高体积分率条件下微流道内粒子迁移运动特性及其影响机理研究

As a new approach to precisely manipulate particles or fluids, the manipulation technology based on micro-scale particle migration has been used to solve numerous micro-fluidic problems in particle transporting, sorting, focusing and sample mixing due to its advantages such as operation without external fields, low cost, inherent miniaturization and portability. Due to the nonlinear interplay between phases, the characterization of particle migration in the dense inertial micro-fluidics flows is rather complex yet necessary to fully understand the intrinsic dynamics. . In this study, the interactions between a viscous fluid phase and rigid particles dispersed within the dense inertial micro-fluidic flow in a 700μm micro-channel will be investigated by using a multi-layer electrical capacitance tomography system. The multi-layer electrical capacitance tomography system is consists of a 700μm micro-channel with multi-layer electrodes array sensor, two micro pumps, a multiplexer, a capacitance measurement system and a process computer. The polystyrene particles as a solid phase and non-conductive deionized water as a liquid phase are non-uniformly injected into the inlets of micro-channel. The data from sample focusing experiments, performed with polystyrene particle samples is analyzed. In order to visualize the particle migration process that particle coincides with the unmixed location within the underlying flow, distribution images of the particle volume fraction along the upstream to downstream cross-section of the micro-channel will be reconstructed. A microscope video system equipped with a 20× objective lens and high speed CCD camera will also used to capture the particle motion spontaneously to compare with the reconstructed particle distribution image. The effect of the initial volume fraction condition, particle diameter and stream transitional on the particles migration in inertial micro-fluidic flow will be discussed quantitatively. Moreover, the particle migration in the dense inertial micro-fluidic flow is numerically simulated by means of the coupling of the lattice-Boltzmann method with the smoothed profile method which provides a coupling scheme between continuum fluid dynamics and rigid-body dynamics through a smoothed profile of the fluid-particle interface. Based on the experimental and simulation results, the effect of particle volume fraction on the inertial lift force and the mixing effect due to particle-particle interaction will be investigated by scaling analysis to clarify the response mechanism of volume fraction on particle migration.. From this study, a technique for real-time monitoring of particle migration in the dense inertial micro-fluidic flow will be proposed. And a more comprehensive understanding and eventual manipulation of hydrodynamic interactions within inertial micro-fluidic yield the spontaneously organized ‘structured suspensions’ will be provided.

基于粒子惯性迁移效应的惯性微流控芯片技术具有无需外场介入、易集成等众多优点，因而被广泛用于微小粒子及细胞的分选、聚焦等微流控领域。本课题以阐明高体积分率条件下微流道内粒子迁移运动特性及其影响机理为研究目标，利用微尺度多层电极阵列传感器在测量原理上不受体积分率制约的特点，实现高体积分率条件下微流道内粒子迁移运动的实时测量，找出体积分率对粒子迁移速率，迁移平衡位置等运动特性的影响规律；综合考虑粒子体积分率对粒子间相互作用及流体流动的影响，建立基于格子玻尔兹曼方法的粒子迁移运动仿真模型，量化粒子体积分率与迁移运动过程中粒子位置，速度及受力等动力学参数之间的关系；建立带有体积分率影响系数的惯性升力和混合效应尺度模型，阐明粒子体积分率对其迁移运动特性的影响机理，修正与完善现有惯性微流控芯片参数设计模型，为高体积分率条件下粒子迁移运动的控制以及高效惯性微流控芯片的设计开发提供理论与实践基础。

基于粒子惯性迁移效应的惯性微流控芯片技术具有无需外场介入、易集成等众多优点，因而被广泛用于微小粒子及细胞的分选、聚焦等微流控领域。但现有的大部分理论和实验成果都是在粒子间不相关假设的前提下获得，仅适用于粒子体积分率较低的条件（通常<5.0vol%），理论体系尚不完善。本课题以阐明高体积分率条件下微流道内粒子迁移运动特性及其影响机理为研究目标，旨在实现高体积分率条件下微流道内粒子迁移运动的实时测量，量化粒子体积分率与粒子迁移速率，迁移平衡位置等运动特性间的关系，建立带有体积分率影响系数的惯性升力和混合效应尺度模型，为高体积分率条件下粒子迁移运动的控制以及高效惯性微流控芯片的设计开发提供理论与实践基础。项目取得的重要结果及其科学意义主要有：.1) 综合考虑微电极抗噪性能要求、微电极三维效应以及充放电流特性、图像重构算法适应性以及测量精度要求等各方面因素，提出了微尺度多层电极阵列传感器电极形状、尺寸参数及传感器外延主板的合理设计方案，优化了测量电路充放电流强度、频率和采集处理速度，并在微尺度下接触阻抗效应对电极阵列传感器测量精度及粒子分布成像精度的影响分析基础上，建立了微尺度条件下的接触阻抗量化模型并将其引入成像算法，提高了颗粒分布图像的成像精度。.2）利用多层电极阵列传感器实现了高体积分率条件下菱形微流道内粒子迁移运动的实时测量，获得了不同粒子体积分率范围内各测量截面的粒子实时分布图像，并利用三维小波变换从重构图像中提取了粒子的时间和空间分布特性，分析了探讨了粒子体积分率对迁移速率，迁移平衡位置等迁移运动特性参数的影响规律。.3) 利用修正的兰纳-琼斯势和半解析模拟手段表征粒子间相互作用力及惯性升力的影响，建立了高浓度条件下粒子迁移特性的仿真分析模型，并以此为基础提出了预测不同体积分率条件下粒子迁移效果的迁移指数模型，与实验结果进行了定性比较，取得了较好的一致性。