JPH0566476U - Cryogenic refrigerator - Google Patents

Abstract

(57) [Abstract] [Purpose] Regarding the novel structure of a refrigerator that cools to an extremely low temperature of about several K in absolute temperature, a cryogenic refrigerator using a regenerator has high refrigeration performance and requires a large number of manufacturing steps. It is an object of the present invention to provide a cryogenic refrigerator, which has a small number and a long maintenance period. A cryogenic refrigerator provided with a regenerator that stores refrigeration in a refrigeration cycle, wherein an outer container that covers the outside of the regenerator is provided, and the outer container cools a portion near an endothermic portion of the refrigerant. Has good thermal conductivity in the temperature range,
A portion far from the heat absorbing portion has good thermal conductivity in a temperature region higher than the cooling temperature region, and an intermediate portion connecting between a portion close to the heat absorbing portion and a far portion has poor thermal conductivity. In addition, it is formed of a functionally graded material whose thermal function changes.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator, and more particularly to a novel structure of a refrigerator that cools to an extremely low temperature of about 10 to 20 ° K in absolute temperature.

[0002]

[Prior Art]

 Cryogenic refrigerators include Gifford-McMahon (GM) cycle refrigerators, Solvay refrigerators and Stirling refrigerators, all of which have a displacer equipped with a regenerator in the refrigeration cycle.

In the refrigeration cycle, the refrigerant gas passes through the regenerator before and after the endothermic process of adiabatically expanding the high-pressure refrigerant gas sent from the compressor, and at that time, heat exchange is performed with the regenerator material. As the refrigerant gas, helium gas or the like that does not liquefy even at an absolute temperature of around 10 to 20 ° K is used.

FIG. 2 shows the structure of a conventional GM cycle refrigerator provided with a regenerator. Reference numeral 10 is a compressor, which compresses helium gas as a refrigerant. The compressed helium gas is cooled by the gas cooler 11, and the oil separator 12 further removes oil mist and the like mixed in the refrigerant gas.

The helium gas discharged from the oil separator 12 is introduced into a cold head 20 having a built-in regenerator through a pipe 14 via an intake valve 13 that opens and closes a pipe passage. The helium gas of the refrigerant that has exited the cold head 20 passes from the pipe 15 through the exhaust valve 16 that opens and closes the pipe passage, passes through the surge tank 17, and then returns to the inlet of the compressor 10 as the refrigerant gas at room temperature and pressure. .. By repeating the above cycle, the tip of the cold head 20 is cooled and reaches an extremely low temperature.

Next, the structure of the cold head 20 will be further described. A displacer 22 having a regenerator as an inner container is arranged inside a cylinder 21 as an outer container. The displacer 22 has a space inside thereof filled with a regenerator material 23.

The regenerator material 23 has a large heat capacity, a high heat exchange efficiency, and a material and structure having a high thermal conductivity, and it is necessary to allow the refrigerant gas to pass therethrough. Therefore, copper alloy meshes are laminated or lead particles with a uniform particle size are filled. Reference numerals 24 and 25 are passages through which the refrigerant gas enters and leaves the regenerator material 23.

The displacer 22 is driven up and down inside the outer container 21 by a power unit (not shown), and reciprocates linearly between a top dead center and a bottom dead center. FIG. 2 shows that the displacer 22 is located approximately in the middle of the top dead center and the bottom dead center.

A gas seal 27 is attached to the upper outer wall of the displacer 22 so as not to move through the gap between the displacer 22 and the outer container 21 when the refrigerant gas in the expansion chamber 28 that generates freezing flows in and out. It is hermetically sealed.

Next, the GM refrigeration cycle will be described. First, the displacer 22 is at the top dead center position, and the intake valve 13 is gradually opened while the exhaust valve 16 is closed. The high-pressure helium refrigerant gas in the compressor 10 is introduced into the cold head 20 through the intake valve 13 and the pipe 14.

Next, when the displacer 22 is moved from the top dead center to the bottom dead center, the refrigerant gas passes through the passage 24 and the cold storage material 23. At that time, the refrigerant gas exchanges heat with the regenerator material 23, the heat is removed by the regenerator material 23, and passes through the passage 25 to reach the lower expansion chamber 28.

Next, when the displacer 22 is at the bottom dead center, the intake valve 13 is closed and the exhaust valve 16 is gradually opened, so that the high-pressure refrigerant gas enters the inlet side of the compressor 10. Due to the pressure difference, the temperature of the expansion chamber 28 is adiabatically expanded and the temperature of the expansion chamber 28 is lowered.

Further, when the displacer 22 is lowered from the bottom dead center toward the top dead center, the cooled refrigerant gas in the expansion chamber 28 passes through the passage 25, the regenerator material 23, the passage 24, the pipe 15, the exhaust valve 16, and the surge. It flows to the tank 17 and the compressor 10. At that time, the refrigerant gas exchanges heat with the cold storage material 23 to cool the cold storage material 23.

Cooling is performed by repeating the above refrigeration cycle.

