Cascade type cryogenic refrigerator

Abstract

To improve the efficiency of extremely-low temperature cooling at a level for enabling superconduction.SOLUTION: A cold-storage type refrigerator 1 and a steam compression-type refrigerator 17 are prepared, and piping for transporting a refrigerant of the steam compression-type refrigerator 17 to a high-temperature part 200 of the cold-storage type refrigerator 1 is arranged. A heat-exchange mechanism for making the refrigerant and a gas of the cold-storage type refrigerator 1 exchange heat between themselves is arranged in the high-temperature part 200. The steam compression-type refrigerator 17 performs cooling down to a prescribed intermediate temperature from a state that a temperature is near room temperature. Since the refrigerant which is cooled down to the intermediate temperature cools the high-temperature part of the cold-storage type refrigerator 1, the cold-storage type refrigerator 1 can perform cooling down to a targeted extremely-low temperature from the intermediate temperature. A control device 100 sets the intermediate temperature so that a total sum of power consumption becomes minimum, and by controlling operations of both the refrigerators, can perform cooling more efficiently than the case for performing the cooling down to the extremely-low temperature by using only the cold-storage type refrigerator 1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technology that realizes extremely low temperature cooling below that of liquid nitrogen (77.3K). [Background technology]

[0002] Generally, to realize superconductivity, an environment of about 20 to 40K is required. A regenerative refrigerator is often used as a device to achieve such cooling. Known examples of regenerative refrigerators include Stirling refrigerators and pulse tube refrigerators. In addition, for freezers in the temperature range used in showcases, etc., a cascade system in which multiple freezers are connected in series is known as a technology for improving the refrigeration efficiency. For example, Patent Document 1 discloses a technology for quickly achieving the cooling function by exchanging heat of the refrigerant between a main cooling machine and a supercooling machine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-82294 A Summary of the Invention [Problem to be solved by the invention]

[0004] Previously, research and development had focused on realizing superconductivity and its application technology, with little consideration given to the efficiency of cooling required to achieve superconductivity. Cryogenic refrigeration requires a large amount of power for cooling and has low cooling efficiency, but these issues were not taken into consideration. As a result, superconductivity was a technology used only in fields where the need for it was so great that cooling efficiency was not an issue, such as MRI, linear motor cars, and nuclear fusion reactors.

[0005] However, superconductivity is a technology that can be applied in areas other than these, and its usefulness is extremely high because it can reduce electrical resistance to zero. In order to apply superconductivity in such a wide range of fields, it is necessary to efficiently achieve the extremely low temperatures required for this. Improvements in the efficiency of refrigeration to extremely low temperatures below the temperature of liquid nitrogen (77.3 K) are required not only for superconductivity but also for other purposes. In view of the above problems, the present invention aims to improve the efficiency of refrigeration to achieve such extremely low temperatures. [Means for solving the problem]

[0006] The present invention relates to A cascade type cryogenic refrigerator that realizes cryogenic cooling lower than the temperature of liquid nitrogen by connecting multiple types of refrigerators, a vapor compression refrigerator that cools a refrigerant to a predetermined intermediate temperature; a regenerative refrigerator designed so that a high temperature section is at the intermediate temperature and a low temperature section is at the extremely low temperature; The present invention may be a cascade type cryogenic refrigerator including a heat exchange mechanism for exchanging heat between the refrigerant of the vapor compression refrigerator and a high temperature portion of the regenerative refrigerator.

[0007] The Carnot efficiency (= low temperature end temperature / (high temperature end temperature - low temperature end temperature)), which is the ideal efficiency of a refrigerator, becomes lower as the low temperature end temperature becomes lower. Therefore, when trying to cool from room temperature to extremely low temperatures using only a regenerative refrigerator, there is a theoretical limit to how much efficiency can be improved. On the other hand, in the present invention, as described above, the regenerative refrigerator and the vapor compression refrigerator are connected via a heat exchange mechanism to achieve extremely low temperatures as a whole. That is, cooling to an intermediate temperature is performed by the vapor compression refrigerator, and cooling from the intermediate temperature to extremely low temperatures is performed by the regenerative refrigerator. In this way, the vapor compression refrigerator can perform cooling more efficiently than the regenerative refrigerator, so that the present invention can improve the overall cooling efficiency to extremely low temperatures.

