JPH11233839A - Low-temperature thermostat - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of entering heat by providing a liquid refrigerant container with first and second baths and an insert, a body that is maintained at a low, constant temperature, a lid, and the like in the insert, and an exhaust port for externally discharging gas being evaporated from the liquid refrigerant in the lid. SOLUTION: A liquid refrigerant container in double structure is constituted of an inner bath 1 of a first bath and an outer bath 2 of a second bath. A heat-insulating material 6 is installed at the gap between the inner layer 2 and the outer layer 2 to maintain vacuum state. An insert 9 is provided in the liquid refrigerant container. The insert 9 is constituted of a sensor part 10 that is a body that is maintained at a low, constant temperature consisting of a superconductive coil and a superconductive quantum interference element circuit, a base plate 11, a support rod 12, a vacuum container 13, a heat insulator 14, and a lid 16 with the exhaust port. The heat insulator 16 is constituted by alternately piling up a mesh material 4 and a metal foil 5, thus reducing the amount of heat being propagated downward in the refrigerant container due to heat radiation. A liquid refrigerant 17 such as liquid helium is sealed to a depth where the sensor part 10 is dipped in the refrigerant container.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature thermostat, and more particularly to a low-temperature thermostat suitable for performing magnetic measurement using a superconducting quantum interference device (SQUID) circuit.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent Application Laid-Open No. Hei 6-331717, a liquid container has a double-walled vacuum heat insulating layer on the side and bottom surfaces. (1987) "Low temperature technology", University of Tokyo Press, p.
As shown in Fig. 7.1 of Fig. 77, the structure used heat insulation material such as expanded styrene to prevent heat from entering.

[0003]

However, in the above-mentioned prior art, heat enters the liquid container from the upper surface of the liquid container due to heat conduction of the heat insulating material, and suppresses the amount of heat infiltration to the same extent as the heat intrusion from the side and bottom surfaces. I couldn't do that. Accordingly, the evaporation amount (consumption amount) of the liquid refrigerant is large, and the liquid refrigerant must be replenished frequently in order to keep the contents inside the liquid container at a low temperature, and the maintenance labor and cost are considerable.

Further, in the liquid container having the conventional structure, the gas in which the refrigerant has evaporated (hereinafter referred to as “evaporated refrigerant”) is discharged to the outside (at a low temperature) without sufficient heat exchange. Was cooled by the exhaust, and phenomena such as dew condensation or freezing were observed.

Further, in the vacuum heat insulating layer of the double-structured liquid container, during a long use period, the evaporative refrigerant diffuses into the vacuum portion through the inner tank wall of the liquid container, and the degree of vacuum is reduced to lower the heat insulating effect. Since the amount of evaporation of the liquid refrigerant increases, it is necessary to redraw the vacuum once every few months.

An object of the present invention is to provide a low-temperature constant-temperature apparatus suitable for reducing the amount of infiltration heat.

[0007]

SUMMARY OF THE INVENTION According to one aspect, the present invention provides a liquid refrigerant containing a liquid refrigerant having a first tank and a second tank, with a vacuum insulation layer formed therebetween. A liquid container having an opening provided in an upper part thereof, wherein the insert is held so as to be immersed in the liquid refrigerant;
A lid coupled to the liquid refrigerant container so as to be able to open and close the opening, a heat insulator made of a heat insulating material provided between the lid and the low-temperature constant temperature maintaining body, and a vacuum container, The lid has an exhaust port for discharging gas evaporating from the liquid refrigerant to the outside of the liquid container.

[0008] According to another aspect, the present invention provides a first method.
A liquid refrigerant container containing a liquid refrigerant, and a gas stagnation portion provided in the vacuum heat insulating layer, and a liquid refrigerant container, A conduit for introducing gas evaporating from the liquid refrigerant into the gas retaining portion; and an insert, wherein the liquid refrigerant container has an opening provided at an upper portion thereof, and the insert is provided to the liquid refrigerant. A low-temperature constant-maintenance body held to be immersed; a lid coupled to the liquid refrigerant container so as to open and close the opening; and a lid interposed between the lid and the low-temperature constant-temperature maintenance body. A heat insulator made of a heat insulating material, wherein the lid has an exhaust port for discharging the gas from the stagnation portion to the outside of the liquid refrigerant container.

