JPH0721359B2 - Cryogenic helium refrigerator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic helium refrigerator, and more particularly to an improvement of a cryogenic helium refrigerator for preventing heat invasion from the outside in a container for storing liquid helium.

(Prior Art) Conventionally, as a cryogenic helium refrigerator, for example, Japanese Patent Publication No. Sho 61-
The one disclosed in Japanese Patent No. 28907 is known.

As shown in Fig. 5, this one is equipped with three compressors (a
Compressor unit (a) having 1), (a2) and (a3)
And a cryostat unit (b) that generates an extremely low temperature and a cryostat (c) that cools an object to be cooled, and connect the refrigerator unit (b) and the cryostat (c) with a connecting pipe (d). It was constructed by contacting them.

Thus, the high-pressure helium gas supplied from the single compressor (a1) of the compressor unit (a) is expanded in the refrigerator unit (b), and the first heat stage is expanded by this expansion action. A precooler (e) that cools (e1) to a temperature of about 60K and also cools the second heat stage (e2) to a lower temperature of about 15K is provided, and in series with the compressor unit (a). Two connected compressors (a
2), J-T valve (f) for pre-cooling the high-pressure helium gas from (a3) in the second heat stage (e2) of the pre-cooler (e) to about 15 K and then expanding the Joule-Thomson.

Further, the refrigerator unit (b) is provided with three heat exchangers (g1), (g2), (g3) for recovering the cold heat of the helium gas returned from the cryostat (c). On the other hand, in the cryostat (c), the container (h) containing the liquefied helium and the object to be cooled, and the helium in the gas-liquid mixed state at the cryogenic temperature expanded by the JT valve (f) And a condensing heat exchanger (i) for cooling the object to be cooled, and surrounding the container (h) outside the container (h) 2
Heavy shield plates (j) and (k) are provided, and the shield heat exchangers (l) and (m) are provided on the shield plates (j) and (k), respectively.
To place.

Then, the process of cooling the helium gas from the two compressors (a2) (a3) connected in series in the compressor unit (a) from the second heat stage (e2) of the precooler (e) to about 5K. Then, the high-pressure helium gas from the compressor (a3) is used as the first heat exchanger (g1) for cold heat recovery of the refrigerator unit (b).
After cooling with the low temperature gas returning from the cryostat (c), the first shield plate (j) is circulated to the first shield heat exchanger (1) of the cryostat (e) to cool the first shield plate (j) to about 80K. After that, after cooling to 60K in the first heat stage (e1) of the precooler (e), it is cooled to a lower temperature by the low temperature gas returned from the cryostat (c) again in the second heat exchanger (g2) for cold heat recovery. Then, the shield plate (k) is circulated to the second shield heat exchanger (m) of the cryostat (c) to cool the shield plate (k) to about 20K, and both shield plates (j),
In (k), heat from the outside is prevented. After that, as usual, after cooling to about 15K in the second heat stage (e2) of the precooler (e), it is further cooled in the third heat exchanger (g3) for cold heat recovery, and then the J-T The valve (f) is used to cause Joule-Thomson expansion to generate a cryogenic temperature.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional one, two shield heat exchangers (i) and (m) of the cryostat (c) and J- are used.
Since the T-valve (f) is connected in series, the cooling capacity of the double shield plates [j] and (k) by the shield heat exchangers (i) and (m) is the J-T valve. It is governed by the amount of helium gas circulating in (f) (JT circulating gas amount).
Therefore, when the JT circulating gas amount is small or when the shield load on the high temperature side shield plate (j) is large (for example, an MRI-CT device), the cooling capacity of the shield plate (j) is required. Due to insufficient cooling capacity, the shield plate (j) cannot be kept at a predetermined temperature (about 80K), and as a result, heat from the outside cannot be effectively prevented and the inside of the cryostat (c) container (h) cannot be effectively prevented. There is a drawback that the temperature rises and the amount of evaporation of liquid helium stored inside increases, which exceeds the recondensing capacity of the refrigerating apparatus and prevents stable operation of the refrigerating apparatus for a long time.

