Better boiling with nanorods could lead to cooler chips

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 Koratka, 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. At the boiling point, 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 miniscule 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 by six to 10 times.

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

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

Placing copper nanorods onto the copper interconnects of chips could greatly reduce the heat build up, 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."

Koratkar said this may increase chip cooling by 6 to 10 times, although at this point that's just an estimate.

Late in June, researchers at Purdue University announced that they had developed a tiny refrigeration system that could be cooling laptops and desktops within two years.

The cooling system, which is the size of a computer processor, should enable PC manufacturers to not only lower the temperature of existing machines, but also build much smaller computers. The new system uses tiny compressors and tubing to pump refrigerants through it. The chip-size systems could be integrated into a CPU, or they could replace the traditional air-cooled heat sink in the computer.