COAGULATION AND FRAGMENTATION - UNIVERSAL STEADY-STATE PARTICLE-SIZE DISTRIBUTION

A population balance model presented describes simultaneous coagulatio n and fragmentation during shear-induced flocculation. Given sufficien t time, a floc-size distribution reaches steady state that reflects th e balance between coagulation and fragmentation. The model agrees with experimental data for the evolution of the average floc size. Higher shear shifts the steady-state size distribution to smaller sizes. When the steady-state size distributions obtained at various shear rates a re scaled with the average flee size, however, they collapse onto a si ngle line. This indicates that the steady-state floc-size distribution is self-preserving with respect to fluid shear. This distribution is universal for the employed coagulation and fragmentation rates provide d that less than 5% (by number) of the particles remain unflocculated. This result is supported with experimental data on shear-induced floc culation of polystyrene particles, although a detailed quantitative co mparison is limited by the irregular structure of the flocs.