Featured Research

from universities, journals, and other organizations

Better way to shed water: Lubricated, nanotextured surfaces boost performance of condensers in power and desalination plants

Date:
October 22, 2012
Source:
Massachusetts Institute of Technology
Summary:
Condensers are a crucial part of today's power generation systems: About 80 percent 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 holds the promise of significantly boosting the performance of such condensers.

On a surface patterned with tiny pillars (white squares), and with a coating of a lubricant liquid that fills the spaces between the pillars, dome-shaped droplets of water condense but remain free to move quickly across the surface, unlike on conventional flat surfaces or ones with just the patterning, where they tend to stay stuck in place. The new surface treatment could provide a significant boost for power plants, water desalination and other applications.
Credit: Image courtesy of the Varanasi Laboratory

Condensers are a crucial part of today's power generation systems: About 80 percent 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 postdoc Sushant Anand; Kripa Varanasi, the Doherty Associate Professor of Ocean Utilization; and graduate student Adam Paxson, postdoc 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."

The amount of lubricant required is minimal: It forms a thin coating, and is securely pinned in place by the posts. Any lubricant that is lost is easily replaced from a small reservoir at the edge of the surface. The lubricant can be designed to have such low vapor pressure that, Varanasi says, "You can even put it in a vacuum, and it won't evaporate."

Another advantage of the new system is that it doesn't depend on any particular configuration of the tiny textures on the surface, as long as they have about the right dimensions. "It can be manufactured easily," Varanasi says. After the surface is textured, the material can be mechanically dipped in the lubricant and pulled out; most of the lubricant simply drains off, and "only the liquid in the cavities is held in by capillary forces," Anand says. Because the coating is so thin, he says, it only takes about a quarter- to a half-teaspoon of lubricant to coat a square yard of the material. The lubricant can also protect the underlying metal surface from corrosion.

Varanasi plans further research to quantify exactly how much improvement is possible by using the new technique in powerplants. Because steam-powered turbines are ubiquitous in the world's fossil-fuel powerplants, he says, "even if it saves 1 percent, that's huge" in its potential impact on global emissions of greenhouse gases.

The new approach works with a wide variety of surface textures and lubricants, the researchers say; they plan to focus ongoing research on finding optimal combinations for cost and durability. "There's a lot of science in how you design these liquids and textures," Varanasi says.

Daniel Beysens, research director of the Physics and Mechanics of Heterogeneous Media Laboratory at ESPCI in Paris, says the concept behind using a lubricant liquid trapped by a nanopatterned surface, is "simple and beautiful. The drops will nucleate and then slide down quite easily. And it works!"

That further research will be aided by a new technique Varanasi has developed in collaboration with researchers including Konrad Rykaczewski, an MIT research scientist currently based at the National Institute of Standards and Technology (NIST) in Gaithersberg, Md., along with John Henry Scott and Marlon Walker of NIST and Trevan Landin of FEI Company. That technique is described in a separate paper also just published in ACS Nano.

For the first time, this new technique obtains direct, detailed images of the interface between a surface and a liquid, such as droplets that condense on it. Normally, that interface -- the key to understanding wetting and water-shedding processes -- is hidden from view by the droplets themselves, Varanasi explains, so most analysis has relied on computer modeling. In the new process, droplets are rapidly frozen in place on the surface, sliced in cross-section with an ion beam, and then imaged using a scanning electron microscope.

"The method relies on preserving the geometry of the samples through rapid freezing in liquid-nitrogen slush at minus 210 degrees Celsius [minus 346 degrees Fahrenheit]," Rykaczewski says. "The freezing rate is so fast (about 20,000 degrees Celsius per second) that water and other liquids do not crystalize, and their geometry is preserved."

The technique could be used to study many different interactions between liquids or gases and solid surfaces, Varanasi says. "It's a completely new technique. For the first time, we're able to see these details of these surfaces."

The enhanced condensation research received funding from the National Science Foundation (NSF), the Masdar-MIT Energy Initiative program, and the MIT Deshpande Center. The direct imaging research used NIST facilities, with funding from an NSF grant and the Dupont-MIT Alliance.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by David L. Chandler, MIT News Office. Note: Materials may be edited for content and length.


Journal Reference:

  1. Sushant Anand, Adam T. Paxson, Rajeev Dhiman, J. David Smith, Kripa K. Varanasi. Enhanced Condensation on Lubricant-Impregnated Nanotextured Surfaces. ACS Nano, 2012; 121010154020005 DOI: 10.1021/nn303867y

Cite This Page:

Massachusetts Institute of Technology. "Better way to shed water: Lubricated, nanotextured surfaces boost performance of condensers in power and desalination plants." ScienceDaily. ScienceDaily, 22 October 2012. <www.sciencedaily.com/releases/2012/10/121022142210.htm>.
Massachusetts Institute of Technology. (2012, October 22). Better way to shed water: Lubricated, nanotextured surfaces boost performance of condensers in power and desalination plants. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2012/10/121022142210.htm
Massachusetts Institute of Technology. "Better way to shed water: Lubricated, nanotextured surfaces boost performance of condensers in power and desalination plants." ScienceDaily. www.sciencedaily.com/releases/2012/10/121022142210.htm (accessed July 28, 2014).

Share This




More Matter & Energy News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins