Process for producing heat exchanger tubes and heat exchanger tubes

Abstract

A process for making heat exchanger tubes comprises the operating steps of cutting a piece of sheet, subjecting the piece of sheet (3) to a forming step to obtain a plurality of first elements (8, 9) which mirror one another, and bending the piece of sheet (3) to create a tubular element (1) which has two flat walls (4) with the raised elements (8, 9) on them, the flat walls being opposite one another and joined by two connecting walls (5), and; the bending step substantially joining the lateral edges (7) to one another; and welding the lateral edges (7) to close the tubular element (1). The first raised elements (8) having an extended shape according to their main direction of extension. Those of the rows closest to the central axis (X) are made in such a way that their main direction of extension is set at an angle to the central axis (X) and to a direction perpendicular to it, while those of the rows closest to the lateral edges (7) are made in such a way that their main direction of extension is set at an angle to the central axis (X) and to a direction perpendicular to it, on the opposite side relative to the first raised elements (8) of the rows closest to the axis (X). The claims also relate to a tube obtained in this way.

Description

TECHNICAL FIELD

The present invention relates to a process for making heat exchanger tubes, as well as heat exchanger tubes of the type in which a plurality of tubes carrying a first fluid are positioned parallel with one another in a chamber in which a second fluid flows. In particular, the present invention is intended for shell and tube heat exchangers made of stainless steel with limited thickness.

In particular, the present invention is intended to be applied to heat exchangers in whose tubes exhaust gases pass, for example from engines, and around which a coolant fluid flows.

BACKGROUND ART

At present, this type of heat exchanger has several problems relative to heat exchange efficiency. Firstly, the current multi-tube heat exchangers cannot guarantee the correct flow of the fluid around all of the tubes. Secondly, there may be thermal gradients between the various tubes which have a negative effect on the general efficiency of the heat exchange.

It should also be noticed that no type of existing tube, if used in a heat exchanger, is able to overcome said problems.

DISCLOSURE OF THE INVENTION

The technical purpose which forms the basis of the present invention is to provide a process for making heat exchanger tubes which overcomes the above-mentioned disadvantages.

In particular, the technical purpose of the present invention is to provide a process for making heat exchanger tubes which allows tubes to be made which guarantee optimum heat exchange.

The technical purpose specified and the aims indicated are substantially achieved by a process for making heat exchanger tubes and by a heat exchanger tube as described in the claims herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention are more apparent in the detailed description below, with reference to several preferred, non-limiting embodiments of a process for making heat exchanger tubes, illustrated in the accompanying drawings, in which:

FIGS. 1 to 5 illustrate, in a plan view, a sequence of operating steps for making the tube in accordance with the present invention;

FIGS. 1 a to 5a illustrate, in an elevated side view, the sequence of operating steps of FIGS. 1 to 5;

FIG. 6 is an enlarged view of the detail VI of FIG. 5a;

FIG. 7 shows a detail of FIG. 2;

FIG. 8 shows the detail of FIG. 7 according to the cross-section VIII-VIII;

FIG. 9 illustrates another detail of FIG. 2;

FIG. 10 shows the detail of FIG. 9 according to the cross-section X-X;

FIG. 11 is a central lateral section of a heat exchanger made with tubes made in accordance with the present invention;

FIG. 12 is an enlarged view of the detail XII-XII of FIG. 11;

FIG. 13 illustrates, in a plan view, a sequence of operating steps for making the tube in accordance with an alternative embodiment of the present invention; and

FIG. 14 illustrates, in a plan view, a sequence of operating steps for making the tube in accordance with another alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference to the accompanying drawings, the numeral 1 denotes as a whole a tube for heat exchangers 2.

In particular, in the embodiment illustrated, the tube 1 consists of a single bent and shaped sheet 3, having two flat walls 4, opposite one another and joined by two connecting walls 5. Each flat wall 4 has a plurality of formed raised elements 8, 9, designed, in practice, as described in more detail below, to space out and maintain in contact with one another two adjacent tubes 1, as well as, in particular first raised elements 8, for suitably conveying and slowing the motion of the fluid to optimise heat exchange. The bent sheet 3 is welded, preferably at the front end, along its lateral edges 7 at one of the connecting walls 5.

