Predictive formulation of high solids content suspensions through understanding the statistics of flow-induced jamming

当流体中的固体颗粒悬浮液以高颗粒浓度运输时，通常会出现重大问题，例如灾难性的增稠或“堵塞”以及高度不稳定和明显不可控的流动。在从陶瓷和油漆制造到石油开采的钻井泥浆等行业，这些问题意味着不可靠的产品质量和不可预测的过程故障。最近的研究表明，尽管这种明显的不可预测性，但这种不稳定的干扰流确实遵循有意义的统计“规则”，可以用来设计更好的工艺和制定更好的产品。因此，利用新颖的实验设备和理论分析，提高对干扰统计的理解是本博士项目的重点。该候选人将探索在高固体含量颗粒悬浮流中不稳定流动和应力驱动的瞬态干扰如何发生的基本原理，以及如何开发工程方法来提高流动可靠性。该项目将影响非常广泛的领域和过程，包括化学过程中的粉末流动和浆液，食品和陶瓷等颗粒产品的配方和制造，地质中土壤和沉积物的稳定性，甚至是动脉中血细胞的流动和拥挤环境中的行人。这样的系统存在许多常见的难题和挑战，例如灾难性崩溃（例如地震、火山喷发、山体滑坡）之后的干扰、不稳定的波动（例如血凝块和中风）和模式形成（例如分层沉积物、粉末分离）。因此，该项目跨越了许多工程和制造部门以及学术学科。该研究将确定“固体”颗粒结构何时出现，这如何取决于流动几何形状、配方（浓度、流速、颗粒相互作用、流体粘度/粘弹性等），以及我们如何开发统计分析来解释明显不可预测的波动，并开发可靠的预测控制方法和策略。实验：采用颗粒和流体性质可控的悬浮液，通过新型剪切和管流池、不同颗粒相互作用、尺寸分布等，获得局部应力波动的统计数据。应力数据将通过使用高速视频的光学显微镜与结构波动联系起来。分析：一个关键的进步将是分析测量的应力波动的统计数据，以得出基于干扰概率的预测方法，这将允许优化流动控制，产品配方和给定工艺和产品的工艺可靠性。基本原理：分析还将使我们能够与相关系统和现象进行类比，例如地震震级分布和行人人群安全设计（例如如何设计建筑物以最大限度地减少疏散期间的干扰概率）。在这些不同的干扰场景中，已经获得的结果显示出明显的相似性，但也有显著的差异，该项目有望在我们对“拥挤”相互作用系统中波动作用的更广泛的基本理解方面取得重大进展。工程与设计：根据实验和分析结果，我们将继续研究如何操纵几何形状和产品配方，以可靠地控制剪切流和沟道流中的易堵塞流，从而为应用中此类流的设计提供新思路。结果将最大限度地提高我们对基础知识的理解，这对未来的创新工程至关重要，并有助于确定潜在的策略，以提高涉及悬液的实际过程的效率和可控性。

When suspensions of solid particles in a fluid are transported at high particle concentration major problems often occur, such as catastrophic thickening or 'jamming' and highly erratic and apparently uncontrollable flow. In industries ranging from ceramics and paint manufacture to drilling muds in oil extraction, these problems mean unreliable product quality and unpredictable process failure. Recent work has shown that despite this apparent unpredictability, such erratic jamming flows do follow meaningful statistical 'rules' which could be used to design better processes and formulate better products. Improved understanding of the statistics of jamming is thus the focus of this PhD project, using novel experimental apparatus and theoretical analysis. The candidate will explore the fundamentals of how erratic flow and stress-driven transient jamming occur in high solids content particulate suspension flow, and thus how to develop engineering methods to improve flow reliability. The project will impact a very wide range of fields and processes, including powder flows and slurries in chemical processes, formulation and manufacture of particle-based products such as foods and ceramics, the stability of soils and sediments in geology, and even the flow of blood cells in arteries and pedestrians in crowded environments. Such systems present many common puzzles and challenges, such as jamming followed by catastrophic collapse (e.g., earthquakes, eruptions, landslides), erratic fluctuations (e.g., blood clots and strokes) and pattern formation (e.g., stratified sediments, segregation in powders). The project thus crosses many engineering and manufacturing sectors and academic disciplines.The research will determine when 'solid' particle configurations appear, how this depends on flow geometry, on formulation (concentration, flow rate, particle interactions, fluid viscosity/viscoelasticity, etc) and how we can develop statistical analyses to interpret apparently unpredictable fluctuations and develop reliable predictive control methods and strategies. Experiment: Using suspensions with controllable particle and fluid properties, statistical data on local stress fluctuations will be obtained via novel shear and pipe flow cells, varying particle interactions, size distributions, etc. Stress data will be linked to structural fluctuations through optical microscopy using high speed video. Analysis: A key advance will be to analyse the statistics of the measured stress fluctuations to arrive at predictive methods based on jamming probabilities, which will allow optimisation of flow control, product formulation and process reliability for given processes and products. Underlying fundamentals: The analysis will also allow us to draw analogies with related systems and phenomena such as earthquake magnitude distributions and pedestrian crowd safety design (for example how to design buildings to minimise probability of jamming during evacuations). Results already obtained show clear similarities, but also significant differences, across these different jamming scenarios, and this project promises a significant advance in our wider fundamental understanding of the role of fluctuations in 'crowded' interacting systems.Engineering and design: Informed by the experimental and analysis results, we will go on to investigate how to manipulate geometry and product formulation, to reliably control jamming-prone flows in shear and channel flows, leading to novel ideas for design of such flows in applications.Results will both maximise our understanding of the fundamentals, vital for future innovative engineering, and help identify potential strategies to improve efficiency and controllability of real processes involving suspensions.