A jet of liquid can bounce off of a hot plate without ever touching it. This extension of the Leidenfrost effect 鈥� the phenomenon that allows beads of water to skitter across a scorching pan 鈥� could help improve cooling processes, like those used in things ranging from nuclear reactors to firefighting.
Though first described nearly 300 years ago, the Leidenfrost effect has only been tested with fluid droplets, not squirts of liquid. Until now.
at C么te d鈥橝zur University in France and his colleagues experimented with ethanol instead of water because it is more volatile 鈥� it vaporises more quickly. They shot a jet of the liquid, about the size of a stream of water from the faucet, onto a plate heated to between 200掳C (400掳F) and 300掳C (570掳F). The researchers varied the speed of the jet and the angle at which it hit the plate, recording the process with a high-speed camera.
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They found that jets could ricochet from the plate without touching it. This strange effect is possible because of a layer of steam that forms above the plate, cushioning the jet. But this 鈥淟eidenfrost jet鈥� did not happen in all instances. Depending on the temperature of the plate, the amount of ethanol being jetted onto it and the jet鈥檚 speed, the fluid only levitated successfully if shot from an angle steeper than 50 degrees.
Though this was tested with ethanol, Celestini says he expects that water jets would behave similarly.
The work could have implications for industrial cooling processes such as cooling nuclear reactors, says at Emory University in Atlanta, Georgia. That is because cooling hot reactors by spraying them with water becomes ineffective if some of the spray never touches the reactors鈥� surface.
at Virginia Tech says the same is true in metal production, where the Leidenfrost effect may interfere with the cooling process, which can be important for the final properties of metals. He says the effect may even be relevant for firefighting in preventing jets of water from bouncing off burning surfaces.
Physical Review Fluids
