EP3865789A1

EP3865789A1 - Cryogenic system

Info

Publication number: EP3865789A1
Application number: EP21157189.8A
Authority: EP
Inventors: Katsuhiro Narasaki
Original assignee: Sumitomo Heavy Industries Ltd
Current assignee: Sumitomo Heavy Industries Ltd
Priority date: 2020-02-17
Filing date: 2021-02-15
Publication date: 2021-08-18
Also published as: JP2021127885A

Abstract

The continuity improvement of cooling operation of a cryogenic system (100, 200) is achieved. The cryogenic system (100, 200) includes a JT circuit (10), a refrigerant circulation type precooling circuit (12) that precools the JT circuit (10), and a plurality of mechanical refrigerators (14) that indirectly cool the JT circuit (10) by cooling the precooling circuit (12) . The cryogenic system (100, 200) may include a first JT circuit (10a) and a second JT circuit (10b). The precooling circuit (12) includes a first precooling loop (12a) that precools the first JT circuit (10a), a second precooling loop (12b) that precools the second JT circuit (10b), and a connection line (13) that disconnectably connects the first precooling loop (12a) and the second precooling loop (12b) to each other.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cryogenic system.

Description of Related Art

In the related art, a cryogenic system including a Joule-Thomson (JT) cryocooler is used in order to cool a highly sensitive electromagnetic wave detection element used in astronomical observation or other objects to be cooled to a desired cryogenic temperature. The cryogenic system usually includes a precooler that precools a JT cryocooler. A two-stage mechanical refrigerator including a two-stage Stirling cryocooler, a two-stage Gifford-McMahon (GM) cryocooler, and a two-stage pulse tube cryocooler can be typically used as the precooler. Such a cryogenic system can cool the object to be cooled to, for example, a temperature range of 1 K to 4 K (for example, Japanese Unexamined Patent Publication No. 2019-078481 ).

SUMMARY OF THE INVENTION

As a result of examining the cryogenic system described above, the present inventor has come to recognize the following problems. A possibility that the cooling capacity which can be provided by the system is reduced or lost during use for a long period of time is considered in terms of design. In a case where a plurality of mechanical refrigerators are mounted on the system, even when any one refrigerator stops cooling operation due to a failure, the remaining refrigerator can supplement the cooling capacity which becomes insufficient accordingly.
The failed refrigerator becomes merely a structure that connects a high-temperature section (for example, a room temperature section) and a low-temperature section (for example, the object to be cooled) to each other, and forms a heat transfer path that can bring about thermal infiltration from the high-temperature section to the low-temperature section. The cryogenic system needs to respond to, with the remaining refrigerator that continues cooling, not only a reduction in the cooling capacity caused by a failure but also this thermal infiltration. When the excess cooling capacity of each of the refrigerators is low, a risk that the cryogenic system becomes unable or difficult to continue desired cryogenic cooling increases. In particular, it can have detrimental consequences in situations where it is difficult to repair or replace during operation, for example, as in a case where the cryogenic system is mounted on a spacecraft.
One exemplary object of an aspect of the present invention is to achieve the continuity improvement of cooling operation of a cryogenic system.
According to an aspect of the present invention, there is provided a cryogenic system including a JT circuit, a refrigerant circulation type precooling circuit that precools the JT circuit, and a plurality of mechanical refrigerators that indirectly cool the JT circuit by cooling the precooling circuit.
Any combination of the components described above and a combination obtained by switching the components and expressions of the present invention between methods, devices, and systems are also effective as an aspect of the present invention.
With the present invention, the continuity improvement of cooling operation of the cryogenic system can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram schematically showing a cryogenic system according to a first embodiment.
Fig. 2 is a table for describing a relationship between an exemplary failure mode of the cryogenic system according to the first embodiment and a flow path switching state.
Fig. 3 is a diagram schematically showing the cryogenic system according to the first embodiment.
Fig. 4 is a diagram schematically showing a modification example of the cryogenic system according to the first embodiment.
Fig. 5 is a diagram schematically showing a cryogenic system according to a second embodiment.
Fig. 6 is a table for describing a relationship between an exemplary failure mode of the cryogenic system according to the second embodiment and a flow path switching state.

