Cooler, cooling system, and cooling method

Abstract

To provide a cooler capable of efficiently cooling an object to be cooled when used in an indirect cooling method.SOLUTION: A cooler has a container, and working fluid stored in the container. The working fluid contains at least two or more kinds of working fluid with a boiling point of less than 300K. The cooler is configured to cool an object to be cooled that is in thermal contact with the container to 300K or less by making at least part of a region in the container dry out.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cooler, a thermal switch mechanism, a cooling system, and a cooling method.

Background Art

[0002] As a method for maintaining a member made of niobium titanium (NbTi) or the like at a superconducting temperature, generally, a method of immersing a superconducting member in a refrigerant such as liquid helium and recondensing the evaporated refrigerant by a refrigerator, and a method of connecting a superconducting member and a refrigerator (cold stage) via a member having a high thermal conductivity (for example, a copper strand or the like) for cooling (hereinafter, also referred to as an "indirect cooling method") are known.

[0003] In recent years, with the development of superconducting materials having a higher transition temperature and the progress of the technology development of small refrigerators, the importance of the indirect cooling method that does not require handling a large amount of refrigerant has been increasing. As one of such methods, Patent Document 1 describes that "a working fluid filling portion is provided around or in the vicinity of a superconducting coil of a superconducting motor, a cooler is disposed in the vicinity of the superconducting motor, and the cooler cools the working fluid in the working fluid filling portion until the working fluid solidifies, and the superconducting coil is directly or indirectly cooled by the solidified solid working fluid. A cooling device for a superconducting motor characterized by such a configuration."

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to Patent Document 1, although it is not necessary to bring a cooled object such as a superconducting member into contact with a refrigerant, the inventors have found that the efficiency of heat transport from the cold stage of the refrigerator to the cooled object is poor, and a lot of time and energy are required to cool the cooled object to a target temperature (for example, several tens of Kelvin).

[0006] Therefore, an object of the present invention is to provide a cooler that can efficiently cool a cooled object when used in an indirect cooling method. Another object of the present invention is also to provide a heat switch mechanism, a cooling system, and a cooling method. [Means for Solving the Problems]

[0007] As a result of intensive studies to achieve the above problems, the present inventors have found that the above problems can be achieved by the following configuration.

[0008] [1] A cooler comprising a container and a working fluid accommodated in the container, the working fluid including at least two or more working fluids having a boiling point of less than 300 K, and using a state where at least a part of the region in the container is in a dry-out state to cool a cooled object thermally contacting the container to 300 K or less.

[0009] [2] The cooler according to [1], comprising at least two of the above containers, each of the containers containing a different one of the above working fluids. According to the above cooler, since the working fluids having different saturation temperatures are accommodated in the respective containers, even when the working fluid solidifies in one container during the cooling process, the working fluid accommodated in the other container is less likely to be affected by the solidified working fluid (such as the influence of wick blockage), and efficient heat transport can continue over a wider temperature range. Therefore, even when a container with a wick having a wick inside is used, efficient heat transport (cooling) can be performed over a wider temperature range.

[0010] [3] The cooler according to [1] or [2], wherein at least one of the above containers contains two or more of the above working fluids. When two or more working fluids are contained in one of the containers, the total number of containers can be reduced, and the cooler can be made smaller. It is more suitable for use in a limited space inside a cryostat or the like. Also, by using a gravity-driven thermosiphon, even after one working fluid solidifies, more efficient heat transport by the other working fluid can continue, which is preferable.

[0011] [4] The cooler according to any one of [1] to [3], wherein the working fluid contains at least one selected from the group consisting of nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, and helium. When the cooler contains the above working fluid, when the object to be cooled is at an extremely low temperature, specifically, when the target temperature is 100 K or lower, it can be cooled more efficiently.

[0012] [5] The cooler according to any one of [1] to [4], wherein the container has a housing made of a metal material, and the residual resistivity ratio of the metal material is 30 or more. When the residual resistivity ratio of the metal material constituting the housing of the container is within the above numerical range, in the extremely low temperature region, an excellent heat transport effect due to the heat conduction of the housing can be obtained. A metal material having a residual resistivity ratio within the above range is generally called "high purity", and particularly in the extremely low temperature region, its thermal conductivity is larger compared to the same type of metal material with low purity, so more excellent heat transport efficiency in the extremely low temperature region can be obtained. However, such metal materials are expensive, and in the region above 100 K, the difference in thermal conductivity from the same type of metal material with low purity is small. Therefore, if only these high-purity metal materials are used as the heat transfer medium for indirect cooling, the cost of cooling in the region above 100 K, so-called precooling, will increase significantly. That is, even if the high-purity metal materials necessary for efficient heat transfer in the cryogenic region are used, the time required for precooling cannot be shortened, and if the high-purity metal materials necessary for efficient heat transfer for precooling are used, the price of the cooler will become too high. When the housing of the container of this cooler is a predetermined metal material, precooling is borne by the heat pipe (heat siphon), and a large amount of high-purity metal is not required. After the working fluid freezes in the cryogenic region, the main body of heat transfer can be switched to the heat conduction of the high-purity metal housing with a greatly improved thermal conductivity in the cryogenic region. Therefore, the above cooler can obtain better heat transfer efficiency in a wide range, especially when the cooling target temperature is cryogenic.

[0013] [6] The cooler according to any one of [1] to [4], wherein the thermal conductivity of the container at 293 K is 24 W / m·K or less. When the thermal conductivity of the container is equal to or less than the above value, when the cooler is used as a heat switch mechanism, more efficient heat transfer to the target temperature and more reliable thermal separation of the cooled object from the heat source after reaching the target temperature can be achieved.

[0014] [7] The cooler according to any one of [1] to [6], wherein the internal pressure of the working fluid in the container at 300 K is 1 MPa or less. When the internal pressure of the working fluid in the container is within the above numerical range, even if the inside of the container is in a complete dry-out state, the rupture of the container is more suppressed. That is, when cooling the cooled object from room temperature (about 300 K), the rupture of the container is more suppressed.

[0015] [8] The cooler according to any one of [1] to [7], which is a heat pipe. [9] The cooler according to any one of [1] to [7], which is a heat siphon.

[10] A thermal switch mechanism including the cooler according to [6].

[11] A cooling system including a refrigerator having a cooler and a cold stage according to any one of [1] to [9], and arranging the cooler between a body to be cooled and the cold stage.

