Refrigerant Materials Research Articles

Feasibility and performance analysis of a novel air separation unit with energy storage and air recovery

The high-purity air output by expansion during energy release is discharged into the ambient for liquid air energy storage (LAES) technology, resulting in a large loss of material resources. Currently, LAES research focuses mostly on enhancing thermally driven power generation while disregarding the use of its discharging air. To address this issue, we proposed a novel air separation unit (ASU) with energy storage and air recovery (ASU-ESAR) based on the matching characteristics of air separation and LAES technologies in refrigeration temperature and material utilization. Except for storing liquid air on large-scale by employing ASU and directly recovering cold energy of liquid air, ASU-ESAR has the benefit and novelty of fully recycling high-purity air outputted during energy release, as well as its low temperature and high pressure energy, into ASU. Its process design and feasibility studies are carried out. Energy conservation efficiency, economic benefits, and its influences on China's power grid and emission reductions are assessed. Without any waste heat usage, an electrical round-trip efficiency of 55.82%–58.72% is presented. Taking Shanghai, China as an example, ASU-ESAR's electricity costs are reduced by 5.77%–7.65% when compared to conventional ASU, and the payback period for LAES system with a power capacity of 70.70–74.38 MWh/day is 2.2–2.9 years. The average peak-valley ratio (PVR) of China's power grid might fall by 13% once ASU-ESAR is implemented across the industry, and the yearly CO2 emissions could be reduced by 12.53-27.71 Mt. Its application can achieve a win-win situation of electricity cost savings in ASU operations as well as energy savings and emission reductions on the power generation side.

Investigation of magnetocaloric effect in La0.67Sr0.33Mn1-xZrxO3

The influence of Zr-doping on the magnetocaloric effect of La0.67Sr0.33Mn1-xZrxO3 manganese perovskites in low magnetic field has been investigated. Using Hamad’s phenomenological model, we have estimated the important magnetocaloric properties, for example, the thermal magnetization, the change of magnetic entropy and the relative cooling power. We have shown that the magnetocaloric properties decrease as the increase of the dopant amount. Tunable magnetocaloric effect in these compounds is advantageous to magnetic refrigeration applications in wide temperature ranges. Therefore, these compounds are good candidates for working materials in magnetic refrigeration.

Estimation of magnetocaloric effect by means of phenomenological model in La0.67Ca0.33-xSrxMnO3 (x=0.035, 0.065) perovskite manganite

The magnetocaloric effect in the perovskite manganite La0.67Ca0.33-xSrxMnO3 with x=0.035, 0.065 have been investigated. Using Hamad’s phenomenological model, we have estimated the important magnetocaloric properties, for example, the thermal magnetization, the change of magnetic entropy and the relative cooling power. Considerable and tunable magnetocaloric effect in these compounds is advantageous to applications in near-room-temperature magnetic refrigeration. Therefore, these compounds are good candidates for working materials in magnetic refrigeration.

Impact of F and S doping on (Mn,Fe)2(P,Si) giant magnetocaloric materials

The quarternary (Mn,Fe)2(P,Si)-based materials with a giant magnetocaloric effect (GMCE) at the ferromagnetic transition TC are promising bulk materials for solid-state magnetic refrigeration. In the present study we demonstrate that doping with the light elements fluorine and sulfur can be used to adjust TC near room temperature and tune the magnetocaloric properties. For F doping the first-order magnetic transition (FOMT) of Mn0.60Fe1.30P0.64Si0.36Fx (x = 0.00, 0.01, 0.02, 0.03) is enhanced, which is explained by an enhanced magnetoelastic coupling. The magnetic entropy change |ΔSm| at a field change (Δμ0H) of 2 T markedly improved by 30% from 14.2 Jkg−1K−1 (x = 0.00) at 335 K to 20.2 Jkg−1K−1 (x = 0.03) at 297 K. For the F doped material the value of |ΔSm| for Δμ0H = 1 T reaches 11.6 Jkg−1K−1 at 294 K, which is consistent with the calorimetric data (12.4 Jkg−1K−1). Neutron diffraction experiments reveal enhanced magnetic moments by F doping in agreement with the prediction of DFT calculation. For S doping in Mn0.60Fe1.25P0.66-ySi0.34Sy (y = 0.00, 0.01, 0.02, 0.03, 0.04) three impurity phases have been found from microstructural analysis, which reduce the stability of the FOMT in the main phase and decrease TC, e.g. the |ΔSm| reduces from 7.9(12.6) Jkg-1K-1 (332 K) for the undoped sample to 3.4(6.2) Jkg-1K-1 (313 K) for the maximum doped sample for Δμ0H = 1(2) T. Neutron diffraction experiments combined with first-principles theoretical calculation, distinguish the occupation of F/S dopants and the tuning mechanism for light element doping, corresponding to subtle structural changes and a strengthening of the covalent bonding between metal and metalloid atoms. It is found that the light elements F and S can effectively regulate the magnetocaloric properties and provide fundamental understanding of (Mn,Fe)2(P,Si)-based intermetallic compounds.

