Refrigeration Devices Research Articles

Highlighting the effects of gravity in a compact thermoacoustic heat pump

We present a numerical study of gravity impact on thermoacoustic heat pumping effects in a compact cavity used as a refrigeration device. More precisely, we show how gravity acts on the temperature distribution, on the mean temperature heat flux along the stack area and on flow dynamics. Studies are performed in a two-dimensional geometrical configuration which is simplified with respect to common experimental devices but sufficiently detailed to take into account the main physical mechanisms. Fluid motion, heat and mass transfer as well as compression/expansion effects are estimated from the computation of the Navier-Stokes equations in the low-Mach number hypothesis coupled with the heat equation in solid parts. The low-Mach number hypothesis is here relevant because the characteristic scale of the acoustic wavelength is much smaller than the geometrical length scales of the cavity. The operating mode is characterized by a moderate drive ratio, a fluid oscillating motion of moderate amplitude and fixed low frequency, typical of such devices. It is shown that when gravity is included, buoyancy effects modify the temperature and velocity fields as well as heat pumping efficiency.

Broad table-like magnetocaloric effect in the full hydrogen liquefaction range in Gd3Ni6XY

Gd3Ni6SiAl, Gd3Ni6SiGa, and Gd3Ni6AlGa (Ce3Ni6Si2-type, Im-3m, N 229, cI44) present a broad table-like magnetocaloric effect in the full hydrogen liquefaction range (20-77K) with a real plateau wide enough to be competitive for refrigeration devices based on the Ericsson cycle. The characterization of the magnetocaloric variables (|ΔSMpk|= 6.60J/kgK, TEC(10)= 6.44J/kgK for Gd3Ni6SiGa, |ΔSMpk|= 6.05J/kgK, TEC(10)= 6.01J/kgK for Gd3Ni6SiAl, all at μ0ΔH=5T) state that they are among the best of table-like magnetocaloric materials in this temperature range. The physical origin of this smooth and wide table-like effect is the combination of a spin reorientation transition (which appears in Gd3Ni6XY when Si or Ga is introduced) with the paramagnetic to ferromagnetic transition, close to each other. The application of the Banerjee criterion and the evolution of the critical exponent with temperature n(T) confirm that both transitions are second order, which is extremely relevant for real applications. From the study of the magnetic properties it has been inferred that the introduction of Si induces a magnetic ground state with combined ferromagnetic and antiferromagnetic components which turns to fully ferromagnetic at very low field. The critical exponents (β, γ, δ, n) have been found for the paramagnetic to ferromagnetic transitions; the values of γ (from 1.22 to 1.36) suggest that the magnetic interactions are short-range, though the ensembles do not correspond to any particular universality class.

Excellent Barocaloric Effect by Modulating Geometrical Frustrations in Mn3Pt.

Barocaloric materials hold great promise for next-generation solid-state cooling devices because of their green and efficient cooling performance. The insights into low-pressure-driven barocaloric materials are expected to pave the way for the widespread application of barocaloric refrigeration technology. Here, we reveal the low-pressure-driven large barocaloric effect (BCE) modulated by geometrical frustrations in Mn3Pt. The highest sensitivity to pressure of Mn3Pt in metal BCE materials results in an excellent temperature-change strength of 9.77 K 100-1 MPa-1. Neutron powder diffraction and first-principles calculations point out the dual effect of geometrical frustration on modulating the unusual BCE, which not only induces giant volume expansion by inspiring strong spin fluctuation and magnetic moment but also enhances the sensitivity of magnetic phase transition. The model of the dual effect of geometrical frustration in magnets with geometrical frustration is established, which will promote the research progress of barocaloric refrigeration devices.

Thermodynamic analysis of a modified two-stage transcritical CO2 refrigeration cycle with an ejector and a subcooler

