In which region does surface dry-out occur, leading to film boiling?

In which region does surface dry-out occur, leading to film boiling?

• A. Film Boiling
• B. Transition Boiling
• C. Nucleate Boiling
• D. Convective Boiling

Answer: (A)

Dry-out of the surface happens when the liquid can no longer wet the hot surface and a continuous vapor layer forms between them. That vapor blanket insulates the surface and keeps it effectively dry from the liquid, which is the defining feature of film boiling. As heat flux climbs from nucleate boiling, boiling becomes unstable and the surface temperature rises in transition boiling; once the vapor layer becomes continuous, you enter film boiling. In this regime, heat transfer is dominated by the vapor film (and radiation), and direct liquid contact is largely eliminated. The other regimes involve varying degrees of liquid touching the surface, so they don’t produce the sustained dry surface characteristic of film boiling.

Dry-out of the surface happens when the liquid can no longer wet the hot surface and a continuous vapor layer forms between them. That vapor blanket insulates the surface and keeps it effectively dry from the liquid, which is the defining feature of film boiling. As heat flux climbs from nucleate boiling, boiling becomes unstable and the surface temperature rises in transition boiling; once the vapor layer becomes continuous, you enter film boiling. In this regime, heat transfer is dominated by the vapor film (and radiation), and direct liquid contact is largely eliminated. The other regimes involve varying degrees of liquid touching the surface, so they don’t produce the sustained dry surface characteristic of film boiling.