JP5649373B2 - Superconducting member cooling apparatus and temperature maintaining method for subcooled liquid nitrogen in a heat insulating container - Google Patents

Description

  The present invention is a superconducting member cooling for cooling and holding a superconducting member such as a superconducting transformer, a superconducting magnet, various other superconducting coils, or a superconducting cable, in particular, a high-temperature superconducting member with subcooled liquid nitrogen (supercooled liquid nitrogen). The present invention relates to a device and a method for maintaining the temperature of subcooled liquid nitrogen in an insulated container.

In cooling a superconducting member such as a superconducting coil, particularly a superconducting member using high-temperature superconductivity, the use of relatively inexpensive liquid nitrogen (LN ₂ ) as a cooling medium is known.
As a method for cooling the high-temperature superconducting member with liquid nitrogen, saturated liquid nitrogen at atmospheric pressure (−196 ° C. (77 K)) is used, or subcooled liquid nitrogen lower than −196 ° C. is used with the liquid nitrogen container in a reduced pressure state. Was. When using the above saturated liquid nitrogen, for example, when using saturated liquid nitrogen at atmospheric pressure, the superconducting member is accommodated in a cooling container substantially open to the atmosphere called a cryostat that is vacuum insulated, Usually, about 77 K atmospheric pressure saturated liquid nitrogen is injected into the cooling container, and the superconducting member is immersed in the liquid nitrogen, and is cooled and held.

By the way, in a high-temperature superconducting member, it is known that the superconducting characteristics will be greatly improved if the temperature is slightly lowered. For example, it is known that the critical current increases several times even if it falls from 77K to 70K.
Therefore, it is conceivable to cool the superconducting member to a temperature lower than 77K by immersing the superconducting member in subcooled liquid nitrogen whose pressure is reduced to about 65K by reducing the pressure of liquid nitrogen at atmospheric pressure. In that case, in a container for immersing the superconducting member in liquid nitrogen, it is necessary to maintain the reduced pressure state of liquid nitrogen. On the other hand, since the cryostat generally used is premised on the use at a pressure substantially close to the atmospheric pressure, if this type of general-purpose cryostat is applied to liquid nitrogen that has been depressurized, a lid or a current introduction terminal is used. It becomes inadequate in terms of sealing at such locations, and atmospheric pressure air containing moisture is sucked into the inside from the outside, clogging due to moisture freezing in the vent hole of the current introduction terminal and ice on the surface of the superconducting member Adhesion may occur and operation may become impossible in practice. Therefore, for the above-mentioned purpose, a special container must be newly designed and manufactured. In this case, there is a problem that causes a significant increase in cost, so that practical use is hesitant. .

  Also, if the superconducting member is operated by immersing the superconducting member in saturated liquid nitrogen at atmospheric pressure, the saturated liquid nitrogen is immediately vaporized by the heat generated by the superconducting member, and gas bubbles are generated. However, even when the superconducting member is immersed in liquid nitrogen whose temperature has been lowered to about 65K by depressurization as described above, there is a problem that the performance is reduced. In saturated liquid nitrogen, liquid nitrogen is immediately vaporized as a result of heat generated by the superconducting member, and bubbles are generated. Therefore, this is also one of the reasons for hesitating to use the reduced pressure liquid nitrogen.

In Patent Document 1, liquid nitrogen for heat exchange is supplied into a decompression container separately from the liquid nitrogen for cooling the superconducting member housed in the cooling container, and the inside of the decompression container is decompressed by a vacuum pump. The temperature of the liquid nitrogen for heat exchange is lowered, and the superconducting member is configured to obtain the liquid nitrogen for cooling in the subcooled state at atmospheric pressure by heat exchange between the liquid nitrogen for heat exchange and the liquid nitrogen for cooling. A cooling device is disclosed.
A heat insulating member is disposed below the liquid surface of the cooling liquid nitrogen, and a thermal gradient is formed between the liquid surface of the liquid nitrogen for cooling (about 77 K because it is a gas-liquid interface) and the lower side of the heat insulating member. In addition, it is described that the presence of the heat insulating member can prevent convective stirring between the bottom side and the liquid surface.
However, in this case, the liquid nitrogen for heat exchange in the decompression vessel is gradually evaporated and evaporated by the decompression, and the vaporized gas is exhausted by the pump, so that the liquid nitrogen liquid level in the decompression vessel rapidly decreases. Eventually, the heat exchanger in the decompression vessel will be exposed. If the heat exchanger is exposed from the liquid surface in this way, a sufficient heat exchange efficiency cannot be obtained, and it becomes difficult to cool the cooling liquid nitrogen to a sufficient subcooled state. Above, there is a problem that before the heat exchanger is exposed from the liquid level, liquid nitrogen must be replenished into the decompression vessel, and the operation must be stopped once when the liquid nitrogen is replenished.

In Patent Document 2, liquid nitrogen is cooled to a temperature at which a subcooled cooling state under atmospheric pressure is achieved with a refrigerator in a supply side container, and the obtained supercooling liquid nitrogen in a subcooled state is directly used as a superconducting member in the cooling container. This is used as a cooling medium for cooling, so that the decompression vessel and the heat exchanger as in Patent Document 1 are not used, and the heat exchange liquid nitrogen is supplied into the decompression vessel. A superconducting member cooling device is disclosed that avoids shutdown and enables continuous operation for a long time.
In the supply side container, by disposing a heat insulating member made of a low thermal conductivity material such as FRP under the liquid nitrogen surface, the vicinity of the liquid surface (about 77 K) and the vicinity of the cooling head of the refrigerator (65 to 70 K). A thermal gradient layer is formed between them. However, in the region where the heat insulating member is arranged, liquid nitrogen is excluded by the volume of the heat insulating member, and the liquid nitrogen can move only in a portion of a small narrow gap around the heat insulating member. Even if liquid nitrogen is slightly evaporated or nitrogen gas is condensed due to the swinging of the supply side container, the position of the liquid level is greatly fluctuated, so that the temperature gradient layer may be fluctuated greatly. Therefore, when the heat insulating member as in the prior art is provided, it is still insufficient to stabilize the operation state and improve the reliability during actual operation.

  In Patent Document 3, liquid nitrogen in a liquid nitrogen container in which liquid nitrogen is stored leaving a space on the liquid surface and nitrogen gas pressure such as atmospheric pressure is applied to the space on the liquid surface is obtained under atmospheric pressure. In the superconducting member cooling device configured to cool the superconducting member with liquid nitrogen at the subcooling temperature under the atmospheric pressure at a subcooling temperature, from the position below the liquid surface of the liquid nitrogen in the liquid nitrogen container, the liquid A superconducting member cooling device is disclosed in which a convection blocking member made of a porous heat insulating material having continuous pores is disposed over a position above the surface. As the porous heat insulating material having continuous pores, in addition to the open-cell urethane foam, for example, open-cell polyethylene foam, acrylonitrile-butadiene rubber foam, ethylene propylene rubber foam, etc. can be used. Have been described.

In Patent Document 3, subcooled liquid nitrogen is not a liquid having a saturation temperature, and therefore does not boil unless extreme heat is generated by the superconducting member. Further, since the gas phase part is at atmospheric pressure, it is easy to handle, and there is an advantage that there is no concern about mixing of outside air (particularly moisture). As described above, the subcooled liquid nitrogen supplies liquid nitrogen having a lower temperature, whereby the superconducting member can be cooled at a lower temperature and the performance of the superconducting power device can be improved.
In Non-Patent Document 1, liquid nitrogen having a saturation temperature (77 K) at atmospheric pressure is stored in a cryostat, and thereafter the pressure on the liquid surface of liquid nitrogen in the cryostat is controlled to 7 kPaG slightly higher than atmospheric pressure. Then, with the cryostat still standing, when 66K liquid nitrogen is gently introduced into the bottom and 77K liquid nitrogen is discharged from the top to keep the liquid level constant, the liquid level is saturated at 7 kPaG. Experimental results are shown in which liquid nitrogen at a temperature (about 77 K) is present and 66 K subcooled liquid nitrogen is present at a depth of about 30 mm or more from the liquid surface. That is, in this case, it can be seen that a temperature gradient layer is formed at a depth of about 30 mm from the liquid surface. Moreover, if the temperature of 66K liquid nitrogen introduced into the bottom is controlled by a heater so that substantially 70K liquid nitrogen is introduced, a temperature gradient layer may be formed to a depth of about 15 to 20 mm from the liquid level. It is shown.
That is, Non-Patent Document 1 shows that a temperature gradient layer is formed between the liquid level of liquid nitrogen and a depth of 15 to 30 mm from the liquid level depending on conditions.

