Posted on 03/21/2008 5:08:59 AM PDT by saganite
Researchers at Boston College and MIT have used nanotechnology to achieve a major increase in thermoelectric efficiency, a milestone that paves the way for a new generation of products -- from semiconductors and air conditioners to car exhaust systems and solar power technology -- that run cleaner.
The team's low-cost approach, details of which are published in the journal Science, involves building tiny alloy nanostructures that can serve as micro-coolers and power generators. The researchers said that in addition to being inexpensive, their method will likely result in practical, near-term enhancements to make products consume less energy or capture energy that would otherwise be wasted.
The findings represent a key milestone in the quest to harness the thermoelectric effect, which has both enticed and frustrated scientists since its discovery in the early 19th century. The effect refers to certain materials that can convert heat into electricity and vice versa. But there has been a hitch in trying to exploit the effect: most materials that conduct electricity also conduct heat, so their temperature equalizes quickly. In order to improve efficiency, scientists have sought materials that will conduct electricity but not similarly conduct heat.
Using nanotechnology, the researchers at BC and MIT produced a big increase in the thermoelectric efficiency of bismuth antimony telluride -- a semiconductor alloy that has been commonly used in commercial devices since the 1950s -- in bulk form. Specifically, the team realized a 40 percent increase in the alloy's figure of merit, a term scientists use to measure a material's relative performance. The achievement marks the first such gain in a half-century using the cost-effective material that functions at room temperatures and up to 250 degrees Celsius. The success using the relatively inexpensive and environmentally friendly alloy means the discovery can quickly be applied to a range of uses, leading to higher cooling and power generation efficiency.
"By using nanotechnology, we have found a way to improve an old material by breaking it up and then rebuilding it in a composite of nanostructures in bulk form," said Boston College physicist Zhifeng Ren, one of the leaders of the project. "This method is low cost and can be scaled for mass production. This represents an exciting opportunity to improve the performance of thermoelectric materials in a cost-effective manner."
"These thermoelectric materials are already used in many applications, but this better material can have a bigger impact," said Gang Chen, the Warren and Towneley Rohsenow Professor of Mechanical Engineering at MIT and another leader of the project.
At its core, thermoelectricity is the "hot and cool" issue of physics. Heating one end of a wire, for example, causes electrons to move to the cooler end, producing an electric current. In reverse, applying a current to the same wire will carry heat away from a hot section to a cool section. Phonons, a quantum mode of vibration, play a key role because they are the primary means by which heat conduction takes place in insulating solids.
Bismuth antimony telluride is a material commonly used in thermoelectric products, and the researchers crushed it into a nanoscopic dust and then reconstituted it in bulk form, albeit with nanoscale constituents. The grains and irregularities of the reconstituted alloy dramatically slowed the passage of phonons through the material, radically transforming the thermoelectric performance by blocking heat flow while allowing the electrical flow.
In addition to Ren and six researchers at his BC lab, the international team involved MIT researchers, including Chen and Institute Professor Mildred S. Dresselhaus; research scientist Bed Poudel at GMZ Energy, Inc, a Newton, Mass.-based company formed by Ren, Chen, and CEO Mike Clary; as well as BC visiting Professor Junming Liu, a physicist from Nanjing University in China.
Thermoelectric materials have been used by NASA to generate power for far-away spacecraft. These materials have been used by specialty automobile seat makers to keep drivers cool during the summer. The auto industry has been experimenting with ways to use thermoelectric materials to convert waste heat from a car exhaust systems into electric current to help power vehicles.
This research will be published online in Science Express on March 20, 2008. The research was supported by the Department of Energy and by the National Science Foundation
I think it’s a company with only one asset .... a website. However any any improvement in this technology with be valuable.
The internal combustion engine in real world conditions gets about 20% Carnot efficiency. It certainly was good enough to build an economy on.
If they can manage 30% efficiency, they have a real chance to replace gasoline engines. At this level, they also compete well with steam turbine electrical generation.
If they can get to 50% then the diesel engine goes too.
At 10% if it is cheap enough, there are many reasonable applications such as alternator replacement and auxilliary electric power on semi trucks.
Peltier effects are cool and some real advances are being made but quantum gap devices offer some real alternatives and theoretical vast improvements in effiency.
Couple this with big advances in Solid Oxide fuel cells, the fundimental technology of modern society is going to change radically in the next twenty years.
Thanks for the ping.
Your comment about solid oxide fuel cells sent me off on a discovery tour from Wikipedia to current articles. As recently as this month some company is claiming 15KW/Litre density with their fuel cell. According to the article that would beat the then current best density by a factor of 4. I can see great applications for these things in generating emergency power, say after a hurricane, and power in remote sites. I’m sure the military is loving it. What is the potential of SOFC for large scale power production?
I was talking about low grade waste heat energy recovery in industry. If I am trying to use waste heat from steam condensate, the maximum heat available is at 212F, usually a bit less. If my heat sink in the summer is a cooling tower, I can manage 80F cool water temperature.
The carnot efficiency in this case is about 20%. This is the theoretical maximum efficiency. Real world efficiency is less, about 10 to 15% at best. The closer you get to perfect, the more it costs. Even at 20% efficiency (impossible under the conditions I just described), the savings on electricity would not pay back the investment before the thermo-electric devices would need replaced unless they become dirt cheap.
I was not talking about higher heat sources, where the carnot efficiency is higher and the economics are more favorable. However, call me a skeptic if you wish, but I'd be surprised that the cost and reliability (they go together) of a large scale generating system would ever compete financially with mechanical electricity generation. It will have it's place, just as solar, hydro, and wind will, but I think it will serve a supporting role and not the main role. For instance, I can see using thermo-electrics to capture heat in a power plant that leaks through insulation, or in vents to capture heat going to atmosphere. They would enhance the overall plant efficiency in that case.
The economics really all depend upon the price of fuel.
With cheap abundant coal and minimal emissions limits, the economics of a coal fired steam turbine are hard to beat.
With government pressure to limit stack emissions, there is going to be a real pressure on the power industry to burn less coal. I know the technology is still a few years away but there is a real posibility for the industry to change from turbine generation to SOFC generation. This has two main benefits, the primary generation is about 70% more efficient and the waste heat is of much higher quality. Instead of a delta of 120 degrees, you are looking at more than 500 degrees. It is enough to drive a secondary steam turbine or if the technology is ready, thermoelectric generators.
There are millions of dollars being invested in SOFC power generation both for small and large scale applications. Money is being invested because the potential benefits are huge. The fuel cells are significantly more efficient than current power plants and they put out high quality heat which in itself is useful.
We are just beginning to see products hitting the streets. The company you read about has the potential to shake up the market. They are expecting to get significantly better power density in the future. Their process is easier to manufacture in industrial quantities and have solved several problems that have plagued SOFC fuel cells most notably, seal leaks and low temperature connections to the cell.
It’s nothing more than a solid state heat pump. They have been using this technology for ages to refrigerate a space, but it had very limited practical applications because it was so inefficient.
If this new version of the tech pans out, we will have refrigerators and airconditioners that have no moving parts and do not utilize freon or refrigerant of any kind. Just simply apply a voltage to a metal plate(or in this case, semiconductor material) and it will get cold.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.