JP2941575B2 - Cryogenic refrigerator and operating method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator,
In particular, the present invention relates to a cryogenic refrigerator including a combination of a Joule-Thomson refrigeration loop and a regenerative refrigerator for pre-cooling, and an operation method thereof.

[0002]

2. Description of the Related Art At present, superconducting magnets are applied to MRI, magnetic levitation trains, and the like, but systems using these superconducting magnets require cooling with liquid helium.

[0003] Since this liquid helium is effective, a cryogenic refrigerator capable of cooling to the temperature of liquid helium to suppress evaporation is used. Helium gas precooled by a regenerative refrigerator such as the Gifford McMahon (GM) refrigerator is one of the cryogenic refrigerators.
T) There is a JT refrigerator to expand. Hereinafter, a GM + JT refrigerator combined with both refrigerators will be described as an example.

In these systems, it is important to increase the efficiency of the refrigerator and reduce the running cost.
Particularly in a magnetic levitation train or the like, since the electric power is limited, it is important to increase the efficiency.

As a method for increasing the efficiency of the GM + JT refrigerator, it is conceivable to first lower the precooling temperature. It has been found that lowering the pre-cooling temperature improves the refrigeration capacity as in the inventor's earlier patent. In the above invention, a magnetic regenerator material such as Er ₃ Ni is used as a method of lowering the precooling temperature. It also shows that when the pre-cooling temperature is lowered, the efficiency is improved by setting the pressure of the JT cooling loop to the optimum pressure at each pre-cooling temperature.

[0006]

Although the refrigerating efficiency is improved by the above-mentioned improvement, it is necessary to further increase the efficiency from an application point of view. As a cause of the decrease in refrigeration efficiency,
Since the temperature difference between the cooling stages of the GM refrigerator is large, there is a problem that the temperature of the helium gas does not fall sufficiently even if the temperature of the refrigerator is lowered. In addition, in order to increase the capacity of the GM refrigerator, the focus has been on improving the refrigeration capacity at 4K in the past, but when using a GM + JT refrigerator, the refrigeration capacity in a temperature band different from that of the GM refrigerator alone is required. Becomes important. Conventionally, there was a problem that this was not taken into account when selecting the cold storage material. An object of the present invention is to improve the refrigeration efficiency of a GM + JT refrigerator by making an improvement in consideration of the above problems.

[0007]

According to the first aspect of the present invention, a compressed refrigerant gas is pre-cooled in a cooling stage portion of a cylinder of a regenerative refrigerator and then expanded by Joule-Thomson to generate cold. In the cryogenic refrigerator described above, the cylinder is formed of a block with good heat conduction and heat, in which a passage for allowing the cooling stage to flow through the refrigerant gas for pre-cooling is integrally formed. It is characterized by being integrally joined to the rest of the cylinder.

According to a second aspect of the present invention, in the cryogenic refrigerator, the compressed helium gas is pre-cooled by a regenerative refrigerator and then expanded by Joule-Thomson to generate cold. Almost 1 in the regenerator
A magnetic material having a magnetic transition point within a temperature range of 0 to 15K is provided as a cold storage material.

According to a third aspect of the present invention, in the cryogenic refrigerator, the compressed refrigerant gas is pre-cooled by a regenerative refrigerator and then expanded by Joule-Thomson to generate cold. And a pressure control means for controlling the pressure of the refrigerant gas.

According to a fourth aspect of the present invention, in the method for operating a cryogenic refrigerator, the compressed refrigerant gas is precooled by a regenerative refrigerator and then expanded by Joule-Thomson to generate cold. The operation speed of the refrigerator is controlled to an operation speed at which the cooling temperature of the refrigerant gas is the lowest, and the pressure of the refrigerant gas is controlled to a pressure at which the cooling gas has the highest efficiency.

[0011]

According to the first aspect of the present invention, the cylinder and the block are connected by electron beam welding or friction welding.
It is directly and integrally joined without any solder. That is, dissimilar metal bonding is performed. A helium gas flow path for pre-cooling the helium gas of the JT refrigerator is formed integrally with the block. Therefore, with such a configuration, it is possible to greatly reduce the thermal resistance and greatly improve the refrigeration capacity.

According to the second aspect of the present invention, the regenerator of the regenerative refrigerator is provided with a magnetic material having a magnetic transition point in a temperature range of approximately 10 to 15K as a regenerator material. If the magnetic transition point is higher than 15K, the efficiency of the JT refrigerator will deteriorate, and if it is lower than 10K, the efficiency of the regenerative refrigerator will deteriorate. Therefore, a magnetic material having a magnetic transition point 10～15K, e.g. ErNi, Er ₃ Co, the individual efficiency of regenerative refrigerator and JT refrigerator by using at least one selected from among such Nd ₃ Ni Therefore, the total performance of the cryogenic refrigerator can be improved.

