Subscribe free to our newsletters via your
. 24/7 Space News .




TECH SPACE
Bubble, bubble ... boiling on the double
by Staff Writers
Boston MA (SPX) Sep 09, 2015


Postdoc Navdeep Singh Dhillon (pictured) studies the fundamental physical mechanisms that dictate the boiling crisis phenomenon. At right is a rig for measuring the critical heat flux (CHF) of thermally saturated water boiling on thin textured substrates, which allows researchers to visualize bubbles and measure real-time spatial substrate temperatures using infrared imaging. Image courtesy Jose-Luis Olivares and MIT.

The boiling of water is at the heart of many industrial processes, from the operation of electric power plants to chemical processing and desalination. But the details of what happens on a hot surface as water boils have been poorly understood, so unexpected hotspots can sometimes melt expensive equipment and disable plants.

Now researchers at MIT have developed an understanding of what causes this extreme heating - which occurs when a value known as the critical heat flux (CHF) is exceeded - and how to prevent it. The new insights could make it possible to operate power plants at higher temperatures and thus significantly higher overall efficiency, they say.

The findings are reported this week in the journal Nature Communications, in a paper co-authored by mechanical engineering postdoc Navdeep Singh Dhillon, professor of nuclear science and engineering Jacopo Buongiorno, and associate professor of mechanical engineering Kripa Varanasi.

"Roughly 85 percent of the worldwide installed base of electricity relies on steam power generators, and in the U.S. it's 90 percent," Varanasi says. "If you're able to improve the boiling process that produces this steam, you can improve the overall power plant efficiency."

The bubbles of vapor that characterize boiling, familiar to anyone who has ever boiled water on a stove, turn out to limit energy efficiency. That's because gas - whether it's air or water vapor - is highly insulating, whereas water is a good absorber of heat. So on a hot surface, the more area that is covered with bubbles, the less efficient the transfer of heat energy becomes.

If those bubbles persist too long at a given spot, it can significantly increase the temperature of the metal underneath, since heat is not transferred away fast enough, Varanasi says - and can potentially melt part of the metal.

"This will most certainly damage an industrial boiler, a potentially catastrophic scenario for a nuclear power plant or a chemical processing unit," says Dhillon. When a layer of bubbles limits heat transfer, "locally, the temperature can increase by several thousand degrees" - a phenomenon known as a "boiling crisis."

To avoid exceeding the CHF, power plants are usually operated at temperatures lower than they otherwise could, limiting their efficiency and power output. Using textured surfaces has been known to help, but it has not been known why, or what the optimal texturing might be.

Contrary to prevailing views, the new work shows that more texturing is not always better. The MIT team's experiments, which use simultaneous high-speed optical and infrared imaging of the boiling process, show a maximum benefit at a certain level of surface texturing; understanding exactly where this maximum value lies and the physics behind it is key to improving boiler systems, the team says.

"What was really missing was an understanding of the specific mechanism that textured surfaces would provide," Buongiorno says. The new research points to the importance of a balance between capillary forces and viscous forces in the liquid.

"As the bubble begins to depart the surface, the surrounding liquid needs to rewet the surface before the temperature of the hot dry spot underneath the bubble exceeds a critical value," Varanasi says. This requires understanding the coupling between liquid flow in the surface textures and its thermal interaction with the underlying surface.

"If anything can enhance the heat transfer, that could improve the operating margin of a power plant," Varanasi says, allowing it to operate safely at higher temperatures.

By improving the overall efficiency of a plant, it's possible to reduce its emissions: "You can get the same amount of steam production from a smaller amount of fuel," Dhillon says. At the same time, the plant's safety is improved by reducing the risk of overheating, and catastrophic boiler failures.

The research was supported by Chevron Corp., the Kuwait-MIT Center for Natural Resources and the Environment, and a Shapiro fellowship from Mechanical Engineering Department. The micro-nano structured surfaces used in the study were fabricated in the Microsystems Technologies Labrotary (MTL) and at Harvard CNS.


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only


.


Related Links
Massachusetts Institute of Technology
Space Technology News - Applications and Research






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TECH SPACE
Using ultrathin sheets to discover new class of wrapped shapes
Amherst MA (SPX) Sep 02, 2015
Materials scientists seeking to encapsulate droplets of one fluid within another often use molecules like soap or micro- or nano-particles to do it. One distinct way of wrapping a droplet is to use a thin sheet that calls on capillary action to naturally wrap a droplet in a blanket of film, but because it takes some force to bend a sheet around a drop, there were thought to be limits on what can ... read more


TECH SPACE
Russia Eyes Moon for Hi-Tech Lunar Base

Russia Gets Ready for New Moon Landing

ASU chosen to lead lunar CubeSat mission

Russia's moon landing plan hindered by financial distress

TECH SPACE
ASU instruments help scientists probe ancient Mars atmosphere

What Happened to Early Mars' Atmosphere

Opportunity brushes a rock and conducts in-situ studies

Destination Red Planet: Will Billionaires Fund a Private Mars Colony

TECH SPACE
New Life for Old Buddy: Russia Tests Renewed Soyuz-MS Spacecraft

Opportunity found in lack of diversity in US tech sector

Boeing Revamps Production Facility for Starliner Flights

In Virginia, TechShop lets 'makers' tinker, innovate

TECH SPACE
Progress for Tiangong 2

China rocket parts hit villager's home: police, media

China's "sky eyes" help protect world heritage Angkor Wat

China's space exploration potential has US chasing its own tail

TECH SPACE
Russian ISS Crew's Next Spacewalk Planned for February 2016

Mogensen begins busy ISS tour

Soyuz rocket with three astronauts launches towards ISS

Soyuz Heads to Space Station with New Crew

TECH SPACE
US Navy to Launch Folding-Fin Ground Attack Rocket on Scientific Mission

US Launches Atlas V Rocket With Navy Communications Satellite After Delay

FCube facility enters operations with fueling of Soyuz Fregat upper stage

SpaceX delays next launch after blast

TECH SPACE
Earth observations show how nitrogen may be detected on exoplanets, aiding search for life

Distant planet's interior chemistry may differ from our own

Earth's mineralogy unique in the cosmos

A new model of gas giant planet formation

TECH SPACE
Billie Holiday to return to New York stage -- by hologram

Half diamond, half cubic boron, all cutting business

Customizing 3-D printing

DNA-guided 3-D printing of human tissue is unveiled




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.