JPH0452467A - Cryogenic refrigerator - Google Patents

Abstract

PURPOSE:To enable an efficient increase in refrigeration quantity by charging a regenerative refrigerator with a specified magnetic material as a cold- accumulating material. CONSTITUTION:A cryogenic refrigerator comprises a regenerative refrigerator (GM refrigerator) A for pre-cooling and a Joule-Thomson refrigeration loop (JT refrigerator) B. Compressed helium gas is pre-cooled by the regenerative refrigerator A, and is then subjected to Joule-Thomson expansion, thereby producing cold. The regenerative refrigerator A is charged with at least one magnetic material selected from Er3Ni, Dy5Er5Ni2 and GdRh, as a cold- accumulating material. The magnetic material has a large specific heat at constant volume at low temperatures of 10 K or below. When an input gas on the high pressure side of a final-stage heat exchanger 43 of the JT refrigerator B is cooled by the regenerative refrigerator A charged with the magnetic material, it is possible to achieve cooling to a temperature by far lower than those attained, for example, by use of lead as a cold-accumulating material. Consequently, it is possible to increase cooling (or cold-producing) capacity under the condition where the pressure on the high side of the JT refrigerator B is low.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a cryogenic refrigerator, and particularly relates to a cryogenic refrigerator that combines a Jull-Thomson freezing loop and a regenerative refrigerator for precooling. Regarding refrigerators.

(Prior Art) There are various types of cryogenic refrigerators. Among these are those that combine a Joule-Thomson refrigeration loop with a regenerative refrigerator. This type of refrigerator is configured to generate cold by pre-cooling compressed gas in a regenerator refrigerator and then subjecting it to Joule-Thomson expansion.

By the way, in a cryogenic refrigerator that combines a Joule-Thomson refrigeration loop and a regenerative refrigerator, a Gifford-McMahon refrigerator (hereinafter abbreviated as GM refrigerator) is usually used as the regenerative refrigerator. Joules in a refrigerator
The inlet gas on the high pressure side of the final stage heat exchanger of the Thomson refrigeration loop is cooled. And with the GM refrigerator,
Lead is generally used as a cold storage material.

However, as described above, the cryogenic refrigerator that combines the Joule-Thompson refrigeration loop and the GM refrigerator that uses lead as a cold storage material has the following problems. That is, although lead is a material with a large specific heat at low temperatures, the specific heat decreases rapidly as the temperature decreases, and below about 15%, it no longer has sufficient heat capacity to exchange heat with the refrigerant. For this reason, it has been difficult to cool the high-pressure side inlet gas temperature of the final stage heat exchanger of the Joule-Thompson refrigeration loop to 15 or below. Therefore, in order to increase the amount of refrigeration obtained by expansion with the Joule-Thompson valve, it is necessary to increase the pressure on the high pressure side of the Joule-Thompson refrigeration loop. Increasing the pressure on the high pressure side of the Joule-Thompson refrigeration loop in this way leads to an increase in input to the compressor, resulting in a problem of poor efficiency.

(Problems to be Solved by the Invention) As mentioned above, in the conventional cryogenic refrigerator that combines a Joule-Thomson refrigeration loop and a regenerator for precooling using lead as a regenerator, the Joule-Thomson refrigeration loop The high-pressure side input gas of the final stage heat exchanger can only be cooled to about 15%, and this is due to the fact that in order to increase the amount of refrigeration obtained by expansion in the Joule-Thomson valve, the Joule-Thomson refrigeration loop is It is necessary to increase the pressure on the high pressure side. For this reason, there was a problem that the input to the compressor increased, resulting in poor efficiency.

Therefore, an object of the present invention is to provide a cryogenic refrigerator that can efficiently increase the amount of refrigeration at 4.2 K, in particular, in a combination of a Joule-Thomson refrigeration loop and a regenerator refrigerator. .

[Structure of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention generates refrigeration by pre-cooling compressed helium gas with a regenerator and then expanding it with Joule and Thomson gas. In the cryogenic refrigerator, Er3Ni, D
The regenerator is characterized in that the regenerator refrigerator is loaded with at least one kind of magnetic material selected from among Y, Er5, Ni2°GdRh.

(Function) Magnetic materials Er3 Ni, Dy5 Er5 Ni2,
GdRh has a much larger constant volume specific heat than lead at low temperatures, ie, below IOK. therefore,
When a regenerator refrigerator loaded with these regenerator materials is used to cool the high-pressure input gas in the final stage heat exchanger of the Joule-Thomson refrigeration loop, it is much more effective than when it is cooled with a regenerator refrigerator that uses lead as the regenerator material. Can be cooled to low temperatures.

As a result, it is possible to increase the amount of refrigeration generated while keeping the pressure on the high pressure side of the Joule-Thompson refrigeration loop low.

