Elastocaloric Effect Research Articles

Elastocaloric heat pump with specific cooling power of 20.9 W g–1 exploiting snap-through instability and strain-induced crystallization

Conventional refrigeration relies on hazardous agents, contributing to global warming. Soft, cheap, biodegradable solid-state elastocaloric cooling based on natural rubber offers an environmentally friendly alternative. However, no such practical cooler has been developed, as conventional soft elastocaloric designs are not fast enough to ensure adiabaticity. Here, we combine snap-through instability with strain-induced crystallization and achieve a sub-100 ms quasi-adiabatic cycling, which is 30 times faster than previous designs. Negligible heat exchange in expansion/contraction stages combined with the latent heat of phase transitions results in a giant elastocaloric crystallization effect. The rubber-based all-soft heat pump enables a specific cooling power of 20.9 W g–1, a heat flux of 256 mW cm–2, a coefficient of performance of 4.7 and a single-stage temperature span between hot and cold reservoirs of 7.9 K (full adiabatic temperature change of rubber membrane exceeding 23 K). The pump permits a compact all-soft voltage-actuated set-up, opening up the opportunity of a viable plug-in-ready cooling device.

Elastocaloric effect with a broad temperature window and low energy loss in a nanograin Ti-44Ni-5Cu-1Al (at·%) shape memory alloy

Superelastic Ti-Ni-based shape memory alloys are promising elastocaloric materials for solid-state refrigeration. In this paper, we studied the mechanical properties and elastocaloric effect of a severely cold rolled Ti-44Ni-5Cu-1Al (at.%) alloy composed of nanograins $(\ensuremath{\sim}5\text{--}16\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$. The alloy exhibits partial stress-induced martensitic transformation with a large quasilinear reversible strain of $\ensuremath{\sim}3.4\phantom{\rule{0.16em}{0ex}}%$ and a small energy dissipation of $\ensuremath{\sim}1.6\phantom{\rule{0.16em}{0ex}}\mathrm{MJ}/{\mathrm{m}}^{3}$ when a maximum stress of 1 GPa is applied. The temperature decrease induced by adiabatic removal of a stress of 1 GPa is of about \ensuremath{-}5 K, which is mainly due to the reverse transition occurring during unloading. The effective working temperature window of elastocaloric effect larger than 200 K. The coefficient of performance of this alloy reaches \ensuremath{\sim}13, which is higher than values reported so far for Ti-Ni alloys.

Electrocaloric cooling over high device temperature span

Summary Electrocaloric cooling demonstrates direct electricity utilization and high energy efficiency, and is often proposed as an environmentally benign, solid-state alternative to the conventional vapor compression cooling technology. As a result, the fabrication of effective electrocaloric materials and engineering of electrocaloric cooling devices have attracted increasing attention in the cooling community. However, the limited material adiabatic temperature change under safe operation field poses a major challenge to practical electrocaloric cooling device development, since real-world applications usually require device temperature span over 20 K. This perspective presents recent efforts devoted to design electrocaloric cooling devices based on active heat regeneration and cascading approaches; both strategies have achieved significant device temperature lift ~10 K with adiabatic temperature change of 2~3 K. The strategies discussed in this work are broadly applicable to the design of efficient and compact cooling systems.

Flexo/elasto-caloric effects in 0.66Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 single crystal

Flexocaloric and elastocaloric effect are investigated in a 0.66Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 single crystal. The maximum flexocaloric temperature (0.43 K) and entropy (0.38 J/kg K) change are obtained at Curie temperature under a strain gradient of 5000 m−1. A peak elastocaloric temperature (1.45 K) and entropy (1.33 J/kg K) change due to strain gradient is evaluated at the Curie temperature under the applied stress of 250 MPa. 0.66Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 encompasses an enormous elastic contribution to the flexocaloric effect instead of the polarization at similar stress level. The formulation used for caloric calculation is based on strong approximation and available data; therefore, further research is warranted to validate this work.

Versatile Device for the Study of Coupling Properties in Multifunctional Materials. Example: Ni-(Co)-Mn-In Heusler Materials

We report on a versatile experimental setup for the study of the electro-magneto-elasto-thermal coupling for bulk materials having coupling properties. The setup enables measurement of stress and electrical resistivity in a 80-450 K temperature range under controlled uniaxial pressure in a magnetic field up to 8 T. The strong influence of uniaxial pressure and magnetic field on strain and transport properties is shown for Ni-Co-Mn-In Heusler single crystal material. Phase transformation, magnetostress and magnetic field-induced phase transformation, and elastocaloric effect can be estimated using this versatile setup. This device is very complementary to the studies focused on the modeling of thermo-electro-magneto-mechanical behavior for functional materials.

