JP4823768B2 - Transfer tube - Google Patents

Description

  The present invention relates to a transfer tube for transporting liquid helium that transports liquid helium from a refrigerator to a liquid helium storage tank.

  Conventionally, in MEG (magnetoencephalograph), NMR (superconducting nuclear magnetic resonance apparatus), MRI (magnetic resonance imaging) apparatus, etc., it is necessary to maintain a cryogenic state to cause superconductivity. Cryogenic liquid helium (approximately 4K) is used. Since this liquid helium is a scarce resource and relatively expensive, it is not preferable to release the helium gas vaporized in the cooling process to the atmosphere. For this reason, helium reliquefaction systems are known in which helium gas vaporized in a storage tank storing cryogenic liquid helium is recovered, reliquefied, and returned to the storage tank (for example, Patent Document 1 and Patent Document 2). And Patent Document 3).

  This helium reliquefaction system is a Gifford McMahon cycle refrigerator (hereinafter referred to as “GM refrigerator”) capable of cooling helium gas to approximately 4K, a condenser connected to the GM refrigerator, and a recovery from a storage tank. And a purifier that cools and solidifies the impurities in the helium gas. The helium gas (approximately 4-10K) generated in the reservoir is sent to the condenser and reliquefied into cryogenic liquid helium. In addition, the relatively high temperature (approximately 300K) helium gas generated in the storage tank removes impurities such as nitrogen and oxygen in the purifier, and is cooled by the GM refrigerator, then sent to the condenser, and into liquid helium. Reliquefied.

Japanese Patent No. 3446883 Japanese Patent No. 3523085 JP 2005-291628 A

  In such a helium reliquefaction system, a transfer tube is used to transport the liquid helium obtained in the condenser to the storage tank, but in order to perform reliable transport in the liquid helium state, the transfer tube is used. It is desirable to reduce the heat absorption in the chamber as much as possible.

The present invention , in a helium liquefaction system comprising a refrigerator and a helium liquefier that includes a heat shield that is connected to the refrigerator and covers the refrigerator, and a liquid helium storage tank that stores liquid helium. protrudes to the outside from the helium liquefier, the liquid helium from said helium liquefier a transfer tube for transporting the liquid helium reservoir, wherein the transfer tube includes a liquid helium transport pipe for transporting liquid helium, the liquid helium A heat shield pipe that insulates the transport pipe from the surroundings, and a flexible heat transfer material is provided on an outer periphery of the heat shield pipe , and one end of the flexible heat transfer material is the refrigeration Connected to the outer periphery of the heat shield pipe of the transfer tube outside the machine, And an end is connected to the heat shield in the interior of the helium liquefier.

  In addition, it is preferable that the heat transfer material is made of a metal net string material.

  Furthermore, a low-temperature helium transport pipe that transports the low-temperature helium gas existing in the space near the liquid surface of the liquid helium storage tank toward the refrigerator, and a cooled helium gas that is higher in temperature than the low-temperature helium gas obtained by the refrigerator A cooling helium transport pipe that transports the liquid helium storage tank to the upper space of the liquid helium storage tank, and the heat shield pipe covers the liquid helium transport pipe, the low temperature helium transport pipe, and the cooling helium transport pipe to insulate from the surroundings Is preferred.

  Further, in the part close to the refrigerator, the three pipes are connected to the refrigerator as independent pipes, and the heat transfer material is connected to the outer periphery of the heat shield pipe of this part. Is preferred.

  In addition, the liquid helium transport pipe, the low temperature helium transport pipe, and the cooled helium transport pipe formed as three independent pipes, the liquid helium transport pipe, the cold helium transport pipe, and the cooled helium transport It is preferable that a multiple pipe in which the pipe and the heat shield pipe are arranged in this order from the inside is connected.

  Thus, according to the present invention, the heat shield pipe of the transfer tube is connected to the heat shield of the refrigerator with a flexible heat transfer material. Since the heat shield of the refrigerator is connected to the low-temperature refrigerator, the temperature is low, and by providing a heat transfer material, a temperature rise due to radiation of the heat shield pipe can be effectively suppressed.

  In addition, by using a metal net string material as the heat transfer material, attachment and the like are facilitated while maintaining heat conduction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

"System configuration"
FIG. 1 is a diagram illustrating a schematic configuration of a helium reliquefaction system using a transfer tube according to an embodiment.

