Using the statistics of jamming to enable predictive formulation of high solids content suspensions

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 products. Improved understanding of the statistics of jamming is the focus of this PhD project, using novel experimental apparatus and theoretical analysis. The PhD dovetails with a newly funded collaboration with the University of Edinburgh and a range of companies including Johnson Matthey, AkzoNobel, Dupont and Schlumberger. 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.

Using experiment and theory, the research will determine when ‘solid’ particle configurations appear, how this depends on flow geometry, concentration, flow rate, particle interactions, fluid viscosity/viscoelasticity, etc, and how we can develop statistical analyses to interpret apparently unpredictable fluctuations and develop reliable control methods and strategies. The project has three major work strands:

• 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. This work has scope for collaboration with the University of Edinburgh’s advanced confocal ‘rheomicroscopy’, with our industry partners to compare across industrial particle systems, and with rheometry companies to develop our methods into new commercial measurement devices.

• 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 and reliability for given processes and product formulations. 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.

• 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.
The project builds on recent high-impact publications on particle network stability and geometry induced jamming and unjamming. 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.