JP2003254653A - Exhaust device for cryogenic cryostat - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To safely deliver helium gas outdoors by reducing line resistance for preventing increase of internal pressure of a Dewar and by heat-exchanging. <P>SOLUTION: This exhaust device for a cryogenic cryostat for processing cryogenic exhaust gas generated during a helium transfer comprises an exhaust pipe 18 connected with the helium cryostat for exhausting helium gas, and a duct having a discharge port of the exhaust pipe 18 for discharging helium gas arranged approximately in the center of section of an opening 23 as one end part and comprising a body part 22 for mixing an inflow air made flow in by a fan 24 placed on a discharge port 25 as the other end part with the discharged helium gas. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for treating cryogenic exhaust gas generated during helium transfer in a liquid helium cryostat used for biomagnetic measurement and the like. More specifically, it relates to a method or structure for constructing an exhaust fan for cryogenic gas.

[0002]

2. Description of the Related Art In the field of biomagnetism measurement such as magnetoencephalography and magnetocardiography, liquid helium is used as a cryogen for handling superconducting quantum interference devices (SQUIDs). Liquid helium is SQU
The liquid helium container is injected (transferred) into the vacuum double-layer structure dewar (liquid storage tank) in which the ID array is stored, and at that time, a large amount of liquid helium is vaporized.
A practical dewar for a magnetoencephalograph used in clinical use has a capacity of 50.
~ 100 L, 50 ~ 1 once or twice per week
Must be transferred from a 00 L liquid helium container.

The dewar for a magnetoencephalograph has a large opening and S
Since the vacuum layer on the measurement surface of the QUID is thin and heat intrusion is large, liquid helium is consumed in large amounts, and transfer is inevitable. Since liquid helium has an extremely small latent heat of vaporization, it tends to vaporize, and the loss during transfer is large. Loss such as vaporization during pressurization in a helium container, vaporization during cooling and transfer of a liquid injection tube having a vacuum insulation layer called a transfer tube, cooling of the vapor layer in the dewar, vaporization by stirring the liquid layer in the dewar, etc. Although there are factors, it is said that the loss during transfer is 20 to 30%.

That is, when transferring from a 100 L liquid helium container, it is converted into a liquid volume of 20 to 3
0L is exhausted from the dewar exhaust port. The helium gas coming out of the exhaust gas port is not liquid helium temperature (4.2K) because it comes out after being heat-exchanged inside the dewar, but the temperature is still as low as several tens of K. Touching this gas may cause low-temperature burns, and since the exhaust gas is a choking gas and is in large quantities, it cannot be directly opened indoors. Furthermore, since cryogenic gas embrittles most resin piping materials, there is a risk of bursting if stress is applied and the conduit must be made of metal. Must be exhausted.

Conventionally, exhaust gas treatment has been performed by the method shown in FIG. Liquid helium is contained in a sump 2 in a liquid helium container 1. Send helium gas from tube 3,
The gas layer 4 is pressurized to deliver liquid helium. Liquid helium is thermally insulated and transferred through a thin tube inside by a double tube 5 having a vacuum layer by a transfer tube. On the upper surface of the dewar 6 having a vacuum heat insulating layer, there is an insertion port 7 (Wilson seal) into which the transfer tube is hermetically inserted.
Mist-like helium is ejected from the tip 8 of the transfer tube and accumulates in the sump 9.

At this time, since excess gas is lost, excess gas is exhausted through the gap 10 and the vacuum double tube 11 for exhaust gas. Exhaust gas (helium gas) is passed through a Teflon (registered trademark) tube or a metal tube 12 in water 14 for heat exchange in a water tank 13 filled with water for heat exchange. However,
In some cases, there is no water tank and heat is exchanged in the air. FIG. 2 shows a structure in which heat is exchanged in air, and only the structure after the exhaust pipe is shown. The metal conduit 15 should be as long as necessary for heat exchange.

[0007]

However, when heat is exchanged indoors, as shown in FIGS. 5 and 6, the pipe length of the heat exchange section becomes long and the pipe resistance becomes large. That is, the pressure on the dewar side becomes high. Liquid helium and room temperature gas helium have a volume ratio of 750 times, but the pressure in the pipeline tends to be high due to expansion in the heat exchange section. Even if the exhaust outlet is open to the atmosphere, the pressure increases on the dewar side, so it is desirable to reduce the line resistance as much as possible, but heat exchange cannot be sufficiently performed with a short line.

When the pressure in the Dewar rises, it takes time to transfer the transfer, and the transfer loss increases due to the effect of heat intrusion into the transfer tube, which is not economical. Therefore, when the pressure of the container is increased, the pressure of Dewar increases. The dewar has a very thin measuring surface and is weak in strength, so the pressure cannot be raised so much and must be suppressed to about 1.1 to 1.3 atm. For this reason, the heat exchange path of the exhaust unit must be shortened.

