In annular flow, which describes the flow pattern?

In annular flow, which describes the flow pattern?

• A. Gas becomes the continuous phase with liquid droplets entrained in the gas.
• B. Liquid forms a continuous core with gas pockets dispersed around it.
• C. Gas becomes the continuous phase, with liquid flowing in an annulus coating the surface of the pipe and droplets entrained in the gas phase.
• D. Gas and liquid separate with a clear, unmixed interface.

Answer: (C)

In annular flow the gas is the continuous phase, while the liquid forms a thin film that coats the pipe wall. As the gas flows, it drags the liquid along the inner surface, creating an annular liquid film around the circumference, and droplets are carried within the flowing gas. This combination—a liquid film on the wall with droplets entrained in the gas—captures the characteristic pattern of annular flow. The other descriptions don’t fit this pattern: having liquid as a continuous core with gas pockets around it describes a different regime, not annular flow; a clear unmixed interface with complete separation describes stratified or segregated flow; and gas with liquid droplets in the gas without the wall film resembles a mist or dispersed regime rather than annular flow.

In annular flow the gas is the continuous phase, while the liquid forms a thin film that coats the pipe wall. As the gas flows, it drags the liquid along the inner surface, creating an annular liquid film around the circumference, and droplets are carried within the flowing gas. This combination—a liquid film on the wall with droplets entrained in the gas—captures the characteristic pattern of annular flow.

The other descriptions don’t fit this pattern: having liquid as a continuous core with gas pockets around it describes a different regime, not annular flow; a clear unmixed interface with complete separation describes stratified or segregated flow; and gas with liquid droplets in the gas without the wall film resembles a mist or dispersed regime rather than annular flow.