JPH0136029B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a helium refrigerator, and more specifically, to a helium refrigerator using a regenerative heat exchanger such as a Gifford-McMahon cycle refrigerator or a Stirling cycle refrigerator. It is.

Fig. 1 shows an example of the structure of a conventional Gifford-McMahon refrigerator (hereinafter referred to as a GM refrigerator). A first displacer 2 having the shape of ) is connected to the first piston rod 4. An O-ring 5 is inserted between the sliding portion of the first cylinder 1 and the first piston rod 4. A first regenerator 6 made of copper mesh or the like is provided inside the first displacer 2, and operating gas is provided at both ends of the first displacer 2 that houses the first regenerator 6. Communication holes 6a and 6b are formed so that the first cylinder 1
A first expansion chamber 7 is formed between the first displacer 2 and the bottom of the first displacer 2 . A second cylinder 8 provided in parallel with the first cylinder 1 accommodates a second displacer 9 that operates within the second cylinder with a constant stroke, and the second displacer 9 and the drive unit ( A second piston rod 10 (not shown) passes through the second cylinder 8. An O-ring 11 is inserted between the sliding portion of the second cylinder 8 and the second piston rod 10. A second expansion chamber 12 is formed between the bottom surface of the second cylinder 8 and the second displacer 9. A second regenerator 14 made of fine particles of lead is contained in a third cylinder 13, which is installed with an opening at the lower end of the first cylinder 1 and whose other end is sealed with a flange.
is formed. Further, the working gas is supplied to the second chamber by penetrating the lower end of the third cylinder 13 and the second expansion chamber 12.
The communication pipe 1 for moving the regenerator 14 through the regenerator 14 of
5 is provided. A high-pressure shutoff valve 16 that cuts off a flow path connected from the upper end flange of the first cylinder 1 to the discharge side of a helium compressor (not shown) via piping, and similarly connected to the suction side of the helium compressor. A low pressure shutoff valve 17 is provided to cut off the flow path.

In the G-M refrigerator having such a configuration, the first displacer 2 and the second displacer 9 are synchronously reciprocated via the drive unit with a constant stroke and rotation speed, Furthermore, by alternately switching the high-pressure shut-off valve 16 and the low-pressure shut-off valve 17 during one cycle of the reciprocating motion of these displacers 2 and 9, the operating gas is expanded adiabatically to generate the required cooling. . That is, first, with the first and second displacers 2 and 9 at the lowest ends of the first and second cylinders 1 and 8, the high pressure shutoff valve 16 is opened and the low pressure shutoff valve 17 is closed, and then the displacer is closed. High pressure helium gas is sucked in this state until the sensors 2 and 9 are near the uppermost position. At this time, the inflowing helium gas cools down the regenerators 6 and 14, and then closes the high-pressure shutoff valve 16 and opens the low-pressure shutoff valve 17. At this time, the high-pressure helium gas in the first expansion chamber 7 and the second expansion chamber 12 expands itself adiabatically (Simon expansion) and becomes low temperature. In this state, when the displacers 2 and 9 are pushed down to the lowest ends of the cylinders 1 and 8, respectively, the low-temperature helium gas in the expansion chambers 7 and 12 is
It flows upstream within the second regenerator 14 and the first regenerator 6, during which cold is released into the regenerator material to reach approximately room temperature, and reaches the suction side of the helium compressor. When the displacers 2 and 9 reach the bottom surfaces of their respective cylinders 1 and 8, the low pressure shutoff valve 17 is closed to complete one cycle. By continuously repeating the above cycle, through the walls of the expansion chambers 7 and 12,
Cold can be extracted and cooled to the desired temperature of the object to be cooled.

However, the conventional G-M configured as described above
In refrigerators, thin fibers or fine particles of metal such as copper alloy or lead are usually used as a cold storage material.

In general, the specific heat of metals gradually decreases as the temperature decreases, and the specific heat of most metals becomes zero below 10K. For this reason, the second regenerator 14 hardly functions in the extremely low temperature range, and in the region below 15K, the COP of the refrigerator drops significantly, and there is a limit to the low temperature that it can reach.

As a measure to improve the above-mentioned drawbacks of the conventional methods, a method using helium gas as a regenerator has been proposed, but this invention is a method in which helium gas-filled tubes are installed in the regenerator section that operates in an extremely low temperature range. death,
The purpose of this invention is to provide a helium refrigerator that has a structure that allows the amount of helium gas to be easily controlled from the outside, improves the performance of the low-temperature regenerator, and improves the COP in the extremely low temperature range.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, a cold storage gas filled tube 18 in which thin tubes made of stainless steel or the like are formed in multiple layers in a spiral shape is housed in a second cold storage device 14.
4. A refrigerant gas introduction pipe 19 is provided which penetrates the wall of the third cylinder 13 from above and connects to the high temperature end of the cold storage gas filling pipe 18. Reference numeral 20 denotes a control valve mechanism whose primary side is connected to a helium gas supply system (not shown) and is provided so that helium gas at a constant pressure can be supplied to the cold storage gas filling pipe 18. This control valve mechanism 20 is operated by the cold storage gas filled pipe 1 due to a rise in temperature of the cold storage device 14, etc.
It is equipped with a pressure reducing function that can release part of the sealed gas to the outside of the system and maintain the pressure below a predetermined level when an abnormal pressure rise occurs within the system. Other configurations are the first
It is similar to the figure.

In the G-M refrigerator configured in this way, cold generation is performed in the same way as in conventional refrigerators, but in the region where the specific heat of metal is extremely small at an operating temperature of 20K or less, the second expansion chamber 12 The cold working gas discharged from the regenerator is stored in helium gas sealed in a regenerator gas filling tube 18 that is thermally coupled to the second regenerator 14 . Next, the working gas flowing into the second expansion chamber 12 exchanges heat with the cold helium gas sealed in the cold storage gas filling tube 18 and is cooled, allowing it to reach a much lower temperature than the conventional one. This makes it possible to improve the COP in the cryogenic operating range of the refrigerator.

