JPS6340712A - Production of pressurized helium having superfluidity - Google Patents

Abstract

PURPOSE:To effectively obtain the titled He at low cost without using a large heat exchanger by allowing a saturated He having superfluidity to boost its pressure with pressurizing by a bellows-type pump. CONSTITUTION:Liquid He IIs obtained by reducing the pressure of liquid He I in a vessel 10 with a vacuum pump 11 is sucked into a working chamber 13A from a suction valve 13C of a bellows-type pump 13 dipped in the liquid He IIs. The titled HE (IIp) is obtained through a delivery pipe 14 via a delivery valve 13D by boosting the pressure of the liquid He (IIs) sucked in the bellows by allowing the internal volume of the bellows to change with the expanding and contracting of the bellows 13B consisting of a stainless steel, etc.

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a method for producing pressurized superfluid helium, which is most suitable as a cooling medium for cooling to extremely low temperatures, such as a cooling medium used in superconducting magnets. .

BACKGROUND OF THE INVENTION Liquid helium has been used as a cooling medium for superconducting magnets and the like. Ordinary liquid helium consists of 41-46 atoms with a mass number of 4, and the phase diagram of 4He is shown in FIG.

There are two types of liquid phases of 4He: a liquid phase called liquid helium (hereinafter referred to as HeI) and a liquid phase called liquid helium (hereinafter referred to as HeII). In particular, the latter HeII is known to have a unique liquid phase that has virtually zero viscosity and exhibits the so-called superfluid phenomenon.
Therefore, this HeII is also generally called superfluid helium. This Hen has much better thermal conductivity than HeI, so if l-1elI is used as a cooling medium for superconducting magnets, the cooling efficiency will be much better than when HeI is used. . Therefore, recently, consideration has been given to using HeII as a cooling medium for superconducting magnets, etc., and practical use has begun in some cases.

By the way, among HeI [particularly, the gas-liquid boundary line (saturated vapor pressure line) A-B between HeII and the gas phase in the phase diagram of FIG.
The above HeII (generally referred to as saturated superfluid helium, hereinafter referred to as HeII) can be obtained relatively easily. In other words, if f-feI (hereinafter referred to as HeI), which is under saturated vapor pressure on the gas-liquid boundary line (saturated vapor pressure line) 8-C between HeI and the gas phase on the phase diagram, is depressurized, it becomes saturated. The temperature drops along the vapor pressure line B-C,
When the transition temperature Tλ (≠2.172K > point B under the saturated vapor pressure is exceeded, the liquid phase becomes HeI. Specifically, for example, the gas phase (He gas) in a container containing HeI is vacuumed. Either use a pump to reduce the pressure, or HeI
By adiabatically expanding , HeII can be obtained.

However, HeII obtained in this way.

If the temperature rises even slightly, gasification will proceed accordingly, so there is a problem of lack of stability when actually using it as a cooling medium for superconducting magnets, etc. Therefore, it is difficult to use it as an actual cooling medium. is under a pressure higher than the saturated vapor pressure (
-1eII at atmospheric pressure = 1 atm),
That is, so-called pressurized superfluid helium (hereinafter referred to as HeII)
(denoted as p) must be used. For example, if we look at HeIIp at point D at 1 atm on the phase diagram in Fig. 4, under equal pressure, until the temperature rises by △t1, HeIIp
Since the state of 1I is maintained and the liquid phase is maintained until the temperature rises by Δt2 even after it becomes roughly l-1eI, there is a margin (Δt1+Δt2) for the temperature rise until gasification, and therefore cooling is possible. It can be said that even if there is a slight temperature rise when used as a medium, stable cooling can be achieved without gasification.

The following methods are known as conventional methods for producing HeII (pressurized superfluid helium) as described above.

That is, the most common method is to use H under pressure such as atmospheric pressure.
This is a method in which eI is heat exchanged with HeI[3 and the temperature is lowered under the pressure to obtain He1I. In principle, this method can be carried out using an apparatus as shown in FIG. 5, for example.

