JPH08226718A - Cold storage material for cryogenic use and cold storage apparatus for cryogenic use using the same - Google Patents

Abstract

PURPOSE: To provide a cold storage material for cryogenic use inexpensive industrially and a cold storage apparatus using the same which enable the setting and maintenance of a gap between particles of a cold storage substance stably and easily and also maintenance of the performance of the cold storage apparatus for a long time. CONSTITUTION: This cold storage material for cryogenic use comprises a particulate body of a cold storage substance having a specific heat exceeding 0.1J/cm<3> K at the temperature of below 30K. When the circumferential length of a projection image of individual particle of the cold storage substance particulate body is represented by L and an actual area of the projection image by A, the particles exceeding 60% of those of the cold storage substance particulate body have a shape with a geometrical factor R expressed by L<2> /4πA meeting 1.1<R<2.0. The cold storage apparatus for cryogenic use employs a sintered cold storage material as cold storage material for cryogenic use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic regenerator material used in refrigerators and the like, and a cryogenic regenerator using the same.

[0002]

2. Description of the Related Art In recent years, the development of superconducting technology has been remarkable, and with the expansion of its application fields, it has become essential to develop a small-sized and high-performance refrigerator. Such refrigerators are required to be lightweight, compact and have high thermal efficiency.

For example, in a superconducting MRI apparatus, a cryopump, etc., a refrigerator having a refrigeration cycle such as Gifford-McMahon method (GM method) or Stirling method is used. High-performance refrigerators are also essential for magnetic levitation trains. In such a refrigerator, the working medium such as compressed He gas flows in one direction in the regenerator filled with the regenerator material, and supplies the thermal energy to the filling material (regenerator material). The expanded working medium flows in the opposite direction and receives heat energy from the regenerator material. As the recuperation effect becomes better in such a process, the thermal efficiency of the working medium cycle is improved, and it becomes possible to realize a lower temperature.

Conventionally, Cu, Pb and the like have been mainly used as the cryogenic regenerator material used in the refrigerator as described above. However, since the specific heat of these regenerator materials becomes extremely small at cryogenic temperatures of 20K or less, the above-mentioned recuperative effect does not function sufficiently, and it was difficult to achieve cryogenic temperatures of 20K or less.

Therefore, recently, in order to realize a temperature closer to absolute zero, an Er-Ni-based intermetallic compound such as Er ₃ Ni, ErNi, ErNi ₂ which exhibits a large volume specific heat in an extremely low temperature region (see Japanese Patent Laid-Open No. H11 (1999) -135242). 1-310269) or ARh such as ErRh
Intermetallic compounds (A: Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb)
The use of a magnetic cold storage material such as JP-A-51-52378) has been studied.

When the regenerator is filled with the magnetic regenerator material as described above, it has been proposed that the regenerator has a particle shape close to a sphere (for example, Japanese Patent Laid-Open No. 3-1744).
(See Publication No. 86, etc.) Then, the spherical granules of the magnetic regenerator material as described above are filled in a regenerator and an appropriate lid is provided so that the particles do not move to form a regenerator. In such regenerators, the He
Gas flows, and heat exchange is performed due to the temperature difference between the regenerator material and the gas.

[0007]

In the operating state of the regenerator described above, the working medium such as He gas is charged into the regenerator such that the flow direction thereof frequently changes at high pressure and high speed. Since the particles pass through the voids between the magnetic regenerator particles, various particles such as mechanical vibration are applied to the particles.

Since various forces act on the magnetic regenerator material particles in this manner, a gap is generated between the magnetic regenerator material particles as the operating time elapses even when the magnetic regenerator material particles are packed in the closest packed state at the beginning of filling. However, there is a problem that the gas flow is changed to affect the performance of the regenerator. Also, Er
₃ Magnetic regenerator materials such as Ni and ErRh are generally fragile in material, so it is easy for the regenerator material to become fine powder due to mechanical vibration etc. during operation of the above-mentioned regenerator, and this fine powder obstructs the gas seal. As a result, there has been a problem that the performance of the regenerator is adversely affected.

