Patent Application
20160097567
Priority is claimed to Japanese Patent Application No. 2014-206156, filed Oct. 7, 2014, the entire content of which is incorporated herein by reference.
1. Technical Field
Certain embodiments of the invention relate to a cryogenic refrigerator.
2.Description of Related Art
Cryogenic refrigerators are used to cool a refrigeration article down to temperatures in a range of, for example, from about 100 K (Kelvin) to about 4 K. Examples of cryogenic refrigerators include Gifford-McMahon (GM) refrigerators, pulse tube refrigerators, Stirling refrigerators, and the Solvay refrigerator. Cryogenic refrigerators are used, for example, for cooling superconducting magnets or detectors, or in cryopumps.
According to a certain embodiment of the invention, there is provided a cryogenic refrigerator including: an axially extending cylinder; an axially reciprocating displacer provided inside the cylinder, at a gap between an inner circumferential surface of the cylinder and an outer circumferential surface of the displacer, for shifting to create an expansion space for refrigerant gas between the displacer and an axial end portion of the cylinder; a regenerator built into the displacer; and a sleeve disposed along the inner circumferential surface of the axial end portion of the cylinder, encompassing the expansion space. A first passage for guiding the refrigerant gas from the regenerator to the gap is provided in the displacer, and a second passage for guiding the refrigerant gas from the gap to the expansion space is provided between the axial end portion of the cylinder and the sleeve, and/or is provided between the outer surface and the inner surface of the sleeve.
According to embodiments of the invention, it is possible to enhance heat exchanging efficiency of a cryogenic refrigerator.
The need for improving heat exchanging efficiency has been felt in the art of cryogenic refrigerators.
Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. In addition, the same reference signs are assigned to the same components in the description, and the duplicated description is appropriately omitted. The configuration described below is an example, and does not limit the scope of the invention.
The regenerator-type cryogenic refrigerator such as the GM refrigerator 10 includes a regenerator 12, an expander 14, and a compressor 16. As illustrated in
The expander 14 includes a cold head including a cylinder 20, a cooling stage 22, and a displacer 24. The cylinder 20 is an air-tight container of the refrigerant gas, and is a hollow member that extends in an axial direction Q. The cylinder 20 has, for example, a cylindrical shape.
The cooling stage 22 is thermally connected to the cylinder 20 by surrounding the expansion space 18. The cooling stage 22 is formed to have, for example, a bottomed cylindrical shape, and is attached to the outer side of the cylinder 20. The cooling stage 22 functions as a heat exchanger that performs heat exchange between the refrigerant gas and a cooling object such as an external heat source. The cooling stage 22 may be called a thermal load flange.
The displacer 24 is arranged on the same axis as the cylinder 20. The regenerator 12 is built in the displacer 24. The displacer 24 has, for example, a cylindrical shape having a diameter that is slightly smaller than that of the cylinder 20. A gap is provided between the inner circumferential surface of the cylinder 20 and the outer circumferential surface of the displacer 24. This gap is referred to as a first clearance 26 below. The outer circumferential surface of the displacer 24 is a side surface of the displacer 24, and the inner circumferential surface of the cylinder 20 is the surface of the cylinder 20 facing the side surface of the displacer 24.
The displacer 24 is a piston that divides the internal space of the cylinder 20 into the expansion space 18 and a room temperature space 28. The expansion space 18 is formed on one side of the cylinder 20 with respect to the displacer 24, and the room temperature space 28 is formed on the other side of the cylinder 20 with respect to the displacer 24. Therefore, one end portion of the cylinder 20 (or the displacer 24) in the axial direction Q can be called a low temperature end, and the other end of the cylinder 20 (or the displacer 24) in the axial direction Q can be called a high temperature end. Accordingly, the expansion space 18 is formed between the low temperature end of the displacer 24 and the low temperature end of the cylinder 20, and the room temperature space 28 is formed between the high temperature end of the displacer 24 and the high temperature end of the cylinder 20.
Hereinafter, for the convenience of description, the relative positional relationship between elements may be described by representing the room temperature side as “upper” and the low temperature side as “lower”. For example, it is possible to describe that the room temperature space 28 is present at the upper portion of the displacer 24 and the expansion space 18 is present at the lower portion of the displacer 24.
The displacer 24 is provided in the cylinder 20 so as to move in the axial direction Q in a reciprocating manner. A driving unit 25 is connected to the high temperature end of the displacer 24 for the reciprocating movement of the displacer 24. By the reciprocating movement of the displacer 24, the volumes of the expansion space 18 and the room temperature space 28 are complementarily changed.
