Heat exchanger

Abstract: A heat exchanger (1) includes a header (2,3) having tube insertion holes (22) and heat transfer tubes (6), wherein each of said heat transfer tubes (6) has an end portion inserted into a corresponding tube insertion hole (19,20). A burr (21) is formed on a wall of the header (2,3) around each tube insertion hole (19,20) to extend in a direction toward an interior of the header (2,3). The burr (21) has a bent tip portion (21a,21b) formed by bending at least a part of a tip portion of the burr inwardly. A tip of the end portion (6a) of each heat transfer tube (6) inserted into a corresponding tube insertion hole (19,20) contacts with the bent tip portion (21a,21b) of the burr (21). The bent tip portion (21a,21b) of the burr seals a gap formed between an outer surface of the inserted end portion of the tube and an inner surface of the burr when the header and the tubes are assembled and brazed, thereby preventing leakage of a heat exchange fluid through such a gap. The insertion depth of the tube (6) is reduced by the bent tip portion (21a,21b) of the burr, thereby decreasing pressure loss in the header.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger, and more particularly to an improved connection structure between a header and a heat transfer tube in the heat exchanger. 2. Description of the Related Art In a conventional heat exchanger having a header and a heat transfer tube connected to the header, a burr for enlarging a connection area between the header and an end portion of the heat transfer tube inserted into the tube insertion hole may be formed on a wall of the header around a tube insertion hole defined on the wall. In such a connection structure, however, it is generally difficult to control the depth of tube insertion into the header. If the tube insertion depth is relatively large, a pressure loss in the header caused by the inserted portion of the tube increases. Further, in the above-described conventional connection structure, when the heat transfer tube is formed as a flat tube, problems may arise due to deformation of the tube. For example, as shown in Fig. 9, when the assembly including header 101 and heat transfer tube 102 is fixed using fixing jigs (not shown) for handling and brazing, heat transfer tube 102 formed as a flat tube may subsequently be deformed by force applied by the fixing jigs, and the end portion of transfer tube 102 inserted into tube insertion hole 103 may also be deformed by the force. As a result, a gap 104 may be created between an outer surface of the inserted end portion of transfer tube 102 and an inner surface of burr 105 formed around tube insertion hole 103. If a brazing material is not supplied in sufficient quantity into gap 104, fluid leaks may occur through the gap 104 during operation of the heat exchanger. In order to avoid this disadvantage, for example, Japanese Utility Model Laid-Open HEI 5-17385 discloses a structure as shown in Fig. 10. In Fig. 10, a burr 111 is formed around tube insertion hole 112 defined on header wall 113. Heat transfer tube 114 is inserted into tube insertion hole 112, so that its end portion 115 extends over burr 111 in header 116. After insertion, end portion 115 of tube 114 is expanded outwardly in order to prevent the creation of a gap between the outer surface of the tube 114 and the inner surface of burr 111. In such a structure, however, because end portion 115 of tube 114 is inserted into header 116 up to a position over burr 111 and the expanded end portion 115 is present at a position over burr 111 in header 116, the pressure loss in header 116 again increases. Further, when heat transfer tube 114 is constructed from an aluminum alloy clad with a corrosion resistant layer (for example, an Al-Zn alloy) on its inner surface for the purpose of avoiding corrosion, because the outer surface and the edge of the inserted end portion 115 of tube 114 protruding into the interior of header 116 are not clad with the corrosion resistant layer and are exposed directly to a fluid in header 116, tube 114 is likely to be corroded from such portions. In particular, when the fluid is water, such a corrosion of the non-protected portions of the tube are likely to occur. Further, generally, clad, corrosion resistant layer may- become delaminated due to a shearing force due to water or the impact of water at a portion of water inlet side of a heat transfer tube. Thus, corrosion, i.e., turbulence corrosion or inlet tube corrosion may be accelerated, and a fluid may be leaked. When a heat transfer tube protrudes in a tank as depicted in the structure of Japanese Utility Model Laid-Open HEI 5-17385, water turbulence is likely to occur near the water inlet of heat transfer tube 114, and turbulence corrosion or inlet tube corrosion also is likely to occur. From JP 61-108 435 A a heat exchanger is known comprising at least one header having at least one tube insertion hole and at least one heat transfer tube having an end portion inserted into the at least one tube insertion hole and at least one burr formed on a wall of the header around the at least one tube insertion hole to extend in a direction toward an interior of the header. From the US patent 