JP7611573B2 - Cascade type cryogenic refrigerator - Google Patents

Description

The present invention relates to technology that achieves extremely low temperatures below that of liquid nitrogen (77.3K).

Generally, to realize superconductivity, an environment of about 20 to 40 K is required. A regenerative refrigerator is often used as a device to realize such cooling. Known examples of regenerative refrigerators include Stirling refrigerators and pulse tube refrigerators.
Furthermore, 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.

JP 2019-82294 A

Traditionally, research and development has focused on realizing superconductivity and its application technologies, with little consideration given to the efficiency of cooling required to achieve superconductivity. Cryogenic refrigeration requires a huge amount of power for cooling and has low cooling efficiency, but these issues have not been taken into consideration. As a result, superconductivity has become a technology used only in fields where the need is so great that cooling efficiency is not an issue, such as MRI, linear motor cars, and nuclear fusion reactors.

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.
Improvement in the efficiency of refrigeration to extremely low temperatures below the temperature of liquid nitrogen (77.3 K) is required not only for superconductivity but also for other purposes. In view of the above problem, the present invention aims to improve the efficiency of refrigeration to achieve such extremely low temperatures.

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.

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.

Various types of regenerative refrigerators can be used, including Stirling refrigerators and pulse tube refrigerators. Conventionally, regenerative refrigerators work on the basic principle of applying a sine wave or other pressure wave to a gas sealed in a pulse tube or the like, and generating a temperature gradient by the compression and expansion that accompanies the local movement of this gas. 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.

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 realize cryogenic freezing in multiple stages, such as 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 plurality of 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.

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.

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.

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.

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.

In a regenerative refrigerator, gas flows inside due to compression and expansion. The above-mentioned configuration has the advantage that the gas flow path does not impede the gas flow, which prevents a significant decrease in the cooling efficiency of the regenerative refrigerator.

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.

This can further promote heat exchange in the high temperature area. The second heat exchange mechanism can have various configurations, but for example, it may have a structure in which the refrigerant piping is wrapped around the outer surface. It may also be a mechanism in which a heat exchange material such as a metal foam, a laminate of metal thin films, or metal microspheres is wrapped around the mechanism, and heat exchange with the refrigerant is performed 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 it may also be a mechanism that exchanges heat with room temperature or outside air, etc.

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.

In this way, the outside means the part of the regenerative refrigerator that is exposed to an environment of above the intermediate temperature, 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 above the intermediate temperature. As a result, the cooling efficiency during operation can be improved. In addition, even when operation is stopped, the high temperature part can be prevented from rising to about room temperature, so that when operation is resumed, the high temperature part can be relatively easily lowered to the intermediate temperature, and the cooling efficiency when restarting the operation can also be improved. As a result, when cooling is not required, it is possible to stop the operation of the refrigerator, and the cooling efficiency can be improved overall.

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.

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, and the power consumption of the vapor compression refrigerator decreases. However, the temperature difference cooled by the regenerative refrigerator increases, and the power consumption of the regenerative refrigerator increases. From this perspective, according to the above aspect, the intermediate temperature is set based on the power consumption of both refrigerators to control operation, making it possible to achieve the target power consumption.

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.

In this way, optimal cooling can be achieved in terms of power consumption. Such intermediate temperatures may be calculated during operation, or may be set in advance based on analysis or experimentation.

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.

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

The setting of the intermediate temperature and the operation control are not limited to the above. For example, a method may be used 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.

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.

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.

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 to the aspect of a cascade-type cryogenic refrigerator, the present invention can also be configured in various other aspects, such as an operation control method for a cascade-type cryogenic refrigerator, and a design method for a cascade-type cryogenic refrigerator.

1 is an explanatory diagram showing the overall configuration of a cascade type cryogenic refrigerator as an embodiment; FIG. 2 is an explanatory diagram showing a configuration of a heat exchange mechanism. 1 is a flowchart of a design process for a cascade type cryogenic refrigerator. 4 is a flowchart of an operation control process. FIG. 11 is an explanatory diagram showing the cooling effect in the embodiment.

Below, we will explain a cascade type cryogenic refrigerator as an example. In the example, we will show an example of a device that cools a superconducting coil and has a target cooling temperature of about 40 K, but regardless of the cooling temperature, it is possible to configure the device to cool various cryogenic temperatures below liquid nitrogen.

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

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 assumed to be a temperature of around 100K.

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.

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, i.e., a temperature of about 100K, during cooling. The heat insulating parts 13A and 13B can suppress the temperature rise of the high temperature part 200, and can improve the cooling efficiency. 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 the operation is restarted can be suppressed. As a result, the operation of the regenerative refrigerator 1 can be stopped when the operation is not required, and power consumption can also be suppressed in this respect.

