Magnetic Refrigeration System Research Articles

Experimental Investigation on Conduction-Cooled Fast-Ramping Layer-Wound (RE)BCO Superconducting Magnet for Magnetic Refrigeration

Magnetic refrigeration requires a strong magnetic field and its alternation for the magnetization and demagnetization processes. A conduction-cooled (RE)BCO coil was designed and fabricated to exert the maximum central magnetic field of 3.5 T with a field homogeneity of 90% on the magnetic refrigerant bed for an adiabatic demagnetization refrigerator (ADR) operating between 22 and 20 K. The polyimide tape insulated (RE)BCO tape conductor was wound on the stainless steel bobbin with standard layer-wound method whose outer diameter and thickness were 25.4 and 0.3 mm, respectively. The fast-ramping (RE)BCO coil was conductively cooled by a GM cryocooler to approximately 20 K. The (RE)BCO coil winding has a novel thermal drain structure to withstand the high thermal loads during alternating current (AC) operation which consists of high purity copper strip arrays installed between the inter-layers of the coil winding. Alternating magnetic field was stably generated with the peak of 3.0 T at the current of 130 A (10.5 A s -1 ). In this paper, the technical issues regarding to the fast-ramping conduction-cooled (RE) BCO coil itself and the integrated operation with the magnetic refrigeration system are discussed.

<b>Research and Development Concerning Superconducting Maglev and Research on Applying Its Technology to the Conventional Railway System</b>

RTRI is promoting the fundamental research and development concerning superconducting maglev. The topics of research are high-temperature superconducting magnet, maglev vehicles motion simulation, evaluation of the ground coil and the diagnostic technology of systems. Research on application of maglev technology to the conventional railway system is advanced in cooperation with other organizations. The main topics of this issue are a flywheel energy storage system using superconducting magnetic bearings and a magnetic refrigeration system for air-conditioners. This paper describes the existing circumstance of these researches and developments.

Cooling factor for magnetic refrigeration systems

AbstractThe adiabatic temperature change (ΔTad) during the magnetization process of polycrystalline gadolinium and Ni51Mn33.4In15.6 Heusler alloy is directly measured near the Curie temperature. The cooling factor (CF) is introduced as the area under the curve of adiabatic temperature change versus ambient temperature. The CF provides more representative measure of cooling performance in the operational temperature range. Selecting different temperature abscissas qualitatively changes the interpretation of the cooling performance of a magnetocaloric material. In particular, plotting ΔTad versus initial temperature gives a measurably different CF compared to that given by plotting ΔTad versus average temperature.

Microstructure and Magnetic Properties of La-Ca-Sr-Mn-O Perovskite Ceramics

A wide range of di erent types of materials, from metals to ceramics, exhibit the magnetocaloric e ect [1]. Generally, the magnetocaloric e ect manifests itself as a reversible increase in temperature when the magnetic material is placed in a magnetic eld, and the maximum magnetocaloric e ect occurs near the Curie temperature. Magnetic ceramics materials are very stable at room temperature, can be compositionally tuned to adjust the Curie temperature, and do not corrode in water. This makes them an attractive option for use as regenerators for magnetic refrigeration systems. Families of functional materials with a large magnetocaloric e ect have been found in several perovskite type manganese oxides such as Caand Sr-doped lanthanum manganites, La0.67Ca0.33−xSrxMnO3 (x = 0; 0.33) [2]. These samples show a substantial magnetocaloric e ect in a temperature range around their respective Curie temperature, which makes the compounds suitable for air-conditioning and refrigeration applications. By varying the composition parameter x the Curie temperature can be adjusted between 267 K (x = 0) and 369 K (x = 0.33) [2]. In this contribution, the structure, microstructure and the in uence of high pressure oxygenation on magnetisation behaviour of La0.67Ca0.33−xSrxMnO3, prepared by solid state synthesis were investigated.

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.

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.

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.

Corrosion behavior of gadolinium and La–Fe–Co–Si compounds in various heat conducting fluids

For successful implementation in magnetic refrigeration systems, the corrosion resistance of gadolinium and La–Fe–Co–Si compounds in different heat conducting fluids has been studied. Two types of tests were used: immersion at room temperature (ASTM G31-72), and accelerated tests at 88 °C during 336 h (ASTM D1384-05). Results were evaluated regarding corrosion and specific heat: the main objective was to increase the heat transfer and to reduce the corrosion rate. We have also tested a protection of gadolinium by passivation with oxalic acid solutions of pH lower than 1.00. This treatment is efficient, and doesn't affect the magnetocaloric effect. Finally, the optimal solutions were selected and proposed for use by thermal engineers. Passivation can be a good solution to protect gadolinium from corrosion but the use of water based fluids with oxygen inhibitors is better. Some fluids (water + additives) gives satisfaction, providing a heat transfer close to that of water and protecting well materials from corrosion.