2,164,629 a heat exchanger according to the preamble of claim 1 is known. The bent tip portion is formed in a U-shape and the at least one heat transfer tube is inserted into the U-shaped bent tip portion. A part from the bent tip portion extends into the at least one heat transfer tube. It is an object of the present invention to provide a heat exchanger having a connection structure between a tank and a heat transfer tube which may readily control an insertion depth of the heat transfer tube into an interior of the tank, thereby decreasing a pressure loss in the tank; in particular, a fluid leakage through a gap which may be formed between a deformed heat transfer tube and a burr provided around a tube insertion hole defined on a header wall should be prevented; turbulence corrosion or inlet tube corrosion at an edge of an outer surface of an inserted end portion of a heat transfer tube clad with a corrosion resistant layer should be reduced or eliminated. This object is solved by a heat exchanger having the features of claim 1. Preferred developments of the invention are given in the dependent claims. In such a heat exchanger, the tip of the end portion of the at least one heat transfer tube inserted into the at least one tube insertion hole engages the bent tip portion of the burr, and the insertion depth thereof may be readily controlled, for example, to a predetermined depth. Therefore, the pressure loss in the header caused by the inserted tube portion may be decreased as compared with a conventional structure having a relatively large insertion depth (for example, 3-5 mm) of a tube. Further, because the bent tip portion of the burr is formed by bending at least a part of the tip portion of the burr inwardly, even if a gap is formed between an outer surface of the inserted tube end portion and an inner surface of the burr by an external force applied from, for example, jigs used for assembling or brazing, the formed bent tip portion may seal the gap. Therefore, such a gap may be sealed by the bent tip portion, and a fluid leakage may be prevented. Moreover, because the tube insertion depth of the end portion of the heat transfer tube may be reduced to a small depth corresponding to about a height of the burr (for example, not more than 3 mm), the outer surface of the end portion of the tube is covered by the inner surface of the burr and at least a part of the edge (tip) of the tube is covered by the bent tip portion of the burr. Therefore, when a heat transfer tube is clad with a corrosion resistant material on its inner surface, an area of a portion of the tube in direct contact with a heat exchange fluid may be reduced in size or minimized. As a result, the corrosion resistant property of the heat transfer tube may be greatly improved. Further, because at least a part of the inlet edge of the inserted tube is covered and protected by the bent tip portion of the burr, turbulence corrosion or inlet tube corrosion at or near the edge may be reduced or eliminated. Further objects, and advantages of the present invention will be understood from the following detailed description of the embodiments of the present invention with reference to the appropriate figures. BRIEF DESCRIPTION OF THE DRAWINGS Some embodiments of the invention will now be described with reference to the appropriate figures, which are given by way of example only, and are not intended to limit the present invention. Fig. 1 is a perspective view of a heat exchanger according to a first embodiment of the present invention. Fig. 2 is a partially cut away perspective view of the heat exchanger depicted in Fig. 1. Fig. 3 is an expanded perspective view of the heat exchanger depicted in Fig. 1. Fig. 4 is an enlarged cross-sectional view of a header of the heat exchanger depicted in Fig. 1. Fig. 5 is an enlarged vertical sectional view of the header and an end portion of a heat transfer tube of the heat exchanger depicted in Fig. 4, as viewed along V-V line of Fig. 4. Fig. 6 is an elevational view of a tube-header connection portion of the heat exchanger depicted in Fig. 5, as viewed along VI-VI line of Fig. 5. Fig. 7 is a perspective view of a part of a header of the heat exchanger depicted in Fig. 5. Fig. 8 is an elevational view of a tube-header connection portion of a heat exchanger according to a second embodiment of the present invention. Fig. 9 is an elevational view of a tube-header connection portion of a conventional heat exchanger. Fig. 10 is a perspective view of a tube-header connection portion of another conventional heat exchanger. