GB2115131A - Heat exchangers - Google Patents

Abstract

A heat exchanger comprises a tubular element 12, forming a closed channel through which a heat exchange fluid may flow, welded to a heat collecting or emitting panel 13. The tubular element and panel are assembled, so that there is point contact therebetween at spaced locations along the length of the tubular element, and are welded together at said locations. The panel may be perforated in order to enhance airflow over the panel. The point contact may be provided via projections (14) formed on the panel against which the tubular element abuts, or by undulations extending from the surface of the tubular element, this undulating surface contacting a flat portion of the panel. <IMAGE>

Description

SPECIFICATION Heat exchangers The present invention relates to heat exchangers and in particular, heat exchangers comprising a tubular element forming a closed channel through which a heat exchange fluid may flow, said tubular element being mounted in thermal contact with a heat collecting or emitting panel.

According to one aspect of the present invention a heat exchanger comprises a tubular element forming a closed channel through which a heat exchange fluid may flow and a heat collecting or emitting panel made of sheet material of substantially uniform thickness, said tubular element and panel being superimposed such that there is point contact between the panel and the tubular element at spaced locations along the length of said tubular element, the tubular element being welded to the panel at said locations.

Preferably a series of projections is formed on the panel against which the tubular element will abut when it is superimposed on the panel, so as to provide point contact with the panel, at spaced locations along its length. In order to obtain maximum thermal contact between the tubular element and the panel, the points of contact between the tubular element and the projections on the panel, should be as close together as possible. In order to achieve this, a series of closely spaced small projections may be provided along the path of the tubular element. The height of the projections should be sufficient to maintain a small contact area between each projection and the tubular element, even if the projections are partially compressed during the welding process.The projections should also be made sufficiently wide to ensure that they will engage the tubular element, although there may be some variation in its path due to manufacturing tolerances. The actual dimensions of the projections depends on the materials used, but are substantially independent of the diameter of the tubular element.

One design of heat emitting or collecting panel may consequently be used with a wide range of diameters of tubular elements. Alternatively the surface of the tubular element which engages the panel may be formed with undulations, so that when superimposed upon a flat surface of the panel there will be point contact between the tubular element and the panel at spaced locations along the length of the tubular element.

Where projections are formed on the panel, these may conveniently be formed by stamping the sheet material using pressing or rolling techniques. Simi marly the undulations in the surface of the tubular element may be formed by a pressing operation, after the tubular element has been manipulated to the desired configuration.

The panel may be in the form of sheet material which is plain apart from the projections which abut the tubular element, where these are used. However, preferably the panel is perforated and in particular louvered in orderto improve the convectional flow over its surface. These perforations may be cut by any suitable method provided that it does not result in any significant thinning of the sheet material around the periphery of the cut. For example, a louvered panel may be formed using a sheering technique in which a sheet of material is stamped between a pair of dies in a press. Where projections are provided on the panel in order to abut the tubular element, these may be formed simultaniously with the perforations or louvers.

According to a further aspect of the present invention a method of manufacturing a heat exchanger, comprises superimposing a heat collecting or emitting panel made of sheet material of substantially uniform thickness and a tubular element so that there is point contact between the panel and tubular element at spaced locations along the length of said tubular element, clamping the panel and tubular element between a pair of electrodes, and applying a current between the electrodes to weld the tubular element to the panel at the points of contact therebetween.

According to one preferred embodiment, the electrodes may be in the form of a longitudinally extending bars, which may be clamped along a length of the tubular element, so that the tubular element may be welded to the panel at all the points of contact therewith along that length, in a single operation. After welding one length of the tubular element to the panel, electrodes would then be moved to the adjoining length and so on until the tubular element had been welded to the panel at all the points of contact therewith, along the length of said tubular element. Alternatively, the electrodes may be in the form of rollers, so that the tubular element and panel may be passed therebetween and welded together progressively, as the points of contact between the tubular element and panel pass between the electrodes.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a plan view of part of the condenser for a refrigerator, formed in accordance with the present invention; Figure 2 shows a sectional elevation, on an enlarged scale, along the line x-x in Figure 1; Figure 3 shows a sectional elevation, on an enlarged scale, along the line y-y in Figure 1; Figure 4 shows a plan view (on enlarged scale) of a modified form of heat emitting panel, that may be used in the embodiment shown in Figure 1; Figures 5 and 6 show alternative arrangements of projections that may be used in accordance with the present invention; and Figure 7shows an alternative method of securing the tubular element to the panel.

