Faster
Computers through Carbon Foam?
When smaller and smaller transistors are packed on a computer chip, electrons don’t have to travel as far, making the chip run faster. As the power density of the chip increases, it can do more and more calculations per second. Faster chips make faster computers.
National security and emergency responder personnel can benefit from faster computers to deal with terrorist attacks. A more rapid computation capability could increase their speed in making emergency plans, communicating with each other during terrorist attacks, and intercepting and decoding messages transmitted between terrorist cells.
But at least one obstacle is slowing down the race to faster computers. As the power density increases, each computer chip gets hotter faster. Current computer chips, which have power densities up to 25 watts per square centimeter (W/cm2), can be cooled effectively using aluminum and copper heat sinks. However, future high-performance computer chips are expected to have power densities up to 50 to 200 W/cm2. Unless it is effectively cooled, the chip will generate enough heat to cause impurities intentionally incorporated in the silicon transistors to diffuse out, rendering the chip nonfunctional or even melting it.
In cooperation with the National Security Agency (NSA), ORNL’s James Klett has demonstrated that using a graphite foam disk for immersion cooling (evaporative cooling) can effectively carry away the heat dissipated by chips having higher power density. This graphite foam, which Klett found in 1996 to have unusually good heat-transfer capabilities, promises to be safer than spray cooling and more effective than diamond spreaders on inverted silicon chips.
As a result of the limited surface area of the diamond spreader, the maximum power density that can be achieved with immersion cooling a chip without overheating it is 28 W/cm2. “When the diamond spreader was replaced with ORNL’s graphite foam, a power density of 100 W/cm2 was attained without overheating the system,” Klett says. “Thanks to our foam, power densities more than 350% of the current designs were safely reached. Theoretically, significantly higher power densities can be achieved with proper design of the evaporative cooling system adjacent to the foam-bonded chip and the system’s fluid content. This system ejects from the computer the heat the graphite foam transfers to it rapidly from the chip.”
ORNL is teaming with NASA, the University of Maryland, and Thermacore to develop and optimize prototype immersion coolers for the NSA and other electronics chip applications. Graphite foam is emerging as a hot new material that may enable “cool” computer technologies.
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