电共轭流体微型泵的实验研究（英文）

为了解决MEMS技术制备具有超厚、高深宽比电极结构的射流发生器中三角柱电极尖端部分出现的弧形缺陷以及脱模时缝隙电极易脱落等问题,提高射流发生器的制作质量以及电共轭流体微型泵的输出性能。结合理论分析与反复试验提出了一系列改进措施:优化涂胶、热处理、显影等工艺的参数以及缝隙电极的形状,采用新型KMPR光刻胶去除方法等。通过应用上述方法获得的射流发生器中,三角柱电极-缝隙电极对厚度约500μm,深宽比高,三角柱电极尖端结构完整,缝隙电极附着率有很大提高。同时,利用制备的射流发生器,设计、装配了电共轭流体微型泵的样机。     

支撑板缝隙对蒸汽发生器热工水力特性的影响

采用CFD方法数值研究支撑板缝隙对蒸汽发生器热工水力特性的影响,获得了一次侧流体温度,二次侧流体温度、传热系数、质量含汽率以及传热管温度等关键热工水力参数的局部分布规律,计算所得出口质量含汽率与大亚湾核电站实际运行参数相符;支撑板缝隙处传热管壁温高于流水孔处,支撑板处传热管外壁温度沿圆周方向变化呈周期性波动,无缝隙结构的波动幅度明显高于有缝隙结构。缝隙处质量含汽率高于流水孔处,而流体平均流速小于流水孔处,导致缝隙中液体不足,增加了支撑板缝隙处杂质浓缩和传热管应力腐蚀的可能。     

微型填充式气相色谱柱的制备（英文）北大核心CSCD

为了分离永久性气体及低碳轻化合物,基于MEMS技术,研究制备了一种微型填充式的气相色谱柱。为了增加色谱柱的长度以及深宽比,色谱柱的沟道制备采用了激光刻蚀技术,这种技术可以方便的在玻璃基底上刻蚀出深沟道,这是其他化学腐蚀技术无法比拟的。研制的色谱柱其沟道横截面为1.2mm(深度)×0.6mm(宽度),深宽比为2∶1。实验结果表明,这种微型填充柱,具有较大的样品容量,能很好的实现CO和SO_2的分离。     

微型填充式气相色谱柱的制备（英文）

为了分离永久性气体及低碳轻化合物,基于MEMS技术,研究制备了一种微型填充式的气相色谱柱。为了增加色谱柱的长度以及深宽比,色谱柱的沟道制备采用了激光刻蚀技术,这种技术可以方便的在玻璃基底上刻蚀出深沟道,这是其他化学腐蚀技术无法比拟的。研制的色谱柱其沟道横截面为1.2mm(深度)×0.6mm(宽度),深宽比为2∶1。实验结果表明,这种微型填充柱,具有较大的样品容量,能很好的实现CO和SO_2的分离。     

不同电极结构下双通道大气压He等离子体射流数值研究

采用二维轴对称流体模型对单电极结构（不锈钢针管）和双电极结构（不锈钢针管-高压环形电极）下同轴双通道进气的大气压氦气等离子体射流进行了对比研究。研究表明:相比于单电极结构,双电极结构下射流的传播速度明显降低,介质管内尤为严重。同时双电极结构下射流的空间结构也发生了显著变化。在单电极结构下,随射流发展由环形中空结构转变为实心圆盘结构;而在双电极结构下则呈现出实心圆盘结构至环形中空结构再至实心圆盘结构的演化过程,改善了射流空间分布的均匀性。此外,还研究了双电极结构下高压环形电极厚度对射流的影响。研究表明,随环形电极厚度的增加,射流的传播速度进一步降低,射流通道径向收缩,同时环形中空结构的射流内径减小,进而改善了射流径向分布的均匀性。     

制备复合液滴的微尺度流动方法

微尺度流动能够一步到位地制备不同结构和功能、尺寸在微米量级的复合液滴.文章回顾了几种常见的基于复合液滴的微尺度流动方法,包括同轴电雾化、复合流动聚焦、微流控芯片、玻璃微毛细管等,并对各种技术的原理和进展进行了简要概括和分析.在这类流动中,不同种类的流体在一定的几何结构通道或外力场作用下平稳地拉伸成微细射流并最终破碎成复合液滴.在同轴电雾化和复合流动聚焦技术中,从毛细管流出的流体能够形成稳定的锥-射流结构,当外力作用改变时能够形成不同的流动模式.在微流控芯片和玻璃微毛细管技术中,流体被约束在固定管道内,不同管道构型下能够形成不同的流动形态.这些方法都采用纯物理机理,过程稳定、易于操作,制备的复合液滴粒径可控,单分散性好,微观结构可设计,在科学研究和工程实际中具有重要的应用价值.      

