Long narrow wires carry heat with little resistance

Enlarge / Tiny wires may boost heat flow. (credit: Rice University)

Getting rid of heat is one of the central challenges with modern technology. It doesn't matter whether the technology is a high-end server CPU or some pathetically anemic processor in a no-brand set-top box-someone has had to think about thermal management. One of the central issues in thermal management is thermal resistance, a material's tendency to limit the flow of heat. The thicker a material, the larger the temperature gradient required to achieve the same amount of cooling because the thermal resistance increases with thickness.

Except when it doesn't. If the heat is carried by ballistic phonons, thermal resistance stays constant.

Energy in motion

Heat is basically energy. In a solid material, energy is stored in two places: the motion of electrons, and the motion of the nuclei. The motion of electrons can pull nuclei into motion, while likewise, nuclei kick electrons around, so energy travels back and forth between the two.

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