[AI] Tiny refrigerator taking shape to cool future computers
saravanan.ramadoss1 at gmail.com
Sat Jun 21 11:46:45 EDT 2008
Sci. & Tech.
Tiny refrigerator taking shape to cool future computers
WEST LAFAYETTE: Researchers at Purdue University are developing a miniature
refrigeration system small enough to fit inside laptops and personal
a cooling technology that would boost performance while shrinking the size
A press release by EurekAlert says, unlike conventional cooling systems,
which use a fan to circulate air through finned devices called heat sinks
to computer chips, miniature refrigeration would dramatically increase how
much heat could be removed, said Suresh Garimella, the R. Eugene and Susie
Goodson Professor of Mechanical Engineering.
The Purdue research focuses on learning how to design miniature components
called compressors and evaporators, which are critical for refrigeration
The researchers developed an analytical model for designing tiny compressors
that pump refrigerants using penny-size diaphragms and validated the model
with experimental data. The elastic membranes are made of ultra-thin sheets
of a plastic called polyimide and coated with an electrically conducting
layer. The metal layer allows the diaphragm to be moved back and forth to
produce a pumping action using electrical charges, or "electrostatic
In related research, the engineers are among the first to precisely measure
how a refrigerant boils and vaporizes inside tiny "microchannels" in an
and determine how to vary this boiling rate for maximum chip cooling.
The research is led by Garimella and Eckhard Groll, a professor of
"We feel we have a very good handle on this technology now, but there still
are difficulties in implementing it in practical applications," said
director of the Cooling Technologies Research Center based at Purdue. "One
challenge is that it's difficult to make a compressor really small that runs
efficiently and reliably."
Findings will be detailed in two papers being presented during the 12th
International Refrigeration and Air Conditioning Conference and the 19th
Compressor Engineering Conference on July 14-17 at Purdue. The papers were
written by doctoral students Stefan S. Bertsch and Abhijit A. Sathe, Groll
New types of cooling systems will be needed for future computer chips that
will likely generate 10 times more heat than today's microprocessors,
in small "hot spots," Garimella said.
Miniature refrigeration has a key advantage over other cooling technologies,
"The best that all other cooling methods can achieve is to cool the chip
down to ambient temperature, whereas refrigeration allows you to cool below
temperatures," he said.
The ability to cool below ambient temperature could result in smaller, more
powerful computers and also could improve reliability by reducing long-term
damage to chips caused by heating.
One complication is that the technology would require many diaphragms
operating in parallel to pump a large enough volume of refrigerant for the
"So you have an array of 50 or 100 tiny diaphragm compressors, and you can
stack them," Groll said.
The researchers conducted laboratory experiments with the diaphragms in
Garimella's Thermal Microsystems Lab, developed a computational model for
the compressor and validated the model with data from the lab. Findings
showed that it is feasible to design a prototype system small enough to fit
a laptop, Garimella said.
The model enables the engineers to optimize the design, determining how many
diaphragms to use and how to stack them, either parallel to each other or in
"If you stack in one direction, you get more pressure rise, and if you stack
in the other direction, you get more volume pumped," Groll said.
Learning how to manufacture the devices at low cost is another major
challenge, with industry requiring a cost of about $30 each.
"We can't currently produce them at this price, but maybe in the future,"
Another portion of the research focuses on learning precisely how
refrigerant boils and turns into a vapor as it flows along microchannels
a human hair. Such evaporators would be placed on top of computer chips.
Bertsch, the doctoral student who led work to set up experiments at the
university's Ray W. Herrick Laboratories, observed how refrigerant boils
the channels and measured how much heat is transferred by this boiling
refrigerant. He also created mathematical equations needed to properly
"This overall project represents the first comprehensive research to
carefully obtain data showing what happens to heat transfer in arrays of
for miniature refrigeration systems and how to design miniature
compressors," Garimella said. "Eventually, we will be able to design both
compressors and evaporators."
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