含荧光颗粒液滴的内部流动特性及最终沉积图案

发布时间：2018-01-27 09:47

本文关键词： 固着液滴荧光颗粒乙醇内部流动特性沉积图案　出处：《华北电力大学(北京)》2016年硕士论文　论文类型：学位论文

【摘要】：固着液滴的蒸发现象在大自然中随处可见,是传热传质领域研究的一个重要方向。含有颗粒的固着液滴在蒸发完毕之后,会在固体基底表面上留下各种各样的沉积图案。这种颗粒沉积的现象在工业生产中发挥着重大的作用,例如在喷墨打印、薄膜涂层、药物发现、新型光电元件的制造等领域。本文利用倒置显微镜来观察含荧光颗粒的液滴在蒸发过程中的内部流动特性以及最终的颗粒沉积图案。通过实验研究及观察发现,纯水液滴的蒸发时间和颗粒浓度有关,颗粒由外到内存在三种不同样式的沉积,而且颗粒的整体沉积图案随着颗粒浓度的升高而有所变化。液滴内部加入乙醇会改变液滴的表面张力,从而改变液滴的铺展半径和蒸发时间。此外,乙醇的加入还会彻底改变液滴内部的流动特性,而且最终的沉积图案也会随着乙醇浓度的变化而显现出巨大的差异。我们同样研究了液滴中不同尺寸颗粒的混合效果,发现颗粒的混合虽然对液滴的蒸发和内部流动没有太大的影响,但是不同大小的颗粒在三相接触线位置能够很好地分离。直径较小的颗粒沉积在三相接触线的附近位置,而直径较大的颗粒则沉积在距离接触线较远的位置。研究发现,位置的远近不但和颗粒的接触半径有关,而且还会受到液滴接触角的影响。最后我们分析了接触线的移动行为,发现接触线的解附和液滴的表面自由能有关,并且受到能量势垒的影响,接触线的移动能够影响颗粒的沉积图案,一般情况下接触线的跳跃步长随着蒸发的进行逐渐减小。
[Abstract]:Evaporation of fixed droplets is widely seen in nature, which is an important research direction in the field of heat and mass transfer. This phenomenon of particle deposition plays an important role in industrial production, such as inkjet printing, film coating, drug discovery. In this paper, inverted microscope is used to observe the internal flow characteristics of droplets containing fluorescent particles in evaporation process and the final particle deposition pattern. The evaporation time of pure water droplets is related to the concentration of the particles, and there are three different types of deposition from outside to inside. Moreover, the overall deposition pattern of the particles changes with the increase of particle concentration. The surface tension of the droplets will be changed by adding ethanol into the droplets, thus changing the spreading radius and evaporation time of the droplets. The addition of ethanol will also completely change the flow characteristics of the droplet. And the final deposition patterns also show great differences with the change of ethanol concentration. We also studied the mixing effect of different size particles in droplets. It is found that the mixing of particles has little effect on the evaporation and internal flow of droplets. However, particles of different sizes can be separated well in the three-phase contact line position. The smaller particles are deposited in the vicinity of the three-phase contact line. On the other hand, the larger particles are deposited in the distance from the contact line. It is found that the distance and proximity of the particles are not only related to the contact radius of the particles. Finally, we analyze the moving behavior of the contact line and find that the solution of the contact line is related to the surface free energy of the droplet and is affected by the energy barrier. The movement of contact line can affect the deposition pattern of particles. In general, the jump step of contact line decreases with evaporation.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK124

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