Active Magnetic Regenerator Research Articles

磁気ヒートポンプ装置におけるAMR 形状に関する考察

This paper discusses the system performance of a magnetic heat pump with an active magnetic regenerator. The heat-transfer coefficient and pressure drop in the AMR are performed analytically. Measurements on the experimental magnetic heat pump test device are performed using distilled water as the working fluid. The coupling of a one-dimensional thermal model is presented. The thermal model takes into consideration the magneto-caloric effect as a source term and the energy conservation between a solid and a fluid. At cyclic steady states, the temperatures of the fluid on both sides of the regenerator are calculated numerically and compared with the measurement results. A reasonable agreement between simulations and experiments confirms the validity of the proposed model.

H232 磁気冷媒の階層構造化によるAMRの高性能化に関する研究(一般講演(13))

H232 磁気冷媒の階層構造化によるAMRの高性能化に関する研究(一般講演(13))

Numerical analysis of a reciprocating active magnetic regenerator

A time-dependent, two-dimensional mathematical model of a configuration system for magnetic refrigeration has been developed, based on a reciprocating active magnetic regenerator operating at room temperature. The model's geometry is made of parallel plates of magnetocaloric material separated by microchannels. Through the microchannels, the flow of a heat transfer fluid has also been simulated. Water has been used as heat transfer fluid and as magnetocaloric material we have used the benchmark material gadolinium. The heat transfer inside the regenerator and the fluid flow are modelled separately and the magnetocaloric effect is taken into account by the inclusion of a variable source term in the energy equation.The model simulates the steps of the active magnetic regenerative refrigeration cycle and evaluates the performance in terms of cooling load, COP, temperature span and pressure drop for the parallel-plate configuration. The model has been validated by comparing the numerical results with the results obtained from an experimental device made by a partner. This parametric study allows us to identify the most important characteristics that have a significant influence on the thermal behaviour of the active magnetic regenerator. Several simulation results are discussed and some optimal solutions are presented.

Lanthanum Concentration Effect of Magnetocaloric Properties in La x MnO3−δ

Magnetocaloric properties of La xMnO 3−δ films in the composition range 0.75 ≤ x ≤ 1 near phase transition from a ferromagnetic to a paramagnetic state were investigated. For x > 0.75 composition, it is showed that the increasing of La concentration improves magnetocaloric properties. It is also showed that post-annealing films in O 2 improves magnetocaloric effect. The magnetocaloric properties are affected by Mn +3/Mn +4 ratios, which can be varied either by changing La concentration or varying the oxygen content in the La xMnO 3−δ system. Moreover, La xMnO 3−δ films can be used as a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas.

Epoxy-bonded La–Fe–Co–Si magnetocaloric plates

We report the processing, analysis and testing of magnetocaloric composite materials consisting of La–Fe–Co–Si particles of various size fractions and a polymer matrix. All of the composites have working temperatures close to room temperature. The composites were pressed into thin plates, a geometry favorable for testing the composites in an active magnetic regenerator (AMR). In order to investigate the influence of particle size and binder type (epoxy), eight different epoxy-bonded La–Fe–Co–Si plates were made and analyzed. We found that the higher filling factor that can be achieved by using a mixture of several particle size fractions has beneficial influence on the thermal conductivity. Tests in the AMR revealed that a maximum temperature span of approximately ΔT=10 K under magnetic field change of μ0H=1.15 T can be obtained at no cooling load conditions. The stability of the measured ΔT values and the mechanical integrity of sample after cyclic application of a magnetic field have been monitored for 90,000 cycles and showed no significant changes. We therefore conclude that epoxy-bonded La–Fe–Co–Si magnetocaloric composites have good magnetocaloric properties at low material-processing costs and hence represent a competitive way to produce magnetocaloric materials to be used in AMR.

Magnetic refrigerator for hydrogen liquefaction

This paper reviews the status of magnetic refrigeration system for hydrogen liquefaction. There is no doubt that hydrogen is one of most important energy sources in the near future. In particular, liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. When we compare the consuming energy of hydrogen liquefaction with high pressurized hydrogen gas, FOM must be larger than 0.57 for hydrogen liquefaction. Thus, we need to develop a highly efficient liquefaction method. Magnetic refrigeration using the magneto-caloric effect has potential to realize not only the higher liquefaction efficiency >50%, but also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and AMR (active magnetic regenerator) cycle for precooling stages. For the Carnot cycle, we develop the high efficient system with >80% liquefaction efficiency by using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems, which transferred the working fluid. We confirmed the AMR effect with the cooling temperature span of 12K for 1.8T of the magnetic field and 6s of the cycle. By using the simulation, we estimate the efficiency of the hydrogen liquefaction plant for 10kg/day. A FOM of 0.47 is obtained for operation temperature between 20K and 77K including LN2 work input.