[0008] As the regenerative refrigerator, various types such as a Stirling refrigerator and a pulse tube refrigerator can be used. Conventionally, the regenerative refrigerator is based on the basic principle of applying a pressure wave of a sine wave or other shape to a gas sealed in a pulse tube or the like, and generating a temperature gradient by compression and expansion accompanying local movement of the gas, and the high-temperature end is equipped with a mechanism such as a fin that exchanges heat with the high-temperature gas and releases the heat to the outside. In the present invention, instead of or in addition to such a mechanism, a heat exchange mechanism with a vapor compression refrigerator is provided in the high-temperature section.

[0009] In the present invention, the number of regenerative refrigerators and vapor compression refrigerators may be one or more. It is not necessary to use the same number of both. When multiple units are provided, the regenerative refrigerator may be configured to achieve cryogenic freezing in multiple stages, for example, by using a refrigerator that freezes from an intermediate temperature to temperature A and a refrigerator that freezes from temperature A to a target cryogenic temperature. The same applies to the vapor compression refrigerator. In addition, a plurality of regenerative refrigerators may be connected in parallel to one vapor compression refrigerator. In this case, each of the regenerative refrigerators is provided with its own heat exchange mechanism, and it is preferable that the vapor compression refrigerator and these heat exchange mechanisms are also connected in parallel.

[0010] In the present invention, the heat exchange mechanism can take various forms, for example: The heat exchange mechanism includes: It is installed inside the high temperature part of the regenerative refrigerator, The regenerative refrigerator may have a structure in which a plurality of gas flow paths through which gas used for cooling passes and a plurality of refrigerant flow paths through which the refrigerant passes are in contact with each other.

[0011] According to this aspect, heat exchange can be performed inside the high-temperature portion, and therefore, compared to the case where heat exchange is performed on the outer surface of the high-temperature portion, heat exchange can be performed more quickly and efficiently. In the present invention, in order to improve the cooling efficiency, it is preferable to reduce the temperature difference between the high temperature section and the low temperature section in the regenerative refrigerator, and in this sense, it is preferable to set the intermediate temperature low. However, unless rapid heat exchange is realized in the high temperature section, it is difficult to maintain the temperature of the high temperature section at the target intermediate temperature. The above embodiment is highly useful for performing such rapid heat exchange.

[0012] In addition, the internal space of the high-temperature section of a regenerative refrigerator is often relatively narrow, and it is often not easy to incorporate a heat exchange mechanism inside the high-temperature section. However, in the above-mentioned embodiment, this can be achieved by adopting a structure in which the gas flow path and the refrigerant flow path are in contact with each other. The gas flow path and the refrigerant flow path may each be one or more. In order to achieve faster heat exchange, it is preferable to provide a structure in which multiple flow paths are provided, each gas flow path is in contact with one or more refrigerant flow paths, and each refrigerant flow path is in contact with one or more gas flow paths. The specific structure can take various forms.

[0013] In addition, when the heat exchange mechanism has the above-mentioned configuration, The heat exchange mechanism includes: The gas flow passage may be formed along a flow direction inside the high temperature portion.

[0014] In the regenerative refrigerator, gas flows inside due to compression and expansion. In the above-described embodiment, the gas flow path does not impede the gas flow, which has the advantage that a significant decrease in the cooling efficiency of the regenerative refrigerator can be avoided.

[0015] In the present invention, Furthermore, a second heat exchange mechanism that is provided on the outer surface of the high temperature portion and performs the heat exchange may be provided.

[0016] This can further promote heat exchange in the high temperature portion. The second heat exchange mechanism can have various configurations, and may have a structure in which refrigerant piping is wrapped around the outer surface. Alternatively, the mechanism may be configured by wrapping a heat exchange material such as metal foam, a laminate of metal thin films, or metal microspheres, and performing heat exchange with the refrigerant through these. Furthermore, if the second heat exchange mechanism is considered as an auxiliary heat exchange mechanism, it is not necessarily limited to heat exchange with the vapor compression refrigerator, and may also perform heat exchange with room temperature or outside air.

[0017] Regardless of the form of the heat exchange mechanism, in the present invention, The regenerative refrigerator may further include a heat insulating mechanism that blocks heat transfer from the outside to the high temperature portion.