In FIG. 5, a partition wall 2 is provided in the middle of the container 1 in the vertical direction.
It is divided into A and Royal 1B, and a communication hole 3 is formed in the partition wall 2, and this communication hole 3 can be opened and closed by a stopper 4.

In addition, the pipe line 5 whose tip opens into the upper ilA is an adiabatic expansion valve 6.
It is connected to a heat exchanger 7 in the lower chamber 1B via the heat exchanger 7, and the tip side of the heat exchanger 7 is connected to a vacuum pump 8.

When manufacturing Hen using such an apparatus, first, with the communication hole 3 open, for example, i at
H in the upper chamber 1A and lower chamber 1B of the container 1 under the pressure of m.
Inject eI. Then, by operating the vacuum pump 8 with the communication hole 3 closed by the stopper 4 while maintaining the pressure of 1 atm, HeI in the upper chamber 1A is removed.
is introduced into the adiabatic expansion valve 6, and the HeI is subjected to adiabatic free expansion (J
Heff1. , change it to H
eI, is guided to the heat exchanger 7 immersed in HeI in the lower chamber 1B to exchange heat with HeI in the lower chamber 1B, thereby lowering the temperature of the HeI under a pressure of 1 atm,
Change to HeII. Therefore, He
n, will be obtained. The communication hole 3 is temporarily closed by the stopper 4, but in reality, the H in the royal room 1B
If the volume of en decreases, HeI in the upper chamber 1A flows into the lower chamber 1B through the gap between the plug 4 and the inner surface of the communication hole 3, the temperature decreases, and it changes to HenD. Replenishment will be provided.

In addition to the methods mentioned above, a method for obtaining HeIIp@ has also been proposed in which HeII is obtained by lowering the temperature of HeI under pressure using a magnetic refrigerator using a GGG (gallium gadolinium garnet) crystal. , In addition, there is also a method of compressing 3He to, for example, 4.2, and then subjecting it to adiabatic free expansion to a temperature sufficiently lower than 4.2 to exchange heat with HeI under pressure, thereby converting HeI into HeII. Proposed.

Problems to be Solved by the Invention Among the methods for obtaining HeIIp (pressurized superfluid helium) as described above, the most common method is to convert HeI under pressure to HeIp.
In the method of obtaining HeII by heat exchange with HeII, a heat exchanger is absolutely necessary. However, in this case, it is necessary to use a heat exchanger with a significantly large surface area. That is, in general, the boundary thermal resistance of a heat transfer wall is Kap
It is known that it is inversely proportional to the cube of the absolute temperature, as expressed by the formula i tZa. Therefore, at extremely low temperatures near absolute zero, the boundary thermal resistance becomes extremely large, and therefore, when exchanging heat at extremely low temperatures, Since the temperature difference due to boundary thermal resistance between the low-temperature fluid and the heat exchanger heat transfer wall in contact with it becomes significantly large, the surface of the heat exchanger heat transfer wall must be significantly enlarged to increase heat exchange efficiency. occurs. Therefore, the entire heat exchanger for heat exchange as described above had to be increased in size, and the entire fruiting device had to be increased in size as well.

On the other hand, the method using the magnetic refrigerator described above has not yet been put into practical use due to technical and cost aspects, and
The actual situation is that the method using e has not been put into practical use because 3He does not exist naturally and is extremely expensive.

This invention was made against the background of the above circumstances, and it is possible to use pressurized superfluid helium (pressurized superfluid helium) without using a large heat exchanger.
The purpose of this invention is to provide a method for efficiently producing HeII, ) at low cost.

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have made various studies, and as a result, they have already published "Cryogenic Engineering" Vol. 20.
．． (1985) It was discovered that pressurized superfluid helium could be efficiently produced without using a heat exchanger by applying a bellows-type liquid helium pump as announced in p. 35 to p. 41, and this invention This is what we came to do.

