Mechanical & Plumbing
Cooling systems made from metal muscles that tense and flex
February 2, 2016 - Researchers are developing a new method of cooling in which heat and cold are transferred using ‘muscles’ made from a ‘shape memory alloy’, with the aim of achieving a cooling process that does not require climatically harmful refrigerants, and should consume less energy than current technologies.
“In our systems, shape memory alloys [SMAs] are used to remove heat,” explained Stefan Seelecke of Saarland University. “Shape memory means that wires or sheets made from a nickel-titanium alloy have a certain ability to remember their original shape […] So they are able to tense and flex like muscles. The fact that they absorb and release heat when they do so is something we exploit to achieve cooling.”
When a nickel-titanium wire or sheet is deformed or pulled in tension, the crystal lattice structure can change, creating strain within the material. This change in the crystal structure—known as a phase transition—causes the SMA to become hotter. When the stressed sample is allowed to relax after temperature equalization with the environment, it undergoes cooling to a temperature about 20 degrees below ambient.
“The basic idea was to remove heat from a space—like the interior of a refrigerator—by allowing a pre-stressed, super-elastic shape memory material to relax and, thus, cool significantly. The heat taken up in this process is then released externally to the surroundings. The SMA is then re-stressed in the surroundings, thereby raising its temperature, before the cycle begins again,” said Seelecke.
PHOTO: Marvin Schmidt and Johannes Ullrich from the research team headed by professors Andreas Schütze and Stefan Seelecke are working on developing an environmentally sustainable and resource-friendly cooling method. Photo Oliver Dietze.