In more detail, each flat wall 4 has on its outer face four longitudinal rows of first raised elements 8, parallel with a tube 1 central axis (usually there are at least two).

The first raised elements 8 positioned on a flat wall 4 equal in number and mirror those positioned on the other flat wall, relative to a plane of symmetry passing through the longitudinal central axis of the tube 1 and parallel with the flat walls 4.

As FIGS. 7 and 8 show more clearly (illustrating an enlarged first raised element 8), each first raised element 8 has a flat upper face 8a, having an extended preferably elliptical shape, and designed to connect with a first raised element 8 of an adjacent tube 1 (FIG. 12).

With reference to FIGS. 4 and 5, it should be noticed that the main directions of extension (greater axis of the ellipse they form) of the upper faces 8a of the first raised elements 8 of the rows closest to a first connecting wall 5a are set at an angle to the longitudinal direction of the tube 1 and to a direction perpendicular to it. In turn, the main directions of extension of the upper faces 8a of the first raised elements 8 of the rows closest to the second connecting wall 5b, are set at an angle both to the longitudinal direction of the tube 1 and to a direction perpendicular to it, but on the opposite side relative to upper faces 8a of the raised elements 8 of the rows closest to the first connecting wall 5a.

There are also other embodiments (FIG. 13 and FIG. 14) in which the first raised elements 8 of one or more central rows are positioned with their main direction of extension parallel with or perpendicular to the longitudinal direction of the tube 1 (for example, embodiments in which on each flat wall 4 there are three rows of first raised elements 8).

Each flat wall 4 preferably has at least one second raised element 9 higher than the first raised element 8 (FIGS. 9 and 10). At the same time, advantageously, the portion 10 of a flat wall 4 which, relative to a plane of symmetry passing through the central axis of the tube and parallel with the flat walls 4, mirrors a second raised element 9 positioned on the other flat wall 4, is made smooth and without any type of raised element (FIGS. 2 and 3).

The second raised element 9 preferably projects from its flat wall 4, by a height equal to the sum of the projections of the pairs of first raised elements 8 so as to make contact with the respective portion 10 of a flat wall 4 belonging to an adjacent tube (FIG. 12).

When the tubes are mounted in a shell and tube heat exchanger, in accordance with the present invention each tube 1 is in contact with the tubes adjacent to it, and in particular the first raised elements 8 of one tube 1 rest against the first raised elements 8 of the tubes adjacent to it, and the second raised elements 9 of one tube are in contact with the flat portions 10 of the tubes adjacent to it (FIG. 12).

As regards the process for obtaining tubes 1 which is the subject matter of the present invention, in accordance with a preferred embodiment, the tube 1 is obtained by means of an initial step in which a substantially rectangular piece of sheet 3 is cut, preferably from a stainless steel plate between 0.1 and 1 mm thick, preferably 0.4 mm.

The sheet 3 has a first main face 11a, and a second main face 11b, a front edge 12, a rear edge 13 and two lateral edges 7 (FIGS. 1 and 1a).

Then, the piece of sheet 3 is subjected to a forming step to obtain a plurality of elements 8, 9 raised relative to the second face 11b (FIGS. 2 and 2a).

The step of forming the raised elements 8, 9 is only carried out at zones of the sheet 3 designed to constitute the flat walls 4.

In detail, the forming step involves the creation of two groups of raised elements 8, 9 positioned respectively in two longitudinal bands of the piece of sheet 3, positioned so that they mirror one another relative to a central axis X of the piece of sheet 3 parallel with the lateral walls 7 (FIGS. 2 and 3).

At least two longitudinal rows of the first raised elements 8 are made on each longitudinal band, parallel with the central axis X.

In this way, the first raised elements 8 are positioned in such a way that they mirror one another relative to the central axis X of the piece of sheet 3.