According to yet another aspect of the present invention, there is provided a liquid containing a liquid refrigerant, comprising a first tank and a second tank disposed outside the first tank, wherein a vacuum heat insulating layer is formed therebetween. A refrigerant container, an insert, and a vacuum isolation wall forming a further vacuum heat insulating layer in the vacuum heat insulating layer so as to cover a portion of the first tank corresponding to the liquid refrigerant; The refrigerant container has an opening provided at an upper part thereof,
The insert is a low-temperature constant-temperature maintaining body held so as to be immersed in the liquid refrigerant, a lid connected to the liquid refrigerant container so as to open and close the opening, and the lid and the low-temperature constant temperature. And a heat insulator made of a heat insulating material interposed between the retainer and the retainer, wherein the lid has an exhaust port for discharging gas evaporating from the liquid refrigerant to the outside of the liquid refrigerant container.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In order to suppress the amount of heat intrusion from the upper side of the liquid refrigerant container to the same level as that from the side or bottom side, the heat insulating means on the upper side should have the same structure as the side or bottom side. do it. That is, a vacuum container is provided on the side surface or the bottom surface of a heat insulator made of a heat insulating material at the upper part of the insert to suppress heat intrusion due to heat conduction. The heat radiation in the vacuum chamber may be suppressed by inserting heat insulating materials alternately stacked in the layers.

In order to promote the heat exchange of the evaporative refrigerant, a gas retaining portion is provided on the side and bottom portions of the vacuum heat insulating layer, and a conduit for guiding the evaporative refrigerant from the liquid refrigerant container to the gas retaining portion is provided. It is sufficient to adopt a configuration in which heat entering from the side and bottom surfaces due to heat radiation is absorbed by the evaporated refrigerant in the gas retaining portion.

[0012] Further, the fact that the degree of vacuum is reduced during long-term use and the heat insulating effect is reduced is described below in a part below the liquid level of the liquid refrigerant in the inner tank of the double-structured liquid container. A vacuum insulation wall is provided so that a further vacuum insulation tank is formed so as to cover the inner tank, and in this further vacuum insulation layer, a mesh material and a metal foil are alternately stacked in layers. What is necessary is just to be the structure which inserts a material.

[0013] With the above structure, the heat intrusion from the upper part of the insert is caused by invasion heat transmitted from the upper surface side of the vacuum vessel through the side wall of the vacuum vessel and thermal radiation passing through the inside of the vacuum vessel. Since the latter has a negligible amount of heat infiltration as compared to the former, it eventually becomes heat infiltration due to heat conduction from a portion corresponding to the cross-sectional area of the side wall of the vacuum vessel, and the amount of heat intruded can be significantly reduced. . In addition, since the path of this heat intrusion is exclusively limited to the side of the vacuum vessel, the side is cooled by the evaporative refrigerant (counter flow) passing from immediately below (liquid level) to above (exhaust port), Further, the amount of invading heat can be reduced.

Further, since the evaporative refrigerant receives heat from the vacuum heat insulating layers on the side and bottom surfaces of the liquid container in the gas retaining portion, the temperature of the evaporative refrigerant when discharged to the outside can be increased, and the evaporative refrigerant near the exhaust port can be increased. The conditions of condensation and freezing are alleviated.
In addition, since heat entering the liquid refrigerant from the outside is reduced, the amount of evaporation of the liquid refrigerant is also suppressed.

