Maximum Refrigeration Research Articles

Critical behavior and tunable magnetocaloric effect in (Gd1-xErx)3Al2 alloys

The magnetic properties, magnetocaloric effect, and the critical behavior near Curie temperature (TC) were systematically studied in a series of (Gd1-xErx)3Al2 (x = 0, 0.1, 0.2, 0.3) alloys. As the Er content increases, both the TC and lattice constant gradually decrease. The maximum magnetic entropy change and refrigerant capacity remain relatively high, ranging from −5.8 to −8.5J/kg K and 209.0 to 290.8 J/kg respectively, for a field change of 5 T. The critical exponents, derived from the field dependence of magnetic entropy change, conform to scaling theory and are consistent with those obtained using the Kouvel–Fisher method. These findings suggest that the reliability of the obtained critical exponents and imply the presence of long-range exchange interactions in (Gd1-xErx)3Al2 alloys.

Enhancing Semiconductor Chiller Performance: Investigating the Performance Characteristics of Ultra-Low-Temperature Chillers Applying a Liquid Receiver

This study investigates the implementation of a cryogenic chiller utilizing a mixed-refrigerant cascade refrigeration cycle (MRCRC). In this setup, R-404A is employed in the high-temperature circuit (HTC), while a mixture of refrigerants is utilized in the low-temperature circuit (LTC). Unlike a conventional MRCRC that operates without a receiver to maintain the composition ratio, this research explores the impact of receiver installation on system performance. Experiments were conducted with and without a receiver to assess performance improvements and device behavior. With a fixed refrigerant charge of 4 kg, the suction and discharge pressures of the LTC compressor remained low and stable after the receiver’s installation. The addition of a receiver significantly reduced the cooling time, with further reductions observed as the refrigerant charge increased. The system achieved evaporative heat capacities of 0.59, 1.76, and 2 kW for refrigerant charges of 4, 7, and 9 kg, respectively. Notably, at the maximum refrigerant charge of 11 kg, the evaporative heat capacity peaked at 3.3 kW. These findings indicate that incorporating a receiver is crucial for enhancing the cooling performance of cryogenic coolers using mixed refrigerants and stabilizing device operation. This contrasts with previous studies that omitted receivers due to concerns over potential alterations in the composition ratio of the mixed refrigerant.

Simulation of diffusion of combustible refrigerants R1234yf and R290 leakage in automotive air conditioning

Electric vehicles that utilize a heat pump system have a refrigerant charge increase of at least 400 g compared to traditional fuel vehicle air conditioning systems. If combustible refrigerants are used, the risk of combustion increases when the refrigerant leaks and spreads to the passenger compartment. This paper dynamically monitored the volume concentrations of combustible refrigerants R1234yf and R290 as they leaked and entered the passenger compartment accompanied by air supply by numerical simulation. The results indicated that refrigerants are more prone to accumulate in the rear row than in the front. After a leak, the average volume concentration of R1234yf at the four air outlets was 1.58 %, and 3.36 % for R290. at the breathing points of four passengers, the average volume concentration was 0.99 % for R1234yf and 2.39 % for R290. Near the feet of the passengers, the average volume concentration was 0.95 % for R1234yf and 2.27 % for R290. The highest volume concentration of R1234yf in the passenger compartment was below its LFL, whereas all monitoring points for R290 exceeded its LFL. Compared to experimental data, the difference in maximum refrigerant volume concentration was approximately 1.2 %.

Excellent magnetocaloric effect near the hydrogen liquefaction temperature of a binary Er67.5Co32.5 metallic glass

We reported the excellent magnetocaloric effect of a binary Er67.5Co32.5 metallic glass (MG) near the hydrogen liquefaction temperature. The binary MG ribbon was fabricated by a melt-spinning method. The Er67.5Co32.5 alloy exhibits a better glass formability than most of other rare earth (RE)-Co binary alloys. The maximum magnetic entropy change (−ΔSmpeak) and refrigeration capacity (RC) of the Er67.5Co32.5 amorphous ribbon under 0–5 T reach to 17.47 J/(kg × K) near its Curie temperature (Tc, ∼ 11 K) and 472 J/kg, both of which are rather high among the RE-based MGs with a Tc around 10 K and imply the potential application perspective as magnetic refrigerants for hydrogen liquefaction. The magnetization as well as magnetocaloric behaviors of the binary MG were observed, and the mechanism involved was investigated.

