GB1575021A

GB1575021A - Tubular heat exchangers

Info

Publication number: GB1575021A
Application number: GB44277A
Authority: GB
Original assignee: Chausson Usines SA
Current assignee: Chausson Usines SA
Priority date: 1976-01-12
Filing date: 1977-01-06
Publication date: 1980-09-17
Also published as: IT1076501B; FR2337867B1; BE850227A; FR2337867A1; DE2700182A1; ES454927A1

Description

(54) IMPROVEMENTS IN OR RELATING TO TUBULAR HEAT EXCHANGERS (71) We, SOCIETE ANONYME DES USINES CHAUSSON, a company organised under the laws of France, of 35 rue Malakoff, Asnieres, Hauts-de-Seine, France, do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to tubular heat exchangers.

Up to now, heat exchangers of the type having tubes mounted in end plates are relatively easy to manufacture when they are only one or two rows of tubes thick but the manufacture becomes far more difficult when the number of rows of tubes is greater. Indeed, it becomes practically impossible to engage the tubes in tube passages in the end plates by swift-acting mechanical means, since the difficulties of accurately centering the tubes increase with the number of rows of tubes. In particular, it is practically possible to position end plates on a completed heat exchanger core of tubes when the tubes are provided with secondary heat exchange elements such as fins.

According to the present invention there is provided a heat exchanger including successive rows of tubes engaged in tube end plates, the end plates being formed by a stack of metal bars, at least one lateral side of each bar having grooves each of which is of a complementary shape to and receives half of the outer cross-section of one of the tubes, adjacent bars being brazed together at least between adjacent tubes of each said row at portions of said lateral sides exclusive of s.aid grooves.

For a better understanding of the invention and to .show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is an exploded partial perspec tive view of a heat exchanger, Figure 2 is a perspective view of part of the heat exchanger shown in Figure 1, Figures 3 to 6 are perspective views showing various developments of the invention, and Figure 7 is a diagrammatic elevation, partially in cross-section, showing a manufacturing operation of a heat exchanger.

Figure 1 shows a heat exchanger which comprises fluid circulation tubes 1 between which are placed secondary heat exchange elements 2, for example constituted as shown in the drawings by corrugated strips.

The elements 2 could, however, be formed alternatively by fins slipped on the tubes 1.

Turbulence-causing members 3 are also advantageously provided inside the tubes 1 although this is not necessary. At their ends, the tubes 1 are engaged in end plates 4,5 on which are placed and fixed header tanks 6,7.

In the example shown in Figure 1, the heat exchanger comprises only two rows a and b of tubes 1, but it could, in the same way, comprise more than two rows, in general up to any desired number.

As shown in Figures 1 and 2, the end plates 4 and 5 are constituted by a stack of bars 8 of any suitable thickness e, for example between 2 and 15 millimetres, according to the intended use of the heat exchanger.

Each bar 8 has, on two opposite sides thereof, notches or grooves 9, 9a whose number corresponds to the number of rows of tubes 1 that the heat exchanger has.

In cross-section, the grooves 9, 9a correspond exactly to the cross-sectional shape of half of a tube 1 so as to receive half of the outer cross-section of one of the tubes.

Thus, in the example shown, the tubes have in cross-section two flat sides and two rounded ends, each groove 9, 9a having a flat base 10 leading into opposed arcuate parts 11, the depth of a groove 9, 9a being equal to half the thickness of a tube across the flat sides. The grooves 9, 9a are separated from each other by plane portions 12 which constitute areas of mutual support for the bars 8 when they are assembled as described hereinbelow with reference to Figure 7.

End bars 8a, having grooves 9 only in one of their sides, are also provided as illustrated in Figure 1, these being intended to be placed at the two ends of each end plate 4, 5 (only one bar 8a being shown).

Preferably, but this is not necessary, the bars 8 have bevelled edges 13 or a groove at their two ends, and a similar bevelled edge or groove 13a is also formed on the end side of each end bar 8a. These bevelled edges or grooves are provided to permit the centering of the header tanks 6,7, which are to be welded or brazed as shown at 14 in Figure 1.

Figure 3 shows a development according to which the bars shown at 8l still have two sets of grooves 9, 9a but also between them, slots 91 which have the same crosssectional shape as that of the tubes 1, and into which the tubes are engaged as illustrated in the Figure.

This latter type of bar permits the formation of sub-units comprising respectively two bars and one, two or more tubes, these sub-units being able subsequently to be built up during as.sembly of the heat exchanger in the a same way as the bars previously described.

With the embodiment shown in Figure 4, the bars 82, are manufactured by stamping plates or metal sheets into a generally channel-shaped cross-section, each bar being thus provided with two folds, 15,16 separated by a gap 17, the two folds being connected by a base portion 18. The outer shape of the bars 82 according to this embodiment is the same as that previously described for the other embodiments, i.e., the bars 82 have opposed grooves 9 and 9a respectively, separated by support portions 12. It is advantageous, in order further to rigidify the bars shown in Figure 4, for slots 19 to be made in the support portions 12, these slots extending from the side of the folds 15, 16 towards the base portion 18.These slots 19 are used to position blades 20, which are then welded or brazed at the same time as the bars themselves, the blades then forming braces between respective folds and respective bars and also braces for each of the header tanks such as that shown at 62.

