Cryogenic freezer, and flexible hose for cryogenic freezer

Abstract

To reduce noise occurring from a flexible hose during operation of a cryogenic freezer.SOLUTION: A cryogenic freezer 10 comprises 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 comprises a conduit for flowing working gas of the cryogenic freezer 10, and a braid externally attached to the conduit. The braid comprises a braided wire woven into a cylindrical shape so as to cover the conduit, and is configured so that tensile stress acting on the braided wire is 85 N / mm2 or less when the working gas flows through the conduit at a nominal pressure.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cryogenic refrigerator and a flexible hose for a cryogenic refrigerator. [Background technology]

[0002] In general, a cryogenic refrigerator such as a Gifford-McMahon (GM) refrigerator includes a working gas pipe that connects a compressor and an expander, also called a cold head, for supplying and discharging a working gas between the compressor and the expander. A bellows-shaped flexible hose is sometimes used as the working gas pipe. Conventionally, it has been proposed to attach a flexible pipe to the inner surface of the bellows-shaped flexible hose in order to reduce noise generated from the flexible hose due to the flow of working gas during operation of the cryogenic refrigerator (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-333224 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventor has studied the above-mentioned flexible hose for cryogenic refrigerators and recognized the following problems. This flexible hose aims to reduce noise caused by gas flow by smoothing the inner surface of the hose using a flexible pipe. However, the inventor's study has revealed that the noise level may worsen depending on the design of the braid that is exteriorized to the flexible hose and the operating conditions of the cryogenic refrigerator, such as the working gas pressure. In addition, the above-mentioned flexible hose requires an additional part, the flexible pipe. This may lead to an increase in the manufacturing cost of the flexible hose. There are also concerns about long-term reliability, such as the progression of wear of the pipe due to long-term operation of the cryogenic refrigerator.

[0005] One exemplary object of an embodiment of the present invention is to reduce noise generated by flexible hoses during operation of a cryogenic refrigerator. [Means for solving the problem]

[0006] According to one aspect of the present invention, a cryogenic refrigerator includes a compressor, a cold head, and a flexible hose connecting the compressor to the cold head, the flexible hose including a conduit for flowing a working gas of the cryogenic refrigerator and a braid exteriorly attached to the conduit. The braid includes a braided wire woven into a cylindrical shape so as to cover the conduit, and when the working gas flows through the conduit at a nominal pressure, the tensile stress acting on the braided wire is 85 N / mm 2 It is configured as follows:

[0007] According to one aspect of the present invention, a cryogenic refrigerator includes a compressor, a cold head, and a flexible hose connecting the compressor to the cold head, the flexible hose including a conduit for flowing a working gas of the cryogenic refrigerator. The conduit includes a corrugated inner surface exposed to the flow of the working gas, and the corrugated inner surface has a gap between the corrugations of 1 mm or less.

[0008] According to one aspect of the present invention, a flexible hose for a cryogenic refrigerator includes a conduit for flowing a working gas of the cryogenic refrigerator and a braid that is fitted around the conduit. The braid includes a braided wire that is woven into a cylindrical shape so as to cover the conduit, and when the working gas flows through the conduit at a nominal pressure, the tensile stress acting on the braided wire is 85 N / mm 2 Additionally or alternatively, the conduit comprises a corrugated inner surface exposed to the flow of working gas, the corrugated inner surface having an inter-corrugation gap of 1 mm or less. Effect of the Invention

[0009] According to the present invention, it is possible to reduce noise generated from a flexible hose during operation of a cryogenic refrigerator. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a schematic diagram of a cryogenic refrigerator according to an embodiment; [Diagram 2] 1 is a diagram illustrating a schematic diagram of a cryogenic refrigerator according to an embodiment; [Diagram 3] 3(a) to 3(c) are schematic diagrams showing a flexible hose for a cryogenic refrigerator according to an embodiment. [Figure 4] 4 is a graph showing the relationship between blade stress and noise level according to the embodiment. [Diagram 5] 5 is a graph showing the relationship between the inter-corrugation gap and the noise level according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience in order to facilitate the description, and are not to be interpreted as being limiting unless otherwise specified. The embodiments are merely examples, and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0012] 1 and 2 are schematic diagrams illustrating a cryogenic refrigerator 10 according to an embodiment. The cryogenic refrigerator 10 is, as an example, a two-stage Gifford-McMahon (GM) refrigerator. FIG. 1 shows the exterior of the cryogenic refrigerator 10, and FIG. 2 shows the internal structure of the cryogenic refrigerator 10.