The performance of a large-scale rotary magnetic refrigerator

Astronautics has constructed a large-scale rotary magnetic refrigerator which was designed to provide 2 kW of cooling power over a temperature span of 12 K with Electrical Coefficient Of Performance (COPe) > 2. The system uses a NdFeB magnet assembly with peak field of 1.44 T which rotates over twelve beds arranged circumferentially. Each bed was packed with six layers of LaFeSiH of different Curie temperatures, chosen to optimize system performance over the desired span. We report here on the performance of this system at flow rates ranging from 12.5 to 21.2 L min−1. At the largest flow rate, the system produced 3042 W of cooling power at zero span and peak performance of 2502 W over a span of 11 K. To our knowledge, this represents the largest cooling power yet observed for a magnetic refrigeration system. We show that the measured performance is in good agreement with theoretical prediction.

Magnetic refrigerator for hydrogen liquefaction

This paper reviews the development 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. Liquid hydrogen is in cryogenic temperatures and therefore high efficient liquefaction method must be studied. Magnetic refrigeration which uses 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 > 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 12 K for 1.8 T of the magnetic field and 6 second of the cycle. By using the simulation, we estimate the total efficiency of the hydrogen liquefaction plant for 10 kg/day. A FOM of 0.47 is obtained in the magnetic refrigeration system operation temperature between 20 K and 77 K including LN2 work input.

A dimensionless numerical analysis for the optimization of an active magnetic regenerative refrigerant cycle

Refrigeration by an active magnetic regenerative system (AMR) is potentially more attractive, as compared to conventional techniques. Indeed, devices based upon an AMR cycle are more efficient, compact, environment-friendly and can operate over a broad range of temperatures. In this paper, attention is focused to the near room-temperature range. On the other hand, however, the AMR cycle poses a variety of complex problems, in terms of fluid dynamics, heat transfer and magnetic field. In order to identify the optimal operational parameters, the design and optimization of a magnetic refrigeration system can be supported by modelling. In this paper, a dimensionless approach was adopted to simulate an AMR cycle following a Brayton regenerative cycle. In the simulation, the temperature range that has been explored is 260 – 280 K and 275 – 295 K. The heat transfer mediums are, respectively, water–glycol mixture (50% by weight) and pure water. The Gd0.8Dy0.2 alloy and pure Gd have been chosen as constituent material for the regenerator of the AMR cycle. With this model, the influence of the different parameters on cycle efficiency has been analysed. In particular, the study has been focused on the influence of the secondary fluid properties, magnetic material particle diameter, fluid blow time, secondary fluid mass flow rate, regenerator geometry and effect of axial thermal conduction. The model enables to find optimal dimensionless numbers in order to maximize the cycle performances. The results can be extended to widely different situations and therefore can be easily employed for the design and the optimization of new experimental prototypes. Copyright © 2012 John Wiley & Sons, Ltd.

Development of a new magnetocaloric material used in a magnetic refrigeration device

Testing directly a magnetocaloric material in a magnetic refrigeration (MR) system is the best way to judge of its applicative potentialities. In this spirit, an oxide expected to show promising magnetocaloric properties around room temperature (Pr0.65Sr0.35MnO3) was produced in large scale and shaped in order to build a regenerator. Magnetization, heat capacity, resistivity, thermal conductivity and a direct test in a MR device were carried out on this manganite. The results were compared to those observed in the reference material which is Gadolinium. The two main conclusions of these preliminary results are: (i) the Pr0.65Sr0.35MnO3 actually displays not only a significant magnetocaloric effect but also a real refrigeration capability at room temperature; (ii) the temperature spans reached in these first experiments are even found to well compare with those obtained with Gd.

MULTIPHYSICS MODELING OF A MAGNETIC REFRIGERATION SYSTEM BASED ON SUPERCONDUCTORS

Based on the magnetocaloric efiect, magnetic refrigeration at room temperature has, for the past decade, been a promising and environmentally friendly technology predicted to have a signiflcantly higher e-ciency than the present conventional methods. However, to the authors' knowledge, so far no prototypes have been presented for large scale applications. This paper presents the modeling of a superconducting-based magnetic refrigeration system for large scale applications. On one hand, electromagnetic computations are undertaken to maximize magnetic fleld produced in order to get the best performance (temperature span and cooling power) and to limit the mechanical efiorts (forces and torque). On the other hand, the thermal modeling aims to evaluate and to optimize the cooling performance.

Solid state magnetic refrigerator

The viability and operation of a fully solid state magnetic refrigeration system with envisaged applications on chip, sensor and device cooling is here tested using numerical simulations. The proposed system relies on the combined use of materials displaying the magnetocaloric effect and of materials whose thermal conductivities are controlled by an external magnetic field. This allows the switching of the heat flow direction in sync with the temperature variation of the magnetocaloric material, removing the necessity to use fluids which has for long hindered the implementation of magnetic refrigeration. We have found the optimum operating conditions of the proposed refrigerator, for which a cooling power density of ∼2.75Wcm−2 was obtained for an operating temperature of ∼296K, using Gadolinium as the magnetocaloric material and an applied magnetic field of 1T. The coefficient of performance (COP) achieved by this refrigerator was found to be COP ∼1.5, making it a viable alternative to thermoelectric refrigeration.