The present invention has been made in view of the above problems, and an object thereof is to provide a first precooler for a cryogenic helium refrigerator.
By separately providing a shield cooling circuit for flowing a part of the helium gas cooled in the heat stage (on the high temperature side) to the shield heat exchanger of the cryostat, the gas circulation amount to the shield heat exchanger is increased. To increase the shield function to prevent heat from entering the lyostat container from the outside, thereby reducing the evaporation amount of liquid helium into the cryostat container and operating the helium refrigerator stably for a long time. It is in.

(Means for Solving the Problem) In order to achieve the above-mentioned object, the solution means of the present invention is, for example, as shown in FIG. 1, a low-stage compressor (2) and a high-stage compressor (2) connected in series ( A precooler (4) that expands high-pressure helium gas compressed in a compressor unit (A) having 3) to generate low temperatures in a plurality of heat stages (5) and (6), and heat exchange for cold heat recovery. A refrigerator unit (B) having a JT valve (10) for expanding the helium gas cooled by the heat stage (6) on the low temperature side (11) and the Joule-Thomson, and containing liquefied helium and an object to be cooled A container (15) having a condensation heat exchanger (18) for condensing helium vapor inside and a shield plate (20) arranged outside the container (15) and receiving cold heat from the shield heat exchanger (22). And a cryostat (C) having The high-pressure helium gas compressed by the high-stage compressor (3) of the compressor unit (A) is sequentially supplied to the heat exchanger (11) for heat recovery of the refrigerator unit (B) and a plurality of heats of the precooler. After cooling in the stages (5) and (6), the above J-
Inflate with the T valve (10), and then use the cryostat (C)
Of the low-stage compressor (2) of the compressor unit (A) through the heat exchanger (11) for heat recovery of the refrigerator unit (B). It is premised on a cryogenic helium refrigerator in which the object to be cooled in the container (15) is cooled to a cryogenic temperature by returning to the suction side. Then, one end of the shield heat exchanger (22) of the cryostat (C) is passed from the high temperature side heat stage (5) of the precooler (4) through the low temperature side heat stage (6) to the J-
The T-valve (10) is connected so as to receive a part of the cold heat, and the other end of the shield heat exchanger (22) is connected to the heat exchanger (11) for heat recovery of the refrigerator unit (B). Connect to release cold heat. Further, a heat exchanger (1) for heat recovery from the high-stage compressor (3) of the compressor unit (A), the heat stage (5) on the high temperature side, and the shield heat exchanger (22).
A shield cooling circuit (30) that circulates gas to 1) and returns it to the discharge side of the low-stage compressor (2) of the compressor unit (A).
And a regulating valve (31) for regulating the gas circulation amount of the shield cooling circuit (30) is arranged in the shield cooling circuit (30).

(Operation) With the above configuration, in the present invention, during operation of the cryogenic helium refrigerator, the helium gas compressed to a high pressure by the high-stage compressor (3) of the compressor unit (A) is used for cold heat recovery. After being cooled by the heat exchanger (11) and the heat stage (5) on the high temperature side of the precooler (4), a part thereof is used as the amount of JT circulation gas on the heat stage on the low temperature side of the precooler (4) ( While flowing to 6), the rest flows into the shield heat exchanger (22) of the cryostat (C) through the shield cooling circuit (30).

Then, the helium gas that has flowed to the heat stage (6) on the low temperature side of the former precooler (4) is further cooled by this heat stage (6), then is throttled by the JT valve (10), and is cooled by the joule. Thomson expands and flows into the condensation heat exchanger (18) of the cryostat (C) to cool the object to be cooled. Then, after that, cold heat is given to the helium gas from the compressor unit (A) by the heat exchanger (11) for cold heat recovery of the refrigerator unit (B), and the low-stage compressor of the compressor unit (A) is given. Repeat returning to the suction side of (2).

Meanwhile, the cryostat (C) shield heat exchanger (2
The high-pressure helium gas in the shield cooling circuit (30) flowing in 2) releases cold heat in the shield heat exchanger (22) to cool the shield plate (20) to a predetermined temperature (about 80K), and then the refrigerator. The heat flows into the heat exchanger (11) for cold heat recovery of the unit (B), where cold heat is given to the helium gas from the compressor unit (A). Further, the throttle valve (31) of the shield cooling circuit (30) is throttled and returned to the discharge side of the low-stage compressor (2) of the compressor unit (A).

