Cryogenic refrigerator and flexible hose for cryogenic refrigerator

Abstract

The present invention addresses the problem of reducing noise generated from a flexible hose during operation of a cryogenic refrigerator. A cryogenic refrigerator (10) is provided with a compressor (12), a cold head (14), and a first flexible hose (63) connecting the compressor (12) to the cold head (14). The first flexible hose (63) is provided with a conduit through which the working gas of the cryogenic refrigerator (10) flows, and a braid covering the conduit. The braid layer is provided with a braided wire braided in a tubular shape so as to cover the conduit, and is configured such that the tensile stress acting on the braided wire when the working gas flows through the conduit at a nominal pressure is 85 N / mm2 or less.

Description

[0001] This application claims priority based on Japanese Patent Application No. 2023-166077 filed on September 27, 2023. The entire contents of the Japanese Patent Application are incorporated herein by reference. Technical Field

[0002] The invention relates to an ultra-low temperature refrigerator and a flexible hose for the ultra-low temperature refrigerator. Background Art

[0003] Typically, a cryogenic refrigerator such as a Gifford-McMahon (GM) refrigerator has a working gas pipe connecting a compressor and an expander, also called a cold head, in order to supply and discharge working gas between the two. A corrugated flexible hose is sometimes used as the working gas pipe. In the past, in order to reduce the noise generated from the flexible hose due to the flow of working gas during the operation of the cryogenic refrigerator, a solution of installing a flexible tube on the inner surface of the corrugated flexible hose has been proposed (for example, refer to Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2002-333224

[0005] The inventor has studied the flexible hose for the ultra-low temperature refrigerator, and thus realized the following problems. In the flexible hose, a flexible pipe is used to smooth the inner surface of the hose, thereby reducing the noise caused by the gas flow. However, according to the research of the inventor, it is found that the noise level may deteriorate depending on the design of the braid layer (braid) of the outer shell of the flexible hose or the use conditions of the ultra-low temperature refrigerator such as the working gas pressure. In addition, the above-mentioned flexible hose also requires additional parts (flexible pipes). This may cause the manufacturing cost of the flexible hose to increase. There is also a concern that the long-term reliability of the ultra-low temperature refrigerator will be reduced due to the long-term operation, such as the wear of the pipe. Summary of the invention

[0006] One of the exemplary purposes of an embodiment of the present invention is to reduce the noise generated from a flexible hose during operation of a cryogenic refrigerator.

[0007] According to one embodiment of the present invention, a cryogenic refrigerator comprises: a compressor; a cold head; and a flexible hose, the compressor is connected to the cold head, and a conduit for allowing a working gas of the cryogenic refrigerator to flow through and a braided layer outer covering the conduit. The braided layer comprises a braided wire braided into a cylindrical shape in a manner of covering the conduit, and the braided layer is configured such that when the working gas flows through the conduit at a nominal pressure, the tensile stress acting on the braided wire becomes 85N / mm 2 the following.

[0008] According to one embodiment of the present invention, a cryogenic refrigerator comprises: a compressor; a cold head; and a flexible hose, the compressor is connected to the cold head, and a conduit for flowing a working gas of the cryogenic refrigerator is provided. The conduit is characterized in that it has a corrugated inner surface exposed to the working gas flow, and the gap between the corrugations on the corrugated inner surface is less than 1 mm.

[0009] According to one embodiment of the present invention, a flexible hose for a cryogenic refrigerator comprises: a conduit for allowing a working gas of the cryogenic refrigerator to flow through; and a braided layer outer covering the conduit. The braided layer comprises a braided wire braided into a cylindrical shape in a manner of covering the conduit, and the braided layer is configured such that when the working gas flows through the conduit at a nominal pressure, the tensile stress acting on the braided wire becomes 85 N / mm 2 At the same time, or instead of this, the conduit has a corrugated inner surface exposed to the working gas flow, and the inter-corrugation gap of the corrugated inner surface is less than 1 mm.

[0010] According to the present invention, it is possible to reduce the noise generated from the flexible hose during the operation of the cryogenic refrigerator. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a diagram schematically showing a cryogenic refrigerator according to an embodiment.

[0012] Figure 2 It is a diagram schematically showing a cryogenic refrigerator according to an embodiment.

[0013] Figure 3 (a) to (c) are views schematically showing a flexible hose for a cryogenic refrigerator according to an embodiment.

[0014] Figure 4 : is a graph showing the relationship between the knitting stress and the noise level according to the embodiment.

[0015] Figure 5 : is a graph showing the relationship between the gap between corrugations and the noise level according to the embodiment.

