WO2024014117A1

WO2024014117A1 - Cryogenic system and control method for cryogenic system

Info

Publication number: WO2024014117A1
Application number: PCT/JP2023/018541
Authority: WO
Inventors: 貴士平山
Original assignee: 住友重機械工業株式会社
Priority date: 2022-07-13
Filing date: 2023-05-18
Publication date: 2024-01-18
Also published as: JP2024010936A

Abstract

A cryogenic system (100) comprises: a cryogenic refrigerator (10); and a controller (60). The cryogenic refrigerator (10) is provided with a first cylinder (16a), a second cylinder (16b) that is provided with, at an axially middle portion, a heat absorption part (46) to be thermally connected to a heat source, a first temperature sensor (51) that measures the temperature at one axial end of the second cylinder (16b), a second temperature sensor (52) that measures the temperature at the other axial end of the second cylinder (16b), and a third temperature sensor (53) that measures the temperature at the heat absorption part (46). The controller (60) is configured to: acquire a first measured temperature from the first temperature sensor (51), a second measured temperature from the second temperature sensor (52), and a third measured temperature from the third temperature sensor (53); set the upper limit temperature for the heat absorption part (46) on the basis of the first measured temperature, the second measured temperature, and the axial position of the heat absorption part (46); and control the heat source such that the third measured temperature is equal to or lower than the upper limit temperature of the heat absorption part (46).

Description

Cryogenic systems and how to control them

The present invention relates to a cryogenic system and a method of controlling a cryogenic system.

Conventionally, cryogenic refrigerators typified by Gifford-McMahon (GM) refrigerators have been known. Cryogenic refrigerators are used to cool a variety of cryogenic systems.

Japanese Patent Application Publication No. 2001-116379

One exemplary objective of certain embodiments of the present invention is to efficiently cool cryogenic systems.

According to an aspect of the invention, a cryogenic system includes a cryogenic refrigerator and a controller. The cryogenic refrigerator includes a first cylinder and a second cylinder provided axially in series with the first cylinder, the second cylinder having an endothermic part thermally connected to a heat source at an axially intermediate portion thereof. and a first temperature sensor that measures a first measurement temperature at one axial end of the second cylinder that is close to the first cylinder, and a second temperature sensor that measures a second measurement temperature at the other axial end of the second cylinder that is remote from the first cylinder. It includes a second temperature sensor that measures temperature, and a third temperature sensor that measures a third measured temperature at the endothermic part. The controller obtains a first measured temperature from the first temperature sensor, a second measured temperature from the second temperature sensor, and a third measured temperature from the third temperature sensor, and obtains the first measured temperature, the second measured temperature, and The upper limit temperature of the heat absorber is set based on the axial position of the heat absorber, and the heat source is controlled so that the third measured temperature is equal to or lower than the upper limit temperature of the heat absorber.

According to one aspect of the present invention, a method of controlling a cryogenic system is provided. The cryogenic system includes a cryogenic refrigerator including a first cylinder and a second cylinder arranged in series in the axial direction, and the second cylinder has a heat absorption part thermally connected to a heat source at an axially intermediate part thereof. Equipped with The method includes: measuring a first measured temperature at one axial end of a second cylinder near the first cylinder; and measuring a second measured temperature at the other axial end of the second cylinder remote from the first cylinder. measuring a third measured temperature at the endothermic part; and setting an upper limit temperature of the endothermic part based on the first measured temperature, the second measured temperature, and the axial position of the endothermic part; controlling the heat source so that the third measured temperature is equal to or lower than the upper limit temperature of the heat absorption section.

Note that arbitrary combinations of the above constituent elements and mutual substitution of constituent elements and expressions of the present invention among methods, devices, systems, etc. are also effective as aspects of the present invention.

According to the present invention, a cryogenic system can be efficiently cooled.

FIG. 1 is a diagram schematically showing a cryogenic system according to an embodiment. 2 is a diagram schematically showing a cryogenic refrigerator that can be applied to the cryogenic system shown in FIG. 1. FIG. FIGS. 3(a) and 3(b) are graphs showing experimental results by the present inventor regarding the embodiment. FIGS. 4(a) and 4(b) are graphs showing experimental results by the present inventor regarding the embodiment. It is a flow chart showing a control method of a cryogenic system concerning an embodiment. 6 is a flowchart showing an example of a control process (S30) for the refrigerant gas line shown in FIG. 5. FIG. FIG. 7 is a diagram schematically showing a cryogenic system according to another embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are denoted by the same reference numerals, and overlapping explanations will be omitted as appropriate. The scales and shapes of the parts shown in the figures are set for convenience to facilitate explanation, and should not be interpreted in a limited manner unless otherwise stated. The embodiments are illustrative and do not limit the scope of the present invention. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

FIG. 1 is a diagram schematically showing a cryogenic system 100 according to an embodiment. FIG. 2 is a diagram schematically showing a cryogenic refrigerator 10 that can be applied to the cryogenic system 100 shown in FIG. 1. The external appearance of the cryogenic refrigerator 10 is shown in FIG. 1, and the internal structure of the cryogenic refrigerator 10 is shown in FIG. The cryogenic refrigerator 10 is, for example, a two-stage Gifford-McMahon (GM) refrigerator.

In this embodiment, cryogenic system 100 may be utilized as a cryogenic liquid storage device. Thus, in addition to the cryogenic refrigerator 10, the cryogenic system 100 includes a vacuum vessel 110 for storing, for example, liquid helium or other cryogenic liquid 102. The cryogenic refrigerator 10 cools the stored cryogenic liquid 102 to a cryogenic temperature below its liquefaction temperature (approximately 4 K in the case of liquid helium).

The vacuum container 110 includes an outer tank 112 and an inner tank 114. A vacuum insulation layer 116 is formed between the outer tank 112 and the inner tank 114, and the outer tank 112 is configured to separate the vacuum insulation layer 116 from the surrounding environment of the cryogenic system 100 (e.g., room temperature, atmospheric pressure environment). be done. The vacuum insulation layer 116 may be provided with an insulation structure such as, for example, multilayer insulation (MLI). Moreover, the inner tank 114 is configured to contain the cryogenic liquid 102 therein and to separate the cryogenic liquid 102 from the vacuum insulation layer 116 . The outer tank 112 and the inner tank 114 are formed of a metallic material, such as stainless steel, or other suitable high-strength material to withstand internal and external pressure differences.