Therefore, as described above, the first raised elements 8 of the rows closest to the central axis X are made in such a way that their main direction of extension (greater axis of the ellipse formed by their upper face 8a) is set at an angle to the central axis X and to a direction perpendicular to it. In turn, the first raised elements 8 of the rows closest to the lateral edges 7 are made in such a way that their main direction of extension is set at an angle to the central axis X and to a direction perpendicular to it, on the opposite side relative to the first raised elements 8 of the rows closest to the axis X.

In some cases, when each flat wall 4 has three or more parallel rows of first raised elements 8, those of the central rows of each longitudinal band of the piece of sheet 3 may instead be made in such a way that their main direction of extension is parallel with or perpendicular to the central axis X, to create, with the adjacent elements, channels for the fluid which, in practice, will envelope the tubes 1. In particular, if the central elements are parallel with the central axis X, said channels will converge from the periphery to the centre of the tube which they will then follow longitudinally (similarly to what happens in the case illustrated in the accompanying drawings). In contrast, if the elements are positioned perpendicularly, the channels will pass across the tube 1 transversally.

The forming step may also involve the production of at least one second raised element 9 as described above.

The forming step is followed by a step of bending the piece of sheet 3 parallel with the lateral edges 7, to create a tubular element whose outer surface consists of the second face 11b and which has two flat walls 4 opposite one another and joined by the connecting walls 5.

This bending step is preferably carried out by placing the lateral edges 7 opposite one another in such a way that the first and second faces 11a, 11b at one lateral edge 7, form a continuation respectively of the first and second faces 11a, 11b at the other lateral edge 7.

In more detail, the bending step involves a first sub-step of partly bending the piece of sheet 3 at the lateral edges 7 so that, when the bending step is complete, the two portions bent in this way form one of the connecting walls 5 of the tubular element 1 (FIGS. 3 and 3a).

Advantageously, the first partial bending sub-step is carried out simultaneously with the step of forming the raised elements 8, 9.

Then a second partial bending sub-step is carried out, partly bending the piece of sheet 3 around a template 14 positioned at an intermediate portion of the first face 11a equidistant from the lateral edges 7 (FIGS. 4 and 4a).

After the partial bending sub-step, there is a template 14 removal sub-step and a bending completion sub-step during which the lateral edges 7 are placed opposite one another (FIGS. 5 and 5a) and the tubular element is gauged.

Finally, the front end lateral edges 7 are welded, preferably with laser welding, to close the tubular element 1 (FIG. 6).

The present invention brings important advantages.

The tubes disclosed guarantee optimum heat exchange thanks to the angled arrangement of the first, outer raised elements, which create channels for the fluid and suitably guide and slow its flow.

Moreover, thanks to the contact between the tubes guaranteed by the raised elements, there is an equalisation of the temperature in the tube bundle which guarantees improved heat exchange compared with conventional exchangers.

It should also be noticed that the present invention is relatively easy to produce and even the cost linked to implementation of the invention is not very high.

The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

All details of the invention may be substituted by other technically equivalent elements and, in practice, all of the materials used, as well as the shapes and dimensions of the various components, may be any according to requirements.

Claims

1. A process for making heat exchanger tubes, characterised in that it comprises the operating steps of: cutting a substantially rectangular piece of sheet which has a first main face (11a), a second main face (11b), a front edge (12), a rear edge (13) and two lateral edges (7);subjecting the piece of sheet (3) to a forming step to obtain a plurality of first elements (8, 9) raised relative to the second face (11b), positioned in such a way that they mirror one another relative to a central axis (X) of the piece of sheet (3) parallel with the lateral edges (7), and each having an upper face (8a) with an extended shape in a main direction of extension;bending the piece of sheet (3) parallel with the lateral edges (7), to create a tubular element (1) whose outer surface consists of the second face (11b) and which has two flat walls (4) with the raised elements on them and opposite one another, joined by two connecting walls (5); the bending step substantially connecting the lateral edges (7) to one another; andwelding the lateral edges (7) to close the tubular element (1);wherein during the forming step at least four rows of first raised elements are produced parallel with the central axis (X);the first raised elements (8) of the rows closest to the central axis (X) being made in such a way that their main direction of extension is set at an angle to the central axis (X) and to a direction perpendicular to it; andthe first raised elements (8) of the rows closest to the lateral edges (7) being made in such a way that their main direction of extension is set at an angle to the central axis (X) and to a direction perpendicular to it, on the opposite side relative to the first raised elements (8) of the rows closest to the axis (X), and wherein the forming step involves making one or more higher second raised elements (9).