[0016]

[12] The refrigerator further includes a condensing unit temperature sensor that detects the temperature TC of a condensing unit configured by thermally contacting the cold stage and the cooler, an evaporating unit temperature sensor that detects the temperature TE of an evaporating unit configured by thermally contacting the cooler and the body to be cooled, and a control device. The control device has a temperature comparison unit that compares the temperature TE with a threshold value predetermined for the working fluid included in the cooler, and a temperature adjustment unit that adjusts the temperature of the condensing unit. The control device adjusts the temperature TC so as to exceed a predetermined temperature TM based on the freezing temperature of the working fluid until the temperature TE becomes less than the threshold value. The cooling system according to

[11] . When the cooling system has the above configuration, until the temperature of the evaporating unit becomes less than the threshold value defined as the lower limit temperature for obtaining efficient heat transport, that is, within the temperature range in which efficient heat transport can be performed by a certain working fluid, the temperature of the condensing unit is controlled so that the working fluid does not solidify. Therefore, more efficient heat transport (cooling) can be performed by the working fluid.

[0017]

[13] The control device adjusts the temperature TC to a range of the formula: TM(i + 1) < TC ≦ TM(i) when the temperature TE is less than the threshold value for the working fluid i. The cooling system according to

[12] . (However, i represents an integer from 1 to n - 1, n represents an integer of 2 or more representing the type of the working fluid included in the cooler, TM(i) represents the temperature TM for the working fluid i, and TM(1), TM(2), ···, TM(n) are in descending order of temperature) When the cooling system has the above configuration, for each of the plurality of working fluids, the region where efficient heat transfer is possible can be fully utilized, and as a result, more efficient heat transfer can be achieved.

[0018]

[14] The control device is the cooling system according to

[13] , which further cools the condensing part when the temperature TE is less than the threshold value for the working fluid n and the temperature TE exceeds the target temperature. When the cooling system has the above configuration, heat conduction of a container or the like can be utilized to further cool the object to be cooled. At this time, if the target temperature of the cooling is an extremely low temperature and at least the housing of the container is made of a high-purity metal material, more efficient heat transfer can be achieved.

[0019]

[15] A cooling method in which a cooler according to any one of [1] to [9] is disposed between the object to be cooled and the cold heat source, and the object to be cooled is cooled by heat transfer between the object to be cooled and the cold heat source.

[16] Until the temperature TE of the evaporation part formed by thermally contacting the object to be cooled and the cooler becomes less than a threshold value predetermined for the working fluid contained in the cooler, The cooling method according to

[15] , including a step A of adjusting the temperature TC of the condensing part formed by thermally contacting the cold heat source and the cooler to exceed a temperature TM predetermined based on the solidification temperature of the working fluid.

[17] The adjustment includes a step A2 of adjusting the temperature TC to a range of the formula: TM(i + 1) < TC ≤ TM(i), which is the cooling system according to

[12] . (However, i represents an integer from 1 to n - 1, n represents an integer of 2 or more representing the types of working fluids contained in the cooler, TM(i) represents the temperature TM for the working fluid i, and in descending order of temperature, they are TM(1), TM(2), ···, TM(n))

[18] The above-described step A2 is the cooling method described in

[17] , which includes a step B of further cooling the condensation part when the temperature TE is less than the threshold value for the working fluid n and the temperature TE exceeds the target temperature.

Advantages of the Invention

[0020] According to the present invention, a cooler that can efficiently cool an object to be cooled when used in an indirect cooling method can be provided. Further, according to the present invention, a thermal switch mechanism, a cooling system, and a cooling method can also be provided.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

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Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0022] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range represented using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0023] [Cooler] Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a first embodiment of the cooler of the present invention, FIG. 2 is a cross-sectional view taken along line A-A' thereof, and FIG. 3 is a front view.

[0024] The cooler 10 includes three long containers 11a, 11b, and 11c (collectively also referred to as container 11) arranged in parallel, a rectangular parallelepiped-shaped condensation block 12 attached to one end thereof, and a rectangular parallelepiped-shaped evaporation block 13 attached to the other end. The three containers 11 are fitted into the groove portions of a long heat conductor 14 having groove portions corresponding to their outer diameters, and the condensation block 12 and the evaporation block 13 are connected and in thermal contact via the containers 11 and the heat conductor 14.

[0025] Each of the containers 11 is a hollow cylindrical shape, and both ends thereof are sealed and airtight. The container 11 has a double structure and includes an outer housing 21 and a wick 22 disposed along the inner wall of the housing, and the interior thereof (indicated as "Cav" in FIG. 2) is a cavity. Further, each container houses a working fluid responsible for heat transport.

[0026] The condensation block 12 disposed at one end of the container 11 thermally contacts a heat source such as a refrigerator, a refrigerant, and a metal container containing the refrigerant to form a condensation section (condenser section), and cools and condenses the working fluid in the container 11 to the saturation temperature by the heat source, thereby realizing the function of condensing. In addition, the evaporation block 13 disposed at the other end thermally contacts the object to be cooled to form an evaporation section (evaporator section), and realizes the function of evaporating the working fluid in the container 11 by the heat input from the object to be cooled.

[0027] The container 11 has a wick 22 inside, and the container 11 filled with the working fluid functions as a heat pipe utilizing capillary action. As a typical operation of the heat pipe, first, the heat input to the evaporation section evaporates the working fluid (liquid) in the wick. Next, the working fluid (gas) enters the cavity Cav and moves to the condensation section. When heat is removed from the working fluid (gas) in the condensation section, the above condenses and the latent heat of vaporization is released. The condensate is sent back to the evaporation section by the capillary force of the wick. By this series of heat transfer, the object to be cooled is cooled.

[0028] Note that the cooler 10 is a parallel-type capillary heat pipe configured by arranging a plurality of long containers 11 having wicks 22 enclosed therein with a working fluid. However, the type of cooler according to the embodiment of the present invention is not limited to the above, and for example, it can be of various types such as a Rotating Heat Pipe type, a Gas-Loaded Heat Pipe type, a Loop Heat Pipe (LHP) type, a Capillary Pumped Loop (CPL) type, a Pulsating Heat Pipe (PHP) type, a Monogroove type, and an Inverted Meniscus Heat Pipe type. The shape of each heat pipe is known and is described, for example, on pages 4 to 9 of Frontiers in Heat Pipes (FHP), 5, 1 (2014), and the above description is incorporated herein.

[0029] Also, the container 11 of the cooler 10 has a double structure. However, the container of the cooler according to the present invention is not limited to the above structure and may not have a wick 22 (such a container is also referred to as a "wickless container"). When the container 11 is a wickless container, the cooler of the present invention is preferably a gravity-assisted heat siphon. In the following description, heat pipes, heat siphons, etc. are also collectively referred to as "heat pipes, etc.".

[0030] In the cooler 10, each of the three containers 11 contains a different working fluid, and all of them are working fluids having a boiling point of less than 300 K at standard atmospheric pressure (1 atm). The working fluid contained in the container 11 of the cooler 10 of the present invention only needs to contain at least two or more working fluids having a boiling point of less than 300 K, and may contain a working fluid having a boiling point of 300 K or more, but it is preferably that no working fluid having a boiling point of 300 K or more is contained. That is, the working fluid contained in the container is preferably only one having a boiling point of less than 300 K.

