In annular flow, how are the phases distributed?

• A. Gas becomes the continuous phase, with liquid droplets entrained in the gas phase
• B. Liquid becomes the continuous phase with gas pockets entrained
• C. Liquid forms a core with a gas film around the outside
• D. Phases separate with no entrainment

Answer: (A)

In annular flow, the gas moves as the continuous phase through the core of the pipe, while the liquid forms a thin film on the pipe walls. The fast gas shear also strips small droplets from that liquid film, carrying them along with the gas stream. So you have a gas-dominated flow with liquid droplets entrained in the gas phase. This is why describing the gas as the continuous phase with liquid droplets dispersed in it best matches the typical distribution.

The other pictures don’t fit the usual annular pattern: having the liquid as the continuous phase with gas pockets, a liquid core with a gas film around it, or complete separation with no entrainment would imply a different flow regime.