Better boiling with nanorods could lead to cooler chips

July 7, 2008 (Computerworld) University researchers have discovered a way to use nanotechnology to enable them to boil water much more quickly. And that, they say, will help them more efficiently cool computer chips, leading to more powerful and smaller machines.

"This would be extremely important," said Nikhil Koratkar, an associate professor in the department of mechanical, aerospace and nuclear engineering at Rensselaer Polytechnic Institute. "A huge problem with making chips smaller is the fact that you get hot spots. The size of computers is going to become smaller and lighter, so it's important to have new strategies to cool them."

Koratkar, who has been working on the project with other researchers at Rensselaer for two years, explained that when water hits the boiling point, there's a phase change, and the water is transformed into vapor. For that phase change to happen, however, you need what he calls an interface — in this case, air. Without air in the equation, the water simply heats up past the boiling point without evaporation.

In any given pot, there are minuscule cavities or divots in the surface that hold tiny pockets of air. When the water boils, the air in those pockets escapes in bubbles that rise to the surface. The cavities then are flooded with water so the interface is lost and the boiling becomes less efficient.

Koratkar said he laid in a layer of copper nanorods all around the inner surface of the pot. Air trapped in the forest of nanorods helps to boost the creation of bubbles and also helps keep the cavities from filling with water, upping the boiling efficiency.

Boiling is a potential heat-transfer technique that can be used to cool chips, Koratkar noted.

As the physical size of chips has continued to shrink, heat has become a bigger problem for processor manufacturers. Faster chips at smaller scales — like 65nm vs. 45nm — generate a lot of heat.

Placing copper nanorods onto the copper interconnects of chips could greatly reduce the heat buildup, according to Koratkar.

"Since computer interconnects are already made of copper, it should be easy and inexpensive to treat those components with a layer of copper nanorods," he said. "When you have a hot spot inside a chip and you want to cool it, the idea is that you insert a coolant inside the chip. ... The coolant vaporizes, and the heat energy needed to vaporize the coolant is taken away from the chip. If you can vaporize more coolant, you naturally extract more heat from the chip. With nanorods, you can vaporize more coolant at any point in time. You'll extract more heat from the chip. You can cool off the chip faster."