The cryogenic refrigerator 10 includes a compressor 12 and an expander 14. The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, increase the pressure of the recovered working gas, and supply the working gas to the expander 14 again. The working gas, also referred to as refrigerant gas, is typically helium gas, although other suitable gases may be used.

The expander 14 includes a refrigerator cylinder 16, a displacer assembly 18, and a refrigerator housing 20. Refrigerator housing 20 is coupled with refrigerator cylinder 16 to thereby define an airtight container housing displacer assembly 18 . Refrigerator cylinder 16 and refrigerator housing 20 are formed of a metallic material, such as stainless steel, or other suitable high strength material.

The expander 14 is installed in the vacuum container 110 with the refrigerator cylinder 16 inserted into the inner tank 114 of the vacuum container 110 and the refrigerator housing 20 attached to the outside of the vacuum container 110. As an example, the expander 14 is installed at the top of the vacuum container 110 so that its central axis coincides with the vertical direction. However, the mounting location and mounting posture of the expander 14 are not limited to this. For example, the expander 14 may be installed at the bottom of the vacuum container 110. Further, the expander 14 can be installed in a desired posture, and may be installed in the vacuum container 110 with its central axis aligned diagonally or horizontally.

The refrigerator cylinder 16 has a first cylinder 16a and a second cylinder 16b that extend in the axial direction (in the vertical direction in FIGS. 1 and 2). The second cylinder 16b is provided in series with the first cylinder 16a in the axial direction. The first cylinder 16a and the second cylinder 16b are, for example, members having a cylindrical shape, and the second cylinder 16b has a smaller diameter than the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are arranged coaxially, and the lower end of the first cylinder 16a is rigidly connected to the upper end of the second cylinder 16b.

The displacer assembly 18 includes a first displacer 18a and a second displacer 18b. The first displacer 18a and the second displacer 18b are, for example, members having a cylindrical shape, and the second displacer 18b has a smaller diameter than the first displacer 18a. The first displacer 18a and the second displacer 18b are coaxially arranged.

The first displacer 18a is housed in the first cylinder 16a, and the second displacer 18b is housed in the second cylinder 16b. The first displacer 18a can be reciprocated in the axial direction along the first cylinder 16a, and the second displacer 18b can be reciprocated in the axial direction along the second cylinder 16b. The first displacer 18a and the second displacer 18b are connected to each other and move together.

In this document, in order to explain the positional relationship between the components of the cryogenic refrigerator 10, for convenience, the side near the top dead center of the reciprocating motion of the displacer in the axial direction is referred to as "upper", and the side closer to the bottom dead center is referred to as "lower". ”. The top dead center is the position of the displacer where the volume of the expansion space is maximum, and the bottom dead center is the position of the displacer where the volume of the expansion space is the minimum. During operation of the cryogenic refrigerator 10, a temperature gradient occurs in which the temperature decreases from the upper side to the lower side in the axial direction, so the upper side can also be called the high temperature side and the lower side can also be called the low temperature side.

The first displacer 18a accommodates the first regenerator 26. The first regenerator 26 is formed by filling the cylindrical main body of the first displacer 18a with, for example, a wire mesh made of copper or other suitable first regenerator material. The upper lid part and the lower lid part of the first displacer 18a may be provided as separate members from the main body part of the first displacer 18a, and the upper lid part and the lower lid part of the first displacer 18a are fastened, welded, etc. as appropriate. The first regenerator material may be fixed to the main body by means such that the first regenerator material is accommodated in the first displacer 18a.

Similarly, the second displacer 18b accommodates the second regenerator 28. The second regenerator 28 is configured by filling the cylindrical main body of the second displacer 18b with a non-magnetic regenerator material such as bismuth, a magnetic regenerator material such as HoCu ₂ , or any other appropriate second regenerator material. is formed by. The second cold storage material may be shaped into particles. The upper lid part and the lower lid part of the second displacer 18b may be provided as separate members from the main body part of the second displacer 18b, and the lower lid part of the upper lid part of the second displacer 18b may be fastened, welded, etc. as appropriate. The second regenerator material may be fixed to the main body by means such that the second regenerator material is accommodated in the second displacer 18b.

The displacer assembly 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. For heat exchange with the desired object or medium to be cooled by the cryogenic refrigerator 10, the expander 14 comprises a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper lid part of the first displacer 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower lid portion of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower lid part of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fixed to the lower part of the first cylinder 16a so as to surround the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower part of the second cylinder 16b so as to surround the second expansion chamber 34. has been done. The first cooling stage 33 and the second cooling stage 35 are formed of, for example, pure copper (eg, oxygen-free copper, tough pitch copper, etc.) or other high heat conductive metal.

The first regenerator 26 is connected to the upper chamber 30 through a working gas passage 36a formed in the upper lid of the first displacer 18a, and is connected to the upper chamber 30 through a working gas passage 36b formed in the lower lid of the first displacer 18a. 1 expansion chamber 32. The second regenerator 28 is connected to the first regenerator 26 through a working gas passage 36c formed from the lower lid of the first displacer 18a to the upper lid of the second displacer 18b. Further, the second regenerator 28 is connected to the second expansion chamber 34 through a working gas flow path 36d formed in the lower lid portion of the second displacer 18b.

The working gas flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 is not limited to the clearance between the refrigerator cylinder 16 and the displacer assembly 18; A first seal 38a and a second seal 38b may be provided to guide the liquid to the vessel 28. The first seal 38a may be attached to the upper lid portion of the first displacer 18a so as to be disposed between the first displacer 18a and the first cylinder 16a. The second seal 38b may be attached to the upper lid portion of the second displacer 18b so as to be disposed between the second displacer 18b and the second cylinder 16b.

Additionally, the expander 14 includes a pressure switching valve 40 and a drive motor 42. The pressure switching valve 40 is housed in the refrigerator housing 20, and the drive motor 42 is attached to the refrigerator housing 20.

