Piping structure of heat exchanger and manufacturing method therefor

Abstract

Provided are a piping structure of a heat exchanger and a manufacturing method therefor which make it possible to eliminate complexity of a manufacturing process and to inhibit thermal deterioration of members in the manufacturing process. Portions between manifolds 4A, 4B and an outer pipe 3, which are externally inserted onto an inner pipe 2, are sealed by annular seal materials S1. Portions between the manifolds 4A, 4B and the inner pipe 2 are sealed by annular seal materials S2. Longitudinal end parts of the outer pipe 3 are shut by the manifolds 4A, 4B, and bead parts 2a, 2b which protrude to the outer circumferential side is formed on the outer circumferential surface of the inner pipe 2 at longitudinally spaced-apart two portions. One manifold 4A is held between one bead part 2a and one longitudinal end of the outer pipe 3, and is located to be regulated from moving in the longitudinal direction, and the other manifold 4B is held between the other bead part 2b and the other longitudinal end of the outer pipe 3, and is located to be regulated from moving in the longitudinal direction. Pipes 5a, 5b are connected to the manifolds 4A, 4B by brazing.

Description

Heat exchanger piping structure and manufacturing method thereof

[0001] The present invention relates to a piping structure of a heat exchanger and a manufacturing method thereof, and more particularly to a piping structure of a heat exchanger that can eliminate the complexity of the manufacturing process and suppress thermal deterioration of components during this manufacturing process, and a manufacturing method thereof.

[0002] Various piping structures for heat exchangers have been proposed (see, for example, Patent Document 1). Patent Document 1 describes a double-pipe structure in which a condenser 320 is disposed around an aluminum alloy pipe 205 between an evaporator 204 and a compressor 201 (see paragraph 0035, FIGS. 1 to 8, etc. of Patent Document 1). In the piping structure described in Patent Document 1, end caps 322 and 323 that close both ends of a main body 321 of the condenser 320 are connected to the pipe 205 by brazing. Furthermore, a refrigerant pipe 330 is connected to the end cap 323 by brazing.

[0003] Brazing has traditionally been used to improve sealing, but the brazing process requires a significant amount of time. Furthermore, the components heated during the brazing process are at risk of thermal degradation. Therefore, there is room for improvement in the manufacture of heat exchanger piping structures, both in reducing the number of brazed parts to eliminate the complexity of the manufacturing process and in suppressing thermal degradation of components during the manufacturing process.

[0004] Japanese Patent Application Publication No. 2021-148374

[0005] An object of the present invention is to provide a piping structure for a heat exchanger that can eliminate the complexity of the manufacturing process and can suppress thermal deterioration of components during the manufacturing process, and a manufacturing method thereof.

[0006] In order to achieve the above object, the piping structure of a heat exchanger of the present invention comprises an inner pipe and an outer pipe that form a double pipe structure, a cylindrical manifold that is inserted onto the inner pipe and installed at both longitudinal ends of the outer pipe, and pipe bodies brazed to each of the manifolds, wherein the longitudinal ends of the outer pipe are sealed by each of the manifolds, flow paths of each of the pipe bodies communicate with the internal space of the brazed manifold, and flow paths between the outer peripheral surface of the inner pipe and the inner peripheral surface of the outer pipe communicate with an outer peripheral region of the inner pipe in the internal space of each of the manifolds. The piping structure of a heat exchanger has an outer pipe annular sealing material interposed between each of the manifolds and the outer pipe, an inner pipe annular sealing material interposed between each of the manifolds and the inner pipe, and bead portions protruding outward from the outer surface of the inner pipe at intervals in the longitudinal direction of the inner pipe, wherein one of the manifolds is sandwiched between one of the bead portions and one longitudinal end of the outer pipe, thereby restricting its longitudinal movement, and the other manifold is sandwiched between the other bead portion and the other longitudinal end of the outer pipe, thereby restricting its longitudinal movement.

