Double-pipe heat exchanger manufacturing method

Abstract

To provide a double-tube heat exchanger having no risk of cracking of an inner tube when a double-tube is bent and capable of reducing the amount of refrigerant by decreasing a flow passage cross section area between an outer tube and the inner tube, as well as a method of manufacturing the double-tube heat exchanger which can easily perform processing of the inner tube and diameter reducing processing of the outer tube.SOLUTION: A double-tube heat exchanger 1 includes an outer tube 2 and an inner tube 3 inserted into the outer tube, with a plurality of bottoms 10a and apexes 10b being formed on an outer surface of the inner tube 3. The outer tube 2 has reduced diameter, with a plurality of points P on an inner surface of the outer tube 2 being in contact with the apexes 10b of the inner tube 3. The diameter of the outer tube 2 is reduced by formation of a recessed groove 6 extending in an axial direction on an outer surface of the outer pipe 2, and the inner surface 7 of the outer tube 2 is in contact with the apexes 10b of the inner pipe 3.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a double-pipe heat exchanger having an outer pipe and an inner pipe. vessel Regarding the manufacturing method. [Background technology]

[0002] Some car air conditioners use an internal heat exchanger that exchanges heat between a high-temperature liquid refrigerant from a condenser, which is part of a refrigeration cycle, and a low-temperature gaseous refrigerant from an evaporator, which is also part of a refrigeration cycle, to improve the cooling efficiency of the evaporator. This internal heat exchanger is a double-pipe heat exchanger consisting of an outer pipe and an inner pipe disposed within the outer pipe, with a flow path for the high-temperature liquid refrigerant from the condenser formed between the outer pipe and the inner pipe, and a flow path for the low-temperature gaseous refrigerant from the evaporator formed inside the inner pipe.

[0003] In double-pipe heat exchangers, if there is a gap between the outer and inner pipes, the inner pipe will not be able to follow the deformation of the outer pipe when an external force is applied, which may result in abnormal deformation or cracking of the inner pipe. Therefore, the outer pipe and the inner pipe are fixed in place by making them contact with each other.

[0004] For example, Patent Document 1 describes a double pipe having an outer pipe and an inner pipe with a groove formed in the inner pipe, in which, in the straight pipe section, the inner pipe is not in contact with the outer pipe or is in contact only in one radial direction, and in the bent section, the inner pipe is in contact with the outer pipe in multiple radial directions.

[0005] In Patent Document 1, the outer and inner pipes are bent while the inner pipe remains positioned inside the outer pipe, so that the outer and inner pipes come into contact with each other. However, when the outer and inner pipes are bent, there is a risk that the inner pipe may break, and there are also places where the outer and inner pipes do not come into contact. Furthermore, if the outer and inner pipes do not come into contact, the cross-sectional area of ​​the flow path between the outer and inner pipes becomes large, and the amount of refrigerant increases.

[0006] Patent document 2 describes a double-pipe heat exchanger in which concave grooves are formed in the inner pipe to increase the heat transfer area and improve heat exchange efficiency, and a manufacturing method in which the inner pipe is moved while a groove-making tool is pressed against the inner pipe to form the concave grooves in the inner pipe.

[0007] In Patent Document 2, the concave grooves in the inner tube are formed by rolling using a grooving tool, which poses problems of expensive manufacturing equipment and a long processing time.

[0008] In Patent Document 3, the applicant of the present application has proposed a method for manufacturing a double-pipe heat exchanger that can form a corrugated portion on the inner pipe in a short time. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 4350079 specification [Patent Document 2] Patent No. 4628858 specification [Patent Document 3] Japanese Patent Publication No. 2020-82192 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in consideration of the problems of the prior art, and is capable of reducing the amount of refrigerant by reducing the cross-sectional area of ​​the flow path between the outer and inner pipes without the risk of the inner pipe being deformed or cracked when bending the double pipe. , outside The present invention addresses the problem of providing a method for manufacturing a double-pipe heat exchanger that allows easy diameter reduction of the pipes. [Means for solving the problem]

[0011] As a means for solving the above problem, (1) The double-pipe heat exchanger according to the present invention is A double-pipe heat exchanger including an outer pipe and an inner pipe inserted inside the outer pipe, a plurality of bottoms and tops are formed on the outer surface of the inner tube; The outer tube is characterized in that its diameter is reduced so that a plurality of points on the inner surface of the outer tube are in contact with the top of the inner tube. Here, "diameter reduction" includes deforming a part of the outer surface of the outer tube inward in the radial direction, and deforming the entire periphery of the outer surface of the outer tube inward in the radial direction.

