An Integrated Approach to Identify the Total Recirculation Regime for a Gas–Liquid System in an Agitated and Sparged Tank Contactor

Mass-transfer rates vary across hydrodynamic regimes in gas–liquid (G–L) systems in an agitated and sparged tank contactor (ASTC). Ideally, kinetics studies should be conducted in the total recirculation regime (TRR) representing intimate G–L contact, minimizing hydrodynamic limitations while offering optimum mass-transfer rates. Our earlier studies indicated the utility of gassed to ungassed power ratio (Pg/Pl) as a means of identifying regimes. Continuing with our efforts, we have used a combined strategy of gassed to ungassed differential pressure ratio (Δpg/Δpl) supported by Pg/Pl profiles to accurately identify the TRR and its point of transition to the flooding regime. We also demonstrate how the TRR offers an optimum interfacial area (Sopt) ideal for mass transport across the G–L interfaces. A standard ASTC of 0.25 m diameter (DT) equipped with turbine impellers and ring spargers containing 10 L or 1 × 10–2 m3 water was used for our studies. The stirring rate (N0) was varied from 1.67 to 41.67 rps for an oxygen flow rate (QG) of 7.5 NLPM or 12.50 × 10–5 Nm3 s–1 at a temperature (T) between 303 and 313 K under atmospheric pressure. This comprehensive approach offers a novel yet simple method for identifying the TRR, applicable to G–L kinetics studies in general and valuable in enhancing energy efficiency in chemical reaction engineering.