JPH0362983B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention attempts to obtain a magnetic refrigerator with a wide cooling temperature range by using a magnetic working material that exhibits uniform cooling efficiency over a wide temperature range.

Compared to conventional gas refrigeration equipment, magnetic refrigeration () has a smaller molar volume of the working medium, which essentially makes the equipment smaller and lighter; () does not require an external field control compressor that is added to the working medium; Therefore, it is possible to manufacture a low-noise, low-vibration refrigeration system.() Since most operations are electromagnetic, computer control is easy, and a highly reliable refrigeration system can be obtained.

It has many features such as, and is expected to bring new developments to the refrigeration industry.

Attempts have begun to use magnetic refrigeration in low-temperature regions of around 20 degrees K or less, but in recent years, the development of superconducting magnets has made it easier to obtain strong magnetic fields, making it difficult to apply it to higher-temperature regions. The possibilities are open. However, if only one type of conventionally known substance is used as the working substance, it is not possible to efficiently operate a magnetic refrigeration system with such a wide range of cooling temperatures.

In other words, in magnetic refrigeration in high-temperature regions, ferromagnetic material is usually used as the magnetic working material, and Ericsson
Configure the cycle. If this cycle is drawn on an entropy-temperature plane, it will look like Figure 1. A
When a strong magnetic field H ₁ is applied at a point to magnetize the working material isothermally (point B), the magnetic entropy decreases by △S ₁ due to the alignment of the magnetic moments of the atoms forming the working material, and accordingly Q ₁ = Only △S ₁ T ₁ of heat is released, and the temperature on the high temperature side rises slightly. Next, while keeping the magnetic field _H1 constant, the work material is transferred to the low temperature _T2 section (point C) and isothermally demagnetized here (point D).
Due to the disordered arrangement of magnetic moments, the magnetic entropy increases by △S ₂ , and along with this, heat of Q ₂ = △S ₂ T ₂ is absorbed, causing a slight temperature drop on the low temperature side. The work material is then transferred to a high temperature section while remaining demagnetized. The high-temperature part has reached a slightly higher temperature than _T1 due to the heat release in _Q1 , so the working material moves to point E. In this way, the state changes from E → F → G → H → I,
The temperature difference ΔT between the high temperature part and the low temperature part gradually expands and finally reaches a stable state.

As is clear from the above cycle diagram, in order to improve the performance of the magnetic refrigeration system, it is desirable that the entropy change ΔS _M of the working substance with respect to a constant magnetic field be as large as possible. Further, in order to increase the cooling temperature width ΔT and improve the refrigeration efficiency, it is desirable that ΔS _M be a substantially constant value at least over this temperature range.

On the other hand, as shown in FIG. 2, ΔS _M of a ferromagnetic material takes a maximum value at the Curie temperature T _c and rapidly decreases when the temperature deviates from this temperature. For this reason, magnetic refrigerators that use a type of ferromagnetic material as a working material are unable to maintain the high cooling capacity exhibited near the Curie point over a wide temperature range.

This invention mixes several ferromagnetic materials having a Curie temperature between T ₁ and _{T 2} of a refrigerator in an appropriate ratio, and produces a constant entropy change ΔS _M for a constant magnetic field in that temperature range. The aim is to synthesize and use such working materials to obtain a magnetic refrigeration system that has a high cooling capacity over a wide range of cooling temperatures.

That is, as shown in Fig. 3, an appropriate amount of ferromagnetic material having the Curie points T _c1 , T _c2 , T _c3 , and T _c4 is mixed between the high temperature side temperature T ₁ and the low temperature side temperature T ₂ of the magnetic refrigeration system. By doing so, it is possible to synthesize a ferromagnetic material having a substantially constant ΔS _M between T ₁ and T ₂ as a whole, as shown by the solid line.

Specifically, as an example, the following series of ferromagnetic materials may be used for each temperature range.

280〜180〓 (G _dx T _b1-x ) ₃ Al ₂ 180〜74〓 (T _bx D _y1-x ) ₃ Al ₂ 74〜33〓 (D _yx H _p1-x ) ₃ Al ₂ in these compounds. By changing X, a working material having a Curie point at any temperature within each temperature range can be obtained.

Of these, the desired working material can be obtained by weighing the materials with a suitable Curie point in a ratio that creates the shape shown in the solid line in Figure 3, crushing and mixing, and sintering as necessary. can get.

Since the mixture is a mixture of several types of pulverized ferromagnetic materials, the individual particles maintain the properties of their parent material and are microscopically heterogeneous, but when the magnetic field of the device is applied. It is sufficient that the particle size is small compared to the size and that it can be effectively considered to be homogeneous.

In this specification, not only the above-mentioned working substances but also the mixture forming the cold storage block are understood as such.

1 of magnetic refrigeration equipment using such working materials
An example is shown in FIG.

5 is a regenerator with an appropriate number of solid blocks 51,5.
2, 53, 54..., and filled with gas such as helium for heat exchange.

