IL100264A

IL100264A - Heat exchanger

Info

Publication number: IL100264A
Application number: IL10026491A
Authority: IL
Original assignee: Gea Luftkuehler Happel Gmbh
Priority date: 1990-12-08
Filing date: 1991-12-06
Publication date: 1995-03-30
Also published as: ATE113708T1; ZW17791A1; AU8880291A; DE4039293C2; AU653755B2; EP0490210B1; IL100264A0; EP0490210A1; ZA919524B; DE4039293A1; ES2063430T3; MX9102394A; DE59103422D1; DE4039293C3

Abstract

The heat exchanger consists of exchange tubes (2) which are narrow in the flow direction (SR) on the outer exchange medium. Two adjacent exchange tubes (2) are connected in each case by ribs (3a, 3b) either from U-shaped individual ribs or as a component of a meandering ribbed strip (14). The connection to the tube flanks (11) and the rib feet (9), and to the contact sections (16) is preferably performed by welding, in particular by fusion welding beams (20) from the insides (22) of the tube flanks (11). After two tube shells (7) have been connected via the ribs (3a, 3b), such a compound component is connected to a further such compound component by welding the longitudinal edges (6) of the tube shells (7). The tube ends are inserted in tube plates. Such a heat exchanger is completely galvanised and requires no supporting structures. <IMAGE>

Description

100264/2 Heat Exchanger GEA LUFTKUHLER GmbH C. 84983/6 - 1 - 100264/2 FIELD OF THE INVENTION The present invention relates to heat exchangers of the kind in which a heat exchanger medium flows in contact with the outer faces of slender, essentially oval heat exchanger tubes having an elongated cross-section in a direction parallel to the flow direction of an external exchanger medium and in which each exchanger tube is equipped with integral ribs projecting traversely from a side wall thereof. In heat exchangers of this kind an array of exchanger tubes are arranged adjacent each other in at least one layer and are held by two suitably slotted tube supporting plates, the ends of each tube being received by and welded to the edge of a slot of such plate.

BACKGROUND OF THE INVENTION AND PRIOR ART German Patent No. 3,419,734 discloses a heat exchanger which capable, for example, of exchanging heat between gases and liquids or between gases and condensing vapors. Such a heat exchanger is used predominantly for cooling air or condensing vapors by means of air and it - 2 - 100264/2 comprises steel ribs connected with steel exchanger tubes. The steel ribs which are punched with appropriate machines from plates or strips, are fitted with cut outs adapted to the cross-section of the exchanger tubes and in the course of assembly the ribs are slid onto the exchanger tubes in longitudinal direction. The subsequent galvanization by dipping not only has the purpose to protect the exchanger tubes and the ribs, but also to produce the metal-to-metal connection of the exchanger tubes with the ribs.

If in such exchanger tubes, a certain width of the sides, for example approximately 200 mm, is exceeded, and if the rib dimensions and rib spacings are conventional, i.e., having a thickness of approximately 0.35 mm, a height of approximately 15 mm and a spacing of approximately 2.5 mm, and the sides of the tubes have a conventional thickness of about 1.5 mm, it may easily occur that the permissible bending stresses of the thin ribs are exceeded and distortions of the ribs are caused as a result. Moreover, the connection between the exchanger tubes and the ribs which is usually effected by zinc, may be damaged. This damage results in a significant impairment of heat flow between the exchanger tubes and the ribs without that the reason for this problem becomes visible or apparent.

In manufacturing heat exchangers of the known type, high precision complicated and cumbersome mechanical procedures of punching out the ribs and sliding the ribs onto the exchanger tubes are required to ensure that the zinc provides as close as possible a connection between the exchanger tubes and the ribs. Moreover, for adapting the ribs to slide over the exchanger tubes, a significant amount of material has to be cut out of the ribs which is wasted and has to be scrapped.

In the manufacture of the known heat exchangers the heat exchanger tubes are galvanized individually. For this purpose, each exchanger tube must be pressed flat and tightly welded at its ends, so that only the outer surfaces are pickled and pasivated and the inner surfaces are - 3 - 100264/2 not galvanized which in itself is also cumbersome and complicated. After the exchanger tubes have been galvanized, it is necessary to remove the ends which have been pressed flat and welded which adds an additional operation and produces more waste material.

Subsequent to the dip-galvanization, it is necessary to join the individual exchanger tubes together by means of the support structures in order to obtain a heat exchanger that is self-supporting over its entire length.

