U.S. patent application number 12/357476 was filed with the patent office on 2009-07-30 for cryogenic container with built-in refrigerator.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Hisashi Isogami, Norihide SAHO, Hiroyuki Tanaka.
Application Number | 20090188260 12/357476 |
Document ID | / |
Family ID | 40578538 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090188260 |
Kind Code |
A1 |
SAHO; Norihide ; et
al. |
July 30, 2009 |
CRYOGENIC CONTAINER WITH BUILT-IN REFRIGERATOR
Abstract
A cryogenic container with a built-in refrigerator according to
the present invention comprises the refrigerator having a first
heat absorbing part and a first heat dissipating part, a vacuum
vessel for containing and thermally insulating an object to be
cooled while holding the object at a cryogenic temperature through
the first heat absorbing part of the refrigerator, and a
pre-cooling unit having a second heat absorbing part and a second
heat dissipating part for cooling the first heat dissipating part,
wherein the first heat dissipating part and the second heat
absorbing part are arranged inside the vacuum vessel, and a part of
a heat dissipating unit including the second heat dissipating part
is exposed outside the vacuum vessel. According to the present
invention, in the cryogenic container with the built-in
refrigerator capable of cooling the object to be cooled to the
cryogenic temperature, the refrigerator efficiency can be improved
by cooling a heat dissipating surface of the first heat dissipating
part of the refrigerator to a level lower than the room
temperature.
Inventors: |
SAHO; Norihide; (Tsuchiura,
JP) ; Isogami; Hisashi; (Ushiku, JP) ; Tanaka;
Hiroyuki; (Mito, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
40578538 |
Appl. No.: |
12/357476 |
Filed: |
January 22, 2009 |
Current U.S.
Class: |
62/3.6 ;
62/51.1 |
Current CPC
Class: |
F25B 9/14 20130101; F25B
21/02 20130101; F25D 19/006 20130101; F25B 2500/13 20130101; F25B
25/00 20130101 |
Class at
Publication: |
62/3.6 ;
62/51.1 |
International
Class: |
F25B 21/02 20060101
F25B021/02; F25B 19/00 20060101 F25B019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2008 |
JP |
2008-015018 |
Claims
1. A cryogenic container with a built-in refrigerator comprising:
the refrigerator having a first heat absorbing part and a first
heat dissipating part; a vacuum vessel for containing and thermally
insulating an object to be cooled while holding the object at a
cryogenic temperature through the first heat absorbing part of the
refrigerator; and a pre-cooling unit having a second heat absorbing
part and a second heat dissipating part for cooling the first heat
dissipating part; wherein the first heat dissipating part and the
second heat absorbing part are arranged inside the vacuum vessel,
and a part of a heat dissipating unit including the second heat
dissipating part is exposed outside the vacuum vessel.
2. The cryogenic container with the built-in refrigerator according
to claim 1, wherein the refrigerator uses a gas as a cooling medium
and has a compressing part for mechanically compressing the cooling
medium; and the compressing part includes the first heat
dissipating part.
3. The cryogenic container with the built-in refrigerator according
to claim 1, wherein the heat dissipating unit includes a thermally
conductive member.
4. The cryogenic container with the built-in refrigerator according
to claim 1, wherein the pre-cooling unit comprises a Peltier
element.
5. The cryogenic container with the built-in refrigerator according
to claim 1, wherein a vibration isolating member is arranged
between the compressing part and an inner wall of the vacuum
vessel.
6. The cryogenic container with the built-in refrigerator according
to claim 1, wherein the first heat absorbing part and the
compressing part are connected by a tube.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese patent
application serial No. 2008-015018, filed on Jan. 25, 2008, the
content of which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a cryogenic container with
a built-in refrigerator.
[0004] 2. Description of Related Art
[0005] Document 1 (Japanese Patent Laid-open No Hei 11-87131)
discloses a refrigerator system, wherein a cryogenic part of a
refrigerator and a object to be cooled are disposed in a vacuum
vessel to prevent heat leak from a room temperature area in order
to keep the object at a lower temperature when the object to be
cooled such as a superconducting magnet is cooled to a cryogenic
temperature.
[0006] When a very small superconducting magnet is to be cooled,
the refrigerator should be very small.
