【作者】 刘华；

【导师】 陈瀚；

【作者基本信息】 华中科技大学 ， 流体力学， 2017， 硕士

【摘要】 微流控芯片中的流体混合是微流控研究领域的一个重要分支。由于微流控芯片中流体通道尺寸很小(通常为微米量级),流动雷诺数较小,流动状态一般为层流,混合只能依靠分子扩散,所需时间较长。利用交流动电效应对微流控芯片中的流体进行混合具有芯片几何结构简单、加工成本低、易于集成、所需电压低、溶液不易电解等优势,因此得到了广泛关注。本文利用交流动电效应中的交流电渗流和交流电热流,设计了两类微流体混合器,并采用数值模拟结合实验的方法对其进行了深入研究。首先,本文详述了微流控芯片及微流体混合器的国内外研究现状,介绍了双电层及交流电渗流的形成机理以及基于等效电路法的交流电渗流速度模型;同时阐述了交流电热效应的产生机理及模型,为本文的微混合器设计提供理论基础。其次,基于非对称电极交流电渗流的流动特征,本文提出并设计了非对称电极交流电渗混合器。建立了该混合器的数学物理模型,通过求解Navier-Stokes方程及对流扩散方程,数值模拟了三维通道中两种溶液的混合。通过对微通道内的流场及浓度场的仿真分析解释了该混合器的工作原理。通过仿真分析,得到了该混合器的关键结构参数(电极宽度比、电极间距、电极长度及电极偏移距离)对混合器性能的影响规律。同时分析了所加电压幅值及频率、流体雷诺数及溶液电导率对该混合器性能的影响规律。再次,基于交流电热流的流动特征,本文设计了用以促进微流体混合的偏场加热的交流电热微混合器。建立了该混合器的数学物理模型,通过多物理场(电场、温度场、流场、浓度场)耦合的仿真分析阐明了该混合器的工作原理,并数值研究了加热片尺寸参数、加热片热通量、流体流量及电导率对混合效率的影响规律。针对混合高电导率溶液时温升较大的问题提出了相应的解决措施。最后,本文对设计的两种混合器分别进行了实验研究。以PDMS及玻璃基底为材料,采用金电极,制作了微混合芯片。分别进行了两种微混合器的荧光素溶液混合实验,验证了本文微混合器设计的可行性及数值计算结论。研究成果为微流体的快速混合提供了理论及实验依据。更多还原

【Abstract】 Chip-scale micromixing is an important branch of microfluidic research.However,mixing in microfluidic chips is limited by small size of microchannels(usually at micro level),as well as the low Reynolds number laminar flow.Since molecular diffusion is the primary mechanism for mixing in laminar flow,it would take a long time to accomplish the mixing process.AC electrokinetic approach have attracted particular recognition due to many advantages,such as simple structure,low cost,low voltage,easy to be integrated and no electrolysis.This paper presents two novel micromixers which utilize AC electroosmosis(ACEO)and AC electrothermal(ACET)effect to promote mixing of fluids in microchannel.These two micromixers are studied by numerical simulation and experiment in this work.At first,this paper summarized the research status of microfluidic chip and micromixer all over the world.The mechanism of electric double layer and ACEO flow as well as the velocity model of ACEO flow based on equivalent circuit method are introduced,besides,the mechanism and model of ACET effect is introduced as theoretical basis for design of micromixers.Then we proposed an ACEO micromixer with asymmetric electrodes based on the characteristics of ACEO flow.The mathematical and physical model of this micromixer is established.The 3D numerical simulations of two solutions’ mixing is performed by solving the Navier-Stokes and convection-diffusion equations in microchannel.The flow field and concentration field is studied to explain the working principle of the micromixer.Influences of several key parameters on mixing efficiency are discussed in our simulation,such as width ratio of electrodes,the gap of electrodes,the length of electrodes and the offset distance of electrodes pair.Furthermore,effects of applied voltage and frequency,Reynolds number,conductivity of fluid on mixing efficiency are also investigated.In this work,another novel micromixer which utilizes thermally biased ACET effect to promote mixing is proposed based on the characteristics of ACET flow and the mathematical and physical model is established.And multiphysics(electrical,temperature,fluid flow and concentration fields)in this mixer is numerically studied to illuminate how the mixer works.Effects of heater’s geometric parameters,heat flux of heater,flow rate and conductivity of fluid on mixing efficiency are also studied.Besides,a solution to the problem that high temperature appears when mixed high conductivity fluid is put forward.At last,the experimental study of these two micromixers is carried out.The micromixers which consist of gold electrodes patterned on to glass wafer substrate and PDMS microchannel aligned onto substrate are fabricated for experiment.And dilution experiment was performed for these mixers by using dye solution as verifications for our designs and numerical simulation.The research results provide a theoretical and experimental basis for the rapid mixing of microfluidics.更多还原