Why Make Nanodroplets Drop Faster?

The condensation of water is crucial to the operation of most of the power plants that provide our electricity and it is also the key to producing potable water from salty or brackish water. MIT mechanical engineering graduate student Nenad Miljkovic discusses his team's work on condensation, nanodroplet formation, and new nanopatterned surfaces that could boost the efficiency of power plants and desalination systems.

Transcript

00:00:07 What you're seeing in this video is a highly magnified view of water droplet condensation on a cool nanostructured surface, kind of like dew formation on a cool spring morning The surface is special in that it consists of an array of very small silicon nanopillars, which are spaced two microns apart, are six microns tall, and are zero point three microns thick, or about three hundred times thinner than human hair. The pillars are chemically coated to be hydrophobic, which means water-hating. This allows the growing droplets

00:00:37 to merge and easily jump from the surface, which results in much more efficient heat transfer. If you look closely, you'll notice that some droplets are very round, and some are balloon-shaped, with a stretched neck at the bottom. The round ones form and grow on the tips of pillars, while the ballon shapes grow from inside the pillared array. What we're studying is the growth difference between these two droplet types: the faster droplets grow, the more heat they can carry away before jumping, which is

00:01:04 actually very important for many industrial applications, such as steam power plant condensers, evaporation-based desalination plants, and solar collectors. Our findings show that contrary to previous intuition, these ballon-shaped droplets are highly favorable for efficient condensation, since they grow six times faster than drops sitting on the pillar tops. In the future, we plan to leverage this new information to create highly efficient, scalable condensing surfaces.