[0012] (2) It is preferable that the outer tube has a reduced diameter by forming a recess extending in the axial direction on the outer surface of the outer tube.

[0013] (3) It is preferable that the outer tube has a reduced diameter by forming a recessed groove extending in the axial direction on the outer surface of the outer tube.

[0014] (4) It is preferable that the outer tube has a reduced diameter by forming a spiral groove extending in the axial direction on the outer surface of the outer tube.

[0015] (5) A method for manufacturing a double-pipe heat exchanger according to the present invention includes the steps of: A method for manufacturing a double-pipe heat exchanger including an outer pipe and an inner pipe inserted into the outer pipe, The method is characterized in that the outer tube is pressed radially inward against an inner tube having a plurality of bottoms and tops formed on its outer surface, thereby reducing the diameter within a predetermined range in the axial direction and bringing multiple points on the inner surface of the outer tube into contact with the tops of the inner tube.

[0016] (6) It is preferable that the diameter of the outer tube is reduced by pressing a plurality of movable pieces arranged at equal intervals around the outer tube radially inward against the outer tube, and then moving the outer tube and the inner tube axially, and repeating this process multiple times to form a recess extending axially on the outer surface of the outer tube, thereby reducing the diameter.

[0017] (7) It is preferable to reduce the diameter by pressing a plurality of rollers having rotation axes on a plane perpendicular to the central axis of the outer tube against the outer tube, moving the outer tube and the inner tube in the axial direction, and forming a recess extending in the axial direction on the outer surface of the outer tube with the rollers.

[0018] (8) It is preferable to reduce the diameter by pressing a plurality of rollers having rotation axes on a plane perpendicular to the central axis of the outer tube against the outer tube, moving the outer tube and the inner tube in the axial direction, and forming a groove extending in the axial direction on the outer surface of the outer tube with the rollers.

[0019] (9) It is preferable to reduce the diameter by pressing a plurality of rollers having rotation axes parallel to the central axis of the outer tube against the outer tube, rotating the rollers around the outer tube, and moving the outer tube and the inner tube axially, so that the rollers form a spiral groove extending axially on the outer surface of the outer tube. [Effects of the Invention]

[0020] Original Clearly Since the inner surface of the outer pipe is in contact with the top of the inner pipe at multiple points and the inner pipe is supported by the outer pipe, there is no risk of the inner pipe being deformed or cracked when the double pipe is bent. In addition, since the diameter of the outer pipe is reduced and the cross-sectional area of ​​the flow path between the outer pipe and the inner pipe is reduced, the amount of refrigerant can be reduced.