On the other hand, it has been proposed to sinter the spherical particles or the like of the magnetic regenerator material so as to fix them between the spherical particles in order to prevent the magnetic regenerator material particles from vibrating or moving with the above. (See Japanese Patent Laid-Open No. 5-203272). However, spherical particles of a magnetic regenerator material such as Er ₃ Ni and ErRh are generally produced using a rapid solidification method such as a rotating disk method, a rotating electrode method, a gas atomizing method, and a water atomizing method. In addition to being expensive from an industrial point of view, the contact area between particles during sintering is large, which makes it difficult to set the required voids.

The present invention has been made in order to solve such a problem, and it is possible to stably and easily set and maintain the voids between the regenerator material particles and maintain the performance of the regenerator for a long period of time. It is an object of the present invention to provide an industrially inexpensive regenerator material for cryogenic temperatures and a regenerator using the same.

[0011]

[Means and Actions for Solving the Problem] The cryogenic regenerator material of the present invention is a cryogenic regenerator material comprising particles of a regenerator material having a specific heat of 0.1 J / cm ³ K or more at a temperature of ³⁰ K or less. , L is the perimeter of the projected image of individual particles of the cold storage material granules, and A is the actual area of the projected image, and 60% or more of the particles in the cold storage material granules are represented by L ² / 4πA. The shape factor R is 1.1 <R <2.0, and the cold storage material particles are fixed by sintering.

Further, the cryogenic regenerator of the present invention is a regenerator filled with granules of a regenerator material having a specific heat of 0.1 J / cm ³ K or more at a temperature of ³⁰ K or less. Assuming that the perimeter of the projected image of each particle is L and the actual area of the projected image is A, 60% or more of the particles in the regenerator material have a shape factor R represented by L ² / 4πA of 1.1. It is characterized in that it has a shape of <R <2.0 and that the particles of the regenerator material are fixed by sintering.

As the cold storage material used in the present invention, 3
Various substances can be used as long as they have a specific heat of 0.1 J / cm ³ K or more at a temperature of 0 K or less, and examples thereof include Pb and Pb alloys, or magnetic intermetallic compounds containing a rare earth element. . Rare earth element magnetic intermetallic compounds include RM _z (R is Y, La, Ce, Pr, Nd, Pm, Sm, E
u, Gd, Tb, Dy, Ho, Er, Tm and at least one rare earth element selected from Yb, M is at least one metal element selected from Ni, Co and Cu, z is 0.001 ~
Intermetallic compounds represented by numbers in the range 9.0), RM _z
Examples include intermetallic compounds in which C and the like are added to R, R / Rh-based intermetallic compounds, and the like. These rare earth element magnetic cold storage materials are
It has a maximum value of specific heat of 20K or less, and since the value is sufficiently large as the specific heat per unit volume (volume specific heat), it becomes possible to reach an extremely low temperature, and therefore, it is a cool storage material suitable for the present invention. is there.

The cryogenic regenerator material of the present invention is one in which the particles of the regenerator material as described above are fixed by sintering, and the projected image of individual particles of the regenerator material before sintering is obtained. When the perimeter is L and the real area of the projected image is A, L ² / 4π
The abundance ratio of cool storage material particles having a shape factor R represented by A of 1.1 <R <2.0 is 60% or more. The shape factor R is a value of 1 when the particle shape is completely spherical, and the shape factor R is 1.1 <R <2.0.
The range is a particle having a relatively irregular shape.

That is, the cryogenic regenerator material of the present invention uses the regenerator material granules mainly composed of irregularly shaped particles to facilitate the setting of interparticle voids after sintering. As the shape of the particles of the cold storage material approximates to a sphere, the contact area between the particles increases, and it is relatively difficult to set the sintering conditions for obtaining the desired interparticle voids. On the other hand, the contact area between particles can be made relatively small by setting the abundance ratio of the cool storage material particles having an irregular shape with the shape factor R of 1.1 <R <2.0 to be 60% or more. Even if the sintering conditions and the like vary to some extent, relatively large desired interparticle voids can be easily obtained.

