Numerical simulation of drag coefficient and hydrodynamics of bubbly flow in two-scale bubble column

Bubbly flow inside a lab-scale bubble column reactor with continuous air feedstock is numerically predicted by presenting the two-fluid model approach coupled with the RNG k–ε method in which the motion of the gas and liquid phases are tracked in the Eulerian–Eulerian frameworks. After validation, the visualization of the hydrodynamics and drag coefficient to bubble diameter ratio (Cd/db) is analyzed, together with the comprehensive discussion of the impacts of the inter-phase interaction forces, apparatus geometrics, and operating parameters. The results indicate that considering both drag and lift forces simultaneously provides improved simulation accuracy, especially in the lower portion of the apparatus. The value of Cd/db increases with increasing height to depth (H/D) ratio of the bubble column. Increasing sparger numbers intensifies liquid circulation but slightly decreases gas holdup. Larger bubbles suppress stagnation zones and improve mixing efficiency. The normalized drag coefficient Cd/db increases with both gas superficial velocity and column aspect ratio, reflecting stronger bubble–liquid momentum coupling under enhanced aeration. Insights into the properties of multiphase interactions in reactors provide a theoretical basis for optimizing fluid dynamics in industrial processes.