As shown in FIG. 2, the pressure switching valve 40 includes a high pressure valve 40a and a low pressure valve 40b, and is configured to generate periodic pressure fluctuations within the refrigerator cylinder 16. A working gas discharge port of the compressor 12 is connected to the upper chamber 30 via a high pressure valve 40a, and a working gas inlet of the compressor 12 is connected to the upper chamber 30 via a low pressure valve 40b. High pressure valve 40a and low pressure valve 40b are configured to open and close selectively and alternately (ie, when one is open, the other is closed). High-pressure (for example, 2 to 3 MPa) working gas is supplied from the compressor 12 to the expander 14 through the high-pressure valve 40a, and low-pressure (for example, 0.5 to 1.5 MPa) working gas is compressed from the expander 14 through the low-pressure valve 40b. It is recovered by machine 12. For understanding, the direction of flow of the working gas is indicated by arrows in FIG.

A drive motor 42 is provided to drive the reciprocating motion of the displacer assembly 18. The drive motor 42 is connected to a displacer drive shaft 44 via a motion conversion mechanism 43 such as a Scotch yoke mechanism. The motion conversion mechanism 43, like the pressure switching valve 40, is housed in the refrigerator housing 20. The displacer drive shaft 44 extends from the motion converting mechanism 43 through the refrigerator housing 20 into the upper chamber 30, and is fixed to the upper lid portion of the first displacer 18a. A third seal 38c is provided to prevent leakage of working gas from the upper chamber 30 to the refrigerator housing 20 (which may be maintained at low pressure as described above). The third seal 38c may be attached to the refrigerator housing 20 so as to be disposed between the refrigerator housing 20 and the displacer drive shaft 44.

When the drive motor 42 is driven, the rotational output of the drive motor 42 is converted into an axial reciprocating motion of the displacer drive shaft 44 by the motion conversion mechanism 43, and the displacer assembly 18 reciprocates in the axial direction within the refrigerator cylinder 16. . Further, the drive motor 42 is connected to the high pressure valve 40a and the low pressure valve 40b so as to selectively and alternately open and close these valves.

When the compressor 12 and the drive motor 42 are operated, the cryogenic refrigerator 10 generates periodic volume fluctuations and working gas pressure fluctuations in synchronization with this in the first expansion chamber 32 and the second expansion chamber 34. , thereby forming a refrigeration cycle, in which the first cooling stage 33 and the second cooling stage 35 are cooled to a desired cryogenic temperature. The first cooling stage 33 may be cooled to a first cooling temperature ranging from about 20K to about 40K, for example. The second cooling stage 35 may be cooled to a second cooling temperature (eg, about 1K to about 4K) lower than the first cooling temperature.

By the way, it is known that in addition to the first cooling stage 33 and the second cooling stage 35, the expander 14 can also absorb heat on the refrigerator cylinder 16, for example, at the axially intermediate portion of the second cylinder 16b. Such a heat absorber 46 is cooled to a cooling temperature based on the axial temperature distribution on the refrigerator cylinder 16, for example the second cylinder 16b, and the axial position of the heat absorber 46, and provides some refrigeration capacity at this cooling temperature. can do. The cooling temperature of the heat absorption section 46 is between the first cooling temperature of the first cooling stage 33 and the second cooling temperature of the second cooling stage 35. The heat absorbing portion 46 is located at a normalized axial position on the second cylinder 16b (that is, a dimensionless axial position where the positions of the first cooling stage 33 and the second cooling stage 35 are 0 and 1, respectively), for example, 1. It may be in the range of /4 to 3/4.

In a typical usage scene of the cryogenic refrigerator 10, an object to be cooled is thermally connected to either the first cooling stage 33 or the second cooling stage 35 and cooled depending on the desired cooling temperature. Nothing is connected to the heat absorption section 46 on the second cylinder 16b, and the refrigerating capacity of the heat absorption section 46 is not utilized.

If the refrigeration capacity of the heat sink 46 could also be utilized in addition to the two cooling stages, this could lead to more efficient cooling of the cryogenic system 100. However, the heat input to the heat absorption part 46 may affect the cooling temperature of the cooling stage, for example, the second cooling stage 35 (the large heat input to the heat absorption part 46 may cause the temperature of the second cooling stage 35 to increase. ). Typically, in the cryogenic system 100, in order to maintain the object to be cooled at a desired cooling temperature, the cryogenic refrigerator 10 is required to operate so that the cooling stage temperature does not exceed a predetermined temperature limit. The reason why cooling using the heat absorbing part 46 has not been used so far is because there is a concern about the risk of temperature increase in the cooling stage due to heat input to the heat absorbing part 46.

As will be described in detail below, the present inventor has discovered that by keeping the temperature of the heat absorbing section 46 below a certain upper limit temperature, the temperature increase in the second cooling stage 35 can be prevented or minimized. . From this point of view, in this embodiment, the cryogenic system 100 is configured to control the heat source so as to optimize the heat input from the heat source (that is, the object to be cooled) to the heat absorption section 46. Optimization of heat input is achieved by keeping the temperature of the heat absorbing section 46 below the upper limit temperature.

FIGS. 3(a) and 3(b) are graphs showing experimental results by the present inventors in accordance with the embodiment. In this experiment, a heater for simulating heat input to the heat absorption part 46 is installed in the heat absorption part 46. The position of the heater, in other words, the position of the heat absorption part 46 is slightly lower temperature side than the center in the axial direction, specifically, the standardized axial position on the second cylinder 16b (as described above, the position of the first cooling stage 33 is 0). , the second cooling stage 35 is about 0.54. Further, a heater is also installed on the second cooling stage 35 in order to apply a heat load (for example, a rated heat load of 1.5 W). The cryogenic refrigerator 10 is operated so as to maintain the first cooling stage 33 at a constant temperature (for example, 43 K) while applying a rated heat load to the second cooling stage 35.