DETAILED DESCRIPTION OF THE INVENTION

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 processing will be assigned with the same reference symbols, and redundant description thereof will be omitted as appropriate. The scales and shapes of shown parts are set for convenience in order to make the description easy to understand, and are not to be understood as limiting unless stated otherwise. The embodiments are merely examples and do not limit the scope of the present invention. All characteristics and combinations to be described in the embodiments are not necessarily essential to the invention.
Fig. 1 is a diagram schematically showing a cryogenic system 100 according to a first embodiment. The cryogenic system 100 includes a JT circuit 10, a refrigerant circulation type precooling circuit 12 that precools the JT circuit 10, and a plurality of mechanical refrigerators 14 that indirectly cool the JT circuit 10 by cooling the precooling circuit 12. A precooling system of the JT circuit 10 is configured by the precooling circuit 12 and the mechanical refrigerators 14. In addition, the cryogenic system 100 includes a vacuum chamber 16 and a cryogenic cooling unit 20 that cools an object to be cooled 18. Although a radiation shield for suppressing radiant heat incident to the object to be cooled 18 and the cryogenic cooling unit 20 is usually provided in the vacuum chamber 16, the illustration thereof is omitted for simplicity.
The cryogenic system 100 is provided with a first JT circuit 10a configuring a first JT cryocooler and a second JT circuit 10b configuring a second JT cryocooler. As described above, the cryogenic system 100 includes the plurality of JT circuits 10 that are separated from each other, and each JT circuit can operate independently as a JT cryocooler. Each JT circuit 10 is configured to cool the cryogenic cooling unit 20 through heat exchange between the cryogenic cooling unit 20 and a refrigerant. The refrigerant circulating in the JT circuit 10 is, for example, helium (helium 3 or helium 4).
The precooling circuit 12 includes a first precooling loop 12a that precools the first JT circuit 10a, a second precooling loop 12b that precools the second JT circuit 10b, and a connection line 13 that disconnectably connects the first precooling loop 12a and the second precooling loop 12b to each other. That is, the precooling circuit 12 includes a plurality of precooling loops, and the plurality of JT circuits 10 are cooled by the corresponding precooling loops. The precooling circuit 12 includes a circulation pump 26 that circulates a refrigerant for each precooling loop. The refrigerant circulating in the precooling circuit 12 is, for example, a refrigerant gas (for example, helium). The precooling circuit 12 and the JT circuit 10 are separated from each other, and refrigerants do not flow between the precooling circuit 12 and the JT circuit 10.
The plurality of mechanical refrigerators 14 cool the corresponding precooling loops, respectively. In the embodiment, two mechanical refrigerators 14 are provided. One mechanical refrigerator cools a refrigerant circulating in the first precooling loop 12a, and the other mechanical refrigerator cools a refrigerant circulating in the second precooling loop 12b.
Exemplary configurations of the JT circuit 10, the precooling circuit 12, and the mechanical refrigerator 14 will be described later. Since the plurality of JT circuits 10 have the same configuration, the configuration of the first JT circuit 10a will be mainly described below, and the description of the second JT circuit 10b will be omitted as appropriate. Regarding the precooling circuit 12, since the first precooling loop 12a and the second precooling loop 12b have the same configuration, the configuration of the first precooling loop 12a will be mainly described below, and the description of the second precooling loop 12b will be omitted as appropriate. The plurality of mechanical refrigerators 14 also have the same configuration.
The vacuum chamber 16 is a cryogenic vacuum chamber such as a cryostat, and divides the cryogenic system 100 into a normal-temperature section 22 and a low-temperature section 24. That is, the normal-temperature section 22 of the cryogenic system 100 is disposed outside the vacuum chamber 16, and the low-temperature section 24 of the cryogenic system 100 is disposed in the vacuum chamber 16. The temperature of the normal-temperature section 22 can become, for example, the room temperature or a temperature of approximately 300 K.
For example, the object to be cooled 18 may be a detection element that detects infrared rays, submillimeter waves, X-rays, or other electromagnetic waves, and such a detection element is a component of an observation device used in astronomical observation. The object to be cooled 18 is physically in contact with the cryogenic cooling unit 20 and is thermally coupled thereto, or is thermally coupled to the cryogenic cooling unit 20 via a heat transfer member.
The cryogenic cooling unit 20 is also called a cooling stage . As shown, the cryogenic system 100 may include one common cooling stage as the cryogenic cooling unit 20. Alternatively, the cryogenic cooling unit 20 may include a plurality of cooling stages. In this case, a cooling stage may be provided for each JT circuit 10.
The cryogenic system 100 is mountable on, for example, a spacecraft such as an artificial satellite, together with the object to be cooled 18. The cryogenic system 100 may be mounted on ground facilities including the object to be cooled 18. The cryogenic system 100 may be mounted on a spacecraft or ground facilities together with, for example, a sensor, a superconductivity device, or other objects to be cooled 18 where a cryogenic environment is desired.
The mechanical refrigerator 14 is, for example, a two-stage Stirling cryocooler. The mechanical refrigerator 14 includes a compressor 30, a two-stage cold head 32, which is an expander, and a connecting pipe 34 that connects the compressor 30 to the two-stage cold head 32. The connecting pipe 34 provides a gas flow path for flowing a refrigerant gas (for example, a helium gas) between the compressor 30 and the two-stage cold head 32. The two-stage cold head 32 includes a first-stage refrigerator stage 36 and a second-stage refrigerator stage 38. The normal-temperature section 22 of the cryogenic system 100 includes the compressor 30, a room temperature section of the two-stage cold head 32, and the connecting pipe 34. The low-temperature section 24 of the cryogenic system 100 includes the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38.
The compressor 30 is configured to generate pressure oscillation of a refrigerant gas. The generated pressure oscillation is transmitted to the two-stage cold head 32 through the connecting pipe 34. The two-stage cold head 32 is configured such that the pressure oscillation transmitted from the compressor 30 induces pressure oscillation having a phase difference at the same frequency as the pressure oscillation in the two-stage coldhead 32. Accordingly, a refrigeration cycle (specifically, a reverse Stirling cycle) is formed between the compressor 30 and the two-stage cold head 32.
In this manner, the first-stage refrigerator stage 36 of the mechanical refrigerator 14 is cooled to a first-stage cooling temperature, and the second-stage refrigerator stage 38 is cooled to a second-stage cooling temperature. The first-stage cooling temperature of the mechanical refrigerator 14 is selected from, for example, a temperature range of 50 K or higher and 150 K or lower. The first-stage cooling temperature may be in, for example, a temperature range of 80 K or higher and 120 K or lower. The second-stage cooling temperature is lower than the first-stage cooling temperature. The second-stage cooling temperature is selected from, for example, a temperature range of 4 K or higher and 25 K or lower. The second-stage cooling temperature may be in, for example, a temperature range of 10 K or higher and 20 K or lower.
The refrigerant circulation of the precooling circuit 12 and the refrigerant circulation of the mechanical refrigerator 14 are separated from each other, and a refrigerant gas does not flow from the mechanical refrigerator 14 to the precooling circuit 12. Similarly, the refrigerant circulation of the JT circuit 10 and the refrigerant circulation of the mechanical refrigerator 14 are separated from each other, and a refrigerant gas does not flow from the mechanical refrigerator 14 to the JT circuit 10.
The circulation pump 26 provided in the precooling circuit 12 is configured to pressurize, for example, a refrigerant gas collected from the low-temperature section 24 to, for example, approximately the atmospheric pressure or approximately several atmospheres . The circulation pump 26 can recover a pressure loss that occurs in a refrigerant in the precooling circuit 12. The circulation pump 26 is a pump of a low output (for example, approximately several W) compared to the compressor 30 described above. The circulation pump 26 is disposed in the normal-temperature section 22 of the cryogenic system 100.
The first precooling loop 12a is provided with a first precooling heat exchanger 40, a first-stage precooling unit 41, a second precooling heat exchanger 42, a second-stage precooling unit 43, a first-stage heat exchanger 44, and a second-stage heat exchanger 46. The components are disposed in the vacuum chamber 16, that is, in the low-temperature section 24 of the cryogenic system 100. The first precooling loop 12a further includes a precooling supply line 50 and a precooling collection line 52. The precooling supply line 50 connects a discharge side of the circulation pump 26 to a supply side of the second-stage heat exchanger 46, and the precooling collection line 52 connects a collection side of the second-stage heat exchanger 46 to a suction side of the circulation pump 26. Accordingly, a part of each of the precooling supply line 50 and the precooling collection line 52 is disposed in the normal-temperature section 22, and the remaining portion is disposed in the low-temperature section 24.
The first precooling heat exchanger 40 cools a high-temperature (for example, a normal temperature, such as approximately 300 K) refrigerant gas flowing from the circulation pump 26 into the vacuum chamber 16. The second precooling heat exchanger 42 further cools the refrigerant, which is cooled by the first precooling heat exchanger 40 and the first-stage precooling unit 41 and has passed through the first-stage heat exchanger 44.
The first precooling heat exchanger 40 and the second precooling heat exchanger 42 are, for example, countercurrent heat exchangers. The precooling supply line 50 includes supply side flow paths of the first precooling heat exchanger 40 and the second precooling heat exchanger 42 respectively, and the precooling collection line 52 includes collection side flowpaths of the first precooling heat exchanger 40 and the second precooling heat exchanger 42 respectively. A refrigerant flowing in the supply side flow path can be cooled through heat exchange between the supply side flow path and the collection side flow path of each heat exchanger.
The first-stage precooling unit 41 is thermally coupled to the first-stage refrigerator stage 36. A refrigerant flowing in the first-stage precooling unit 41 is cooled through heat exchange with the first-stage refrigerator stage 36. On the precooling supply line 50, the first-stage precooling unit 41 is disposed between the first precooling heat exchanger 40 and the first-stage heat exchanger 44. The first-stage heat exchanger 44 of the first precooling loop 12a is thermally coupled to the first JT circuit 10a.
The second-stage precooling unit 43 is thermally coupled to the second-stage refrigerator stage 38. Arefrigerant flowing in the second-stage precooling unit 43 is cooled by the second-stage refrigerator stage 38. On the precooling supply line 50, the second-stage precooling unit 43 is disposed between the second precooling heat exchanger 42 and the second-stage heat exchanger 46. The second-stage heat exchanger 46 of the first precooling loop 12a is thermally coupled to the first JT circuit 10a.
Similarly, the second precooling loop 12b includes the circulation pump 26 and the mechanical refrigerator 14. The mechanical refrigerator 14 includes the compressor 30, the two-stage cold head 32, and the connecting pipe 34. The two-stage cold head 32 includes the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38. In addition, the second precooling loop 12b includes the first precooling heat exchanger 40, the first-stage precooling unit 41, the second precooling heat exchanger 42, the second-stage precooling unit 43, the first-stage heat exchanger 44, the second-stage heat exchanger 46, the precooling supply line 50, and the precooling collection line 52. The first-stage heat exchanger 44 and the second-stage heat exchanger 46 of the second precooling loop 12b are thermally coupled to the second JT circuit 10b.
