Heat Transfer Through Edges Can Lead to Thermal Transistors

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Researchers can make heat transistors for next-generation computer and diodes by controlling the flow of heat

Researchers at the University of Michigan have reported that 100 times more heat can flow between two nanoscale objects, even at bigger than nanoscale distances.
The new results could have implications for better solar cells, materials that behave like one-way valves for heat flow and perhaps even a heat-based computing platform.

What could the findings enable?

Researchers proposed that you can control the flow of heat in a way similar to how electronics manage electrons, can make heat transistors for next-generation computers and diodes (like one-way valves).

Using the concept, future building materials could let heat out during cool summer nights but keep it in during the winter. Solar cells could harness the portion of the sun’s spectrum that isn’t converted to electricity for other purposes. A roof installation could send this lost energy to heat water.

Heat shoots out the edges in thin plates

To illustrate the concept, Pramod Reddy, professor of mechanical engineering, produced two cards from his wallet, laying one on his palm and the other across his fingers with a gap between them. He made matched pairs of semiconductor plates similar in shape to the cards but about a thousand times smaller in length and width.

The thickness of the rectangular plates was anywhere between 10,000 nanometers (0.01 millimetres) to 270 nanometers. He suspended these on narrow beams about a hundred times thinner than a human hair.

In an object which is similar to the size and shape of a credit card, heat would radiate from each of the six sides in proportion to the surface area. But the team found that when the structures are thinnest or about half the wavelength of green light, those edges release and absorb much more heat than anticipated.

Reddy along with Zhu built a detailed mathematical model of the two thin plates and the physics that govern heat transfer between these structures.
After running the model on a supercomputer, they confirmed that the 100-fold enhancement in heat flow occurs because of the way that waves move in the very thin plates. Since the waves run parallel to the plate’s longer dimensions, the heat shoots out the edges. In the identical plate absorbing the energy, the same concept was at work.