CN218523812U - Ultralow temperature storage system - Google Patents

Abstract

The application discloses an ultralow temperature storage system, which comprises a low-temperature storage tank and a refrigeration host, wherein the refrigeration host comprises a storage tank, a pump, a refrigerator, a low-temperature refrigerator and a heat insulation device; the low-temperature storage tank comprises an inner shell, an outer shell wrapped outside the inner shell and a heat exchange pipeline arranged in the inner shell and used for secondary refrigerant to flow in the heat exchange pipeline; the heat exchange pipeline, the storage tank, the pump, the cold end of the refrigerator and the cold disc of the low-temperature refrigerator are sequentially communicated to form a secondary refrigerant circulating loop, and the refrigerator and the low-temperature refrigerator are both arranged in the heat insulation device; the storage tank is used for storing gas-phase secondary refrigerant in the secondary refrigerant flowing out of the heat exchange pipeline, the pump provides power for the flow of the secondary refrigerant in the secondary refrigerant circulation loop, the cold end of the refrigerator is used for pre-cooling the secondary refrigerant passing through the interior of the refrigerator, and the cold plate of the low-temperature refrigerator is used for refrigerating the secondary refrigerant passing through the interior of the refrigerator. By the design, the low-temperature storage tank can keep low temperature for a long time, and the problems that the storage time of low-temperature media in the low-temperature storage tank is short and the stored low-temperature media are easy to volatilize are solved.

Description

Ultralow temperature storage system

Technical Field

The application relates to the technical field of ultralow temperature storage, in particular to an ultralow temperature storage system.

Background

In the prior art, cryogenic storage tanks are typically double walled with a vacuum interlayer between the two walls and a silver plating on the inner wall.

However, such cryogenic storage tanks have a limited storage time and cannot store fluids for long periods of time, and the stored fluids are volatile.

SUMMERY OF THE UTILITY MODEL

Therefore, the technical problem that this application will be solved lies in overcoming the limited, easy volatile defect of depositing fluid of storage time of low temperature storage jar in the prior art to provide an ultra-low temperature storage system.

In order to solve the technical problem, the technical scheme of the application is as follows:

an ultra-low temperature storage system comprises a low-temperature storage tank and a refrigeration host, wherein the refrigeration host comprises a storage tank, a pump, a refrigerator, a low-temperature refrigerator and a heat insulation device; the low-temperature storage tank comprises an inner shell for storing a low-temperature medium, an outer shell wrapping the periphery of the inner shell and a heat exchange pipeline arranged on the inner side of the inner shell and used for secondary refrigerant to flow in the heat exchange pipeline; the heat exchange pipeline, the storage tank, the pump, the cold end of the refrigerator and the cold disc of the low-temperature refrigerator are sequentially communicated to form a secondary refrigerant circulating loop; the storage tank is used for storing gas-phase secondary refrigerant in the secondary refrigerant flowing out of the heat exchange pipeline, the pump provides power for the flow of the secondary refrigerant in the secondary refrigerant circulation loop, the cold end of the refrigerator is used for pre-cooling the secondary refrigerant passing through the refrigerator, and the cold plate of the low-temperature refrigerator is used for refrigerating the secondary refrigerant passing through the refrigerator; the refrigerator and the low-temperature refrigerator are both arranged in the heat insulation device.

Further, the secondary refrigerant circulation loop further comprises a gas-liquid separator arranged between the cold plate of the low-temperature refrigerator and the heat exchange pipeline, and the gas-liquid separator is used for separating gas-phase secondary refrigerant and liquid-phase secondary refrigerant entering the gas-liquid separator and enabling the separated liquid-phase secondary refrigerant to flow into the heat exchange pipeline.

Furthermore, the pipeline communicated between the gas-liquid separator and the low-temperature storage tank comprises a first pipeline and a second pipeline which are connected in parallel; the first pipeline is communicated between the upper part of the gas-liquid separator and the heat exchange pipeline and is used for allowing gas-phase secondary refrigerant to flow to the heat exchange pipeline; the second pipeline is communicated between the lower part of the gas-liquid separator and the heat exchange pipeline, and liquid-phase secondary refrigerant flows to the heat exchange pipeline; the first pipeline is provided with a first switch valve for controlling the on-off of the first pipeline, and the second pipeline is provided with a second switch valve for controlling the on-off of the second pipeline.

