Caloric cooling: state of the art and perspectives
In their review article (1) recently published in the International Journal of Refrigeration, A. Greco et al stress that since 1976, year of the development of the first room-temperature magnetic refrigerator, up to a few years ago, magnetocaloric cooling was among the most investigated alternative solid-state technologies to vapour-compression refrigeration. During this period, a remarkable number of prototypes of magnetic refrigerators or heat pumps has been built.
In the last few years, the attention on solid-state cooling was progressively extended from magnetocaloric to three other caloric effects applicable to refrigeration and heat pumps, namely electro-, elasto- and baro-caloric effects. As highlighted by the authors, this has been illustrated by the subtitle change of the IIR Thermag conferences – launched in 2005 to gather the scientific community and to disseminate a periodic overview of the latest developments on magnetocaloric materials and prototypes – which became “International Conference on Caloric Cooling” in 2018 and now includes magnetocaloric, electrocaloric, elastocaloric and barocaloric cooling. The next Thermag IX conference will take place in College Park, Maryland, US, on June 7-11, 2020. (2)
In their paper, the authors provide an overview of the progresses made by the scientific community on solid-state caloric effect-based cooling in device realization. By retracing the entire history of prototype development, they have seen how research has developed through sudden steps leading to major breakthroughs. For example, the introduction of rotative permanent magnets systems has drastically changed the design of magnetocaloric devices, or the discovery of Giant Electrocaloric Effect paved the way for the use of this phenomenon for cooling applications.
Important steps have been taken particularly in magnetocaloric prototype development with the design of devices that can produce cooling power up to 3042 W, or temperature spans as high as around 40 K.
The major bottleneck of elastocaloric cooling is fatigue resistance of the elastocaloric materials employed; it currently does not allow for the construction of long-lasting devices. Further research needs to be done in this field.
Less remarkable results were obtained in the development of electrocaloric devices, based on active regeneration, because of the high losses related to electric-field generation that drastically bring down the energy performances of the realized prototypes.
Barocaloric seems to be a promising technology on which scientific community is now laying the first bases for the realization of heating and cooling devices.
Nowadays, researchers are moving toward further promising directions, alongside active regeneration. One of these is represented by thermoelectric switches employed for magnetocaloric and electrocaloric cooling applications. Such technology has the advantage of presenting no moving parts that allows the miniaturization and the operation of the devices at higher frequencies.
An interesting perspective on the synergic application of magnetocaloric and thermoelectric for cooling was also recently presented. Likewise, a model of a small-scale heat pump based on thermoelectric and electrocaloric materials was introduced. Another way is the simultaneous employment of several caloric effects for cooling – multicaloric effect – generated by different-nature fields.
Most of the studies published up to now are still theoretical; but more practical applications for cooling purposes have been presented by researchers that modeled an efficient solid-state cooler based on layered multiferroics. Other researchers proposed a proof of concept based on multicaloric cooling cycle in which also thermal hysteresis is accounted.
The authors conclude that solid-state refrigeration and heat pumping technology have made great strides in the last decade and hope that the research work carried out will allow for a large-scale implementation as well as boost the competitiveness of the solid-state prototypes based on caloric effects.
(1) A. Greco a , C. Aprea b , A. Maiorino b , C. Masselli; A review of the state of the art of solid-state caloric cooling processes at room-temperature before 2019: Available in Fridoc database (free for IIR members).