The Coalescence of Drying Droplets

摘要：韦伯数（We）是一个用于描述流体惯性与其表面张力之比的无量纲数，通常被绘制为碰撞参数(B)的函数，该参数衡量了正面碰撞的程度，是绘制两个液滴碰撞结果的一种方式。这些已知的状态图已经被实验研究过，并且已经提出了预测碰撞结果的模型。然而，先前工作的重点是亚毫米液滴的碰撞。本文提出的初步实验将集中在~ 30- 80um半径的水滴之间的碰撞。这种新颖的尺寸使得所提出的工作与气溶胶及其微物理性质的研究相关。可以与现有的水碰撞状态图进行比较，以确定液滴大小和动力学状态的变化是否会影响碰撞结果。这将研究使用两个微液滴分配器碰撞液滴，通过频闪成像技术成像。在此之后，粘度对状态图的影响可以用相同的方法确定，不同浓度的蔗糖液滴。这可能受到点胶器喷射高粘度液滴（bbb20 mPa）的能力的限制。S)，这可能导致使用电动捕集器，以便控制液滴在聚结之前的干燥时间。这两种仪器都有可能与腔增强拉曼光谱相结合，以确定液滴的组成和非均质性。

Abstract: The Weber number (We), a dimensionless number used to describe the ratio of a fluid's inertia to its surface tension, is often plotted as a function of the impact parameter (B), a measure of how head-on a collision is, as a way of mapping collisional outcomes of two fluid droplets. These regime maps, as they are known, have been studied experimentally and models have been suggested for predicting the collisional outcome. However, the focus of previous work has been the collisions of submillimetre droplets. The initial experiment proposed here will focus on the collisions of water-water droplets of ~ 30-80 um radius. This novel size makes the proposed work relevant to the research of aerosols and their microphysical properties. A comparison can be made with existing collisional regime maps of water to determine whether droplet size, and the shift in the kinetic regime, influences the collisional outcome. This will be investigated using two microdroplet dispensers to collide droplets, imaged by a stroboscopic imaging technique. Following this, the effect of viscosity on the regime map can be determined using the same method, with varying concentrations of aqueous sucrose droplets. This is likely to be limited by the ability of the dispensers to eject high viscosity droplets (> 20 mPa.s), which may lead to the use of an electrodynamic trap in order to have control over droplet drying time prior to coalescence. Both instrumentations have the potential to be combined with cavity enhanced Raman spectroscopy to determine droplet composition and heterogeneity.