Further, the evaporative refrigerant passes through the inner tank wall of the liquid refrigerant container near the upper portion of the container where the temperature is high, and does not occur near the liquid refrigerant where the temperature is low. Therefore, in the vacuum heat insulating layer, the evaporating refrigerant that has penetrated through the wall at the upper portion is diffused to cause a reduction in the degree of vacuum, and heat intrusion occurs between the outer tank and the inner tank by convective heat transfer. In order to cope with this, a vacuum in which a further vacuum heat insulating layer is formed so as to cover the inner tank in a portion below the liquid level of the liquid refrigerant in the inner tank of the liquid refrigerant container having a double structure. By providing a separating wall and inserting a heat insulating material in which a mesh material and a metal foil are alternately stacked in multiple layers also in this further vacuum heat insulating layer, vacuum isolation connected to the liquid container inner tank is performed. Since the walls are kept at a low temperature, the evaporated refrigerant does not pass through the vacuum isolation wall, the degree of vacuum in the further vacuum insulation layer is maintained and the amount of heat entering can be suppressed, so the amount of evaporation of the liquid refrigerant can be reduced. it can.

FIG. 1 shows an embodiment of a low-temperature constant temperature apparatus according to the present invention. The inner tank 1 and the outer tank 2 made of a non-conductive material such as glass fiber reinforced plastic (GFRP) constitute a liquid refrigerant container having a double structure in which a sealing material 3 such as an O-ring is sandwiched. The non-conductive material used for the inner tank 1 and the outer tank 2 is such that when the low-temperature constant temperature apparatus of the present invention is used for magnetic measurement, the inner tank 1 and the outer tank 2 are made of a conductive material (for example,
This is because, when made of metal, an eddy current is generated in the material, magnetic noise is generated, and accurate magnetic measurement cannot be performed.

The space between the inner tank 1 and the outer tank 2 is maintained in a vacuum state, and includes a mesh material 4 woven in a mesh shape with a vinyl chloride wire and a metal foil 5 such as a copper foil or an aluminum foil. The heat insulating material 6 is formed by alternately stacking any number of layers (for example, 30 layers). Copper foil and aluminum foil are suitable as metal foils because they have a low injection rate ε at low temperature (“Superconductivity and Low Temperature Engineering Handbook”, 1st edition, 1st printing (1993) Co., Ltd.)
See Table 3.4 on p.1092 of Ohmsha). Some of the metal foils are connected to a copper plate 7 attached to the outer surface of the inner tank 1. In this way, the heat that has entered from the outside by heat radiation is captured by the metal foil 5, and this heat is transmitted to the inner wall of the inner tank 1 via the copper plate 7 by heat conduction, and the evaporating refrigerant is transferred to the inner wall. This is because they take away the transmitted heat. In the lower part of the vacuum heat insulating layer, a sheet-like coil foil 8 formed by bonding a number of mutually insulated copper wires is used in place of the metal foil 5. This is because when the metal foil 5 is used, an eddy current is generated on the foil, and this causes noise in magnetic measurement.

There is an insert 9 in the liquid refrigerant container.
The diameter of the insert 9 is substantially equal to the inner diameter of the refrigerant vessel,
Large enough to close. When there is a gap between the insert 9 and the inner tank 1, the gas in which the refrigerant evaporates causes convection in the gap, and the amount of heat that carries the heat of the upper space in the refrigerant container downward and enters the liquid refrigerant is increased. This is because the consumption amount (evaporation amount) of is increased. The insert 9 includes a sensor unit 10 and a sensor unit, which are a low-temperature constant-temperature holding body including a superconducting detection coil made of a manganin wire for capturing magnetism and a SQUID (superconducting quantum interference device) circuit arranged in order from the bottom. 10, a base plate 11 for fixing the support 10, a support rod 12 for supporting the base plate 11, a vacuum container 13 for preventing heat from entering by heat conduction, and a heat insulator 1 made of a heat insulating material such as foamed polyurethane to be connected to the vacuum container
4. It comprises a lid 16 of a liquid container having an exhaust port 15. Here, the mesh members 4 and the metal foils 5 are alternately stacked inside the vacuum container 13 so as to reduce the amount of heat transmitted downward by heat radiation inside the refrigerant container. And in the refrigerant container, the lower part of the insert and the superconducting coil and
The liquid refrigerant 17 such as liquid helium is filled to a depth at which the sensor unit including the SQUID circuit is immersed.