In practice, the blades 20 can be of a length that is greater than the height of the stack of bars 82 so that the blades can be used as guides for the bars during assembly thereof by brazing and during which operation clearances which can exist between the successive bars are progressively reduced. After brazing, the protruding ends 20 of the blades 20 are trimmed to the level of the.ends of the bars 82.

It is also possible for the blades 20 to have a length smaller than the height of the stack of bars 82 and then it is only during brazing that the ends of the blades 20 are introduced into the slots 19 of the outer bars 82. The complete side edges of the bars 82 from the two sides of the respective channel sections to the respective bases 18, are engaged with the inner wall of the header tank 62 in order for the whole length of the side edges of the bars 82 to be welded or brazed to the adjacent inner wall of the header tank.

It is advantageous that the bars have protuberances to ensure their mutual selfcentering. This is shown in Figure 5 according to which the bars 82 have protruding ribs 21 and corresponding recesses 22 in their support portions 12 and 12a respectively. This thus ensures that the bars are correctly aligned when they are stacked upon one another.

Other means to ensure alignment of the bars can be provided; for example, Figure 2 shows that holes 23 can be provided through the bars so as to open on either side of the support portions 12 to permit engagement of a centering pin in the holes.

Figure 3 shows centering means in the form of protrusions 24 on the support portions 12 and corresponding recessed holes 25 on the support portions 12a into which holes the protrusions 24 can engage.

The above described bars can be made of various metals such as brass, copper, steel (which can be stainless steel) or aluminium, or alloys of these metals.

Depending on the nature of the metal utilised to make the bars, various brazing methods can be used. In all cases, it is important that the surfaces of the portions to be brazed are not polished but, on the contrary, these surfaces must be slightly roughened to form scratches grooves or other roughened forms enabling the brazing alloy to defuse by capill.ary action when it has melted during brazing. It is especially important that the support portions or areas 12 be roughened, since these are the surfaces upon which the brazing alloy must diffuse and which provide a relatively great area where the brazing alloy is not able to be provided by a layer of plating alloy, as is the case for the grooves 9, where the brazing alloy can be provided by a layer of plating alloy covering the tubes 1.

Besides, it is important, as has already been explained, for the bases 10 and the arcuate parts 11 of the grooves 9 to have a good machining accuracy.

When the bars are solid, as is the case with the bars of Figures 2, 3 and 5, 6 and 7, they can be manufactured or shaped in various ways. For example, they can be cast, especially if the bars are of aluminium, but then their surfaces will have a crust (oxide layer) which hinders brazing. They can be obtained through drawing of a plate having longitudinal grooves corresponding to the grooves 9, 9a, the plate so produced being then cut into sections. They can also be manufactured from a bar by stamping or cutting When the bars are manufactured by stamping a.s described with reference to Figure 4, the dimensions are sometimes not very accurate and often they have to be corrected or adjusted. It is advantageous, in order to obtain the desired roughnesses, to carry out a grinding step which is dia gr.ammatically shown in Figure 5.Above the bars there is diagrammatically shown a grinding machine or a milling machine 26 which has a shape complementary to the profile to be obtained. The milling machine has largediameter parts 261, 262, corresponding to the grooves 9, and parts 26,, 264 and 265 of a smaller diameter, which correspond to the support areas, the latter parts being grooved at 27 to correspond to the ribs 21.

Thus, by causing the bars to be milled by the machine shown or to be acted upon by a set of grinding machines or milling machines or other tools (the bars being placed in a carrier during such a process), the support areas and the bases 10 of the grooves are roughened or scratched while dimensionally adjusting the bases 10 and also the arcuate portions 11.

In the embodiment shown in Figure 4, it is possible to adjust only the parts forming the bases 10 of the grooves 9 and the arcuate portions 11. To permit brazing of the bars with one another and with the tubes 1, it is advantageous to utilise tubes which have been, at least on their outsides, coated with a brazing plating alloy. In such a case, the brazing alloy originating from the layer of brazing alloy on the tubes is sufficient to ensure the brazing of the tubes with the bars.

To braze the support areas 12 together, it is necessary to add some brazing alloy, however. When the bars of Figure 2 are provided with the holes 23 used for passage of a centering pin 24 (Figure 3), then the pin 24 can be made of a brazing alloy or coated with the alloy. In addition, in the embodiment shown in Figure 3, small brazing rods can be engaged in the recessed holes 25.

In the embodiment of Figure 4, the blades 20 can be coated with brazing alloy or the sheet or plate from which the bars are formed can be coated initially with a layer of brazing alloy and the grinding process will then remove only the layer of plated brazing alloy in the grooves 9 and 9a whilst leaving it on the support areas 12.

