JP2005331180A - Multi-stage refrigerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-stage refrigerator capable of surely cutting off thermal connection in a thermal switch when the thermal switch is off even in the case where axial direction of the thermal switch is arbitrarily positioned, and capable of exercising sufficient convection heat transmission effect. <P>SOLUTION: The multi-stage refrigerator is equipped with a first refrigerating end of which lowest achieving temperature and refrigerating performance are high and a second refrigerating end of which lowest achieving temperature and refrigerating performance are low and a thermal switch for being switched from thermal-connection-on to thermal-connection-off at a predetermined temperature with which the first refrigerating end and the second refrigerating end can be thermally connected. The multi-stage refrigerator refrigerates an object to be refrigerated to a cryogenic temperature by attaching the object to be refrigerated to the second refrigerating end in a thermally connected manner. A gas solidification chamber for communicating with inside of the thermal switch via a tube at a side of the second refrigerating end of the thermal switch is also provided and at least part of the gas solidification chamber is thermally connected to the second refrigerating end. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multistage refrigerator that cools an object to be cooled to a cryogenic temperature, and more particularly to a multistage refrigerator that cools a superconducting magnet to a cryogenic temperature.

  In general, a multistage refrigerator that cools an object to be cooled to a cryogenic temperature has a plurality of cooling ends, for example, a first cooling end having a high minimum temperature and a second cooling end having a low minimum temperature. The object to be cooled which is in thermal contact with the second cooling end is cooled to a cryogenic temperature by a structure in which the two are connected in series. However, since the second cooling end having the lowest minimum temperature has a low cooling capacity, there is a problem that it takes time to cool the object to be cooled which is in thermal contact with the second cooling end. The first cooling end has a high cooling capacity but has a high minimum temperature, and it is difficult to obtain an extremely low temperature.

For this reason, as disclosed in Patent Document 1 below, there has been proposed one in which a thermal switch is arranged between the first cooling end and the second cooling end of the multistage refrigerator described above. This thermal switch has the following functions. In the initial stage of cooling, the object to be cooled and the first cooling end are thermally connected via the thermal switch, and the object to be cooled can be cooled more quickly by the first cooling end having a high cooling capacity. In addition, when the temperature reaches the minimum temperature at the first cooling end, the thermal switch automatically changes from the on state to the off state, disconnects the thermal connection between the object to be cooled and the first cooling end, and the minimum temperature is low. Cooling to a cryogenic temperature can be performed only by the second cooling end.
Japanese Patent No. 2835305

  However, in Patent Document 1, even when the heat switch is turned off, the gas inside the heat switch is liquefied and solidified, and the solidified gas component is converted into the heat transfer surface on the first cooling end side and the second cooling end. When it remains so as to fill the space between the heat transfer surface on the side, heat conduction occurs through the solidified gas component, and the thermal connection in the heat switch may not be cut off. In particular, when the axial direction of the thermal switch is horizontally arranged, the solidified gas remains in a place where the gap between the heat transfer surfaces is small, so that it is easy for the thermal connection in the thermal switch to be disconnected. Further, since this thermal switch is of a cylindrical type, a sufficient convective heat transfer effect could not be obtained unless the axial direction is vertical.

  Therefore, even if the axial direction of the thermal switch is arbitrarily arranged, the object of the present invention is to reliably disconnect the thermal connection in the thermal switch when the thermal switch is turned off. Then, it is providing the multistage refrigerator which can acquire sufficient convection heat-transfer effect.

Means and effects for solving the problems

The multi-stage refrigerator of the present invention includes a first cooling end having a high minimum temperature and a high cooling capacity, a second cooling end having a low minimum temperature and a low cooling capacity, the first cooling end and the second cooling end. A thermal switch that is provided so as to be thermally connectable to the cooling end, and that switches from thermal connection ON to thermal connection OFF at a predetermined temperature, and to which an object to be cooled is thermally connected to the second cooling end A multi-stage refrigerator that cools the object to be cooled to an extremely low temperature, and is a tube at the second cooling end side of the thermal switch, preferably at the side surface of the second cooling end side end. A gas solidification chamber that communicates with the inside of the thermal switch is further provided, and at least a part of the gas solidification chamber is in thermal contact with the second cooling end.
With the above configuration, even if the thermal switch is in a vertical arrangement, horizontal arrangement, or inclined arrangement, the multistage refrigerator that reliably disconnects the thermal connection in the thermal switch when the thermal switch is turned off. Can be provided.