[0015]

[Problems to be solved by the device]

 The cylinder 21 of the cold head 20 shown in FIG. 2 is in contact with high-pressure refrigerant gas, and when the displacer 22 equipped with a regenerator reciprocates, the cylinder 21 is slid to generate heat due to frictional heat to a high temperature. It includes a portion H, a lower portion C that surrounds the expansion chamber 28 and contacts the cryogenic refrigerant gas, and an intermediate portion M between the upper portion H and the lower portion C.

Conditions required for a cylinder of a refrigerating cycle refrigerator using such a regenerator include the following items. That is, (1) sufficient mechanical strength is maintained even at cryogenic temperatures, (2) cryogenic parts are normally placed in a vacuum, but refrigerant gas inside the cylinder does not leak to the vacuum area around the cylinder. Airtightness, (3) Keep the gas seal on the inner surface of the upper part H that becomes high temperature, and (4) Have a high thermal conductivity in the lower part C that generates extremely low temperature in order to efficiently absorb heat from the refrigeration load. (5) Reduction of cooling loss due to heat conduction from the upper high temperature part H to the lower low temperature part C.

In a conventional GM cycle refrigerator, a cylinder 21 satisfying the above conditions is manufactured by integrally cutting a strip of stainless steel SUS304. Since SUS304 has excellent mechanical strength even at low temperatures and has a low thermal conductivity, it has an effect of hindering heat transfer from the high temperature portion H to the low temperature portion C and reducing freezing loss.

Further, since it has relatively good workability and is easily available, it is airtight by integrally cutting, airtight welding, improving the surface finish of the sliding portion of the gas seal, selecting an appropriate sealing material, etc. I was dealing with sexual problems.

Further, as shown in FIG. 2, the wall thickness of the cylinder 21 is cut only in the middle portion M thinner than the other portions so that the heat conduction from the high temperature portion H to the low temperature portion C is deteriorated. Further, in order to enhance the heat absorption effect in the low temperature portion C, a copper flange 29 having good thermal conductivity is inserted to enhance the thermal conductivity.

However, since SUS304 material has a low thermal conductivity from the beginning, it is preferable as a material used for the middle portion M, but as a material for the high temperature portion H and the low temperature portion C, due to poor thermal conductivity, it is as follows. There is a problem. (1) Since the frictional heat due to the sliding movement of the gas seal portion of the high temperature portion H is difficult to radiate, the temperature becomes high, the gas seal material deteriorates, and the life is shortened. Therefore, replacement and maintenance of the gas seal is necessary frequently. (2) Cooling efficiency is low due to poor heat conduction in the low temperature portion C. (3) Since the thickness of the intermediate portion M is reduced or the copper flange 29 is attached to the low temperature portion, the number of manufacturing steps and cost increase.

An object of the present invention is to provide a cryogenic refrigerator using a regenerator, which has a high refrigerating performance, a small number of manufacturing steps, and a long maintenance period. To do.

[0022]

[Means for Solving the Problems]

 The cryogenic refrigerator of the present invention is a cryogenic refrigerator having a regenerator for storing refrigerating refrigerant during a refrigeration cycle, wherein the cryogenic refrigerator is provided with an outer container covering the outside of the regenerator, and the external container comprises the refrigerant. The part close to the heat absorption part is made of a material having good thermal conductivity in the cooling temperature range, and the part far from the heat absorption part is made of a material having good heat conductivity in the temperature range higher than the cooling temperature range. The intermediate portion connecting between the portion close to the heat absorbing portion and the portion far from the heat absorbing portion is formed of a material having poor thermal conductivity, and each material is connected by a functionally graded material whose composition gradually changes.

[0023]

[Action]

 The low temperature part has good thermal conductivity at low temperature, and the part that requires higher heat dissipation apart from the low temperature part also has good thermal conductivity, and the intermediate part has poor thermal conductivity. Therefore, the heat absorption efficiency is improved in the low temperature part, the heat dissipation is good in the part distant from the low temperature part, and the heat conduction between the both ends is hindered in the intermediate part.

[0024]

【Example】

 An embodiment of the cryogenic refrigerator of the present invention will be described below with reference to FIG. The compressor, the gas cooler, the oil separator, the intake valve, the piping, the exhaust valve, the surge tank, the power unit, etc. of the refrigeration cycle are the same as those in FIG. Omitted in.

A displacer 2 which is an inner container is arranged inside a cylinder 1 which is an outer container. The displacer 2 is filled with the regenerator material 3 in its internal space. The regenerator material 3 has a large heat capacity, a high heat exchange efficiency, and a material and a structure with high thermal conductivity, and a copper alloy mesh is laminated on top of it to allow the refrigerant gas to pass therethrough. Alternatively, it has a structure in which lead particles having a uniform particle size are filled. Reference numerals 4 and 5 are passages through which the refrigerant gas enters and leaves the regenerator material 3.

The displacer 2 having a regenerator is made of bakelite or the like, and reciprocates linearly inside the cylinder 1 between a top dead center and a bottom dead center. FIG. 1 shows that the displacer 2 is located approximately in the middle of the top dead center and the bottom dead center.

