JPH0629636Y2 - Cryogenic refrigerator - Google Patents

Description

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

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

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

(Problems to be solved by the invention) By the way, the liquid helium in the cryostat is
It is evaporated and consumed little by little due to the heat entering from the outside.
For this reason, it is necessary to periodically replenish the liquid helium, which has been reduced due to the evaporation, from the outside of the cryostat, but since the liquid helium is expensive, the MR
There is a problem that the lining cost of the I-CT becomes high and the replenishing work of liquid helium is troublesome.

In addition, in order to prevent heat from entering the cryostat from the outside, radiation around the liquid helium in the cryostat is also shielded by a low-temperature radiation shield part obtained by a refrigerator,
In that case, it is only necessary to control the evaporation amount of liquid helium, and it is necessary to replenish liquid helium.

Therefore, the refrigerator is attached to the cryostat, and the low temperature part of the refrigerator is placed directly above the liquid helium storage part of the cryostat, and the low temperature part cools the evaporated helium gas and recondenses it into liquid helium. However, it is necessary to widen the opening of the cryostat as a mounting part of the refrigerator, and the heat entering from the opening is large, and it is necessary to change the structure of the cryostat. there were.

The present invention has been made in view of these points, and an object thereof is to recondense the helium gas inside the cryostat by the low temperature part of the refrigerator as described above.
By improving the arrangement structure of the refrigerator low temperature part with respect to the cryostat, the size of the refrigerator mounting opening in the cryostat can be reduced, and the labor of replenishing expensive liquid helium can be eliminated and low temperature such as MRI-CT. The purpose is to reduce the lining cost of the operating equipment.

(Means for Solving Problems) In order to achieve the above-mentioned object, a solution means of the present invention is, for example, as shown in FIG.
5) is a cryostat that stores liquid helium (2)
Re-condensers (23) for cooling and re-condensing the helium gas evaporated from liquid helium are arranged inside the cryostat (2) respectively, and the refrigerator main body (15) is provided outside.
The re-condenser (23) and the re-condenser (23) are connected in an adiabatic state by a cylindrical heat insulating part (24) made of a material having a low heat conductivity and a vacuum inside, and the inside of the heat insulating part (24) is frozen. The recondensing refrigerant pipes (26) and (27) for transferring the refrigerant between the machine body (15) and the recondenser (23) are arranged.

Further, the heat insulating part (24) has a built-in radiation shield part (28) extending from the refrigerator main body (15) to a portion where the atmosphere around the heat insulating part (24) reaches a predetermined level, and the recondensing refrigerant pipe ( 26) and (27) have a structure in which the spacers (29) and (30) support the heat insulating portion (24) in a heat insulating state.

(Operation) With the above configuration, in the present invention, the helium gas evaporated from the liquid helium stored inside the cryostat (2) is cooled by the recondenser (23) of the refrigerator and re-converted into the original liquid helium. Be condensed. Therefore, since expensive liquid helium is not consumed, it is not necessary to periodically replenish the liquid helium, and MRI-based liquid helium is used as a cooling source.
It is possible to reduce the lining cost of low temperature operation equipment such as CT, and to eliminate the trouble of replenishing operation of the liquid helium.

And in that case, the refrigerator body (15) in the refrigerator
Are arranged outside the cryostat (2) and the re-condenser (23) inside the cryostat (2). The refrigerator main body (15) and the re-condenser (23) are heated in a vacuum state. Since they are connected in an adiabatic state by the tubular heat insulating part (24) made of a material having a low conductivity, the insertion part of the refrigerator into the cryostat (2) is recondensed (2).
3) only, and the opening portion of the cryostat (2) as a mounting portion of the refrigerator is narrow, and it is not necessary to greatly change the cryostat (2).

Moreover, the recondensing refrigerant pipes (26) and (27) are arranged in the heat insulating part (24), and the atmosphere around the heat insulating part (24) from the refrigerator body (15) is arranged in the heat insulating part (24). The radiation shield part (2
8) is built in, and the recondensing refrigerant pipes (26), (2
7) are spacers (29), (3) with respect to the heat insulating part (24).
Since they are supported in a heat-insulating state by means of 0), the heat-insulating structure can suppress the heat entering from the opening of the cryostat (2) as much as possible.

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

FIG. 2 shows the entire structure of a refrigerator using helium as a refrigerant according to an embodiment of the present invention, in which (1) is a superconducting magnet (1
In the MRI-CT as a medical device containing a), the superconducting magnet (1a) is arranged in a cryostat (2) for storing liquid helium,
Due to the cold heat of the liquid helium, the cryogenic level (4.
It is kept cooled at 3K).

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). The 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 so as to penetrate in the vertical direction, and a cylindrical insertion member (13) is fitted in the 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.
4) is, as shown in FIG. 1, a pre-cooling 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). From the JT circuit (19) for precooling the helium gas compressed by 1. by the precooling refrigeration circuit (16) and expanding the precooled helium gas by JT to generate a cryogenic state at an extremely low temperature level. Become. The refrigerator body (15) of the refrigerator (14) has the mounting flange portion (15b) at the lower end of the case (15a) of the refrigerator body (15) attached to the upper surface of the cryostat (2). 13) Mounting flange part (13a) provided on the upper end
It is attached by fastening it confidentially.