[0018] In this way, the outside means a part of the regenerative refrigerator that is exposed to an environment of the intermediate temperature or higher, or the outside air other than the regenerative refrigerator. According to the above-mentioned embodiment, the provision of a heat insulating mechanism can prevent the high temperature part from rising to the intermediate temperature or higher. As a result, the cooling efficiency during operation can be improved. Even when the operation is stopped, the high temperature part can be prevented from rising to about room temperature, so that when the operation is resumed, the high temperature part can be relatively easily lowered to the intermediate temperature, and the cooling efficiency when the operation is resumed can be improved. As a result, when cooling is not required, the operation of the refrigerator can be stopped, so that the cooling efficiency as a whole can be improved.

[0019] In the present invention, The refrigerator may further include a control device that controls operation of the regenerative refrigerator and the vapor compression refrigerator based on the intermediate temperature that is set based on power consumption of the regenerative refrigerator and the vapor compression refrigerator.

[0020] The cooling efficiency of the regenerative refrigerator and the vapor compression refrigerator depends on the intermediate temperature. As the intermediate temperature increases, the temperature difference cooled by the vapor compression refrigerator decreases, so the power consumption of the vapor compression refrigerator decreases, but the temperature difference cooled by the regenerative refrigerator increases, so the power consumption of the regenerative refrigerator increases. From this perspective, according to the above-mentioned aspect, the intermediate temperature is set based on the power consumption of both refrigerators to control the operation, so that it is possible to achieve the target power consumption.

[0021] When performing the above-mentioned control, The control device may use the intermediate temperature that is set so that the sum of the power consumption becomes a minimum value.

[0022] In this way, optimal cooling can be achieved from the viewpoint of power consumption. The intermediate temperature may be calculated during operation, or may be set in advance based on analysis or experimentation.

[0023] The above control can be realized in various ways. The control device includes: a power consumption data storage unit that stores in advance power consumption data indicating a relationship between power consumption and an operating temperature for each of the cold storage refrigerator and the vapor compression refrigerator; The power consumption control device may further include an intermediate temperature setting unit that sets the intermediate temperature based on the power consumption data.

[0024] In this way, it is possible to obtain the intermediate temperature that minimizes the total power consumption of the regenerative refrigerator and the vapor compression refrigerator based on the power consumption data prepared in advance. Also, according to this aspect, it is possible to calculate the optimal intermediate temperature during operation. Therefore, for example, even if the extremely low temperature that is the cooling target is modified, it is possible to dynamically calculate the optimal intermediate temperature.

[0025] The setting of the intermediate temperature and the operation control are not limited to the above, and for example, a method may be adopted in which the intermediate temperature is changed parametrically during operation, the associated power consumption is measured, and the intermediate temperature at which power consumption is minimized is searched for based on the results. Furthermore, a learning model may be generated by machine learning regression based on past operation results of the target cooling temperature, intermediate temperature, and power consumption to obtain the intermediate temperature at which power consumption is optimal according to the target cooling temperature, and this model may be used to set the intermediate temperature.

[0026] The cascade type cryogenic refrigerator of the present invention can be constructed in various ways, the regenerative refrigerator is selected to achieve the desired cryogenic cooling; The vapor compression refrigerator and the intermediate temperature may be selected so that a sum of power consumption of the regenerative refrigerator and power consumption of the vapor compression refrigerator is minimized.

[0027] In this way, a cascade type cryogenic refrigerator with high cooling efficiency as a whole can be constructed. In other words, in the case of the present invention, the factors that affect power consumption include the selection of the regenerative refrigerator and the vapor compression refrigerator, as well as the intermediate temperature during operation, and it becomes necessary to carry out the design while considering the effects in multiple dimensions. In the above embodiment, first, a regenerative refrigerator is selected so as to achieve the target cooling to a very low temperature. It is best to select one that consumes low power for this cooling. In the case of a regenerative refrigerator, the temperature of the high temperature part has a lower limit according to the temperature of the low temperature part, and the lower limit of the intermediate temperature is determined as a candidate value based on this. If the temperature of the high temperature part drops too low, it may have a negative effect on the motor and compressor of the regenerative refrigerator, so it is desirable to take these negative effects into consideration when determining the lower limit. When the candidate value for the intermediate temperature is determined, the vapor compression refrigerator selects a candidate unit that consumes the least amount of power when cooling to the candidate value. Then, the intermediate temperature and the vapor compression refrigerator are selected so that the power consumption of the regenerative refrigerator and the vapor compression refrigerator are minimized.