To sum up, the manufacture of a heat exchanger of the known type is relatively cumbersome and requires time-consuming working steps.

Moreover, when a reduced pressure prevails within the tubes and/or in case of an excess outer pressure, significant forces act on the large-area sides of the slender exchanger tubes. Consequently, when a certain degree of slenderness is exceeded, the sides of the tubes may sag or warp unless suitable preventive measures are taken, e.g. the provision of supports. Accordingly, in one embodiment of a known heat exchanger of the kind specified, at least one internal transverse web is provided in each tube for supporting the large area side walls against sagging or warping.

DE 3,044,507 discloses a heat exchanger having an array of adjacent tubes connected with each other by corrugated strips whose ridges are fixed to the tubes by welding, soldering, hard-soldering or the like. Any reference in this connection to conventional welding clearly means a method of fixation whereby the upstream and downstream rib edges (relative to direction of the exterior exchanger medium) are welded to the tube sides at the sites where the ridge constituting bends of the ribs come into contact with the tube sides. As a rule, the inner parts of the ridges between the outer edges of the strips are not accessible to welding because the V-shaped channels between the rib webs cannot accommodate a welding electrode, - 4 - 100264/2 particularly in mass production, and it is accordingly evident that in the context of the disclosure in DE 3,044,507 "welding" means spot-welding.

It follows from the foregoing that from the point of view of heat transfer technology, the teachings of DE 3044507 are unsatisfactory and do not enable to establish a satisfactory contact between the rib strips and the tube side walls along the ridges beyond the two spot- welded sites at the two opposite ends of each ridge. Indeed, it is quite likely that when galvanizing the heat exchanger tubes and the ridge strips spot-welded to them, the required heat transfer connection via the zinc will not be achieved. This in turn impairs the desired heat flow between the heat exchanger tubes and the corrugated rib strips without, however, there being any discernable cause for such impairment. Such a defect occurs in particular in cases where upon dipping of the heat exchanger assembly into a zinc bath, the tube side walls sag or warp, making it impossible to achieve a perfect heat conducting connection via the zinc solder between the rib strips and the tube side walls.

SUMMARY OF THE INVENTION It is the object of the present invention to provide an improved and simplified heat exchanger of the kind specified in which with the aid of simple manufacturing methods the ribs are fastened to the wide side walls of the tubes in a manner which ensures a satisfactory heat transfer, whereby bending stresses and sagging or warping of the exchanger tubes and ribs are largely avoided.

In accordance with the present invention there is provided a heat exchanger of the kind that comprises an array of parallel heat exchanger tubes extending in a direction which in operation is transversal to the flow direction of an external exchanger medium, each heat exchanger tube having a first dimension transversal to and a second dimension parallel to the said flow direction, said second dimension being several times larger than said - 5 - 100264/2 first dimension whereby each tube has wide and narrow side walls, each end of each heat exchanger tube being received by and circumferentially welded to a slot in a tube supporting plate, every two adjacent heat exchanger tubes being connected to each other by a corrugated rib strip; which heat exchanger is characterized in that each exchanger tube consists of two trough like shells welded to each other along their longitudinal edges to form welding seams extending along the narrow side walls, and in that each of said corrugated rib strips is welded along its ridges to opposite external faces of the wide side walls of adjacent heat exchanger tubes.

Due to the fact that in a heat exchanger according to the invention the ridges of the corrugated rib strips are each welded to the wide tube side wall, in case of a pressure difference between the exterior and interior of the tubes, the individual ribs and the tube side walls are subjected only to tensile or compression stresses as the case may be. Preferably the welding of the ridge of the rib strips to the tubes is by fusion. The welding along the ridges may either be by way of continuous stretches or a plurality of fusion spots.

Furthermore, because of the multiple spot sites along the ridges, it is possible in accordance with the invention to produce heat exchangers with extremely broad tubes having, for example side walls that are 300 mm wide or even more. In this way a high section modulus (moment of inertia) is obtained and it is possible to combine slender exchanger tubes that offer a low flow resistance with large heat exchange surfaces.

Due to the fact the corrugated rib strips are welded along their ridges to the wide side walls of the tube at several spots, the heat exchangers according to the invention achieve such a stiffness that it is possible to galvanize the entire exchanger in one go and with no danger that the high temperature yield points are exceeded. Consequently, the galvanization is significantly simpler as compared to the galvanization of the individual - 6 - 100264/2 tubes. The width of such a heat exchanger can easily be adapted to the width of a zinc bath because due to its stiffness, the heat exchanger does not require an auxiliary support structure.