Further, in particular, the spherical particles of the magnetic regenerator material need to be produced by a rapid solidification method such as a rotating disk method, a rotating electrode method, a gas atomizing method and a water atomizing method, whereas the spherical particles of the present invention are not specified. Regular shape cold storage material granules,
By crushing the pre-produced mother alloy using a stamp mill, a jet mill, a ball mill or the like, it can be easily and industrially obtained at low cost.

In the cryogenic regenerator material of the present invention, the shape factor R of the regenerator material particles is defined in the range of 1.1 <R <2.0 for the following reasons. That is, the form factor R is 1.1
When it is below, interparticle voids as described above cannot be easily obtained, and when the shape factor R is 2.0 or more, conversely, the contact area between particles becomes too small and the sinterability deteriorates. If the abundance ratio of such irregularly shaped cool storage substance particles is less than 60%, it becomes impossible to easily obtain the desired interparticle voids as described above. A more preferable abundance ratio of the irregularly shaped cool storage material particles is 70% or more, and further preferably 80% or more.

Further, since the particle size of the cold storage substance particles has a great influence on the heat transfer characteristics and the like, in the present invention, 70% by weight or more of the total particles are stored in the cold storage material having a particle size of 0.01 to 0.3 mm. It is preferably composed of material particles. Here, the particle size as referred to in the present invention means the diameter of the smallest sphere capable of encapsulating the particles. If the particle size of the cool storage substance particles is less than 0.01 mm, the packing density becomes too high, which may lead to an increase in pressure loss, and if the particle size exceeds 3.0 mm,
Since the heat transfer area becomes small, the heat transfer efficiency is likely to decrease. Therefore, such particles are 30 weight of the whole particle.
If it exceeds%, the cold storage performance may be deteriorated. A more preferable particle size is in the range of 0.1 to 2 mm. Particle size is 0.
The ratio of particles in the range 01 to 3.0 mm in the whole particle is 80
The content is more preferably at least wt%, further preferably at least 90 wt%.

The cryogenic regenerator material of the present invention is obtained by sintering the particles of the regenerator material mainly composed of irregularly shaped particles as described above at a temperature lower than the melting point thereof so as to fix the particles to each other. It is a cold storage material. In this way, by sintering the regenerator material particles and fixing the particles, the desired interparticle voids can be easily obtained, and even if a force or thermal shock due to a gas flow is applied, the regenerator material particles It is possible to prevent vibration and movement. Therefore, the voids between the particles of the cold storage material are kept stable, and the change of the gas flow and the generation of fine powder can be effectively suppressed. The degree of sintering may be such that particles are fixed to each other, and it is preferable to set the sintering conditions so that the porosity is about 15 to 80%. Porosity after sintering
If it is less than 15%, the gas flow may be obstructed and the cold storage performance may be deteriorated. If it exceeds 80%, the structure becomes unstable.

Further, the fixation due to the sintering of the cold storage material granules is
It may be carried out directly between the particles of the cold storage material, or the surface of the particles of the cold storage material may be previously covered with a material that liquefies, softens or self-melts at a temperature lower than the melting point of the cold storage material, and then liquid phase baking is performed through such a material. You may carry out by binding. Examples of such intervening substances include lead, silver, tin, indium,
Examples are low melting point alloys made of zinc or the like. By performing liquid phase sintering through the above-mentioned substances, it is possible to fix the cold-storage substance particles at a lower temperature and to improve the fixing strength.

The cryogenic regenerator material of the present invention, that is, the sintered regenerator material is manufactured, for example, as follows. That is, first, the regenerator substance granules mainly composed of irregularly shaped particles as described above are housed in a sintering container made of a material that does not easily react with the regenerator substance, and the regenerator substance particles are appropriately contacted. The above-mentioned granules are pressed by a lid or the like with a pressure to such an extent that they are heat-treated in this state to be sintered. As the above-mentioned sintering container, spraying fine particles of oxide, plating with Ni, Co, or the like, or using an oxide container is also effective so that the container and the regenerator material particles are not fused. That's the method. The firing atmosphere is preferably performed in vacuum or in an inert gas so that the cold storage material is not oxidized.