[0021] Original Clearly According to this, the diameter of the outer tube can be easily reduced by simply pressing the outer tube inward in the radial direction using a plurality of drawing tools that are movable in the radial direction. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a longitudinal cross-sectional view of a double-pipe heat exchanger according to the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the double-pipe heat exchanger taken along line II-II in FIG. 1. [Figure 3] FIG. 10 is a perspective view showing the double-pipe heat exchanger in a bent state. [Figure 4] 4A is a side view showing a first embodiment of a method for reducing the diameter of an outer tube to bring the inner surface of the outer tube into contact with the top of the wave-shaped portion of an inner tube, and FIG. 4B is a cross-sectional view taken along line IVb-IVb thereof. [Figure 5] 5A to 5C are cross-sectional views sequentially showing a method for reducing the diameter of the outer tube by the movable piece of FIG. 4. [Figure 6] 5 is an enlarged cross-sectional view of the outer tube and the inner tube after the diameter is reduced by the movable piece in FIG. 4. [Figure 7] 5 is a front view showing a recess formed in the outer tube after the diameter is reduced by the movable piece in FIG. 4. [Figure 8] FIG. 10 is a side view showing a second embodiment of a method for reducing the diameter of the outer tube to bring the inner surface of the outer tube into contact with the top of the wave-shaped portion of the inner tube. [Figure 9] 9A to 9C are cross-sectional views sequentially illustrating a method for reducing the diameter of the outer tube by the roller of FIG. 8. [Figure 10] 9 is an enlarged cross-sectional view of the outer tube and the inner tube after the diameter is reduced by the rollers in FIG. 8. [Figure 11] 9 is a front view showing recesses formed in the outer tube after the diameter is reduced by the rollers of FIG. 8. [Figure 12] FIG. 10 is a side view showing a third embodiment of a method for reducing the diameter of the outer tube to bring the inner surface of the outer tube into contact with the top of the wave-shaped portion of the inner tube. [Figure 13] 13A to 13C are cross-sectional views sequentially illustrating a method for reducing the diameter of the outer tube by the roller of FIG. 12. [Figure 14] 13 is an enlarged cross-sectional view of the outer tube and the inner tube after the diameter is reduced by the rollers in FIG. 12. [Figure 15] 13 is a front view showing the grooves formed in the outer tube after the diameter is reduced by the rollers of FIG. 12. [Figure 16] FIG. 11 is a front view showing a modified example of the third embodiment. [Figure 17] 17 is an enlarged cross-sectional view of the outer tube and the inner tube after the diameters are reduced by the rollers in FIG. 16. [Figure 18] FIG. 10 is a side view showing a fourth embodiment of a method for reducing the diameter of the outer tube to bring the inner surface of the outer tube into contact with the top of the wave-shaped portion of the inner tube. [Figure 19] 19A to 19C are cross-sectional views sequentially showing a method for reducing the diameter of the outer tube by the roller of FIG. 18. [Figure 20] 19 is an enlarged cross-sectional view of the outer tube and the inner tube after the diameter is reduced by the rollers in FIG. 18. [Figure 21] 19 is a front view showing the grooves formed in the outer tube after the diameter is reduced by the rollers of FIG. 18. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0024] 1 shows a double-pipe heat exchanger 1 according to a first embodiment of the present invention. This double-pipe heat exchanger 1 comprises an outer pipe 2 and an inner pipe 3 inserted inside the outer pipe 2. In this embodiment, the double-pipe heat exchanger 1 is an internal heat exchanger for a car air conditioner, and is described as having a first flow path 4 between the outer pipe 2 and the inner pipe 3, in which a high-temperature, high-pressure liquid refrigerant flows, and a second flow path 5 within the inner pipe 3, in which a low-temperature, low-pressure gas refrigerant flows in a counter-flow manner. However, conversely, the low-temperature, low-pressure gas refrigerant may flow in the first flow path 4, and a high-temperature, high-pressure refrigerant may flow in the second flow path 5, or the two may flow in parallel.

[0025] As shown in Fig. 2, the outer pipe 2 is made of an aluminum extrusion with a circular cross section, and has a reduced diameter portion 6 within a predetermined axial range, the diameter of which is reduced by a method described below. The inner surface 7 of the reduced diameter portion 6 of the outer pipe 2 contacts, at multiple locations P, crests 10b of corrugated portions 10 of the inner pipe 3, which will be described later. As shown in Fig. 1, both ends of the outer pipe 2 are joined to the outer surface of the inner pipe 3 and closed. The outer pipe 2 is formed with an outer pipe inlet 8 through which high-temperature, high-pressure liquid refrigerant flows in, and an outer pipe outlet 9 through which the liquid refrigerant flows out after heat exchange with the gas refrigerant in the inner pipe 3.

