Applied Scientific Research

, Volume 59, Issue 2–3, pp 255–268 | Cite as

Modelling the Aggregation and Break-up of Fractal Aggregates in a Shear Flow

  • Teresa Serra
  • Xavier Casamitjana


A population balance model has been proposed to describe simultaneous coagulation and fragmentation of fractal aggregates during shear-flocculation induced by means of a Couette-flow system. Given enough time, a floc-size distribution achieves the steady state, which reflects the balance between coagulation and fragmentation forces. Experimental results obtained recently show that higher shear rate values shift the steady state to smaller aggregate sizes. Also, for a fixed value of the shear rate, when the volume fraction of the particles increases, the steady state size increases if the flow is laminar, and decreases if the flow is turbulent. In order to model the fragmentation of the aggregates, a power dependence between the breakage rate coefficient and the shear rate has been proposed. The model is adjusted by using two different parameters: the effective probability of success for collisions αeff, and the break up coefficient for shear fragmentation, B′. The dependence of these two parameters on the shear rate and the volume fraction of the particles is discussed.

coagulation fragmentation shear rate concentration Couette latex 


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Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • Teresa Serra
    • 1
  • Xavier Casamitjana
    • 1
  1. 1.Department of Environmental SciencesUniversity of Girona, Campus MontiliviGironaSpain

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