Modelling an active magnetic refrigeration system: A comparison with different models of incompressible flow through a packed bed

Abstract Active Magnetic Regenerative refrigeration system (AMR) is an environmentally attractive refrigeration alternative to vapour compression plants. A magnetic refrigerator is composed of a regenerator that is a solid packed bed made of a magnetic material and a secondary heat transfer fluid flowing in the porous matrix. The secondary fluid can be a liquid (water or water anti-freezing mixture). Modelling is a particularly cost-effective method for studying, designing and optimizing a magnetic refrigeration system. In this paper a comparison between three different models to simulate the thermo-fluidodynamic behaviour of an AMR cycle is carried out. Each model simulates both the magnetic material and the secondary fluid of an AMR operating in conformity with a Brayton regenerative cycle. In the reported models Gd x Dy 1−x alloys are the constituent materials for the regenerator over the temperature range 260–280 K. The heat transfer medium is a water-glycol mixture (50% by weight).With these models, the refrigeration capacity, the power consumption and consequently the coefficient of performance of the cycle can be predicted.

Design of a new magnetic refrigeration field source running with rotating bar-shaped magnets

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) is a prime candidate for the next generation of cooling systems. The essential components of magnetic refrigeration are the magnetic field generator and the magnetocaloric material. Although, several permanent magnet systems (magnetic field sources) for MR have been developed, recent development in magnetic refrigeration technology has encouraged researchers all over the world to think about new and original systems. This paper aims to describe a new and original magnetic refrigeration system based on a simple principle of magnetism called the Halbach effect. The proposed system is running with rotating bar-shaped magnets. This structure provides the desired varying magnetic field to the magnetocaloric material. Several configurations for the proposed systems have been investigated and presented in this paper. The design and modeling have been accomplished by using the finite elements method.

Magnetocaloric Properties Desired for Magnetic Refrigeration System near Room Temperature

ABSTRACTIn order to realize the magnetic refrigeration system, it is necessary to develop a 100 W class refrigerator with COP > 7.5. This requires us to find new magnetic refrigerant materials, of which cooling capacity is 2.5 times higher than that of Gd. In this paper, first we discuss the cooling capacity of magnetic refrigerant materials to achieve COP = 7.5. Then, we compare the experimental results of MnAsSb, MnFe(PGe) and La(FeCoSi)13 compounds with the calculated cooling capacity. It is suggested that a composite layer material of MnFe(PGe) would show excellent cooling capacity in the temperature span of 20 K.

SMART ELECTROMAGNETIC SIMULATIONS: GUIDELINES FOR DESIGN OF EXPERIMENTS TECHNIQUE

Electromagnetic design problems usually involve a large number of varying parameters. A designer can use difierent kinds of models in order to achieve optimum design. Some models, e.g., flnite-element model, can be very precise: however, it requires large computational costs (i.e., CPU time). Therefore, the designer should use a screening process to reduce the number of parameters in order to reduce the required computational time. In this paper, using the Design of Experiments (DOE) approach to reduce the number of parameters is explored. The beneflts of this technique are tremendous. For example, once researchers realize how much insight and information can be obtained in a relatively short amount of time from a well-designed experiment, DOE would become a regular part of the way they approach their simulation projects. The main objective of this paper is to apply the DOE technique to electromagnetic simulations of difierent systems and to explore its efiectiveness on a new fleld, namely the magnetic refrigeration systems. The methodology of the DOE is presented to assess the efiects of the difierent variables and their interaction involved in electromagnetic simulations design and optimization processes.

DESIGN AND OPTIMIZATION OF A PERMANENT MAGNET ROTATING MACHINE FOR POWER COOLING GENERATION

Magnetic refrigeration is an innovative, revolutionary, e-cient and environmentally friendly cooling technology which is on the threshold of commercialization. The essential components of magnetic refrigeration system are the magnetic fleld generator and the magnetocaloric material. The two main goals of this paper are to design and to optimize a permanent magnet magnetic refrigeration machine for power cooling generation, where an initial conflguration is studied and based on this study two other conflgurations are presented. Both electromagnetic and thermal studies are explored. The electromagnetic design part has been accomplished by using the flnite elements method and the thermal design part has been achieved using the flnite difierence method.

Numerical simulation of magnetocaloric system behaviour for an industrial application

This paper presents a numerical model conceived for a multi-physics evaluation of a magnetic refrigeration system. The model takes into account the variable magnetic field, the characteristics of the magnetocaloric materials (MCM) as well as the efficiency of the fluid flow heat transfer between the hot and the cold sources via the MCM. This model allows us to optimize these elements and to determine their impact on the overall performance of a magnetocaloric device. We present here a finite-difference model of AMRR cycles for a sub-unit of MCM crossed by micro-channels of fluid connected to cold and hot regenerative receivers. Thus, the calculation of the output parameters such as the temperature span, and thermal power passing from the cold receiver to the hot receiver has been performed. The influence of the geometry of the MCM and the fluid flow were investigated over the working domain highlighting the current technological achievements and indicating possible improvements.