When water is heated in a pot, as the temperature rises to 100 degrees Celsius, the water boils and bubbles rise from the bottom and turn into water vapor, but if the pot is heated to a temperature much higher than the boiling point, a strange behavior is observed. When a drop of water is dropped into a hot pan, the water molecules break up and spread out.
Why do water droplets jump in a hot pan
Water droplets in a pan
The water droplet does not turn into steam but instead dances on the pot like a ping-pong ball. This is because the lower part of the water droplet on the overheated surface instantly turns into steam, creating an invisible vapor layer, which keeps the droplet from direct contact with the hot pot.
Since this vapor layer is weak in heat transfer, the water droplet absorbs heat very slowly and does not evaporate immediately; rather, it runs around inside the pot as friction becomes almost zero. In scientific terms, this phenomenon is called the Leidenfrost effect, first explained by the German scientist Johann Gottlob Leidenfrost in 1756, and the temperature at which this effect begins is called the Leidenfrost point.
This point depends on the nature of the liquid, the volume of the droplet, and the surface area of the container; in general, liquids with high surface area require relatively high temperatures for the Leidenfrost effect to occur. For example, in pure water and copper containers, this effect occurs at about 257 degrees Celsius, but in the case of glycerol or ordinary alcohols, it is possible at much lower temperatures. Even cryogenic substances such as liquid nitrogen (N2) exhibit the Leidenfrost effect at ordinary room temperature, because their boiling points are very low.
Using this idea, scientists have developed special thermostats and heat-insulating systems, where the movement of water droplets is used to control temperature, and the Leidenfrost effect may also play an important role in the future in protecting engine parts operating at high temperatures from overheating.
