Which flow regime is characterized by bulk boiling occurring but bubbles are NOT yet coalescing?

• A. Bubble Flow
• B. Slug Flow
• C. Subcooled Boiling
• D. Mist Flow

Answer: (A)

Bubbly flow is the pattern where many small vapor bubbles are dispersed throughout the liquid, produced by bulk boiling, yet the bubbles remain separate and do not coalesce into larger gas pockets. This regime shows vapor generation throughout the liquid volume with discrete bubbles rising, rather than a continuous gas phase or large gas slugs forming.

This differs from mist flow, where vapor carries liquid droplets; from slug flow, where large gas pockets dominate and coalesce into long slugs; and from subcooled boiling, which occurs mainly near the heated surface with little bulk vapor in the liquid.