Experimental investigation of an active magnetic regenerative heat circulator applied to self-heat recuperation technology

An experimental investigation into an active magnetic regenerative (AMR) heat circulator based on self-heat recuperation technology, was conducted to evaluate its energy saving potential in heat circulation. In an AMR heat circulator, magnetocaloric effect is applied to recuperate the heat exergy of the process fluid. The recuperated heat can be reused to heat the feed process fluid and realize self-heat recuperation. In this paper, AMR heat circulator has newly been constructed to determine the amount of heat circulated when applied to self-heat recuperation and the energy consumption of the heat circulator. Gadolinium and water was used as the magnetocaloric working material and the process fluid, respectively. The heat circulated amount was determined by measuring the temperature of the process fluid and gadolinium. The net work input for heat circulation was obtained from the magnetizing and demagnetizing forces and the distance travelled by the magnetocaloric bed. The results were compared with the minimum work input needed for heat circulation derived from exergy loss during heat exchange. It was seen that the experimentally obtained value was close to the minimum work input needed for heat circulation.

Development of an active magnetic regenerator for space applications

This paper discusses the design of a micromachined regenerator in an Active Magnetic Regenerative Refrigeration (AMRR) system for space applications. The AMRR system is designed to provide continuous remote/distributed cooling at about 2K and reject heat at temperatures of about 15K. This paper first discusses the general thermal and fluid performance requirements for an AMRR regenerator, a unique structured bed configuration that enables the regenerator to meet these requirements, and its thermal and fluid performance based on numerical analyses. The paper then discusses the general design consideration for the magnetic field driving the regenerator for optimal thermal performance, and the analysis processes to optimize the variation rate of the magnetic field in an actual superconducting magnet during the isothermal processes of the AMRR cycle to enhance the performance of an actual regenerator. The paper finally presents the thermal performance of the regenerator from such iterative design optimization processes.

Modeling of Thermomagnetic Phenomena in Active Magnetocaloric Regenerators

The active magnetic regenerator (AMR) consists of a porous matrix heat exchanger whose solid phase is a magnetocaloric material (solid refrigerant) that undergoes a reversible magnetic entropy change when subjected to a changing magnetic field. The cooling capacity of the cycle is proportional to the mass of solid refrigerant, operating frequency, volumetric displacement of the heat transfer fluid and regenerator effectiveness. AMRs can be modeled via a porous media approach and a model has been developed in this work to simulate the time-dependent fluid flow and heat transfer processes in the regenerator matrix. Gadolinium (Gd) is usually adopted as a reference material for magnetic cooling at near room temperature and its magnetic temperature change and physical properties were accounted for through a combination of experimental data and the Weiss-Debye-Sommerfeld (WDS) theory. In this paper, the interaction of the applied magnetic field waveform with the heat transfer fluid displacement profile and the influence of demagnetizing effects on the AMR performance are investigated numerically. The numerical model is evaluated against experimental data for a regenerator containing spherical Gd particles.

AMR (Active Magnetic Regenerative) refrigeration for low temperature

This paper reviews AMR (Active Magnetic Regenerative) refrigeration technology for low temperature applications that is a novel cooling method to expand the temperature span of magnetic refrigerator. The key component of the AMR system is a porous magnetic regenerator which allows a heat transfer medium (typically helium gas) to flow through it and therefore obviate intermittently operating an external heat switch. The AMR system alternatingly heats and cools the heat transfer medium by convection when the magneto-caloric effect is created under varying magnetic field. AMR may extend the temperature span for wider range than ADR (Adiabatic Demagnetization Refrigerator) at higher temperatures above 10K because magneto-caloric effects are typically concentrated in a small temperature range in usual magnetic refrigerants. The regenerative concept theoretically enables each magnetic refrigerant to experience a pseudo-Carnot magnetic refrigeration cycle in a wide temperature span if it is properly designed, although adequate thermodynamic matching of strongly temperature-dependent MCE (magneto-caloric effect) of the regenerator material and the heat capacity of fluid flow is often tricky due to inherent characteristics of magnetic materials. This paper covers historical developments, fundamental concepts, key components, applications, and recent research trends of AMR refrigerators for liquid helium or liquid hydrogen temperatures.

