US3383874A - Cryostat - Google Patents

Description

May 21, 1968 ROYET 3,383,874

CRYOSTAT Filed July 14, 1966 I 4 Sheets-Sheet l FIG .1

May 21, 1968 J. ROYET 3,383,874

CRYOSTAT Filed July 14, 1966 4 Sheets-Sheet 2 J- ROYET CRYOSTAT May 21, 1968 4 Sheets-Sheet 4 Filed July 14, 1966 FIGS FIGQ

FIGJiO' United States Patent 19 Claims. CI. 62-45) ABSTRACT OF THE DISCLOSURE This invention relates to cryostats including an inner container arranged Within a casing with a heat screen being provided in the space between the lateral walls of the casing and container and with an insulating material filling the space between the casing and the heat screen. The heat screen comprises a double-walled jacket made of a high thermal conductivity material which defines an annular space for circulating a cryogenic fluid. The bottom part of the jacket is connected to the top of the container through a plurality of pipes, the upper part of the jacket being connected to a discharge pipe for the cryogenic fluid.

The present invention relates principally to a novel cryostat for cryogenic fluids at very low temperatures (liquid hydrogen, or liquid helium).

The cryostats of the prior art comprise generally a container surrounded with a jacket filled with an auxiliary refrigerant or guard liquid and arranged within an evac uated vessel which may or may not be filled with an insulating material. In such apparatuses, the guard-liquid is generally liquid nitrogen, while the refrigerant liquid proper is liquid helium poured from the top of the container, the escaping vapours being collected also at the top of said container. It is to be noted that the current use of high performance insulating materials known as super insulations makes it necessary to provide between the container and the heat insulation a cold screen which absorbs the heat which, as a result of solid conduction, has passed through the insulation, since this heat can no longer be channelled to the outside. In conventional containers, an adequate screen against infrared radiations is provided by an ordinary jacket cooled at its top, but in the case of super insulations, it is necessary to cool the screen on its full height. For that reason, some cryostats of the prior art are provided both with a jacket filled with a guard liquid and super insulation. In such cases, two independent supplies must be provided, a nitrogen and a helium one, and the consumption of both these refrigerants is relatively high.

To avoid this drawback, it has already been suggested to design cryostats wherein the vapours emitted by the refrigerant liquid are collected at the top of the container and discharged to the atmosphere after circulating in a helical tube surrounding the container and attached to a heat screen thereby cooled all over its height. This dispenses from using a guard liquid and also reduces the consumption of the refrigerant liquid proper.

Such an arrangement however entails certain drawbacks. In particular, the pressure drop in the discharge tube or coil is relatively high, since the tube must have a great length and a small diameter. As a result, undesirable over-pressures may occur within the cryostat container whenever, for any reason, the liquid evaporation rate departs from a rather small value. Besides, the attachment joining, the cooling coil and screen must provide a very good thermal bond, this being diflicult to achieve. Moreover, the heat drainage through the screen is performed only by conduction, thereby decreasing the conductivity of the screen.

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The primary object of the invention is to provide a cryostat comprising an inner container arranged within a casing, a heat screen located in the space between the casing and the container, and an insulation filling the space between the casing and the heat screen.

It is another object of the invention to provide a cryostat wherein said heat screen is a double-walled jacket, the two walls defining an empty space which is connected through appropriate pipes respectively to the top of said container to a discharge.

It is a further object of the invention to provide transversal wrinkles or the like in the walls of said jacket, the Wrinkles of both walls being preferably located at the same levels and protruding inside said jacket so as to make up constrictions.

It is still a further object of the invention to provide a sheet, gauze, wire-netting or membrane, made of a high heat conductivity material, such as aluminium, which is arranged within said jacket.

It is obvious that such arrangements provide a heat screen made up by the liquid refrigerant vapours carrying away the heat which has passed through the super-insulation by convection effect, which greatly improves the efliciency of said screen. In addition, no overpressure is to be feared, since the section provided for the flow of the vapours within the heat screen is relatively large.

It is a still further object of the inventionto provide a compact cryostat, easy to build and capable of being entirely demounted.

These and other objects of the invention will be apparent from the following description, taken in connection with the accompanying drawings, given merely as illustrative examples.

FIGURE 1 is a broken-away side elevation and partial section of a cryostat according to the invention.

FIGURE 2 is a section according to line 22 of FIGURE 1.

FIGURE 3 is a broken-away side elevation and partial section of a variant of the cryostat according to the invention.

FIGURE 4 is a section according to line 4--4 of FIGURE 3.

FIGURE 5 is an enlarged section of the connection arrangement of the discharge pipe of the jacket making up the heat screen.

FIGURES 6 and 7 are enlarged sections of details of the cryostat of FIGURE 3 respectively along lines 66 and 77 of FIGURE 4.

