JPH0797664B2 - Superfluid helium cooling device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a superfluid helium cooling device that cools an object to be cooled with superfluid helium, and is suitable for cooling a superconducting coil, for example.

[Conventional technology]

It is known that helium exhibits a state called superfluidity, which has different properties from ordinary helium at temperatures below 1.8K to 2.1K. Since such superfluid helium has a viscosity almost close to zero and excellent heat transfer characteristics, it is particularly effective for cooling superconducting coils.

Conventionally, as a method of generating or maintaining a superfluid state of helium, for example, depressurizing the inside of a container containing helium in which the object to be cooled is immersed, and using the latent heat of evaporation of helium as a cooling source is performed. Was there.

[Problems to be solved by the invention]

However, this method has a problem that continuous use is limited because the amount of superfluid helium in the container is reduced. Also. In this case, continuous supply of helium may be considered, but due to the large amount of evaporation due to heat intrusion from the helium supply pipeline for supply, the capacity of the pressure reducing pump for maintaining a reduced pressure state increases, etc. ,
Especially, in a small-sized device, there is a problem that the cooling efficiency and the capacity are significantly lowered.

Incidentally, a method of producing superfluid helium under atmospheric pressure, regardless of the above method, is described in Japanese Patent Publication No. 60-4121. However, when it is used for cooling a superconducting coil or the like, the structure shown in FIG. 6 (d) or (c) of the publication must be adopted in order to be able to take the superconducting coil in and out of the cryostat. That is, one container is divided into upper and lower parts through a partition plate, the upper part is a normal liquid helium chamber, the lower part is a superfluid helium chamber, and the lower superfluid helium is cooled by another cooling source. To ensure a sufficient temperature gradient in the helium passage formed in the gap with the container, make the gap very small (for example, 10 to 50 μm).
m).

However, forming such a minute gap is
It is possible if the inner diameter of the container is small, but the inner diameter is several 10 cm ~
If the length is more than 1 m, there is a problem that it is difficult due to processing technology.

An object of the present invention is to solve the above-mentioned conventional problems, in other words, to enable continuous use and to increase the size without making the processing technique a problem, and to improve the cooling capacity of superfluid helium. It is to provide a cooling device.

[Means for solving problems]

The present invention, in order to achieve the above object, a closed container for storing superfluid helium in which the object to be cooled is immersed, a liquid helium supply pipe inserted and opened above the superfluid helium liquid level in the container, A gas-liquid separator provided at the open end of the supply pipe, an expansion valve communicating with the bottom of the gas-liquid separator and having the other end opened into the container, and a gas in the gas-liquid separator. The superfluid helium cooling device includes an exhaust pipe line that sends helium to the outside, and a decompression pump that evacuates the gaseous helium in the container and holds the decompression at a predetermined pressure.

[Action]

With this structure, the liquid helium replenished from the liquid helium supply pipe is in a gas-liquid mixed phase due to heat entry or the like, but is completely separated into a gas phase and a liquid phase by the gas-liquid separator. . Further, since the gaseous helium is sent out of the container through the exhaust pipe line, it does not become a load on the decompression pump. On the other hand, the liquid helium separated and accumulated at the bottom of the gas-liquid separator flows through the expansion valve into the container. At this time, since the inside of the container is kept at a predetermined low pressure by the decompression pump, that is, the liquid helium accumulated at the bottom of the container is maintained at a pressure in a superfluid state, the liquid helium discharged into the container through the expansion valve is It undergoes enthalpy expansion and is cooled efficiently to become superfluid helium, which cools the object to be cooled.

That is, replenishment of liquid helium enables continuous use, and the heat intrusion in the replenishment pipeline, etc. is separated by the gas-liquid separator and discharged to the outside of the system, so high cooling efficiency is maintained. become. Further, since the gas-liquid separator has a simple structure and is designed to generate superfluid helium by decompression, there is no problem in upsizing.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

(First Embodiment) FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention. As shown in FIG. 1, the super-electric coil 1 as the cooled object can be housed in the bottom of a vertical cylindrical container 2. Superfluid helium 3 is stored at the bottom of the container 2 so as to immerse the superconducting coil 1. The outer skin of the container 2 is covered with a laminated heat insulating material (not shown), and the whole is housed in the vacuum container 4 to maintain high heat insulating properties.

