EP4248160B1 - Tube bundle heat exchanger - Google Patents

Description

The invention relates to a tube bundle heat exchanger according to the preamble of claim 1. US 2008/235950 A1 eg discloses such a tube bundle heat exchanger.

Shell-and-tube heat exchangers are used to transfer heat from a first fluid to a second fluid. For this purpose, a shell-and-tube heat exchanger usually has a hollow cylinder inside which a large number of tubes are arranged. One of the two fluids can be passed through the tubes, the other fluid through the hollow cylinder, in particular around the tubes. The tubes are attached by their ends to one or more tube plates of the shell-and-tube heat exchanger along their circumference.

During the manufacturing process of a tube bundle heat exchanger, the tubes are, for example, firmly bonded to the tube sheet at their ends. In general, it is desirable to provide a way to connect tubes of a tube bundle heat exchanger to a tube sheet of the tube bundle heat exchanger in a low-effort and cost-effective manner with high quality.

From the publication WO 2017/ 025 184 A1 A method for connecting tubes of a tube bundle heat exchanger to a tube sheet is described. The tubes and the tube sheet are each made of aluminum or an aluminum alloy and are bonded to the tube sheet by means of laser welding. The intensity of the laser beam generated is over 1 MW/cm2. It is also planned that the tubes of the tube bundle heat exchanger are bonded to the tube sheet before laser welding. be connected in a form-fitting manner.

The tube bundle heat exchanger to be manufactured has, in its finished, operational state, a large number of tubes arranged inside a hollow cylinder. The tube sheet can be designed as a plate and has holes whose diameters essentially correspond to the outside diameters of the tubes. Each tube is attached with one of its ends to one of these holes.

The tubes can run in a straight line within the hollow cylinder as a straight tube heat exchanger. In this case, two tube plates are provided, which are arranged at opposite ends of the straight tube heat exchanger. Each tube is attached at one of its ends to one of these two tube plates.

The tubes can also run in a U-shape within the hollow cylinder as a U-tube heat exchanger. Such a U-tube heat exchanger usually has only one tube plate. Since the tubes are bent in a U-shape in this case, they can each be attached to the same tube plate at both ends.

From the DE 10 2006 031 606 A1 A method for laser welding a heat exchanger for exhaust gas cooling is known, in which a pendulum motion is superimposed on the feed motion of the laser beam. This pendulum motion is essentially perpendicular to the feed direction. The pendulum motion is used to better bridge gaps.

Furthermore, the publication WO 2017/ 125 253 A1 a method for connecting tubes of a tube bundle heat exchanger to a tube sheet is known. The tubes are connected to the tube sheet by means of laser welding bonded together. To create the connection, a laser beam is generated and focused on a spot to be welded in a connection area between the pipe and the tube sheet. The laser beam is moved in such a way that it makes a first movement across the connection area and a second movement superimposed on the first movement, which is different from the first movement. The second movement specifically influences the melt pool dynamics and advantageously modifies a vapor capillary that is formed.

The invention is based on the object of connecting tubes of a tube bundle heat exchanger to a tube sheet reliably and with little effort in high quality.

The invention is represented by the features of claim 1. The further dependent claims relate to advantageous developments and refinements of the invention.

The invention includes a tube bundle heat exchanger with an enveloping outer shell and at least one tube sheet, which together define an interior of the tube bundle heat exchanger. The tube bundle heat exchanger comprises a tube bundle with a plurality of heat exchanger tubes, which are arranged in the interior through which a first fluid can flow and are optionally supported by additional support plates. The heat exchanger tubes have integral ribs formed on the outside of the tube that run helically around the tube, with a rib base, rib flanks and rib tip, and a channel with a channel base is formed between the ribs. The tube bundle heat exchanger comprises at least one inlet on the outer shell, via which a second fluid can be introduced into the interior, and at least one outlet, via which the second fluid can be discharged from the interior. The tube bundle heat exchanger comprises optionally at least one connection box arranged on the at least one tube sheet for distribution, deflection or collection of the first fluid. The at least one tube sheet has recesses as passage points, each recess having an inner surface. The heat exchanger tubes protrude with their outer ribbing at least into the recesses of the tube sheet, whereby a joint gap is formed between the inner surface of a recess and the outer ribbing of a heat exchanger tube located within the recess. The heat exchanger tubes have a material connection with the tube sheet by means of joining material and including the external ribbing, which is formed only in a first partial section of the recess extending from the front side of a heat exchanger tube in the axial direction, in that the joining gap is filled with joining material in this first partial section, so that a second partial section of the recess remains in which the joining gap is not filled with joining material, wherein the heat exchanger tube in the region of the second partial section on the outside of the tube still has external ribbing.