[0007] FIG. 4 shows an example of refrigerator cooling performance.
The figure shows refrigerator cooling performance in relation to
refrigerator cooling temperature where a parameter is an ambient
temperature for the refrigerator, or a temperature of helium gas as
a cooling medium at an inlet of the refrigerator in cooling
operation in the environment in which the refrigerator is
installed. For example, if heat leak into a cryogenic part of a
vacuum vessel is 0.3 W, regarding the cooling temperature of the
refrigerator in the refrigerator system, the superconducting magnet
cooling temperature is 48 K at the ambient temperature Tr of 296 K
but it is 55 K at the ambient temperature of 318 K in summer.
[0008] If the superconducting magnet is prepared by magnetizing a
cylindrical yttrium oxide bulk superconductor in a high magnetic
field, an intensity of the magnetized field sharply decreases when
the bulk superconductor cooling temperature exceeds 50 K. For
example, if a diameter of the cylindrical bulk superconductor is 45
mm, the intensity of the magnetized field is 6 Tesla at the bulk
superconductor cooling temperature of 48 K but it is 4 Tesla at the
bulk superconductor cooling temperature of 55K, leading to a
serious decline in the magnetic field performance of the
superconducting magnet. Once the magnetic field performance
declines, even if the cooling temperature goes down to 48K again,
the magnetic field intensity will remain 4 Tesla, namely the
magnetic field performance will remain low.
[0009] On the contrary, when the ambient temperature goes down to
273 K in winter, the superconducting magnet cooling temperature is
45 K and the intensity of the magnetized field goes up to 6.5
Tesla.
[0010] As described above, if adiabatic expansion of helium gas as
a cooling medium is used for cooling, the lower the temperature of
the helium gas as cooling medium at the inlet of the refrigerator
is, the lower the temperature of the cryogenic part of the
refrigerator is. In a process of compressing the helium gas
supplied to the refrigerator by a compressor, the gas is heated to
approximately 353 K by compression heat and if this heat is
directly or indirectly discharged to the room, the ambient
temperature as shown in FIG. 4 may actually become 10-20 K higher
than the room temperature.
[0011] Therefore, there is a problem that the inlet temperature of
the helium gas as the cooling medium for the refrigerator may be
higher than the room temperature and the cooling temperature of the
refrigerator may be higher than when the inlet temperature of the
refrigerator is lower than the room temperature.
[0012] In decreasing the cooling temperature of the refrigerator by
further decreasing the helium gas inlet temperature, the helium gas
heated by the compression heat is cooled by cooling water whose
temperature is lower than the room temperature, so that the helium
gas inlet temperature is made lower than the room temperature
before the gas is supplied to the refrigerator.
[0013] As disclosed in Document 1, since an inlet portion of a
refrigerator is located outside a vacuum vessel and exposed to a
room temperature area, if helium gas inlet temperature is lower
than the dew point in the room, condensation of moisture in the air
occurs at the inlet portion, resulting in water drops outside of
the refrigerator. Also, as a result of the condensation of moisture
in the air at the inlet portion, a problem may arise that the
temperature of the helium gas at the inlet of the refrigerator
rises and the cooling temperature of the refrigerator rises.
[0014] On the other hand, Document 2 (Japanese Patent Laid-open No.
2004-144399) discloses a means for controlling a temperature using
an electronic device such as a Peltier element without using
cooling water. This means comprises a refrigerating cycle using
carbon dioxide as a refrigerant, where a motive energy recovered by
an expansion device is used for refrigerant heat exchange between a
dissipating heat exchanger in an atmospheric air and an outlet of
the expansion device using the Peltier element.
[0015] Document 3 (Japanese Patent Laid-open No. 2002-181437)
discloses a means for dissipating exhaust heat from a compressor of
a refrigerator system through a heat pipe. In this means, a
cryogenic part and a hot part of the refrigerator are disposed in a
hermetically sealed case in order to prevent penetration of
raindrops and a heat dissipating part for the heat pipe is provided
outside the case, and the hot part and the heat dissipating part
are connected by the heat pipe. The heat in the hot part is
discharged through the cooling medium in the heat pipe to an
atmosphere of a room temperature and the temperature of the hot
part is always kept higher than the room temperature. In this means
as well, no dew condensation occurs since the refrigerant used for
the temperature control is higher lo than the room temperature.