As illustrated in Figures 1 to 3 of the accompanying drawings, a condenser for a refrigeratorcornpris- es a serpentine tube 10 having a plurality of substantially parallel straight runs 11, interconnected by curved sections 12. A heat emitting panel 13 is provided with a plurality of rows of closely spaced projections 14, these rows corresponding in position to the straight runs 11 of the serpentine tube 10, so that the straight runs 11 of the tube 10 may be arranged to engage the projections 14 and provide point contact between the tube 10 and panel 13 at spaced locations along the length of the tube 10. The tube 10 is welded to the panel 11 at the points of contact therewith, so as to provide thermal contact therebetween.Columns of louvers 15 are provided between each pair of parallel runs 11 oftheserpen- tine tube 10, in order to improve the convection currents over the panel 13 and thereby the extraction of heat from a refrigerant flowing through the serpentine tube 10.

In orderto produce condensers of the type described above, the panel 13 is first formed from sheet metal, the rows of projections 14 and columns of louvers 15 being formed by stamping the sheet between a pair of dies mounted on opposed platens of a press. By this means, the sheet material may be indexed between the dies to form a complete panel our a continuous length of formed sheet, from which panels of the required length may be cut. The serpentine tube 10 is then assembled with the panel 13, so that it engages the projections 14 and one run 11 of the tube 10 is clamped to a corresponding row of projections 14 on the panel 13, between a pair of longitudinally extending electrodes, which cover the full length of the run 11.A current is then passed between the electrodes so that the run 11 of the tube is welded to the panel 13, where it contacts the projections 14. The condenser is then indexed through the welding maching, until the next run 11 of the tube 10 is clamped between the electrodes, this run 11 is then welded to the panel 13 and the process is continued until all the runs 11 have been welded to the panel 13. Alternatively, the welding machine may be provided with a plurality of pairs of electrodes, each pair corresponding in position to one run 11 of the serpentine tube 10 and covering the full length of the run 11,so that all the runs 11 may be welded in a single operation.With longer condensers, the plurality of pairs of electrodes may only be of sufficient length to cover a portion of each of the runs 11 of the tubular element 10, the condenser may then be gradually indexed through the welding machine, so that successive lengths of each run 11 are welded to the panel 13. In a further alternative, the welding machine may be provided with electrodes in the form of rollers, so that each run 11 of the tube 10 and the adjacent section of the panel 13, may be clamped between a pair of rollers and then fed between the rollers, so that each point of contact between the tube 10 and panel 13 will pass in turn between the rollers and a weld will be formed therebetween.

When forming the projections 14 on the panel 13 material is displaced, thus reducing the overall length of the sheet along the row of projections 14.

As a result of this shortening in length as compared with the edges of the sheet, which remain flat, the panel 13 will tend to distort.

This distortion problem may be overcome or reduced significantly by providing slits or apertures 20 at regular intervals along each row of projections 14, as illustrated in Figure 4. These slits or apertures 20 will open up to compensate for the reduction in length due to the formation of the projections 14.

As an alternative, or in addition to the use of slits or apertures 20, the orientation and/or shape of the projections may be designed to provide a more balanced arrangement which will give reduced distortion of the panel. For example, the projections 21 may be arranged in rows, along the path of the tubular element, so that each projection 21 is inclined to the axis of the row, as illustrated in Figure 5. With this arrangement of projections 21, alternate rows of projections 21 may be inclined in opposite directions. Alternatively V-shaped projections 22 may be arranged transverse to the path of the tubular element, the vertices of successive projections being directed to opposite sides of the path of the tubular element, as illustrated in Figure 6.

The panels 13 of the form described above may be made individually. However it is convenient to form such panels from a roll of sheet material and cut the panels to the required length from the formed sheet.

In order to avoid the formation of sharp edges when the sheet is cut, it is necessary to ensure that the cut is made between successive louvers, across the sheet. This is extremely difficult to achieve on a mechanised basis and is almost impossible when the sheet is subjected to the slightest distortion. In order to overcome this difficulty, at regular intervals along each column of louvers 15, a blank 23 may be left between adjacent louvers 15, so as to provide a flat strip which extends across the full width of the sheet. The sheet may then be cut across one of these strips without difficulty, to provide a panel 13 of the required length.

The problem of distortion of the panel 13 due to the formation of rows of projections 14 may be avoided by providing an undulating surface 30 on the tubular element 10, as illustrated in Figure 7. The tubular element 10 may then be assembled with the panel 13, so that the undulating surface 30 engages flat portions of the panel 13 to provide point contact therebetween, at spaced locations along the length of the tubular element 10. The tubular element 10 may then be welded to the panel 13 at the points of contact therebetween, by any of the methods described above.

Only the surface 30 of the tubular element 10, which is to engage the panel 13 need be undulated.