[0028] The present invention does not necessarily have to have all of the above-mentioned features, and may be configured by omitting or combining some of them as appropriate. In addition, the present invention can be configured in various forms, such as a cascade type cryogenic refrigerator, an operation control method for a cascade type cryogenic refrigerator, and a design method for a cascade type cryogenic refrigerator, in addition to the form of a cascade type cryogenic refrigerator. [Brief description of the drawings]

[0029] [Figure 1] 1 is an explanatory diagram showing the overall configuration of a cascade type cryogenic refrigerator as an embodiment; [Diagram 2] FIG. 2 is an explanatory diagram showing a configuration of a heat exchange mechanism. [Diagram 3] 1 is a flowchart of a design process for a cascade type cryogenic refrigerator. [Figure 4] 4 is a flowchart of an operation control process. [Diagram 5] FIG. 11 is an explanatory diagram showing a cooling effect in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The following describes a cascade type cryogenic refrigerator as an embodiment. In the embodiment, the cooling target is a superconducting coil, and an example of a device with a target cooling temperature of about 40 K is shown, but it can be configured as a device that can cool various cryogenic temperatures below liquid nitrogen regardless of the cooling temperature.

[0031] FIG. 1 is an explanatory diagram showing the overall configuration of a cascade type cryogenic refrigerator as an embodiment. The cascade type cryogenic refrigerator includes a regenerative refrigerator 1, a vapor compression refrigerator 17, a control device 100, and a refrigerant pipe 20.

[0032] The vapor compression refrigerator 17 is a device that performs cooling by compressing and expanding a gaseous refrigerant. In this embodiment, the cascade type cryogenic refrigerator performs cooling from the temperature of the place where the cascade type cryogenic refrigerator is installed (hereinafter simply referred to as room temperature) to a predetermined intermediate temperature. The intermediate temperature can be set arbitrarily, and the method for setting it will be described later, but it is expected to be set at a temperature of around 100K.

[0033] Various types of refrigerators, such as a Stirling refrigerator and a pulse tube refrigerator, can be used as the regenerative refrigerator 1. In this embodiment, a pulse tube refrigerator is used. In this embodiment, the regenerative refrigerator 1 performs cooling from an intermediate temperature to a very low temperature. As shown in the figure, the regenerative refrigerator 1 has a structure in which a pulse tube 14 and a regenerator 16 are connected. The space between the two is called a low-temperature section 15. In addition, high-temperature sections 200 are provided on both ends of the pulse tube 14 and the regenerator 16. The pulse tube 14 and the regenerator 16 are filled with a gas such as helium, and are connected to a compressor 19 via a switching valve 18. The compressor 19 applies a pressure wave to the gas, with a sine wave or other shape. The gas flows in response to this pressure, thereby cooling it. In addition, a buffer tank 10 is connected to the end of the pulse tube via an orifice valve 12 in order to adjust the phase difference of the pressure wave applied to the gas.

[0034] Heat insulating sections 13A and 13B are provided between the high temperature section 200 and the orifice valve 12 and between the high temperature section 200 and the switching valve 18. The heat insulating sections 13A and 13B are filled with various types of heat insulating materials. Even when the buffer tank 10, compressor 19, etc. of the regenerative refrigerator 1 are installed in a room temperature environment, the heat transfer from the outside to the high temperature part 200 is almost blocked by the action of the heat insulating parts 13A and 13B. Since the regenerative refrigerator 1 performs cooling from an intermediate temperature to an extremely low temperature, the high temperature part 200 is kept at an intermediate temperature, that is, a temperature of about 100K, during cooling. The action of the heat insulating parts 13A and 13B can suppress the temperature rise of the high temperature part 200, and the cooling efficiency can be improved. In addition, even when the operation is stopped, the temperature rise of the high temperature part 200 due to heat from the outside can be suppressed, and the power consumption required to lower the high temperature part 200 to the intermediate temperature when restarting the operation can be suppressed. As a result, the operation of the regenerative refrigerator 1 can be stopped when operation is not required, and power consumption can also be suppressed in this respect.