In that case, the gas circulation amount to the shield heat exchanger (22) of the cryostat (C) is a part of the helium gas after being cooled by the heat stage (5) on the high temperature side of the precooler (4), that is, independent. The amount of gas flowing through the shield cooling circuit (30) provided in the irrespective of the JT circulation gas amount, and the gas circulation amount of this shield cooling circuit (30) is adjusted by the adjusting valve (31). Since this is possible, the cooling capacity of the shield plate (20) can be adjusted to an appropriate value, and heat can be effectively prevented from entering the cryostat (C) from the outside. As a result, the evaporation amount of liquid helium in the container (15) is prevented from increasing, and the cryogenic helium refrigerator can be stably operated for a long time.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows a schematic circuit configuration of a cryogenic helium refrigerator as an embodiment of the present invention, (A) is a compressor unit,
The compressor unit (A) includes a compressor (1) for a precooler.
And a low-stage compressor (2) and a high-stage compressor (3) connected in series, and the compressor (1) for the precooler brings the low-pressure helium to a predetermined pressure (for example, 1 atm to 10 atm). It is to compress. The low-stage compressor (2) compresses the low-pressure helium gas to a predetermined pressure (1 atm to 10 atm), and the high-stage compressor (3) further compresses the helium gas compressed by the low-stage compressor (2). It is compressed to (for example, 24 atmospheres).

Further, (B) is a refrigerator unit that generates an extremely low temperature, and in the refrigerator unit (B), a precooler (4) for expanding the helium gas from the precooler compressor (1).
The precooler (4) generates a low temperature of 60K in the first heat stage (5) and a low temperature of 15K in the second heat stage (6) by the expansion action of helium gas. Have a function. Further, the refrigerator unit (B) is equipped with a JT valve (10) for expanding the helium gas by Joule-Thomson, and three countercurrent heat exchangers (11) for cold heat recovery. , (12), (13) are provided.

Further, in FIG. 1, (C) is a cryostat for cooling an object to be cooled, and the cryostat (C)
Has a container (15) for containing liquefied helium (L) and an object to be cooled. Inside the container (15), a helium connecting Joule-Thomson expanded by the JT valve (10) is connected ( A condensing heat exchanger (18) is arranged to receive via the (17) and condense the helium vapor in the container (15). Also,
A first shield plate (20) surrounding the container (15) and a second shield plate (21) surrounding the container (15) are arranged outside the container (15), and each shield plate (20). , (21) are arranged in thermal contact with shield heat exchangers (22), (23) for cooling the shield plates (20), (21), respectively.

Next, connection between the three heat exchangers (11) to (13) for cold heat recovery of the refrigerator unit (B) and the two shield heat exchangers (22) and (23) of the cryostat (C). Explain the relationship.

That is, three heat exchangers (11) to (13) for cold heat recovery
Is connected to the secondary sides (11b) to (13b) in series, and the third heat exchanger (13) located on the lower side in the drawing has a condensing heat exchanger (18) of the cryostat (C). ) From the low temperature helium gas flows in through the connecting pipe (17), and in the first heat exchanger (11) located on the upper side in the figure, the inflowing helium is compressed by the low-stage compression of the compressor unit (A). It is connected so as to return to the suction side of the machine (2), and the cold heat is recovered from the low temperature helium after the object to be cooled is cooled by the cryostat (C). Also, the helium gas from the high-stage compressor (3) of the compressor unit (A) is received by the first heat exchanger for cold heat recovery (11), and its primary side (11a).
Through the first heat stage (5) of the precooler (4)
After pre-cooling to about 60K, the second part located in the middle of the figure
Is cooled to a lower temperature by the cold heat recovered in the primary side (12a) of the heat exchanger (12) and is transferred to the second shield heat exchanger (23) of the cryostat (C) via the communication pipe (17). Let it flow
It is configured to cool the second shield plate (21) to a predetermined temperature (about 20K).

