Multitubular heat exchanger

Abstract

 Provided is a heat exchanger including a plurality of inner tubes (114) through which a first fluid passes and an outer tube (117) through which a second fluid passes, the inner tubes (114) including thick tube portions (114a) at both ends, a thin tube portion (114b) at the middle, and a tapered tube portion (114c) between the thin tube portion (114b) and the thick tube portion (114a). Provided is a multitubular heat exchanger for which the inner tubes (114) are in sealed contact at the thick tube portions (114a) and held and integrated by the outer tube (117), so that a second fluid pass-through gap (S) is formed between the outside of each inner tube (114) and the inside of the outer tube (117). The inner tube (114) is tapered at one side in the upper and lower direction of the tapered tube portion (114c), and its surface (bottom surface) to be on the downside when the inner tube (114) is used is provided as a longitudinal flat surface. Thus, the multitubular heat exchanger according to the present invention does not allow forming between the thick tube portion (114a) and the tapered tube portion (114c) a recess portion forming a condensed water pool in the heat exchanger when used.

Description

[0001] The present invention relates to a multitubular heat exchanger which includes an inner tube (heat transfer tube) group through which a first fluid passes and an outer tube (shell) through which a second fluid passes, and for which the group of a plurality of heat transfer tubes are held in the outer tube.

[0002] Particularly, the invention is, in a multitubular heat exchanger such as, for example, an exhaust gas recirculation system (hereinafter, abbreviated as "an EGR system") which performs heat exchange by passing of a high-speed high-temperature gas (gas) through the heat transfer tubes and passing of cooling water (liquid) through the shell, suitable for an exhaust cooler (a high degree of heat exchange capability is required) and the like which cools exhaust gas of an internal combustion engine by cooling water.

[0003] For one for which a high degree of heat exchange capability is required as in the above, for example, a multitubular heat exchanger having an external form as shown in Fig. 1 to Fig. 2 has been frequently used. The heat exchanger has had an internal structure as shown in Fig. 3 to Fig. 6.

[0004] The heat exchanger includes a plurality of inner tubes (heat transfer tubes) 14, 14... through which a first fluid (high-temperature gas) passes, an outer tube (shell) 17 which holds the heat transfer tubes and for which a second fluid (cooling water) forms a pass-through gap, and rectifying cylinders 20, 21 attached at both ends of the outer tube 17. The inner tube 14 includes thick tube portions 14a at both ends, a thin tube portion 14b at the middle, and a tapered tube portion 14c between the thin tube portion 14b and the thick tube portion 14a. The inner tubes 14 are in sealed contact at the thick tube portions 14a and held and integrated by the outer tube 17, so that the second fluid pass-through gap S is formed between the outsides of each inner tube 14 and the inside of the outer tube 17. Usually, in the inner tube 14, a heat transfer fin 22 is inserted from the viewpoint of heat conductivity.

[0005] Here, a heat exchanger is usually produced, after mutually assembling the members, by integration through brazing or welding.

[0006] From the viewpoint of assembling workability, the inner tube 14 is formed divided into portions of a receiving inner tube portion 15 and a covering inner tube portion 16, and the outer tube 17, of a receiving outer tube portion 18 and a covering outer tube portion 19.

[0007] That is, after setting the heat transfer fin 22 in the covering inner tube portion 16, the receiving inner tube portion 15 is fitted therein. The inner tubes 14, 14... thus prepared are fitted in plural numbers with the receiving outer tube portion 18 and the covering outer tube portion 19, respectively, and then the covering outer tube portion 19 is inverted, and placed to cover the receiving outer tube portion 18 (refer to Fig. 5).

[0008] Thereafter, the outer tube 17 with the rectifying cylinders 20, 21 fitted at both ends is, as a heat exchanger assembly, passed through a brazing furnace so as to be integrated. Also, in this case, the receiving outer tube portion 18 and the covering outer tube portion 19 may be integrated in advance by spot welding and the like.