[0016] In the figure: 10 - ultra-low temperature refrigerator, 12 - compressor, 14 - cold head, 22 - air inlet, 24 - exhaust port, 50 - delivery port, 52 - recovery port, 70 - flexible hose, 72 - catheter, 74 - braided layer, 76 - braided wire. DETAILED DESCRIPTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, identical or equivalent components, parts, and processes are marked with the same symbols, and repeated descriptions are appropriately omitted. For ease of explanation, in each of the accompanying drawings, the scale or shape of each part is appropriately set, and unless otherwise specifically stated, it is not interpreted as limiting. The embodiments are illustrative and do not limit the scope of the present invention in any way. All features or combinations thereof described in the embodiments are not necessarily the essence of the invention.

[0018] Figure 1 and Figure 2 1 is a diagram schematically showing a cryogenic refrigerator 10 according to an embodiment. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator. Figure 1 FIG. 4 shows the appearance of the ultra-low temperature refrigerator 10. Figure 2 The internal structure of the cryogenic refrigerator 10 is shown in FIG.

[0019] The cryogenic refrigerator 10 includes a compressor 12 and a cold head 14. The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the cold head 14, and to supply the working gas to the cold head 14 again after the recovered working gas is pressurized. The cold head 14 is also called an expander. The compressor 12 and the cold head 14 constitute a refrigeration cycle (for example, a GM cycle) of the cryogenic refrigerator 10, whereby the cryogenic refrigerator 10 can provide ultra-low temperature cooling. The working gas is also called a refrigerant gas, which is usually helium, but other suitable gases may also be used.

[0020] Typically, the pressure of the working gas supplied from the compressor 12 to the cold head 14 and the pressure of the working gas recovered from the cold head 14 to the compressor 12 are both much higher than the atmospheric pressure, and they can be referred to as the first high pressure and the second high pressure, respectively. The first high pressure (i.e., the nominal pressure of the working gas on the supply side) can be selected from, for example, a first pressure range of more than 1.5 MPa and less than 3.5 MPa. The first nominal pressure can be, for example, 2.2 MPa. The second high pressure (i.e., the nominal pressure of the working gas on the recovery side) is lower than the first high pressure. The second high pressure is, for example, selected from a second pressure range of more than 0.2 MPa and less than 2.0 MPa. The second nominal pressure can be, for example, 0.8 MPa. In the following, for the sake of convenience of explanation, the first high pressure and the second high pressure can also be referred to as high pressure and low pressure, respectively. For ease of understanding, the flow direction of the working gas is indicated by an arrow.

[0021] like Figure 1As shown, the compressor 12 includes a delivery port 50 for delivering the working gas and a recovery port 52 for recovering the working gas. The delivery port 50 is provided on the frame of the compressor 12 as a port of the compressor 12 for the high-pressure working gas compressed by the compressor 12. The recovery port 52 is provided on the frame of the compressor 12 as an inlet of the compressor 12 for recovering the low-pressure working gas into the compressor 12.

[0022] The compressor 12 may be, for example, a vortex pump, a rotary pump, or other appropriate pump that increases the pressure of the working gas. In this embodiment, the compressor 12 is configured to discharge a constant flow rate of the working gas. Alternatively, the compressor 12 may be configured to make the flow rate of the discharged working gas variable. A cooling device such as a cooler may be attached to the compressor 12 to remove the compression heat generated by the compression of the working gas.

[0023] The cold head 14 includes a refrigerator cylinder 16 and a displacer assembly 18. The refrigerator cylinder 16 guides the linear reciprocating motion of the displacer assembly 18, and expansion chambers 32 and 34 of the working gas are formed between the refrigerator cylinder 16 and the displacer assembly 18. In addition, the cold head 14 includes a pressure switching valve 40, which determines the start time of supplying the working gas to the expansion chamber and the start time of exhausting the working gas from the expansion chamber.

[0024] In this specification, in order to explain the positional relationship between the components of the ultra-low temperature refrigerator 10, for convenience, the side close to the upper dead point of the axial reciprocating movement of the displacer is marked as "up", and the side close to the lower dead point is marked as "down". The upper dead point is the position of the displacer when the volume of the expansion space becomes the maximum, and the lower dead point is the position of the displacer when the volume of the expansion space becomes the minimum. When the ultra-low temperature refrigerator 10 is running, a temperature gradient is generated in which the temperature decreases from the upper side to the lower side in the axial direction, so the upper side can also be called the high temperature side, and the lower side can be called the low temperature side.

[0025] The refrigerator cylinder 16 has a first cylinder 16a and a second cylinder 16b. As an example, the first cylinder 16a and the second cylinder 16b are cylindrical components, and the diameter of the second cylinder 16b is smaller than the diameter of the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are coaxially arranged, and the lower end of the first cylinder 16a and the upper end of the second cylinder 16b are rigidly connected together.