FIG. 3(a) shows the relationship between the normalized heater output representing the heat input to the heat absorption section 46 and the temperature rise of the second cooling stage 35. The temperature rise of the second cooling stage 35 represents a temperature rise with respect to the target cooling temperature (for example, 4K) of the second cooling stage 35. FIG. 3(b) shows the relationship between the normalized axial position on the second cylinder 16b and the temperature, that is, how the axial temperature distribution on the second cylinder 16b changes depending on the normalized heater output. shown. In FIGS. 3(a) and 3(b), the temperature measurement results when the normalized heater output is zero (that is, there is no heat input to the heat absorption part 46) are shown with circle symbols, and the normalized heater output The temperature measurement results when is 0.085, 0.31, and 0.45 are shown by square, triangle, and diamond symbols, respectively.

Referring to FIG. 3(a), when the normalized heater output is zero, the temperature rise of the second cooling stage 35 is 0K (circle symbol), and the normalized heater output is 0.085, 0.31, 0.45. It can be seen that as the temperature increases, the temperature rise of the second cooling stage 35 also increases (square, triangle, and diamond symbols). Specifically, when the standardized heater output is 0.085, the temperature rise is about 0.04 K (square symbol), and when the standardized heater output is 0.31, the temperature rise is about 0.09 K (triangle symbol), and the standardized heater At an output of 0.45, the temperature rise is approximately 0.17K (diamond symbol).

Based on the inventor's knowledge and experience, in some applications of the cryogenic refrigerator 10, such as liquid helium cooling, where the target cooling temperature of the second cooling stage 35 is approximately 4K, the second cooling stage 35 is often The permissible temperature rise of the stage 35 is desirably up to about 0.1K, and is required to be up to about 0.2K at the maximum.

It is understood from FIG. 3(a) that the normalized heater output threshold Th1 indicated by the broken line in FIG. 3(a) represents one important boundary. If the heat input to the heat absorption section 46 is below this threshold value Th1, the temperature rise in the second cooling stage 35 is suppressed to a relatively small value within about 0.1K. On the other hand, when the heat input to the heat absorbing section 46 exceeds this threshold value Th1, the temperature rise in the second cooling stage 35 changes its aspect, becomes proportionally larger in conjunction with the increase in the normalized heater output, and is easily exceeds 0.2K.

Referring to FIG. 3(b), it is possible to understand the relationship between the normalized heater output and the temperature of the heat absorption section 46 (temperature at the normalized axial position of about 0.54). When the standardized heater output is zero, the temperature of the heat absorbing part 46 is approximately 8 K (circle symbol), and as the standardized heater output increases to 0.085, 0.31, and 0.45, the temperature of the heat absorbing part 46 also increases. (square, triangle, diamond symbols). More specifically, when the normalized heater output is 0.085, the temperature of the heat absorption part 46 is about 13K (square symbol), and when the normalized heater output is 0.31, the temperature of the heat absorption part 46 is about 20K (triangle symbol). The normalized heater output is 0.45, and the temperature of the heat absorbing portion 46 is approximately 24K (diamond symbol).

A broken line L1 shown in FIG. 3(b) represents a straight line connecting the measured temperature of the first cooling stage 33 and the measured temperature of the second cooling stage 35. From FIGS. 3(a) and 3(b), it is important to note that the temperature of the heat absorbing section 46 at the normalized heater output threshold Th1 is on or near this straight line L1 (the square in FIG. 3(b) symbol and triangle symbol).

From this, if the heat input to the heat absorption part 46 is large (that is, exceeds the threshold value Th1), and as a result, the temperature of the heat absorption part 46 exceeds the upper limit temperature of this straight line L1 or its vicinity, the heat absorption part 46 A significant temperature increase may occur in the second cooling stage 35 due to the heat input. Furthermore, if the heat input to the heat absorption part 46 is such that the temperature of the heat absorption part 46 does not exceed this upper limit temperature, the temperature of the second cooling stage 35 due to the heat input to the heat absorption part 46 is The increase may be substantially absent or within an acceptable range (eg, within 0.2K, or preferably within 0.1K).

FIGS. 4(a) and 4(b) are graphs showing experimental results by the present inventors in accordance with the embodiment. The experimental results shown in FIGS. 4(a) and 4(b) were obtained by changing the axial position of the heat absorption part 46 from the experimental results shown in FIGS. 3(a) and 3(b), Other experimental conditions were the same. In FIGS. 4(a) and 4(b), the position of the heat absorption part 46 is on the high temperature side compared to FIGS. 3(a) and 3(b), specifically, on the normalized axis on the second cylinder 16b. The direction position is approximately 0.35.

Similarly to FIG. 3(a), FIG. 4(a) shows the relationship between the normalized heater output representing the heat input to the heat absorption section 46 and the temperature rise of the second cooling stage 35. Similar to FIG. 3(b), FIG. 4(b) shows the relationship between the normalized axial position on the second cylinder 16b and the temperature. In FIGS. 4(a) and 4(b), the temperature measurement results when the normalized heater output is zero (that is, there is no heat input to the heat absorption part 46) are shown with circle symbols, and the normalized heater output The temperature measurement results when is 0.31, 0.55, and 0.72 are shown by square, triangle, and diamond symbols, respectively.

Referring to FIG. 4(a), when the normalized heater output is zero, there is no temperature rise in the second cooling stage 35 (circle symbol), and as the normalized heater output increases, the temperature rise in the second cooling stage 35 also increases. I understand that. Specifically, when the normalized heater output is 0.31, the temperature rise is about 0.02K (square symbol), and when the normalized heater output is 0.55, the temperature rise is about 0.07K (triangle symbol). At an output of 0.72, the temperature rise is approximately 0.09K (diamond symbol). In FIG. 4A, the heat absorption part 46 is on the high temperature side compared to FIG.

Also in FIG. 4(a), the normalized heater output threshold Th2 indicated by the broken line is an important boundary. If the heat input to the heat absorbing section 46 is below this threshold value Th2, the temperature rise in the second cooling stage 35 is suppressed to a very small value within about 0.02K. On the other hand, when the heat input to the heat absorption section 46 exceeds this threshold value Th2, the temperature rise of the second cooling stage 35 changes in aspect and increases proportionally in accordance with the normalized heater output.