2. The process according to claim 1, characterised in that the forming step involves forming the first raised elements (8, 9) only at zones of the piece of sheet (3) designed to constitute the flat walls (4) after the bending step.

3. The process according to claim 2, characterised in that the forming step involves forming two groups of first raised elements (8, 9) positioned respectively in two longitudinal bands of the piece of sheet (3), mirroring one another relative to the central axis (X) of the piece of sheet (3).

4. The process according to claim 3, characterised in that the forming step involves making, for each longitudinal band, at least three longitudinal rows of first raised elements (8) parallel with the central axis (X).

5. The process according to claim 4, characterised in that the step of forming the raised elements (8, 9) is carried out in such a way that the sum of projections, relative to the second face (11b), of each pair of first raised elements (8) which mirror one another relative to the central axis (X), is the same.

6. The process according to claim 1, characterised in that during the forming step each first raised element (8) is made with a flat upper face (8a).

7. The process according to claim 6, characterised in that each first raised element (8) is made with an elliptical upper face (8a).

8. The process according to claim 4, characterised in that the first raised elements (8) of the central rows of each longitudinal band of the piece of sheet (3) are made in such a way that their main direction of extension is substantially parallel with or perpendicular to the central axis (X).

9. The process according to claim 1, characterised in that the second raised element (9) is made in such a way that the second face (11b) is flat at its zones which, relative to the central axis (X), mirror the second raised elements.

10. The process according to claim 5, characterised in that the second raised element (9) is made in such a way that the second face (11b) is flat at its zones which, relative to the central axis (X), mirror the second raised elements, and in that the second raised element (9) is made with a projection equal to the sum of the projections of the pairs of first raised elements (8).

11. The process according to claim 1, characterised in that the bending step is carried out in such a way that, at one lateral edge (7), the first and second faces (11a, 11b) form a continuation, respectively, of the first and second faces (11a, 11b) at the other lateral edge (7).

12. The process according to claim 1, characterised in that the welding step is carried out by welding the front end of the lateral edges (7).

13. The process according to claim 1, characterised in that the welding step is carried out by laser welding.

14. The process according to claim 1, characterised in that the bending step involves several sub-steps one after another.

15. The process according to claim 14, characterised in that the bending step comprises a first sub-step of partly bending the piece of sheet (3) at the lateral edges (7) so that, when the bending step is complete, the two portions bent in this way form one of the connecting walls (5) of the tubular element (1).

16. The process according to claim 15, characterised in that the first partial bending sub-step is carried out by forming, simultaneously or not with the step of forming the raised elements (8, 9).

17. The process according to claim 14, characterised in that the bending step comprises a second partial bending sub-step obtained by partly bending the piece of sheet (3) about a template (14) positioned at an intermediate portion of the first face (11a) between the lateral edges (7).

18. The process according to claim 17, characterised in that the template (14) is positioned at a portion of the first face (11a) equidistant from the lateral edges (7).

19. The process according to claim 17, characterised in that the bending step involves, after the partial bending sub-step, a template (14) removal sub-step and a bending completion sub-step during which the lateral edges (7) are placed opposite one another.

20. The process according to claim 19, characterised in that the bending completion sub-step also involves gauging of the tubular element (1).

21. The process according to claim 1, characterised in that the piece of sheet (3) is cut from a steel plate between 0.1 and 1 mm thick.

22. The process according to claim 1, wherein the piece of sheet (3) is cut from a steel plate 0.4 mm thick.