A displacer upper opening 30 is provided to the high temperature end of the displacer 24 in order to cause the refrigerant gas to flow between the room temperature space 28 and the regenerator 12. The displacer upper opening 30 is formed along the axial direction Q. A displacer lower opening 32 is provided to the low temperature end of the displacer 24 in order to cause the refrigerant gas to flow between the regenerator 12 and the expansion space 18. The displacer lower opening 32 is a passage that guides the refrigerant gas from the low temperature end of the regenerator 12 to the first clearance 26. The displacer lower opening 32 is formed along a radial direction that is orthogonal to the axial direction Q.
A seal 34 may be provided at the upper portion of the first clearance 26. The flow of the gas that has passed through the first clearance 26 is blocked by the seal 34. Accordingly, the flow of the refrigerant gas between the room temperature space 28 and the expansion space 18 passes through the regenerator 12. In a case where the seal 34 is a contact seal such as a seal ring, the seal 34 may be provided to the high temperature end of the displacer 24. The seal 34 may be a non-contact seal. In addition, in a certain embodiment, the flow or leaking of the refrigerant gas that has passed through the first clearance 26 may be allowed.
In addition, the expander 14 includes a sleeve 36 that is arranged around the expansion space 18 at the inside of the low temperature end of the cylinder 20. The sleeve 36 is arranged on the same axis as the cylinder 20. The sleeve 36 is mounted to the low temperature end of the cylinder 20. Therefore, at least one contacting portion (not illustrated) that is in contact with the inner surface of the cylinder 20 may be provided on the outer surface of the sleeve 36. The sleeve 36 may be formed of the same material (for example, stainless steel) as the cylinder 20.
The sleeve 36 defines the passage that guides the refrigerant gas from the first clearance 26 to the expansion space 18. This gas passage is a gap formed between the low temperature end of the cylinder 20 and the sleeve 36. Hereinafter, this gap is called a second clearance 38. The second clearance 38 is narrower than the first clearance 26. That is, the width of the second clearance 38 in the radial direction is smaller than the width of the first clearance 26 in the radial direction. The sleeve 36 configures a flow velocity increasing mechanism for the refrigerant gas in the cooling stage 22.
As illustrated in
The position of a sleeve upper end 50 in the axial direction is substantially the same as that of a cooling stage upper end 23 in the axial direction. Accordingly, a gas inlet from the first clearance 26 to the second clearance 38 is provided at substantially the same height as that of the cooling stage upper end 23. The gas inlet may be provided at a height different from the height of the cooling stage upper end 23. In addition, a gas outlet (that is, the through hole 48) from the second clearance 38 to the expansion space 18 is provided at the same position as that of a bottom center 49 of the cooling stage 22 in the radial direction. The gas outlet may be provided at a position different from the position of the bottom center 49.
In this manner, the sleeve 36 forms the flow path of the refrigerant gas between the cooling stage 22 and the sleeve 36. This flow path reaches the bottom center 49 of the cooling stage 22 from the cooling stage upper end 23 along the inner surface of the cylinder 20. The sleeve 36 provides the flow path that causes the refrigerant gas to flow in parallel with the inner surface of the cooling stage 22 in almost the entire area of the inner surface of the cooling stage 22. In
In the movable range in the axial direction (hereinafter, referred to as a stroke) of the displacer 24, the displacer lower opening 32 is usually positioned at the upper portion of the sleeve upper end 50 in the axial direction Q. The displacer lower opening 32 is usually positioned at the upper portion of the second clearance 38 and does not enter the inside of the sleeve 36. Therefore, the displacer lower opening 32 is not hidden by the sleeve 36 from the cylinder 20 (or the cooling stage 22). In addition, in a certain embodiment, in at least a portion of the stroke (for example, when the displacer 24 is at the bottom dead center), the displacer lower opening 32 may be positioned at the lower portion of the sleeve upper end 50 in the axial direction Q.
The sleeve upper end 50 defines an opening that receives the low temperature end of the displacer 24. In the stroke of the displacer 24, the low temperature end of the displacer 24 is usually inserted into the sleeve 36. In other words, the movable range of a displacer bottom surface 33 is in the sleeve 36. The sleeve upper end 50 is inserted into the lower portion of the first clearance 26, and the sleeve cylindrical portion 40 surrounds the low temperature end of the displacer 24. In addition, in a certain embodiment, in at least a portion of the stroke (for example, when the displacer 24 is at the top dead center) or entire stroke, the displacer bottom surface 33 may be at the outside of the sleeve 36.