[0026] As shown in FIG. 2, the inner pipe 3 is made of an aluminum extrusion with a circular cross section and has an outer diameter smaller than the inner surface of the outer pipe 2. When viewed from the outside, the inner pipe 3 has eight corrugated portions 10 formed thereon, each of which has a plurality of axially extending bottom portions 10a and top portions 10b that alternate in the circumferential direction. The corrugated portions 10 are formed by a known method such as pressing or rolling. The corrugated portions 10 may also extend spirally in the axial direction. As shown in FIG. 1, the inner pipe 3 has an inner pipe inlet 11 at one end through which a low-temperature, low-pressure gas refrigerant flows in, and an inner pipe outlet 12 at the other end through which the gas refrigerant flows out after heat exchange with the liquid refrigerant between the outer pipe 2 and the inner pipe 3.

[0027] Next, the operation of the double-pipe heat exchanger 1 will be described.

[0028] In FIG. 1, the heat held by the high-temperature, high-pressure liquid refrigerant flowing in the first flow path 4 between the outer pipe 2 and the inner pipe 3 is transferred to the low-temperature, low-pressure gas refrigerant flowing in the second flow path 5 of the inner pipe 3 by heat transfer to the outer surface of the pipe wall of the inner pipe 3, heat conduction within the pipe wall of the inner pipe 3, and heat transfer from the inner surface of the pipe wall of the inner pipe 3.

[0029] As a result, heat exchange takes place between the high-temperature, high-pressure liquid refrigerant flowing through the first flow path 4 between the outer pipe 2 and the inner pipe 3 and the low-temperature, low-pressure gas refrigerant flowing through the second flow path 5 within the inner pipe 3, cooling the high-temperature, high-pressure liquid refrigerant in the first flow path 4 between the outer pipe 2 and the inner pipe 3 and heating the low-temperature, low-pressure gas refrigerant in the second flow path 5 within the inner pipe 3. In particular, the inner pipe 3 has a larger heat transfer area in the central portion having the corrugated portions 10 than a pipe without the corrugated portions 10, resulting in good heat exchange efficiency.

[0030] According to the double-pipe heat exchanger 1 of the above embodiment, as shown in Fig. 2, the inner surface of the outer pipe 2 is in contact with the crests 10b of the corrugated portions 10 of the inner pipe 3 at multiple points, and the inner pipe 3 is supported by the outer pipe 2, so there is no risk of the inner pipe 3 being deformed or cracked when the double pipe is bent, as shown in Fig. 3. Furthermore, the diameter of the outer pipe 2 is reduced, and the cross-sectional area of ​​the flow path for high-pressure liquid refrigerant between the outer pipe 2 and the inner pipe 3 is reduced, so the amount of refrigerant injected into the refrigeration cycle in which the double-pipe heat exchanger 1 is installed can be reduced.

[0031] Next, an embodiment of a method for manufacturing the double-pipe heat exchanger 1, in particular, a method for bringing the outer pipe 2 into contact with the inner pipe 3, will be described.

[0032] First Embodiment 4 shows the multiple movable pieces 21 of the first embodiment that bring the outer tube 2 into contact with the inner tube 3. Eight of the multiple movable pieces 21 are arranged at equal intervals around the outer tube 2. Each movable piece 21 has a sector-shaped cross section in the radial direction, and the inner surface on the radially inner side is a curved surface with a radius slightly smaller than the outer peripheral surface of the outer tube 2, and has a predetermined length in the axial direction. Each movable piece 21 is movable in the radial direction of the outer tube 2 and can simultaneously press against the outer tube 2.

[0033] The inner pipe 3 is inserted inside the outer pipe 2, with both ends of the inner pipe 3 protruding from both ends of the outer pipe 2. A plurality of movable pieces 21 are positioned at one end of a predetermined range L for reducing the diameter of the outer pipe 2. Preferably, the movable pieces 21 face the crests 10b of the corrugated portion 10 of the inner pipe 3. When the movable pieces 21 are moved radially inward to press the outer pipe 2, as shown in FIG. 6 , the portions of the outer pipe 2 pressed by the movable pieces 21 move radially inward toward the inner pipe 3 and undergo plastic deformation while in contact with the crests 10b of the corrugated portion 10 of the inner pipe 3, forming recesses 6a on the outer surface of the outer pipe 2. A plurality of these recesses 6a are formed in the circumferential direction to form the reduced diameter portion 6.