Tailored martensitic transformation and enhanced magnetocaloric effect in all-d-metal Ni35Co15Mn33Fe2Ti15 alloy ribbons

The crystal structure, martensitic transformation and magnetocaloric effect have been studied in all-d-metal Ni35Co15Mn33Fe2Ti15 alloy ribbons with different wheel speeds (15 m/s (S15), 30 m/s (S30), and 45 m/s (S45)). All three ribbons crystalize in B2-ordered structure at room temperature with crystal constants of 5.893(2) Å, 5.898(4) Å, and 5.898(6) Å, respectively. With the increase of wheel speed, the martensitic transformation temperature decreases from 230 K to 210 K, the Curie temperature increases slightly from 371 K to 378 K. At the same time, magnetic entropy change (ΔS m) is also enhanced, as well as refrigeration capacity (RC). The maximum ΔS m of 15.6(39.7) J/kg⋅K and RC of 85.5 (212.7) J/kg under ΔH = 20 (50) kOe (1 Oe = 79.5775 A⋅m−1) appear in S45. The results indicate that the ribbons could be the candidate for solid-state magnetic refrigeration materials.

Tunable nucleation process of nano-sized NaZn13-type and α-(Fe,Si) phases by doping boron in La–Fe–Si alloys during rapid solidification

The effect of a small dose of boron-doping on the nucleation process of nano-sized 1:13 phase (NaZn13-type phase) and α-(Fe,Si) phase of the La–Fe–Si alloys during the rapid solidification was investigated. The simulation of classical nucleation theory indicates a competitive nucleation relationship between 1:13 and α-(Fe,Si) phases during the rapid solidification. Compared to the La–Fe–Si alloys undoped with boron atom, the undercooled temperature change (ΔT) for the same nucleation rate conditions of the 1:13 and α-Fe phases was significantly decreased from 673 K (x = 0) to 639 K (x = 0.3) during the rapid solidification of La–Fe–Si–B alloys. The analysis of the microstructure and phase structure of the La–Fe–Si alloys ribbons by scanning electron microscope , x-ray diffraction, and transmission electron microscope also concludes that the doping of boron promoted the formation of the 1:13 phase. The results of this study have considerable meaning for the engineering application of magnetic refrigeration materials (La–Fe–Si) in the future.

Electric hysteresis and validity of indirect electrocaloric characterization in antiferroelectric ceramics

Antiferroelectric (AFE) materials have garnered considerable attention in electrocaloric (EC) refrigeration owing to the large entropy change accompanying their transitions and the coexistence of positive and negative EC effects. Almost all studies to date of EC response in AFEs have employed the indirect characterization of thermodynamic behavior based on the Maxwell relation, regardless of the significant electric hysteresis behavior of AFEs in unipolar polarization. Herein, using direct isothermal heat flow measurements in the AFE ceramic Pb0.99Nb0.02[(Zr0.6Sn0.4)0.94Ti0.06]0.98O3 as the benchmark, we discover the large deviation in carrying out indirect EC characterization on AFEs. The electric hysteresis also results in self-heating due to the asymmetric exothermic and endothermic cyclic response, and can be calculated quantificationally from the hysteresis area of P-E loops. Our work emphasizes the necessity in carrying out direct EC characterization on AFEs, and suggests the importance in designing AFE EC refrigeration materials with low electric hysteresis.

Observation of the magnetic entropy change in Zn doped MnFe2O4 common ceramic: Be cool being environmental friendly

We report the detail investigation on the magnetic and magnetocaloric behaviour of polycrystalline Mn1-xZnxFe2O4 (0.0 ≤ x ≤ 0.7) ferrite. The magnetization analysis shows that the increase of Zn concentration in the samples results in decrease of saturation magnetization. The maximum magnetic entropy change, |ΔSMmax| is evaluated through M-H isotherms measurements and takes values of 1.25, 1.11, 1.07, and 0.64 Jkg−1K−1 for x = 0.0, 0.3, 0.5, and 0.7, respectively under a maximum applied magnetic field of 2.5 T. The corresponding relative cooling power (RCP) for these samples were found to be 102, 162, 96, and 89 Jkg-1 for x = 0.0, 0.3, 0.5, and 0.7, respectively. After the comparison of the obtained values of |ΔSMmax| and RCP with those reported earlier for the other compounds, recommend to explore such common soft ferrites based materials for magnetic refrigeration.

