In which region is the heat transfer mechanism unfavorable but increases with larger temperature difference?

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

Answer: (A)

In the film boiling regime, a continuous vapor layer forms between the hot surface and the liquid. That vapor film acts as an insulating barrier, so heat transfer is very poor and this mechanism is considered unfavorable. However, as the temperature difference between the surface and the liquid grows, more energy goes into generating and sustaining that vapor layer, so the rate of heat transfer through the film increases with larger temperature difference—even though it remains much lower than in nucleate boiling. This combination—unfavorable due to the insulating film, but increasing with delta T—identifies film boiling.