What is bubble flow?

• A. A continuous gas phase with dispersed liquid droplets
• B. Dispersed bubbles of gas in a continuous liquid phase
• C. A homogeneous gas-liquid mixture
• D. A single bubble rising in liquid

Answer: (B)

Bubble flow means gas exists as many discrete bubbles dispersed within a liquid that acts as the continuous phase. The bubbles rise through the liquid due to buoyancy, and the liquid forms the surrounding matrix through which they move. This is different from a situation where the gas would be the continuous phase with liquid droplets dispersed in it (that would be a mist or spray rather than bubbles), or from a truly single-phase mixture where gas and liquid are not separated into distinct phases, or from having only one bubble with nothing else of interest in the flow. Bubble flow is common in aeration and reactor processes, where bubble size, rise speed, and how densely the bubbles occupy the volume (void fraction) govern the behavior of the system.