[0013] The cryogenic refrigerator 10 includes a compressor 12 and a cold head 14. The compressor 12 is configured to recover a working gas of the cryogenic refrigerator 10 from the cold head 14, pressurize the recovered working gas, and supply the working gas to the cold head 14 again. The cold head 14 is also called an expander. The compressor 12 and the cold head 14 form a refrigeration cycle (e.g., a GM cycle) of the cryogenic refrigerator 10, which enables the cryogenic refrigerator 10 to provide cryogenic cooling. The working gas, also called a refrigerant gas, is typically helium gas, but other suitable gases may be used.

[0014] In general, 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 significantly higher than atmospheric pressure and can be referred to as a first high pressure and a second high pressure, respectively. The first high pressure, i.e., the nominal pressure of the working gas on the supply side, may be selected from a first pressure range, for example, 1.5 MPa to 3.5 MPa. This first nominal pressure may 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 selected from a second pressure range, for example, 0.2 MPa to 2.0 MPa. This second nominal pressure may be, for example, 0.8 MPa. Hereinafter, for convenience of explanation, the first high pressure and the second high pressure are also simply referred to as a high pressure and a low pressure, respectively. For understanding, the flow direction of the working gas is indicated by an arrow.

[0015] 1, 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 in a housing of the compressor 12 as an outlet from the compressor 12 for the high-pressure working gas compressed by the compressor 12. The recovery port 52 is provided in a housing of the compressor 12 as an inlet to the compressor 12 for the low-pressure working gas recovered by the compressor 12.

[0016] The compressor 12 may be, for example, a scroll type, a rotary type, or any other suitable pump for pressurizing the working gas. In this embodiment, the compressor 12 is configured to discharge a fixed constant flow rate of the working gas. Alternatively, the compressor 12 may be configured to vary the flow rate of the working gas that it discharges. The compressor 12 may be provided with a cooling device, such as a chiller, to remove heat of compression generated by compression of the working gas.

[0017] 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 forms an expansion chamber (32, 34) for the working gas between the refrigerator cylinder 16 and the displacer assembly 18. The cold head 14 also includes a pressure switching valve 40 that determines the timing at which the working gas is sucked into the expansion chamber and the timing at which the working gas is exhausted from the expansion chamber.

[0018] In this document, in order to explain the positional relationship between the components of the cryogenic refrigerator 10, for convenience, the side closer to the top dead center of the axial reciprocating motion of the displacer will be referred to as "top" and the side closer to the bottom dead center as "bottom." The top dead center is the position of the displacer where the volume of the expansion space is maximum, and the bottom dead center is the position of the displacer where the volume of the expansion space is minimum. During operation of the cryogenic refrigerator 10, a temperature gradient occurs in which the temperature decreases from the top to the bottom in the axial direction, so the top side can also be called the high temperature side and the bottom side the low temperature side.

[0019] The refrigerator cylinder 16 has a first cylinder 16a and a second cylinder 16b. The first cylinder 16a and the second cylinder 16b are, for example, members having a cylindrical shape, and the second cylinder 16b has a smaller diameter than the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are arranged coaxially, and the lower end of the first cylinder 16a is rigidly connected to the upper end of the second cylinder 16b.

[0020] The displacer assembly 18 includes a first displacer 18a and a second displacer 18b that are connected to each other and move together. The first displacer 18a and the second displacer 18b are, for example, cylindrical members, and the second displacer 18b has a smaller diameter than the first displacer 18a. The first displacer 18a and the second displacer 18b are arranged coaxially.

