JPH0452468A - Cryogenic refrigerator - Google Patents

Abstract

PURPOSE:To contrive a higher refrigeration capacity without any complication of construction by providing a main body of a cryogenic refrigerator of the single-stage expansion type and a cooling means for pre-cooling a heat- exchanging stage. CONSTITUTION:A main body 51 of a cryogenic refrigerator is composed of a single-stage expansion type GM refrigerator. When a pre-cooling refrigerator 52 is operated, a heat-transmitting block 86 is cooled to about 40K, and a heat- transmitting block 87 is cooled to about 8K. When a displacer 62 is moved toward the top dead center, a high-pressure helium gas is cooled by a cold- accumulating material 70 in a fluid passage 74, before flowing to a heat- exchanging stage 72. The stage 72 is kept at about 45K, so that the helium gas flowing out of a passage has a temperature of about 45K. A heat-exchanging stage 73 is kept at about 12K, so that the helium gas passed through a fluid passage 78 has a temperature of about 12K. The helium gas is then cooled to about 4.2K by a cold-accumulating material 81 in a fluid passage 76, before flowing into an expansion chamber 90. When a high-pressure valve 66 is closed and a low-pressure valve 67 is opened, the helium gas is expanded to produce cold, whereby a cooling stage 83 is cooled to a low temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a cryogenic refrigerator whose main refrigerator is a regenerator refrigerator.

(Prior Art) There are various types of cryogenic refrigerators. Among these are regenerator cryogenic refrigerators, such as the Gifford-McMahon refrigerator. This regenerator type cryogenic refrigerator, for example, a two-stage expansion type Gift-McMahon type refrigerator (hereinafter abbreviated as GM refrigerator), is constructed as shown in FIG.

That is, this refrigerator is broadly composed of a cold head 1 and a refrigerant gas introduction and discharge system 2.

The cold head 1 includes a closed cylinder 11, a piston housed in the cylinder 11 so as to be able to reciprocate, that is, a displacer 12 made of a heat insulating material, and a motor that provides the power necessary for the reciprocating motion to the displacer 12. It consists of 13.

The cylinder 11 includes a large-diameter first cylinder 14 and a first cylinder 14 having a large diameter.
It is composed of a small diameter second cylinder 15 coaxially connected to the cylinder 14. The first cylinder 14 and the second cylinder
The cylinder 15 is usually made of a thin stainless steel plate or the like. Then, the first cylinder 14 and the second cylinder 1
A first cooling stage 16 is configured by the boundary wall portion with 5,
Further, the tip wall portion of the second cylinder 15 constitutes a second cooling stage 17 having a lower temperature than the first cooling stage 16.

The displacer 12 includes a first displacer 18 that reciprocates within the first cylinder 14 and a second displacer 19 that reciprocates within the second cylinder 15.

The first displacer 18 and the second displacer 19 are coupled in the axial direction by a coupling mechanism 20.

Inside the first displacer 18, a fluid passage 21 for forming a regenerator is formed in the axial direction, and a regenerator material 22 formed of copper mesh or the like is accommodated in this fluid passage 21. There is.

Inside the second displacer 19, a fluid passage 23 is formed in the axial direction to constitute a final stage regenerator.
In this fluid passage 23, there is a regenerator material 24 made of spherical lead.
is accommodated.

Seal devices 25 are provided between the outer circumferential surface of the first displacer 18 and the inner circumferential surface of the first cylinder 14 and between the outer circumferential surface of the second displacer 19 and the inner circumferential surface of the second cylinder 15, respectively. .26 is installed.

The upper end of the first displacer 18 in the figure is connected to a connecting rod 31.
, is connected to the rotating shaft of the motor 13 via a Scotch choke or crankshaft 32.

Therefore, when the motor 13 rotates, the displacer 12 reciprocates in the direction shown by the solid arrow 33 in the figure in synchronization with this rotation.

