JPH04142083A - Cryostat - Google Patents

Abstract

PURPOSE:To inhibit the penetration of heat and avoid the clogging of piping by maintaining in the piping a gap through which gas flows and laying out a thin wall cylindrical vessel coaxially. CONSTITUTION:A vacuum cylindrical vessel 11 is coaxially laid out in a pipeline 7 used for the injection of very low temperature refrigerant 2, the collection of vapor gas, and the guide of current lead in order to prevent the generation of convection. The optimum value is available, which specifies the diameter, material, and thickness of the cylindrical vessel in conformity with the penetration heat of cryostats used. More specifically, when the diameter of a vacuum cylindrical vessel exceeds a certain level, the clearance between the pipe and the vacuum cylindrical vessel is narrower than a total thickness of a natural convection border layer which develops on the pipe wall of both the pipeline and the vessel, which inhibits the generation of downstream. On the other hand, it is desirable to take up a large gas flow passage cross section area as much as possible in order to protect the pipeline from being clogged. This construction makes it possible to prevent the introduction of hot gas in an ambient temperature section into a low temperature section and inhibit the penetration of heat from the piping.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a taliostat used in superconducting equipment and the like.

(Prior Art) Conventionally, a cryostat for maintaining a superconducting magnet or the like at a cryogenic temperature has the following configuration in order to minimize evaporation of a cryogenic refrigerant. That is, a refrigerant container containing a cryogenic refrigerant, covering this refrigerant container,
A vacuum container that forms a vacuum insulation layer between itself and the refrigerant container, a heat shield provided within the insulation layer, one end communicating with the refrigerant container, and the other end connecting the vacuum insulation layer, thermal silt, and the vacuum container. The pipe is installed so as to penetrate the wall of the pipe and is located in the normal temperature part, and is used for injection of cryogenic refrigerant, recovery of evaporated gas, guidance of current leads, etc.

In the cryostat configured in this manner, the heat that enters the refrigerant container other than the piping can be suppressed to several mw by installing a small refrigerator or the like. However, the intrusion heat related to the piping is generally several tens of mW, which poses a big problem in reducing the amount of evaporation of the refrigerant. A major factor in the intrusion heat related to this piping is probably due to the convection of evaporated gas within the piping. For example, in the case of vertical piping, the heat intruding from the pipe causes an upward flow near the pipe wall and a downward flow in the center of the pipe, and due to this convection phenomenon, warm gas from the normal temperature area is brought to the low temperature area and evaporates. amount or increase.

The increase in evaporation due to convection of evaporated gas can be suppressed by reducing the cross-sectional area of the piping, so convection can be suppressed accordingly.
It can be suppressed. However, in order to suppress the rise in internal pressure of the refrigerant container due to quenching of the superconducting magnet, the pipe diameter cannot be reduced to a certain level. Furthermore, if the pipe diameter is made smaller, the pipe becomes more likely to become clogged when air gets mixed in, and in the worst case, the cryostat will be damaged.

For this reason, conventional cryostat
It has been proposed to arrange a cylindrical body having a large number of small holes in the tube axis direction, as shown in No. 59911.

However, such a configuration as described above does not provide such a great effect. This is explained as follows.

By inserting the above-mentioned convection prevention plate into the piping, the heat intrusion due to convection is reduced, but the heat intrusion due to conduction through the inserted cylindrical body with many small holes increases, so the intrusion heat is not so much. Does not decrease.

Furthermore, a structure in which a large number of small holes are provided has a small cross-sectional area for each flow path, which promotes clogging of the piping due to intrusion of air and the like.

Also, JP-A-57-62580, JP-A-56-28384,
57-89277, etc., as a measure to prevent convection in the piping, the emergency discharge pipe is separated from the piping related to refrigerant injection, recovery, etc., and the emergency discharge pipe has a rupture plate on the low temperature side and the normal temperature side. It is constructed by providing a vacuum inside.

On the other hand, a method has been proposed in which the diameter of the piping for liquid injection and collection is made as small as possible to prevent convection within the piping.

