What is Leidenfrost point and Pool boiling?

The Leidenfrost point is a temperature above which a liquid produces an insulating vapor layer that keeps that liquid from boiling rapidly. This is due to the Leidenfrost effect, a physical phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly.

On the other hand, pool boiling is a type of boiling that takes place when the heater is submerged in a large amount of liquid, such as a pool. The process can be divided into four stages: natural convection, nucleate boiling, transition boiling, and film boiling.

1. Natural convection: This is the initial stage where heat transfer occurs mainly through natural convection, where the fluid in contact with the heater gets heated, decreases in density and rises.

2. Nucleate boiling: As the temperature increases, boiling starts and vapor bubbles start to form. These bubbles rise to the surface and the heat transfer occurs through both convection and boiling.

3. Transition boiling: As the temperature continues to increase, a mixture of nucleate boiling and film boiling occurs. The heat transfer rate decreases in this stage.

4. Film boiling: At very high temperatures, a stable vapor film forms around the heater, which acts as an insulator and significantly reduces the rate of heat transfer. This is also known as the Leidenfrost effect.