JP2001248930A - Cryogenic refrigeration unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cryogenic refrigeration unit which is simple of structure and is capable of obtaining ultralow temperature. SOLUTION: A displacer is inserted into a cylinder, and an expansion chamber is demarcated at one end of the cylinder. A drive means reciprocates the displacer. A first gas passage leads to the expansion chamber. Cold accumulating material is filled in a first gas passage. The gas flowing in the first gas passage performs heat exchange with the cold accumulating material. A gas supply system supplies refrigerating gas into the expansion chamber through the first gas passage, and recovers refrigerant gas from the expansion chamber. The supply and recovery of the refrigerant gas are performed synchronously with the reciprocation of the displacer. A refrigerant gas container is coupled with the expansion chamber through the second gas passage having flow resistance. A third gas passage leads to a refrigerant gas container. A gas pressure reducing means reduces the pressure within the refrigerant container through the third gas passage.

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 particularly to a cryogenic refrigerator that generates heat by expansion of a refrigerant gas.

[0002]

2. Description of the Related Art There is known a refrigerator which obtains a cryogenic temperature by combining a Gifford McMahon (GM) refrigerator with a Joule Thomson (JT) circuit. A GM refrigerator pre-cools the helium gas flowing through the JT circuit. Helium gas cooled after passing through the JT valve is liquefied and accumulated in the refrigerant gas container. By reducing the pressure in the refrigerant gas container using a vacuum pump, an extremely low temperature of about 2K can be obtained.

[0003]

In a refrigerator in which a GM refrigerator and a JT circuit are combined, the structure is complicated because both must be thermally coupled.

[0004] It is an object of the present invention to provide a cryogenic refrigerator having a simpler structure and capable of obtaining a cryogenic temperature.

[0005]

According to one aspect of the present invention, a cylinder, a displacer inserted into the cylinder and defining an expansion chamber at one end of the cylinder;
Driving means for reciprocatingly driving the displacer in the axial direction of the cylinder, a first gas flow path communicating with the expansion chamber, and a first gas flow path filled in the first gas flow path. A cold storage material for exchanging heat with a gas flowing through the inside;
A gas supply system for supplying the refrigerant gas into the expansion chamber and recovering the refrigerant gas from the expansion chamber in synchronization with the reciprocating motion of the displacer; A refrigerant gas container coupled through a second gas flow path having flow resistance, and a third refrigerant gas container connected to the refrigerant gas container.
And a cryogenic refrigerator having gas pressure reducing means for reducing the pressure in the refrigerant gas container via the third gas flow path.

Heat is absorbed in the expansion chamber, and the cooled refrigerant gas in the expansion chamber leaks into the refrigerant gas container through the second gas flow path. By reducing the pressure in the refrigerant gas container, heat is absorbed in the refrigerant gas container, and an extremely low temperature can be obtained.

[0007]

FIG. 1 is a schematic sectional view of a cryogenic refrigerator according to an embodiment of the present invention. The cryogenic refrigerator according to the embodiment includes a GM refrigerator 1, a refrigerant gas container 50, and a gas exhaust system 80.

The configuration of the GM refrigerator 1 will be described. G
The M refrigerator 1 has a two-stage configuration including a first-stage cylinder 10a and a second-stage cylinder 10b. The high temperature end of the second stage cylinder 10b is connected to the low temperature end of the first stage cylinder 10a. The second stage cylinder 10b is
It has a smaller diameter than the stage cylinder 10a. A first-stage displacer 11a and a second-stage displacer 11b are inserted into the first-stage cylinder 10a and the second-stage cylinder 10b, respectively. The first-stage displacer 11a and the second-stage displacer 11b are connected to each other, and are driven by the drive mechanism 3 to reciprocate in the axial direction of the cylinder.

The gas passages 1 are provided inside the first-stage displacer 11a and the second-stage displacer 11b, respectively.
2a and 12b are formed. The gas flow paths 12a and 12b are filled with cold storage materials 13a and 13b, respectively.

