Active Magnetic Regenerator Cycle Research Articles

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.

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.

Magnetocaloric Effect of Perovskite Eu0.5Sr0.5CoO3

Magnetocaloric properties of the Eu0.5Sr0.5CoO3 system near a phase transition from a ferromagnetic to a paramagnetic state are investigated. It is shown that the magnetic entropy change (ΔSM) peak spanning over a broad range of temperature leads to a remarkably wide working temperature region, yielding a significant performance in terms of refrigerant efficiency. Moreover, ΔSM distribution is very uniform, which is desirable for Ericsson-cycle magnetic refrigerator. Eu0.5Sr0.5CoO3 can be used as a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas.

Simulation of Magnetocaloric Effect in La0.7Ca0.3MnO3 Ceramics Fabricated by Fast Sintering Process

The enhanced low-field magnetocaloric effect (MCE) is simulated for La0.7Ca0.3MnO3 (LCMO) ceramics that were fabricated by fast sintering process with different Al2O3 contents. It is shown that LCMO exhibits magnetic entropy change (ΔSM) much more uniform than that of gadolinium. The results show that the peak in the MCE at the ferromagnetic to paramagnetic phase transition is improved as the sintering temperature decreases. Furthermore, the samples open up a new way in which to tune the intrinsic properties of mixed-valence manganites. Through these results, LCMO has some potential applications for magnetic refrigerants in an extended high-temperature range. It is suggested that the fast sintering process with different Al2O3 contents for LCMO is an efficient way to obtain a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas.

Magnetocaloric Effect in Nanopowders of Pr0.67Ca0.33Fe x Mn1−x O3

Magnetocaloric effect in nanopowders of Pr0.67Ca0.33Fe x Mn1−x O3 (x=0,0.1,0.3,0.4), in the vicinity of magnetic phase transitions, was investigated. It is shown that Pr0.67Ca0.33MnO3 exhibits the largest magnetic entropy change (ΔS M ) of 0.61 J/kg/K at 208 K upon 0.5 T magnetic field variation. Furthermore, the ΔS M distribution of the Pr0.67Ca0.33Fe x Mn1−x O3 is much more uniform than that of gadolinium. Because of these results, nanopowders of Pr0.67Ca0.33Fe x Mn1−x O3 have some potential applications for magnetic refrigerants in an extended high-temperature range. Moreover, it can be used as a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas.

Magnetocaloric Effect of Perovskite Manganites Ce0.67Sr0.33MnO3

Magnetocaloric properties of the Ce0.67Sr0.33MnO3 system near a phase transition from a ferromagnetic to a paramagnetic state are investigated. The value of the magnetocaloric effect has been determined from the calculation of magnetization as a function of temperature under different external magnetic fields. The ΔSM distribution is uniform, which is desirable for an Ericson-cycle magnetic refrigerator. The data show that Ce0.67Sr0.33MnO3 can be used as a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas from the temperature of liquid natural gas to nearly the boiling point of hydrogen.

Fundamental characteristics of Room-temperature Magnetic Refrigerator with Active Magnetic Regenerator

The purpose of this study is to understand the fundamental cooling characteristics of room temperature magnetic refrigerator using an active magnetic regenerator (AMR). The AMR is one of the regeneration cycles and has four sequential processes: adiabatic magnetization, heat exchange fluid flow, adiabatic demagnetization, and fluid flow. Gadolinium particles of 0.6mm diameter are adopted as a magnetic refrigerant and fully packed into a test section. The temperature change based on the magnetocaloric effect is distributed to the hot end and the cold end with heat transport fluid. The results reveal that the AMR cycle shows the improvement of the cooling performance of the room temperature magnetic refrigerator. In addition, it is found that the temperature difference between the hot and cold ends is strongly affected by the fluid transfer volume.

Preliminary experimental results from a linear reciprocating magnetic refrigerator prototype

A linear reciprocating magnetic refrigerator prototype was designed and built with the aid of an industrial partner. The refrigerator is based on the Active Magnetic Regenerative cycle, and exploits two regenerators working in parallel. The active material is Gadolinium in plates, 0.8 mm thick, for a total mass of 0.36 kg. The device is described and results about magnetic field and temperature span measurements are presented. The designed permanent magnet structure, based on an improved cross-type arrangement, generates a maximum magnetic field intensity of 1.55 T in air, over a gap of (13 × 50 × 100) mm3. The maximum temperature span achieved is 5.0 K, in a free run condition.

The influence of the solid thermal conductivity on active magnetic regenerators

The influence of the thermal conductivity of the regenerator solid on the performance of a flat plate active magnetic regenerator (AMR) is investigated using an established numerical AMR model. The cooling power at different (fixed) temperature spans is used as a measure of the performance for a range of thermal conductivities, operating frequencies, a long and short regenerator, and finally a regenerator with a low and a high number of transfer units (NTU). In this way the performance is mapped out and the impact of the thermal conductivity of the solid is probed.Modelling shows that under certain operating conditions, the AMR cycle is sensitive to the solid conductivity. It is found that as the operating frequency is increased it is not only sufficient to have a high NTU regenerator but the regenerator performance will also benefit from increased thermal conductivity in the solid. It is also found that a longer regenerator is generally better performing than a shorter one under the otherwise exact same conditions. This suggests that the thermal conductivity of candidate magnetocaloric materials should be considered when selecting them for use in a device.