By the way, what is important when subcooled liquid nitrogen is used is how to stabilize the temperature gradient layer formed on the surface of liquid nitrogen. If the liquid cannot be stabilized, the whole liquid is agitated, so that the liquid temperature near the liquid surface becomes a temperature equal to or lower than the saturation temperature with respect to the nitrogen gas pressure, and the gas in the gas phase is condensed and decompressed. In other words, boiling of the liquid nitrogen is likely to occur due to the saturation of the entire liquid nitrogen. Moreover, there is a possibility that outside air (especially moisture) may be mixed into the container.
In situations where the liquid nitrogen container itself oscillates and vibrates during actual operation, the liquid nitrogen inside the container is greatly agitated and the temperature gradient layer is disturbed. Even if heat insulating material is provided, the operation status becomes unstable, and the liquid surface position fluctuates due to vaporization of liquid nitrogen on the liquid surface and conversely condensation of nitrogen gas. The gradient layer becomes unstable, the operation status becomes unstable, and cooling efficiency and system reliability may be reduced.

Japanese Patent Laid-Open No. 10-054637 Japanese Patent Laid-Open No. 10-325661 JP 2001-345208 A

S. Yoshida, etc., “1 ATM SUBCOOLED LIQUID NITROGEN CRYOGENIC SYSTEM FOR OXIDE SUPERCONDUDUTING POWER TRANSFORMER”, Advances in Cryogenic Engineering Vol.43, 1998, p.1191-1198

When a low thermal conductivity material such as FRP is disposed in the temperature gradient layer forming part, liquid nitrogen is excluded by the volume of the heat insulating member, so that the liquid nitrogen moves only in a small narrow gap around the heat insulating member. In the situation where it is possible to obtain the liquid level, the liquid level position fluctuates greatly and the temperature gradient layer may fluctuate greatly even if the liquid nitrogen is slightly evaporated or the nitrogen gas is condensed.
In addition, an open-cell resin foam such as a sponge-shaped porous heat insulating material plays a role of maintaining a liquid nitrogen temperature gradient layer against small turbulence generated inside the container when the container is left standing, but the container itself is always shaken. In a situation involving dynamics and vibrations, the liquid nitrogen inside the porous heat insulating material sways greatly, so it was insufficient to maintain the temperature gradient layer.
Therefore, the present invention maintains the temperature gradient layer of subcooled liquid nitrogen in the heat insulating container even under vibration and swinging, and prevents pressure reduction due to nitrogen gas condensation near the liquid surface and saturation of liquid nitrogen due to pressure reduction. An object of the present invention is to provide a superconducting member cooling apparatus capable of stably supplying subcooled liquid nitrogen and a method for maintaining the temperature of subcooled liquid nitrogen in a heat insulating container.

  The present invention has been made against the background described above. From the position above the liquid nitrogen level of the heat insulating container containing the subcooled liquid nitrogen, the upper surface of the cooling head or the upper surface of the cooling head. Over the range up to the position, the glass fiber paper having absorptivity to liquid nitrogen is filled and a glass fiber paper packed layer is disposed, and a temperature gradient layer is formed and held in the glass fiber paper packed layer (hereinafter referred to as “the glass fiber paper packed layer”). , “Form and hold” is sometimes referred to as “hold”.), The present inventors have found that the above problems can be solved, and have completed the present invention.

That is, the gist of the present invention is the invention described in the following <1> to <5>. <1> At least a heat insulating container (V1) that stores subcooled liquid nitrogen leaving a nitrogen gas space, a refrigerator that immerses a cooling head for cooling to a position below the liquid surface of liquid nitrogen, and the subcooled liquid In a superconducting member cooling device composed of a superconducting member to be cooled, which is immersed in nitrogen,
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V1) to a position above the upper surface of the cooling head or the upper surface of the cooling head. Glass fiber paper-filled layer for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the glass fiber paper and between the glass fiber paper and the wall surface of the heat insulating container (V1). has established the L1),
A superconducting member cooling device (hereinafter sometimes referred to as a first embodiment), wherein the glass fiber paper packed layer includes at least one partition plate .

<2> At least the subcooled liquid nitrogen is stored leaving a nitrogen gas space, and a liquid feed pump for supplying the subcooled liquid nitrogen to the heat insulating container (V3) is inserted into the subcooled liquid nitrogen, A heat insulating container (V2) equipped with a refrigerator that immerses the cooling head for cooling to a position below the liquid nitrogen liquid level;
A subcooled liquid nitrogen is circulated and accommodated from the heat insulating container (V2) leaving a nitrogen gas space on the liquid surface, and a heat insulating container (V3) for immersing the superconducting member to be cooled in the subcooled liquid nitrogen; In a superconducting member cooling device comprising:
Absorptive to liquid nitrogen over a range from the position above the liquid nitrogen liquid level in the heat insulating container (V2) to the upper surface of the cooling head or the position above the upper surface of the cooling head. Glass fiber paper filled layer (L2) for holding a temperature gradient layer of subcooled liquid nitrogen filled with glass fiber paper so that no gap is formed between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V2). ),
And the glass which has an absorptivity with respect to liquid nitrogen over the range from the position above the liquid level of the liquid nitrogen in the said heat insulation container (V3) to the upper surface part of the said superconducting member, or a position above an upper surface part. Glass fiber paper filled layer (L3) for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V3) so as not to form voids. , it has established a,
The glass fiber paper filling layer (L2) and the glass fiber paper filling layer (L3) each include at least one partition plate , a superconducting member cooling device (hereinafter referred to as a second conductive material cooling device). Sometimes referred to as an aspect).

<3> At least the subcooled liquid nitrogen is stored leaving a nitrogen gas space, and a liquid feed pump for supplying the subcooled liquid nitrogen to the heat insulating container (V4) is inserted in the subcooled liquid nitrogen, A heat insulating container (V2) equipped with a refrigerator that immerses the cooling head for cooling to a position below the liquid nitrogen liquid level;
The subcooled liquid nitrogen is circulated from the heat insulating container (V2) and filled so that no space is formed on the liquid surface, and the superconducting member to be cooled is immersed in the subcooled liquid nitrogen (V4). A superconducting member cooling device comprising:
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V2) to a position above the upper surface of the cooling head or the upper surface of the cooling head. Glass fiber paper packed layer (L2) for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V2) so as not to form a void. Has been established ,
A superconducting member cooling device (hereinafter sometimes referred to as a third mode), wherein the glass fiber paper packed layer includes at least one partition plate .
<4> From <1> to <3> , the thickness in the vertical direction of the glass fiber paper filling layer (L1, L2 and L3, or L2) is 20 mm or more and 50 mm or less excluding the thickness of the partition plate. The superconducting member cooling device according to any one of the above.
<5> In the method for maintaining the temperature of the subcooled liquid nitrogen in the heat insulating container (V0) accommodated at least leaving the nitrogen gas space,
Immerse the cooling head of the refrigerator for cooling the subcooled liquid nitrogen to a position below the liquid surface of the liquid nitrogen,
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V0) to a position above the upper surface of the cooling head or the upper surface of the cooling head. at least fiber paper to said fiber sheet and between said fiber paper and the heat insulating container glass fiber paper packed bed filled so voids are not formed between the wall surface of (V0) (L0) and provided Rutotomoni the glass fiber paper packed bed A method for maintaining the temperature of subcooled liquid nitrogen in a heat insulating container (hereinafter referred to as the following), characterized in that a temperature gradient layer of subcooled liquid nitrogen is retained in the glass fiber paper packed layer (L0) by including one partition plate. , Sometimes referred to as a fourth aspect).

