨损部位主要在周壁、隔舌及泵体口环处。本研究可为固液两相双流道离心泵的理论研究与设计应用提供试验依据。     

双钩波形板分离器的冷态试验研究

对双钩波形板分离器进行了冷态试验研究,对不同入口速度下波形板的总分离效率、单级分离效率和压降进行了分析,并对不同入口湿度下的总分离效率进行了研究。结果表明:在低速时,提高入口速度有助于提高分离效率,但流速超过临界破膜速度(6m/s)后,二次携带现象明显,导致分离效率降低;增加波形板入口湿度时,总分离效率呈先增后减的趋势;波形板前三级的分离水量显著高于后三级;入口速度对波形板压降的影响较为明显。试验结果对波形板分离器的优化设计具有一定的指导意义。     

进水温度对水润滑轴承润滑特性的影响

为研究进水温度变化对水润滑轴承润滑特性的影响,采用有限差分法建立水润滑轴承弹流润滑模型,分析不同进水温度和载荷条件下水润滑轴承润滑特性的差异,并且通过试验验证摩擦因数的变化规律。研究发现：随着进水温度升高,轴承的水膜压力下降,但在水膜压力峰区域最大水膜压力升高、最小水膜厚度减小、偏心率增大,表明进水温度升高对润滑性能有着负面影响;在相同的载荷和转速下,轴承摩擦因数随着进水温度升高而下降,且高载荷下进水温度对摩擦因数的影响更大。通过试验发现进水温度越高对摩擦因数变化的影响越大,不同进水温度下载荷越低,载荷的变化对摩擦因数变化量的影响越大。     

平纹编织碳纤维/Kevlar纤维增强混杂复合材料微-宏观切削去除机理研究

由于碳纤维和Kevlar纤维力学性能相差迥异,在C-K纤维混杂增强复合材料(Carbon-Kevlar fiber hybrid composite,CKFH)加工中易产生加工缺陷,比单种纤维复合材料的加工缺陷更难控制。由此,从微观和宏观角度,构建CKFH三维有限元切削模型,分析CKFH的切削去除机理及平纹编织结构对切削过程的影响机制。结果表明,在不同纤维取向下,Kevlar纤维均易产生抽丝拉毛现象,尤其当纤维取向θ=0°/180°时最为明显;纤维取向θ=0°/180°时,切屑多为卷曲片状切屑,纤维取向θ=45°、90°、135°时,两种纤维的断裂相互影响,切削表面、切屑形态均与切削方向存在密切关系,当纤维取向θ=45°时,多为细小片状切屑,纤维取向θ=90°时,切屑多为絮状块状切屑,纤维取向θ=135°时,切屑多为成块状切屑;从碳纤维切向Kevlar纤维时,Kevlar纤维出现松散、抽丝拉毛现象明显,从Kevlar纤维切向碳纤维时,在Kevlar纤维的韧性弯曲区碳纤维发生弯曲脆断、碎裂,易出现凹坑;平纹编织结构对切削应力的传递具有明显的阻断作用,有限元仿真结果与试验观测结果基本吻合。     

台阶式斜篦齿封严压降与风阻温升数值分析

为研究转速、进口压力及齿隙和齿宽的比对斜篦封严压降与风阻温升特性的影响,建立二维阶梯式斜篦齿封严模型,对台梯式斜篦齿封严进行数值仿真计算,获得不同转速、进口压力及齿隙和齿宽的比下的进出口压差和风阻温升,以及最后一级齿隙处射流的温度和压力。结果表明：斜篦齿的背风面存在高温带,主要是由于旋转的摩擦效应、阶梯几何结构和2个大尺寸涡相遇处的掺混效应所导致;贴壁大尺寸涡与主流的动量交换随着转速的增加而增强,主流与齿腔大尺寸涡的动量交换随着转速的增加而减弱;风阻温升随着齿隙和齿宽的比的增大而降低,随着转速的增加而升高,但与进口压力的关系不明显;进出口压差随着转速的增加而增大,随着齿隙和齿宽的比的增大而减小;出口射流的压力随着进口压力的增加而增加。分别得到压差比和风阻温升系数的拟合式,拟合效果符合预期。     

电动汽车涡旋压缩机内油气分离器的研究

通过数值模拟的方法研究了电动汽车涡旋压缩机在不同转速工况下,进口结构对油气分离器的流场和性能的影响.采用RSM模型对油气分离器内的气相流场进行模拟计算,同时利用DPM模型对4种分离器的油滴轨迹进行追踪.研究结果表明:进口结构变窄将促使油气分离器内部流场具有良好的对称性,并随着转速的提高,不同进口结构分离器的压降都呈抛物...     

Numerical study of droplet dynamics in a PEMFC gas channel with multiple pores

The water droplet motion in a PEMFC gas channel with multiple pores, through which water emerges, is studied numerically by solving the equations governing the conservation of mass and momentum. The liquid-gas interface is tracked by a level set method which is based on a sharp-interface representation for accurately imposing the matching conditions at the interface. The method is modified to implement the contact angle conditions on the walls and pores. The dynamic interaction between the droplets growing on multiple pores is investigated by conducting the computations until the droplet growth and sliding motion exhibits a periodic pattern. The numerical results show that the configuration subject to droplet merging is not effective for water removal and that the wettability of channel wall strongly affects water management in the PEMFC gas channel. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Gihun Son received his B.S. and M.S. degrees in Mechanical Engineering from Seoul National University in 1986 and 1988, respectively, and Ph.D. degree in Mechanical Engineering from UCLA in 1996. Dr. Son is currently a professor of Mechanical Engineering at Sogang University in Seoul, Korea. His research interests are in the area of multiphase dynamics, heat transfer, and power system simulation. Jiyoung Choi received a B.S. degree in Mechanical Engineering from Sogang University in 2005. He is a graduate student of Mechanical Engineering at Sogang University in Seoul, Korea. Choi’s research interests are in the area of PEM fuel cell and microfluidics.     

Novel liquid flow sensor based on differential pressure method

In this article, a novel liquid flow sensor which is composed of a special structure conduit main body and a differential pressure sensor was designed, fabricated, and calibrated. The conduit main body includes an inlet channel section with a branch conduit connecting one end of the pressure sensor, a throat channel section, and an outlet channel section with a branch conduit connecting another end of the pressure sensor. The basic principle is to employ a differential pressure sensor to measure the pressure difference between the inlet channel and outlet channel of the conduit main body when fluid passes through it. The pressure difference between the two ends of the differential pressure sensor (i.e., the two branch conduits located in the inlet and outlet channel sections) is of either forward or backward flow and directly interrelates with the volume flow rate (mass flow rate or flow velocity) via the conduit main body, so the volume flow rate or mass flow rate or flow velocity can be calculated and the flow direction can be determined from the detected pressure difference. This liquid flow sensor is characterized by using only one differential pressure sensor of a simple structure, the error of which is less than 1%.