[0021] 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 can reciprocate in the axial direction along the first cylinder 16a, and the second displacer 18b can reciprocate in the axial direction along the second cylinder 16b.

[0022] As shown in Fig. 2, the first displacer 18a accommodates the first regenerator 26. The first regenerator 26 is formed by filling a tubular main body of the first displacer 18a with a wire mesh such as copper or other suitable first regenerator material. The upper and lower lids of the first displacer 18a may be provided as separate members from the main body of the first displacer 18a, and the upper and lower lids of the first displacer 18a may be fixed to the main body by suitable means such as fastening or welding, thereby accommodating the first regenerator material in the first displacer 18a.

[0023] Similarly, the second displacer 18b accommodates the second regenerator 28. The second regenerator 28 is formed by filling the cylindrical main body of the second displacer 18b with a non-magnetic regenerator material such as bismuth, a magnetic regenerator material such as HoCu2, or other suitable second regenerator material. The second regenerator material may be formed in a granular shape. The upper and lower lids of the second displacer 18b may be provided as separate members from the main body of the second displacer 18b, and the lower lid of the upper lid of the second displacer 18b may be fixed to the main body by suitable means such as fastening or welding, thereby accommodating the second regenerator material in the second displacer 18b.

[0024] The displacer assembly 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. For heat exchange with a desired object or medium to be cooled by the cryogenic refrigerator 10, the cold head 14 includes 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 fixed to the lower part of the first cylinder 16a so as to surround the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower part of the second cylinder 16b so as to surround the second expansion chamber 34.

[0025] The first regenerator 26 is connected to the upper chamber 30 through a working gas passage 36a formed in the upper lid of the first displacer 18a, and is connected to the first expansion chamber 32 through a working gas passage 36b formed in the lower lid of the first displacer 18a. The second regenerator 28 is connected to the first regenerator 26 through a working gas passage 36c formed from the lower lid of the first displacer 18a to the upper lid of the second displacer 18b. The second regenerator 28 is also connected to the second expansion chamber 34 through a working gas passage 36d formed in the lower lid of the second displacer 18b.

[0026] A first seal 38a and a second seal 38b may be provided so that the working gas flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 is guided to the first regenerator 26 and the second regenerator 28, instead of through the clearance between the refrigerator cylinder 16 and the displacer assembly 18. The first seal 38a may be attached to an upper cover of the first displacer 18a so as to be disposed between the first displacer 18a and the first cylinder 16a. The second seal 38b may be attached to an upper cover of the second displacer 18b so as to be disposed between the second displacer 18b and the second cylinder 16b.

[0027] 1, the cold head 14 includes a refrigerator housing 20 that houses a pressure switching valve 40. The refrigerator housing 20 is coupled to the refrigerator cylinder 16, thereby forming an airtight container that houses the pressure switching valve 40 and the displacer assembly 18.

[0028] The cold head 14 also has an intake port 22 for receiving the working gas, and an exhaust port 24 for discharging the working gas. The intake port 22 is provided in the refrigerator housing 20 as an inlet for the high-pressure working gas supplied from the compressor 12 to the cold head 14. The exhaust port 24 is provided in the refrigerator housing 20 as an outlet for the low-pressure working gas discharged from the cold head 14.

[0029] 2, the pressure switching valve 40 includes a high-pressure valve 40a and a low-pressure valve 40b, and is configured to generate a periodic pressure fluctuation in the refrigerator cylinder 16. A delivery port 50 of the compressor 12 is connected to the upper chamber 30 via the high-pressure valve 40a, and a 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 and alternately open and close (i.e., when one is open, the other is closed).

[0030] The pressure switching valve 40 may take the form of a rotary valve. That is, the pressure switching valve 40 may be configured so that the high pressure valve 40a and the low pressure valve 40b are alternately opened and closed by the rotational sliding of a valve disc relative to a stationary valve body. In this case, the expander motor 42 may be connected to the pressure switching valve 40 so as to rotate the valve disc of the pressure switching valve 40. For example, the pressure switching valve 40 is arranged so that the valve rotation axis is coaxial with the rotation axis of the expander motor 42.

