Jumping Droplets

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Condensation, which removes heat by changing a vapor into a liquid, is a common feature in industrial heat transfer. When droplets form on surfaces, they typically have to grow to millimeter size before gravity causes them to slide off and open up the surface to new droplet formation. Hydrophobic surfaces can shed droplets a little sooner. Droplets only 100 micrometers in size will spontaneously jump off hydrophobic surfaces due to the release of excess surface energy during droplet coalescence, but this only happens when those droplets have a small contact area with the surface. Defects in the nanoscale structure of the surface can allow water to squeeze in between posts and hold on.

To counter this, new experiments packed copper nanowires into a dense 3D array. This permits fewer defects and helps condensing droplets leap from the surface sooner. Each droplet carries away a bit of the surface’s heat. The new method is impressively efficient at it. Researchers found the new heat exchanger could remove 100% more heat than previous hydrophobic designs. (Video credit: Science; research credit: R. Wen et al.)

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