Закономерности проявления эластокалорического эффекта в [001]-монокристаллах никелида титана, содержащих наноразмерные частицы Ti3Ni4

The temperature dependence of the elastocaloric effect were studied and experimental values of the adiabatic cooling Δ T ad in loading/unloading cycles up to 13.3 K in quenched and 16.4 K in aged at 573 K, 1 h Ni50.6Ti49.4 single crystals were obtained. In aged crystals, a specific feature of the elastocaloric effect temperature dependence (an increase in Δ T ad above the temperature T R = 273 K) was found, which is associated with a change in the sequence of stress-induced martensitic transformation from R-B19' to B2-B19'. The factors (the value of the dissipated energy in the working cycle, the strain hardening coefficient during the stress-induced martensitic transformation), that affect the elastocaloric effect, are discussed. It is shown, that aged single crystals have a high coefficient of performance value up to 31, which characterizes the efficiency of converting mechanical energy into thermal energy, and are promising for solid-state cooling technologies.

Enhanced Superelasticity and Reversible Elastocaloric Effect in Nano-NiTi Alloys with Low Stress Hysteresis

Enhanced Superelasticity and Reversible Elastocaloric Effect in Nano-NiTi Alloys with Low Stress Hysteresis

Temperature dependence of martensite variant reorientation in stress-induced martensite aged Ni49Fe18Ga27Co6 single crystals

In the present study, the temperature dependence of martensite variant reorientation in stress-induced martensite aged at 423 K along the [110]B2||[100]L10-direction Ni49Fe18Ga27Co6 single crystals was investigated in compression. This martensite aging induces a rubber-like behavior with a reversible strain of up to –16.0% along the [001]B2-direction in the temperature range from 248 K to 344 K, which is caused by L10-martensite variant reorientation. At higher temperatures between the forward and reverse transformation from 344 K to 382 K, the stress-induced martensite aged crystals demonstrate a two-stage stress-strain response with a reversible strain of up to –13.5%. The first stage is characterized by low critical stresses of σcr1 ≈ 1 – 15 MPa and an inverse elastocaloric effect (heat absorption) under loading. Superelasticity is observed in the second stage with σcr2 ≥ 100 MPa. In this temperature range, the martensite variant reorientation occurs through reverse and then forward martensitic transformation.

Elastocaloric properties of thermoplastic polyurethane

Very few studies have explored the elastocaloric effect of elastomers other than natural rubber (NR). The aim of the present article is thus to evaluate the elastocaloric properties of a thermoplastic polyurethane (TPU) in terms of microstructural characteristics and thermoelastic coupling. Calorimetric measurements showed two successive peaks at 240 K and 282 K, attributed to the crystallization and melting of soft segments, respectively. X-ray diffraction indicated that TPU exhibited a fully reversible strain-induced crystallization at room temperature. Thermomechanical experiments performed at different elongations revealed a minimum adiabatic temperature variation of about −8 K after retraction of a sample initially elongated at λ = 5. This is comparable to NR performances. However, for cycles carried out between λ = 1 and λ = 5, tensile stress/elongation curves showed a non-elastic behavior of TPU. A pseudo-elastic response was obtained for cyclic elongation when unloading was incomplete, in our case, when λ was between 3 and 5. The recorded peak-to-peak temperature variation decreased from 4.5 K to 3.3 K when the number of cycles was increased to 5000. Despite the fact that the issue of fatigue resistance for TPU needs to be addressed, this work opens new perspectives for studying the elastocaloric properties of various polyurethanes (whether crosslinked or thermoplastic) as well as other materials with a tendency for strain-induced crystallization, such as polychloroprene, hydrogenated acrylonitrile butadiene rubber, and others.

Inhomogeneous martensitic transformation behavior and elastocaloric effect in a bicrystal Cu-Al-Mn shape memory alloy

The inhomogeneous distributions of strain and temperature of a bicrystal Cu-Al-Mn shape memory alloy were investigated. A large strain gradient was observed near the grain boundary. During the compression test, the top and bottom grains underwent outward and inward out-of-plane deformations, respectively, which led to the formation of cracks.

