Incredibly Hot Balls Boil Water Without Making It Bubble, Make Nuclear Reactors Safer

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Here’s something fun you can do at home. Heat up a frying pan to a very high temperature, well over 100 degrees Centigrade. Then throw a droplet of water on it.

The droplet of water will skitter around the pan instead of evaporating instantly. What’s happening is a phenomenon called the Leidenfrost Effect: the droplet, when it hits a much hotter surface, has its underside immediately flash to vapor, creating what amounts to a little water-droplet hovercraft. The droplet floats around on a cushion of its own vapor, slowly evaporating instead of vanishing all at once.

Drop the temperature and the vapor layer disappears, meaning the droplet will flash into steam all at once, which is basically a little explosion. Look neat? It is.

It gets a bit less neat when, say, this happens to a lot of water at a nuclear reactor, which is why the seemingly silly achievement of dumping something really hot into water and not having it flash to steam is such a big deal.

Researchers at Northwestern University coated steel balls with a nanoparticle coating that gave them a rough texture, and then heated them to 400 degrees C. Then they dumped them in water.

The Leidenfrost effect kicked in and the heat flashed some water around the balls to vapor, where it filled in the valleys and crags on the balls. While the balls cooled down to water’s boiling point, the vapor kept the water from touching the steel directly, meaning it couldn’t flash to vapor all at once.

The nanoparticles mean safer nuclear reactors and chemical plants. And, hey, bubble-free boiling is a neat trick.

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Dan Seitz is a grad student and freelance writer. He currently lives in Boston.

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