Elastocaloric Cooling: State-of-the-art and Future Challenges in Designing Regenerative Elastocaloric Devices

Abstract

The elastocaloric cooling, utilizing latent heat associated with martensitic transformation in shape-memory alloys, is being considered in the recent years as one of the most promising alternatives to vapour compression cooling technology. It can be more efficient and completely harmless to the environment and people. In the first part of this work, the basics of the elastocaloric effect (eCE) and the state-of-the-art in the field of elastocaloric materials and devices are presented. In the second part, we are addressing crucial challenges in designing active elastocaloric regenerators, which are currently showing the largest potential for utilization of eCE in practical devices. Another key component of elastocaloric technology is a driver mechanism that needs to provide loading for active elastocaloric regenerators in an efficient way and recover the released energy during their unloading. Different driver mechanisms are reviewed and the work recovery potential is discussed in the third part of this work.

Numerical Optimization of a Single Bunch of NiTi Wires to Be Placed in an Elastocaloric Experimental Device: Preliminary Results

“…(a) The elastocaloric benchmark material is the Nickel-Titanium (NiTi) binary alloy, whose elastocaloric properties were open to the scientific community in 1963 [46]. It is the most investigated shape memory alloy in the panorama of elastocaloric applications [47] because of its remarkable adiabatic temperature change (∆T ad ) at room temperature due to eCE. Cui et al conducted Ni-Ti wires showing a ∆T ad of 25.5 K during loading and 17 K during unloading [48].…”

“…Next to the binary Ni-Ti, ternary or quaternary Ni-Ti alloys can improve the performance of the SMAs for different applications. With respect to the binary version, copper or vanadium addition to Ni-Ti alloys has the purpose to minimize the stress hysteresis and to enhance fatigue life [47]. Other popular SMA are the Cu-based as Cu-Zn and Cu-Sn, even if the ternary alloys (Cu-Zn-Al, Cu-Al-Ni) and others are more interesting, since they offer increased mechanical and thermal properties; i.e., the presence of Aluminum ensures an enhancement of the heat transfer coefficients [49,50].…”

“…(b) To date, the elastocaloric prototypes developed so far in the world do not exceed ten units and are still far from prospects of use for residential or commercial cooling applications [42,47]. As maximal subclassification, the concepts for cooling or heat pumping by means of the elastocaloric technology can be implemented based disjunctively on: conductive heat transfer though the placement of chains of solid elements (eCE material and thermal diodes); convective heat exchange establishing itself between the eCE refrigerant and a Heat Transfer Fluid (HTF), in an Active elastocaloric Regenerator (AeR).…”

Toward a solid-state thermal diode for room-temperature magnetocaloric energy conversion

“…Caloric refrigeration is seen as one of the promising alternatives to vapor-compression refrigeration technology [1][2][3] . This technology is based on exploiting the so-called caloric effect, where the temperature of a caloric material changes with a changing external parameter: i) magnetic field for a magnetocaloric material [4][5][6][7] ; ii) electric field for an electrocaloric material [8][9][10][11] ; iii) applied stress for an elastocaloric material [12][13][14] ; iv) applied pressure for a barocaloric material 15,16 or; v) a combination of some or all of them for a multicaloric material [17][18][19] under adiabatic conditions. A caloric refrigeration or heat-pump system typically consists of a caloric material, heat source, heat sink, and heat-transfer medium, and its thermodynamic cycle comprises the following four stages:…”

Utilizing Incomplete Phase Transformation to Characterize Elastocaloric Effect of Shape Memory Alloys

“…To effectively utilize the caloric effect in a required temperature span compared with conventional cooling, heat recovery, [15] active regenerative, [16] and cascade [17,18] cycles are applied to execute a multi-stage of caloric refrigeration cycles. [19][20][21] As most caloric devices configured with active regeneration, [22,23] SMAs can be operated in an active elastocaloric cycle as follows: 1) loading from an austenitic to a martensitic phase; 2) releasing heat crossed by fluid flow under stress; 3) unloading from a martensitic to an austenitic phase; and 4) absorbing heat during a reverse fluid flow under the stress-free condition. [24] The eCE is commonly characterized by adiabatic temperature change (ΔT adi ) and isothermal entropy change (Δs iso ) as a function of temperature and applied stress/strain.…”