[0035] The high temperature section 200 of the regenerative refrigerator 1 and the vapor compression refrigerator 17 are connected by a refrigerant pipe 20. In this way, the refrigerant cooled to an intermediate temperature by the vapor compression refrigerator 17 can cool the high temperature section 200 to the intermediate temperature. In order to exchange heat with the refrigerant in the high temperature section 200, a heat exchange mechanism is built inside the high temperature section 200. The structure of the heat exchange mechanism will be described later.

[0036] The control device 100 controls the operation of the cascade type cryogenic refrigerator. The control device 100 can be realized by installing a computer program that realizes each of the functions shown in the figure in a computer equipped with a CPU and a memory. In this embodiment, each of the functions shown in the figure is configured as software, but some or all of these may be configured as hardware.

[0037] The power consumption data storage unit 116 stores the relationship between the cooling temperature difference and the power consumption for each of the cold storage refrigerator 1 and the vapor compression refrigerator 17 as power consumption data. The setting input unit 114 inputs settings such as a target cooling temperature through an operator's operation. The intermediate temperature setting unit 112 sets an intermediate temperature that minimizes power consumption according to the input cooling temperature. The method of setting the intermediate temperature will be described later, but the intermediate temperature is set based on the power consumption data so as to minimize the total power consumption. Based on the set intermediate temperature, the operation control unit 110 controls the operation of the vapor compression refrigerator 17 and the cold storage refrigerator 1. When the target cooling temperature is fixed in advance and the intermediate temperature is also set in advance, the setting input unit 114, the intermediate temperature setting unit 112, and the power consumption data storage unit 116 may be omitted.

[0038] 2 is an explanatory diagram showing the configuration of the heat exchange mechanism. The heat exchange mechanism is incorporated inside the high temperature section 200, cooled by the vapor compression refrigerator 17, and exchanges heat with the refrigerant flowing through the refrigerant pipe 20. FIG. 2(a) shows a perspective view of the heat exchange mechanism 210. The heat exchange mechanism 210 has a structure in which a plurality of flow passage layers 211a to 211d are laminated, each of which is formed by sandwiching a triangular corrugated metal plate between flat metal plates from above and below. In this embodiment, an example is shown in which the flow passages of the flow passage layers 211a and 211c and the flow passages of the flow passage layers 211b and 211d are laminated so as to be perpendicular to each other. Gas from the regenerative refrigerator 1 flows through the flow passage layers 211a and 211c, and refrigerant cooled by the vapor compression refrigerator 17 flows through the flow passage layers 211b and 211d. Since the flow passages of both are in contact with each other, heat exchange is performed, and the high temperature section 200 is cooled to the temperature of the refrigerant, that is, to the intermediate temperature. In the embodiment, the flow paths of the flow path layers 211a and 211c and the flow paths of the flow path layers 211b and 211d may be arranged in the same direction. In this case, the gas of the regenerative refrigerator 1 and the refrigerant cooled by the vapor compression refrigerator 17 may flow in the same direction or in opposite directions.

[0039] The heat exchange mechanism is not limited to the structure shown in Fig. 2(a). For example, the gas and refrigerant flow paths may be formed of through holes formed in a single metal plate. Alternatively, cylindrical pipes forming each flow path may be arranged. In this case, since a circular cross section of the pipe reduces the contact area with adjacent pipes, it is preferable to make the cross section rectangular or hexagonal so that the pipes can be arranged without gaps, or to fill the gaps between the pipes with metal or other material with high thermal conductivity.

[0040] 2(b) shows a schematic diagram of the internal structure of the high temperature section 200 in which the heat exchange mechanism is installed. The heat exchange mechanism 210 is attached inside the high temperature section 200 as shown in the figure. Since the gas in the regenerative refrigerator 1 flows in the vertical direction as indicated by the arrow A, the flow path layers 211a and 211c are installed along this direction. The flow path layers 211a and 211c through which the refrigerant flows are installed facing the direction of the arrow B. In the figure, the structure connecting the flow path layers 211a and 211c to the refrigerant pipes 20 is omitted. This allows heat exchange to be performed inside the high temperature section 200 without impeding the flow of gas in the regenerative refrigerator 1. However, the method of installing the heat exchange mechanism is not limited to this embodiment, and it can be incorporated in various embodiments.

