Koji Kamiya

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.

Magneto caloric effect in (DyxGd1−x)3Ga5O12 for adiabatic demagnetization refrigeration

Abstract Gadolinium and dysprosium gallium garnet single crystals ( Dy x Gd 1−x ) 3 Ga 5 O 12 (x=0,0.5 and 1) have been investigated for adiabatic demagnetization refrigeration used as magnetic materials between 0.5 and 5 K . Specific heat measurement of (Dy 0.5 Gd 0.5 ) 3 Ga 5 O 12 showed a large and broad peak similar to that of Gd 3 Ga 5 O 12 and it suggests that the geometrical frustration in Gd 3 Ga 5 O 12 still remains in (Dy 0.5 Gd 0.5 ) 3 Ga 5 O 12 . Magneto caloric effect of (Dy 0.5 Gd 0.5 ) 3 Ga 5 O 12 was about four times larger than that of Gd 3 Ga 5 O 12 for the magnetic field of 1 T between 0.5 and 5 K . Therefore, the magnetic entropy change of Gd 3 Ga 5 O 12 by the external magnetic fields could be enhanced by substituting Dy 3+ ion for Gd 3+ ion for the magnetic fields of T between 0.5 and 5 K .

Specific heat and thermal conductivity of HoN and ErN at cryogenic temperatures

The rare earth nitrides, HoN and ErN, were synthesized by the hot isostatic pressing method. Their specific heat CH(T) and the thermal conductivity κ were measured at cryogenic temperatures. In zero field, the peak values of the C0(T) of HoN and ErN are larger than those of the magnetic regenerators such as Er3Ni. The peak values of the adiabatic temperature change ΔT(T) of HoN and ErN showed similar or larger values compared with those of the candidate materials for the magnetic refrigerants such as ErAl2. The thermal conductivity of HoN and ErN are comparable to those of the magnetic regenerators such as Er3Ni. The present results indicate that HoN and ErN are promising materials as the magnetic refrigerant and regenerator for the cryogenic refrigeration system.

Magnetocaloric Effect, Specific Heat, and Entropy of Iron-Substituted Gadolinium Gallium Garnets Gd3(Ga1-xFex)5O12

A series of Gd3(Ga1-xFex)5O12 (GGIG) compounds for magnetic refrigerants were characterized by magnetization and specific heat measurements. For comparison, the base compound gadolinium gallium garnet (GGG) was also measured. From the magnetization measurements, the entropy change by external magnetic field was confirmed to be enhanced by the addition of iron, as previously reported by the National Institute of Standards and Technology (NIST) group. The specific heat data obtained in various magnetic fields enabled the establishment of temperature entropy (T–S) diagrams, which are essential for thermal cycle analysis. It has been shown that GGIGs with high iron content have a large specific heat in zero field, and are suitable for regenerative thermal cycle.

DEVELOPMENT OF A MAGNETIC REFIRGERATOR FOR HYDROGEN LIQUEFACTION

This paper describes recent progress on a hydrogen magnetic refrigerator. Magnetic refrigeration makes use of the magnetocaloric effect, and is well known as an efficient method in principal because its cooling cycle can most closely follow the Carnot cycle with appropriate heat switches. A liquefaction principal of our magnetic refrigerator is based on the thermo-siphon method, in which liquid hydrogen is condensed directly on the surface of magnetic refrigerants and drops downward. In liquefaction experiments, we have successfully liquefied hydrogen gas preliminarily cooled to a temperature slightly above the boiling point. To improve liquefaction efficiency, the filling factor and spherical form of the magnetic material have been considered. Increasing the filling factor from 0.34 to 0.45 resulted in increasing %Carnot and cooling power by ∼50%. Spherical magnetic material DGAG with a 0.4 mm diameter was successfully developed. The thermal efficiency during the liquefaction process was increased largel...

Design and Build of Magnetic Refrigerator for Hydrogen Liquefaction

National Institute for Materials Science (NIMS) and Kanazawa University have been developing a magnetic refrigerator for hydrogen liquefaction since it is possible more efficient than conventional liquefaction systems around the hydrogen liquefaction temperature (20K). The magnetic refrigerator consists of a magnet, heat switches and a magnetic material that exhibits magnetocaloric effect (MCE) which heats up and cools down when magnetized and demagnetized, respectively. This paper describes outline of our magnetic refrigerator as well as newly developed magnetic materials, poly crystal 20% Gadolinium doped Dysprosium Aluminum Garnet (DGAG). Cooling power of the system and the magnetic force acts on the DGAG in the field are also calculated for system evaluation.

Thermal Property of DyxEr1−xAl2 and Gd5(SixGe1−x)4 for Hydrogen Magnetic Refrigeration

The New Energy and Industrial Technology Development Organization (NEDO) in Japan has built a project called World Energy Network (WE‐NET). The aim of WE‐NET is development of a new infrastructure of hydrogen technology for the upcoming hydrogen energy society. Among several element technologies to be achieved, high efficient liquefaction and storage of hydrogen have been identified as key technologies. Active Magnetic Regenerative Refrigeration (AMRR) is thought to have the best performance in cooling efficiency for hydrogen liquefaction. AMRR makes use of magnetic materials so that a magnetic field can create the cooling power. Therefore, magnetic and thermal properties of the materials are of crucial importance to the design and development of the AMRR system. In this paper, we focused specially on thermal expansion among the thermal properties of magnetic materials for AMRR to provide a fundamental database for the design of the AMRR. Correlation between magnetic property and thermal expansion of the ...