JPH09145180A - Cryogenic refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent eddy current from being generated in a cryogenic freezer in which refrigerant gas of which temperature is decreased is passed through a cold heat accumulator stored in a displacer so as to store cold heat therein by a method wherein the cold heat accumulator is constructed such that many metallic cold heat accumulating members are stored in a container and some partition members having aeration characteristic are arranged at predetermined positions. SOLUTION: A Solvay-cycle type helium freezer is operated such that a temperature in an expansion chamber of a cylinder is decreased as an adiabatic expansion of refrigerant gas is performed in it so as to generate cold heat and the refrigerant gas of which temperature is decreased is passed through a cold heat accumulator stored in a displacer so as to accumulate cold heat. This cold heat accumulator is constructed such that a plurality of partition members 32 having aeration characteristic and non-conductive characteristic such as mesh made of Bakelite, urethane coated copper wire, mesh made of polyimide amide coated copper wire or the like are arranged in a cylindrical container 30 in a predetermined spaced-apart interval so as to be crossed with a central axis of the container 30 and to divide an inner side of the container 30 into a plurality of segments, and a limitless number of lead balls 31 with a diameter of about 0.1mm are filled and enclosed in each of the segments.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator, and more specifically, to a cryogenic refrigerator for expanding and refrigerating a refrigerant gas by a reciprocating motion of a displacer (replacer) in a cylinder to generate cold. Therefore, the present invention relates to an improved technology of a cryogenic refrigerator of a type in which a displacer has a built-in regenerator that stores a part of the generated cold.

[0002]

2. Description of the Related Art Conventionally, as a cryogenic refrigerator having an expander for expanding a high-pressure refrigerant gas in a cylinder to generate cold, as disclosed in, for example, JP-A-58-214758. A compressor that compresses helium gas as a refrigerant gas and an expander that expands the compressed helium gas are connected to a closed circuit by high-pressure piping and low-pressure piping, and the high pressure by a switching valve in the expander. The piping and low-pressure piping are alternately communicated with the cylinder of the expander, and the slack piston is reciprocated in the cylinder according to the switching operation of this switching valve, and the slack piston reciprocally drives the displacer to expand the helium gas. A so-called improved solve cycle helium refrigerator that generates cold by It is known. In addition, a GM cycle (Gifford-McMahon cycle) in which a displacer is directly driven by gas pressure without using a slack piston is also well known.

In such a refrigerator, the temperature of the refrigerating machine is lowered due to the adiabatic expansion of the refrigerant gas in the in-cylinder expansion chamber, and cold is generated. And, in order to make the expander compact, usually, a regenerator that contains a large number of metal regenerator materials such as lead balls and copper nets in a container is built in the displacer. In the exhaust process of discharging the refrigerant gas whose temperature has dropped due to expansion from the expansion chamber of the cylinder, the refrigerant gas is discharged through the regenerator in the displacer, and when the refrigerant gas passes, part of the cold is stored in the regenerator. To do. Next, in the intake step of supplying the refrigerant gas to the expansion chamber in the cylinder, the refrigerant gas reaching the expansion chamber is supplied through the regenerator, and the temperature of the refrigerant gas is lowered by heat exchange between the refrigerant gas and the regenerator. By repeating the intake process and the exhaust process, it is possible to gradually obtain a cryogenic level of cold.

By the way, generally, when a metal placed in a magnetic field moves, a loop of induced electromotive current (eddy current) is generated in the metal, and the larger the area of this loop is, the larger the eddy current is and the magnetic field of the magnetic field increases. There is a phenomenon that fluctuations become large. Therefore, as the displacer reciprocates, the regenerator material in the regenerator therein moves in a magnetic field such as geomagnetism, and an eddy current flows in the regenerator material. This eddy current is divided into those generated in individual cool storage materials and those generated in the aggregate of cool storage materials.
Since the former eddy currents cancel each other out between the adjacent regenerator materials, only the latter eddy currents become a problem. Specifically, the magnetic field generated by the latter eddy current is proportional to the fourth power of the radius of the displacer.

