Researchers look to air-condition computer chips

[July 16, 2008]  CINCINNATI (AP) -- Purdue University scientists have taken a page from air conditioner technology in their quest for a new way to cool down ever-more powerful computer chips. Their experimental system, which flushes a refrigerant through tiny channels cut into chips, is intended for the high-power electronics found in radar and advanced weapons systems such as lasers, said Issam Mudawar, a mechanical engineering professor at Purdue.

Mudawar, who's leading the research, said the new cooling system should be able to cool chips that produce more than 1,000 watts of heat for about every half-inch square of circuitry.

He said that would be a fivefold increase over the heat-removing abilities of existing systems that typically rely on air-cooling to waft heat away from microprocessors.

"Basically what we're doing is opening the window of opportunity in terms of heat dissipation, so that chip developers can make more aggressive chips, more demanding chips," Mudawar said.

The new cooling system uses tiny parallel grooves called microchannels cut in a chip's surface and covered with a metal plate. Hydrofluorocarbons -- a liquid used in air conditioners to cool air -- are flushed through tiny holes in the metal plate called microjets and into the channels to draw heat away from the chip.

As it flows through the grooves, the liquid bubbles and partially vaporizes, adding to its ability to cool. After each pass, the fluid and vapor leaves the chip and enters a loop where it is returned to an all-liquid state and then comes back into the channels to cool again.

Personal computers get their brain power from conventional microprocessors that rarely dissipate more than 100 watts of heat for about every half-inch square. But computing systems needed for complex devices such as weapons systems generate far more heat.

And as chips used in those advanced computers become smaller and more powerful, scientists must find a way to remove the additional heat that puts those electronics at risk of a meltdown.

Mudawar said the goal is remove the greatest number of watts -- a measure of the rate of heat coming from a chip's surface -- to keep it below a certain temperature. That's typically no greater than 257 degrees Fahrenheit, he said.

Mudawar developed the new cooling technique with mechanical engineering doctoral students Myung Sung and Jaeseon Lee.

The Purdue colleagues, who are still working to refine the system, hope their idea catches the interest of a defense contractor.

Some of their work was presented in May during a gathering in Orlando, Fla., of scientists who study ways of reducing heat in computer electronics. Over the past four years, the Purdue team has received about $500,000 in funding from the Office of Naval Research.

Mark S. Spector, the ONR's program officer for advanced naval power systems, said the new research holds promise in the government's push with academia and private industry to find new ways cool down microprocessors needed for future military applications.

He said those include the high-power electronics found in lasers, propulsion and military sensor arrays.

"The rapidly increasing use of electronics in military hardware is resulting in unprecedented thermal management needs," Spector said.

[Associated Press; By RICK CALLAHAN]

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