[0009] In the case of using the heat exchanger thus prepared as an exhaust cooler of an EGR system, when its tilt angle is smaller than the tapered angle, a recess portion C with respect to a horizontal plane is formed at a boundary portion between the tapered tube portion 14c and the thick tube portion 14a of the inner tube 14. Condensed water is likely to pool in the recess portion C. This condensed water pool promotes corrosion if exhaust gas and the like contains sulfides etc. (refer to Fig. 7 and paragraph [0002] of Patent JP2002-28775 A).

[0010] For preventing the above-described condensed water pool from occurring, it is necessary to tilt the heat exchanger at an angle α (for example, 15°) or more of a sloping portion as shown in Fig. 7. However, from the viewpoint of effective use of the space in an engine compartment, a setting to tilt the heat exchanger at an angle or more where no condensed water pool occurs is difficult in some cases.

[0011] JP2002-28775 A, JP2005-37002 A and JP2004-317002 A can be mentioned as prior art documents related to measures against condensed water of heat exchangers although these have no effect on the patentability of the present invention.

[0012] Patent JP2002-28775 A discloses a technique regarding brazing when producing an EGR gas heat exchanger and the like by brazing using stainless steel.

[0013] JP2005-37002 A and JP2004-317002 A disclose a technique for securing the drainage of condensed water in a heat exchanger composed of flat tubes and corrugated fins to be used for an outdoor unit of a cooling and heating air conditioner.

[0014] In view of the above, it is an object of the present invention to provide a multitubular heat exchanger that does not allow forming between the thick tube portion and the tapered tube portion a recess portion to form a condensed water pool in the heat exchanger when used.

[0015] In order to solve the problems described above, the present inventors have arrived at a multitubular heat exchanger having the following configuration as a result of keen efforts for development. For the sake of reference, reference signs are used with parentheses.

[0016] A multitubular heat exchanger including a plurality of inner tubes through which a first fluid passes and an outer tube through which a second fluid passes,
the inner tubes including thick tube portions at both ends, a thin tube portion at a middle, and a tapered tube portion between the thin tube portion and the thick tube portion, and
the inner tubes being in sealed contact at the thick tube portions and held and integrated by the outer tube, so that a second fluid pass-through gap is formed between an outside of each inner tube and an inside of the outer tube, characterized in that
the inner tube is tapered at one side in an upper and lower (vertical) direction of the tapered tube portion, and its surface (bottom surface) to be on a downside when the inner tube is used is provided as a longitudinal flat surface.

[0017] Since the surface (bottom surface) to be on the downside when the inner tube is used is provided as a flat surface, irrespective of the tilt angle with respect to the tapered angle at one side, no recess portion with respect to a horizontal plane is formed at a boundary portion between the tapered tube portion and the thick tube portion of the inner tube. Therefore, no condensed water (condensate) pool occurs, and as a result, advanced anticorrosion measures caused by pooling of condensed water are no longer necessary. Moreover, in the case of application to a refrigerating machine and the like, degradation in heat exchanging performance due to condensed water freezing to obstruct the first fluid flowing can also be prevented.

[0018] The term "tapered tube portion" is intended to refer preferable to a reduced cross-sectional shape along the length of the portion without implying a conical shape. Rather, the inner tube preferably has in the tapered portion a reduced cross-sectional shape on a top surface only, while the bottom surface, and optionally the side surfaces, remain substantially planar or flat.

[0019] In the above-described configuration, it is desirable that the outer tube is formed divided into portions of a receiving outer tube portion and a covering outer tube portion (119), and the receiving outer tube portion holds all of the inner tubes in a stacked manner to be closed with the covering outer tube portion so as to be integrated.

[0020] As compared with the case of assembly by inverting the covering outer tube portion with respect to the receiving outer tube portion, the assembling workability of a heat exchanger is improved. This is because assembly of the inner tubes with respect to the outer tube can be performed by making the receiving outer tube portion hold all of the inner tubes in a stacked manner, and then closing the receiving outer tube portion by fitting the covering outer tube portion (refer to Fig. 5 and Fig. 12).
In the following reference will be made to the drawings, in which: Fig. 1 is a front view showing an example of a conventional multitubular heat exchanger.

