Swap metal heat exchangers for plastic

HEAT exchangers could one day be made from polyethylene after engineers at the Massachusetts Institute of Technology found a way to make it conduct heat very efficiently in one direction.

Carrying heat in one direction is not a property associated with polymers, or even metals used to make heat exchangers used today, which conduct heat equally well in all directions. The MIT team found that they could make heat travel in a straight line along a polymer fibre if they could make all the molecules in the fibre line up unidirectionally, rather than forming a jumbled mass as is the norm.

In the first stage of the production process, the team slowly drew a polyethylene fibre out of a heated solution using the finely controllable cantilever of an atomic force microscope. In the second stage it was heated once more to restretch it. “Once it solidifies at room temperature, you can't do any large deformation,” says lead author Sheng Shen, “so we heat it up twice.”

The resulting fibre was around 300 times more thermally conductive than normal polyethylene making it the highest thermal conductivity ever seen in any polymer. The team says this outperforms almost half of all pure metals, including iron and platinum.

The team will now work to scale up its production process, which has so far only produced individual fibres. The team thinks modified polyethylene could eventually replace the metals used in heat exchanger fins, solar hot water collectors and microchips.
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