Flow-induced heterogeneity in applications of complex fluids: causes, consequences and engineering

Complex fluids include emulsions, pastes, particulates, foams, polymers, grains, colloids, nanofluids, and medical fluids such as blood. Complex fluid flow is ubiquitous in everyday technologies, from food processing to minerals to ceramics to pharmaceuticals. Assumptions of homogeneous fluid response--that a fluid deforms and flows evenly throughout a flow geometry--are often violated by flow-induced heterogeneity in complex fluids, e.g. jamming of grains in hoppers, liquid/solid phase separation in food processing. Flow thus induces variations of composition and concentration across the flow geometry, as well as complicated variations of flow rate over time, leading to often serious problems with product quality and processing. This research will investigate the causes, consequences and engineering of flow-induced heterogeneity, in complex fluid flows relevant to important applications and technologies. The project has a twin focus: both solving application problems through basic experiment, measurement and understanding of key example flows; and investigating new control and design opportunities arising from control and use of flow-induced heterogeneity, by applying external fields such as ultrasound and microwaves.The research programme focuses around three flow situations that are key examples of applications: jamming in channels, in granulation (an important industrial process for turning fine powders into stable larger grains, e.g. in washing powder), and in squeeze flows (common e.g. in food processing).Direct optical measurements and observations will compare the heterogeneous response of 'model' complex fluids with controllable properties (colloids and polysaccharides, a key component of foods), to quantify the role of system properties and flow geometry as causes of flow-induced heterogeneity.The project will go on to investigate control and use of flow-induced heterogeneity, to solve process problems and generate desirable product attributes, e.g. texture in foods, by application of external fields (acoustic, microwaves). The possibilities of engineering heterogeneous response will be investigated by experimenting with the field geometry, strength, and protocol (changing field with time).Understanding the causes and consequences of flow-induced heterogeneity in complex fluids, and finding ways to use it to engineer the properties of complex fluid products, will aid a broad range of industries from foods to cosmetics to pharmaceuticals, enabling better design, testing and characterisation of products and processes. The results of this research will help turn heterogeneous flow responses such as jamming from a potentially serious and unpredictable problem, to a well-understood, predictable and useful engineering phenomenon.