Although magnetocaloric cooling is considered a promising long-term alternative to vapor compression, recent prototype developments have not yet made this technology commercially competitive, ...primarily due to its high energy consumption and lack of cost-effective, long-term mechanically-chemically stable materials. To address the first issue and understand how the efficiency of magnetocaloric systems can be improved, dynamic models can offer valuable insights into their transient operation. This work focuses on the development of an artificial neural network with experimental data to model the dynamic operation of a magnetic refrigeration system. Through a design of experiments approach, we propose excitation signals for the identification experiment, involving five manipulated variables and one selected disturbance as inputs, with the output temperature of the cold manifold and power consumption as the target parameters. We chose a nonlinear autoregressive artificial neural network with exogenous inputs to model the transient operation of the system. The temperature model achieved R2 values of 0.995 and 0.955 for the 1-step and 90-step ahead predictions, respectively. Similarly, the power consumption model achieved R2 values of 0.988 and 0.949 for the 1-step and 90-step ahead predictions, respectively. These performance metrics were evaluated on the test sets that were not used for training the models, highlighting the robustness and accuracy of the models in both short-term and long-term predictions.
•Dynamic-model-predicted magnetic refrigerator’s temperature and power consumption.•A nonlinear autoregressive with exogenous inputs neural network modeled the system.•Experimental design methodology collected data for training and testing the model.•Model predicted system’s long-term dynamics with MSE of 0.091 °C and 70.38 W.
The study of magnetic measurements and magnetic memory effect was performed on nanocrystalline single-phase powders of GdMnO3 synthesized by the sol–gel method. They were structurally characterized ...via X-ray diffraction patterns and scanning electron microscopy images. The sol–gel method was coupled with mixing and blending the material powder using two techniques: (a) agate mortar and (b) corn flour. Zero-field cooling and field cooling magnetizations of both types of samples were also investigated thermally, and the susceptibility inverse was used to study the existence of the Griffiths phase. The corn flour technique showed a comparable particle quality and magnetic properties to the traditional mixing technique using an agate mortar. The GdMnO3 exhibited a large magnetocaloric effect with a magnetic entropy change in the range of 24.5–26.9 J/(kg·K) at an applied magnetic field of 5 T at low temperatures. The results surpassed the values reported in the literature by more than 44% at 5 T. The proposed method represents a scalable efficient method to produce a strong candidate material for cryogenic cooling in addition to other applications in electrical machines.
•Single crystallographic structure of GdMnO3 produced by two blending techniques.•Agate mortar sample resulted in better homogeneity than corn flour mixing.•Superior magnetic properties and smaller crystallites of agate mortar than corn flour sample.•More than 50% in entropy change compared to the literature.•Superior enhanced giant magnetocaloric effect for cryogenic cooling applications.
•New insights into the part-load operation of a magnetocaloric cooling device.•Experimental capacity modulation by tuning the fluid flow rate and cycle frequency.•Reducing the capacity to 54 % of the ...maximum load nearly doubles the efficiency.•A maximum second-law efficiency of 29.7 % was achieved at a 14 K temperature span.•Part-load operation with large energy-saving potential.
Magnetocaloric energy conversion devices (e.g., room air conditioners and household refrigerators) have the potential to significantly reduce the emissions associated with refrigerant leakage into the atmosphere but still have lower efficiencies compared to mature vapor compression systems. The efficiency of a magnetocaloric cooling device derives not only from its design characteristics (e.g., solid refrigerant, hydraulic system, and magnet system) and its operating temperature span but also from its modulating capability. Owing to the lack of experimental data regarding this topic, the advantage of modulating the cooling capacity (i.e., the part-load performance) of an active magnetic regenerator prototype is demonstrated experimentally for the first time. The capacity modulation is carried out by means of regulating both the cycle frequency of the device and the volumetric flow rate of the heat transfer fluid. At a 14 K temperature span and a 1.4 Hz frequency, the magnetocaloric refrigerator prototype using 3.8 kg of gadolinium provided a maximum cooling capacity of 452 W with an appreciable coefficient of performance of 3.2, which corresponds to a second-law efficiency of 15.5 %. At part-load operating conditions, the device can produce a cooling capacity of 245 W with an increased second-law efficiency of 29.7 %, or a coefficient of performance of 6.2, making it more competitive with traditional vapor compression systems. In future studies, the experimental data obtained may be implemented in a dynamic building energy model to quantify the energy-saving benefits of part-load operation by estimating the overall system efficiency during a typical cooling season.
The exponential rise of power dissipation in electric devices has so far vastly surpassed the performance of power converter systems. New thermal management solutions are therefore in high demand to ...maintain devices at their optimal temperature and efficiency. Here, we present an innovative magnetically actuated thermal switch (MATS) based on nanofluids capable of controlling both the magnitude and direction of the heat flux. When in the OFF state (zero applied magnetic field), the nanofluid captures the heat being generated at the heat source. When an external magnetic field is applied (ON state), the nanofluid is transported from the heat source to the heat sink where it releases the carried heat. This work (i) provides a detailed description of the MATS operating principles, (ii) studies the effect of thickness and operation frequency in its cooling power, (iii) presents numerical simulations to forecast MATS behavior and (iv) demonstrates the MATS applicability in the thermal management of a 10W Light Emitting Diode. The versatility, simple design, unique operating mode and high performance of the MATS suggests that the proposed approach is a promising technology to be used in a vast number of electronic devices, thermal storage systems and thermal management applications.