In other words: The heat exchanger tubes have external ribbing within the passage points where they enter or pass through a tube sheet. This external ribbing is enclosed by the material for a material-locking connection, thus hermetically sealing the passage of gas or liquid. For pure material-locking, a combination of force-locking and form-locking can also be used to advantage.

The joining material penetrates in the axial direction only to a certain extent in a first section from the front side into the joint gap, since the outer ribs prevent free passage, as is the case with a smooth tube, for example. The outer ribs therefore form barriers that must be flowed around or melted. Flowing around is particularly important in the joining processes of soldering and gluing. During welding, the outer fins of the heat exchanger tube are partially melted. The melt flow is then preferably stopped at one of the outer fins as soon as the temperature of the melt is no longer sufficient to melt a fin further inside. This barrier stops the melt from penetrating further into the joint gap. In this way, a defined flow process of the joining material is provided during the joining process, which completely closes the joint point at or near the front of the tube.

In addition to the external fins, a heat exchanger tube can optionally have an internal structure. The internal structure can be designed in the form of an internally rotating helix with a predetermined twist angle. In the event that the outside of the heat exchanger tubes has spirally rotating external fins, the pitch of the rotating external fins can be the same, less than or greater than the pitch of the rotating helix specified by the twist angle. The two structures can therefore differ in that the design of the external fins and the internal structure can be designed independently of one another and thus optimized in order to ensure a material bond between the outside of a heat exchanger tube and the vessel wall.

However, to optimize heat exchange, certain limits are imposed on both structures. For example, the ratio of the maximum structural height of the external fins and the maximum structural height of the internal structure is preferably in the range of 1.25 to 5 for condenser tubes and preferably in the range of 0.5 to 2 for evaporator tubes.

Above all, investment costs are to be saved, since the tube bundle heat exchangers according to the invention can be built much more compactly. The external finning continues into the tube sheet, which means that the number of heat exchanger tubes per unit can be significantly reduced. Depending on the requirements, the finned tubes enable more efficient use of energy or the reduction of filling quantities, which reduces operating costs.

The invention is based on the idea that a material-locking connection between the heat exchanger tubes and the tube sheets can be achieved in a particularly reliable and high-quality manner with little effort. According to the invention, a heat exchanger tube with its external ribbing enters the tube sheet or passes through the tube sheet. The external ribbing then remains immediately adjacent to the material-locking connection between the tubes and the tube sheet. This has the particular advantage that the heat exchanger tubes inside the tube bundle heat exchanger have continuous external ribbing for efficient heat transfer.

In an advantageous embodiment of the invention, the first section filled with joining material can be less than 70% of the length of the entire joint gap in the axial direction. The filled first section of the joint gap advantageously comprises only less than 50% of the total length. In particular in the case of welded joints, a filling level of 20% of the first section can be sufficient to produce a fluid-tight, material-tight connection.

Advantageously, the clear width between the fin tips of a heat exchanger tube and the inner surface of the recess can be a maximum of 30% of the fin height measured from the channel base to the fin tip. The barrier effect of the outer fins is increased by this clear width. varies. Particularly with the joining processes of soldering and gluing, the joining material can be introduced in a targeted manner via this clear width of the joining gap to form the filled first section. Another flow channel for the joining material is the channel formed by the integral ribs that are formed in a helical shape. The channel cross-section is, however, determined by the rib height and the distance between adjacent ribs and is usually smaller than the selected clear width.

The material connection can advantageously be designed to be gas-tight and pressure-resistant. In addition to the functions of mechanical stability combined with efficient heat transfer, a hermetic seal is important to prevent fluid exchange with the environment in every operating mode.

In an advantageous embodiment of the invention, the heat exchanger tubes in the passage points have an inner tube diameter D2 which is larger than the inner tube diameter D1 of the heat exchanger tubes outside the passage points.

If the heat exchanger tubes still have external fins within the passage points where they enter or pass through the tube sheet, the process involves an expansion of the heat exchanger tube, resulting in an increased internal passage diameter D2. The expansion then causes the external fins to be squeezed within a passage point. Nevertheless, the material-tight connection ensures a stable hermetic seal.

In an advantageous embodiment of the invention, the heat exchanger tubes can be soldered, glued or welded into the tube sheet.

In addition to the preferred types of connection mentioned above, there may also be others which reliably join the heat exchanger tubes to the tube sheet by means of a material-locking connection.

In principle, the external ribbing on the outside of the heat exchanger tubes can preferably run in the circumferential direction or in the axial direction parallel to the tube axis. In an advantageous embodiment of the invention, the outside of the heat exchanger tubes can have spirally circumferential external ribbing. With spirally circumferential external ribbing, only a residual gap and the channel spirally circumferential with external ribbing must be reliably sealed by the material-locking connection.

