Magnetic Field Effect and Heat Transfer of Nanofluids within Waveform Microchannel

In this research,a numerical study of mixed convection of non-Newtonian fluid and magnetic field effect along a vertical wavy surface was investigated.A simple coordinate transformation to transform wavy surface to a flat surface is employed.A cubic spline collocation numerical method is employed to analyze transformed equations.The effect of various parameters such as Reynolds number,volume fraction 0-,Hartmann number,and amplitude of wave length was evaluated in improving the performance of a wavy microchannel.According to the presented results,the sinusoidal shape of the microchannel has a direct impact on heat transfer.By increasing the microchannel wave amplitude,the Nusselt number has risen.On the other hand,increasing the heat transfer in the higher wavelength ratio corrugated channel is seen as an effective method of increasing the heat transfer,especially at higher Reynolds numbers.The results showed that with increasing Hartmann numbers,the flow line near thewall becomesmore regular and,according to the temperature gradient created,theNusselt number growth.

Reversal current observed in micro-and submicro-channel flow under non-continuous DC electric field

In practical applications of biochips and bio-sensors, electrokinetic mechanisms are commonly employed to manipulate and analyze the characteristics of single bio-molecules. To accurately and flexibly control the movement of single molecule within micro-/submicro-fluidic channels, the characteristics of current signals at the initial stage of the flow are systematically studied based on a three-electrode system. The current response of micro-/submicro-fluidic channels filled with different electrolyte solutions in non-continuous external electric field are investigated. It is found, there always exists a current reversal phenomenon, which is an inherent property of the current signals in micro/submicro-fluidics Each solution has an individual critical voltage under which the steady current value is equal to zero The interaction between the steady current and external applied voltage follows an exponential function. All these results can be attributed to the overpotentials of the electric double layer on the electrodes. These results are helpful for the design and fabrication of functional micro/nano-scale fluidic sensors and biochips.

Ball Tips of Micro/Nano Probing Systems:A Review

To satisfy the measuring demands for the micro components of the industry, micro/nano probing systems with various ball tips have been developed. However, most of them cannot be used to measure the real micro geometrical features high precisely because the parameters of the ball tips are not appropriate. The ball tips with a diameter of less than 100 μm, a sphericity and eccentricity of far less than 1 μm are required urgently. A review on the state-of-the-art of ball tips of micro/nano probing systems is presented. The material characteristics and geometric parameters of now available ball tips are introduced sepa- rately. The existing fabrication methods for the ball tips are demonstrated and summarized. The ball tips＇ future trends, which are smaller diameter, better sphericity and smaller eccentricity, are proposed in view of the practical requirements of high-precision measurement for micro geometrical features. Some challenges have to be faced in future, such as the promotion and high-precision measurement for the small ball tip＇s sphericity and eccentricity. Fusion method without the gravity effect when the molten ball tip solidifying is a more suitable way to fabricate a small diameter ball tip together with a shaft.

微通道反应器制备纳米硫酸钡的工艺研究

利用微通道反应器,以硫酸钠和硫化钡为原料反应并进行纳米硫酸钡粒子制备研究,考察了微通道反应器制备纳米硫酸钡粒子的影响因素,并对产品进行激光粒度检测和TEM测试。结果表明,该法可以制备出平均粒径50~80 nm、分布窄的纳米硫酸钡粒子。

Monte Carlo simulations of dense gas flow and heat transfer in micro-and nano-channels

The dense gas flow and heat transfer in micro- and nano-channels was simulated using the Enskog simulation Monte Carlo (ESMC) method. The results were compared with those from the direct simulation Monte Carlo (DSMC) method and from the consistent Boltzmann algorithm (CBA). The dense gas flow and heat transfer characteristics were thus analyzed. The results showed that when the gas density was large enough, the finite gas density effect on the flow and heat transfer cannot be ignored, which decreased the skin friction coefficient and changed the heat transfer characteristics on the channel wall surfaces.

Observation of the induced pressure in a hybrid micro/nano-channel

This paper studies the flow characteristics in micro/nano-channels subjected to an applied electric field. The nano-channel flow was observed by means of the fluorescence Calcein. A Fluorescence Concentration Gradient Interface （FCGI） was observed across the nano-channel array. The front of the FCGI was shown to have an analogous parabolic shape. The propagation of this interface reflects indirectly the induced pressure at the micro/nano-channel junction, where the enrichment-depletion processes are known to take place. This induced pressure was predicted by numerical simulations, and this paper gives the first experimental evidence.

