Two-Dimensional Simulation of the Breakup Process of Aggregates in Shear and Elongational Flows.

A modified discrete element method in which the hydrodynamic contribution is taken into account is proposed to simulate the deformation and breakup process of coagulated particles in two-dimensional shear and elongational flows. The simulation was performed for aggregates of various sizes, constitutive particles and fractal dimensions, and the followings were found: (i) the average number of particles in broken fragments <i> is related with the intensity of flow field Gamma by <i> ~ Gamma-P, where the value of P for aggregates of fractal dimension 1.8 is about 0.86 in the shear flow and about 1.0 in the elongational flow, (ii) aggregates are fragmented in the same fashion if their fractal dimension is the same, and a scaling law for fragmentation will hold if their fractal dimension, particle number and ratio of the minimum gap between neighboring particles to the particle size are the same among aggregates, (iii) aggregates in flow fields are broken by splitting into the smaller fragments but not by eroding particles one by one from their surface, and (iv) the elongational flow is more effective to break up aggregates than the shear flow under usual flow conditions. Copyright 1998 Academic Press.