A gap in the radial direction, which is formed between the sleeve cylindrical portion 40 and the low temperature end of the displacer 24 when the displacer 24 is inserted into the sleeve 36, is narrower than the lateral gap 44. That is, the width of the gap in the radial direction is smaller than the width of the lateral gap 44 in the radial direction. In this manner, it is possible to increase the flow rate of the gas passing through the lateral gap 44.
The sleeve 36 may provide a seal between the low temperature end of the displacer 24 and the sleeve 36. The seal may be a contact seal or a non-contact seal. A direct gas flow from the first clearance 26 to the expansion space 18 is blocked by the seal. Accordingly, all the flow of the refrigerant gas between the first clearance 26 and the expansion space 18 passes through the second clearance 38. In this case, the inner surface of the sleeve cylindrical portion 40 may be in contact with the outer circumferential surface of the low temperature end of the displacer 24. Otherwise, the inner surface of the sleeve cylindrical portion 40 may be in non-contact with the outer circumferential surface of the low temperature end of the displacer 24 by providing a slight gap therebetween. According to the reciprocating movement of the displacer 24, the low temperature end of the displacer 24 moves in a sliding manner or in a non-contact manner with respect to the sleeve 36.
In addition, the GM refrigerator 10 includes a piping system 52 that connects the compressor 16 to the expander 14. In the piping system 52, a high pressure valve 54 and a low pressure valve 56 are provided. The piping system 52 is connected to the high temperature end of the cylinder 20. The GM refrigerator 10 is configured to supply the high-pressure refrigerant gas from the compressor 16 to the expander 14 via the high pressure valve 54 and the piping system 52. In addition, the GM refrigerator 10 is configured to discharge the low-pressure refrigerant gas from the expander 14 to the compressor 16 via the piping system 52 and the low pressure valve 56.
The GM refrigerator 10 includes a valve driving unit (not illustrated) that selectively closes and opens the high pressure valve 54 and the low pressure valve 56 in synchronization with the reciprocating movement of the displacer 24, and switches between the supply and the discharge of the refrigerant gas with respect to the expansion space 18. The valve driving unit may be the driving unit 25 described above. The high pressure valve 54, the low pressure valve 56, and the valve driving unit may be incorporated in the expander 14.
Next, the operation of the GM refrigerator 10 is described. When the displacer 24 is positioned at the bottom dead center or in the vicinity of the bottom dead center of the cylinder 20, the high pressure valve 54 is opened. The high-pressure refrigerant gas is supplied from the compressor 16 to the cylinder 20 via the high pressure valve 54 and the piping system 52. The refrigerant gas flows into the regenerator 12 from the room temperature space 28 via the displacer upper opening 30. The refrigerant gas is cooled while passing through the regenerator 12. The refrigerant gas flows into the expansion space 18 via the displacer lower opening 32, the first clearance 26, and the second clearance 38. While the refrigerant gas flows into the expansion space 18, the displacer 24 moves toward the top dead center of the cylinder 20. In this manner, the volume of the expansion space 18 is increased. Accordingly, the expansion space 18 is filled with the high-pressure refrigerant gas.
When the displacer 24 is positioned at the top dead center or in the vicinity of the top dead center of the cylinder 20, the high pressure valve 54 is closed. At the same timing as, or slightly after, the high pressure valve 54 is closed, the low pressure valve 56 is opened. The refrigerant gas of the expansion space 18 is expanded and cooled. The refrigerant gas absorbs the heat from the cooling stage 22.
The low-pressure refrigerant gas is collected in a reversed route. The refrigerant gas flows into the regenerator 12 from the expansion space 18 via the second clearance 38, the first clearance 26, and the displacer lower opening 32. The refrigerant gas cools the regenerator 12 while passing through the regenerator 12. The refrigerant gas is discharged from the cylinder 20 via the displacer upper opening 30 and the room temperature space 28. The refrigerant gas is collected by the compressor 16 via the low pressure valve 56 and the piping system 52. While the refrigerant gas flows out from the expansion space 18, the displacer 24 moves toward the bottom dead center of the cylinder 20. In this manner, the volume of the expansion space is decreased, and the low-pressure refrigerant gas is discharged from the expansion space 18.