Further, the gas-liquid separator, the first switch valve and the second switch valve are all arranged in the heat insulation device.

Further, the low-temperature refrigerator is a thermoacoustic refrigerator, and the refrigerator is any one of a compression refrigerator, a semiconductor refrigerator and a steam jet refrigerator.

The system further comprises a heat regenerator arranged in the heat insulation device, wherein the cold end of the heat regenerator acts on the inlet end of the storage tank, and the hot end of the heat regenerator acts on a pipeline between the cold end of the refrigerator and the cold plate of the low-temperature refrigerator.

Furthermore, a temperature sensor for detecting the temperature of the secondary refrigerant is arranged on a pipeline between the cold plate of the refrigerating machine and the gas-liquid separator.

Further, the temperature sensor is electrically connected with the controller; the controller responds to a temperature detection signal sent by the temperature sensor to control the on-off of the ultra-low temperature storage system.

Further, the cryogenic storage tank further comprises a thermal insulation layer filled between the inner shell and the outer shell.

Further, the heat exchange pipeline is spiral.

The technical scheme of the application has the following advantages:

1. according to the ultralow temperature storage system provided by the application, the heat exchange pipeline is arranged in the low temperature storage tank, the heat exchange pipeline is communicated with the external storage tank, the pump, the cold end of the refrigerator and the cold plate of the low temperature refrigerator to form a secondary refrigerant circulation loop, the pump drives the secondary refrigerant to circularly flow in the secondary refrigerant circulation loop, the cold end of the refrigerator precools the secondary refrigerant in the refrigerator, the cold plate of the low temperature refrigerator refrigerates the secondary refrigerant in the low temperature refrigerator, the secondary refrigerant after being refrigerated twice can continuously enter the heat exchange pipeline and exchanges heat with a cooled medium in the low temperature storage tank through the heat exchange pipeline, the secondary refrigerant returns after absorbing heat and is conveyed to the cold end of the refrigerator through the storage tank and the pump to refrigerate, and the closed type cyclic utilization of the secondary refrigerant is realized; the low-temperature storage tank can keep low temperature for a long time by the arrangement, and the problems that the storage time of low-temperature media in the low-temperature storage tank is short and the stored low-temperature media are easy to volatilize are solved. In addition, the storage tank can store the gas-phase secondary refrigerant in the secondary refrigerant flowing out of the heat exchange pipeline, so that the gas-phase secondary refrigerant is prevented from entering the pump, and the whole system is more stable; the heat insulation device can reduce the heat exchange between the refrigerator and the low-temperature refrigerator and the outside.

2. The application provides an ultra-low temperature storage system, through set up vapour and liquid separator between cryocooler's cold dish and heat transfer pipeline, vapour and liquid separator can separate gaseous phase secondary refrigerant and the liquid phase secondary refrigerant in the secondary refrigerant, adopts the liquid phase secondary refrigerant to provide cold energy to the heat transfer pipeline, can avoid gaseous phase secondary refrigerant to cause the problem that the service environment is unstable to service environment.

3. The application provides an ultra-low temperature storage system, vapour and liquid separator, first ooff valve and second ooff valve all set up in heat-proof device, can reduce with external environment's heat transfer.

4. The application provides an ultra-low temperature storage system, whole refrigerating system is simple, and control mode is simple.

5. The application provides an ultra-low temperature storage system, through setting up the regenerator, the cold junction of carrying behind the cold junction heat absorption of backward flow through storage tank, pump, refrigerator behind the cold junction heat absorption of regenerator behind the secondary refrigerant heat absorption is exothermic, can get into the precooling of low temperature refrigerator refrigeration front realization secondary refrigerant at the secondary refrigerant.