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to Figs. 1-3, a heat exchanger 1 is provided according to a first embodiment. Heat exchanger 1 includes a pair of headers 2 and 3. Each of headers 2 and 3 is constructed from tank member 14 or 17 and seat member 15 or 16 to form barrel 12 or 13. Each of inlet pipe 4 and outlet pipe 5 is connected to pipe insertion hole 19 or 20, respectively, defined on tank member 14 of header 2. A plurality of flat heat transfer tubes 6 (for example, refrigerant tubes) are fluidly interconnected between headers 2 and 3. In this embodiment, flat heat transfer tube 6 is formed as a flat tube. Corrugated fins 7 are disposed on both surfaces of each heat transfer tube 6. Side members 8 and 9 are provided on the upper surface of the uppermost fin 7 and on the lower surface of the lowermost fin 7, respectively. Each of headers 2 and 3 is sealed at both open ends by caps 10 and 11, respectively. The interior of header 2 is divided into two sections 12a and 12b by partition 18 provided in header 2. As depicted in Fig. 4, header 2 has a substantially rectangular cross-section and is formed as barrel 12 when tank member 14 and seat member 15 are joined to each other. In this embodiment, seat member 15 has curved portions 15a provided on both end portions thereof in the radial direction for forming grooves 15b open toward tank member 14. Tank member 14 has a U-shape cross section and has side walls 14a on both end portions in its radial direction. Each side wall 14a has free end portion 14b extending toward the tip of the side wall 14a. Each free end portion 14b is offset inwardly by an amount substantially equal to the thickness of bent portion 15c of seat member 15 measured at the tip portion of curved portion 15a. Free end portions 14b of tank member 14 are inserted into the respective grooves 15b of seat member 15. Seat member 15 and tank member 14 are brazed to each other to form barrel 12 having a substantially rectangular cross-section, as described above. Burr 21 is formed on wall 15d of seat member 15 at a position around tube insertion hole 22, so as to extend toward an interior of header 2. End portion 6a of heat transfer tube 6 is inserted into tube insertion hole 22 along burr 21. Although Fig. 4 shows the side of header 2, the side of header 3 may have substantially the same structure with respect to the tube connection structure. As depicted in Figs. 5-7, tube insertion hole 22 is formed as a slot having two lateral edges and two longitudinal edges, and burr 21 has a cross-section along the tube insertion hole 22. Burr 21 has a pair of first tip portions 21a and a pair of second tip portions 21b, wherein a first length of first tip portions 21a is greater than a second length of second tip portions 21b. Each of the pair of first tip portions 21a is bent inwardly to form a bent tip portion. The pair of bent tip portions 21a extend along the lateral edges of the slot of tube insertion hole 22. Each bent tip portion 21a extends inwardly by a length "α" equal to or less than thickness "t" of end portion 6a of heat transfer tube 6. A tip of end portion 6a of heat transfer tube 6 inserted into tube insertion hole 22 contacts with bent tip portions 21a of burr 21. In such a condition, heat transfer tube 6 is brazed to seat member 15 of header 2. Heat transfer tube 6 may also be connected to header 3 by the same connection structure. The respective members described above are constructed from aluminum or an aluminum alloy. After the members are assembled, the assembly may be temporarily fixed and placed in a furnace for heating and brazing. In such a heat exchanger 1, the tip of end portion 6a of heat transfer tube 6 inserted into tube insertion hole 22 contacts with bent tip portions 21a of burr 21, and the insertion depth of the end portion 6a may be readily controlled to a predetermined small depth (for example, not more than 2.5 mm). Therefore, the pressure loss in header 2 caused by the inserted tube portion may be decreased as compared with a conventional structure having a relatively large insertion depth (for example, 3-5 mm) of a tube. Further, because the bending length "α" of each bent tip portion 21a of burr 21 is equal to or less than thickness "t" of end portion 6a of heat transfer tube 6, the bent tip portion 21a does not protrude into the interior of heat transfer tube 6. Therefore, the pressure loss in heat transfer tube 6 does not increase due to bent tip portion 21a of burr 21. As mentioned above, end portion 6a of heat transfer tube 6 may be deformed inwardly when applied with external force for fixing the assembly of header 2 and tube 6 for heating and brazing. Thus, a gap may form between the outer surface of the end portion 6a and the inner surface of burr 21, as shown by dashed lines in Fig. 6. In this embodiment, however, each bent tip portion 21a of burr 21 extends along the lateral edge of the slot of tube insertion hole 22 and may cover and seal such a gap. Heat transfer tube 6 is brazed to header 2 maintaining such a gap-sealed condition. Therefore, fluid leakage through the gap may be appropriately prevented. Further, because the tube insertion depth of end portion 6a of heat transfer tube 6 is reduced to a small depth corresponding to about a height of burr 21, the outer surface of end portion 6a is covered by burr 21. The height of burr 21 may be controlled, for example, in the range of 2-3 mm. Moreover, at least a part of the edge (tip) of inserted end portion 6a of heat transfer tube 6 is covered by bent tip portion 21a of burr 21 (in the embodiment of Fig. 6, most of the edge is covered). Therefore, even when heat transfer tube 6 is clad with a corrosion resistant material on its inner surface, an area of a portion of the tube 6 directly exposed to a heat exchange fluid along non-clad portions may be reduced to