[0016] However, since the temperature of the cooling medium at the
inlet of the refrigerator is higher than the room temperature,
there is a problem that the cooling temperature of the refrigerator
is higher than when the temperature of the cooling medium at the
inlet of the refrigerator is lower than the room temperature. In
addition, since the case is hermetically sealed, the air
temperature inside the case is always higher than the room
temperature and there is more heat leak into the cryogenic part of
the refrigerator than the air temperature inside the case is equal
to the room temperature, leading to a temperature rise in a cooling
part of the refrigerator.
[0017] In the means disclosed in Document 3, when the refrigerator
is hermetically sealed by the case, the cryogenic part of the
refrigerator must be insulated sufficiently and thus the case must
be large and the volume and weight of the entire refrigerator
system must be larger.
[0018] Instead of using the hermetically sealed case, it is also
possible to cover the refrigerator with a foaming agent or the like
and fill gaps with an adhesive agent. However, since foaming agents
are usually flammable, possibility of burning of such covered
portions cannot be eliminated and safety is not ensured in a place
where a high degree of fire protection is required.
[0019] The problem inherent to the above related art is as follows.
When the inlet temperature of the helium gas as the cooling medium
for the refrigerator is decreased to a level lower than a dew point
in the room in order to make the cooling temperature of the
refrigerator system lower and an inlet portion of the cooling
medium is exposed to the air, moisture in the air may result in dew
condensation and the condensation may cause the temperature of the
cooled helium gas to go up again.
[0020] An object of the present invention is to provide a cryogenic
container with a built-in refrigerator capable of cooling an object
to a cryogenic temperature, wherein a temperature of a heat
dissipating surface of a compressing part of the refrigerator is
decreased to a level lower than the room temperature to improve an
efficiency of the refrigerator, and also a temperature of a cooling
medium at an inlet of the refrigerator is controlled to a level
lower than the room temperature without causing a dew condensation
on an outer surface of the cryogenic container and heat leak into
the refrigerator from the room temperature area is reduced to keep
the cooling temperature of the refrigerator low enough.
SUMMARY OF THE INVENTION
[0021] A cryogenic container with a built-in refrigerator according
to the present invention comprises the refrigerator having a first
heat absorbing part and a first heat dissipating part, a vacuum
vessel for containing and thermally insulating an object to be
cooled while holding the object at a cryogenic temperature through
the first heat absorbing part of the refrigerator, and a
pre-cooling unit having a second heat absorbing part and a second
heat dissipating part for cooling the first heat dissipating part,
wherein the first heat dissipating part and the second heat
absorbing part are arranged inside the vacuum vessel, and a part of
a heat dissipating unit including the second heat dissipating part
is exposed outside the vacuum vessel.
[0022] According to the present invention, in the cryogenic
container with the built-in refrigerator capable of cooling the
object to be cooled to the cryogenic temperature, the refrigerator
efficiency can be improved by cooling a heat dissipating surface of
the first heat dissipating part of the refrigerator to a level
lower than the room temperature. Furthermore, since the compressing
part of the refrigerator to be pre-cooled by the pre-cooling unit
to the temperature lower than the room temperature is contained
inside the vacuum space, there is no possibility that condensation
of moisture in the air occurs and thus electric short-circuiting
due to dew condensation and failures due to dew condensation in
transportation can be prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic sectional view illustrating a
structure of a cryogenic container with a built-in refrigerator
according to a first embodiment of the present invention.
[0024] FIG. 2 is a schematic sectional view illustrating the
structure of a cryogenic container with a built-in refrigerator
according to a second embodiment of the present invention.
[0025] FIG. 3 is a schematic sectional view illustrating the
structure of a cryogenic container with a built-in refrigerator
according to a third embodiment of the present invention.
[0026] FIG. 4 is a graph illustrating a cooling characteristics of
the refrigerator used in the embodiments of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] A cryogenic container with a built-in refrigerator is
characterized in that it uses gas as a cooling medium and comprises
a compressing part and a vacuum vessel. The compressing part has a
function of compressing the cooling medium mechanically and
comprises a first heat dissipating part. A vacuum vessel contains
the refrigerator including a first heat absorbing part for
generating cryogenic energy by adiabatic expansion of the cooling
medium, and an object to be cooled and kept at a cryogenic
temperature by the refrigerator, and insulates the refrigerator and
the object. Further, A vacuum vessel contains a pre-cooling unit
for cooling the first heat dissipating part. And the cryogenic
container with a built-in refrigerator can discharge exhaust heat
from the pre-cooling unit to the air.
