Role of turbulent shear rate distribution in aggregation and breakage processes

The effect of spatial flow heterogeneity on shear-induced aggregation and breakage of fine particles in turbulent flow conditions is investigated using computational fluid dynamics (CFD) and population balance modeling. The quadrature method of moments (QMOM), particularly suitable for implementation in commercial CFD codes, has been used to solve the corresponding population balance equation. QMOM is first tested and compared with alternative numerical methods (sectional/fixed-pivot methods) for a specific set of realistic operating conditions. Then QMOM is implemented in a CFD code and the effect of spatial heterogeneities on the cluster mass distribution in a Taylor-Couette vessel is investigated. Simplified models have been derived based on the separation of the timescales of mixing on one hand and of aggregation and breakage on the other and compared with the full CFD model. Guidelines for use and limitations of such models and the identification of the underlying aggregation and breakage kernels are discussed. (c) 2005 American Institute of Chemical Engineers AIChE J, 52: 158-173, 2006.