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

Computational Fluid Dynamics Study of Flow Induced by a Grooved High‐Shear Impeller in an Unbaffled Tank

“…The study was carried out in the transitional flow regime (20 ≤ Re ≤ 133). In previous works , , it has been reported that in this flow regime the laminar model practically delivers the same predictions as a transitional flow model, but with a lower computational cost. Therefore, in this study only the laminar model was used in all simulations.…”

“…These authors defined the term effective circulating capacity as the circulating capacity that exerts a maximum shear on the material treated, and not the total circulation that the impeller induces, i.e., they refer to the circulation that forces the material to pass through the high‐shear zone induced by the impeller. As was pointed out previously, for the HockD‐2R HSI, the region of maximum effective viscous dissipation for breaking particle agglomerates is the volume swept by the blades . Thus, from the Bates and Fondy definition, the effective circulation for the HockD‐2R impeller will correspond to the liquid circulation throughout the volume swept by the blades.…”

“…The energy transferred from the impeller toward the mixture induces high‐velocity gradients on the fluid passing through this volume. This fluid acceleration induces, in turn, local high viscous dissipation (or shear) values responsible for the dispersion , .…”

“…They pointed out that it is likely that the ultimate particle size due to the breakage of particle agglomerates is mainly correlated with the energy dissipation in this region. In a later work, Ramírez‐Muñoz et al performed experiments to investigate the influence of the viscous dissipation on the amount of fines generated from mineral powders. In agreement with Ramírez‐Gómez et al , they found that, based on the effects on the breakage of particle agglomerates, the volume swept by the blades is the region of maximum effective viscous dissipation.…”

“…It is the purpose of the present study to provide a deeper understanding of the flow field induced by these impellers, and to compare their performance with existing data of HSIs operating at the same flow regime. By taking into account that viscous dissipation can be considered the energy source for particle‐size reduction in dispersion systems carried out in laminar flow , different volume regions were defined near the impeller swept volume, and average viscous dissipation corresponding to these volumes extracted from simulations were used to compare the impellers' performance. Moreover, average viscous dissipation values for each of the studied impellers were determined at different constant power draw and fluid viscosities.…”