[0021] Fig. 2 is a side view of the same.

[0022] Fig. 3 is a sectional view taken along arrows 3-3 of Fig. 1.

[0023] Fig. 4 is a sectional view taken along arrows 4-4 of Fig. 3.

[0024] Fig. 5 is a sectional view taken along arrows 5-5 of Fig. 1 and a view for explaining assembly of a heat exchanger using the sectional view.

[0025] Fig. 6 is a sectional view taken along arrows 6-6 of Fig. 1.

[0026] Fig. 7 is a view for explaining occurrence of condensed water pooling in the inner tubes of a conventional heat exchanger and for elimination thereof.

[0027] Fig. 8 is a front view showing an example of a multitubular heat exchanger of the present invention.

[0028] Fig. 9 is a side view of the same.

[0029] Fig. 10 is a sectional view taken along arrows 10-10 of Fig. 8.

[0030] Fig. 11 is a sectional view taken along arrows 11-11 of Fig. 10.

[0031] Fig. 12 is a sectional view taken along arrows 12-12 of Fig. 8 and a view for explaining assembly of a heat exchanger using the sectional view.

[0032] Fig. 13 is a sectional view taken along arrows 13-13 of Fig. 8.

[0033] Fig. 14 is a view for explaining elimination of condensed water pooling in the inner tubes of a heat exchanger in an embodiment of the present invention.

[0034] An embodiment of a multitubular heat exchanger of the present invention will be described based on illustration (Fig. 8 to Fig. 14). Here, description will be given, by way of example, of a heat exchanger to be applied to EGR (exhaust gas). Of the reference signs numbered in the hundreds for parts corresponding to the conventional example, the hundreds place digits are provided as "1," and the same numbers are used for the last two digits, whereby the whole or part of description of those is omitted.

[0035] The multitubular heat exchanger includes a plurality of inner tubes 114, 114... through which exhaust gas (first fluid) passes and an outer tube 117 through which cooling water (second fluid) passes.

[0036] The inner tube 114 includes thick tube portions 114a at both ends, a thin tube portion 114b at the middle, and a tapered tube portion 114c between the thin tube portion 114b and the thick tube portion 114a. The inner tubes 114 are in sealed contact at the thick tube portions 114a and held and integrated by the outer tube 117, so that a second fluid pass-through gap S is formed between the outside of each inner tube 114 and the inside of the outer tube 117.

[0037] In the above, the inner tube 114 is formed of divided portions of a receiving inner tube portion 115 and a covering inner tube portion 116, and a heat transfer fin 122 is inserted in and integrated with the inner tube 114. In the case of a configuration without a heat transfer fin, the inner tube may be formed of a pultruded article or a seamless tube. In such a case, for an improvement in the efficiency of heat transfer, projections to produce longitudinal eddies may be formed inside (refer to Abstracts etc., of JP2002-350081 A and JP2002-181468 A).

[0038] So far, the present embodiment has substantially the same configuration as that of the conventional example.

[0039] In the above-described configuration, the inner tube 114 is tapered at one side in the upper and lower direction of the tapered tube portion 114c, and its surface (bottom surface) to be on the downside when the inner tube 114 is used is provided as a longitudinal flat surface.

[0040] The outer tube 117 is a divided body of a receiving outer tube portion 118 and a covering outer tube portion 119, which is the same as in the conventional example, but is different in sectional shape. That is, the receiving outer tube portion 118 has a U-shaped section that can hold all of the inner tubes 114, 114... , and holds all (in the illustration, five) of the inner tubes 114, 114... in a stacked manner to be closed with the covering outer tube portion so as to be integrated.