Referring to FIG. 4(b), it is possible to understand the relationship between the normalized heater output and the temperature of the heat absorption section 46 (temperature at a normalized axial position of about 0.35). When the standardized heater output is zero, the temperature of the heat absorbing part 46 is approximately 16 K (circle symbol), and as the standardized heater output increases, the temperature of the heat absorbing part 46 also increases. Specifically, when the standardized heater output is 0.31, the temperature of the heat absorbing part 46 is about 27 K (square symbol), and when the normalized heater output is 0.55, the temperature of the heat absorbing part 46 is about 33 K (triangle symbol). The heating output is 0.72, and the temperature of the heat absorbing section 46 is approximately 38K (diamond symbol).

A broken line L2 shown in FIG. 4(b) represents a straight line connecting the measured temperature of the first cooling stage 33 and the measured temperature of the second cooling stage 35. From FIG. 4(a) and FIG. 4(b), the temperature of the heat absorbing part 46 at the normalized heater output threshold Th2 is on or near this straight line L2 (in the square symbol and triangular symbol in FIG. 4(b)). It is thought to be located between

Therefore, if the heat input to the heat absorption part 46 is large (that is, exceeds the threshold value Th2), and as a result, the temperature of the heat absorption part 46 exceeds the upper limit temperature of this straight line L2 or its vicinity, the heat input to the heat absorption part 46 will decrease. A significant temperature increase may occur in the second cooling stage 35 due to heat. Furthermore, if the heat input to the heat absorption part 46 is such that the temperature of the heat absorption part 46 does not exceed this upper limit temperature, the temperature of the second cooling stage 35 due to the heat input to the heat absorption part 46 is It is believed that the increase may be substantially non-existent or within an acceptable range.

In addition to the experimental results shown in FIGS. 3(a) to 4(b), the inventor conducted the same experiment by variously changing the axial position of the heat absorption part 46 and the temperature of the first cooling stage 33. Is going. As a result, the inventor has determined the relationship between the heat input to the heat absorption part 46 and the temperature rise of the second cooling stage 35, and the relationship between the normalized axial position on the second cylinder 16b and the temperature as described above. We have confirmed that the same behavior as the results is observed.

Therefore, the upper limit temperature of the heat absorption part 46 for preventing or minimizing the temperature rise of the second cooling stage 35 due to heat input to the heat absorption part 46 is determined by the temperature measured at both ends of the second cylinder 16b, and It can be set based on the axial position of the heat absorbing portion 46.

In one exemplary method, the upper limit temperature of the heat absorption part 46 may be set based on the reference temperature distribution of the second cylinder 16b and the axial position of the heat absorption part 46. Here, the reference temperature distribution of the second cylinder 16b has a first measured temperature at one axial end of the second cylinder 16b (for example, the first cooling stage 33) and a temperature distribution at the other axial end of the second cylinder 16b. The temperature distribution may have a second measured temperature at the end (for example, the second cooling stage 35) and vary linearly depending on the axial position in the second cylinder 16b.

An exemplary configuration for optimizing heat input to the heat absorption section 46 will be described below. Referring to FIG. 1 again, the cryogenic refrigerator 10 includes a first temperature sensor 51, a second temperature sensor 52, a third temperature sensor 53, and a controller 60.

The first temperature sensor 51 measures a first measurement temperature T1 at one axial end of the second cylinder 16b near the first cylinder 16a. The first temperature sensor 51 may be provided on the first cooling stage 33 and may measure the first measurement temperature T1 on the first cooling stage 33. The second temperature sensor 52 measures a second measured temperature T2 at the other axial end of the second cylinder 16b that is far from the first cylinder 16a. The second temperature sensor 52 may be provided on the second cooling stage 35 and may measure the second measurement temperature T2 on the second cooling stage 35. The third temperature sensor 53 is provided in the heat absorption section 46 and measures the third measurement temperature T3 at the heat absorption section 46.

The controller 60 receives the first measured temperature T1, the second measured temperature T2, and the third measured temperature T3 from the first temperature sensor 51, the second temperature sensor 52, and the third temperature sensor 53, respectively. is connected to enable communication.

The internal configuration of the controller 60 is realized as a hardware configuration by elements and circuits such as a computer's CPU (Central Processing Unit) and memory, and as a software configuration by a computer program, etc.; It is depicted as a functional block that is realized by their cooperation. Those skilled in the art will understand that these functional blocks can be realized in various ways by combining hardware and software.

The cryogenic system 100 includes a refrigerant gas line 118 that is cooled by the cryogenic refrigerator 10. The refrigerant gas in refrigerant gas line 118 is condensed by cooling, and cryogenic liquid 102 is produced. The refrigerant gas line 118 includes a supply line 120 that supplies the cryogenic liquid 102 to the inner tank 114 of the vacuum vessel 110, and a return line 122 for the cryogenic liquid 102 (ie, refrigerant gas) vaporized in the inner tank 114. Supply line 120 and return line 122 may each be rigid or flexible piping through which refrigerant gas flows.

The supply line 120 includes a first heat exchanger 124, a second heat exchanger 126, and a recondensing section 128. It flows through the recondensing section 128 in the order described.

The first heat exchanger 124 is provided outside the first cooling stage 33 within the inner tank 114, and is configured to pre-cool the refrigerant gas to a first cooling temperature through heat exchange between the first cooling stage 33 and the refrigerant gas. be done. The second heat exchanger 126 is provided outside the second cylinder 16b in the inner tank 114, and exchanges heat between the heat absorption part 46 of the second cylinder 16b and the refrigerant gas to bring the refrigerant gas to the cooling temperature of the heat absorption part 46. It is further configured to pre-cool.

The recondensing section 128 serves as an outlet for the supply line 120 to the inner tank 114. The recondensing section 128 is provided outside the second cooling stage 35 in the inner tank 114, cools the refrigerant gas to a second cooling temperature through heat exchange between the second cooling stage 35 and the refrigerant gas, and cools the refrigerant gas to an extremely low temperature. It is configured to recondense into a cryogenic liquid 102. The recondensed cryogenic liquid 102 is stored in the inner tank 114 as described above. The recondensing section 128 may be integral with the second cooling stage 35, as shown, and may have fin-like protrusions or asperities to increase the surface area in contact with the refrigerant gas or cryogenic liquid 102. Good too. Like the second cooling stage 35, the recondensing section 128 is formed of, for example, pure copper (eg, oxygen-free copper, tough pitch copper, etc.) or other high heat conductive metal.

