微细通道内液滴生成及内部混合强化

发布时间：2018-10-30 17:17

【摘要】：随着微机电系统的快速发展,仪器设备微型化和高度集成化已经成为现代设备发展的主流趋势之一。微流控芯片就是将混合、分离、稀释、检测等功能集成在一块微小芯片上,正被广泛的应用于生物化学分析以及医药和生命科学等领域。液滴式微流控芯片是近年来微流控领域内一个新的分支。每一个液滴均可被视为独立的反应器,和传统生物化学反应器相比,液滴式微流控芯片具有样品消耗低、反应快、无交叉污染等优点,可以被广泛应用到化学合成、纳米材料制备、细胞分析、药物筛选等诸多领域。其中液滴的形成和内部混合的控制是实现上述功能的关键,但其相关系统研究却不深入。因此本文以此为切入点,针对液滴的形成及内部混合性能展开研究。本文采用可视化实验的方法针对微通道内液滴的生成及其内部混合的强化开展研究。首先在200*200μm的T型微通道内通过连续相二甲基硅油剪切分散相去离子水生成微液滴,研究了连续相流速、分散相流速以及连续相粘度对微液滴生成尺寸的影响;并提出了一种利用光热效应致相变的方法在大尺度T型微通道内生成超微液滴的新方法;其次,研究了螺旋型微通道对液滴内部混合的强化作用,并进行了量化分析;最后,利用PIV技术测量了微液滴受到侧向剪切时其内部流动状况的变化并分析了这一变化对液滴内部混合性能的影响。通过对以上内容的研究,本文得出了以下结论:①在T型微通道内液滴的生成尺寸随连续相流速的上升而减小;随分散相流速的上升而增大;随连续相粘度的增大而减小。同时提出了利用激光的光热效应致T型结构中水相相变蒸发冷凝形成超微液滴。在工作过程中,液态水通过激光加热生成水蒸汽,水蒸汽被连续相剪切生成汽塞,汽塞冷凝后可以形成超微液滴。由于液滴是通过冷凝形成,汽塞的大小直接决定了液滴的大小,研究发现汽塞大小随激光功率上升而变大,随连续相流速增大而减小。②通过研究直微通道和螺旋形微通道中液滴的混合性能,发现具有T型结构入口的直微通道内液滴生成时的混合效率随连续相的增大而得到强化,随分散相流速的增大而减弱。螺旋形微通道也具有相同的变化趋势。更重要的是,研究发现无论在单位时间内还是在单位长度上,相对于直微通道,螺旋型微通道内由于螺旋结构所产生的二次流使得液滴的混合效率得到提高。③利用流体侧向剪切微液滴时,液滴受到剪切力的作用,其内部流场向剪切方向偏转,同时可以提升液滴内的流速,从而可以强化液滴内的混合。其强度随流体流速的增强而变大,随分散相的流速的增大也增强。
[Abstract]:With the rapid development of MEMS, the miniaturization and high integration of instrument and equipment have become one of the mainstream trends in the development of modern equipment. The microfluidic chip integrates the functions of mixing, separating, diluting and detecting on a microchip, which is widely used in biochemistry analysis, medicine and life science and so on. Droplet microfluidic chip is a new branch in the field of microfluidic in recent years. Each droplet can be regarded as an independent reactor. Compared with the traditional biochemical reactor, the droplet microfluidic chip has the advantages of low sample consumption, fast reaction and no cross contamination, so it can be widely used in chemical synthesis. Preparation of nanomaterials, cell analysis, drug screening and many other fields. The formation of droplets and the control of internal mixing are the key to achieve the above functions, but the related system research is not thorough. In this paper, the formation of droplets and their internal mixing properties are studied. In this paper, the method of visualization experiment is used to study the formation of droplets in microchannels and the enhancement of their internal mixing. At first, microdroplets were formed in 200 渭 m T microchannels by continuous phase dimethyl silicone oil shearing dispersed phase deionized water. The effects of continuous phase flow rate, dispersed phase flow rate and continuous phase viscosity on the formation size of microdroplets were studied. A new method for the formation of ultrafine droplets in large scale T microchannels by photothermal effect is proposed. Secondly, the enhancement effect of spiral microchannels on the internal mixing of droplets is studied, and the quantitative analysis is carried out. Finally, the change of the internal flow state of microdroplets under lateral shear was measured by PIV technique and the influence of this change on the internal mixing performance of droplets was analyzed. Based on the above research, the following conclusions are drawn: 1 the size of droplet formation decreases with the increase of the flow rate of the continuous phase, increases with the increase of the velocity of the dispersed phase, and decreases with the increase of the viscosity of the continuous phase in the T-shaped microchannel. At the same time, the superfine droplets were formed by evaporating and condensing water phase change in T type structure by the photothermal effect of laser. During the working process, liquid water is heated by laser to form steam, which is shearing by continuous phase to form steam plug, which can form ultramicro droplets after condensing. Since the droplet is formed by condensation, the size of the steam plug directly determines the size of the droplet. It is found that the size of the steam plug increases with the increase of laser power. By studying the mixing performance of droplets in straight microchannels and spiral microchannels, it is found that the mixing efficiency of droplets in the straight microchannels with T-shaped structure increases with the increase of the continuous phase. With the increase of the velocity of the dispersed phase, it weakens. The spiral microchannels have the same trend. More importantly, the study found that both in unit time and in unit length, relative to straight microchannels, The secondary flow caused by helical structure in the spiral microchannel improves the mixing efficiency of the droplets. 3 when the droplets are shearing laterally, the droplets are subjected to shear force, and the internal flow field deflects to the shear direction. At the same time, the flow rate in the droplet can be increased, thus the mixing in the droplet can be enhanced. The strength increases with the increase of the flow velocity of the fluid and the velocity of the dispersed phase.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN492

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