Effect of the shear and volume fraction on the aggregation and breakup of particles

The aggregation and breakup of particles in a Couette flow system were studied for different values of the shear rate (G) and the volume fraction of particles ϕ o . After a certain time, an initial distribution of 2‐μm‐dia. latex particles achieves the steady state, reflecting the balance between coagulation and fragmentation forces. Higher G values shift the steady state to smaller aggregate sizes. For a fixed value of G, when ϕ o increases, the steady‐state size increases if the flow is laminar and decreases if the flow is turbulent. The population balance model proposed describes simultuneous coagulation and fragmentation during shear flocculation. A power dependence between the breakage rate coefficient and the shear rate was found. The model is adjusted by using two parameters: the probability of success for collisions α and the effective breakup coefficient for shear fiagmentation B' eff depends on both G and ϕ o , while α is nearly constant.