[0034] As shown in FIG. 5(a), the first recesses 6a are formed by the multiple movable pieces 21, and then, as shown in FIG. 5(b), the multiple movable pieces 21 are moved in the axial direction of the outer tube 2 to form the second recesses 6a, and this process is repeated multiple times. The axial length s of the recesses 6a formed first by the multiple movable pieces 21 and the axial length s of the recesses 6a formed next are made to overlap by a predetermined dimension ΔL. By repeating the formation of the recesses 6a with length s multiple times, the recesses 6a are formed within a predetermined range L, as shown in FIG. 5(c). Note that the recesses 6a with length s may be spaced apart in the axial direction so as not to overlap, or may be offset in the circumferential direction.

[0035] 7, multiple pressing by the multiple movable pieces 21 forms multiple recesses 6a extending in the axial direction on the outer surface of the outer tube 2, and multiple points P on the inner surface of the outer tube 2 come into linear contact with the peaks 10b of the wave-shaped portion 10 of the inner tube 3. Between the recesses 6a adjacent in the circumferential direction, which are not pressed by the multiple movable pieces 21, protrusions 13 extending in the axial direction are formed.

[0036] 1, both ends of the outer pipe 2 are radially fastened to the outer periphery of the inner pipe 3 in the range where the corrugated portions 10 are not formed at both ends, and then fixed by brazing or welding. Next, an outer pipe inlet 8 is attached to one end of the outer pipe 2, and an outer pipe outlet 9 is attached to the other end.

[0037] According to the manufacturing method of the double-pipe heat exchanger 1 of the first embodiment, the outer pipe 2 can be easily reduced in diameter simply by pressing the outer pipe 2 radially inward with the plurality of movable pieces 21 that are movable in the radial direction.

[0038] Second Embodiment In the second embodiment and the following embodiments, the process of inserting and positioning the outer tube 2 into the inner tube 3 and the process of fixing the outer tube 2 to the inner tube 3 are the same as those in the first embodiment, so the explanation will be omitted and only the process of bringing the outer tube 2 into contact with the inner tube 3 will be explained.

[0039] FIG. 8 shows a second embodiment of rollers 22 for bringing the outer tube 2 into contact with the inner tube 3. Four rollers 22 are arranged at equal intervals around the outer tube 2. Each roller 22 has a rotation axis 22a that is perpendicular to the central axis of the outer tube 2 and perpendicular to a line passing through the center of the outer tube 2, and is rotatable around this rotation axis 22a. The rollers 22 have a small diameter in the center and a gradually increasing diameter toward both ends, forming a so-called hourglass-shaped outer surface. The cross section of the roller 22, including its axis, is slightly smaller than the radius of curvature of the outer tube 2 and has a length approximately one-quarter of the outer circumference of the outer tube 2. Each roller 22 is movable radially around the outer tube 2 and can simultaneously press the outer tube 2. Preferably, the rollers 22 face the crests 10b of the corrugated portions 10 of the inner tube 3.

[0040] As shown in FIG. 9( a), rollers 22 are positioned at one end of a predetermined range L for reducing the diameter of the outer tube 2, and the multiple rollers 22 are moved radially inward to press the outer tube 2. As a result, the outer tube 2 is plastically deformed radially inward toward the crests 10 b of the corrugated portion 10 of the inner tube 3, and multiple locations P on the inner surface of the outer tube 2 come into contact with the crests 10 b of the inner tube 3, as shown in FIG. 10. As shown in FIG. 9( b), when the outer tube 2 is slid in the axial direction while the rollers 22 are pressed against the inner tube 3, the rollers 22 form recesses 6 b extending in the axial direction on the outer surface of the outer tube 2, and multiple locations on the inner surface of the tube 2 come into linear contact with the crests 10 b of the corrugated portion 10 of the inner tube 3, as shown in FIG. 11. Axial protrusions 14 are formed between circumferentially adjacent recesses 6 b because they are not pressed by the multiple rollers 22.