A refrigerant gas inlet 34 is provided in the upper part of the side wall of the first cylinder 14.
and a discharge port 35 are provided, and these inlet port 34 and discharge port 35 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 11, and has a discharge port 35 connected to the inlet port 34 via a low pressure valve 36, a compressor 37, and a high pressure valve 38. ing. That is, the refrigerant gas introduction and discharge system 2 compresses helium gas at a low pressure (approximately 5 atm) to a high pressure (approximately 18 aLs) using the compressor 37 and sends it into the cylinder 11. The low-pressure valve 36 and the high-pressure valve 38 are controlled to open and close in relation to the reciprocating movement of the displacer 12, as will be described later.

The operation of this refrigerator is briefly explained below.

In this refrigerator, the parts where cold is generated, that is, the parts that serve as cooling surfaces are the first cooling stage 16 and the second cooling stage 17.

When the motor 13 starts rotating, the displacer 12 reciprocates between the bottom dead center and the top dead center. Displacer 1
2 is at bottom dead center, the high pressure valve 38 opens and high pressure helium gas flows into the cold head 1. Next, the displacer 12 moves to top dead center. As mentioned above, the first
Between the outer circumferential surface of the displacer 18 and the inner circumferential surface of the first cylinder 14 and between the outer circumferential surface of the second displacer 19 and the second
A sealing device 2 is provided between the inner peripheral surface of the cylinder 15 and the inner circumferential surface of the cylinder 15.
5.26 is installed. Therefore, when the displacer 12 moves toward the top dead center, the high-pressure helium gas flows through the fluid passage 21 formed in the first displacer 18 and the second displacer 18.
The first expansion chamber 39 formed between the first displacer 18 and the second displacer 19 and the second displacer 19 pass through the fluid passage 23 formed in the displacer 19 . It flows into a two-stage expansion chamber 40 formed between the cylinder 15 and the tip wall thereof. Along with this flow, the high-pressure helium gas is cooled by the cold storage material 22, 24, and eventually the high-pressure helium gas that has flowed into the first stage expansion chamber 39 is
The high pressure helium gas flowing into the two-stage expansion chamber 40 is cooled to a level of 15.

Here, high pressure valve 38 is closed and low pressure valve 36 is opened.

When the low-pressure valve 36 opens in this way, the high-pressure helium gas in the first-stage expansion chamber 39 and the second-stage expansion chamber 40 expands to generate cold. Due to this cold, the first cooling stage 16
The second cooling stage 17 is further cooled to a lower temperature. Then, when the displacer 12 moves to the bottom dead center again, the helium gas in the first-stage expansion chamber 39 and the second-stage expansion chamber 40 is eliminated. The expanded helium gas passes through the fluid passageway 23.21 while passing through the regenerator material 24.2.
2 is cooled down to room temperature and discharged. Thereafter, the above-described cycle is repeated to perform the refrigeration operation.

However, the conventional cryogenic refrigerator configured as described above has the following problems.

That is, as shown in FIG. 6, the volumetric specific heat of the lead filled in the second displacer 19 as the cold storage material 24 decreases as the temperature decreases, and the heat capacity decreases.

Therefore, the amount of heat exchanged with helium gas is significantly reduced. On the other hand, helium gas has a property that its volumetric specific heat increases as the temperature decreases. Due to these properties, it is difficult to lower the temperature of the second cooling stage 17 below 8 in the conventional regenerator type cryogenic refrigerator.

Therefore, in order to lower the lowest temperature reached by the second cooling stage 17, a refrigerator using GdRh or GdErRh, which has a higher specific heat than lead at low temperatures as the regenerator material 24, and three or more stages of regenerators and displacers are installed. A refrigerator is being considered. However, even with such improved refrigerators, it is difficult to exhibit a large refrigerating capacity, especially near the liquid helium temperature of 4.2.