Novel Fluorite-Structured Materials for Solid-State Refrigeration.

Refrigeration based on the electrocaloric effect can offer many advantages over conventional cooling technologies in terms of efficiency, size, weight, and power source. The discovery of ferroelectric and antiferroelectric properties in fluorite-based materials in 2011 has led to diverse applications related to memory (e.g., ferroelectric tunnel junctions, nonvolatile memory, and field-effect transistors) and energy fields (e.g., energy storage and harvesting, electrocaloric refrigeration, and infrared detection). Fluorite-based materials exhibit several properties not shared by most conventional materials (such as in terms of compatibility with complementary metal-oxide semiconductors and 3D nanostructures, deposition thickness at the nanometer scale, and simple composition). Here, the electrocaloric refrigeration properties of fluorite-based ferroelectric/antiferroelectric materials are reviewed by focusing on the advantages of ZrO2 - and HfO2 -based materials (e.g., relative to conventional perovskite- and polymer-based counterparts). Finally, the recent progress made in this research field are also discussed along with its future perspectives.

Novel approach in fabricating microchannel-structured La(Fe,Si)13Hy magnetic refrigerant via low-contamination route using dissolutive mold

Herein, as the fabrication of the microchannels for fluid flow using La(Fe,Si)13 magnetic refrigerant material is required while maintaining its superior magnetocaloric performance, sinter molding of the microchannel-designed La(Fe,Si)13 was investigated using a dissolutive mold comprised of NaCl to develop a molding process without contamination by carbon and other light elements. In addition, to avoid the thermal decomposition of fine particles of La(Fe,Si)13, a solid-state reaction was conducted during sintering using a mixture of α-Fe and La-rich compounds as the initial powder. After sintering, the sample shape exhibited channel widths and depths of 200 μm and pillar widths of 300 μm, which were originally designed for the NaCl dissolutive mold. The metallographic microstructure mostly comprised the La(Fe,Si)13 phase, and the volume fractions of the extra phases, such as α-Fe and La2O3, were suppressed to 1.1 % and 3.2 %, respectively. The maximum of the magnetic entropy change in a single pillar reached −19 J/kg K. Direct observation of magnetic nucleation/growth confirmed the smooth emergence of the first-order transitions in multiple pillars. Consequently, this fabrication approach promoted micro-channel-designed La(Fe,Si)13Hy while maintaining a large magnetocaloric effect via low carbon contamination.

Magnetic refrigeration material operating at a full temperature range required for hydrogen liquefaction

Magnetic refrigeration (MR) is a key technique for hydrogen liquefaction. Although the MR has ideally higher performance than the conventional gas compression technique around the hydrogen liquefaction temperature, the lack of MR materials with high magnetic entropy change in a wide temperature range required for the hydrogen liquefaction is a bottle-neck for practical applications of MR cooling systems. Here, we show a series of materials with a giant magnetocaloric effect (MCE) in magnetic entropy change (-∆Sm > 0.2 J cm−3K−1) in the Er(Ho)Co2-based compounds, suitable for operation in the full temperature range required for hydrogen liquefaction (20-77 K). We also demonstrate that the giant MCE becomes reversible, enabling sustainable use of the MR materials, by eliminating the magneto-structural phase transition that leads to deterioration of the MCE. This discovery can lead to the application of Er(Ho)Co2-based alloys for the hydrogen liquefaction using MR cooling technology for the future green fuel society.