Thermodynamics of active magnetic regenerators: Part I

Cycle-averaged relationships for heat transfer, magnetic work, and temperature distribution are derived for an active magnetic regenerator cycle. A step-wise cycle is defined and a single equation describing the temperature as a function of time and position is derived. The main assumption is that the convective interaction between fluid and solid is large so that thermal equilibrium between fluid and solid exists during a fluid flow phase (regeneration). Relations for the temperatures at each step in the cycle are developed assuming small regenerative perturbations and used to derive the net cooling power and magnetic work at any location in the AMR. The overall energy balance expression is presented with transformations needed to relate the boundary conditions to effective operating temperatures. An expression is derived in terms of operating parameters and material properties when each location is regeneratively balanced; this relation indicates needed conditions so the local energy balance will satisfy the assumed cycle. By solving the energy balance expression to determine temperature distribution one can calculate work, heat transfer, and COP.

Cooling Characteristics of Regenerative Magnetic Refrigeration With Particle-Packed Bed

The aim of our study was to elucidate the fundamental cooling characteristics and to improve the cooling characteristics of a room-temperature magnetic refrigerator operated under an active magnetic regenerator (AMR) cycle. The AMR refrigeration cycle, which includes a thermal storage process and a regeneration process, is used to realize a practical magnetic refrigerator operating near room-temperature. The basic components of the target AMR system are a magnetic circuit, test section, fluid-displacing device, and associated instrumentation. Spherical gadolinium particles are packed in the test section as the magnetic working substance, and air and water are used as heat transfer fluids. The cooling characteristics of the target AMR system under various operating conditions are investigated. The results show that the AMR cycle is very effective in improving the cooling performance of the room-temperature magnetic refrigerator.

Performance predictions of a first stage magnetic hydrogen liquefier

This work deals with the study of the first stage hydrogen magnetic liquefier operating through an active magnetic regenerator (AMR) cycle, over the temperature range: 298–233K. For this purpose, an unsteady and one-dimensional numerical model has been developed for predicting the thermal performances of such a liquefier. The transient energy equations are considered to account for the heat transfer between magnetic refrigerant and hydrogen flowing throughout the regenerator bed. The gadolinium has been chosen as a constitute material for the regenerator bed. Simulation results including mainly the cooling capacity and the coefficient of performance (COP) of the AMR cycle as functions of the cycle frequency, the mass flow rate, and the applied magnetic field, are presented and discussed. The capability of the numerical model of predicting consistent results has been shown.

Magnetic refrigeration with GdN by Active Magnetic Refrigerator cycle

ABSTRACTA magnetic refrigeration test was performed using a test device filled with spherical GdN material synthesized by the hot isostatic pressing (HIP) method. Refrigeration with an active magnetic regenerator cycle was tested in the temperature range between 48 and 66 K, with the field changing from 1.2 to 3.7 T and 2.0 to 4.0 T at upper and lower sides of the regenerator bed filled with the GdN spheres, respectively. Temperature spans about of 2 K were obtained at both sides, and the total temperature span in each cycle attained about 5 K. The specific heat of the material was measured to calculate the magnetic entropy change ΔS and the adiabatic temperature change ΔT induced by the magnetic field change ΔH. It was suggested that for a given ΔH, larger ΔS and ΔT can be exploited when demagnetized to lower H, especially, to zero field.

Development and Fundamental Characteristics of a Prototype Magnetocaloric Heat Pump

ABSTRACTThe primary objective of this study is to discuss the optimum operating conditions of magnetocaloric heat pumps according to the fundamental heat transfer characteristics of an active magnetic regenerator (AMR) bed. The AMR cycle has four sequential processes: magnetization, heat exchange fluid flow, demagnetization, and heat exchange fluid blow. The fundamental heat transfer characteristics of each process of the AMR cycle is investigated minutely. Moreover, the cooling power and the overall system performance are evaluated when the system is running continuously.In addition to the aforementioned investigation, we have developed a prototype rotational magnetocaloric heat pump having a compact component arrangement and an uncomplicated control system. A performance evaluation has been conducted to obtain the optimum conditions for practical operation. The operation parameters such as the heat transfer fluid flow rate, rotational frequency, and initial temperature of the heat transfer fluid are examined, and the variations of the maximum temperature span between the inlet and outlet for the heat transfer fluid are discussed. As a result, the values of the optimum rotational frequency and flow rate are obtained to obtain the maximum temperature span between the inlet and outlet of the present magnetocaloric heat pump.