The intrusion of heat in the low-temperature constant-temperature apparatus having the above configuration will be described below. First, heat intrusion from the side and bottom sides of the refrigerant container will be described. Since the side and bottom sides of the refrigerant container are constituted by a double-structured tank having a vacuum heat insulating layer, heat only enters by heat radiation in the vacuum heat insulating layer space. However, heat radiation is small because the mesh material 4 and the metal foil 5 are alternately layered in multiple layers in the vacuum heat insulating layer space as described above. For example, the inner wall of the outer tank 2, the outer wall of the inner tank 1, and the injection rate of the metal foil 5 have the same value ε.
Then, when 30 layers of the mesh material 4 and the metal foil 5 are stacked, the heat radiation is 1/31 =
It is as small as about 3.2%.

At the position (height) where the copper plate 7 to which the metal foil 5 is connected is a liquid refrigerant instead of a liquid refrigerant, there is an evaporative refrigerant. The heat from the metal foil 5 is received by the evaporative refrigerant through the copper plate 7. To release the refrigerant to the outside of the refrigerant container, the metal foil 5 in the vacuum heat insulating layer can be kept at a low temperature, heat intrusion due to heat radiation can be reduced, and at the same time, the metal foil 5 enters the inner tank 1 of the refrigerant container from the copper plate 7. Consumption of liquid refrigerant by heat
(Evaporation) is prevented from increasing.

Next, the heat entering from the upper surface side of the liquid refrigerant container will be described. The heat of penetration from the upper surface side of the refrigerant container mainly enters the heat insulating material 14 by heat conduction, but the heat of penetration enters the side wall of the vacuum container 13 downward by heat conduction.
As described above, since the mesh members 4 and the metal foils 5 are alternately layered in several layers inside the vacuum container 13, the amount of heat that enters the inside of the refrigerant container downward by heat radiation will be described later. This is because it is negligible compared to the amount of heat that penetrates the side wall of the vacuum vessel 13 downward by heat conduction.

On the other hand, the amount of heat that penetrates the side wall of the vacuum vessel 13 downward by heat conduction is controlled (proportional) by the cross-sectional area of the side wall. Therefore, to reduce the amount of heat
It is only necessary to reduce the wall thickness of the side wall, but since the inside of the side wall is vacuum, it is necessary to have strength enough to withstand pressure from the outside and strength enough to ensure maintenance of vacuum, The wall thickness is 3m if the refrigerant container is made of GFRP, for example.
about 0.2 m, and about 0.2 mm when made of stainless steel.

The reason for using GFRP is that the thermal conductivity is extremely small in the low temperature region as compared with stainless steel.
(For example, "Superconductivity and Low Temperature Engineering Handbook" 1st edition 1st edition
According to Figure 3.28 on p.1090 of Ohm Co., Ltd. (1993), high-strength CFRP is 0.09W / (mK) at 20K, 0.07W / (mK) or less at 10K,
GFRP is 0.18 W / (m · K) at 20-10 K, whereas stainless steel is 2-1 W / (m · K) according to Figure 3.28 on p.

In addition, stainless steel can be used in terms of magnetic noise because it is far from the magnetic measurement unit, but since this part is not immersed in liquid helium, the temperature is relatively high (for example, 30 to 90K). ), GFRP having lower thermal conductivity is suitable for the material of the vacuum vessel.

For example, when a cylindrical vacuum container having an outer diameter of 200 mm and a height of 100 mm is considered, the thickness of the GFRP is reduced due to strength.
Assuming 3 mm, (200-3) x π (pi: 3.14) x 3 (thickness) = approx.
It has a cross-sectional area of 1855.74 mm ² and a thermal conductivity of 0.4 to 0.8 W / (m
K) (100-130K), the invading heat is 0.6W / (mK) x 1
855.74 × 10 ⁻⁶ / (100 × 10 ⁻³ ) × (130-100) = 0.334 W, whereas when the thickness is 0.2 mm with stainless steel, the thermal conductivity is 15 W / (mK ) (100-130K), the amount of invading heat is 10W / (mK) x ((200-0.2) x π x 0.2) x ^10-6 / (100 x ^10-3 )
× (130-100) = 0.3764W. Therefore, even if the plate thickness of GFRP is made larger than that of stainless steel (for example, 3 mm), there is no significant difference from the relation with the amount of heat that enters.