Furthermore, it is also possible to galvanize the two tube supporting plates together with any distributor and collector chambers connected thereto. In other words, the distributor and collector chamber may be galvanized together with the heat exchanger tubes, which further improves the efficiency of the manufacturing process. In this connection it is of particular advantage that the gap between the end of each tube and the edge of the suitably dimensioned slot in a tube supporting plate is completely filled out with zinc in consequence of capillary forces. Due to this, problematic zones present in known heat exchangers are eliminated in a satisfactory fashion.

The welding of the ridges of the corrugated rib strips to the wide side walls of the tubes along the ridges, is readily achieved due to the fact that the heat exchanger tubes are made of tube shells. Before the tube shells are welded together along their edges so as to form a heat exchanger tube, it is possible to bring about an immaculate connection between the ridge regions of the corrugated rib strips and the tube side walls by welding, e.g. means of a fusion inducing radiation such as a laser or electron beam.

To this end, each corrugated rib strip is first applied to the wide outer side of a tube shell so that its ridges are in contact therewith. Subsequently, the assembly of corrugated rib strip and tube shell is advanced at uniform speed in the shell's longitudinal direction across a skew fusion-welding inducing beam which is directed to the inner face of the shell and is guided so as to move back and forth over the entire width of the shell. Subsequently, the ribbed tube shell is turned by 180° and the free ridges of the corrugated rib strip are put in contact with the wide outer side of another tube shell whereupon the first, ribbed shell and the second shell are jointly - 7 - 100264/2 advanced at constant speed in the longitudinal direction of the shells across a skew fusion-welding inducing beam which is directed on the inner face of the second shell and is guided so as to move back and forth over the entire width thereof until the desired degree of fusion has been achieved.

In a subsequent manufacturing step, pairs of complementary ribbed shells are welded together at their edges to form the desired heat exchanger tubes.

DESCRIPTION OF THE DRAWINGS For better understanding, the invention will now be described, by way of example only, with reference to the annexed drawings in which: Fig. 1 is a perspective partial view of a heat exchanger according to the present invention; Fig. 2 is a horizontal cross-sectional view, drawn to a larger scale, along sectional line II— II of Fig. 1, showing the manner of fastening a tube end to a tube supporting plate; Fig. 3 is a perspective partial view showing two manners of connection of tube shells and ribs; and Fig. 4 is a perspective view, drawn to a larger scale, showing a detail of the heat exchanger of Fig. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Fig. 1 of the drawings shows a heat exchanger generally designated at 1 which comprises an array of eight exchanger tubes 2 arranged next to each other in one plane with ribs 3 extending between adjacent tubes 2. As shown in Fig. 2, the tube ends 4 are received in suitably dimensioned slots of tube supporting plates 5 one of which forms part of a distribution chamber and the other of a collection chamber (both not shown). The exchanger tubes 2 have a slender cross-section in the flow - 8 - 100264/2 direction SR of the external exchanger medium, with the dimension L signifying the width of the wide side walls of a tube short of the rounded end portions 12 thereof being several times larger than the width B of the narrow side walls thereof. As seen in Figs. 3 and 4, each heat exchanger tube 2 is formed of two tube shells 7 which are welded to each other at their longitudinal edges to form welding seams extending along the two narrow side walls of each tube 2.

The two parts A and B of Fig. 3 show different embodiments of ribs 3. In accordance with part A, the ribs consist of a plurality of individual, unconnected U-shaped ribs 3a comprising each a web 8 and flanges 9. Each web 8 is fitted with trapezoidal spacers 13 punched out of the web and folded open by about 90°. Preferably the spacers 13 protrude slightly beyond the edges of flanges 9. Due to the fact that the ribs are not connected to each other, a heat exchanger fabricated in this manner does not have the desired degree of stiffness. Furthermore, the production of a heat exchanger with such a rib configuration involves a cumbersome manufacturing procedure apt to lead to defects which in practice impair the heat conduction. This design is therefore outside the scope of the present invention.

