Thursday, October 30, 2014 Headlines & Global News

Discovery Of Charged Particles In'Jumping' Droplets Could Make For More Efficient Power Plants (VIDEO)

By Rebekah Marcarelli r.marcarelli@hngn.com | Oct 02, 2013 02:07 PM EDT

Jumping droplets.
Jumping droplets. (Photo : MIT/ NENAD MILJKOVIC AND DANIEL PRESTON)

Researchers were surprised to find that they could create charged droplets on a metal plate.

The team noticed that water droplets that form on a superhydrophobic surface and "jump" away carry an electric charge, a Massachusetts Institute of Technology (MIT) press release reported.

The finding could help us draw energy from the environment, and could improve the function of power plants.

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Past studies have found that instead of sliding down a surface with a superhydrophobic coating because of gravity, the drops would sometimes "leap away" from the plate due to "a release of excess surface energy." The phenomenon occurs when at least two of the droplets coalesce.

"We found that when these droplets jump, through analysis of high-speed video, we saw that they repel one another midflight," MIT postdoc Nenad Miljkovic, who worked on the study, said. "Previous studies have shown no such effect. When we first saw that, we were intrigued."

The researchers performed a number of experiments on the droplets using charged electrodes. They found that when the electrode held a positive charge the droplets were repelled it and by each other. When the electrode was negatively charged the droplets were drawn towards it. The experiment confirmed that the liquid was positively charged when it "jumped" away from the surface.

The droplets obtain an "electric double layer," that is made from paired positive and negative charges, when they form on the surface. When the drops coalesce and jump from the surface "so fast that the charge separates. It leaves a bit of charge on the droplet, and the rest on the surface," Miljkovic said.

The finding that droplets can jump off condenser surfaces, which are used in power plants, "provided a mechanism for enhancing the efficiency of heat transfer on those condensers, and thus improving power plants' overall efficiency."

This new finding could improve the efficiency of the system even more. When the correct amount charge is applied to the metal plate it reduces the risk of droplets being pushed back into the condenser.

The team came up with another use for the system as well.

"[By placing two parallel metal plates out in the open, with] one surface that has droplets jumping, and another that collects them ... you could generate some power," the researchers said.

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