JPH0645812Y2 - Cryogenic refrigerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a cryogenic refrigerator for cooling and re-condensing helium gas evaporated from liquid helium stored in a cryostat.

(Prior Art) In recent years, as a medical device, a so-called magnetic resonance image CT (in which the content of hydrogen in a molecule in a human body is detected by an electromagnetic coil and a high-frequency generator, and the inside of the human body is imaged to examine its abnormality) Magnetic Resonance Imaging-Computer Tomo
graph. Hereinafter, abbreviated as MRI-CT) is well known and used.

Since this MRI-CT uses a superconducting magnet that operates at a cryogenic level, the magnet is cooled to a cryogenic level by liquid helium stored in a cryostat (cryostat).

(Problems to be solved by the invention) By the way, in the cryostat, a refrigerant having a relatively high liquefaction temperature such as liquid nitrogen is usually stored in an upper portion of a storage tank for a refrigerant having a very low liquefaction temperature such as helium. In this way, a temperature gradient is provided so that the temperature decreases from the upper side to the lower side, so that good heat insulation from the outside is maintained. However, even in such a case, there is a considerable temperature gradient between the refrigerant storage tank and the outside, and for example, when helium that liquefies at a cryogenic temperature of 4.2 K level is used as the refrigerant, the outside Even if a shield part is maintained at 77K level by liquid hydrogen, a temperature gradient of about 73K exists between the shield part and the helium tank.

Then, due to the temperature gradient as described above, for example, when the temperature in the vicinity of the recondenser becomes about 7.5 K, the latent heat of condensation of helium and the amount of sensible heat become almost equal, so that the recondensation amount of helium has an ambient temperature of 4.2 K. It is about 1/2 of that of Therefore, there is a problem that the recondensing ability is reduced.

The present invention has been made in view of these points, and an object thereof is a means for keeping the temperature around the recondenser low when the helium gas in the cryostat is recondensed by the recondenser as described above. This is to improve the recondensing ability.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the first solution means of the present invention is to store a liquid refrigerant such as liquid helium inside as shown in FIG. Of the cryostat (2), which is maintained at a predetermined cryogenic temperature, and a cryostat (2) disposed inside the cryostat (2) for cooling and re-condensing the helium gas evaporated from the liquid helium in the cryostat (2). A refrigerant pipe (26) for recondensing, which is arranged outside the condenser (23) and the cryostat (2), cools compressed refrigerant gas such as helium by expansion.
It is premised on a cryogenic refrigerator provided with a refrigerator main body (15) which supplies the recondenser (23) via the (27).

A tubular heat insulating part (24), which is made of a low thermal conductivity material whose inside is in a vacuum state and which adiabatically connects the refrigerator body (15) and the recondenser (23), is further provided. A cylindrical shielding tube (31) is provided continuously with the tip of the cylindrical heat insulating part (24), extends downward, and surrounds the entire lateral side of the recondenser (23) with a predetermined gap. It is configured.

A second solving means is the same as the first solving means, in which the outer diameter of the shield tube (31) is set to be equal to or less than the outer diameter of the heat insulating section (24).

(Operation) With the above structure, in the device of claim (1), the helium gas evaporated from the liquid helium stored inside the cryostat (2) is cooled by the recondenser (23) of the refrigerator and is then recovered. Recondensed into liquid helium. Therefore, since expensive liquid helium is not consumed, it is not necessary to periodically replenish it, and liquid helium is used as a cooling source.
It is possible to reduce the running cost of low-temperature operating equipment such as MRI-CT, and to eliminate the trouble of replenishing liquid helium.

The refrigerator body (15) of the refrigerator is arranged outside the cryostat (2), and the recondenser (23) is arranged inside the cryostat (2).
Since the 5) and the re-condenser (23) are connected in an adiabatic state by a cylindrical heat insulation part (24) made of a material having a low heat conductivity and a vacuum state, the re-condenser (23) is connected to the cryostat (2). Only the re-condenser (23) is inserted into the refrigerator, and the opening portion of the cryostat (2) as the attachment portion of the refrigerator can be narrowed, so that the cryostat (2) does not need to be largely changed.