[0026] The displacer assembly 18 includes a first displacer 18a and a second displacer 18b connected to each other, and they move integrally. As an example, the first displacer 18a and the second displacer 18b are both cylindrical components, and the diameter of the second displacer 18b is smaller than the diameter of the first displacer 18a. The first displacer 18a and the second displacer 18b are coaxially arranged.

[0027] The first displacer 18a is accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b. The first displacer 18a is reciprocable in the axial direction along the first cylinder 16a, and the second displacer 18b is reciprocable in the axial direction along the second cylinder 16b.

[0028] like Figure 2 As shown, the first displacer 18a accommodates the first cold storage device 26. The first cold storage device 26 is formed by filling a metal wire mesh such as copper or other appropriate first cold storage material in the cylindrical main body of the first displacer 18a. The upper cover and the lower cover of the first displacer 18a can be provided as components different from the main body of the first displacer 18a, and the upper cover and the lower cover of the first displacer 18a can be fixed to the main body by an appropriate method such as fastening and welding, so that the first cold storage material is accommodated in the first displacer 18a.

[0029] Similarly, the second displacer 18b accommodates the second cold storage device 28. The second cold storage device 28 is formed by filling the cylindrical main body of the second displacer 18b with a non-magnetic cold storage material such as bismuth, a magnetic cold storage material such as HoCu2, or other appropriate second cold storage material. The second cold storage material can be formed into a granular form. The upper cover and the lower cover of the second displacer 18b can be provided as components different from the main body of the second displacer 18b, and the upper cover and the lower cover of the second displacer 18b can also be fixed to the main body by an appropriate method such as fastening or welding, so that the second cold storage material is accommodated in the second displacer 18b.

[0030] The displacer assembly 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. In order to perform heat exchange with a desired object or medium to be cooled by the ultra-low temperature refrigerator 10, the cold head 14 has a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper cover of the first displacer 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower cover of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower cover of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fastened to the lower part of the first cylinder 16a in a manner surrounding the first expansion chamber 32, and the second cooling stage 35 is fastened to the lower part of the second cylinder 16b in a manner surrounding the second expansion chamber 34.

[0031] The first regenerator 26 is communicated with the upper chamber 30 through a working gas flow path 36a formed on the upper cover portion of the first displacer 18a, and is communicated with the first expansion chamber 32 through a working gas flow path 36b formed on the lower cover portion of the first displacer 18a. The second regenerator 28 is communicated with the first regenerator 26 through a working gas flow path 36c formed from the lower cover portion of the first displacer 18a to the upper cover portion of the second displacer 18b. Furthermore, the second regenerator 28 is communicated with the second expansion chamber 34 through a working gas flow path 36d formed on the lower cover portion of the second displacer 18b.

[0032] In order to prevent the working gas flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 from being introduced into the gap between the refrigerator cylinder 16 and the displacer assembly 18 and being introduced into the first cold storage device 26 and the second cold storage device 28, a first seal 38a and a second seal 38b may be provided. The first seal 38a may be installed on the upper cover of the first displacer 18a in a manner arranged between the first displacer 18a and the first cylinder 16a. The second seal 38b may be installed on the upper cover of the second displacer 18b in a manner arranged between the second displacer 18b and the second cylinder 16b.

[0033] like Figure 1 As shown, the cold head 14 includes a refrigerator housing 20 that accommodates a pressure switching valve 40. The refrigerator housing 20 is combined with the refrigerator cylinder 16 to form an airtight container that accommodates the pressure switching valve 40 and the displacer assembly 18.

[0034] In addition, the cold head 14 includes an air inlet 22 for receiving the working gas and an exhaust port 24 for exhausting the working gas. The air inlet 22 is provided on the refrigerator housing 20 as an inlet of the high-pressure working gas supplied from the compressor 12 to the cold head 14. The exhaust port 24 is provided on the refrigerator housing 20 as an outlet of the cold head 14 for the low-pressure working gas exhausted from the cold head 14.

[0035] like Figure 2 As shown, the pressure switching valve 40 is configured to include a high-pressure valve 40a and a low-pressure valve 40b and to generate periodic pressure fluctuations in the refrigerator cylinder 16. The delivery port 50 of the compressor 12 is connected to the upper chamber 30 via the high-pressure valve 40a, and the recovery port 52 of the compressor 12 is connected to the upper chamber 30 via the low-pressure valve 40b. The high-pressure valve 40a and the low-pressure valve 40b are configured to selectively open and close alternately (that is, during the period when one valve is open, the other valve is in a closed state).