Even if a suitable uniform material is generally preferred for the heat exchanger tubes, in an advantageous embodiment of the invention at least one first heat exchanger tube can consist of a first material and at least one second heat exchanger tube can consist of a second material that differs from the first material. With regard to mechanical stability, steel tubes with particularly high strength can offer a particular advantage. Copper tubes, on the other hand, optimize efficient heat transfer. Other materials, such as titanium, aluminum, aluminum alloys and copper-nickel alloys, can also be considered.

Embodiments of the invention are explained in more detail with reference to the schematic drawings.

Fig. 1

schematisch eine Seitenansicht eines Rohrbündelwärmetauschers mit Detailansicht eines Wärmeaustauscherrohrs mit Außenrippen,

Fig. 2

schematisch eine Frontansicht eines Ausschnitts eines Rohrbodens mit Du rchtrittsstelle,

Fig.3

schematisch einen senkrechten Schnitt des Rohrbodens in der Ebene der Durchtrittsstelle der Wärmeaustauscherrohre, und

Fig. 4

schematisch eine Detailansicht eines Schnittes einer stoffschlüssigen Verbindung des Rohrbodens mit einem Wärmeaustauscherrohr.

Showing:

Fig. 1

schematically a side view of a tube bundle heat exchanger with detailed view of a heat exchanger tube with external fins,

Fig. 2

schematically a front view of a section of a tube sheet with passage point,

Fig.3

schematically a vertical section of the tube sheet in the plane of the passage point of the heat exchanger tubes, and

Fig. 4

schematically a detailed view of a section of a material connection of the tube sheet with a heat exchanger tube.

Corresponding parts are provided with the same reference numerals in all figures.

Fig. 1 shows a schematic side view of a tube bundle heat exchanger 1 with an enveloping outer shell 2 and two tube plates 3, which together define an interior 4 of the tube bundle heat exchanger 1. The tube bundle heat exchanger 1 comprises a tube bundle with a large number of heat exchanger tubes 5, which are arranged in the interior 4 and through which a first fluid for heat transfer can flow and are supported by additional support plates 6. Such support plates 6 are often also used as baffles for the fluid flow. The tube bundle heat exchanger 1 also comprises connection boxes 7, which distribute, divert or collect the first fluid inside the heat exchanger tubes as required. There is at least one inlet 8 on the outer shell 2, via which a second fluid for heat transfer can be introduced into the interior, and at least one outlet 9 via which the second fluid can be discharged from the interior. In the detailed view, a heat exchanger tube 5 with outer fins 51 is enlarged. By means of a rolling process which is otherwise known, integral ribs 51 are formed on the outside of the pipe and run helically around the pipe axis A.

Fig. 2 shows schematically a front view of a section of a tube sheet 3 with passages 31. At a passage 31, the recess in the Tube sheet 3 is preferably just large enough for a heat exchanger tube 5 with its external ribbing 51 to be inserted and connected there in a materially bonded manner. Welded, adhesive and soldered connections as a materially bonded connection 20 can be made at the passage point 31, starting from the front side, over a first section of the wall thickness of a tube sheet 3 and form a fluid-tight connection. In a second section reaching into the depth, a Figure 2 not visible, unfilled remainder of the joint gap in the tube sheet wall 3 preserved.

Fig. 3 shows schematically a vertical section of the tube sheet 3 in the plane of the passage point 31 of a heat exchanger tube 5. The heat exchanger tube 5 shown has an external ribbing 51 on the outside. The heat exchanger tube 5 passes through the tube sheet 3 at the recess 31 as a passage point in the illustrated embodiment. At this passage point 31, the heat exchanger tube 5 has a continuous external ribbing 51. A Figure 3 A material-locking connection 20 that has not yet been made, for example in the form of a weld seam with the tube sheet 3 that runs around the circumference of the tube, is located in a section of the joint gap 10 after the joining process. Depending on the material combination of the tube sheet 3 and the heat exchanger tube 5, advantageous new intermetallic phases can form in the melt bath at the weld point 20. Laser welding is a particularly suitable method for producing a material-locking connection with a locally limited melt flow.

Fig. 4 shows schematically a detailed view of a section of a material connection 20 of the tube sheet 3 with a heat exchanger tube 5. In the embodiment shown, the heat exchanger tube 5 is inserted in the direction of the tube axis A into the recess 31 made in the tube sheet 3 and ends with the front side 53 with the outer tube sheet surface.

