FLOW OF GAS-LIQUID FOAMS IN NARROW COMPLEX GEOMETRIES

气液泡沫在我们的日常生活和工业中无处不在。应用范围从食品、消费品、药品、聚合物和陶瓷到消防、提高石油采收率和矿物颗粒输送。近年来，在医学领域也出现了应用，如泡沫硬化治疗静脉曲张，膨胀聚合物泡沫治疗脑动脉瘤等。因此，泡沫对许多工业都是至关重要的，对世界经济作出了相当大的贡献。例如，到2018年，聚氨酯泡沫的全球市场价值将达到619亿美元，剃须泡沫将达到79亿美元，冰淇淋将达到740亿美元。2016年巧克力市场将达到983亿美元，其中相当一部分是充气产品（如慕斯）。泡沫是一种具有挑战性的复杂流体，由于其重量轻、微观结构复杂、流变性和瞬态性等多种原因，其许多方面还没有得到很好的理解，因此目前的模型无法很好地预测。因此，泡沫现象的复杂性与目前的知识水平之间存在着巨大的差距，这使得泡沫设计和控制在商业应用中更多的是艺术而不是科学。特别是，在许多工业过程中，泡沫被迫流过复杂的通道，进入具有狭窄复杂横截面的容器或通过喷嘴。例如，充气糖果在狭窄通道和复杂模具中的流动，用保温泡沫填充空腔，在狭窄的油井环空中发泡水泥浆的流动，用聚氨酯泡沫填充空心机翼部分以制造用于通信和地球工程应用的气动系绳，以及生产用于区域供热的预保温管道。这些流动的典型特征是收缩和膨胀，它们会产生复杂的现象，对泡沫结构和流动产生重要影响，并可能导致剧烈的不稳定性和形态变化，对泡沫在流动和加工过程中的可持续性产生严重的实际影响。在这里，泡沫在气泡尺度上的流动特性是重要的，但所发生的拓扑变化及其对泡沫流变学和流动的影响却知之甚少。本提案旨在通过实验研究，使用一系列先进的诊断技术，并通过理论和计算机模拟与三维泡沫通过包含各种复杂几何形状的狭窄通道的流动，稳定性和行为相关的一些基本方面来解决这种缺乏理解的问题。将实验研究含水泡沫的流动以及不同复杂程度配方的聚合物泡沫。我们将开发气泡规模的模拟与任意液体馏分跨越整个范围从干到湿，以涵盖工业相关的泡沫。在这个项目中产生的广泛的实验信息和数据将使这些模拟得到指导和严格的测试，反过来，模拟将巩固我们在复杂几何形状中泡沫流动行为的工程理论。这些基础知识，从理论、建模到实验，将使基础科学得到进一步的提高，并将帮助泡沫产品的设计者和制造商，以及泡沫产生或加工设备的设计者和用户。更具体地说，该项目的实际目标是开发预测工具，作为工业从业者的辅助工具，根据从实验和建模工作中获得的知识，从配方特性和流动参数方面描述泡沫的结构和动态特性。我们还将与我们的工业合作伙伴合作，帮助他们提高对基础科学的理解，这些基础科学支撑着他们特定的泡沫流应用，从而使他们能够提高它们。

Gas-liquid foams are ubiquitous in our daily life and in industry. Applications range from food, consumer goods, pharmaceuticals, polymers and ceramics to fire-fighting, enhanced oil recovery, and mineral particle transport. Recently, applications have also emerged in the medical field, e.g. foam sclerotherapy of varicose veins, and expanding polymer foam for treating brain aneurysms. Thus, foams are crucial to a wide range of industries and contribute considerably to the world economy. For example, by 2018 the global market will be worth $61.9 billion for polyurethane foam, $7.9 billion for shaving foam, and $74 billion for ice cream. The chocolate market will reach $98.3 billion in 2016, and a considerable part of it is due to aerated products (e.g. mousse).Foams are challenging complex fluids which are used for a variety of reasons including their light weight, complex microstructure, rheology, and transience, many aspects of which are not well understood and, thus, not well predicted by current models. A wide gap therefore exists between the complexity of foam phenomena and the present state of knowledge, which makes foam design and control in commercial applications more art than science.In particular, in many industrial processes foams are forced to flow through intricate passages, into vessels with narrow complex cross-sections or through nozzles. Examples include flow of aerated confectionary in narrow channels and complex moulds, filling of cavities with insulation foam, flow of foamed cement slurries in narrow oil-well annuli, filling of hollow aerofoil sections with polyurethane foam to make aerodynamic tethers for communication and geoengineering applications, and production of pre-insulated pipes for district heating. These flows are typified by contractions and expansions which generate complex phenomena that can have important effects on foam structure and flow, and can lead to dramatic instabilities and morphological transformations with serious practical implications for foam sustainability during flow and processing. Here, the flow characteristics of the foam at bubble scale are important, but the topological changes incurred and their effects on the rheology and flow of the foam are poorly understood. This proposal seeks to address this lack of understanding by studying experimentally, using a range of advanced diagnostic techniques, and via theory and computer simulation a number of fundamental aspects related to the flow, stability and behaviour of three-dimensional foams through narrow channels containing a variety of complex geometries. The flow of aqueous foams as well as setting polymer foams with formulations of varying degrees of complexity will be experimentally studied. We will develop bubble-scale simulations with arbitrary liquid fractions spanning the whole range from dry to wet, to cover foams of industrial relevance. The wide range of experimental information and data to be generated in this project will allow these simulations to be guided and critically tested and, conversely, the simulations will underpin our engineering theory of the behaviour of foam flows in complex geometries.This basic knowledge, from theory, modelling and experiment, will give a step improvement in fundamental science, and will assist designers and manufacturers of foam products, as well as designers and users of foam generating or processing equipment. More specifically, the practical aim of the project is to develop predictive tools as an aid to industrial practitioners, to describe the structural and dynamical properties of foams in terms of formulation properties and flow parameters, based on the knowledge gained from the experimental and modelling work. We will also work with our industrial partners to help them improve their understanding of the fundamental science which underpins their particular foam flow applications and, thus, enable them to enhance them.