Water-repellent balls make liquid boil with no bubbles

IMAGINE water boiling without bubbling. Although the effect has been achieved before, a new version allows water to maintain its bubble-free state even as the hot materials around it cool.

The phenomenon is based on the Leidenfrost effect. If a frying pan is hot enough, droplets of water will skitter around rather than spreading into a puddle. That is because high heat evaporates enough of the water to create a vapour layer. The liquid floats on this cushion and boils without bubbling, says Neelesh Patankar of Northwestern University in Evanston, Illinois. As the surface cools, the vapour layer can collapse and the water will bubble, triggering a violent outburst.

The Leidenfrost effect is a concern in chemical plants and nuclear reactors, where liquid water touching hot metal may cause explosions.

But if hot water can be kept away from the material long enough, the team hypothesised, the vapour might stay in place past when the material cools to the boiling point of water, and there is no more explosion risk.

To test this, the team covered steel balls in a nanoparticle-based coating that gave them a rough texture (Nature, DOI: 10.1038/nature11418). They heated the balls to 400??C and submerged them in hot water.

Rather than bubbling against the scorching metal, water droplets stretched across the grooves in the rough coating and cavities beneath them filled with vapour. This kept the surrounding water undisturbed as the temperature of the balls fell all the way to 100??C.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.

Have your say

Only subscribers may leave comments on this article. Please log in.

Only personal subscribers may leave comments on this article

Subscribe now to comment.

All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.

If you are having a technical problem posting a comment, please contact technical support.

Source: http://feeds.newscientist.com/c/749/f/10897/s/235a7add/l/0L0Snewscientist0N0Carticle0Cmg215288250B0A0A0A0Ewaterrepellent0Eballs0Emake0Eliquid0Eboil0Ewith0Eno0Ebubbles0Bhtml0DDCMP0FOTC0Erss0Gnsref0Fonline0Enews/story01.htm

cpac powell the last lecture kim jong un josh powell madonna halftime show linsanity