Large room-temperature elastocaloric effect in a bulk polycrystalline Ni-Ti-Cu-Co alloy with low isothermal stress hysteresis

Development of high-performance advanced elastocaloric materials is essential for the execution of elastocaloric refrigeration that can be an environment-friendly and high-efficiency substitute for the widely used traditional vapor-compression cooling technology. Here we have developed a bulk polycrystalline Ni-Ti-Cu-Co shape memory alloy exhibiting large elastocaloric effect, low stress hysteresis and room-temperature working temperature, all of which are of great importance to and urgently demanded for high-efficiency room-temperature elastocaloric refrigeration. This newly developed (Ni42.5Ti50Cu7.5)99Co1 alloy shows a large room-temperature elastocaloric effect with directly measured adiabatic temperature change up to −14.4 K during unloading. The stress hysteresis of the isothermal superelastic stress-strain curve is as low as 60 MPa when the maximum tensile strain is 2.7%. Owing to the large elastocaloric effect and low stress hysteresis, a very high coefficient of performance up to 19 is achieved on the material level. This newly developed (Ni42.5Ti50Cu7.5)99Co1 alloy is a robust candidate for efficient elastocaloric refrigeration. Advanced in-situ synchrotron high-energy X-ray diffraction technique was employed to reveal the phase transformation sequence and to accurately determine the crystal structure of different phases, based on which the lattice compatibility between the transforming phases was evaluated and the phase transformation strain was predicted, providing in-depth fundamental understanding of the martensitic transformation in this newly developed alloy. This work could be useful for designing high-performance elastocaloric materials for solid-state cooling applications.

Comparative analysis of elastocaloric and barocaloric effects in single-crystal and ceramic ferroelectric (NH4)2SO4

We report the influence of anisotropy and texture on elasto(ElCE)- and baro(BCE)-caloric effects in single-crystal and ceramic (NH4)2SO4. Inverse extensive and intensive ElCE in ceramics, (ΔSElCE)cer = 87 J/kg·K; ΔTAD = - 11.6 K), as well as in a single crystal along the ferroelectric axis a, (ΔSElCE)a = 115 J/kg·K; (ΔTAD)a = - 16 K, significantly exceed BCE, ΔSBCE = 75 J/kg·K; ΔTAD = - 9.8 K, even at low pressure ~ 0.3 GPa. Caloric parameters of ammonium sulphate are comparable with those for promising solid-state refrigerants.

Enhanced cyclability of elastocaloric effect in a directionally solidified Ni55Mn18Ga26Ti1 alloy with low hysteresis

Enhanced elastocaloric properties in a directionally solidified Ni55Mn18Ga26Ti1 alloy were achieved by combining composition tuning and microstructural control. Owing to the introduction of Ti and the microstructural feature with coarse columnar grains and strong <001>A preferred orientation, the thermal hysteresis and the stress hysteresis were successfully reduced to 4K and 16MPa, respectively. Large adiabatic temperature change of −6.2K was obtained on removing a low stress of 120MPa, resulting in the specific adiabatic temperature change of 51.7K/GPa. Moreover, the alloy demonstrated enhanced cyclability of elastocaloric effect up to 497 loading/unloading cycles and high coefficient of performance value of 25.6.

Elastocaloric switching effect induced by reentrant martensitic transformation

Vapor compression technologies widely used for refrigeration, heating, and air-conditioning have consumed a large fraction of global energy. Efforts have been made to improve the efficiency to save the energy, and to search for new refrigerants to take the place of the ones with high global warming potentials. The solid-state refrigeration using caloric materials are regarded as high-efficiency and environmentally friendly technologies. Among them, the elastocaloric refrigeration using shape memory alloys has been evaluated as the most promising one due to its low device cost and less of a demand for an ambient environment. General caloric materials heat up and cool down when external fields are applied and removed adiabatically (conventional caloric effect), while a few materials show opposite temperature changes (inverse caloric effect). Previously reported shape memory alloys have been found to show either a conventional or an inverse elastocaloric effect by the latent heat during uniaxial-stress-induced martensitic transformation. In this paper, we report a self-regulating functional material whose behavior exhibits an elastocaloric switching effect in Co-Cr-Al-Si Heusler-type shape memory alloys. For a fixed alloy composition, these alloys can change from conventional to inverse elastocaloric effects because of the change in ambient temperature. This unique behavior is caused by the sign reversal of latent heat from conventional to the re-entrant martensitic transformation. The realization of the elastocaloric switching effect can open new possibilities of system design for solid-state refrigeration and temperature sensors.

Exploring the elastocaloric switching effect and its mechanism

Researchers observe the elastocaloric switching effect in Co-based alloys, a phenomenon that could have applications in more efficient and environmentally friendly refrigeration technology of the future.

Elastocaloric effect in bamboo-grained Cu71.1Al17.2Mn11.7 microwires

Bamboo-grained Cu71.1Al17.2Mn11.7 microwires with diameter ∼150 μm were created by Taylor-Ulitovsky method and subsequent annealing. The grain architecture dependent superelasticity (SE) and elastocaloric effects (eCE) were confirmed. The bamboo-grained microwires exhibited low stress hysteresis loss during SE due to the reduced constraints caused by grain boundary, which is favorable for the mobility of martensite-austenite interface. Consequently, a large isothermal entropy change ∼21 J/kg K with a wide temperature range 90 K was achieved. The produced adiabatic temperature change (ΔTad) reached −11.9 K under a maximum stress 400 MPa. A stable ΔTad of −5.6 K showing little degradation in 200 eCE cycles was found with applied stress 325 MPa. This work reveals a fact that the bamboo-grained Cu–Al–Mn microwire may act as a desirable material for miniature solid-state refrigeration devices.