In the case (15a) of the refrigerator body (15), as shown in enlarged detail in FIG. 1, constituent units respectively constituting a precooling refrigeration circuit (16) and a JT circuit (19) are housed. ing. That is, although shown only partially, as a constituent unit on the side of the pre-cooling refrigeration circuit (16),
An expander (18) for expanding a helium gas from the compressor to generate a low temperature state of a predetermined temperature level is disposed at a heat station (not shown). On the other hand, as a constituent unit on the JT circuit (19) side, the expansion (18) is used.
A plurality of JT heat exchangers (20), (20), ... for cooling the helium gas cooled by heat exchange with the helium gas on the return side in order to cool the helium gas on the return side.
A JT valve (21) (Joule Thomson valve) for expanding the helium gas cooled by the JT heat exchangers (20), (20), ...
Further, inside the refrigerator body (15), a radiation shield part (22) having a predetermined temperature level for shielding heat from the outside is arranged.

Further, (23) is a re-condenser as a cooler that evaporates the helium gas expanded by the J-T valve (21) and is cooled 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).

Then, the recondenser (23) and the refrigerator main body (1
The case (15a) of 5) is integrally connected by a cylindrical heat insulating portion (24) made of a material having a low thermal conductivity. The heat insulating portion (24) is concentrically fitted and inserted into the insertion member (13), and a vacuum chamber (25) is formed inside thereof.

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. Further, in the heat insulating part (24), the atmosphere around the heat insulating 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). A cylindrical radiation shield portion (28) extending to a portion having a temperature level of 77K is incorporated.

Further, the recondensing refrigerant pipes (26) and (27) are supported in the heat insulating portion (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 insertion member (13) are formed in a substantially quadrangular shape so as to have a minimum contact area.

On the other hand, the inner spacer (30) has a pair of through holes (30a), (30a) through which the recondensing pipes (26), (27) are inserted, as shown in FIG. , The through holes (30a), (30a) in the refrigerant pipe (26),
By bringing both ends into contact with the inner peripheral surface of the heat insulating section (24) with the (27) inserted, the recondensing refrigerant pipe (2
6) and (27) are held in the substantially central part of the heat insulating part (24), and both ends thereof are tapered so that the contact area with the inner peripheral surface of the heat insulating part (24) becomes the minimum area. Has been formed.

In FIG. 2, reference numeral (40) is a liquid helium supply port opened in a portion of the insertion member (13) located outside the cryostat (2), and (41) is a precooling refrigeration circuit (16).
Helium gas supply port to the expander (18) of (4)
2) is the same outlet. Further, (43) is a supply port of helium gas in the JT circuit (19), and (44) is the discharge port thereof.

Therefore, in the above-described embodiment, the temperature of the heat station of the expander (18) in the pre-cooling refrigeration circuit (16) of the refrigerating machine (14) decreases to a low temperature level and the JT circuit (19) in the above embodiment. ) Side helium gas is pre-cooled in the heat station of the expander (18), the pre-cooled helium gas is cooled in the JT heat exchanger (20), and the JT valve (21) is used in the Joule Thomson. After the expansion, the recondenser (23) expands, and the latent heat of vaporization at that time reduces the temperature of the recondenser (23) to a cryogenic level of 4.3K. Therefore, even if liquid helium stored inside the cryostat (2) is evaporated into helium gas by the heat of entry from the outside of the cryostat (2), the helium gas is recondensed (23) at the cryogenic level. ) Will be re-condensed to the original liquid helium. as a result,
Since there is no consumption of expensive liquid helium due to evaporation, periodical replenishment of the liquid helium is not necessary, the running cost of the MRI-CT (1) using liquid helium as a cooling source can be reduced, and the liquid helium It is possible to eliminate the trouble of refilling operation.

In that case, the refrigerator main body (15) in the refrigerator (14)
Are arranged outside the cryostat (2) and the re-condenser (23) inside the cryostat (2). The refrigerator main body (15) and the re-condenser (23) are heated in a vacuum state. Since they are connected in a heat-insulated state by the tubular heat insulating portion (24) made of a material having low conductivity, the insertion portion of the refrigerator (14) into the cryostat (2) is inserted into the insertion member (13) again. Compared with the case where only the condenser (23) is provided and the entire refrigerator (14) is equipped in the cryostat (2), the opening portion as the attachment portion of the refrigerator (14) in the cryostat (2) may be narrower, This is advantageous because it is not necessary to significantly change the structure of the cryostat (2).

In addition, the recondensing refrigerant pipes (26) and (27) are arranged in the heat insulating part (24), and the heat insulating part (24) is provided around the heat insulating part (24) from the refrigerator main body (15). Radiation shield part (2
8) is built in, and the recondensing refrigerant pipes (26), (2
7) are spacers (29), (3) with respect to the heat insulating part (24).
Since it is supported in a heat-insulating state by means of (0), the heat-insulating structure can suppress the heat of invasion from the opening of the cryostat (2) as much as possible, and thus more surely suppress the evaporation of the liquid helium. be able to.