One cooling cycle in the GM refrigerator 10 is described above. The GM refrigerator 10 repeatedly performs this cooling cycle, and therefore, the cooling stage 22 is cooled to a desired temperature. In this manner, the GM refrigerator 10 can absorb the heat from the cooling object (not illustrated) that is thermally connected to the cooling stage 22 and can cool the cooling object. The cooling stage 22 may be cooled to a target temperature selected from a range of, for example, about 10 K to about 30 K. Otherwise, the cooling stage 22 may be cooled to a target temperature selected from a range of, for example, about 50 K to 100 K.
As described above, according to the embodiment, the passage of the refrigerant gas from the first clearance 26 to the expansion space 18 (that is, the second clearance 38) is defined by providing the sleeve 36 to the inside of the cylinder 20 to be adjacent to the cooling stage 22. By defining the gas passage in this manner, the lowering of the velocity component in a direction along the surface of the cooling stage 22 is suppressed compared to a case in the related art in which the gas is directly blown from the low temperature end of the displacer 24 to the expansion space 18. Since the velocity can be increased compared to that in the related art, it is possible to enhance the heat exchanging efficiency of the cooling stage 22.
The second clearance 38 is narrower than the first clearance 26. Specifically, the gas passage defined in an outside region of the sleeve 36 by the sleeve 36 is narrower than the gap between the cylinder 20 and the displacer 24 in the radial direction. Accordingly, when the gas flows in the gas passage from the gap, the velocity is increased, and therefore, it is possible to enhance the heat exchanging efficiency. According to a trial calculation, if the velocity of the refrigerant gas flowing in the expansion space 18 is doubled, the refrigerating capacity of the refrigerator is improved by about 5% to about 10%. Therefore, as the refrigerator is a large-sized refrigerator having a high refrigerating capacity, the increasing amount of the refrigerating capacity by the application of the sleeve 36 according to the embodiment becomes large. Typically, such a large-sized refrigerator is a single-stage refrigerator. Accordingly, the embodiment is preferable for a single-stage refrigerator having a high capacity (for example, a single-stage refrigerator having a refrigerating capacity of 100 W to 300 W at 10 K, or a single-stage refrigerator having a refrigerating capacity of 500 W to 1 kW at 70 K) .
In addition, according to the embodiment, it is possible to enhance the heat exchanging efficiency of the refrigerator by a relatively simple operation such as mounting of the sleeve 36 to the cylinder 20. By adding the sleeve 36 to the existing refrigerator, it is possible to easily enhance the heat exchanging efficiency of the refrigerator.
Herein before, the invention is described based on the embodiments. The invention is not limited to the embodiments described above. Those skilled in the art can understand that various changes in design and various modification examples are possible, and such modification examples are in the scope of the invention.
It is not essential that the sleeve 36 includes the sleeve bottom plate 42. In a certain embodiment, the sleeve 36 includes only the sleeve cylindrical portion 40. It can be said that the diameter of the through hole 48 at a sleeve lower end is equal to the diameter of the sleeve cylindrical portion 40.
Similarly, the unevenness may be formed on the bottom surface of the sleeve bottom plate. In this case, a gas passage formed between the sleeve bottom plate and the cylinder may be provided along the radial direction.
As an alternative, the unevenness may be formed on the inner surface of the cylinder. In this case, a convex portion may be in contact with the outer surface of the sleeve, and a passage of the refrigerant gas may be formed between a concave portion and the outer surface of the sleeve.
In a certain embodiment, the gas passage defined between the cylinder and the sleeve (for example, the gas passage illustrated in
In a certain embodiment, in a case where the sleeve is necessarily accommodated, the outer diameter of the low temperature end of the displacer may be slightly smaller than that of the high temperature end. Otherwise, the inner diameter of the low temperature end of the cylinder or the inner diameter of the cooling stage may be slightly greater than that of the high temperature end of the cylinder.
In a certain embodiment, the sleeve may be provided at the low temperature end of at least a stage in a two-stage (or multiple-stage) refrigerator.
In the above embodiment, the GM refrigerator 10 is described as an example, but it is not limited thereto. In a certain embodiment, a sleeve may be provided in another type of refrigerator that includes a displacer in which a regenerator is built, and a cylinder that accommodates the displacer.
The GM refrigerator 10 or another refrigerator including the sleeve according to the embodiment may be used as cooling means or liquefying means in a superconducting magnet, a cryopump, an X-ray detector, an infrared sensor, a quantum photon detector, a solid state detector, a dilution refrigerator, an He3 refrigerator, an insulated demagnetized refrigerator, a helium liquefier, and a cryostat.
It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-206156 | Oct 2014 | JP | national |