[0031] Alternatively, the high pressure valve 40a and the low pressure valve 40b may each be a valve that can be controlled individually, in which case the pressure switching valve 40 does not need to be connected to the expander motor .

[0032] The expander motor 42 may be an electric motor, for example, a permanent magnet type motor driven by three-phase AC. The expander motor 42 is connected to a displacer drive shaft 44 via a motion conversion mechanism 43, for example, a Scotch yoke mechanism. The expander motor 42 is attached to the refrigerator housing 20. The motion conversion mechanism 43 is accommodated in the refrigerator housing 20, similar to the pressure switching valve 40. 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 into the upper chamber 30 and is fixed to the upper cover part of the first displacer 18a. The rotation of the expander motor 42 is converted into an axial reciprocating motion of the displacer drive shaft 44 by the motion conversion mechanism 43, and the displacer assembly 18 linearly reciprocates in the axial direction within the refrigerator cylinder 16.

[0033] The cryogenic refrigerator 10 also includes a working gas line 62 that circulates the working gas between the compressor 12 and the cold head 14. The working gas line 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 intake port 22 of the cold head 14. Thus, the first flexible hose 63 is supplied with high pressure working gas from the compressor 12 to the cold head 14. The second flexible hose 64 connects the recovery port 52 of the compressor 12 to the exhaust port 24 of the cold head 14. Thus, the second flexible hose 64 is supplied with low pressure working gas recovered from the cold head 14 to the compressor 12. Details of these flexible hoses will be described later.

[0034] When the compressor 12 and the expander motor 42 are operated, the cryogenic refrigerator 10 generates periodic volume fluctuations and pressure fluctuations of the working gas synchronized therewith in the first expansion chamber 32 and the second expansion chamber 34. Typically, in the intake stroke, the low pressure valve 40b is closed and the high pressure valve 40a is opened, so that the high pressure working gas flows from the compressor 12 through the high pressure valve 40a into the upper chamber 30, is supplied to the first expansion chamber 32 through the first regenerator 26, and is supplied to the second expansion chamber 34 through the second regenerator 28. In this way, the first expansion chamber 32 and the second expansion chamber 34 are pressurized from low pressure to high pressure. At this time, the displacer assembly 18 is moved upward from the bottom dead center to the top dead center, and the volumes of the first expansion chamber 32 and the second expansion chamber 34 are increased. When the high pressure valve 40a is closed, the intake stroke ends.

[0035] In the exhaust stroke, 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 opened to the low-pressure working gas intake port of the compressor 12, and the working gas expands in the first expansion chamber 32 and the second expansion chamber 34, and the low-pressure working gas is discharged from the first expansion chamber 32 and the second expansion chamber 34 to the upper chamber 30 through the first regenerator 26 and the second regenerator 28. At this time, the displacer assembly 18 is moved downward from the top dead center to the bottom dead center, and the volumes of the first expansion chamber 32 and the second expansion chamber 34 are reduced. The working gas is collected from the cold head 14 to the compressor 12 through the low-pressure valve 40b. When the low-pressure valve 40b is closed, the exhaust stroke is completed.

[0036] In this manner, a refrigeration cycle such as a GM cycle is configured in the cryogenic refrigerator 10, and the first cooling stage 33 and the second cooling stage 35 are cooled to a desired cryogenic 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 in the range of, for example, about 30K to about 80K. The second cooling temperature may be in the range of, for example, about 1K to about 20K. The second cooling temperature may be the liquid helium temperature of about 4.2K or a temperature lower than that.

[0037] Meanwhile, during operation of the cryogenic refrigerator 10, the working gas line 62 may generate noise due to the flow of the working gas. In the intake stroke, the working gas flows from the compressor 12 to the cold head 14 through the first flexible hose 63, so that noise associated with the flow of the working gas may be generated from the first flexible hose 63. In the exhaust stroke, the working gas flows from the cold head 14 to the compressor 12 through the second flexible hose 64, so that noise associated with the flow of the working gas may be generated from the second flexible hose 64. Such noise may be perceived as noise by a user of the cryogenic refrigerator 10 or a user of an apparatus (e.g., a magnetic resonance imaging (MRI) apparatus) equipped with the cryogenic refrigerator 10. Therefore, this document proposes a technology for reducing such noise.