In the application scope of large-scale supermarkets, the practicality of transcritical CO2 refrigeration device has been confirmed to be quite satisfying. A modified two-stage transcritical CO2 refrigeration cycle with an ejector and a subcooler (MTC) is proposed in this paper. In the modified cycle, the ejector recovers expansion works and reduces irreversible losses in the throttling process. The subcooler provides subcooling degree for the CO2 entering the low-temperature (LT) evaporator, thus increasing the refrigeration capacity and improving the COP of the modified cycle. Thermodynamic analysis has shown that the exergy efficiency (ηex) and COP of MTC under given operating condition has been enhanced by 13.7 % and 14.2 % compared to BTC. The discharge temperature at the outlet of high-pressure compressor in MTC is decreased by 8.3℃. Under typical operating condition, the optimal discharge pressure of MTC is 9.07 MPa, which is lower than that of BTC. The correlation to calculate optimal discharge pressure for single-stage CO2 refrigeration cycle is also suitable for MTC under given operating conditions. The MTC has also shown better performance under variable operating conditions. For MTC, when the temperature at the outlet of gas cooler increases from 35 – 45℃, the COP and ηex are enhanced by 14.1 % - 16.1 % and 12.8 % - 14.2 % compared to BTC, respectively. When gas cooler outlet pressure decreases from 11.0 to 7.5 MPa, the COP and ηex are enhanced by 14.0 % - 22.8 % and 13.4 % - 18.7 %. As the evaporating temperature at the cold side of subcooler increases from -25 to -15℃, the COP and ηex increase from 1.82 to 1.98 and 27.4 % to 29.7 %. With the ratio of refrigeration capacity (Rec) between medium-temperature evaporator and low-temperature evaporator varies from 0.7 to 1.2, the COP and ηex are improved by 10.7 % - 16.3 % and 10.7 % - 15.4 % compared to BTC. There is the maximum exergy loss at gas cooler in the MTC, whereas that of BTC is located in the expansion valve before LT evaporator. The economic analysis shows the cost per unit of exergy of MTC is decreased by 11.5 % under typical operation condition. According to simulation results, the modified cycle has better performance in severe working conditions such as high gas cooler outlet temperature and low gas cooler outlet pressure in the given range of working conditions compared to BTC.

Giant Photocaloric Effects across a Vast Temperature Range in Ferroelectric Perovskites.

Solid-state cooling presents an energy-efficient and environmentally friendly alternative to traditional refrigeration technologies that rely on thermodynamic cycles involving greenhouse gases. However, conventional caloric effects face several challenges that impede their practical application in refrigeration devices. First, operational temperature conditions must align closely with zero-field phase-transition points; otherwise, the required driving fields become excessively large. However, phase transitions occur infrequently near room temperature. Additionally, caloric effects typically exhibit strong temperature dependence and are sizable only within relatively narrow temperature ranges. In this Letter, we employ first-principles simulation methods to demonstrate that light-driven phase transitions in polar oxide perovskites have the potential to overcome such limitations. Specifically, for the prototypical ferroelectric KNbO_{3} we illustrate the existence of giant "photocaloric" effects induced by light absorption (ΔS_{PC}∼100 J K^{-1} kg^{-1} and ΔT_{PC}∼10 K) across a vast temperature range of several hundred Kelvin, encompassing room temperature. These findings are expected to be generalizable to other materials exhibiting similar polar behavior.

Cutting-edge technologies and recent modernization on multifunctional perovskite materials for green energy conversion and spintronic applications

This featured letter summarizes the recent developments in green energy and spintronic technologies based on multifunctional i.e., multiferroic (MF) and magnetoelectric (ME) materials. These are non-toxic materials, find applications in spintronic, non-volatile memory devices, microelectromechanical systems (MEMS), photovoltaics and next generation IC miniaturization devices. Recent studies on MF and ME materials have probed and analyzed significant properties such as evidence of photo-response and significant power conversion efficiency (PCE) of multiferroic-based solar cells (SCs), evidence of electro-caloric effect (ECE) which find usage in non-toxic solid state refrigeration devices, photo- and electro-catalytic activities for green hydrogen generation, magnon-phonon coupling and existence of magnon polarons which can facilitate spintronic device technology and thermal Hall effect and, hybrid nano-generators utilized to empower portable electronic devices. All such applications are comprehensively analyzed in-depth in this letter.

Band Structure Calculations, Magnetic Properties and Magnetocaloric Effect of GdCo1.8M0.2 Compounds with M = Fe, Mn, Cu, Al

The magnetic properties, band structure results, and magnetocaloric effect of GdCo1.8M0.2 with M = Fe, Mn, Cu, and Al are reported. The band structure calculations demonstrate that all the samples have a ferrimagnetically ordered ground state, in perfect agreement with the magnetic measurements. Calculated magnetic moments and variation with the alloy composition are strongly influenced by hybridisation mechanisms as sustained by an analysis of the orbital projected local density of states. The XPS measurements reveal no significant shift in the binding energy of the investigated Co core levels with a change in the dopant element. The Co 3s core-level spectra gave us direct evidence of the local magnetic moments on Co sites and an average magnetic moment of 1.3 µB /atom was found, being in good agreement with the theoretical estimation and magnetic measurements. From the Mn 3s core-level spectra, a value of 2.1 µB/Mn was obtained. The symmetric shapes of magnetic entropy changes, the Arrott plots, and the temperature dependence of Landau coefficients clearly indicate a second-order phase transition. The relative cooling power, RCP(S), normalized relative cooling power, RCP(∆S)/∆B, and temperature-averaged entropy change values indicate that these compounds could be promising candidates for applications in magnetic refrigeration devices.

