SHELL AND TUBE HEAT EXCHANGER, FINNED TUBES FOR SUCH HEAT EXCHANGER AND CORRESPONDING METHOD

Abstract

A shell and tube longitudinal flow heat exchanger comprising a containment casing 101 within which a first fluid can flow substantially parallel to the longitudinal axis of said casing 101, said containment casing 101 accommodating in its interior a bundle of tubes 2 substantially parallel to one another and parallel to the longitudinal axis of said casing 101 and a plurality of grid-shaped baffles 102 substantially transverse to the longitudinal axis of said casing 101 supporting said tubes 2, a second fluid flowing in said bundle of tubes 2. Said tubes 2 are provided on at least a part of their outside surface with a plurality of low fins 21, which are helically arranged on the outer surface of said tubes 2 with a first angle of advancement and having a profile interrupted by helical grooves 22 having a second angle of advancement , with .

Claims

1. A shell and tube longitudinal flow heat exchanger comprising a containment casing within which a first fluid can flow substantially parallel to the longitudinal axis of said casing, said containment casing accommodating in its interior a bundle of tubes substantially parallel to one another and parallel to the longitudinal axis of said casing and a plurality of grid-shaped baffles substantially transverse to the longitudinal axis of said casing supporting said tubes, said bundle of tubes being adapted to the flow of a second fluid therein, characterized in that said tubes are provided on at least a part of their outside surface with a plurality of low fins, said low fins being helically arranged on the outer surface of said tubes with a first angle of advancement and having a profile interrupted by helical grooves having a second helical angle of advancement , with .

2. A shell and tube longitudinal flow heat exchanger according to claim 1, characterized in that said low fins have a height H between 0.5 and 1.5 mm.

3. A shell and tube longitudinal flow heat exchanger according to claim 1, characterized in that said first advance angle is 2045.

4. A shell and tube longitudinal flow heat exchanger according to claim 1, characterized in that the relative angle between said first angle of advancement and said second angle of advancement is between 30 and 60.

5. A shell and tube longitudinal flow heat exchanger according to claim 1, characterized in that said tubes are provided on their internal surface of a plurality of low fins.

6. A shell and tube longitudinal flow heat exchanger according to claim 1, characterized in that said tubes are provided with finned portions alternated by smooth portions.

7. A method for manufacturing a finned tube using a machine comprising a working assembly and at least one support assembly, said first working assembly comprising a first rotating finning tool and a second rotating finning tool mounted in sequence on the same driving axis, said first rotating finning tool being provided with a first helical working profile having a first angle of advancement at and said second rotating finning tool being provided with a second helical working profile having a second angle of advancement .sub.2, with .sub.2.sub.1, the method comprising advancing said tube on a plane defined by said support assembly, forming a first fin on said tube by means of said first rotating finning tool, forming a second fin on said tube by means of said second rotating finning tool, the formation of said second fin being immediately subsequent to the formation of said first fin, the height of said first fin being lower than the height of said second fin.

8. A method for manufacturing a finned tube according to claim 7, characterized in that the relative angle between said first angle of advancement at and said second angle of advancement .sub.2 is between 30 and 60, and in that the height h of said first fin is 0.5 mm, and the height H of said second fin is 2 mm.

9. A finned tube for heat exchangers, in particular for a shell and tube heat exchanger, obtained by a method for manufacturing the finned tube using a machine comprising a working assembly and at least one support assembly, said first working assembly comprising a first rotating finning tool and a second rotating finning tool mounted in sequence on the same driving axis, said first rotating finning tool being provided with a first helical working profile having a first angle of advancement at and said second rotating finning tool being provided with a second helical working profile having a second angle of advancement .sub.2, with .sub.2.sub.1, the method comprising advancing said tube on a plane defined by said support assembly, forming a first fin on said tube by means of said first rotating finning tool, forming a second fin on said tube by means of said second rotating finning tool, the formation of said second fin being immediately subsequent to the formation of said first fin, the height of said first fin being lower than the height of said second fin.

10. A finned tube for heat exchangers according to claim 9, characterized in that it is provided on at least a part of its outside surface with a plurality of low fins, said low fins being helically arranged on the outer surface of said tube with a first angle of advancement and having a profile interrupted by helical grooves having a second helical angle of advancement , with , said first angle of advancement being 1560, the relative angle between said first angle of advancement and said second angle of advancement being between 30 and 60, said low fins having a height H between 0.5 and 1.5 mm.

