New refrigerator runs by flexing its artificial muscles

A team of researchers from Saarland University and the Center for Mechatronics and Automation Technology (ZeMa) has developed what it claims is the world’s first refrigerator that cools using artificial muscles composed of nitinol — a nickel-titanium alloy.

According to its developers, the refrigerator is a compact prototype that demonstrates the new cooling technology, which works according to the elastocaloric principle wherein heat is removed from a region via stretching wires and thus releasing them. The team explained that the shape-memory wires featuring the super-elastic nitinol — which are also called “artificial muscles” — accumulate heat within the cooling chamber and subsequently release it into the surrounding air. This process, researchers suggest, offers environmentally friendly and energy efficient cooling and heating technology when compared against conventional technologies.

Source: Saarland University and the Center for Mechatronics and Automation Technology (ZeMa)

“Our elastocaloric process enables us to achieve temperature differences of around 20 degrees Celsius without using climate-damaging refrigerants in a far more energy-efficient manner than today’s conventional technologies,” the researchers added in a statement.

While engineers currently demonstrate elastocalorics within small cooling chambers, the material can also reportedly extract heat from and supply it to larger spaces. As such, the research team is also using the superelastic wires for heat transfer in heating applications.

The researchers accomplish this by harnessing the shape memory characteristics of the nitinol-based artificial muscles to transfer heat. The alloy’s wires can reportedly “remember” their initial configuration and can subsequently return to it after stretching or distorting, much like muscles flexing.

The researchers explained that this is due to the fact that nitinol features two crystal lattices — or phases — that can transform into one another deep within. Further, the wires absorb heat and then release it at such crystalline structure phase transitions.

Specifically, the shape-memory material will release heat when stretched in a superelastic state, and will absorb heat when released. This effect is amplified when several wires are grouped together, with their increased surface area enabling them to absorb and release more heat, thereby intensifying the impact.

As such, the research team developed its mini-fridge featuring a patented cam drive that rotates bundles of 200 micron-thin nitinol wires around a circular cooling chamber.

The researchers added that as the wires rotate, they take turns being mechanically loaded and unloaded, absorbing heat from the circulating air within the chamber. Meanwhile, the cooled air circulates around unloaded wires and the rotating wires release heat outside the chamber when stretched.

Going forward, the team wants to leverage the potential of elastocalorics in applications including industrial cooling, electric vehicle cooling and household appliances.

For more information on this research, watch the accompanying video that appears courtesy of Saarland University and ZeMa.

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