FIGURE 8 is an enlarged section along line 8-8 of FIGURE 3.

7 FIgURE 9 is a section along line 99 of FIGURE FIGURE 10 is a view of details according to arrow F of FIGURE 6-.

The cryostat shown as a merely illustrating example in FIGURE 1 comprises an outer casing 10 resting on a conventional support 12. The cryostat is open at its top and closed by a lid 14, resting on a flange 16 making up the upper rim of the cryostat. The lid 14 is attached by means of U-shaped clamps 18, an O-ring joint ensuring leak-tightness between the lid and the flange 16. A container or vessel 26 is arranged within the casing 10; on its top is arranged an outer flange 24, on the outer edge of which is attached a cylindrical section 22, which itself is attached at its top to the underside of the flange 16. The flange 24 thus makes up a step and is provided with a plurality of holes (six in the example shown here); in which are fitted tubes 28 arranged in a circle around the vessel or container 26. The bottom parts of the tubes 28 are fitted into blank holes provided in an annular part 30 surrounding the vessel 26 near its bottom but which are not in contact with said vessel. The outer edge of the annular part as is welded to the lower edge of a double-walled jacket 52, the inside of which communicates with the inside of the tubes 28 by means of drillings 34 provided for in the part 30 which supports the jacket 32. The jacket 32, which surrounds the container 26 and the cylindrical section 22 runs up close to the underside of the flange 16. The two walls of the jacket 32 join up at their top so as to close up the inner space between them. The jacket 32 is provided, also at its top, with a discharge pipe 36 which passes through the casing 19 at 38.

In addition, a gauze, sheet, wire netting or preferably a membrane made of aluminium or any other high heat condutivity material 31 is laid within the jacket 32 on its full height.

The annular part 30 on which the jacket 32 and the tubes 28 are resting is also used for fitting an auxiliary bottom part 40 prolonging said jacket substantially at a constant distance from the wall of the casing 10. A partition 42 defines in the auxiliary bottom part a space 44 which is isolated from the container 26 and which contains an absorbent. Openings or slots 46 are provided in the partition 42 as well as in the auxiliary bottom wall 40. In addition, the auxiliary bottom 40 is provided with another opening 47 closed by a plug 48.

The bottom of the casing 10 is also provided with an opening fitted with a nozzle 56 closed by a check-valve 58 covered with a cap 66'. In addition, a tube 62, emerging from the base of the container 26, runs up between the jacket 32 and the casing 10 and reaches the upper part of the cryostat where it leaves it so as to be connected to a supply by any conventional means 64. Between the casing wall it), the jacket 32 and the auxiliary bottom part .0, an insulating material, which may, for instance, be a snperinsulation cladding onto the jacket, is provided.

Preferably, the casing 10 as well as the container 26 and the cylindrical part 22 are provided with horizontal annular beads 66, which reinforce them and prevent their being deformed as a result of pressure gradients. Likewise, each of the walls of the jacket 32 is provided also with horizontal wrinkles 68 protruding towards the inside of said jacket so that their tops make up a constriction facilitating in particular the holding in place of the aluminium membrane 31.

It is to be noted that the casing 10 of the cryostat is, in the example shown herein, made up of two parts made integral by means of flanges 70 held together by means of U-shaped clamps 72, obviously to facilitate the assembling and disassembling operations.

The cryostat which has been described hereabove operates as follows:

An adsorbent of any usual type is placed within the space 44, the plug 48 is placed into position, and the opening 56 provided for at the base of the casing 10 is connected to vacuum equipment, which enables the positioning of the check-valve 58. Once the space between the container 26 and the casing 16 has been evacuated, the check-valve 58 is applied on its seat by the atmospheric pressure and the cap 60 may be placed. The apparatus is then ready to operate. A liquid refrigerant such as helium, for instance, is fed at the base of the container 26 via the tube 62. The refrigerant partially evaporates, and the vapours emerging at the top of the vessel or container 26 pass through the tubes 28, the openings 34 of the annular support and the jacket 32. They are disposed of at the top of said jacket through the connecting arrangement 36. The aluminium membrane provided for within the jacket 32 enables to achieve a uniform temperature distribution over the full surface of the jacket, while the adsorbent provided for in the space 44 enables to hold an acceptable vacuum for a very long time.

In the example which has been described hereabove, the jacket 32 is made up of two concentric cylindrical walls defining an annular space for the flow of vapours escaping from the tank.

According to a variant of the invention (not shown here), said jacket is obtained by applying the process known as Roll bond. In such a case, the jacket is made up of two thin plates, of aluminium for instance, welded together in places by hot rolling and thereafter inflated by injecting a compressed gas between said plates, which results in a permanent deformation of the latter in their non-welded areas.