[0031] The working fluid with a boiling point of less than 300 K is not particularly limited. For example, nitrous oxide, sulfur dioxide, argon, arsine, allene, ammonia, carbon monoxide, nitric oxide, ethane, ethylacetylene, ethylene, ethyl chloride, hydrogen chloride, vinyl chloride, methyl chloride, chlorine, xenon, krypton, germane, boron pentafluoride, phosphorus pentafluoride, boron trichloride, ethylene oxide, oxygen, nitrogen trifluoride, boron trifluoride, phosphorus trifluoride, cyclopropane, dichlorosilane, disilane, sulfur tetrafluoride, silicon tetrafluoride, diborane, dimethyl ether, dimethylpropane, hydrogen bromide, vinyl bromide, methyl bromide, silane, hydrogen, hydrogen selenide, carbon dioxide (sublimation point), nitrogen, trimethylamine, neon, 1,3 - butadiene, sulfuryl fluoride, vinyl fluoride, methyl fluoride, fluorine, propane, propylene, normal butane, isobutane, helium, phosgene, phosphine, methane, methylacetylene, methyl mercaptan, carbonyl sulfide, hydrogen sulfide, sulfur hexafluoride, and tungsten hexafluoride, etc. can be mentioned.

[0032] Also, considering safety, handling properties, etc., as the working fluid with a boiling point of less than 300 K, for example, helium (melting point 1 K, boiling point 4.21 K, the same hereinafter in this paragraph), hydrogen (13.8 K, 20.38 K), neon (24 K, 27.9 K), nitrogen (63.1 K, 77.35 K), argon (83.9 K, 87.29 K), oxygen (54.7 K, 90.18 K), methane (90.6 K, 111.4 K), krypton (115.8 K, 119.7 K), ethane (89.9 K, 184.6 K), chlorodifluoroethane (113.1 K, 322.2 K), and ammonia (195.5 K, 239.9 K), etc. are preferable. In this paragraph, the numerical values in parentheses represent the melting point and boiling point at standard atmospheric pressure, respectively. Also, it is preferable to use carbon dioxide as the working fluid.

[0033] Among them, in terms of obtaining a cooler having a more excellent effect of the present invention, it is more preferable to include at least one working fluid selected from the group consisting of nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, and helium. It is still more preferable to include at least one working fluid selected from the group consisting of nitrogen and argon, and it is particularly preferable to include nitrogen and argon.

[0034] Note that the cooler 10 has three containers 11a, 11b, and 11c and three types of working fluids respectively accommodated therein. However, the cooler of the present invention is not limited to the above, and it is sufficient to have at least two or more types of working fluids (boiling point less than 300K) accommodated in the container.

[0035] The cooler of the present invention may have, for example, a mixture of two or more types of working fluids accommodated in one container. Also, it may have three or more containers. In this case, a mixture of the above working fluids may be accommodated in one or more of the containers.

[0036] The number of containers of the cooler is not particularly limited. However, when a mixture of working fluids is accommodated, it may be one or more. When each different working fluid (including the mixture) is accommodated, it may be two or more. The upper limit is not restricted, but for example, 20 or less is preferable, and 10 or less is more preferable.

[0037] The cooler 10 of the present invention can be manufactured by accommodating each working fluid in a gaseous state in the container 11 at room temperature and assembling each member. The cooler 10 having such characteristics suppresses breakage of the container 11 due to an unintended increase in internal pressure even if all the working fluids are vaporized in the container 11 up to the temperature at which at least the working fluid is accommodated (for example, 300K).

[0038] Generally, in a heat pipe or the like, when the heat load increases and exceeds the heat transport capacity, all of the working fluid contained inside evaporates, and the excellent heat transport function as a heat pipe or the like stops (entering a dry-out state). When in the dry-out state, the internal pressure of the container rises, posing a risk of rupture. Therefore, in general heat pipes or the like, especially those manufactured by containing a working fluid that is liquid at normal temperature, not only the dry-out state, but also even when at least a part inside the container (typically, the periphery of the evaporation section) is in a dry-out state (partial dry-out state), this has not been actively used.

[0039] Also, in the cryogenic region where the target temperature for cooling the object to be cooled is 100 K or lower, helium, argon, oxygen, etc. have been used as the working fluid. However, since these have a small heat of vaporization, a high viscosity, and furthermore, a small surface tension, it has been considered that the amount of heat that can be transported even when using a heat pipe or the like is small, thus becoming an obstacle to the consideration of using a heat pipe or the like for cooling in the cryogenic region.

[0040] The inventors of the present invention have not been bound by the above-mentioned common technical knowledge and have continuously intensively studied a more efficient cooling method in the cryogenic region.

[0041] First, the inventors of the present invention reexamined the problems of the conventional indirect cooling method. As a result, it was found that there is a problem with the thermal conductivity of the heat conductor (generally, copper strands or the like) connecting the object to be cooled and the heat source.

[0042] Generally, in the cryogenic region of 100 K or lower, the thermal conductivity of a metal material is greatly affected by the purity of the metal material. That is, for metal materials such as copper and aluminum, the thermal conductivity increases with higher purity in the cryogenic region. However, in the region exceeding 100 K, the influence of purity on the thermal conductivity is small, and it has been difficult to shorten the time for cooling the object to be cooled from 300 K to the cryogenic region only by increasing the purity of the metal material (for example, copper strands).

[0043] Reducing the cooling time from about 300K to about 100K (hereinafter also referred to as "pre-cooling") has a great impact on reducing the cooling time. Therefore, the inventors further studied the method of pre-cooling, and more particularly, reducing the cooling time to the target temperature.

[0044] As a result, the inventors finally found that by using a heat pipe or the like, which has not been studied conventionally, and further by using it in a partially dried-out state that was conventionally considered to be outside the usable range, an efficient heat transport far exceeding that of a metal strand can be realized, and thus the present invention was completed.

[0045] That is, by using a heat pipe composed of a container containing a working fluid with a boiling point of less than 300K to cool the object to be cooled to 300K or less, excellent heat transport efficiency by the heat pipe can be obtained even in the pre-cooling region where it was difficult to obtain the benefits of conventional high-purity metals, and as a whole, the cooling time to the target temperature can be significantly shortened.

[0046] Figure 8 shows the comparison results of the thermal resistance (K / W) with respect to the heat input (W) by a heat pipe (triangular plots marked "N" and star plots marked "Ar", respectively) containing nitrogen or argon in a copper container, a copper rod (solid) of the same shape, and a copper pipe (hollow). 2 Figure 8 shows the comparison results of the thermal resistance (K / W) with respect to the heat input (W) by a heat pipe (triangular plots marked "N" and star plots marked "Ar", respectively) containing nitrogen or argon in a copper container, a copper rod (solid) of the same shape, and a copper pipe (hollow).