(A) In the superconducting member cooling device according to <1> to <4> above, from the liquid nitrogen liquid level in a heat insulating container (V1 or the like) in which a cooling head for cooling liquid nitrogen is immersed in liquid nitrogen. By providing a glass fiber paper filling layer (L1 etc.) over the range from the upper position to the upper surface of the cooling head or the position above the upper surface of the cooling head,
Liquid nitrogen in the container is absorbed by the glass fiber paper in the glass fiber paper filling layer (L1 etc.), so that a temperature gradient layer is formed downward from the liquid level in the glass fiber paper filling layer (L1 etc.). Due to the fine glass fiber structure of the glass fiber paper that is held and forms the glass fiber paper filled layer (L1 etc.), the temperature gradient layer is not It is stably maintained as compared with a porous heat insulating member having continuous pores. Further, since the glass fiber paper filling layer (L1 or the like) is filled so as not to form a large gap with the container wall surface, convection of liquid nitrogen in the vertical direction can also be suppressed.
As a result, the gas phase portion in the container is not suddenly depressurized, and the saturation of the temperature of the liquid nitrogen in the lower part of the glass fiber paper packed layer (L1 etc.) is suppressed, so that the subcooled liquid nitrogen It becomes possible to maintain the temperature.

(B) In the temperature maintenance method for subcooled liquid nitrogen described in <5> above, from the position above the liquid nitrogen liquid level in the heat insulating container (V0) to the position above the cooling head or above the top. A glass fiber paper filling layer (L0) is provided over the range, and a temperature gradient layer of subcooled liquid nitrogen is retained in the glass fiber paper filling layer (L0). Due to the fine glass fiber structure of the glass fiber paper to be formed, even if convection or agitation of liquid nitrogen occurs due to rocking for some reason in the lower part of the heat insulating container (V0), convection to liquid nitrogen near the liquid surface In addition, the temperature gradient layer can be stably held and the liquid surface position can be stabilized.

It is a schematic diagram which shows an example of the superconducting member cooling device of this invention which cools a superconducting member by subcooled liquid nitrogen within the heat insulation container (V1) in which the cooling head is immersed. It is a schematic diagram which shows an example of the superconducting member cooling device of this invention which cools a superconducting member in the heat insulating container (V3) by which the subcooled liquid nitrogen cooled by the cooling head is circulated in the heat insulating container (V2). It is a schematic diagram which shows an example of the superconducting member cooling device of this invention which cools a superconducting member in the heat insulation container (V4) by which the subcooled liquid nitrogen cooled by the cooling head in the heat insulation container (V2) is circulated.

Hereinafter, [1] “superconducting member cooling device” of the first aspect of the present invention, [2] “superconducting member cooling device” of the second aspect, [3] “superconducting member cooling device” of the third aspect, And [4] "Method for controlling temperature of subcooled liquid nitrogen in heat insulating container" of the fourth aspect will be described.
[1] “Superconducting member cooling device” according to the first aspect
The “superconducting member cooling device” according to the first aspect of the present invention includes at least a heat insulating container (V1) that stores subcooled liquid nitrogen leaving a nitrogen gas space, and a cooling head for cooling than the liquid nitrogen level. In a superconducting member cooling device comprising a refrigerator immersed in a lower position and a superconducting member to be cooled, which is immersed in the subcooled liquid nitrogen, the upper part of the liquid nitrogen in the heat insulating container (V1) Glass fiber paper that absorbs liquid nitrogen over the range from the position to the upper surface of the cooling head or the position above the upper surface of the cooling head, and between the glass fiber paper and the glass fiber paper and the heat insulating container gap between the wall surface of (V1) is filled so as not to be formed, and provided with a glass fiber paper filling layer (L1) to maintain the temperature gradient layer of subcooled liquid nitrogen, the glass fiber paper packed bed The, it contains at least one partition plate.

Hereinafter, the first aspect of the present invention will be described with reference to the drawings. However, the first aspect of the present invention is not limited to the illustration of FIG. 1 below.
FIG. 1 is a schematic diagram for explaining the superconducting member cooling device according to the first embodiment. The superconducting member cooling device includes a heat insulating container (V1) 11 and subcooled liquid nitrogen 14 accommodated in the container. The refrigerator 21, the glass fiber paper packed layer (L 1) 16, and the superconducting member 27 to be cooled are included, and liquid nitrogen supply means 51 and nitrogen gas supply means 55 can be provided as additional equipment.
In the heat insulating container (V1) 11, the glass fiber paper packed layer (L1) is in a range from a position above the liquid nitrogen liquid level to a position above the upper surface of the cooling head 25 or the upper surface of the cooling head. The superconducting member 27 is disposed in a lower direction than the glass fiber paper filling layer (L1).
The superconducting member cooling device according to the first aspect will be specifically described below.

(B) Insulated container (V1)
The heat insulating container (V1) 11 is made of a general-purpose cryostat, and the outer peripheral wall portion and the bottom wall portion thereof are a vacuum heat insulating structure 13 including an inner tank 19A and an outer tank 19B, A lid 12 that can be opened and closed is provided. The lid is preferably mounted in a state where it can be vacuum-sealed with bolts, nuts, etc. with a gasket such as an O-ring sandwiched between the main body of the heat insulating container (V1). In addition, a through joint for a current introduction terminal or the like similar to that of a general-purpose cryostat is disposed in the lid portion in a sealed structure. For example, the liquid nitrogen supply means 51 can supply the liquid nitrogen 14 from the liquid nitrogen tank 52 in which the liquid nitrogen (LN ₂ ) is stored to the heat insulating container (V1) through the control valve 53 and the supply pipe 54. Further, the nitrogen gas can be supplied from the nitrogen gas tank 56 in which nitrogen gas (GN ₂ ) is stored by the nitrogen gas supply means 55 through the control valve 57 and the supply pipe 58. be able to.
Although a safety valve 26 that can withstand negative pressure can be provided in the lid, this safety valve is opened when the internal pressure exceeds, for example, +10 kPa with respect to the external atmospheric pressure, and the internal pressure is reduced. The pressure can be made to function within the range of the pressure to the atmospheric pressure + 10 kPa, that is, between the negative pressure and a pressure slightly higher than the atmospheric pressure. And a superconducting member can be immersed in the subcooled liquid nitrogen accommodated in this container and cooled with a refrigerator, and can be cooled and held.

(B) In the refrigerator, the subcooled liquid nitrogen insulated container (V1), the liquid nitrogen 14 in the container is cooled to a temperature lower than the temperature of saturated liquid nitrogen (about 77K) under atmospheric pressure (for example, 65 to 70K). ) Is provided with a refrigerator 21 for cooling. This refrigerator is not particularly limited. For example, a compressor (compressor) for compressing a refrigeration medium gas (usually helium gas) and a compressed high-pressure refrigeration medium gas are expanded to lower the temperature. A cooling head 25 for obtaining, a heat exchanger 23 for closely contacting the cooling head and exchanging the low temperature with the object to be cooled (liquid nitrogen), a high-pressure medium gas from the compression section, and an expanded low-pressure returning from the cooling head It is possible to use a refrigerator having a cylinder portion 22 in which a passage for reciprocating the refrigeration medium gas is formed between a switching portion such as a motor valve for switching the flow of the medium gas and the cooling head. The cooling head 25 can be provided with a heater 24 to maintain the subcooled liquid nitrogen at a predetermined temperature.
As shown in FIG. 1, the cooling head 25 of the refrigerator 21 is immersed in the liquid nitrogen in the heat insulating container (V1) 11.