[0028] The cryogenic container with the built-in refrigerator
according to the present invention is also characterized in that
the helium gas at the inlet of the refrigerator is cooled to a
temperature lower than the room temperature in order to decrease
its cooling temperature. Further, an isolating means for isolating
the refrigerator inlet portion for helium gas from the air is
arranged in the cryogenic container and a space inside the
isolating means is an insulating space and the thermally conductive
medium in the insulating space is removed.
[0029] The cryogenic container with the built-in refrigerator
according to the present invention is also characterized in that
the pre-cooling unit for cooling the helium gas as the refrigerator
cooling medium at the refrigerator inlet to a level lower than the
room temperature is located inside the insulating space, and a hot
part of the pre-cooling unit with a temperature higher than the
room temperature and a partition for constituting the isolating
means and being contact with the air are thermally connected by a
thermally conductive member with a high thermal conductivity. A
leak of a heat into a cooling part of the pre-cooling unit is
prevented by dissipating the heat of the hot part of the
pre-cooling unit through the partition (room temperature) to the
air, and a rise of the temperature of the helium gas at the
refrigerator inlet is controlled.
[0030] The cryogenic container with the built-in refrigerator
according to the present invention is characterized in that a high
insulating performance with a small space is assure by evacuating
the insulating space, and discharging air and keeping a vacuum
condition prevent combustion or ignition even if the temperature
inside the space is higher. And a compact and fireproof cryogenic
container is obtained thereby.
[0031] Next, the preferred embodiments of the present invention
will be described in detail.
First Embodiment
[0032] FIG. 1 is a sectional view illustrating a small
superconducting magnet system wherein an object to be cooled is a
cylindrical yttrium-based bulk superconductor including Y
(yttrium), Ba (barium), Cu (copper) and O (oxygen).
[0033] A cryogenic container with a built-in refrigerator according
to a first embodiment is a small and light container for cooling a
bulk superconductor 1 as the object to be cooled. This cryogenic
container with the built-in refrigerator contains a Stirling
refrigerator as a cooling means for cooling the object, the
Stirling refrigerator generating cryogenic energy by compressing
helium gas as a cooling medium and adiabatically expanding the
compressed helium gas. The refrigerator comprises a cooling part 2,
a compressing part 3, a pre-cooling stage 4 included in the
compressing part 3 for dissipating a compression heat of the
compressing part 3 to an outside of the refrigerator, a thermally
conductive plate 5 located in contact with the pre-cooling stage 4,
a Peltier element 6 as a pre-cooling unit located in contact with
the thermally conductive plate 5, a thermally conductive plate 7
located in contact with a hot heat dissipating surface of the
Peltier element 6, a vacuum vessel 10, a thermally conductive plate
9 located in contact with an inner wall of the vacuum vessel 10,
and a copper net 8 located in contact with the thermally conductive
plate 7 and thermally conductive plate 9. The pre-cooling stage 4
cools the compressing part 3 of the refrigerator in combination
with the thermally conductive plate 5 by transferring the heat
generated in the compressing part 3 to the cooling surface of the
Peltier element 6. The hot helium gas without expanding inside the
compressing part 3 is thus cooled.
[0034] Here, the cooling part 2 of the refrigerator is defined as a
first heat absorbing part. The pre-cooling stage 4 included in the
compressing part 3 of the refrigerator is defined as a first heat
dissipating part. The cooling surface of the Peltier element 6 for
cooling the pre-cooling stage 4 is defined as a second heat
absorbing part. And a hot heat dissipating surface of the Peltier
element 6 is defined as a second heat dissipating part.
[0035] The copper net 8 is a thermally conductive member for
transferring the exhaust heat of the Peltier element 6 from the
thermally conductive plate 7 to the thermally conductive plate 9.
