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Article

Near-Wall Convection in a Sedimenting Suspension of fibres

Authors: Zhang, F.Z., Gustavsson, K, Dahlkild, A. A.
Document Type: Article
Pubstate: Published
Journal: AIChE Journal
Volume: 60   4253-4265
Year: 2014

Abstract

The sedimentation of a fiber suspension near a vertical wall is investigated numerically. Initially, the near-wall convection is an upward backflow, which originates from the combined effects of the steric-depleted layer and a hydrodynamically depleted region near the wall. The formation of the hydrodynamically depleted region is elucidated by a convection-diffusion investigation, in which fibers are classified according to the different directions in which they drift. For fibers with sufficiently large aspect ratio, the initial near-wall backflow keeps growing. However, the backflow reverses to downward flow at later times if the aspect ratio is small. This is due to the fiber-wall interactions which rotate fibers to such angles that make fibers drift away from the wall, inducing a dense region and a correspondingly downward flow outside the initial backflow. Moreover, the steric-depleted boundary condition is of secondary importance in the generation and evolution of the near-wall convection. © 2014 American Institute of Chemical Engineers AIChE J 60: 4253–4265, 2014