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Big Step Forward in Use of 'Wasted' Heat

Copyright 2001 by United Press International.

SALT LAKE CITY, Nov 27, 2001 (United Press International via COMTEX) -- Technology that could greatly increase the efficiency of engines and power plants while at the same time cutting polluting emissions has taken a significant step forward, according to scientists at MIT and a small Utah research company.
    Researchers announced Tuesday at a scientific meeting in Boston that they had developed a semiconductor that will capture heat from machinery that is normally vented into the air and "recycle" it into electricity.
    "Our approach is the first to yield high efficiency heat energy conversion," said Lew Brown, president of Eneco, Inc., a Salt Lake City company that specializes in such energy conversion technology.
    Tests on early prototypes resulted in the capture of about 17 percent of the lost heat compared to 10 percent in most current models, and Eneco told the New York Times it was confident it could improve that level to near the 50-percent barrier that the laws of physics set as the maximum amount of heat that can be recovered by a thermoelectric device.
    While still in a primitive state, the so-called solid-state thermionics technology has the capacity to capture and reuse larger amounts of heat and also use heat at a lower temperature than currently possible.
    Working in reverse, the technology also could improve the efficiency of refrigerators, air conditioners and other cooling equipment.
    "Potentially, it's an enormous deal," MIT professor Peter L. Hagelstein told the Times. "This opens a door."
    The use of thermionic devices is limited to heat sources of around 2,000 degrees Fahrenheit, which Eneco said in a release limits their use to nuclear-powered converters in space probes and a few specialty military and satellite systems. By bringing the usable heat threshold down to around 400-800 degrees, a wide range of more earthbound uses opens up.
    Eneco said that the technology is well suited for use in power plants where significant amounts of heat are lost in the process of generating electricity. Capturing the heat before it is expelled into the atmosphere would allow it to be used to augment the coal, gas or other primary fuel being burned.
    "The heat of external combustion of these primary fuels, when channeled through Eneco devices, can not only produce electricity but also can simultaneously co-generate useful heat and reduce pollution," the company said.
    Taking the idea further, Eneco engineers believe that the size of their devices can be reduced enough to make them fit in small-scale equipment, including appliances, small-scale power plants and even planes, ships and automobiles.
    "Vehicles of all sizes strive for efficient use of fuel energy, yet often do little to recover waste exhaust heat," the company touted. "The heat lost through engine exhausts may be captured ... and converted into electricity to augment or replace a vehicle's electrical and air conditioning systems."
    The idea of compact, efficient power source with virtually no working parts has attracted the interest of Pentagon officials who see thermionics as a key to developing silent engines.
    Hagelstein called the technology relatively simple; using three layers of semiconductors, the devices capture radiating heat on one outside layer and transfer to the other side. Heat gives off large numbers of electrons that take the form of an electrical current.
    Eneco added a number of impurities to the heated layers in a process called doping that is aimed at increasing the flow of electrons.
    "The region near the hot part is heavily doped, so it boils off electrons," Hagelstein told the Times. "We get more voltage and more current."

United Press International