金刚石刀具的圆柱母光栅微加工基础研究

精密长光栅作为高档数控机床中的核心部件,其制造能力和精度直接影响着数控机床的制造水平.针对纳米滚压印技术制备长光栅中的核心部件即圆柱母光栅的制造开展了深入研究,探讨了母光栅刻划用金刚石刀具的聚焦离子束(FIB)制备技术,以及微刻划过程中切削参数对圆柱母光栅加工质量的影响规律.研究发现,聚焦离子束加工单晶金刚石材料时会存在沟道效应,影响所制备的金刚石刀具及其加工母光栅的形状精度.从改善离子束束流分布的均匀性、FIB加工参数优化等角度建立了有效克服FIB加工沟道效应的方法.通过DEFORM有限元模拟实验和超精密母光栅刻划实验,优化金刚石刀具刀尖角和微刻划加工速度,研究了抑制母光栅加工中微尺度毛刺的有效方法,最终获得了高精度母光栅刻划结果.

微槽道中纳米流体沸腾换热特性研究

为研究纳米流体在微槽道中的沸腾换热特性及规律,分别以去离子水和体积浓度为0.2%、0.5%的水基A l2O3纳米流体为工质进行试验,研究质量流速、热流密度、进口过冷度、槽道尺寸等因素对沸腾传热系数的影响及其两相摩擦压降与出口干度的关联分析和沸腾换热关联式对比拟合。试验结果表明:在一定热流密度和质量流速下,传热系数随槽道尺寸的减小而增大;质量流速和进口过冷度对水基A l2O3纳米流体和去离子水的传热系数均无明显的影响。研究表明,在本实验的给定条件下,水基A l2O3纳米流体相对于去离子水可以明显强化微槽道沸腾换热特性,传热系数可提高10%-15%。

微纳米通道电场调控电渗流研究及控制

在通道壁面垂直施加一个调控电场可以改变双电层电荷密度和Zeta电位势,实现对电渗流的调控。采用离子输运Nernst-Planck方程、液体流动Navier-Stokes方程、以及介电层-电解液耦合双电层Poisson方程,数值求解外加均匀调控电压下微纳米通道的电渗流动,得到表面Zeta电位势、电渗流速度与外加调控电压的关系特性。数值解与基于Poisson-Boltzmann方程双电层弱重叠近似和双电容串联模型的解析解相对比,进一步研究了控制外加调控电压以及控制电渗流的方法。

微纳通道谐振器检测与表征中的动力学问题

微纳通道机械谐振器在液体环境中具有超高的谐振频率、品质因子和灵敏度,常用于液体环境中的高精度检测与表征,在生物、医药、化工等领域有着广阔的应用前景.微纳通道机械谐振器的检测与表征功能高度依赖其动力学特性,而此类器件是由谐振结构、内部流体、被检测物和外部激励等多因素组成的耦合系统,涉及的动力学问题较为复杂,已成为谐振器件研究中的前沿热点和瓶颈问题.本文综述了微纳通道机械谐振器的研究进展,总结了谐振器件实现高精度检测与表征功能时的动力学设计原理,详细讨论了谐振器件的稳定性、频响特性、能量耗散、频率波动等动态特性,阐明了不同动力学问题的物理机制及其对谐振器性能的影响规律,可为深入厘清微纳通道机械谐振器的动力学设计问题,提高器件动态性能提供理论参考和技术支撑,对超高频、超高灵敏度谐振器的设计、制造及应用发展具有重要意义.

矩形微槽道内磁纳米流体传热与流阻特性研究

以浓度为0.5%的Fe3O4-水磁纳米流体为工质,研究其在0.6mm×2mm、1mm×2mm、2mm×2mm三种不同微槽内的两相流沸腾传热和压降特性。实验结果表明:在施加磁场前后,其饱和沸腾传热系数和两相流压降梯度均随热流密度的增加而增大;施加磁场后,饱和沸腾传热系数和两相流压降梯度较无磁场时有所提高,并且随着磁场强度的增加进一步提高;通过不同尺寸的槽道对比发现,槽道尺寸越小,其传热强化作用越大,其两相流压降越大。

新型超高压微型撞击流发生器制备微乳液的研究

提出一种集撞击流、超高压和微通道三者优势的新方法,超高压提供动力,颗粒在微通道中保持能量集中,受剪切力的作用得到初步粉碎细化,从微通道喷出的两股高速流体相互撞击,颗粒被进一步粉碎、分散。根据新方法设计了超高压微通道撞击流发生器,从模拟、理论和实验3个方面对结果进行了研究,成功制备了微纳米颗粒。

适用微纳卫星的便携测控站设计

针对微纳卫星的测控数传需求,利用业务无线电及ISM(Industrial-Scientific-Medical,工业-科学-医疗)频段和设备,设计了适用微纳卫星的便携式测控站,包括ISM和VHF/UHF(Very High Frequency/Ultra High Frequency,甚高频/超高频)2个通道;优选了COTS(Commercial Off The Shelf,商用现货)ISM通信电台和VHF/UHF全模式电台、VHF/UHF八木天线、S频段花瓣式网状抛物面天线等部组件,3副天线共用1个伺服机构;并对ISM和VHF/UHF信道的上/下行链路电平进行估算。结果表明:该多频段多通道便携测控站的设计方案可行性好,效费比高,并已在相关微纳卫星的测控应用中得到验证。

