Assessment of the effective viscous dissipation for deagglomeration processes induced by a high shear impeller in a stirred tank

摘要

A ring-style high shear impeller Hockmeyer (R) type (HockD-2R) of practical importance (Hockmeyer (R) Equipment Corp. D-Blade), commonly used in the paint and coatings industry to rapidly break lumps of powdery material in a liquid was investigated, and its performance compared against the classical Rushton turbine (RT). A numerical and experimental study in an unbaffled tank, operating in the laminar to transitional flow regime (50 <= Re <= 125) was carried out. Simulations were conducted using commercial Computational Fluid Dynamics (CFD) solver ANSYS Fluent 14.5. Local hydrodynamics (velocity vectors and viscous dissipation), averaged viscous dissipation values and pumping capacities, obtained from simulations, were firstly used to compare the impeller's performance. After that, experiments were performed to investigate the influence of the viscous dissipation on the amount of fines generation from mineral powders. It was found that the volume swept by the blades is the region of maximum effective viscous dissipation, considering its effects on breakage of particle agglomerates. Further experiments were conducted to investigate the influence of the power input on the powder dispersion efficiency. At the same power draw and higher speeds, the HockD-2R was found to be more efficient than the RT for fine aggregates production. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.