A group of researchers, operating from Massachusetts Institute of Technology (MIT), have found that water droplets that jump from a superhydrophobic surface can carry their own electrical charge. This finding could offer improved condenser systems in power plants, as well as a new means of generating electrical power.
It seems, with scientists already looking to exploit these superhydrophobic surfaces for various uses, including de-icing and condensation-based heat transfer applications, researchers are keen to explore the physics of droplet interactions upon these materials.
Specifically, the researchers found that two coalescing droplets will discharge surplus surface energy, resulting in the droplets spontaneously launching off of a superhydrophobic surface. According to the research paper, the findings of which were published in the latest issue of the journal Nature Communications, the group showed that the tiny water droplets gained a net positive charge; these charged drops then repelled one another.
Nenad Milijkovic, of MIT’s Department of Mechanical Engineering, explained how his latest study was actually an expansion of prior work that the MIT group had conducted. During Milijkovic’s research, he collected high-speed video imagery of the phenomenon, whereby charged droplets would repel each other in mid-flight.
To better appreciate the repelling mechanism, identified during the experimenter’s observations, they employed electric fields to determine the charge of the jumping droplets.
The following video adequately demonstrates the team’s observations, where an electrically charged wire is deployed to attract the jumping water droplets:
When a positively charged electrode was presented below the superhydrophobic surface, the positively charged droplets were repelled. In stark contrast, as was expected, the water was attracted to a negatively charged electrode.
Mechanism & Applications
Milijkovic describes the charging process, which occurs on the superhydrophobic surface. Two coalescing droplets on the material’s surface, will develop an electric double layer on their surface. Electric double layers consist of coupled positive and negative electric charges. The rapidity of fusion between the two drops on the surface causes a separation of charge, with a small amount of charge remaining on the jumping droplet, and the remainder on the surface.
The potential applications could be incredible. Firstly, this technique could be exploited in power plants. The jumping water droplet mechanism could be used to improve the exchange of heat in condensers within these power plants.
Surface condensers operate by condensing exhaust steam produced by a steam turbine, which is subsequently recycled as water. If a suitable charge is applied to a neighboring metal plate, scientists could force the water to jump off the cool pipes of the condenser, limiting the possibility that this water will fall back onto the condenser’s surface. This will improve the efficiency of the condenser, as more room will be cleared to permit formation of new droplets along its surface.
In addition to this, Milijkovic claims that two adjacent plates, including a capture plate and a source plate, could facilitate the generation of power, using the movement of these water droplets:
“You just need a cold surface in a moist environment… We’re working on demonstrating this concept.”
This would provide mankind with the ability to yield power, using condensation of water within the atmosphere.
Meanwhile, Johnathan Boreyko, a post doctorate at Oak Ridge National Laboratory, who remains unaffiliated with the latest study, boasts about the high quality findings. He indicates, although the afore-mentioned jumping phenomenon has been well-documented, Milijkovic’s work represents the first knowledge that they possessed a new charge.
By: James Fenner