In the multistage refrigerator of the present invention, it is preferable that the thermal switch includes a flat heat transfer fin having a vertical heat transfer surface.
With the above configuration, not only the effect of the multi-stage refrigerator, but also the heat switch installation posture is tilted vertically, horizontally, or in the middle as long as the heat transfer surface of the heat switch is arranged in the vertical direction. However, when the thermal switch is turned on, a sufficient convective heat transfer effect can be obtained.

The multi-stage refrigerator of the present invention includes a first cooling end having a high minimum temperature and a high cooling capacity, a second cooling end having a low minimum temperature and a low cooling capacity, the first cooling end, and the second cooling end. A thermal switch that is provided so as to be thermally connectable to the cooling end, and that switches from thermal connection ON to thermal connection OFF at a predetermined temperature, and to which an object to be cooled is thermally connected to the second cooling end A multi-stage refrigerator that cools the object to be cooled to a cryogenic temperature, wherein the heat switch has a flat plate heat transfer fin having a vertical heat transfer surface inside, and an internal The thermal connection is turned on when the gas enclosed in the gas is vaporized, and the thermal connection is turned off when the gas is liquefied.
With the above configuration, as long as the heat transfer surface of the heat switch is arranged in the vertical direction, the heat switch is turned on even if the installation posture of the heat switch is inclined vertically, horizontally, or in the middle. In this case, a sufficient convective heat transfer effect can be obtained.

In the multistage refrigerator of the present invention, the gas is preferably nitrogen gas, neon gas, or hydrogen gas.
Since these gases have a boiling point near the lowest temperature reached at the first cooling end, the heat switch can be operated reliably. Neon gas or hydrogen gas is preferable for increasing the cooling rate of the object to be cooled.

  Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the arrangement of thermal switches in the multistage refrigerator according to the embodiment of the present invention, FIG. 2 is a transparent perspective view showing the structure of the thermal switch in the multistage refrigerator of FIG. 1, and FIG. It is sectional drawing which shows the structure of the heat switch in this multistage refrigerator.

  In the multistage refrigerator 1, most of the refrigerator main body 1 a is protruded into the container 2. The container 2 is usually formed as a vacuum container. The refrigerator main body 1a in the container 2 includes a first cooling unit 3 having a first cooling end 3a on the lower surface and a second cooling unit 4 having a second cooling end 4a on the lower surface. A first cooling plate 5 is screwed to the lower part of the first cooling end 3a, and a second cooling plate 6 is screwed to the lower part of the second cooling end 4a. Further, a radiation shield 7 is connected to the first cooling plate 5 to form a cooling space 8, and an object 9 to be cooled is provided on the surface of the second cooling end 6 a opposite to the refrigerator main body 1 a at the second cooling end 4 a. Are connected. The thermal switch 10 is disposed by connecting the first cooling plate 5 and the second cooling plate 6. Further, the heat switch 10 is provided with a gas solidification chamber 11 that communicates with the inside of the heat switch 10 near the second cooling end 4a via a pipe 11a. A part of the outer periphery of the gas solidifying chamber 11 is in thermal contact with the second cooling end 4a through the heat transfer path 11b. Further, in the heat switch 10 and the gas solidification chamber 11, a gas (medium) having a boiling point in the vicinity of the lowest temperature reached by the first cooling end 3a is enclosed.

  As shown in FIG. 2, the thermal switch 10 includes a first member 12 and a second member 13.

  The first member 12 includes a columnar first pure copper block 14 and pure copper cylindrical fins 15a to 15c (heat exchange members). On the first pure copper block 14, the fins 15 a, 15 b, 15 c are arranged concentrically with each other in order of increasing diameter, and are joined by welding or the like.

  The second member 13 includes a columnar second pure copper block 16, pure copper cylindrical fins 17 a to 17 c (heat exchange members), and a cylindrical stainless steel tube 23. On the second pure copper block 16, the fins 17a, 17b and 17c are arranged concentrically on the second pure copper block 16 in the order of decreasing diameter, and are joined by welding or the like. Further, a thin stainless steel tube 23 is concentrically joined to the outer side of the fin 17c on the second pure copper block 16, and the length of the stainless steel tube 23 is longer than the lengths of the fins 15a to 15c and the fins 17a to 17c. long. Moreover, the 2nd pure copper block 16 has the recessed part 16a provided in the radial direction in the inner surface of the thermal switch 10 so that a part may be penetrated. The recess 16a communicates with a hole 16b provided on the outer periphery of the second pure copper block 16 so as to communicate with the outside.