[0047] According to Figure 8, it can be seen that regardless of the magnitude of the input heat (Heat input), the heat resistance of the heat pipe containing each working fluid is smaller compared to the calculated values of the copper rod (Cal.Copper Tube) and the copper pipe (Cal.Copper Rod). Furthermore, surprisingly, in the region to the right of the horizontal axis compared to the arrows D1 and D2, that is, in the partially dried-out state (although liquefaction of the working fluid occurs in the condensation part, there is a region where no liquid working fluid exists in the container), it is also clear that the heat resistivity is smaller compared to the copper rod and the copper pipe.

[0048] Furthermore, since the cooler of the present invention uses heat pipes or the like in parallel, or heat pipes or the like in which a plurality of working fluids are mixed (in this case, a heat pipe type is preferred), etc., it is possible to take a wider operating temperature range for efficient heat transport by heat pipes or the like, which also contributes to shortening the cooling time.

[0049] The working fluid may be appropriately selected according to the target temperature of cooling. However, from the viewpoint of further improving the cooling rate in the precooling region where it is difficult to sufficiently take advantage of the high thermal conductivity of high-purity metals, the working fluid preferably contains at least one selected from the group consisting of nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, helium, methane, krypton, ethane, chlorodifluoroethane, and ammonia. More preferably, it contains at least one selected from the group consisting of nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, helium, methane, krypton, ethane, and chlorodifluoroethane. Even more preferably, it contains at least one selected from the group consisting of nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, helium, methane, krypton, and ethane. Particularly preferably, it contains at least one selected from the group consisting of nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, and helium. Most preferably, it contains nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, and helium.

[0050] Furthermore, if the container (and the heat conductor 14) is formed of a high-purity metal material, efficient heat transport by heat pipes or the like can be achieved during preheating, and in the temperature range of approximately 100 K or lower, the effect of heat transport by efficient heat conduction by a higher-purity metal can be obtained, and the entire cooling from precooling to the target temperature can be performed more efficiently.

[0051] The material of the container is not particularly limited, but copper, aluminum, etc. are preferred. It is preferably a material having a residual resistance ratio (RRR) of 30 or more (hereinafter, also simply referred to as "high purity"), more preferably 100 or more, and still more preferably 300 or more. The upper limit is not particularly limited, but generally 30,000 or less is preferred.

[0052] In particular, when the target temperature for cooling the object to be cooled is lower than the freezing point of the working fluid having the lowest freezing point among the working fluids contained in the container, and / or when the above target temperature is 100 K or lower (preferably 90 K or lower, more preferably 80 K or lower, still more preferably 70 K or lower, particularly preferably 60 K or lower, and most preferably 50 K or lower), when the material of the container is a metal material having the above residual resistance ratio (RRR) of 30 or more, more efficient cooling can be performed.

[0053] In the above case, in a temperature range (pre-cooling) exceeding 100 K where the superiority of the thermal conductivity of the high-purity metal material is difficult to exhibit, more efficient heat transport can be achieved by the operation of a heat pipe or the like in which the working fluid is contained, and the cooling of the object to be cooled proceeds. Even when all of the working fluid solidifies in the region where the superiority of the thermal conductivity of the high-purity metal material is exhibited, more efficient heat transport can be achieved by the heat conduction of the container. That is, by combining a heat pipe or the like and a high-purity metal material, more efficient cooling becomes possible particularly when the target temperature is in the cryogenic region.

[0054] The thermal conductivity of the high-purity metal has a maximum value with respect to temperature, and it is known that the peak temperature shifts to the low-temperature side as the purity increases. Therefore, the purity of the metal material of the container may be determined according to the target temperature so that the region where the thermal conductivity is maximum can be used more efficiently. That is, it is preferable that the target temperature is selected to be equal to or higher than the peak temperature of the thermal conductivity (on the high-temperature side above the peak temperature).

[0055] On the one hand, when the working fluid contains at least one selected from the group consisting of helium, hydrogen, and neon, the efficient heat transfer effect of the heat pipe can be obtained even if the target temperature is lower.

[0056] FIG. 9 shows a cooler (Parallel heat pipe) of the present invention having copper containers containing nitrogen and argon respectively, and a simulation result of calculating the time taken for the temperature of the object to be cooled (evaporation section) to decrease when using a copper rod (2 of OFHCs·Rod) of the same dimensions and setting the temperature of the low-temperature end (condensation section) to 77K. From the results of FIG. 9, it became clear that when using the cooler of the present invention, the cooling time can be reduced to approximately 1 / 3 compared to the case of using a copper rod of the same dimensions.

[0057] Next, a method of using a typical cooler 10 will be described. The cooler 10 is disposed so as to be in thermal contact with the object to be cooled and the heat source respectively. Typically, the object to be cooled and the evaporation block 13 are in contact to form an evaporation section, and the heat source and the condensation block 12 are in contact to form a condensation section. A method of cooling the object to be cooled to a target temperature of 300K or lower will be described with such a configuration.

[0058] First, the container 11 of the cooler 10 contains working fluids having different boiling points. Therefore, the saturation temperatures of the respective working fluids in the container 11 are also different. Here, the working fluids contained in the container 11 are respectively referred to as working fluids 1, 2, and 3, and their saturation temperatures are k(1), k(2), and k(3) [unit: K] from the high-temperature side.

[0059] First, when the temperature of the condensation section is higher than the saturation temperature of the working fluid 1, all the working fluids are vaporized and in a so-called dry-out state. Conventionally, in the dry-out state, it was considered that the efficiency of heat transport decreases and the internal pressure increases, potentially causing the container to rupture. However, in the cooler of the present invention, since each container contains a working fluid with a boiling point of 300 K or higher, there is almost no risk of rupture even in the dry-out state.

[0060] Next, when the temperature of the condensation part reaches about the saturation temperature [k(1)] K of the working fluid 1, the working fluid 1 starts to condense around the condensation part inside the container 11, and from the dry-out state where the wick 22 is completely dry, liquid working fluid 1 starts to be generated in at least a part of the container (a part of the wick 22). This state can be said to be a partially dry-out state inside the container, and by actively utilizing this region, excellent heat transport efficiency can be obtained.

[0061] After passing through this partially dry-out state and the state of operating as a normal heat pipe, when the object to be cooled (evaporation part) is cooled to a certain level, depending on the temperature of the cold heat source, etc., the temperature of the condensation part becomes lower than the solidification temperature of the working fluid 1. Then, the working fluid 1 solidifies inside the container 11. Then, the heat transport by the container 11 containing the working fluid 1 mainly relies on the heat conduction of the housing (housing 21) of the container 11, and the efficiency decreases.

[0062] On the other hand, the cooler 10 further has containers 11 containing a working fluid 2 and a working fluid 3 with a saturation temperature lower than that of the working fluid 1. Therefore, as the temperature of the condensation part decreases, sequentially, the containers 11 containing the working fluid 2 and the containers 11 containing the working fluid 3 operate in the same manner as described above.

[0063] In this way, when the cooler of the present invention is applied to the indirect cooling method, the temperature of the object to be cooled can be efficiently lowered.

