Issue
EPL
Volume 83, Number 6, September 2008
Article Number 64001
Number of page(s) 6
Section Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
DOI http://dx.doi.org/10.1209/0295-5075/83/64001
Published online 09 September 2008
EPL, 83 (2008) 64001
DOI: 10.1209/0295-5075/83/64001

Intriguing viscosity effects in confined suspensions: A numerical study

Y. Davit and P. Peyla

Laboratoire de Spectrométrie Physique, Université Joseph Fourier - Grenoble 1, BP87, F-38402 Saint Martin d'Hères, France, EU

philippe.peyla@ujf-grenoble.fr

received 6 May 2008; accepted in final form 4 August 2008; published September 2008
published online 9 September 2008

Abstract
The effective viscosity of dilute and semi-dilute suspensions in a shear flow in a microfluidic configuration is studied numerically. The suspension is composed of monodisperse and non-Brownian hard spherical buoyant particles confined between two walls in a shear flow. An abrupt change of the viscosity behaviour occurs with strong confinements: when the wall-to-wall distance is below five times the radius of the particles, we obtain a change of the sign of the contribution of the hydrodynamic interactions to the effective viscosity. This effect is the macroscopic counterpart of the peculiar micro-hydrodynamics of confined suspensions due to the influence of walls. In addition, for higher concentrations (above 25%), we find that the viscosity meets a minimum when the inter-wall distance is around five times the sphere radius. This phenomenon is reminiscent of the Fahraeus-Lindqvist effect for blood confined in small capillaries. However, we show that for sheared confined semi-dilute suspensions, the physical origin of this minimum is not due to a migration effect but to the change of hydrodynamic interactions.

PACS
47.57.E- - Suspensions.
47.57.Qk - Rheological aspects.
47.11.-j - Computational methods in fluid dynamics.

© EPLA 2008