The above sintering temperature and time are appropriately set depending on the presence or absence of the cold accumulating substance and inclusions used so that the porosity as described above can be obtained. However, since the contact area between particles is smaller than that in the case of using spherical particles of the cold storage substance, the sintering temperature is set slightly higher or the sintering time is set slightly longer. The above-mentioned sintering step also functions as a stabilization treatment for the cool storage material, particularly the rare earth element-based magnetic cool storage material.

The cryogenic regenerator of the present invention is obtained by filling the regenerator cylinder with the sintered regenerator material whose particles are fixed by the above-mentioned sintering. For example, by filling a plurality of sintered regenerator materials. Various forms can be adopted, such as a regenerator for cryogenic temperature can be configured. Further, not all of the regenerator material to be filled must be composed of the above-mentioned sintered regenerator material, but it is also possible to fill it as a mixture of the sintered regenerator material and granules. Then, by using the above-described sintered regenerator material, it becomes possible to greatly improve the reproducibility of the initial performance of the regenerator and the stability of the refrigerating performance. That is, excellent initial performance can be obtained with good reproducibility, the change in refrigeration temperature with time is stable, and after optimally adjusting the operating conditions, always operate without adjusting the stable conditions and maximum output conditions. Is possible.

[0024]

Embodiments of the present invention will be described below.

Example 1 First, an Er ₃ Ni mother alloy (melting point: 1123K) was produced by high frequency melting. Particle size of this Er ₃ Ni mother alloy was measured by a stamp mill.
After crushing to 0.2 to 0.3 mm, shape classification was performed using an inclined vibrating plate. The perimeter L of the projected image of each particle of the obtained Er ₃ Ni particles and the actual area A of the projected image are measured by image processing,
When the form factor R represented by L ² / 4πA is evaluated,
The abundance ratio of particles falling within the range of 1.1 <R <2.0 was 91%.

Next, the Er ₃ Ni granules described above were filled in a graphite mold while vibrating, and a graphite cap was placed on the mold so as to exert a force to lightly press it. I placed it. The filling rate when filling granules is about 6
It was set to 2%. Then, the furnace was evacuated sufficiently and Ar gas was introduced, followed by firing in this Ar atmosphere at a temperature of 1023K for 1 hour, cooling to room temperature, and then taking it out of the mold to obtain an outer diameter.
A sintered Er ₃ Ni regenerator material having a filter shape of 20.0 mm and a height of 50.0 mm was obtained. The obtained sintered Er ₃ Ni regenerator material had a porosity of about 32%.

Next, a cryogenic regenerator was constructed using the above sintered Er ₃ Ni regenerator material, and its stability and refrigerating capacity were evaluated as follows. First, the outer diameter of the sintered Er ₃ Ni regenerator material is ground to the inner diameter of the regenerator, and fine powder is completely removed by ultrasonic waves, and then a pressure of approximately 1 kg / cm ² is applied to the regenerator. did. This was incorporated into a GM refrigerator and a freezing test was conducted. As a result, 250 mW was obtained as the initial refrigeration capacity at 4.2 K, and stable output could be obtained during continuous operation for 2000 hours.

Example 2 Five types of Er ₃ Ni particles were produced in the same manner as in Example 1 above, and then sintered Er ₃ having a filter shape under the sintering conditions shown in Table 1.
Each Ni cold storage material was produced. The abundance ratio of particles in which the shape factor R of each Er ₃ Ni particle falls within the range of 1.1 <R <2.0 is shown together with the porosity after sintering.

Next, a freezing test was conducted in the same manner as in Example 1 using each of the filter-like sintered Er ₃ Ni regenerator materials. As a result, Table 1 shows the initial cooling capacity and the cooling capacity after 2000 hours of continuous operation.

[0030]

[Table 1] As is clear from Table 1, by using the regenerator material granules mainly composed of irregularly shaped particles, the inter-particle voids of the sintered regenerator material can be stably set, and such sintering By using the regenerator material, it is possible to obtain an excellent initial refrigerating capacity with good reproducibility, and it is possible to maintain such performance for a long period of time.

