A Saarland University research team has revealed a prototype device that can be used to heat or cool air or liquids using artificial nickel-titanium (nitinol) “muscles.” The device takes advantage of nitinol’s memory material ability to absorb or release heat depending on whether it is moving towards a superelastic “relaxed” state or returning to a “loaded” state.
The Saarbrücken researchers report that their prototype is environmentally friendly and has twice to three times the efficiency of conventional heating or cooling equipment. Already, the US Department of Energy and the EU Commission have declared the new technology to have great promise as a more sustainable alternative to current refrigeration techniques.
The most significant difference between the new technology and the old, is that refrigerants used in air conditioning are known to be harmful to the environment. The new method can achieve the same effect using less energy and without the harmful gases. As an added bonus, the same principle can be used for heating.
Professor Stephan Seeleke of Saarland University (Germany) explains that when pre-stressed nitinol wires are unloaded, they will cool dramatically, with a 20 degree drop in temperature having been observed. When the wires are loaded up again, the rise in temperature is similar.
Just as muscles fibers work in bundles, so the new cooling method consists of bundles of fibers that load an unload in concert, ensuring efficient heat transference. When air is blown through the mechanical muscles, two separate chambers house the resulting heated and cooled air, allowing the operator to choose between heated or refrigerated output.
However, the theory is a lot simpler than the implementation as the researchers have found during an ongoing project in which various problems had to be overcome. For example, calibrating the wires’ loading so that they produced a desired level of cooling presented challenges and the team had to determine how many wires to include in each bundle to get the necessary surface-area for heating and cooling.
Now, exact parameters have been captured and the team has developed software that will allow for precise tuning of the device’s heating and cooling.
The efficiency of the novel technology is unquestionable. It can produce as much as thirty times more cooling or heating power than the mechanical energy it takes to load the wires.
Nevertheless, the researchers believe that there is room for improvement. They are currently working on improving the device still further so that the phase transition’s energy will almost exclusively be used for heating or cooling.