If a resin tube is used for the conduit, it may be ruptured due to pressure fluctuation, internal pressure or vibration, which is dangerous. In addition to the problem of poor operability of metal pipes, they are subject to repeated stress due to expansion and contraction due to heat, and there is a risk of breakage over a long period of time due to low temperature brittleness, although not as much as resin. Therefore, if it is attempted to exchange heat with a conduit as short as possible, a water tank as shown in FIG. 1 must be prepared, but it must be complicated when it is used.
In other words, in the past, since the duct resistance of the exhaust pipe is high and the pressure in the Dewar tends to rise, the loss is tolerated and transferred slowly, and a large space is taken in an inconvenient way to secure safety.

The present invention has been made in view of the above circumstances, and it is possible to reduce the duct resistance of the exhaust pipe so that the pressure in the Dewar does not rise, and to exchange the heat safely to lead it out of the room. An object is to provide a possible cryogenic cryostat exhaust device.

[0011]

In order to achieve the above object, the invention according to claim 1 is an exhaust for a cryogenic cryostat for treating cryogenic helium gas generated during helium transfer in a helium cryostat. A device, which is connected to a helium cryostat, has an exhaust pipe for exhausting helium gas, and an exhaust port for exhausting the helium gas. And a duct having a body for mixing the inflowing air introduced by the fan provided at the other end of the exhaust port and the exhausted helium gas. And

Therefore, according to the invention described in claim 1,
Helium gas from the dewar (storage tank) is sent to the duct through the exhaust pipe, and indoor air is taken in from the opening.
Helium gas and room air are mixed in the body of the duct, and heat is exchanged and helium gas is confined, so safety can be ensured and heat exchange efficiency for heat exchange is performed in the body of the duct. It will be possible to improve. Further, since the duct is located immediately after the exhaust port of the exhaust pipe, the cross-sectional area becomes large and it becomes possible to prevent the pressure on the dewar side.

The invention described in claim 2 is the same as claim 1
In addition to the configuration described in (1), a heat exchanger that is attached to the exhaust port of the exhaust pipe so as to be incorporated in the opening of the duct and that has a radial heat radiating plate arranged in parallel to the flow of the air taken in And

Therefore, according to the invention described in claim 2,
Since the fins, which are heat exchangers, are radially arranged in parallel with the flow of air, it is possible to efficiently perform heat exchange between the helium gas and the room air taken in through the openings.

Further, in addition to the structure of claim 1, the invention of claim 3 is close to the opening of the duct,
A straightening vane is provided along the inner surface of the duct from the exhaust port of the exhaust pipe.

Therefore, according to the invention of claim 3,
Since a straightening plate is provided along the inner surface of the duct from the exhaust port of the exhaust pipe, the flow of air becomes a laminar flow so that it does not touch the inner surface of the duct immediately after exiting the exhaust pipe. It is possible to prevent dew condensation from concentrating on a part of the duct.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows an overall view of an exhaust system for a cryogenic cryostat which is an embodiment of the present invention. A dewar (liquid storage tank) 16 equipped with a vacuum heat insulation layer contains a double tube 17 having a vacuum layer as a transfer tube. In this tube 17, liquid helium is thermally insulated and transferred through an internal thin tube. It will be. Further, an insertion port 17 (Wilson seal) into which the transfer tube is hermetically inserted is provided on the upper surface of the dewar 16.

Mist-like helium is ejected from the tip of the transfer tube inserted into the insertion port 17 and collected in the liquid reservoir 29 in the dewar 16. A gap 27 is provided above the liquid sump 29 for discharging the exhaust gas (helium gas) from the dewar 16.
Is connected to one end of the (insulated) exhaust pipe 18.
The fin 2 is provided at the other end (exit) of the (insulated) exhaust pipe 18.
A conduit with 0 is attached. 2 is a view of the portion AA ′ of the fin 20 in FIG. The fins 20 are radially arranged so as to be parallel to the inflow air, and heat exchange between the inflow air and the helium gas can be efficiently performed. The fins 21 are made of a material having high heat conductivity such as aluminum or copper, and helium gas is discharged through the holes (conduit) 19 inside.

An opening 23 is formed by an aluminum exhaust duct 21 having a body 22 so as to surround the conduit 20 having the fins 21. Further, a fan 24 for pulling air in the exhaust duct 21 is provided at the rear of the exhaust duct 21 made of aluminum. Fan 2
An exhaust port 25 for exhausting the air in the exhaust duct 21 is provided in the rear of 4.

Next, an exhaust method using the exhaust device for the cryogenic cryostat shown in FIG. 3 will be described. First, in the dewar 16, helium is injected from the double pipe 17,
(Adiabatic) Exhaust pipe 18 is the same as in FIG. Helium gas from the sump 29 passes through the gap 27,
(Insulation) Enters the exhaust pipe 18 and reaches a conduit 19 having fins 20. In this way, partial heat exchange takes place while the helium gas passes through. Then, in the exhaust duct 21 made of aluminum, the indoor air is taken in from the opening 23 so as to surround the fin.