  A small cryogenic refrigerator represented by a GM refrigerator (Gifford McMahon refrigerator) can be used as a refrigerator for setting liquid nitrogen to a subcool temperature. In this case, the refrigerator includes a compressor, an expander, a circulating refrigerant pipe, a power source, and the like, and circulates gas refrigerant (mainly helium gas) compressed by the compressor to cool the cold generated by the expander. Heat is exchanged at the head, and the heated gas is returned to the compressor for circulation. The compressor of the refrigerator is placed on the lid portion of the heat insulating container and secured by securing the container seal. The cooling head 25 is arranged in a state of being immersed in liquid nitrogen facing vertically downward, and a heat exchanger 23 for improving heat exchange with liquid nitrogen is attached. As a refrigerating capacity, for example, there are a cooling head of 60 K, a frequency of 50 Hz and a refrigerating output of 200 W, and a refrigerating output of 1 kW class.

(C) Glass fiber paper packed layer (L1)
The glass fiber paper filling layer (L1) extends over a range from a position above the liquid nitrogen level in the heat insulating container (V1) to a position above the top surface of the cooling head or the top surface of the cooling head. A temperature gradient layer of liquid nitrogen filled with glass fiber paper having absorbability with respect to liquid nitrogen so that no gap is formed between the glass fiber paper and between the glass fiber paper and the wall surface of the heat insulating container (V1). It is a layer for forming and holding.
(I) Glass fiber paper Glass fiber paper is a sheet-like material obtained by bonding glass fibers to a heat-fusible or bonded material using a binder, and its production method is, for example, Japanese Patent Publication No. 36-9601, It is described in JP-A-5-86567. Glass fiber paper is known in the form of a roll or paper, and is a commercial product made by Rydal Thermal Co. (trade name): CryoTherm 233 (registered trademark), CryoTherm 234 (registered). Trademarks), trade names manufactured by Nippon Sheet Glass Co., Ltd .: AGM separator, MC paper and the like are known. Such glass fiber paper generally has a high space ratio (for example, 85% or more), can hold a large amount of liquid, has a high affinity for liquid nitrogen, etc., and has a fine glass fiber of several tens of μm or less. Due to its structure, it consists of fine capillaries, which can hold a large amount of liquid nitrogen uniformly, and is characterized by extremely little shrinkage even when cooled with subcooled liquid nitrogen.

(Ii) Glass fiber paper packed layer (L1)
The glass fiber paper-filled layer (L1) has an absorbability with respect to liquid nitrogen, and is a layer filled so that no gap is formed between the glass fiber paper and between the glass fiber paper and the wall surface of the heat insulating container (V1). If it is, it will not restrict | limit in particular, For example, the said glass fiber paper wound in roll shape is extended flatly, between glass fiber paper in the horizontal direction, and between the wall surface of this glass fiber paper and a heat insulation container (V1) It can be formed by filling so as not to form voids. In order to prevent the fiber from peeling due to the long-term use of the glass fiber paper, the upper surface and the lower surface of the glass fiber paper filling layer (L1) have a flat plate having an opening made of stainless steel, a wire mesh, or It is desirable to hold it with a resin net. Glass fiber paper absorbs liquid nitrogen well and has a high space ratio, so it can hold a large amount of liquid nitrogen uniformly, suppresses convection of liquid nitrogen due to the fine glass fiber structure, and is cooled to the subcooled liquid nitrogen temperature. However, it has a low thermal shrinkage rate as its outer shape, so it is suitable as a material for forming the glass fiber paper filled layer (L1) that holds the temperature gradient layer, and a slight change in the liquid amount affects the change in the liquid surface position. Since the influence is small, the liquid surface position can be stabilized. Further, the glass fiber paper-filled layer (L1) can maintain the temperature gradient layer in the layer relatively stably with the porous heat insulating member having the continuous pores even with respect to vibration, swinging, and the like. .
Therefore, since the glass fiber paper filled layer (L1) suppresses the fluctuation of the liquid nitrogen itself forming the temperature gradient layer, the conventionally known open-cell urethane foam, open-cell polyethylene foam, acrylonitrile The stability of the temperature gradient layer is superior to that of a butadiene rubber foam, an ethylene propylene rubber foam, or the like.

The glass fiber paper-filled layer (L1) maintains a temperature gradient layer of liquid nitrogen in the layer, thereby setting the temperature of liquid nitrogen near the liquid surface to a saturation temperature (about 77 K) at atmospheric pressure, While subcooling the temperature of the lower layer from the glass fiber paper packed layer (L1) in which the superconducting member is immersed to a temperature of about 65 to 70 K, for example, a liquid nitrogen temperature gradient layer is formed by suppressing convection and stirring of liquid nitrogen. Stabilize.
The glass fiber paper filling layer (L1) is a glass fiber paper that is suspended from a lid by a support member (not shown) such as a stud bolt or in a wire mesh suspended from a lid. It can arrange | position by installing.
Although the glass fiber paper-filled layer (L1) can stably hold the temperature gradient layer without providing a partition plate in the layer , as described below, one or two or more partitions It is provided with a plate. In addition, it is preferable to provide a glass fiber paper filling layer (L1) of at least 5 mm in the nitrogen gas space on the liquid surface from the viewpoint of preventing intrusion heat from the nitrogen gas space.
Furthermore, in order to prevent convection heat from the nitrogen gas space part which is one factor of intrusion heat, a glass fiber paper filling layer having a thickness of about 10 to 50 mm is further provided on the upper part of the glass fiber paper filling layer (L1), Alternatively, other heat insulating materials such as polyethylene foam can be provided.
As described in Non-Patent Document 1, a temperature gradient layer is formed between the liquid surface of liquid nitrogen and a depth of 15 to 30 mm from the liquid surface depending on the temperature condition of the subcooled liquid nitrogen. In view of the fact, the thickness in the vertical direction of the glass fiber paper filling layer (L1) below the liquid surface of liquid nitrogen is preferably 15 mm or more. Accordingly, considering the thickness in the nitrogen gas space, the thickness of the glass fiber paper filling layer (L1) is preferably 20 mm or more. By providing the glass fiber paper-filled layer (L1) having such a thickness, the liquid nitrogen temperature gradient layer can be stabilized by suppressing convection and stirring of liquid nitrogen. On the other hand, the upper limit of the thickness is not particularly limited, and even if the thickness exceeds 50 mm, there is no particular problem in exerting the effect of the glass fiber paper filling layer (L1), but the above functions are further improved. Cannot be expected.

The vertical thickness of the glass fiber paper filling layer (L1) when no partition plate is provided in the glass fiber paper filling layer (L1) is as described above.
On the other hand, when a partition plate is provided in the glass fiber paper filling layer (L1), the vertical thickness of one block of the glass fiber paper filling layer (L1) is set to about 5 to 10 mm, and the partition plates are provided and stacked. By setting it as a structure, it can suppress that glass fiber paper absorbs liquid nitrogen and raises, and liquid nitrogen evaporates on a liquid level. In this case, the number of partition plates is preferably 2 to 6, more preferably 3 to 4, and the total thickness is preferably 20 to 50 mm (excluding the thickness of the partition plate).
The material of the partition plate is not particularly limited, but a material having a low expansion coefficient at the temperature when liquid nitrogen is subcooled is desirable. For example, the partition plate is preferably made of a stainless partition plate having a thickness of about 1 mm. A partition plate can be arrange | positioned in the state hung from the cover part by support members (not shown), such as a stud bolt.

If there is an air gap between the partition plate and the heat insulating container (V1) wall, the liquid nitrogen easily moves through the glass fiber paper through the narrow air gap portion and evaporates, so the air gap with the heat insulating container (V1) wall. It is preferable to install the partition plate so as to minimize the size of the plate. In this case, the gap is preferably 0.5 to 5 mm, more preferably 1 to 2 mm.
(D) Superconducting member The superconducting member to be cooled in the present invention is not particularly limited, and is effective for cooling superconducting members such as superconducting transformers, superconducting magnets, other various superconducting coils, or superconducting cables, particularly high-temperature superconducting members. It is. As shown in FIG. 1, the superconducting member 27 can be suspended from the lid by the supporting members 20A and 20B.