[0036] The pressure switching valve 40 may be in the form of a rotary valve. That is, the pressure switching valve 40 may be configured so that the valve disc rotates and slides relative to the stationary valve body, thereby alternately opening and closing the high-pressure valve 40a and the low-pressure valve 40b. In this case, the expander motor 42 may be connected to the pressure switching valve 40 in such a way that the valve disc of the pressure switching valve 40 rotates. For example, the valve rotation axis of the pressure switching valve 40 and the rotation axis of the expander motor 42 are coaxially arranged.

[0037] Alternatively, the high-pressure valve 40 a and the low-pressure valve 40 b may be valves that can be controlled individually. In this case, the pressure switching valve 40 may not be connected to the expander motor 42 .

[0038] The expander motor 42 can be an electric motor, for example, a permanent magnet motor driven by three-phase alternating current. The expander motor 42 is connected to the displacer drive shaft 44 via a motion conversion mechanism 43 such as a scotch yoke mechanism. The expander motor 42 is mounted on the refrigerator housing 20. Like the pressure switching valve 40, the motion conversion mechanism 43 is accommodated in the refrigerator housing 20. The motion conversion mechanism 43 converts the rotational motion output by the expander motor 42 into a linear reciprocating motion of the displacer drive shaft 44. The displacer drive shaft 44 extends from the motion conversion mechanism 43 toward the upper chamber 30 and is fixed to the upper cover of the first displacer 18a. The rotation of the expander motor 42 is converted by the motion conversion mechanism 43 into an axial reciprocating motion of the displacer drive shaft 44, whereby the displacer assembly 18 performs a linear reciprocating motion along the axial direction in the refrigerator cylinder 16.

[0039] Furthermore, the cryogenic refrigerator 10 includes a working gas pipeline 62 for circulating the working gas between the compressor 12 and the cold head 14. The working gas pipeline 62 includes a first flexible hose 63 on the high-pressure side and a second flexible hose 64 on the low-pressure side. The first flexible hose 63 connects the delivery port 50 of the compressor 12 to the air inlet 22 of the cold head 14. Therefore, the high-pressure working gas supplied from the compressor 12 to the cold head 14 flows through the first flexible hose 63. The second flexible hose 64 connects the recovery port 52 of the compressor 12 to the exhaust port 24 of the cold head 14. Therefore, the low-pressure working gas recovered from the cold head 14 to the compressor 12 flows through the second flexible hose 64. The details of these flexible hoses will be described in detail later.

[0040] When the compressor 12 and the expander motor 42 are running, the cryogenic refrigerator 10 generates periodic volume changes and pressure changes of the working gas synchronized therewith in the first expansion chamber 32 and the second expansion chamber 34. Typically, in the intake process, by closing the low-pressure valve 40b and opening the high-pressure valve 40a, the high-pressure working gas flows from the compressor 12 through the high-pressure valve 40a into the upper chamber 30, and is supplied to the first expansion chamber 32 through the first cold storage device 26, and then supplied to the second expansion chamber 34 through the second cold storage device 28. As a result, the first expansion chamber 32 and the second expansion chamber 34 are boosted from low pressure to high pressure. At this time, the displacer assembly 18 moves from the lower dead center toward the upper dead center, and the volume of the first expansion chamber 32 and the second expansion chamber 34 increases. If the high-pressure valve 40a is closed, the intake process ends.

[0041] In the exhaust process, the high-pressure valve 40a is closed and the low-pressure valve 40b is opened, so that the high-pressure first expansion chamber 32 and the second expansion chamber 34 are connected to the low-pressure working gas suction port of the compressor 12, so that the working gas expands in the first expansion chamber 32 and the second expansion chamber 34, and as a result, the low-pressure working gas is discharged from the first expansion chamber 32 and the second expansion chamber 34 toward the upper chamber 30 through the first regenerator 26 and the second regenerator 28. At this time, the displacer assembly 18 moves from the top dead center to the bottom dead center, and the volume of the first expansion chamber 32 and the second expansion chamber 34 decreases. The working gas is recovered from the cold head 14 through the low-pressure valve 40b to the compressor 12. If the low-pressure valve 40b is closed, the exhaust process is completed.

[0042] Thus, a refrigeration cycle such as a GM cycle is formed in the ultra-low temperature refrigerator 10, and the first cooling stage 33 and the second cooling stage 35 are cooled to a desired ultra-low temperature. The first cooling stage 33 is cooled to a first cooling temperature, and the second cooling stage 35 is cooled to a second cooling temperature lower than the first cooling temperature. The first cooling temperature may be, for example, in the range of about 30K to about 80K. The second cooling temperature may be, for example, in the range of about 1K to about 20K. The second cooling temperature may be a liquid helium temperature of about 4.2K or a temperature lower than the liquid helium temperature.

