Featured Research

from universities, journals, and other organizations

Jumping droplets take a lot of heat, as long as it comes in a cool way

Date:
January 1, 2012
Source:
Duke University
Summary:
Microscopic water droplets jumping from one surface to another may hold the key to a wide array of more energy efficient products.

Chuan-Hua Chen, foreground, and Jonathan Boreyko.
Credit: Image courtesy of Duke University

Microscopic water droplets jumping between surfaces that repel and attract moisture could hold the key to a wide array of more energy efficient products, ranging from large solar panels to compact laptop computers.

Related Articles


Duke University engineers have developed a new way of producing thermal diodes, devices which regulate heat to preferentially flow in a certain direction, effectively creating a thermal conductor in the forward direction and an insulator in the reverse direction. While thermal diodes can be made from solid materials, these solid-state diodes are not nearly as effective as "phase-change" thermal diodes that rely on vaporization and condensation to transport heat.

These phase-change diodes can transfer over a hundred times more heat in the forward direction compared to the reverse, but with major limitations -- they are dependent on gravity or restricted by a tubular configuration. These limitations severely constrain the application of phase-change thermal diodes, for example, in mobile electronics which require orientation independence or solar panels which require a large surface area.

The Duke engineers believe they have figured out a way to solve these limitations to existing thermal diodes by exploiting self-propelled water droplets, which can jump from a superhydrophobic (highly water-repellent) surface to a superhydrophilic (highly absorbent) surface, but not the other way around. The results of the Duke experiments were published online in the journal Applied Physical Letters.

Chuan-Hua Chen, assistant professor of mechanical engineering and materials science at Duke's Pratt School of Engineering, and his research group was the first to actually videotape the self-propelled jumping motion of water droplets on a superhydrophobic surface. They found that the droplets literally jumped straight up and off the surface. In their current experiments, a superhydrophilic plate was placed opposite to the superhydrophobic one, creating an asymmetry crucial for the directional transport of heat in their thermal diode.

"When the superhydrophobic surface is colder than the superhydrophilic surface, the heat transport is very effective with phase-change processes, much like sweat taking away body heat; when the superhydrophobic surface is hotter, the heat flow is blocked and the diode behaves like a double-paned window," said Chen. "Because the jumping droplets in our system are very small, gravity has negligible effect on them. Therefore, devices based on this approach can be oriented in any direction without the need to worry about gravity."

Furthermore, Chen said, this approach can be easily scalable, which means technology based on this design can be used for thermal management of devices as small as computer chips and as large as building roofs. The jumping-drop approach uniquely combines large-area scalability, orientation independence, and effective thermal rectification into one device. This combination of properties is extremely useful for thermal diodes but has remained elusive until Chen's invention.

Typical phase-change thermal diodes rely on evaporating water to transfer heat from one surface to another, with gravity pulling the subsequent condensate down to restart the cycle again. For example, these so-called thermosyphons are in use in the Alaskan oil pipeline, in order to keep the heat from the pipes from melting the permafrost.

Chen believes that this new approach could make thermal diodes more practical and effective for a variety of applications. These applications range from energy-efficient solar panels to smart "skins" of thermally adaptive buildings. For example, in the summertime a diode panel on a building could let heat escape out but prevent heat from creeping in. In space vehicles, thermal diodes can be used to regulate diurnal thermal fluctuations in the outer space, or even to harvest solar energy for powering satellites.

Chen's research is supported by the Defense Advanced Research Projects Agency. Other Duke members of the team are and Yuejun Zhao.


Story Source:

The above story is based on materials provided by Duke University. The original article was written by Richard Merritt. Note: Materials may be edited for content and length.


Journal Reference:

  1. Jonathan B. Boreyko, Yuejun Zhao, Chuan-Hua Chen. Planar jumping-drop thermal diodes. Applied Physics Letters, 2011; 99 (23): 234105 DOI: 10.1063/1.3666818

Cite This Page:

Duke University. "Jumping droplets take a lot of heat, as long as it comes in a cool way." ScienceDaily. ScienceDaily, 1 January 2012. <www.sciencedaily.com/releases/2011/12/111212124516.htm>.
Duke University. (2012, January 1). Jumping droplets take a lot of heat, as long as it comes in a cool way. ScienceDaily. Retrieved November 27, 2014 from www.sciencedaily.com/releases/2011/12/111212124516.htm
Duke University. "Jumping droplets take a lot of heat, as long as it comes in a cool way." ScienceDaily. www.sciencedaily.com/releases/2011/12/111212124516.htm (accessed November 27, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Thursday, November 27, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

NASA's First 3-D Printer In Space Creates Its First Object

NASA's First 3-D Printer In Space Creates Its First Object

Newsy (Nov. 26, 2014) The International Space Station is now using a proof-of-concept 3D printer to test additive printing in a weightless, isolated environment. Video provided by Newsy
Powered by NewsLook.com
Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Reuters - Innovations Video Online (Nov. 26, 2014) Innovative recycling project in La Paz separates city waste and converts plastic garbage into school furniture made from 'plastiwood'. Tara Cleary reports. Video provided by Reuters
Powered by NewsLook.com
Blu-Ray Discs Getting Second Run As Solar Panels

Blu-Ray Discs Getting Second Run As Solar Panels

Newsy (Nov. 26, 2014) Researchers at Northwestern University are repurposing Blu-ray movies for better solar panel technology thanks to the discs' internal structures. Video provided by Newsy
Powered by NewsLook.com
Today's Prostheses Are More Capable Than Ever

Today's Prostheses Are More Capable Than Ever

Newsy (Nov. 26, 2014) Advances in prosthetics are making replacement body parts stronger and more lifelike than they’ve ever been. 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:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

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