Large Refrigerant Capacity Research Articles

HoDyGdCoAl high-entropy amorphous alloys working at full temperature range for hydrogen liquefaction with large magnetocaloric effects

Cryogenic magnetic refrigeration materials based on magnetocaloric effect can be used for hydrogen liquefaction. In this work, glass formation ability (GFA), magnetocaloric effect (MCE), refrigeration performance of melt-extracted HoDyGdCoAl amorphous ribbons have been investigated. Amorphous ribbons undergo a second order magnetic phase transition which achieve a table-like behavior broaden the range of magnetic transition temperature in hydrogen liquefaction.The maximum magnetic entropy change (-ΔSmaxM), the δTFWHM and the refrigeration capacity (RC) achieved 10.9 J/ (kg K), 84.2 K and 742.4 J/ kg (x = 5) and 11.2 J/ (kg K), 69.8 K and 643.0 J/ kg (x = 20) under a magnetic field change of 7 T, respectively. Combining wide magnetic transition temperature and large refrigerant capacity, the present amorphous ribbons can be used as potential magnetic refrigerant materials in hydrogen liquefaction temperature region.

A novel Fe87Pr11B2 amorphous alloy with outstanding magnetocaloric properties near 325 K

A novel Fe87Pr11B2 metallic glass that exhibits outstanding magnetocaloric effect near room temperature was prepared into the shape of amorphous ribbons. The ribbon exhibits soft magnetic properties and high saturation magnetization at 200 K, which is much lower than its Curie temperature at 325 K. No obvious spin-glass-like behavior was found above 200 K. The almost highest maximum magnetic entropy change (−ΔSmpeak) among Fe-based metallic glasses near the hot end of a residential magnetic refrigerator is most likely attributed to the high concentration of Pr and low content of B in the Fe87Pr11B2 amorphous ribbon. The high −ΔSmpeak, large refrigeration capacity (RC) and adiabatic temperature rise (ΔTad) make the Fe87Pr11B2 amorphous alloy better candidate for the potential component of a refrigerant working in a high-efficiency residential magnetic refrigerator.

Giant magnetocaloric effect and hysteresis loss in MnxFe2-xP0.5Si0.5 (0.7 ≤ x ≤ 1.2) microwires at ambient temperatures

Magnetocaloric microwires are very promising for energy-efficient magnetic refrigeration in micro electromechanical systems (MEMS) and nano electromechanical systems (NEMS). Creating microwires that exhibit large magnetocaloric effects around room temperature represents an important but challenging task. Here, we report a tunable giant magnetocaloric effect around room temperature in MnxFe2-xP0.5Si0.5 (0.7≤x ≤ 1.2) microwires by utilizing a melt-extraction technique paired with thermal treatment and chemical engineering. The isothermal magnetic entropy change (ΔSiso) and Curie temperature (TC) can be tuned by adjusting the Mn/Fe ratio. The TC varies from 351 to 190 K as x increases from 0.8 to 1.2. Among the compositions investigated, the x = 0.9 sample shows the largest value of ΔSiso = 18.3 J kg−1 K−1 for a field change of 5 T around 300 K. After subtracting magnetic hysteresis loss, a large refrigerant capacity of ∼284.6 J kg−1 is achieved. Our study paves a new pathway for the design of novel magnetocaloric microwires for active magnetic refrigeration at ambient temperatures.

The GdMn1-xRuxSi compounds cassette for magnetocaloric nitrogen liquefaction

New intermetallic compounds GdMn1-xRuxSi, x = 0–1 with a tetragonal structure of the CeFeSi-type (P4/nmm) have been synthesized. For GdMn1-xRuxSi, Curie temperature TC drops sharply from 320 K (x = 0) to 78.3 K (x = 1), while the magnetocaloric effect varies from 1.84 J/kgK (x = 0) to 4.94 J/kgK (x = 1) with a change in the magnetic field of 0–17 kOe. Thus, the GdMn1-xRuxSi magnetic refrigeration compounds operate at temperatures from 320 K to 78.3 K, close to the nitrogen liquefaction temperature of 77.4 K. Therefore, the GdMn1-xRuxSi system, where x ranges from 0 to 1, could be of practical interest for nitrogen liquefaction, provided that these alloys are assembled into a cassette with a single large refrigerant capacity. The electronic structure and magnetic moments of the GdMn1-xRuxSi intermetallic compounds were calculated using the DFT + U theoretical method.