[0043] During the operation of the cryogenic refrigerator 10, the working gas pipeline 62 may generate sound caused by the flow of the working gas. In the intake process, since the working gas flows from the compressor 12 to the cold head 14 through the first flexible hose 63, a sound accompanying the flow of the working gas may be generated from the first flexible hose 63. In the exhaust process, since the working gas flows from the cold head 14 to the compressor 12 through the second flexible hose 64, a sound accompanying the flow of the working gas may be generated from the second flexible hose 64. For the user of the cryogenic refrigerator 10 or the user of the device equipped with the cryogenic refrigerator 10 (for example, a magnetic resonance imaging (MRI) device), this sound may be perceived as noise. Therefore, in this specification, a technology for reducing this noise is proposed.

[0044] Figure 3 (a) to (c) are diagrams schematically showing a flexible hose for a cryogenic refrigerator according to an embodiment of the present invention. Figure 3 As shown in (a) to (c), the flexible hose 70 includes a conduit 72 for allowing the working gas of the cryogenic refrigerator to flow through and a braided layer 74 that is sheathed on the conduit 72. The flexible hose 70 shown in the figure can be used for the above-mentioned reference Figure 1 and Figure 2 The first flexible hose 63 or the second flexible hose 64 described, or both thereof.

[0045] In this embodiment, the conduit 72 is a corrugated tube (ie, a corrugated tube). Figure 3 As shown in (c), the inner surface (hereinafter also referred to as the corrugated inner surface) 72a of the conduit 72 (ie, the corrugated tube) is exposed to the working gas flow 80. The conduit 72 is made of, for example, stainless steel. Alternatively, the conduit 72 may also be made of other appropriate materials.

[0046] The conduit 72 can be designed according to several conduit design parameters. The conduit design parameters may include, for example: the maximum inner diameter D of the corrugated tube imax (mm), inner diameter D of corrugated tube i (mm), corrugation pitch q (mm), and corrugated tube gap g (mm). On the tube wall of the corrugated tube, a plurality of convex portions 73 protruding toward the inside of the tube are formed along the tube axis direction, such as Figure 3 As shown, the corrugated tube gap g refers to the distance between two adjacent protrusions 73 in the tube axis direction.

[0047] The braided layer 74 includes a braided wire 76 braided into a cylindrical shape so as to cover the catheter 72. The braided layer 74 is woven so as to envelop the corrugated shape of the catheter 72. Therefore, unlike the catheter 72, the outer surface of the braided layer 74 has a substantially constant outer diameter D. oThe braided wire 76 is made of, for example, stainless steel. Alternatively, the braided wire 76 may be made of other appropriate materials.

[0048] The braided layer 74 can be designed according to several braiding design parameters. The braiding design parameters may include, for example: braid wire diameter d (mm), number of braids b1, number of braid bundles b2, braiding cross angle b3 (rad), and number of braiding layers b4. Number of braids b1 indicates the number of braided wires 76 constituting a bundle of braided wires 76 for braiding the braided layer 74. Number of braiding bundles b2 indicates the number of bundles of braided wires 76 used for braiding the braided layer 74. Braiding cross angle b3 indicates the angle between bundles of braided wires 76 when braiding the braided layer 74. Number of braiding layers b4 indicates the number of layers of the braided layer 74 covering the catheter 72. Figure 3 (b) illustrates a case where the number of braided layers b4 is 2.

[0049] The inventors of the present invention have experimentally investigated the noise of flexible hoses 70 of various braiding designs and found that a major parameter related to the braid 74 that affects the noise level is the tensile stress acting on the braided wire 76 (hereinafter also referred to as "braiding stress").

[0050] When the working gas flows through the conduit 72 of the flexible hose 70, the pressure of the working gas generates a force to extend the conduit 72, and this force is transmitted to the braided layer 74, which may cause tensile stress on the braided wire 76. The braiding stress σ (N / mm) can be calculated by the following formula: 2 ) (ie, tensile stress acting on one braided wire 76 in the extending direction).

[0051] σ=P·π(D imax / 2) 2 / (b1·b2) / b4 / cos(b3 / 2) / π(d / 2) 2

[0052] Here, P (MPa) represents the internal pressure of the conduit 72 generated by the working gas during the operation of the cryogenic refrigerator 10. For calculating the braiding stress σ, the first nominal pressure (for example, 2.2 MPa) mentioned above can be used as the internal pressure P.