an extremely small area or minimized. The directly exposed area may be controlled to be not more than 20 mm 2 per one end portion of tube 6. Thus, only a small part of the edge of end portion 6a of heat transfer tube 6 contacts the heat exchange fluid. As a result, the corrosion resistant abilities of heat transfer tube 6 may be greatly improved. Moreover, in this embodiment, because a pair of bent tip portions 21a are formed along the lateral edges of the slot of tube insertion hole 22, the entrance shape of heat transfer tube 6 as an water inlet port becomes a smooth shape. Therefore, turbulence of the heat exchange fluid is reduced or eliminated. In addition, most of the edge of end portion 6a of heat transfer tube 6 is covered with bent tip portion 21a of burr 21, as described above. As a result, turbulence corrosion or inlet tube corrosion at or near the edge is reduced or eliminated. Fig. 8 shows a tube-header connection structure according to a second embodiment of the present invention. In this embodiment, a pair of bent tip portions 31a of burr 31 are formed on the respective second tip portions of burr 31 positioned along the longitudinal edges of a slot of tube insertion hole 22. Even in such a structure, however, the tube insertion length of heat transfer tube 6 may be controlled to a predetermined desired small length. Although the side of header 2 has been explained hereinabove, the side of header 3 may be substantially the same structure as that of header 2. Although several embodiments of the present invention have been described in detail herein, the scope of the invention is not limited thereto.

Claims: A heat exchanger (1) comprising: at least one header (2, 3) having at least one tube insertion hole (22) and at least one heat transfer tube (6) having an end portion inserted into said at least one tube insertion hole (22); and at least one burr (21,31) formed on a wall of said header (2, 3) around said at least one tube insertion hole (22) to extend in a direction toward an interior of said header; said burr (21,31) having a bent tip portion (21a, 21b) formed by bending at least a part of a tip portion (21a, 21b) of said burr (21) inwardly, a tip of said end portion (6a) of said at least one heat transfer tube (6) inserted into said at least one tube insertion hole (22) comes into contact with said bent tip portion (21a, 21b) of said at least one burr (21); characterized in that said bent tip portion extends inwardly to a depth (α) equal to or less than a thickness (t) of said end portion (6a) of said at least one heat transfer tube (6). The heat exchanger of claim 1, wherein said at least one burr (21) has a first tip portion (21a) and a second tip portion (21b), wherein a first length of said first tip portion (21a) is greater than a second length of said second tip portion (21b), and said first tip portions (21a) is bent for forming said bent tip portion. The heat exchanger of claim 1, wherein said at least one burr (21) has a pair of first tip portions (21a) and a pair of second tip portions (21b), wherein a first length of said first tip portions (21a) is greater than a second length of said second tip portions (21b), and each of said pair of first tip portions (21a) is bent for forming said bent tip portion. The heat exchanger of one of claims 1 to 3, wherein said at least one heat transfer tube (6) is formed as a flat tube, and said at least one tube insertion hole (22) is formed as a slot having two lateral edges and two longitudinal edges. The heat exchanger of claim 4, wherein said bent tip portion is formed on each of said first tip portions (21a) of said at least one burr (21) positioned along said lateral edges of said at least one slot, and/or said bent tip portion is formed on each of said second tip portions (31a) of said at least one burr (31) positioned along said longitudinal edges of said at least one slot. The heat exchanger of one of claims 1 to 5, wherein said header further comprises a tank member (14, 17) and a seat member (15, 16) connected to each other to form a barrel (12), and said seat member includes said at least one tube insertion hole (22) and said at least one burr (21). The heat exchanger of claim 1, wherein said end portion (6a) of said at least one heat transfer tube (6) is brazed to said header. The heat exchanger of one of claims 1 to 7, wherein a corrosion-resistant layer is clad on an inner surface of said at least one heat transfer tube (6), preferably formed from an Al-Zn alloy. The heat exchanger of one of claims 1 to 8, wherein said heat exchanger (1) has a pair of headers (2, 3), a plurality of heat transfer tubes (6) interconnected between said pair of headers (2, 3), and a plurality of fins (7), such that at least one of said fins (7) is disposed between adjacent heat transfer tubes (6), preferably each of said pair of headers (2, 3) having a plurality of tube insertion holes (22) and a plurality of said burrs (21), each of said burrs (21) being formed around a corresponding tube insertion hole (22).

Inventors: KADO HIROTAKA, WATANABE AKIMICHI, KADO, HIROTAKA, WATANABE, AKIMICHI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1996
Main classification: F28F9
IPC codes: F28F9