EFFECT OF THE SHEAR AND VOLUME FRACTION ON THE AGGREGATION AND BREAKUP AT 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 fra ction of particles phi(0). After a certain time, an initial distributi on of 2-mu m-dia. latex particles achieves the steady state, reflectin g the balance between coagulation and fragmentation forces. Higher G v alues shift the steady state to smaller aggregate sizes. For a fixed v alue of G, when phi(0) increases, the steady-state size increases if t he flow is laminar and decreases if the flow is turbulent The populati on balance model proposed describes simultaneous coagulation and fragm entation during shear flocculation. A power dependence between the bre akage rare coefficient and the shear rate was found. The model is adju sted by wing two parameters: the probability of success for collisions a and the effective breakup coefficient for shear fragmentation B'(ef f) depends on both G and phi(0), while alpha is nearly constant.