This thermally conductive member is not limited to the copper net 8
but may be any flexible member with a high thermal conductivity
such as a bundle of copper wires, an aluminum net or a bundle of
aluminum wires. It should be flexible enough to absorb vibrations
of the refrigerator and reduce vibrations transmitted to an outside
of the vacuum vessel 10 and prevent collapse due to vibrations of
the refrigerator.
[0036] In this embodiment, the thermally conductive plate 9 is
tightly fixed on the inner wall of the vacuum vessel 10 with a bolt
11. It is desirable that a heat dissipating surface of the vacuum
vessel 10 be made of a metal with a high thermal conductivity such
as copper.
[0037] The second heat dissipating part (hot heat dissipating
surface of the Peltier element 6), thermally conductive plate 7,
the copper net 8 (the thermally conductive member), thermally
conductive plate 9, and the heat dissipating surface of the vacuum
vessel 10 are collectively defined as a heat dissipating unit. This
heat dissipating unit may lack one or some or all of following
components: the thermally conductive plate 7, the copper net 8 (the
thermally conductive member), the thermally conductive plate 9, and
the heat dissipating surface of the vacuum vessel 10 except the
second heat dissipating part (the hot heat dissipating surface of
the Peltier element 6). In other words, the heat dissipating unit
may only consist of the second heat dissipating part.
[0038] The hot heat dissipating surface of the Peltier element 6,
the thermal conductors 5 and 7 are fastened through an indium sheet
or the like with a bolt or connected by soldering (not shown).
[0039] The bulk superconductor 1 is fixed on an inside of a holder
12 of copper or stainless steel with an adhesive agent or the like.
The holder 12 is formed of a material functioning both as a
reinforcing member and a thermally conductive member. The holder 12
is coupled with a support 13 made of a material with a high thermal
conductivity such as aluminum or copper using screws or the like.
The support 13 is fixed on a top of a supportive cylinder 14 of a
glass fiber-filled epoxy resin with a low thermal conductivity by
an adhesive agent or the like. And the supportive cylinder 14 is
fixed on a flange 15 at its bottom by an adhesive agent and
fastened to an inner wall of the vacuum vessel 10 with a bolt or
the like (not shown).
[0040] A thermal conductor 16 formed of a flexible copper net or a
ring made of a copper thin belt with a high thermal conductivity is
arranged between the support 13 and the cooling part 2 of the
Sterling refrigerator and they are connected with each other by
soldering or another method. Soldering operation here can be done
using a hole 17 in the supportive cylinder 14 and a soldering
iron.
[0041] Electric power is supplied from a power supply unit 18 to
the compressing part 3 of the refrigerator and Peltier element 6
through wires 19a and 19b.
[0042] An upper part 20 of the vacuum vessel 10 is made of, for
example, a glass fiber-filled epoxy resin. A flange 21 is joined to
a lower part 110 of the vacuum vessel 10 by welding or blazing, and
a flange 22 is joined to an upper part 20 of the vacuum vessel 10
with an adhesive agent. These flanges 21 and 22 are coupled through
an O ring (not shown) with a bolt 23 and a nut 24. This ensures an
air tightness of the vacuum vessel 10.
[0043] The compressing part 3 of the refrigerator is fixed on a
retaining plate 25 joined to an inner wall of the vacuum vessel 10
through a vibration isolating cushion 33 with a bolt (not shown). A
space 26 inside the vacuum vessel 10 is evacuated by a vacuum pump
30 through a nozzle 27, a valve 28 and a tube 29. The vibration
isolating cushion 33 is not limited to a rubber but may be any
flexible member for suppressing transmission of vibrations. Such a
member is defined as a vibration isolating member. Activated carbon
particles 32, for example, are contained inside the vacuum vessel
10 for the purpose of absorbing a residual gas (air, etc) in the
space 26 and keeping the required degree of vacuum.
[0044] A distance between a upper end of the cooling part 2 of the
refrigerator and a bottom of the support 13 changes from before an
operation of the refrigerator to during the operation because of
thermal deformation. However, the flexible thermal conductor 16
reduces a large thermal stress on the cooling part 2 and the
support 13.