A gas seal 7 is attached to the upper outer wall of the displacer 2, so that the refrigerant gas flowing into and out of the expansion chamber 8 for generating refrigeration creates a gap between the displacer 2 and the cylinder 1 when opening and closing the intake valve and the exhaust valve. It is hermetically sealed so as not to move through it.

The cylinder 1 is made of functionally graded material. The functionally gradient material is described, for example, on pages 72 and 73 of "Industrial Materials" Vol. 36, No. 12 (August 1988 separate volume).

The functionally gradient material is different from a generally used homogeneous material or a composite material in which different materials are bonded together, and the composition interface of a plurality of materials having different physical properties, properties, or functions is clearly defined. It is a material that is formed as a single material while gradually changing (gradienting) the concentration gradient in the absence of any condition, and it is possible to realize different characteristics and functions with one material.

As the method for producing the functionally graded material, there are a chemical vapor deposition method, a gradient composition controlled sintering (added by changing the component composition and sintered as a graded concentration), a gradient composition controlled self-heating method (between materials). There is a method for synthesizing by utilizing heat generated by a chemical reaction), and any method may be used in the present embodiment.

In the cylinder 1 of the present embodiment, the high temperature portion H of the sliding portion of the gas seal has high thermal conductivity in that temperature range, and the low temperature portion C has high thermal conductivity even at an extremely low temperature. The intermediate portion M connecting the high temperature portion H and the low temperature portion C has characteristics of low thermal conductivity in any temperature range.

In order to have these thermal gradient functions, a gradient function material in which the composition of some materials gradually shifts is integrally manufactured, and the cylinder 1 is manufactured by cutting.

The vertical lengths of the high temperature portion H and the low temperature portion C are selected so as to cover the stroke length of the displacer 2. The inner wall surface of the high temperature portion H of the cylinder 1 has a good surface finish so as to have abrasion resistance against the gas seal 7, and the surface hardness is further increased.

According to the structure of the above-described embodiment, the heat generated by the friction between the gas seal 7 and the cylinder 1 is quickly dissipated in the high temperature portion H having high thermal conductivity to prevent the temperature rise of the gas seal 7, and The contact surface of the seal has high wear resistance, which improves the life of the gas seal.

Furthermore, the cooling efficiency of the low temperature portion C is increased due to the high thermal conductivity. That is, heat can be absorbed even with a small temperature difference. Further, the temperature difference between the high temperature portion H and the low temperature portion C is 200 ° C. or more, but the intermediate portion M has a low thermal conductivity, and the flow of heat from the high temperature portion H to the low temperature portion C is reduced, Increase the freezing effect.

In the embodiment of the invention described above, the cold head has a one-stage configuration. However, the present invention also applies to a cold head having a multi-stage configuration in which two or more stages of regenerators are connected in cascade. Applicable.

Further, it goes without saying that the present invention can be applied not only to the GM cycle refrigerator, but also to other refrigerators / coolers using a regenerator, for example, a solver refrigerator or a Stirling refrigerator.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0039]

[Effect of the device]

 As described above, according to the present invention, since the functional material is used for the outer container surrounding the regenerator, the high temperature portion, the middle portion, and the low temperature portion can have different characteristics, so that the refrigerating efficiency is high. Moreover, the number of manufacturing steps is small, and the maintenance period can be extended.

Further, since it is possible to perform cutting work from an integrally peeled material, it is possible to obtain sufficient accuracy and strength.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a cold head in a cryogenic refrigerator according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a structure of a GM cycle refrigerator according to a conventional technique.

[Explanation of symbols]

 1 ... Cylinder (outer container) 2 ... Displacer (regenerator) 3 ... Regenerator material 4, 5 ... Refrigerant gas passage 7 ... Gas seal 8 ... ... Expansion chamber

Claims (2)

[Scope of utility model registration request] 1. A cryogenic refrigerator provided with a regenerator for storing refrigerating refrigerant during a refrigeration cycle, comprising an outer container for covering an outer side of the regenerator, the outer container being a portion close to an endothermic portion of the refrigerant. Has good thermal conductivity in the cooling temperature range, and the part far from the heat absorbing part has good heat conductivity in the temperature range higher than the cooling temperature range, between the part close to the heat absorbing part and the far part. The cryogenic refrigerator in which the intermediate portion connecting the two is formed of a functionally graded material having a gradient function of heat conduction characteristics so as to have poor thermal conductivity. 2. The regenerator stores an inner container arranged to make a reciprocating linear motion inside the outer container, a regenerator material filled inside the inner container, and a regenerator during the reciprocating linear motion. A gas seal member for keeping airtightness of the refrigerant between the outer side of the inner container and the inner side of the outer container, the refrigerant passing through the regenerator during the reciprocating linear motion, and the regenerator. 2. A portion having good thermal conductivity in a high temperature region far from the endothermic portion of the outer container, which performs heat exchange between the gas container and the outer container, includes a range in which the gas seal slides during the reciprocating linear motion. The cryogenic refrigerator described.