The impact of refrigerant leakage on the dynamic operating performance of R600a refrigerator systems

Refrigerant leakage in refrigeration and freezing systems reduces efficiency and even results in reliable risks like insufficient cooling and component damage. This paper establishes a dynamic model of a dual-temperature zone refrigerator that combines physical and control models. It investigates the impact of refrigerant micro-leakage on the system’s dynamic operational performance, studies the effects of different leakage areas and compressor speeds on leakage performance, and identifies the critical leakage area (Ac) and critical compressor speed (Rc) based on the temperature variation patterns within the cabinets. Furthermore, this paper analyzes the coupled influence of the compressor speed and leakage area on the cabinet’s temperature. The findings reveal that after leakage occurs, the first noticeable deviations are in system pressure and the amount of refrigerant in the accumulator. Once the refrigerant in the accumulator fully vaporizes, the temperature in the cabinets is affected. Throughout the leakage process, both the system pressure and the heat exchange capacity of the evaporator decrease. At a compressor speed of 2000 rpm, the critical leakage area is 0.013 mm2, and the maximum refrigerant leakage that allows the refrigerator cabinet to cool to the shutdown temperature is 67.6 %. If the leakage area is larger than Ac, it reduces the time for alternating cooling between the freezer and refrigeration cabinets, resulting in a rapid rise in the comprehensive weighted average temperature deviation (CATD). For smaller leakage areas (<0.015 mm2), Rc exists. Operating the compressor at Rc can significantly reduce CATD. For larger leakage areas (≥0.015 mm2), Rc does not exist, increasing compressor speed has a lesser impact on CATD. The research results provide guidance for establishing a refrigerant leakage detection system and improving its accuracy, enhancing the operational reliability of refrigeration systems.

Magnetocaloric effect and phase transformation of Zn-doped Ni–Mn–Ti all-d metal Heusler alloys

Ni–Mn–Ti Heusler alloys have gained a great consideration recently due to their important magnetoresistance and magnetocaloric properties. Herein, the structure, martensitic transition (MT), and magnetocaloric effect (MCE) of Ni50-xZnxMn35Ti15 (x = 0, 2, 4, and 6) Heusler alloys have been studied. XRD results show that the studied alloy with x = 0 display a monoclinic (5 M) martensite phase. Besides, the examined alloy with x = 2 presents a combination of monoclinic (5 M) martensite and cubic (B2) austenite phases, whereas the alloys with x = 4 and x = 6 exhibit only a cubic (B2) austenite phase. By increasing Zn content x up to 6, the Curie temperature of austenite decreases from 283 K to 132 K, and the MT temperatures decrease from ferromagnetic austenite to weak-magnetic martensite, which is apparently due to the exchange interaction of Mn–Mn and the low power of d-d hybridization between the A/C and B(D) sites. The best maximum magnetic entropy change (ΔSM, max) and refrigeration capacity (RC) are for the studied alloy with x = 4 (5.22 J kg−1K−1 and 217 J kg−1 at 120 kOe, respectively). The Zn addition not only facilitates the formation of B2-type Heusler phases but also offer the possibility to tune the MT and establish strong ferromagnetic coupling.

Magnetic phase transition and large cryogenic magnetocaloric effect in the gallides RE2Rh3Ga (RE = Gd, Dy, Ho, Er)

We herein provide an experimental investigation of the gallides RE2Rh3Ga (RE = Gd, Dy, Ho, Er) regarding their magnetic properties and magnetocaloric effect (MCE). All of these RE2Rh3Ga intermetallic compounds crystallized with the Mg2Ni3Si type structure, space group R–3 m and are ordered magnetically at low temperatures. Large reversible MCEs around their own ordering temperature were observed in all RE2Rh3Ga compounds and their magnetocaloric parameters including the maximum magnetic entropy change, refrigerant capacity, and temperature-averaged entropy change are comparable to those of some recently reported candidate materials with prominent performances, making them considerable for cryogenic MR applications.