These undulations may conveniently be formed by stamping the tubular element between the platen of a press and a suitable die mounted on the opposite platen, after the tubular element 10 has been manipulated to the required configuration. The criteria governing the depth and pitch of the undulations on the surface 30 of the tubular element 10, are the same as those governing the corresponding dimensions of the projections formed on the panel 13 in the embodiments described above. However, in addition care must be taken to ensure that the undulations do not significantly restrict the flow of heat exchange fluid, through the tubular elements.

Various modifications may be made without do- parting from the invention, for example, while in the above embodiments we have described the use of a serpentine tube 10, the shape of the tube may be varied as desired and/or several lengths of tube may be secured to the heat collecting or emitting panel.

Also while the tubular element described above is formed from plain tube, tube of any cross-section may be used and it is advantageous to use tube with annular or longitudinal serrations or corrugations so as to obtain a greater surface area. While we have described the use of a louvered panel, other forms of panel, for example perforated or plain, may be used.

Claims (24)

1. A heat exchanger comprising atubularelement forming a closed channel through which a heat exchange fluid may flow and a heat collecting or emitting panel made of sheet material of substantially uniform thickness, said tubular element and panel being superimposed such that there is point contact between the panel and the tubular element at spaced locations along the length of said tubular element, the tubular element being welded to the panel at said locations.

2. A heat exchanger according to Claim 1 in which projections are formed on the panel, against which the tubular element will abut, to provide point contact at spaced locations along the length of the tubular element.

3. A heat exchanger according to Claim 2 in which a series of closely spaced small projections are provided along the path of the tubular element.

4. A heat exchanger according to Claim 3 in which slits are provided in the panel, these slits positioned between successive projections, at spaced intervals along the series of projections.

5. A heat exchanger according to Claim 3 or 4 in which the projections are arranged to minimise distortion of the panel.

6. A heat exchanger according to Claim 5 in which the projections are of elongated configuration and are inclined to the path of the tubular element.

7. A heat exchanger according to Claim 5 in which the projections are of V-shaped configuration and are arranged transverse to the path of the tubular element, the vertices of successive projections being directed to opposite sides of the path of the tubular element.

8. A heat exchanger according to Claim 1 in which the surface of the tubular element which engages the panel is provided with undulations, this undulating surface engaging a flat portion of the panel to provide point contact with the panel, at spaced locations along the length of the tubular element.

9. A heat exchanger according to any one of the preceding claims in which the panel is perforated, there being no significant thinning of the sheet material about the periphery of the perforations.

10. A heat exchanger according to Claim 9 in which the panel is louvered.

11. A heat exchanger according to any one of the preceding claims in which the tubular element has a series of parallel runs.

12. A heat exchanger according to Claim 11 in which the tubular element is of surpentine configuration.

13. A heat exchanger according to Claim 12 in which columns of perforations or louvers are provided between adjacent runs of the tubular element.

14. A method of manufacturing a heat exchanger comprising, superimposing a heat collecting or emitting panel made of sheet material of substantially uniform thickness and a tubular element so that there is point contact between the panel and tubular element at spaced locations along the length of said tubular element, clamping the panel and tubular element between a pair of electrodes and applying a current between the electrodes to weld the tubular element to the panel at the points of contact therebetween.

15. A method according to Claim 14 in which the electrodes are in the form of longitudinally extending bars which are clamped along a length of the tubular element, a current being passed between said electrodes, so that the tubular element will be welded to the panel at all the points of contact therewith, along that length.

16. A method according to Claim 14 in which the electrodes are in the form of rollers, the assembled tubular element and panel being passed between the rollers so that they are clamped together and welded at the points of contact therebetween.

17. A method according to any one of Claims 14 to 16 in which projections are formed on the panel in order to provide point contact between the panel and the tubular element at spaced locations along the length of the tubular element.

18. A method according to any one of Claims 14 to 16 in which undulations are formed on the surface of the tubular element which engages the panel and the tubular element, is assembled with the panel such that its undulating surface engages a flat portion of the panel.

19. A method according to any one of Claims 14 to 18 in which perforations are cut in the panel, the perforations being formed without any significant thinning of the sheet material about the periphery of the perforations.

20. A method according to Claim 19 in which the perforations are formed by stamping the sheet material between a pair of dies, located on the platens of a press.

21. A method according to Claim 20 in which a continuous length of sheet is formed with perforations, from which panels of the required length may be cut, prior to assembly with the tubular element

22. A method according to Claim 21 in which flat strips extending fully across the width of the sheet are provided at regular intervals defining unit lengths, so that the sheet may be cut across one of these strips to form a panel of the required length.

23. A method of manufacturing a heat exchanger substantially as described herein with reference to the accompanying drawings.

24. A heat exchanger substantially as described herein with reference to, and as shown in, Figures 1 to 3,4,5,6 or 7 of the accompanying drawings.