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Long-lived and unstable modes of Brownian suspensions in microchannels

Published online by Cambridge University Press:  10 May 2012

Atefeh Khoshnood
Affiliation:
Computational Mechanics Laboratory, Department of Mechanical Engineering, Sharif University of Technology, Azadi Avenue, PO Box 11155-9567, Tehran, Iran Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544-5263, USA
Mir Abbas Jalali*
Affiliation:
Computational Mechanics Laboratory, Department of Mechanical Engineering, Sharif University of Technology, Azadi Avenue, PO Box 11155-9567, Tehran, Iran
*
Email address for correspondence: [email protected]

Abstract

We investigate the stability of the pressure-driven, low-Reynolds-number flow of Brownian suspensions with spherical particles in microchannels. We find two general families of stable/unstable modes: (i) degenerate modes with symmetric and antisymmetric patterns; (ii) single modes that are either symmetric or antisymmetric. The concentration profiles of degenerate modes have strong peaks near the channel walls, while single modes diminish there. Once excited, both families would be detectable through high-speed imaging. We find that unstable modes occur in concentrated suspensions whose velocity profiles are sufficiently flattened near the channel centreline. The patterns of growing unstable modes suggest that they are triggered due to Brownian migration of particles between the central bulk that moves with an almost constant velocity, and a highly-sheared low-velocity region near the wall. Modes are amplified because shear-induced diffusion cannot efficiently disperse particles from the cavities of the perturbed velocity field.

Type
Papers
Copyright
Copyright © Cambridge University Press 2012

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