With a simple twist, a rubber band could power future eco-fridges

11 Oct 2019

Image: © Duangjit/Stock.adobe.com

An international research team has discovered new refrigeration technology achieved just by twisting and untwisting fibres.

A breakthrough in refrigeration technology has shown it possible to create a cooling effect using objects as common as fishing line or rubber, just by twisting and untwisting them. Writing in Science, an international team led by researchers from the University of Texas and Nankai University in China described this newly discovered method as ‘twistocaloric cooling’ and anything that uses twist changes for cooling as ‘twist fridges’.

Existing science has shown that stretching a rubber band will heat the rubber, while releasing the stretch will cool it, referred to as elastocaloric cooling.

“This elastocaloric behaviour of natural rubber has been known since the early 1800s,” said Dr Ray Baughman, a corresponding author of the study.

“But to get high cooling from a rubber band, you have to release a very large stretch. With twistocaloric cooling, we found that all you have to do is release twist.”

Such efforts are expected to play an important part in significantly reducing electricity consumption of refrigeration units and air conditioners, which amount to some of the largest consumers in the world. These units also release tonnes of harmful gases that are contributing to the climate emergency.

Twists and turns

As part of this latest study, the team stretched rubber fibres, then twisted them until they not only coiled, but supercoiled. When the twist was released, it cooled the rubber fibres’ surface temperature by 15.5 degrees Celsius. Releasing both the twist and the stretch from the rubber produced even higher cooling of 16.4 degrees Celsius.

The phenomenon was also seen in non-elastic polymer fishing lines that were twisted until coils formed. This caused the fibres to heat up, but releasing them saw it cool by 5.1 degrees Celsius.

By analysing the rubber and fishing lines at a molecular level, it showed releasing stretch from a coiled fibre results in partial conversion of a low entropy phase into a high entropy phase, resulting in twistocaloric cooling.

Even more impressive cooling was seen in nickel titanium wires with a maximum surface cooling of 17 degrees Celsius in one untwisted wire, while 20.8 degrees Celsius was seen in a four-wire bundle. The researchers placed a three-ply nickel titanium wire cable in a device they built that cooled a stream of water by up to 7.7 degrees Celsius when the cable was unplied.

“Many challenges and opportunities exist on the path from these initial discoveries to commercialisation of twist fridges for diverse large- and small-scale applications,” Baughman said.

Colm Gorey was a senior journalist with Silicon Republic