  As shown in FIG. 3, the upper and lower two first members 12 and the second member 13 are overlapped, and the first pure copper block 14 and the stainless steel pipe 23 are fixed by welding or the like. Thus, a sealed space is formed by the outer stainless steel tube 23, the first pure copper block 14, and the second pure copper block 16. In this space, the fins 15a to 15c and the fins 17a to 17c are concentrically arranged alternately. The fins 15a to 15c and the second pure copper block 16 and the fins 17a to 17c and the first pure copper block 14 are opposed to each other so as to have a gap.

  As shown in the multistage refrigerator 1 of FIG. 1, the thermal switch 10 includes a first pure copper block 14 on the first cold plate 5 on the high temperature side in the vertical direction, and a second pure copper block 16 on the low temperature side in the vertical direction. The second cooling plate 6 is connected.

  As shown in FIG. 3, the gas solidification chamber 11 communicates with the inside of the thermal switch 10 through a pipe 11 a connected to the recess 16 a in the hole 16 b of the second pure copper block 16. In addition, a part of the outer periphery of the gas solidification chamber 11 is in thermal contact with the second cooling end 4a through a heat transfer path 11b (for example, a pure copper plate or a pure copper wire). In addition, 18 in FIG. 3 has shown the solidified gas.

  Next, the operation of the thermal switch 10 will be described. The thermal switch 10 according to the present invention is a gas conduction type switch in which a gas having a boiling point in the vicinity of the lowest ultimate temperature of the first cooling end 3a is sealed in a space sealed by a stainless steel tube 23. The upper and lower heat conduction is performed through the gaps between the fins 15a to 15c and the fins 17a to 17c using the internal gas as the heat conduction medium. Switching of the on / off state of the thermal switch 10 occurs at the boiling point of the gas. When the temperature of the heat switch is equal to or higher than the boiling point of the gas, heat conduction using the gas as a heat medium is turned on, and when the temperature is equal to or lower than the boiling point, the gas is condensed and the inside is evacuated, so that it is turned off. In addition, since the heat conductivity of the stainless steel pipe 23 of the outermost layer is small, heat transfer through this can be ignored. In particular, in the present apparatus, the place where the gas is below the boiling point is the gas solidification chamber 11 partially connected to the second cooling plate 6, so that the liquefied or solidified gas accumulates in the gas solidification chamber 11. The gas does not liquefy or solidify in the gaps between the fins 15a to 15c and the fins 17a to 17c, the gap between the fins 17c and the stainless steel pipe 23, or the like.

  Here, when the lowest temperature reached at the first cooling end 3a is 30K and the lowest temperature reached at the second cooling end 4a is 4K, neon gas having a boiling point of about 30K at normal pressure is in a state of normal temperature and 4 atm. An example using a thermal switch enclosed inside will be described. In the initial stage of cooling, neon gas is in a gaseous state, the heat switch 10 can transmit heat (the heat switch 10 is in an on state), and the object 9 is cooled by the first cooling end 3a and the second cooling end 4a. Is done. Since the first cooling end 3a has a higher cooling capacity than the second cooling end 4a, the first cooling end 3a can be cooled more quickly than when the thermal switch 10 is not used. The neon gas of 4 atm at normal temperature becomes 0.4 atm at the lowest temperature (30K) of the first cooling end 4a, and the boiling point of the neon gas changes from 27K to 24K.

  Further, when the cooling progresses and the temperature in the thermal switch 10 becomes equal to or lower than the lowest temperature (30K) of the first cooling end 3a and reaches the boiling point of the neon gas, the gas is liquefied and the inside of the thermal switch 10 becomes vacuum, (The heat switch 10 is in an off state), and thereafter, the object 9 is cooled to an extremely low temperature only by the second cooling end 4a. The liquefied or solidified gas remains in the gas solidification chamber 11, and the thermal switch 10 can be kept completely off.

  In addition, although not shown in figure, the multistage refrigerator which made the axial direction of the thermal switch of the said embodiment horizontal, or inclined the axial direction of the thermal switch by arbitrary angles may be sufficient. Even in such a multistage refrigerator, the heat switch can be kept in the OFF state completely as in the above embodiment.