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•A novel remotely operated magnetic thermal switch was developed based on ferrofluids.•The temperature difference between hot and cold sides is significantly reduced.•The temperature control of a high power Light Emitting Diode was demonstrated.•We discuss the prospects and challenges of the MATS for future developments.
Structural martensitic transformations enable various applications, which range from high stroke actuation and sensing to energy efficient magnetocaloric refrigeration and thermomagnetic energy ...harvesting. All these emerging applications benefit from a fast transformation, but up to now their speed limit has not been explored. Here, we demonstrate that a thermoelastic martensite to austenite transformation can be completed within 10 ns. We heat epitaxial Ni-Mn-Ga films with a nanosecond laser pulse and use synchrotron diffraction to probe the influence of initial temperature and overheating on transformation rate and ratio. We demonstrate that an increase in thermal energy drives this transformation faster. Though the observed speed limit of 2.5 × 10
27
(Js)
1
per unit cell leaves plenty of room for further acceleration of applications, our analysis reveals that the practical limit will be the energy required for switching. Thus, martensitic transformations obey similar speed limits as in microelectronics, as expressed by the Margolus - Levitin theorem.
La
0.63
Gd
0.37
MnO
3
material was synthesized using the Pechini-modified-sol–gel method at different sintering temperatures 600, 650, 750, 800, and 900 °C. After characterizing the samples ...structurally and magnetically, we report a direct relation between the crystallite size, particles agglomeration level, and material performance in field-cooling/zero-field-cooling magnetization modes, in addition to an inverse relation between the existence of Griffith phase and the samples’ magneto-caloric performance. The material sintered at 800 °C presents the maximum isothermal entropy change among others that is 7.57 J kg
−1
K
−1
at 7 T, in addition to a good performance shown at higher temperatures, making it a promising candidate for different cooling applications.
The influence of the synthesis and sintering methods on the structural, microstructural, stoichiometry and thus the magnetocaloric properties of the La0.7Ca0.3MnO3 compound has been thoroughly ...studied. Soft-chemistry (sol-gel and polyol) synthesis and spark plasma sintering (SPS) procedures, used to obtain nanostructured materials, were compared to the traditional ceramic ones. This work evidences that SPS treatment not only reduces the grain size but also leads to oxygen sub-stoichiometry. This entails a lower Mn4+ content in the manganite, and probably heterogeneity in the Mn4+ grain distribution, which have consequences on the magnetic and magnetocaloric properties: a lower maximum entropy variation which is compensated by a larger transition temperature range. The sample prepared by combining polyol soft-chemistry synthesis and SPS sintering displays a higher maximum relative cooling power value, equal to 70% of that of gadolinium, the most effective material for domestic magnetic refrigeration.
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•Preparation of a same manganite by different synthesis and sintering methods.•Effect of the reductive atmosphere during Spark Plasma Sintering treatment.•Influence on the composition, structure, microstructure and magnetic properties.•Enlargement of the transition magnetic temperature range induced by SPS.
•Material model for a first-order magnetocaloric material.•Model tailored for an easy integration into system simulations.•Model based only on the specific heat, providing a built-in model ...consistency.•Parameters are determined from experimental data.•Consistency of the model is verified with experimental data.
In order to predict the potential of magnetocaloric heating and cooling devices, system simulations are an essential instrument. These simulations, in turn, depend to a large extent on the model implemented for the magnetocaloric material. Magnetocaloric materials with a first-order phase transition, such as found in some La(Fe,Mn,Si)13-based alloys, show excellent magnetocaloric properties. The aim of this work is thus to provide a material model for a first-order La(Fe,Mn,Si)13-based alloy. The model is tailored to be used in system simulations. This includes thermodynamic consistency of the model and a relatively simple implementation. All relevant equations of the material model are determined from the specific heat capacitance as function of the temperature and the magnetic field. Since all equations are derived from the same base equation, they are consistent in terms of the first and second law of thermodynamics. As base function for the specific heat capacitance, a modified Cauchy–Lorentz function is used. The model parameters are determined from experimental data. Consistency of the model is verified with further data. The present model enables the simulation of the exergetic efficiency of a magnetocaloric cooling or heating device based on first-order La(Fe,Mn,Si)13 alloys.
Modern society relies on readily available refrigeration. The ideal cooling machine would be a compact, solid state, silent and energy-efficient heat pump that does not require maintenance. Magnetic ...refrigeration has three prominent advantages compared to compressor-based refrigeration. First, there are no harmful gases involved, second it may be built more compact as the working material is a solid and third magnetic refrigerators generate much less noise. Recently, a new class of magnetic refrigerant materials for room-temperature applications was discovered. These new materials have important advantages over existing magnetic coolants: They exhibit a large magnetocaloric effect (MCE) in conjunction with a magnetic phase transition of first order. This MCE is, larger than that of Gd metal, which is used in the demonstration refrigerators built to explore the potential of this evolving technology. In the present review, we compare the different materials considering both scientific aspects and industrial applicability.
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