[0007] The method for manufacturing a piping structure of a heat exchanger of the present invention is a method for manufacturing a piping structure of a heat exchanger having a double pipe structure consisting of an inner pipe and an outer pipe, a cylindrical manifold inserted onto the inner pipe and installed at both longitudinal ends of the outer pipe, and a pipe body brazed to each of the manifolds, the method comprising the steps of: forming one bead portion protruding outward on an outer circumferential surface of the inner pipe; inserting one of the manifolds onto the inner pipe and abutting the one bead portion; and forming an annular inner pipe joint between the one of the manifolds and the inner pipe at a position where the one of the manifolds is inserted onto the inner pipe and abuts the one of the bead portions. The outer pipe is fitted onto the inner pipe, and at a position where one of the manifolds is sandwiched between the one bead portion and one longitudinal end of the outer pipe, the gap between one of the manifolds and the outer pipe is sealed with an annular sealing material for the outer pipe, the one longitudinal end of the outer pipe is sealed with one of the manifolds, and the other manifold is fitted onto the inner pipe, and at a position where the outer pipe is sandwiched between the respective manifolds, the gap between the other manifold and the inner pipe is sealed with another annular sealing material for the inner pipe. and a second bead portion is formed on the outer circumferential surface of the inner pipe at a position spaced apart in the longitudinal direction from the first bead portion, the second bead portion protruding outward from the outer circumferential surface of the inner pipe, the first manifold being sandwiched between the first bead portion and one longitudinal end of the outer pipe to restrict movement in the longitudinal direction, and the second manifold being mounted between the second bead portion and the outer circumferential end of the outer pipe. The manifold is characterized in that the manifold is clamped between the other longitudinal end of the pipe to restrict longitudinal movement, and is installed to connect a flow path between the outer peripheral surface of the inner pipe and the inner peripheral surface of the outer pipe to the outer peripheral region of the inner pipe in the internal space of one of the manifolds and the other of the manifolds, connect a flow path of one of the pipe bodies brazed to one of the manifolds to the internal space of one of the manifolds, and connect a flow path of the other pipe body brazed to the other of the manifolds to the internal space of the other of the manifolds.

[0008] According to the present invention, the two bead portions formed at intervals along the longitudinal direction of the inner pipe are used to install each of the manifolds together with the outer pipe while restricting longitudinal movement, and the manifolds and the inner pipe are sealed by the inner pipe annular seal material, and the manifolds and the outer pipe are sealed by the outer pipe annular seal material. Because brazing is required only for connecting each of the manifolds to each of the pipe bodies, the complexity of the manufacturing process for this piping structure is eliminated. This is advantageous for suppressing thermal degradation of the inner pipe and the outer pipe during the manufacturing process.

[0009] FIG. 1 is an explanatory diagram illustrating an embodiment of a piping structure for a heat exchanger, as seen from the front. FIG. 2 is an explanatory diagram illustrating the piping structure of FIG. 1, as seen from the longitudinal cross section. FIG. 3 is a cross-sectional view taken along the line A-A in FIG. 2. FIG. 4 is an enlarged view of a portion of FIG. 2. FIG. 5 is an explanatory diagram illustrating an inner pipe, as seen from the front, before the piping structure of FIG. 1 is manufactured, with the lower half cross-sectionally arranged. FIG. 6 is an explanatory diagram illustrating a state in which one bead portion has been formed on the inner pipe of FIG. 5. FIG. 7 is an explanatory diagram illustrating a step of inserting one manifold onto the inner pipe of FIG. 6. FIG. 8 is an explanatory diagram illustrating a step of inserting an outer pipe onto the inner pipe of FIG. 7. FIG. 9 is an explanatory diagram illustrating a step of inserting the other manifold onto the inner pipe of FIG. 8. FIG. 10 is an explanatory diagram illustrating a state in which the other manifold of FIG. 9 is abutted against the other longitudinal end of the outer pipe. FIG. 11 is an explanatory diagram illustrating a portion of another embodiment of a piping structure, as seen from the longitudinal cross section.

[0010] Hereinafter, a piping structure of a heat exchanger and a manufacturing method thereof according to the present invention will be described based on an embodiment shown in the drawings.

[0011] The embodiment of the piping structure of the heat exchanger 1 illustrated in Figures 1 to 4 includes an inner pipe 2 and an outer pipe 3 constituting a double-pipe structure, two cylindrical manifolds 4A and 4B, and two pipes 5a and 5b. This piping structure also includes an annular seal S1 for the outer pipe, an annular seal S2 for the inner pipe, and bead portions 2a and 2b protruding outward from the outer surface of the inner pipe 2 at intervals along its length. One manifold 4A, the outer pipe 3, and the other manifold 4B are arranged in this order between the bead portions 2a and 2b. While Figure 4 shows the area around the other manifold 4B, the area around the one manifold 4A has a similar structure. The dashed-dotted line CL in the figure indicates the cylindrical axes of the inner pipe 2, the outer pipe 3, and the manifolds 4A and 4B.

[0012] The inner tube 2, manifolds 4A and 4B, and tube bodies 5a and 5b are each made of metal or a known material, while the outer tube 3 is made of metal or a polymer material such as resin or a known material. Although the outer tube 3 may be made of stainless steel, the inner tube 2, outer tube 3, manifolds 4A and 4B, and tube bodies 5a and 5b are preferably made of, for example, aluminum or an aluminum alloy, and these components are preferably made of the same material.

[0013] The sizes of the inner pipe 2, the outer pipe 3, and the pipe bodies 5a, 5b vary depending on the performance required of the heat exchanger 1, but the outer diameter of the inner pipe 2 is, for example, about 4 mm to 500 mm, the outer diameter of the outer pipe 3 is, for example, about 8 mm to 500 mm, and the outer diameter of the pipe bodies 5a, 5b is, for example, about 4 mm to 500 mm. The sizes of the manifolds 4A, 4B are appropriately set based on the sizes of the inner pipe 2 and the outer pipe 3, etc.

[0014] In this embodiment, the bead portions 2a, 2b extend annularly in the circumferential direction on the outer peripheral surface of the inner pipe 2. The bead portions 2a, 2b are formed by processing the inner pipe 2. As will be described later, the protruding height of the bead portions 2a, 2b toward the outer periphery may be any height that is capable of restricting the movement of the respective manifolds 4A, 4B in the longitudinal direction of the inner pipe 2. The protruding height of the bead portions 2a, 2b varies depending on the outer diameter of the inner pipe 2, etc., but is, for example, 2 mm or more. The bead portions 2a, 2b are not limited to the specifications exemplified in this embodiment, and may be any height that is capable of restricting the movement of the respective manifolds 4A, 4B in the longitudinal direction of the inner pipe 2.

[0015] Each of the manifolds 4A, 4B is fitted onto the inner tube 2 and installed at both longitudinal ends of the outer tube 3. Each of the manifolds 4A, 4B has through holes 4c, 4d at one end and the other end in the cylindrical axis direction, respectively, and the space between the through holes 4c and 4d in the cylindrical axis direction forms an internal space P3. In this embodiment, each of the manifolds 4A, 4B has a cylindrical flange portion 4f with a reduced diameter at one end in the cylindrical axis direction, and the inner peripheral surface of this flange portion 4f forms the through hole 4c.

[0016] The inner pipe 2 passes through the through holes 4c, 4d of one manifold 4A and the through holes 4c, 4d of the other manifold 4B. The flange portion 4f of one manifold 4A is inserted into one longitudinal end of the outer pipe 3, and the flange portion 4f of the other manifold 4B is inserted into the other longitudinal end of the outer pipe 3. Both longitudinal ends of the outer pipe 3 are sealed by the manifolds 4A, 4B. It is preferable to make the gap between the inner circumferential surface of the outer pipe 3 and the outer circumferential surface of each flange portion 4f as small as possible, for example, 1 mm or less. It is also preferable to make the gap between the outer circumferential surface of the inner pipe 2 and the inner circumferential surface of each through hole 4d as small as possible, for example, 1 mm or less.

[0017] More specifically, seal materials S1, S1 are interposed between each manifold 4A, 4B and the outer pipe 3, and seal materials S2, S2 are interposed between each manifold 4A, 4B and the inner pipe 2. In this embodiment, seal materials S1, S1 are disposed between the outer peripheral surface of each flange portion 4f, 4f and the inner peripheral surface of the outer pipe 3 to seal the gaps between them. Furthermore, seal materials S2, S2 are disposed between the outer peripheral surface of the inner pipe 2 and the inner peripheral surface of each through hole 4d, 4d to seal the gaps between them. Each seal material S2, S2 is disposed in a position where it does not come into contact with the adjacent bead portions 2a, 2b.

[0018] One longitudinal end face of the outer pipe 3 abuts against an end face of one manifold 4A that is closer to the outer periphery than the flange portion 4f. Similarly, the other longitudinal end face of the outer pipe 3 abuts against an end face of the other manifold 4B that is closer to the outer periphery than the flange portion 4f. One manifold 4A is engaged with one bead portion 2a, with its end face abutting against the bead portion 2a. Similarly, the other manifold 4B is engaged with the other bead portion 2b, with its end face abutting against the bead portion 2b. As a result, both longitudinal ends of the outer pipe 3 are airtightly sealed by the manifolds 4A, 4B.

[0019] The seals S1 and S2 may be made of various known seals that seal gaps airtightly, such as O-rings made of various known elastic materials such as silicone rubber, various gaskets, various packings, and various adhesives.