At this time, since it passes through the fin 20, the interface of the fin 20 is always warmed to near room temperature. Further, the body portion 22 of the exhaust duct plays a role of exchanging heat with room air and confining helium gas. At this time, inside the body 22 of the exhaust duct, the room air introduced through the opening 23 and the helium gas are mixed, and the temperature rises. Then, the air in the exhaust duct 21 is pulled by the fan 24, and the helium gas is finally discharged from the discharge port 25 to the outside.

The exhaust duct 21 shown in FIG. 1 has the role of a heat exchanger, but since the exhaust gas (helium gas) is in direct contact (insulation), the temperature is low near the exhaust port of the exhaust pipe 18 and the temperature near the fan 24. Becomes higher. Therefore,
(Insulation) The exhaust duct 21 near the exhaust port of the exhaust pipe 18 is liable to cause dew condensation, which causes problems such as mold. Therefore, it is desirable that heat can be evenly exchanged in the exhaust duct 21.

FIG. 3 shows a structure therefor.
Air rectified is provided so that the air taken in from the room is made to follow the inner side surface (inner wall) of the exhaust duct 21 and a part of the air flow becomes a laminar flow. Therefore, the inner surface (inner wall) of the exhaust duct 21 is prevented from coming into contact with the exhaust port of the (insulated) exhaust pipe 18 immediately after it exits. Therefore, it is not possible to form dew condensation spots concentrated on a part of the exhaust duct 21. In FIG. 3, the rectifying plate 3 is provided only at one location immediately after the fin 20.
Although the example in which 0 is provided is shown, the flow straightening plate 3 is provided downstream along the flow.
By providing 0 at a plurality of points, heat exchange points can be dispersed in the pipeline (pipe of the duct).

1 and 3, the exhaust port 2 of the exhaust duct is shown.
5 is provided with a fan 24, but the inlet (the duct opening 2
Even if it is provided on the 3) side, the same effect can be obtained. The structure is shown in FIG. 4, and since the fan 24 is provided at a position close to the discharge pipe 21, the effect of not cooling the fan 24 is added.

[0026]

According to the present invention, since the exhaust pipe is provided with the fins for heat exchange, heat is efficiently exchanged at the exhaust port of the exhaust pipe. Further, the helium gas is diluted with the indoor air that flows in immediately after the fin, and the temperature can be rapidly raised, which is safe. Furthermore, since helium gas is confined in the aluminum exhaust duct, it is safe because it is not opened indoors.

In the past, helium gas was confined in the conduit in the air or liquid for heat exchange. However, in the present invention, heat is exchanged in the body of the large-area aluminum exhaust duct, so that the pipe Road resistance is also reduced and heat exchange efficiency is improved. In particular, since the duct immediately after the exhaust port of the exhaust pipe has a large cross-sectional area, it is possible to prevent an increase in pressure on the dewar side. In the past, 100% helium exhaust gas was exhausted, so it was necessary to be careful. However, in the present invention, the exhaust gas, helium gas, is exhausted after it has been sufficiently diluted with the atmosphere, so not only the temperature but also the gas concentration. Is low and safe.

[Brief description of drawings]

FIG. 1 is an overall view of an exhaust system for a cryogenic cryostat according to the present invention.

FIG. 2 is a cross-sectional view of fins that are heat exchangers taken along the line AA ′ in FIG.

FIG. 3 is a partially enlarged view of an exhaust device for a cryogenic cryostat in which a current plate is provided in a duct.

FIG. 4 is a partially enlarged view of an exhaust device for a cryogenic cryostat in which a fan is provided on the air inlet side of the room.

FIG. 5 is an overall view of a conventional exhaust gas (helium gas) treatment apparatus.

FIG. 6 is a partially enlarged view of a conventional exhaust gas (helium gas) treatment device in which a conduit for heat exchange is deformed.

[Explanation of symbols]

16 Dewar 17 double tube 18 (insulated) exhaust pipe 19 conduits 20 fins 21 Exhaust duct 22 Body of exhaust duct 23 opening 24 fans 25 Exhaust duct outlet 27 Gap 29 liquid reservoir 30 current plate

Claims (3)

[Claims] 1. An exhaust device for a cryogenic cryostat for treating cryogenic helium gas generated during helium transfer in a helium cryostat, the exhaust device being connected to the helium cryostat and for exhausting the helium gas, An exhaust port of the exhaust pipe for exhausting the helium gas is arranged substantially at the center of the cross section of the opening which is one end, and an inflow which is introduced by a fan provided at the exhaust port which is the other end. An exhaust system for a cryogenic cryostat, comprising: a duct having a body for mixing air and the discharged helium gas. 2. A heat exchanger, which is attached to an exhaust port of the exhaust pipe so as to be incorporated in an opening of the duct, and which has a radial heat radiating plate arranged in parallel to a flow of air taken therein. The exhaust device for a cryogenic cryostat according to claim 1. 3. The exhaust for a cryogenic cryostat according to claim 1, wherein a rectifying plate is provided in the vicinity of the opening of the duct and along the inner surface of the duct from the exhaust port of the exhaust pipe. apparatus.