射流式氧发生器的三维模拟研究

实现了对射流式氧发生器的三维仿真模拟,给出了氧发生器内部流场结构、各组分的分布状态等信息。研究了射流孔结构对氧发生器性能的影响。指出即便是具有相同比表面积的不同射流孔排布方式,也会对发生器性能产生影响。此外,逆向射流式氧发生器反应器中气体从双侧进入对于减小发生器对气体的阻力具有重要作用。     

纳米级激光发生器

研究人员成功打造出纳米级激光发生器，这种微型装置是由两个金三角形组成，金三角的尖端彼此相对形成一个三维蝴蝶结的形状。这种特殊的几何学能够在两个金属三角尖端之间形成小范围集中磁场的“热点”。西北大学化学和材料科学家TeriOdom说道：“形状真的很重要。”     

电液动力微泵的实验分析

本实验运用MEMS技术在硅片上加工了一种新型电子冷却微泵-电液动力微泵,微泵由一组平面电极组成,施加直流来驱动流体.相关实验研究表明微泵的性能与施加电压、工作介质,电极结构和材料以及工作环境有关.     

直流纯氮层流等离子体射流特性的实验研究

采用自行研制的直流非转移型等离子体发生器,对其产生的层流等离子体射流特性进行了实验研究。实验结果表明:该等离子体发生器在以纯氮气为工作气体时,呈现出高电压低电流的等离子体射流特性,该特性有助于提高等离子体发生器的电极寿命;在弧电流和工作气流量由小向大变化过程中,等离子体射流长度均呈现出先由短变长、再由长变短的变化规律;在等离子体射流长度由长变短的过程中,射流的形貌从相对集中、轴对称和稳定的状态向分散、非轴对称和不稳定的状态变化,即等离子体射流由层流形态向湍流形态转变,并且在此过程中射流产生的噪音逐渐增强。     

Multiple beams surface plasmon interference generation: A theoretical analysis

In this paper, multiple beams surface plasmon (SP) interference generation based on prism coupling technique is theoretically analyzed and presented. The proposed multiple beams SP interference configuration is investigated for nanolithography application for two-dimensional feature fabrication. The configuration is then numerically and experimentally analyzed by employing aluminum metal at 364-nm illumination wavelengths to realize high resolution and high aspect ratio two-dimensional periodic nanoscale dot array patterns on the recording medium.     

Numerical heat transfer analysis in turbulent channel flow over a side-by-side triangular prism pair

Heat transfer and flow behavior in a channel fitted with a transverse triangular prism pair is numerically investigated in the turbulent flow regime for the Reynolds number ranging from 10000 to 50000. The aspect ratio of channel height to the prism base is fixed at 4.0 throughout the study. The Navier-Stokes equation, along with the energy equation, is solved using a finite volume method with the SIMPLE technique and the QUICK numerical scheme for coupling the discretized equations while the standard k-ɛ turbulence model is used for closure of the problem. The numerical result reveals that heat transfer augmentation in the channel with the built-in prism pair can be obtained. It is observed that as compared to a channel, the heat transfer is enhanced by about 17% for a single triangular prism and by some 85% for a triangular prism pair mounted on the channel wall. Effects of the clearance between the prisms on the heat transfer augmentation are presented. The heat transfer enhancement is due to the vortex formation or recirculation zone downstream of the prism elements. However, the presence of the prisms also leads to higher values of friction loss over the channel.     

Acoustic-excited vortex shedding and acoustic nonlinearity at a rectangular slit with bias flow

The acoustical response of a slit with a mean bias flow is numerically studied. By means of a potential flow model based on the discrete vortex method and a spanwise-averaged three-dimensional Green?s function, both unsteady vortical flow and slit impedance are obtained in a unified theoretical framework. The numerical simulation focuses on the acoustic-excited vortex structures of the slit flow while neglecting the viscous damping effect. Three representative flow features are demonstrated, which are the destabilized jet flow, the rolling up of vortex sheets and formation of vortex pairs, and the reversal flow with alternating vortex shedding on both sides of the slit. These features are corresponding to low, moderate, and high sound amplitude, respectively. The acoustic behavior of the slit can be divided into linear, transition, and nonlinear regimes. During its evolution through the three regimes, the resistance exhibits a constant value, a slight decrease, and a significant increase with the increasing sound amplitude. Correspondingly, the reactance first remains constant and then shows a modest decrease as the sound amplitude increases. The nonlinear effect also causes the gradual decrease of the mean bias velocity in company with the marked increase of the amplitude of the fluctuating velocity in the slit. The mean bias velocity decreases to about 80 percent of its linear value at the transition point where reversal flow begins to occur, and further decreases to only 10 percent in the highly nonlinear region. The slit impedance is also presented as a function of frequency and for different aspect ratios. And the effects of frequency and slit geometry are discussed.     