That is, the method for producing pressurized superfluid helium of this invention is as follows:
The action is characterized by obtaining pressurized superfluid helium by pressurizing saturated superfluid helium with a bellows pump and increasing the pressure. As already mentioned, it becomes saturated superfluid! Noumu (HeII3)
can be easily obtained. Therefore, in the present invention, HeII obtained in advance is pressurized to a predetermined pressure using a bellows pump to produce pressurized superfluid helium (HeIIp). That is, as shown in the phase diagram of 4He in Figure 1, for example, the saturated vapor pressure of 1.8 HeI is 12T
orr, therefore Hell5 at that temperature
The vapor pressure of HeII is also 12 Torr, so by pressurizing HeII at an isothermal temperature as shown by the arrow, for example, 1
ATM, HeII of 1.8 can be obtained. Therefore, in principle, the method of this invention does not require heat exchange. In other words, the conventional heat exchanger method required a large heat exchanger with a large heat transfer area to increase heat exchange efficiency at extremely low temperatures, but with this invention, the heat exchanger itself is not required, so the equipment This made it possible to downsize the entire system.

In addition, conventional piston-cylinder type pumps generate a lot of heat due to the friction between the cylinder and the piston, so if it is actually applied to pressurize He, the temperature rise due to heat generation will cause He to gasify. Just H
e II o @ There are also rotary pumps, but rotary pumps have a small pressurizing force, so you can sufficiently pressurize Hell 3, which is at a low pressure of about 12 Torr, to 1 atm, and generate a sufficiently high pressure HeIIp. It was difficult to obtain.

On the other hand, according to the bellows-type pump that the present inventors developed earlier, there is no frictional part in principle, so there is no heat generation, and it is possible to obtain a large pressure increase, so it can be used without causing gasification. -16I[.

It became possible to obtain HeIIp at a sufficiently high pressure.

Embodiment FIG. 2 shows the principle of an apparatus for carrying out the method of the present invention.

In FIG. 2, a container 10 contains HeI. This HeII can be obtained, for example, by reducing the pressure of HeI in the container 10 using the vacuum pump 11. He II in the container 10, inside the bellows type pump 1
3 is immersed in the container 10, and this bellows pump is immersed in the container 10.
By taking in the Hen inside and pressurizing it, HeII
, and the HeII is discharged from the discharge pipe 14.

The most basic configuration example of the bellows pump 12 is shown in the third example.
As shown in the figure. This bellows type pump 13 has a bellows 1 made of stainless steel or the like, with an internal volume of an inner working chamber 13A.
A suction valve 13C consisting of a one-way valve is provided between the actuator 3A and the outside, and a one-way valve 13C is provided between the actuator 13A and the discharge pipe 14. A discharge valve 13D consisting of a directional valve is provided. Therefore, when the bellows 13B is extended, the external He
II, is sucked into the actuator 13A through the suction valve 13C, and when the bellows 13B is contracted, He in the actuator i aA
Pressure is applied to II, and it changes to HeII, and the Hen is discharged to the discharge pipe 14 via the discharge valve 13B.

Effects of the Invention According to the production method of the present invention, pressurized superfluid helium (HeII) can be obtained without heat exchange in principle, and therefore it is possible to obtain pressurized superfluid helium (HeII) without performing heat exchange. Since it is no longer necessary to use a large heat exchanger with a large surface to achieve sufficient heat exchange efficiency in consideration of thermal resistance, it is possible to downsize the manufacturing equipment, and
HeIIp can be obtained efficiently.

[Brief explanation of the drawing]

Figure 1 shows 4H for explaining the principle of the method of this invention.
Fig. 2 is a schematic diagram showing the principle of an example of an apparatus for carrying out the method of the present invention; Fig. 3 is a schematic diagram showing an example of a bellows pump used in the method of the present invention; 4
The figure is a 4He state diagram for explaining the conventional method.
The figure is a schematic diagram showing the principle of an apparatus for carrying out an example of a method for producing pressurized superfluid helium using a conventional heat exchange method.

Claims (1)

[Claims] A method for producing pressurized superfluid helium, characterized in that pressurized superfluid helium is obtained by pressurizing saturated superfluid helium with a bellows pump to increase the pressure.