The cryostat shown in FIGURES 3 to 10 is in its principle identical to that of FIGURES 1 and 2, only, different assembling provisions have been made, which are nevertheless of great interest, as they enable to disassemble the apparatus entirely and to have access to all its parts without any difiiculty.

The cryostat of FIGURE 3 has an outer casing mounted on a support 102.

At its open top, the casing 100 has an outer brim on which rests the brim 106 of a container 108 housed Within the casing 100. Both brims 104 and 106 are held together by means of bolts or screws 110, a sealing gasket being provided between said brims. A cover 114 rests on the brim 106 of the inner container 108 and is attached thereon by means of bolts 116, a sealing gasket being provided between them.

The container 108 is made up of two parts assembled together by a ring on which they are welded. Drillings are provided in the edge of the ring .120 surrounding the container and serve for fitting vertical tubes 122 arranged concentrically around the container 108, said drillings emerging in an annular groove 123 provided in the bore of said ring and thus enabling the tubes 122 to communicate with the inside of the container 108.

At their bottom, which is close to the bottom of the container 108, the tubes 122 are fitted in openings provided for in a ring 124 surrounding the bottom of the container 108, with suificient clearance to prevent any contact between said ring and the container. The ring 124 rests on an annular part 126 on which it is attached by means of screws 128, sealing gaskets 1130 being provided for (FIGURES 6 and 7).

The base of a double-walled jacket 132 is attached to the outer part of the annular part 126, the inside of the jacket 1'32 communicating with the tubes 122 by means of channels or pipes 134 provided for within the annular part 126 (FIGURE 7).

The walls of the jacket 132 join up at their tops, the jacket comprising at its upper part a discharge 136 con nected by means of a flange and screw assembly to the collar 138 of a demountable connection arrangement 139, of a type known of the prior art, screwed up on the casing 10 (FIGURE 5).

In addition, the annular part 126 on which the jacket 132 and the tubes 122 rest has a lower skirt 140 making up a cylindrical section on which pins or screw heads 142 are arranged at regular intervals (FIGURES 6 and 10). An auxiliary bottom part 144 prolongs the jacket 132 and is placed on this skirt 140. To this effect, the edge of the auxiliary bottom part 144 is provided with a plurality of vertical slots 146 as well as curved slots 147 arranged at regular intervals and into which the pins or screw heads 142 are engaged. Such an arrangement thus makes it possible to attach the auxiliary bottom part by means of a bayonet type assembly. A metallic clamping ring 148 surrounds the top of the auxiliary bottom part 144 and holds it tight against the edge of the annular part 126. The clamping ring 148 is provided with a clamping device made up of a bolt 150 fastening two lugs 152-154 provided at its ends (FIGURE 9).

The refrigerant is fed into the container 108 by means of a tube 156 which runs in the space 158 filled with an insulation and defined by the casing 100 and the container 1G8. Said tube passes through the auxiliary bottom part 144 through a relatively large opening 160 and is connected to a coupling arrangement made up of two parts 162-164, one of which (164) is welded on the container 108 while the other (162) is made integral with the tube 156, the two parts -162-164 being so assembled that they can be dissociated, by means of a screw assembly 166 for instance (FIGURE 8). At its top, the tube 156 is connected to a connecting arrangement 167 Which is also attached on the casing 100 in such a way as to be demountable (FIGURE 3).

It is to be noted that, as for the cryostat shown in FIGURE 1, the casing 100 itself is made up of two parts made integral by means of U-shaped clamps 168 holding together flanges 170-172 (FIGURE 3).

The apparatus which has been described hereabove is disassembled as follows:

The U-sh'aped members 168 are first removed and the parts of the casing 100 are thus separated. The container 108 and the various other parts of the cryostat thus remain integral with the upper part of the casing. Then, the insulation arranged in the space 158 between the casing 100 and the container 108 is removed, which enables to free the tube 156 from the insulation. The two parts 162-164 of the coupling arrangement connecting the tube 156 to the container '108 are subsequently taken apart by unscrewing the screws 166 which make the two parts integral through the opening 160 provided for in the auxiliary bottom 144.

The auxiliary bottom may then be removed, once the clamping ring 148 has been released and the pins or screw heads 142 have come out of the corresponding curved slots 147.

After taking off from the casing the vapour discharge connecting arrangement 139 and separated its inner collar 138 from the cylindrical part 136 attached to the jacket 132, the annular part 126 and the ring 124 can come apart by unscrewing the screws 128 which make them fast; the jacket 132 can then be loosened and removed by making it slide around the container 108.

After unscrewing the screws 116, which hold them at their top, the container 108 and the casing come apart.

The advantages offered by such an embodiment, which enables easy access to all the parts of the cryostat, are obvious.

It is evident that various modifications and changes may be made in the embodiments of the invention herein illustrated and described without departing from the spirit and scope of the invention 'as described in the following claims.