Structural and magnetic properties of Gd4Ga2O9 oxide with a large cryogenic magnetocaloric effect

The magnetocaloric effect has been extensively investigated in various types of magnetic solids to not only develop practical magnetic cooling applications but also deepen the understanding of these materials’ underlying inherent properties. Through experimental determination and theoretical calculation, we conducted a systematic investigation of Gd4Ga2O9 oxide in terms of its structural, magnetic, and magnetocaloric properties and found it to crystallize in a monoclinic structure belonging to the space group P21/c and to possess an antiferromagnetic semiconducting ground state. The consistent elements were uniformly distributed up to the nanoscale and presented as Gd3+, Ga3+, and O2 states, respectively. The magnetocaloric performances of Gd4Ga2O9 oxide were checked according to the parameters of maximum magnetic entropy change, refrigerant capacity, and temperature-averaged entropy changes (lift of 5 K), which were determined to be 25.77 J/kgK, 218.27 J/kg, and 23.43 J/kgK under 0–7 T magnetic field change. These parameters of Gd4Ga2O9 oxide are comparable to those of some recently reported materials with prominent performances, which means that it can be considered for cryogenic magnetic cooling applications.

Large reversible magnetocaloric effects originating from ferromagnetic phase transition in Gd(Cu1−xNix)2 (x = 0.12, 0.15)

Here, the significant increase in MCE without any hysteresis loss was achieved through the substitution of nickel for a portion of the copper in GdCu2 compound. The values of maximum magnetic entropy changes (−ΔSMmax) and refrigeration capacity (RC) for Gd(Cu1-xNix)2 (x = 0.12, 0.15) compounds are 10.3 J/kg K, 455.3 J/kg, 9.3 J/kg K and 461.2 J/kg under varying magnetic fields from 0 to 5 T, respectively. The refrigeration capacity of Gd(Cu1−xNix)2 (x = 0.12, 0.15) is improved by an order of magnitude compared to the GdCu2 compound under varying magnetic fields from 0 to 5 T. While providing an ideal magnetocaloric refrigerated material for hydrogen liquefaction, our work also suggests a promising approach to the development of new magnetocaloric refrigerated materials.

Wearable active-cooling garment for personalized thermoregulation in vehicle

The issue of energy waste caused by automobile air conditioning while improving the thermal environment of the compartment necessitates immediate attention. In this study, a liquid cooling garment (LCG) for vehicles was designed based on the heat flow field in the compartment. The silicone tubes (with inner diameter of 0.5 mm and a total length of 71.5 m, respectively) are woven into a T-shirt and used as heat exchange pipelines in eleven regions (including the chest and belly). We adopted the thermoelectric cooler with a maximum refrigeration coefficient of 0.68 for the active cooling supply, and the maximum energy consumption of the LCG system is 0.15 kW∙h. The temperature distribution of an outdoor parking compartment was monitored in the summer to verify the simulation results. The experiment results have shown that the maximum temperature difference between the subject wearing LCG and the reference group was 3 °C under the high-temperature environment (37–42 °C). The thermal sensation score of the subject ranged from −1 to 3, and the thermal comfort and thermal acceptability scores ranged from −0.01 to 1. The LCG has been demonstrated to meet human cooling needs. This work provides a new idea for designing personal temperature control systems and establishes a foundation for the wide application of cooling garments.

Wide temperature span and giant refrigeration capacity magnetic refrigeration materials for hydrogen liquefaction

Based on theoretical calculations and experiments, the crystal structure, electronic structure, magnetism, and magnetocaloric effect (MCE) of the Ho5B2C5 compound have been systematically investigated. The Ho5B2C5 compound with a typical metallic nature was found to crystallize in a tetragonal structure belonging to space group P4/ncc (No. 130), and its magnetic ground state was identified as ferromagnetic (FM) ordering based on theoretical and experimental results. Additionally, a second-order magnetic phase transition from FM to paramagnetic around approximately 27 K was observed in the Ho5B2C5 compound, resulting in a large MCE. Under varying magnetic fields (ΔH) from 0 to 7 T, the maximum magnetic entropy change (−ΔSMmax), refrigeration capacity (RC), and δTFWHM are 21.3 J/kg K, 1001.6 J/kg, and 60.2 K (a wide temperature range from 15.2 to 75.4 K), respectively. The outstanding MCE performance of the Ho5B2C5 compound is expected to facilitate the progress of magnetic refrigeration for hydrogen liquefaction.

