JPS62216304A - Cryostat - Google Patents

Abstract

PURPOSE:To improve the heat insulating performance of a cryostat by so varying one of porosity and pore diameter that the exhausting performance of a laminated heat insulator nearer to an inside vessel becomes easier to reduce transmitting heat due to remaining gas between the layers of the insulators, thereby decreasing an increase in radiation heat. CONSTITUTION:Laminated heat insulators 2-4 are formed by depositing metal such as aluminum on one or both side surfaces of a Myler sheet and perforating pores 9. The pores 9 are smaller at the inner positions, the number of the pores is increased, the porosity of the pores is stepwisely varied in the layers of the insulators, and increased more at the inner side of the vessel. The porosity is approx. 0.5-1.0% at the outer layer of the insulator and 2-4% at the inner layer side, and stepwisely varied in the range of this porosity in the layers therebetween. Since the porosity is increased larger and the diameters of the pores are reduced toward the inner layer insulators 4 of low temperature side, vacuum at the inner layer is improved to reduce transmitting heat due to gas between the layers.

Description

[Detailed description of the invention] 〔the purpose〕 (Industrial application field) TECHNICAL FIELD This invention relates to cryogenic vessels containing cryogenic refrigerants.

(Prior art) Conventionally, cryogenic containers that contain cryogenic refrigerants such as liquid nitrogen and liquid helium have been constructed by creating a vacuum between the inner container and the outer container, and by interposing a laminated insulation material in the vacuum space to maintain the cryogenic temperature. The inner container containing the refrigerant is insulated from the outer container. This laminated heat insulating material has a structure in which a metal such as aluminum is vapor-deposited on one or both sides of a plastic film or Mylar sheet, and a perforated reflective film and a plastic net are alternately laminated. This perforated laminated insulation material improves ventilation between the layers and reduces conduction heat due to residual gas. However, the area that reflects the radiant heat from the outer container becomes smaller by the total fractional integral of the perforations, and the radiant heat increases. Therefore, the ratio of the total area of the perforations to the total area of the reflective film, that is, the perforation rate, must be determined taking into consideration the improvement in exhaust performance and the increase in heat intrusion due to radiation.

However, in general, the degree of vacuum between the layers of a laminated insulation material differs from layer to layer, and becomes worse as the temperature decreases. That is, on the low temperature side, the ratio of conduction heat due to residual gas to the total intrusion heat is larger than on the high temperature side, and conversely, on the high temperature side, radiant heat is dominant.

(Problem to be solved by the invention) For the above reasons, in the high temperature side of conventional laminated insulation materials in which the same number of perforations of the same diameter are provided in each layer, the effect of radiation passing through the perforations is large, and the vacuum on the low temperature side To compensate for the reduction in conductive heat due to the direction of the hole, the effectiveness of the perforation is lost.

An object of the present invention is to provide a cryogenic container with improved heat insulation performance by reducing conduction heat due to residual gas between layers of a laminated insulation material with perforations, and by reducing an increase in radiant heat due to perforations.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an inner container containing a cryogenic refrigerant, an outer container surrounding the inner container whose inside is evacuated, and a space between the two containers. In a cryogenic container consisting of a cryogenic laminated insulation material interposed in a vacuum space,
The laminated heat insulating material is characterized in that at least one of the perforation rate and the perforation diameter is changed so that the closer to the inner container, the easier the exhaust performance becomes.

(Function) With this structure, by improving the exhaust performance of the laminated insulation material near the inner container, the degree of vacuum does not decrease much compared to the outside, and the insulation effect is comparable to that of the conventional one. Significant improvement in comparison.

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

FIG. 1 is a sectional view of a cryogenic container provided with a laminated heat insulating material according to this embodiment, and FIG. 2 is an enlarged sectional view of the laminated heat insulating material. In Figure 1, (1) is a vacuum boat, (2)
, (3) and (4) are typical outer, middle, and inner three layers out of dozens of laminated insulation layers, and (5) is for storing cryogenic refrigerant (6) such as liquid nitrogen or liquid helium. (7) indicates an outer container whose interior is evacuated.

In Figures 1 and 2, laminated insulation material (2),
(3) and (4) are plastic films or
This is a mylar sheet with metal such as aluminum vapor-deposited on one or both sides and perforations (9). The diameter of the perforations is made smaller on the inside and the number of holes is increased, the perforation rate of the perforations is changed stepwise in each layer of the laminated insulation material, and the diameter is made larger on the inner side of the container. The perforation rate is the outer layer of laminated insulation (
0.5-1.0% on the outer container side) 2-4% on the inner layer side
The perforation rate is changed in stages within this range for layers in between.

In the laminated insulation material according to this example, the perforation rate of the outer laminated material (2) on the high temperature side is the same as or lower than that of the conventional type, and the perforation diameter is increased, so that radiant heat passes through this layer. can be reduced. In addition, the inner laminated material (4) on the low temperature side has a large perforation rate and a small perforation diameter, so the vacuum in the inner layer of the laminated material is better than that of conventional types, and the gas between the laminated materials is reduced. Conductive heat is reduced. That is, in this example, it is possible to reduce the heat intrusion by reducing radiant heat, which is the main cause of heat intrusion into the laminated material, and by reducing conduction heat due to residual gas, which is the main cause on the low temperature side of the laminated material. can.

Therefore, in the laminated heat insulating material according to the present invention, the heat insulating performance is improved. It is obvious that the present invention can also be applied to laminated heat insulating materials without inclusions such as plastic nets.

Other examples include the following.

=4- In the above example, the perforation rate and perforation diameter of the laminated material were changed,
It is possible to reduce the intrusion heat due to radiation on the high temperature side of the laminated material and reduce the intrusion heat due to gas conduction on the low temperature side, but it is possible to keep the perforation rate constant and change only the perforation diameter.

That is, on the high temperature side of the laminated material, the diameter of the perforations (9) is large and the number of perforations is small, and on the inner layer side, the perforation diameter is small and the number of perforations is large. This is due to the basic property that if the perforation rate (total perforation area) in each layer of laminated material is the same, the larger the perforation diameter, the better the insulation performance, and the larger the number of perforations, the better the exhaust performance. By using this, the same effects as in the above embodiment can be obtained.

It is also conceivable to keep the perforation diameter constant and increase the number of perforations on the low temperature side, thus increasing the perforation rate.

It is also possible that the perforation positions overlap in each layer, increasing the intrusion heat due to radiation, but this is because the perforation rate is a few percent.
Since the number of layers is small and the number of calendar layers is large, such as several tens, the above possibility is small and does not pose a problem.

〔Effect of the invention〕

As explained above, according to the present invention, the exhaust performance is improved and the sum of radiant heat and conductive heat can be reduced, so that a cryogenic container with improved heat insulation performance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the cryogenic container of the present invention;
FIG. 2 is an enlarged sectional view of the laminated insulation material of FIG. 1. 1... Vacuum port, 2.3.4... Laminated insulation material, 5... Inner container, 6
...Cryogenic refrigerant, 7.Outer container, 8.
...Spacer, 9...perforation.

Claims (1)

[Claims] In a cryogenic container consisting of an inner container containing a cryogenic refrigerant, an outer container surrounding it and evacuated inside, and a cryogenic laminated insulation material interposed in the vacuum space between both containers, a laminated A cryogenic container characterized in that at least one of the perforation rate and the perforation diameter of the insulating material is changed so that the closer the insulating material is to the inner container, the easier the exhaust performance is.