  The storage tank 10 incorporates a dewar that stores liquid helium, covers the periphery with a heat insulating material, and insulates the periphery from the surroundings by maintaining a vacuum. In the case of a biomagnetic measurement system such as MEG, a superconducting quantum interferometer (SQUID) is installed in the dewar and isolated from the surroundings by a magnetic shield. In addition, the storage tank 10 should just store liquid helium, and can be used for various uses, such as cooling of a superconducting motor.

  In the upper part of the storage tank 10, helium gas of about 300 K that is vaporized inside and rises in temperature is generated. This high-temperature helium gas is supplied to the helium liquefier 30 through a recovery line 22 having a circulation pump 20.

  The helium liquefier 30 has a cold chamber 32 that is vacuum insulated from the surroundings and accommodates two GM refrigerators 34 and 36 therein. The GM refrigerators 34 and 36 include first refrigeration units 34a and 36a and second refrigeration units 34b and 36b. The first refrigeration units 34a and 36a cool helium gas of about 300K to helium gas of about 40K. The second freezing sections 34b and 36b cool helium gas of about 40K to 4K.

  A heat transfer tube 38 in the cold chamber 32 is connected to the recovery line 22, and the heat transfer tube 38 is cooled to about 40K by the first freezing unit 34a and cooled to 4K by the second freezing unit 34b. Then, helium cooled to 4K is supplied to the condenser 40. And this condenser 40 is maintained by the 2nd freezing parts 34b and 36b at the low temperature below 4K, and liquid helium below 4K is obtained here.

  Moreover, the heat transfer tube 42 in the cold chamber 32 is connected to the recovery line 22, and the inside of the heat transfer tube 42 is cooled to about 40K by the first refrigeration unit 36a to obtain cooled helium gas.

  The helium liquefier 30 and the storage tank 10 are connected by a transfer tube 50 for transporting liquid helium. Here, the transfer tube 50 has a multi-tube structure, and a liquid helium transport pipe 52 that transports liquid helium from the condenser 40 to the storage tank 10, and 4 near the liquid helium level in the storage tank 10. A low-temperature helium transport pipe 54 that transports low-temperature liquid helium of about 10 K to the condenser 40, a cooling helium transport pipe 56 that transports a cooling helium gas of about 40 K obtained in the heat transfer tube 42 to an intermediate portion of the storage tank 10, Is included.

  In particular, since the transfer tube 50 is disposed in an atmosphere at room temperature (about 300 K), it is preferable to configure the transfer tube 50 so that the temperature is lower toward the inner side. The liquid helium transport pipe 52, the low temperature helium transport pipe 54, the cooling It is preferable that the helium transport pipe 56 has a multi-tube structure in which the helium transport pipe 56 is sequentially positioned outside in this order. This configuration will be described later.

"Structure on the helium liquefier 30 side"
FIG. 2 shows a configuration of a portion of the transfer tube 50 that is connected to the helium liquefier 30.

  The helium liquefier 30 is isolated from the surroundings by an outer wall 60, and the inside is maintained in a vacuum. That is, the inside of the outer wall 60 is a cold chamber 32. Inside the outer wall 60, there is provided a heat shield 62 that is connected to and covers the refrigerators 34 and 36. The heat shield 62 is maintained at about 40K, for example. A part of the heat shield 62 has a hole, and the inside of the heat shield 62 is also maintained in a vacuum. From this hole, a liquid helium transport pipe 52, a low-temperature helium transport pipe 54, and a cooled helium transport pipe 56 connected to the condenser are exposed.

  Further, a part of the outer wall 60 corresponding to the hole of the heat shield 62 protrudes outward, and a flange 60a connected to the transfer tube 50 is formed there. And this flange 60a and the flange 64a of the casing pipe 64 used as the outermost pipe of the transfer tube 50 are connected, The inside of the casing pipe 64 is connected with the inside of the outer wall 60, and this is also maintained in vacuum. The The flanges 60a and 64a may be connected by welding, but in the case of an MEG set in a shield room, it is preferable that the flanges 60a and 64a be removable by bolting.

