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Barbeque hotplates-inspired discovery may make ships move faster


June 8, 2011 - Washington

Sizzling barbeque hotplates have inspired scientists to discover a new way to reduce drag of fast moving projectiles in water.

The findings could lead to more efficient pumping of fluids or help give underwater vehicles a temporary boost, said Dr Derek Chan, a professor of mathematics from the University of Melbourne.

"The genesis [of the idea] came from having a drink at the Intercontinental Hotel in Singapore," Chan told the ABC News.

He and co-author Dr Ivan Vakarelski of King Abdullah University of Science and Technology in Saudi Arabia were mulling over what happens when one throw a drop of water onto a barbeque plate.

"On a very hot plate the water does not evaporate instantaneously but stays around for a very long time," said Chan, adding the water drops appear to slide around on the hot plate.

The research was based on the 255-year-old Leidenfrost effect.

The Leidenfrost effect describes the phenomenon where a liquid produces an insulating vapour layer when it comes in contact with a solid surface that is hotter than its boiling point.

Chan and colleagues decided to turn the Leidenfrost effect 'inside out'.

Instead of dropping water onto a hot surface, they dropped a hot object into a liquid to see if the vapour layer that formed around it would reduce its drag as it moved through the water.

Chan and colleagues heated up ball bearings and dropped them into cylinders of liquid.

Instead of water they used fluorocarbon liquid, which has a relatively low boiling point of 56 degrees Celsius, making it easier to heat the solid to the desired temperature.

They used high-speed video footage to assess the drag produced from polished balls dropped into liquid. The results found that the drag on the ball is reduced to almost the minimum possible through the creating of an insulating vapour as it falls through the liquid.

"We found that it doesn't matter if the sphere rises or falls, the drag reduction is the same," said Chan.

Chan says the drag coefficient of the hot vapour-covered sphere reduced from 0.4 to 0.07. By comparison a sports car has a drag coefficient of 0.3, he said.

While the theoretical calculation of the limit to drag reduction was made in the 1960s, this is the first time it has been actually demonstrated.

The finding appears in a recent issue of Physical Review Letters.

ANI

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