Theoretical investigation of a novel distributed compression cycle for CO2 trans-critical system

Efficient cooling of the trans-critical CO2 vapor compression cycle to improve system performance is a crucial research topic. This paper proposes an innovative approach called distribution compression (DC) to achieve the same effect as subcooling in a trans-critical CO2 thermodynamic cycle. In the DC system, the trans-critical CO2 at the gas cooler outlet is no longer further cooled but subjected to a secondary pressure boost and releases heat in ordinary heat sink conditions as in the gas cooler. Thermodynamics calculated the change in performance of the DC system under different working conditions with different secondary boost ratios. The optimal secondary boost ratio related to evaporation and gas cooler outlet temperatures under optimal discharge pressure based on the baseline system was obtained. The results show that compared with the baseline system, the DC system can effectively improve the system performance, and the maximum refrigeration COP increase is between 8.2 % ∼ 10.76 %, and the maximum heating COP increase is between 5.37 % ∼ 6.34 %. The cooling or heating capacity increase can reach up to about 26 %. The ideal secondary boost ratio in a DC system is not highly demanding, and the increased input power for the second input power for the secondary boost will not exceed 20 % relative to the baseline system. Comparing the COP of the DC system over current systems that only use a single subcooling technology still shows advantages. The DC system provides a new idea to improve the performance of the trans-critical CO2 vapor compression cycle.

Magneto-structural transitions driven giant magnetocaloric effect in Ni42Mn43Cr4Sn11 Shape Memory Heusler Alloy near room temperature

In the current work, a Ni–Mn-X (X = Sn, In) type off-stoichiometric, polycrystalline magnetic shape memory alloy (MSMA) having nominal composition Ni42Mn43Cr4Sn11 (at. %) has been thoroughly investigated in terms of its crystal structure, microstructure, magnetic properties, and magnetocaloric effect (MCE). X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), differential scanning calorimetry (DSC), and magnetic and magneto-transport measurements are used to characterize it. By offering a significant value of parameters related to MCE at the first-order martensite transition (FOMT) and the second-order magnetic transition (SOMT), the “Cr” doping at the “Ni” site enables considerable magnetic refrigeration to occur close to room temperature (RT). The alloy crystallises into coexisting cubic L21 austenite and tetragonal L10 martensite phases, among which the first one prevails as the leading phase at room temperature (RT) without exhibiting any geometric frustration. Lattice strain is enumerated using the Williamson-Hall method. A huge working temperature spans of 29.65 K and 26.16 K; the maximum magnetic entropy changes of +8.70 J kg−1.K−1 and −5.04 J kg−1.K−1 and the maximum refrigerant capacities (RC) of 284.24 J. Kg−1 and 234.10 J. Kg−1 across FOMT and SOMT, respectively at an applied magnetic field of 6 T are found to be most suitable for real technological applications. This MSMA offers a comparatively low cost of the constituent elements (Ni, Mn, Cr, and Sn), as well as exhibits giant MCE and RC across both FOMT and SOMT, making it an excellent candidate for magnetic refrigeration near RT. It also opens up new avenues for future research on novel Heusler alloys of this type.

Optimization method for mixed refrigerants in Joule–Thomson refrigerators with fixed-temperature heat loads