The refrigerant gas line 118 also includes a flow regulator 130 configured to adjust the refrigerant gas flow rate of the refrigerant gas line 118. In the illustrated example, a flow regulator 130 is provided on the refrigerant gas line 118 to connect the return line 122 to the supply line 120. Flow regulator 130 receives refrigerant gas from return line 122, regulates the refrigerant gas flow rate, and delivers refrigerant gas to supply line 120 at the regulated flow rate. Flow regulator 130 may be a circulating flow generator, such as a pump, a compressor, or a mechanism for regulating gas flow, such as a flow control valve, variable orifice, or the like.

The flow regulator 130 may be placed outside the vacuum vessel 110, as shown, or may be placed within the vacuum vessel 110. Additionally, the flow regulator 130 may be provided anywhere on the refrigerant gas line 118, may be provided on the supply line 120, or may be provided on the return line 122.

As described below, under the control of the controller 60, the flow regulator 130 can adjust the flow rate of the refrigerant gas circulating through the refrigerant gas line 118. By adjusting the flow rate, heat input from the refrigerant gas line 118 to the heat absorption section 46 is controlled.

The refrigerant gas line 118 serves as a heat source for the cryogenic refrigerator 10. The heat source includes a first portion (e.g., first heat exchanger 124), a second portion (e.g., recondensing section 128), and a third portion of the heat source (e.g., second heat exchanger 128) connecting the first and second portions. exchanger 126). One axial end of the second cylinder 16b (e.g., the first cooling stage 33) is thermally connected to the first portion of the heat source, and the other axial end of the second cylinder 16b (e.g., the second cooling stage 35) is thermally connected to the second part of the heat source. The heat absorbing portion 46 is thermally connected to the third portion of the heat source. The refrigerant gas line 118 passes through the first, third, and second portions of the heat source in the order listed.

FIG. 5 is a flowchart showing a method of controlling the cryogenic system 100 according to the embodiment. This method includes obtaining a first measured temperature T1 from the first temperature sensor 51, a second measured temperature T2 from the second temperature sensor 52, and a third measured temperature T3 from the third temperature sensor 53 (S10). , setting the upper limit temperature of the heat absorbing part 46 based on the first measured temperature T1, the second measured temperature T2, and the axial position of the heat absorbing part 46 (S20), and setting the third measured temperature T3 of the heat absorbing part 46. Controlling the heat source, that is, the refrigerant gas line 118, so that the temperature is below the upper limit temperature (S30).

In S10, the first measured temperature T1 is measured by the first temperature sensor 51 at one axial end (for example, the first cooling stage 33) of the second cylinder 16b near the first cylinder 16a. A signal indicating the first measured temperature T1 is input from the first temperature sensor 51 to the controller 60. Further, the second measured temperature T2 is measured by the second temperature sensor 52 at the other axial end of the second cylinder 16b that is far from the first cylinder 16a. A signal indicating the second measured temperature T2 is input from the second temperature sensor 52 to the controller 60. The third measured temperature T3 is measured by the third temperature sensor 53 at the heat absorption section 46. A signal indicating the third measured temperature T3 is input from the third temperature sensor 53 to the controller 60.

In S20, the controller 60 first determines the reference temperature distribution of the second cylinder 16b based on the first measured temperature T1 and the second measured temperature T2. This reference temperature distribution has a first measured temperature T1 at one axial end of the second cylinder 16b, a second measured temperature T2 at the other axial end of the second cylinder 16b, and a second measured temperature T2 at the other axial end of the second cylinder 16b. This is a temperature distribution that changes linearly depending on the axial position in the cylinder 16b. The reference temperature distribution is a straight line passing through the points (0, T1) and (1, T2) on the XY plane with the normalized axial position on the second cylinder 16b as the X axis and the temperature as the Y axis. (Y=(T2-T1)X+T1).

The controller 60 sets the upper limit temperature of the heat absorption section 46 based on the reference temperature distribution and the axial position of the heat absorption section 46. By substituting the axial normalized position of the heat absorbing portion 46 into the above equation representing the reference temperature distribution, a candidate value for the upper limit temperature of the heat absorbing portion 46 is determined. The controller 60 may employ this candidate value as the upper limit temperature.

Alternatively, if it is important to reliably prevent the temperature of the second cooling stage 35 from rising due to heat input to the heat absorption section 46, the controller 60 may set a value somewhat smaller than this candidate value (for example, A value selected from the range of 70% to 100%, 80% to 100%, or 90% to 100%) may be adopted as the upper limit temperature of the heat absorbing portion 46.

Alternatively, if the temperature increase of the second cooling stage 35 due to heat input to the heat absorption part 46 is allowed to some extent, the controller 60 sets a value somewhat larger than this candidate value (for example, 100 to 100 of the candidate value). 130%, or a value selected from the range of 100 to 120%, or 100 to 110%) may be adopted as the upper limit temperature of the heat absorbing portion 46.

In S30, the controller 60 controls the refrigerant gas flow rate of the refrigerant gas line 118 so that the third measured temperature T3 is equal to or lower than the upper limit temperature of the heat absorption section 46. An example of this control will be described later with reference to FIG.

The controller 60 may update the upper limit temperature of the heat absorption section 46 according to the first measured temperature T1 and the second measured temperature T2 by periodically repeating the process shown in FIG. 5. In addition, when the cryogenic refrigerator 10 is operated to maintain the cooling temperature of the first cooling stage 33 (and/or the second cooling stage 35) at a certain target temperature, unless the target temperature is changed, The temperature distribution also remains roughly unchanged. In this case, the upper limit temperature of the heat absorption section 46 that has been set once may be used continuously thereafter.