Design of polar boundaries enhancing negative electrocaloric performance by antiferroelectric phase-field simulations

Electrocaloric refrigeration which is environmentally benign has attracted considerable attention. In distinction to ferroelectric materials, which exhibit an extremely high positive electrocaloric effect near the Curie temperature, antiferroelectric materials represented by PbZrO3 have a specific negative electrocaloric effect, i.e., electric field decreases the temperature of the materials. However, the explanation of the microscopic mechanism of the negative electrocaloric effect is still unclear, and further research is still needed to provide a theoretical basis for the negative electrocaloric effect enhancement. Herein, the antiferroelectric phase-field model has been proposed to design polar boundaries enhancing antiferroelectric negative electrocaloric performance in PbZrO3-based materials. Based on this, we have simulated the polarization response and domain switching process of the temperature and electric field-induced antiferroelectric—ferroelectric phase transition. It is shown that the temperature range tends to increase as the density of polar boundaries increases from the antiferroelectric stripe domain, polymorphic domain to the nanodomain. Among them, the peak adiabatic temperature change of antiferroelectric nanodomains can reach −13.05 K at 84 kV/cm, and a wide temperature range of about 75 K can be realized at 42 kV/cm. We expect these discoveries to spur further interest in the potential applications of antiferroelectric materials for next-generation refrigeration devices.

Improved Drycooler control by custom hybrid controller

Refrigeration devices designed for use in industrial environments are typically equipped with universal control algorithms, which require a minimal number of signals and parameters to ensure satisfactory device operation. These algorithms are typically of the PID type. This study elaborates upon the impact of using a dedicated hybrid controller, which was designed with specific consideration of the operating conditions of a given refrigeration device. The identified nonlinear Drycooler characteristics were used to support the controller at steady-state operating conditions. The system dynamics were supervised by a dedicated, experience-based designed hybrid fuzzy logic Mamdani type controller for both freecooling and compressor modes. The switchable configuration of the MISO control architecture results in a reduction in overshoots and oscillations in the system, a decrease in the time necessary for stabilization, a reduction in CO2, and an increase in control quality and energy efficiency.

Magnetic phase diagrams and magnetocaloric effect of alternate layers of nanoborophene like: A Monte Carlo study

Here, we have investigated the magnetic properties and magnetocaloric effect of the alternate layers of nanoborophene like of a ferrimagnetic mixed spin 2 and 3/2 in a Blume–Capel model, employing the Monte Carlo method. The ground states at different parameters planes are found. Besides, we also determined the reduced compensation temperature and critical temperature to vary the number of layers (L). The impact of L, reduced exchange couplings Rσσ, RSσ, and reduced crystal field on the total magnetizations. In addition, the various parameters L, Rσσ, RSσ, and t also have distinct influences on the hysteresis loop are also analyzed. The Cp, -ΔSm, and ΔTa as a function of reduced temperature under the effect of several reduced external magnetic fields were discussed. Lastly, the impacts of the reduced external magnetic field on the relative cooling power were also studied. We hope that these results can be used as a basis for the application of materials, spintronics, energy storage, and magnetic refrigeration devices.

Analysis of the influence and mechanism of the pollution condensation environment on the electrochemical migration behaviour of printed circuit board with immersion silver

A refrigeration device was developed to induce condensation on printed circuit board with immersion silver (PCB-ImAg). Results show that in a condensation environment with low relative humidity, an electrolyte film can still be formed that allows conduction between the two poles of PCB-ImAg, allowing the thermodynamic conditions for electrochemical migration (ECM) to be reached and creating the risk of short-circuit failure. Under high relative humidity, the main body of ions that underwent ECM on the surface of PCB-ImAg was Cu2+ and as the relative humidity of the environment increases, the short-circuit failure time shortens, and the initial current density increases.

Effect of Magnetic Flow and Convective Heat Transfer Enhancement Using Hybrid Nanofluid: A Structured Review

Convective heat transfer is vital in a variety of engineering applications, including thermal management systems, electronic refrigeration, and energy conversion devices. Improving the rate of heat transfer in these systems is of the utmost significance for increasing their efficiency. This review focuses on the single and combined effects of these parameters on improving heat transmission in such systems. The heat and mass transfer of nanofluid is greatly influenced by various factors, including the intrinsic features of the nanofluid, the process used for synthesising the nanofluid, the impact of magnetic force, the concentration and size of nanoparticles, and the Reynolds number (Re). Furthermore, it is important to note that the material characteristics, thermal properties, and performance of magnetic nanofluids are significantly influenced by slight variations in the magnetic force and magnetic field gradient. Multiple research projects have reached the agreement that the inclusion of a magnetic field within magnetic nanoparticles enhances the convective heat transfer capabilities of a nanofluid, resulting in an improvement ranging from around 13% to 75%. Moreover, several applications of hybrid nanofluids in thermal systems have been introduced.