Pipes of the JT circuit 10 and the precooling circuit 12 are formed of, for example, a material having thermal conductivity lower than the thermal conductivity of a material for a cryocooler stage of the mechanical refrigerator 14. Since the cryocooler stage is usually formed of copper, such pipes may be made of, for example, stainless steel. Thermal infiltration caused by thermal conduction through the pipes to the JT circuit 10 (furthermore, the cryogenic cooling unit 20) can be reduced.
In addition, the precooling circuit 12 may be formed by a flexible pipe at least in the low-temperature section 24 of the cryogenic system 100. For example, at least one of a pipe from the first precooling heat exchanger 40 (or the first-stage precooling unit 41) to the first-stage heat exchanger 44, a pipe from the first-stage heat exchanger 44 to the second precooling heat exchanger 42, a pipe from the second precoolingheat exchanger 42 (or the second-stage precooling unit 43) to the second-stage heat exchanger 46, and a return pipe from the second-stage heat exchanger 46 to the second precooling heat exchanger 42 may be a flexible pipe.
By doing so, thermal infiltration caused by thermal conduction from the cryocooler stage of the mechanical refrigerator 14 to the JT circuit 10 (furthermore, the cryogenic cooling unit 20) through the precooling circuit 12 can be reduced. At the same time, oscillation transmission from the mechanical refrigerator 14 to the JT circuit 10 (furthermore, the cryogenic cooling unit 20) can also be suppressed.
In addition, connecting various components of the cryogenic system 100 with a pipe leads to an increase in a degree of freedom in terms of component disposition places. This is advantageous in a large-scale cryogenic system in which a distance from the normal-temperature section 22 to the cryogenic cooling unit 20 is large.
Including the first-stage heat exchanger 44 and the second-stage heat exchanger 46, the heat exchangers provided in the JT circuit 10 and the precooling circuit 12 may be formed of a material excellent in thermal conduction, such as copper, just as the cryocooler stage, in order to facilitate heat exchange between a high temperature side flow path and a low temperature side flow path.
The precooling circuit 12 is provided with a flow path switching device formed by a group of valves (V1 to V6). The flow path switching device is configured to switch between connecting and disconnecting of the plurality of precooling loops in the precooling circuit 12.
The first precooling loop 12a includes a set of circulation pump shutoff valves (V1 and V2). The first valve V1 is provided on the precooling collection line 52, and the second valve V2 is provided on the precooling supply line 50. In the shown example, the two circulation pump shutoff valves (V1 and V2) are provided on an upstream side and a downstream side of the circulation pump 26, respectively. This is advantageous from a perspective of redundancy in that in a case where one of the two valves is not closed due to a failure, the circulation pump 26 can be shut off by closing the other valve. However, only one circulation pump shutoff valve may be provided, and in this case, any one of the circulation pump shutoff valves (V1 and V2) may be provided. Similarly, the second precooling loop 12b also includes a set of circulation pump shutoff valves (V5 and V6).
The circulation pump shutoff valves (V1, V2, V5, and V6) are opened in a disconnected state of the connection line 13. The circulation pump shutoff valves (V1, V2, V5, and V6) can be closed in a connected state of the connection line 13. Details of the disconnected state and the connected state of the connection line 13 will be described later.
The connection line 13 is configured to be switchable from the disconnected state to the connected state. The connection line 13 disconnects the plurality of precooling loops from each other such that the circulation pump 26 of each precooling loop circulates a refrigerant in the precooling loop in the disconnected state. On the other hand, the connection line 13 connects the plurality of precooling loops such that the circulation pump 26 of at least one precooling loop circulates the refrigerant in at least the other precooling loop in the connected state. The connection line 13 can be returned from the connected state to the disconnected state.
The connection line 13 includes a connection flow path that connects the two precooling loops to each other, and connection opening and closing valves (V3 and V4) that are provided in the connection flow path, are closed in the disconnected state, and are opened in the connected state. With a relatively simple configuration of opening and closing of the connection opening and closing valves (V3 and V4), the connected state and the disconnected state of the connection line 13 can be switched.
More specifically, the connection line 13 includes a supply side connection flow path 13a that connects the precooling supply lines 50 of the two precooling loops to each other and a collection side connection flow path 13b that connects the precooling collection lines 52 of the two precooling loops to each other. The supply side connection flow path 13a joins the precooling supply line 50 between the second valve V2 (the sixth valve V6) and the supply side flow path of the first precooling heat exchanger 40. The collection side connection flow path 13b joins the precooling collection line 52 between the first valve V1 (the fifth valve V5) and the collection side flow path of the first precooling heat exchanger 40.
The third valve V3 is provided on the supply side connection flow path 13a, and the fourth valve V4 is provided on the collection side connection flow path 13b. Both of the third valve V3 and the fourth valve V4 are closed in the disconnected state and are opened in the connected state.
The flow path switching devices (V1 to V6) are disposed in the normal-temperature section 22 of the cryogenic system 100. For this reason, for the flow path switching devices, general-purpose parts whose operation reliability is guaranteed at the normal temperature can be adopted. Such general-purpose parts can be obtained at affordable prices compared to parts whose reliability in the cryogenic environment is guaranteed. If possible, at least some of the flow path switching devices (V1 to V6) may be disposed in the low-temperature section 24 of the cryogenic system 100.
For each of the opening and closing valves (V1 to V6) provided in the precooling circuit 12 and the connection line 13, the opening and closing valve allows a refrigerant to flow therein when opened, and the opening and closing valve does not allow the refrigerant to flow therein when closed. Each of the opening and closing valves (V1 to V6) maybe an electromagnetic, mechanical, manual or other drive type opening and closing valve.
In addition to the first-stage heat exchanger 44 and the second-stage heat exchanger 46 which are described above, the first JT circuit 10a includes a JT compression system 56, a JT heat exchanger group 58, a JT valve 60, a cooling-stage heat exchanger 61, and a JT circulation line 62 that connects the components to each other. The first-stage heat exchanger 44 and the second-stage heat exchanger 46 are, for example, countercurrent heat exchangers. The JT heat exchanger group 58 is formed by a series of countercurrent heat exchangers (58a to 58c). The JT circulation line 62 includes a JT supply line 62a that connects a discharge side of the JT compression system 56 to a supply side of the cooling-stage heat exchanger 61 and a JT collection line 62b that connects a collection side of the cooling-stage heat exchanger 61 to a suction side of the JT compression system 56.
The JT compression system 56 is configured to pressurize a refrigerant gas collected from the JT collection line 62b to send the refrigerant gas out to the JT supply line 62a. The JT compression system 56 operates as a refrigerant source that circulates a refrigerant in the JT circulation line 62. The JT compression system 56 is disposed outside the vacuum chamber 16, that is, in the normal-temperature section 22 of the cryogenic system 100. For example, the JT compression system 56 includes a two-stage compression configuration that has a low pressure stage compressor and a high pressure stage compressor which are connected to each other in series. For example, a low pressure refrigerant gas which has approximately the atmospheric pressure is collected from the JT supply line 62a to the JT compression system 56. The JT compression system 56 pressurizes the collected refrigerant gas to, for example, approximately several tens of atmospheres, and sends out the refrigerant gas to the JT supply line 62a.
On the JT circulation line 62, the JT heat exchanger group 58 is disposed between the JT compression system 56 and the cooling-stage heat exchanger 61. The JT heat exchanger group 58 has a three-stage configuration including a first JT heat exchanger 58a, a second JT heat exchanger 58b, and a third JT heat exchanger 58c. The first JT heat exchanger 58a cools a high-temperature (for example, a normal temperature, such as approximately 300 K) refrigerant gas flowing from the outside of the vacuum chamber 16 into the vacuum chamber 16. The second JT heat exchanger 58b further cools the refrigerant which is cooled by the first JT heat exchanger 58a and the first-stage heat exchanger 44. The third JT heat exchanger 58c further cools the refrigerant which is cooled by the second JT heat exchanger 58b and the second-stage heat exchanger 46. The JT heat exchanger group 58 may have other multi-stage configurations.
The JT supply line 62a includes a high pressure side flow path of each of the first JT heat exchanger 58a, the second JT heat exchanger 58b, and the third JT heat exchanger 58c, and the JT collection line 62b includes a low pressure side flow path of each of the first JT heat exchanger 58a, the second JT heat exchanger 58b, and the third JT heat exchanger 58c. A refrigerant flowing in the high pressure side flow path can be cooled through heat exchange between the high pressure side flow path and the low pressure side flow path of each heat exchanger. The high pressure side flow path and the low pressure side flow path can also be called a high temperature side flow path and a low temperature side flow path, respectively.
The first-stage heat exchanger 44 is disposed between the first JT heat exchanger 58a and the second JT heat exchanger 58b on the JT supply line 62a. The first-stage heat exchanger 44 can cool the JT supply line 62a through heat exchange between a refrigerant cooled by the first-stage precooling unit 41 and the JT supply line 62a.
The second-stage heat exchanger 46 is disposed between the second JT heat exchanger 58b and the third JT heat exchanger 58c on the JT supply line 62a. The second-stage heat exchanger 46 can further cool the JT supply line 62a through heat exchange between a refrigerant cooled by the second-stage precooling unit 43 and the JT supply line 62a.
The JT valve 60 is disposed between the heat exchanger (the third JT heat exchanger 58c in the present example) at the last stage of the JT heat exchanger group 58 and the cooling-stage heat exchanger 61 on the JT supply line 62a. The JT valve 60 is, for example, a fixed orifice. The cooling-stage heat exchanger 61 is thermally coupled to the cryogenic cooling unit 20. A refrigerant flowing in the cooling-stage heat exchanger 61 cools the cryogenic cooling unit 20.
Similarly, in addition to the first-stage heat exchanger 44 and the second-stage heat exchanger 46, the second JT circuit 10b includes the JT compression system 56, the JT heat exchanger group 58 (58a to 58c), the JT valve 60, the cooling-stage heat exchanger 61, and the JT circulation line 62 (62a and 62b) that connects the components to each other.
Without being limited to the specific configuration described above, various typical configurations can be adopted as appropriate for the JT circuit 10.
Fig. 2 is a table for describing a relationship between an exemplary failure mode of the cryogenic system 100 according to the first embodiment and a flow path switching state. The open and closed state of each of the opening and closing valves (V1 to V6) is shown to correspond to each of several failure modes. In the table, "open" means that the opening and closing valve is open, and "close" means that the opening and closing valve is closed.