  Next, the multistage refrigerator according to another embodiment of the present invention will be described. FIG. 4 is a view showing heat transfer fins and stainless steel pipes having a heat transfer surface in the vertical direction in a heat switch of a multistage refrigerator according to another embodiment of the present invention, wherein (a) is a transparent perspective view, (b) ) Is a cross-sectional view. In addition, description may be abbreviate | omitted about the part similar to the multistage refrigerator 1 of the said embodiment.

  The multistage refrigerator according to another embodiment of the present invention is a flat plate type having a surface in the vertical (perpendicular to the ground) direction shown in FIG. 4 instead of the cylindrical fins 15a to 15c and 17a to 17c of the thermal switch 10. This is the same as the multistage refrigerator 1 except that the multistage refrigerator 1 of the above embodiment has a horizontal arrangement so that the heat switch has a horizontal arrangement in the axial direction by having the fins 21a, 21b, 22a, and 22b. It is the composition.

  Each fin is arranged in the order of the fin 21b, the fin 22b, the fin 21a, and the fin 22a from the front side in FIG. Although not shown, the fins 21a and 21b are fins attached to the first pure copper block 14 on the high temperature side (first cooling plate 5 side), and the fins 22a and 22b are on the low temperature side (second cooling plate 6 side). These fins are attached to the second pure copper block 16. Further, the length of the fins 21 a, 21 b, 22 a, 22 b in the thermal switch axial direction is shorter than that of the stainless steel pipe 23.

  Next, the operation of the thermal switch according to another embodiment of the present invention will be described. Although the basic operation is the same as that of the above embodiment, the fins 21a and 21b are hotter than the fins 22a and 22b, and each fin is a fin having a plane perpendicular to the ground surface. Such gas convection is generated and the convection is sufficiently performed.

  With the above configuration, not only the effects similar to those of the above-described embodiment, but also the thermal switch installation posture is tilted vertically, horizontally, or in the middle as long as the heat transfer surface of the thermal switch is arranged in the vertical direction. However, when the thermal switch is turned on, a sufficient convective heat transfer effect can be obtained.

  In addition, it is good also as a thing which does not have a gas solidification chamber as a modification of the multistage refrigerator of embodiment by this invention. For example, the interval between the fins may be increased so that the solidified gas does not fill between the fins.

  Next, the present invention will be specifically described using examples. In addition, the magnitude | size and shape of each part of the superconducting electromagnet apparatus of Examples 1 and 2 and the comparative example 1 shown below are the things of the same structure except a part with a difference.

Example 1
The superconducting electromagnet apparatus according to Example 1 has the same configuration as the multi-stage refrigerator (FIG. 1) of the above embodiment, and the multi-stage refrigerator has a heat switch arranged horizontally by arranging the multi-stage refrigerator horizontally. A refrigerator is used. The gas solidification chamber may be located at any position as long as it is arranged in the same manner as in FIG.

(Example 2)
The superconducting electromagnet apparatus according to Example 1 uses a multistage refrigerator (using the thermal switch of FIG. 4) having the same configuration as that of the above-described another embodiment.

(Comparative Example 1)
The superconducting electromagnet apparatus according to Comparative Example 1 uses a multistage refrigerator (not shown) in which conventional heat switches having no gas solidification chamber are horizontally arranged.

  Objects to be cooled in the superconducting electromagnet apparatus of Examples 1 and 2 and Comparative Example 1 (superconducting electromagnet connected to the second cooling plate, the same applies to Example 2 and Comparative Example 1 below) and radiation shield (first Connected to the cooling plate, the same applies to the following Example 2 and Comparative Example 1), and the resistance value of the ruthenium oxide sensor embedded in the object to be cooled and the resistance value of the platinum resistance sensor embedded in the radiation shield were external to the superconducting electromagnet apparatus. It was measured by converting the temperature with a monitor installed in the above. The results are shown in the graphs of FIGS. 5 to 7 in the order of Examples 1 and 2 and Comparative Example 1. 5 to 7, (a) indicates all data from the start of cooling to the final temperature, (b) indicates enlarged data near the final temperature, the solid line indicates the temperature of the object to be cooled, and the dotted line indicates the radiation. It shows the temperature of the shield.