A cavity 14 is defined at a high temperature end in the first stage cylinder 10a, and a first stage expansion chamber 15a is defined at a low temperature end. At the low temperature end in the second stage cylinder 10b, the second
A stage expansion chamber 15b is defined. First stage expansion chamber 1
A first cooling stage 18 is thermally coupled around 5a. A second cooling stage 19 is disposed around the second expansion chamber 15b. The second cooling stage 19 is thermally connected to the second expansion chamber.

A plurality of gas flow paths L1 to L4 are provided in the first stage displacer 11a and the second stage displacer 11b. The gas flow path L1 connects the cavity 14 and the gas flow path 12a, the gas flow path L2 connects the gas flow path 12a and the first-stage expansion chamber 15a, and the gas flow path L3 is connected to the first-stage expansion chamber 15a. The gas flow path L4 connects the gas flow path 12b and the second-stage expansion chamber 15b.

A cavity 14 on the high temperature end side of the first stage cylinder 10a is connected to the refrigerant gas supply system 5. The refrigerant gas supply system 5 includes a gas compressor 6, valves 7, 8, and a gas flow path 9. The valves 7 and 8 are mounted on the exhaust port side and the intake port side of the gas compressor 6, respectively. When the valve 7 is opened and the valve 8 is closed, refrigerant gas (generally helium gas) is supplied from the gas compressor 6 into the cavity 14 through the valve 7 and the gas passage 9. When the valve 7 is closed and the valve 8 is opened, the refrigerant gas in the cavity 14 is collected in the gas compressor 6 through the gas passage 9 and the valve 8.

The opening and closing of the valves 7 and 8 and the reciprocating drive of the displacers 11a and 11b are performed in synchronization with a predetermined phase difference, so that the first stage expansion chamber 15a and the second stage
Endothermic occurs in the stage expansion chamber 15b.

Next, the refrigerant gas container 50 and the gas exhaust system 8
0 will be described. A refrigerant gas container 50 is attached to the low temperature end of the second stage cylinder 10b. The space in the refrigerant gas container 50 communicates with the second-stage expansion chamber 15b via the gas flow path 51. A gas flow channel 52 provided on the wall of the refrigerant gas container 50 communicates the inside and outside of the container.

The gas exhaust system 80 includes a gas flow path 81, a pump 82, and a gas flow path 83. The gas passage 81 connects the intake port of the pump 82 and the gas passage 52. Further, the gas passage 81 is provided in the second cooling stage 19.
And is thermally coupled to the first cooling stage 18.
The refrigerant gas flowing in the gas passage 81 and the first-stage expansion chamber 1
Heat exchange is performed between the refrigerant gas in the expansion chamber 5a and the second stage expansion chamber 15b. The gas passage 83 connects an exhaust port of the pump 82 and an intake port of the gas compressor 6.

The pump 82 reduces the pressure in the refrigerant gas container 50 through the gas flow paths 52 and 81. Refrigerant gas container 5
The refrigerant gas exhausted from the inside is returned to the gas supply system 5 through the gas passage 83.

FIG. 2 is a detailed sectional view of the refrigerant gas container 50. The partition 55, the cylindrical side wall 56, and the lid 57
A cavity for storing the refrigerant gas is defined. Partition wall 55 and lid 5
7 is formed of a material having high thermal conductivity, for example, copper. The side wall 56 is formed of a material having low thermal conductivity, for example, stainless steel. These parts are mutually silver brazed. The partition wall 55 blocks the low temperature end of the second stage cylinder 10b. In the lid 57, the gas flow path 52 also shown in FIG. 1 is formed.

A fin 5 made of copper is provided on the inner surface of the lid 57.
9 is attached. The fins 59 increase the heat exchange efficiency between the refrigerant gas in the refrigerant gas container 50 and the lid 57. The lid 57 functions as a third cooling stage.

