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.     

微型直接甲醇燃料电池极板结构的研究

极板结构直接影响微型直接甲醇燃料电池的极化特性,采用微机械加工技术制作几种不同极板流场结构的直接甲醇燃料电池.通过对不同极板结构的微型直接甲醇燃料电池的性能比较,发现栅型阳极流场结构的电池输出特性明显优于螺旋蛇型和点型流场结构.另外对采用不同极板材料制作的直接甲醇燃料电池也进行比较,发现不锈钢微型直接甲醇燃料电池的性能明显优于硅基结构的燃料电池.     

集成毛细管电泳芯片的设计

利用ANSYS软件对集成毛细管电泳芯片微沟道内样品流动情况进行模拟,获得了不同进样模式下微沟道的结构与流体流速之间的关系,并以此为依据对芯片整体结构参数进行设计:毛细管沟道最终尺寸为宽度16μm,深度10μm,有效分离长度为3.5cm的圆角转弯形沟道,从而确定整个芯片设计。     

一种新颖的基于离子束刻蚀的纳米沟道制备技术

研究了一种新颖的基于MEMS工艺中离子束刻蚀的纳米沟道制备技术,通过研究离子束刻蚀微米级线条时,离子束刻蚀角度与刻蚀的轮廓形状之间的关系,在2μm线条内刻蚀出纳米沟道所需要的掩模图形,并结合KOH的各向异性腐蚀,成功获得了纳米沟道阵列.在两种不同的离子束刻蚀条件下,在2 μm图形内分别制备出单纳米沟道和双纳米沟道,最小宽度可达440 nm.     

电泳微芯片进样口与微沟道形状的优化设计

基于电渗流场的理论,建立电泳芯片的不同结构模型,以计算流体力学(CFD)方法来模拟不同设计参数和电压组合下的电泳微芯片微沟道中流体流动现象.最终优化基本型毛细管微沟道交叉口形状为矩形,微沟道宽度为20 μm,进样与分离场强为200～250V/cm.为在有限芯片面积下增加有效分离距离,设计螺旋形沟道电泳芯片模式.     

光电导开关中的隧穿现象

采用光刻和大气环境下原子力显微镜(AFM)阳极诱导氧化加工相结合的加工方法,加工由Ti-TiOx-Ti纳米级隧道结构成其基本结构的微型光电导开关(PCSS),并对其电特性进行了研究和分析.研究结果表明在大气室温条件下,微型PC-SS的输出特性随氧化物宽度不同而不同,当宽度小于100 nm时,其输出特性表现为在一个线性峰值的输出过后,又出现了一个非线性的峰值;在一定条件下Ti-TiOx-Ti纳米级隧道结存在隧穿效应,且其隧穿特性随绝缘金属氧化物的宽度不同而不同.     

MEMS半填充气相色谱柱研究

采用MEMS技术设计了一种微型半填充气相色谱柱,运用深反应离子刻蚀(DRIE)技术,对器件刻蚀深250μm,其微型色谱柱总长度为1m,宽度为160μm,槽道内部填充20μm×20μm微型柱。采用静态涂覆法对色谱柱涂覆SE—54固定相。通过理论模拟分析柱结构,得出微型半填充色谱柱具有高分离效率能力。在对酯类化合物分离测试中,选取了含酯类的化学战剂模拟剂和几种酯类食品添加剂,分别对其进行分离,所有组分在75s内被完全分离。实现了微型半填充色谱柱快速并具有高分离率。     

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.     

电介质击穿对MOSFET器件漏电流的影响

栅电介质击穿是MOSFET器件工作中主要的失效模式之一。由击穿而引起的栅泄漏不仅是电损耗增加的问题,而且对漏电流造成很大的影响。采用最新工艺制成的超薄栅电介质,把由击穿产生的漏电流作为因击穿点的扩展而损伤的沟道电流的一部分。制作栅氧厚度为2.2nm和3.5nm、不同沟道宽度的器件,使用专门的装置给器件施加应力,用统计方法研究晶体管性能的退化。分析表明,使漏电流退化的损伤半径大约在1.4μm-1.8μm之间。     

Simulation of the filling process in molding components with micro channels

In micro molding of components with micro features, the ability for the polymer melt to flow into the micro channels is a crucial factor for successful molding. In this case, the molded volume is about the same as the conventional molding. The penetration distance into the microstructure depends on the flow rate and the cooling rate of the micro features, which is function of the geometric dimensions. In this study, a simplified model was established to estimate the injection distance into the micro channels of a mold insert. The effect of the mold temperature, injection rate, and micro channel dimension on the filling distance was investigated based on the model. The filling distance increases dramatically with respect to the increase of the channel width. In molding of components with micro features as those analyzed in this study, decrease of the part thickness could enhance the filling in the micro features.The authors would like to thank for the financial support from National Science Council in Republic of China under the contract number of NSC 91-2212-E006-131.     