Drawings

In order to more clearly illustrate the detailed description of the present application or the technical solutions in the prior art, the drawings needed to be used in the detailed description of the present application or the prior art description will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic structural diagram of an ultra-low temperature storage system according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of an ultra-low temperature storage system according to a second embodiment of the present application.

Description of the reference numerals: 1. a low-temperature storage tank; 1-1, an inner shell; 1-2, a shell; 1-3, a heat exchange pipeline; 1-4, a heat insulating layer; 2. a storage tank; 3. a pump; 4. a refrigerator; 5. a cryogenic refrigerator; 6. a gas-liquid separator; 6-1, a first pipeline; 6-2, a second pipeline; 7-1, a first switch valve; 7-2, a second switch valve; 8. a heat regenerator; 9. a heat insulation device.

Detailed Description

The technical solutions of the present application will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present application, it should be noted that, unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, a fixed connection, a detachable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in this application will be understood to be a specific case for those of ordinary skill in the art.

In addition, the technical features mentioned in the different embodiments of the present application described below may be combined with each other as long as they do not conflict with each other.

Example one

An ultra-low temperature storage system as shown in fig. 1 comprises a refrigeration host 100 and an application end 200, wherein the application end 200 comprises a low temperature storage tank 1, and the refrigeration host 100 comprises a storage tank 2, a pump 3, a refrigerator 4, a low temperature refrigerator 5 and a heat insulation device 10. The low-temperature storage tank 1 comprises an inner shell 1-1 for storing low-temperature media, an outer shell 1-2 wrapping the periphery of the inner shell 1-1, and a heat exchange pipeline 1-3 arranged on the inner side of the inner shell 1-1 and used for secondary refrigerant to flow in the heat exchange pipeline. The heat exchange pipelines 1-3, the storage tank 2, the pump 3, the cold end of the refrigerator 4 and the cold plate of the low-temperature refrigerator 5 are communicated in sequence to form a secondary refrigerant circulation loop. The storage tank 2 is used for storing gas-phase secondary refrigerants in the secondary refrigerants flowing out of the heat exchange pipelines 1-3, the pump 3 provides power for the flow of the secondary refrigerants in the secondary refrigerant circulation loop, the cold end of the refrigerator 4 is used for precooling the secondary refrigerants passing through the interior of the refrigerator, and the cold plate of the low-temperature refrigerator 5 is used for refrigerating the secondary refrigerants passing through the interior of the refrigerator; the refrigerator 4 and the cryocooler 5 are both arranged in a heat insulation device 9.

The ultralow temperature storage system is characterized in that a heat exchange pipeline 1-3 is arranged in a low temperature storage tank 1, the heat exchange pipeline 1-3 is communicated with an external storage tank 2, a pump 3, the cold end of a refrigerator 4 and a cold plate of the low temperature refrigerator 5 to form a secondary refrigerant circulation loop, the pump drives secondary refrigerant to circularly flow in the secondary refrigerant circulation loop, the cold end of the refrigerator 4 precools the secondary refrigerant in the secondary refrigerant circulation loop, the cold plate of the low temperature refrigerator 5 refrigerates the secondary refrigerant in the secondary refrigerant circulation loop, the secondary refrigerant after twice refrigeration can continuously enter the heat exchange pipeline 1-3 and exchanges heat with a cooled medium in the low temperature storage tank 1 through the heat exchange pipeline 1-3, the secondary refrigerant returns after absorbing heat and is conveyed to the cold end of the refrigerator 4 through the storage tank 2 and the pump 3 to refrigerate, and closed circulation utilization of the secondary refrigerant is realized; the low-temperature storage tank 1 can keep low temperature for a long time by the arrangement, and the problems that the storage time of low-temperature media in the low-temperature storage tank 1 is short and the stored low-temperature media are easy to volatilize are solved; in addition, the storage tank 2 can store the gas-phase secondary refrigerant in the secondary refrigerant flowing out of the heat exchange pipelines 1-3, so that the gas-phase secondary refrigerant is prevented from entering the pump 3, and the whole system is more stable; the heat insulation device 9 can reduce the heat exchange between the refrigerator and the low-temperature refrigerator and the outside.