The reason why the vacuum vessel 13 is arranged under the heat insulating material is that the thermal conductivity of GFRP is low only at a low temperature.
At high temperatures, it is high (according to the above data, the thermal conductivity of GFRP is 0.18 W / (m ・ K) at 20 ~ 10K, 0.7 ~ 0.8W /
(m · K)), because if the vacuum container 13 made of GFRP is arranged above the insert (that is, in a high-temperature region), the amount of invading heat increases.

By the way, 0.75 W / (m · K) × 1855.74 × 10 ⁻⁶ / (100 × 10 ⁻³ ) × (250-200) =
If heat intrusion of about 0.6959W can be tolerated, the vacuum vessel 13 can be arranged above the insert (not shown).

FIG. 2 shows another embodiment of the low-temperature constant temperature apparatus according to the present invention. In this figure, only the characteristic portions are shown, and other components (such as a seal, a heat insulating material, and an insert as shown in FIG. 1) are omitted for simplification.

A gas retaining section 18 is provided in the vacuum heat insulating layer. At least a part of the gas retaining portion 18 is provided below the liquid surface of the liquid refrigerant 17 in the vacuum heat insulating layer. This is because there is a liquid refrigerant below the refrigerant container and the amount of heat entering the liquid refrigerant is reduced. The conduit 19 for guiding the evaporated refrigerant from the inner tank 1 of the refrigerant container to the gas retaining portion 18 is not located at the upper part of the refrigerant container but at a position slightly higher than the liquid level of the liquid refrigerant (the height of the middle of the refrigerant container). )It is in. This is because the evaporated refrigerant at the top of the refrigerant container has a high temperature (200 to
250K), and the effect of absorbing heat from external heat radiation cannot be expected even when the refrigerant is led to the gas retaining portion 18, whereas the evaporated refrigerant near the liquid surface has a low temperature (20% when the refrigerant is liquid helium). ~ 70K). And the gas retaining section 1
Exhaust port 2 for discharging evaporative refrigerant from the refrigerant container 8 to the outside of the refrigerant container
0 is provided. The reason why the conduit 19 extends to the vicinity of the bottom surface of the gas retaining portion 18 is that the low-temperature evaporating refrigerant flowing out of the conduit 19 receives heat and expands and rises. This is because the staying portion 18 can be kept at a low temperature. On the other hand, the reason why the exhaust port 20 emerges from the upper portion of the gas retaining portion 18 is that the evaporative refrigerant that has received heat and has become high temperature accumulates in the upper portion.

The flow of the evaporating refrigerant and the intrusion of heat in the low-temperature constant-temperature apparatus having the above configuration will be described below.

The evaporating refrigerant moves through the conduit 19 to the gas retaining section 18 provided in the vacuum heat insulating layer. As described above, since the conduit 19 extends to near the bottom surface of the gas retaining portion 18, the low-temperature evaporated refrigerant accumulates near the bottom surface. Then, the heat accumulates in the gas accumulating portion 18 and expands by receiving heat that has entered through the vacuum heat insulating layer by heat radiation from the outer tank of the refrigerant container, and rises in the gas accumulating portion 18 by convection. The evaporated refrigerant that has received sufficient heat in the gas retaining portion 18 and has become high temperature is discharged to the outside from the exhaust port 20 provided at the upper portion.

Now, suppose that the refrigerant is helium and the refrigerant container is placed at room temperature (300 K). When there is no shielding plate in the vacuum heat insulating layer of the refrigerant container, the heat flux q ₀ due to heat radiation to the inner tank wall from the outer tub wall of the coolant container, from the expression of _{Stefan-Boltzmann, q 0 = σ × (T} h ⁴ -T _c ⁴ ) / [(1 / ε _h ) + (1 / ε _c ) -1] σ: Stefan-Boltzmann constant (5.67 × 10-8 [J / K4m2
s]) ε _h , ε _c : Injection rate of outer and inner tank walls, respectively, _Th , T _c : Evaporated gas is guided to the gas stagnation part because given by wall temperature of outer and inner tank walls, respectively In this way, the heat flux when keeping the wall temperature of the gas retaining portion facing the side and bottom surfaces of the refrigerant container inner tank at 150 K, as compared with the case where the gas retaining portion is not provided, is (300 ⁴ -4.2 ⁴ ) / (150 ⁴ -4.2 ⁴ ) = 6.25 × 10 ^-2 = 6.25%.