Here, adjusting and controlling the amount of helium gas filled into the refrigerant gas filling tube 18 is an important issue. first,
During the cooling down process from room temperature to steady cooling temperature of the refrigerator, the volume of sealed helium gas decreases, so it is necessary to replenish it. If the amount of helium gas required for steady operation were to be sealed at room temperature, the pressure would be several hundred atmospheres of helium, which would be technically extremely difficult.
Further, as shown in FIG. 3, which shows the specific heat characteristics of helium gas at low temperatures as a pressure parameter, the maximum value of the specific heat changes depending on the sealing pressure. This means that
It can be seen that when the operating temperature of the refrigerator during steady operation is determined, by adjusting and setting the helium gas filling pressure of the cold storage gas filling tube 18 to an optimum value, the refrigerator can be operated with high efficiency.

According to this invention, the amount of helium gas filled in the cold storage gas filling tube 18 can be maintained at a predetermined pressure by the regulating valve mechanism 20 even if the temperature of the cold storage gas filling tube 18 changes, and in a steady cooling state, The helium gas filling pressure of the cold storage gas filling tube 18 can be arbitrarily adjusted and set so that the refrigerator can be operated in an optimal state.

FIG. 4 shows another embodiment of the present invention, and a second embodiment of the invention is shown in FIG.
A refrigerant gas filled pipe 18 is provided on the outer surface of the wall of the third cylinder 13 that houses the regenerator 14. In this case, consideration must be given to increasing the heat exchange efficiency between the helium gas in the refrigerant gas filled tube 18 and the operating gas passing through the regenerator 14, and the third
It is also an idea to provide an enlarged heat transfer surface such as heat transfer fins 21 on one or both of the inner wall of the cylinder 13 and the inner side of the refrigerant gas filling tube 18 . By providing the refrigerant gas filling tube 18 outside the cylinder tube of the refrigerator working gas, the refrigerant gas filling tube 18 does not have to penetrate the wall of the third cylinder 13, making the work easier and improving the durability. This has the effect of improving vacuum reliability.

FIG. 5 shows another embodiment, in which a refrigerant introduction pipe 19 is connected via a heat exchanger 22 provided in contact with the outer wall of the first cylinder 1. In this case, the helium gas supplied into the cold storage gas filling tube 18 is cooled to a low temperature during the inflow process, so the refrigeration load on the cold storage gas filling tube 18 can be reduced. When the gas is released outside the system, the cold of the sealed gas itself can be collected into the refrigerator, which has the effect of increasing the efficiency of the refrigeration system.

Although the above embodiments have been described with respect to a GM refrigerator, it goes without saying that the present invention can be widely applied to other helium refrigerators using a regenerator, such as a Stirling cycle refrigerator.

As explained above, in the final stage regenerator section of a helium refrigerator using a regenerator, the regenerator gas filled tubes made of thin metal tubes are provided in parallel, and the regenerator gas filled tubes are connected to the regenerator gas filled tubes through a control valve mechanism. By filling it with helium gas and making it possible to adjust and maintain a constant pressure of your choice, the minimum temperature range that can be reached is expanded compared to conventional refrigerators of this type, and it is also possible to operate in cryogenic temperatures. It has great effects, such as being able to rationally and stably control the refrigeration capacity with only simple valve adjustments.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a conventional device, FIG. 2 is a longitudinal sectional view of an embodiment of the present invention, FIG. 3 is a specific heat characteristic curve of helium gas at low temperature, and FIG. 4 is a diagram of another embodiment of the present invention. FIG. 5 is a sectional view of the main part of the embodiment, and FIG. 5 is a schematic diagram of the main part of another embodiment. DESCRIPTION OF SYMBOLS 1... First cylinder, 2... First displacer, 4... First piston rod, 6... First regenerator, 7... First expansion chamber, 8... Second Cylinder, 9...Second displacer, 10...
...Second piston rod, 12...Second expansion chamber, 13...Third cylinder, 14...Second regenerator, 15...Communication pipe, 16...High pressure shut-off valve, 1
7...Low pressure shutoff valve, 18...Cold storage gas filled pipe, 1
9... Refrigerant gas introduction pipe, 20... Control valve mechanism, 2
1... Heat transfer fin, 22... Heat exchanger. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In a helium refrigerator equipped with a plurality of stages of regenerators, a regenerator gas-filled tube that is provided in the regenerator section of the final stage and is filled with a certain amount of helium gas by forming multiple thin tubes. and a refrigerant gas introduction pipe having one end connected to the refrigerant gas filling pipe, and a regulating valve mechanism connected to the other end of the refrigerant gas introduction pipe for maintaining the internal pressure of the cold storage gas filling pipe at a predetermined level. A helium refrigerator featuring 2. Claim 1, wherein a cold storage gas filling tube is disposed in a cold storage device, and a refrigerant gas introduction tube penetrates a container wall of the cold storage device and is connected to the cold storage gas filling tube.
Helium refrigerator as described in section. 3. The helium refrigerator according to claim 1, wherein the cold storage gas filling tube is disposed on the outer surface of the container wall of the regenerator. 4. The helium refrigerator according to claim 3, comprising heat transfer fins provided on at least one of the inner wall of the container and the inner side of the cold storage gas filled tube. 5. The helium refrigerator according to claim 1, wherein the refrigerant gas introduction pipe is connected to the cold storage gas filling pipe via a heat exchanger disposed in contact with the outer wall of the pre-stage regenerator.