Measurement of rheological properties in raw and cooked meat aged with a controlled dry-aging system

Texture of meat is a critical parameter of consumer’s acceptability. In this regard, aging technology has become essential to enhance meat tenderness and flavour. The present study evaluated the effect of dry-aging on the rheological properties of cooked and raw meat (Longissiumus dorsi) using objective instrumental measurements: colorimeter (CIEL*a*b*), texture profile analysis (TPA-test) and Warner Bratzler shear force test (WBSF-test). In this study, a monitored refrigeration device was used for 60 days of dry aging of meat. Physical-chemical analyses were also evaluated on raw meat. The analyses were carried out at 2 (T0), 15 (T1), 30 (T2) and 60 (T3) days post-slaughter. During dry aging, aw values tended to decrease while the pH values increased. The mayor color changes occurred in the first 15 days of dry aging. As regard the texture traits, significant differences were found between the cooked and raw meat mainly due to the effect of temperatures on collagen. The correlation data showed significant positive correlations between WBSF and hardness values. Results showed that aging time and cooking tended to decrease the hardness and shear force implying more tender meat for the consumer.

Natural rubber based elastocaloric solid-state refrigeration device: design and performances of a single stage system

The elastocaloric effect denotes the ability of a material to release or absorb heat when the material is stretched and released respectively. This effect may be used to design an alternative cooling device. This work focuses on the development of a cooling device using natural rubber (NR) as the elastocaloric material. It consists of a solid–solid heat exchange between a cyclically stretched elastocaloric material and two exchangers, respectively put in contact with the elastocaloric material when it is stretched or released. An experimental device was designed and tested in order to assess the temperature span and cooling power (PC) achievable by NR based single stage device. The effect of the thickness of the NR is also discussed. It is shown that it was possible to transfer nearly 60% of the heat absorption potential of the NR from the cold heat exchanger. From the measurements, the highest PC was found to be 390 mW (430 W kg−1) for a 600 µm thick sample, and 305 mW (540 W kg−1) for a 400 µm thick sample. The temperature span was found to be similar for both materials, ranging 1.5 °C–1.9 °C.

Experimental research on the cooling effect of a novel two-phase closed thermosyphon with semiconductor refrigeration in permafrost regions

Hybrid two-phase closed thermosyphon (TPCT) artificial ground freezing technique is an effective cooling strategy adaptable to different geological and meteorological conditions in permafrost regions. Previous studies have focused on the feasibility of hybrid TPCT with little attention given to the cooling characteristics and long-term effects of this technique under actual environmental conditions. In this study, a novel structured semiconductor refrigeration device, with simple structure, small size, and wide operating temperature range, was designed and manufactured to act as the active condenser of a hybrid TPCT, and the cooling effect of this device was investigated during a two-year field test under stable power supply. This study showed that: 1) The minimum (maximum) average temperature of the semiconductor refrigeration two-phase closed thermosyphon (SRTPCT) evaporator was 0.5 (2.1) °C lower than the TPCT evaporator. The average ground temperature decreased by 0.3 °C, and the permafrost table rose to 0.2 m at 1 m from the evaporators around SRTPCT. The semiconductor refrigeration device added more than 9.75 MJ of cold storage to the soil around the TPCT evaporator during an operating cycle. 2) The optimal working period for the semiconductor refrigeration device was from June to October, and the cooling effect was better when the ambient temperature was low in the warm season. 3) As active condenser of hybrid TPCT in permafrost regions, semiconductor refrigeration device has a larger heat transfer power enhancement for TPCTs than vapor compression refrigeration device in the warm season, and vice versa in the cold season, as well as a higher heat transfer power enhancement for TPCTs than adsorption refrigeration device. The results of this study provide relevant parameters and references for the design and engineering application of future SRTPCT.