Observation of Griffiths phase, critical exponent analysis and high magnetocaloric effect near room temperature at low magnetic field in V-doped La0.7Sr0.3MnO3

We report on observation of the Griffiths phase (GP), high magnetocaloric properties at low magnetic fields and temperature-dependent critical exponents of La0.7Sr0.3V x Mn1−x O3 (x = 0, 0.05 and 0.1) perovskite bulk materials. The Curie temperature (T C) of pure La0.7Sr0.3MnO3 (LMSO) is seen to be 368.7 K and decreases toward room temperature (RT) (342.2 K) by 10 mol% V doping at the Mn site. V doping leads to an enhancement in magnetic entropy change (−ΔS M) from 1 J kg−1 K−1to 1.41 J kg−1 K−1. V doping at a Mn site leads to the formation of GP, a magnetic disorder due to the coexistence of a paramagnetic (PM) matrix and short-range ferromagnetic (FM) clusters. X-ray photoelectron spectroscopy analysis confirms the presence of mixed-valence V4+/V5+along with Mn3+/Mn4+ ions contributing to various double exchange interactions. The natures of phase transitions and magnetic interactions are analyzed by evaluating critical exponents δ, β, and γ. All the samples show second-order FM to PM phase transition, confirmed from the modified Arrott plots and critical exponent analysis carried out using the Kouvel–Fisher method. The enhancement in magnetic entropy change along with the decrease in Curie temperature toward RT by V doping in the LMSO oxides indicates the possible application of these materials in magnetic refrigeration at low magnetic fields.

Study on the Magnetocaloric Effect of Room Temperature Magnetic Refrigerant Material La0.5Pr0.5(Fe1-xCox)11.4Si1.6 and the Effect Arising from Co Doping on Its Curie Temperature.

The arc-melting method was adopted to prepare the compound La0.5Pr0.5(Fe1−xCox)11.4Si1.6 (x = 0, 0.02, 0.04, 0.06, 0.08), and the magnetocaloric effect of the compound was investigated. As indicated by the powder X-ray diffraction (XRD) results, after receiving 7-day high temperature annealing at 1373 K, all the compounds formed a single-phase cubic NaZn13 crystal structure. As indicated by the magnetic measurement, the most significant magnetic entropy change |∆SM(T)| of the sample decreased from 28.92 J/kg·K to 4.22 J/kg·K with the increase of the Co content under the 0–1.5 T magnetic field, while the Curie temperature TC increased from 185 K to the room temperature 296 K, which indicated that this series of alloys are the room temperature magnetic refrigerant material with practical value. By using the ferromagnetic Curie temperature theory and analyzing the effect of Co doping on the exchange integral of these alloys, the mechanism that the Curie temperature of La0.5Pr0.5(Fe1−xCox)11.4Si1.6 and La0.8Ce0.2(Fe1−xCox)11.4Si1.6 increased with the increase in the Co content was reasonably explained. Accordingly, this paper can provide a theoretical reference for subsequent studies.

Understanding electrocaloric cooling of ferroelectrics guided by phase‐field modeling

AbstractWith the urgent need to explore low‐cost, high‐efficiency solid‐state refrigeration technology, the electrocaloric effects of ferroelectric materials have attracted much attention in the past decades. With the development of modern computing technology, the phase‐field method is widely used to simulate the evolution of microstructure at mesoscale and predict the properties of different types of ferroelectric materials. In this article, we review the recent progress of electrocaloric effects from phenomenological Landau thermodynamics theory to phase‐field simulation by discussing the microcosmic composition, mesoscopic domain structures, macroscopic size/shape, and external stimulus of strain/stress. More importantly, in searching for new ferroelectric electrocaloric cooling materials, it is possible to find materials whose free energy barrier height changes rapidly with temperature, such materials have a faster change rate with polarization temperature in terms of ferroelectric macroscopic properties, from them could get superior electrocaloric effects. We compile a relatively comprehensive computational design on the high performance of electrocaloric effects in different types of ferroelectrics and offer a perspective on the computational design of electrocaloric refrigeration materials at the mesoscale microstructure level.

NaGdS2: A Promising Sulfide for Cryogenic Magnetic Cooling

The development of effective and eco-friendly cooling technology demands an investigation of new magnetocaloric materials. Compounds containing gadolinium are one of the best candidates due to the large spin-only magnetic moment of Gd3+ ions. This work reports on the magnetocaloric properties of the AGdS2 family (A = Li, Na, K, Rb) in relation to the crystal chemistry of these compounds. These sulfides crystallize in two different structure types: NaCl (A = Li) and α-NaFeO2 (A = Na, K, Rb). Although one would expect the larger magnetocaloric effect to be associated with LiGdS2 due to its higher magnetic/non-magnetic mass ratio, our study demonstrates that the NaGdS2 member leads to the best properties among the investigated series. The change in structure from the three-dimensional (3D) NaCl structure of LiGdS2 to the layered α-NaFeO2 structure of NaGdS2 drastically improves the magnetocaloric properties. Hence, thanks to its structural features associated with negligible exchange interactions, NaGdS2 exhibits a magnetic entropy change up to 54 J kg–1 K–1 at 2.5 K for μ0ΔH = 5 T, which is comparable to that of the top-ranked inorganic Gd-based materials operating in the cryogenic temperature range. These magnetocaloric figures of merit provide evidence that Gd-based sulfides are promising materials for magnetic refrigeration, and, more broadly, this highlights the potential of sulfides in that field.

