Break up of nano-particle clusters in high-shear devices

Formulation of stable nano-suspensions by breaking up nano-particle clusters is considered. Two devices of practical importance are investigated: the Silverson 150/250MS rotor-stator mixer and the high-pressure nozzle disintegrator. The main part of the work is related to model formulation and simulation of the processes of disintegration of Aerosil 200 V agglomerates in both systems. The population balance modelling is applied to account for effects of breakage and restructuring of aggregates on their size distribution. Effects of resulting structure of aggregated suspension on its rheology and details of the flow are simulated as well. Effects of the flow on creation of local stresses include hydrodynamic stresses and stresses generated by cavitation. Population balances are solved using the QMOM that is linked to the CFD code FLUENT. Results of numerical simulations show that the high-pressure system is more efficient than the rotor-stator device; one pass through the high-pressure system gives better disintegration than several passes through the rotor-stator. This may result from the fact that in the high-pressure system disintegration results from both: hydrodynamic stresses and effects of cavitation, whereas, in the case of the rotor-stator mixer only hydrodynamic stresses are active. Simulations are based on models validated earlier by comparison with experimental data. (C) 2007 Elsevier B.V. All rights reserved.