Study of trailing vortices and impeller jet instabilities of a flat blade impeller in small-scale reactors

Abstract

The design of economically feasible and profitable production processes has driven companies toward integrated continuous manufacturing by reducing working volumes and increasing operating frequencies. Thus, the development of robust small-scale devices capable of multivariate process optimization is essential. The aim of this work is to characterize the flow developed in a ml-scale stirred tank operating at intermediate Re ~3732, and assess trailing vortex stability with respect to baffle presence and size. Velocity characteristics are computed via computational fluid dynamics (CFD) and validated experimentally for an unbaffled (UB) and two baffled configurations. Proper orthogonal decomposition (POD) is used to extract dominant spatial–temporal flow features affecting the underlying flow patterns. Results show very good agreement between simulations and experiments, while POD analysis revealed the existence of highly energetic and periodic modes, linked to interactions between impeller jet and reactor walls. These modes are responsible for an impeller jet instability, which is amplified by the presence and size of baffles.