Editing Refrigeration (section)

===Elastocaloric refrigeration===
Another potential solid-state refrigeration technique and a relatively new area of study comes from a special property of [[pseudoelasticity|super elastic]] materials. These materials undergo a temperature change when experiencing an applied mechanical [[stress (mechanics)|stress]] (called the elastocaloric effect). Since super elastic materials deform reversibly at high [[strain (mechanics)|strains]], the material experiences a flattened [[elasticity (physics)|elastic]] region in its [[stress-strain curve]] caused by a resulting phase transformation from an [[austenite|austenitic]] to a [[martensite|martensitic]] crystal phase.

When a super elastic material experiences a stress in the austenitic phase, it undergoes an [[exothermic]] [[phase transition|phase transformation]] to the martensitic phase, which causes the material to heat up. Removing the stress reverses the process, restores the material to its austenitic phase, and [[endothermic process|absorbs heat]] from the surroundings cooling down the material.

The most appealing part of this research is how potentially energy efficient and environmentally friendly this cooling technology is. The different materials used, commonly [[shape-memory alloy]]s, provide a non-toxic source of emission free refrigeration. The most commonly studied materials studied are shape-memory alloys, like [[nitinol]] and Cu-Zn-Al. Nitinol is of the more promising alloys with output heat at about 66 J/cm<sup>3</sup> and a temperature change of about 16–20 K.<ref>{{cite journal|last1=Tušek|first1=J.|last2=Engelbrecht|first2=K.|last3=Mikkelsen|first3=L.P.|last4=Pryds|first4=N.|title=Elastocaloric effect of Ni-Ti wire for application in a cooling device|journal=Journal of Applied Physics|date=February 2015|volume=117|issue=12|pages=124901|doi=10.1063/1.4913878|bibcode=2015JAP...117l4901T|s2cid=54708904 }}</ref> Due to the difficulty in manufacturing some of the shape memory alloys, alternative materials like [[natural rubber]] have been studied. Even though rubber may not give off as much heat per volume (12 J/cm<sup>3</sup> ) as the shape memory alloys, it still generates a comparable temperature change of about 12 K and operates at a suitable temperature range, low stresses, and low cost.<ref>{{cite journal|last1=Xie|first1=Zhongjian|last2=Sebald|first2=Gael|last3=Guyomar|first3=Daniel|title=Temperature dependence of the elastocaloric effect in natural rubber|journal=Physics Letters A|date=21 February 2017|volume=381|issue=25–26|pages=2112–2116|doi=10.1016/j.physleta.2017.02.014|arxiv=1604.02686|bibcode=2017PhLA..381.2112X|s2cid=119218238}}</ref>

The main challenge however comes from potential energy losses in the form of [[hysteresis]], often associated with this process. Since most of these losses comes from incompatibilities between the two phases, proper alloy tuning is necessary to reduce losses and increase reversibility and [[energy conversion efficiency|efficiency]]. Balancing the transformation strain of the material with the energy losses enables a large elastocaloric effect to occur and potentially a new alternative for refrigeration.<ref>{{cite journal|last1=Lu|first1=Benfeng|last2=Liu|first2=Jian|title=Elastocaloric effect and superelastic stability in Ni–Mn–In–Co polycrystalline Heusler alloys: hysteresis and strain-rate effects|journal=Scientific Reports|date=18 May 2017|volume=7|issue=1|pages=2084|doi=10.1038/s41598-017-02300-3|pmid=28522819|pmc=5437036|bibcode=2017NatSR...7.2084L}}</ref>