Editing Shape-memory alloy (section)

=== Heating and cooling ===

German scientists at [[Saarland University]] have produced a prototype machine that transfers heat using a nickel-titanium ("nitinol") alloy wire wrapped around a rotating cylinder.  As the cylinder rotates, heat is absorbed on one side and released on the other, as the wire changes from its "superelastic" state to its unloaded state.  According to a 2019 article released by Saarland University, the efficiency by which the heat is transferred appears to be higher than that of a typical heat pump or air conditioner.<ref>{{cite web |author=Saarland University |date=March 13, 2019 |title=Research team uses artificial muscles to develop an air conditioner for the future |url=https://phys.org/news/2019-03-team-artificial-muscles-air-conditioner.html |website=phys.org }}</ref>

Almost all air conditioners and [[heat pumps]] in use today employ vapor-compression of [[refrigerants]].  Over time, some of the refrigerants used in these systems leak into the atmosphere and contribute to [[global warming]].  If the new technology, which uses no refrigerants, proves economical and practical, it might offer a significant breakthrough in the effort to reduce climate change.{{citation needed|date=December 2019}}