According to the third and fourth aspects of the invention, the regenerative refrigerator has an optimum operation speed depending on each temperature range, and the gas pressure on the high pressure side of the JT refrigerator also There is an optimal gas pressure. Therefore, by controlling the operating speed of the regenerative refrigerator to the operating speed at which the cooling temperature of the refrigerant gas is the lowest, and by controlling the refrigerant gas pressure to a pressure at which the cooling gas is most efficient with respect to the cooling temperature, The refrigeration efficiency of the cryogenic refrigerator can be dramatically improved.

[0014]

Embodiments will be described below with reference to the drawings. FIG. 1 shows a cryogenic refrigerator according to one embodiment of the present invention.

The cryogenic refrigerator is roughly divided into a regenerative refrigerator for precooling, in this example, a GM refrigerator A, and a Joule-Thomson refrigeration loop (hereinafter, JT) precooled by the GM refrigerator A. B).

The GM refrigerator A is mainly composed of a cold head 1 and a refrigerant gas guide / discharge system 2.
As shown in FIG. 2, the cold head 1 includes a closed cylinder 3, a piston housed reciprocally in the cylinder 3, that is, a displacer 4 formed of a heat insulating material, and a reciprocating motion of the displacer 4. And a motor 5 for providing necessary power.

The cylinder 3 includes a first cylinder 6 having a large diameter,
It is composed of a small-diameter second cylinder 7 coaxially connected to the first cylinder 6. And the first cylinder 6
A first-stage cooling stage 8 is constituted by a boundary wall portion between the first and second cylinders 7, and a first-stage cooling stage 8 is formed by
A second cooling stage 9 having a lower temperature than the stage cooling stage 6 is configured.

The displacer 4 includes a first displacer 10 reciprocating in the first cylinder 6 and a second cylinder 7
And a second displacer 11 that reciprocates inside. First displacer 10 and second displacer 1
1 is connected in the axial direction by a connecting mechanism 12. A fluid passage 13 extending in the axial direction is formed inside the first displacer 10, and the fluid passage 13 accommodates a cold storage material 15 formed of a copper mesh or the like. Similarly, a fluid passage 14 extending in the axial direction is formed inside the second displacer 11. The fluid passage 14 is formed of a magnetic material having a magnetic transition point of 10 to 15K, such as Er ₃ Co or ErNi. The regenerator 16 formed of at least one selected from the group consisting of, for example, ErNi spheres is accommodated therein. The outer peripheral surface of the first displacer 10 and the first
Between the inner peripheral surface of the cylinder 6 and the second displacer 1
Sealing devices 17 and 18 are mounted between the outer peripheral surface of the first cylinder 1 and the inner peripheral surface of the second cylinder 7, respectively.

The upper end of the first displacer 10 in the figure is connected rod 20, scotch yoke or crankshaft 21.
And is connected to the rotating shaft of the motor 5 through. Therefore, when the motor 5 rotates, the displacer 4 reciprocates in the direction indicated by the solid arrow 22 in FIG.

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

The JT refrigerator B is roughly divided into a compressor 40 for compressing helium gas, one end connected to a gas discharge port 48 of the compressor 40, and the other end connected to a gas suction port 49 of the compressor 40. Gas guide tube 50 and the gas guide tube 5
Jul. Thomson expansion valve (hereinafter referred to as JT)
Abbreviated as valve. ) 44, the JT valve 44 and the compressor 40
Between the first, second, and third gas guide tubes 50
And the heat exchangers 41, 42, and 43 of FIG. First
The heat exchanger 41 is disposed on the compressor 40 side, the third heat exchange 43 is disposed on the JT valve 44 side, and the second heat exchanger 42 is disposed between the heat exchanger 41 and the heat exchanger 43. I have.

A first heat exchanger 41 and a second heat exchanger 42
The high pressure side pipe in the gas guide pipe 50 between the
It is thermally connected to the first cooling stage 8 of the refrigerator A. Further, the high-pressure side pipe of the gas guide pipe 50 between the second heat exchanger 42 and the third heat exchanger 43 is thermally connected to the second cooling stage 9 of the GM refrigerator A. In this refrigerator, a portion located below a line indicated by 51 in FIG. 1 is accommodated in the cryostat. Next, the operation of the refrigerator configured as described above will be described.

