[AI] Tiny refrigerator taking shape to cool future computers

Saravanan Ramadoss 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 
computers,
a cooling technology that would boost performance while shrinking the size 
of computers.

A press release by EurekAlert says, unlike conventional cooling systems, 
which use a fan to circulate air through finned devices called heat sinks 
attached
to computer chips, miniature refrigeration would dramatically increase how 
much heat could be removed, said Suresh Garimella, the R. Eugene and Susie 
E.
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 
systems.
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 
metallic
layer. The metal layer allows the diaphragm to be moved back and forth to 
produce a pumping action using electrical charges, or "electrostatic 
diaphragm
compression."

In related research, the engineers are among the first to precisely measure 
how a refrigerant boils and vaporizes inside tiny "microchannels" in an 
evaporator
and determine how to vary this boiling rate for maximum chip cooling.

The research is led by Garimella and Eckhard Groll, a professor of 
mechanical engineering.

"We feel we have a very good handle on this technology now, but there still 
are difficulties in implementing it in practical applications," said 
Garimella,
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 
International
Compressor Engineering Conference on July 14-17 at Purdue. The papers were 
written by doctoral students Stefan S. Bertsch and Abhijit A. Sathe, Groll 
and
Garimella.

New types of cooling systems will be needed for future computer chips that 
will likely generate 10 times more heat than today's microprocessors, 
especially
in small "hot spots," Garimella said.

Miniature refrigeration has a key advantage over other cooling technologies, 
Groll said.

"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 
surrounding
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 
cooling
system.

"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 
designing
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 
in
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
series.

"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," 
Groll said.

Another portion of the research focuses on learning precisely how 
refrigerant boils and turns into a vapor as it flows along microchannels 
thinner than
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 
inside
the channels and measured how much heat is transferred by this boiling 
refrigerant. He also created mathematical equations needed to properly 
design the
miniature evaporators.

"This overall project represents the first comprehensive research to 
carefully obtain data showing what happens to heat transfer in arrays of 
microchannels
for miniature refrigeration systems and how to design miniature 
compressors," Garimella said. "Eventually, we will be able to design both 
the miniature
compressors and evaporators."
_______
 If it is repeated message,  please excuse me.
Thanks with regards
Saravanan.





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