Description

[0043] Further characteristics and advantages of the present invention will be more apparent from the description of preferred, but not exclusive, embodiments of a shell and tube longitudinal flow heat exchanger according to the present invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

[0044] FIG. 1 shows a perspective view of a shell and tube longitudinal flow heat exchanger:

[0045] FIG. 2 shows a schematic view of a shell and tube longitudinal flow heat exchanger:

[0046] FIG. 3 shows a schematic view of a shell and tube tortuous flow heat exchanger:

[0047] FIG. 4 shows a schematic view of a shell and tube helical flow heat exchanger;

[0048] FIG. 5 shows a portion of finned tube that can be used in a shell and tube longitudinal flow heat exchanger according to the present invention:

[0049] FIG. 6a schematically shows the helical trend of the fins of a finned tube that can be used in a shell and tube longitudinal flow heat exchanger according to the present invention;

[0050] FIG. 6b schematically shows the helical trend of the grooves that interrupt the profile of the fins of a finned tube that can be used in a shell and tube longitudinal flow heat exchanger according to the present invention;

[0051] FIGS. 7a-7c show sections of alternative profiles of fins of a finned tube that can be used in a shell and tube longitudinal flow heat exchanger according to the present invention;

[0052] FIG. 8 shows a portion of finned tube with finned portions alternated by smooth portions that can be used in a shell and tube longitudinal flow heat exchanger according to the present invention;

[0053] FIG. 9 is a schematic side view of a first embodiment of a machine for implementing the method for manufacturing finned tubes according to the present invention;

[0054] FIG. 10 is a schematic front view of the machine of FIG. 9;

[0055] FIG. 11a schematically illustrates the formation of a first fin/groove on a tube with the method for manufacturing finned tubes according to the present invention;

[0056] FIG. 11b schematically illustrates the formation of a second (main) fin on a tube with the method for manufacturing finned tubes according to the present invention:

[0057] FIG. 12 is schematic side view of a second embodiment of a machine for implementing the method for manufacturing finned tubes according to the present invention:

[0058] FIG. 13 is a schematic front view of the machine of FIG. 12;

[0059] FIG. 14 shows a schematic view of a shell and tube longitudinal flow heat exchanger according to the present invention;

[0060] FIG. 15 shows a detail of the shell and tube longitudinal flow heat exchanger of FIG. 14.

[0061] With reference to the appended figures, a shell and tube longitudinal flow heat exchanger of EMBaffle type comprises, in its more general embodiment, a containment casing 101 within which a first fluid can flow substantially parallel to the longitudinal axis of said casing 101. Inside the containment casing 101 there is positioned a bundle of tubes 2, which are substantially parallel to one another and parallel to the longitudinal axis of the casing 101; the casing 101 also contains a plurality of grid-shaped baffles 102 transverse to the longitudinal axis of said casing 101, said baffles 102 supporting said tubes 2.

[0062] With particular reference to FIG. 14, a second fluid flows inside the tubes 2, generally in counterflow (see arrows 210) to the direction of flow of the first fluid inside the shell 101 (see arrows 110).

[0063] With reference to FIG. 7, one of the peculiar characteristics of the shell and tube longitudinal flow heat exchanger 1 according to the present invention is given by the fact that said tubes 2 are provided on at least a part of their outer surface with a plurality of low fins 21 that are helically arranged on the outer surface of said tube 2 according to a first angle of advancement . This angle of advancement is generally less than 80, and preferably between 15 and 60, more preferably between 20 and 45.

[0064] A further peculiar characteristic of the shell and tube longitudinal flow heat exchanger 1 according to the present invention is given by the fact that the low fins 21 have a profile interrupted by helical grooves 22 having a second angle of advancement , with .

[0065] To illustrate the characteristics of the tube 2 more clearly, in FIGS. 6a and 6b the fins and the grooves have been schematically represented separately. Also with reference to FIG. 11a, a first machining phase of the tube 2 allows the base of the tube to be lowered (by an amount h) and raised (by the same amount h) so as to produce a corrugated profile having helical fins 22 and corresponding helical grooves with angle of advancement , as shown in FIG. 6b. The height h with respect to the base profile is preferably less than 0.5 mm.

[0066] With reference now to FIG. 11b, a second machining phase of the tube 2 allows the final fin 21 to be obtained by lowering (by an amount H) and raising (by the same amount H) the corrugated profile of the tube 2 of FIG. 11a according to a helical machining operation with angle of advancement (see FIG. 6a).

[0067] The final structure of the fin 21, in terms of height and of number of interruptions, will thus depend on the composition of the two deformations, in particular on the amounts h and H, and on the angles and . When the relative angle between and is close to 0 the maximum increase in the height of the fin 21 will be obtained, while when it is close to 90 the maximum number of interruptions on the profile of the fin 21 due to the grooves 22 will be obtained.

