Breakup of Fractal Flocs in a Turbulent Flow

Abstract

A simple model of the breakup of a floc in a turbulent flow is proposed by analogy with that of a droplet. In the model, the strength of a floc is expressed as a product of the cohesive force between primary particles and the number of contacts between clusters in the floc. To confirm the validity of this model, three types of polystyrene latex flocs with different fractal dimensions were broken up in the turbulent flow generated with a Rushton type agitator in a mixing vessel. The relation of the maximum diameter of the floc vs the turbulent shear stress was confirmed to obey the scaling law predicted by the proposed model. The power of the relation was also consistent with theoretical prediction.

Initial Stage Dynamics of Bridging Flocculation of Polystyrene Latex Spheres with Polyethylene Oxide

“…This can be obtained from measurement of the rate of rapid coagulation of well-defined colloidal particles. If we assume that (i) the hypothesis of isotropic turbulence proposed by Kolmogorov is applicable, (ii) the size of the collision radius is sufficiently small in comparison with the size of the smallest eddy of the turbulence, (iii) all particles move following fluid motion, (iv) all collisions lead to coagulation and coagulated flocs will never be broken up, (v) the effects of Brownian motion and sedimentation are negligibly small, (vi) the coagulation is in the early stage where most particles remain as singlets of radius a 0 , we can derive the equation for the temporal variation of the number concentration of colloidal particles (19,20), N (t), as…”

“…where A and µ denote the Hamaker constant and the viscosity of the fluid (19,20). When the collision between colloidal particles with attached polymer takes place, the collision radius effectively increases, reflecting the protruding part of the attached polymer on the colloidal surface.…”

Modeling particle-size distribution dynamics in a shear-induced breakage process with an improved breakage kernel: Importance of the internal bonds

“…S3). As the fractal dimension decreased from 3.0, 2.5 to 2.0, according to the numerical simulation results, the mean size also reduced from 115 m, 39 m to 12 m. It is well known that fractal aggregates become more porous as they increase in size [7,23,[36][37][38]. Therefore, large aggregates with a lower fractal dimension would be much weaker in structure and hence more vulnerable to shear breakage.…”

Effect of dosage strategy on Al-humic flocs growth and re-growth

“…Kobayashi et al [19] considered that, the number of cluster-cluster bond(s) and the magnitude of cohesive force dominated the breakage of a floc. The large flocs will then be broken at the points corresponding to cluster-cluster bonds, depending on the relative magnitude of the cohesive force and the applied shear force.…”