Specially coated surface boils water without making bubbles

Scientists have created a surface that will allow water to boil without bubbling, which could someday help prevent bubbling explosions.
Written by Laura Shin, Contributor

After experiencing the torture of having to clean up an exploded coffee pot from the walls of a rented Italian villa, I can say that water that boils without bubbling is a godsend.

Northwestern University scientists have created a surface that allows you to boil water without it bubbling, a discovery that could help prevent bubbling explosions and someday lead to breakthroughs in anti-frost technologies, help reduce drag on ships or augment heat transfer equipment.

How it works

This specially engineered coated surface, described in the September 13 edition of Nature, can create a "vapor cushion" between the surface and a hot liquid, which prevents bubbles from being created during boiling.

The scientists based their work on a phenomenon called the Leidenfrost effect. You might have noticed that on a hot skillet, water drops will bounce across its surface. This was noticed by Johann Leidenfrost in 1756. (Hence, the name.) Why does it bounce? The water skitters on a vapor cushion, or a film of steam.

The problem is, though, that at water boiling temperature, 100 degrees Celsius, water bubbles.

In order to prevent the boiling water from bubbling, the scientists -- Neelesh A. Patankar, of Northwestern, Ivan U. Vakarelski of King Abdullah University of Science and Technology, Saudi Arabia and Derek Chan from the University of Melbourne in Australia -- coated little steel spheres with a hydrophobic coating and other water-repellant chemicals to create some roughness in addition to water repellancy. On a small scale, this roughness meant that the coated surface contained peaks and valleys that could hold a Leidenfrost vapor film.

When the steel sphere was heated to 400 degrees Celsius and then dropped into room temperature water, the Leidenfrost vapor film didn't collapse even when the water temperature was cooled to just boiling.

In the video below, the left ball is coated with a water loving material, and the ball on the right is coated with the water-repellant material. Both were heated to 700 degrees Celsius and then doppred into room temperature water: At one point in the middle of the video, the ball on the left releases a bunch of bubbles, signifying that the Leidenfrost vapor has collapsed.

“This is a dramatic result and there are many applications in which a vapor-loving, water-hating surface is beneficial,” Patankar told Northwestern News.

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via: Northwestern News

photo: screenshot

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