Effect of shear rate on aggregate size and morphology investigated under turbulent conditions in stirred tank

Miroslav Soos, Amgad S. Moussa, Lyonel Ehrl, Jan Sefcik, Hua Wu, Massimo Morbidelli

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130 Citations (Scopus)

Abstract

Aggregation and breakage of aggregates produced from fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tank. Detailed investigation of the initial kinetics showed that the collision efficiency, alpha, depends on the shear rate G according to alpha proportional to G(-b), with a power law exponent, b, equal to 0.18. After steady state was reached the dynamic response of the system on a change in stirring speed and solid volume fraction was investigated. It was found that the steady-state values of two measured moments of the cluster mass distribution (CMD) are fully reversible upon a change in stirring speed. This indicates that although the moments of CMD at steady-state depend on the applied shear rate, the aggregate structure is independent of the shear rate in the given range of stirring speeds. This was proved by independent measurement of the fractal dimension, d(f), using image analysis which provided a df equal to 2.62 +/- 0.18 independent of applied stirring speed. The critical aggregate size, below which breakage is negligible, determined by dilution experiments was consequently used to evaluate the aggregate cohesive force holding the aggregate together, which was found to be independent of the aggregate size and equal to 6.2 +/- 1.0 nN.
Original languageEnglish
Pages (from-to)577-589
Number of pages13
JournalJournal of Colloid and Interface Science
Volume319
Issue number2
DOIs
Publication statusPublished - 15 Mar 2008

Keywords

  • aggregation
  • breakage
  • turbulent conditions
  • polystyrene particles
  • shear rate effect
  • solid volume fraction effect
  • aggregation efficiency
  • steady-state reversibility
  • aggregate morphology
  • light scattering
  • image analysis
  • aggregate cohesive force

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