[2] “Superconducting member cooling device” of the second aspect
In the “superconducting member cooling device” according to the second aspect of the present invention, at least the subcooled liquid nitrogen is accommodated leaving the nitrogen gas space, and the liquid feed for supplying the subcooled liquid nitrogen to the heat insulating container (V3). A heat insulating container (V2) having a pump inserted in subcooled liquid nitrogen and having a cooling head for cooling to a position below the liquid level of liquid nitrogen, and nitrogen gas on the liquid level Supercooling member cooling apparatus comprising subcooled liquid nitrogen circulated and accommodated from the heat insulating container (V2) leaving a space, and a heat insulating container (V3) for immersing the superconducting member to be cooled in the subcooled liquid nitrogen In
Absorptive to liquid nitrogen over a range from the position above the liquid nitrogen liquid level in the heat insulating container (V2) to the upper surface of the cooling head or the position above the upper surface of the cooling head. Glass fiber paper filled layer (L2) for holding a temperature gradient layer of subcooled liquid nitrogen filled with glass fiber paper so that no gap is formed between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V2). ),
And the glass which has an absorptivity with respect to liquid nitrogen over the range from the position above the liquid level of the liquid nitrogen in the said heat insulation container (V3) to the upper surface part of the said superconducting member, or a position above an upper surface part. Glass fiber paper filled layer (L3) for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V3) so as not to form voids. , it has established a,
Each of the glass fiber paper filling layer (L2) and the glass fiber paper filling layer (L3) includes at least one partition plate .

Hereinafter, the second aspect of the present invention will be described with reference to FIG. 2, but the second aspect is not limited to the following example of FIG. 2.
FIG. 2 is a schematic diagram for explaining the superconducting member cooling device according to the second embodiment. As described above, the superconducting member cooling device includes a liquid nitrogen supply-side heat insulating container for cooling the superconducting member. , A heat insulating container (V2) 31, a subcooled liquid nitrogen 14 accommodated in the container, a refrigerator 21, a glass fiber paper packed layer (L2) 16, and a liquid feed pump 32, and liquid nitrogen as ancillary equipment. Supply means 51 and nitrogen gas supply means 55 can be provided. In addition, as a cooling side heat insulating container that cools the superconducting member with liquid nitrogen transferred from the supply side heat insulating container, the heat insulating container (V3) 41, a glass fiber paper packed layer (L3) 46 in the container, and a cooling target The superconducting member 27 is included.
In the first mode, the cooling of the superconducting member is natural convection heat transfer, whereas in the second mode, liquid nitrogen that is forcibly cooled by the pump is sent to the cooling-side heat insulating container, so that it is close to forced convection heat transfer. Since it is a state, the 2nd aspect can cool a superconducting member more. Further, since the supply-side heat insulation container and the cooling-side heat insulation container are separated, maintenance is facilitated. The superconducting member cooling device according to the second aspect will be specifically described below by dividing it into a supply side heat insulating container and a cooling side heat insulating container.

(1) Supply side insulated container (b) Insulated container (V2)
The heat insulating container (V2) is composed of a general general-purpose cryostat, like the heat insulating container (V1), and a vacuum heat insulating structure whose outer peripheral wall portion and bottom wall portion are composed of an inner tank 19A and an outer tank 19B. 13 and a lid 12 that can be opened and closed can be provided at the upper end. It is preferable that the lid is mounted in a vacuum sealable state with respect to the container main body in the same manner as the heat insulating container (V1). The lid can be provided with a safety valve 26 that can withstand negative pressure, liquid nitrogen supply means 51 and nitrogen gas supply means 55, but these are the same as described in the heat insulating container (V1), Further, a liquid feeding pipe 33 and a reflux pipe 34 can be provided.

(B) Refrigerator, liquid nitrogen in the subcooled liquid nitrogen insulated container (V2) is cooled by the cooling head 25 and the heat exchanger 23 of the refrigerator 21 in the same manner as described in the insulated container (V1). The temperature of the liquid nitrogen 14 that has been subcooled is lowered to a temperature (for example, 65 to 70 K) lower than a saturated liquid nitrogen temperature (for example, about 77 K) under atmospheric pressure, and is near the bottom of the heat insulating container (V2) by the liquid feed pump 32. The superconducting member 27 is cooled and held at a subcooling temperature (for example, about 67 to 72K) through the liquid feeding pipe 33 and led into the heat insulating container (V3). Further, the liquid nitrogen (for example, about 70 K or more) whose temperature has been increased by heat from the superconducting member 27 in the heat insulating container (V3) is returned to the heat insulating container (V2) through the reflux pipe. The liquid nitrogen refluxed to the heat insulating container (V2) in this way is cooled again to a subcooling temperature (for example, about 65 to 70K) under a pressure between negative pressure and atmospheric pressure by the cooling head of the refrigerator. As mentioned above, it is sent to the heat insulating container (V3) by the liquid feed pump. The refrigerator is the same as the refrigerator provided in the heat insulating container (V1).

(C) Glass fiber paper packed layer (L2)
The glass fiber paper filling layer (L2) provided in the heat insulation container (V2) is the same as the glass fiber paper filling layer (L1) in the heat insulation container (V1) described in the first aspect.
(D) The liquid feed pump 32 disposed in the liquid feed pump heat insulating container (V2) can be fixed in a state of being suspended from the lid portion 12, for example. This liquid feed pump is disposed so that its inlet (pump outlet) is located below the glass fiber paper packed layer (L2) 16 in the heat insulating container (V2). The outlet side of the liquid feeding pump is connected to the liquid feeding pipe 33, and the liquid feeding pipe 33 is led into the heat insulating container (V3) as described above. Further, a reflux pipe 34 from the heat insulating container (V3) is led into the heat insulating container (V2), and the opening end of the reflux pipe 34 is an upper part of the heat insulating container (V2) (the heat exchanger of the refrigerator). The liquid nitrogen introduced from the reflux pipe 34 is cooled by the heat exchanger 23. In addition, liquid nitrogen is recirculated through the reflux pipe 34 by setting the pressure in the heat insulation container (V3) slightly higher than the pressure in the heat insulation container (V2).

(2) Cooling side insulated container (b) Insulated container (V3)
A heat insulating container (V3) 41 for immersing the superconducting member in liquid nitrogen and cooling the superconducting member in the cooling side heat insulating container is provided.
The heat insulating container (V3) has a vacuum heat insulating structure 43 whose outer peripheral wall portion and bottom wall portion are composed of an inner tank 49A and an outer tank 49B in the same manner as the heat insulating container (V1) and the heat insulating container (V2). Is provided with a lid 42 that can be opened and closed. It is preferable that the lid is connected to the container body in a vacuum sealable state, similarly to the heat insulating container (V1) and the heat insulating container (V2). A safety valve 66, a nitrogen gas supply means 61, a liquid feeding pipe 33, and a reflux pipe 34 can be provided on the lid of the heat insulating container (V3). The safety valve 66 has an internal pressure with respect to an external atmospheric pressure. For example, it is opened when it exceeds +30 kPa, and can function so that the internal pressure is maintained within the range of atmospheric pressure to atmospheric pressure +30 kPa, that is, slightly higher than the heat insulating container (V2). The superconducting member is immersed in subcooled liquid nitrogen sent from the heat insulating container (V2) in the heat insulating container (V3) and cooled.

(B) Glass fiber paper packed layer (L3)
For the glass fiber paper filled layer (L3) in the heat insulating container (V3), as described above, the nitrogen gas space part, the temperature gradient layer described in Non-Patent Document 1, the liquid level of liquid nitrogen, Considering the fact that the temperature gradient layer is formed from the liquid surface to a depth of 15 to 30 mm, the thickness is preferably 20 mm or more, more preferably 20 to 50 mm. About another point, it is the same as that of the glass fiber paper filling layer (L1) in the heat insulation container (V1) described in the said 1st aspect.
(C) The superconducting member to be cooled and disposed in the superconducting member heat insulating container (V3) is the same as the superconducting member described in the first aspect. In addition, as shown in FIG. 2, it is preferable that the superconducting member 27 is disposed in a lower direction than the glass fiber paper filling layer (L3). As shown in FIG. 2, the superconducting member 27 can be suspended from the lid by the supporting members 20A and 20B.

