collaboration of university researchers and top industry experts has created a
pumpless liquid cooling system that uses nanotechnology to
push the limits of past designs.
One fundamental computing problem is that there are only two ways to increase
computing power -- increase the speed or add more processing circuits.
Adding more circuits requires advanced chip designs like 3D chips or, more
traditionally, die shrinks that are approaching the limits of the laws of physics as applied to
current manufacturing approaches. Meanwhile, speedups are constrained by
the fact that increasing chip frequency increases power consumption and heat,
as evidence by the gigahertz war that peaked in the Pentium 4 era.
A team led by Suresh V. Garimella, the R. Eugene and Susie E. Goodson
Distinguished Professor of Mechanical Engineering at Purdue University, may
have a solution to cooling higher frequency chips and power electronics.
His team cooked up a bleeding edge cooler consisting of tiny copper spheres
and carbon nanotubes, which wick coolant passively
towards hot electronics.
The coolant used is everyday water, which is transferred to an ultrathin
"thermal ground plane" -- a flat hollow plate.
The new design can handle an estimated 10 times the heat of current computer
chip designs. That opens the door to higher frequency CPUs and GPUs, but
also more efficient electronics in military and electric vehicle applications.
The new design can wick an incredible 550 watts per square centimeter.
Mark North, an engineer with Thermacore comments, "We know the wicking part of the
system is working well, so we now need to make sure the rest of the system
The design was first verified with computer models made by Gamirella, Jayathi
Y. Murthy, a Purdue professor of mechanical engineering, and doctoral student
Ram Ranjan. Purdue mechanical engineering professor Timothy Fisher's team
then produced physical nanotubes to implement the cooler and test it in an
advanced simulated electronic chamber.
Garimella describes this fused approach of using computer modeling and
experimentation hand in hand, stating, "We have validated the models
against experiments, and we are conducting further experiments to more fully
explore the results of simulations."
Essentially the breakthrough offers pumpless water-cooling, as the design
naturally propels the water. It also uses microfluidics and advanced
microchannel research to allow the fluid to fully boil, wicking away far more
heat than similar past designs.
This is enabled by smaller pore size than previous sintered designs.
Sintering is fusing together tiny copper spheres to form a cooling
surface. Garimella comments, "For high drawing power, you need small
pores. The problem is that if you make the pores very fine and densely
spaced, the liquid faces a lot of frictional resistance and doesn't want to
flow. So the permeability of the wick is also important."
To further improve the design and make the pores even smaller the team used
50-nm copper coated carbon nanotubes.
The research was published in this month's edition of the
peer-reviewed journal International Journal of Heat and Mass Transfer.
Raytheon Co. is helping design the new cooler. Besides Purdue, Thermacore
Inc. and Georgia Tech Research Institute are also aiding the research, which is
funded by a Defense Advanced Research Projects Agency (DARPA) grant. The
team says they expect commercial coolers utilizing the tech to hit the market
within a few years. Given that commercial cooling companies (Thermacore,
Raytheon) were involved, there's credibility in that estimate.
quote: The researchers are creating smaller pores by "nanostructuring" the material with carbon nanotubes, which have a diameter of about 50 nanometers, or billionths of a meter. However, carbon nanotubes are naturally hydrophobic, hindering their wicking ability, so they were coated with copper using a device called an electron beam evaporator.
quote: The carbon nanotubes were produced and studied at the university's Birck Nanotechnology Center in work led by mechanical engineering professor Timothy Fisher.
quote: The findings are detailed in a research paper appearing online this month in the International Journal of Heat and Mass Transfer and will be published in the journal's September issue. The paper was written by mechanical engineering doctoral student Justin Weibel, Garimella and Mark North, an engineer with Thermacore, a producer of commercial heat pipes located in Lancaster, Pa.