Amazing leidenfrost effect



Johann Gottlieb Leidenfrost (November 27, 1715 – December 2, 1794) was a German doctor and theologian who first described the scientific phenomenon  named the Leidenfrost effect.
The effect Leidenfrost described is a phenomenon in which a liquid, in near contact with a mass significantly hotter than its boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly. It is most commonly seen when cooking; one sprinkles drops of water in a skillet to gauge its temperature. If the skillet's temperature is at or above the Leidenfrost point, the water skitters across the metal and takes longer to evaporate than it would in a skillet that is hot, but at a temperature below the Leidenfrost point. It has also been used in some dangerous demonstrations, such as dipping a wet finger in molten lead or blowing out a mouthful of liquid nitrogen, both enacted without injury to the demonstrator.

The Leidenfrost point signifies the onset of stable film boiling. It represents the point on the boiling curve where the heat flux is at the minimum and the surface is completely covered by a vapor blanket. Heat transfer from the surface to the liquid occurs by conduction and radiation through the vapor.  As the surface temperature is increased, radiation through the vapor film becomes more significant and the heat flux increases with increasing excess temperature.


Leidenfrost effect is the reason why the sprinkled water drops skitters on a hot cooking pan, the liguid nitogen floats above the ground when spilled,and many more.It also  has a variety of usage and can be used for levitating small objects on a hot surface by means of vapour. 


References:Wikipedia

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