Моделирование системы магнитного охлаждения и синтез регулятора ее холодопроизводительности

The article reviews existing designs of cooling systems and analyzes problems in their development and operation. As a result, a magnetocaloric refrigerator is selected as a research object. The refrigerator device under study and the processes occurring therein are investigated to develop a mathematical apparatus for simulating an active magnetic regenerator as the most problematic part of the refrigerator device. Subsequently, the system for controlling cooling capacity is synthesized and implemented in software form to regulate temperature fluctuations in steady-state mode at the boundary with heat dissipation. Simulation of transient heat transfer processes between a magnetic material and a coolant is carried out taking into account the spatial distribution of the object under consideration. The setting of the regulator is based on the static characteristic of changes in the coolant temperature on the value of magnetic induction in the orthocenter of the boundary plane with the cold heat exchanger.

Frost-Preventing Design for Space Station Refrigerator

Different preservation temperatures for sample storage in space stations and corresponding refrigerator devices have been designed. In the below-freezing environment, frost will occur on the inner wall surface and the sealing place of the refrigerator device, which may have an impact on the operating performance and sealing performance of the refrigerator device. This paper analyzes the impact of frost on refrigerator storage devices, and designs and verifies a scheme of air cooling with a hollow seal method to reduce the impact of frost. The designed refrigerator was tested for air cooling, sealing, and long-term performance. The tests show that the air-cooling structure designed in this paper can effectively reduce the frost on the sample surface. A cumulative helium mass spectrometry leak detection method is applied to verify that the hollow seal structure designed has a better sealing property, which can prevent the diffusion of water vapor and frosting at the sealing position. The design with air cooling and hollow sealing has less frost and more stable performance for long-term operation. The results demonstrate this refrigerator would have the capability of operating on-orbit. The frost-preventing method for space station refrigerator designed in this paper has significance for the design of similar cryogenic equipment in microgravity environments.

Study of an integrated vortex tube used in hydrogen pre-cooling system

In hydrogen refueling stations, a hydrogen pre-cooling system is essential to protect the onboard hydrogen storage cylinder from high-temperature damage during refueling. To address the high power consumption of existing systems, this study proposes an integrated vortex tube hydrogen pre-cooling system. This system combines the vortex tube with a two-stage compression refrigeration cycle to create a new refrigeration device. The vortex tube component is numerically simulated using the standard k-ε turbulence model. Comparative analysis of power consumption and coefficient of performance (COP) is conducted between the new system, single-stage, and two-stage hydrogen pre-cooling systems. The results indicate that the vortex tube, as the pressure ratio increases from 1.5 to 20, reduces power consumption by 26.37%–41.52% compared to the single-stage system. Additionally, it improves the COP by 30.9%–53.8% compared to the single-stage system. Furthermore, compared to the two-stage system, the vortex tube achieves power savings of 4.08%–10.44% and COP improvements of 4.3%–11.7%.

Giant magnetocaloric effect and second order phase transition in PrMnO3

Magnetocaloric effect and the order of magnetic phase transitions of polycrystalline PrMnO3 have been investigated through magnetization measurements. The amount of magnetic entropy-change has been calculated by Maxwell relation and the maximum value of -△SMmax was found to be 23.4 Jkg-1K−1 at 5 T applied magnetic field. Near Curie temperature (TC = 104 K), PrMnO3 exhibits a second order paramagnetic to ferromagnetic phase transition. The order of magnetic phase transition is determined with the help of Arrott plot and Landau temperature dependent coefficient b(T). A 3D magnetic entropy plot is also implemented to further evaluate the order of magnetic phase transition. The fact that this material has large value of magnetic entropy change pairedwith second order magnetic phase transitionat a low strength appliedmagnetic field indicates its potential suitability for use in magnetic refrigeration devices.

Solar adsorption refrigeration system: Comparison between equilibrium, universal and transient model

Three models of different level of complexity are detailed in order to predict the cold production of a solar cooling device. The transient model consists on a heat and mass transfer model of the absorber, coupled with a solar collector model which conceives the ambient temperature as variable along the day and comprehends the evolution of the solar radiation throughout the day according the locations of the prototype to be analyzed in addition to the ideal models of the condenser and evaporator. The Equilibrium and Universal Model are both lumped models in which the spacial distributions of the variables and the heat and mass transfer resistance in the system are disregarded. The advantages and disadvantages of each model are discussed.The results of the models are compared with experimental data obtained from four methanol/activated-carbon adsorption refrigerator prototypes. The cold generated is underestimated 12%–20% by the transient model, while it is overestimated 22%–46% by the equilibrium model and 53%–66% by the universal model. Even when the transient model allows some improvements, is a useful tool to analyze the impact that different variables of a solar adsorption refrigeration system have in the generation of cold. The simpler models can be used for preliminary design and feasibility studies of solar adsorption refrigeration devices (SARS) whose results can be extrapolated on the premise of its overestimation of cold generation approximately given by this work.