[0041] In this embodiment, a heat exchange mechanism 220 is further provided on the outer surface of the high temperature section 200. The heat exchange mechanism 220 is configured by filling with metal foam, a laminate of metal thin films, metal microspheres, or the like, and is wrapped around the outer periphery of the high temperature section 200. The heat exchange mechanism 220 is connected to the refrigerant pipe 20 via a refrigerant inlet 221 and an outlet 222. The refrigerant flows into the heat exchange mechanism 220 as indicated by arrow C, and after heat exchange, is discharged as indicated by arrow D. The heat exchange mechanism 220 is auxiliary and may be omitted.

[0042] FIG. 3 is a flowchart of the design process for a cascade type cryogenic refrigerator. In the cascade type cryogenic refrigerator of the embodiment, elements such as the regenerative refrigerator 1, the vapor compression refrigerator 17, and the intermediate temperature setting must be determined while taking into consideration the overall power consumption. The design process shown in Figure 3 shows an example of the procedure for a designer to determine these elements.

[0043] First, a target cooling temperature is set (step S1). When a cascade type cryogenic refrigerator is used to realize superconductivity, a temperature of 20 to 40 K or the like is set as the target cooling temperature depending on the superconducting material.

[0044] Next, a regenerative refrigerator is selected based on this temperature (step S2). When using an existing regenerative refrigerator, one that can achieve the target cooling temperature is selected. When not limited to an existing regenerative refrigerator, a new refrigerator may be designed.

[0045] Then, a candidate for the intermediate temperature is set based on the regenerative refrigerator (step S3). The curve C1 in step S5 shows the relationship between the temperature and power consumption of the high-temperature part of the regenerative refrigerator. It shows that the higher the temperature of the high-temperature part, the greater the power consumption required for cooling. However, in the case of a regenerative refrigerator, it is known that the high-temperature part does not become lower than a certain temperature in principle. This is shown by the curve C1 in the figure being represented by a dashed line below a certain temperature. That is, when the target cooling temperature is determined, the lower limit temperature of the high-temperature part is determined, and generally, the higher the temperature of the high-temperature part, the greater the power consumption required for cooling to the target cooling temperature. Therefore, if only the power consumption of the regenerative refrigerator is taken into consideration, it is preferable to set the lower limit value of the high-temperature part as the intermediate temperature. In the embodiment, this temperature is set as the intermediate temperature candidate.

[0046] Next, candidates for vapor compression chillers are selected based on the intermediate temperature candidate (step S4). At this stage, it is not necessary to narrow down the candidates for vapor compression chillers to one. It is sufficient to select several types of existing vapor compression chillers that have the smallest power consumption for cooling near the intermediate temperature candidate as candidates. Of course, it is not limited to existing ones, and it is also possible to design a new one. The curve C2 in step S5 in the figure shows the power consumption required for cooling from room temperature to each temperature by the vapor compression refrigerator. As shown in the figure, it is generally known that power consumption is minimum within a certain temperature range. The reason why power consumption increases when the temperature is lower than this temperature range is because cooling to an extremely low temperature requires cooling at a low cooling efficiency. On the other hand, the reason why power consumption increases when the temperature is higher is because the structure of the vapor compression refrigerator determines the cooling temperature that can be efficiently achieved by the compression and expansion of the refrigerant, and therefore, in order to cool to a higher temperature, it becomes necessary to add heat to the refrigerant that has been cooled once. Thus, there is a temperature range in which power consumption is minimum in the vapor compression refrigerator. In step S4, a selection or design is made so that the intermediate temperature candidate falls within this temperature range in which power consumption is minimum.

[0047] Next, the vapor compression refrigerator and the intermediate temperature are set based on the total power consumption (step S5). The setting method is shown in the figure. In the figure, curve C1 represents the power consumption when cooling from each temperature to the target cooling temperature by the regenerative refrigerator. Curve C2 represents the power consumption when cooling from room temperature to each temperature. Curve Ctotal is the sum of curves C1 and C2, and represents the total power consumption required to cool from room temperature to the target cooling temperature when each temperature is the intermediate temperature. Since curve C2 has a minimum value, curve Ctotal also has a minimum value. The temperature corresponding to this minimum value is the optimal intermediate temperature in the sense that the power consumption is minimized.