[3] "Superconducting member cooling device" of the third aspect
In the “superconducting member cooling device” according to the third aspect of the present invention, at least the subcooled liquid nitrogen is accommodated leaving the nitrogen gas space, and the liquid feed for supplying the subcooled liquid nitrogen to the heat insulating container (V4). A heat insulating container (V2) provided with a refrigerator in which a pump is inserted into the subcooled liquid nitrogen and the cooling head for cooling is immersed to a position below the liquid surface of the liquid nitrogen;
The subcooled liquid nitrogen is circulated from the heat insulating container (V2) and filled so that no space is formed on the liquid surface, and the superconducting member to be cooled is immersed in the subcooled liquid nitrogen (V4). A superconducting member cooling device comprising:
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V2) to a position above the upper surface of the cooling head or the upper surface of the cooling head. Glass fiber paper packed layer (L2) for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V2) so as not to form a void. Has been established ,
The glass fiber paper packed layer includes at least one partition plate .

Hereinafter, the third aspect of the present invention will be described with reference to FIG. 3, but the third aspect is not limited to the following example of FIG. 3.
FIG. 3 is a schematic diagram for explaining the superconducting member cooling device according to the third embodiment. As described above, the superconducting member cooling device includes a liquid nitrogen supply-side heat insulating container for cooling the superconducting member. , A heat insulating container (V2) 31, a subcooled liquid nitrogen 14 accommodated in the container, a refrigerator 21, a glass fiber paper packed layer (L2) 16, and a liquid feed pump 32, and liquid nitrogen as ancillary equipment. Supply means 51 and nitrogen gas supply means 55 can be provided,
As a cooling side heat insulating container that cools the superconducting member with liquid nitrogen transferred from the supply side heat insulating container, a heat insulating container (V4) 71 and a superconducting member 27 to be cooled are provided.
Since the superconducting member cooling device of the third aspect is filled with liquid nitrogen so that a nitrogen gas phase portion is not formed inside the heat insulating container (V4) as compared with the superconducting member cooling device of the second aspect, It has a feature that there is no temperature gradient layer. The superconducting member cooling device according to the third aspect will be described below by dividing it into a supply side heat insulating container and a cooling side heat insulating container.

(1) Supply side heat insulating container As a liquid nitrogen supply side heat insulating container for cooling the superconducting member, (a) heat insulating container (V2), (b) glass fiber paper packed layer (L2), (c) refrigerator , And (d) The liquid feed pump is substantially the same as the contents described in the supply side heat insulating container of the second aspect. As described in the first aspect, the heat insulating container (V2) is provided with a safety valve 26 that can withstand negative pressure, a liquid feeding pipe 33, and a reflux pipe 34 in the lid portion 12, and as ancillary equipment. Liquid nitrogen supply means 51 and nitrogen gas supply means 55 similar to those described in the first embodiment can be provided.
(2) Cooling side heat insulating container As a cooling side heat insulating container that cools the superconducting member with subcooled liquid nitrogen transferred from the supply side heat insulating container, the heat insulating container (V4) 71 has an outer peripheral wall portion and The bottom wall portion is a vacuum heat insulating structure 73 including an inner tank 79A and an outer tank 79B, and a sealed structure is formed except for the liquid feeding pipe 33 and the reflux pipe 34.
The subcooled liquid nitrogen fed from the heat insulating container (V2) to the heat insulating container (V4) through the liquid feeding pipe 33 by the liquid feeding pump is heated by the superconducting member in the heat insulating container (V4), and the temperature of the subcooled liquid nitrogen is increased. Since the heat insulation container (V4) has the above-mentioned sealed structure, it is refluxed to the heat insulation container (V2) via the reflux pipe. The superconducting member 27 to be cooled and disposed in the heat insulating container (V4) is the same as the superconducting member described in the first aspect and the second aspect. As shown in FIG. 3, the superconducting member 27 can be suspended from the inner tank 79A by the supporting members 20A and 20B.

[4] Method for maintaining temperature of subcooled liquid nitrogen “Method for maintaining temperature of subcooled liquid nitrogen in a heat insulating container” according to the fourth aspect of the present invention includes:
At least in the temperature maintaining method of the subcooled liquid nitrogen in the heat insulating container (V0) accommodated leaving the nitrogen gas space,
Immerse the cooling head of the refrigerator for cooling the subcooled liquid nitrogen to a position below the liquid surface of the liquid nitrogen,
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V0) to a position above the upper surface of the cooling head or the upper surface of the cooling head. at least fiber paper to said fiber sheet and between said fiber paper and the heat insulating container glass fiber paper packed bed filled so voids are not formed between the wall surface of (V0) (L0) and provided Rutotomoni the glass fiber paper packed bed One partition plate is included and a temperature gradient layer of subcooled liquid nitrogen is held in the glass fiber paper packed layer (L0) .

The temperature maintaining method of subcooled liquid nitrogen can be applied to any of the first to third embodiments. For example, as shown in FIG. 1, in a heat insulating container (V0 (V1 in FIG. 1, the same shall apply hereinafter)) Insert the cooling head of the refrigerator into the stored liquid nitrogen, and the glass covers the range from the position above the liquid nitrogen liquid level to the upper surface of the cooling head or the position above the upper surface of the cooling head. An apparatus capable of providing, for example, liquid nitrogen supply means and nitrogen gas supply means as ancillary equipment in a heat insulating container (V0) by providing a fiber paper packed layer (L0 (L1 in FIG. 1; the same applies hereinafter)). In
The liquid nitrogen liquid surface is disposed on the glass fiber paper packed layer (L0), and the temperature gradient layer is held downward from the liquid surface of the packed layer. This is a method of maintaining the temperature (including temperature control) by cooling the liquid nitrogen in the lower layer from the glass fiber paper filled layer (L0) to the subcooled liquid nitrogen.
The heat insulating container (V0), the refrigerator, and the glass fiber paper packed layer (L0) are respectively the heat insulating containers (V1, V2, or V3) described in the first aspect, the second aspect, or the third aspect, It is the same as that of a refrigerator and a glass fiber paper filling layer (L1, L2, or L3). In the heat insulating container (V0) usable for the superconducting member cooling device, a nitrogen gas supply means 55 as shown in FIG. 1 is used to supply a control valve 57 and a control valve 57 from a nitrogen gas tank 56 in which nitrogen gas (GN ₂ ) is stored. A structure in which nitrogen gas can be supplied through the supply pipe 58 can be adopted.

As shown in FIG. 1, the lid can be provided with a safety valve 26 that can withstand negative pressure, but this safety valve is opened when the internal pressure exceeds +10 kPa, for example, with respect to the external atmospheric pressure. Thus, the internal pressure can be made to function so as to be maintained within the range of the large negative pressure to the atmospheric pressure + 10 kPa, that is, between the negative pressure and a pressure slightly higher than the atmospheric pressure.
(A) Method of disposing the liquid nitrogen liquid level on the glass fiber paper packed layer (L0) Although not shown, it is preferable to provide a liquid level gauge in the heat insulating container (V0). When filling the heat insulating container (V0) with nitrogen, the liquid level can be set to a position where a temperature gradient layer can be formed and held in the glass fiber paper packed layer (L0).
(B) Retention of the temperature gradient layer in the glass fiber paper filling layer (L0) For example, when the thickness of the glass fiber paper filling layer (L0) in the vertical direction is 20 mm, the upper surface of the glass fiber paper filling layer (L0) Is filled with liquid nitrogen so that the position of about 5 mm becomes the liquid nitrogen liquid surface, and when the liquid nitrogen is subcooled, a temperature gradient layer is formed and held in the glass fiber paper filled layer (L0).
Hereinafter, a start method and a continuous operation method in the temperature control method of the subcooled liquid nitrogen in the heat insulating container will be described with reference to FIG. In addition, the following description is an illustration and the temperature maintenance method of the subcooled liquid nitrogen of the 4th aspect of this invention is not limited to the method described below.