Fig. 2 shows normal operation and four failure modes of the cryogenic system 100 as examples. "Normal operation" means that both of the circulation pump 26 and the mechanical refrigerator 14 which are provided in the cryogenic system 100 operate normally without a failure. A "ST1 failure" means that the mechanical refrigerator 14 of the first precooling loop 12a has failed, and a "ST2 failure" means that the mechanical refrigerator 14 of the second precooling loop 12b has failed. A "P1 failure" means that the circulation pump 26 of the first precooling loop 12a has failed, and a "P2 failure" means that the circulation pump 26 of the second precooling loop 12b has failed.
Since a temperature sensor 64 that measures the temperature of the cryocooler stage is usually provided in at least one of the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38, it is possible to determine whether or not the mechanical refrigerator 14 has failed based on the measurement results from the temperature sensor 64. Since a refrigerant sensor 66, such as a pressure sensor that measures the pressure of a refrigerant (and/or a flow rate sensor that measures the flow rate of the refrigerant), is usually provided in the precooling circuit 12, it is possible to determine whether or not the circulation pump 26 has failed based on the measurement results from the refrigerant sensor 66.
As shown in the field of the "normal operation" in Fig. 2, in a case where the cryogenic system 100 operates normally without a failure or an abnormality, all of the circulation pump shutoff valves (V1, V2, V5, and V6) are opened, and the connection opening and closing valves (V3 and V4) are both closed. This is the disconnected state of the connection line 13. This open and closed state may be a nominal state of each of the opening and closing valves (V1 to V6). That is, the circulation pump shutoff valves (V1, V2, V5, and V6) may be normally open valves, and the connection opening and closing valves (V3 and V4) may be normally closed valves. By doing so, it is guaranteed that each of the opening and closing valves (V1 to V6) takes an open and closed state during normal operation as an initial state.
Therefore, in the disconnected state of the connection line 13, the circulation pump 26 of the first precooling loop 12a circulates a refrigerant in the first precooling loop 12a, and the circulation pump 26 of the second precooling loop 12b circulates a refrigerant in the second precooling loop 12b, as shown by arrows in Fig. 1. The refrigerant does not flow in the connection line 13, and the refrigerant does not flow between the first precooling loop 12a and the second precooling loop 12b. In this manner, the plurality of precooling loops are operated independently of each other.
During the normal operation of the cryogenic system 100, in each precooling loop, a refrigerant sent out from the circulation pump 26 to the precooling supply line 50 flows into the vacuum chamber 16, and is first supplied to the supply side flow path of the first precooling heat exchanger 40. The refrigerant flowing in the supply side flow path of the first precooling heat exchanger 40 is cooled by exchanging heat with a returning refrigerant flowing in the collection side flow path of the first precooling heat exchanger 40. The refrigerant cooled by the first precooling heat exchanger 40 flows into the first-stage precooling unit 41 through the precooling supply line 50.
A refrigerant is cooled by the first-stage refrigerator stage 36 at the first-stage precooling unit 41, and is supplied to the first-stage heat exchanger 44. The refrigerant is sent from the first-stage heat exchanger 44 into the supply side flow path of the second precooling heat exchanger 42. The refrigerant flowing in the supply side flow path of the second precooling heat exchanger 42 is cooled by exchanging heat with a returning refrigerant flowing in the collection side flowpath of the second precooling heat exchanger 42. The refrigerant cooled by the second precooling heat exchanger 42 flows into the second-stage precooling unit 43 through the precooling supply line 50.
A refrigerant is cooled by the second-stage refrigerator stage 38 at the second-stage precooling unit 43, and is supplied to the second-stage heat exchanger 46. The refrigerant flows from the second-stage heat exchanger 46 to the precooling collection line 52. The refrigerant flows in the precooling collection line 52 in the order of the second precooling heat exchanger 42 and the first precooling heat exchanger 40. As described above, a returning refrigerant cools a refrigerant flowing in the precooling supply line 50 while being heated in each of the heat exchangers (42 and 40). The refrigerant that has returned to a normal temperature in this manner exits the vacuum chamber 16 to be collected in the circulation pump 26, and is again send out. In this manner, each of the precooling loops operates individually during normal operation.
On the other hand, in the first JT circuit 10a and the second JT circuit 10b, a refrigerant flows in the JT circulation line 62 as follows. A high pressure refrigerant compressed by the JT compression system 56 is first supplied to the high pressure side flow path of the first JT heat exchanger 58a. The high pressure refrigerant flowing in the high pressure side flow path of the first JT heat exchanger 58a is cooled by exchanging heat with a low pressure returning refrigerant flowing in the low pressure side flow path of the first JT heat exchanger 58a. The high pressure refrigerant cooled by the first JT heat exchanger 58a flows into the first-stage heat exchanger 44 through the JT supply line 62a.
A high pressure refrigerant in the JT supply line 62a is cooled by exchanging heat with a refrigerant in the precooling circuit 12 cooled by the first-stage precooling unit 41 at the first-stage heat exchanger 44, and is sent into the high pressure side flow path of the second JT heat exchanger 58b. The high pressure refrigerant flowing in the high pressure side flow path of the second JT heat exchanger 58b is cooled by exchanging heat with a low pressure returning refrigerant flowing in the low pressure side flow path of the second JT heat exchanger 58b. The high pressure refrigerant cooled by the second JT heat exchanger 58b flows into the second-stage heat exchanger 46 through the JT supply line 62a.
A high pressure refrigerant in the JT supply line 62a is cooled by exchanging heat with a refrigerant in the precooling circuit 12 cooled by the second-stage precooling unit 43 at the second-stage heat exchanger 46, and is sent into the high pressure side flow path of the third JT heat exchanger 58c. The high pressure refrigerant flowing in the high pressure side flow path of the third JT heat exchanger 58c is cooled by exchanging heat with a low pressure returning refrigerant flowing in the low pressure side flow path of the third JT heat exchanger 58c. In this manner, the high pressure refrigerant is cooled to a temperature or less at which the Joule-Thomson effect is expected, and is sent to the JT valve 60.
When passing through the JT valve 60, a cooled high pressure refrigerant becomes a mist-like low pressure refrigerant in a gas-liquid mixed state due to the Joule-Thomson effect, generating a cooling capacity in a temperature range of a liquefied refrigerant. The mist-like low pressure refrigerant is sent to the cooling-stage heat exchanger 61. In a case where the refrigerant is helium as described above, the cooling-stage heat exchanger 61 is cooled to a liquid helium temperature range, and accordingly the cryogenic cooling unit 20 can be cooled to the temperature.
When cooling the cooling-stage heat exchanger 61, a mist-like low pressure refrigerant evaporates and vaporizes again. A refrigerant yet to be liquefied and the refrigerant vaporized through evaporation at the JT valve 60 are returned to the low pressure side flow path of the third JT heat exchanger 58c. The low pressure refrigerant flows in the JT collection line 62b in the order of the second JT heat exchanger 58b and the first JT heat exchanger 58a. In this case, the low pressure refrigerant cools a high pressure refrigerant while being heated in each of the heat exchangers (58c, 58b, and 58a), as described above. The low pressure refrigerant that has returned to a normal temperature in this manner exits the vacuum chamber 16 to be collected in the JT compression system 56, and is again compressed.
In this manner, the cryogenic system 100 can cool the cryogenic cooling unit 20 and the object to be cooled 18 to a temperature lower than the second-stage cooling temperature of the mechanical refrigerator 14, for example, a desired temperature of less than 4 K (for example, 1 K to 4 K).
As shown in Fig. 2, the connection line 13 takes the disconnected state also in cases of the ST1 failure and the ST2 failure. However, in these cases, it is not necessary to circulate a refrigerant in a precooling loop to which the failed mechanical refrigerator 14 belongs, unlike the normal operation. Accordingly, in the case of the ST1 failure, the operation of the circulation pump 26 of the first precooling loop 12a is stopped, and in the case of the ST2 failure, the operation of the circulation pump 26 of the second precooling loop 12b is stopped. In this manner, the circulation pump 26 of the precooling loop to which the failed mechanical refrigerator 14 belongs is stopped, and the operation of the circulation pump 26 of the other precooling loop is continued.
In the case of the ST1 failure, the operation of the circulation pump 26 of the first precooling loop 12a is stopped, and the circulation pump shutoff valves (V1 and V2) of the first precooling loop 12a may be closed. Similarly, in the case of the ST2 failure, the operation of the circulation pump 26 of the second precooling loop 12b is stopped, and the circulation pump shutoff valves (V5 and V6) of the second precooling loop 12b may be closed. By doing so, a refrigerant gas that passes through and flows in the failed circulation pump 26 can be reliably shut off.
In the cases of the ST1 failure and the ST2 failure, the mechanical refrigerator 14 can no longer be cooled. The mechanical refrigerator 14 is a heat transfer path from the normal-temperature section 22 to the cryocooler stage. The failed mechanical refrigerator 14 can also be called a thermal infiltration source. Heat infiltrates from the normal-temperature section 22 into the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38 via a structural member (for example, a cylinder and a displacer) of the mechanical refrigerator 14 through thermal conduction. As a result, the temperatures of the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38 gradually increase to a normal temperature. When the cryogenic cooling unit 20 is directly attached to the cryocooler stage, the cryogenic cooling unit 20 is also heated together with the cryocooler stage due to a failure in the mechanical refrigerator 14. The cooling capacity of the cryogenic system 100 reduces, and it can be difficult to maintain the cooling of the object to be cooled 18 in the end.
However, in the present embodiment, the cryocooler stage of the mechanical refrigerator 14 is physically separated from the JT circuit 10 and the cryogenic cooling unit 20. The mechanical refrigerator 14 is merely thermally coupled to the JT circuit 10 indirectly via the precooling circuit 12. In the cases of the ST1 failure and the ST2 failure, the amount of heat transmitted from the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38 to the first-stage heat exchanger 44 and the second-stage heat exchanger 46 through thermal conduction is limited. In addition, the first-stage heat exchanger 44 and the second-stage heat exchanger 46 are also merely connected to the cryogenic cooling unit 20 via the JT circuit 10 (the JT circulation line 62) as a path for thermal conduction. For this reason, even when any mechanical refrigerator 14 of the plurality of mechanical refrigerators 14 has failed, thermal infiltration from the failed mechanical refrigerator 14 to the cryogenic cooling unit 20 is significantly suppressed. In fact, the cryogenic system 100 can thermally disconnect the failed mechanical refrigerator 14 from the cryogenic system 100. The cryogenic cooling of the cryogenic cooling unit 20 and the object to be cooled 18 can be continued using the other normal mechanical refrigerator 14, the precooling circuit 12, and the JT circuit 10.
In addition, in general, the existing JT cryocooler only includes a mechanical refrigerator as precooling means. Since the JT cryocooler is thermally coupled to the cryocooler stage of the mechanical refrigerator directly, thermal infiltration into the JT cryocooler at the time of a failure in the mechanical refrigerator tends to increase. In such an existing method, according to the estimation by the present inventor, at least three mechanical refrigerators may be necessary in order to ensure redundancy for two systems of JT cryocoolers as in Fig. 1. In other words, when one mechanical refrigerator has failed, not only the cooling capacity of a failed refrigerator is lost from the entire system, but also thermal infiltration, which is caused by thermal conduction with the failed refrigerator as a heat transfer path, needs to be dealt with. For this, at least two normal refrigerators may be necessary.