Reference numeral 7 denotes an upper heat exchange chamber for heat dissipation, in which heat is exhausted by gas flowing back from an inlet 71 to an outlet 72. 8
is a lower heat exchange chamber, and the gas flowing back from the inlet 81 to the outlet 82 is guided to the object to be cooled. 3 in the diagram
4 is an electromagnet, and 9 is an operating rod.

The magnetic working substance 1 and the electromagnet 4 move relative to the regenerator, the magnetic field is removed at the upper block 51 of the regenerator 5, and after heat exchange, it is demagnetized at the lower block 54.

At this time, the solid blocks 51 and 52 of the regenerator 5
. . . After all, it is advantageous to use a substance with a high specific heat in order to make the refrigerator compact.

However, in general, the specific heat is
As shown in FIG. 5, C _L rapidly decreases as the temperature decreases. In the case of an antiferromagnetic material or a ferromagnetic material, specific heat derived from the above-mentioned magnetic entropy is added, resulting in a shape having a peak at the phase transition point _Tt , as shown by the dotted line in FIG.

In a real refrigerator, each cold storage block 5
1, 52, 53... are conveniently made of the same material, and therefore it is convenient to make them have a constant specific heat within the operating temperature range of the refrigerator _T1 to _T2 . Therefore, by mixing appropriate amounts of several antiferromagnetic substances or ferromagnetic substances with different T _t similar to the above-mentioned working substance,
A block material having a specific heat as shown in FIG. 6 is synthesized. In particular, in the case of magnetic refrigeration, an external magnetic field is used, so it is better to use antiferromagnetic materials that have little entropy change due to this.

In this case, unlike the working material, the contribution of the specific heat of the crystal lattice is large, and only the difference from the lattice specific heat shown by the chain line needs to be given by the magnetic specific heat, so the proportion of the antiferromagnetic material with a high Neel temperature is It will be smaller than the case.

Of course, there are various types of magnetic refrigeration cycles, and depending on the type of cycle (Ericson, etc.), it may be better to have heat capacity that has a certain temperature dependence in order to increase efficiency. By changing the mixing ratio of different antiferromagnetic materials, it is possible to create regenerator materials with any temperature dependence.

A regenerator using such a regenerator material is often used as equipment for other types of refrigeration (gas, etc.). (In this case, it may be either antiferromagnetic or ferromagnetic.) In this refrigerator, the gas sealed in the heat insulating container 3 is solid blocks 51, 52, which are cold storage media.
The heat capacity is extremely small compared to the solid block and the magnetic working material 1, and it acts only as a heat exchange medium between the solid block and the magnetic working material 1, and even some mixing of the upper and lower parts does not reduce the cooling effect. In addition, solid block 5
Since blocks 1, 52, 53, etc. are arranged at regular intervals, even if there is a temperature difference between adjacent blocks, heat conduction between them is blocked, thereby preventing the cold storage effect from decreasing. I can do it.

As in this invention, when the cooling temperature range is wide and the solid cold storage block is made relatively small and the working material and the solid cold storage block exchange heat using gas as a medium, the top view shown in FIG. 7 is used to promote heat exchange. As shown in the figure, it is desirable that the fins of the cold storage blocks 51, 52, . By creating a shape that allows for rapid heat exchange, it is possible to operate at a relatively high speed using a solid having a large specific heat.

Note that the above embodiment has been described as a refrigeration apparatus using an Ericsson cycle. Although the present invention is theoretically valid not only in the Ericsson cycle but also in the Stirling cycle, the device for realizing the Stirling cycle is complicated and is generally not used as it is not an industrially effective cycle.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of magnetic refrigeration, Fig. 2 is an entropy change-temperature diagram of a ferromagnetic material, Fig. 3 is an explanatory diagram of the principle of the working material used in the magnetic refrigeration system of this invention, and Fig. 4 is an illustration of the principle of magnetic refrigeration. A side view of the structure of an embodiment of the magnetic refrigeration system of the invention, FIG. 5 is an explanatory diagram of the lattice specific heat of the solid, FIG. 6 is an explanatory diagram of the specific heat of the cold storage solid block of the magnetic refrigeration system of the invention, and FIG. FIG. 3 is a top view showing the structure of the cold storage solid block and the working material. 1: Magnetic working material, 3: Heat insulating container, 4: Electromagnet, 5: Solid regenerator, 7, 8: Heat exchange chamber.

Claims (1)

[Scope of Claims] 1. Ericsson characterized by using a magnetic working material made of a mixture of a plurality of ferromagnetic materials having a Kyrie point between the high temperature side temperature T ₁ and the low temperature side temperature T ₂ of the refrigeration device. A magnetic refrigeration system that uses a cycle and has a large cooling temperature range and refrigeration output. 2. Cooling temperature range and refrigeration output using the Ericsson cycle according to claim 1, characterized in that a plurality of antiferromagnetic substances or a mixture of ferromagnetic substances having different transition temperatures are used as a solid cold storage block. Large magnetic refrigeration system. 3. Claim 1, characterized in that the magnetic working material and the cold storage block each have fins, and the fins are structured so as to face each other.
A magnetic refrigeration device with a large cooling temperature range and a large refrigeration output using the Ericsson cycle described in the above or the second term.