A team of researchers in Germany has developed a prototype of an advanced heating/cooling system that can heat and cool air by compressing and unloading nitinol “muscle lines” at twice the efficiency of heat pumps or three times the efficiency of air conditioners. The device does not use refrigerant gas, which means it is a more environmentally friendly way to heat or cool a space.
The device is based on the special properties of certain shape memory metal alloys. In some cases, especially nickel-titanium alloys, these metals absorb a lot of heat when bent out of shape, and then release the heat when they are allowed to return to their normal shape. The difference between the loaded line and the released line can be as much as 20°C. So this cooling device is very simple in concept, it uses a rotating cylinder covered with bundles of nitinol wires. The wires are loaded when passing through one side, sucking heat from the air and storing it. Then when they rotate past the other side, they are allowed to spring back into shape, dumping the heat on the second side. Air is blown through chambers on each side, heating the air on one side and cooling it on the other side.
Heating/cooling system that exploits the superior properties of shape memory NiTi alloy for environmentally friendly cooling and heating
The research team at Saarland University in Germany has been experimenting with this device to determine the wire load, rotation speed, and how many wires should be bundled to achieve the best convergence, thereby creating the maximum possible thermal difference between the two sides for a given energy input. Ultimately, the Saarland University team claims that the system’s heating or cooling power is thirty times higher than the mechanical power required to load and unload the alloy wire bundles, depending on the type of alloy used. They say this makes their new system twice as efficient as a conventional heat pump and three times as efficient as a conventional refrigerator.
This new technology is also environmentally friendly and does not harm the climate because the heat transfer mechanism does not use liquids or steam. Therefore, the air in the air conditioning system can be cooled directly without intermediate heat exchangers and without the need for leak-free high-pressure pipes. And nickel-titanium alloy is the most resistant metal known to date in high-amplitude strain-controlled fatigue environments, so theoretically there is no need to worry about its metal fatigue problem, but this still requires subsequent commercial applications for actual evaluation.