On the other hand, in the present embodiment, thermal infiltration from the failed mechanical refrigerator 14 to the cryogenic cooling unit 20 is significantly suppressed as described above. According to the estimation by the present inventor, in the JT circuit 10 having two systems of JT cryocoolers as in Fig. 1, redundancy can be ensured by the two mechanical refrigerators 14. That is, when one mechanical refrigerator 14 has failed, the cooling operation of the cryogenic system 100 can be continued using the remaining one normal mechanical refrigerator 14.
Further, as shown in Fig. 2, in the case of the P1 failure, the circulation pump shutoff valves (V1 and V2) of the first precooling loop 12a to which the failed circulation pump 26 belongs are closed, and the connection opening and closing valves (V3 and V4) are both opened. The circulation pump shutoff valves (V5 and V6) of the second precooling loop 12b to which the normal circulation pump 26 belongs are opened. In addition, in the case of the P2 failure, the circulation pump shutoff valves (V5 and V6) of the second precooling loop 12b to which the failed circulation pump 26 belongs are closed, and the connection opening and closing valves (V3 and V4) are both opened. The circulation pump shutoff valves (V1 and V2) of the first precooling loop 12a to which the normal circulation pump 26 belongs are opened. These are the connected state of the connection line 13.
In Fig. 3, the flow of a refrigerant in the connected state of the connection line 13 is shown by arrows. For example, the P2 failure, that is, a case where the circulation pump 26 of the second precooling loop 12b has failed is shown. Accordingly, while the circulation pump 26 of the first precooling loop 12a operates normally, the circulation pump 26 of the second precooling loop 12b does not operate. As shown, the circulation pump 26 of the first precooling loop 12a circulates the refrigerant in both of the first precooling loop 12a and the second precooling loop 12b. In the first precooling loop 12a, the refrigerant circulates as in normal times.
In the second precooling loop 12b, a refrigerant is supplied from the precooling supply line 50 of the first precooling loop 12a to the precooling supply line 50 of the second precooling loop 12b through the supply side connection flow path 13a. Also in the second precooling loop 12b, the refrigerant is supplied to the first-stage heat exchanger 44 and the second-stage heat exchanger 46 as in normal times. The refrigerant returns from the precooling collection line 52 of the second precooling loop 12b to the precooling collection line 52 of the first precooling loop 12a through the collection side connection flow path 13b, and is collected in the circulation pump 26 of the first precooling loop 12a. Since the circulation pump shutoff valves (V5 and V6) of the second precooling loop 12b are closed, the backflow in the second precooling loop 12b is prevented.
In the case of the P1 failure, the circulation pump 26 of the second precooling loop 12b circulates a refrigerant in both of the first precooling loop 12a and the second precooling loop 12b.
The precooling circuit 12 has no element having a high flow path resistance unlike the JT valve 60 of the JT circuit 10. For this reason, the precooling circuit 12 has a small pressure loss as a whole, and a refrigerant gas can be circulated by a small-scale pump having a relatively low power consumption like the circulation pump 26.
In this manner, during a failure in the circulation pump 26 of one precooling loop, the plurality of precooling loops can be operated using the normal circulation pump 26 of the other precooling loop. Accordingly, the cryogenic system 100 can precool the JT circuit 10. Even when any circulation pump 26 fails, the cooling operation of the cryogenic system 100 can be continued.
As described above, in the cryogenic system 100 according to the first embodiment, the cooling operation of the cryogenic system 100 can be continued in a form corresponding to each of the plurality of failure modes.
The cryogenic system 100 can be expanded in various ways. For example, the cryogenic system 100 may include more than two JT circuits (10a, 10b, 10c, ...). The precooling circuit 12 may be configured to precool the multiple JT circuits . The precooling circuit 12 may include more than two precooling loops (12a, 12b, 12c, ...), and more than two JT circuits may be cooled by corresponding precooling loops, respectively. The cryogenic system 100 may include more than two mechanical refrigerators 14 in order to cool the precooling circuit 12. The plurality of mechanical refrigerators 14 may cool corresponding precooling loops (12a, 12b, 12c, ...), respectively.
Fig. 4 is a diagram schematically showing a modification example of the cryogenic system 100 according to the first embodiment. From a perspective of increasing redundancy, the third valve V3 disposed on the supply side connection flow path 13a may be a plurality of (for example, two) valves disposed in parallel. Similarly, the fourth valve V4 disposed on the collection side connection flow path 13b may be a plurality of (for example, two) valves disposed in parallel. By doing so, when one of the two parallel valves is opened, the connection line 13 can be switched from the disconnected state to the connected state even when the other valve remains closed due to a failure.
Fig. 5 is a diagram schematically showing a cryogenic system 200 according to a second embodiment. Fig. 6 is a table for describing a relationship between an exemplary failure mode of the cryogenic system according to the second embodiment and a flow path switching state. The cryogenic system 200 according to the second embodiment is different from the cryogenic system 100 according to the first embodiment in terms of connection between the JT circuit and the precooling circuit, and the rest is mostly the same. Hereinafter, different configurations will be mainly described, and common configurations will be briefly described or description thereof will be omitted.
The cryogenic system 200 includes the JT circuit 10, the refrigerant circulation type precooling circuit 12 that precools the JT circuit 10, and the plurality of mechanical refrigerators 14 that indirectly cool the JT circuit 10 by cooling the precooling circuit 12. In addition, the cryogenic system 200 includes the vacuum chamber 16 and the cryogenic cooling unit 20 that cools the object to be cooled 18.
The JT circuit 10 includes, as components provided in the low-temperature section 24 of the cryogenic system 200, the JT heat exchanger group 58 (58a, 58b, and 58c), the JT valve 60, the cooling-stage heat exchanger 61, and the JT circulation line 62 (62a and 62b) that connects the components to each other. In addition, the JT circuit 10 includes the first-stage heat exchanger 44 and the second-stage heat exchanger 46 in order to precool the JT circuit 10 with the precooling circuit 12. While the plurality of JT circuits (10a and 10b) separated from each other are provided in parallel in the first embodiment, one JT circuit is provided in the second embodiment. If necessary, a plurality of JT circuits may be provided also in the second embodiment.
In the embodiment, the JT circuit 10 includes a plurality of JT compressor systems, for example, a first JT compressor 56a and a second JT compressor 56b in the normal-temperature section 22 of the cryogenic system 200. The first JT compressor 56a and the second JT compressor 56b are provided in parallel. The JT supply line 62a branches off at a first connection point 72 and is connected to each of discharge sides of the first JT compressor 56a and the second JT compressor 56b. The JT collection line 62b branches off at a second connection point 73 and is connected to each of collection sides of the first JT compressor 56a and the second JT compressor 56b.
The first JT compressor 56a includes, for example, a front stage compressor 70 and a rear stage compressor 71, and the compressors are connected to each other in series. For example, a low pressure refrigerant gas which has approximately the atmospheric pressure is collected from the JT collection line 62b to the front stage compressor 70. The front stage compressor 70 pressurizes the collected refrigerant gas to, for example, approximately several atmospheres. The rear stage compressor 71 pressurizes the refrigerant gas pressurized by the front stage compressor 70 to, for example, approximately several tens of atmospheres. The high pressure refrigerant gas obtained in this manner is sent out from the rear stage compressor 71 to the JT supply line 62a. Similarly, the second JT compressor 56b also has a two-stage compression configuration, and includes the front stage compressor 70 and the rear stage compressor 71 which are connected to each other in series. The first JT compressor 56a and the second JT compressor 56b may have other multi-stage compression configurations, or may have a single-stage compression configuration.
While the JT circuit 10 and the precooling circuit 12 are completely separated from each other in the cryogenic system 100 according to the first embodiment, the cryogenic system 200 according to the second embodiment includes flow path switching devices (V1 to V12) that connect the JT circuit 10 to the precooling circuit 12. Although details will be described later, the flow path switching devices are configured to switch between a first state where the JT circuit 10 is operated by the first JT compressor 56a and the precooling circuit 12 is operated by the second JT compressor 56b and a second state where the JT circuit 10 is operated by the second JT compressor 56b and the precooling circuit 12 is operated by the first JT compressor 56a.
The precooling circuit 12 includes the first precooling loop 12a and the second precooling loop 12b that precool the JT circuit 10 and the connection line 13 (13a and 13b) that connects the first precooling loop 12a and the second precooling loop 12b to each other. A dedicated circulation pump for circulating a refrigerant in the precooling circuit 12 is not provided in the second embodiment unlike the first embodiment. Any one of the first JT compressor 56a and the second JT compressor 56b is used in circulating the refrigerant in the precooling circuit 12.
In addition to the first-stage heat exchanger 44 and the second-stage heat exchanger 46 which are described above, the first precooling loop 12a includes the first precooling heat exchanger 40, the first-stage precooling unit 41, the second precooling heat exchanger 42, and the second-stage precooling unit 43, and the components are disposed in the low-temperature section 24 of the cryogenic system 200. The first precooling loop 12a further includes the precooling supply line 50 and the precooling collection line 52. The precooling supply line 50 of the first precooling loop 12a connects a discharge side of the first JT compressor 56a to the supply side of the second-stage heat exchanger 46 of the first precooling loop 12a. The precooling collection line 52 of the first precooling loop 12a connects the collection side of the second-stage heat exchanger 46 of the first precooling loop 12a to a suction side of the first JT compressor 56a. The JT supply line 62a branches off (a third connection point 74) from the precooling supply line 50 on the discharge side of the first JT compressor 56a. The third connection point 74 is on the upstream side from the first connection point 72 (that is, close to the discharge side of the first JT compressor 56a). In addition, the JT collection line 62b joins the precooling collection line 52 (a fourth connect ion point 75) on a collection side of the first JT compressor 56a. The fourth connection point 75 is on the downstream side from the second connection point 73 (that is, close to the collection side of the first JT compressor 56a).
The second precooling loop 12b also includes the same components. However, the precooling supply line 50 of the second precooling loop 12b connects a discharge side of the second JT compressor 56b to the supply side of the second-stage heat exchanger 46 of the second precooling loop 12b. The precooling collection line 52 of the second precooling loop 12b connects the collection side of the second-stage heat exchanger 46 of the second precooling loop 12b to a suction side of the second JT compressor 56b. The JT supply line 62a branches off (a fifth connection point 76) from the precooling supply line 50 on the discharge side of the second JT compressor 56b. The fifth connection point 76 is on the upstream side from the first connection point 72 (that is, close to the discharge side of the second JT compressor 56b). In addition, the JT collection line 62b joins the precooling collection line 52 (a sixth connection point 77) on a collection side of the second JT compressor 56b. The sixth connection point 77 is on the downstream side from the second connection point 73 (that is, close to the collection side of the second JT compressor 56b) .