In this embodiment, the coolant circulation circuit further includes a gas-liquid separator 6 connected between the cold plate of the cryocooler 5 and the heat exchange lines 1-3, and the gas-liquid separator 6 can separate gas-phase coolant and liquid-phase coolant in the coolant. The gas-liquid separator 6 can adopt liquid-phase secondary refrigerant to provide cold energy for the heat exchange pipelines 1-3, and can avoid the problems that the gas-phase secondary refrigerant causes interference to the use environment and causes unstable use environment.

Further, the pipeline communicated between the gas-liquid separator 6 and the low-temperature storage tank 1 comprises a first pipeline 6-1 and a second pipeline 6-2 which are mutually connected in parallel; the first pipeline 6-1 is communicated between the upper part of the gas-liquid separator 6 and the heat exchange pipeline 1-3, and gas-phase secondary refrigerant flows to the heat exchange pipeline 1-3; the second pipeline 6-2 is communicated between the lower part of the gas-liquid separator 6 and the heat exchange pipeline 1-3, and liquid-phase secondary refrigerant flows to the heat exchange pipeline 1-3; the first pipeline 6-1 is provided with a first switch valve 7-1 for controlling the on-off of the first pipeline 6-1, and the second pipeline 6-2 is provided with a second switch valve 7-2 for controlling the on-off of the second pipeline 6-2. By the arrangement, the flow of the gas-phase refrigerating medium or the liquid-phase refrigerating medium to the heat exchange pipelines 1-3 can be selectively controlled.

In this embodiment, the gas-liquid separator 6, the first switch valve 7-1 and the second switch valve 7-2 are all disposed in the heat insulation device 10, so that heat exchange between the above components and the external environment can be reduced.

In the present embodiment, the cryocooler 5 is specifically a thermoacoustic cryocooler. The water cooling and air cooling modes at the heat dissipation end of the thermoacoustic refrigerator are not limited, and the circulating medium in the thermoacoustic refrigerator is not limited. The refrigerator 4 is a non-thermoacoustic refrigerator, specifically any one of a compression refrigerator, a semiconductor refrigerator, and a steam jet refrigerator. The refrigerating temperature interval of the low-temperature refrigerator 5 is lower than that of the refrigerator 4.

In this embodiment, the cryogenic storage tank 1 further includes a thermal insulation layer 1-4 filled between the inner shell 1-1 and the outer shell 1-2, and the heat exchange pipeline 1-3 is located in the inner shell 1-1 and is in a spiral shape.

In the present embodiment, a temperature sensor for detecting the temperature of the coolant is provided in the pipe between the cold plate of the cryocooler 5 and the gas-liquid separator 6. The ultra-low temperature storage system also comprises a controller which is electrically connected with the temperature sensor; the controller responds to a temperature detection signal sent by the temperature sensor to control the on-off of the ultra-low temperature storage system.

In this embodiment, a heat regenerator 8 is further disposed in the heat insulation device 9, a cold end of the heat regenerator 8 acts on the inlet end of the storage tank 2, and a hot end of the heat regenerator 8 acts on a pipeline between the cold end of the refrigerator 4 and the cold plate of the cryocooler 5.

The operation and principle of such an ultra-low temperature storage system are as follows:

the ultra-low temperature storage system receives the starting command, starts the pump 3, then starts the refrigerator 4, and then starts the thermoacoustic refrigerator. The cold end of the refrigerator 4 generates cold energy to pre-cool the secondary refrigerant in the refrigerator, the cold plate of the thermoacoustic refrigerator generates cold energy to refrigerate the secondary refrigerant in the thermoacoustic refrigerator, the secondary refrigerant in the cold plate enters the gas-liquid separator 6 after being cooled, the separated liquid-phase secondary refrigerant enters the low-temperature storage tank 1 and exchanges heat with the cooled medium in the low-temperature storage tank 1 through the heat exchange pipeline 1-3, the secondary refrigerant flows back to the storage tank 2 after absorbing heat, the gas-phase secondary refrigerant is stored in the storage tank 2, and the liquid-phase secondary refrigerant enters the cold end of the refrigerator 4 after being driven by the pump 3 to pre-cool and then enters the cold plate of the thermoacoustic refrigerator to refrigerate. The temperature sensor detects the temperature of the refrigerating medium output by the cold plate of the thermoacoustic refrigerator and sends a temperature detection signal to the controller, and when the temperature of the output refrigerating medium reaches the required temperature, the controller sends a shutdown instruction to shut down the low-temperature refrigerator 5, shut down the refrigerator 4 and finally shut down the pump 3.