The upper end of the container 2 is an opening through which the superconducting coil 1 can be inserted and withdrawn, and the opening is sealed by a flange 5. A gas-liquid separator 6 having a double pipe structure is attached so as to hang down from the flange 5. The gas-liquid separator 6 is formed of stainless steel or the like having a low thermal conductivity in order to prevent heat from entering from the outside. As shown in FIG. 2 (A), the gas-liquid separator 6 has an inner tube and an outer tube 6a each having a bottom.
6b is inserted concentrically, and a blowout hole 6c is appropriately formed in the circumferential direction of the lower pipe wall of the inner pipe 6b. Further, as shown in the sectional view taken along the line IIB-IIB in the figure (A) shown in FIG. 9B, the blowout hole 6c is formed so as to be inclined in the tangential direction so that the blowout flow becomes a swirl flow. . On the other hand, an expansion valve 8 is connected to the bottom of the outer pipe 6a via a pipe line 7, and the other end of the expansion valve 8 is opened near the liquid surface of the superfluid helium 3. An initial injection pipe 10 having a valve 9 is provided in a branched manner in the pipe line 7, and its tip is located at the bottom of the container 2. In addition,
The exhaust gas of the helium gas separated by the gas-liquid separator 6 is discharged to the atmosphere via the exhaust pipe 11 which is in communication with the outer pipe 6a.

A porous plate having high thermal conductivity so that it is positioned above the liquid surface of the superfluid helium 3 in the container 2 and cooled by vaporized gas.
12 are arranged in multiple layers, and the perforated plate 12 is provided in thermal contact with the pipe 7.

A decompression pump 13 is provided in the upper part of the container 2, and the decompression pump 13 is driven by a variable speed motor 14 attached to the flange 5. Vacuum pump 13 suction pipe 15
Is opened at the inside of the container 4, and the blow-out pipe 16 is drawn out to the outside.

On the other hand, helium is supplied from the liquid helium dewar 20 through the liquid helium supply pipe 21.
One end of the liquid helium supply pipe 21 is inserted up to near the bottom of the dewa 20, and the other end is connected to the inner pipe 6b of the gas-liquid separator 6. Further, a pressurized gas system for supplying a pressurized gas through a sluice valve 22 is connected to the mouth of the dewa 20. Double heat shield plates 23 and 24 are concentrically provided on the outer periphery of the liquid helium supply pipe 21 to reduce heat intrusion, and a gap between them is evacuated. The heat shield plate 23 is provided with the exhaust pipe 11 of the gas-liquid separator 6, and the heat shield plate 24 is provided with the discharge pipe 16 of the decompression pump 13.
Are provided in thermal contact with each other along the longitudinal direction.

Here, details of the decompression pump 13 and the variable speed motor 14 will be described with reference to FIGS. As shown in FIG. 3, the motor 14 is attached through a motor flange 40 to an opening provided in the flange 5 of the container 2 with a motor shaft 41 protruding into the container 2. On the other hand, the decompression pump 13 includes an impeller 31 made of a metal such as aluminum alloy and a pump case 32 that cooperates with the impeller 31 to form a pump chamber.
Is a motor flange through a support case 33 made of heat insulating material.
It is fixed to 40 and the impeller 31 is fixed to the tip of the motor shaft 41.

The motor 14 includes a rotor 42 attached to a motor shaft 41, a stator 43 facing the rotor 42, a housing 44 supporting the stator 43, an end plate 45, a cooling fan 46 for cooling the motor, and a cooling fan. The case 48 is configured to include a case 48 that functions as a guide for circulating the air flow 47 of the 46 along the outer surface of the housing 44. The motor shaft 41 is axially supported by the motor flange 40 and the end plate 45 via a ball bearing 49. A seal disk 50 that hermetically seals the inside and outside of the housing 44 is attached to the outside of the end plate 45, and is in close contact with the housing 44 via an O-ring, an indium seal, a metal gasket, and the like. Similarly, the housing 44 and the motor flange 40, the pump case 32 and the support case 33, and the support case 33 and the motor flange 40 are also hermetically sealed.

As shown in FIG. 5, the impeller 31 of the decompression pump 13 has a large number of radial blades (for example, 50 to 60) 31a on the peripheral edge of the lower surface and is made of a light metal such as an aluminum alloy. As shown in FIG. 4, an annular helium gas flow path 34 is formed with the case 32, and a suction port 35 and a discharge port 36 are arranged so as to face the flow path 34. Incidentally, FIG. 4 shows a view of the pressure reducing pump 13 of FIG. 3 as seen from below. Since the impeller 31 is rotated at a high speed (for example, 200 to 400 Hz), the axial length between the impeller 31 and the ball bearing 49 is set to 3 to 6 cm in consideration of the critical speed of the rotating body. The temperature of the impeller 31 is about 4K.
Since the temperature of the ball bearing 49 is 300 K, the motor shaft 41 is made of a titanium alloy, which is a low heat conductive material, in order to minimize the heat entering the impeller through the motor shaft 41. Since the decompression pump 13 is installed in the container, low temperature (about 4K) helium gas can be exhausted at a low pressure, and it is small in size and requires less power than the one that exhausts the gas at room temperature. The pressure can be reduced. Further, since there is almost no pressure difference between the helium gas inside and outside the pump, the requirement for the sealing property of the pump itself is relaxed.