Further, the helium that has flowed through the second shield heat exchanger (23) is returned to the refrigerator unit (B) through the communication pipe (17) again, and then the second heat stage (6) of the precooler (4) is used. After cooling to a low temperature (about 15K), it is made to flow to the primary side (13a) of the third heat recovery heat exchanger (13), and then subjected to Joule-Thomson expansion by the JT valve (10),
It is made to flow to the condensation heat exchanger (18) of the cryostat (C) to cool the object to be cooled in the container (15), and then the three heat exchangers (11) for cold heat recovery of the refrigerator unit (B) to. (13)
The JT circuit (24) is configured so that the cold heat is recovered and returned to the suction side of the low-stage compressor (2) of the compressor unit (A).

Thus, in the refrigerator unit (B), a pipe (25) from the first heat stage (5) of the precooler (4) to the heat exchanger (12) for recovering cold heat is separately provided as a pipe ( One end of 26) is connected, the other end is connected to one side of the first shield heat exchanger (22) of the cryostat (C) via the connecting pipe (17), and the other side is connected to the connecting pipe (17) again. ) And another pipe (27) for the first heat exchanger (11) for recovering cold heat.
Connected to the tertiary side (11c) of the first heat exchanger (1c
From 1) is connected to the suction side of the high-stage compressor (3) of the compressor unit (A). With the above configuration, the helium gas from the high-stage compressor (3) is supplied to the precooler (4), and the first (high temperature side) heat stage (5) of the precooler (4) is supplied.
The first shield heat exchanger (22) of the cryostat (C) independently of a part of the helium gas cooled to about 60K by
To cool the first shield plate (20) effectively, and then to the tertiary side (11c) of the first heat exchanger (11) for cold heat recovery.
The shield cooling circuit (30) is configured to circulate the helium gas by recovering the cold heat by the above, raising the temperature to room temperature and returning it to the suction side of the high-stage compressor (3) of the compressor unit (A). ing.

In the compressor unit (A), as shown in FIG.
It has a built-in ballast tank (35). The ballast tank (35) absorbs the amount of helium that fluctuates in the circuit due to the temperature of the cryostat (C) being different between when the refrigerator is stopped and when it is in operation. That is, the two compressors (2) of the compressor unit (A),
A solenoid valve unit (3) having three solenoid valves (36a), (36b), (36c) between the ballast tank (35) and (3).
6), when the operation of raising the temperature of the cryostat (C) is stopped, the helium pressure in the JT circuit (24) increases as the evaporation amount of liquid helium in the container (15) increases. , Open the solenoid valve unit (36) and collect more helium than necessary in the ballast tank (35). When the operation is started, the electromagnetic valve unit (36) is closed to start the operation, and when the amount of helium in the JT circuit (24) begins to become insufficient due to the decrease in the helium gas pressure, the electromagnetic valve unit (36 ) Is opened and helium in the ballast tank (35) is replenished to ensure normal operation. Therefore, compared to the case where the ballast tank (35) is installed separately from the compressor unit (A), it is not necessary to connect the ballast tank each time the operation is stopped or started, and the operating efficiency is improved and the circuit is improved. The configuration is simple.

Further, in FIG. 2, the compressor unit (A) is provided with a connection port (37) communicating with the ballast tank (35) incorporated therein. This connection port (37) is
Pipe (2) on the low temperature side (about 20K) of the shield cooling circuit (30)
If 6) becomes long, the fluctuation range of the required helium amount between the time of the above operation and the time of stop becomes large, and when the capacity of the built-in ballast tank (35) is insufficient, the connection port (37) This is for connecting another ballast tank (38) in communication with each other to increase the capacity thereof.

Thus, in the compressor unit (A) of FIG. 1, the shield cooling circuit (30) has a helium circulating in the shield cooling circuit (30) near the suction side of the high-stage compressor (3). A pressure reducing valve (31) is interposed as a regulating valve for regulating the gas amount.