[0041] According to the manufacturing method of the double-pipe heat exchanger 1 of the second embodiment, the outer pipe 2 can be easily reduced in diameter simply by pressing the outer pipe 2 radially inward with a plurality of rollers 22 that can move radially and moving the outer pipe 2 axially.

[0042] <Third embodiment> FIG. 12 shows a third embodiment of rollers 23 for bringing the outer tube 2 into contact with the inner tube 3. Four rollers 23 are arranged at equal intervals around the outer tube 2. Each roller 23 has a rotation axis 23a that is on a plane perpendicular to the central axis of the outer tube 2 and perpendicular to a line passing through the center of the outer tube 2, and is rotatable around this rotation axis 23a. The rollers 23 are narrower than the rollers 22 of the second embodiment and have an arcuate or flat outer peripheral surface. Each roller 23 is movable in the radial direction of the outer tube 2 and can simultaneously press the outer tube 2. Preferably, the rollers 23 face the peaks 10b of the corrugated portion 10 of the inner tube 3.

[0043] As shown in Fig. 13(a), when multiple rollers 23 are positioned at one end of a predetermined range L in which the outer pipe 2 is reduced in diameter, and the multiple rollers 23 are moved radially inward to press the outer pipe 2, the outer pipe 2 is plastically deformed radially inward toward the crests 10b of the corrugated portions 10 of the inner pipe 3, and multiple points P on the inner surface of the outer pipe 2 come into contact with the crests 10b of the corrugated portions 10 of the inner pipe 3, as shown in Fig. 14. As shown in Fig. 13(b), when the outer pipe 2 is slid in the axial direction while the rollers 23 are pressed against the inner pipe 3, the rollers 23 form grooves 6c extending in the axial direction on the outer surface of the outer pipe 2, and multiple points on the inner surface of the outer pipe 2 come into linear contact with the crests 10b of the corrugated portions 10 of the inner pipe 3, as shown in Fig. 15.

[0044] According to the manufacturing method of the double-pipe heat exchanger 1 of the third embodiment, the diameter of the outer pipe 2 can be easily reduced by simply pressing the outer pipe 2 radially inward with a plurality of radially movable rollers 23 and moving the outer pipe 2 in the axial direction. In addition, since a plurality of points on the inner surface of the outer pipe 2 are brought into contact with the crests 10b of the corrugated portions 10 of the inner pipe 3, the first flow path 4 between the outer pipe 2 and the inner pipe 3 does not become narrow.

[0045] In the third embodiment, as shown in Figure 12, rollers 23 are arranged circumferentially so as to face the crests 10b of the corrugated portion 10, and the multiple rollers 23 press the outer tube 2 radially inward, plastically deforming the outer tube 2 and bringing multiple points on the inner surface of the outer tube 2 into contact with the crests 10b of the corrugated portion 10 of the inner tube 3. However, as shown in Figure 16, rollers 23 may be arranged circumferentially so as to face the bottom 10a of the corrugated portion 10, and the multiple rollers 23 may press the outer tube 2 radially inward, plastically deforming the outer tube 2, and as shown in Figure 17, multiple points P on the inner surface of the outer tube 2 on both sides of the rollers 23 may come into contact with the crests 10b of the corrugated portion 10 of the inner tube 3.

[0046] <Fourth embodiment> FIG. 18 shows a fourth embodiment of rollers 24 that bring the outer tube 2 into contact with the inner tube 3. Four rollers 24 are arranged at equal intervals around the outer tube 2. Each roller 24 has a rotation axis 24a parallel to the central axis of the outer tube 2 and is rotatable around this rotation axis 24a. The rollers 24 are narrower than the rollers 22 of the second embodiment and have an arcuate or flat outer peripheral surface. Each roller 24 is movable in the radial direction of the outer tube 2, allowing them to simultaneously press against the outer tube 2, and is also capable of rotating around the outer tube 2. In FIG. 18, the number of rollers 24 is not limited to four and can be any number, but three is preferable.