[0048] By performing the above-mentioned evaluation for each candidate vapor compression chiller, the optimal intermediate temperature and total power consumption can be obtained for each vapor compression chiller. Then, by determining the vapor compression chiller and intermediate temperature that minimizes the total power consumption, this is the optimal cascade type cryogenic chiller configuration that achieves the target cooling temperature. Note that it is not necessary to prepare multiple candidate vapor compression chillers. When there is only one type of candidate, it is sufficient to set the optimal intermediate temperature for that vapor compression chiller.

[0049] Once the regenerative refrigerator, vapor compression refrigerator, and intermediate temperature have been set in this way, the next step is to design the heat exchange mechanisms of the regenerative refrigerator and vapor compression refrigerator (step S6). The heat exchange mechanism may adopt various structures, such as the structure explained in Fig. 2, but it is desirable to configure it so that it can achieve sufficiently fast and efficient heat exchange so that the high temperature part of the regenerative refrigerator can be maintained at the intermediate temperature.

[0050] Next, a refrigeration operation control process of the cascade type cryogenic refrigerator of the embodiment will be described. 4 is a flowchart of the operation control process. This process is executed by the control device 100. When the process starts, the control device 100 receives an operation from an operator and inputs a target cooling temperature (step S10). As explained above in step S1 of Fig. 3, the target cooling temperature is set at the design stage of the cascade cryogenic refrigerator, but the setting in step S10 of the control process assumes that a different cooling temperature will be set during actual operation. If operation is always performed only at the cooling temperature set at the design stage, the processes from step S10 to step S16 described below may be omitted.

[0051] Next, the control device 100 reads the power consumption data of the regenerative refrigerator that has been stored in advance (step S12). In this embodiment, the data is stored in advance in the power consumption data storage unit 116 of the control device 100 (see FIG. 1), but it may be downloaded from a server or the like via a network as necessary.

[0052] The control device 100 also reads the power consumption of the vapor compression refrigerator (step S14). This data may also be downloaded from a server or the like via a network as necessary.

[0053] Then, the intermediate temperature is set based on the total power consumption obtained by using these (step S16). The method of setting the intermediate temperature is shown in the figure. It is the same as the setting at the time of designing the cascade type cryogenic refrigerator (step S5 in FIG. 3). That is, the curve C1 shown in step S16 in FIG. 4 represents the power consumption when cooling from each temperature to the target cooling temperature by the regenerative refrigerator. Since the target cooling temperature is different from the design time, the curve is different from step S5 in FIG. 3. If the power consumption data of the regenerative refrigerator is prepared in the form of power consumption relative to the temperature difference between the high temperature part and the low temperature part, the set target cooling temperature becomes the temperature of the low temperature part, and the temperature on the horizontal axis when drawing the curve C1 becomes the temperature of the high temperature part, so the curve C1 can be obtained by shifting the power consumption data stored in advance left and right according to the cooling temperature.

[0054] Curve C2 in step S16 of Fig. 4 represents the power consumption when cooling from room temperature to each temperature. This curve C2 can be drawn directly from the power consumption data previously stored for the vapor compression refrigerator. Curve Ctotal is the sum of curves C1 and C2, and represents the total power consumption required to cool from room temperature to the target cooling temperature when each temperature is set as an intermediate temperature. By selecting the temperature at which the power consumption of curve Ctotal is minimized, it is possible to set the optimal intermediate temperature in the sense of minimizing the total power consumption. Once the intermediate temperature is set in this manner, the control device 100 controls the operation of each refrigerator (step S18).

[0055] According to the cascade type cryogenic refrigerator of the embodiment described above, the cooling efficiency as a whole can be improved, one example of which is shown below. FIG. 5 is an explanatory diagram showing the cooling effect in the embodiment. The left side shows the cooling efficiency COP when cooling from 300K to 20K using only a regenerative refrigerator. It is known that the cooling efficiency of existing regenerative refrigerators is about 0.03. Based on this cooling efficiency, the power consumption is calculated to be 333W. Meanwhile, on the right side, the cooling efficiency of the cascade type cryogenic refrigerator of the embodiment is shown. When the intermediate temperature is 100K, the vapor compression refrigerator cools from 300K to 100K, and the regenerative refrigerator cools from 100K to 20K. The regenerative refrigerator can achieve a cooling efficiency of about 0.15, which is higher than 0.03. The vapor compression refrigerator can achieve a cooling efficiency of 0.4. When the power consumption is calculated based on these cooling efficiencies, it is 168W + 67W, totaling 235W. Therefore, by using a cascade-type cryogenic refrigerator, power consumption can be reduced from 333 W to 235 W, making it possible to achieve a power saving of approximately 29% (=(333-235) / 333×100).