MEMS-based combustor with hairpin-shape design of gas recirculation channel

This paper describes the design, fabrication and test of a silicon-based micro combustor, which is a part of a micro power generation system under development. Based on the three-dimensional computational fluid dynamics (CFD) simulation and analysis of different micro combustor design, a hairpin-shape design for air/fuel recirculation channel is adopted. The combustor is fabricated from seven single crystal silicon wafers using deep reactive ion etching (DRIE) process. It has been assembled successfully with gas tubing and thermal couplers for monitoring the exit gas temperature. The effect of mass flow rate on the combustion characteristics is studied experimentally and numerically under several operating conditions. The exhaust gas temperature can reach the range from 870 to 1,100 K. The results indicate that with the increases of the mass flow rate, the combustor exhaust gas temperature increase as well in both experimental and the simulated results. This is due to the heat released in the combustor increases with the fuel/air mass flow rate.

     

MEMS-based combustor with hairpin-shape design of gas recirculation channel

This paper describes the design, fabrication and test of a silicon-based micro combustor, which is a part of a micro power generation system under development. Based on the three-dimensional computational fluid dynamics (CFD) simulation and analysis of different micro combustor design, a hairpin-shape design for air/fuel recirculation channel is adopted. The combustor is fabricated from seven single crystal silicon wafers using deep reactive ion etching (DRIE) process. It has been assembled successfully with gas tubing and thermal couplers for monitoring the exit gas temperature. The effect of mass flow rate on the combustion characteristics is studied experimentally and numerically under several operating conditions. The exhaust gas temperature can reach the range from 870 to 1,100 K. The results indicate that with the increases of the mass flow rate, the combustor exhaust gas temperature increase as well in both experimental and the simulated results. This is due to the heat released in the combustor increases with the fuel/air mass flow rate.     

磁力驱动微泵设计及优化

为提高收缩/扩散管无阀微泵的性能,设计了磁力驱动式无阀微泵,并利用ANSYS软件对微泵的整流部件收缩/扩散管和单腔微泵整体结构进行流体仿真,得到了微泵的结构优化参数.仿真和实验结果表明,流量随着管长、最小宽度、扩张角、泵腔半径的增大存在极大值.磁驱动微泵的流量在驱动电压12 V、驱动频率为25 Hz时达到最大值.     

Effects of interface curvature on Poiseuille flow through microchannels and microtubes containing superhydrophobic surfaces with transverse grooves and ribs

This paper presents numerical results pertaining to the effects of interface curvature on the effective slip behavior of Poiseuille flow through microchannels and microtubes containing superhydrophobic surfaces with transverse ribs and grooves. The effects of interface curvature are systematically investigated for different normalized channel heights or tube diameters, shear-free fractions, and flow Reynolds numbers. The numerical results show that in the low Reynolds number Stokes flow regime, when the channel height or tube diameter (normalized using the groove–rib spacing) is sufficiently large, the critical interface protrusion angle at which the effective slip length becomes zero is θ _c ≈ 62°–65°, which is independent of the shear-free fraction, flow geometry (channel and tube), and flow driving mechanism. As the normalized channel height or tube diameter is reduced, for a given shear-free fraction, the critical interface protrusion angle θ _c decreases. As inertial effects become increasingly dominant corresponding to an increase in Reynolds number, the effective slip length decreases, with the tube flow exhibiting a more pronounced reduction than the channel flow. In addition, for the same corresponding values of shear-free fraction, normalized groove–rib spacing, and interface protrusion angle, longitudinal grooves are found to be consistently superior to transverse grooves in terms of effective slip performance.     

薄肋高速空切的颤振实验研究

薄肋在高速空切时产生的颤振将影响零件加工质量、表面粗糙度和刀具寿 命,为了克服此影响,对薄肋空切时,在不受外力直接激振的情况下的薄肋振幅变化进行分 析;运用有限元方法和田口实验法对薄肋进行仿真实验和动态位移激振研究,得出结论：薄 肋的宽、高、厚度尺寸会直接影响薄肋位移量,当高度一定时,宽度增加位移量会减少;当 宽度与高度一定时,随着厚度的减少,其位移量会变大;当宽度与厚度一定时,随着高度的 增加,其位移量亦会变大。探讨了薄肋动态位移内部能量的变化状态,并获得其能量完全衰 减的时间,进而设计其加工路径以避开颤振。     

Microfluidic analysis of CO<Subscript>2</Subscript> bubble dynamics using thermal lattice-Boltzmann method

By means of microfluidic analysis with a thermal lattice-Boltzmann method, we investigated the hydrophilic, thermal and geometric effects on the dynamics of CO₂ bubbles at anode microchannels (e.g., porous layers and flow channels) of a micro-direct methanol fuel cell. The simulation results show that a more hydrophilic wall provides an additional attractive force to the aqueous methanol in the flow direction and that moves the CO₂ bubble more easily. The bubble propagates quicker in the microchannel with a positive temperature gradient imposed from the inlet to the exit, mainly due to the Marangoni effect. Regarding the geometric effect of the microchannel, the bubble moves more rapidly in a divergent microchannel than in a straight or convergent channel. On the basis of the quantitative evaluation of hydrophilic, thermal and geometric effects, we are able to design the bubble-removal technique in micro fuel cells.