The supply side connection flow path 13a branches off (a seventh connection point 78) from the precooling supply line 50 of the second precooling loop 12b, and joins the precooling supply line 50 of the first precooling loop 12a (an eighth connection point 79). The seventh connection point 78 is on the downstream side from the fifth connection point 76 on the precooling supply line 50 of the second precooling loop 12b. The eighth connection point 79 is on the downstream side from the third connection point 74 on the precooling supply line 50 of the first precooling loop 12a. In addition, the collection side connection flow path 13b branches off (a ninth connection point 80) from the precooling collection line 52 of the first precooling loop 12a, and joins the precooling collection line 52 of the second precooling loop 12b (a tenth connection point 81). The ninth connection point 80 is on the upstream side from the fourth connection point 75 on the precooling collection line 52 of the first precooling loop 12a. The tenth connection point 81 is on the upstream side from the sixth connection point 77 on the precooling collection line 52 of the second precooling loop 12b.
The plurality of mechanical refrigerators 14 cool the corresponding precooling loops, respectively. In the embodiment, two mechanical refrigerators 14 are provided. One mechanical refrigerator cools a refrigerant circulating in the first precooling loop 12a, and the other mechanical refrigerator cools a refrigerant circulating in the second precooling loop 12b. The mechanical refrigerator 14 is, for example, a two-stage Stirling cryocooler. The mechanical refrigerator 14 includes the compressor 30, the two-stage coldhead 32, which is an expander, and the connecting pipe 34 that connects the compressor 30 to the two-stage cold head 32. The two-stage cold head 32 includes the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38. Similarly, the refrigerant circulation inside the mechanical refrigerator 14 is separated from the JT circuit 10 and the precooling circuit 12, and a refrigerant gas does not flow from the mechanical refrigerator 14 to the JT circuit 10 (or the precooling circuit 12).
The temperature sensor 64 that measures the temperature of the cryocooler stage is usually provided in at least one of the first-stage refrigerator stage 36 and the second-stage refrigerator stage 38. The refrigerant sensor 66, such as a pressure sensor that measures the pressure of a refrigerant (and/or a flow rate sensor that measures the flow rate of the refrigerant), is usually provided in the precooling circuit 12. For example, in order to check the operation of the first JT compressor 56a, a first pressure sensor may be provided on the discharge side of the first JT compressor 56a, and a second pressure sensor may be provided on the collection side of the second JT compressor 56b. A third pressure sensor may be provided between the front stage compressor 70 and the rear stage compressor 71.
The first-stage heat exchanger 44 is configured to exchange heat with both of the first precooling loop 12a and the second precooling loop 12b. The first-stage heat exchanger 44 is provided between the first JT heat exchanger 58a and the second JT heat exchanger 58b on the JT supply line 62a in the JT circuit 10. The first-stage heat exchanger 44 is provided between the first-stage precooling unit 41 and the second precooling heat exchanger 42 on the precooling supply line 50 in the first precooling loop 12a, and is also provided between the first-stage precooling unit 41 and the second precooling heat exchanger 42 on the precooling supply line 50 in the second precooling loop 12b. Therefore, the first-stage heat exchanger 44 can further cool a refrigerant in the JT supply line 62a cooled by the first JT heat exchanger 58a with both of the first precooling loop 12a and the second precooling loop 12b. The refrigerant cooled by the first-stage heat exchanger 44 flows to the second JT heat exchanger 58b.
The second-stage heat exchanger 46 is also configured to exchange heat with both of the first precooling loop 12a and the second precooling loop 12b. The second-stage heat exchanger 46 is provided between the second JT heat exchanger 58b and the third JT heat exchanger 58c on the JT supply line 62a in the JT circuit 10. In each of the first precooling loop 12a and the second precooling loop 12b, a refrigerant cooled by the second-stage precooling unit 43 is supplied to the second-stage heat exchanger 46. Therefore, the second-stage heat exchanger 46 can further cool the refrigerant in the JT supply line 62a cooled by the second JT heat exchanger 58b with both of the first precooling loop 12a and the second precooling loop 12b. The refrigerant cooled by the second-stage heat exchanger 46 flows to the third JT heat exchanger 58c.
The first-stage heat exchanger 44 and the second-stage heat exchanger 46 each may include a heat transfer member 82 which is a part of a refrigerant flow path of the JT circuit 10. The JT supply line 62a is configured to pass through the inside of the heat transfer member 82 in the first-stage heat exchanger 44. Similarly, the JT supply line 62a is configured to pass through the inside of the heat transfer member 82 in the second-stage heat exchanger 46. In the first-stage heat exchanger 44 and the second-stage heat exchanger 46, the first precooling loop 12a and the second precooling loop 12b are provided outside the JT supply line 62a, and exchange heat with the JT supply line 62a via the heat transfer member 82. The heat transfer member 82 is formed of a material excellent in thermal conduction, such as copper, just as the cryocooler stage. By doing so, the first precooling loop 12a and the second precooling loop 12b can equally precool the JT circuit 10.
As described above, the first-stage heat exchanger 44 and the second-stage heat exchanger 46 can precool the JT circuit 10 with both of the first precooling loop 12a and the second precooling loop 12b. For this reason, even in a case where any one of the precooling loops does not operate, the precooling circuit 12 can precool the JT circuit 10 using the other precooling loop operating normally.
The role and disposition of a group of valves (V1 to V12) configuring the flow path switching devices will be described. The valves are disposed in the normal-temperature section 22 of the cryogenic system 200 just as the first JT compressor 56a and the second JT compressor 56b.
In order to select which one of the JT circuit 10 and the precooling circuit 12 is to be connected to the first JT compressor 56a, four opening and closing valves including the first valve V1, the second valve V2, the third valve V3, and the fifth valve V5 are provided. The second valve V2 is provided on the JT supply line 62a, the third valve V3 is provided on the precooling supply line 50 of the first precooling loop 12a, and the valves are connected to the discharge side of the first JT compressor 56a in parallel. The second valve V2 is disposed between the third connection point 74 and the first connection point 72, and the third valve V3 is disposed between the third connection point 74 and the eighth connection point 79. The first valve V1 is provided on the precooling collection line 52 of the first precooling loop 12a, the fifth valve V5 is provided on the JT collection line 62b, and the valves are connected to the collection side of the first JT compressor 56a in parallel. The first valve V1 is disposed between the fourth connection point 75 and the ninth connection point 80, and the fifth valve V5 is disposed between the fourth connection point 75 and the second connection point 73.
Therefore, when the second valve V2 is opened and the third valve V3 is closed, the discharge side of the first JT compressor 56a is connected to the JT supply line 62a of the JT circuit 10. When the fifth valve V5 is opened and the first valve V1 is closed, the collection side of the first JT compressor 56a is connected to the JT collection line 62b of the JT circuit 10. In this manner, the cryogenic system 200 can operate the JT circuit 10 with the first JT compressor 56a.
Conversely, when the second valve V2 is closed and the third valve V3 is opened, the discharge side of the first JT compressor 56a is connected to the precooling supply line 50 of the first precooling loop 12a. When the fifth valve V5 is closed and the first valve V1 is opened, the collection side of the first JT compressor 56a is connected to the precooling collection line 52 of the first precooling loop 12a. In this manner, the cryogenic system 200 can operate the precooling circuit 12 with the first JT compressor 56a.
In order to select which one of the JT circuit 10 and the precooling circuit 12 is to be connected to the second JT compressor 56b, four opening and closing valves including the sixth valve V6, the seventh valve V7, the eighth valve V8, and the ninth valve V9 are provided. The eighth valve V8 is provided on the JT supply line 62a, the ninth valve V9 is provided on the precooling supply line 50 of the second precooling loop 12b, and the valves are connected to the discharge side of the second JT compressor 56b in parallel. The eighth valve V8 is disposed between the fifth connection point 76 and the first connection point 72, and the ninth valve V9 is disposed between the fifth connection point 76 and the seventh connection point 78. The sixth valve V6 is provided on the JT collection line 62b, the seventh valve V7 is provided on the precooling collection line 52 of the second precooling loop 12b, and the valves are connected to the collection side of the second JT compressor 56b in parallel. The sixth valve V6 is disposed between the sixth connection point 77 and the second connection point 73, and the seventh valve V7 is disposed between the sixth connection point 77 and the tenth connection point 81.
Therefore, when the eighth valve V8 is opened and the ninth valve V9 is closed, the discharge side of the second JT compressor 56b is connected to the JT supply line 62a of the JT circuit 10. When the sixth valve V6 is opened and the seventh valve V7 is closed, the collection side of the second JT compressor 56b is connected to the JT collection line 62b of the JT circuit 10. In this manner, the cryogenic system 200 can operate the JT circuit 10 with the second JT compressor 56b.
Conversely, when the eighth valve V8 is closed and the ninth valve V9 is opened, the discharge side of the second JT compressor 56b is connected to the precooling supply line 50 of the second precooling loop 12b. When the sixth valve V6 is closed and the seventh valve V7 is opened, the collection side of the second JT compressor 56b is connected to the precooling collection line 52 of the second precooling loop 12b. In this manner, the cryogenic system 200 can operate the precooling circuit 12 with the second JT compressor 56b.
Further, in order to select whether to connect or disconnect the first precooling loop 12a and the second precooling loop 12b to or from each other, four opening and closing valves including the fourth valve V4, the tenth valve V10, the eleventh valve V11, and the twelfth valve V12 are provided. The fourth valve V4 is provided on the downstream side from the eighth connection point 79 on the precooling supply line 50 of the first precooling loop 12a, and the tenth valve V10 is provided on the downstream side from the seventh connection point 78 on the precooling supply line 50 of the second precooling loop 12b. The eleventh valve V11 is provided on the upstream side from the tenth connection point 81 on the precooling collection line 52 of the second precooling loop 12b, and the twelfth valve V12 is provided on the upstream side from the ninth connection point 80 on the precooling collection line 52 of the first precooling loop 12a.
Therefore, when all of the fourth valve V4, the tenth valve V10, the eleventh valve V11, and the twelfth valve V12 are opened, the first precooling loop 12a and the second precooling loop 12b are connected to each other through the connection line 13. In addition, when at least one of the fourth valve V4 and the tenth valve V10 is closed and at least one of the eleventh valve V11 and the twelfth valve V12 is closed, the first precooling loop 12a and the second precooling loop 12b are disconnected from each other.
