New Accoustic Sterling Engine
Two scientists at Los Alamos National Laboratory
have developed a low-tech engine that performs work using simple sound waves and
has no moving parts. Scott Backhaus and Gregory Swift believe it has the
potential to provide alternative energy, significantly save energy supplies and
reduce global pollution.
They said in their study published Thursday in
the journal Nature that the revolutionary engine, which is as efficient as a
typical car engine, might be used to cool refrigerators or to cryogenically
recover a form of natural gas wasted and burned off in oil production.
They already have developed a working collaboration with Denver-based
Cryenco Co. to produce a machine for liquefying the natural gas usually burned
off or "flared" in oil production.
"We expect our engine to find many
additional uses throughout the global power-production environment, ranging from
the separation of air into nitrogen and oxygen, to the generation of
electricity," they said in their report.
Swift suggested in a statement
issued by the lab Wednesday that "small low-cost engines like this could be used
in homes for (electrical) cogeneration. That is, they could be used to generate
electricity while at the same time to produce heat for warming the home or for
Their "thermo acoustic Stirling engine" is a long,
steel, baseball-bat-shaped resonator with an oval handle on the lower end, which
is filled with compressed helium. Electronic devices generate sound waves, which
stimulate the gas to alternately expand and contract.
operation is based on the Stirling principle, named for the Scottish 19th
century scientist Robert Stirling, who showed that a confined volume of gas
expands at high pressure and contracts at low pressure, creating an alternating
cycle that can do work when the gas is heated or cooled through exchangers.
In a separate article published in the same issue of Nature, the
research is praised for its ingenuity and environmentally favorable qualities by
Steven L. Garrett of the acoustics program at Pennsylvania State University.
Garrett expresses admiration for the invention's simplicity, efficiency and lack
of environmental intrusiveness.
"The working fluid is pressurized
helium, an inert gas, which neither depletes stratospheric ozone nor contributes
to global warming," he said.
Garrett said the Los Alamos researchers provide
"elegant acoustic solutions" to problems that have vexed acoustic-engine
researchers for decades. Researchers, he adds, will soon "exploit this
technology for applications that need mechanical or electrical energy."
An obvious drawback of the new thermo acoustic engines is that acoustic
amplitudes can reach levels of 190 decibels. That, Garrett said, is "about 10
million times as intense as the front-row levels at a rock concert and 300 times
the intensity required to ignite human hair." Fortunately, he said, the sound is
produced inside a rigid pressurized vessel, and because the engines only radiate
a "single-frequency tone," any escaping sound waves are easily canceled by a
complimentary frequency or tone.
Lawrence Spohn writes for The Tribune
in Albuquerque, N.M.
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