Les faits marquants de la conférence Thermag VIII de l’IIF sur le froid calorique (en anglais)

Thermag VIII took place in Darmstadt (Germany) on September 16-20, 2018. It is the 8th IIR conference on magnetic refrigeration but this time, it was also largely dedicated to other not in kind technologies such as electrocaloric and elastocaloric refrigeration.

Even if these technologies currently only represent niche applications possibilities, it is crucial to explore all technologies for the future because of increasing refrigeration uses and environmental constraints. We thus decided to continue the Thermag series of conferences, dedicated to all these technologies with solid materials and the next one will take place in the university of Maryland (USA) in June 7-10, 2020.

The high number of papers (43) presented at the IIR Thermag VIII International Conference on Caloric Cooling illustrates the great attention paid by researchers to the development of cooling devices based on the magnetocaloric, electrocaloric and (elasto)barocaloric effects. These effects rely on the temperature change of the material exposed to different physical fields (magnetic, electrical and mechanical). But, as highlighted by Sergio L. Dutra et al.¹, the magnitude of these effects (in common less than 5 K) is not sufficient for the development of efficient solid-state cooling devices where a temperature change in the range 30-50 K is required. To solve this problem, it is necessary to organize an efficient thermodynamic cycle.

Magnetic cooling using an Active Magnetic Regenerator has been the first caloric technology to capture the attention of the scientific community. Magnetocaloric materials have aroused high research interest. According to Sandra Wieland et al.² and other authors, La(FeSi)13-based alloys came into focus during the last years and are considered as very promising since they show high magnetocaloric effect in a broad temperature range and are at the same time composed of relatively cheap and abundant elements.

Regarding magnetocaloric devices, it may be noted that Cooltech Applications announced³ that they had assembled and tested a new type of a magnetocaloric rotating system which is said by its designers to be "the largest scale magnetocaloric machine ever built by the community". It meets the requirements for an actual industrial chiller: both a temperature span of more than 20 K and a cooling capacity of 15 kW, with an efficiency around 60% of the COP of Carnot.

Electrocaloric cooling is a promising candidate for novel sustainable solid state cooling technologies. According to Y. Wang et al⁴, the electrocaloric effect, a material property that can be described as an adiabatic temperature change with an applied electric field, can be exploited to design solid-state cooling systems that are compact, efficient, reliable, and environmentally benign.

Regeneration has been explored by the authors as a means for increasing the system temperature lift. They report a solid-state regenerative EC cooling system design capable of a very high regeneration factor.

Regarding elastocaloric cooling, Susanne-Marie Kirsch, Felix Welsh et al.^{5, 6} have presented the modeling and development of a novel continuous operating elastocaloric air cooling device based on Shape memory alloys (SMA). A novel mechanical loading concept and a novel bundle concept of thin NiTi SMA wires enable a thermodynamically optimised cooling process by utilising a minimal amount of SMA material in a compact design space and high cooling capability.

Ciro Aprea et al.⁷ stressed that, for all caloric cooling technologies, the cooling capacities and, more generally, the energy performances of caloric refrigerators are limited by the not so wide amplitude of caloric effect materials which constitutes an obstacle to the development of large-scale application coolers. Caloric materials are generally tested numerically through models before being employed in real experimental prototypes. A large number of Active Magnetocaloric Regenerator models has been proposed over the years. On the other side, electrocaloric and elastocaloric models presented in the literature are many less, whereas there is not any numerical model of Active barocaloric refrigerator, yet. Inherent literature does not contain any model of Active Caloric Cooler which can reproduce the behaviour of any caloric refrigerant regardless of the specific caloric effect shown. In this context, the authors proposed a two-dimensional model of an Active Caloric Regenerator which has been employed to investigate the caloric effects and energy performances of the most promising magnetocaloric, electrocaloric, elastocaloric and barocaloric materials reported in the literature. Based on this model, the results show that electrocaloric materials give the largest cooling power and COP with a cooling power of around 1500 W vs 36 K as temperature span.

¹ Dutra S. L . et al. Solid-state magnetocaloric cooler without heat switches. Available in Fridoc.

² Wieland S. et al. Powder, process parameters and heat treatment conditions for Laser Beam Melting of LaFeSi-based alloys. Available in Fridoc.

³ Chaudron J. B. et al. Performance measurements on a large-scale magnetocaloric cooling application at room temperature. Available in Fridoc.

⁴ Wang Y. et al. A self-regenerating electrocaloric cooler. Available in Fridoc.

⁵ Kirsch S. M. et al. Continuously operating elastocaloric cooling device based on shape memory alloys: development and realization. Available in Fridoc.

⁶ Welsh F. et al. Continuously operating elastocaloric cooling device based on shape memory alloys: modeling. Available in Fridoc.

⁷ Aprea C. et al. A numerical investigation upon the energy performances of caloric materials working in an Active Regenerator. Available in Fridoc.

Download other Thermag VIII papers in Fridoc.