Pumping into a cool future: electrocaloric materials for zero-carbon refrigeration

Pumping into a cool future: electrocaloric materials for zero-carbon refrigeration

Study of magnetic and magnetocaloric effect of REMnO3(RE=Dy,Eu)manganites

We have systematically investigated the magnetic and magnetocaloric effect (MCE) of REMnO3 (RE = Dy, Eu) manganites sintered by solid-state reaction method. The Neel temperature (TN), the maximum magnetic entropy change (-ΔSmmax) and the relative cooling power (RCP) of the sample were obtained by measuring the magnetization and heat capacity. Under the magnetic field change of 50 kOe, large -ΔSmmax of 8.93J/kg K and 9.31J/kg K are achieved around the TN of 14 K and 50 K for DyMnO3 and EuMnO3, respectively. It is proved by the slope of the Arrott plot and the universal phenomenological curve that the sample undergoes second order phase transition. The critical behavior of antiferromagnetic to paramagnetic phase transition is studied by modifying Arrott plot, which shows that the spin order of the sample decreases at the phase transition temperature and tends to change into shortrange order. The large magnetic entropy change calculated by Landau theory and experimental data indicates that the sample has a large magnetocaloric effect and has potential application in low temperature magnetic refrigeration materials.

Magnetic and magnetocaloric properties of nanocrystalline sample of a glassy ferromagnetic compound: Modification of short range ordering

The modification of magnetic interactions due to the reduction of particle size has been explored in the case of nanocrystalline Gd0.5Sr0.5MnO3 compound. In contrast to the normal ferromagnetic or antiferromagnetic compounds, the studied nanoparticle exhibits quite different magnetic and magnetocaloric properties. The experimental outcomes are also compared with its bulk counterparts having disordered ferromagnetic ground state. Additionally, at the cryogenic temperature range, the significant magnetocaloric effect in both the samples indicate the applicability as a suitable magnetic refrigerant material. Moreover, the desertion nature of the magnetic hysteresis loop due to the field cycling indicates the superiority of the nanocrystalline compound over its bulk counterpart.

Effect of Bi doping on the crystal structure, magnetic and magnetocaloric properties of La0.7-xBixSr0.15Ca0.15MnO3 (x = 0, 0.05, 0.10, 0.15) manganites

The influence of Bi3+ doping on the structure, magnetic and magnetocaloric properties of La0.7-xBixSr0.15Ca0.15MnO3 (x = 0, 0.05, 0.10, 0.15) was studied. The samples were prepared by the Pechini sol–gel method. The powder X-ray diffraction data demonstrates that the major phase of samples possesses a single perovskite structure with the Pbnm orthorhombic space group. Rietveld refined data shows that the lattice parameters and unit cell volume become large with an increase of Bi3+. The magnetization measurement demonstrates that the Curie temperature and relative cooling power decrease with the increase of Bi3+ content, while the maximum magnetic entropy change first increases with the increase of Bi3+ content, and then decreases. La0.6Bi0.1Sr0.15Ca0.15MnO3 exhibits a giant value of magnetic entropy (2.16 J/kg·K at around 291 K) under an applied magnetic field of 2 T, and the RCP for this compound is found accordingly as 99 J/kg, which can be used as one of the potential magnetic refrigerant materials close to room temperature.

Magnetic refrigeration down to 0.2 K by heavy fermion metal YbCu4Ni

Ytterbium-based heavy-fermion metals have recently attracted attention as magnetic refrigeration materials generating low-temperature environments below 1 K without using expensive 3He. YbCu4Ni is known to exhibit a giant value of specific heat divided by temperature C/T∼7.5J/K2mol below 0.2 K, implying high potential of magnetic refrigeration. In this paper, we report magnetic refrigeration down to 0.2 K from the initial temperatures of 1.8 K by YbCu4Ni ingots installed in a commercial 4He refrigerator. The performance is consistent with that evaluated by our DC magnetization and specific heat measurements. Our study demonstrates the high performance of YbCu4Ni without precious metals as a magnetic refrigeration material with moderately high density of Yb atoms (∼0.02Ybmol/cm3) and high thermal conductivity.