  Inside the casing pipe 64, a heat shield pipe 66 is arranged concentrically. The heat shield pipe 66 is open on the helium liquefier 30 side, and the inside thereof communicates with the inner space of the casing pipe 64 and the inner space of the outer wall 60. Further, a liquid helium transport pipe 52, a low temperature helium transport pipe 54, and a cooling helium transport pipe 56 coming out of the holes of the heat shield 62 are accommodated in the heat shield pipe 66. The heat shield pipe 66 is formed by bolting a half pipe. Accordingly, the heat shield pipe 66 can be installed after the liquid helium transport pipe 52, the low temperature helium transport pipe 54, and the cooling helium transport pipe 56 are installed.

  In this example, the casing pipe 64 is formed of a bellows that can be removed at both ends and can expand and contract in the axial direction. Therefore, the inside can be exposed by removing at least one end of the casing pipe 64 and moving it to one side. Further, the liquid helium transport pipe 52, the low temperature helium transport pipe 54, and the cooling helium transport pipe 56 are provided with a connecting portion (VCR) in the middle thereof. Therefore, after connecting the liquid helium transport pipe 52, the low temperature helium transport pipe 54, and the cooling helium transport pipe 56 at the connecting portion, the half heat shield pipe 66 is bolted and the casing pipe 64 is closed, whereby the transfer tube 50. Can be connected to the refrigerator.

  The liquid helium transport pipe 52, the low-temperature helium transport pipe 54, and the cooling helium transport pipe 56 are three independent pipes inside the heat shield pipe 66 on the helium liquefier 30 side. It has become.

  On the outer periphery of the heat shield pipe 66, a string-like and net-made string material 68 made of copper is provided as a heat transfer material. One end of the net string material 68 is bolted to the outer periphery of the heat shield pipe 66, and the other end is bolted to the heat shield 62. Therefore, the heat shield pipe 66 is in a low temperature state equivalent to that of the heat shield 62 due to the heat transfer of the netting material 68, and the intrusion of radiant heat into the heat shield pipe 66 is performed in the first stage of the refrigerator having a large refrigerating capacity. Absorbs. Further, the netting material 68 is flexible, can be easily fixed to the heat shield 62, and can secure sufficient heat conduction.

  Further, the outer peripheral surface of the heat shield pipe 66 is subjected to a finishing process such as buffing to have a mirror-like surface, thereby reducing intrusion of radiant heat from the outside. It is also preferable to apply nickel plating or the like.

  In addition, although copper is used as the netting material 68 as a material having good heat transfer, other metal or non-metal may be used as long as sufficient heat transfer is possible. Moreover, if it has flexibility, it may not be a net string material. In addition, it is preferable that a portion to be bolted is provided with a crimp terminal or the like.

"Multi-tube structure"
In the right part of FIG. 2, the structure of the multi-tube structure part is shown. An independent liquid helium transport pipe 52 that transports liquid helium from the condenser 40 is connected to a liquid helium transport pipe 70 having a double tube structure in which a vacuum chamber is formed on the outer periphery.

  A low temperature helium transport pipe 72 connected to a low temperature helium transport pipe 54 for transporting a low temperature helium gas from the storage tank 10 is provided concentrically on the outer peripheral side of the liquid helium transport pipe 70 so as to surround the liquid helium transport pipe 70. Yes. Around the low-temperature helium transport pipe 72, a cooling helium transport pipe 74 connected to the cooling helium transport pipe 56 that transports the cooling helium gas is provided concentrically. The cooling helium transport pipe 74 has a double tube structure having a vacuum chamber around it. Further, the cooling helium transport pipe 74 is provided concentrically and spaced outside the low temperature helium transport pipe 72. Therefore, the outer space of the low temperature helium transport pipe 72 is a vacuum chamber communicating with the inside of the heat shield pipe 66.

  The end of the cooling helium transport pipe 74 is connected to the inside of the heat shield pipe 66. The casing pipe 64 extends as it is, and is arranged concentrically at intervals outside the cooling helium transport pipe 74 having a double tube structure. Therefore, the casing pipe 64 is positioned outside the cooling helium transport pipe 74 having a double-pipe structure through the vacuum chamber.

  Thus, in this example, the transfer tube 50 has a liquid helium transport pipe 70, a low-temperature helium transport pipe 72, and a cooled helium transport pipe 74 in a double tube structure each having a vacuum chamber around them, It has a seven-pipe structure in which a heat shield pipe 66 and a casing pipe 64 are arranged around it. And since 4K liquid helium, 4-10K low temperature helium gas, and about 40K cooling helium gas are located through the vacuum chamber from the innermost side, it is effective in reducing heat transfer to liquid helium. Liquid helium can be transported. Furthermore, the penetration of radiant heat can be reduced by the heat shield pipe 66 disposed inside the casing pipe 64.