The operation of the embodiment shown in FIG. 1 having such a configuration will be described below.

Liquid helium in normal condition Liquid helium in Dewa 20 25
Is extruded by the pressurized gas that is press-fitted through the gate valve 22, passes through the liquid helium supply pipe 21, and is the inner pipe of the gas-liquid separator 6.
It is discharged into 6b. At this time, the liquid helium 25 is a gas-liquid two-phase flow 26 that is partially vaporized due to heat penetration.
The two-layer flow 26 is blown into the outer pipe 6a from the blowout hole 6c and collides with the inner wall of the outer pipe 6a, and is separated into a helium gas 27 and a liquid helium 25 due to the difference in density between them. Helium gas 27
Is released into the atmosphere through the exhaust pipe 11 as it rises in the outer pipe 6a. By cooling the heat shield plate 23 in this process, it contributes to preventing heat from entering the liquid helium supply pipe 21. On the other hand,
The liquid helium 25 flows down along the inner wall while rotating, and collects at the bottom of the gas-liquid separator 6. This accumulated liquid helium 25
Through the expansion valve 8 to the bottom of the container 4. At this time, the pressure in the container 2 is reduced by the decompression pump 13, and the stored liquid helium is maintained at a value that maintains the superfluid state. Therefore, liquid helium that has passed through the expansion valve 8
25 is isenthalpic expanded and a part thereof is vaporized, and its latent heat further lowers the temperature to form superfluid helium 3 which accumulates at the bottom of the container 2. This will be further described with reference to FIG.

FIG. 6 shows the relationship between the enthalpy H of liquid helium and the temperature T. In FIG. 6, the A region shown in FIG. 6 is the gas phase (100%), the B region is the liquid phase (100%), and the (A + B) region is the gas-liquid mixed phase. The liquid helium 25 whose gas phase has been separated by the gas-liquid separator 6 is in the state of the intersection a of the boundary line of the liquid phase B and the temperature of 4.2K. And liquid helium 25 discharged from the expansion valve 8
Is isenthalpic expansion, and the temperature (1.
8K) and superfluid helium-3 is produced. The cooling capacity of the superfluid helium 3 thus generated is
The heat quantity Qa from point a'to the complete vaporization in the isothermal state is Qa, and the mass flow rate of liquid helium is m, and the enthalpy difference is ΔHa.

Qa = mΔHa (1) On the other hand, when the expansion valve 8 is passed without separating and removing the helium gas from the liquid helium 25 by the gas-liquid separator 6,
The points a and a'are points b and b ', respectively, and the cooling capacity Qb is given by the following equation.

Qb = mΔHb (2) That is, even if the superfluid helium 3 is produced using a pump having the same performance, it is clear from FIG. 6 depending on the presence or absence of the gas-liquid separator 6. As described above, ΔHa has a difference in cooling capacity corresponding to ΔHb. As an example, using a liquid helium supply pipe 21 with an invasion heat of 1 w,
When liquid helium 25 is supplied at 20 to 2.8 / hour to generate superfluid helium 3, ΔHb becomes about 29% of ΔHa.
When gas-liquid separation is performed, the flow rate m decreases, but even if this is taken into consideration, the refrigerating capacity increases by nearly 80%.

Furthermore, since the helium gas (temperature 1.8K) evaporated from the liquid surface of the superfluid helium 3 accumulated at the bottom of the container 2 cools the pipeline 7 through the porous plate 12, it flows down the pipeline 7. The liquid helium 25 is cooled, and the point a in FIG. 6 becomes the state of point c in FIG. Therefore, the superfluid helium discharged and generated from the expansion valve 8 has the enthalpy at the point c ', and the cooling capacity is further improved.

Further, the helium gas sucked by the decompression pump 13 is guided to a room temperature decompression pump (not shown) through the discharge pipe 16, but in this process, the heat shield plate 24 of the liquid helium supply pipe 21 is cooled by sensible heat, Reduces heat penetration.
On the other hand, when viewed from the room temperature decompression pump side, the helium gas is heated, which is convenient. Therefore, the liquid helium supply pipe 21 may be a double pipe, and the discharge gas of the decompression pump 13 may be passed through the outer pipe to positively heat.