[0045] The compressing part 3 of the refrigerator is joined to the
retaining plate 25 joined to an inner wall of the vacuum vessel 10
with a bolt (not shown) through the rubber cushion 33. Since the
compressing part 3 of the Sterling refrigerator considerably
vibrates during operation and the vibration is directly transmitted
to the vacuum vessel 10 and the vacuum vessel 10 itself vibrates,
resonates and generates a noise, the rubber cushion 33 is used to
reduce the vibration. A fin 31 is disposed on the vacuum vessel 10
to improve a heat dissipating performance.
[0046] In this embodiment, if a heat leaking into a cryogenic zone
inside the vacuum vessel 10 is 0.3 W, a compression heat 7 W
generated in the compressing part 3 of the refrigerator must be
dissipated to the outside of the refrigerator. If the Peltier
element 6 generates a temperature difference of 50 K at a cooling
power of 7 W, the thermally conductive plate 5 cooled by the
Peltier element 6 is cooled to 273 K. The heat dissipated by the
Peltier element 6 here is estimated to be 20 W. A temperature of
the thermally conductive plate 7 being in contact with the hot heat
dissipating surface of the Peltier element 6 becomes 323 K, and the
heat is dissipated through the copper net 8 to heat dissipating
surface of the vacuum vessel 10 whose temperature is 10 K lower, or
313 K (room temperature).
[0047] In the above case, the temperature of pre-cooling stage 4 of
the refrigerator disposed inside the vacuum vessel 10 is 273 K and
the bulk superconductor 1 is cooled to approximately 45 K. If a
diameter of the cylindrical bulk superconductor 1 is 45 mm, a
magnetized field intensity is higher than 6 Tesla, or 6.5 Tesla, at
a bulk superconductor cooling temperature of 48 K.
[0048] In a related art, in order to remove the compression heat (7
W) generated in the compressing part 3 without using the Peltier
element 6 at a room temperature of 313K, the compressing part 3 is
exposed outside the vacuum vessel 10 to dissipate the heat. In this
case, however, a heat dissipating surface area is small and a
temperature of the compressing part 3 is approximately 318 K. Since
this temperature is the ambient temperature for the refrigerator,
the cooling temperature of the bulk superconductor 1 is 55 K and
the magnetized field intensity is 4 Tesla.
[0049] In this embodiment, the compressing part 3 of the
refrigerator is pre-cooled by the Peltier element 6 to make its
temperature lower than the room temperature and the bulk
superconductor 1 being cooled by the refrigerator is cooled to 50 K
or less. Therefore, the magnetized field intensity of the bulk
superconductor 1 is increased.
[0050] Furthermore, in this embodiment, since the Peltier element 6
for cooling the compressing part 3 of the refrigerator is disposed
inside the vacuum vessel 10, there is no possibility that a
condensation of moisture in the air occurs on the cooling surface
of the Peltier element 6 and thus electric short-circuiting due to
the dew condensation and failures due to the condensed moisture in
transportation can be prevented.
[0051] Furthermore, since the Peltier element 6 is disposed inside
the vacuum vessel 10, the cryogenic part of the Peltier element 6
is thermally insulated from the room temperature area. Therefore,
the cooling efficiency of the Peltier element 6 is improved and the
compressing part 3 of the refrigerator is cooled to a lower
temperature and the bulk superconductor 1 can be cooled to 50 K or
less by the refrigerator.
[0052] In addition, since the Peltier element 6 is disposed inside
the vacuum vessel 10, there is no air layer around the hot part of
the Peltier element 6. This prevents a transfer of the heat from
the hot part of the Peltier element 6 to the compressing part 3
(located near to the hot part) through an air layer. For this
reason, the compressing part 3 of the refrigerator can be cooled to
a lower temperature and the bulk superconductor 1 can be cooled to
50 K or less by the refrigerator. Since the magnetization
performance is enhanced, it is possible to provide a
superconducting magnet generating a higher-intensity magnetic
field.
Second Embodiment
[0053] FIG. 2 shows another embodiment of the present invention.