However, in this method, it is not possible to cool the intruding heat due to conduction from the large-diameter emergency discharge pipe with the evaporative gas, so this intruding heat becomes a big problem in a cryostat with low intrusive heat.

(Problems to be Solved by the Invention) As described above, if the piping is provided with a convection prevention plate or a separate emergency release piping, it is not possible to suppress the intrusion heat, and the piping The possibility of blockage increases.

Therefore, the present invention can reliably suppress the intrusion heat that enters the cryogenic refrigerant container through the piping, and at the same time has a low possibility of clogging the piping, and even if the piping is clogged, the cryostat will not be damaged. The purpose is to provide a rhiostat that is easy to restore.

[Structure of the Invention] (Means for Solving the Problems) In the cryostat of the present invention, evaporation is carried out in the piping used for injection of cryogenic refrigerant, collection of evaporated gas, discharge of gas in an emergency, guidance of current leads, etc. A thin-walled cylindrical container is coaxially arranged to maintain a gap for gas flow, and safety valves such as rupture discs are provided on the low-temperature side and the room-temperature side of the cylindrical container.

(Function) By providing a cylindrical container coaxially within the pipe, a boundary layer due to natural convection develops over the entire cross section of the flow path, and upward flow flows over the entire cross section of the flow path, reducing convection within the pipe. It can be suppressed. That is, warm gas from the normal temperature section is not brought into the low temperature section, and heat intrusion from the piping section can be suppressed.

Even if the superconducting magnet is quenched, the safety valve provided in the vacuum cylindrical container can reliably suppress an increase in the internal pressure of the refrigerant container.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a cryostat according to an embodiment of the present invention. The basic configuration is the same as a conventional cryostat, but the difference between the present invention and the conventional cryostat is that there is a vacuum inside the pipe 7. This is because the cylindrical containers 11 are arranged coaxially.

That is, in the cryostat of this embodiment, a vacuum cylindrical container 11 is disposed coaxially inside the pipe 7, which is used for injecting the cryogenic refrigerant 2, recovering evaporated gas, guiding the current lead, etc., for the purpose of preventing convection. do.

In the first place, the reason why convection occurs inside the pipe 7 is that the heat that enters through the pipe causes an upward flow near the wall due to natural convection, and the mass of the gas carried out of the system by this upward flow is due to the intruding heat other than the convection. Therefore, when the mass of the gas is greater than the mass of the gas to be evaporated, a downward flow occurs in the center of the pipe in order to balance the mass flow rate in the pipe cross section. This downward flow brings heat to the low-temperature part, increases the amount of evaporation of the refrigerant, and balances the system.

Since convection occurs due to the process described above, the diameter, material, thickness, etc. of the vacuum cylinder 11 disposed within the pipe 7 have optimum values depending on the intrusion heat of the cryostat used. An example is shown in FIG.

In the figure, the horizontal axis is the diameter of the vacuum cylinder, and the vertical axis is the amount of refrigerant evaporation. As shown in Figure 2, as the diameter of the vacuum cylindrical container to be inserted increases (as the gap between the piping and the vacuum cylinder to be inserted decreases), the amount of evaporation decreases up to a certain value. After that, it hardly changes. As shown in Figures 3 and 4, when the diameter of the vacuum cylindrical container exceeds a certain level, the gap between the piping and the vacuum cylinder becomes narrower than the total thickness of the natural convection boundary layer that develops on the walls of both pipes, and the downward flow or will no longer occur. Therefore, after that, almost no heat enters due to convection, so the amount of evaporation does not change.

On the other hand, in order to prevent clogging of the pipe 7, it is desirable to make the cross-sectional area of the gas flow path as large as possible.

Therefore, there is an optimum value for the diameter of this vacuum cylindrical container, and that value is the point at which there is almost no change in the amount of evaporation, as shown in FIG.

In this manner, according to this configuration, convection within the pipe is suppressed, the amount of evaporation is reduced, and the possibility of blockage can be reduced.