Optimization and fabrication of a planar thermoelectric generator for a high-performance solar thermoelectric generator

A planar thermoelectric generator (TEG) could be used as an energy harvester for wireless sensor networks (WSNs). Its planar configuration offers the advantages of miniaturization and low-cost fabrication. Herein, we report the fabrication of a device based on a co-evaporated thick film of Bi–Te. Before fabrication we studied quantitative optimization dimensions for the planar TEG via finite element method (FEM) simulations. The planar TEG was also used in a high-performance solar thermoelectric generator (STEG) that concentrated heat from solar radiation via a solar absorber to generate a temperature difference (ΔT) between two thermoelectric and electrode junctions. When exposed to a solar simulator, the STEG produced a ΔT of about 6 °C and generated 2.3 μW of power. The demonstrated high flexibility and mechanical stability of this device suggests applications in wearable electronics.     

Control of the cross-sectional shape of a hollow microchannel embedded in photostructurable glass by use of a femtosecond laser

Theoretical and experimental investigations have been made of the three-dimensional microchannel fabrication of photostructurable glass by use of a femtosecond (fs) laser. Generally, a microchannel fabricated inside glass by the scanning focal spot of a fs laser perpendicular to the direction of laser propagation assumes an elliptical shape with a cross section of large aspect ratio. We demonstrate that one can greatly reduce the aspect ratio merely by inserting a slit, which is oriented parallel to the laser's scanning direction, before the focusing lens. Computer simulations show that a more symmetrical pattern is obtained in the vicinity of the focal point with the help of such a slit, owing essentially to a diffraction effect.     

A unipolar pulsed plasma generator in combination with a laser as a plasma jet source

A pulsed plasma generator ignited by plasma produced by laser radiation is described. The plasma generator can provide a relatively high-velocity plasma jet of specific chemical composition. The principal parameters of the plasma jet (its velocity, charged particle concentration, and temperature) have been measured and the properties of the plasma jet have been found to be independent of the polarity of the plasma generator ring electrode.The authors are grateful to M. A. El'yashevich for discussing the present paper.     

Fabrication of two-dimensional infrared photonic crystals by deep reactive ion etching on Si wafers and their optical properties

We report the fabrication and characterization of two-dimensional silicon-based photonic crystal structures realized by deep reactive ion etching. Photonic crystals with square and triangular lattices with very high aspect ratios up to 33 have been achieved. Photonic bandgap behaviors are identified by the transmission and reflection spectra measured by using a Fourier transform infrared spectrometer. The experimental results are in good agreement with the calculated band structures.     

Selective ablation-assisted two-photon stereolithography for effective nano- and microfabrication

The two-photon stereolithography (TPS) process has strong merits for the direct fabrication of 2-D and 3-D microstructures with sub-100-nm resolution. In this paper, we report an effective fabrication process in which selective ablation-assisted TPS (SA-TPS) was used to ameliorate some of the limitations of the TPS process. In SA-TPS, two processes (namely, an additive process of two-photon induced photocuring and a subtractive process of selective laser ablation) were performed sequentially using a single femtosecond laser optical scanning system. The effectiveness of the proposed process was demonstrated in several applications, including precise high-resolution patterning at resolution levels higher than those achievable using the TPS process, and the fabrication of structures with high mechanical sensitivity.     

流经矩形喷嘴的超音速射流啸叫模式切换的实验研究

通过实验分析比较了对于相同高度不同宽度的四种矩形喷嘴, 当压力在0.2 MPa到0.8 MPa 之间变动时, 欠膨胀超音速自由射流的啸叫特性和对应的流场纹影结构.结果表明: 不同宽高比喷嘴的超音速自由射流辐射噪声中的单频离散啸叫存在两种不同的啸叫模式, 且随着射流压力的变化会出现模式间的切换.所谓模式切换是指不同模式的轮流占优和消失的现象.啸叫模式间的切换及占优区间的宽度随着喷嘴宽高比的减小而缩短.其中, 宽高比为2的射流啸叫模式中的一种模式所占的射流压降区间异常小, 此现象未在相关文献中提及; 喷嘴宽高比为4的射流啸叫占优区间内, 啸叫基频-射流压力曲线在0.49 MPa时出现了间断、跳跃现象.随着压力的降低激波纹影的轴线出现了抖动, 不同宽高比下流场结构的稳定性随压力变化的规律各异.射流压力在0.70 MPa到0.45 MPa区间内, 随着宽高比减小, 第一波节格栅的激波致密度减弱, 且出现轴向脉动, 第二波节后方的流场变得紊乱; 当射流压力低于0.45 MPa 时, 激波串结构随着宽高比的增大而趋于稳定, 在此压力区间内周期性激波格栅结构较射流压力在0.45 MPa以上时有所减弱.结合啸叫频谱及纹影图分析, 可初步认为, 第二、三波节也会对啸叫频率的声压幅值起到反馈增强作用.