Fig. 6 shows normal operation and five failure modes of the cryogenic system 200 as examples. "Normal operation (1)" and "normal operation (2)" mean that both of the circulation pump 26 and the mechanical refrigerator 14 which are provided in the cryogenic system 200 operate normally without a failure. A"ST1 failure (1)" and a "ST1 failure (2)"mean that the mechanical refrigerator 14 of the first precooling loop 12a has failed during the "normal operation (1)" and the "normal operation (2)", respectively. A "ST2 failure (1)" and a "ST2 failure (2)" mean that the mechanical refrigerator 14 of the second precooling loop 12b has failed during the "normal operation (1)" and the "normal operation (2)", respectively.
As shown in the field of the "normal operation (1)", in a case where the cryogenic system 200 operates normally without a failure or an abnormality, the first valve V1, the third valve V3, the sixth valve V6, and the eighth valve V8 are closed, and the other opening and closing valves (V2, V4, V5, V7, and V9 to V12) are opened. Therefore, the cryogenic system 200 can operate the precooling circuit 12 with the second JT compressor 56b while operating the JT circuit 10 with the first JT compressor 56a (the first state) . This open and closed state maybe a nominal state of each of the opening and closing valves (V1 to V12). That is, the first valve V1, the third valve V3, the sixth valve V6, and the eighth valve V8 may be normally closed valves, and the other opening and closing valves may be normally open valves . By doing so, it is guaranteed that each of the opening and closing valves (V1 to V12) takes an open and closed state of the normal operation (1) during normal operation as an initial state.
In the first state, in order to operate the JT circuit 10, both of the front stage compressor 70 and the rear stage compressor 71 of the first JT compressor 56a are operated. On the other hand, the second JT compressor 56b operates at lower output than the first JT compressor 56a in the first state. For example, the front stage compressor 70 can pressurize a collected refrigerant gas to, for example, approximately the atmospheric pressure or approximately several atmospheres, and this is sufficient to recover a pressure loss that occurs in a refrigerant in the precooling circuit 12. Accordingly, the second JT compressor 56b can operate the precooling circuit 12 by stopping the rear stage compressor 71 and operating only the front stage compressor 70. Alternatively, the second JT compressor 56b may stop the front stage compressor 70 and operate only the rear stage compressor 71 at a low output. In a case where any one of the front stage compressor 70 and the rear stage compressor 71 has failed or deteriorated, the precooling circuit 12 can be operated by the other normal compressor.
During the "normal operation (2)", the second valve V2, the fifth valve V5, the seventh valve V7, and the ninth valve V9 are closed, and the other opening and closing valves are opened. Therefore, the cryogenic system 200 can operate the precooling circuit 12 with the first JT compressor 56a while operating the JT circuit 10 with the second JT compressor 56b (the second state) . The second state can be used in a case where the cryogenic system 200 operates normally without a failure or an abnormality as in the first state.
Alternatively, it is also possible to switch from the first state to the second state when a reduction or a deterioration in the performance of the first JT compressor 56a is found as the first state is continued for a long period of time. By doing so, a cooling operation of the JT circuit 10 can be continued using the second JT compressor 56b. The first JT compressor 56a operates at lower output than the second JT compressor 56b in the second state. As described above, since the precooling circuit 12 does not require as a high pressure as the JT circuit 10, the operation of the precooling circuit 12 can also be continued with the first JT compressor 56a. Similarly, it is also possible to switch from the second state to the first state when a reduction or a deterioration in the performance of the second JT compressor 56b is found as the second state is continued for a long period of time.
In addition, the flow path switching devices (V1 to V12) are configured to disconnect any one of the first precooling loop 12a and the second precooling loop 12b from the precooling circuit 12 while operating the other one of the first precooling loop 12a and the second precooling loop 12b with the first JT compressor 56a or the second JT compressor 56b.
In a case where the mechanical refrigerator 14 that cools the first precooling loop 12a has failed in the first state (that is, the "normal operation (1)"), the fourth valve V4 and the twelfth valve V12 are closed as shown in the field of the "ST1 failure (1)" in Fig. 6. The other opening and closing valves are maintained at valve open and closed states of the first state. In this manner, the first precooling loop 12a is disconnected from the precooling circuit 12 while operating the second precooling loop 12b with the second JT compressor 56b.
In a case where the mechanical refrigerator 14 that cools the second precooling loop 12b has failed in the first state, the tenth valve V10 and the eleventh valve V11 are closed as shown in the field of the "ST2 failure (1)". The other opening and closing valves are maintained at valve open and closed states of the first state. In this manner, the second precooling loop 12b is disconnected from the precooling circuit 12 while operating the first precooling loop 12a with the second JT compressor 56b.
In addition, in a case where the mechanical refrigerator 14 that cools the first precooling loop 12a has failed in the second state (that is, the "normal operation (2)"), the fourth valve V4 and the twelfth valve V12 are closed as shown in the field of the "ST1 failure (2)". The other opening and closing valves are maintained at valve open and closed states of the second state. In this manner, the first precooling loop 12a is disconnected from the precooling circuit 12 while operating the second precooling loop 12b with the first JT compressor 56a.
In a case where the mechanical refrigerator 14 that cools the second precooling loop 12b has failed in the second state, the tenth valve V10 and the eleventh valve V11 are closed as shown in the field of the "ST2 failure (2)". The other opening and closing valves are maintained at valve open and closed states of the second state. In this manner, the second precooling loop 12b is disconnected from the precooling circuit 12 while operating the first precooling loop 12a with the first JT compressor 56a.
As described above, the cryogenic system 200 according to the second embodiment includes the JT circuit 10, the precooling circuit 12, and the mechanical refrigerators 14 in order to precool the JT circuit. Accordingly, the cryogenic system 200 can cool the cryogenic cooling unit 20 and the object to be cooled 18 to, for example, a desired temperature of less than 4 K (for example, 1 K to 4 K).
Also in the second embodiment, the cryocooler stage of the mechanical refrigerator 14 is physically separated from the JT circuit 10 and the cryogenic cooling unit 20. The mechanical refrigerator 14 is merely thermally coupled to the JT circuit 10 indirectly via the precooling circuit 12. For this reason, even when any mechanical refrigerator 14 of the plurality of mechanical refrigerators 14 has failed, thermal infiltration from the failed mechanical refrigerator 14 to the cryogenic cooling unit 20 is significantly suppressed. In fact, the cryogenic system 100 can thermally disconnect the failed mechanical refrigerator 14 from the cryogenic system 100. Accordingly, also in the cryogenic system 200 according to the second embodiment, redundancy can be ensured by the two mechanical refrigerators 14. That is, when one mechanical refrigerator 14 has failed, the cooling operation of the cryogenic system 200 can be continued using the remaining one normal mechanical refrigerator 14.
Also in the cryogenic system 200 according to the second embodiment, the cooling operation of the cryogenic system 200 can be continued in a form corresponding to each of the plurality of failure modes. For example, as described above, in a case where a performance deterioration is found in the JT compressor operating the JT circuit 10, it is possible to respond to the performance deterioration by switching between the first state and the second state. Unlike the first embodiment, a dedicated circulation pump for the precooling circuit 12 is unnecessary. Redundancy can be ensured while reducing the total number of pumps and compressors included in the cryogenic system 200. In addition, in a case where the mechanical refrigerator 14 of any one of the plurality of mechanical refrigerators 14 has failed, it is possible to respond to the failure by disconnecting the corresponding precooling loop.
Various configurations and characteristics which are described above in relation to the first embodiment can be similarly applied to the second embodiment as well if applicable. For example, the pipes of the JT circuit 10 and the precooling circuit 12 may be formed of, for example, a material having thermal conductivity lower than the thermal conductivity of a material for the cryocooler stage of the mechanical refrigerator 14, and for example, may be made of stainless steel. In addition, the precooling circuit 12 may be formed by a flexible pipe at least in the low-temperature section 24 of the cryogenic system 100.
The cryogenic system 200 according to the second embodiment can be expanded in various ways. For example, the cryogenic system 200 may include the plurality of JT circuits 10 that are separated from each other, and each JT circuit can operate independently as a JT cryocooler, as in the first embodiment. In this case, each of the plurality of JT circuits 10 may include a plurality of JT compressor systems, (for example, the first JT compressor 56a and the second JT compressor 56b). Alternatively, two or more JT circuits 10 may be connected to the plurality of JT compressor systems, (for example, the first JT compressor 56a and the second JT compressor 56b) in parallel. In this case, the JT compressor system is shared by two or more JT circuits 10. The two or more JT circuits 10 may be connected to the JT compressor system so as to be selectively disconnectable from the JT compressor system.
The cryogenic system 200 may include a plurality of precooling circuits 12. Each of the plurality of precooling circuits 12 may include the plurality of precooling loops (for example, the first precooling loop 12a and the second precooling loop 12b) that precool the corresponding JT circuits 10 and the connection line that connects the plurality of precooling loops to each other. The cryogenic system 200 may include the plurality of flow path switching devices (V1 to V12), and each of the plurality of flow path switching devices may connect a set of the corresponding JT circuit 10 and the precooling circuit 12 to each other and be configured to switch between the first state and the second state for this set. The cryogenic system 200 may include more than two mechanical refrigerators 14 in order to cool the plurality of precooling circuits 12. The plurality of mechanical refrigerators 14 may cool the corresponding precooling loops, respectively.
The present invention has been described hereinbefore based on the examples. It is clear for those skilled in the art that the present invention is not limited to the embodiments, various design changes are possible, various modification examples are possible, and such modification examples are also within the scope of the present invention. Various characteristics described in relation to one embodiment are also applicable to other embodiments. A new embodiment generated through combination also has the effects of each of the combined embodiments.
Although a case where the mechanical refrigerator 14 is a two-stage Stirling cryocooler has been described as an example in the embodiments described above, the invention is not limited thereto. The mechanical refrigerator 14 may be a two-stage GM cryocooler, a two-stage pulse tube cryocooler, and other two-stage mechanical refrigerators. In addition, the mechanical refrigerator 14 may be a mechanical refrigerator having a multi-stage configuration having more than two stages or a single-stage mechanical refrigerator, depending on a target cooling temperature.
Although the present invention has been described using specific phrases based on the embodiments, the embodiments merely show one aspect of the principles and applications of the present invention, and many modification examples and changes in disposition are allowed without departing from the scope of the present invention defined in the claims.

