【作者】 王瑞金；

【导师】 林建忠；

【作者基本信息】 浙江大学 ， 流体力学， 2005， 博士

【摘要】 本文是以数值模拟为主对影响微通道中流体扩散和混合规律的因素进行研究,并在此基础上设计出高效率的微混合器。 首先,在介绍微通道在流体扩散和混合规律的应用背景和研究状况的基础上,利用流体力学的基本方程,对通道宽度在50-500微米的微通道中流体扩散和混合进行数值模拟和实验研究,模拟结果显示:Reynolds数对扩散具有决定性的影响,Reynolds数越大,扩散越小,混合越不充分。此外,T-sensor的结构参数对扩散的效率有很大影响,如扩散通道宽度小时扩散快,入流角度大时扩散快,弯曲通道的扩散和混合效果比直通道要好得多。扩散尺寸/通道深度(d/w)对扩散也有一定的影响,当(d/w)较大时,沿w的浓度分布明显为抛物线,此时上下壁面的影响是主要的;反之,当d/w较小时,沿d、w二个方向的速度分布都为抛物线,上下左右壁面影响都不可忽略。实验研究结果部分验证了数值模拟结果。 其次,在介绍和了解微混合器的原理和混沌混合理论的基础上,根据马蹄型混沌对流循环的理论设计了一种新型的螺旋式微混合器,为说明其混合效果,对不同组分流体在分合式微通道中的扩散和混合进行了数值模拟,结果发现在小Reynolds数下,由于流体分层增加了接触面积,大大加快了流体混合的速度,其混合效果不仅比直通道,而且比蛇形通道明显好。随着Reynolds数的增大,对流作用得到加强,分合式通道的混合效果与直通道相比提高更明显,但与蛇形通道相差无几,所得结果为微流芯片的被动式混合提供了一种新的形式。同时还设计了一种主动式磁性混合器,分析了影响其混合效果的主要因素。 第三,为了解和解决毛细管电泳通道接头带来的ζ势的变化和管径变化对毛细管电泳分离效率和采样的影响,分别利用流体力学的全N-S方程(把电场力考虑为体积力加到方程内),结合电势方程,对毛细管内的流场进行数值模拟,结果显示:在ζ势较小的情况下,由于速度剖面的内凹不明显,这时ζ和尺寸的增大对速度剖面的畸变影响不大,但是在ζ势较大的情况下,由于沿程反向压更多还原

【Abstract】 This thesis is mainly related to the numerical study on the diffusion and mixing in the micro-channel flow. Based on it, the micro-mixers with high efficiency are designed. The thesis can be divided into three parts.In the first part, the numerical simulation of the diffusion-based mixing of the species in the micro-channel with the width of 50-500 microns and some experiments were carried out on the basis of the introduction of the research background about this theme, using the basic equations of the fluid dynamics. The numerical results show that the Reynolds number crucially influences the diffusion and mixing in the micro-channel, the lower the Reynolds is, the wider the species diffuse, furthermore, the dimension and shape of the micro-channel of T-sensor also play an important role in the diffusion of the flow. The smaller the channel width is, the more obviously the species diffuse, and the inlet angle has a reversed impact on the diffusion process. The ratio of the diffusion dimension (d) to the channel width (w) also plays a role in diffusion, the velocity distribution along diffusion dimension is almost the same, and the velocity contribution along channel width is obviously parabola when the ratio d/w is large, so the influence of upper and lower wall is primary. Conversely, when d/w is small, the velocity contribution along both directions are parabola, thereby the influence of all walls (upper and lower, right and left) could not be ignored. The experimental results validate partially the numerical results.In the second part, after introducing the various mixing principles and chaotic mixing theory, a new helical micro-mixer with horseshoe map was designed. In order to illuminate the mixing efficiency of the helical micro-mixer, the diffusion and mixing of the multi-species in the helical micro-channel were simulated numerically, the numerical results show that the mixing efficiency is much better than that in the straight micro-channel and obviously better than that in the serpentine micro-channel because of the layered structure and more contact areas when the Reynolds number islow. The mixing efficiency is also much better than that in the straight channel, but no obvious difference from that in serpentine micro-channel when the Reynolds number is high because the convection dominates the flow. A new micro-channel type with good passive mixing efficiency is provided. An active micro-mixer with magnetic bead and external magnetic field was designed, and then the factors impacting on the mixing efficiency for the micro-mixer were analysed.In the third part, the numerical simulation of Electroosmosis flow in a micro-channel was carried out by using the full Navier-Stokes equation (the electric force is considered as the volume force in this equation) in order that the separating efficiency and sampling quality can be improved when the zeta potential along the micro-channel wall becomes non-uniform because of the joint of different capillaries with different material and dimension. The numerical results indicate that a step change in ^-potential causes a significant variation in the velocity profile and in the pressure distribution. A step change both in ^-potential and dimension will result in more violent variation of the velocity profile near the joint. This variation will reduce the separation efficiency and sampling quality. However, the small difference between the maximum velocity and minimum velocity is benefit to the separation efficiency of the capillary electrophoresis when narrowing channel with bigger step-changed ^-potential.更多还原