For this reason, for example, SQUID (superconducting quantum interference device; Superconducting QUAa)
ntum Interference Device)
To cool to a cryogenic level by the cryogenic refrigerator, the magnetic field due to the eddy current generated in the regenerator is detected as noise, and the magnetic field detection sensitivity and accuracy of the magnetometer using the SQUID. However, there is an inconvenience that

Further, when an eddy current is generated when the superconducting magnet is operated in a strong magnetic field, such as cooling, it causes heat generation and reduces the cooling efficiency of the cryogenic refrigerator. In consideration of such inconvenience, JP-A-2-
As described in Japanese Patent No. 85652, it has been proposed to coat the surface of a regenerator material with a coating film having heat transfer, heat storage and non-conductivity.

If this structure is adopted, it is possible to eliminate eddy currents generated in the regenerator material aggregate.

[0008]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2-85652
In the case of adopting the configuration shown in the publication, the surface of each of the many regenerator materials housed in the regenerator must be coated with a coating film having heat conductivity, heat retentivity and non-conductivity. Is difficult to process, and the coating film may peel off when the cryogenic refrigerator is used for a long period of time.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is sufficient to perform simple processing for the regenerator as a whole without processing the regenerator material itself, and moreover, due to eddy current. It is an object of the present invention to provide a cryogenic refrigerator capable of significantly suppressing magnetism.

[0010]

The cryogenic refrigerator according to claim 1 is a regenerator, in which a large number of metallic regenerator materials are accommodated in a container and which has air permeability and non-conductivity at predetermined positions. A partition member is provided. In the cryogenic refrigerator according to the second aspect, as the partition member, a plurality of partition members are provided at rotationally symmetric positions with respect to the central axis parallel to the refrigerant gas passage direction of the regenerator.

The cryogenic refrigerator of claim 3 employs, as the partition member, a partition member arranged in a state orthogonal to the refrigerant gas passage direction of the regenerator.

[0012]

According to the cryogenic refrigerator of claim 1, when the displacer reciprocates in the cylinder during differential operation of the refrigerator, an eddy current flows in each regenerator material in the regenerator incorporated in the displacer. Occurs. And the whole cold storage material is 1
Since only the regenerator material located in the space partitioned by the partition member does not constitute one aggregate but one aggregate, an eddy current is generated in each compartment. Become. Here, each partition has a radius smaller than the radius of the entire regenerator, and since the magnetic field generated by each eddy current is proportional to the fourth power of the radius, it is partitioned by the partition member as described above. As a result, the generated magnetic field as a whole can be significantly reduced. Of course, since the eddy current is suppressed, heat generation can be suppressed and the cooling efficiency can be improved.

Further, heat transfer to each of a large number of regenerator materials,
It is not necessary to provide a coating film having heat storage properties and non-conductivity, and it is only necessary to provide a partition plate to divide a large number of regenerator materials into a plurality of parts, so that the configuration can be simplified. As the partition member, a plurality of partition members are provided at rotationally symmetric positions with reference to the central axis parallel to the refrigerant gas passage direction of the regenerator, and those arranged in a state orthogonal to the refrigerant gas passage direction of the regenerator. It is possible to employ any of the above, and a combination of both, and it is possible to achieve the same effect as in claim 1.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 3 is a longitudinal cross-sectional view of a main part showing a main part of a helium refrigerator having an improved solve cycle which is one embodiment of the cryogenic refrigerator of the present invention. 1
Is an expander for expanding helium gas (refrigerant gas) compressed by a compressor not shown. The expander 1 is connected to the compressor by a high pressure gas pipe (not shown) and a low pressure gas (not shown). As a result, a closed circuit is formed.

The expander 1 has a valve housing 4 having a high-pressure gas inlet 2 to which the high-pressure gas pipe is connected and a low-pressure gas outlet 3 to which the low-pressure gas pipe is connected, and a lower part of the valve housing 4 integrally formed therewith. A cylinder 5 having a two-stage structure that is airtightly joined and has an upper large diameter portion 5a and a lower small diameter portion 5b is provided. Inside the valve housing 4, a motor chamber 6 that communicates with the high pressure gas inlet 2 is provided. A vertical through hole 7 communicating with the motor chamber 6 and a surge volume chamber 9 communicating with the low pressure gas outlet 3 via an auxiliary orifice 8 are formed.

