JPH03293784A - Cryostat - Google Patents

Abstract

PURPOSE:To reliably suppress intrusion of heat into piping and to lower the possibility of clogging of piping by coaxially arranging one or a plurality of thin tubes in the piping for injecting cryogenic refrigerant, recovering evaporated gas, guiding a current lead, or the like. CONSTITUTION:One or a plurality, as required, of tubes 11 made of low heat conductivity material, e.g. FRP, are arranged coaxially in a pipe 7 for injecting cryogenic refrigerant 2, recovering evaporated gas, guiding current lead, or the like. Consequently, a boundary layer develops due to natural convection on the entire cross section of the flow path to produce an updraft across the entire cross section of the flow path thus suppressing convection in the pipe. According to the arrangement, convectional intrusion of heat through the pipe, for injecting cryogenic refrigerant, recovering evaporated gas, guiding current lead, or the like, can drastically be reduced and the possibility of clogging is lowered.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a cryostat 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 cryogenic refrigerant.

a vacuum container that covers the refrigerant container and forms a vacuum insulation layer between it and the refrigerant container; a heat shield provided within the insulation layer; one end communicates with the refrigerant container; It is installed so that it penetrates the vacuum insulation layer, heat shield and wall of the vacuum container and is located in the room temperature area.
It consists of piping used for injection of cryogenic refrigerant, collection of evaporated gas, guidance of current leads, etc.

In a cryostat configured as above,
The heat that enters the refrigerant container other than through the piping can be suppressed to several milliwatts 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 due to 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 this convection phenomenon brings warm gas from the normal temperature area to the low temperature area. The amount of evaporation increases.

This increase in the amount of evaporation due to the convection of the evaporated gas can be suppressed by reducing the cross-sectional area of the piping, since the convection is also suppressed accordingly. However, in order to suppress an increase in the internal pressure of the refrigerant container due to quenching of the superconducting magnet, the pipe diameter cannot be reduced to a certain level. For this reason, a conventional cryostat has been proposed in which a cylindrical body having a large number of small holes is arranged in the tube axis direction, as shown in Japanese Patent Laid-Open No. 64-59911.

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

Inserting a cylindrical body like the one described above into the pipe reduces the amount of heat intrusion due to convection, but the amount of heat intrusion due to conduction through the inserted cylindrical body, which has a large number of small holes, increases, so the amount of heat intrusion is not that much. Does not decrease.

Furthermore, a structure with a large number of small holes promotes clogging of the piping due to intrusion of air and the like.

(Problems to be Solved by the Invention) As described above, simply providing the above-mentioned cylindrical body inside the pipe cannot suppress the heat intruding from the pipe, and there is a high possibility that the pipe will be blocked. Become.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cryostat that can reliably suppress the intrusion heat that enters the cryogenic refrigerant container through the inside of the pipe, and at the same time has a low possibility of clogging the pipe.

[Structure of the invention]

(Means for Solving the Problems) In the cryostat of the present invention, one or more thin-walled tubes are provided in the piping used for injection of cryogenic refrigerant, recovery of evaporated gas, guidance of current leads, etc.

Arrange coaxially.

(Function) As mentioned above, by providing one or more cylinders coaxially within the pipe, a boundary layer due to natural convection develops over the entire cross section of the flow path, and an upward flow flows over the entire cross section of the flow path. It is possible to suppress the convection phenomenon inside the piping. 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. Furthermore, with such a coaxial cylinder configuration, the cross section of the flow path within the pipe can be made large, reducing the possibility of blockage.

(Example) An embodiment 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 present invention differs from the conventional cryostat in that the inside of the pipe 7 is made of FRP. The cylinders 11 made of a material with low thermal conductivity, such as, are arranged coaxially.

That is, in the cryostat according to this embodiment,
One tube or a plurality of tubes as necessary are arranged coaxially with the tube 7 inside the tube 7 which is used for injecting the cryogenic refrigerant 2, recovering evaporated gas, guiding current leads, etc.

The reason why convection occurs inside the pipe 7 is as follows. As shown in Figure 3, the heat penetrating through the pipe 7 causes an upward flow near the wall due to natural convection, and the mass of gas carried out of the system by this upward flow is greater than the mass of gas evaporated by intruding heat other than convection. If it is large, 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 the convection phenomenon occurs due to the above-mentioned process, the number, material, diameter, thickness, etc. of the cylinders placed in the pipe 7 are
There is an optimum value depending on the intrusion heat of the cryostat used. An example of this is shown in Figure 2. In the figure, the horizontal axis is the number of cylinders, and the vertical axis is the amount of refrigerant evaporation. As shown in Figure 2, as the number of inserted cylinders increases, the amount of evaporation increases up to a certain value. It decreases, but after that it increases. That is, when the number of cylinders is small, the effect of preventing convection is small, and when the number of cylinders increases.

The amount of heat that enters through the cylinder increases, and the amount of evaporation increases.

Furthermore, as the number of cylinders increases, the cross-sectional area of each divided flow path becomes smaller, increasing the possibility of blockage.

In addition, the number of inserted cylinders, position, material, thickness, etc.
As shown in FIG. 4, it is necessary to determine so that the boundary layer developed from the inner wall of the pipe and the cylindrical surface closes the entire flow path, that is, the flow is upward across the entire cross section of the flow path. In this way, the coaxial cylindrical structure of this embodiment can suppress convection within the pipe, reduce the amount of evaporation of the refrigerant, and reduce the possibility of blockage.

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. Furthermore, in low-temperature areas where the boundary layer due to natural convection or the like is not sufficiently developed, by increasing the number of cylinders inserted only on the low-temperature side, it is possible to form only upward flow in the entire channel cross section even on the low-temperature side. In particular, the above-described configuration is particularly effective when a thermal anchor is installed in the middle of piping using a shield cooler such as a small refrigerator.

Further, instead of the cylinder 11, a square cylinder, a hexagonal cylinder, or the like may be used.

〔Effect 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., and to prevent blockages. We can provide a cryostat that is unlikely.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of a fly-stat according to an embodiment of the present invention, Figure 1 is a diagram showing changes in the amount of evaporation depending on the number of inserted cylinders, Figure 1 is the velocity of evaporated gas in the cylinders. The distribution diagram, Figure 4, is a schematic diagram of the velocity distribution in the pipe when the convection prevention part of the present invention is inserted. 1...Superconducting coil, 2...Cryogenic refrigerant. 3... Refrigerant container, 4... Vacuum insulation layer, 5...
...Vacuum container, 6...Heat shield, 71. ,
Piping, 8...Thermal anchor. 9...Small refrigerator, 11...Cylinder.

Claims (4)

[Claims] (1) A refrigerant container that accommodates a cryogenic refrigerant, a vacuum container that covers the refrigerant container and forms a vacuum insulation layer between it and the refrigerant container, one end of which communicates with the refrigerant container and the other end of which is connected to the vacuum A cryostat comprising a heat insulating layer and a pipe that penetrates the wall of a vacuum container and is located in a room temperature region, characterized in that a thin-walled cylinder made of a low thermal conductive material is coaxially disposed within the pipe. (2) The cryostat according to claim (1), wherein the tubes in the pipe are a plurality of coaxial tubes having different diameters. (3) Claim (1) characterized in that the number of tubes is arranged to be different between the low temperature side and the normal temperature side of the pipe.
) Cryostat described. (4) The cryostat according to claim 1, wherein when the cross section of the pipe is not circular, the tube is formed by coaxially disposing partition plates having a cross section similar to the cross section of the pipe.