Therefore, in the above embodiment, when the refrigerator is operating,
The helium gas compressed to high pressure by the two compressors (2) and (3) of the compressor unit (A) is cooled by the first heat exchanger (11) for cold heat recovery of the refrigerator unit (B). After being processed, the first heat stage (5) of the precooler (4)
It is cooled to about 60K.

After that, a part of the helium gas cooled to about 60 K is further cooled by the second heat exchanger (12) for cold heat recovery, and then the second helium gas of the cryostat (C) is passed through the communication pipe (17). The second shield plate (21) is circulated to the shield heat exchanger (23) to cool the second shield plate (21) to about 20K, and then, the connecting pipe (17) is again provided.
After reaching the second heat stage (6) of the pre-cooler (4) via the heat exchanger and being cooled to about 15K, and then being cooled by the third heat exchanger (13) for cold heat recovery, the J-T valve ( In 14), it is squeezed and expands by Joule-Thomson, and becomes helium in a gas-liquid mixed state at an extremely low temperature (1 atm 4.2K). After that, the connecting pipe (17)
Condensation heat exchanger (18) for cryostat (C) via
To cool the object to be cooled in the container (15), and then
It again flows into the three heat exchangers (11) to (13) for cold heat recovery of the refrigerator unit (B) through the communication pipe (17), and cools the helium gas from the compressor unit (A) to the helium gas. Is given to raise the temperature, and becomes room temperature low-pressure helium gas, which is sucked into the suction side of the low-stage compressor (2) in the compressor unit (A) and compressed again by the high-stage compressor (3). repeat.

On the other hand, the remaining helium gas cooled to about 60 K in the first heat exchanger (11) for cold heat recovery has a shield cooling circuit (30) partially forming the pipe (26) and the connecting pipe (17). Through the first shield heat exchanger (22) of the cryostat (3) to cool the first shield plate (20) to about 80K. After that, the helium gas from the compressor unit (A) flows through the communication pipe (17) and the pipe (27) to the tertiary side (11c) of the first heat exchanger (11) for cold heat recovery. After applying cold heat to raise the temperature to room temperature, it is sucked into the suction side of the high-stage compressor (3) of the compressor unit (A) through the pressure reducing valve (31) and circulated again.

Here, the amount of gas circulated in the cryostat (C) first shield heat exchanger (22) is a part of the helium gas cooled in the first heat stage (5) of the precooler (4), and -Shield cooling circuit (30) different from T circuit (24)
The amount of gas flowing through the shield cooling circuit (30) can be increased or decreased by the adjustment valve (31) provided in the shield cooling circuit (30). Therefore, the first shield heat exchanger (22) of the cryostat (C) is The cooling capacity of the first shield plate (2
0) can be reliably cooled to a predetermined temperature (about 80K) As a result, it is possible to effectively suppress the invasion of heat from the outside into the cryostat (C) and increase the shield function, and it is possible to suppress an increase in the evaporation amount of helium in the container (15) due to the invasion of heat. The helium refrigerator can be operated stably for a long time. In this case, since the relationship between the circulation amount of helium gas flowing through the JT circuit (24) and the cooling capacity depends on the capacity of the precooler (4) and the capacity of the low-stage compressor (2), the cryostat (C The cooling capacity in () is about the same as the normal one without the shield cooling circuit (30), and the cooling capacity is not deteriorated.

FIG. 3 shows a modified example of the shield cooling circuit (30). In the above-mentioned embodiment, the first heat exchanger (11) for recovering cold heat is provided with three components.
While the secondary side (11c) is provided, the other heat exchanger (11) is attached to the normal heat exchanger (11 ') of only the primary side and the secondary side. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 4 shows another modified example of the shield cooling circuit (30), which is applied to the compressor unit (A ') in which the precooling compressor is omitted. That is, the high-stage compressor (3) of the compressor unit (A ') is also used as a precooler, and the helium gas returned from the tertiary side (11c) of the first heat exchanger (11) for cold heat recovery. The pressure is reduced by the pressure reducing valve (31 '), and then the helium gas returned from the precooler (4) is merged and returned to the suction side of the high-stage compressor (3). It is similar to the figure. Therefore, as in the above-mentioned embodiment, the shield cooling circuit (30 ') independent of the J-T circuit (24) is used for the first operation of the cryostat (C).
The cooling performance of the shield heat exchanger (22) can be enhanced to improve the shielding performance against invasion heat, and the refrigerator can be stably operated for a long time.