A through hole 60 is formed in the partition wall 55. The through hole 60 allows the second-stage expansion chamber 15b to communicate with the cavity in the refrigerant gas container 50. The inner peripheral surface of the through hole 60 has a tapered shape in which the refrigerant gas container 50 side is narrowed. A plug 58 having a tapered outer peripheral surface aligned with the inner peripheral surface of the through hole 60 is inserted into the through hole 60 from the second-stage expansion chamber 15b side. The stopper 58 is formed of, for example, stainless steel. The diameter of the narrow end of the plug 58 is 6 mm, the length of the plug is 20 mm, and the inclination of the tapered surface is 1/50. The tip of the stopper 58 projects into the refrigerant gas container 50.

At the tip of the stopper 58, a disc-shaped stopper 61 is provided.
Are fixed by bolts 62. The stopper 61 prevents the stopper 58 from coming off. The stopper 58 is provided with a play so that the stopper 58 can slightly move toward the second-stage expansion chamber 15b. A groove 63 in the radial direction is formed on the surface of the stopper 61 on the partition 55 side.

When the pressure in the second stage expansion chamber 15 b is higher than the pressure in the refrigerant gas container 50, the outer peripheral surface of the plug 58 comes into close contact with the inner peripheral surface of the through hole 60. In this state, the stopper 58
The refrigerant gas leaks from the second-stage expansion chamber 15b into the refrigerant gas container 50 through a slight gap between the outer peripheral surface of the second hole and the inner peripheral surface of the through hole 60. The inside of the refrigerant gas container 50 is set to the atmospheric pressure,
Helium gas pressure (gauge pressure) in the second stage expansion chamber 15b
To 1 MPa (about 10 kgf / cm ² ), 1.5 MPa
(About 15 kgf / cm ² ) and 2 MPa (about 20 kg
f / cm ² ), the leakage amount of helium gas at room temperature is 76 sccm and 155.4 sccc, respectively.
m, and 307 sccm.

When the pressure in the refrigerant gas container 50 is higher than the pressure in the second-stage expansion chamber 15b, the stopper 58 moves toward the second-stage expansion chamber 15b, and the stopper 61 contacts the partition wall 55. Since the gap between the plug 58 and the through hole 60 is widened,
The flow resistance of the gas flow path 51 is reduced. Refrigerant gas container 5
The refrigerant gas in the chamber 0 returns to the second-stage expansion chamber 15b through the groove 63 and the gap between the plug 58 and the through hole 60. Therefore, when the pressure in the refrigerant gas container 50 rises for some reason, the refrigerant gas returns to the GM refrigerator 1 through the gas flow path 51. In this way, an increase in the pressure in the refrigerant gas container 50 is prevented.

The cryogenic refrigerator according to the above embodiment has a simple structure as compared with the system in which the refrigerant gas flowing through the JT circuit is precooled by the GM refrigerator.

Next, the operation of the cryogenic refrigerator according to the embodiment will be described. When the GM refrigerator 1 shown in FIG. 1 is operated, heat is absorbed in the first-stage expansion chamber 15a and the second-stage expansion chamber 15b. In a normal operation state, the pressure in the second-stage expansion chamber 15b (0.6 to 2 MPa in gauge pressure) is higher than the pressure in the refrigerant gas container 50. Therefore, the cooled refrigerant gas in the second-stage expansion chamber 15 b leaks into the refrigerant gas container 50.

A pump 82 reduces the pressure inside the refrigerant gas container 50. The pressure in the refrigerant gas container 50 decreases, and the temperature in the refrigerant gas container 50 decreases. The ultimate temperature can be controlled by adjusting the flow resistance of the gas flow path 51 and the suction flow rate by the pump 82. In the experiment of the inventor, the temperature in the second expansion chamber 15b when the refrigerating capacity was 50 mW was 2.4K, and the temperature in the refrigerant gas container 50 was 1.88K. At this time, the suction flow rate of the pump 82 was 104 liter / h. ⁴ He 1.88K of
Is about 10 Torr. Therefore, it is considered that the pressure in the refrigerant gas container 50 is about 10 Torr.