The latent heat of vaporization at the boiling point of helium (4.22 K) is 20.8 J / g, and the latent heat of vaporization at the boiling point of nitrogen (77.41 K) is less than 199 J / g. This indicates that the liquid helium easily evaporates even with a small amount of heat. On the other hand, the constant pressure specific heat of the evaporated gas is 1 atm, 0 ° C, and that of helium gas is 5.
It is 193 J / gK and that of nitrogen gas is 1.040 J / gK. The temperature rise when latent heat of vaporization is given to a boiling gas
In contrast to 3.2K, it is 190K with nitrogen gas. This indicates that the amount of heat required to raise the temperature of the helium gas is larger than the amount of heat required to raise the nitrogen gas of the same mass by the same temperature (the temperature of the helium gas hardly increases). Therefore, providing the gas retaining portion 18 in the vacuum heat insulating layer in order to reduce heat penetration is particularly effective when the refrigerant is helium.

FIG. 3 is a developed sectional view of the gas retaining section 18 shown in FIG. A labyrinth 21 is provided in the gas retaining section 18 to suppress the rising speed of the evaporative refrigerant and promote heat exchange.

FIG. 4 shows still another embodiment of the low temperature constant temperature apparatus according to the present invention. In the figure, only characteristic portions are shown, and others (such as seal materials and inserts) are omitted for simplification. The feature of this embodiment is that a further vacuum insulated tank is formed so as to cover the inner tank in a portion below the liquid level of the liquid refrigerant in the inner tank of the dual structure refrigerant container so as to cover the inner tank. A vacuum insulation wall 22 is provided, and a heat insulating material (not shown) in which a mesh material and a metal foil are alternately stacked in multiple layers is inserted into the vacuum heat insulating layer.
The vacuum insulation layer is separated into two parts, and the lower part of the inner tank containing the liquid refrigerant has a structure surrounded by a double vacuum insulation layer.

To explain the effect of this embodiment, when helium is used as the refrigerant, the degree of vacuum in the vacuum heat insulating layer decreases during a long use period because the evaporating refrigerant in the refrigerant container
This is because (helium gas) passes through the inner tank wall and enters the vacuum heat insulating layer. This is because even if air enters the vacuum insulation layer from the outside, the amount is very small, and the air molecules are liquid refrigerant (liquid helium, 4.2K) 1.
Wall of inner tank 1 containing 7 (wall temperature on the vacuum insulation layer side is around 10K)
This is because they are caught and condensed. That is, the amount of air that enters is very small because air (main components are nitrogen, oxygen, carbon dioxide, and argon) has a large molecular weight and does not enter through the outer tank 2 wall. Yes, and therefore only enters from the contact sealing surfaces of the inner and outer tanks by leak. On the other hand, the evaporative refrigerant (helium gas) passing through the wall of the inner tank 1 does not condense at around 10K, and once the evaporative refrigerant enters the vacuum heat insulating layer, it causes a decrease in the degree of vacuum. Because.

The evaporative refrigerant (helium gas) has a low temperature.
(Near the liquid surface), it does not pass through the wall of the inner tank 1, but has a property of passing through the wall in a high temperature portion (150K or more) above the inner tank 1. Therefore, the vacuum isolation wall 22 functions to prevent the evaporated refrigerant (helium gas) that has passed through the upper part of the refrigerant container inner tank 1 and entered the vacuum heat insulating layer from diffusing to the lower part of the vacuum heat insulating layer. Also,
Since the vacuum isolation wall 22 is connected near the liquid surface of the inner tank 1, the entire vacuum isolation wall 22 is maintained at a low temperature (100K or less),
Little helium gas passes through the vacuum isolation wall 22. As a result, the degree of vacuum in the vacuum heat-insulating layer at the lower part of the vessel inner tank 1 containing the liquid refrigerant (liquid helium) 17 is maintained, heat intrusion due to convective heat transfer of gas is prevented, and the amount of evaporation of the liquid refrigerant (liquid helium) 17 Can be kept low.