[0064] Note that the cooler 10 is an example of an embodiment of the present invention, and various modifications are possible as long as the effects of the present invention are achieved. Also, regarding the dimensions of each part, etc., they can be appropriately changed by known methods according to the application, etc.

[0065] For example, although the cooler 10 has a condensation block 12, an evaporation block 13, and a heat conductor 14, the cooler according to the embodiment of the present invention may not have some or all of the above members. In that case, one end of a plurality of containers 11 arranged in parallel may be in thermal contact with the cold stage of the refrigerator, and / or the other end may be in thermal contact with the object to be cooled.

[0066] Also, in the cooler 10, the condensation block 12 and the evaporation block 13 are arranged at both ends of the container 11, respectively. However, the relative positional relationship between the condensation block 12, the evaporation block 13, and the container 11 can be arbitrarily changed. Also, although the present cooler 10 has one set of a condensation block 12 and an evaporation block 13, it is not limited to the above. The cooler may have a plurality of condensation blocks and evaporation blocks.

[0067] Also, the shape and size of the container 11 are not particularly limited and can be appropriately changed according to the application. Although the container 11 is in a hollow cylindrical shape, it may be in any shape such as rectangular, conical, annular, and corrugated. When the cooler according to the present embodiment is used in an indirect cooling method for cooling a superconducting member or the like, cooling can be performed efficiently, and the time required for cooling (especially the time required for precooling) can be significantly reduced compared to the conventional method.

[0068] [Cooling System] FIG. 4 is an explanatory diagram of the hardware configuration of a cooling system according to an embodiment of the present invention. The cooling system 40 has a cooler 10 disposed between a refrigerator 52 and an object to be cooled 44.

[0069] The refrigerator 52 includes a refrigeration unit 43 including a cold head 41, a first-stage cold stage 42a, and a second-stage cold stage 42b, a compression unit 50, and a control device 51.

[0070] The object to be cooled 44 is disposed within a radiation shield 48 arranged within a cryostat 49, and is in thermal contact with the evaporation block 13 of the cooler 10 to form an evaporation section. The second cold stage 42b inserted into the radiation shield 48 within the cryostat 49 is in thermal contact with the condensation block 12 to form a condensation section. Although not shown, a heat conductor 14 is also disposed between the condensation block 12 and the evaporation block 13. Note that the cooling system may not have the heat conductor 14.

[0071] The container 11 containing the working fluid is connected via a buffer tank 45 for each working fluid, a valve 46, and a pipe 47, and is configured to be able to adjust the amount of the internal working fluid. Note that the cooling system may not have the buffer tank 45. Further, the cooler 10 according to the present embodiment is a heat pipe having a wick inside the container, but may be a heat syphon (gravity reflux type wickless heat pipe).

[0072] The cooling system 40 also has a condensation section temperature sensor for detecting the temperature TC of the condensation section and an evaporation section temperature sensor for detecting the temperature TE of the evaporation section. The cooling system 40 also has a reheater for heating the condensation section. Note that all are not shown in the drawings.

[0073] Next, the function of the cooling system 40 will be described. FIG. 5 is a functional block diagram of the cooling system 40. The cooling system 40 includes a control device 51, a cooling unit 61, a temperature control unit 62, and a temperature comparison unit 63, and each unit is configured to be able to exchange data with each other.

[0074] First, the control device 51 is composed of a well-known computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and its peripheral circuits. The control device 51 performs various calculations and processes based on the control program stored in its ROM. The control device 51 controls the cooling unit 61, the temperature control unit 62, and the temperature comparison unit 63 based on the inputs from the condensation unit temperature sensor and the evaporation unit temperature sensor, and realizes each function of the cooling system 40.

[0075] Note that all or part of the control device 51 can also be configured using circuits such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). That is, the functions of each functional block described in FIG. 9 can be configured based on the illustrated computer, or all or part of them can be configured using circuits such as an FPGA and an ASIC. Also, at least a part of the functions of each functional block can be configured by an analog circuit.

[0076] An evaporation unit temperature sensor 64 for detecting the temperature TE of the evaporation unit and a condensation unit temperature sensor 65 for detecting the temperature TC of the condensation unit are connected to the input side of the control device 51. And the detection signals of these sensor groups are input to the control device 51.

[0077] The function of the cooling unit 61 is realized when the program (cooling unit control PG61a) stored in the storage device of the control device 51 is executed by the CPU, and the first-stage cold stage 42a and the second-stage cold stage 42b connected to the refrigeration unit 43 and the compression unit 50 are controlled.

[0078] The function of the temperature control unit 62 is realized by the program (temperature control unit control PG62a) stored in the storage device of the control device 51 being executed by the CPU to control the reheater 62b. The temperature of the condenser is adjusted (typically heated) by the temperature control unit 62. Although the present cooling system 40 has a reheater 62b, when the cooling system 40 does not have a reheater 62b, the temperature control unit 62 can also be configured to control the outputs of the compression unit 50 and / or the refrigeration unit 43 to adjust the temperature of the condenser.

[0079] The function of the temperature comparison unit 63 is realized by the program stored in the storage device of the control device 51 being executed by the CPU. The temperature comparison unit 63 includes a TE / threshold comparison unit 63a that compares the detection signal of the evaporator temperature sensor (the temperature TE of the evaporator) with a threshold value (details will be described later) predetermined for each working fluid and stored in the ROM, and a TC / TM comparison unit 63b that compares the detection signal of the condenser temperature sensor (the temperature TC of the condenser) with a temperature TM predetermined based on the freezing temperature of the working fluid.

[0080] Next, the operation of the cooling system 40 will be described based on the operation flow of the control device 51.

[0081] FIG. 6 is an operation flowchart of the control device 51 of the cooling system 40 when cooling the object to be cooled from 300K to the target temperature. In the following description, the working fluids contained in the container 11 of the cooler 10 are referred to as working fluid 1, working fluid 2, ···, working fluid n in descending order of boiling point (for the cooler 10, n = 3).

[0082] First, in step S71, the control device 51 controls the cooling unit 61 to start cooling the first-stage cold stage 42a and the second-stage cold stage 42b. When the cooling of the cold stages (42a, 42b) starts, the condenser is cooled, and the evaporator is also cooled by the heat transfer of the cooler 10.

[0083] When cooling starts and the temperature TC of the condensation part reaches the saturation temperature of the working fluid 1, condensation of the working fluid 1 starts in the condensation part. In the container in which the working fluid 1 is contained, it enters a partial dry-out state and starts operating as a heat pipe. Efficient heat transport starts between the condensation part and the evaporation part, and the temperature of the evaporation part rapidly decreases.

[0084] Next, in step S72, the temperature comparison unit 63 is controlled by the control device 51, and the temperature TE of the evaporation part detected by the evaporation part temperature sensor is compared with a threshold value predetermined for the working fluid 1. This threshold value is a value predetermined as the lower limit temperature for obtaining efficient heat transport.