The difference from FIG. 1 is that the refrigerator is a split-type
Sterling refrigerator wherein its cooling part 34 and compressing
part 35 are separate from each other and connected by a tube 36. In
this embodiment, the cooling part 34 of the refrigerator and the
compressing part 35 of the refrigerator are fixed through a
supportive plate 37 and through a rubber cushion 33 respectively on
a retaining plate 38 fixed on the inner wall of the vacuum vessel
10 with bolts or the like (not shown). In this embodiment, the
cooling part 34 and the hot compressing part 35 are separated from
each other through the tube 36 with a small sectional area so that
a heat leak from the compressing part 35 into the cooling part 34
by thermal conduction can be reduced. Consequently, the cooling
part 34 can be cooled to a lower temperature and the magnetization
performance can be enhanced by decreasing the temperature of the
bulk superconductor 1 to realize a superconducting magnet with a
higher magnetic field intensity. In addition, a transmission of
vibrations of the compressing part 35 to the bulk superconductor 1
as the object to be cooled is reduced.
[0054] Even when the refrigerator is of the split type, since the
Peltier element 6, the temperature of which becomes lower than the
room temperature, is disposed inside the vacuum vessel 10, there is
no possibility that the condensation of moisture in the air occurs
on the cooling surface of the Peltier element 6 and thus electric
short-circuiting due to the dew condensation and the failures due
to the condensed moisture in the transportation can be
prevented.
Third Embodiment
[0055] FIG. 3 shows another embodiment of the present invention.
The difference from FIG. 1 is that a fan 39 is arranged on the
bottom of the vacuum vessel 10. An electric power is supplied to
the fan 39 from the power supply 18 by wire 19C and the fan 39 send
air to the fin 31. This improves the heat dissipating performance
of the fin 31.
[0056] In this embodiment, since an operation of the fan 39
improves the heat dissipating performance of the fin 31, the
temperature of the thermally conductive plate 7 becomes further
lower and thus the temperature of the thermally conductive plate 5
also becomes lower. Consequently the temperature of the cooling
part 34 of the refrigerator becomes further lower and the
temperature of the bulk superconductor 1 becomes lower so that the
magnetization performance is enhanced and a superconducting magnet
generating a higher-intensity magnetic field is realized.
[0057] The above embodiments assume that the refrigerator for
cooling the object to be cooled is a Sterling refrigerator.
However, even if the refrigerator is another type of refrigerator
such as a Gifford-McMahon refrigerator, a pulse tube refrigerator
or a thermoacoustic refrigerator, a similar advantageous effect can
be achieved.
[0058] Besides, although the above embodiments assume that the
object to be cooled is a bulk superconductor, the invention can be
applied even when the object to be cooled is a cell sample or a
protein sample. If that is the case, it is desirable that one end
of the cryogenic container be open to the air to allow a user to
take in and out the sample to be kept cold. In this case as well,
since the pre-cooling unit decreases the helium gas inlet
temperature to a level lower than the room temperature and thereby
further decreases the temperature of the cryogenic container, the
same advantageous effect that no dew condensation occurs on the
cooling surface of the pre-cooling unit is achieved.
[0059] In the above embodiments, the entire Peltier element 6 as
the pre-cooling unit is disposed inside the vacuum vessel 10.
However, it is also possible that the cooling surface of the
Peltier element 6 as the second heat absorbing part is disposed
inside the vacuum vessel 10 and the hot heat dissipating surface of
the Peltier element 6 as the second heat dissipating part is
exposed outside the vacuum vessel 10. In this case as well, the
temperature of the pre-cooling stage 4 as the first heat
dissipating part can be below the dew point in the room and the dew
condensation can be reduced.
[0060] According to the present invention, in a cryogenic container
with a built-in refrigerator capable of cooling the object to be
cooled to a cryogenic temperature, the efficiency of the
refrigerator is improved by cooling the heat dissipating surface of
its first heat dissipating part to a level lower than the room
temperature.
[0061] Furthermore, according to the present invention, since
compressing part of the refrigerator to be pre-cooled by the
pre-cooling unit to below the room temperature is disposed in the
vacuum space, there is no possibility that the condensation of
moisture in the air occurs and thus the electric short-circuiting
due to the dew condensation and the failures due to the dew
condensation in transportation can be prevented. Moreover,
according to the present invention, the helium gas temperature at
the inlet of the refrigerator is kept lower than the room
temperature so that the object to be cooled by the refrigerator can
be cooled to a lower temperature.
[0062] Also, according to the present invention, since the
insulating vacuum vessel contains no oxygen, it is excellent in
fire protection and assures safety in a place where a high degree
of fire protection is required.
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