As described above, the embodiment of the present invention is particularly effective when helium is used as a refrigerant because of the property that air entering from outside is trapped in the vicinity of liquid helium. When nitrogen is used, it does not pass through the wall due to its molecular weight,
Since the degree of vacuum may be reduced by air entering from the outside, the embodiment of the present invention is effective in such a case.

As shown in FIG. 5, it is appropriate to adopt a configuration in which the vacuum heat insulating layer is divided into an upper part and a lower part, instead of forming a further vacuum heat insulating tank so as to cover the inner tank 1. is not. This is because a large amount of heat penetrates through the wall 23 that separates the vacuum heat insulating layer due to heat conduction.

As can be understood from the above description, in the embodiment of FIG. 1, heat enters due to heat conduction from the portion corresponding to the cross-sectional area of the side wall of the vacuum vessel, and the amount of heat entering can be significantly reduced. In addition, since the path of this heat intrusion is exclusively limited to the side of the vacuum vessel,
Evaporative refrigerant passing through (exhaust port) (counter flow)
As a result, the side surface is cooled, so that the amount of penetrated heat can be further reduced.

In the embodiment shown in FIGS. 2 and 3, the temperature of the evaporated refrigerant when discharged to the outside can be increased,
Condensation and freezing near the exhaust port are alleviated. In addition, since heat entering the liquid refrigerant from the outside is reduced, the amount of evaporation of the liquid refrigerant is also suppressed.

In the embodiment shown in FIG. 4, the degree of vacuum in the vacuum heat-insulating layer is maintained and the amount of heat that enters can be suppressed.
The amount of evaporation of the liquid refrigerant can be reduced.

[0043]

According to the present invention, there is provided a low-temperature constant-temperature apparatus suitable for reducing the amount of infiltration heat.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of a low-temperature constant temperature apparatus according to the present invention.

FIG. 2 is a longitudinal sectional view of another embodiment of the low-temperature constant temperature apparatus according to the present invention.

FIG. 3 is a developed cross-sectional view of a part of a gas retaining section shown in FIG. 2;

FIG. 4 is a longitudinal sectional view of still another embodiment of the low temperature constant temperature apparatus according to the present invention.

FIG. 5 is a reference longitudinal sectional view of a low-temperature constant-temperature apparatus for explaining the effect of the embodiment shown in FIG. 4;

[Explanation of symbols]

1: inner tank, 2: outer tank, 3: seal material, 4: mesh material,
5: metal foil, 6: heat insulating material, 7: copper plate, 8: coil foil, 9: insert, 10: sensor part, 11: base plate, 12: support bar, 13: vacuum vessel, 14: heat insulating material, 1
5: exhaust port, 16: lid, 17: liquid refrigerant, 18: gas retaining part, 19: conduit, 20: exhaust port, 21: labyrinth, 22: vacuum isolation wall, 23: wall.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiji Tsukada 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. Central Research Laboratory

Claims (12)