Further, considering the characteristics of adiabatic expansion cooling, it is advisable to operate at a low pressure level in order to obtain a large refrigerating capacity in a low temperature range of 10 to 10 degrees or less. However, when conventional refrigerators are operated at low pressure, the upper cooling stage (
The pressure level also becomes low in the 1st cooling stage in a 2-stage cooling GM refrigerator, and in the 1.2 cooling stage in a 3-stage GM refrigerator. On the upper stage side, that is, in the region where the temperature exceeds IOK, on the contrary, a higher pressure is preferable in order to improve the refrigerating capacity. Therefore, as mentioned above, when the pressure on the upper stage side is also lowered, the refrigerating capacity on the upper stage side decreases, leading to a rise in temperature on the upper stage side, which causes the problem of lowering the refrigerating capacity on the low temperature side.

(Problems to be Solved by the Invention) As mentioned above, with conventional regenerator cryogenic refrigerators, it is not possible to obtain high refrigerating capacity, especially near the industrially useful liquid helium temperature (4°2K). There was a problem.

Therefore, the present invention provides 4.2 without complicating the structure.
The purpose of the present invention is to provide a cryogenic refrigerator that can significantly improve the refrigerating capacity in the vicinity of the refrigerator.

[Configuration of the Invention (Means for Solving the Problem) In order to achieve the above object, the cryogenic refrigerator according to the present invention generates cold by passing compressed helium gas through a regenerator and then expanding it. a one-stage expansion type cryogenic refrigerator body, at least one heat exchange stage inserted between the room temperature side and the lowest temperature side of the regenerator, and a cooling means for precooling the heat exchange stage. We are prepared.

(Function) Helium gas passing through the regenerator is cooled to a lower temperature than when no heat exchange stage is provided. Therefore, by selecting the temperature of the heat exchange stage, it is possible to select the operating conditions (pressure level, rotation speed, etc.) most suitable for generating cold in the low-temperature section, which improves the refrigerating capacity in the vicinity of 4.2. becomes possible.

(Example) Examples will be described below with reference to the drawings.

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

This cryogenic refrigerator is broadly divided into two parts: the cryogenic refrigerator main body 5
1, and a refrigerator 52 for pre-cooling. A portion of the cryogenic refrigerator main body 51 and the refrigerator 52 located below the boundary wall 53 in the figure is disposed within a heat insulating layer.

The cryogenic refrigerator main body 51 is configured as follows. In other words, the cylinder 6 is made of a thin stainless steel plate or the like.
1, this cylinder 6] - a displacer 62 housed in a reciprocating manner, a motor 64 and a crank coupling mechanism 65 for reciprocating this displacer 62 in the direction shown by the solid line arrow 63 in the figure, and the cylinder 61. It is comprised of a high pressure valve 66, a low pressure valve 67, and a compressor 68 for introducing and discharging helium gas between them.

The displacer 62 is made up of cylindrical heat insulating blocks 69, 70, 71 and cylindrical heat exchange stages 72, 73 made of a good heat conductive material, which are alternately and coaxially connected. There is. Each insulation block 69, 70.7
1 are formed with axially extending fluid passages 74, 75, 76.

Each heat exchange stage 72,73 also includes fluid passages 74.
75 and 76 are connected in series to form fluid passages 77 and 78 that connect the upper end side and the lower end side of the displacer 62. A cold storage material 79 made of copper mesh or the like is housed in the fluid passage 74, and a cold storage material 80 made of lead balls or the like is housed in the fluid passage 75.
Further, inside the fluid passage 76, a cool storage material 81 formed of Er, Ni balls, etc. having a large specific heat near 4.2 is accommodated. Note that 82 in the figure indicates a sealing mechanism that seals between the displacer 62 and the cylinder 61.

As can be seen from the above configuration, the cryogenic refrigerator main body 51 is composed of a one-stage expansion type GM refrigerator. Therefore, in this cryogenic refrigerator main body 51, an expansion chamber 90 is formed between the tip wall 83 of the cylinder 61 and the displacer 62, and the tip wall 83 serves as a cooling stage.