The design of a heat exchanger according to the invention with a corrugated rib strip as shown in Part B of Fig. 3. As shown adjacent heat exchanger tubes 2 are connected to one another by means of ribs 3b which are components of a corrugated or meander-like rib strip 14. In this rib strip 14, the width Bl of the spacer side 15 which determines the distance between two adjacent exchanger tubes 2, is greater than the width B2 of the contact ridges 16 are placed on the outer faces 10 of the tube wide side walls 11. It can in addition be seen in Fig. 3 that each spacer side 15 has several bends 17 which divide it and the contact ridges 16 into sections that are offset relative to each other. Such offset causes turbulence of the - 9 - 100264/2 throughflowing exterior exchanger medium whereby the heat transfer is improved. As shown, ridges 16 that bear on one of the tube shells 7 alternate with ridges 16 that bear on the adjacent tube shell 7.

For fastening the ribs 3 to the tube shells 7 longitudinal slots 18 may be provided in the tube side walls 11 of the tube shells 7 extending parallel to the longitudinal edges 6 thereof. After the ribs 3b and the tube shells 7 have been placed so as to bear against each other in the manner shown in Fig. 3, a conventional welding process can be used for filling the longitudinal slots 18 with welding material thus obtaining an excellent connection and heat content between the contact ridges 16 with the tube shells 7. The welding seams are schematically indicated in Fig. 3 by reference numeral 19.

According to another embodiment of fastening ribs 3 of a rib strip 14 to the outer face 10 of a tube side wall 11, a fusion welding inducing beam 20, for example, a laser beam, is guided in a zig-zag fashion over the inner face 22 of the tube side wall 11 as indicated by dash-dot lines 21 in Fig. 3, so that the ridges 16 are connected to the tube shell 7.

As shown in Figs. 1 and 2 of the drawings, the tube ends 4 are placed in the tube plates 5 within slots 23 which substantially have the cross-section of the heat exchanger tubes 2. The tube ends 4 are welded at the area of the end faces 24 to the circumference of slots 23 in tube plates 5. A conventional welding process or a fusion welding process can be used for welding the tube ends 24 to the tube plates 5.

Assembling a heat exchanger according to the present invention is carried out by first bringing each rib strip 14 into contact with the external face 10 of a tube shell 7 via contact ridges 16. Then, the rib strip together with the tube shell 7 are shifted in the longitudinal direction of the tube shell, and they are connected to each other by fusion with a fusion welding inducing beam 20. Fusion is performed by advancing the shell/rib i - 10 - 100264/2 strip assembly across the fusion inducing beam 20 which latter is applied to the inner side of shell 7 and is moved back and forth over the entire width of the tube side walls 11. Once fusion of rib strips 14 to the shells is completed, all shells are rotated by 180°, and the free contact ridges 16 of each rib strip is placed in contact with the external face 10 of an adjacent tube shell 7. The first tube shells with the ribs welded thereto and the additional tube shells are then subjected to the same treatment as before for the fusion of a second shell 7 to each rib strip 14. Finally, the fabrication of the heat exchanger is completed by welding together the longitudinal edges 6 of each pair of complementary shell tubes 7.

While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

- 11 - 100264/2 CLAIMS:

1. A heat exchanger of the kind that comprises an array of parallel heat exchanger tubes extending in a direction which in operation is transversal to the flow direction of an external exchanger medium, each heat exchanger tube having a first dimension transversal to and a second dimension parallel to said flow direction, said second dimension being several times larger than said first dimension whereby each tube has wide and narrow side walls, each end of each of the heat exchanger tubes being received by and circumferentially welded to a slot in a tube supporting plate, and every two adjacent heat exchanger tubes being connected to each other by a corrugated rib strip; which heat exchanger is characterized in that each exchanger tube consists of two trough like shells welded to each other along their longitudinal edges to form welding seams extending along the narrow side walls and in that each of said corrugated rib strips is welded along its ridges to opposite external faces of the wide side walls of adjacent heat exchanger tubes.

2. A heat exchanger according to Claim 1, wherein the rib strips have a meander-like configuration comprising spacer side walls and contact ridges, each spacer side wall comprising transversal bends whereby each spacer side wall and contact ridge is divided into mutually offset portions.

3. A heat exchanger according to Claim 1 or 2, wherein the welding of the ridges of said corrugated rib strips to the opposite external faces of the wide side walls of adjacent heat exchanger tubes is by fusion welding directed at an inner surface of the tube shells. For the Applicants, AND PARTNERS 84983-6SPC DD/MC/be 4.12.1994