Comparative Example 1 An extremely low temperature regenerator was produced in the same manner as in Example 1 except that the Er ₃ Ni particles produced in Example 1 above were used as they were as a regenerator material without being sintered. The filling rate of Er ₃ Ni particles in the cold storage cylinder was set to 65%. This cryogenic regenerator is G
It was incorporated into an M refrigerator and a freezing test was conducted in the same manner as in Example 1 above. As a result, the initial refrigeration capacity was about 250 mW, and the refrigeration capacity after continuous operation for 2000 hours was 20 mW.

Comparative Example 2 The same Er ₃ Ni mother alloy as in Example 1 above was melted at 1373 K, and this molten metal was dropped and sprayed onto a rotating disk in an Ar atmosphere to rapidly solidify. The obtained granules are sieved and classified by shape,
Spherical Er ₃ Ni particles having a particle size of 0.2 to 0.3 mm were obtained. This spherical Er
_{The 3} Ni particles were fired under the same conditions as in Example 1 to prepare a filter-like sintered Er ₃ Ni regenerator material. The porosity of this sintered Er ₃ Ni regenerator material was 28%.

A cryogenic regenerator was prepared in the same manner as in Example 1 using the above-mentioned filter-like sintered Er ₃ Ni regenerator material, and a freezing test was conducted in the same manner.
At 50mW, stable output could be obtained during 2000 hours of continuous operation. However, the manufacturing cost of the cryogenic regenerator was about twice that of Example 1.

Example 3 First, the surface of an Er ₃ Ni grain produced in the same manner as in Example 1 was preliminarily plated with Sn to a thickness of 5 to 10 μm. Then, the Er ₃ Ni granules having this Sn plating film were filled into a graphite mold while applying vibration, and the graphite lid was placed on top of it so that the force of pressing it lightly acted, and in this state, in the firing furnace. Placed in. The filling rate when filling granules is approx.
It was set to 65%. Then, after evacuation of the furnace, it was fired at a temperature of about 573 K for 0.5 hour, cooled to room temperature, and then taken out of the mold to obtain a sintered Er ₃ Ni regenerator material having a target Sn plating layer.

The sintered Er ₃ Ni regenerator material having the Sn plating layer thus obtained had a porosity of about 31%. Further, this sintered Er ₃ Ni regenerator material was press-fitted into a regenerator cylinder in the same manner as in Example 1 to form a cryogenic regenerator, and this cryogenic regenerator was incorporated into a GM refrigerator. A freezing test was conducted in the same manner as in Example 1. As a result, the initial refrigeration capacity was 230 mW, and stable output could be obtained during 2000 hours of continuous operation.

[0036]

As described above, according to the present invention,
It becomes possible to provide a low temperature cryogenic regenerator material that can stably and easily set and maintain the voids between the regenerator material particles at low cost. Therefore, it is possible to effectively suppress the change in gas flow and the generation of fine powder, and thus it is possible to provide a regenerator excellent in initial performance and its continuous stability.

[0037]

Claims (2)

[Claims] 1. A cryogenic regenerator material comprising particles of a cold storage material having a specific heat of 0.1 J / cm ³ K or more at a temperature of ³⁰ K or less, wherein a perimeter of a projected image of individual particles of the cold storage material particles L,
Assuming that the real area of the projected image is A, 60% or more of the particles in the regenerator material have a shape factor R represented by L ² / 4πA.
Has a shape of 1.1 <R <2.0, and the particles of the cold storage material are firmly fixed by sintering. 2. A regenerator filled with particles of a cool storage material having a specific heat of 0.1 J / cm ³ K or higher at a temperature of ³⁰ K or lower, wherein a perimeter of a projected image of each particle of the cool storage material particles is L,
Assuming that the real area of the projected image is A, 60% or more of the particles in the regenerator material have a shape factor R represented by L ² / 4πA.
Has a shape of 1.1 <R <2.0, and the regenerator material particles are firmly fixed by sintering.