Mixed-refrigerant Joule–Thomson refrigeration is a widely used and effective method for refrigeration in the temperature range of 80–230 K. The demand for cooling heat loads at fixed temperatures, such as biological storage and cryogenic treatment of materials, is significant. The mixed refrigerant determines the refrigeration temperature and capacity in many cases; therefore, optimizing the mixed refrigerant composition is essential. The current mathematical approach for optimizing mixed refrigerants is not well-defined, owing to the challenge of determining how to adjust the concentrations of the components in the optimization process. Therefore, the current approach may exhibit poor robustness or a longer optimization time. This study proposes an alternative optimization method based on the effective refrigeration effect. The method aims to overcome the challenges associated with complex algorithms typically used in optimizing mixed refrigerants. The maximum refrigeration capacity was achieved by optimizing the isothermal throttling effect in the full-temperature zone without cycle simulations. Only one component with a significant refrigeration effect was changed at each optimization step. The proposed method was applied to a cryogenic refrigerator at 120 K, achieving a higher coefficient of performance than a genetic algorithm and other references. The study determined that varying the initial concentrations of the refrigerant components changed the performance coefficient to less than 0.002, indicating good robustness of the proposed optimization approach. Thus, our proposal is reliable for optimizing the composition of mixed refrigerants and can be extended to all mixed-refrigerant Joule–Thomson refrigeration systems with fixed-temperature heat loads.

Structure, magnetism and magnetocaloric effects in Er5Si3B x (x = 0.3,0.6) compounds

We investigate the structure, magnetic properties, magnetic phase transitions and magnetocaloric effects (MCEs) of Er5Si3B x (x = 0.3, 0.6) compounds. The Er5Si3B x (x = 0.3, 0.6) compounds crystalize in a Mn5Si3 type hexagonal structure (space group: P63/cm) and exhibit a successive complicated magnetic phase transition. The extensive magnetic phase transitions contribute to the broad temperature range of MCEs exhibiting in Er5Si3B x (x = 0.3, 0.6) compounds, with maximum magnetic entropy change () and refrigeration capacity of 10.2 J⋅kg−1⋅K−1, 356.3 J/kg and 11.5 J⋅kg−1⋅K−1, 393.3 J/kg under varying magnetic fields 0–5 T, respectively. Remarkably, the δT FWHM values (the temperature range corresponding to ) of Er5Si3B x (x = 0.3, 0.6) compounds were up to 41.8 K and 39.6 K, respectively. Thus, the present work provides a potential magnetic refrigeration material with a broad temperature range MCEs for applications in cryogenic magnetic refrigerators.

Effect of Ni alloying on the microstructure and magnetocaloric properties of Gd-based metallic microfibers

Gd-based metallic microfibers have been the research highlights due to the significant magnetocaloric effect. Herein, the atomic cluster micro-regions are constructed in Gd-based microfibers to further improve the magnetocaloric effect. The results show that the continuous and amorphous microfibers with excellent softly magnetic and thermal stability properties are obtained. The maximum magnetic entropy change -ΔSmmax of Gd-based microfibers increases first and then decreases with Ni alloying degree increase. Among which, the better magnetocaloric properties is obtained in (Gd60A20lCo20)95Ni5 microfibers. The maximum magnetic entropy change, refrigeration capacity (RC), and relative cooling power (RCP) at 5 T reach 11.57 J/kg K, 834.14 J/kg, and 1138.16 J/kg, respectively. The outstanding magnetocaloric properties of microfibers are attributed to the indirect interaction coupling caused by Ni elements and the atomic cluster micro-regions, which lead to a fundamental shift in magnetic entropy. The findings of this study promote the application of Gd-based microfibers in the field of magnetic refrigeration.

Advanced Method of Variable Refrigerant Flow (VRF) System Design to Forecast on Site Operation—Part 3: Optimal Solutions to Minimize Sizes

Outdoor air conditioning systems (ACS) are used as autonomic systems as well as in combined outdoor and indoor ACS of the variable refrigerant flow (VRF) type, with variable speed compressors (VSC) as their advanced version. Methods for determining the optimal value of refrigeration capacity and providing the maximum rate of the summarized annual refrigeration energy generation increment, according to its needs at minimum compressor sizes and rational values, are applied to reveal the reserves for reducing the designed (installed) refrigeration capacity, thus enabling us to practically achieve maximum annual refrigeration energy generation as the primary criterion at the second stage of the general design methodology previously developed by the authors. The principle of sharing the total thermal load on the ACS between the ranges of changeable loads for outdoor air precooling, and a relatively stable load range for further processing air are used as its basis. According to this principle, the changeable thermal load range is chosen as the object for energy saving by recuperating the excessive refrigeration generated at lowered loading in order to compensate for the increased loads, thereby matching actual duties at a reduced designed refrigeration capacity. The method allows us to determine the corresponding level of regulated loads (LRL) of SRC and the load range of compressor operation to minimize sizes.

