Nanotextured surfaces improved performance of condensers

MIT researchers find that lubricated, nanotextured surfaces improved performance of condensers in power and desalination plants.

Condensers are a crucial part of today's power generation systems: About 80 per cent of all the world's powerplants use them to turn steam back to water after it comes out of the turbines that turn generators. They are also a key element in desalination plants, a fast-growing contributor to the world's supply of fresh water.

Now, a new surface architecture designed by researchers at MIT holds the promise of significantly boosting the performance of such condensers. The research is described in a paper just published online in the journal ACS Nano by MIT post-doc Sushant Anand; Kripa Varanasi, the Doherty Associate Professor of Ocean Utilisation; and graduate student Adam Paxson, post-doc Rajeev Dhiman and research affiliate Dave Smith, all of Varanasi's research group at MIT.

The key to the improved hydrophobic (water-shedding) surface is a combination of microscopic patterning - a surface covered with tiny bumps or posts just 10 micrometers (millionths of a meter) across, about the size of a red blood cell - and a coating of a lubricant, such as oil. The tiny spaces between the posts hold the oil in place through capillary action, the researchers found.

The team discovered that droplets of water condensing on this surface moved 10,000 times faster than on surfaces with just the hydrophobic patterning. The speed of this droplet motion is key to allowing the droplets to fall from the surface so that new ones can form, increasing the efficiency of heat transfer in a powerplant condenser, or the rate of water production in a desalination plant.

With this new treatment, ''drops can glide on the surface,'' Varanasi says, floating like pucks on an air-hockey table and looking like hovering UFOs - a behavior Varanasi says he has never seen in more than a decade of work on hydrophobic surfaces. ''These are just crazy velocities.''