A valve stem 10 constituting an upper closed end portion of the cylinder 5 is fitted in a connecting portion between the valve housing 4 and the cylinder 5, and the valve stem 10 has a through hole 7 in the valve housing 4. The valve seat portion 10a that is airtightly fitted to the valve seat portion 10a and the hanging portion 10b that is formed in a subtotal smaller than the inner diameter of the cylinder large diameter portion 5a and hangs above the inside of the cylinder large diameter portion 5a.
A valve chamber 11 that communicates with the high-pressure gas pipe via the motor chamber 6 is formed by the space surrounded by the upper surface of a and the wall surface of the through hole 7.

In addition, the valve stem 10 has a first gas passage 1 whose upper half is branched into two branch passages 12a and 12b and which communicates the valve chamber 11 with the cylinder 5.
2, and one end communicates with the first gas flow path 12 via a low pressure port 27 of a rotary valve 24 described later,
The other end is formed to penetrate through the low pressure gas outlet 3 and the second gas flow path 13 communicating with the valve housing 4 through the communication path 14 formed in the valve housing 4.
0 upper surface with respect to the valve chamber 11, the second gas flow path 13
Then, in the central portion of the valve stem 10, the branch flow passages 12a and 12b of the first gas flow passage 12 are opened at positions symmetrical to the opening of the second gas flow passage 13, respectively. .

On the other hand, at the upper end of the large-diameter portion 5a of the cylinder 5, the drive space 1 is provided above the large-diameter portion 5a of the cylinder.
A cup-shaped slack piston 1 that divides and forms 5
Reference numeral 6 designates the inner surface of the upper end of the valve stem 10.
0b is fitted in the airtight manner in a reciprocating manner, and the drive space 15 is always in communication with the surge volume chamber 9 in the valve housing 4 through the orifice 17. The slack piston 16 has a bottom wall 16a, and a center hole 16b and a communication hole 16c that communicate the inside and outside of the slack piston 16 are formed through the bottom wall 16a.

A displacer 18 is reciprocally fitted in the cylinder 5. The displacer 18 is integrally formed with a large-diameter portion 18a of a closed cylindrical shape that slides in the lower half of the large-diameter portion 5a of the cylinder 5 and the lower end of the large-diameter portion 18a, and slides in the small-diameter portion 5b of the cylinder 5. And a small-diameter portion 18b in the shape of a closed cylinder. The displacer 18 allows the inner space of the cylinder 5 below the slack piston 16 to be intermediate chamber 19 and first-stage expansion chamber 20 in order from the top.
And the second expansion chamber 21. The space inside the large-diameter portion 18a of the displacer 18 is always communicated with the first-stage expansion chamber 20 by a communication hole (not shown), and the space inside the small-diameter portion 18b is the first-stage expansion chamber 20.
And it is always connected to the second expansion chamber 21.

Further, at the upper end of the large-diameter portion 18a of the displacer 18, a tubular locking piece 22 for communicating the space inside the large-diameter portion 18a with the intermediate chamber 19 is integrally projected, and the locking piece 22. Extends through the central hole 16b of the slack piston bottom wall 16a and extends into the slack piston 16 by a predetermined dimension, and a flange-shaped engaging portion 22a that engages with the piston bottom wall 16a is integrally formed at the upper end thereof. And
When the slack piston 16 rises, the slack piston 16
Is moved by a predetermined stroke, the displacer 18 is driven by the slack piston 16 to start rising by engaging the bottom wall 16a with the locking portion 22a of the locking piece 22, that is, the displacer 18 is moved by a predetermined stroke. With a delay of, the slack piston 16 is made to follow the movement.

Further, a rotary valve 24 as a switching valve, which is rotationally driven by a valve motor 23 arranged in the motor chamber 6, is provided in the valve chamber 11 of the valve housing 4, and the rotary valve 24 performs a switching operation. The high pressure gas pipe, that is, the valve chamber 11 that communicates with the high pressure gas pipe, and the communication passage 14 that communicates with the low pressure gas pipe, that is, the low pressure gas pipe, are connected to the intermediate chamber 19, the first expansion chamber 20, and the second expansion chamber in the cylinder 5. The chambers 21 are alternately communicated with each other.

