气泡对固着液滴蒸发特性影响仿真研究
Simulation study on effect of bubbles on evaporation characteristics of sessile droplets
摘要：
提出了一种气泡液滴的蒸发模型,旨在不改变液滴属性和外部蒸发条件的前提下,探究气泡对液滴在固着基板上蒸发特性的影响。开展了相应的气泡液滴实验,对数值模型及其结果进行了验证。结果显示:气泡的加入增大了液滴的初始体积和表面积;液滴内部流场从单一Marangoni(马兰戈尼)流动转变为逆时针Marangoni流动与顺时针气泡诱导对流的双涡结构,增强了流动传热;液滴内部温度分布更加不均匀,并在蒸发过程中一直保持着比纯液滴更大的温差进行蒸发;会影响液滴蒸发模式,加快液滴从CCR(恒接触半径模式)到CCA(恒接触角模式)蒸发模式的变化,导致CCA模式在整个蒸发过程中的占比变大;加快了液滴的蒸发,气泡体积比为4%、7%、10%的气泡液滴的平均蒸发速率比纯液滴分别提高了17.88%、32.77%和53.19%。
Abstract：
In this study, a bubble droplet evaporation model is developed, which aims to investigate the effect of bubbles on the evaporation characteristics of liquid droplets fixed on a substrate without changing the properties of droplets and external evaporation conditions. Corresponding bubble droplet experiments are carried out to verify the numerical model and its results. The results show that the introduction of bubbles increases the initial volume and surface area of the liquid droplet, and the flow field inside the liquid droplet changes from a single Marangoni flow to a double vortex structure with counterclockwise Marangoni flow and clockwise bubble-induced convection, which enhances the flow and heat transfer. The internal temperature distribution of the liquid droplet is more uneven, and the temperature difference is greater than that of pure liquid droplets during the evaporation process. The droplet evaporation mode will be affected, and the change of the droplet from CCR to CCA evaporation mode is accelerated, resulting in a larger proportion of CCA mode in the entire evaporation process. The evaporation of liquid droplets is accelerated, and the average evaporation rate of bubble droplets with bubble volume ratios of 4%, 7%, and 10% is increased by 17.88%, 32.77% and 53.19%, respectively, compared with pure liquid droplets.
Keywords:bubble; bubble droplet; evaporation characteristic; evaporation rate; contact angle; contact radius; temperature distribution; bubble volume ratio