What I claim is:

1. A cryostat including an inner container arranged within a casing, a heat screen in the space between the lateral walls of said casing and said container and an insulating material filling the space only between said casing and said heat screen, said heat screen being a double-walled jacket made of a high thermal conductivity material, and defining an annular space -for circulating a cryogenic fluid, a bottom part of said jacket being connected to the top of said container through a plurality of circumferentially arranged pipes, the upper part of said jacket being connected to a discharge pipe for said cryogenie fluid.

2. A cryostat including an inner container arranged within a casing, a heat screen in the space between the lateral walls of said casing and said container and an insulating material filling the space between said casing and said heat screen, said heat screen being a doublewalled jacket, defining an annular space, for circulating a cryogenic fluid, a bottom part of said jacket being connected to the top of said container through a plurality of pipes, the upper part of said jacket being connected to a discharge pipe, said jacket being made of a high thermal conductivity material, the walls of said jacket being provided with substantially facing each other wrinkles, said wrinkles protruding inside said jacket so as to make up constrictions, said jacket being provided with means allowing a good axial repartition of cold.

3. A cryostat as claimed in claim 2 in which said means allowing a good axial repartition of cold include a sheet of a high thermal conductivity material placed in said annular space between the walls of said jacket.

4. A cryostat as claimed in claim 2 in which said means allowing a good axial repartition of cold include a fabric made of interlaced metallic wires of a high thermal conductivity metal, said fabric being inserted between the walls of said double-walled jacket.

5. A cryostat as claimed in claim 1 in which said jacket is made of two metallic sheets spaced apart and comprising partitions formed by local welding of said sheets and defining a plurality of communicating chambers.

6. A cryostat as claimed in claim 1, wherein said pipes connecting the bottom part of said jacket to the top of said container are placed in the space between said heat screen and said container, said tubes being spaced apart from said screen and said container.

7. A cryostat as claimed in claim 6 in which a refrigerant liquid supply pipe arranged within said insulating material emerges into said container near its bottom and runs through said casing near its top.

8. A cryostat as claimed in claim 1 in which said jacket is a substantially cylindrical annulus extended by a bottom provided with openings for communication with the free space between said bottom and said container, in which an adsorbent material is placed.

9. A cryostat as claimed in claim 8, in which a wall provided with apertures divides said free space into two chambers, said adsorbent material being arranged in the lower chamber, at a distance from said container, without any contact with the wall of the latter.

10. A cryostat as claimed in claim 9, in which said inner container has a wider part at its top, the upper ends of said pipes being fixed in drillings provided for in the wall of said wider part.

11. A cryostat as claimed in claim 10, in which said jacket is closed at its bottom by an annular part the inner diameter of which is slightly larger than the outer diameter of said container so that said annular part protrudes inside said jacket without being in contact with the container, said annular part comprising ports emerging on one side within said jacket and, on the other side, connected to the lower of said tubes.

12. A cryostat as claimed in claim 11 in which the lower ends of said pipes are mounted in a ring resting on the protruding part of said annular part and attached to the latter by means of screws and sealing gaskets.

13. A cryostat as claimed in claim 6, in which a refrigerant liquid supply pipe arranged within said insulating material emerges into said container near its bottom and runs through said casing near its top, said jacket being substantially cylindrical annulus extended by a bottom provided with openings for communication with the free space between said bottom and said container, in which an adsorbent material is placed, said refrigerant liquid supply pipe running through said bottom provided for under said jacket, through a relatively large opening and is connected to the inside of the container by means of a demountable coupling arrangement fixed on the wall of the container.

14. A cryostat as claimed in claim 7, in which said supply and discharge pipes run through said outer casing via dismountable coupling arrangements attached on said casing.

15. A cryostat as claimed in claim 8, in which the bottom provided for under said jacket is attached on said annular part by dismountable means.

16. A cryostat as claimed in claim 1, in which said inner container comprises an outer brim at its top as does said casing, said brims being applied one on top of the other, and being made integral by means of a screw arrangement or the like, sealing gaskets being interposed between said brims.

17. A cryostat as claimed in claim 1, in which transversal annular beads are provided in the wall of said casing.

7 8 18. A cryostat as claimed in claim 1, in which trans- 3,174,300 3/1965 Webb 62-259 versal annular beads are provided in the wall of said 3 274 7 9 19 H ffm et 1 62 45 container. 7 I

19. A cryostat as claimed in claim 1, in which said 2/1967 De Haan n 62 casing is made up of two parts assembled by means of 5 FOREIGN PATENTS flanges and U-shaped clamps.

1,000,882 8/1965 Great Britain. References Cited UNITED STATES PATENTS LLOYD L. KING, Primary Examiner.

3,122,004 2/1964- Aberle 61231 62259 10

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