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 displacer 4 is at bottom dead center,
Helium gas (about 18 atm) compressed to high pressure by opening the high pressure valve 27 flows into the cold head 1. next,
When the displacer 4 moves to the top dead center, the high-pressure helium gas passes through the fluid passage 13 formed in the first displacer 10, the one-stage expansion chamber 28, and the second displacer 1.
1 through the fluid passage 14 formed in the two-stage expansion chamber 29
Flows to With this flow, the high-pressure helium gas is cooled by the cold storage materials 15 and 16.

Here, the high pressure valve 17 is closed and the low pressure valve 25 is opened. As a result, the first-stage expansion chamber 28 and the two-stage expansion chamber 2
The helium gas inside 9 expands to a low pressure (approximately 5 atm) to generate cold, and this cold causes the first cooling stage 8 and the second cooling stage 9 to have a temperature of 40K or less and 15K, respectively.
It is cooled to about K or less. The displacer 4 moves to the bottom dead center again, and accordingly, the helium gas in the first-stage expansion chamber 28 and the second-stage expansion chamber 29 is removed. The expanded helium gas passes through the fluid passages 13 and 14 while the cold storage material 1 is kept.
5 and 16 are cooled and discharged at normal temperature. Hereinafter, the above-described cycle is repeated.

On the other hand, when the compressor 40 of the JT refrigerator B is operated, the helium gas compressed to a high pressure becomes the first, second and second helium gases.
Via the high pressure side of the third heat exchangers 41, 42, 43, J
It flows to the T valve 44. On the way, the first cooling stage 8
, And further cooled to a lower temperature in the second cooling stage 9. Then, it is expanded to a low pressure (about 1 atm) through the JT valve 44. At this time, the helium gas is cooled to a saturation temperature of about 4.2 K at 1 atm by the Joule-Thomson effect, and becomes a gas-liquid two-phase flow. The object 45 to be cooled such as a superconducting magnet and helium gas is cooled by the cold generated by the gas-liquid two-phase flow. The helium gas that has cooled the cooled object 45 sequentially passes through the low-pressure sides of the third, second, and first heat exchangers 43, 42, 41, and flows through the high-pressure sides of the heat exchangers 43, 42, 41. After cooling the high-pressure helium gas, it flows into the compressor 40 and is compressed again.

The performance of the refrigerator configured as described above is as follows.
It 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 the amount of cold generated at 4.2 K per 1 g of helium gas and the pressure of the helium gas flowing into the high pressure side of the third heat exchanger 43 and the high pressure side of the third heat exchanger 43. 2 shows the result obtained by calculating the relationship between the temperature of the helium gas flowing into and the temperature of the helium gas. Here, the heat exchange efficiency of the third heat exchanger 43 is set to 99% for convenience.
And In the figure, curves a, b, c, d, e, and f are pressures 10, 12, 14, 16, 18, and 20 (at, respectively).
m). As can be seen from this figure, the third
When the temperature of the helium gas flowing into the high pressure side of the third heat exchanger 43 is high (for example, 18 K or higher), the higher the pressure of the helium gas flowing into the high pressure side of the third heat exchanger 43, the larger the amount of cold generated. Become. However, conversely, the third heat exchanger 4
When the temperature of the helium gas flowing into the high-pressure side of the third heat exchanger 43 is low (for example, 9 K or less), the lower the pressure of the helium gas flowing into the high-pressure side of the third heat exchanger 43, the greater the amount of cold generated. As can be seen from this, the third heat exchanger 4
If the temperature of the helium gas flowing into the high pressure side of 3 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 generated cold can be obtained and the compressor 4
The input of 0 can be reduced. That is, the GM refrigerator A
If the cooling temperature of the second cooling stage 9 is reduced by improving the capacity of the JT refrigerator B,
Performance is improved. An object of the present invention is to improve the total performance of a GM + JT cryogenic refrigerator, and three specific invention items will be described below. The first invention is
This is to optimally control the operation speed of the GM refrigerator A and the gas pressure on the high pressure side of the JT refrigerator B, respectively.

In the GM refrigerator A, the refrigerating capacity differs depending on the operation speed. FIG. 4 shows the results of measurement of the refrigerating capacity at each temperature by changing the operation speed of the GM refrigerator A at various temperatures.