[0041] At both ends of the outer tube 117, rectifying cylinders 120, 121 are connected and integrated. The rectifying cylinders are also formed, in consideration of drainage when condensed water occurs, with circular connection ports 120a, 121 a eccentrically located so that the sides to serve as lower surfaces (bottom surfaces) when used have linear sections. In the illustration, reference sign 117a denotes a positioning protrusion when assembling by fitting the rectifying cylinders 120, 121 with the outer tube 117.

[0042] Next, a method for manufacturing a heat exchanger having the above-described configuration will be described.

[0043] As the material of the members of the heat exchanger, stainless steel is usually used, and the plate thickness of the outer tube and rectifying cylinders is provided as 0.5mm to 3mm (desirably, 1 mm to 2mm), and the inner tubes and heat transfer fins: as 0.05mm to 1 mm (desirably, 0.1 mm to 0.8mm).

[0044] First, the heat transfer fin 122 is set (inserted for assembly) in the covering inner tube portion 116, and then the receiving inner tube portion 115 is fitted for assembly. The mode of bonding of the members is brazing at this time. When the material of these members is stainless steel as described above, usually, a copper brazing filler or a nickel brazing filler is used.

[0045] The plurality of (in the illustration, five) inner tubes 114, 114... thus prepared are all set in the receiving outer tube portion 118, and then covered with the covering outer tube portion 119. Bonding of the inner tubes 114, 114... and of the inner tube 114 and the outer tube 117 is performed by the same brazing as described above.

[0046] In addition, bonding of the receiving outer tube portion 118 and the covering outer tube portion 119 is also performed, usually, by the same brazing as described above.

[0047] Further, the rectifying cylinders 120, 121 are inserted in the outer tube 117, and brazed in the same manner as described above.

[0048] Then, the heat exchanger assembly is passed through a brazing furnace (vacuum furnace) so that the members are mutually brazed and integrated. Heating and cooling conditions during brazing are set in consideration of the type and heat capacity of the brazing filler metal.

[0049] Thus, the manufactured multitubular heat exchanger is, with its side to be a flat surface located on the downside, mounted on the piping system of an EGR system.

[0050] In the heat exchanger of the present embodiment, no such recess portion as has been conventionally formed is formed, on the downside of the inner tube (bottom portion side), at a boundary portion between the thick tube portion 114a and the tapered tube portion 114c, so that no condensed water pool occurs (Fig. 14). Therefore, the freedom of setting of the mounting tilt angle of the heat exchanger is increased.

Claims

1. A multitubular heat exchanger including a plurality of inner tubes (114) through which a first fluid passes and an outer tube (117) through which a second fluid passes,
the inner tubes (114) including thick tube portions (114a) at both ends, a thin tube portion (114b) at a middle, and a tapered tube portion (114c) between the thin tube portion (114b) and the thick tube portion (114a), and
the inner tubes (114) being in sealed contact at the thick tube portions (114a) and held and integrated by the outer tube (117), so that a second fluid pass-through gap (S) is formed between an outside of each inner tube (114) and an inside of the outer tube (117), characterized in that
the inner tube (114) is tapered at one side in an upper and lower direction of the tapered tube portion (114c), and its surface (bottom surface) to be on a downside when the inner tube (114) is used is provided as a longitudinal flat surface.

2. The multitubular heat exchanger as set forth in claim 1, characterized in that the outer tube (117) is formed divided into portions of a receiving outer tube portion (118) and a covering outer tube portion (119), and the receiving outer tube portion (118) holds all of the inner tubes (114) in a stacked manner to be closed with the covering outer tube portion (119) so as to be integrated.

3. The multitubular heat exchanger as set forth in claim 1 or 2, characterized in that the inner tube (114) is formed divided into portions of a receiving inner tube portion (115) and a covering inner tube portion (116), and a heat transfer fin (122) is held by and integrated with the inner tube (114).

4. A method for assembling the multitubular heat exchanger as set forth in claim 2 or 3, comprising a step of making the receiving outer tube portion (118) hold all of the inner tubes (114) in a stacked manner, and then closing the receiving outer tube portion (118) by fitting the covering outer tube portion (119).

Drawing