Monte Carlo simulation of ammonia adsorption in high-silica zeolites for refrigeration applications

Climate change and the continual rise in cooling demand means more efficient and environmentally friendly refrigeration technologies are required more than ever. One attractive route to reducing future demand is to improve adsorption refrigeration technologies based on natural refrigerants such as ammonia. The choice of ammonia adsorbent plays an important role in achieving improved refrigeration efficiency and suitable operating conditions. This paper reports a detailed study on the suitability of zeolites as an adsorbent of ammonia in refrigeration applications. Systematic Monte Carlo simulations were conducted to study ammonia adsorption in five high-silica zeolites with a wide range of pores sizes and porosities. Simulations were carried out at temperatures between -50 and 50°C and pressures up to 4.0 bar. It is found that zeolites, in particular the ones with large porosities, could be very good ammonia adsorbents for adsorption refrigeration applications, since their use allows for large refrigeration capacities and tuneable operating conditions with good coefficients of performance (COP).

The large magnetocaloric effect in GdErHoCoM (M = Cr and Mn) high-entropy alloy ingots with orthorhombic structures

High-entropy alloys (HEAs) with significant magnetocaloric effects (MCEs) have attracted widespread attention due to their potential magnetic refrigeration applications over a much more comprehensive temperature range with large refrigerant capacity (RC). However, most of them are metallic glasses (MGs) with problems of limited size, resulting in the difficulty of further applications. Therefore, research on HEAs with crystalline structures and giant MCE is urgently needed. In this paper, GdErHoCoM (M = Cr and Mn) rare-earth HEA ingots with orthorhombic structures are developed, and their magnetic behavior and MCE are studied in detail. Phase investigations find that the main phase of GdErHoCoM ingots is probably (GdErHo)Co with an orthorhombic Ho3Co-type structure of a space group of Pnma. The secondary phases in GdErHoCoCr and GdErHoCoMn are body-center-cubic Cr and Mn-rich HoCo2-type phases, respectively. Magnetic investigations reveal that both ingots undergo a first-order magnetic phase transition below their respective Neel temperatures. Above their respective Neel temperatures, a second-order transition is observed. The Neel temperatures are 40 and 56 K for GdErHoCoCr and GdErHoCoMn, respectively. Additionally, the GdErHoCoCr and GdErHoCoMn ingots exhibit maximum magnetic entropy changes and RC values of 12.29 J/kg/K and 746 J/kg and 10.13 J/kg/K and 606 J/kg, respectively, under a magnetic field of 5 T. The ingots GdErHoCoM (M = Cr and Mn) show excellent MEC properties and can be manufactured easily, making them promising for magnetic refrigerant applications.

Analysis of the performance of mixed refrigerant chillers based on the impact of exergy glide temperature matching coefficient

A glide temperature matching model based on the exergy matching coefficient was established for the phase change heat transfer process of non-azeotropic mixed refrigerants. The exergy loss rate of the temperature difference and the exergy loss rate of the glide temperature in the condenser and evaporator were analyzed, and the temperature matching coefficient of mixed refrigerants parameter πglide was derived to indicate mixed refrigerants with large refrigeration capacity. The model was experimentally verified by the performance of three types of mixed refrigerants in chillers. The results show that the higher the glide temperature, the bigger the condenser πglide of the mixed refrigerants and the worse the temperature-matching effect. The smaller the πglide of the evaporator, the better the temperature-matching effect, and at the same time, the greater the cooling capacity. This model can be used for predicting the different component mixtures of working fluids.

Magnetic and magnetocaloric effect of Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass

Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass exhibited excellent magnetic refrigeration material with a wide temperature range and high refrigeration capacity (RC) was reported. Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass was observed with typical spin glass behavior around 15.5 K. In addition, we find that the magnetic entropy change (−ΔS M) originates from the sample undergoing a ferromagnetic (FM) to paramagnetic (PM) transition around 20 K. Under a field change from 0 T to 7 T, the value of maximum magnetic entropy change ( −ΔSMmax ) reaches 12.5 J/kg⋅K, and the corresponding value of RC reaches 487.7 J/kg in the temperature range from 6 K to 60 K. The large RC and wide temperature range make the Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass be a promising material for application in magnetic refrigerators.