(Example) An embodiment will be described below with reference to one drawing.

FIG. 1 shows a cryogenic refrigerator according to an embodiment of the present invention.

This cryogenic refrigerator can be broadly divided into a regenerator refrigerator for precooling, in this example, GM refrigerator A, and a Joule-Thomson refrigerator loop (hereinafter abbreviated as JT refrigerator) that is precooled by GM refrigerator A. ) and B.

GM refrigerator A can be broadly divided into cold head 1,
It is composed of a refrigerant gas introduction and discharge system 2.

As shown in FIG. 2, the cold head 1 includes a closed cylinder 3, a piston housed in the cylinder 3 so as to be able to reciprocate, that is, a displacer 4 made of a heat insulating material, and the displacer 4. and a motor 5 that provides the power necessary for reciprocating motion.

The cylinder 3 is comprised of a large diameter first cylinder 6 and a small diameter second cylinder 7 coaxially connected to the first cylinder 6. The boundary wall between the first cylinder 6 and the second cylinder 7 constitutes a first stage cooling stage 8, and the tip wall of the second cylinder 7 constitutes a second stage cooling stage which is lower temperature than the first stage cooling stage 6. Stage 9 is configured.

The displacer 4 includes a first displacer 10 that reciprocates within the first cylinder 6 and a second displacer 11 that reciprocates within the second cylinder 7. The first displacer 10 and the second displacer 11 are coupled in the axial direction by a coupling mechanism 12. Inside the first displacer 10, a fluid passage 13 extending in the axial direction is provided.
A cool storage material 15 made of copper mesh or the like is accommodated in this fluid passage 13. Similarly, a fluid passage 14 extending in the axial direction is formed inside the second displacer 11, and this fluid passage 14 is made of magnetic materials such as Er3NiDy5Er5Ni2. A cold storage material 16 formed of at least one type of GdRh, for example, Er3Ni balls is accommodated. Seal devices 17 are provided between the outer circumferential surface of the first displacer 10 and the inner circumferential surface of the first cylinder 6 and between the outer circumferential surface of the second displacer 11 and the inner circumferential surface of the second cylinder 7, respectively. .18 is installed.

The upper end of the first displacer 10 in the figure is connected to a connecting rod 20.
, is connected to the rotating shaft of the motor 5 via a Scotch choke or a crankshaft 21.

Therefore, when the motor 5 rotates, the displacer 4 reciprocates in the direction shown by the solid line arrow 22 in the figure in synchronization with this rotation.

A refrigerant gas inlet 23 and an outlet 24 are provided in the upper part of the side wall of the first cylinder 6 , and these inlet 23 and outlet 24 are connected to the refrigerant gas introduction and discharge system 2 . The refrigerant gas introduction and discharge system 2 constitutes a helium gas circulation system via the cylinder 3, and has a discharge port 24 connected to the inlet port 23 via a low pressure valve 25, a compressor 26, and a high pressure valve 27. ing. That is, the refrigerant gas introduction and discharge system 2 compresses low-pressure helium gas to high pressure using the compressor 26 and sends it into the cylinder 3.

JT refrigerator B is broadly divided into a compressor 40 that compresses helium gas, and a gas compressor 40 that compresses helium gas, one end of which is connected to the gas discharge port 48 of the compressor 40, and the other end of which is connected to the gas suction port 49 of the compressor 40. A guide pipe 50, a Joule-Thomson expansion valve (hereinafter abbreviated as JT valve) 44 inserted into the gas guide pipe 50, and a gas guide pipe 50 between the JT valve 44 and the compressor 40. The first provided. Second. Third heat exchanger 4
1.42.43. First heat exchanger 4
1 is on the compressor 40 side, and the third heat exchanger 43 is on the JT valve 44.
On the side, and a second heat exchanger 42 is arranged between heat exchanger 41 and heat exchanger 43.

The high pressure side piping of the gas guide pipe 50 between the first heat exchanger 41 and the second heat exchanger 42 is thermally connected to the first cooling stage 8 of the GM refrigerator A described above. Also, the second
The high pressure side piping of the gas guide pipe 50 between the heat exchanger 42 and the third heat exchanger 43 is thermally connected to the second cooling stage 9 of the GM refrigerator A. Note that the portion of this refrigerator located below the line 51 in FIG. 1 is housed in a cryostat.

Next, the operation of the refrigerator configured as described above will be explained.

In the GM refrigerator A, when the motor 5 starts rotating,
The displacer 4 reciprocates between the bottom dead center and the top dead center. When the displacer 4 is at the bottom dead center, the high pressure valve 27 is opened and helium gas (approximately 18 atm) is compressed to high pressure.
flows into the cold head 1. Next, when the displacer 4 moves to the top dead center, high pressure helium gas flows through the fluid passage 13 formed in the first displacer 10, the first stage expansion chamber 28, and the second displacer 11. It flows through the fluid passageway 14 to the two-stage expansion chamber 29 .