[0038] Figures 3(a) to 3(c) are schematic diagrams showing a flexible hose for a cryogenic refrigerator according to an embodiment. As shown in Figures 3(a) to 3(c), a flexible hose 70 includes a conduit 72 for flowing a working gas of the cryogenic refrigerator, and a braid 74 that is fitted to the exterior of the conduit 72. The illustrated flexible hose 70 can be used as the first flexible hose 63 or the second flexible hose 64 described above with reference to Figures 1 and 2, or both.

[0039] In this embodiment, the conduit 72 is a corrugated pipe, i.e., a bellows-shaped pipe. As shown in Fig. 3(c), the inner surface 72a of the conduit 72, i.e., the corrugated pipe (hereinafter also referred to as the corrugated inner surface) is exposed to the flow 80 of the working gas. The conduit 72 is made of, for example, stainless steel. Alternatively, the conduit 72 may be made of other suitable materials.

[0040] The conduit 72 may be designed based on several conduit design parameters, such as the maximum inner diameter D of the corrugated pipe. imax (mm), inner diameter of corrugated pipe D iThe corrugated pipe wall has a large number of protrusions 73 formed along the pipe axis direction toward the inside of the pipe, and the corrugated pipe gap g, as shown in the figure, indicates the distance in the pipe axis direction between two adjacent protrusions 73.

[0041] The braid 74 includes a braided wire 76 braided into a cylindrical shape so as to cover the conduit 72. The braid 74 is braided so as to envelop the corrugated shape of the conduit 72. Therefore, unlike the conduit 72, the outer surface of the braid 74 has a generally constant outer diameter D o (mm). The braided wire 76 is made of, for example, stainless steel. Alternatively, the braided wire 76 may be made of other suitable materials.

[0042] The braid 74 may be designed based on several braid design parameters. The braid design parameters may include, for example, the braid wire diameter d (mm), the braid number b1, the braid number b2, the braid crossing angle b3 (rad), and the number of braid layers b4. The braid number b1 represents the number of braid wires 76 constituting one bundle of braid wires 76 used to weave the braid 74. The braid number b2 represents the number of bundles of braid wires 76 used to weave the braid 74. The braid crossing angle b3 represents the angle between the bundles of braid wires 76 when weaving the braid 74. The number of braid layers b4 represents the number of layers of the braid 74 that cover the conduit 72, and FIG. 3(b) illustrates an example in which the number of braid layers b4 is 2.

[0043] The inventors have experimentally investigated noise from flexible hoses 70 with various braid designs, and as a result have found one main parameter that influences the noise level in relation to the braid 74. This is the tensile stress acting on the braid wire 76 (hereinafter also referred to simply as "braid stress").

[0044] When the working gas flows through the conduit 72 of the flexible hose 70, the conduit 72 is subjected to a force that tends to expand due to the pressure of the working gas. This force is transmitted to the braid 74 and can cause tensile stress in the braid wire 76. 2 ), that is, the tensile stress acting on one braid wire 76 in its extending direction can be calculated by the following formula. σ=P π(D imax / 2) 2 / (b1·b2) / b4 / cos(b3 / 2) / π(d / 2) 2 Here, P (MPa) represents the internal pressure of the conduit 72 due to the working gas during operation of the cryogenic refrigerator 10. To calculate the braid stress σ, the above-mentioned first nominal pressure (e.g., 2.2 MPa) can be used as this internal pressure P.

[0045] Fig. 4 is a graph showing the relationship between braid stress and noise level according to the embodiment. The braid stress was calculated and the noise value (dBA) was measured for nine samples 1a to 1i of the first flexible hose 63 prepared by the inventor, and the results are plotted in Fig. 4.

