Dynamic settling of particles in shear flows of shear-thinning fluids

L. H. Childs, A. J. Hogg, D. Pritchard

Research output: Contribution to journalArticle

1 Citation (Scopus)
39 Downloads (Pure)

Abstract

Dynamic settling is the phenomenon whereby a relatively dense particle settles through a sheared flow of a non-Newtonian fluid at a speed that depends on the shear rate of the background flow. This means that due to the non-linear rheology, the settling velocity may vary spatially and temporally as the background shear rate of the suspending fluid varies, an effect which does not occur in Newtonian fluids. In this contribution, the consequences of this dependency are explored for a dilute suspension of particles released uniformly from a source in a sustained and externally-driven flow of shear-thinning fluid. It is shown theoretically that the concentration field does not remain uniform, but evolves downstream, allowing calculation of the runout length, settling times and distribution of the deposited particles. Flows with a velocity maximum are demonstrated to affect the concentration field very strongly as they develop a ‘kinematic barrier’ over which settling times are considerably lengthened. Flows with bidisperse suspensions are shown to produce deposits that vary non-monotonically in thickness and composition with distance downstream, an effect which is solely due to dynamic settling. Finally flows of viscoplastic fluids which exhibit yielded and unyielded regions may accentuate the role and effects of the kinematic barrier to settling.
Original languageEnglish
Pages (from-to)83-94
Number of pages12
JournalJournal of Non-Newtonian Fluid Mechanics
Volume235
Early online date26 Jul 2016
DOIs
Publication statusE-pub ahead of print - 26 Jul 2016

Fingerprint

Shear Thinning
shear thinning
Shear thinning
settling
Shear flow
Shear Flow
shear flow
Fluid
Fluids
fluids
Shear deformation
Suspensions
Kinematics
Vary
kinematics
Viscoplastic Fluid
Rheology
shear
Flow of fluids
Deposits

Keywords

  • particle settling
  • suspensions
  • deposits
  • shear thinning
  • viscoplastic
  • shear flows
  • dynamic settling
  • non-Newtonian fluids
  • settling velocity

Cite this

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title = "Dynamic settling of particles in shear flows of shear-thinning fluids",
abstract = "Dynamic settling is the phenomenon whereby a relatively dense particle settles through a sheared flow of a non-Newtonian fluid at a speed that depends on the shear rate of the background flow. This means that due to the non-linear rheology, the settling velocity may vary spatially and temporally as the background shear rate of the suspending fluid varies, an effect which does not occur in Newtonian fluids. In this contribution, the consequences of this dependency are explored for a dilute suspension of particles released uniformly from a source in a sustained and externally-driven flow of shear-thinning fluid. It is shown theoretically that the concentration field does not remain uniform, but evolves downstream, allowing calculation of the runout length, settling times and distribution of the deposited particles. Flows with a velocity maximum are demonstrated to affect the concentration field very strongly as they develop a ‘kinematic barrier’ over which settling times are considerably lengthened. Flows with bidisperse suspensions are shown to produce deposits that vary non-monotonically in thickness and composition with distance downstream, an effect which is solely due to dynamic settling. Finally flows of viscoplastic fluids which exhibit yielded and unyielded regions may accentuate the role and effects of the kinematic barrier to settling.",
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Dynamic settling of particles in shear flows of shear-thinning fluids. / Childs, L. H.; Hogg, A. J.; Pritchard, D.

In: Journal of Non-Newtonian Fluid Mechanics, Vol. 235, 26.07.2016, p. 83-94.

Research output: Contribution to journalArticle

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AU - Hogg, A. J.

AU - Pritchard, D.

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AB - Dynamic settling is the phenomenon whereby a relatively dense particle settles through a sheared flow of a non-Newtonian fluid at a speed that depends on the shear rate of the background flow. This means that due to the non-linear rheology, the settling velocity may vary spatially and temporally as the background shear rate of the suspending fluid varies, an effect which does not occur in Newtonian fluids. In this contribution, the consequences of this dependency are explored for a dilute suspension of particles released uniformly from a source in a sustained and externally-driven flow of shear-thinning fluid. It is shown theoretically that the concentration field does not remain uniform, but evolves downstream, allowing calculation of the runout length, settling times and distribution of the deposited particles. Flows with a velocity maximum are demonstrated to affect the concentration field very strongly as they develop a ‘kinematic barrier’ over which settling times are considerably lengthened. Flows with bidisperse suspensions are shown to produce deposits that vary non-monotonically in thickness and composition with distance downstream, an effect which is solely due to dynamic settling. Finally flows of viscoplastic fluids which exhibit yielded and unyielded regions may accentuate the role and effects of the kinematic barrier to settling.

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