Flow regime identification in a dual impeller gas-liquid stirred tank reactor using time-series analysis of radioactive particle tracking data

Abstract

Accurate characterization of flow regimes in gas–liquid stirred tank reactors (STRs) is critical for the design, scale-up, and optimization of multiphase mixing systems. This study investigates three-dimensional liquid flow fields in a lab-scale dual impeller gas–liquid STR (T = 0.19 m), equipped with radial and mixed flow impellers. A non-invasive Radioactive Particle Tracking (RPT) technique was used to capture detailed flow behavior under varying operating conditions. Velocity vector plots, mean liquid velocity, and turbulent kinetic energy (TKE) profiles were analyzed to evaluate the hydrodynamic influence of impeller configuration and impeller spacing. To further understand the chaotic nature of the flow, time-series data from the tracked particle were processed, using Kolmogorov entropy, following the approach of Nedeltchev et al. (2003) for bubble columns. This entropy based method enabled identification of flow regimes across different impeller speeds and superficial gas velocities, and impeller-to-impeller spacing to impeller diameter ratio (S/D). Additionally, the individual contributions of the lower and upper impellers to local Kolmogorov entropy were assessed, revealing their distinct roles in flow and bubble dispersion. The integration of RPT measurements with Kolmogorov entropy analysis provides a robust framework for understanding complex flow patterns and enhancing hydrodynamic design in dual impeller STRs.