[0053] Figure 4 Graph showing the relationship between braiding stress and noise level according to the embodiment. Braiding stress was calculated and noise level (dBA) was measured for nine samples 1a to 1i of the first flexible hose 63 prepared by the present inventors, and the results were plotted on Figure 4 middle.

[0054] The knitting design parameters of the nine samples 1a to 1i are shown in the following table.

[0055] [Table 1]

[0056]

[0057] The braiding stress σ (N / mm) was calculated for samples 1a to 1i. 2 ) and the measured noise level (dBA) are as follows, and these are shown in Figure 4 middle.

[0058] [Table 2]

[0059] <![CDATA[Weaving stress (N / mm 2 )]]> Noise level(dBA) Sample 1a 94.3 61.1 Sample 1b 79.2 56.2 Sample 1c 63.3 55.6 Sample 1d 75.5 55.7 Sample 1e 59.2 53.5 Sample 1f 63.3 56.7 Sample 1g 68.6 56.2 Sample 1h 83.9 55.7 Sample 1i 47.2 56.2

[0060] In the calculation of the braiding stress σ, the design of the conduit 72 of each sample is the same, and the maximum inner diameter D of the corrugated tube is imax is 25.2mm. The operating conditions of the ultra-low temperature refrigerator 10 are the same in each sample, and the nominal pressure of the working gas in the first flexible hose 63 is 2.2MPa. In addition, the ultra-low temperature refrigerator 10 is operated in a state where both the first flexible hose 63 and the second flexible hose 64 are accommodated in a soundproof box, and the noise value is measured in the soundproof box. In the noise measurement of each sample, the same flexible hose is used for the second flexible hose 64. Due to the soundproof box, external noise is not included in the measurement results. As described above, since the sound generation time in the first flexible hose 63 and the second flexible hose 64 is different, the sound from the first flexible hose 63 can be separated and measured from the sound from the second flexible hose 64. In addition, the noise measurement method is described later. Figure 5 The same is true in Chinese.

[0061] Depend on Figure 4 It can be seen that the noise value is when the weaving stress is 85N / mm 2 When the braiding stress exceeds the threshold value (i.e., 85 N / mm), the braiding stress is generally suppressed to the upper limit value of about 56 dBA or below. 2 ), the noise value exceeds the upper limit and becomes higher. Specifically, when the braiding stress is 94.3N / mm 2 When the noise level is low, it reaches 61.1dBA.

[0062] The sound emitted by the first flexible hose 63 is caused by the impact of the gas flow generated in the conduit 72 when the high-pressure valve 40a is opened to allow the high-pressure working gas to flow from the compressor 12 into the first flexible hose 63 when the air intake process of the ultra-low temperature refrigerator 10 is started. The impact is transmitted to the braided wire 76 of the braided layer 74 via the conduit 72, and is perceived as noise from the first flexible hose 63. The transmission of sound using the braided wire 76 as a medium is promoted as the tension (i.e., braiding stress) acting on the braided wire 76 increases. The braided wire 76 acts like a guitar string. According to the analysis of the inventors, it can be considered that the sound pressure of the sound emitted from the braided wire 76 increases significantly when the braiding stress exceeds a certain threshold. Figure 4 In the measurement results shown, it can be read that the threshold is 85N / mm 2 .

[0063] Therefore, it is preferable that the braided layer 74 of the first flexible hose 63 is configured so that the tensile stress acting on the braided wire 76 when the working gas flows through the conduit at the nominal pressure becomes 85 N / mm. 2 The proposal is based on the following concept independently discovered by the inventors: noise can be managed by focusing on the braiding stress σ calculated using the braiding design parameters rather than focusing on the braiding design parameters (e.g., d, b1, b2, etc.) themselves. By this braiding design, the noise generated from the first flexible hose 63 during the operation of the cryogenic refrigerator 10 can be reduced.

[0064] From the perspective of reducing noise, the lower the braiding stress, the better. However, from the perspective of ease of manufacturing and other reasons, it is considered that the braiding stress is 30N / mm 2 The above is reasonable in design. Therefore, the braided layer 74 can be constructed so that when the working gas flows through the conduit 72 at the nominal pressure, the tensile stress acting on the braided wire 76 becomes 30N / mm 2 above.

[0065] During operation of the cryogenic refrigerator 10, the internal pressure of the first flexible hose 63 is higher than the internal pressure of the second flexible hose 64, so the impact sound caused by the working gas flow is more likely to become noticeable in the first flexible hose 63. Therefore, the braid stress management proposed in this specification is effective as a noise countermeasure in the pipeline on the high pressure side of the working gas pipeline 62 (for example, the first flexible hose 63).