In the embodiment of Figure 5, holes similar to the holes 23 (Figure 2) can be provided for a brazing rod, or a brazing sheet can be placed between the support areas 12, 12a.

Figure 6 shows another embodiment according to which the bars 84 are multilayered, the layers being constituted by plates 27 made of basic metal and by sheets 28 made of brazing alloy. In such a case, the above described machinings can be achieved whilst ensuring that there is always some brazing alloy present.

To assemble a heat exchanger as shown in Figure 7, a frame 29 is provided which comprises four uprights 30 constituted by U-shaped sections supported by a base 31.

In each set of two uprights 30, whose openings face each other, there is placed a first bar A, then a row of tubes a b, and then a secondary heat exchanger element 2. The stacking is continued in thus manner.

Possibly rods or pins 33 for centering purposes and /our for -providing the brazing material are placed in the holes 23 and the successive bars such as B, C are then slipped on the rods or pins 33 while being guided by the uprights 30. When the core of the heat exchanger is entirely built, it is tightened by means of a plate 34 resiliently urged by springs 35, which are themselves supported by a cover 36 fixed on the uprights 30. The bars being mutually tiehtened, it is possible, if so desired, to widen the ends of the tubes 1 in their housings formed by the complementary grooves of two adjacent bars. The assembly formed by the heat exchanger and the frame are then submitted to conventional steps usual in the art to effect brazing.

It will be appreciated that it is possible to provide the tube end plates by using bars such as those shown at 8a in Figure 1 and at 8b in Figure 4, i.e. bars which have only one set of grooves 9, two such bars being placed back to back to constitute a complete bar 8 or 8,.

It will be further appreciated that it is possible to construct the heat exchangers described in various sizes, using standardised elements which are easily assembled together and, not only can the heat exchangers be made of various metals but each heat exchanger can be made-up of parts of different metals. The heat exchangers described should be able to withstand relatively high inner pressures, for example up to 30 bars, without risk of distortion.

WHAT WE CLAIM IS-: - 1. A heat exchanger including successive rows. of tubes engaged in tube end plates, the end plates being formed by a stack of metal bars, at least one lateral side of each bar having grooves each of which is of a complementary shape to and receives half of the outer cross-section of one of the tubes, adjacent bars being brazed together at least between adjacent tubes of each said row at portions of said lateral sides exclusive of said grooves.

2. A heat exchanger as claimed in claim 1, wherein said portions of said lateral sides constitute support areas for the bars.

3. A heat exchanger as claimed in claim 1, wherein said portions of- said lateral sides have means to assist in their mutual self-centering,upon assembly.

4. A heat exchanger as claimed in claim 3, wherein said means are provided by apertures in said portions, through which apertures pins, wires or rods can be passed to connect the bars together.

5. A heat exchanger as claimed in claim 4, wherein at least a part of each pin, wire or rod that extends into .a respective aperture is formed of brazing material.

6. A heat exchanger as claimed in claim 3, wherein said means are formed by ribs and- complementary recesses on said portions.

7. A heat exchanger as claimed in any one of the preceding claims, wherein each said bar has two of said grooves on each lateral side thereof.

8. A heat exchanger as claimed in any one of the preceding claims, wherein at least one end edge of each bar has a bevelled edge or a groove for housing a corresponding edge of a header tank for the heat exchanger.

9. A heat exchanger as claimed in any one of the preceding claims, wherein at least one of: said bars has- two said grooves, one on each said lateral: side and, between these grooves, a. sl'ot having in cross-section the same shape as that as one of said tubes to receive this tube.

10. A heat exchanger as claimed in any one of the preceding claims, wherein each bar has been formed from a solid element, the or each groove- having been formed by drawing, cutting or grinding said element.

1.1. A heat exchanger as claimed in any one of claims 1 to. 9, wherein each. bar has been- made by stamping a metal sheet or plate that has been folded to define two folds, each of them forming a set of said grooves, the two folds forming a said bar, which is of generally channel-shaped section in end view.

12. A heat exchanger as claimed in any one of claims 1 to 9, wherein each bar is multi-layered, the layers being constituted by plates of basic metal and by sheets of brazing alloy.

13. A heat exchanger as claimed in any one- of the preceding claims, wherein at least said portions of each bar have been roughened to enable brazing alloy to defuse across them by capillary action.

14. A heat exchanger as claimed in any one of the preceding claims, wherein at least the or each groove has been machined in order dimensionally to adjust its shape.

15. A- heat exchanger, substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. for example up to 30 bars, without risk of distortion. WHAT WE CLAIM IS-: -

1. A heat exchanger including successive rows. of tubes engaged in tube end plates, the end plates being formed by a stack of metal bars, at least one lateral side of each bar having grooves each of which is of a complementary shape to and receives half of the outer cross-section of one of the tubes, adjacent bars being brazed together at least between adjacent tubes of each said row at portions of said lateral sides exclusive of said grooves.