Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. Space Industry and Business News .




TECH SPACE
International team of physicists makes discovery about temperature in convection
by Staff Writers
Santa Barbara CA (SPX) Sep 19, 2012


This is Guenter Ahlers with the container used to study convection. Credit: UCSB.

An international team of physicists is working to ascertain more about the fundamental physical laws that are at work in a process known as convection, which occurs in a boiling pot of water as well as in the turbulent movement of the liquid outer core of the Earth.

The team's new finding specifies the way that the temperature of a gas or liquid varies with the distance from a heat source during convection. The research is expected to eventually help engineers with applications such as the design of cooling systems, for instance, in nuclear power plants.

Guenter Ahlers, professor of physics at UC Santa Barbara, worked with his team at the Max Planck Institute for Dynamics and Self-Organization in Goettingen, Germany, on this important discovery about turbulent convection. The results will be published in the September 7 issue of Physical Review Letters, and are available online now.

The experiments took place in a cylinder that was placed under the turret of a large pressure container. The 8-foot tall cylinder was heated at the bottom and cooled at the top. There were about 100 thermometers inside it, and it was pressurized with sulfur hexafluoride, an inert gas. Convection occurred inside the cylinder because, in the presence of gravity, the warmer gas at the bottom tends to rise to the top, while the colder gas tends to sink.

"We like sulfur hexafluoride because it is harmless - not poisonous, not chemically reacting - and because it is a heavy molecule," said Ahlers.

"A heavy molecule enables us to produce more vigorous convection with the same temperature difference. The strength of the convection is measured by a parameter called the Rayleigh number. We go to Rayleigh numbers as high as 10 to the 15 - a million billion - which is very large by our standards."

Ahlers enjoys the ability to oversee and even run the continuing experiments remotely on a computer in his office at UCSB (or anywhere else in the world), even though the laboratory is 5,000 miles away.

He explained that convection occurs naturally in astrophysics and in Earth systems. For example, the outer layer of the sun is composed of convection cells. Convection occurs in the Earth's atmosphere and oceans. The liquid iron in the outer core of the Earth undergoes vigorous convection and has Rayleigh numbers well above 10 to the 20. That convection generates the magnetic field of the Earth.

In their paper, the scientists present experimental and numerical data that show that, except for a very thin layer in the immediate vicinity of the plates, the temperature of this system varies linearly with the logarithm of the distance from the confining plates. They discovered this profile and measured it in detail.

The findings are especially intriguing because they echo an important discovery from 1930 by Theodore von Karman and Ludwig Prandtl, known as the "Law of the Wall." This discovery involved the study of a gas or liquid flowing along a wall, where its speed must be zero at the wall because of friction.

The speed of the fluid parallel to the wall increases as the distance from the wall increases. Von Karman and Prandtl showed more specifically that the speed increases linearly with the logarithm of this distance when the flow is fast enough so that the fluid becomes turbulent. This result is called the Law of the Wall and is of great importance in many engineering applications.

Ahlers compared the new findings about the way temperature varies in convection to the way speed varies with the Law of the Wall, noting that they are similar, although the precise relationship has yet to be understood.

"They behave in the same way," said Ahlers. "But just because two things look the same doesn't mean they are the same, so we still need to build the theoretical foundation that connects them. That's what makes this a very active, very exciting field, with theorists as far apart as Beijing (China), Marburg (Germany), and Twente (the Netherlands) already trying to explain the experimental results. You make an experimental discovery, and then theorists get excited. Then they start working on it, and who knows what we will have six months down the road?"

He explained how the Law of the Wall is of importance in engineering applications. "Pumping oil from Alaska down to the United States costs billions of dollars," said Ahlers. "And if you can understand what causes the resistance that you have to overcome, then maybe you can reduce that. Even if you only reduce it by 2 or 3 percent, you've saved hundreds of millions. So it's very, very important."

Ahlers went on to say that understanding the temperature in turbulent convection is also very important because there are many applications where turbulent convection is used to cool things. In nuclear reactors, for instance, cooling is done by turbulent convection.

"There are many applications of this turbulent convection system in industry, where you would also like to understand what's going on inside, what the temperature gradients are," he said. "So I can see relevance for this in applications. Although I must say that is not our motivation; our motivation is to understand the fundamental physics."

Eberhard Bodenschatz, one of the authors, was a postdoctoral fellow with Ahlers at UCSB about 20 years ago and is now director of the Max Planck Institute for Dynamics and Self-Organization in Goettingen. Co-author Xiaozhou He is a postdoctoral fellow with Ahlers and is based in Goettingen. Scientists from The Netherlands, Italy, and France are also involved.

.


Related Links
University of California - Santa Barbara
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
Boiling Water Without Bubbles
Evanston IL (SPX) Sep 18, 2012
Every cook knows that boiling water bubbles, right? New research from Northwestern University turns that notion on its head. "We manipulated what has been known for a long, long time by using the right kind of texture and chemistry to prevent bubbling during boiling," said Neelesh A. Patankar, professor of mechanical engineering at Northwestern's McCormick School of Engineering and Applied Scien ... read more


TECH SPACE
e2v chosen to supply high performance imaging sensors for Japan's X-ray Free-Electron Laser

Less wear, longer life for memory storage device

Solving bubble troubles: new surface can prevent liquid explosions or even frost

International team of physicists makes discovery about temperature in convection

TECH SPACE
Hughes Awarded Custom SATCOM Solutions Contract by GSA

4 SOPS begins testing newest AEHF satellite

SES Government Solutions Awarded Custom Satellite Solutions Contract in the US

Boeing Chosen for US Government's COMSATCOM Services Acquisition Program

TECH SPACE
Failure Review Oversight Board Establishes Proton Return to Flight Schedule

HISPASAT chooses Arianespace to launch its Amazonas 4A and AG1 satellites

Arianespace signs multi-launch services agreement with SKY Perfect JSAT of Japan

Vandenberg's Fifth Atlas V lifts off

TECH SPACE
Improved positioning indoors

ITT Exelis announces new capability in GPS interference, detection and geolocation

Countdown: a month to go to Galileo's next launch

Monitech Announces Zero-Installation Tracking System for Automotive Industry

TECH SPACE
Boeing Business Jets proves range capability with record-setting trans-Pacific flight

DLR and NASA announce partnership in aeronautics research

Sikorsky explores broader Polish network

Chile in talks to buy Dutch Cougar copters

TECH SPACE
Radiation-Enabled Computer Chips Could Lead to Low-Cost Security Imaging Systems

Memristors based on transparent electronics offer technology of the future

Needle beam could eliminate signal loss in on-chip optics

Samsung starts to build $7bn chip plant in China

TECH SPACE
Pioneering UK project to improve land carbon intelligence accuracy and reliability

More satellite launches planned for upgrading maritime monitoring

Astrium installs new terminal in Mexico to receive SPOT 6 and SPOT 7 imagery

Suomi NPP Captures Smoke Plume Images from Russian and African Fires

TECH SPACE
Measuring mercury levels: Nano-velcro detects water-borne toxic metals

Indonesian lives risked on 'world's most polluted' river

Oil spill ship's officers deported from New Zealand

Chemical use inflicts mounting bill on poor countries: UN




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal 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