[0066] However, the braiding stress management (specifically, setting the braiding stress to 85 N / mm 2The following) can also be applied to the second flexible hose 64. During the operation of the cryogenic refrigerator 10, the nominal pressure of the working gas flowing through the second flexible hose 64 is low, the braiding stress is reduced, and therefore the noise value can be expected to be reduced. In addition, by also using a flexible hose of the same design as the first flexible hose 63 in the second flexible hose 64, it is also possible to achieve a reduction in product cost based on the commonality of parts.

[0067] Figure 5 : is a graph showing the relationship between the gap between corrugations and the noise level involved in the embodiment. The gap between corrugations of the duct 72 is also a major parameter affecting the noise level. As shown below, the five samples 2a to 2e of the second flexible hose 64 prepared by the present inventor have gaps between corrugations of different sizes. Regarding samples 2a to 2e, the specifications other than the gap between corrugations, such as the weaving design, are the same. Specifically, the weaving design of samples 2a to 2e is the same as the weaving design of sample 1c. The noise values ​​(dBA) of these samples 2a to 2e were measured and the results were plotted on Figure 5 The noise measurement method is the same as the above Figure 4 The same method was used in the noise measurement of each sample. The same flexible hose was used as the first flexible hose 63 .

[0068] [Table 3]

[0069] Gap between corrugated sheets (mm) Noise level(dBA) Sample 2a 1.5 57.9 Sample 2b 0.25 55.6 Sample 2c 0.55 55.9 Sample 2d 0.35 56.2 Sample 2e 0.45 55.6

[0070] Depend on Figure 5 It can be seen that when the gap between the corrugations is less than 1 mm (preferably less than 0.6 mm), the noise value is about 56 dBA. In contrast, if the gap between the corrugations exceeds this threshold, the noise value increases. Specifically, when the gap between the corrugations is 1.5 mm, the noise value is 57.9 dBA.

[0071] The sound emitted by the second flexible hose 64 is caused by the gas flow generated in the conduit 72 when the low-pressure valve 40b is opened at the start of the exhaust process of the ultra-low temperature refrigerator 10, allowing the working gas expanded in the cold head 14 to flow into the second flexible hose 64. A part of the gas enters the gap between the corrugations and generates turbulence, thereby generating sound. According to the analysis of the inventors, it can be considered that the sound pressure of the sound emitted from the conduit 72 does not increase linearly with the increase of the gap between the corrugations, but is maintained at a substantially constant level when the gap between the corrugations is below a certain threshold, and increases significantly when the gap between the corrugations exceeds the threshold. Figure 5 In the measurement results shown, the threshold value can be read as, for example, 1 mm or preferably 0.6 mm.

[0072] Therefore, it is preferred that the conduit 72 of the second flexible hose 64 is configured such that the gap between the corrugations of the corrugated inner surface 72a is, for example, 1 mm or less, or preferably 0.6 mm or less. In this way, the gap between the corrugations on the corrugated inner surface 72a is sufficiently narrowed, and the working gas entering therein can be reduced. Thus, turbulence in the second flexible hose 64 can be suppressed, and the noise generated from the second flexible hose 64 during the operation of the cryogenic refrigerator 10 can be reduced.

[0073] From the viewpoint of reducing noise value, the smaller the gap between the corrugations, the better. Therefore, the gap between the corrugations only needs to be greater than 0 mm. However, from other reasons such as ease of manufacturing, it can be considered that the gap between the corrugations is 0.01 mm or more in design. Therefore, the duct 72 can be constructed so that the gap between the corrugations on the corrugated inner surface 72a is greater than 0 mm, or preferably greater than 0.01 mm.

[0074] During operation of the cryogenic refrigerator 10, the mass flow rates of the working gas in the second flexible hose 64 and the first flexible hose 63 are equal, and the pressure in the second flexible hose 64 is lower than the pressure in the first flexible hose 63. Therefore, the volume flow rate in the exhaust process of the working gas through the second flexible hose 64 becomes larger than that in the intake process of the working gas through the first flexible hose 63. Therefore, the second flexible hose 64 is more likely to generate turbulent sound than the first flexible hose 63. Therefore, the management of the gap between corrugations proposed in this specification is effective as a noise countermeasure in the pipeline on the low pressure side of the working gas pipeline 62 (for example, the second flexible hose 64).

[0075] However, the above-mentioned management of the gap between the corrugations can also be applied to the first flexible hose 63, which can help reduce the turbulent sound that may be generated in the first flexible hose 63. In addition, by adopting a flexible hose of the same design as the second flexible hose 64 in the first flexible hose 63, it is also possible to achieve a reduction in product cost based on the commonality of parts.