On the other hand, the precooling refrigerator 52 is composed of a two-stage expansion type GM refrigerator shown in FIG. Therefore, in this figure, the same parts as in FIG. 5 are indicated by the same reference numerals. One end of a heat transfer member 84.85 is thermally connected to the first cooling stage 16 and second cooling stage 17 of the refrigerator 52, respectively, and the other end of the heat transfer member 84.85 is connected to the first cooling stage 16 and the second cooling stage 17 of the refrigerator 52, respectively. The cylinder 61 is thermally connected to heat transfer blocks 86 and 87 which are provided in close thermal contact with the outer peripheral surface of the cylinder 61.

The heat transfer block 86 is provided to be located just outside the heat exchange stage 72 when the displacer 62 is at the bottom dead center, and the heat transfer block 87 is provided to be located just outside the heat exchange stage 72 when the displacer 62 is at the bottom dead center. , heat exchange stage 7
It is provided so as to be located outside of 3.

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

As mentioned above, the cryogenic refrigerator main body 51 is a one-stage expansion type GM.
Consists of a refrigerator. Therefore, the basic operation is the same as that of the refrigerator shown in FIG. Further, the precooling refrigerator 52 operates in the same manner as the refrigerator shown in FIG.

When the precooling refrigerator 52 is operated, the heat transfer block 86
is cooled to about 40°C, and the heat transfer block 87 is cooled to about 8°C. Assuming that the displacer 62 is now at the bottom dead center, the heat exchange stage 72 is cooled to about 45 degrees via the heat transfer block 86, and the heat exchange stage 73 is cooled to about 12 degrees via the heat transfer block 87. be done.

When the displacer 62 is at the bottom dead center, the high pressure valve 66 opens and high pressure helium gas flows into the cylinder 61. Next, the displacer 62 moves to top dead center. When the displacer 62 moves toward the top dead center, the high-pressure helium gas is cooled by the cold storage material 79 filled in the fluid passage 74, and then flows into the fluid passage 77 formed in the heat exchange stage 72. Since the heat exchange stage 72 is cooled to about 45°C as described above, the helium gas exiting the fluid passage 77 has a temperature of about 45°C.

This helium gas is then further cooled to a low temperature by the cold storage material 80 filled in the fluid passage 75, and then flows into the fluid passage 78 formed in the heat exchange stage 73. As described above, the heat exchange stage 73 is cooled to about 12°C, so the helium gas exiting the fluid passage 78 is about 12°C.
The temperature will be around 2. This helium gas is then cooled to a temperature of 4.2 mm by the cool storage material 81 filled in the fluid passage 76 and then flows into the expansion chamber 90 .

Here, the high pressure valve 66 is closed and the low pressure valve 67 is opened.

When the low pressure valve 67 opens in this way, the high pressure helium gas in the expansion chamber 90 expands and generates cold. This cooling further cools the cooling stage 83 to a lower temperature. Then, when the displacer 62 moves to the bottom dead center again, the helium gas in the expansion chamber 90 is removed through the opposite route. The expanded helium gas flows through fluid passages 76, 75.
While passing through 74, the cold storage material 81, 80, 79 is cooled and discharged at room temperature. Thereafter, the above-described cycle is repeated to perform a refrigeration operation.

As can be seen from the above operation, in this cryogenic refrigerator, high-pressure helium gas flowing through a so-called regenerator is cooled to a desired temperature by heat exchange stages 72 and 73 at intermediate positions in the regenerator.

Therefore, the temperature of the high-pressure helium gas flowing into the expansion chamber 90 can be lowered than in the case where the heat exchange stages 72 and 73 are not provided.

As mentioned above, in the region below 10, the lower the helium gas pressure flowing into the expansion chamber 90, the higher the refrigerating capacity can be. However, if the pressure is lowered, the refrigerating capacity on the upper stage side is lowered, so the temperature of the helium gas flowing into the expansion chamber 90 increases. By arranging the heat exchange stages 72 and 73 in the middle as in this embodiment, the temperature of the helium gas flowing into the expansion chamber 90 can be controlled, which ultimately makes it possible to reduce the pressure of the helium gas. .