The heat exchanger tubes 5 have integral ribs 51 formed on the outside of the tube in a helical shape with a rib base 511, rib flanks 512 and rib tip 513. A channel 52 with a channel base 521 is formed between adjacent ribs 51. In Figure 4 a weld seam is shown as a material-locking connection 20, which is formed, for example, during laser welding. If necessary, suitable welding additives are used on the material side during joining. In this way, the material flow and the quantity can be precisely tailored to the desired joint connection. In the material-locking connection shown, due to the process, certain areas of the tube sheet 3 as well as some outer ribs 51 on the heat exchanger tube 5 are at least partially melted by the heat input of a laser and integrated as joining material 20. During joining, the melt enters the joining gap 10 starting from the front side 53, but is blocked after a certain penetration depth, so that only a first front-side section 101 of the joining gap 10 is filled, including the outer ribbing 51. Further passage of the melt is prevented by a rib 51, which is no longer melted or flowed around due to the decreasing temperature at the melt front and thus acts as a barrier. In this way, a defined flow process of the joining material 20 is provided during the joining process, which can completely close the joint point already at or near the pipe front side 53.

The heat exchanger tubes 5 thus have a material connection 20 with the tube sheet 3, which is formed only in a first partial section 101 of the recess 31 extending in the axial direction from the end face 53 of a heat exchanger tube 5. A second partial section 102 of the recess 31 is not filled with joining material. In the second partial section 102, the heat exchanger tube 5 also has an external ribbing 51 on the outside of the tube.

List of reference symbols

1

shell-and-tube heat exchangers

2

outer shell

3

tube sheet

31

recess, passage point

311

inner surface of the recess

4

interior

5

heat exchanger tube

51

integral ribs, external ribs

511

rib foot

512

rib flank

513

rib tip

52

channel

521

canal bottom

53

front side

6

support plate

7

junction box

8

inlet

9

outlet

10

joint gap

101

first section

102

second section

20

material-locking connection, joining material

A

pipe axis, axial direction

D1, D2

pipe inner diameter

Arrow

fluid flow

Claims (6)

1. Tube bundle heat exchanger (1) having a surrounding outer covering (2) and at least one tube base (3) which together define an inner space (4) of the tube bundle heat exchanger (1), comprising

   - a tube bundle having a large number of heat exchange tubes (5) which in a state arranged in the inner space (4) can be flowed through by a first fluid and are optionally supported by additional metal support sheets (6),
   wherein the heat exchange tubes (5) have integral ribs (51) which are formed on the outer side of the tube and which extend in a helical line and which have a rib base (511), rib flanks (512) and a rib tip (513) and between the ribs (51) a channel (52) having a channel base (521) is formed,

   - on the outer covering (2) at least one inlet (8), via which a second fluid can be introduced into the inner space (4), and at least one outlet (9), via which the second fluid can be discharged from the inner space (4),

   - optionally at least one connection box (7) which is arranged on the at least one tube base (3) for distributing, redirecting or collecting the first fluid,

   wherein the at least one tube base (3) has recesses (31) as passage locations, wherein each recess (31) has an inner surface (311),

   characterised in that

   - the heat exchange tubes (5) at least protrude with the outer ribbing (51) thereof into the recesses (31) of the tube base (3), whereby a joint gap (10) is formed in each case between the inner surface (311) of a recess (31) and the outer ribbing (51), which is located inside the recess (31), of a heat exchange tube (5),

   - in that the heat exchange tubes (5) by means of joining material (20) and incorporating the outer ribbing (51) have a materially engaging connection (20) to the tube base (3), which is formed only in a first part-portion (101), which extends from the front face (53) of a heat exchange tube (5) in an axial direction (A), of the recess (31) by the joint gap (10) being filled with joining material (20) in this first part-portion (101) so that a second part-portion (102), in which the joint gap (10) is not filled with joining material, of the recess (31) remains, wherein the heat exchange tube (5) in the region of the second part-portion (102) at the outer tube side further has an outer ribbing (51) .
2. Tube bundle heat exchanger (1) according to claim 1, characterised in that the first part-portion (101) which is filled with the joining material (20) in an axial direction (A) is less than 70% of the length of the entire joint gap (10) .
3. Tube bundle heat exchanger (1) according to claim 1 or 2, characterised in that the clear width between the rib tips (513) of a heat exchange tube (5) and the inner surface (311) of the recess (31) is a maximum of 30% of the rib height measured from the channel base (521) up to the rib tip (513).
4. Tube bundle heat exchanger (1) according to any one of claims 1 to 3, characterised in that the materially engaging connection (20) is configured to be gas-tight and pressure-resistant.
5. Tube bundle heat exchanger (1) according to any one of claims 1 to 4, characterised in that the heat exchange tubes (5) have in the recesses as passage locations (31) a tube inner diameter D2 which is greater than the tube inner diameter D1 of the heat exchange tubes (5) outside the passage locations (31).
6. Tube bundle heat exchanger (1) according to any one of claims 1 to 5, characterised in that the heat exchange tubes (5) are soldered, adhesively bonded or welded in the tube base (3).

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