Beyond boiling, bubbles vanish when the heat is up

Joanna Carver, reporter

You may use your kettle every day but have you ever seen what goes on inside it? Now Sander Wildeman from the University of Twente in?Enschede, the Netherlands,?and colleagues have captured its inner activity to better understand the dynamics of boiling.

To observe the process, the team built a transparent "kettle" with an open top. It was filled with ethanol instead of water: because water has a high surface tension, it would fog up the glass. The container was then heated on a hot plate at a temperature of 200??C, 120??C above the boiling point of ethanol.

The number of bubbles initially increases as the liquid boils, enhancing heat transport by dragging hot liquid upwards. But as the liquid overheats, a thin film of vapour takes shape, covering the ethanol and limiting the movement of heat. At this point, far fewer bubbles form and boiling slows down while waves periodically pulse on the surface, a condition known as the boiling crisis. The difference in density between the two layers causes this instability. "The movie shows that boiling is a complex phenomenon that involves many different mechanisms and regimes," says Wildeman.

The team is investigating boiling to see how to make the process more energy efficient, which could, for example, help improve cooling systems in nuclear power plants or steam turbines in power stations of various types.

The research was recently presented at the American Physical Society's Division of Fluid Dynamics conference in San Diego, California.

If you enjoyed this post, watch exploding bubbles create powerful jets or see how a "freeze ray" powder can create bizarre drops.

Source: http://feeds.newscientist.com/c/749/f/10897/s/2639310e/l/0L0Snewscientist0N0Cblogs0Cnstv0C20A120C120Cboiling0Ecrisis0Ekettle0Bhtml0Dcmpid0FRSS0QNSNS0Q20A120EGLOBAL0Qonline0Enews/story01.htm

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