Incidentally, the outer spacer (29) and the inner spacer (30) in the above embodiment can be changed to other structures. That is, FIGS. 6 to 10 show the spacer (2
9) and (30) are shown as modified examples, and in the examples shown in FIGS. 6 and 7, the outer spacer (29 ') is composed of three push-pin-shaped support members (31), (31), .... Then, the three support members (31), (31), ... Are equally divided in the circumferential direction, and the rod portion (31a) of each support member (31) is arranged.
The head portion (31b) to the inner peripheral surface of the radiation shield portion (28) by penetrating the inside of the radiation shield portion (28) from the outside, and the tip of the rod portion (31a) to the inner periphery of the heat insulating portion (24). The radiation shield part (28) is adiabatically supported by the heat insulating part (24) by abutting against the surface.

Further, in the structure shown in FIG. 8, the inner spacer (3
0 ') through holes (30'a), (30'a) are opened to one side of the spacer (30') so that the spacer (30 ') for the recondensing refrigerant pipes (26), (27). It is designed to be easily attached and detached.

Further, in the example shown in FIG. 9, the inner spacer (3
0 '), the first support rod (32) having elasticity and bent to approximately 120 ° (triangular division of a circle), and the second elasticity having a support portion (33a) at the tip. Of the first support rod (32), the both ends of the first support rod (32) are brought into contact with and fixed to the inner peripheral surface of the radiation shield part (28), respectively, while the second support rod (33) is fixed. The base end of is joined to the inner peripheral surface of the radiation shield (28), and the support portion (33
The recondensing refrigerant pipes (26) and (27) are pressed and supported between a) and the intermediate portion of the first support rod (33), and are held at approximately the center of the radiation shield part (28). It is the one.

Therefore, also in each of the above examples, it is possible to obtain the same operational effects as those of the above-described embodiment.

(Effect of the Invention) As described above, according to the present invention, the refrigerator main body of the refrigerator is arranged outside the cryostat, and the recondenser is arranged inside the cryostat, respectively, and the refrigerator main body and the recondenser are cylindrical. A radiation shield part which is connected in a vacuum adiabatic state by a heat insulating part, and which is provided with a recondensing refrigerant pipe in the heat insulating part, and which extends from the refrigerator body to a part where the atmosphere around the heat insulating part reaches a predetermined level in the heat insulating part. With the structure that the recondensing refrigerant pipe is supported in a heat insulating state by a spacer to the heat insulating portion, the size of the refrigerator mounting opening in the cryostat is reduced, and the structure of the cryostat is changed. And, while suppressing the heat intrusion from the opening portion thereof, eliminating the trouble of replenishing expensive liquid helium, the temperature of low temperature operating equipment such as MRI-CT is reduced. It is possible to reduce the training cost.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is an enlarged cross-sectional view of a main part of the present invention, FIG. 2 is a cross-sectional view showing the entire structure, FIG. 3 is a perspective view of an outer spacer, and FIG. The figure is the same front view, and FIG. 5 is a perspective view of the inner spacer. FIG. 6 is a perspective view showing a mounting structure of a modified outer spacer to a radiation shield portion, and FIG. 7 is a sectional view taken along line VII-VII in FIG. FIG. 8 is a perspective view showing a modified example of the inner spacer. FIG. 9 is a perspective view showing another modified example of the inner spacer, and FIG. 10 is a front view of the same. (2) ... Cryostat, (14) ... Refrigerator, (1
5) ... Refrigerator body, (23) ... Recondenser, (24) ... Insulating section, (26), (27) ... Refrigerant piping, (28) ... Radiation shield section, (29), (29 ') ... Inner spacer,
(30), (30 '), (30 ") ... Outer spacer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-261868 (JP, A) JP-A-62-116868 (JP, A)

Claims (1)

[Scope of utility model registration request] 1. A refrigerator in which helium gas evaporated from liquid helium stored inside a cryostat (2) is cooled by a recondenser (23) and recondensed,
The refrigerator body (15) is placed outside the cryostat (2),
The re-condensers (23) are arranged inside the cryostat (2), respectively, and the refrigerator main body (15) and the re-condenser (23) are made of a material having a low heat conductivity in a vacuum state. The heat insulation unit (24) is connected in a heat insulating state by the cylindrical heat insulation unit (24), and the refrigerator main body (15) is provided in the heat insulation unit (24).
The recondensing refrigerant pipes (26) and (27) for exchanging the refrigerant between the recondenser (23) and the recondenser (23) are arranged, and the heat insulating section (24) is insulated from the refrigerator main body (15). Division (24)
A radiation shield portion (28) extending to a portion where the surrounding atmosphere reaches a predetermined level is built in, and the recondensing refrigerant pipes (26) and (27) are spacers (29) and (30) with respect to the heat insulating portion (24). ) Is supported in a heat-insulated state by a refrigerator.