In that case, at the tip of the cylindrical heat insulation part (24), the recondenser (2
Shield tube (31) that surrounds the entire side of 3) and shields heat
Is provided, the temperature of the evaporated helium gas in the vicinity of the recondenser (24) is maintained at substantially the same level as the temperature of 4.2K in the recondenser (31). Therefore, the sensible heat load of helium is almost eliminated, so that the recondensing capacity of the recondenser (23) does not decrease due to the sensible heat amount of helium,
The recondensing ability will be effectively improved. Further, since the periphery of the recondenser (23) is protected by the shield tube (31), damage to the recondenser component due to contact with the cryostat or the like during plug-in is prevented.

Further, in the invention of claim (2), since the side of the recondenser (23) is heat shielded by the shield tube (31) having a diameter equal to or smaller than the diameter of the heat insulating portion (24), the first embodiment described above. As with the example, the recondensing capacity can be improved, and the cryostat for plugging in the recondenser (23) can be installed even if it has a small opening, thus improving the compatibility when plugging in. Will be done.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows the whole construction of the plug-in type refrigerator according to the first embodiment to which the invention of claim (1) is applied, and (1) shows an MRI as a medical device incorporating a superconducting magnet (1a). -
In the CT, the superconducting magnet (1a) is placed in a cryostat (2) that stores liquid helium as a refrigerant, and is cooled to a cryogenic level (4.3K) by the cold heat of the liquid helium. Is held.

The cryostat (2) has a liquid helium container (3) for storing the liquid helium, and an inner shield part (3) concentrically arranged and supported around the container (3) via an inner vacuum chamber (4). 5) and an outer shield part (7) which is concentrically arranged and supported around the inner shield part (5) through an outer vacuum chamber (6) are arranged in the liquid helium container (3). Above superconducting magnet (1
a) is housed. Further, a liquid nitrogen storage chamber (8) for storing liquid nitrogen with the upper wall of the outer shield part (7) as a bottom wall is provided above the outer shield part (7).
The outer shield part (7) is maintained at a predetermined temperature level (77K) by the liquid nitrogen in the storage chamber (8).

Further, the liquid helium container (3) of the cryostat (2), the inner shield part (5), the outer shield part (7) and the liquid nitrogen storage chamber (8) have circular openings (9) on their respective upper walls. ) To (12) are formed penetratingly in the vertical direction, and a cylindrical insertion member (13) is fitted and inserted into these openings (9) to (12) in an airtight state. ), The upper end is open to the outside of the cryostat (2), and the lower end is open to the liquid helium container (3).

(14) is a refrigerator for cooling the evaporated helium gas in the liquid helium container (3) of the cryostat (2) and recondensing it into liquid helium, the refrigerator (14)
As shown in FIG. 1, a precooling refrigeration circuit (16) for expanding a helium gas compressed by a compressor (not shown) to generate a low temperature state of a predetermined temperature level, and a compressor (not shown) for compression. The precooled refrigeration circuit (1
6) and a JT circuit (19) for expanding the precooled helium gas by JT to generate a cryogenic state at an extremely low temperature level. The refrigerator body (15) of the refrigerator (14) is a cryostat (2).
By securely fastening the mounting flange portion (15b) at the lower end of the case (15a) of the refrigerator body (15) to the mounting flange portion (13a) provided at the upper end of the insertion member (13) with respect to the upper surface of the It is installed.

In the case (15a) of the refrigerator body (15), as shown in an enlarged detail in FIG.
The constituent units that respectively configure the T circuits (19) are housed. That is, although only partially shown, as a constituent unit on the side of the pre-cooling refrigeration circuit (16), the helium gas from the compressor is expanded to generate a low temperature state of a predetermined temperature level in the heat station (not shown). An expander (18) is arranged. On the other hand, as a constituent unit on the JT circuit (19) side, a plurality of J units for cooling the helium gas cooled by heat exchange in the heat station of the expander (18) with the helium gas on the return side for cooling.
-T heat exchangers (20), (20), ... and J-T valve (21) for expanding the helium gas cooled by the J-T heat exchangers (20), (20), ... by Joule-Thomson. (Joule Thomson valve) is built in. In addition, a radiation shield part (22) of a predetermined temperature level is provided in the refrigerator body (15) to shield heat from the outside.

Further, (23) is a re-condenser as a cooler which evaporates the helium gas expanded by the J-T valve (21) and cools it to a cryogenic level by its latent heat. (23) is arranged in the upper part of the liquid helium container (3) of the cryostat (2).

