A magnetically, electrically or mechanically responsive material can undergo significant thermal changes near a ferroic phase transition when its order parameter is modified by the conjugate applied field. The resulting magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects are compared here in terms of history, experimental method, performance and prospective cooling applications.

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Caloric materials near ferroic phase transitions

Magnetocaloric effect: From materials research to refrigeration devices

The elastocaloric effect in the vicinity of the martensitic transition of a Cu-Zn-Al single crystal has been studied by inducing the transition by strain or stress measurements. While transition trajectories show significant differences, the entropy change associated with the whole transformation (DeltaS_(t)) is coincident in both kinds of experiments since entropy production is small compared to DeltaS_(t). The values agree with estimations based on the Clausius-Clapeyron equation. The possibility of using these materials for mechanical refrigeration is also discussed.

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Elastocaloric effect associated with the martensitic transition in shape-memory alloys.

The search for materials with large caloric effects has become a major challenge in material science due to their potential in developing near room-temperature solid-state cooling devices, which are both efficient and clean, and that can successfully replace present refrigeration technologies. There are three main families of caloric materials: magnetocaloric, electrocaloric, and mechanocaloric. While magnetocaloric and electrocaloric materials have been studied intensively in the last few decades, mechanocaloric materials are only very recently receiving a great deal of attention. The mechanocaloric effect refers to the reversible thermal response of a solid when subjected to an external mechanical field, and encompasses both the elastocaloric effect, corresponding to a uniaxial force, and the barocaloric effect, which corresponds to the response to hydrostatic pressure. Here, the state of the art in giant mechanocaloric effects is reviewed and a critical analysis of the thermodynamic quantities that characterize the major families of barocaloric and elastocaloric materials is provided. Finally perspectives for further development in this area are given.

Materials with Giant Mechanocaloric Effects: Cooling by Strength.

Elastocaloric cooling is a new alternative solid-state cooling technology undergoing early stage research and development. This study presents a comprehensive review of key issues related to achieving a successful elastocaloric cooling system. Fundamentals in elastocaloric materials are reviewed. The basic and advanced thermodynamic cycles are presented based on analogy from other solid-state cooling technologies. System integration issues are discussed to characterize the next generation elastocaloric cooling prototype. Knowledge acquired from the elastocaloric heat engines is provided as the basis for the design of cooling system configuration. Commercially available drivers enabling proper compression and tension are also presented. A few performance assessment indices are proposed and discussed as guidelines for design and evaluation of future elastocaloric cooling system. A brief summary of the up-to-date elastocaloric cooling prototypes is presented as well.

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A review of elastocaloric cooling: materials, cycles and system integrations.

Giant elastocaloric effect in FeRh alloy

The heat-pumping scheme based on the 1st order antiferromagnetism–ferromagnetism transition induced in FeRh alloy by one-dimensional tensile stress is proposed. Using the model S–T diagram for this alloy, the heat-pump cycles are drawn up based both on the transition latent heat absorption and emission when the transition is induced isothermally and on the change in alloy's temperature when the transition is induced adiabatically by applying tensile stress. The calculated values of heat coefficient φ for the cycles are ∼30 at ΔT=5 К and ∼20 at ΔT=10 К, where ΔT is the difference between the temperature surrounding and that of the heat receiver. These values are achieved using the tensile stress of ∼1·109 Pa. The high values of φ make it possible to consider Fe–Rh alloys near the equiatomic composition as an effective refrigerant for elastocaloric heat-pumping near the room temperature.

Heat pump cycles based on the AF-F transition in Fe-Rh alloys induced by tensile stress

A cooling scheme based on the first-order antiferromagnetism-ferromagnetism transition induced in the Fe-Rh alloy by one-dimensional tensile stress is proposed. Using the model S-T diagram for this alloy, the cooling cycles are drawn up based both on the latent heat of transition absorption and emission when the transition is induced isothermally and on the change in temperature of the alloy when the transition is induced adiabatically by applying tensile stress. The calculated values of the efficiency e for the cycles are ∼35 at ΔT = 5 K and ∼27 at ΔT = 10 K, where ΔT is the difference between the temperature of the surroundings and that of the cooled body. These values are achieved using a tensile stress of ∼1 x 10 9 Pa. The high values of e make it possible to consider Fe-Rh alloys near the equiatomic composition as an effective refrigerant for elastocaloric cooling near room temperature.

S.A. Akopyan

Papers

Giant elastocaloric effect in FeRh alloy

Heat pump cycles based on the AF-F transition in Fe-Rh alloys induced by tensile stress

Cooling Scheme Based on the AF–F Transition in Fe–Rh Alloys Induced by Tensile Stress