[0068] With regard to the shape of the fin 21, this can be chosen at will according to needs. FIGS. 7a-7c show some possible sections of the fin 21, without being in any way limited to these embodiments.

[0069] With reference to FIG. 8, in a preferred embodiment of the shell and tube longitudinal flow heat exchanger 1 according to the present invention, the tubes 2 are provided with finned portions 20 alternated by smooth portions 200. In this way, also with reference to FIG. 15, stable positioning of the baffle 102 will be facilitated.

[0070] With reference to FIGS. 9 and 10, there will now be described a first embodiment of a method for manufacturing a finned tube 2 provided on at least one part of its outer surface with a plurality of low fins 21. These fins 21 are helically arranged on said outer surface with a first angle of advancement and have a profile interrupted by helical grooves 22 having a second angle of advancement .

[0071] The method according to the invention is carried out using a machine 3 comprising a working assembly 30 and at least one support assembly 40. The first working assembly 30 comprises a first rotating finning/grooving tool 32 and a second rotating finning tool 31 mounted in sequence on the same driving axis 33. The support assembly 40 comprises two smooth surface cylindrical guides 34 and 36, the purpose of which is to maintain the tube 2 in position during machining, supporting the thrust load of the working assembly 30.

[0072] The first rotating finning/grooving tool 32 is provided with a first helical working profile symmetrical to the helical grooves 22 to be generated on the outer surface of the tube 2 and that has a first angle of advancement .sub.1.

[0073] The second rotating finning tool 31 is provided with a second helical working profile symmetrical to the low fins 21 to be generated on the outer surface of the tube 2 and that has a second angle of advancement .sub.2, with .sub.2.sub.1.

[0074] The method according to the invention comprises advancing the tube 2 on a plane defined by the support assembly 40 and forming a first fin/groove 22 on said tube 2 by means of the first rotating tool 32. Advantageously, the fin/groove 22 has a depth preferably 0.5 mm to limit hardening of the material.

[0075] Immediately after the first fin/groove 22 has been formed, a second fin 21 (main fin) is formed on said tube 2 by means of said second rotating finning tool 31. The height of said second main fin 21 is greater than the height of said first fin 22, even if it is normally less than 2 mm.

[0076] As explained above, depending on the relative angle between said first angle of advancement .sub.1 and said second angle of advancement .sub.2 it is possible to obtain a greater or lesser height of the main fin 21 and a greater or lesser number of its interruptions by the groove 22.

[0077] With reference to FIGS. 12 and 13, in a second embodiment of a method for manufacturing a finned tube 2 according to the present invention, a plurality of low fins are formed both on its outer surface and on its internal surface.

[0078] In this case, the method according to the invention is carried out using a machine 5 comprising a first working assembly 50 and a support assembly 70, similar to the first working assembly 30 and to the support assembly 40 described previously. With regard to the outer part of the tube 2, machining takes place in the same manner as described previously.

[0079] The machine 5 also comprises a second working assembly that is adapted to produce the internal fins of the tube 2. The internal fin is obtained by means of a finning tool 61 with profile symmetrical to what is to be obtained on the internal surface of the tube 2. The tool 61 is inserted into the tube and is actuated by the pressure exerted by the first 32 and second 31 rotating tool on the tube 2 resting on the smooth surface cylindrical guides 71 and 72 of the support assembly 70. This causes a reduction in the internal diameter of the tube 2, which is thus finned by the internal tool 61.

[0080] The internal fin has a wrap angle contrary to that of the external fin 21 so as to prevent the external or internal tool from binding. Angle of advancement, height of fin and density of fins on the internal part are obtainable in the ranges known in the state of the art.

[0081] In brief, the method described uses two profiled tools for external (or external and internal) cold forming of a tube made of low or high alloy steel. This configuration allows high productivity, preventing the otherwise frequent risks of damage/breakage of the tools and reducing to a minimum the complexity of the mechanical apparatus employed. It is also suitable for machining alloy steels, such as copper-nickel, stainless, duplex, titanium steels, which are critical for many alternative methods, as known from the state of the art.

[0082] Based on the description above, it has been seen how the method for manufacturing a finned tube, a finned tube thus obtained, and a heat exchanger, in particular a shell and tube longitudinal flow heat exchanger according to the present invention, achieve the intended aims and objects.

[0083] On the basis of the description provided, other characteristics, modifications or improvements are possible and evident to a person skilled in the art. These characteristics, modifications and improvements should therefore be considered part of the present invention.

[0084] In practice, the materials used, the dimensions and contingent shapes can be any according to requirements and to the state of the art.