[0056] It is not necessary to have all of the various features described in the above embodiments, and some of them may be omitted or combined as appropriate. Furthermore, the cascade type cryogenic refrigerator of the present invention is not limited to the embodiment, and various modified examples can be configured. For example, in the embodiment, a structural example using one regenerative refrigerator and one vapor compression refrigerator is shown, but a plurality of refrigerators may be used. In this case, the plurality of regenerative refrigerators may be connected in parallel to one vapor compression refrigerator. [Industrial Applicability]

[0057] The present invention can be utilized to achieve cryogenic cooling below liquid nitrogen. [Explanation of symbols]

[0058] 1 Cold storage refrigerator 10 Buffer Tank 12 Orifice valve 13A, 13B Insulation section 14 Pulse tube 15 Low temperature section 16 Regenerator 17 Vapor compression refrigerator 18 Switching valve 19 Compressor 20 Refrigerant piping 100 Control device 110 Operation control unit 112 Intermediate temperature setting section 114 Setting input section 116 Power consumption data storage unit 200 High temperature section 210 Heat exchange mechanism 211a~211d Flow path layer 220 Heat exchange mechanism 221 Inlet 222 Outlet

Claims

1. A cascade type cryogenic refrigerator that realizes cryogenic cooling lower than the temperature of liquid nitrogen by connecting multiple types of refrigerators, a vapor compression refrigerator that cools a refrigerant to a predetermined intermediate temperature; a regenerative refrigerator designed so that a high temperature section is at the intermediate temperature and a low temperature section is at the extremely low temperature; a heat exchange mechanism for exchanging heat between the refrigerant of the vapor compression refrigerator and a high-temperature portion of the regenerative refrigerator, The heat exchange mechanism includes: It is installed inside the high temperature part of the regenerative refrigerator, A cascade type cryogenic refrigerator has a structure in which a plurality of gas flow paths through which the gas used for cooling in the regenerative refrigerator passes and a plurality of refrigerant flow paths through which the refrigerant passes are in contact with each other.

2. A cascade type cryogenic refrigerator according to claim 1, The heat exchange mechanism includes: The gas flow path is formed along a flow direction inside the high temperature portion.

3. A cascade type cryogenic refrigerator according to claim 1 or 2, The cascade type cryogenic refrigerator further comprises a second heat exchange mechanism provided on an outer surface of the high temperature portion and performing the heat exchange.

4. A cascade type cryogenic refrigerator according to any one of claims 1 to 3, a cascade type cryogenic refrigerator comprising a heat insulating mechanism for blocking heat transfer from the outside to the high temperature portion of the regenerative refrigerator.

5. A cascade type cryogenic refrigerator according to any one of claims 1 to 4, a cascade type cryogenic refrigerator comprising a control device that controls operation of the regenerative refrigerator and the vapor compression refrigerator based on the intermediate temperature that is set based on the power consumption of the regenerative refrigerator and the vapor compression refrigerator.

6. A cascade type cryogenic refrigerator according to claim 5, The control device is a cascade type cryogenic refrigerator using the intermediate temperature that is set so that the sum of the power consumption is a minimum value.

7. A cascade type cryogenic refrigerator according to claim 5 or 6, The control device includes: a power consumption data storage unit that stores in advance power consumption data indicating a relationship between power consumption and an operating temperature for each of the cold storage refrigerator and the vapor compression refrigerator; and an intermediate temperature setting unit that sets the intermediate temperature based on the power consumption data.

8. A cascade type cryogenic refrigerator according to any one of claims 1 to 7, the regenerative refrigerator is selected to achieve the desired cryogenic cooling; A cascade type cryogenic refrigerator, wherein the vapor compression refrigerator and the intermediate temperature are selected so that a sum of power consumption of the regenerative refrigerator and power consumption of the vapor compression refrigerator is minimized.

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