[0085] Typically, this threshold value is determined in consideration of the temperature difference, saturation pressure, etc. between the evaporation part and the condensation part necessary for the container containing the working fluid 1 to efficiently transport heat as a heat pipe. There is no particular limitation on how the threshold value is determined, but as an example, it can also be determined based on the following experimental results.

[0086] Figures 10 to 13 show experimental results of the heat transport capacity with respect to the temperature of the evaporation part when the temperature of the condensation part is maintained at 77K (Figure 10), 82K (Figure 11), 84K (Figure 12), and 87K (Figure 13) in a cooling system equipped with a cooler having two heat pipes configured by arranging containers containing argon and nitrogen in parallel. The horizontal axis represents the temperature (K) of the evaporation part, and the vertical axis represents the heat transfer rate (W). In each figure, "Parallel-Heat pipe" represents the measured value of the above cooler, "OFHCs-Rod" represents the measured value of a copper rod, and "OFHCs-Tube" represents the measured value of a copper tube.

[0087] As is clear from the results of FIGS. 10 to 13, when cooling is started from a state where the temperature of the evaporation section is near room temperature (about 300 K), it can be seen that the heat transfer coefficient is maintained at a high level when the temperature of the evaporation section is approximately 90 K or higher. This is presumably because excellent heat transport efficiency can be obtained by the operation as a heat pipe that starts through a partial dry-out state.

[0088] On the other hand, when the temperature of the evaporation section becomes less than approximately 90 K, it can be seen that the temperature difference between the condensation section and the evaporation section gradually decreases, and as a result, the heat transfer coefficient decreases. According to such experimental results, when argon is used as the working fluid, there is a method of setting the threshold value to 84 to 89 K.

[0089] Although the threshold values of the respective working fluids vary depending on the pressure of the working fluid enclosed in the container, as an example, helium is 2 to 3 K, hydrogen is 14 to 20 K, neon is 27 to 32 K, nitrogen is 70 to 75 K, argon is 84 to 89 K, oxygen is 73 to 78 K, methane is 91 to 96 K, krypton is 116 to 121 K, ethane is 150 to 155 K, chlorodifluoroethane is 193 to 198 K, and ammonia is 213 to 218 K, etc.

[0090] Next, as a result of the above comparison, when the temperature TE is equal to or higher than the threshold value of the working fluid 1, that is, when the temperature TE is not less than the threshold value (step S73: NO), the temperature of the evaporation section is still sufficiently high, and it is a region where efficient heat transport by the working fluid 1 is possible. Therefore, the control device 51 adjusts the temperature TC of the condensation section detected by the condensation section temperature sensor so as to exceed a temperature TM(1) predetermined based on the solidification temperature of the working fluid 1 (step S74). That is, the control device 51 monitors the temperature TC so that the working fluid 1 does not solidify in the condensation section and the heat transport efficiency does not decrease, and controls the temperature control unit 62 as necessary to adjust the temperature of the condensation section (step A).

[0091] As described as the function of the temperature control unit 62, the method for controlling the temperature of the condensing unit is not particularly limited. For example, methods such as heating by a reheater or adjusting the output of the cold stage by adjusting the power supply can be mentioned. By doing so, the container in which the working fluid 1 is accommodated can operate sufficiently as a heat pipe, and efficient heat transport between the condensing unit and the evaporating unit can be obtained.

[0092] Note that this temperature TM(1) can be determined with reference to the freezing point of the working fluid 1 and the like. For example, in the experimental results of FIGS. 10 to 13, focusing on argon as the working fluid, the temperature TM(1) is preferably a value exceeding 77K, and more preferably a value of 82K or more. Note that the upper limit of TM(1) is not particularly limited, but is preferably equal to or lower than the saturation temperature of the working fluid 1.

[0093] On the other hand, as a result of the above comparison, when the temperature TE is less than the threshold value (step S73: YES), the cooling of the evaporating unit has progressed, so that the difference between the temperature TC and the temperature TE has become small, and the temperature TE has fallen below the lower limit of the range in which efficient heat transport can already be performed with the working fluid 1. Therefore, next, the main body of heat transport is switched to the container in which the working fluid 2 is accommodated.

[0094] That is, the control device 51 controls the temperature control unit 62 to adjust the temperature TC to a range of the formula: TM(i + 1) < TC ≦ TM(i) (step S75, process A2). In the formula, i represents an integer from 1 to n - 1, n represents an integer of 2 or more representing the types of working fluids included in the cooler (that is, the total number of types), TM(i) represents the temperature TM for the working fluid i, and in descending order of temperature, they are TM(1), TM(2), ···, TM(n).

[0095] Specifically, in step S73, when TE is less than the threshold value determined for the working fluid 1 (that is, i = 1) (step S73: YES), the control device controls the temperature TC to a range of TM(2) < TC ≦ TM(1) as the first step S75.

[0096] When the condensation part becomes TM(1) or less, the working fluid 1 has already started to solidify (or has completely solidified) in the container. Therefore, the container containing the working fluid 1 cannot perform efficient heat transport by the heat pipe operation. On the other hand, by maintaining the temperature TC within the operating range of the working fluid 2, which has the next highest TM among the contained working fluids, efficient heat transport can be performed by the heat pipe operation of the container containing the working fluid 2.

[0097] Next, in step S76, the temperature TE of the evaporation part is compared again with a predetermined threshold value for the working fluid i + 1 (in the first step S76, i + 1 is 2). This threshold value can be determined in the same manner as in the case of the working fluid 1.

[0098] As a result, when the temperature TE is less than the threshold value of the working fluid i + 1 (step S76: YES), the temperature TE exceeds the target temperature, that is, when it is not "below" the target temperature (step S77: No), and i + 1 is less than n (that is, it is not the last type of working fluid) (step S78: YES), 1 is added to i (i = i + 1) (step S79), and steps S75 to S78 are repeated. By this repetition, each of the working fluids contained in the cooler can be sequentially utilized in a state of being in a partial dry-out state to an efficiently operating state as a heat pipe, and cooling can be performed in a shorter time.

[0099] On the other hand, when the temperature TE is not less than the threshold value of the working fluid i + 1, that is, when it is equal to or greater than the threshold value (step S76: NO), efficient heat pipe operation of the container containing the working fluid i + 1 is still possible. Therefore, again, the temperature TC is controlled within the range of TM(i + 1) < TC ≦ TM(i) (step S75).

[0100] Also, when the temperature TE is less than the threshold value of the working fluid i + 1 (step S76: YES), and the temperature TE has reached the target temperature, that is, when the temperature TE is below the target temperature (step S77: YES), the cooling ends.

[0101] Also, as a result of the above repetition, when i + 1 becomes equal to n, that is, when i + 1 is not less than n (step S78: No), the repetition ends. This state indicates that the evaporation section is further cooled than the region where efficient heat pipe operation is possible with the working fluid n having the lowest threshold value (i.e., the lowest temperature TM).