  And as FIG. 3 shows, the spacer 76 is arrange | positioned between each pipe which comprises a 7-fold pipe | tube. The spacer 76 has a cylindrical shape in the radial direction, and an outer tip portion thereof is tapered. Therefore, it is possible to position the pipe by reducing the contact area with the outer pipe. In addition, the spacer 76 is preferably made of a low thermal conductivity such as Teflon resin, so that the pipe can be reliably supported and the thermal conduction can be suppressed.

  Here, FIG. 5 shows a configuration of the spacer 76 viewed from the axial direction. As described above, the spacer 76 includes the ring-shaped base portion 76a, the trapezoidal protrusion portion 76b facing inward, and the trapezoidal protrusion portion 76c facing outward. Therefore, the contact between the spacer 76 and the inner and outer pipes is only the projecting portions 76b and 76c, and the contact area is small and the heat conduction is small. Further, in this example, the positions of the protrusion 76b in the inner direction and the protrusion 76c in the outer direction are shifted (in this example, they are shifted by 45 degrees from each other), and the spacer 76 of the outer pipe and the inner pipe is moved. The distance of the path of heat conduction through is long.

  As described above, according to the present embodiment, the spacer 76 can sufficiently receive the pressure for holding the pipe, and at the same time, the contact area with the pipe can be reduced and the heat transfer path can be enlarged to conduct heat conduction. Can be small.

  Further, as is apparent from FIG. 3, the positions where the spacers 76 are arranged are shifted in the axial direction between adjacent ones and arranged in a staggered manner. Thereby, the heat transfer path can be lengthened, and the heat conduction to the inside can be reduced.

  The protrusions 76b and 76c can have various shapes such as a spherical shape, a truncated cone shape, and a polygonal truncated cone shape, and may have a structure in which a vertical hole is formed in the central portion.

  In addition, as described above, the spacer in the present embodiment is preferably made of resin. And as a whole, it is ring-shaped, has protrusions 76b, c on its outer peripheral surface and inner peripheral surface, and is point-symmetric with respect to the center. Such a spacer can be manufactured at a relatively low cost by being manufactured using a laser or pressurized water. For example, it can be manufactured by cutting a resin plate having a predetermined thickness using a laser or pressurized water. Further, according to this processing method, spacers having different diameters can be manufactured from one resin plate.

  Further, it is also preferable to wrap a super insulator (SI) around the outer periphery of the cooling helium transport pipe 74, whereby heat penetration from the outside can be reduced. In addition, the super insulator SI is usually obtained by vapor-depositing aluminum on a synthetic fiber such as polyester.

“Structure on the storage tank 10 side”
In FIG. 4, the structure of the transfer tube 50 of the part connected to the storage tank 10 is shown. The end portion of the casing pipe 64 is bent downward in an L shape, and a pipe-like protrusion 80 is provided at the upper portion of the portion, and a removable lid 82 is bolted and fixed to this portion. . Therefore, by removing the lid 82, this portion functions as an inspection port.

  Further, the end portion of the casing pipe 64 is configured as a separate L-shaped portion 84, and the L-shaped portion 84 is connected to the casing pipe 64 by bolting. The L-shaped portion 84 is fixed to the outer wall 86 of the transfer tube inserted into the storage tank 10. It is also preferable that the L-shaped portion 84 be removable from the outer wall 86.

  In the casing pipe 64, a heat shield pipe 88 connected to the outer periphery of a seven-pipe cooling helium transport pipe 74 is arranged, and a corner portion 88a of the heat shield pipe 88 is bent downward in an L shape. ing. The corner portion 88a bent in an L shape of the heat shield pipe 66 is removed from the straight pipe portion. In particular, by making it possible to divide, after removing the lid 82, the corner 88a can be removed to expose the inside. In addition, it is preferable to provide a super insulator around the heat shield pipe 88.

  Inside the heat shield pipe 66, a liquid helium transport pipe 90, a low temperature helium transport pipe 92, and a cooling helium transport pipe 94 are arranged as independent pipes, and these are also bent in an L shape.