The recondenser (23) and the case (15a) of the refrigerator body (15) are integrally connected by a tubular heat insulating section (24) made of a material having a low thermal conductivity. The heat insulation part (24) is concentrically inserted into the insertion member (13), and a vacuum chamber (25) is formed therein.

A recondensing refrigerant pipe (26) for exchanging refrigerant between the JT heat exchanger (20) and the recondenser (23) in the refrigerating machine body (15) in the heat insulating section (24), (27) is provided. In the heat insulation part (24), the atmosphere around the heat insulation part (24) from the radiation shield part (22) in the refrigerator body (15) is cooled by the liquid nitrogen in the liquid nitrogen storage chamber (8). It has a built-in cylindrical radiation shield part (28) that extends to the temperature level of 77K.

Further, the recondensing refrigerant pipes (26) and (27) are supported in the heat insulating section (24) in a heat insulating state by two kinds of spacers (29) and (30) of outer and inner. That is, the outer spacer (29) is made of Teflon resin, and as shown in enlarged detail in FIGS. 3 and 4, the outer peripheral surface of the radiation shield part (28) and the inner peripheral surface of the insertion member (13). The outer peripheral surface of the radiation shield part (28) and the inner peripheral surface of the insert member (13) are formed in a substantially quadrangular shape so as to have a minimum contact area.

Here, as a feature of the present invention, at the lower end of the cylindrical heat insulating part (24), the diameter is the same as the diameter of the heat insulating part (24) and extends downward by a predetermined length, and then the diameter is expanded by a predetermined taper. The re-condenser (2
A cylindrical shield pipe (31) extending below the tip of 3) is provided, and the shield pipe (31) surrounds the entire recondenser (23) laterally. . That is, the surroundings of the recondenser (23) are heat shielded to maintain the ambient temperature at an extremely low temperature near 4.2K.

In FIG. 2, (40) is a liquid helium supply port opened in a portion of the insertion member (13) located outside the cryostat (2), and (41) is an expander (18) of the pre-cooling refrigeration circuit (16). ) Is a supply port of helium gas, and (42) is the discharge port. Further, (43) is a supply port of helium gas in the JT circuit (19), and (44) is an exhaust port thereof.

Therefore, in the above embodiment, the expander (1) in the pre-cooling refrigeration circuit (16) is associated with the operation of the refrigerator (14).
As the temperature of the heat station of 8) decreases to a low temperature level, the helium gas on the JT circuit (19) side is precooled by the heat station of the expander (18), and this precooled helium gas is cooled by JT. Heat exchanger (2
It is cooled by 0) and expanded by the J-T valve (21) by Joule-Thomson and then expanded by the re-condenser (23). The latent heat of evaporation at that time causes the temperature of the re-condenser (23) to reach 4.2K level. It becomes extremely low. Therefore, the cryostat (2)
Even if the liquid helium stored inside the helium vaporizes into helium gas due to the heat of penetration from the outside of the cryostat (2), the helium gas is cooled by the re-condenser (23) at the cryogenic level and the original helium gas is cooled. It will be recondensed into liquid helium. As a result, there is no consumption of expensive liquid helium due to evaporation, so periodic replenishment is not required, and MRI-CT using liquid helium as a cooling source.
The running cost of (1) can be reduced, and the labor for replenishing the liquid helium can be eliminated.

The refrigerator body (15) of the refrigerator (14) is arranged outside the cryostat (2), and the recondenser (23) is arranged inside the cryostat (2), respectively, and the refrigerator body (15) and the recondenser are arranged. (23) has a so-called plug-in type structure in which the inside is connected in a heat-insulated state by a cylindrical heat-insulating part (24) made of a material having a low heat conductivity and a vacuum state. Refrigerators (14)
The insertion part of is only the re-condenser (23) inserted into the insertion member (13), and compared with the case where the entire cryostat (14) is equipped in the cryostat (2), the cryostat in the cryostat (2) is This is advantageous because the opening as the mounting portion of (14) can be made narrow and there is no need to change the structure of the cryostat (2) much.