The initial injection pipe 10 is used at the beginning of operation,
When cooling the superconducting coil 1 for the first time, the expansion valve 8 is closed, the valve 9 is opened, and the entire liquid helium 25 is initially injected.
The sensible heat of helium is sufficiently utilized for cooling the superconducting coil 1.

As described above, according to the present embodiment, in the case where the pressure inside the container is reduced to generate superfluid helium, the liquid helium to be replenished is supplied only in the liquid phase through the gas-liquid separator. The enthalpy of the superfluid helium produced is significantly increased, which has the effect of significantly improving the cooling capacity. This makes it possible to use it continuously, and the processing technology for large-sized parts becomes a problem. Since it does not have any, there is an effect that it can be easily enlarged.

Further, according to the present embodiment, since the heat shield plate of the liquid helium supply pipe is cooled by the sensible heat of the helium gas discharged from the gas-liquid separator and the pressure reducing pump, it is possible to reduce heat intrusion. Therefore, the cooling capacity can be further enhanced.

Further, the sensible heat of the helium gas evaporated from the superfluid helium liquid surface by the perforated plate cools the liquid helium pipeline reaching the expansion valve, so that the cooling capacity can be further improved.

(Second Embodiment) FIG. 7 shows a schematic block diagram of another embodiment of the present invention. This embodiment differs from the embodiment shown in FIG. 1 in that a liquid helium supply pipe
In the double pipe part formed from 21 and its heat shield plate 23,
In order to allow the helium gas discharged from the gas-liquid separator 6 to flow, a heat shield plate 23 is provided extending in the gas-liquid separator 6 along the supply line 21 and the helium gas is exhausted by two systems. What to do, lead wire 1a of superconducting coil 1
Is arranged along the side wall of the gas-liquid separator 6 so as to maintain thermal contact therewith to reduce heat intrusion by the lead wire 1a, and to reduce the decompression pump 13 and the motor 14 in the container 2 Board
The reason is that the exhaust efficiency was improved by inserting the decompression pump 13 to the upper position of 12 and letting the decompression pump 13 as much as possible absorb helium gas.

As the thermal contact method of the lead wire 1a, a method by an adhesive method that maintains electrical insulation, a method of flowing the helium gas separated by the gas-liquid separator 6 into the lead wire 1a, and the like can be considered.

The decompression pump 13 and the motor 14 have a cylindrical body 17 made of a heat insulating material or the like.
A cylindrical body 17 housed inside and provided so as to hang down from the flange 5 is covered with a cylindrical body 18 via a vacuum space, and prevents the motor 14 and the ball bearings 49 and the like from becoming cold.

〔The invention's effect〕

As described above, according to the present invention, in which the pressure inside the container is reduced to generate superfluid helium, a liquid helium supply pipe is inserted into the container, and a gas-liquid separator is provided at the tip of the pipe, and continuous. The liquid phase of liquid helium that is supplied is separated and exhausted to the outside of the container, and only the liquid phase is replenished through the expansion valve, so the cooling capacity can be greatly improved and continuous. In addition to being usable, there is no problem in processing technology in upsizing, so there is an effect that upsizing can be performed easily.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 (A),
FIG. 3B is a partial sectional view of the gas-liquid separator of FIG.
1 is a detailed sectional view of a pressure reducing pump and a variable speed motor according to the embodiment of FIG. 1, FIG. 4 is a view of the pressure reducing pump as seen from below, FIG. 5 is a view showing an impeller of the pressure reducing pump, and FIG. 6 is the present invention. FIG. 7 is a diagram showing the relationship between the enthalpy of helium and temperature for explaining the operation of FIG. 7, and FIG. 7 is a configuration diagram of another embodiment of the present invention. 1 ... Super-electric coil, 2 ... Container, 6 ... Gas-liquid separator, 8 ... Expansion valve, 11 ... Exhaust pipe, 12 ... Perforated plate, 13 ... Decompression pump, 16 ... Discharge pipe, 21 …… Liquid helium supply pipe, 23, 24 …… Heat shield plate.

Claims (1)

[Claims] 1. A closed container for storing superfluid helium in which an object to be cooled is immersed, a liquid helium supply pipe inserted and opened above a liquid surface of superfluid helium in the container, and an open end of the supply pipe. A gas-liquid separator, an expansion valve communicating with the bottom of the gas-liquid separator and having the other end opened into the container, and helium gas in the gas-liquid separator is delivered to the outside. A superfluid helium cooling device comprising: an exhaust pipe line; and a decompression pump that decompresses gaseous helium in the container and holds the decompression at a predetermined pressure.