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 smallscale 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.

Exploration of Multishafts Stirred Reactors: An Investigation on Experiments and Large Eddy Simulations for Turbulent Chaos and Mixing Characteristics

“…These issues collectively contribute to a decrease in both transport and reaction efficiency. 15 Traditional methods for enhancing mixing efficiency primarily revolve around the design of impellers, the geometric configuration of the tank, fluid properties, and operational conditions. The choice of impeller type, size, quantity, and rotational speed significantly influences the flow field structure and mixing performance.…”

“…Furthermore, single-shaft stirred reactors face additional challenges, including substantial flow velocity gradients, rapid energy dissipation, and a susceptibility to phenomena such as “columnar recirculation” or “trailing vortices”. These issues collectively contribute to a decrease in both transport and reaction efficiency . Traditional methods for enhancing mixing efficiency primarily revolve around the design of impellers, the geometric configuration of the tank, fluid properties, and operational conditions.…”

Study of fluid turbulence characteristics and structural evolution in a reciprocating mixing tank

“…In addition, single-axis stirred reactors face additional challenges, including significant flow gradients, rapid energy dissipation, and sensitivity to phenomena such as "column recirculation" or "trailing vortices". At the same time, long cycle times lead to the formation of "isolated mixing regions (IMR)" 3,[9][10][11][12] . Together, these issues result in decreased transport and reaction efficiencies between reactants.…”

Proper orthogonal decomposition modal analysis in a baffled stirred tank: a base tool for the study of structures

“…During the last two decades or so, the POD procedure has been implemented for the study of stirred tanks in transitional (see e.g. Charalambidou, Micheletti, & Ducci, 2023; Fan et al., 2022; Hasal, Montes, Boisson, & Fořt, 2000; Raju, Balachandar, Hill, & Adrian, 2005) and turbulent (see e.g. de Lamotte, Delafosse, Calvo, & Toye, 2018; Doulgerakis, Yianneskis, & Ducci, 2011; Hasal et al., 2000; Moreau & Liné, 2006; Raju et al., 2005) flow regimes.…”