FIG. 6 is a flowchart showing an example of the control process (S30) for the refrigerant gas line 118 shown in FIG. In this process, the controller 60 controls the flow rate regulator 130 of the refrigerant gas line 118 based on the comparison between the third measured temperature T3 and the upper limit temperature of the heat absorption section 46, thereby controlling the refrigerant gas flow rate of the refrigerant gas line 118. Control. This process is repeatedly executed by the controller 60 at predetermined intervals while the cryogenic refrigerator 10 is in operation.

Therefore, as shown in FIG. 6, the controller 60 first compares the third measured temperature T3 with the upper limit temperature T _lim of the heat absorption section 46 (S31). The third measured temperature T3 is measured by the third temperature sensor 53 as described above (S10 in FIG. 5). The upper limit temperature of the heat absorption part 46 is set based on the measured temperature at both ends of the second cylinder 16b and the axial position of the heat absorption part 46 (S20 in FIG. 5).

The controller 60 compares the third measured temperature T3 with the upper limit temperature _Tlim of the heat absorption section 46, and outputs the magnitude relationship between the two as a comparison result. That is, the comparison result by the controller 60 is in the following three states: (i) the third measured temperature T3 is higher than the upper limit temperature T _lim , (ii) the third measured temperature T3 is lower than the upper limit temperature T _lim , (iii) The third measured temperature T3 is equal to the upper limit temperature _Tlim .

Controller 60 controls flow regulator 130 based on the comparison result. Specifically, (i) when the third measured temperature T3 is higher than the upper limit temperature _Tlim , the controller 60 controls the flow regulator 130 to reduce the refrigerant gas flow rate (S32). Thereby, the heat input from the second heat exchanger 126 to the heat absorption section 46 can be reduced, and the third measured temperature T3 can be lowered. (ii) When the third measured temperature T3 is lower than the upper limit temperature _Tlim , the controller 60 controls the flow regulator 130 to increase the refrigerant gas flow rate (S33). Thereby, heat input from the second heat exchanger 126 to the heat absorption section 46 can be increased, and the refrigerant gas line 118 can be cooled more efficiently. (iii) If the third measured temperature T3 is equal to the upper limit temperature _Tlim , there is no need to increase or decrease the refrigerant gas flow rate, so the controller 60 controls the flow regulator 130 to maintain the current refrigerant gas flow rate. . Note that the case (iii) may be included in either (i) or (ii).

As described above, according to the embodiment, in addition to the first cooling stage 33 and the second cooling stage 35, the refrigerant gas line 118 is can be cooled. Cryogenic system 100 can be cooled more efficiently than typical cooling configurations that do not utilize heat sink 46.

Further, in the embodiment, the upper limit temperature T _{lim of the heat absorbing portion 46 is set based on the first measured temperature T1, the second measured temperature T2, and the axial position of the heat absorbing portion 46, and the third measured temperature T3 is set as the upper limit temperature T lim} of the heat absorbing portion 46. A heat source (for example, refrigerant gas line 118) for cryogenic refrigerator 10 in cryogenic system 100 is controlled so that the temperature is below T _lim . In this way, by keeping the temperature of the heat absorbing section 46 below the upper limit temperature T _lim , the temperature rise of the second cooling stage 35 can be prevented or minimized.

Furthermore, in the embodiment, the upper limit temperature T _lim is based on the above-mentioned linear reference temperature distribution and the axial position of the heat absorption section 46 . In this way, even if the temperatures of the first cooling stage 33 and the second cooling stage 35 change depending on various operating conditions of the cryogenic refrigerator 10, the heat absorbing portion 46 can be provided at various axial positions. Even if the upper limit temperature T lim is determined, the upper limit temperature T _lim can be clearly and easily determined.

FIG. 7 is a diagram schematically showing a cryogenic system 100 according to another embodiment. The cryogenic system 100 shown in FIG. 7 differs from the cryogenic system 100 shown in FIG. 1 with respect to the object to be cooled, and the rest is generally the same. Below, different configurations will be mainly explained, and common configurations will be briefly explained or their explanations will be omitted.

Although the above-described embodiments are described with reference to the case where the cryogenic system 100 is a storage device for the cryogenic liquid 102, other configurations are also possible. For example, the cryogenic system 100 may be applied to a superconducting device, and the cryogenic refrigerator 10 is configured to provide a superconducting coil 150 disposed within a vacuum container 110 and a current for supplying power to the superconducting coil 150. It may also be used to cool the leads 152. Superconducting coil 150 is cooled by second cooling stage 35 , and current lead 152 is cooled by first cooling stage 33 , heat absorption section 46 , and second cooling stage 35 .

The current lead 152 electrically connects a power source 154 placed outside the vacuum vessel 110 to the superconducting coil 150, and serves as a current path from the power source 154 to the superconducting coil 150. Therefore, since the current lead 152 can generate heat when energized, it functions as a heat source for the cryogenic refrigerator 10. The current lead 152 has a first portion 152a, a second portion 152b, and a third portion 152c connecting the first portion 152a and the second portion 152b.

One axial end of the second cylinder 16b (for example, the first cooling stage 33) is thermally connected to the first portion 152a of the current lead 152, and the other axial end of the second cylinder 16b (for example, the first cooling stage 33) is thermally connected to the first portion 152a of the current lead 152. 2 cooling stage 35) is thermally connected to the second portion 152b of the current lead 152. The heat absorbing portion 46 is thermally connected to the third portion 152c of the current lead 152.

As an example of thermal connection, the first cooling stage 33 is connected to the first portion 152a of the current lead 152 by the first heat transfer member 156, and the second cooling stage 35 is connected to the first portion 152a of the current lead 152 by the second heat transfer member 158. It may be connected to the second portion 152b. Further, the second cooling stage 35 may be connected to the superconducting coil 150 by a second heat transfer member 158. The heat absorbing portion 46 of the second cylinder 16b may be connected to the third portion 152c of the current lead 152 by a heat bridge 160.

The controller 60 is configured to control the current in the current lead 152 so that the third measured temperature T3 is equal to or lower than the upper limit temperature. The controller 60 may control the power supply 154 based on a comparison between the third measured temperature T3 and the upper limit temperature of the heat absorption section 46, thereby controlling the current in the current lead 152.

