Smooth-walled wire traps high energy phonons, low energy phonons carry heat.
Tiny wires may boost heat flow.
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.