Thermodynamic analysis of a solar refrigeration system based on combined supercritical CO&lt;SUB align="right"&gt;2 power and cascaded refrigeration cycle

This communication proposed a solar driven system based on supercritical CO2 (sCO2) power cycle integrated with cascaded refrigeration cycle (CRC) to refrigerate a thermal load of below than -40°C. The impact of varying solar irradiance (DNI), type of solar heat transfer fluid (SHTF), and the working fluid of CRC on refrigeration capacity and exergy efficiency of combined system are investigated. Results indicate helium as the most efficient SHTF with air to follow. It is shown that maximum refrigeration is produced when operating with helium as SHTF and propylene as the refrigerant for CRC. From exergetic point of view, propylene provides higher exergy efficiency; CO2 is the one with lower, while N2O presents intermediate results. The exergy efficiency of the system for the propylene, N2O and CO2 is determined as 9.64%, 8.73%, and 8.47%, respectively.

Performance assessment of a perovskite solar cell-driven thermionic refrigerator hybrid system

To develop a high-performance solar refrigeration technology, a novel refrigeration system composed of a perovskite solar cell (PSC) and a thermionic refrigerator (TIR) is constructed. Based on theories of photovoltaic effect, thermionic emission and non-equilibrium thermodynamics, the coefficient of performance (COP) and refrigerating capacity of the integrated system are mathematically expressed, in which the various irreversible losses are taken into consideration. The integration characteristics and coupling relationships between the PSC and TIR are investigated, and the working voltage regions for the combined operation of the subsystems are determined. Furthermore, the impacts of the area ratio, the work function, the environment temperature, the cold reservoir temperature and the heat transfer coefficient on systemic performance are evaluated in detail. Numerical calculation examples illustrate that the maximum COP and maximum refrigerating capacity of the integrated system are 0.81 and 81.2 W, respectively. Analysis results show that there exist optimal area ratio and work function to optimize the system performance. The present study may offer some fresh perspectives on the evolution of the solar refrigeration system.

Realization of Enhanced Refrigeration Capacity with Non-Hysteretic Behavior in Ni40Gd5Co5Mn37In12Si1 Alloy Near Room Temperature at 2T

Ni–Co–Mn–In–Si-based Heusler alloys have recently attracted a lot of attention because of their superior magnetocaloric properties around the second-order magnetic transformation near room temperature. In this paper, the effects of Gd substitution (Ni45–xGdxCo5Mn37In12Si1; x = 0 and 5) and Gd addition (Ni45Co5Mn37In12Si1 + Gdx; x = 0 and 5) on thermal and magnetic hysteretic behavior of temperature- and field-dependent magnetization of Ni45Co5Mn37In12Si1 Heusler alloy were investigated. The as-prepared Ni45–xGdxCo5Mn37In12Si1 Heusler alloys crystalize into a high-temperature austenite cubic L21 crystal structure, confirmed by powder X-ray diffraction. Microstructural and elemental composition analyses from field emission scanning electron microscopy reveal that parent Ni45Co5Mn37In12Si1 alloy shows single phase with larger grains in its as-cast form, whereas the Gd-doped Ni45Co5Mn37In12Si1 sample possess some dendritic well-distinguishable Gd-rich and deficient regions. Thermomagnetic measurements show that substitution of Gd at the Ni site in Ni45Co5Mn37In12Si1 notably reduces the Curie temperature, TC, from 333 to 317 K. Thermodynamic analyses of isothermal field-dependent magnetization result in significantly large magnetic entropy change, ΔSM = −0.842 J kg–1 K–1 under an applied field change, ΔH = 2 T at 305 K across the austenite regime for Ni40Gd5Co5Mn37In12Si1. Furthermore, the maximum refrigeration capacity of ∼47 J kg–1 was achieved for the composition of Ni40Gd5Co5Mn37In12Si1 at 305 K.