  FIG. 5 shows that when the superconducting electromagnet apparatus according to Example 1 is used, the final temperature reached is about 4K. On the other hand, when the superconducting electromagnet apparatus of Comparative Example 1 is used, as shown in FIG. 6, the final reached temperature is only about 7K. This is because the solidified working gas remained so as to fill the space between the heat transfer surfaces, and there was heat penetration from the first cooling end to the second cooling end due to heat conduction therethrough. When the multistage refrigerator according to Example 1 is used, it is understood that such a problem does not occur and the heat switch is completely turned off.

  Further, in the case of using the superconducting electromagnet apparatus according to the second embodiment, a sufficient heat transfer effect can be obtained in the on state of the thermal switch by providing a flat plate heat transfer fin having a heat transfer surface in the vertical direction. . As a result, the time to reach the final temperature reached about 50 hours in the superconducting electromagnet apparatus of Example 1 and Comparative Example 1, but was shortened to about 43 hours in the superconducting electromagnet apparatus of Example 2. Note that the final temperature reached about 4K due to the same effect as when the multistage refrigerator of Example 1 was used.

  The present invention can be changed in design without departing from the scope of the claims, and is not limited to the above-described embodiments and examples.

It is arrangement | positioning sectional drawing of the heat switch in the multistage refrigerator which concerns on embodiment of this invention. It is a permeation | transmission perspective view which shows the structure of the heat switch in the multistage refrigerator of FIG. It is sectional drawing which shows the structure of the heat switch in the multistage refrigerator of FIG. In the thermal switch of the multistage refrigerator according to another embodiment of the present invention, it is a view showing a heat transfer fin and a stainless steel pipe having a heat transfer surface in the vertical direction, (a) is a transparent perspective view, (b) is a sectional view. It is. It is a graph which shows the temperature data at the time of cooling of the to-be-cooled object and radiation shield in the superconducting electromagnet apparatus of Example 1. It is a graph which shows the temperature data at the time of cooling of the to-be-cooled object in the superconducting electromagnet apparatus of Example 2, and a radiation shield. It is a graph which shows the temperature data at the time of cooling of the to-be-cooled object and radiation shield in the superconducting electromagnet apparatus of the comparative example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multistage type refrigerator 1a Refrigerator main body 2 Container 3 1st cooling part 3a 1st cooling end 4 2nd cooling part 4a 2nd cooling end 5 1st cooling plate 6 2nd cooling plate 7 Radiation shield 8 Cooling space 9 Cooled Object 10 Heat switch 11 Gas solidification chamber 11a Pipe 11b Heat transfer path 12 First member 13 Second member 14 First pure copper block 15a-15c, 17a-17c, 21a, 21b, 22a, 22b Fin 16 Second pure copper block 16a Recess 18 Solidified gas 23 Stainless steel pipe

Claims (4)

A first cooling end having a high minimum temperature and a high cooling capacity; a second cooling end having a low minimum temperature and a low cooling capacity;
A thermal switch provided so as to be thermally connectable between the first cooling end and the second cooling end, and switching from thermal connection on to thermal connection off at a predetermined temperature;
A multi-stage refrigerator that attaches the object to be cooled to the second cooling end so as to be thermally connected and cools the object to be cooled to an extremely low temperature,
A gas solidification chamber that communicates with the inside of the heat switch via a pipe on the second cooling end side of the thermal switch; and at least a part of the gas solidification chamber is in thermal contact with the second cooling end. Multistage refrigerator.   The multistage refrigerator according to claim 1, wherein the heat switch includes a flat heat transfer fin having a vertical heat transfer surface. A first cooling end having a high minimum temperature and a high cooling capacity; a second cooling end having a low minimum temperature and a low cooling capacity;
A thermal switch provided so as to be thermally connectable between the first cooling end and the second cooling end, and switching from thermal connection on to thermal connection off at a predetermined temperature;
A multi-stage refrigerator that attaches the object to be cooled to the second cooling end so as to be thermally connected and cools the object to be cooled to an extremely low temperature,
The thermal switch has a flat plate heat transfer fin having a vertical heat transfer surface inside, and is thermally connected by vaporization of the gas enclosed therein, and is thermally connected by liquefaction of the gas. A multistage refrigerator that turns off.   The multistage refrigerator according to any one of claims 1 to 3, wherein the gas is neon gas, hydrogen gas, or nitrogen gas.

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