[0046] The braid design parameters of the nine samples 1a to 1i are as set forth in the table below. [Table 1]

[0047] Braid stress σ (N / mm 2 ) and the measured noise levels (dBA) are as follows, which are shown in Figure 4. [Table 2]

[0048] In calculating the braid stress σ, the design of each sample conduit 72 is the same, and the maximum inner diameter D imaxis 25.2 mm. The operating conditions of the cryogenic refrigerator 10 are the same for each sample, and the nominal pressure of the working gas in the first flexible hose 63 is 2.2 MPa. The cryogenic refrigerator 10 is operated with both the first flexible hose 63 and the second flexible hose 64 housed in one sound-proof box, and the noise value is measured in this sound-proof box. The same second flexible hose 64 is used for the noise measurement of each sample. The sound-proof box prevents external noise from being included in the measurement results. Since the sound generation timing of the first flexible hose 63 and the second flexible hose 64 is different as described above, the sound from the first flexible hose 63 can be measured separately from the sound from the second flexible hose 64. This noise measurement method is also the same in FIG. 5 described later.

[0049] As can be seen from Fig. 4, the noise value is 2 When the braid stress is below this threshold (i.e. 85 N / mm 2 ), the noise level exceeds this upper limit and increases. Specifically, when the blade stress exceeds 94.3N / mm 2 At this time, the noise level reaches 61.1 dBA.

[0050] The sound emitted by the first flexible hose 63 is caused by the shock of the gas flow generated in the conduit 72 when the high-pressure valve 40a is opened at the start of the intake stroke of the cryogenic refrigerator 10 and the high-pressure working gas flows from the compressor 12 into the first flexible hose 63. This shock is transmitted to the braided wire 76 of the braid 74 via the conduit 72, and is sensed as noise from the first flexible hose 63. Sound transmission through the braided wire 76 is promoted as the tension acting on the braided wire 76, i.e., the braid stress, increases. The braided wire 76 acts like a guitar string, so to speak. According to the inventor's analysis, the sound pressure of the sound emitted from the braided wire 76 in this way is considered to become significantly large when the braid stress exceeds a certain threshold value. From the measurement results shown in FIG. 4, this threshold value is considered to be 85 N / mm 2This can be read as follows.

[0051] Therefore, the braid 74 of the first flexible hose 63 has a tensile stress of 85 N / mm acting on the braid wire 76 when the working gas flows through the conduit at the nominal pressure. 2 It is preferable that the configuration is as follows. This proposal is based on the idea that the present inventors have independently discovered that noise can be controlled by focusing on the braid stress σ calculated using the braid design parameters, rather than on the braid design parameters themselves (e.g., d, b1, b2, etc.). Such a braid design can reduce the noise generated from the first flexible hose 63 during operation of the cryogenic refrigerator 10.

[0052] From the viewpoint of reducing noise levels, the lower the braid stress, the better. However, due to other factors such as ease of manufacture, the braid stress is set at 30N / mm 2 It is considered reasonable from a design point of view to set the above value. Therefore, the braid 74 is designed so that the tensile stress acting on the braid wire 76 is 30 N / mm when the working gas flows through the conduit 72 at the nominal pressure. 2 The above may be configured.

[0053] During operation of the cryogenic refrigerator 10, the internal pressure of the first flexible hose 63 is higher than that of the second flexible hose 64, and therefore, the impact noise caused by the working gas flow is more likely to be noticeable in the first flexible hose 63. Therefore, the braid stress management proposed in this specification is effective as a noise countermeasure in the high-pressure side line of the working gas line 62, such as the first flexible hose 63.

[0054] However, the above-mentioned braid stress management, specifically, the braid stress is set at 85N / mm 2The following settings may be similarly applied to the second flexible hose 64. The second flexible hose 64 is expected to have a low noise level because the nominal pressure of the working gas flowing inside during operation of the cryogenic refrigerator 10 is low and the braid stress is small. In addition, by using a flexible hose with the same design as the first flexible hose 63 for the second flexible hose 64, it may be possible to reduce product costs by standardizing parts.