AMR thermodynamics: Semi-analytic modeling

Temperature span, cooling power, work, and efficiency are key performance metrics describing active magnetic regenerators used as refrigerators. Numerical methods to calculate these parameters efficiently and accurately are needed. This paper proposes a set of semi-analytic relationships to determine cooling power and magnetic work as a function of temperature span, regenerator characteristics, operating conditions, and magnetic field waveform. Appropriate effective values for magnetocaloric effect and specific heat are defined. Semi-analytic predictions for cooling power and work are validated against experimental data for room-temperature tests as well as a more complex numerical model describing magnetic work. The semi-analytic approach is found to predict performance well over the range of operating conditions considered.

An idea of the test stand for studies of magnetobarocaloric materials properties and possibilities of their application

AbstractThe paper presents an idea of the laboratory test stand for evaluation of the application potential of magnetobarocaloric materials. These materials are characterized by the temperature change under stimulation by a magnetic field and mechanical loading. This property of the material can be used for construction of cooling and heating devices. Thanks to the ecofriendly character of the solutions based on this material it may replace, in the near future, nowadays solutions based on the gas compression–decompression method. The presented laboratory test stand will allow comparison of the several groups of materials in terms of their application in modern cooling systems. The paper shows the main ideas behind the construction and working principles of the system. To obtain a change in the temperature of the tested material it will be subjected to the magnetic field generated by permanent magnets and mechanical loading generated with use of a universal testing machine. Loading will cause a uniaxial tension state in the material. Magnetobarocaloric material, working as a refrigerant in the device, will be applied as a multiflow system. The test stand will work in a modified active magnetic regenerator (AMR) cycle that is most commonly used in prototypes of magnetic refrigerators. This cycle will be adapted for the use of mechanical loading in addition to magnetic stimulation. The test stand presented in this paper is currently under construction. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modelling of a magnetocaloric system for cooling in the kilowatt range

A numerical time-dependent model of an active magnetic regenerator (AMR) was developed for cooling in the kilowatt range. Earlier numerical models have been mostly developed for cooling power in the 0.4 kW range. In contrast, this paper reports the applicability of magnetic refrigeration to the 50 kW range. A packed bed active magnetic regenerator was modelled and the influence of parameters such as geometry and operating parameters were studied for different geometries. The pressure drop for AMR bed length and particle diameter was also studied.High cooling power and coefficient of performance (COP) were achieved by optimization of the diameter of the magnetocaloric powder particles and operating frequency. The optimum operating conditions of the AMR for a cooling capacity of 50 kW was determined for a temperature span of 15 K. The predicted coefficient of performance (COP) was found to be ∼6, making it an attractive alternative to vapour compression systems.

Microstructure and magnetocaloric properties of melt-extracted La–Fe–Si microwires

LaFe11.6Si1.4 microwires with an average diameter of 50μm have been fabricated by utilizing the melt-extraction method. The geometry of wires fits the requirement of magnetic refrigerants when applied in active magnetic regenerator (AMR) systems. Magnetocaloric properties of these wires are comparable to those for the bulk sample with the equivalent NaZn13-type phase (i.e. the 1:13 phase), making them the promising refrigerants toward application.

Measurement and numerical simulation on the heat transfer characteristics of reciprocating flow in microchannels for the application in magnetic refrigeration

Experimental and numerical studies were conducted on the heat transfer characteristics of reciprocating flow in different types of microchannels for the application in the active magnetic regenerator (AMR) of magnetic refrigeration systems. Experimental measurements were performed for a flat plate type microchannel fabricated using MEMS technique, and with intermittent heating as the boundary condition. The results of the experiments are in good accordance with those of 2-D numerical simulations conducted using the same conditions as the experiments. Therefore, it is considered that the numerical mode is effective for evaluation of the heat transfer for reciprocating flow. Furthermore, numerical simulations on two types of microchannel (flat plate type and staggered mini-plates type) were conducted with alternative heating and cooling conditions which corresponding to the volumetric temperature rise/drop of solid material as a result of magnetocaloric effect. The influence of various factors on the heat transport of reciprocating flow was analyzed. It was found that enhancement of the heat transport could be realized by utilizing the microchannel of staggered mini-plates type, and there is an optimum ratio of amplitude to flow channel length (ΔL/L) to achieve high efficiency heat transport.