[0102] At this time, if the temperature TE of the evaporation section is below the target temperature (step S80: YES), the cooling ends. On the other hand, when TE exceeds the target temperature, that is, when it is not below the target temperature (step S80: NO), the control device 51 controls the temperature control section 62 to further cool the cold stage 42b to further cool the condensation section (step S81, process B).

[0103] In this process B, typically, each working fluid including the working fluid n in the container is solidified at least in the condensation section, and therefore, it is difficult to exhibit excellent heat transport efficiency as a heat pipe. At this time, if at least one material of the container 11 of the cooler 10 is a high-purity metal, better cooling efficiency can be obtained. This tendency is particularly remarkable when the target temperature is below the cryogenic region (specifically, 100 K). The reason is that the thermal conductivity of metals such as copper and aluminum varies greatly depending on purity in the cryogenic region.

[0104] As already explained, the thermal conductivity of metal materials such as copper and aluminum has a maximum value in the cryogenic region, and it is known that the maximum temperature shifts to the low-temperature side as the purity of the metal material increases. In terms of the relationship with the target temperature of cooling, from the viewpoint of realizing more efficient heat transport and performing cooling in a shorter time, it is preferable to set the target temperature to a temperature higher than the maximum temperature of the thermal conductivity determined by the material of the container.

[0105] Note that, as already described, this cooler can be used in combination with a refrigerator 52 like the cooling system 40, but it can also be used in combination with a heat source other than a refrigerator to cool a body to be cooled. Examples of such heat sources include, for example, a metal container containing various refrigerants, and the various refrigerants themselves. Even when such a heat source is used, the same cooling method as described above can be applied.

[0106] [Thermal Switch Mechanism] Next, a thermal switch mechanism using the cooler of the present invention will be described. The thermal switch mechanism means, for example, a heat conduction switching mechanism that places a cooler between a heat source and a body to be cooled, cools the body to be cooled to a predetermined temperature, and then reduces (blocks) the heat conduction between the two.

[0107] When cooling a superconducting member or the like that is a body to be cooled, if the refrigerator continues to operate even after the cooling is completed up to the target temperature, the energy consumption will increase. Generally, since superconducting members etc. have a small resistance and a small heat generation amount, once the target temperature of cooling is reached, even if the operation of the refrigerator is stopped, if the heat conduction between the refrigerator and the body to be cooled can be thermally separated, an extremely low-temperature operating environment can be maintained.

[0108] Such thermal separation can also be performed with a mechanical mechanism. However, especially when the body to be cooled is a superconducting member or the like, the heat and vibration generated by the mechanical mechanism may become a major problem. Also, there are structural constraints for housing a mechanical mechanism in a cryostat, and a thermal switch mechanism that does not involve physical contact and its release is required.

[0109] FIG. 7 is an explanatory diagram of the thermal switch mechanism of the present invention incorporated in a cooling system. In the following, the differences from the already described cooling system 40 will be mainly described, and the parts similar to the already described cooling system 40 will be omitted from the description.

[0110] The cooling system 90 is equipped with a thermal switch mechanism 92, and the thermal switch mechanism 92 has a container 91, condensation blocks 12 arranged at both ends thereof, and an evaporation block 13. In this container 91, different types of working fluids are accommodated in the same manner as the cooler 10 described above.

[0111] One of the characteristic points of the thermal switch mechanism 92 is that the thermal conductivity of the container 91 at 293K is 24 W / m·K or less. Due to the low thermal conductivity of the container 91, the heat transport between the condensation part and the evaporation part due to heat conduction by the container 91 itself is negligibly small. Note that the lower limit of the thermal conductivity is not particularly limited, but generally, it may be 0.01 W / m·K (293K) or more.

[0112] The cooling system 90 is set to use the target temperature of cooling to a temperature at which the working fluid n solidifies in the condensation part.

[0113] When cooling starts, the cooling of the evaporation part proceeds efficiently in the same manner as the cooling system 40 described above. And when the target temperature is reached, since the working fluid n solidifies in the condensation part, the operation as a heat pipe of each container 91 stops.

[0114] At this time, although the condensation part and the evaporation part are connected by the container 91, since the thermal conductivity of the container 91 is low, after the operation as a heat pipe stops, the heat transport between the condensation part and the evaporation part hardly occurs. Thereby, a thermal switch mechanism is realized without having any mechanical mechanism at all.

[0115] Note that the material of the container 91 of the thermal switch mechanism 92 is not particularly limited as long as the thermal conductivity is within a predetermined range, but stainless steel or the like is preferable.

Industrial Applicability

[0116] According to the cooler of the present invention, by combining multiple types of working fluids with boiling points at extremely low temperatures for the conventionally known heat pipes / heat syphons, high thermal conductivity can be achieved in a wide operating range, and the cooling rate of cryogenic equipment can be dramatically shortened.

[0117] As one form, by arranging in parallel containers filled with gases (argon, oxygen, nitrogen, neon, xenon, and hydrogen) that liquefy at about 15 to 90 K respectively, or by combining containers filled with a mixture of these, a dramatic improvement in heat transport capacity in a wide temperature range becomes possible.

[0118] When the cooler of the present invention is used, even in the horizontal direction where the heat transport efficiency has conventionally been considered difficult to improve, the cooling time from 300 K to a temperature of about 80 K is shortened to about 1 / 3 of the conventional time, and the energy required for cooling can also be significantly reduced. In addition, since the technologies of various conventionally known heat pipes / heat syphons can be applied as they are, the scope of application is wide.

[0119] Also, focusing on the fact that the (partial) dry-out state of the heat pipe can also be utilized in cryogenic heat pipes, and experimentally proving this has expanded the operable region of the heat pipe.

[0120] The cooler, heat switch mechanism, cooling system, and cooling method of the present invention can be used in the fields of space science (cooling of cryogenic equipment mounted on artificial satellites, etc.), medical fields (cooling of magnetic resonance imaging devices using superconducting members, etc.), and physical property science fields (cooling of devices using various superconducting members, etc.).

Explanation of Symbols

[0121] 1: Actuating fluid, 2: Actuating fluid, 3: Actuating fluid, 10: Cooler, 11: Container, 12: Condensing block, 13: Evaporating block, 14: Heat conductor, 21: Housing, 22: Wick, 40, 90: Cooling system, 41: Cold head, 42a, 42b: Cold stage, 43: Refrigeration unit, 44: Object to be cooled, 45: Buffer tank, 46: Valve, 47: Pipe, 48: Radiation shield, 49: Cryostat, 50: Compression unit, 51: Control device, 52: Refrigerator, 61: Cooling section, 62: Temperature control section, 63: Temperature comparison section, 91: Container, 92: Thermal switch mechanism

Claims

1. A cooler having a container and a working fluid contained in the container, wherein the working fluid includes at least two or more working fluids having a boiling point of less than 300 K, and which cools a cooled object in thermal contact with the container to a target temperature of 100 K or less by utilizing a state in which at least a part of the region inside the container is in a dry-out state, wherein at least two containers are provided, wherein the working fluids having different saturation temperatures are contained in each of the containers, and the working fluid includes at least one selected from the group consisting of helium, hydrogen, neon, nitrogen, argon, oxygen, methane, krypton, ethane, chlorodifluoroethane, and ammonia, wherein the container has a housing made of a metal material, the residual resistivity ratio of the metal material is 300 or more, and the metal material is copper or aluminum, and a cooler in which the peak temperature of the thermal conductivity of the metal material is lower than the target temperature.

