Define intermittent flow.

• A. Gas and liquid phase alternates.
• B. The two phases are separate.
• C. One phase is dispersed in the other.
• D. The flow is steady and uniform.

Answer: (A)

Intermittent flow is a two-phase flow regime in which the gas and liquid do not stay mixed as a single, steady stream. Instead, segments of the flow alternate between being dominated by gas and being dominated by liquid, so you get gas pockets followed by liquid slugs that move through the pipe. This alternating pattern means the flow is not steady or uniform and the phases take turns occupying the space as the fluid travels.

That’s why the option describing the gas and liquid phases alternating is the best match. If the phases were simply separate, you’d have a stable segregated arrangement rather than an alternation of phases over time. If one phase were dispersed in the other, you’d have a bubbly or mist-like regime with droplets or bubbles throughout, not clear alternating segments. And if the flow were steady and uniform, it would be a homogeneous mix, not intermittent.