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 April 18, 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 April 18, 2014).

Share This



More Matter & Energy News

Friday, April 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Small Reactors Could Be Future of Nuclear Energy

Small Reactors Could Be Future of Nuclear Energy

AP (Apr. 17, 2014) After the Fukushima nuclear disaster, the industry fell under intense scrutiny. Now, small underground nuclear power plants are being considered as the possible future of the nuclear energy. (April 17) Video provided by AP
Powered by NewsLook.com
Horseless Carriage Introduced at NY Auto Show

Horseless Carriage Introduced at NY Auto Show

AP (Apr. 17, 2014) An electric car that proponents hope will replace horse-drawn carriages in New York City has also been revealed at the auto show. (Apr. 17) Video provided by AP
Powered by NewsLook.com
Honda's New ASIMO Robot, More Human-Like Than Ever

Honda's New ASIMO Robot, More Human-Like Than Ever

AFP (Apr. 17, 2014) It walks and runs, even up and down stairs. It can open a bottle and serve a drink, and politely tries to shake hands with a stranger. Meet the latest ASIMO, Honda's humanoid robot. Duration: 00:54 Video provided by AFP
Powered by NewsLook.com
German Researchers Crack Samsung's Fingerprint Scanner

German Researchers Crack Samsung's Fingerprint Scanner

Newsy (Apr. 16, 2014) German researchers have used a fake fingerprint made from glue to bypass the fingerprint security system on Samsung's new Galaxy S5 smartphone. Video provided by Newsy
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