Evaporative Drying of Droplets and the Formation of Micro-structured and Functional Particles and Films

液滴的蒸发干燥以及微结构和功能颗粒和薄膜的形成

基本信息

批准号：
EP/N025245/1
负责人：
Colin Bain
金额：
$ 289.28万
依托单位：
Durham University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FN025245%2F1
关键词：
Evaporative Drying Droplets Formation Micro

项目摘要

'Watching paint dry' is a metaphor for a boring and pointless activity. In reality, the drying of liquids is a complex process and the imperturbable appearance to the eye can hide a wealth of dynamics occurring inside the liquid. The effect of these internal processes is to change the distribution of materials in the deposit left after drying. We are all familiar with the coffee-ring effect, where split coffee dries to form a ring of solids at the edge of the spill - of little use if you are trying to coat a surface uniformly. This project is all about the drying of droplets, either in air or on a surface; one isolated droplet, two droplets merging or many droplets in a spray. We seek to understand how drops dry and how to control where the particles or molecules in the drop end up after the drop evaporates. When do you get a solid particle or a hollow particle? A round one or a spiky one? A uniform particle or one with shells? Or on a surface: a coffee-ring or a pancake? A uniform deposit, a layered one or a bull's eye? Are particles crystalline or amorphous, are different components mixed or separated? There are a myriad of possibilities for controlling the microstructure and properties of the final particle or film. Drying is complicated for three main reasons. First, many transport processes (evaporation, heat flow, diffusion, convection) occur simultaneously and are strongly coupled. For example, in a small droplet of alcohol and water evaporating on a surface, the liquid inside the drop will flow around in a doughnut pattern tens of times each second. Second, the conditions in a drying droplet are often far from equilibrium. For example, a small water droplet in air or on a smooth clean surface can be cooled to -35 degrees C without freezing. So to understand drying one needs to understand the properties of fluids far from equilibrium. It is generally not possible to predict the final outcome of drying from the properties of simple solutions near equilibrium. Third, drops do not dry in isolation. They may merge or bounce, coalesce or chase each other across a surface. The evaporation of one droplet affects its neighbours. Moving droplets change the flow of air around other droplets, coupling the motion of droplets.Why does anyone care, beyond the intellectual fascination with the bizarre outcomes of droplet drying? Drying of droplets turns out to be a rather important process in practical applications: spray painting, graphics printing, inkjet manufacturing, crop spraying, coating of seeds or tablets, spray cooling, spray drying (widely used in food, pharmaceutical and personal care products), drug inhalers and disinfection, to give a few examples. The physics and chemistry underlying all these applications is the same, but if manifests itself in different ways and the desired outcome varies between applications.The first challenge addressed by this project is one of measurement: how do you work out what is going on in a droplet that is less than a tenth of a millimetre across and may dry in less than a second? We have already developed sophisticated measurement tools but will need to extend these further. Another challenge is one of modelling: to understand the drying process we need a theoretical framework and computer models to explain - and predict - experimental observations. We will begin looking at the fundamental processes occurring in single drops in air and on a surface and then explore what happens when drops interact or coalesce. This fundamental understanding will be fed into improved models of arrays, clouds or sprays of droplets that are encountered in most practical applications (such as spray coating, spray drying, inhalers or inkjet manufacturing).We will use an Industry Club to engage with companies from a range of different sectors. This Club will provide a forum for sharing problems, ideas and solutions and for disseminating the knowledge generated in the project.

“看着油漆变干”比喻无聊且毫无意义的活动。事实上，液体的干燥是一个复杂的过程，眼睛看似平静的外观可能隐藏着液体内部发生的大量动态。这些内部过程的作用是改变干燥后留下的沉积物中材料的分布。我们都熟悉咖啡环效应，即分离的咖啡干燥后在溢出物的边缘形成一圈固体 - 如果您试图均匀地涂覆表面，则几乎没有用处。该项目的重点是干燥空气中或表面上的液滴；一个孤立的液滴、两个液滴合并或喷雾中的许多液滴。我们试图了解液滴如何干燥以及如何控制液滴蒸发后液滴中的颗粒或分子的最终位置。什么时候得到实心颗粒或空心颗粒？是圆的还是尖的？是均匀的颗粒还是带壳的颗粒？或者在表面上：咖啡圈还是煎饼？均匀沉积、分层沉积还是靶心沉积？颗粒是结晶的还是无定形的，不同的成分是混合的还是分离的？控制最终颗粒或薄膜的微观结构和性能有多种可能性。由于三个主要原因，干燥变得复杂。首先，许多传输过程（蒸发、热流、扩散、对流）同时发生并且强耦合。例如，在表面蒸发的一小滴酒精和水中，液滴内的液体每秒会以环形图案流动数十次。其次，干燥液滴中的条件通常远离平衡。例如，空气中或光滑清洁表面上的小水滴可以冷却至-35摄氏度而不冻结。因此，要了解干燥，就需要了解远离平衡状态的流体的特性。通常不可能从接近平衡的简单溶液的性质来预测干燥的最终结果。第三，水滴不会单独干燥。它们可能会合并或弹跳、合并或在表面上相互追逐。一滴水滴的蒸发会影响其邻近的水滴。移动的液滴会改变其他液滴周围的空气流动，从而耦合液滴的运动。除了对液滴干燥的奇异结果的智力迷恋之外，为什么还有人关心呢？液滴干燥在实际应用中是一个相当重要的过程：喷涂、图形印刷、喷墨制造、农作物喷雾、种子或片剂包衣、喷雾冷却、喷雾干燥（广泛用于食品、药品和个人护理产品）、药物吸入器和消毒，举几个例子。所有这些应用程序背后的物理和化学原理都是相同的，但如果以不同的方式表现出来，并且不同应用程序所需的结果也有所不同。该项目解决的第一个挑战是测量：如何计算出一个应用程序中发生了什么？直径小于十分之一毫米并且可以在不到一秒的时间内干燥的水滴？我们已经开发了复杂的测量工具，但需要进一步扩展。另一个挑战是建模：为了理解干燥过程，我们需要一个理论框架和计算机模型来解释和预测实验观察结果。我们将开始研究空气中和表面上的单个液滴发生的基本过程，然后探索当液滴相互作用或合并时会发生什么。这种基本的理解将被纳入大多数实际应用（例如喷涂、喷雾干燥、吸入器或喷墨制造）中遇到的液滴阵列、云或喷雾的改进模型。我们将利用行业俱乐部与来自以下领域的公司进行互动：一系列不同的部门。该俱乐部将为分享问题、想法和解决方案以及传播项目中产生的知识提供一个论坛。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Evaporation of a thin droplet in a shallow well: theory and experiment

DOI：
10.1017/jfm.2021.772
发表时间：
2021-10
期刊：
Journal of Fluid Mechanics
影响因子：
3.7
作者：
Hannah-May D'Ambrosio;Teresa Colosimo;B. Duffy;Stephen K. Wilson;Lisong Yang;C. Bain;Daniel E. Walker
通讯作者：
Hannah-May D'Ambrosio;Teresa Colosimo;B. Duffy;Stephen K. Wilson;Lisong Yang;C. Bain;Daniel E. Walker

Inertial stretching separation in binary droplet collisions

二元液滴碰撞中的惯性拉伸分离