In that case, at the tip of the cylindrical heat insulation part (24), the recondenser (2
Shield tube (31) that surrounds the entire side of 3) and shields heat
Is provided, the temperature of the evaporated helium gas in the vicinity of the recondenser (24) is maintained at substantially the same level as the temperature of 4.2 K in the recondenser (31). That is, the sensible heat load of helium is almost eliminated, and the recondensing capacity of the recondenser (23) does not decrease due to the sensible heat amount of helium. Therefore, it is possible to effectively improve the recondensing capacity. is there.

Moreover, since the re-condenser (23) is surrounded by the shield pipe (31) as described above, when the refrigerator is mounted on the cryostat (2), the fins of the re-condenser (23) are not replaced by other elements. It protects from damage due to contact with parts, and can also serve as a device protection function.

Next, a second embodiment according to the invention of claim (2) will be described. FIG. 2 shows only the vicinity of the recondenser (23) of the cryogenic refrigerator according to the second embodiment, and at the lower end of the heat insulating section (24),
A shield tube (31) is provided in which the cylinder forming the heat insulating section (24) extends downward as it is, and the shield tube (31) shields the entire side of the recondenser (23) from heat. There is. Other configurations are similar to those of the first embodiment.

Therefore, in this embodiment, since the side of the recondenser (23) is heat shielded by the shield tube (31), the above first
As with the embodiment, the recondensing capacity can be improved, and since the diameter of the shield tube (31) is set to be less than or equal to the diameter of the heat insulating portion (24), the device such as the above MRI-CT (1) When it is used for the cryostat arranged in the above, the cryostat for plugging in the recondenser (23) can be mounted even if the opening is small, and therefore the adaptability at the time of plug-in is improved.

In the second embodiment, the case where the diameter of the shield tube (31) is the same as the diameter of the heating section (24) has been described.
It goes without saying that the same effect can be obtained even when the diameter of 1) is small.

(Effects of the Invention) As described above, according to the invention of claim (1), the re-condenser for refrigerant re-condensation connected to the cryogenic refrigerator main body by the heat insulating section is provided at the cryogenic temperature of the cryostat. In the plug-in type cryogenic refrigerator that is plugged into the state part,
Since a shield tube for heat shielding the entire side of the recondenser is provided, the temperature of the refrigerant recondensed by the recondenser can be maintained at a value near its boiling point and the recondenser can be protected. Therefore, it is possible to improve the recondensing capacity of the recondenser and prevent damage to parts.

Further, according to the invention of claim (2), since the diameter of the shielding tube in the invention of claim (1) is set to a diameter other than the diameter of the heat insulating portion, the range of application of the shape of the opening or the like when plugged into the device to be used. Therefore, in addition to the same effect as the invention of claim (1), it is possible to improve the adaptability to the device to be used.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is an enlarged cross-sectional view of the essential part of a cryogenic refrigerator according to the first embodiment, and FIG. 2 is a cryogenic refrigerator according to the second embodiment. FIG. 3 is an enlarged sectional view showing the vicinity of a recondenser of the machine, and FIG. 3 is a sectional view showing an overall configuration common to both embodiments. (2) …… Cryostat, (14) …… Refrigerator, (1
5) …… Refrigerator body, (23) …… Recondenser, (24) ……
Heat insulation part, (26), (27) …… Refrigerant pipe, (31) …… Shield pipe.

Claims (2)

[Scope of utility model registration request] 1. A liquid refrigerant such as liquid helium is stored inside,
A cryostat (2) whose inside is maintained at a predetermined cryogenic temperature, and a cryostat (2) arranged inside the cryostat (2) for cooling and re-condensing helium gas evaporated from liquid helium in the cryostat (2). The recondenser (23) is arranged outside the cryostat (2) and cools compressed refrigerant gas such as helium by expansion, and the refrigerant gas for recondensation is passed through the refrigerant pipes (26) and (27). A cryogenic refrigerator having a refrigerator body (15) for supplying to a re-condenser (23), which is made of a low thermal conductivity material whose inside is in a vacuum state, and which is reconstituted with the refrigerator body (15). A tubular heat insulating part (24) for adiabatically connecting with the condenser (23) is provided, and it is continuously provided at the tip of the tubular heat insulating part (24) and extends downward to form the recondenser. Surround the entire side of (23) with a specified gap A cryogenic refrigerator comprising a tubular shield tube (31). 2. The cryogenic refrigerator according to claim 1, wherein the outer diameter of the shield tube (31) is set to be equal to or less than the outer diameter of the heat insulating section (24).