[0020] In this piping structure, one manifold 4A is sandwiched between one bead portion 2a and one longitudinal end of the outer pipe 3, and is installed so that its longitudinal movement is restricted. The other manifold 4B is sandwiched between the other bead portion 2b and the other longitudinal end of the outer pipe 3, and is installed so that its longitudinal movement is restricted. Therefore, one manifold 4A, the outer pipe 3, and the other manifold 4B are installed between the bead portions 2a and 2b, and are substantially fixed in place with respect to the longitudinal direction of the inner pipe 2.

[0021] One pipe 5a is brazed to the outer circumferential surface of one manifold 4A, and the other pipe 5b is brazed to the outer circumferential surface of the other manifold 4b. These manifolds 4A, 4B and the pipes 5a, 5b are brazed together using a known brazing material that is suitable for the materials of these manifolds.

[0022] The flow path P2 of one tube 5a is in communication with the internal space P3 of one manifold 4A brazed to this tube 5a. The flow path P2 of the other tube 5b is in communication with the internal space P3 of the other manifold 4B brazed to this tube 5b. The flow path P1 between the outer peripheral surface of the inner tube 2 and the inner peripheral surface of the outer tube 3 is in communication with the outer peripheral region of the inner tube 2 in the internal spaces P3, P3 of each manifold 4A, 4B. Therefore, the flow path P2 of one tube 5a is in communication with the outer peripheral region of the inner tube 2 in the internal space P3 of one manifold 4A, the flow path P1 between the outer peripheral surface of the inner tube 2 and the inner peripheral surface of the outer tube 3, the outer peripheral region of the inner tube 2 in the internal space P3 of the other manifold 4B, and the flow path P2 of the other tube 5b.

[0023] As shown in FIG. 2 , the high-temperature fluid HF flows from the flow path P2 of one pipe body 5a through the outer peripheral region of the inner pipe 2 in the internal space P3 of one manifold 4A, the flow path P1 between the outer peripheral surface of the inner pipe 2 and the inner peripheral surface of the outer pipe 3, the outer peripheral region of the inner pipe 2 in the internal space P3 of the other manifold 4B, and then into the flow path P2 of the other pipe body 5b. The low-temperature fluid LF flows through the flow path of the inner pipe 2. Between the inner pipe 2 and the outer pipe 3 of the double-pipe structure, the thermal energy of the high-temperature fluid HF is transferred to the low-temperature fluid LF, so that the temperature of the high-temperature fluid HF decreases and the temperature of the low-temperature fluid LF increases. In this way, heat exchange between the high-temperature fluid HF and the low-temperature fluid LF occurs in the heat exchanger 1. This heat exchanger 1 is applicable to, for example, air conditioners installed in vehicles such as automobiles, and air conditioners installed in homes, factories, and various facilities.

[0024] An example of a procedure for manufacturing the piping structure of the heat exchanger 1 will now be described.

[0025] As shown in Fig. 5, an inner pipe 2 of a predetermined length is prepared. Next, as shown in Fig. 6, one bead portion 2a that protrudes outward is formed at one location on the outer circumferential surface of the inner pipe 2. The bead portion 2a may be formed by a known method. For example, the inner pipe 2 is subjected to bead processing (stringing processing) to cause a portion of the inner pipe 2 to protrude outward, thereby forming the bead portion 2a.

[0026] Next, as shown in Fig. 7, one manifold 4A is fitted onto the inner pipe 2. Seal materials S1 and S2 are attached to this manifold 4A in advance. One pipe body 5a is brazed to the outer circumferential surface of the manifold 4A. The end face of the manifold 4A facing one bead portion 2a is then abutted against the bead portion 2a. As a result, the gap between the manifold 4A and the inner pipe 2 is sealed by the seal material S2, as shown in Fig. 8.

[0027] Next, as shown in Fig. 8, the outer pipe 3 is fitted onto the inner pipe 2, and the longitudinal end face of the outer pipe 3 facing the manifold 4A is abutted against the end face of the manifold 4A. As a result, as shown in Fig. 9, the gap between the manifold 4A and the outer pipe 3 is sealed with the seal material S1 at a position where the manifold 4A is sandwiched between one bead portion 2a and one longitudinal end of the outer pipe 3. As a result, one longitudinal end of the outer pipe 3 is sealed by the manifold 4A.

