from the april 2003 issue of Road & Track magazine.

Brrrr ... and it's loud in here too!

Researchers have developed thermo-acoustic cooling.
That is, sound waves are used to bring about the temperature
differential.

Both this new approach and conventional refrigeration depend on
the inherent heating a gas undergoes when compressed and the
subsequent cooling that occurs when it's allowed to expand.  But
conventional systems use environmentally sensitive refrigerants
(R12 in the past, R134a now).  By contrast, the thermo-acoustic
approach uses nothing more exotic than air.

The air is pressurized and blasted into an enclosure as
high-pitched 173-dBA sound waves. (This is REALLY loud  ... a jet
plane taking off 80 ft. away is perhaps 140 dBA.)  The sound
waves alternately compress and expand the air as it travels down
and rebounds within the heat exchanger.  The shape of this
enclosure is carefully tuned so that the compressed hot air
accumulates in one location; the expanding, cooler air in
another.  The cold side can drop as low as -8 degrees Fahrenheit;
furthermore, no sound is heard outside the sealed enclosure.

Energy efficiency still lags behind that of conventional systems,
but steady improvements are being made.  What's more, there are
some tantalizing advantages.  Merely upping the frequency can
lead to downsized units.  Changes in sound volume vary the
output, unlike conventional systems that operate as bang-bang
controllers, needing to cycle either full-on or full-off.

Penn State University researchers are involved, as are those at
Los Alamos National Laboratory.

Part of the funding comes from Ben & Jerry's, a company known for
its environmental commitment (and tasty ice cream as well).
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unca joel's comments ...

ok, so now we know ... all those big boom-box woofers in the
cheap 1970's chevrolets really are 'cool'!!!
;)

does anyone remember the Rovox air conditioning that was
developed in the 70's? Chrysler bought it and it disappeared. it
also used only air, but had a 1/4hp drain on the engine to power
the compressor/expander. it's biggest problem, said the inventor,
was that it tended to create a lot of ice on the outside of the
hoses in humid climates. at one point, Chrysler claimed the seals
didn't last long enough to make it commercially viable. to me,
that was hogwash ... it had a simple box compressor/expander and
even if you had to replace the seals every year, it would have
been a lot cheaper than recharging with freon!!  my personal
feeling was that some company who happened to own Frigidaire ..
the refrigerator and home/business air conditioning company ...
didn't want competition. :(

joel