FIG. 4 shows that the operating speed of the GM refrigerator A is 18r.
pm, 24 rpm, 36 rpm, 48 rpm, 60 rpm
FIG. 7 is a characteristic diagram showing the results of measuring the refrigerating capacity at each temperature while changing each of the five types of m, with the horizontal axis representing the temperature (K) and the vertical axis representing the refrigerating capacity (W). As can be seen from FIG. 4, 48 rpm in a region where the temperature is higher than approximately 5.8 K, 36 rpm between approximately 5.8 K and approximately 4.3 K, and 24 rpm between approximately 4.3 and approximately 3.1 K.
It can be seen that the optimum operating speed decreases as the temperature decreases to 18 rpm at pm, and below 3.1K. Although the specific rotation speed of this operation speed varies depending on various conditions of the GM refrigerator A, the GM refrigerator A has an optimum operation speed depending on each temperature range, and the rotation speed decreases as the temperature becomes lower. The better the performance is,
It has been confirmed from many other experiments by the present inventors.

The gas pressure on the high pressure side of the JT refrigerator B also has an optimum gas pressure according to the inlet temperature on the high pressure side of the third heat exchanger 43, as is apparent from FIG. Although these optimum gas pressures also differ depending on the conditions of the JT refrigerator, these trends have been confirmed by many other experiments by the present inventors.

Therefore, in the present invention, as shown in FIG. 5, the optimum operation speed of the GM refrigerator A of the GM + JT refrigerator and the optimum high-pressure side pressure of the JT refrigerator B are previously measured at each temperature. Are stored in storage devices 60 and 61 such as a ROM or a RAM. In FIG. 5, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

When the cryogenic refrigerator of the present invention is actually operated, the temperature of the second cooling stage 9 of the GM refrigerator A is detected by the temperature sensor 64 by the third heat exchanger 4 of the JT refrigerator B.
The temperature of the helium gas flowing into the high pressure side 3 is measured by the temperature sensor 65.

Then, the measurement result of the temperature sensor 64 is fed back to the speed control device 68 including the storage device 60, and the rotation speed of the motor 5 of the GM refrigerator A is controlled so as to be the above-described optimum rotation speed. On the other hand, the temperature sensor 65
Pressure control device 69 with built-in storage device 61
And the opening degree of the JT valve 44 of the JT refrigerator B is controlled so that the above-described optimum pressure is obtained.

Note that the optimum operation speed of the GM refrigerator A and J
The optimum control of the high-pressure side gas pressure of the T refrigerator B is not limited to the above embodiment as long as its characteristics are grasped in advance. For example, an operator may directly control the optimum gas pressure. As described above, according to the first aspect, the performance of the entire cryogenic refrigerator can be maximized. Next, the second invention will be described.

As described above, in the fluid passage 14 inside the second displacer 11 of the GM refrigerator A, a magnetic material having a magnetic transition point at 10 to 15K, for example, ErNi or Er ₃ Co
The cold storage material 16 formed of a sphere such as the above is stored. Here, when the magnetic transition point is higher than 15K, the efficiency of the JT refrigerator B is deteriorated, and when it is lower than 10K, the efficiency of the GM refrigerator A is deteriorated.

Therefore, as shown in FIG.
Magnetic material having a magnetic transition point at K, for example, ErNi, Er
₃ Co, it is possible to improve the individual efficiency of GM and JT refrigerator by using at least one selected from among such Nd ₃ Ni, it is possible to improve the total performance of the GM + JT cryocooler . Next, a third invention will be described with reference to FIG. In the present invention, a part of the second cylinder 7 of the GM refrigerator A constitutes a second cooling stage 9 for pre-cooling the JT refrigerator B.

First, a conventional cooling stage is shown in FIG. 8 as a comparative example in order to make the third invention easier to understand. Conventionally, a copper block 10 is attached to the tip of the second cylinder 7.
0 is inserted and attached so as to cover the tip of the second cylinder 7 and fixed with solder. And the copper block 100
A copper pipe 101 is fixed to the outer periphery of the pipe by soldering, and helium gas of the JT refrigerator B is guided and cooled in the copper pipe 101. According to such a configuration, since the second cylinder 7 and the copper block 100 and the copper block 100 and the copper pipe 101 are respectively connected by solder, the heat resistance is large at each connection portion, and this heat The resistance creates a large temperature difference between the two sides,
This has contributed to a decrease in refrigeration capacity.