[0028] Next, as shown in Fig. 9, the other manifold 4B is fitted onto the inner pipe 2. Seal materials S1 and S2 are attached to this manifold 4B in advance. The other pipe body 5b is brazed to the outer peripheral surface of the manifold 4B. The end face of the manifold 4B facing the outer pipe 3 is then abutted against the outer pipe 3. As a result, as shown in Fig. 10, at the position where the outer pipe 3 is sandwiched between the manifolds 4A and 4B, the gap between the manifold 4B and the inner pipe 2 is sealed with the seal material S2, and the gap between the manifold 4B and the outer pipe 3 is sealed with the seal material S1. As a result, the other longitudinal end of the outer pipe 3 is sealed by the manifold 4B.

[0029] Next, the other bead portion 2b that protrudes outward is formed on the outer circumferential surface of the inner pipe 2 so as to be adjacent to the manifold 4B, thereby manufacturing the piping structure illustrated in Fig. 2. The method for forming the other bead portion 2b is the same as that for the one bead portion 2a.

[0030] According to the piping structure of the heat exchanger 1 described above, the two bead portions 2a, 2b formed at intervals along the longitudinal direction of the inner pipe 2 allow the installation of the manifolds 4A, 4B together with the outer pipe 3 while restricting their longitudinal movement. Additionally, the manifolds 4A, 4B are sealed between the inner pipe 2 and the manifolds 4A, 4B by the respective seal materials S2, S2, and the manifolds 4A, 4B are sealed between the outer pipe 3 and the manifolds 4A, 4B by the respective seal materials S1, S1. Brazing is required only for connecting the manifolds 4A, 4B to the corresponding pipe bodies 5a, 5b. Brazing and connecting the manifolds while ensuring airtightness requires a considerable amount of time and high skill. Therefore, this embodiment, which requires only two brazing locations, significantly contributes to eliminating the complexity of the manufacturing process of this piping structure. Accordingly, the inner pipe 2 and the outer pipe 3 are not heated by the brazing process during this manufacturing process, which is advantageous for suppressing thermal degradation of the inner pipe 2 and the outer pipe 3.

[0031] In this embodiment, one manifold 4A is brazed to one of the tubes 5a before being fitted onto the inner tube 2. Also, the other manifold 4B is brazed to the other tube 5b before being fitted onto the inner tube 2. As in this embodiment, brazing the manifolds 4A, 4B to the corresponding tubes 5a, 5b before assembling the inner tube 2, outer tube 3, and manifolds 4A, 4B further simplifies the assembly process.

[0032] It is also possible to install one manifold 4A by clamping it between one bead portion 2a and one longitudinal end of the outer pipe 3 to restrict its longitudinal movement, and install the other manifold 4B by clamping it between the other bead portion 2b and the other longitudinal end of the outer pipe 3 to restrict its longitudinal movement, and then braze each manifold 4A, 4B to the corresponding pipe bodies 5a, 5b. By using this procedure, it is possible to prevent the pipe bodies 5a, 5b from getting in the way during the assembly process of the inner pipe 2, outer pipe 3, and manifolds 4A, 4B.

[0033] The embodiment illustrated in FIG. 11 differs from the previous embodiment only in the arrangement of the sealant S2. In this embodiment, sealants S2 are arranged between the outer circumferential surface of the inner pipe 2 and the inner circumferential surfaces of the through holes 4d of each manifold 4A, 4B, sealing the gaps between them. Each sealant S2 is arranged in a position where it contacts the adjacent bead portion 2a, 2b. That is, the other sealant S2 is arranged so as to be exposed on the end surface of the manifold 4B facing the bead portion 2b. Similarly, one sealant S2 is arranged so as to be exposed on the end surface of the manifold 4A facing the bead portion 2a. In this embodiment, the sealant S2 simultaneously seals the gaps between the manifolds 4A, 4B and the outer circumferential surface of the inner pipe 2 and the gaps between the manifolds 4A, 4B and the opposing bead portions 2a, 2b.