Modeling of Graded Active Magnetic Regenerator for Room-Temperature, Energy-Efficient Refrigeration

It has been demonstrated experimentally that grading the regenerator along the flow direction with multiple magnetocaloric materials (MCMs) with varying Curie temperatures improves the performance of magnetic refrigeration significantly. The optimization of the graded active magnetic regenerator (AMR) is a multiphysics problem, which is crucial to the realization of room-temperature magnetic refrigeration. Until now, only a few models have been built and further work to understand the grading effects is urgently needed. In addition to the challenges of the coupling of magnetic, heat transfer and fluid dynamic phenomena and the vast parameter space of the graded regenerator (e.g. composition and geometry), relevant material properties of the MCMs may not yet be available for modeling. To address these issues, a COMSOL model with key material properties estimated by the mean field theory and the de Gennes model has been built. In this paper, two-segment regenerators composed of GdxTb(1 - x) alloys are studied first. Compared to a pure Gd regenerator, it is demonstrated that a two-segment one can achieve a > 3-time increase in cooling capacity. Furthermore, the temperature profile of a graded regenerator, which can be estimated using a first-order approximation, is found to correlate strongly with the cooling capacity, and could potentially serve as an index for performance prediction. The finding is applied to the study of three-segment regenerators. It is demonstrated that three-segment regenerators can cool a space faster and achieve cooling capacities higher than these of two-segment ones, especially for large temperature spans.

Design improvements of a permanent magnet active magnetic refrigerator

A second-generation room-temperature permanent magnet active magnetic regenerator test apparatus using Halbach arrays is described. The magnet arrays consist of three concentric cylinders. Each cylinder is constructed using 12 permanent magnet segments. The inner magnet array is stationary while the intermediate and outer arrays are designed to rotate in opposite directions so as to create a sinusoidal magnetic field waveform with a stationary field direction. The fluid flow system utilizes a novel check valve configuration so that fluid dead volumes are minimized. The system construction is modular to allow for quick replacement of material or system components. Fringing fields near the outer and inner diameters of the arrays are found to create large forces between arrays leading to large torques. Test results using 650 g of gadolinium spheres produce a no-load temperature span of 33 K at 0.8 Hz.

The influence of non-magnetocaloric properties on the performance in parallel-plate AMRs

The performance of Active Magnetic Regenerators (AMR) does not depend solely on the magnetocaloric effect of their constituents. Rather, it depends on several additional parameters, including, magnetic field, geometry (hydraulic diameter, cross-sectional area, regenerator length etc.), thermal properties (conductivity, specific heat and mass density) and operating parameters (utilization, frequency, number of transfer units etc.). In this paper we focus on the influence of three parameters on regenerator performance: 1) Solid thermal conductivity, 2) magnetostatic demagnetization and 3) flow maldistribution due to geometrically non-uniform regenerators. It is shown that the AMR performance is optimal at an intermediate value of the solid thermal conductivity for many operating conditions. The magnetostatic demagnetization is shown to have a significant influence on the AMR performance, giving a strong dependence on the orientation of the applied field and the regenerator geometry. Finally, the flow maldistribution of non-uniform regenerator geometries is found to degrade the AMR performance even at minor deviations from perfectly homogeneous regenerator matrices. This paper reflects a summary of various recently published results.

Fluid choice and test standardization for magnetic regenerators operating at near room temperature

Numerical simulations are performed to investigate the performance of an active magnetic regenerator (AMR) operating near room temperature. A two-dimensional porous model is established to analyze the impact different heat transfer fluids (HTFs) have on the performance of the AMR. The internal temperature distribution and cooling capacity of the system are analyzed and the influence of the HTF discussed. The simulation results show that when mercury is substituted in place of water as the HTF, the cooling capacity can be enhanced by nearly 600%. A fluid with high conductivity, high density, and low specific heat is most suitable for use as the HTF. Furthermore, as the environmental conditions have a great impact upon the performance of the AMR, three feasible methods of standardization testing are proposed. These involve: the evaluation index under fixed test environment conditions, a maximum exergy method, and a maximum specific exergy method around the Curie temperature.

1D model of an active magnetic regenerator

The 1D active magnetic regenerator model developed at the University of Applied Sciences of Western Switzerland is described. The system of two partial differential equations is discretized with the finite differences method backward in time and solved with the tridiagonal matrix algorithm. New features, not found in the literature in 1D models, are thermal losses in the regenerator, parasitic heat exchange, and the calculation of the AMR cycle output power in steady state. The model is implemented in MATLAB and it has a graphical user interface.