Nanowick Cooling explained.
Some of the biggest breakthroughs in future tech revolve around some of the smallest materials on Earth. Even calling these technologies “micro” is magnitudes of measure larger than their actual tiny sizes. From the nano-scaled heat transfer of Nanowick Cooling down to the single atomic-level of Graphene and Quantum Computing, these white papers will help you wrap your head around the maximum potential of these miniscule technologies…
A micro solution to a macro problem
Heat is the enemy of modern electronics. As integrated circuits consume more electrical power and become ever smaller, with their constituent components packed closer and closer together, they generate more and more heat. If that thermal energy isn’t effectively dissipated, it will damage and eventually destroy the circuitry.
Today’s most popular cooling solutions utilize heatsinks and heat pipes, often augmented by powered fans. But that technology is rapidly reaching its practical limit and is threatening to impede the chip industry’s progress. Enter nanowick cooling: While fundamentally based on the same mechanics as the heat pipe, a nanowick cooler is capable of dissipating 10 times more heat. We’ll explain conventional cooling techniques, how nanowick cooling functions, and why it performs so much better.
Look inside your PC and you’ll find passive heatsinks and/or heat pipes, typically fabricated from aluminum or copper, clinging to your motherboard chipset and maybe even your RAM. For components that generate even more heat-your CPU and videocard, for example-the coolers are usually augmented by fans. A heatsink simply uses thermal conductivity to draw heat from the point-of-contact to a cooler area at the opposite end of the metal. Segmenting that far end into a host of very thin fins increases the heatsink’s total overall surface area, making it easier for the heat to pass into the air; adding a fan draws the heat away even faster.
Heat pipes, typically fabricated from copper, operate on a similar principle, and are often used in conjunction with a heatsink. The pipes contain a small amount of fluid-often water-and are sealed at a low atmosphere pressure, which means the fluid will boil at a relatively low temperature while it’s in close proximity to the heat source. The resulting steam transfers the heat to the far end of the tube, where it condenses back into a liquid. Gravity and other forces cause the liquid to flow back to the heat source and the cycle repeats.
A nanowick cooling system is based on the same physics; but as its name implies, it operates on a vastly smaller scale, with pipes and fins that are nearly as thin as cell membranes. A nanowick draws a liquid coolant toward the hot surface of the chip via capillary action, a phenomenon that moves fluids through small spaces based on molecular charges. Since capillary pressure increases as the channel through which the fluid moves narrows, nanowick pressure can be orders of magnitude greater than a conventional heat pipe.
Nanowicks are created through a sintering process in which tiny copper spheres are fused together to form a porous sponge. To make the pathways even smaller, carbon nanotubes with a diameter of about 50 nanometers are inserted into the mix. Since carbon repels liquid, the nanotubes are coated with another substance, often copper. The specific pattern and channel size affects the wicking speed. Nanowicks can even be designed to separate different fluids or to filter substances.
The ultimate nanowick design will be the perfect balance of material, surface area, and capillary channel size: A thick wick has a large contact patch that increases the area over which it can draw heat, but the corresponding downside is a reduced capillary effect. Researchers are still searching for the perfect balance.
The rest of a nanowick system echoes the design of a typical heat pipe. The heated liquid-often water-evaporates and travels to the opposite end of a sealed tube, where the liquid condenses. The nanowick then draws the fluid back to a plate-also known as a thermal ground plane-that’s in direct contact with the component that’s being cooled. And then the process repeats.
A conventional heat pipe is capable of absorbing roughly 50 watts of energy per square centimeter. Researchers at Purdue University’s Birck Nanotechnology Center recently developed new nanowick materials that have proven capable of absorbing more than 550 watts per square centimeter without any occurrence of dryout, the point at which the coolant completely disappears from the loop and the system fails. This suggests that the researchers have only scratched the surface of nanowick technology’s capacity for absorbing heat.
Applying the Science
The first nanowick cooling systems are being deployed in high-power electronic devices developed from the automobile and defense industries. In the auto industry, such applications include the switching transistors that drive the electric motors in hybrid and battery-powered cars. Military applications include the electronic components embedded in radar and laser devices used in vehicles and aircraft. The integrated circuits used in both applications can generate more than 300 watts per square centimeter-far more than conventional heat pipes are capable of dissipating.
Nanowick coolers for consumer-electronics devices will likely reach the market within the next two years, a development that could enable the design and manufacture of even faster CPUs. GPUs, and other chips-especially those designed for mobile applications where cooling is always a challenge. One day, even your smartphone might harbor one of these small wonders.