[0034] REFERENCE SIGNS LIST 1 heat exchanger 2 inner pipe 2a, 2b bead portion 3 outer pipe 4A, 4B manifold 4c, 4d through hole 4f flange portion 5a, 5b pipe body S1 annular seal material for outer pipe S2 annular seal material for inner pipe P1, P2 flow path P3 internal space LF low temperature fluid HF high temperature fluid

Claims

1. A piping structure for a heat exchanger comprising an inner pipe and an outer pipe forming a double pipe structure, a cylindrical manifold fitted onto the inner pipe and installed at both longitudinal ends of the outer pipe, and pipe bodies brazed to each of the manifolds, wherein the longitudinal ends of the outer pipe are sealed by each of the manifolds, flow paths of each of the pipe bodies communicate with the internal space of the brazed manifolds, and flow paths between the outer circumferential surface of the inner pipe and the inner circumferential surface of the outer pipe communicate with an outer peripheral region of the inner pipe in the internal space of each of the manifolds, A piping structure for a heat exchanger having annular sealing material for an outer pipe interposed between each of the manifolds and the outer pipe, annular sealing material for an inner pipe interposed between each of the manifolds and the inner pipe, and bead portions protruding outward from the outer surface of the inner pipe at intervals in the longitudinal direction of the inner pipe, wherein one of the manifolds is sandwiched between one of the bead portions and one longitudinal end of the outer pipe, thereby restricting its longitudinal movement, and the other manifold is sandwiched between the other bead portion and the other longitudinal end of the outer pipe, thereby restricting its longitudinal movement.

2. A piping structure for a heat exchanger as described in claim 1, wherein each of the manifolds has a cylindrical flange portion that is inserted into the outer pipe, and an annular sealing material for the outer pipe is disposed between the outer peripheral surface of each of the flange portions and the inner peripheral surface of the outer pipe.

3. A piping structure for a heat exchanger as described in claim 1 or 2, wherein each of the manifolds has a through hole through which the inner tube passes near the adjacent bead portion, and an annular sealing material for the inner tube is disposed between the inner surface of each of the through holes and the outer surface of the inner tube.

4. A piping structure for a heat exchanger according to claim 3, wherein each of said annular sealing materials for the inner pipe is disposed at a position where it does not come into contact with an adjacent one of said bead portions.

5. A method for manufacturing a piping structure of a heat exchanger having a double pipe structure consisting of an inner pipe and an outer pipe, a cylindrical manifold inserted onto the inner pipe and installed at both longitudinal ends of the outer pipe, and a pipe body brazed to each of the manifolds, comprising the steps of: forming one bead portion protruding outward on the outer circumferential surface of the inner pipe; inserting one of the manifolds onto the inner pipe and sealing the gap between the one of the manifolds and the inner pipe with an annular sealing material for the inner pipe at a position where the one of the manifolds is abutted against the one of the bead portions; inserting the outer pipe onto the inner pipe and sealing the gap between the one of the manifolds and the outer pipe with an annular sealing material for the outer pipe at a position where the one of the manifolds is sandwiched between the one of the bead portions and one longitudinal end of the outer pipe, and sealing one longitudinal end of the outer pipe with one of the manifolds; the other manifold is inserted onto the inner pipe at a position where the outer pipe is sandwiched between the two manifolds, the other manifold and the inner pipe are sealed with another annular sealing material for the inner pipe, and the other manifold and the outer pipe are sealed with another annular sealing material for the outer pipe, and the other longitudinal end of the outer pipe is sealed with the other manifold; the other bead portion protruding outward is formed on the outer circumferential surface of the inner pipe at a position spaced in the longitudinal direction from the one bead portion of the inner pipe, and one of the manifolds is sandwiched between the one bead portion and one longitudinal end of the outer pipe to restrict its longitudinal movement, and the other manifold is sandwiched between the other bead portion and the other longitudinal end of the outer pipe to restrict its longitudinal movement, A manufacturing method for a piping structure of a heat exchanger, which connects a flow path between the outer peripheral surface of the inner tube and the inner peripheral surface of the outer tube with an outer peripheral region of the inner tube in the internal space of one of the manifolds and the other of the manifolds, connects a flow path of one of the tube bodies brazed to one of the manifolds with the internal space of one of the manifolds, and connects a flow path of the other of the tube bodies brazed to the other manifold with the internal space of the other manifold.

6. A method for manufacturing a piping structure of a heat exchanger as described in claim 5, wherein one of the manifolds is brazed to one of the pipe bodies before inserting one of the manifolds onto the inner pipe, and the other of the manifolds is brazed to the other of the pipe bodies before inserting the other of the manifolds onto the inner pipe.

7. A method for manufacturing a piping structure of a heat exchanger as described in claim 5, wherein one of the manifolds is clamped between one of the bead portions and one longitudinal end of the outer tube to restrict longitudinal movement and the other of the manifolds is clamped between the other of the bead portions and the other longitudinal end of the outer tube to restrict longitudinal movement, and then one of the manifolds is brazed to one of the tube bodies and the other of the manifolds is brazed to the other of the tube bodies.

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