Hydrodynamic Regulation and Gas–Liquid Mass Transfer in a Spatially Configured Multiscale Bubble Distributor

An experimental investigation was conducted in a bubble column to clarify how bubble-source composition and spatial configuration regulate multiscale bubble dynamics and gas–liquid mass transfer. A combined bubble distributor containing different pore-size generators and adjustable vertical arrangements was developed to regulate bubble-source composition and spatial configuration. The final bubble size was found to result from continuous generation, transport, collision/coalescence, and size redistribution rather than from sparger pore size alone. Small- and large-scale bubbles exhibited clearly differentiated hydrodynamic characteristics; in particular, the Weber number of large-scale bubbles ranged from 0.44 to 2.02, indicating a stronger competition between inertia and surface tension and a greater potential for interfacial renewal. Convex configurations generally favored large-scale-bubble transport, whereas concave configurations enhanced small-scale-bubble retention and interfacial-area preservation. The experimental results demonstrate that mass-transfer enhancement arises from the coordinated balance between bubble-population structure and hydrodynamic renewal rather than from maximizing a single bubble parameter.