Effect of heat treatment on coupled magnetostructural transition and magnetocaloric effect of MnNiGe system

Material with coupled magnetic and structural transition is of significant interest in the field of energy-efficient technology. In this work, a sharp first-order magneto-structural transition (MST) from a ferromagnetic orthorhombic TiNiSi-type martensite phase to a paramagnetic hexagonal Ni2In-type austenite phase is observed in hexagonal Mn0.85Fe0.15NiGe compound through the heat treatment technique. Through heat treatment, the first-order MST for Mn0.85Fe0.15NiGe sample is observed to decrease drastically from 279.1 K to 211.8 K for the elevated annealing temperatures from 873 K to 1173 K. Furthermore, total entropy change (ΔS) is synergistically associated with the magnetic and structural entropy change in this system. This synergic feature governs a large ΔS ∼ 62.7 Jkg-1K−1, while magnetic entropy change is about 31.3 Jkg-1K−1 (∼52.1%) and the lattice part contributes the remaining ∼48.7% for the sample annealed at 1073 K due to the field change of 5T. In addition, a large effective refrigerant capacity reaches 226.7 Jkg−1 at 226 K for the sample due to the field change of 5T. Henceforth, this work shows an effective and efficient scheme to control the MST temperature of hexagonal phase-transition families using heat treatment method without changing the chemical composition of the sample. Our results based on heat treatment methodology provide a feasible platform for tuning MST and the associated caloric properties.

Large Refrigerant Capacity Induced by Table‐Like Magnetocaloric Effect in High‐Entropy Alloys TbDyHoEr

Rare‐earth‐based high‐entropy alloys (HEAs) with large magnetocaloric effect (MCE) have been recently recognized as good candidates for magnetic refrigeration. Herein, the complex magnetic transition, MCE, refrigerant capacity (RC), and magnetic‐phase diagram of single‐phase TbDyHoEr HEA are studied. It is showed in the results that due to complex magnetic transition and an ideal table‐like MCE, the RC of TbDyHoEr is significantly improved from 883.19 to 1049.22 J kg−1by melt‐spun treatment. In terms of RC value and hysteresis performance, the melt‐spun treatment significantly improves the application potential of TbDyHoEr HEA as a high‐efficient magnetic refrigeration material, and the ideal table‐like MCE in a large temperature range enables this material to meet the requirements of both cryogenic refrigeration and mesothermal refrigeration for an Ericsson cycle.

Magnetocaloric properties of Co-doped Mn0.5Fe0.5Ni1−xCoxSi0.94Al0.06 intermetallic alloys

We have synthesized a series of Co-doped Mn0.5Fe0.5Ni1−xCoxSi0.94Al0.06 (0.025 ≤ x ≤ 0.05) alloys by arc melting followed by a rapidly quenched vacuum suction casting technique and studied the magnetic and magnetocaloric properties of the system. All measurements were performed on the as-cast and annealed samples. X-ray diffraction data indicated that the samples exhibited a hexagonal phase at room temperature. Magnetization data showed that the annealed samples exhibited significantly larger transition temperatures than the as-cast samples. All samples showed the first-order phase transition with a thermomagnetic hysteresis of more than 20 K. The phase transitions were accompanied by isothermal entropy changes of as large as −16.4 J kg−1 K−1 and −42.4 J kg−1 K−1 for field changes of 20 and 50 kOe, respectively. Large refrigeration capacities and temperature averaged entropy changes of up to 201 J/kg and 34.05 J kg−1 K−1, respectively, were observed for a field change of 50 kOe.

Design and experimental study of an outdoor portable thermoelectric air-conditioning system

This study aims to identify suitable microclimate cooling systems to reduce heat stress and improve human thermal comfort. A portable thermoelectric air conditioner was developed for local cooling of the human body. Effects of core components thermoelectric refrigerators (TECs), hot end heat dissipation, intake flow and cold end heat exchangers on TEAC performance. It is shown that, remarkably, this operating voltage can be distinguished from the optimal voltage for the maximum operational performance of TEAC. When the TECs operating voltage is 4V, the maximum COP is 2.2, and the best operating voltage is 10V, the maximum cooling capacity is 26.7 W (COP=0.92). Simulation data show that the area of the diffuser can effectively control the contact between the air and the cooling surface with an error of less than 10% compared to the experimental results. The fans and radiators attached to the hot side of the TEM play an important role in keeping the temperature difference on the hot side of the TECs as small as possible, by dissipating the heat generated on the hot side of the TEM to the external environment. In addition, the experimental refrigeration capacity is greater than 26.7 W and the new system has ultra-quiet operation at large refrigeration capacity, which has promising potential for advanced refrigeration, building air conditioning, ventilation systems and other applications. • Thermalelecrtic air conditioner (TEAC) can achieve a cooling capacity of 26.7W and a cooling coefficient of 0.92, enabling local cooling of the human body. • The maximum cooling capacity of thermoelectric refrigerator varies nonlinearly with the surface area and height of thermoelectric leg. • The increase of cooling capacity decreases with the increase of intake flow rate. • Increasing the strength of heat dissipation at the hot end of the thermoelectric cooler has a larger effect on the TEAC cooling capacity than on the cooling coefficient.