Along with this flow, high pressure helium gas is transferred to the cold storage material 15.
16.

Here, the high pressure valve 27 is closed and the low pressure valve 25 is opened.

As a result, the helium gas in the first-stage expansion chamber 28 and the second-stage expansion chamber 29 expands to a low pressure (approximately 5 atm) and generates cold, and this cold causes the first-stage cooling stage 8 and the second-stage cooling stage 9 are cooled to below 40 and below 15, respectively. The displacer 4 moves to the bottom dead center again, and along with this, the helium gas in the first-stage expansion chamber 28 and the second-stage expansion chamber 29 is removed. The expanded helium gas cools the cold storage material 15.16 while passing through the fluid passage 13.14, reaches room temperature, and is discharged. Thereafter, the above-described cycle is repeated.

On the other hand, when the compressor 40 of JT refrigerator B is operated, helium gas compressed to high pressure is released into the first. It flows to the JT valve 44 via the high pressure side of the second and third heat exchangers 41, 42, 43. During this process, it is cooled at the first cooling stage 8, and further cooled to a lower temperature at the second cooling stage 9. Then, low pressure (approximately latm) is applied via the JT valve 44.
). At this time, due to the Joule-Thomson effect, the helium gas is cooled to about 4.2, which is the saturation temperature at latm, and becomes a gas-liquid two-phase flow. The object to be cooled 45 such as a superconducting magnet or helium gas is cooled by the cold generated by this gas-liquid two-phase flow. Cooled object 4
The helium gas that cooled No. 5 was added to No. 3. Second. After cooling the high-pressure helium gas that passes through the low-pressure side of the first heat exchanger 43, 42.41 and the high-pressure side of each heat exchanger 4B, 42.41, it flows into the compressor 40 again. Compressed.

The performance of the refrigerator configured as described above largely depends on the helium gas pressure at the gas discharge port 48 of the compressor 40 and the temperature of the helium gas flowing into the high pressure side of the third heat exchanger 43.

FIG. 3 shows 1 g of helium gas, with the pressure of helium gas flowing into the high pressure side of the third heat exchanger 43 as a parameter.
The figure shows the result of calculation of the relationship between the amount of cold generated at 4.2K per hour and the temperature of the helium gas flowing into the high pressure side of the third heat exchanger 43. In addition, here, the third
For convenience, the heat exchange efficiency of the heat exchanger 43 is assumed to be 99%. Curves a, b, c, d, e, and f in the figure indicate pressures of 10.12, 14, 16, and 18.20 (atm), respectively. As can be seen from this figure, the temperature of the helium gas flowing into the high pressure side of the third heat exchanger 43 is high (
18 or more), the higher the pressure of the helium gas flowing into the high-pressure side of the third heat exchanger 43, the greater the amount of cold generation. However, on the contrary, when the temperature of the helium gas flowing into the high pressure side of the third heat exchanger 43 is low (for example, below 9), the pressure of the helium gas flowing into the high pressure side of the third heat exchanger 43 is low. The more cold weather occurs, the more cold generation occurs. As can be seen from this, if the temperature of the helium gas flowing into the high pressure side of the third heat exchanger 43 is low, even if the pressure of the helium gas flowing into the high pressure side of the third heat exchanger 43 is low, The required amount of refrigeration can be obtained and the compressor force can be reduced by 400 Å.

In the refrigerator according to this embodiment, the second
In the fluid passage 14 of the displacer 11, E is used instead of lead.
It houses a cold storage material 16 made of Ni. Er
As shown by curve g in Figure 4, the specific heat at volume Cv of 3Ni is slightly smaller than the specific heat at volume Cv of lead (curve h) at temperatures above about 15, but when the temperature drops below about 15, On the contrary, it becomes larger than the constant volume specific heat of lead.

Therefore, when Er3Ni is used as the cold storage material 16, the temperature of the second cooling stage 9 can be made lower than when lead is used as the cold storage material, and as a result, the third heat exchanger The temperature of the helium gas flowing into the high pressure side of the vessel 43 can be made below IOK.

