Jumping Water Droplets Could Charge Future Power Plants

It turns out that some droplets are a bit more powerful than others. Scientists have discovered that tiny water droplets that form on a superhydrophobic surface and then "jump" away carry an electric charge. The findings could lead to more efficient power plants and even result in a new way of drawing power from the atmosphere.

When droplets of water condense onto a metal surface with a specific kind of superhydrophobic coating and at least two of the droplets coalesce, they can spontaneously jump from the surface. As they do so, they release an excess surface energy. Yet scientists wanted to find out the reason for the repulsion between jumping droplets after they leave the surface.

In order to discover the reason behind this phenomenon, the researchers performed a series of experiments using a charged electrode. They found that when the electrode had a positive charge, droplets were repelled by it as well as by each other. When it had a negative charge, the droplets were drawn toward it. This showed that the effect was caused by a net positive electrical charge forming on the droplets as they jumped away from the surface.

"We found that when these droplets jump, through analysis of high-speed video, we saw that they repel one another midflight," said Nenad Miljikovic, one of the researchers, in a news release. "Previous studies have shown no such effect. When we first saw that, we were intrigued."

So what exactly happens? The charging process takes place because as droplets form on a surface, they naturally form an electric double layer--a layer of paired positive and negative charges--on their surfaces. When neighboring drops coalesce, this leads to the leap from the surface.

This particular finding has a few implications for the future. In fact, if droplets can jump from a condenser surface, which is a component at the heart of most of the world's electricity-generating power plants, they could provide a mechanism for enhancing the efficiency of heat transfer on those condensers. This, in turn, would improve overall efficiency.

Yet there's also a possible new application. By placing two parallel metal plates out in the open with one surface that has jumping droplets and another that collects them, you could potentially generate power just from condensation from the ambient air.

The findings are important for understanding how to generate power. Of course, more research will need to be conducted before this method can be used on any kind of large scale. Even so, it could be useful in the future.

The findings are published in the journal Nature Communications.