The operation and principle of such an ultra-low temperature storage system are as follows:

the ultra-low temperature storage system receives the start command, starts the pump 3 first, then starts the refrigerator 4, and then starts the cryocooler 5. The cold end of the refrigerator 4 generates cold to pre-cool the secondary refrigerant in the refrigerator, the cold plate of the low-temperature refrigerator 5 generates cold to refrigerate the secondary refrigerant in the refrigerator, the secondary refrigerant in the cold plate is cooled and then enters the gas-liquid separator 6, the separated liquid-phase secondary refrigerant enters the low-temperature storage tank 1 and exchanges heat with the cooled medium in the low-temperature storage tank 1 through the heat exchange pipeline 1-3, the secondary refrigerant flows into the cold end of the heat regenerator 8 after absorbing heat and then flows back to the storage tank 2, the gas-phase secondary refrigerant is stored in the storage tank 2, the liquid-phase secondary refrigerant enters the cold end of the refrigerator 4 after being driven by the pump 3 to be pre-cooled, and then enters the cold plate of the low-temperature refrigerator 5 to refrigerate after being further pre-cooled by the hot end of the heat regenerator 8. The temperature sensor detects the temperature of the refrigerating medium output by the cold plate of the thermoacoustic refrigerator and sends a temperature detection signal to the controller, and when the temperature of the output refrigerating medium reaches the required temperature, the controller sends a shutdown instruction to shut down the low-temperature refrigerator 5, shut down the refrigerator 4 and finally shut down the pump 3.

The ultra-low temperature storage system has the following beneficial effects:

firstly, the heat exchange pipelines 1-3 are additionally arranged in the low-temperature storage tank 1, so that the low-temperature storage tank 1 can keep low temperature for a long time, the storage time of a medium in the low-temperature storage tank 1 is prolonged, and the waste of the medium caused by volatilization is reduced;

secondly, the secondary refrigerant circularly flows in the closed circulation pipeline, so that the cyclic utilization of the secondary refrigerant can be realized;

thirdly, a gas-liquid separator 6 is added into the system, and cold energy is provided for the heat exchange pipelines 1-3 by adopting a liquid-phase secondary refrigerant, so that the problems that the gas-phase secondary refrigerant causes interference to the use environment and causes the instability of the use environment can be solved;

fourthly, a pump 3 is added, so that the whole refrigerating system is simpler, and the control mode is simpler;

and fifthly, the storage tank 2 is added, and the storage tank 2 can temporarily store the gas-phase secondary refrigerant in the secondary refrigerant circulation pipeline, so that the influence of the gas-phase secondary refrigerant entering the pump 3 and the refrigerator on the refrigeration system is avoided, and the refrigeration system is more stable.

And sixthly, a heat insulation device 9 is arranged, and the gas-liquid separator 6, the refrigerator 4, the low-temperature refrigerator 5, the heat regenerator 8, the first switch valve 7-1, the second switch valve 7-2 and related pipelines are arranged in the heat insulation device 9, so that the heat exchange between each component and the external environment can be reduced.

Example two

An ultra-low temperature storage system as shown in fig. 2 is different from embodiment 1 in that the hot end of the regenerator 8 acts on the piping between the cold end of the refrigerator 4 and the pump 3.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of this invention are intended to be covered by the scope of the invention as expressed herein.