Evaluation of fundamental performance on magnetocaloric cooling with active magnetic regenerator

This paper deals with the cooling characteristics of a magnetocaloric cooling technique refrigerator an active magnetic regenerator (AMR). The AMR-based refrigeration cycle, which has a thermal storage process and a regeneration process, realizes a practical magnetic refrigerator running near room temperature. The AMR cycle has four sequential processes: adiabatic magnetization, fluid flow, adiabatic demagnetization, and fluid flow. We devise an appropriate simulation model of the cyclic heat transfer process inside the particle bed as the target AMR. Then, the temperature profile inside the AMR particle bed and the cooling characteristics of the room-temperature magnetic regenerator are studied analytically. In addition, the validity of the analytical model by molecular field approximation theory is verified by comparing the experimental results with the analytical results. The results show that, when a higher magnetic field is applied to the magnetocaloric material, a greater temperature difference is obtained.

Magnetic refrigerator for hydrogen liquefaction

Magnetic refrigeration which is based on the magnetocaloric effect of solids has the potential to achieve high thermal efficiency for hydrogen liquefaction. We have been developing a magnetic refrigerator for hydrogen liquefaction which cools down hydrogen gas from liquid natural gas temperature and liquefies at 20 K. The magnetic liquefaction system consists of two magnetic refrigerators: Carnot magnetic refrigerator (CMR) and active magnetic regenerator (AMR) device. CMR with Carnot cycle succeeded in liquefying hydrogen at 20K. Above liquefaction temperature, a regenerative refrigeration cycle should be necessary to precool hydrogen gas, because adiabatic temperature change of magnetic material is reduced due to a large lattice specific heat of magnetic materials. We have tested an AMR device as the precooling stage. It was confirmed for the first time that AMR cycle worked around 20 K.

404 AMR磁気冷凍法の特性解析(省エネルギー(1),環境保全型エネルギー技術)

This paper deals with the cooling characteristics of a room-temperature magnetic refrigerator using an active magnetic regenerator (AMR): The AMR-based refrigeration cycle, which consists of a thermal storage process and a regeneration process, realizes a practical magnetic refrigerator running at temperatures close to room temperature. The AMR cycle has four sequential processes: adiabatic magnetization, fluid flow, adiabatic demagnetization, and fluid flow. We devise an appropriate simulation model of the cyclic heat transfer process inside the AMR particle bed. Then, the temperature profile inside the AMR bed and the cooling characteristics of the room-temperature magnetic regenerator are studied analytically. In addition, the validity of the analytical model is verified by comparing the experimental results with the analytical results. The results show that the larger the transferred fluid volume, the larger is the temperature difference between the hot and the cold ends.

Two-dimensional mathematical model of a reciprocating room-temperature Active Magnetic Regenerator

A time-dependent, two-dimensional mathematical model of a reciprocating Active Magnetic Regenerator (AMR) operating at room-temperature has been developed. The model geometry comprises a regenerator made of parallel plates separated by channels of a heat transfer fluid and a hot as well as a cold heat exchanger. The model simulates the different steps of the AMR refrigeration cycle and evaluates the performance in terms of refrigeration capacity and temperature span between the two heat exchangers. The model was used to perform an analysis of an AMR with a regenerator made of gadolinium and water as the heat transfer fluid. The results show that the AMR is able to obtain a no-load temperature span of 10.9 K in a 1 T magnetic field with a corresponding work input of 93.0 kJ m −3 of gadolinium per cycle. The model shows significant temperature differences between the regenerator and the heat transfer fluid during the AMR cycle. This indicates that it is necessary to use two-dimensional models when a parallel-plate regenerator geometry is used.

Static and rotating active magnetic regenerators with porous heat exchangers for magnetic cooling

The operation behaviour of an active magnetic regenerator (AMR) with a wavy-structure, or a honeycomb-like regenerator bed was numerically investigated. The thermodynamic model was applied to a static regenerator and – in a generalized version – to a rotary type. The models take two-dimensional unsteady heat conduction in the magnetic material during the four basic processes of the AMR cycle into account. The numerical results were used to determine optimal arrangements of different magnetic materials in order to obtain larger temperature spans between both ends of the porous beds. Furthermore, a first study of magnetic flux lines in a porous rotary heat exchanger was performed.

Numerical modeling for active magnetic regenerative refrigeration

A one dimensional time-dependent model of the active magnetic regenerator (AMR) cycle is developed and is validated by experimental measurements. The active regenerator is made of gadolinium in sheets of 50 mm length (L) and 1 mm thickness (y/sub r/). The circulating fluid consists of a thin film of water (y/sub r/ = 0.1 mm). In this study, a uniform flow with a constant velocity /spl nu/ is considered. In addition the model assumes that the diffusion phenomenon is negligible along the bed and considers only convection exchanges between the regenerator and the fluid which is verified in this study regarding the geometry and the characteristics of the used materials. This model can and will be used to optimize the AMR cycle for a given magnetic refrigeration application. This model can be improved to take into account diffusion phenomena.