Volume 83, Number 6, September 2008
|Number of page(s)||6|
|Section||Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics|
|Published online||09 September 2008|
Intriguing viscosity effects in confined suspensions: A numerical study
Laboratoire de Spectrométrie Physique, Université Joseph Fourier - Grenoble 1, BP87, F-38402 Saint Martin d'Hères, France, EU
Corresponding author: firstname.lastname@example.org
Accepted: 4 August 2008
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
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