In the present invention, as shown in FIG. 7, the tip of a second cylinder 7 made of stainless steel, titanium, a titanium alloy or the like is made of a material having good heat conductivity such as copper, copper alloy, aluminum, or aluminum alloy. The block 80 is directly joined at a portion A surrounded by a circle in the figure. That is, the second
The portion near the head wall of the cylinder 7 is made of stainless steel or the like having poor heat conductivity, and the tip of the second cylinder 7 is made of a block made of copper or the like having good heat conductivity. The two-cylinder 7 and the block 80 are directly joined by electron beam welding, friction welding, or the like without using solder or the like. That is, dissimilar metal bonding is performed. And, in block 80, JT
A helium gas passage 81 for pre-cooling the helium gas of the refrigerator B is integrally formed. With this configuration, it is possible to greatly reduce the thermal resistance and greatly improve the refrigeration capacity.

FIG. 9 shows the configuration of the present invention shown in FIG.
A comparison characteristic between the heat transfer amount and the temperature difference with the conventional configuration shown in FIG. 8 as a comparative example is shown. It is apparent from this figure that the configuration of the present invention shown in FIG. 7 is effective.

The present invention is not limited to the embodiment described above. That is, although the Gifford McMahon cycle (GM refrigerator) is used as the regenerative refrigerator for precooling, another regenerative refrigerator such as a Stirling cycle may be used. In addition, various modifications can be made without departing from the scope of the present invention.

[0041]

As described above in detail, according to the present invention, it is possible to improve the refrigeration efficiency of a cryogenic refrigerator, and to obtain a cryogenic refrigerator with high energy efficiency and a method of operating the cryogenic refrigerator.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a cryogenic refrigerator as a premise of the present invention.

FIG. 2 is a diagram showing an example of a regenerative refrigerator incorporated in the cryogenic refrigerator shown in FIG.

FIG. 3 is a diagram showing the relationship between the amount of cold generated at 4.2K per gram of helium gas and helium gas flowing into the high pressure side of a third heat exchanger.

FIG. 4 is a characteristic diagram showing a result of measuring a refrigerating capacity at each temperature by changing an operation speed of the regenerative refrigerator according to the present invention.

FIG. 5 is a schematic configuration diagram showing a cryogenic refrigerator according to the present invention.

FIG. 6 is a characteristic diagram of a magnetic material having a magnetic transition point at 10 to 15 K according to the present invention.

FIG. 7 is a partial sectional view showing a cooling stage of the regenerative refrigerator according to the present invention.

8 is a partial sectional view showing a cooling stage of a conventional regenerative refrigerator shown as a comparative example of the one shown in FIG.

FIG. 9 is a characteristic diagram showing a relationship between a heat transfer amount and a temperature difference of the refrigerator having the configuration shown in FIGS. 7 and 8;

[Explanation of symbols]

 A GM refrigerator B JT refrigerator 3 cylinder 4 displacer 5 motor 6 first cylinder 7 second cylinder 8 first stage cooling stage 9 second stage cooling stage 10 first displacer 11 second displacer 15 cold storage material 16 cold storage material 44 joules・ Thomson expansion valve 68 Speed controller 69 Pressure controller 80 Block 81 Flow path

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-52467 (JP, A) JP-A-4-335959 (JP, A) JP-A-5-322343 (JP, A) 100235 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F25B 9/00 395 F25B 9/00

Claims (4)

(57) [Claims] 1. A cryogenic refrigerator in which compressed refrigerant gas is precooled in a cooling stage portion of a cylinder of a regenerative refrigerator and then expanded by Joule-Thomson to generate cold, wherein the cylinder comprises the cooling stage. A part is composed of a block with good heat conduction and heat, in which a flow path for allowing the refrigerant gas to flow and pre-cooling is integrally formed, and this block is integrally joined to the rest of the cylinder. A cryogenic refrigerator characterized by: 2. A cryogenic refrigerator in which compressed helium gas is pre-cooled by a regenerative refrigerator and then expanded by Joule-Thomson to generate cold. A cryogenic refrigerator comprising a magnetic material having a magnetic transition point within the temperature range as a cold storage material. 3. An operation speed for controlling an operation speed of the regenerative refrigerator in a cryogenic refrigerator in which compressed refrigerant gas is precooled by a regenerative refrigerator and then expanded by Joule-Thomson to generate cold. A cryogenic refrigerator comprising a control means and a pressure control means for controlling a pressure of the refrigerant gas. 4. A method of operating a cryogenic refrigerator in which compressed refrigerant gas is precooled by a regenerative refrigerator and then expanded by Joule-Thomson to generate cold, wherein the operating speed of the regenerative refrigerator is controlled by A method for operating a cryogenic refrigerator, comprising: controlling an operation speed at which a cooling temperature of a refrigerant gas is the lowest, and controlling the pressure of the refrigerant gas to a pressure at which the cooling gas has the highest efficiency.