That is, the rotary valve 24 is non-rotatably and slidably connected to the output shaft 23a of the valve motor 23. A spring 25 is compressed between the upper surface of the valve 24 and the valve motor 23, and the rotary valve 2 is compressed by the spring force of the spring 25 and the pressure of the high-pressure helium gas introduced into the valve chamber 11.
The lower surface of the valve 4 is pressed against the upper surface of the valve stem 10 with a constant pressing force.

On the other hand, on the lower surface of the rotary valve 24,
A pair of high pressure ports 26, 26 formed by cutting a predetermined length in the center direction from the outer peripheral edges facing each other in the radial direction, and an angular interval of about 90 ° with respect to the high pressure ports 26, 26 in the rotation direction of the rotary valve 24. A low pressure port 27 is formed by diametrically cutting from the center of the lower surface of the rotary valve 24 toward the vicinity of the outer peripheral edge.

When the rotary valve 24 is rotated by the drive of the valve motor 23 while pressing its lower surface against the upper surface of the valve stem 10 to perform a switching operation, the slack piston 1 responds to the switching operation of the rotary valve 24.
6 and the displacer 18 are reciprocated in the cylinder 5, and the high pressure ports 26, 26 on the lower surface of the rotary valve 24 are
The inner ends of the valve stems open on the upper surface of the valve stem 10, respectively.
When it matches the gas passage 12, the valve chamber 11 is transferred to the intermediate chamber 19, the first stage expansion chamber 20 and the second stage expansion chamber 21 in the cylinder 5 through the high pressure ports 26, 26 and the first gas passage 12. High pressure helium gas is introduced and filled into each of the chambers 19, 0 and 21 so that the slack piston 16 and the displacer 18 driven by the slack piston 16 are raised. On the other hand, when the outer end of the low-pressure port 27, which is always in the center and communicates with the second gas flow passage 13 opening on the upper surface of the valve stem 10, matches the first gas flow passage 12, each chamber 1 in the cylinder 5 is
9, 20, 21 are the first gas flow path 12, the low pressure port 27,
By communicating the low pressure gas outlet 3 through the second gas flow path 13 and the communication passage 14 and discharging the helium gas filled in the chambers 19, 20, 21 to the low pressure gas pipe, the slack piston 16 and The displacer 18 is lowered, and cold is generated by the expansion of the helium gas into the first-stage expansion chamber 20 and the second-stage expansion chamber 21 accompanying the downward movement of the displacer 18.

Further, in the space inside the large diameter portion 18a of the displacer 18, the first stage regenerator 18 and the small diameter portion 1 are provided.
The second-stage regenerator 19 is fitted in the space inside 8b, and these regenerators 28 and 29 are cylindrical containers 30.
A large number of lead balls 31 each having a predetermined diameter as a regenerator material,
.. (lead shots) are filled and sealed, and the gaps between the lead balls 31, 31, ... Are gas passages, and the cold heat of the helium gas flowing through the gas passages is used for each lead ball 31. I am trying to store it in. That is, when the displacer 18 is in the intake stroke in which the displacer 18 rises in the cylinder 5, the lead balls 31, 31, ... Which have decreased in temperature to the cryogenic level in the previous exhaust stroke are transferred from the intermediate chamber 19 to the first-stage expansion chamber 2.
The helium gas is brought into contact with 0 or the helium gas at room temperature toward the second expansion chamber 21, and the helium gas is cooled to near the cryogenic level by heat exchange between the two. On the other hand, the displacer 18
Is in the exhaust process of descending, the expansion chambers 20 and 2
In the middle of discharging the helium gas whose temperature has dropped to the cryogenic level due to the expansion in No. 1 to the outside of the cylinder 5, the lead balls 31, 31,
·······
1, ... Is configured to recool to near the cryogenic level.

