New design will help cool microelectronics more efficiently

October 12, 1999

9/29/99, COLUMBUS, Ohio -- As microelectronics pack more high-powered computer chips into ever-shrinking spaces, cooling these devices becomes more difficult. Ohio State University researchers have developed a heat sink, or cooling system, that is more efficient than current designs.

In simulations, a microelectronic circuit using the new heat sink design heated up only about one third as much as a circuit using a conventional heat sink. Makers of computers, lasers, and other devices may benefit from the new design.

Kambiz Vafai, professor of mechanical engineering, and graduate student Lu Zhu improved upon a conventional heat sink design. Called a micro-channel heat sink, this early design circulated coolants such as water through a network of tiny tubes to absorb heat from electronics, much like the coolant system in an automobile cools an engine. Vafai and Zhu's two-layered micro-channel design doubles the number of tubes, which measure only one-sixteenth of an inch in diameter.

"Micro-channels are useful for electronics because they provide a great deal of cooling, and multiplying the number of channels allows coolant to penetrate much more effectively into the system," said Vafai.

The new design solves some problems of the old one. For instance, to make such small tubes remove a large amount of heat, manufacturers were forced to pump coolant through them at high pressure, which required a large power supply and bulky packaging.

Vafai and Zhu found that if they layered an identical second bed of cooling channels on top of the first, they could dissipate more heat and eliminate the need for a bulky power supply. In the two-layer heat sink design, coolant flows through micro-channels directly next to a heat source, into a heat exchanger, then through the second layer of micro-channels.

The Ohio State researchers modeled the cooling properties of the two-layer heat sink on computer, and compared the results to that of a conventional single-layer heat sink.

They began both models with a hypothetical microelectronic circuit starting at an ambient temperature of approximately 77°F. The conventional, one-layer heat sink allowed the circuit's temperature to increase 27°F, while the new, two-layer heat sink allowed an increase of only 9°F -- about one third as much.

"By designing this two-layer structure, we haven't significantly complicated the manufacturing process, but we've substantially eliminated the problems associated with the one-layer micro-channels," said Vafai. He said the design may cost a little more to manufacture than traditional heat sinks, but the cost would decrease if it were mass-produced. Vafai said the new heat sink could cool all sorts of high-tech devices such as computers, lasers, diodes, and mirrors in sensitive optical equipment. He added that he got the idea for the new design from his related research in the flow of fluids through porous media.

"One can look at a micro-channel heat sink as a pseudo-porous structure, only more organized. In an extremely porous medium, coolant bathes an object and pulls away a tremendous amount of heat. So, to a certain extent, our design takes advantage of that knowledge and increases the number of channels to increase the heat transfer." So if two layers of channels are better than one, then why not stack three or four, or more? "Our results open up the possibility of adding more layers of channels, but that may not be necessary. With just the two layers we've achieved most of the cooling we wanted to achieve," said Vafai.

Vafai has filed a patent application for the design, and several companies have inquired about commercializing the technology. Vafai said he can't estimate when the technology will be available to the general public until the patent process is finished and commercialization begins.

These results appeared in a recent issue of the International Journal of Heat and Mass Transfer. The work was partially funded by the Department of Energy and by a grant from Italy for international exchange with Universita delgi studi Federico II.

Ohio State University

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