Brief Description of the Reference Symbols

10:: JT circuit
10a:: first JT circuit
10b:: second JT circuit
12:: precooling circuit
12a:: first precooling loop
12b:: second precooling loop
13:: connection line
14:: mechanical refrigerator
30:: compressor
56a:: first JT compressor
56b:: second JT compressor
100,: 200: cryogenic system

Claims

A cryogenic system (100, 200) comprising:
a JT circuit (10);

a refrigerant circulation type precooling circuit (12) that precools the JT circuit (10); and

a plurality of mechanical refrigerators (14) that indirectly cool the JT circuit (10) by cooling the precooling circuit (12).
The cryogenic system (100, 200) according to claim 1,
wherein the cryogenic system (100, 200) includes a first JT circuit (10a) and a second JT circuit (10b), and

the precooling circuit (12) includes a first precooling loop (12a) that precools the first JT circuit (10a), a second precooling loop (12b) that precools the second JT circuit (10b), and a connection line (13) that disconnectably connects the first precooling loop (12a) and the second precooling loop (12b) to each other.
The cryogenic system (100, 200) according to claim 1,
wherein the JT circuit (10) includes a first JT compressor (56a) and a second JT compressor (56b) that are provided in parallel, and

the cryogenic system (100, 200) further comprises a flow path switching device (V1 to V12) that connects the JT circuit (10) to the precooling circuit (12), the flow path switching device (V1 to V12) being configured to switch between a first state where the JT circuit (10) is operated by the first JT compressor (56a) and the precooling circuit (12) is operated by the second JT compressor (56b) and a second state where the JT circuit (10) is operated by the second JT compressor (56b) and the precooling circuit (12) is operated by the first JT compressor (56a).
The cryogenic system (100, 200) according to claim 3,
wherein the first JT compressor (56a) operates at lower output than the second JT compressor (56b) in the second state, and the second JT compressor (56b) operates at lower output than the first JT compressor (56a) in the first state.
The cryogenic system (100, 200) according to claim 3 or 4,
wherein the precooling circuit (12) includes a first precooling loop (12a) and a second precooling loop (12b) that each precool the JT circuit (10), and

the flow path switching device (V1 to V12) is configured to disconnect any one of the first precooling loop (12a) and the second precooling loop (12b) from the precooling circuit (12) while operating the other one of the first precooling loop (12a) and the second precooling loop (12b) with the first JT compressor (56a) or the second JT compressor (56b).
The cryogenic system (100, 200) according to claim 5,
wherein the JT circuit (10) includes a heat exchanger (44, 46) configured to exchange heat with both of the first precooling loop (12a) and the second precooling loop (12b).
The cryogenic system (100, 200) according to any one of claims 1 to 6,
wherein the plurality of mechanical refrigerators (14) are two mechanical refrigerators (14).