  The outer wall 86 has a central portion extending downward, and this portion is a casing pipe, and this portion has a six-pipe structure including a liquid helium transport pipe, a low-temperature helium transport pipe, and a cooling helium transport pipe. Yes. This 6-pipe structure is basically the same as that shown in FIGS. 2 and 3 except that only one vacuum chamber is provided outside the cooling helium transport pipe through which cooling helium gas flows. . Also, this portion may have a seven-pipe structure. And the connection part to a 6-fold pipe can also be removed, respectively.

  In addition, an opening for a cable is provided in an end wall on the side portion of the L-shaped portion 84, and a cable hermetic connector 96 is fitted therein. This cable hermetic connector 96 is for leading out the cable from the temperature sensor 98 provided inside while maintaining the inside in a vacuum state.

  In the present embodiment, the temperature sensor 98 can be maintained and inspected and replaced by removing the lid 82 and partially removing the heat shield pipe 88. The temperature sensor 98 can be formed of a silicon diode or the like, and can detect various temperatures such as liquid helium, low-temperature helium gas, and cooling helium gas near the storage tank 10.

It is a figure which shows the whole structure of a system. It is a figure which shows the structure of the transfer tube by the side of helium liquefier. It is a figure which shows the structure of the transfer tube of a multi-tube structure. It is a figure which shows the structure of the transfer tube by the side of a storage tank. It is a figure which shows the structure of a spacer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Reservoir, 20 Circulation pump, 22 Recovery line, 30 Helium liquefier, 32 Cold chamber, 34, 36 Freezer, 34a, 36a 1st freezing part, 34b, 36b 2nd freezing part, 38, 42 Heat transfer tube, 40 Condenser, 50 Transfer tube, 52, 70, 90 Liquid helium transport pipe, 54, 72, 92 Low temperature helium transport pipe, 56, 74, 94 Cooling helium transport pipe, 60 Outer wall, 60a flange, 62 Heat shield, 64 Casing pipe , 64a flange, 66 heat shield pipe, 68 mesh string material, 76 spacer, 78 super insulator, 80 protrusion, 82 lid, 84 L-shaped part, 86 outer wall, 88 heat shield pipe, 88a corner, 96 hermetic connector for cable 98 Temperature sensor.

Claims (5)

A helium liquefaction system comprising: a refrigerator, a helium liquefaction device that includes a heat shield connected to the refrigerator and covers the refrigerator, and liquefies helium gas; and a liquid helium storage tank that stores liquid helium. A transfer tube that protrudes from the outside and transports liquid helium from the helium liquefier to a liquid helium storage tank,
The transfer tube is
A liquid helium transport pipe for transporting liquid helium;
A heat shield pipe that insulates this liquid helium transport pipe from the surroundings;
Including
A flexible heat transfer material is provided on the outer periphery of the heat shield pipe, and one end of the flexible heat transfer material is provided on the outer periphery of the heat shield pipe of the transfer tube outside the refrigerator. It is connected to, tiger emission scan fur tube and the other end is connected to the heat shield in the interior of the helium liquefier. The transfer tube according to claim 1, wherein
The transfer tube, wherein the heat transfer material is made of a metal netting material. The transfer tube according to claim 1 or 2,
further,
A low-temperature helium transport pipe for transporting low-temperature helium gas present in the space near the liquid surface of the liquid helium storage tank toward the refrigerator;
A cooling helium transport pipe for transporting a cooling helium gas having a temperature higher than that of the low temperature helium gas obtained by the refrigerator to an upper space of the liquid helium storage tank;
Including
The transfer tube, wherein the heat shield pipe covers the liquid helium transport pipe, the low-temperature helium transport pipe, and the cooling helium transport pipe to insulate from the surroundings. The transfer tube according to claim 3,
In the part close to the refrigerator, the three pipes are connected to the refrigerator as independent pipes,
The transfer tube is characterized in that the heat transfer material is connected to the outer periphery of the heat shield pipe of this portion. The transfer tube according to claim 4, wherein
For the liquid helium transport pipe, the cold helium transport pipe and the cooled helium transport pipe formed as three independent pipes,
A transfer tube comprising: a plurality of pipes in which the liquid helium transport pipe, the low-temperature helium transport pipe, the cooling helium transport pipe, and the heat shield pipe are arranged in this order from the inside.

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