Flow induced heterogeneity in applications of complex fluids" - Transfer of Mark Haw's grant from Nottingham

Project: Research

Description

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.

Key findings

Understanding and controlling the flow and deformation of
particle suspensions through confined geometries is of significant
technological importance. Soft matter materials consisting of
colloidal particles or droplets suspended in a liquid medium are
frequently encountered in industrial products and applications.
e.g. foods, paints, building materials, pharmaceuticals. Process-
ing of such concentrated colloidal dispersions often involves
driving under pressure through complex geometries, namely
convergent and divergent pipe sections, generating extensional
components of strain. Under suitably low flow rates concen-
trated dispersions exhibit a constant viscosity; i.e. they behave as
a Newtonian fluid. However, under higher stress or shear rate
they can also exhibit shear thickening i.e. increase in viscosity
with stress. Extreme or ‘discontinuous’ shear thickening has been
reported where apparent viscosity increases very suddenly,
accompanied by subsequent large fluctuations in viscosity and
stress. Such extreme thickening has been linked with flow-
induced jamming. Jamming can be defined as the transformation
of a liquid system to a solid by an applied stress. Whilst there
have been some studies of concentrated colloidal systems under
Poiseuille flow, the conditions under which jamming occurs are
still not properly understood. Jamming is relevant to major process problems such as uncontrolled variations in pressure which could cause significant damage; there are even indications that jamming is relevant to geological processes such as earthquakes and volcano eruptions.

In this project we demonstrated experimentally a novel behav-
iour of concentrated jamming suspensions, i.e. a ‘self-lubrication’
effect that enables a jamming suspension to revert to an
unjammed simple fluid flow behaviour. Associated with this is
the creation of rotating vortex-like flow patterns, consistent with
effects seen in computer simulations of granular systems (related to geology) but not to our knowledge observed before in experiment.
At the highest applied pressures the system is thus able to ‘perma-
nently’ unjam, reverting from granular-like behaviour
back to a simple hard-sphere liquid like system. In the experi-
ments the important role played by the geometry in imposing
a rotation on the flow pattern, thus rotating force chains and
taking advantage of the ‘fragility’ of the jammed system, suggests
a simple technical solution to jamming problems in processes
involving channels: insert similar ‘turns’ in straight channels to
enable the jamming fluid to self-lubricate and revert to simple
viscous flow.
StatusFinished
Effective start/end date15/09/0814/10/09

Funding

  • EPSRC (Engineering and Physical Sciences Research Council): £94,213.00

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Fluids
Food processing
Jamming
Geometry
Colloids
Drug products
Flow of fluids
Microwave acoustics
Powders
Granulation
Hoppers
Cosmetics
Acoustic fields
Polysaccharides
Washing
Phase separation
Emulsions
Foams
Blood
Minerals