Film boiling occurs at __________ pressure.

ANS:D - very high

Film boiling typically occurs at very high pressures. In film boiling, a vapor film forms between the heated surface and the liquid, creating a barrier that inhibits direct contact between the surface and the liquid. This phenomenon is often observed under conditions of high heat flux or when the surface temperature is significantly higher than the boiling point of the liquid. Film boiling is characterized by the formation of a stable vapor layer on the surface, which can insulate the surface from the liquid and reduce heat transfer efficiency. It is commonly encountered in high-temperature processes such as industrial boilers, nuclear reactors, and rocket engine combustion chambers.