[Claims] 1. A liquid refrigerant container having a first tank and a second tank, between which a vacuum heat insulating layer is formed and containing a liquid refrigerant, and an insert, wherein the liquid refrigerant container is The insert has an opening provided at an upper portion thereof, and the insert is connected to the low-temperature constant-temperature maintaining body held so as to be immersed in the liquid refrigerant, and to the liquid refrigerant container so as to open and close the opening. Provided, a heat insulator made of a heat insulating material and a vacuum container provided between the lid and the low-temperature constant temperature maintaining body, wherein the lid removes gas evaporating from the liquid refrigerant to the outside of the liquid container. A low temperature constant temperature device having an exhaust port for discharging. 2. The low-temperature constant temperature apparatus according to claim 1, wherein the vacuum vessel is closer to the liquid refrigerant than the heat insulator. 3. A liquid refrigerant container having a first tank and a second tank and having a vacuum heat insulating layer formed therebetween and containing a liquid refrigerant, and a gas retaining section provided in the vacuum heat insulating layer. A conduit for guiding gas evaporating from the liquid refrigerant from the liquid refrigerant container to the gas retaining portion; and an insert, wherein the liquid refrigerant container has an opening provided at an upper portion thereof, and -A low-temperature constant-temperature maintaining body held so as to be immersed in the liquid refrigerant; a lid coupled to the liquid refrigerant container so as to open and close the opening; and the lid and the low-temperature constant-temperature maintaining body. And a heat insulator made of a heat insulating material interposed between the liquid refrigerant container and the lid, the lid having an exhaust port for discharging the gas from the stagnation portion to the outside of the liquid refrigerant container. 4. The low-temperature constant temperature apparatus according to claim 3, wherein at least a part of the gas stagnation portion is provided below the liquid surface of the liquid refrigerant in the vacuum heat insulating layer. . 5. The low-temperature constant-temperature apparatus according to claim 4, wherein the conduit extends to near the bottom of the gas retaining section. 6. The method of claim 3, wherein the conduit is positioned to draw the gas above and near the level of the liquid refrigerant. Low temperature constant temperature equipment. 7. A liquid refrigerant container for holding a liquid refrigerant, comprising a first tank and a second tank disposed outside the first tank and having a vacuum heat insulating layer formed therebetween, an insert, A vacuum isolation wall forming a further vacuum heat insulating layer so as to cover a portion of the first tank corresponding to the liquid refrigerant in the vacuum heat insulating layer, wherein the liquid refrigerant container has an opening provided at an upper portion thereof. A low temperature constant temperature maintaining body which is held so as to be immersed in the liquid refrigerant, and a lid coupled to the liquid refrigerant container so as to open and close the opening.
A heat insulator made of a heat insulating material interposed between the lid and the low-temperature constant temperature maintaining body, wherein the lid has an exhaust port for discharging gas evaporating from the liquid refrigerant to the outside of the liquid refrigerant container. Constant temperature equipment. 8. A liquid refrigerant container for storing a liquid refrigerant, comprising a first tank and a second tank disposed outside the first tank, and a vacuum heat insulating layer formed between the first tank and the second tank. A gas reservoir provided, a conduit for guiding gas evaporating from the liquid refrigerant from the liquid refrigerant container to the gas reservoir, an insert, and a first tank in the vacuum heat insulating layer.
A vacuum isolation wall forming a further vacuum insulation layer so as to cover a portion corresponding to the liquid refrigerant, wherein the liquid refrigerant container has an opening provided at an upper portion thereof, and the insert is provided with the liquid. A low-temperature constant-temperature maintaining body held so as to be immersed in a refrigerant; a lid coupled to the liquid refrigerant container so as to open and close the opening; and a lid interposed between the lid and the low-temperature constant-temperature maintaining body. And a vacuum container, wherein the lid discharges gas from the liquid refrigerant contained in the liquid refrigerant container to the outside of the liquid container and an exhaust port for discharging gas from the retaining portion. A low-temperature constant temperature apparatus having an exhaust port for discharging the liquid refrigerant outside the container. 9. The low-temperature constant temperature apparatus according to claim 8, wherein the vacuum vessel is closer to the liquid refrigerant than the heat insulator. 10. The low-temperature low-temperature apparatus according to claim 8, wherein at least a part of the gas retaining section is provided below the liquid surface of the liquid refrigerant in the vacuum heat insulating layer. Constant temperature equipment. 11. The low-temperature constant-temperature apparatus according to claim 10, wherein the conduit extends to near the bottom of the gas retaining section. 12. The system according to claim 8, wherein said conduit is positioned to draw said gas above and near the level of said liquid refrigerant.
A low-temperature constant-temperature apparatus described in 9, 10 or 11.