As a feature of the present invention, as shown in FIG. 1, bakelite, a urethane-coated copper wire mesh, a polyimideamide-coated copper wire mesh, a Tetoron mesh, etc. are provided in the cylindrical container 30. , A plurality of partition members 32 having air permeability and non-conductivity are arranged at rotationally symmetric positions with respect to the central axis of the cylindrical container 30, and at predetermined intervals so as to be orthogonal to the central axis of the cylindrical container 30. Place the cylindrical container 30
The interior is divided into a plurality of compartments, and each compartment is filled with lead balls 31, 31, ... However, it is also possible to omit either the partition member 32 arranged at the rotationally symmetrical position or the partition member already positioned at predetermined intervals.

Next, the operation of this embodiment will be described.
However, since the operation of the refrigerator is conventionally known as disclosed in, for example, Japanese Patent Application Laid-Open No. 2-85652, detailed description thereof will be omitted, and only the eddy current and magnetic field generated in the regenerator will be described below. . As the displacer 18 reciprocates in the cylinder 5 as described above, the lead balls 31, 31, ... (Cold storage material) in the regenerators 28, 29 built in the displacer 18 are in a magnetic field such as geomagnetism. , So that an eddy current is generated in the lead balls 31, 31, .... Then, the eddy current generated in each lead ball 31 flows into the adjacent lead ball 31. However, in this embodiment, the partition member 32 arranged at a rotationally symmetrical position with respect to the central axis of the cylindrical container 30 and the partition member arranged at predetermined intervals so as to be orthogonal to the central axis of the cylindrical container 30. Three
Since 2 has breathability and non-conductivity,
The phenomenon that the eddy current generated in each lead ball 31 flows to the adjacent lead ball 31 can be blocked by these partition members 32, and the eddy current flowing in the outermost peripheral edge of each section can be reduced. That is, the radius of each section is the cylindrical container 3
Since the radius is smaller than 0, the eddy current also decreases in proportion to the decrease in radius. Since the magnetic field generated by the eddy current is proportional to the fourth power of the radius, the displacer 1
The magnetic field generated by the reciprocating motion of 8 is significantly reduced. Specifically, when the cylindrical container 30 is divided into four sections by the partition member 32, the radius of each section becomes approximately 1/4, so that the magnetic field generated by the eddy current in each section is 1/1.
6 and the magnetic field generated by all the eddy currents in the four sections is 1/16 × 4 = 1/4. Since the heat generated by the eddy current is proportional to the cube of the eddy current, the amount of heat generated by the eddy current in each section is 1/8, and the amount of heat generated by all the eddy currents in the four sections is 1 / 8x4
= 1/2.

A more detailed description will be given. A magnetic field of B = B0sin ωt is applied perpendicularly to a conductor disk having a radius r and a thickness d. At this time, the distribution of the eddy current flowing in the disk is obtained and the Joule heat generated is obtained. However, the electrical conductivity of the disk is σ
And It is clear that the electric field created inside the disk has point symmetry. Therefore, the electric field E on the point P (r)
Find (r).

The electromotive force ε of the circular circuit having the radius r ′ is ε = 2π
r′E, and the magnetic flux Φ in this ring circuit is Φ = πr ′ ²
(B + B '). However, B'is a magnetic field created by the eddy current. Therefore, 2πr′E = πr ′ ² (dB / d
t) = πr ′ ² ωB0cosωt. As a result, the electric field E becomes E = (1 / 2πr ′) πr ′ ² ωB0cosωt = (r ′ / 2) ωB0cosωt.

The current density j is j = σE = (r '/
2) ωB0cosωt. Here, since the current density j is proportional to the radius r, the generated Joule heat W is given by Equation 1, which is proportional to the cube of the radius.

[0031]

(Equation 1)

Letting m be the magnetic moment created by the eddy current flowing in the ring circuit of radius r ', m = μ0πr ² i, and the current i flowing in the ring circuit is i = dr.dz.j.
= Dr · dz · (σ / 2) · ω · r ′ · B0. Therefore, m = μ0π · (σ / 2) · ω · B0 · r ² ·
r ′ · dr · dz = (1/2) μ0πσωB0r ³ dr
dz, and the total magnetic moment is given by the equation 2.

[0033]

(Equation 2)

Therefore, it is understood that the magnetic moment produced by the eddy current on the disk is given by Equation 3, which is proportional to the fourth power of the radius and the thickness.