(1) Start method The start method when the superconducting member cooling device shown in FIG. 1 is used is described below.
<1> Liquid nitrogen (LN ₂ ) at a position below the glass fiber paper filling layer (L 0) in the heat insulating container (V 0) from the liquid nitrogen tank 52 of the liquid nitrogen supply means 51 through the control valve 53 and the supply pipe 54. ) Until the liquid surface position is formed in the glass fiber paper filled layer (L0).
At this time, when the pressure in the heat insulating container (V0) rises above 10 kPa, nitrogen gas is released from the safety valve, and the pressure in the container is controlled within a range of negative pressure to atmospheric pressure + 10 kPa.
On the other hand, when the inside of the heat insulating container (V0) is lower than a predetermined pressure, the nitrogen gas supply means 55 connects the control valve 57 and the supply pipe 58 from the nitrogen gas tank 56 in which the nitrogen gas (GN ₂ ) is stored. Through which nitrogen gas is supplied.

<2> When the liquid surface position is stably formed in the glass fiber paper packed layer (L0), the refrigerator is started and cooling of liquid nitrogen is started. When the liquid nitrogen is subcooled to reduce the volume and the liquid level is formed in the lower part of the glass fiber paper filling layer (L0) or below the filling layer, liquid nitrogen is replenished from the liquid nitrogen tank 52. When the gas phase part in the heat insulating container (V0) becomes lower than a predetermined pressure, nitrogen gas supply means 55 is supplied with nitrogen gas. In this way, the liquid nitrogen liquid level is formed in the glass fiber paper packed layer (L0), and the pressure is balanced at almost atmospheric pressure. If the liquid level rises too much, the distance from the lid part to the liquid level is shortened, so that intrusion heat increases, so that liquid nitrogen is likely to evaporate, and the pressure in the heat insulating container (V0) rises above 10 kPa. In some cases, nitrogen gas is released from the safety valve.
<3> Liquid nitrogen on the liquid surface reaches a saturation temperature at atmospheric pressure, a temperature gradient layer is held immediately below the liquid surface in the glass fiber paper layer, and subcooled liquid nitrogen is contained below the temperature gradient layer become.
Normally, since the cooling head of the refrigerator continues to be cooled with a constant capacity, the temperature adjustment of the subcooled liquid nitrogen is provided with a heater above the cooling head, and is controlled to a predetermined temperature by turning on / off the heater. .
If the operation of the refrigerator is continued, the temperature gradient layer in the glass fiber paper layer is stably maintained in the subcooled liquid nitrogen, and it becomes possible to continue cooling the superconducting member at the subcooled temperature of the liquid nitrogen.

(2) Continuous operation Since the glass fiber paper layer used in the subcooled liquid nitrogen temperature maintaining method of the present invention has high liquid nitrogen absorbability, the insulation container (V0) can be vibrated and swung while the operation is continued. On the other hand, the fluidity of liquid nitrogen in the fiber paper layer is extremely low due to the fine glass fiber structure. As compared with a porous heat insulating member having Therefore, it is possible to stabilize the operating condition, improve the cooling efficiency of the superconducting member, and improve the reliability.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.
Based on the start method described in the fourth aspect above, the cooling head of the refrigerator is immersed in liquid nitrogen and the glass fiber paper packed layer is provided with a liquid in the glass fiber paper packed layer. While the surface was provided and the temperature gradient layer was held downward from the liquid surface, the heat insulating container was vibrated to evaluate the stability of the temperature gradient layer.
(1) Apparatus <1> Heat insulation container A heat insulation container (cryostat) is a vacuum heat insulation structure in which the outer peripheral wall part and the bottom wall part shown in FIG. 1 consist of an inner tank (height: 400 mm, inner diameter: 352 mm) and an outer tank. A lid that can be opened and closed is provided at the upper end.
In this heat insulating container, liquid nitrogen can be supplied from a liquid nitrogen tank in which liquid nitrogen (LN ₂ ) is stored by liquid nitrogen supply means, and nitrogen gas (GN ₂ ) is stored by nitrogen gas supply means. Ancillary equipment that can supply nitrogen gas from a nitrogen gas tank through a control valve and a supply pipe is provided. The lid is provided with a safety valve, which is opened when the internal pressure exceeds +10 kPa with respect to the external atmospheric pressure, and the internal pressure is within the range of atmospheric pressure to atmospheric pressure +10 kPa, that is, The pressure is set to be maintained at atmospheric pressure or slightly higher than atmospheric pressure.

<2> A refrigerator GM type refrigerator (180W @ 80K) manufactured by Suzuki Shokan was used. The upper part of the cooling head of the refrigerator is fixed at a position of 160 mm from the upper part of the container.
<3> Glass fiber paper-filled layer The glass fiber paper constituting the glass fiber paper-filled layer is a product name (CryoTherm 233 (registered trademark)) manufactured by Rydal Thermal Co. (outer diameter: 12). Inch (304.8 mm), inner diameter: 3 inches (76.2 mm), thickness: 35 inches (889 mm)) were cut and filled so that the shape of the glass fiber paper packed layer could be formed.
(2) Vibration and rocking method Vibration was applied at an amplitude of 3 mm (6 mm in total width) and a frequency of 4 Hz (the acceleration at this time is 0.193 G). Incidentally, it is known that the influence of vibration and swinging becomes large when the amplitude is 0.5 to 10 mm and the frequency is 1 to 10 Hz.
The relational expression of vibration frequency, amplitude and acceleration is as follows.
^{A = [(2πf) 2/} 1000 × g] × d
A: Acceleration (G)
f: Frequency (Hz)
d: Amplitude (mm) (* It is a single amplitude. The actual fluctuation width is 2d.)
g: Gravity acceleration 9.8 (m / sec ² )
* Vibration test of railway parts (JIS)
JIS E 4031 (1989) "Railway vehicle parts vibration test method" (Type 1 test)
The temperature of liquid nitrogen in the heat insulation container was measured using a platinum resistance temperature detector (100 ohm).

[Example 1]
(1) Experimental method (1-1) A space part of 50 mm was provided in the vertical direction above the space part of the apparatus heat insulating container (cryostat) and filled with a 40 mm thick glass fiber paper filling layer (no partition plate). The fiber paper filling layer has a structure in which the upper surface and the lower surface are sandwiched between stainless plates, and the stainless plate is structured to be fixed with a suspending nut from a lid portion with a stat bolt. A heater (amount of heat: 200 W at the maximum) was provided below the cooling head in the heat insulating container instead of the superconducting member.
(1-2) Experimental method Liquid nitrogen at a saturation temperature (about 77 K) at atmospheric pressure is supplied into the heat insulation container until a liquid surface is formed 10 mm below the upper surface of the glass fiber paper packed layer. Stabilized. The liquid level was confirmed by a liquid level gauge.
When the operation of the refrigerator was started, a temperature gradient layer was quickly formed and held in the glass fiber paper packed layer. The liquid nitrogen at the liquid level was maintained at a saturation temperature (about 77 K) at atmospheric pressure, the liquid nitrogen below the glass fiber paper packed layer was cooled to a subcool (about 64 K), and the temperature gradient layer was stabilized.
Sixty minutes after the temperature gradient layer was stabilized, the stirring state of liquid nitrogen was observed by measuring the reduced pressure state of the gas phase portion where the heat insulating container was vibrated.
(2) Experimental results No decompression occurred in the heat insulating container until 45 minutes after starting vibration. From this, it was confirmed that the temperature gradient layer was stably maintained for 45 minutes.