2. In at least one of the containers, The cooler according to claim 1, in which two or more of the working fluids are contained.

3. The cooler according to claim 1 or 2, wherein the working fluid includes at least one selected from the group consisting of nitrogen, hydrogen, xenon, argon, neon, oxygen, carbon dioxide, and helium.

4. The cooler according to any one of claims 1 to 3, wherein the internal pressure of the working fluid in the container at 300 K is 1 MPa or less.

5. The cooler according to any one of claims 1 to 4, which is a heat pipe.

6. The cooler according to any one of claims 1 to 5, which is a thermosyphon.

7. A cooling system comprising the cooler according to any one of claims 1 to 6 and a refrigerator having a cold stage, wherein the cooler is disposed between the cooled object and the cold stage.

8. The refrigerator further includes a condensing portion temperature sensor that detects the temperature TC of a condensing portion configured by thermally contacting the cold stage and the cooler, an evaporating portion temperature sensor that detects the temperature TE of an evaporating portion configured by thermally contacting the cooler and the cooled object, and a control device, wherein the control device has a temperature comparison unit that compares the temperature TE with a threshold value predetermined for the working fluid included in the cooler, and a temperature control unit that adjusts the temperature of the condensing portion. The cooling system according to claim 7, wherein the control device adjusts the temperature TC so that the temperature TE exceeds a temperature TM determined in advance based on the solidification temperature of the working fluid until the temperature TE becomes less than the threshold value.

9. When the temperature TE is less than the threshold value for the working fluid i, the control device adjusts the temperature TC to a range of the formula: TM(i + 1) < TC ≤ TM(i), the cooling system according to claim 8. (However, i represents an integer from 1 to n - 1, n represents an integer of 2 or more representing the types of working fluids included in the cooler, TM(i) represents the temperature TM for the working fluid i, and in descending order of temperature, they are TM(1), TM(2),..., TM(n))

10. The cooling system according to claim 9, wherein the control device further cools the condensation part when the temperature TE is less than the threshold value for the working fluid n and the temperature TE exceeds the target temperature.

11. A cooling method, comprising disposing the cooler according to any one of claims 1 to 6 between a body to be cooled and a heat source, and cooling the body to be cooled by heat transfer between the body to be cooled and the heat source.

12. Until the temperature TE of the evaporation part configured such that the body to be cooled and the cooler are in thermal contact becomes less than a threshold value determined in advance for the working fluid included in the cooler, The cooling method according to claim 11, including a step A of adjusting the temperature TC of the condensation part configured such that the heat source and the cooler are in thermal contact to exceed a temperature TM determined in advance based on the solidification temperature of the working fluid.

13. The adjustment is The cooling method according to claim 12, including a step A2 of adjusting the temperature TC to a range of the formula: TM(i + 1) < TC ≤ TM(i). (However, i represents an integer from 1 to n - 1, n represents an integer of 2 or more representing the types of working fluids included in the cooler, TM(i) represents the temperature TM for the working fluid i, and in descending order of temperature, they are TM(1), TM(2),..., TM(n))

14. The step A2 includes a step B of further cooling the condensation part when the temperature TE is less than the threshold value for the working fluid n and the temperature TE exceeds the target temperature, the cooling method according to claim 13.

15. A cooler and a refrigerator having a cold stage, A cooling system, wherein the cooler is disposed between the body to be cooled and the cold stage. The cooler has a container and a working fluid accommodated in the container. The working fluid includes at least two or more working fluids having a boiling point of less than 300 K. By utilizing the fact that at least a part of the region in the container is in a dry-out state, a body to be cooled that is in thermal contact with the container is cooled to 300 K or less. The refrigerator further includes a condensing portion temperature sensor that detects the temperature TC of a condensing portion configured by thermally contacting the cold stage and the cooler, an evaporating portion temperature sensor that detects the temperature TE of an evaporating portion configured by thermally contacting the cooler and the body to be cooled, and a control device. The control device has a temperature comparison unit that compares the temperature TE with a predetermined threshold value for the working fluid included in the cooler. The control device has a temperature adjustment unit that adjusts the temperature of the condensing portion. The control device adjusts the temperature TC so as to exceed a predetermined temperature TM based on the solidification temperature of the working fluid until the temperature TE becomes less than the threshold value. When the temperature TE is less than the threshold value for the working fluid i, the control device adjusts the temperature TC to a range of the formula: TM(i + 1) < TC ≤ TM(i), a cooling system. (However, i represents an integer from 1 to n - 1, n represents an integer of 2 or more representing the types of working fluids included in the cooler, TM(i) represents the temperature TM for the working fluid i, and in descending order of temperature, they are TM(1), TM(2),..., TM(n)).

16. The cooling system according to claim 15, wherein when the temperature TE is less than the threshold value for the working fluid n and the temperature TE exceeds the target temperature, the control device further cools the condensing portion.

17. A cooling method in which a cooler is disposed between a body to be cooled and a heat source, and the body to be cooled is cooled by heat transfer between the body to be cooled and the heat source, wherein the cooler has a container and a working fluid accommodated in the container, the working fluid includes at least two or more working fluids having a boiling point of less than 300 K, and the cooler is configured to cool a body to be cooled that is in thermal contact with the container to 300 K or less by utilizing the fact that at least a part of the region in the container is in a dry-out state. until the temperature TE of an evaporating portion configured by thermally contacting the body to be cooled and the cooler becomes less than a predetermined threshold value for the working fluid included in the cooler. Including step A of adjusting the temperature TC of the condensation part, in which the heat source and the cooler are thermally in contact, so that the temperature TC exceeds a temperature TM predetermined based on the solidification temperature of the working fluid. The adjustment includes Step A2 of adjusting the temperature TC to a range of the formula: TM(i + 1) < TC ≤ TM(i), a cooling method. (However, i represents an integer from 1 to n - 1, n represents an integer of 2 or more representing the types of working fluids included in the cooler, TM(i) represents the temperature TM for the working fluid i, and in descending order of temperature, they are TM(1), TM(2),..., TM(n))

18. The cooling method according to claim 17, wherein step A2 includes step B of further cooling the condensation part when the temperature TE is less than the threshold value for the working fluid n and the temperature TE exceeds the target temperature.

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