[0035]

(Equation 3)

If a partition member 32 having both heat transfer and cold storage properties is adopted, the regenerators 28, 29 will be used.
The cold storage capacity of can be secured. Here, since the partition member 32 described above also has a heat transfer property and a cold storage property, the cold storage capabilities of the regenerators 28 and 29 can be secured. Further, it is extremely difficult to cover the lead spheres having a diameter of about 0.1 mm with the coating film, but in this embodiment, since the partition member 32 is simply arranged in the cylindrical container 30, the regenerators 28, 29 are provided. Can be significantly simplified.

In the above-described embodiment, the regenerators 28 and 29 in which a large number of lead balls 31, 31, ... Are filled and sealed in the cylindrical container 30 are adopted, but the regenerator containing a regenerator material other than the lead balls is used. You can also use a container. For example, as shown in FIG. 2, in the case of adopting a regenerator in which a large number of copper nets 33, 33, ... As shown, a plurality of partition members 32a, 32b (here, the partition member 32a is arranged at a rotationally symmetrical position based on the central axis parallel to the refrigerant gas passage direction of the regenerators 28, 29). The partition member 32b is arranged in parallel with the copper net 33, and the partition member 32a does not need to allow the passage of the refrigerant gas, but the partition member 32b allows the passage of the refrigerant gas like the copper net 33. , And a large number of copper nets 33, 33, ... Are stacked in multiple layers in each space partitioned by the partition member 32. The eddy current, the magnetic field generated by the eddy current, and the eddy current Heat generated by the electric current It is possible to win.

The present invention can be applied not only to the helium refrigerator having the improved solve cycle but also to those using a refrigerant gas other than helium gas and those having a cycle other than the improved solve cycle. Is.

[0039]

According to the cryogenic refrigerator of claim 1, since the regenerator is partitioned by the partition member, the generated magnetic field as a whole can be remarkably reduced, and the eddy current is suppressed. It also has a unique effect that the cooling efficiency can be suppressed, the cooling efficiency can be improved, and the manufacturing of the regenerator can be simplified.

The invention of claim 2 has the same effect as that of claim 1. The invention of claim 3 has the same effect as that of claim 1.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an example of the configuration of a regenerator.

FIG. 2 is a perspective view schematically showing another example of the configuration of the regenerator.

FIG. 3 is a longitudinal cross-sectional view of a main part showing a main part of a helium refrigerator having an improved solve cycle, which is one embodiment of the cryogenic refrigerator of the present invention.

[Explanation of symbols]

 5 cylinder 18 displacer 20 first stage expansion chamber 21 second stage expansion chamber 28 first stage regenerator 29 second stage regenerator 30 cylindrical container 31 lead ball 32, 32a. 32b partition member

Claims (4)

[Claims] 1. A displacer (1) which is reciprocally fitted in a cylinder (5) and which defines an expansion chamber (20) (21) in the cylinder (5).
8), and the refrigerant gas supplied from the compressor is reciprocated by the reciprocating movement of the displacer (18).
0) Expand the inside of (21) to lower the temperature,
In the cryogenic refrigerator in which the refrigerant gas whose temperature has dropped is stored by passing through the regenerator (28) (29) built in the displacer (18), the regenerator (28) (29) is a container A partition member (3) having a large number of metal cold storage materials (31) housed in (30) and having air permeability and non-conductivity at a predetermined position.
2) A cryogenic refrigerator comprising (32a) and (32b). 2. The partition members (32) (32a) are
The cryogenic refrigerator according to claim 1, wherein the cryogenic refrigerator is arranged in a state parallel to the refrigerant gas passage direction of the regenerator (28) (29). 3. The partition members (32) (32a) are
The cryogenic refrigerator according to claim 1, wherein a plurality of the cryogenic refrigerators are provided at rotationally symmetric positions with respect to a central axis parallel to the refrigerant gas passage direction of the regenerators (28) (29). 4. The cryogenic temperature according to any one of claims 1 to 3, wherein the partition member (32b) is arranged in a state orthogonal to a refrigerant gas passage direction of the regenerator (28) (29). refrigerator.