Break-up of nano-particle clusters in high-shear devices
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: Intensified Hydrodynamics & Structured Environments (IHSE-2)
Keywords: aggregates, agglomerates, high-shear-device, nanoparticles, suspension,
The subject of high shear dense suspension flows represents a vast field, which is characterized by a wide spectrum of different length and time scales, and a broad ranges of engineering disciplines and technological applications. In present we consider formulation of stable suspensions of nano-particles of specific rheological properties by breaking-up nano-particle clusters and stabilizing resulting suspensions. Two devices of practical importance are considered: the Silverson 150/250MS rotor-stator mixer and the high pressure nozzle disintegrator. The rotor–stator system consists of a rotor equipped with four inner blades and a stator equipped with a disintegrating head and a square hole disintegration screen. The high pressure system was equipped with a nozzle of diameter equal to 80 μm and the working pressure was as high as 2400 bar. The main part of the work is related to model formulation and model application to simulate the processes of disintegration of Aerosil 200V agglomerates in both considered systems. Accordingly the population balance modelling is applied to account for effects of breakage and restructuring of aggregates; on the other hand the structure of aggregated suspension affects suspension rheology and thus the flow. Rheological models include the effect of clustering of primary nano-particles. Effects of the flow on creation of local stresses includes hydrodynamic stresses and stresses generated by cavitation. Population balances are solved using 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: the hydrodynamic stresses and effects of cavitation, whereas in the case of the rotor-stator mixer only the hydrodynamic stresses are active. The model predictions are validated by comparison with experimental data for both systems considered.
Presented Wednesday 19, 16:00 to 16:20, in session EPIC-1: Intensified Hydrodynamics & Structured Environments (IHSE-2).