[0055] FIG. 5 is a graph showing the relationship between inter-corrugation gaps and noise level according to an embodiment. The inter-corrugation gaps of the conduit 72 are also one of the main parameters that affect the noise level. Five samples 2a to 2e of the second flexible hose 64 prepared by the inventor have inter-corrugation gaps of different sizes, as shown below. The specifications of the samples 2a to 2e, such as the braid design, are the same as those of the sample 1c. Specifically, the braid design of the samples 2a to 2e is the same as that of the sample 1c. The noise values ​​(dBA) of the samples 2a to 2e were measured, and the results are plotted in FIG. 5. The noise measurement method is the same as that used in FIG. 4 described above. The same first flexible hose 63 is used for the noise measurement of each sample. [Table 3]

[0056] As can be seen from Fig. 5, the noise level is about 56 dBA when the inter-corrugation gap is 1 mm or less, preferably 0.6 mm or less. On the other hand, when the inter-corrugation gap exceeds this threshold, the noise level increases. Specifically, when the inter-corrugation gap is 1.5 mm, the noise level is 57.9 dBA.

[0057] The sound generated by the second flexible hose 64 is due to the gas flow generated in the conduit 72 when the low pressure valve 40b is opened at the start of the evacuation process of the cryogenic refrigerator 10 and the working gas expanded in the cold head 14 flows into the second flexible hose 64. A part of the gas enters the gap between the corrugations, causing turbulence, which generates the sound. According to the analysis by the inventor, the sound pressure of the sound generated from the conduit 72 in this way does not increase linearly as the gap between the corrugations increases, but remains approximately constant when the gap between the corrugations is below a certain threshold value and increases significantly when the gap exceeds this threshold value. From the measurement results shown in FIG. 5, this threshold value can be read as, for example, 1 mm, or preferably 0.6 mm.

[0058] Therefore, the conduit 72 of the second flexible hose 64 is preferably configured so that the inter-corrugation gaps on the corrugated inner surface 72a are, for example, 1 mm or less, and preferably 0.6 mm or less. In this way, the inter-corrugation gaps on the corrugated inner surface 72a become sufficiently narrow, and the amount of working gas entering therein can be reduced. This makes it possible to suppress the generation of turbulence in the second flexible hose 64, and reduce noise generated from the second flexible hose 64 during operation of the cryogenic refrigerator 10.

[0059] From the viewpoint of reducing noise levels, the smaller the inter-corrugation gap, the better. Thus, the inter-corrugation gap should be greater than 0 mm. However, from the viewpoint of ease of manufacture and other factors, it is considered reasonable from a design perspective for the inter-corrugation gap to be 0.01 mm or greater. Thus, the conduit 72 may be configured such that the inter-corrugation gap on the corrugated inner surface 72a is greater than 0 mm, or preferably 0.01 mm or greater.

[0060] During operation of the cryogenic refrigerator 10, the mass flow rate of the working gas is equal in the second flexible hose 64 and the first flexible hose 63, and the pressure in the second flexible hose 64 is lower than that in the first flexible hose 63. Therefore, in the exhaust process of the working gas through the second flexible hose 64, the volumetric flow rate is larger than that in the intake process of the working gas through the first flexible hose 63. Thus, turbulent noise is more likely to occur in the second flexible hose 64 than in the first flexible hose 63. Therefore, the management of the inter-corrugated gap proposed in this specification is effective as a noise countermeasure in the low-pressure side line of the working gas line 62, such as the second flexible hose 64.

[0061] However, the above-mentioned management of the inter-corrugation gaps may be similarly applied to the first flexible hose 63, and may be useful in reducing turbulent noise that may occur in the first flexible hose 63. In addition, by using a flexible hose with the same design as the second flexible hose 64 for the first flexible hose 63, it may be possible to reduce product costs by standardizing parts. stomach.