[Example 2]
Using the same insulated container and refrigerator as used in Example 1, 1 mm thick stainless steel partition plates (clearance with container wall: 1 mm) were disposed between four 10 mm thick glass fiber paper filled layers. .
In the same manner as in Example 1, liquid nitrogen at a saturation temperature (about 77 K) at atmospheric pressure was supplied into the heat insulating container until a liquid level was formed 10 mm below the upper surface of the glass fiber paper packed layer. Stabilized the surface. Next, the refrigerator is operated to subcool the liquid nitrogen, the liquid nitrogen at the liquid level is maintained at the saturation temperature (about 77K) at atmospheric pressure, and the liquid nitrogen below the glass fiber paper packed layer is subcooled (64K). The temperature gradient layer was stabilized.
60 minutes after the temperature gradient layer was stabilized, the stirring state of liquid nitrogen was observed by measuring the reduced pressure state of the gas phase portion where the heat insulating container was vibrated.
No decompression occurred in the heat insulating container until 60 minutes had elapsed after the start of vibration. From this, it was confirmed that the temperature gradient layer was stably maintained for 60 minutes.

[Comparative Example 1]
Using the same insulated container and refrigerator as used in Example 1, a polyurethane foam layer having a thickness of 20 mm (made by INOAC, trade name: malt filter (model number: MF-) instead of the glass fiber paper packed layer was used. 20) was laminated on both sides of a partition plate, and a foamed polyethylene layer (made by Asahi Kasei Co., Ltd., trade name: Suntec foam (model number: Q-25) having a thickness of 30 mm was sandwiched on the polyurethane foam layer. )).
Liquid nitrogen at a saturation temperature (about 77 K) at atmospheric pressure was supplied into the heat insulating container until the liquid level was formed 30 mm above the bottom surface of the polyurethane foam layer, thereby stabilizing the liquid level. The liquid level was confirmed by a liquid level gauge.
Except for the above, the refrigerator was operated in the same manner as described in Example 1 to subcool the liquid nitrogen, and the liquid nitrogen on the liquid surface was maintained at the saturation temperature (about 77 K) at atmospheric pressure, and filled with glass fiber paper The liquid nitrogen below the layer was cooled to a subcool (about 64K), and the temperature gradient layer was stabilized.
Sixty minutes after the temperature gradient layer was stabilized, the stirring state of liquid nitrogen was observed by measuring the reduced pressure state of the gas phase portion where the heat insulating container was vibrated.
Immediately after the start of vibration, a pressure reduction of -80 kPa was instantaneously generated in the heat insulating container. From this, it was confirmed that the temperature gradient layer in the polyurethane foam layer was not retained immediately after the start of vibration.

11 Insulated container (V1)
12 Lid 13 Vacuum insulation structure 14 Liquid nitrogen 15 Space 16 Glass fiber paper packed layer (L1, L2)
17 Partition plate 18 Liquid nitrogen liquid surface 19A Inner tank 19B Outer tank 20A Support member 20B Support member 21 Refrigerator 22 Cylinder part 23 Heat exchanger 24 Heater 25 Cooling head 26 Safety valve 27 Superconducting member 31 Heat insulation container (V2)
32 Liquid feed pump 33 Liquid feed pipe 34 Reflux pipe 41 Thermal insulation container (V3)
42 Lid 43 Vacuum insulation structure 44 Liquid nitrogen 45 Space 46 Glass fiber paper packed layer (L3)
47 Partition plate 48 Liquid nitrogen liquid surface 49A Inner tank 49B Outer tank 51 Liquid nitrogen supply means 52 Liquid nitrogen tank 53 Control valve 54 Supply pipe 55 Nitrogen gas supply means 56 Nitrogen gas cylinder 57 Control valve 58 Supply pipe 61 Nitrogen gas supply means 62 Nitrogen Gas cylinder 63 Control valve 64 Supply pipe 66 Safety valve 71 Thermal insulation container (V4)
73 Vacuum insulation structure 74 Liquid nitrogen 79A Inner tank 79B Outer tank

Claims (5)

At least a heat insulating container (V1) that stores subcooled liquid nitrogen leaving a nitrogen gas space, a refrigerator that immerses a cooling head for cooling to a position below the liquid level of liquid nitrogen, and the subcooled liquid nitrogen In the superconducting member cooling device composed of the superconducting member to be cooled that is immersed,
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V1) to a position above the upper surface of the cooling head or the upper surface of the cooling head. Glass fiber paper-filled layer for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the glass fiber paper and between the glass fiber paper and the wall surface of the heat insulating container (V1). has established the L1),
The superconducting member cooling device according to claim 1, wherein the glass fiber paper packed layer includes at least one partition plate . At least a subcooled liquid nitrogen is accommodated leaving a nitrogen gas space, and a liquid feed pump for supplying the subcooled liquid nitrogen to the heat insulating container (V3) is inserted into the subcooled liquid nitrogen, and is used for cooling. A heat insulating container (V2) provided with a refrigerator that immerses the cooling head to a position below the liquid nitrogen liquid level;
A subcooled liquid nitrogen is circulated and accommodated from the heat insulating container (V2) leaving a nitrogen gas space on the liquid surface, and a heat insulating container (V3) for immersing the superconducting member to be cooled in the subcooled liquid nitrogen; In a superconducting member cooling device comprising:
Absorptive to liquid nitrogen over a range from the position above the liquid nitrogen liquid level in the heat insulating container (V2) to the upper surface of the cooling head or the position above the upper surface of the cooling head. Glass fiber paper filled layer (L2) for holding a temperature gradient layer of subcooled liquid nitrogen filled with glass fiber paper so that no gap is formed between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V2). ),
And the glass which has an absorptivity with respect to liquid nitrogen over the range from the position above the liquid level of the liquid nitrogen in the said heat insulation container (V3) to the upper surface part of the said superconducting member, or a position above an upper surface part. Glass fiber paper filled layer (L3) for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V3) so as not to form voids. , it has established a,
The superconducting member cooling device, wherein each of the glass fiber paper filling layer (L2) and the glass fiber paper filling layer (L3) includes at least one partition plate . At least the subcooled liquid nitrogen is accommodated leaving a nitrogen gas space, and a liquid feed pump for supplying the subcooled liquid nitrogen to the heat insulating container (V4) is inserted into the subcooled liquid nitrogen, and is used for cooling. A heat insulating container (V2) provided with a refrigerator that immerses the cooling head to a position below the liquid nitrogen liquid level;
The subcooled liquid nitrogen is circulated from the heat insulating container (V2) and filled so that no space is formed on the liquid surface, and the superconducting member to be cooled is immersed in the subcooled liquid nitrogen (V4). A superconducting member cooling device comprising:
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V2) to a position above the upper surface of the cooling head or the upper surface of the cooling head. Glass fiber paper packed layer (L2) for holding a temperature gradient layer of subcooled liquid nitrogen, in which fiber paper is filled between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V2) so as not to form a void. Has been established ,
The superconducting member cooling device, wherein the glass fiber paper packed layer includes at least one partition plate . The vertical thickness of the glass fiber paper filling layer (L1, L2 and L3, or L2) is 20 mm to 50 mm in thickness excluding the thickness of the partition plate , according to claim 1, The superconducting member cooling device according to any one of the above. At least in the temperature maintaining method of the subcooled liquid nitrogen in the heat insulating container (V0) accommodated leaving the nitrogen gas space,
Immerse the cooling head of the refrigerator for cooling the subcooled liquid nitrogen to a position below the liquid surface of the liquid nitrogen,
Glass having absorptivity to liquid nitrogen over a range from a position above the liquid nitrogen level in the heat insulating container (V0) to a position above the upper surface of the cooling head or the upper surface of the cooling head. A glass fiber paper filling layer (L0) in which fiber paper is filled between the fiber paper and between the fiber paper and the wall surface of the heat insulating container (V0) so as not to form voids is provided , and at least 1 is provided in the glass fiber paper filling layer. A temperature maintaining method for subcooled liquid nitrogen in a heat insulating container, characterized in that a temperature gradient layer of subcooled liquid nitrogen is retained in the glass fiber paper packed layer (L0) by including a number of partition plates .

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