Machine Design

Heat pipes keep laptops cool

ICs in today's laptop computers generate about 50 W/cm2 of heat. To prevent overheating, a fan, often a noisy one, blows heat down onto a copper heat sink on the bottom of the computer, which can really warm up the users lap.

As chips get stacked and circuits are downsized, next-generation ICs might produce 100 W/cm2, the heat levels produced by a light bulb and enough to damage the chips. This could cause some real discomfort. Heat pipes are one possible solution being studied at Sandia National Laboratory. Self-powered with no moving parts, they can direct heat to specific areas where it can be safely, and comfortably, dispersed. Heat pipes can also easily retrofit into existing laptop designs. In the heat pipe, heat converts liquid methanol into vapor, which travels the length of the pipe. At the cool end, which can be made cooler by using a small external fan if necessary, the vapor condenses to a liquid and is wicked back to the hot end. Wicks in this design are finely etched lines about as deep as fingerprints. Methanol travels up the wick using capillary action and defying gravity if necessary.

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