Heat flux will reach the DNB value again during which phenomenon?

• A. Boiling Crisis
• B. Stable Nucleate Boiling
• C. Critical Heat Flux
• D. Transition Boiling

Answer: (A)

Departure from nucleate boiling is reached when the heat flux is high enough that nucleate boiling can no longer be sustained and a continuous vapor film starts to form on the heated surface. This changeover is the boiling crisis, the moment called the critical heat flux. It marks the limit of heat removal by nucleate boiling, after which heat transfer worsens as the surface becomes insulated by vapor. So the DNB value is reached during the boiling crisis. Stable nucleate boiling stays below this limit, transition boiling occurs during the unstable shift between boiling regimes, and while the critical heat flux refers to the same limit value, the phenomenon name most directly associated with reaching DNB is the boiling crisis.