Study of the dispersed and flooded aeration regimes in two-phase gas-liquid stirred tanks using Positron Emission Particle Tracking

This investigation employs Positron Emission Particle Tracking (PEPT) to provide insights into the hydrodynamics and mixing behaviour of two-phase gas-liquid stirred tank systems. Using a T = 0.2 m diameter tank agitated by a standard Rushton turbine (D = C = T/3), industrially relevant superficial gas velocities (U SG = 0–1.67 cm s -1 ) are investigated across the dispersed and flooded aeration regimes in a viscous Newtonian fluid. In the dispersed regime, the impeller discharge angle is quantitatively measured for the first time, revealing a non-linear dependence on gas flow rate. In the flooded regime, impeller bypassing is evident, accompanied by a stagnation zone forming at the fluid surface and a dominant re-circulation loop that deviates significantly from the classical toroidal flow structure exhibited from a Rushton turbine. Additionally, a Lagrangian-based method is applied for the first time to assess the mixing performance of aerated systems, demonstrating that an increase in gas flow rate profoundly influences the mixing dynamics, regardless of the aeration regime. • PEPT used to study gas-liquid flow in stirred tanks at high gas flow rates. • Distinct hydrodynamic regimes imaged in flooded and dispersed aeration regimes. • Lagrangian mixing metric shows effect of aeration on mixing performance. • Power input shifts from impeller-driven to buoyancy-driven with increased gassing.