(Effects of the Invention) As described above, according to the present invention, in the cryogenic helium refrigerator, a shield plate surrounding the container of the cryostat is provided independently of the JT circuit for cooling the object to be cooled. Since the shield cooling circuit is provided for the shield heat exchanger and the gas circulation amount of the shield cooling circuit can be adjusted by the adjusting valve, the amount of helium gas circulating in the shield heat exchanger is increased and It is possible to enhance the shielding function of the shield plate against the invasion heat and to reduce the evaporation amount of liquid helium in the container of the cryostat, and to stably operate the refrigerator for a long time.

[Brief description of drawings]

1 to 4 show an embodiment of the present invention, FIG. 1 is an overall schematic configuration diagram, FIG. 2 is a configuration diagram showing details of the inside of a compressor unit, and FIG. 3 is a modification of a shield cooling circuit. FIG. 4 is a main part configuration diagram showing an example, and FIG. 4 is a main part configuration diagram showing another modified example of the shield cooling circuit. FIG. 5 is an overall circuit configuration diagram showing a conventional example. (A) ... Compressor unit, (B) ... Refrigerator unit, (C) ... Cryostat, (2) ... Low-stage compressor, (3) ... Post-stage compressor, (4) ... Pre-cooling Machine, (5)
...... First heat stage, (6) ...... Second heat stage, (10) ...... JT valve, (11) ...... Cold heat recovery heat exchanger, (15) …… Vessel, (20) ・ ・ ・… The first shield plate, (2
2) …… First shield heat exchanger, (30), (30 ′) ……
Shield cooling circuit, (31), (31 ') ... Pressure reducing valve.

Claims (1)

[Claims] 1. A plurality of heat stages (5) by expanding high-pressure helium gas compressed in a compressor unit (A) having a low-stage compressor (2) and a high-stage compressor (3) connected in series. , (6) for generating a low temperature, a heat exchanger (11) for recovering cold heat, and a JT for expanding the helium gas cooled by the heat stage (6) on the low temperature side by Joule-Thomson expansion A refrigerator unit (B) having a valve (10), a container (15) having a condensing heat exchanger (18) for accommodating liquefied helium and an object to be cooled and condensing helium vapor therein, and the container (15) And a cryostat (C) having a shield plate (20) arranged outside and receiving cold heat from the shield heat exchanger (22), and compressed by the high-stage compressor (3) of the compressor unit (A). High-pressure helium gas is sequentially frozen Unit (B)
After being cooled by the heat exchanger (11) for heat recovery and a plurality of heat stages (5), (6) of the precooler, it is expanded by the JT valve (10), and then cooled by the cryostat (C). It is made to flow through the condensing heat exchanger (18), and then, through the heat exchanger (11) for heat recovery of the refrigerator unit (B), suction of the low-stage compressor (2) of the compressor unit (A). It is a cryogenic helium refrigerator which is cooled to the side to cool the object to be cooled in the container (15) to a cryogenic temperature, the shield heat exchanger (22) of the cryostat (C).
One end of the JT through the heat stage (5) on the high temperature side of the precooler (4) to the heat stage (6) on the low temperature side.
The shield heat exchanger (22) is connected to receive a part of the cold heat toward the valve (10), and the other end of the shield heat exchanger (22) transfers the cold heat to the heat exchanger (11) for heat recovery of the refrigerator unit (B). The heat exchange for heat recovery from the high-stage compressor (3) of the compressor unit (A), which is connected so as to discharge the heat, passes through the high-temperature side heat stage (5) and the shield heat exchanger (22). A shield cooling circuit (30) is provided which circulates the gas in the device (11) and returns it to the discharge side of the low-stage compressor (2) of the compressor unit (A). The shield cooling circuit (30) includes: A cryogenic helium refrigerator, characterized in that a regulating valve (31) for regulating the gas circulation amount of the shield cooling circuit (30) is arranged.