Graphene heat management may be useful if graphene could rapidly carry off heat as waves. That might allow even more miniaturisation. This phenomenon (called “second sound”) could help cool future electronics.
“Graphite is a very common material, and the effect was observed at a relatively balmy (by low-temperature physics standards) temperature of around -240 degrees F.
The team’s theoretical models indicate it might be possible to produce the effect in graphene at something closer to room temperature in the future, thereby opening up any number of potential practical applications.
For instance, microelectronics just keep getting smaller, making heat management a daunting challenge. If room-temperature graphene could rapidly carry off heat as waves, it might allow even more miniaturisation….
So, what exactly are we talking about when discussing “second sound”? Technically, it’s an exotic mode of heat transport. Normally, “heat doesn’t just travel like a bullet in a straight direction,” said Nelson. Rather, it’s transported through the air by molecules moving around, constantly colliding with each other and scattering in all directions as it diffuses outward.
Sound, or acoustic waves, can carry heat energy through a solid via packets of vibrational energy known as “phonons.” Sound waves typically have long wavelengths, capable of traveling long distances, but the heat-carrying phonons in a solid have very short wavelengths, on the nanometer scale….
“Normally, if you put heat somewhere, it will cool and spread around, but where you put it [the source] is always the warmest place,” said Nelson. “That’s because all these acoustic wavelets that are carrying the heat around are also constantly getting scattered back toward the origin, so it remains warm. That’s what isn’t happening when there is second sound.”
Instead, the backscattering is suppressed and you get an unusual effect whereby the heat source actually cools faster than the surrounding region nearby—almost instantly, in fact.
That’s because the phonons are conserving momentum and carrying away heat en masse as a wave. “It’s counterintuitive to our experience and our intuition,” said Nelson. “I mean, waves do that all the time, but heat isn’t supposed to move like a wave.”
This kind of graphene heat management could have major potential for use in cooling future electronics.
Image: Graphite rods ready to be encased in wood to make pencils. MIT scientists have shown that heat behaves like sound when moving through graphite.
Source: Ars Technica