[0047] As shown in Figure 19(a), when the roller 24 is rotated around the outer tube 2 while being pressed against the outer tube 2 and the outer tube 2 is slid in the axial direction, the roller 24 forms a spiral groove 6d extending in the axial direction on the outer surface of the outer tube 2, as shown in Figures 19(b) and 21, and multiple points P on the inner surface of the outer tube 2 come into contact with the top 10b of the inner tube 3, as shown in Figure 20.

[0048] According to the manufacturing method of the double-pipe heat exchanger 1 of the fourth embodiment, the outer pipe 2 can be easily reduced in diameter simply by pressing the outer pipe 2 radially inward with a plurality of radially movable rollers 24 and rotating them around the outer pipe 2 while moving the outer pipe 2 in the axial direction.

[0049] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above embodiment, eight corrugated portions 10 are provided on the inner pipe 3, but the number is not limited to eight and any number may be provided. The height between the bottom 10a and the peak 10b of each corrugated portion 10 can also be changed as appropriate. Furthermore, the corrugated portion 10 may have a plurality of bottoms 10a and peaks 10b extending spirally in the axial direction, repeated in the circumferential direction. [Explanation of symbols]

[0050] 1…Double pipe heat exchanger 2…Outer tube 3…Inner tube 4...First flow path 5...Second flow path 6...Reduced diameter part 6a, 6b...recesses 6c, 6d...Concave groove 7...Inner 8…Outer pipe inlet 9…Outer pipe outlet 10...Wave shaped part 10a...bottom 10b…Top 11…Inner pipe inlet 12…Inner pipe outlet 13, 14...Convex part 21...Movable piece 22, 23, 24...Laura

Claims

1. A method for manufacturing a double-pipe heat exchanger having an outer pipe and an inner pipe inserted inside the outer pipe, A method for manufacturing a double-pipe heat exchanger, characterized in that a plurality of movable pieces arranged at equal intervals around the outer pipe are pressed radially inward against the outer pipe, and the outer pipe and the inner pipe are moved axially, and this is repeated multiple times to form axially extending recesses on the outer surface of the outer pipe, thereby reducing the diameter of the outer pipe relative to the inner pipe, which has a plurality of bottoms and tops formed on its outer surface, and bringing multiple points on the inner surface of the outer pipe into contact with the tops of the inner pipe.

2. A method for manufacturing a double-pipe heat exchanger having an outer pipe and an inner pipe inserted inside the outer pipe, A method for manufacturing a double-pipe heat exchanger, characterized in that: while pressing a plurality of rollers, each having a rotation axis on a plane perpendicular to the central axis of the outer tube, against the outer tube, the outer tube and the inner tube are moved axially, and the rollers form recesses extending in the axial direction on the outer surface of the outer tube, thereby reducing the diameter of the outer tube relative to the inner tube, which has a plurality of bottoms and tops formed on its outer surface, and bringing multiple points on the inner surface of the outer tube into contact with the tops of the inner tube.

3. A method for manufacturing a double-pipe heat exchanger having an outer pipe and an inner pipe inserted inside the outer pipe, A method for manufacturing a double-pipe heat exchanger, characterized in that a plurality of rollers having rotation axes on a plane perpendicular to the central axis of the outer tube are pressed against the outer tube, and the outer tube and the inner tube are moved axially, so that the rollers form axially extending grooves on the outer surface of the outer tube, thereby reducing the diameter of the outer tube relative to the inner tube, which has a plurality of bottoms and tops formed on its outer surface, and bringing multiple points on the inner surface of the outer tube into contact with the tops of the inner tube.

4. A method for manufacturing a double-pipe heat exchanger having an outer pipe and an inner pipe inserted inside the outer pipe, A method for manufacturing a double-pipe heat exchanger, comprising the steps of: pressing a plurality of rollers, each having a rotation axis parallel to the central axis of the outer tube, against the outer tube; rotating the rollers around the outer tube while moving the outer tube and the inner tube axially; forming a spiral groove extending in the axial direction on the outer surface of the outer tube with the rollers; thereby reducing the diameter of the outer tube relative to the inner tube, which has a plurality of bottoms and tops formed on its outer surface, and bringing multiple points on the inner surface of the outer tube into contact with the tops of the inner tube.

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