Featured Research

from universities, journals, and other organizations

Altering surface textures in 'counterintuitive manner' may lead to cooling efficiency gains

Date:
November 12, 2013
Source:
American Institute of Physics (AIP)
Summary:
Researchers across the globe are racing to find ways to improve the cooling of hot surfaces -- for technologies ranging from small electronics to nuclear power plants. Zeroing in on the physics at play underlying surface phenomena, researchers made a significant breakthrough. Although somewhat counterintuitive, they discovered that by creating sparsely packed textures on surfaces rather than densely packed ones, they were able to hold droplets in place and enable cooling.

These are micrographs showing water droplets landing on specially designed silicon surfaces (top images) at different temperatures. At higher temperatures, the droplets begin to exhibit a new behavior: instead of boiling, they bounce on a layer of vapor, never really wetting and cooling the surface. At 400 C, the droplet continues to boil only on the surface that combines microscale posts with a coating of nanoscale particles (last column). These results demonstrate that this micro nano surface can be effectively cooled even at high temperatures.
Credit: K.Varanasi/MIT

Researchers across the globe are racing to find ways to improve the cooling of hot surfaces -- for technologies ranging from small handheld electronics all the way to industrial-sized applications such as nuclear power plants.

By zeroing in on the physics at play underlying surface phenomena, a team of Massachusetts Institute of Technology (MIT) and Boston University researchers made a significant breakthrough. Although somewhat counterintuitive, they discovered that by creating sparsely packed textures on surfaces rather than densely packed ones, they were able to hold droplets in place and enable cooling.

Their findings, described in Applied Physics Letters, which is produced by AIP Publishing, have the potential to enabling cooling efficiency gains in a wide variety of applications.

Worldwide, nearly 86 percent of our energy is currently derived from steam cycles. "If we're able to improve this efficiency by even 1 percent and deploy it to all of the power plants, it could have a significant impact," explains Kripa K. Varanasi, Doherty Chair in Ocean Utilization, as well as an associate professor of mechanical engineering at MIT.

Varanasi's lab is known for tailoring or modifying surfaces to significantly improve efficiency. One of their recent creations was a slippery surface coating, which is now being commercialized by a spinoff called LiquiGlide. They're commercializing a container liner that makes toothpaste and other difficult-to-remove products, such as ketchup, slide right out of their tubes and containers -- greatly reducing waste.

For this particular study, the goal was the exact opposite of creating slippery surfaces. The researchers wanted to make liquid come into direct contact with hot surfaces so cooling could occur. They began by exploring the physics of surface phenomena, because whether focusing on mass transfer, momentum transfer, energy transfer, or charge transfer, the commonality is that the transfer occurs on a surface.

"Vapor films are created beneath the droplets, which is a critical problem in boiling. Once the vapor films start forming, they act as a barrier to heat transfer because vapor has a lower thermal conductivity than liquid," Varanasi says.

In boiling, ideally the liquid will make contact with the solid. But this phenomenon has a certain threshold known as a "critical heat flux" -- once it's reached, a catastrophic event may occur. For example, in the absence of cooling fluid during an emergency situation in a nuclear power plant, a nuclear fuel rod's surface can become very hot. Pouring water on it to attempt to cool it results in the formation of a vapor film that actually interferes with cooling. As a result, droplets float on the hot surface, which is known as the "Leidenfrost effect."

To overcome the vapor film issue, Varanasi and colleagues textured surfaces using sparsely packed micron-scale structures coated with nanoparticles to create a capillary attraction effect to hold droplets in place.

"Vapor that forms as the evaporation of the droplet is able to escape through the surface texture," Varanasi explains. "Interestingly, there are two simultaneous competing forces occurring in this situation. As the vapor forms, it exerts an upward force on these droplets. And the texture pulls on the droplet with capillary attraction. This allows the liquid to come into contact with the surface and cool it."

They can engineer similar structures using a variety of materials and techniques, according to Varanasi. Right now, the team's focus is on exploring the energy, water and agriculture nexus because it's all interrelated. "We're hoping in our own humble way -- since many phenomena occur upon surfaces -- to improve them and enable big efficiencies in this nexus," he says.

Key markets that may benefit from greater cooling efficiency gains include, but aren't limited to, nuclear power plants, semiconductors and electronics, oil and gas, fire suppression, desalinization, and metallurgy.


Story Source:

The above story is based on materials provided by American Institute of Physics (AIP). Note: Materials may be edited for content and length.


Journal Reference:

  1. Hyuk-min Kwon, James C. Bird, Kripa K. Varanasi. Increasing Leidenfrost point using micro-nano hierarchical surface structures. Applied Physics Letters, 2013; 103 (20): 201601 DOI: 10.1063/1.4828673

Cite This Page:

American Institute of Physics (AIP). "Altering surface textures in 'counterintuitive manner' may lead to cooling efficiency gains." ScienceDaily. ScienceDaily, 12 November 2013. <www.sciencedaily.com/releases/2013/11/131112123325.htm>.
American Institute of Physics (AIP). (2013, November 12). Altering surface textures in 'counterintuitive manner' may lead to cooling efficiency gains. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2013/11/131112123325.htm
American Institute of Physics (AIP). "Altering surface textures in 'counterintuitive manner' may lead to cooling efficiency gains." ScienceDaily. www.sciencedaily.com/releases/2013/11/131112123325.htm (accessed July 29, 2014).

Share This




More Matter & Energy News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Climate Change Could Cost Billions, According To White House

Climate Change Could Cost Billions, According To White House

Newsy (July 29, 2014) A report from the White House warns not curbing greenhouse gas emissions could cost the U.S. billions. Video provided by Newsy
Powered by NewsLook.com
Stranded Whale Watching Boat Returns to Boston

Stranded Whale Watching Boat Returns to Boston

Reuters - US Online Video (July 29, 2014) Passengers stuck overnight on a whale watching boat return safely to Boston. Linda So reports. Video provided by Reuters
Powered by NewsLook.com
Baluchistan Mining Eyes an Uncertain Future

Baluchistan Mining Eyes an Uncertain Future

AFP (July 29, 2014) Coal mining is one of the major industries in Baluchistan but a lack of infrastructure and frequent accidents mean that the area has yet to hit its potential. Duration: 01:58 Video provided by AFP
Powered by NewsLook.com
Easier Nuclear Construction Promises Fall Short

Easier Nuclear Construction Promises Fall Short

AP (July 29, 2014) The U.S. nuclear industry started building its first new plants using prefabricated Lego-like blocks meant to save time and prevent the cost overruns that crippled the sector decades ago. So far, it's not working. (July 29) Video provided by AP
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