【作者】 李健；

【导师】 夏国栋；

【作者基本信息】 北京工业大学 ， 热能工程， 2013， 博士

【摘要】 随着工程技术和自然科学的发展，机械产品已经开始向微型化发展，而流体控制微型化是其中一个重要的方向。微流控装置通常是一种以微通道网络和各种功能单元集成化为特点的微流控芯片，可以实现样品的制备、反应、分离和检测的集成，还可对这些过程进行调控。微流控系统主要应用于生物、化学和医学领域，其主要作用是感测、反应、控制和分析微量流体，应用于纳米颗粒的制备、DNA采样、化学合成、药品的采样和分析等方面。微流体技术作为生物芯片的一项关键支撑技术也得到了人们越来越多的关注。与微电子技术不同，微流体技术不强调减小器件的尺寸，它着重于构建微流体通道系统来实现各种复杂的微流体操纵功能。在微流体系统中，经常涉及到流体的扩散和混合问题，有效地控制扩散和混合对化学分析和生物分析的速度和效率的提高。而微混合器的引入使得微流体层流混合有了突破性的发展。微混合的传质特性极佳，参与混合的流体能达到常规混合设备无法实现的流体间均匀、快速混合，因而在乳状液制备、化学合成、医药制备、高通量筛选、生化等方面有很大的应用前景。本文采用模拟与实验相结合的方法，针对传统微混合器设计理念，使用优化方法对被动式混合器进行优化设计，并对不同的控制参数进行分析；在此基础上设计了两种平面被动式微混合器，并借助自主搭建的聚二甲基硅氧烷（polydimethylsiloxane，PDMS）芯片加工系统制作出PDMS芯片并开展实验研究。此外，利用微混合器的高效混合特点，搭建微混合/反应合成系统，采用一步法生成单金属银纳米颗粒。同时，对纳米流体的热物性能做出了定性和定量的评价与分析，为开发新型换热工质提供基础数据。主要包括以下几个方面内容：分析Telsa型微混合器、非对齐入口式T型通道微混合器、布置成涡单元的微混合器和布置矩形肋的T型微混合器内的强化传质传热混合机理，对影响混合器混合性能的结构参数和流体参数进行数值模拟，揭示不同参数对混合效果的影响规律，掌握平面被动式被动混合器的强化混合方法，为后续新型微混合器的设计及流动与混合特性实验研究提供理论基础。分析表明：通过改变局部通道宽度和在微混合器通道内增加障碍物的结构优化方式均可形成混沌对流以促进流体混合。而由于通道结构的变化实现了不同维度涡系间的共同作用，从而强化流体在通道内的扰动达到充分混合。设计两种加工方便、高效混合的新型平面被动式微混合器，根据优化方法对其几何结构参数进行了数值优化。优化后加工而成的非对称分离重组式和基于成涡结构强化混合式平面被动式微混合器内的混合性能得到强化。布置扇形空腔结构的非对称圆形通道分离重组微混合器混合效果显著，由于突扩和突缩结构产生的水平面内扩展涡系与竖直面内Dean涡系，使通道内的混合工质流动形态发生了明显改变，对于典型平面T型微混合器的优化设计提供较高参考价值。而基于成涡结构设计的微混合器在弯曲通道内形成了扩展涡，加大了流体间的扰动；在挡板后侧形成分离涡；在弯曲通道垂直于流体流动方向的截面上出现二次流现象，形成Dean涡。通过简单的通道结构实现了涡系的叠加和强化，从而增加了流体的接触面积，使得混合效果获得显著提高。对于典型平面弯曲微混合通道的优化设计提供参考。提出了一种基于PDMS和玻璃材质的芯片加工工艺。整个工艺流程包括SU-8硅片模具快速制作、复制压模技术和表面改性键合等步骤。通过研究各个工艺参数对流程的影响，对各个加工环节进行优化。对于本实验中200μm厚SU-8胶，采用365nm紫外光曝光时间约为180s,显影时间为10min左右；PDMS树脂与固化剂最佳质量配比为10:1，在75℃条件下固化时间为30min；最后，对PDMS基片表面进行氧等离子体轰击40至100s后直接与玻璃粘接，在100～120℃保温4h完成芯片键合。采用微混合/反应法一步制备粒径均匀、稳定分散的单金属银纳米流体。通过对现有微混合器与微反应器组合方式与制备条件（反应物浓度和反应物注入方式）的优化，实现对其粒径分布和化学稳定性的有效控制。通过对比分析纳米流体制备方法等优缺点，进一步优化了制备单金属纳米颗粒的加工工艺。同时，对其热物性参数进行定性和定量分析。系统分析了颗粒浓度和制备方式等对其热物性的影响。随着温度的升高，不同浓度的银纳米流体导热系数均有提高。不同粒径纳米流体的导热系数均随着颗粒体积分数的增加而增加。同时，纳米颗粒的粒径大小对纳米流体的导热系数影响较大。随着粒径的减小，纳米颗粒受布朗力的作用更加明显，而流体中颗粒的布朗运动和热扩散效应得以增强。更多还原

【Abstract】 With the development of the technology and science, machinery products havealready been minimized. Among these, the miniaturization of fluid control is one ofthe important directions. The characteristic of microfluidic device, i.e., microfluidicchip, is consisted of microchannel network and a variety of functional unitsintegration, which can be achieved the integration of the sample of preparation,reaction, separation and detection, as well as the regulation of these processes.Microfluidic system is mainly applied in the fields of biological, chemical andmedical, with the analysis and measurement of fluid in the aspects of sense, responseand control. Moreover, it also applied in the areas of nanoparticle synthesis, DNAsampling, chemical synthesis, pharmaceutical sampling and analysis, etc. Microfluidictechnology is considered as a key supporting technology, which has been given moreand more attention about it. Unlike microelectronic technology, microfluidictechnology does not emphasis on the size of reduction, but focuses on achievingcomplex manipulated function according to build a microchannel. In microfuildicsystem, it is advantage to improve velocity and efficiency in the chemical analysis andbiological analysis according to effectively control diffusion and mixture.Furthermore, the introduction of micromixer makes a breakthrough in the laminarflow mixing. The characteristic of mass and heat transfer is excellent, which helps themixing fluid more uniform and speedy than other conventional mixing equipment.Therefore, great applications are applied to the preparation of the emulsion, chemicalsynthesis, pharmaceutical preparation, high-throughput screening and biochemical.In this paper, the method of simulation and experiment is used to optimize thepassive micromixer, and analyze the effect of control parameters. Twopolydimethylsiloxane-based (polydimethylsiloxane, PDMS) passive planar passivemicromixers are devised according to the PDMS chip processing system. Furthermore,according to the efficient mixing characteristic in the micromixer, the synthesissystem of micro-mixing/reacting is established and the silver nanoparticle is made byusing one-step method. The thermal performance of nanofluids is evaluated by thequalitative and quantitative analysis, which may offer some data in the design of newworking fluid. The main contents include the following aspects:The mechanisms of enhanced mixing in the Telsa micromixer, the T-shapedmicromixer with non-aligned inputs and the micromixer with vortex-generated unitsare analyzed. The effect of structural and flowing parameters on the performance ofmixer is also simulated using numerical simulation. The results reveal that the effectof different parameters on mixing. To know the method of mixing in the passiveplanar mixer may offer some theoretical basis in design of the new-typed mixer in the further. The results also show that changing the local width of channel and addingobstacle into the mixer can form a chaotic convection so that promoting fluid mixing.Due to the change of structural channel, the interaction of vortices in the differentdimensions is achieved. Hence, it can strengthen the disturbance of the fluid in thechannel to achieve fully mixing.Two kinds of novel passive planar micromixers have been designed which canbe processed easily and achieved fast mixing. The geometry parameters are numericaloptimized according to the optimization method. The mixing performances of passiveasymmetric split-and-recombine micromixer with fan-shaped cavities and micromixerarranged with vortex-generated units are strengthened further. The mixing effect ofasymmetric split-and-recombine micromixer with fan-shaped cavities is significant.The extension vortex in the horizontal plane and the Dean vortex in the vertical planecaused by the sudden enlargement and sudden reduction structure obviously affect theflow pattern changing of mixing fluids in the microchannel. This provides a highreference value to the optimization design of typical planar T-shaped micromixer. Themicromixer arranged vortex-generated units could form extension vortex in thecurved channel, which can increase the disturbance between fluids; form separationvortex behind the baffle; emerge secondary flow and form Dean vortex in the crosssection perpendicular to the direction of fluid flow in the curved channel. The newmicromixers achieve superposition and strengthening of vortices using simple channelstructures. So the contact area of fluids is increased and the mixing effect is improvedsignificantly. This provides reference to the optimization design of typical planarmicromixer with curved channel.The microchip processing technology based on the PDMS and glass is putforward. The whole technological process includes fast making SU-8silicon wafer,replication molding technology and the surface modification bonding and so on.Through researching the influence of various process parameters on the technologicalprocess, the production process has been optimized. To the200μm SU-8glue in theexperiment, the365nm ultraviolet light is adopted and the exposure time is about180s,developing time is about10min; The best quality ratio of PDMS and curing agent is10:1, the curing time of75℃is30min; Finally, the PDMS substrate surface bondswith glass directly after bombarding40~100s by Oxygen plasma, the chip is bondedsuccessfully after thermal insulation4h at100~120℃.The single metallic silver nanofluids are composed which has uniform particlesize and stable dispersion by one step of micro-mixing/reaction method. Throughoptimizing the combination of micromixer and microreactor and the preparationcondition (reactant concentration and the reactant injection pattern), the particle sizedistribution and chemical stability can be controlled effectively. The processing technology of composing single metal nanoparticles is optimized further bycomparative analysis the advantages and disadvantages of nanofluid preparationmethods. At the same time, the thermal physical parameters have been analyzedqualitatively and quantitatively. The influence of particle concentration and synthesismethods on the thermal physical parameters has been analyzed systematically. As thetemperature increasing, the heat conductivity coefficients of silver nanofluids withdifferent concentrations increase. The heat conductivity coefficients of nanofluidswith different partical sizes increase as the particle volume fraction increases.Meanwhile, the particle size of nanoparticle has a great influence on the heatconductivity coefficient. With the decrease of the particle size, the influence of Brownforce on the nanoparticles is more obvious, while the Brownian motion and thethermal diffusion effect of particles in fluid enhance.更多还原