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 in the high temperature section 200. The structure of the heat exchange mechanism will be described later.

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 memory. In this embodiment, each of the functions shown in the figure is configured as software, but some or all of these may also be configured as hardware.

The power consumption data storage unit 116 stores the relationship between the cooling temperature difference and the power consumption for each of the regenerative 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 at which power consumption is minimized 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 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.

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 stacked, 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 stacked 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, i.e., 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.

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.

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 so as to follow this direction. The flow path layers 211a and 211c through which the refrigerant flows are installed in the direction indicated by the arrow B. In the figure, the structure connecting the flow path layers 211a and 211c to the refrigerant pipe 20 is omitted.
This makes it possible to perform heat exchange 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.

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 constructed by filling it with foamed metal, a laminate of thin metal films, metal microspheres, etc., and is wrapped around the outer circumference of the high temperature section 200. The heat exchange mechanism 220 is connected to the refrigerant piping 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, so it may be omitted.

FIG. 3 is a flow chart of a design process for a cascade 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 Fig. 3 shows an example of the procedure by which a designer determines these elements.

First, the target cooling temperature is set (step S1). When using a cascade-type cryogenic refrigerator to achieve superconductivity, the target cooling temperature is set to a temperature of 20 to 40 K depending on the superconducting material.

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 existing regenerative refrigerators, a new one may be designed.

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 of the high-temperature part of the regenerative refrigerator and the power consumption. 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 in principle the high-temperature part does not drop below a certain temperature. This is shown by the curve C1 in the figure being shown as a dashed line below a certain temperature. In other words, 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.

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 a new one may be designed.
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 needs to be performed with 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, in the vapor compression refrigerator, there is a temperature range in which power consumption is minimum. In step S4, a temperature range in which the intermediate temperature candidate falls within this temperature range in which power consumption is minimum is selected or designed.

Next, the vapor compression refrigerator and 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 using 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 set as the intermediate temperature. Since curve C2 has a minimum value, a minimum value also appears in curve Ctotal. The temperature corresponding to this minimum value is the optimal intermediate temperature in the sense that it minimizes power consumption.

By performing the above evaluation for each candidate vapor compression refrigerator, the optimal intermediate temperature and total power consumption can be determined for each vapor compression refrigerator. Then, by determining the vapor compression refrigerator and intermediate temperature that minimizes the total power consumption, this will be the optimal cascade type cryogenic refrigerator configuration that achieves the target cooling temperature. Note that it is not necessary to prepare multiple candidate vapor compression refrigerators. If there is only one type of candidate, it is sufficient to set the optimal intermediate temperature for that vapor compression refrigerator.

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 for the regenerative refrigerator and vapor compression refrigerator (step S6). The heat exchange mechanism can adopt various structures, including the structure described 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.

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, which 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.

Next, the control device 100 reads the power consumption data of the regenerative refrigerator that has been stored in advance (step S12). In the 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 also be downloaded from a server or the like via a network as necessary.

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 the network as necessary.

Then, the intermediate temperature is set based on the total power consumption obtained by using these (step S16). The method for 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 will be 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 will be the temperature of the low temperature part, and the temperature on the horizontal axis when drawing the curve C1 will be 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.

The 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. The curve Ctotal is the sum of the curves C1 and C2, and represents the total power consumption required for cooling from room temperature to the target cooling temperature when each temperature is set as the intermediate temperature. By selecting the temperature at which the power consumption of the curve Ctotal is the minimum, it is possible to set the optimal intermediate temperature in the sense of the minimum total power consumption.
When the intermediate temperature is set in this manner, the control device 100 controls the operation of each refrigerator (step S18).

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 an actual regenerative refrigerator is about 0.03. Based on this cooling efficiency, the power consumption is calculated to be 333W.
On the other hand, the right side shows the cooling efficiency of the cascade type cryogenic refrigerator of the embodiment. 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, which is a total of 235W.
Therefore, by using a cascade type cryogenic refrigerator, the 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).

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.

The present invention can be used to achieve extremely low temperatures below liquid nitrogen.

Reference Signs List 1 Regenerative 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 section 112 Intermediate temperature setting section 114 Setting input section 116 Power consumption data storage section 200 High temperature section 210 Heat exchange mechanism 211a to 211d Flow passage layer 220 Heat exchange mechanism 221 Inlet 222 Outlet

Claims (8)

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. The 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. The 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. The 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. The 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. The 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. The 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. The 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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