Frequency-dependent sensitivity of AC elastocaloric effect measurements explored through analytical and numerical models.

We present a comprehensive study of the frequency-dependent sensitivity for measurements of the AC elastocaloric effect by applying both exactly soluble models and numerical methods to the oscillating heat flow problem. These models reproduce the finer details of the thermal transfer functions observed in experiments, considering here representative data for single-crystal Ba(Fe1-xCox)2As2. Based on our results, we propose a set of practical guidelines for experimentalists using this technique. This work establishes a baseline against which the frequency response of the AC elastocaloric technique can be compared and provides intuitive explanations of the detailed structure observed in experiments.

Modeling the two-way shape memory and elastocaloric effects of bamboo-grained oligocrystalline shape memory alloy microwire

Recent experimental studies reported that the bamboo-grained oligocrystalline shape memory alloy (SMA) microwire showed excellent two-way shape memory effect (TWSME) and elastocaloric effect (eCE) due to the reduced constraints from grain boundary. In this paper, a theoretical model is established to predict the TWSME and eCE of such a kind of SMAs. At single crystal scale, an anisotropic thermo-mechanically coupled constitutive model is proposed to describe the thermo-elastic martensitic transformation based on the crystal plasticity theory. The driving force of martensite transformation, the internal heat release/absorption, and the evolutions of internal variables and temperature are deduced within the framework of irreversible thermodynamics. To calculate the temperature, stress and strain fields in the bamboo-grained oligocrystalline SMA microwire and obtain the overall thermo-mechanical response of the microwire, the proposed constitutive model is implemented into the finite element program ABAQUS/Explicit by writing a user-defined material subroutine. Meanwhile, to reduce the computational cost faced in the fully coupled thermo-mechanical analysis by using the finite element method, a scale transition rule from single crystal scale to macroscopic oligocrystalline one is constructed based on a new proposed sub-region integral method by considering the special geometric characteristics of the microwire. The capability of proposed model to describe the TWSME and eCE of bamboo-grained oligocrystalline SMA microwire is validated by comparing the predictions with the experimental data. In addition, the effect of grain orientation is discussed. The proposed model can provide a theoretical guidance for the optimal design of grain microstructures to obtain the SMAs with excellent TWSME and eCE.

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

This study reports a correction to assist the elastocaloric effect characterization of shape memory alloys and obtain the latent heat of stress‐induced martensitic transformation. The incomplete phase transformation analysis (IPTA) correction is developed based on the assumptions of linear transformation plateau of stress–strain and identical heat capacities for austenite and martensite phases. Taking Ni50.8Ti49.2 alloy as a demonstration, an integrated test rig is built to validate IPTA correction and study the heat leak effect. Using water as heat transfer fluid and heat leak compensation it is possible to further improve the accuracy of imposing IPTA correction. The predictions of latent heat from direct and indirect approaches with IPTA correction are validated from the experimental data. The required minimum martensitic phase fraction is only 10–20% when applying the IPTA correction, compared with 84–93% in traditional approaches. The IPTA correction extends the precondition of complete transformation to incomplete transformation in elastocaloric characterization.

Enhanced elastocaloric effect and mechanical properties of Gd-doped Ni–Mn–Sn-Gd ferromagnetic shape memory alloys

The effect of Gd substitution for Sn on martensitic transformation (MT) temperature, microstructure, elastocaloric effect (eCE) and mechanical properties of Mn49Ni41Sn10 ferromagnetic shape memory alloy has been systematically investigated. These alloys undergo MT from L21 austenite to 5 M martensite during the cooling process. MT temperature can be tuned to the vicinity of room temperature by alloying Gd. The substitution of Gd for Sn introduces γ phase (Gd-rich second phase in Gd-doping alloys), and the volume fraction of the γ phase increases with the increase of Gd content from 0.3 at.% to 0.9 at.%. Among these alloys, Mn49Ni41Sn9.4Gd0.6 alloy shows prominent eCE and stable superelasticity, making it a promising candidate for the elastocaloric cooling application. A large adiabatic temperature change of −11.4 K is obtained by the stress (500 MPa) removal, and a constant temperature change of −9.6 K shows no apparent degradation under the compressive stress of 400 MPa during 200 cycles for this alloy. The underlying mechanism of the enhanced eCE and mechanical properties is also revealed.