改性对硅胶纳米通道润湿性的影响规律研究

研究了多孔硅胶在改性前后不同的壁面特征对纳米通道润湿性的影响规律。采用非平衡分子动力学方法研究了水分子在改性前羟基化及改性后不同链长硅烷化壁面的纳米通道内密度、速度的分布状况,并分析了氢键的径向分布函数。结果表明:羟基化壁面通道的固液界面处流体出现高密度层,几乎无速度滑移,流体密度最大值为1.24g/cm^3,滑移速度仅为0.056?/ps;链长为C_4、C_8、C_(12)的硅烷化壁面通道的固液界面处水的密度分别为1.18g/cm^3、1.12g/cm^3、1.01g/cm^3,滑移速度分别为0.402?/ps、1.211?/ps、1.810?/ps;随烷基链长的增加,固液界面处水的密度接近纯水的密度1.0g/cm^3,固液界面处出现了速度滑移;羟基化通道壁面由于较强的固液相互作用势呈强亲水性;改性后的硅烷化壁面呈疏水性,并随改性层烷基链长度的增加而增强,且固液界面处出现"滑移效应";羟基化通道壁面与水分子存在较强的氢键作用,而改性后硅烷化通道壁面与水分子无氢键的形成,改性层烷基链长的增加减弱了两者的相互作用势,进一步揭示了其疏水机理。

微流控通道加工技术的研究进展

在微流控芯片中,微通道是进行微分析的重要保证,其成型质量直接影响芯片的分析性能。从加工机理、技术特点以及适用范围等方面对激光直写加工、光刻加工、热压印技术、微细铣削加工和3D打印等微流控通道主要加工方法进行了阐述,并总结了这几种加工技术的优缺点,这为实际生产提供了一定参考。最后,对微流控通道加工技术的发展进行了展望,未来微流控芯片将会向三维化、精密化以及微小化方向发展,芯片材料也趋于多样化,这些发展将不断推动微流控通道加工技术的发展。

微纳通道中牛顿及非牛顿流体流动分析

基于润滑近似理论,建立了毛细管力作用下牛顿及非牛顿流体在微纳米通道中的流动控制方程,其时间依赖性的接触角由实验数据拟合,弯月面曲率的变化规律可由其末点与初点曲率比值控制;并利用圆弧分割近似的方法得到不同时刻液体弯月面的动态变化,将该算法应用于求解牛顿流体酒精毛细作用下的液柱高度,结果与Hamraoui的实验吻合很好。该算法进一步扩展到求解非晶材料PC(聚碳酸酯)热压印过程中在微纳通道中的流动高度。通过模拟分析得知:当非牛顿指数n为0.715时,材料易流动且柱体高度上升快;Bond数为0.1时,毛细力对柱体弯月面的作用效果更强,弯月面高度值更大。

矩形微槽道纳米流体沸腾传热压降特性研究

为研究纳米流体微尺度沸腾传热流阻及压降特性,文中以体积浓度为0.2%的水基Al2O3纳米流体为试验工质,在尺寸为0.6mm×2mm矩形微槽道中进行沸腾传热实验,建立实验模型,分析纳米流体沸腾传热两相摩擦乘子的影响因素及进出口压降组成,并将本实验的两相摩擦压降值与现有理论模型及参数修正后理论模型预测值进行比较。结果显示,在本实验给定的条件下,实验段两相流压降中88.6%为两相摩擦压降。与L-M模型相比,M-H修正模型和Z-M修正模型都能较好地预测实验结果。其中经M-H修正模型能更好地预测本实验的实验值,使得平均误差减小为21.2%,大大降低了原L-M模型的误差。

Y型微管道中磁性纳米液体对混合率的影响

利用流动显示手段观测了Y型微管道内含纳米磁性颗粒的液体与去离子水的混合．研究了在Re=0．5～4，磁性颗粒体积分数0.38％-1．54％时，外加静磁场（场强40 Gs）对液体混合地影响．证实了磁场作用可以使完全混合长度大大缩短．同时初步分析了Re和体积分数φ对混合长度的影响．

微纳通道型真空漏孔研究进展

传统真空漏孔存在难以实现尺寸可控制作、分子流压力范围有限等问题,而利用微纳通道型真空漏孔可以有效解决上述问题。本文阐述了一维/二维微纳通道型真空漏孔的加工方法,即使用光学曝光、刻蚀工艺在硅基底上制备微纳沟槽,结合键合技术实现微纳通道密封;通过金属封装、玻璃浆料键合、毛细管连接工艺实现硅基微纳通道型真空漏孔与金属真空法兰的封装连接。该类型漏孔有望在真空计量、极小流量控制和漏率测试等方面取得应用。