Shear-induced flocculation of colloidal particles in stirred tanks

Ching Ju Chin, Sotira Yiacoumi, Costas Tsouris

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Colloidal polystyrene and paramagnetic particles consisting of mixtures of polystyrene and magnetite are used to experimentally investigate flocculation kinetics in a stirred tank under turbulent shear flow. The effects of various parameters - agitation speed, solution pH, ionic strength, particle size, and particle concentration - on the flocculation rate are investigated. A trajectory model applicable for shear-flow systems is formulated to describe particle flocculation in stirred tanks. The collision efficiency of particles is obtained from the limiting trajectory of one particle moving toward another and is a function of interparticle forces and flow properties. The collision frequency is determined as a function of particle size and energy dissipation. The flocculation frequency is then determined by multiplying the collision frequency by the collision efficiency and is incorporated into a population balance model to predict the particle size evolution. Results suggest that the flocculation rate is enhanced by increasing the agitation speed, even though the collision efficiency is decreased at a higher agitation speed. It is also found that the collision rate increases and the collision efficiency decreases as the particle size ratio is increased. Results also suggest that the breakup rate of aggregates in a turbulent shear flow could be significant and may need to be included in the population balance modeling to correctly predict the evolution of particle size distribution.

Original languageEnglish
Pages (from-to)532-545
Number of pages14
JournalJournal of Colloid and Interface Science
Issue number2
StatePublished - 15 Oct 1998


  • Particle aggregation
  • Population balance equation
  • Shear flocculation
  • Trajectory analysis


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