Claims (10)

1. An ultralow temperature storage system is characterized by comprising a low-temperature storage tank (1) and a refrigeration host, wherein the refrigeration host comprises a storage tank (2), a pump (3), a refrigerator (4), a low-temperature refrigerator (5) and a heat insulation device (9); the low-temperature storage tank (1) comprises an inner shell (1-1) for storing a low-temperature medium, an outer shell (1-2) wrapping the periphery of the inner shell (1-1), and a heat exchange pipeline (1-3) arranged on the inner side of the inner shell (1-1) and used for a secondary refrigerant to flow in the heat exchange pipeline; the heat exchange pipelines (1-3), the storage tank (2), the pump (3), the cold end of the refrigerator (4) and the cold plate of the low-temperature refrigerator (5) are communicated in sequence to form a secondary refrigerant circulation loop; the storage tank (2) is used for storing the secondary refrigerant flowing out of the heat exchange pipelines (1-3), the pump (3) provides power for the flow of the secondary refrigerant in the secondary refrigerant circulation loop, the cold end of the refrigerator (4) is used for pre-cooling the secondary refrigerant passing through the refrigerator, and the cold plate of the low-temperature refrigerator (5) is used for refrigerating the secondary refrigerant passing through the refrigerator; the refrigerator (4) and the low-temperature refrigerator (5) are both arranged in the heat insulation device (9).

2. The ultra-low temperature storage system of claim 1, wherein the coolant circulation loop further comprises a gas-liquid separator (6) disposed between the cold plate of the cryocooler (5) and the heat exchange lines (1-3), the gas-liquid separator (6) being configured to separate gas-phase coolant and liquid-phase coolant entering the gas-liquid separator (6) and to cause the separated liquid-phase coolant to flow into the heat exchange lines (1-3).

3. The ultra-low-temperature storage system according to claim 2, wherein the piping communicating between the gas-liquid separator (6) and the cryogenic storage tank (1) comprises a first piping (6-1) and a second piping (6-2) connected in parallel with each other; the first pipeline (6-1) is communicated between the upper part of the gas-liquid separator (6) and the heat exchange pipeline (1-3) and used for allowing gas-phase secondary refrigerant to flow to the heat exchange pipeline (1-3); the second pipeline (6-2) is communicated between the lower part of the gas-liquid separator (6) and the heat exchange pipeline (1-3) to supply liquid-phase secondary refrigerant to the heat exchange pipeline (1-3); the first pipeline (6-1) is provided with a first switch valve (7-1) for controlling the first pipeline (6-1) to be switched on and off, and the second pipeline (6-2) is provided with a second switch valve (7-2) for controlling the second pipeline (6-2) to be switched on and off.

4. The ultra-low temperature storage system according to claim 3, wherein the gas-liquid separator (6), the first switching valve (7-1) and the second switching valve (7-2) are provided in the heat insulating device (9).

5. An ultra-low temperature storage system according to claim 1, wherein the cryogenic refrigerator (5) is a thermoacoustic refrigerator; the refrigerator (4) is any one of a compression refrigerator, a semiconductor refrigerator and a steam jet refrigerator.

6. An ultra-low temperature storage system according to claim 1, further comprising a regenerator (8) disposed within the thermal insulation means (9), the cold end of the regenerator (8) acting on the inlet end of the storage tank (2), the hot end of the regenerator (8) acting on the line between the cold end of the refrigerator (4) and the cold plate of the cryocooler (5).

7. An ultra-low-temperature storage system according to claim 2, wherein a temperature sensor for detecting the temperature of the secondary refrigerant is provided on a pipe between the cold plate of the refrigerator and the gas-liquid separator (6).

8. The ultra-low temperature storage system of claim 7, further comprising a controller electrically connected to said temperature sensor; the controller responds to a temperature detection signal sent by the temperature sensor to control the on-off of the ultra-low temperature storage system.

9. The ultra-low temperature storage system as claimed in claim 1, wherein the cryogenic storage tank (1) further comprises an insulation layer (1-4) filled between the inner casing (1-1) and the outer casing (1-2).

10. The ultra-low temperature storage system of claim 1, wherein the heat exchange tubes (1-3) are helical.

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