The refrigerant gas exhausted from the refrigerant gas container 50 and flowing through the gas passage 81 is supplied to the second cooling stage 1.
9 and the first cooling stage 18 are cooled. For this reason,
The refrigeration efficiency can be improved. In addition, even when these thermal couplings are not performed, extremely low temperatures can be obtained. In this case, the refrigeration capacity is slightly sacrificed, but the structure is simplified.

From the second stage expansion chamber 15b to the refrigerant gas container 5
If the amount of the refrigerant gas leaking into zero increases, the refrigeration capacity of the GM refrigerator decreases. For this reason, it is preferable that the amount of leakage be 1% or less of the average flow rate of the refrigerant gas flowing through the gas flow path in the GM refrigerator.

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

[0029]

As described above, according to the present invention,
Using a cryogenic refrigerator having a relatively simple configuration, it is possible to obtain a cryogenic temperature of the order of 2K.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a cryogenic refrigerator according to an embodiment of the present invention.

FIG. 2 is a sectional view of a refrigerant gas container of the cryogenic refrigerator according to the embodiment.

[Explanation of symbols]

 Reference Signs List 1 GM refrigerator 3 drive mechanism 5 gas supply system 6 gas compressor 7, 8 valve 9 gas flow path 10a, 10b cylinder 11a, 11b displacer 12a, 12b gas flow path 13a, 13b cold storage material 15a, 15b expansion chamber 18, 19 Cooling stage 50 Refrigerant gas container 51, 52 Gas flow path 57 Cover 59 Fin 80 Gas exhaust system 81, 83 Gas flow path 82 Pump

Claims (5)

[Claims] A cylinder; a displacer inserted into the cylinder to define an expansion chamber at one end of the cylinder; a driving means for reciprocatingly driving the displacer in an axial direction of the cylinder; A first gas flow path communicating with the chamber; a cold storage material filled in the first gas flow path and performing heat exchange with gas flowing in the first gas flow path; A gas supply system for supplying refrigerant gas to the expansion chamber through the passage and recovering the refrigerant gas from the expansion chamber in synchronization with the reciprocating motion of the displacer; A refrigerant gas container coupled via a second gas flow path having: a third gas flow path communicating with the refrigerant gas container; and a refrigerant gas container through the third gas flow path. Cryogenic refrigeration having gas decompression means for depressurizing . 2. The second gas flow path penetrates a partition wall between the expansion chamber and the refrigerant gas container,
A through hole having a tapered inner peripheral surface having a narrower refrigerant gas container side; and a tapered outer peripheral surface matching the inner peripheral surface of the through hole, being inserted into the through hole from the expansion chamber side. A stopper projecting into the refrigerant gas container, the stopper defining a passage for the refrigerant gas between the outer peripheral surface and the inner peripheral surface of the through hole; and a protrusion of the stopper into the refrigerant gas container. The cryogenic refrigerator according to claim 1, further comprising: a stopper attached to the refrigerator and configured to prevent the stopper from coming off. 3. The stopper is attached so that the stopper can move from the state in which the stopper is in close contact with the inner peripheral surface of the through hole toward the expansion chamber by a certain distance, and the stopper restricts the movement of the stopper. 3. The cryogenic refrigerator according to claim 2, wherein a gas passage is defined such that the gas flows from the refrigerant gas container into the expansion chamber when the refrigerant gas is in the state. 4. The cryogenic refrigerator according to claim 1, further comprising a fourth gas flow path for returning the refrigerant gas exhausted by the gas pressure reducing means to the gas supply system. 5. The third gas flow path is thermally coupled to the expansion chamber, and heat exchange occurs between the refrigerant gas flowing in the third gas flow path and the refrigerant gas in the expansion chamber. The cryogenic refrigerator according to any one of claims 1 to 4, which is performed.