JPH0428985B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic refrigerator that generates refrigeration by adiabatic demagnetization of a magnetic material, and particularly to a rotary magnetic refrigerator suitable for generating superfluid helium.

Reciprocating type and rotary type types are known as conventional magnetic refrigerators. The reciprocating type moves the magnetic material in and out of a high magnetic field by reciprocating motion, but motor drive requires a mechanism to convert rotational motion into linear motion and requires a large stroke. The driving part becomes complicated and large.
In addition, the rotary type has a problem in ensuring airtightness because the working fluid flows through the rotating body, and requires means for fluid circulation, and has an extremely complicated structure.

An object of the present invention is to provide a rotary magnetic refrigerator with a simple structure that solves these problems.

In the rotary magnetic refrigerator of the present invention, a plurality of magnetic bodies whose outer surfaces are partially exposed are embedded in the circumferential surface of an insulating cylindrical body, and an extremely small gap is maintained on the outer periphery of the cylindrical body. A part of the stationary cylinder has at least an opening connected to a high-temperature liquid helium bath and an opening connected to a low-temperature superfluid helium bath, and an electromagnet that generates a high magnetic field is arranged around the opening connected to the liquid helium bath, The exposed outer surface of the magnetic material embedded in the circumferential surface of the cylindrical body is in direct contact with the helium at each opening, and the magnetic material alternates between the openings connected to the high magnetic field part and the superfluid helium bath. The feature is that the cylindrical body is rotated so that it passes through.

In other words, a magnetic material whose outer surface is partially exposed is embedded in the circumferential surface of a heat-insulating cylindrical body, and the cylindrical body is constructed such that the magnetic material portion alternately passes through a high magnetic field section and a cold extraction section (low magnetic field section). The cylindrical body is rotated and surrounded by a cylinder with an extremely small gap.

Taking a superfluid helium compatible refrigerator as an example, the high temperature section (high magnetic field section) opens into a 4.2K liquid helium bath, and the low temperature section (low magnetic field section) opens into a superfluid helium bath below 2K. It will be opened.

Note that on the low-temperature liquid helium side, the magnetic material is in a low magnetic field, so it is at a lower temperature than the liquid helium. If this liquid helium is superfluid helium, Kapitatsu heat transfer (like contact heat transfer between solids). Superfluid helium is a form of liquid helium, but it is different from normal liquids and has the same heat transfer as solids. ) occurs and cools the liquid helium.
If the liquid helium is not superfluid helium, it is cooled by natural convection near the surface of a magnetic material (this is the same as when hot water is poured into a cold container and the water is cooled by natural convection). In the present invention, since the rotational speed is very slow, the "rotating case" in cooling is substantially the same as the "stationary case".

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Two magnetic bodies 1a and 1b are embedded in a cylindrical body 2 with their surfaces exposed. As the magnetic materials 1a and 1b, Gd ₃ Ga ₅ O ₁₂
(gadolium gallium garnet) or Gd ₂
(SO ₄ ) ₃ 8H ₂ O and copper mesh are used.
The cylinder 2 is made of a material such as alumina, crystallized glass, or fiber-reinforced resin that has a coefficient of expansion comparable to that of the magnetic material 1 and has a low thermal conductivity. Magnetic materials 1a and 1
The surface of b has the same outer diameter as the cylinder 2. The inner diameter of the cylinder 3 is 20 to 40 μm larger than the outer diameter of the cylinder 2. cylinder 3
The material should have low thermal conductivity. Openings 4a and 4b provided in the cylinder 3 are provided at axially symmetrical positions and communicate with the surrounding liquid helium 5. Two superconducting coils 6a and 6b wound in a saddle shape constitute a two-pole magnet and generate a unidirectional magnetic field 7.
On the other hand, openings 8a and 8b are provided at positions shifted by 90 degrees from the openings 4a and 4b of the cylinder 3, and are connected to cold generation chambers 9a and 9b consisting of heat insulating walls.

FIG. 2 shows an A-O-B cross section centered on the rotating shaft 10. However, both assume that the magnetic material is within the cross section.

In the state shown in FIG. 1, the magnetic bodies 1a and 1b are magnetized and generate heat, and are cooled by boiling of the liquid helium 5. The cylinder 2 is then rotated 90°, and the magnetic body is at position 11, indicated by the dotted line. As the magnetic field becomes smaller, heat absorption occurs in the magnetic material, and the cold generation chambers 9a, 9
The temperature of liquid helium 12 in b decreases. The cold generation chambers 9a and 9b are connected by piping or the like. By repeating such a cycle, the liquid helium 12 can be made into superfluid helium of 2.2K or less. The periphery of the cold generation chambers 9a and 9b is formed by a wall with low thermal conductivity or a vacuum insulation wall, and thermal isolation between the liquid helium 5 and the liquid helium 12 is achieved by making the gap between the cylinder 3 and the cylinder 2 minute. It has been realized.

FIG. 3 shows another embodiment of the present invention, in which a pole piece is used as the magnetic field generating section. That is, pole pieces 13a and 13b and superconducting coils 14a and 14b are provided in place of superconducting coils 6a and 6b in FIG. 1, and the direction of the magnetic field is oriented to connect the tips of the pole pieces.

FIG. 4 shows another embodiment using pole pieces. The high magnetic field generation part and the cold generation part are shown in the same cross section. Here, the pole piece 15 is combined with the superconducting coil 16, and can apply a magnetic field parallel to the rotation axis to the magnetic body.

As described above, in the present invention, since the fluid is in direct contact with the working substance, direct thermal contact between the working substance and the fluid can be achieved, and there is no contact thermal resistance. Moreover, in the present invention, since the magnetic body itself is rotated and brought into contact with the fluid, and the structure is not such that the fluid flows through the rotating body, there is an effect that cooling can be generated with a simple device configuration. Further, although there is a gap between the cylindrical bodies for rotation, this gap is made extremely small, so that heat leakage due to direct contact of the rotating body with the fluid can be prevented.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 2 is a vertical cross-sectional view taken along line A-O-B in FIG. 1, and FIG. 3 is a cross-sectional view showing another embodiment of the present invention. 4 are longitudinal sectional views showing other embodiments of the present invention. 1a, 1b...Magnetic material, 2...Cylinder, 3...Cylinder, 6a, 6b, 14a, 14b, 16...Superconducting coil, 9a, 9b...Cold generation part.

Claims (1)

[Claims] 1. A plurality of magnetic bodies whose outer surfaces are partially exposed are embedded in the circumferential surface of a heat-insulating cylinder, and at least a part of a stationary cylinder provided with an extremely small gap on the outer circumference of the cylinder is heated to a high temperature. It has an opening connected to a liquid helium bath and an opening connected to a low-temperature superfluid helium bath, and an electromagnet that generates a high magnetic field is arranged around the opening connected to the liquid helium bath, and is embedded in the circumferential surface of the cylindrical body. The cylindrical body is rotated so that the exposed outer surface of the magnetic body is in direct contact with the helium at each opening, and the magnetic body passes alternately through the high magnetic field section and the opening leading to the superfluid helium bath. A rotating magnetic refrigerator with special features.