Investigation on Magnetization, Magnetocalory, Magnetoresistance, and Electric Properties of Ni-Mn Based Heusler Alloy

The magnetic and electrical characteristics of Ni-Mn quinary Heusler alloys are studied in the current work. The results concern the materials’ magnetic and electrical behavior. The physical property measurement system (PPMS) and superconducting quantum interference device (SQUID) were used at various magnetization levels to determine the results. The addition of Fe helps to form the alloy into a smart memory alloy with magnetocrystalline anisotropy, twin border mobility, and varied magnetic and martensite transition temperature characteristics. Character changes in the superparamagnetic (SPM) and paramagnetic (PM) alloys occur between 26 and 34 °C. The curves are supported by the alloy’s martensitic transition temperature change. A large refrigeration capacity is identified in the alloy. These properties are an indication of the alloys’ application prospects. Entropy change helps to detect the inverse magnetocaloric effect in the alloy, whereas adiabatic temperature change helps identify the origin and validity of reverse magnetic properties. The transition temperature changes occur when austenite’s sigma is larger than that of martensite, and as the magnetic field increases, the temperature declines. Isothermal magnetization curves, a large (MR)/B value at low and high magnetic fields, and temperatures near the transformation point suggest that small-crystal Heusler alloys have tremendous promise for low and high magnetic field magnetoresistance applications.

Large refrigerant capacity in superparamagnetic iron nanoparticles embedded in a thin film matrix

A magnetocaloric effect (MCE) with sizable isothermal entropy change (ΔS) maintained over a broad range of temperatures above the blocking temperature is reported for a rare earth-free superparamagnetic nanoparticle system comprising of Fe–TiN heterostructure. Superparamagnetic iron (Fe) particles were embedded in a titanium nitride (TiN) thin film matrix in a TiN/Fe/TiN multilayered pattern using a pulsed laser deposition method. High angle annular dark-field images in conjunction with dispersive energy analysis, recorded using scanning transmission electron microscopy, show a clear presence of alternating layers of Fe and TiN with a distinct atomic number contrast between Fe particles and TiN. Quantitative information about the isothermal entropy change (ΔS) and the magnetocaloric effect in the multilayer Fe–TiN system has been obtained by applying Maxwell relation to the magnetization vs temperature data at various fields. With the absence of a dynamic magnetic hysteresis above the blocking temperature, the negative ΔS as high as 4.18 × 103 J/Km3 (normal or forward MCE) is obtained at 3 T at 300 K.

Peculiarity of magnetocaloric and magnetoresistance effects in Ni–Mn–Sn–Fe alloy with successive metamagnetic structural transitions

Magnetocaloric and magnetoresistance properties originated from a metamagnetic structural transition were investigated in a Fe-doped Ni46.8Mn38.1Sn11.6Fe3.5 alloy. After annealing, the alloy exhibited the intermartensite phase that contributed to the multiple abrupt magnetization and resistivity changes during heating process of martensite transformation. As a result, three successive magnetic entropy change ΔSM peaks of 10.7, 14.5 and 9.7 J/kg·K at temperatures 275, 279 and 285 K respectively were observed, which was responsible for a wide working temperature span ΔTFWHM of 273–287 K and thus a large effective refrigeration capacity RCeff of 98.1 J/kg under 5.0 T. At the same time, a large negative magnetoresistance MR (e.g. over 26.7% at 275 K) was also revealed during heating process under 5.0 T. Such multi-functional magnetocaloric and magnetoresistance effects render Ni–Mn–Sn–Fe alloys promising working materials for magnetic refrigerants, information storage and thermal magnetoelectricity conversions.

Multiple magnetic phase transitions and magnetocaloric effects of perovskite manganite

Perovskite La0.7Ca0.3Mn0.9Cu0.1O3 manganite was prepared and examined by X-ray diffraction. Multiple magnetic phase transitions and magnetocaloric effect were represented based on magnetic and specific heat measurements. The sample undergoes a first-order ferromagnetic - paramagnetic transition with a large thermal hysteresis, where the Arrott plots show negative slopes. A charge ordered phase occurs at TCO = 162 K, which can be melted under a sufficiently large magnetic field (µ0H ≥ 1 T) and thus result in a spin reorientation. The step-like jump of magnetization at Tb = 42 K in warming curves is caused by a blocked state, which is overcome by applying a magnetic field and leads to a metamagnetic transition. The successive multiple magnetic phase transitions broaden the operating temperature span and contribute to a large refrigerant capacity, in spite of mediocre magnetic entropy change and adiabatic temperature change. The adiabatic temperature change and phase transition mechanism were also discussed based on the recorded specific heat data.

