Posted on 02/22/2007 6:35:15 AM PST by aculeus
Inside fossil-fuel and nuclear-power plants, as well as in cars and trucks, the lion's share of energy in fuel is wasted as heat rather than converted into electricity or mechanical power. But the search for a practical material that can convert at least some of this waste heat into electricity has been long and frustrating.
Researchers have long known that some inorganic semiconductors can do this. Indeed, deep-space probes have been powered by using such materials. But these inorganic materials are costly and difficult to make, and have low efficiencies. Now, new research shows that certain organic molecules produce voltage when exposed to heat. Ultimately, they could be much cheaper and thus more practical to implement.
"This is the first demonstration that you can use organic molecules in this kind of energy generation," says Rachel Segalman, professor of chemical engineering at the University of California, Berkeley, who with her colleagues reported new measurements last week in Science Express. "That's really significant because they are so inexpensive and abundant," she says.
Experts had previously theorized that some organic molecules could have the qualities necessary to generate electricity from heat. But until now, they lacked experimental proof, which the Berkeley researchers were able to provide by isolating and measuring the properties of just a few molecules of organic substances called benzene dithiols at a time.
These were "very difficult experiments," says Brian Sales, a senior research scientist at the Oak Ridge National Laboratory, who was not involved with the work. The researchers trapped a few molecules between a sheet of gold and the ultrafine gold tip of a scanning tunneling microscope, which is so sharp it can end in a single atom. They heated up the gold surface and measured, via the microscope tip, the voltage that was created. "These are the type of difficult experiments that get nanotechnology past the 'picture' stage [and] into the realm of real science," Sales says.
The experiments showed that the organic molecules have the three qualities that make for good thermoelectric materials. The first is the ability to create a voltage. But this works best when the materials have two other qualities: they do not conduct heat, but they do conduct electrons. That way, applying heat, rather than just raising the temperature of the material, actually drives electrons, creating a current.
The results confirmed that the organic molecules could indeed be used to generate electricity from heat. Before they can be put to use, however, it will be important, Sales says, to design the molecules so that they arrange themselves between metal layers to make large-scale thermoelectric materials. What's more, so far the efficiency is very low, the researchers say. To improve this, they are creating and testing new versions of the molecules.
"These are very simple molecules that the group is looking at," says J. Fraser Stoddart, professor of chemistry at the University of California, Los Angeles. He's interested in the researchers' plans to alter the molecules to improve their thermoelectric properties. "That's where my heart starts to beat," he says. "I hope they follow this research up."
The research is only the first step, the researchers say, and, because much work remains, applications will be many years away.
If all goes well, though, so-called thermoelectric devices based on the molecules could prove to be an important source of power--and a way to reduce greenhouse-gas emissions by making far more efficient use of fossil fuel. "Ninety percent of the world's electricity is generated by thermal-mechanical means," says Arun Majumdar, professor of mechanical engineering at UC Berkeley and another researcher on the project. "And a lot of the heat is wasted. One and a half times the power that is generated is actually wasted."
For example, a typical way to generate electricity is by heating up steam to drive a turbine. After the steam passes through the turbine, it still contains energy in the form of heat, although not enough to drive a turbine, Segalman says. That heat typically escapes into the atmosphere and is wasted. By wrapping thermoelectric materials around exhaust pipes, that heat could be put to work. In cars, thermoelectrics could replace the alternator and save hundreds of millions of gallons of gas a year, according to an estimate from a General Motors researcher. (See "Free Power for Cars.")
Organic materials are appealing because they cost much less than thermoelectric inorganic materials: even if they are inefficient, they might still be economical. "These molecules are dirt cheap," Majumdar says. "If the efficiency is low, that's fine. You're throwing that heat away anyway."
Copyright Technology Review 2007.
This has been discussed for decades. An assembly of thermoelectric modules, if clamped to a flat cast into the exhaust manifold, can generate clean DC from the waste heat. But regardless of the semiconductor's Figure Of Merit, the overall perfomance depends on temperature difference between the heat source and sink. If people take the easy way out, and use the engine's coolant as a sink, it is already at 165-195°F.
If the manifold reached 500°, then there is only a 300° Delta T.
One factor that has limited the usual bismuth telluride materials is their poor mechanical properties. After so many expansion/contraction cycles, they fail, because the hundred+ dies are connected in series, and it only takes one to open the circuit and render the device inoperable.
An organic thermoelectric will have limitations on it maximum temperature, limiting the Delta T, and the poorer Figures-Of-Merit, added to this limitation, probably just relegates this to a NanoDream™.
Thanks.
Thanks.
Grant applications, however, will begin at once!
Energy can neither be created or destroyed, so, it is not wasted.
Bump
I worked in thermoelectrics for quite a few years. We would love to have sold modules to GM. Where they DO work well is in the little beer cooler refrigerators. Quiet, no moving parts, and they do not see big temperature cycles.
The Russians, years ago did make a successful TE Generator. They had a kerosene lamp with a bunch of modules and heat dissipating fins on the lamp chimney. It generated "A", "B" and "C" voltages for old tube-type farm radios so the Worker Heroes never missed a Radio Moscow broadcast.
The thing was as ugly as a barrel of )*)'s and wieghed 25 pounds or more but it did work.
But when you put them in a vibrating environment like an auto engine, those semiconductor dice are as fragile as old cheddar cheese.
You need to check up on your thermodynamics. Wasted energy is essentially energy that cannot be exploited to do work.
Reminds me of our old scoutmaster ('way back in antediluvian times). He liked to make up bundles of "Go-lite" or "Hobo" Stew (chunks of seasoned meat and vegetables sealed up in aluminum foil) and put them atop the exhaust manifold of his old truck's straight six engine.
It was always a great treat to arrive at our campsite with a delicious, well-cooked, nourishing meal -- all piping hot and ready to eat!
Why do I remember these things?
http://www.amazon.com/Manifold-Destiny-Guide-Cooking-Engine/dp/0375751408
bttt
"11 used & new available from $74.99"
"Also Available in Paperback 5 used & new from $50.00"
Who says that waste heat from engines isn't valuable!?! '-)
Boy, somebody in GM's SUV marketing department sure missed the boat!
Funny you would put it that way, because they have been selling them in the Boating/Marine market for years.
You know how it is..Sun, and boat, some bait, a COOLER.
You might want to look at powerchips.gi. They make the claim of 70% heat to electricity via the Josephson Junction process(hot electrons tunnel thru the nano-scale barrier, leaving the cold electrons behind). It's already in product testing, getting ready for mass production in europe. It will first appear in german cars. They also claim 40% efficiency in the cooling mode.
Took a few minutes to peruse the Powerchips site.
Very interesting to say the least.
Depending on the efficiency, those could potentially rival photovoltaics in a solar reflector setup.
Going to keep watching that site to see if it pans out.
When I left the field about 15 years ago, there was a lot of interest in quantum dots..is that related?
I'm on the borelius mailing list, get regular updates. They are actually a metals/mining company. This is a sideline to them. They are also doing this wheel tug thing for big jets wherein the jet can move around the airport tarmac on its own w/o ground tugs.
I first heard about this powerchips thing in Infinite Energy Magazine, Eugene Mallove editor. Eugene was murdered in may of 2003 by some druggies. It was really a super magazine then on new energy concepts but has since gone downhill. See infinite_energy.com; the back issues pre-2003 have some real WOW stuff.
Good question. The Josephson Effect is a quantum tunneling effect and as you know the QM world is WEIRD. I can tell you much more about it but in a private post only.
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