In addition, by configuring the vacuum cylinder to have safety valves such as rupture discs on the low-temperature side and the normal-temperature side, even if the piping is blocked or the superconducting magnet is quenched, the safety valves installed in the vacuum cylinder container can be used. The rupture disc ruptures,
Evaporated gas can be safely led out of the system, and an increase in internal pressure in the refrigerant container can be suppressed.

Furthermore, in order to maintain the vacuum cylindrical container at a high vacuum, it is a very effective method to apply activated carbon to the inner wall of the vacuum cylindrical container on the low temperature side.

Note that the present invention is not limited to the embodiments described above, and various modifications can be made.

That is, the same configuration can be used regardless of the shape of the flow path cross section of the pipe 7.

(Other Embodiments) When the pipe 7 is installed at an angle with respect to the direction of gravity, the configurations shown in FIGS. 5(a) and 5(b) are effective. In other words, the evaporative gas conduit is spirally arranged on the inner or outer wall of the vacuum cylindrical container 11. With such a configuration, convection that occurs when the pipe 7 is tilted can be suppressed. Naturally, this configuration is also effective when the pipe 7 is placed in the direction of gravity.

[Effects of the Invention] As described above, according to the present invention, it is possible to significantly reduce the amount of heat that enters by convection through piping used for injection of cryogenic refrigerant, recovery of evaporated gas, guidance of current leads, etc. In addition, it is possible to provide a cryostat that has a low possibility of blockage and can suppress an increase in the internal pressure of the refrigerant container even if the pipe is blocked or the superconducting magnet is quenched.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a cryostat according to an embodiment of the present invention, FIG. 2 is a curve diagram showing changes in the amount of evaporation depending on the diameter of the vacuum cylinder, and FIG. 3 is a diagram of the velocity distribution of evaporated gas in the pipe. FIG. 4 is a diagram showing the velocity distribution in the piping when the vacuum container of this embodiment is inserted, and FIGS. 5(a) and (b) are diagrams showing the piping section of the cryostat according to another embodiment of the present invention. . 1... Superconducting coil, 2... Cryogenic refrigerant, 3
... Cryogenic refrigerant container, 4... Vacuum insulation layer, 5...
・Vacuum container, 6... Heat shield, 7...
Piping, 8... Thermal anchor, 9...
・Small refrigerator, 11... Vacuum cylindrical container, 12.
...Rupture disc, 13...Activated carbon, 15...
spiral tube.

Claims (1)

[Scope of Claims] (1) A refrigerant container containing a cryogenic refrigerant; a vacuum container that covers the refrigerant container and forms a vacuum insulation layer between the refrigerant container; one end communicates with the refrigerant container and the other In a cryostat, the end side of which is provided with a pipe that penetrates the vacuum insulation layer and the wall of the vacuum container and is located in a room temperature section, a thin-walled cylindrical container with a vacuum inside is arranged in the pipe, and the pipe A cryostat characterized in that a gap between the cylindrical container and the cylindrical container is configured as an evaporative gas flow path of the cryogenic refrigerant. (2) Claim (1) characterized in that the cylindrical container in the pipe has a rupture disc or a safety valve at the low temperature end and the normal temperature end.
) Cryostat described. (3) The cryostat according to claim (2), wherein the rupture disc or the safety valve installed at the normal temperature end is a safety valve that closes when the pressure falls below a certain value. (4) The cryostat according to claim (1), characterized in that an adsorbent such as activated carbon is coated on the low temperature side of the inner wall of the cylindrical container. (5) The cryostat according to claim (1), wherein when the cross section of the pipe is not circular, a cylindrical container having a cross section similar to the cross section of the pipe is disposed coaxially within the pipe. (6) The cryostat according to claim (1), wherein the gap between the pipe and the cylindrical container is made smaller than the total thickness of boundary layers developed on each wall surface. (7) The cryostat according to claim (1), characterized in that an evaporative gas pipe is spirally attached to the inner or outer circumference of the cylindrical container. (8) The cryostat according to claim (1), wherein the cylindrical container is removable.