Please use this identifier to cite or link to this item: http://buratest.brunel.ac.uk/handle/2438/9466
Title: Macroscopic effects of microscopic roughness in suspensions
Authors: Wilson, HJ
4th Micro and Nano Flows Conference (MNF2014)
Keywords: Suspensions;Surface roughness;Rheology;Stokesian dynamics;Contact
Issue Date: 2014
Publisher: Brunel University London
Citation: 4th Micro and Nano Flows Conference, University College London, UK, 7-10 September 2014, Editors CS König, TG Karayiannis and S. Balabani
Series/Report no.: ID 233
Abstract: We study a model suspension consisting of a monolayer of identical spheres in a viscous medium without Brownian effects. In the absence of inertia, and under the influence of finite forces, perfectly smooth spheres will never come into contact because of the strength of the lubrication interaction. Indeed, an interaction between two spheres is perfectly reversible. However, this ideal is not achieved in practice: careful experiments with just two spheres show that some irreversible interaction occurs. We treat this interaction as a simple contact between the spheres: we assume that they are microscopically rough and have surface asperities which are too sparse to affect the hydrodynamics of the system, but which prevent the particles from approaching beyond some nominal surface separation. For a dilute suspensions in steady shear flow, a calculation to order c(2) in the particle area concentration shows that roughness actually lowers the viscosity of the suspension relative to its value for smooth spheres; this is because the excluded parts of configuration space are those with very close particles, where the lubrication layers cause high dissipation. Negative normal stress differences are also introduced by the roughness. At higher concentrations we use Stokesian Dynamics to simulate the suspension dynamics. We find that rough- ness increases the viscosity above an area concentration of around 40% and the normal stress differences be- come very sensitive to particle configuration, and fluctuate strongly with time.
Description: This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.
URI: http://bura.brunel.ac.uk/handle/2438/9466
ISBN: 978-1-908549-16-7
Appears in Collections:Brunel Institute for Bioengineering (BIB)
The Brunel Collection

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