Therefore, it is possible to freely select a low pressure (for example, high pressure 10 atm, low pressure 2 ata) that sufficiently generates cold in the vicinity of 4.2, and it is possible to improve the refrigeration capacity in the vicinity of 4.2. .

FIG. 2 shows an example in which the cryogenic refrigerator according to the present invention is actually incorporated into a cryostat.

The cryostat 100 has an inner tank 101 and an outer tank 102.
, a vacuum insulation layer 103 formed between the inner and outer tanks, and a radiant heat shield plate 104 disposed within this vacuum insulation layer 103.
, 105. The inner tank 101 houses, for example, a superconducting coil 106 and liquid helium 107 for cooling it.

In this example, the cooling stage 83 of the cryogenic refrigerator main body 51
The helium gas generated by the evaporation of liquid helium is recondensed, and the radiant heat shield plates 104 and 105 are cooled by the first cooling stage 16 and second cooling stage 17 in the precooling refrigerator 52. There is. Heat transfer blocks 86 and 87 fixed to the outer peripheral surface of the cylinder 61 are thermally connected to the radiant heat shield plates 104 and 105.

With this configuration, the helium gas can be efficiently recondensed in the cooling stage 83, and the refrigerator 52 for precooling can also be used for cooling the radiant heat shield plate, so the overall configuration can be simplified. I can do it.

Note that the present invention is not limited to the embodiments described above. That is, in the embodiment described above, the regenerator material and the heat exchange stage are incorporated in the displacer, but as shown in FIG. Cold storage material 79°80.81 and heat exchange stage 72.7 on the outside
3 may be arranged and the displacer 61a may be made independent. With such a configuration, the cooling stages 72 and 73 can be cooled without using a gap, so efficiency can be improved. Also, the fourth
As shown in the figure, the cylinder 61b accommodating the displacer 62a and the cylinder 61c accommodating the cold storage material 79, 80, 81 and the heat exchange stage 72, 73 may be made independent and connected in series.

In addition, in the above embodiment, a GM refrigerator is used for pre-cooling, but instead of using a refrigerator, a refrigerant such as liquid nitrogen or liquid oxygen is used to cool the heat transfer block, that is, the heat exchange stage. It's okay.

Further, in the above embodiment, two heat exchange stages are provided, but one or three or more stages may be provided.

Further, in the above-described embodiment, the cryogenic refrigerator main body is constructed of a GM Psail refrigerator, but it may be constructed of a cycle using another regenerator, such as a Stirling cycle or a Vilmya cycle.

[Effects of the Invention] As described above, according to the present invention, since the precooling system cools between the normal temperature side and the low temperature side of the heat storage device, operating conditions such as pressure level can be freely selected. As a result, the refrigerating capacity in the vicinity of 4.2 can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a cryogenic refrigerator according to an embodiment of the present invention, FIG. 2 is a diagram showing an example in which the cryogenic refrigerator is incorporated into a taliostat, and FIGS. 3 and 4 are FIG. 5 is a diagram for explaining the configuration of a conventional regenerator refrigerator, and FIG. 6 is a diagram for explaining problems with the conventional refrigerator. 51...Cryogenic refrigerator main body, 52...Freezer for precooling, 61, 61a, 61b, 61cm...Cylinder, 6
2.62a... Displacer, 72.73... Heat exchange stage, 79, 80.81... Cold storage material, 83.
... Cooling stage, 86.87 ... Heat transfer block, 9
0...Inflation chamber. Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (1)

[Claims] A single-stage expansion type cryogenic refrigerator body that generates cold by passing compressed helium gas through a regenerator and then expanding it to generate cold;
A cryogenic refrigerator comprising at least one heat exchange stage inserted between the room temperature side and the lowest temperature side of the regenerator, and a cooling means for precooling the heat exchange stage. .