The typical refrigerator or freezer uses a refrigerant to produce cold temperatures. Refrigerants make use of a cycle of evaporation and condensation to cool the contents inside. Evaporation is an endothermic process, which absorbs heat from the surroundings. The result is a cool refrigerator interior.
Once the refrigerant warms up, it becomes a gas. A compressor then pressurizes the gaseous refrigerant, and it will be condensed back into a liquid ready to cool the interior of the refrigerator again. This refrigeration cycle is what drives the cooling effect in modern fridges and freezers.
Now, a new innovation can potentially change how refrigeration works.
Metal shapeshifter
Nitinol is an alloy composed of nickel and titanium. It is a shapeshifting metal – nitinol can be bent, then snapped back into shape when exposed to heat. It “remembers” its original form no matter how bent and warped it becomes. This behavior is called the shape memory effect.
Hot and cold
Nitinol transitioning from bent to back in shape has another interesting effect. When it is bent, it absorbs heat from its environment. Conversely, when it snaps back into its original shape, it releases heat.
Nitinol coolant
What if nitinol was used instead of a refrigerant? This is possible, and a team of German scientists from Saarland University has built a proof of concept.
The team took bundles of nitinol wire and wrapped it around a cylinder. On one side, the wires were being bent, and on the other side, they were being snapped back. Fans were then put on both sides. Cool air flowed out of the side where the wires were bent, while warm air flowed out of the other side.
In other words, the shape memory effect of nitinol is acting as a heat pump. The bent wire absorbed heat from one side of the cylinder and transferred it to the other side as the wire sprung back into its original shape.
Is this the future of refrigeration?
The nitinol-powered cooling system may eliminate the need for refrigerants and compressors. This way, refrigeration systems can be radically simplified, making them easier to build and maintain. They could become cheaper as well, as fewer parts are needed.
The results of the scientists’ experiments with nitinol cooling are also remarkable. According to the team, the cooling output is up to 30 times more than the mechanical energy needed to bend and snap back the wires. They further say that this system can be three times more efficient than a typical refrigerator. As a bonus, it is also eco-friendly as no chemical refrigerants are needed.
Once this system is scaled up and commercialized, we may be seeing a new breed of refrigerators, chillers, and ultralow temperature freezers.