As an example, (i) if the third measured temperature T3 is higher than the upper limit temperature _Tlim , the controller 60 controls the power supply 154 to reduce the current in the current lead 152. Thereby, the heat input from the second heat exchanger 126 to the heat absorption section 46 can be reduced, and the third measured temperature T3 can be lowered. (ii) If the third measured temperature T3 is lower than the upper limit temperature _Tlim , the controller 60 controls the power supply 154 to increase the current in the current lead 152. Thereby, the heat input from the second heat exchanger 126 to the heat absorption section 46 can be increased, and the current lead 152 can be cooled more efficiently. (iii) If the third measured temperature T3 is equal to the upper limit temperature _Tlim , there is no need to increase or decrease the current in the current lead 152, so the controller 60 controls the power supply 154 to maintain the current current.

In this way, in addition to the first cooling stage 33 and the second cooling stage 35, the current lead 152 can be cooled using the refrigerating capacity of the heat absorbing section 46 on the second cylinder 16b. Cryogenic system 100 can be cooled more efficiently than typical cooling configurations that do not utilize heat sink 46. By keeping the temperature of the heat absorption section 46 below the upper limit temperature T _lim , the temperature rise of the second cooling stage 35 can be prevented or minimized.

The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above embodiments, and that various design changes and modifications are possible, and that such modifications also fall within the scope of the present invention. By the way. Various features described in connection with one embodiment are also applicable to other embodiments. A new embodiment resulting from a combination has the effects of each of the combined embodiments.

In the embodiment described above, one temperature sensor (third temperature sensor 53) is provided to measure the temperature of the heat absorption section 46, but other configurations are also possible. In some embodiments, the temperature of the heat absorbing portion 46 may be measured at multiple temperature measurement locations. Therefore, a plurality of temperature sensors (for example, two third temperature sensors 53) may be provided in the heat absorption section 46. These temperature sensors are provided at different positions in the axial direction on the second cylinder 16b. As an example, one third temperature sensor 53 is arranged on the high temperature side with respect to the other third temperature sensor 53.

In this case, the controller 60 may set the upper limit temperature for each temperature measurement position (temperature sensor) based on the measured temperature at both ends of the second cylinder 16b and the temperature measurement position. The controller 60 may control the heat source so that any measured temperature among the plurality of measured temperatures is equal to or lower than the corresponding upper limit temperature.

In the above embodiment, the cryogenic refrigerator 10 is a two-stage GM refrigerator, but other configurations are also possible. For example, the cryogenic refrigerator 10 may be a single-stage GM refrigerator. Alternatively, the cryogenic refrigerator 10 may be another type of cryogenic refrigerator, such as a Solvay refrigerator, a Stirling refrigerator, a pulse tube refrigerator, etc., for example.

Although the present invention has been described using specific words based on the embodiments, the embodiments merely illustrate one aspect of the principles and applications of the present invention, and the embodiments do not include the claims. Many modifications and changes in arrangement are possible without departing from the spirit of the invention as defined in scope.

The present invention can be used in the fields of cryogenic systems and cryogenic system control methods.

10 cryogenic refrigerator, 16a first cylinder, 16b second cylinder, 46 heat absorption section, 51 first temperature sensor, 52 second temperature sensor, 53 third temperature sensor, 60 controller, 100 cryogenic system, 118 refrigerant gas line , 152 Current lead.

Claims

a first cylinder;
a second cylinder provided in series with the first cylinder in the axial direction, the second cylinder having a heat absorption part thermally connected to a heat source at an axially intermediate portion thereof;
a first temperature sensor that measures a first measurement temperature at one axial end of the second cylinder near the first cylinder;
a second temperature sensor that measures a second measurement temperature at the other axial end of the second cylinder that is far from the first cylinder;
a cryogenic refrigerator comprising: a third temperature sensor that measures a third measurement temperature in the heat absorption part;
obtaining the first measured temperature from the first temperature sensor, the second measured temperature from the second temperature sensor, and the third measured temperature from the third temperature sensor;
setting an upper limit temperature of the heat absorption part based on the first measured temperature, the second measurement temperature, and the axial position of the heat absorption part;
A cryogenic system comprising: a controller configured to control the heat source so that the third measured temperature is equal to or lower than the upper limit temperature of the heat absorption section.
The controller includes:
the first measured temperature at the one axial end of the second cylinder and the second measured temperature at the other axial end of the second cylinder; determining a reference temperature distribution of the second cylinder that changes linearly depending on the directional position;
The cryogenic system according to claim 1, wherein the cryogenic system is configured to set an upper limit temperature of the heat absorption part based on the reference temperature distribution and the axial position of the heat absorption part.
the one axial end of the second cylinder is thermally connected to the first portion of the heat source;
the other axial end of the second cylinder is thermally connected to a second portion of the heat source;
The cryogenic system according to claim 1 or 2, wherein the heat absorption part is thermally connected to a third part of the heat source that connects the first part and the second part.
The heat source includes a refrigerant gas line passing through the first part, the third part, and the second part in the order described,
The cryogenic system according to claim 3, wherein the controller is configured to control the refrigerant gas flow rate of the refrigerant gas line so that the third measured temperature is equal to or lower than the upper limit temperature.
The heat source includes a current lead passing through the first part, the third part, and the second part in the order described,
4. The cryogenic system according to claim 3, wherein the controller is configured to control the current in the current lead so that the third measured temperature is equal to or lower than the upper limit temperature.
A method for controlling a cryogenic system, wherein the cryogenic system includes a cryogenic refrigerator including a first cylinder and a second cylinder arranged in series in the axial direction, and the second cylinder is axially intermediate. a heat absorbing part thermally connected to a heat source;
Measuring a first measurement temperature at one axial end of the second cylinder close to the first cylinder;
measuring a second measured temperature at the other axial end of the second cylinder that is far from the first cylinder;
Measuring a third measurement temperature at the endothermic part;
setting an upper limit temperature of the heat absorption part based on the first measurement temperature, the second measurement temperature, and the axial position of the heat absorption part;
A method comprising: controlling the heat source so that the third measured temperature is equal to or lower than an upper limit temperature of the heat absorption section.