Development of a Replaceable Microreactor Coated with a CuZnFe Nanocatalyst for Methanol Steam Reforming

A methanol steam microreactor with a replaceable catalytically coated plate structure was designed. A splitting‐jointing flow (SJF) design was proposed to increase the efficiency. Stainless‐steel plates were coated with a Cu/Zn/Fe nanocatalyst. Electrophoretic deposition served as a uniform and controllable coating technique to evaluate the performance of the nanocatalyst and the microchannel design. The functioning of the SJF design for methanol conversion was found to be only slightly dependent on the plate length. The yield of H₂ varied with different lengths in the SJF, while the direct parallel microchannel showed a lower performance by reducing the plate length. Comparing a quartz packed‐bed reactor with a microreactor proved the strong dependency of methanol conversion on the accessibility of the reactants to the nanocatalyst sites.     

Development and Characterization of a Novel Polymer Microchannel Tube

This article establishes a novel polymer microchannel tube (MCT) with a channel (0.9–3.0 mm in diameter) in the center surrounded by an array of microchannels (50–300 µm) using extrusion technology. The draw ratio and melt drawing length are demonstrated to significantly affect the cross-sectional parameters of MCT, which is consistent with numerical simulations using Polyflow and theoretical analysis. It was found that the process parameters negligibly influence the relative proportions between cross-sectional parameters. Based on a simplified drawing model, a prediction function of high reliability (R-square >95%) for cross-sectional parameters is set up. The MCTs are formed more uniformly compared with microcapillary films (MCFs) because of the elimination of the sharp boundary effect. Each of the microchannels is formed elliptically as a result of the non-uniform velocity distribution around the injector tip exit. The mechanism where the ambient air is automatically entrained into the microchannels at atmospheric pressure was elucidated.     

Thermal performance of U-shaped serpentine microchannel heat sink using various metal oxide nanofluids

This study aims to evaluate the thermal performance and friction factor characteristics of the U-shaped serpentine microchannel heat sink using three different nanofluids. Two distinct nanoparticles, namely Al₂O₃ (alumina) and CuO (copper oxide), were used for the preparation of nanofluids using water and ethylene glycol (EG) as base fluids. Three nanofluids, namely nanofluid I (Al₂O₃ + water), nanofluid II (CuO + water), and nanofluid III (CuO + EG), have been prepared. The results showed that the thermal conductivity of nanofluids was increased for all concentrations (from 0.01 to 0.3%), compared with base fluids. The theoretical values derived from the relationship between the Darcy friction factor showed a clear understanding of the fully developed laminar flow. Thermal resistance for nanofluid III was lower than other nanofluids, resulting in a higher cooling efficiency. The nanofluid mechanism and the geometry of the U-shaped serpentine heat sink have led to the improvement in the thermal performance of electronic cooling systems.     

EXAMINATION OF THE LBM IN SIMULATION OF MICROCHANNEL FLOW IN TRANSITIONAL REGIME

The gas flows in micro-electro-mechanical systems possess relatively large Knudsen number and usually belong to the slip flow and transitional flow regimes. Recently the lattice Boltzmann method (LBM) was proposed by Nie et al. in Journal of Statistical Physics, vol. 107, pp. 279–289, in 2002 to simulate the microchannel and microcavity flows in the transitional flow regime. The present article intends to test the feasibility of doing so. The results of using the lattice Boltzmann method and the direct simulation Monte Carlo method show good agreement between them for small Kn (Kn = 0.0194), poor agreement for Kn = 0.194, and large deviation for Kn = 0.388 in simulating microchannel flows. This suggests that the present version of the lattice Boltzmann method is not feasible to simulate the transitional channel flow.     

矩形微流道内电渗流影响因素的数值模拟

针对电渗泵的设计参数优化问题,建立电渗驱动流的数学模型,应用有限控制容积法对矩形流道断面上双电层场和速度场的耦合控制方程进行数值求解.详尽分析流道断面深宽比、流道当量直径、电解质溶液浓度和外加电场强度对电势、速度和流量的影响,并给出电渗流量和平均速度与影响因素之间的拟合公式.仿真结果表明:流量随流道深宽比的增大而减小,当流道深宽比为1时,流量最小;流量随流道当量直径的平方增加;平均速度与电解质溶液浓度和外加电场强度有关、与流道深宽比和当量直径的大小基本无关.     

微管道散热器换热性能的有限元分析

利用伽辽金有限元公式计算了微管道散热器中的管道表面温度分布、流体温度分布及流动阻力系数和换热系数等。与现有的分析方法对比发现，利用有限元方法可对热负荷任意分布工况下的微管道散热器进行传热性能分析，而且使用范围比现行的大型CFD软件更广，也可用于分析微管道散热器的几何参数对散热器传热性能的影响。     

微通道板电子透射膜及其粒子透过特性的研究

文中介绍了微光像管中微通道板电子透射膜及其形成技术,研究了粒子(电子和离子)透过特性.给出了死电压概念、死电压曲线、死电压与膜厚关系曲线以及半视场对比测试结果;给出了采用XPS进行成分分析的结果.介绍了电子透射膜的离子透过特性,给出了表征膜层对离子阻止能力的离子透过率的概念,提出了离子透过率测试的原理方案和相关技术等问题.     

基于狄恩流的微混合器的研究

所设计的微混合器是一种基于狄恩流的被动式混合器,该混合器的结构特点是由多个不同半径的弯曲管道双螺旋而成,中部通过"S"形管道将输入管道和输出管道相连。首先分析了狄恩流形成的机理及特点,再通过流体计算软件CFD-ACE+三维模拟并分析了不同流速对二次流强弱以及混合程度的影响,最后利用微细加工技术制作微混合器,罗丹明B溶液与去离子水用作待混合液体,利用Image J软件获取混合图像的灰度值来分析混合器的性能。     

Endoscopic Visualization of Contact Line Dynamics during Pool Boiling on Capillary-Activated Copper Microchannels

Microchannel surfaces are common to microfluidics, biofluidics, thermal management, and energy applications. Due to processing limitations for the majority of metallic materials, the majority of hyperfine microchannels used in microfluidics and thermo-fluids are fabricated on non-metallic substrates, for example, silicon and polydimethylsiloxane. Here, a technique to fabricate ultrasmall microchannels on arbitrary metallic materials is developed using photolithography in combination with electrochemical deposition. The technique is used to prepare copper microchannels and to investigate the pool boiling heat transfer performance with a focus on the three-phase contact line dynamics. The hydrodynamics of nucleating bubbles during boiling are observed in situ using in-liquid endoscopy. The results show that the variation of critical heat flux enhancement has a linear relationship with the contact line increase ratio. The scalable microchannel surfaces exhibit superior heat transfer performance with a maximum heat transfer coefficient) enhancement of 930% with ultra-low wall superheat of 5  ° C. This work not only develops a scalable manufacturing method to develop ultra-small microchannels on metallic materials, it outlines design guidelines for structure optimization of pool boiling heat transfer for temperature sensitive applications, such as electronics thermal management.