## Leidenfrost Effect

July 21, 2020 by Aaruni Kaushik

Can you heat water so quickly, that it refuses to boil? If you think not, I have some news for you!

Enter Dr Johann Gottlob Leidenfrost. In 1756, Dr Leidenfrost wrote the book De Aquae Communis Nonnullis Qualitatibus Tractatus. In the book, he recorded over a hundred properties relating to the behaviour water, including the property later dubbed as the Leidenfrost Effect.

The effect in itself is simple to explain, and fascinating to observe. When cool water touches a surface much hotter than its boiling point, some of the water is immediately turned into steam. This steam forms a layer of insulation between the hot surface and the cool water, significantly slowing down the heat transferred to the cool water. When this happens, the water appears to simply float over the hot surface.

The temperature above which this effect is observed is called the Leidenfrost point. This temperature is not easily calculable. A rough estimate for the Leidenfrost point of water is around 193°C . In an experiment, a drop of water that was vaporized almost immediately at 168°C persisted for 152 seconds at 202°C.

The droplets of liquid on a surface can be directed to move in different directions by varying the temperature and texture of the heated surface at different places. This can have practical applications, like designing a thermostat with no moving rigid parts. Or just, designing a fun maze to watch water run around!

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Post written by Aaruni Kaushik

Aaruni is currently pursuing his master's course in mathematics at Technische Universität Kaiserslautern. An avid reader of trivia and a techno enthusiast in his spare time, he occasionally also writes on a variety of topics. His personal blog can be found here.