Competing ferromagnetic and antiferromagnetic interactions drive the magnetocaloric tunability in Gd55Co30NixAl15−x microwires

We have employed Gd55Co30NixAl15−x (x = 10, 5 and 0) amorphous microwires as a model system to unravel the impact of multiple magnetic interactions on the magnetism and the magnetocaloric behavior in Gd-alloy microwire systems. Our study shows that in addition to the RKKY ferromagnetic (FM) interaction (Gd-Gd), antiferromagnetic (AFM) interactions (Gd-Co, Gd-Ni) coexist and contribute to the magnetic and magnetocaloric response of the system. The dilution effect of Al element on the FM Gd-Gd interaction is responsible for the decrease of the Curie temperature (TC), whereas the increase of the saturation magnetization (MS) is originated from the reduced AFM Gd-Ni interaction. A thorough analysis of critical exponents suggests that the presence of the AFM interactions hinders the system to exhibit a long-range FM order below the TC. Adjusting these interactions is shown to preserve the large refrigerant capacity (RC) while tuning the TC over a wide temperature range, which is desirable for active magnetic refrigeration.

Near room temperature magnetocaloric properties in Ni deficient (Mn0.525Fe0.5)Ni0.975Si0.95Al0.05

We present an experimental study on the crystalline, magnetic, and magnetocaloric properties of Ni deficient (Mn-rich) (Mn0.525Fe0.5)Ni0.975Si0.95Al0.05. The study has been performed by x-ray diffraction, scanning electron microscopy, and dc magnetization measurements. X-ray diffraction measurements showed that the sample primarily exhibited the orthorhombic structure at room temperature. The coupled structural and ferromagnetic transition occurred at ∼338 K, which is significantly larger than ∼320 K observed in (Mn0.50Fe0.5)NiSi0.95Al0.05. Maximum magnetic entropy changes of ΔSM = −9.5 and 25 J kg−1K−1 for ΔH = 20 kOe and 50 kOe, respectively, have been observed in the material. Large refrigeration capacities of 60 J/kg and 160 J/kg for field changes of ΔH = 20 kOe and 50 kOe, respectively, have also been observed.

Spin-glass behavior and magnetocaloric properties of high-entropy perovskite oxides

The high-entropy concept has been recently proposed to be a promising paradigm to enhance the magnetocaloric properties of materials. Motivated by this, the magnetic properties and the magnetocaloric performance of two high-entropy perovskites (Dy1/4Ho1/4Er1/4Tb1/4)FeO3 and (Gd1/5Dy1/5Ho1/5Er1/5Tb1/5)FeO3 have been investigated. The magnetic measurements indicate that a spin-glass phase occurs at low temperatures in the high-entropy compounds, which is induced by the strong compositional disorder of rare-earth sublattice. The glassy state can lead to a sluggish magnetic transition and consequently a potential improvement in the magnetocaloric performance. Due to the increase in configurational entropy, large refrigerant capacity of 247 and 203 J/kg for a magnetic field change of 70 kOe is obtained in the (Gd1/5Dy1/5Ho1/5Er1/5Tb1/5)FeO3 and (Dy1/4Ho1/4Er1/4Tb1/4)FeO3 compounds, respectively. Our findings highlight the availability of spin order control through tuning the configurational entropy and demonstrate the key role of high-entropy design in enhancing the magnetocaloric properties of materials.

Enhanced magnetocaloric performance in nanocrystalline/amorphous Gd3Ni/Gd65Ni35 composite microwires

A novel class of nanocrystalline/amorphous Gd 3 Ni/Gd 65 Ni 35 composite microwires were created directly from melt-extraction through controlled solidification. X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) confirmed the formation of a biphase nanocrystalline/amorphous structure in these wires. Magnetic and magnetocaloric experiments indicate a large magnetic entropy change (-Δ S M ~9.64 J/kg K), large refrigerant capacity ( RC ~742.1 J/kg), and large maximum adiabatic temperature change ( Δ T a d max ~5 K) around the Curie temperature of ~120 K for a field change of 5 T. These values are ~1.5 times larger relative to its bulk counterpart and are superior to other candidate materials being considered for active magnetic refrigeration in the liquid nitrogen temperature range. • Novel nanocrystalline/amorphous Gd 3 Ni/Gd 65 Ni 35 microwires. • Large magnetic entropy change and refrigerant capacity. • Magnetic refrigerators for nitrogen liquefaction.