Skip to comments.A Practical Way to Make Power From Wasted Heat [New Thermoelectric Method (my title)]
Posted on 11/27/2001 8:36:20 PM PST by Diogenesis
Scientists at M.I.T. and a small company in Salt Lake City are scheduled to
announce today that they have developed technology that can efficiently and
inexpensively transform heat pollution into electricity.
Although only a few crude samples have been built, Dr. Yan Kucherov,
director of research and development at the Salt Lake City company, Eneco
Inc., and Dr. Peter L. Hagelstein, professor of electrical engineering at
M.I.T. and a technical consultant at Eneco, say that their devices improve
the efficiency of the conversion by more than half.
"It's really first-generation, very primitive implementation," Dr.
Hagelstein said. "Potentially, it's an enormous deal. This opens a door."
While the heat generated by car engines and power plants usually does
nothing but warm the surrounding air, scientists have long dreamed of
building so-called thermoelectric devices that can capture the wasted heat
and convert a portion of it into electricity.
Such devices could significantly increase the electrical output of existing
power plants or power the electrical systems of automobiles, replacing
alternators and increasing gas mileage.
The Pentagon, which partly financed the new research, has been interested in
using the devices for silent motors. Operating in reverse, thermoelectric
devices can also be used as refrigerators.
Another advantage of thermoelectric devices is that they produce electricity
without generating additional pollution.
Current thermoelectric technology converts only about 10 percent of the heat
it absorbs into electricity, too inefficient a return for widespread use.
The new devices, however, reach about 17 percent, and Dr. Hagelstein said
future devices should be able to improve upon that significantly.
It is impossible to transform 100 percent of the heat into electricity. The
laws of physics dictate a theoretical maximum of about 50 percent at the
temperature a thermoelectric device operates at. Current commercial
thermoelectric devices, at 10 percent efficiency, get only one-fifth the
maximum. Using the new technology, future devices should be able to achieve
more than half the maximum.
.... If borne out, the findings would be significant, said Dr. George S. Nolas, a
professor of physics at the University of South Florida and an organizer of
a symposium about thermoelectric devices at the Materials Research Society
meeting. Dr. Nolas had not seen the Eneco paper but said the reported
efficiency was high enough to find practical use and "would be pretty good
Eneco's thermoelectric device is a sandwich of three layers of
semiconductor. One outer layer is heated; the other is kept at room
temperature. The middle layer acts as an insulator to maintain the
The heat causes electrons to shoot out, some crossing the sandwich to
generate an electrical current. The Eneco researchers added impurities a
process called doping to the heated layer to increase the flow of
"The region near the hot part is heavily doped, so it boils off electrons,"
Dr. Hagelstein said. "We get more voltage and more current."
He added: "The underlying technology is really very simple. It should be a
very practical, relatively cheap technology."
Waste Heat Conversion Is Improved
Scientists Announce Advance in Converting Waste Heat to Energy
By JAY LINDSAY Associated Press Writer
BOSTON (AP) -- Heat emitted by everything from power plants to car exhausts could be efficiently and cheaply converted into power with new technology announced Tuesday by a
Massachusetts Institute of Technology scientist and a Utah company.
The devices, built by Yan Kucherov of Salt Lake City-based Eneco Inc. and MIT electrical engineering professor Peter Hagelstein, are as much as 70 percent more efficient than current technology that
harnesses unused heat.
The science at work has been used for decades, but has been refined to produce more power from less heat.
And because it produces energy directly from heat, without moving parts, it could be used to develop quieter, low-cost power generators that are easy to maintain.
``It's potentially very important,'' Hagelstein said. ``We've demonstrated basic effects that can be exploited by one and all.''
Eneco's technology, called ``solid state thermionics,'' combines thermoelectrics and thermionics, century-old technologies that convert heat into electricity, but which both have practical drawbacks.
Thermoelectrics joins two conductive surfaces together, one of which is heated to produce a low-wattage current that's too inefficient to be useful.
In thermionics, a vacuum separates the two surfaces. It requires temperatures as high as 1,100 degrees Celsius, or 2,000 degrees Fahrenheit. That's far hotter than most waste heat, and limits its uses to nuclear
powered converters, such as those in space probes, satellites and some military systems.
In Eneco's device, impurities are added to the heated surface to increase the flow of electrons to the cooler side, generating a stronger electrical current at lower heat. A semiconductor, rather than a vacuum, lies
between the two surfaces and helps maintain the temperature difference between the heated and cooler sides.
At 250 to 300 degrees Celsius, Eneco's devices convert about 17 percent of the heat it absorbs into energy, compared to about 10 percent for current thermoelectric devices. Hagelstein said improvements
could soon raise that efficiency to 20 to 25 percent.
The devices -- about a millimeter wide and a half millimeter thick -- could be used in a variety of situations, said Eneco president Lew Brown.
Power plants could use them to convert heat pouring from smokestacks into energy, leading to lower emissions and less fuel use. Or they could be fitted for a car's exhaust system, and use that energy to power
the car's electronics, he said.
Eneco's testing has been independently confirmed by U.S. government labs, but the company is about two years from producing something for sale, said marketing director Leroy Becker.
Louis Smullen, an electrical engineering professor emeritus at MIT who had no connection to the research, said he envisioned the devices being used produce power to cool ever-smaller computer chips, so
they don't overheat.
Its efficiency would need improvement for the technology to be practical, Smullen said, but said the technology appears promising.
``What they've demonstrated is good enough to be exciting in the field,'' he said. ``I don't know how to forecast whether it will be part of everybody's home. I think it will be important.''
The findings were presented on Tuesday at the meeting of the Materials Research Society in Boston.
I think they are at least one, perhaps two ordeers of magnitude off on this. Any thermocouple is a "thermionic" electrical generator - a few millivolts at a few microamps. Like to watch their invention work with MY meters attached and we'll just see about that 17 percent efficiency!
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