[0076] In addition, the gap between corrugations is a dimension related to the internal structure of the flexible hose, so it is difficult to measure directly from the outside of a certain flexible hose. Therefore, in order to determine the gap between corrugations of the flexible hose, the gap between corrugations can be measured according to the following procedure.

[0077] (1) Arrange the flexible hose in a straight line.

[0078] (2) Cut the flexible hose at three different locations in the axial direction. The cutting surface is a plane including the central axis of the hose. The cutting positions of the three locations can be, for example, the two ends and the middle of the hose.

[0079] (3) At each cutting position, measure the average value of the gaps between ten corrugations arranged continuously along the axial direction of the hose.

[0080] (4) The average of the average values ​​of the inter-corrugation gaps obtained from the cutting positions at three locations is used. The average value thus obtained can be regarded as the inter-corrugation gap of the flexible hose.

[0081] The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that the present invention is not limited to the above-mentioned embodiments, and various design changes can be made, and various modifications can exist, and such modifications are also within the scope of the present invention. Various features described in one embodiment can also be applied to another embodiment. The new embodiment generated by the combination has the effects of each of the combined embodiments.

[0082] In the above embodiment, the first flexible hose 63 and the second flexible hose 64 are each a single flexible hose, but the present invention is not limited thereto. At least one of the first flexible hose 63 and the second flexible hose 64 may be a hose formed by connecting a plurality of flexible hoses, and the braid stress management according to the embodiment may be applied to each of these flexible hoses or at least one flexible hose.

[0083] In the above embodiment, the case where the cryogenic refrigerator 10 is a two-stage GM refrigerator is described as an example, but the present invention is not limited to this. The cryogenic refrigerator 10 may also be a single-stage or multi-stage GM refrigerator, and may also be other types of cryogenic refrigerators such as a pulse tube refrigerator and a Stirling refrigerator. The flexible hose for a cryogenic refrigerator involved in the embodiment can be used in various cryogenic refrigerators.

[0084] The present invention has been described above based on the implementation method and using specific sentences. However, the implementation method only represents one aspect of the principle and application of the present invention. Without departing from the scope of the idea of ​​the present invention defined by the technical solution, the implementation method may have many variations or configuration changes.

Claims

1. A cryogenic refrigerator, characterized in that: have: compressor; Cold head; and A flexible hose connects the compressor to the cold head and includes a conduit for allowing the working gas of the ultra-low temperature refrigerator to flow through and a braided layer covering the conduit. The braided layer includes a braided wire braided into a cylindrical shape so as to cover the conduit, and the braided layer is configured so that when the working gas flows through the conduit at a nominal pressure, the tensile stress acting on the braided wire becomes 85 N / mm 2 the following.

2. The ultra-low temperature refrigerator according to claim 1, characterized in that: The braided layer is configured so that when the working gas flows through the conduit at the nominal pressure, the tensile stress acting on the braided wire becomes 30 N / mm 2 above.

3. The ultra-low temperature refrigerator according to claim 1, characterized in that: The compressor has a delivery port for delivering the working gas. The cold head has an air inlet for receiving the working gas, The flexible hose connects the delivery port to the air inlet.

4. The ultra-low temperature refrigerator according to any one of claims 1 to 3, characterized in that: The compressor is provided with a recovery port for recovering the working gas. The cold head has an exhaust port for exhausting the working gas. The cryogenic refrigerator further includes another flexible hose, which connects the recovery port to the exhaust port and includes a conduit for allowing the working gas to flow. The conduit of the other flexible hose has a corrugated inner surface exposed to the flow of the working gas, and the gap between the corrugations on the corrugated inner surface is 1 mm or less.

5. The ultra-low temperature refrigerator according to claim 4, characterized in that: The gap between the corrugations on the inner surface of the corrugations is less than 0.6 mm.

6. A cryogenic refrigerator, characterized in that: have: compressor; Cold head; and A flexible hose connects the compressor to the cold head and is provided with a conduit for allowing the working gas of the cryogenic refrigerator to flow through. The conduit has a corrugated inner surface exposed to the working gas flow, and the gap between the corrugations on the corrugated inner surface is less than 1 mm.

7. A flexible hose for a cryogenic refrigerator, characterized in that: have: a conduit for the flow of a working gas of a cryogenic refrigerator; and A braided layer is placed on the catheter. The braided layer includes a braided wire braided into a cylindrical shape so as to cover the conduit, and the braided layer is configured so that when the working gas flows through the conduit at a nominal pressure, the tensile stress acting on the braided wire becomes 85 N / mm 2 The following, and / or The conduit has a corrugated inner surface exposed to the working gas flow, and the gap between the corrugations on the corrugated inner surface is less than 1 mm.

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