Figure 5 shows a GM refrigerator (solid line) that uses Er and Ni as the cold storage material 16, and a GM refrigerator that also uses lead as the cold storage material 16.
The refrigeration capacity curve with the M refrigerator (dashed line) is shown. The horizontal axis shows the temperature (K) of the second cooling stage 9, and the vertical axis shows the refrigerating capacity (W). As can be seen from this figure, the refrigerator that incorporates the cold storage material 16 made of Er and Ni has a greater ability to freeze at the same temperature, and the refrigerator that incorporates the cold storage material 16 that is made of lead. It has the ability to freeze to lower temperatures. Also, based on the relationship between the amount of cold generated at 4.2 K per gram of helium gas shown in FIG. GM who did
In a cryogenic refrigerator using a refrigerator, in order to obtain the same amount of refrigeration, a compressor 26 with a lower pressure and a smaller flow rate than the conventional compressor 26 can be used in the JT refrigerator B.

The inventors have developed a cryogenic refrigerator that combines a JT refrigerator and a regenerator refrigerator that uses Er3Ni as a regenerator material, and a combination of a JT refrigerator and a regenerator refrigerator that uses lead as a regenerator material. The characteristics with cryogenic refrigerators were investigated using an actual machine. The input power of both regenerator refrigerators is 3.3kW,
The JT refrigerator has the same configuration except for the compressor.

Then, in 4.2, the helium gas pressure and flow rate on the high-pressure side, the temperature of the second cooling stage 9, and the power consumption of the compressor 40 necessary to exhibit a refrigeration capacity of 2 W were measured.

Refrigerators that use lead as a cold storage material have a refrigerating capacity of 2W at 4.2, so the helium gas pressure on the high pressure side is 1.
The flow rate was 8 atm and 0.17 g/sec.

Moreover, the input power of the compressor 40 was 1.1 kW. At this time, the temperature of the second cooling stage 9 was 15. That is, the total power consumption of the compressor 26.40 is 4.
It was 4 (-3, 3 + 1.1) kW.

On the other hand, in a refrigerator using Er3Ni as a cold storage material, the helium gas pressure on the high pressure side is 10 atm.

The flow rate was 0.12 g/sec. The input power to the compressor 40 at that time was 0.5 kW. Further, the temperature of the second cooling stage 9 at this time was 8. Therefore, the compressor 26 when using Er3Ni regenerator material.
The total power consumption of 40 is 3.8 (-3, 3 + 0.5)
kW, which means that power consumption can be reduced by approximately 14% compared to using lead regenerator material.

Note that the present invention is not limited to the embodiments described above. Although Er3Ni is used as the cold storage material in the embodiment, the same effect as in the previous embodiment can be obtained by using a magnetic material such as Dy, Er5Ni2, or GdRh. Further, in the embodiment, a Gifford-McMahon cycle is used as a regenerative refrigerator for precooling, but other regenerative refrigerators such as a Stirling cycle may be used. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, the amount of cold generated especially at 4.2 K can be efficiently increased, and a cryogenic refrigerator with high energy efficiency can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a cryogenic refrigerator according to an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view of a regenerator refrigerator incorporated in the cryogenic refrigerator, and FIG. 3 is a helium FIG. 4 is a diagram showing the relationship between the amount of cold generation at 4.2 K per gram of gas and the temperature of helium gas flowing into the high pressure side of the third heat exchanger. Figure 5 is a diagram showing the specific heat of Ni in comparison with that of lead. Figure 5 is a diagram showing the refrigeration capacity of a cryogenic refrigerator using Er3Ni as a cold storage material in comparison with that of a cryogenic refrigerator using lead as a cold storage material. It is. A... Gifford McMahon refrigerator, B... Joule Thomson refrigeration loop, 1... cold head,
2... Refrigerant gas conduction and discharge system, 3... Cylinder, 4...
・Displacer, 5... Motor, 6... First cylinder, 7... Second cylinder, 8... First stage cooling stage, 9... Second stage cooling stage, 10... Third stage 1 displacer, 11... 2nd displacer, 12...
...Connection mechanism, 13.14...Fluid passage, 15.16
...Cold storage material, 17゜18...Seal device, 19...
- Annular groove, 20... Connecting rod, 21... Crankshaft, 23... Inlet, 24... Outlet, 25...
Low pressure valve, 26... Compressor, 27... High pressure valve, 28.
...1st stage expansion chamber, 29...2nd stage expansion chamber, 41.42.
43... Heat exchanger, 44... Joule-Thompson expansion valve, 45... Cooled object, 48... Gas discharge port, 4
9... Gas suction port, 50... Gas guide pipe. Figure 1

Claims (2)

[Claims] (1) In a cryogenic refrigerator in which compressed helium gas is precooled in a regenerative refrigerator and then expanded by Joule-Thomson to generate cold, the regenerator material loaded in the regenerative refrigerator is a magnetic material. Some Er_3Ni, Dy_5
A cryogenic refrigerator characterized by being at least one selected from Er_5Ni_2 and GdRh. (2) The cryogenic refrigerator according to claim 1, wherein the regenerator refrigerator is a Gifford-McMahon refrigerator.