Which description best defines slug flow in two-phase gas–liquid flow inside a pipe?

Which description best defines slug flow in two-phase gas–liquid flow inside a pipe?

• A. At higher gas rates, the bubbles coalesce into larger bubbles, called Taylor bubbles, that eventually fill the entire pipe cross section. Between the large gas bubbles are slugs of liquid that contain smaller bubbles of gas entrained in the liquid.
• B. With a further increase in gas rate, the larger gas bubbles become unstable and collapse, resulting in churn flow, a highly turbulent flow pattern with both phases dispersed.
• C. At higher gas rates, gas becomes the continuous phase, with liquid flowing in an annulus coating the surface of the pipe and with liquid droplets entrained in the gas phase.
• D. The two-phase pressure gradient correlation used for any pipe orientation is Beggs and Brill.

Answer: (A)

Slug flow is defined by large gas bubbles that nearly fill the pipe cross-section (Taylor bubbles) separated by liquid slugs. Between these gas pockets, the liquid forms distinct segments, which can contain smaller gas pockets entrained in the liquid. This alternating pattern of gas-filled plugs and liquid slugs is the hallmark of slug flow as gas flow rate rises — the gas bubbles coalesce into the large Taylor bubbles and the liquid forms the separating slugs. The description that highlights Taylor bubbles filling the cross-section with liquid slugs in between best captures this regime. In contrast, churn flow describes a highly turbulent, dispersed mix of phases; annular flow has gas as the continuous phase with a liquid film around the pipe wall and droplets carried in the gas; and Beggs and Brill refers to a pressure-gradient correlation, not a flow pattern description.

Slug flow is defined by large gas bubbles that nearly fill the pipe cross-section (Taylor bubbles) separated by liquid slugs. Between these gas pockets, the liquid forms distinct segments, which can contain smaller gas pockets entrained in the liquid. This alternating pattern of gas-filled plugs and liquid slugs is the hallmark of slug flow as gas flow rate rises — the gas bubbles coalesce into the large Taylor bubbles and the liquid forms the separating slugs.

The description that highlights Taylor bubbles filling the cross-section with liquid slugs in between best captures this regime. In contrast, churn flow describes a highly turbulent, dispersed mix of phases; annular flow has gas as the continuous phase with a liquid film around the pipe wall and droplets carried in the gas; and Beggs and Brill refers to a pressure-gradient correlation, not a flow pattern description.