The movement of solid-liquid suspensions in pipes and vessels is a generic complex problem which is commercially challenging and technically important. Industrial applications are numerous, e.g. chemicals, consumer goods, food, pharmaceuticals, oil, mining, river engineering, construction, power generation, biotechnology and biomedical. Despite such large markets, industrial practice and processes are neither efficient nor optimal because of a severe lack of fundamental understanding of these flows. Such flows involve complex phenomena on a wide range of scales as flow conduits generally vary from the micron scale to the centimetre scale, and vessels vary from the millilitre scale to the cubic metre scale. Flows may be turbulent or viscous and the carrier fluid may exhibit complex non-Newtonian rheology. Particles occur in various shapes, sizes, densities, bulk and surface properties which exacerbates the complexity of the problem. The design of processes for conveying or processing solid-liquid suspensions requires information about particle behaviour such as particle trajectory, radial migration across streamlines, particle velocity distribution, and solids distribution. There are, however, huge practical difficulties in imaging solid-liquid flows and measuring local fluid and solid velocities, since little of the available instrumentation is applicable. Mixtures of practical interest are often concentrated and opaque so that flow visualisation is impossible, and particles may be deformable, breakable or prone to aggregation. Such complex phenomena are presently difficult to predict. They have hampered fundamental research and the development of rigorous holistic modelling strategies and, as a result, work has generally followed a piecemeal empirical approach. This proposal will use a multiscale approach to study the flow of solid-liquid suspensions including fluids of complex non-Newtonian rheology and particles with complex properties: (i) experimentally via a unique and accurate Lagrangian technique of positron emission particle tracking, which can measure local 3-D phase velocities as well as phase distribution in opaque systems; and (ii) by developing and validating novel modelling approaches to predict such flows including detailed interactions between particles, fluid and walls. A number of advanced modelling techniques will be used including principally the Discrete Element Method (DEM), Computational Fluid Dynamics (CFD), Smooth Particle Hydrodynamics (SPH), Lattice Boltzmann Method (LBM) and Coarse-Grained Molecular Dynamics (CGMD). None of these methodologies on its own, however, is able to effectively model these complex flows as they all enjoy strengths as well as weaknesses. We will, therefore, exploit the strengths of each technique by assembling these methods in an efficient hybrid fashion to produce an integrated multiscale modular framework to be made available free of charge within the unique and well-known open source code DL_MESO. Thus, we will evaluate the best hybrid approaches and develop a paradigm for modelling these complex flows by mapping the model hybrids against flow characteristics. The use of a hybrid modelling methodology and a multiscale approach to include concentrated turbulent flows, fluids of non-Newtonian rheology, particles of complex shapes and properties will produce a quantum leap advance in the modelling of these complex flows. In the medium to long-term, the findings from this work should improve the competitiveness of the UK solid-liquid processing technologies. Our industrial and academic partners, however, will be able to draw immediate benefits through engagement with the project.

A vital challenge for modern engineering is the modelling of the multiscale complex particle-liquid flows at the heart of numerous industrial and physiological processes. Industries dependent on such flows include food, chemicals, consumer goods, pharmaceuticals, oil, mining, river engineering, construction, power generation, biotechnology and medicine. Despite this large range of application areas, industrial practice and processes and clinical practice are neither efficient nor optimal because of a lack of fundamental understanding of the complex, multiscale phenomena involved. Flows may be turbulent or viscous and the carrier fluid may exhibit complex non-Newtonian rheology. Particles have various shapes, sizes, densities, bulk and surface properties. The ability to understand multiscale particle-liquid flows and predict them reliably would offer tremendous economic, scientific and societal benefits to the UK. Our fundamental understanding has so far been restricted by huge practical difficulties in imaging such flows and measuring their local properties. Mixtures of practical interest are often concentrated and opaque so that optical flow visualisation is impossible. We propose to overcome this problem using the technique of positron emission particle tracking (PEPT) which relies on radiation that penetrates opaque materials. We will advance the fundamental physics of multiscale particle-liquid flows in engineering and physiology through an exceptional experimental and theoretical effort, delivering a step change in our ability to image, model, analyse, and predict these flows. We will develop: (i) unique transformative Lagrangian PEPT diagnostic methodology for engineering and physiological flows; and (ii) innovative Lagrangian theories for the analysis of the phenomena uncovered by our measurements. The University of Birmingham Positron Imaging Centre, where the PEPT technique was invented, is unique in the world in its use of positron-emitting radioactive tracers to study engineering processes. In PEPT, a single radiolabelled particle is used as a flow follower and tracked through positron detection. Thus, each component in a multiphase particle-liquid flow can be labelled and its behaviour observed. Compared with leading optical laser techniques (e.g. LDV, PIV), PEPT has the enormous and unique advantage that it can image opaque fluids, and fluids inside opaque apparatus and the human body. To make the most of this and image fast, complex multiphase and multiscale flows in aqueous systems, improved tracking sensitivity and accuracy, dedicated new radiotracers and simultaneous tracking of multiple tracers must be developed, and new theoretical frameworks must be devised to analyse and interpret the data. By delivering this, we will enable multiscale complex particle-liquid flows to be studied with unprecedented detail and resolution in regimes and configurations hitherto inaccessible to any available technique. The benefits will be far-reaching since the range of applications of PEPT in engineering and medicine is extremely wide. This multidisciplinary Programme harnesses the synergy between world-leading centres at Birmingham (chemical engineering, physics), Edinburgh (applied maths) and King's College London (PET chemistry, biomedical engineering) to develop unique PEPT diagnostic tools, and to study experimentally and theoretically outstanding multiscale multiphase flow problems which can only be tackled by these tools. The advances of the Programme include: a novel microPEPT device designed to image microscale flows, and a novel medical PEPT validated in small animals for translation to humans. The investigators' combined strengths and the accompanying wide-ranging industrial collaborations, will ensure that this Programme leads to a paradigm-shift in complex multiphase flow research.