[0062] Since the inter-corrugation gap is a dimension related to the internal structure of the flexible hose, it is difficult to directly measure the inter-corrugation gap of a given flexible hose from the outside of the hose. Therefore, in order to specify the inter-corrugation gap of a flexible hose, the inter-corrugation gap may be measured by the following procedure. (1) Arrange the flexible hose in a straight line. (2) The flexible hose is cut at three different positions in the axial direction. The cut surfaces are planes including the central axis of the hose. The three cut positions may be, for example, both ends and the middle of the hose. (3) At each cut position, measure the average inter-corrugation gap of 10 consecutive corrugations arranged in the axial direction of the hose. (4) The average of the inter-corrugation gaps obtained from the three cut positions is taken. The average value thus obtained can be regarded as the inter-corrugation gap of this flexible hose.

[0063] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment resulting from a combination has the combined effects of each of the combined embodiments.

[0064] 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 to this. At least one of the first flexible hose 63 and the second flexible hose 64 may be a connection of multiple flexible hoses, and the braid stress management according to the embodiment may be applied to each of these flexible hoses, or to at least one of them.

[0065] In the above-described embodiment, the cryogenic refrigerator 10 is described as a two-stage GM refrigerator, but the present invention is not limited to this. The cryogenic refrigerator 10 may be a single-stage or multi-stage GM refrigerator, or may be another type of cryogenic refrigerator, such as a pulse tube refrigerator or a Stirling refrigerator. The flexible hose for a cryogenic refrigerator according to the embodiment can be used in such various cryogenic refrigerators.

[0066] The present invention has been described using specific terms based on the embodiments, but the embodiments merely show one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments without departing from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0067] 10 cryogenic refrigerator, 12 compressor, 14 cold head, 22 intake port, 24 exhaust port, 50 delivery port, 52 recovery port, 70 flexible hose, 72 conduit, 74 braid, 76 braided wire.

Claims

1. A compressor; Cold head and a flexible hose for connecting the compressor to the cold head, the flexible hose including a conduit for flowing a working gas of the cryogenic refrigerator and a braid externally attached to the conduit; The braid has a braided wire woven into a cylindrical shape so as to cover the conduit, and when the working gas flows through the conduit at a nominal pressure, a tensile stress acting on the braided wire is 85 N / mm ２ A cryogenic refrigerator characterized by being configured as follows.

2. The braid has a tensile stress of 30 N / mm when the working gas flows through the conduit at the nominal pressure. ２ 2. The cryogenic refrigerator according to claim 1, characterized in that the cryogenic refrigerator is configured as described above.

3. The compressor includes a delivery port for delivering the working gas, the cold head includes an intake port for receiving the working gas; 2. The cryogenic refrigerator of claim 1, wherein the flexible hose connects the outlet port to the intake port.

4. The compressor includes a recovery port that recovers the working gas, the cold head includes an exhaust port for exhausting the working gas; the cryogenic refrigerator further comprises another flexible hose connecting the recovery port to the exhaust port, the another flexible hose comprising a conduit for flowing the working gas; 4. The cryogenic refrigerator according to claim 1, wherein the conduit of the other flexible hose has a corrugated inner surface exposed to the flow of the working gas, and the inter-corrugation gap on the corrugated inner surface is 1 mm or less.

5. 5. The cryogenic refrigerator according to claim 4, wherein the gap between the corrugations on the inner surface of the corrugation is 0.6 mm or less.

6. A compressor; Cold head and a flexible hose connecting the compressor to the cold head, the flexible hose comprising a conduit for flowing a working gas of the cryogenic refrigerator; The conduit has a corrugated inner surface exposed to the flow of the working gas, and the corrugated inner surface has a gap between the corrugations of 1 mm or less.

7. A flexible hose for a cryogenic refrigerator, A conduit for flowing a working gas of the cryogenic refrigerator; a braid attached to the conduit; The braid has a braided wire woven into a cylindrical shape so as to cover the conduit, and when the working gas flows through the conduit at a nominal pressure, a tensile stress acting on the braided wire is 85 N / mm ２ and / or configured to: The conduit has a corrugated inner surface exposed to the flow of the working gas, and the inter-corrugation gap on the corrugated inner surface is 1 mm or less.

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