DE29516927U1 - Pipe for heat exchangers with vortex-generating current disturbance elements - Google Patents

Description

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SGL TECHNIK GMBH D-86405 Meitingen

Tube for heat exchanger with vortex-generating flow disturbance elements

Description

The invention relates to a tube for tube bundles of heat exchangers with elements located inside the tube that generate turbulence in the flow in the tube.

It is known to improve the heat transfer between fluids and the walls that delimit them by increasing the flow velocity or by generating turbulence in the flow. Such turbulence is achieved by vortex-generating flow disturbance elements. Previously known pipes of this type basically have profiles on the inner surface of the pipe in the form of corrugations, projections, ribs or the like.

The arrangement of vortex-generating flow disturbance elements on the inner surface of the tubes becomes problematic when the individual tube of the heat exchanger is made of a material whose wall cannot be deformed in the conventional way. This applies in particular to tubes that have to be manufactured using the extrusion process. For this purpose, DE-OS 35 21 914 discloses the arrangement of webs in the individual tube that do not completely penetrate the tube and are shaped in a wave-like manner. However, such a shape is only conceivable in the extrusion process for light metal, especially aluminum, where it is possible to produce such wavy webs by appropriately designing the recipient.

However, this known method cannot be used where the material of the pipe cannot be deformed in the known manner by extrusion or another method. This is particularly the case with pipes made of metallic materials such as titanium, high-alloy steels, nickel-based alloys or pipes made of silicon carbide and graphite. Heat exchangers with graphite pipes are preferably used for heat exchange between liquids, vapors or gases that require a chemically resistant pipe material.

The invention is based on the object of designing tubes for use in the tube bundles of tube bundle heat exchangers in such a way that they have elements inside them that generate vortices and/or increase the flow rate and disrupt the fluid flow, without the deformability of the tube material being important. In particular, the invention is intended to make it possible to produce tubes made of materials that are difficult to deform, in particular tubes made of graphite, which have improved heat transfer performance.

The problem is solved according to the characterizing part of claim 1 in that the inner wall of the tube is free of elevations and depressions that influence the fluid flow in the tube and in the interior of the tube there is a strand whose outer surface is provided with profiles that generate turbulence in the fluid flow and that between the outer circumference of this strand and the inner surface of the heat exchanger tube there is a space for a fluid to flow through the heat exchanger tube.

The subordinate claims represent embodiments of the invention and applications of the inventive solution

They are hereby introduced into the descriptive part.

The measures according to claim 1 generate turbulence in the flow passing through the pipe using the simplest of means. At the same time, the flow speed in the pipe can be increased. Both measures, generating turbulence and increasing the flow speed in the pipes, each lead to an improvement in the heat transfer performance of the pipes. If both measures are applied simultaneously, the heat transfer performance is correspondingly higher. To achieve the effects described, all that is required is to insert a suitably profiled strand into the pipe. Since this measure is not linked to the pipe production, heat exchanger pipes can be equipped with the strands according to the invention at any time during their operational existence. Both new systems and systems that have already been in operation can be equipped with them. The latter option is particularly advantageous for adapting existing heat exchangers to changed operating conditions. But even when designing new systems, the designer is often confronted with constraints that he can use the invention to an advantage in order to circumvent. If, for example, he is limited to a certain heat exchange surface for spatial reasons, which cannot provide the required or necessary exchange performance with normal pipes, he can now resort to the solution according to the invention and increase the performance in a simple way. If necessary, the performance can be reduced again at a later point in time by removing all or part of the strands and adapted to other conditions. From this example it is easy to deduce that

With the means of the invention, while keeping the heat exchange performance constant, the dimensions of heat exchangers can also be reduced in comparison to conventional heat exchangers by using the performance gain achieved by applying the inventive measure to reduce the length of the tubes used or to reduce their number in the heat exchanger. In the first case, the exchanger becomes shorter, in the other, slimmer. In some cases, the process design results in tubes with very small internal diameters being required. Such tubes cannot be manufactured at an economically viable cost for production reasons and/or because of their high fragility if they are made of silicon carbide or carbon or graphite, for example. The invention now makes it possible to also advance into the field of application of such pipes, which are difficult to manufacture and practically unusable, by using larger, mechanically more stable pipes that can be manufactured with reasonable effort and by modifying these by using strands according to the invention so that they fully correspond to the technical range of action of the smaller pipes.

The invention is applicable to all types of tubes for heat exchangers that allow the introduction of strands according to the invention.

However, the invention is of particular importance for heat exchangers through which liquid, gaseous or vaporous materials must be passed, which require chemically resistant material for the tubes. For such heat exchangers, tubes made of special, difficult-to-process metallic materials such as titanium, titanium-palladium alloys, high-

alloyed steels or nickel-based alloys or ceramics such as silicon carbide and in particular graphite. A special feature of these materials, and here especially graphite, is that they cannot be provided with vortex-generating flow disturbance elements in the extrusion production process. Pipes made of these materials are essentially smooth pipes on the inside. If the strands according to the invention, which have profiles on the outer circumference, are used in such pipes, the advantage of the resistant material is combined with the improvement in heat transfer performance.

The profiles with which the strands inserted into the pipes are provided can have a variety of shapes. They only have to ensure that laminar flows are converted into turbulent and slightly turbulent flows into more turbulent flows. The following surface designs of the strands are examples: various thread-like shapes, ribs, knobs, spikes and, as the preferred shape, waves. Other shapes that can be used include strips twisted into snail-like structures, e.g. made of sheet metal, plastic or a fiber-reinforced composite material, the wings of which can also be perforated, or hollow or solid bodies arranged one behind the other in the form of a "string of pearls", for example made of glass, ceramic, plastic or carbon, which are either bonded to one another or can be arranged one behind the other using a wire or a strand made of fibers or wires, such as a cord. The strands can be hollow inside or made of solid material. If hollow strands are used, they are preferably closed on at least one side to prevent the formation of a second

To prevent a flow line in the pipe and to prevent fluid from the heat exchanger from accumulating or remaining in the strand. Where this makes sense, both ends of the hollow strand can be closed. However, if this is advantageous, it is also possible to leave the ends open. Preferably, commercially available, relatively inexpensive corrugated pipes are used as hollow strands. The hollow strands can be filled either partially or completely with a suitable material. For example, the part of the strand pointing downwards in the heat exchanger can contain a filling that simply weighs it down to tighten the hanging strand and prevent it from moving too much back and forth, or the interior of the strand is completely foamed with a specifically light material to give the strand good longitudinal stability with an overall low weight.

A particularly preferred solution to the problem is to use U-shaped strands, for example corrugated pipes bent into a U-shape. The legs of such a U-shaped strand are inserted into two adjacent pipes of the heat exchanger and the part connecting the legs naturally remains outside the exchanger pipes. Here, the ends do not need to be closed if the U-shaped strands are arranged so that their openings point in the direction of gravity, so that any process medium that has entered the interior of the strands can flow out again. In this way, a heat exchanger can be equipped with the strands according to the invention using the simplest means and without great effort.

The strands are attached to the heat exchanger tubes using simple, well-known means such as

hangers or webs attached to the pipe ends or pins passed through the string ends which rest on the pipe ends.

In order to facilitate the flow of the respective fluids exchanging heat in the heat exchangers into the heat exchanger tubes equipped with the strands according to the invention, according to another advantageous variant, the heat exchanger tubes or the flow channels aligned with the tube ends of these tubes in the upper and lower tube sheets of the tube bundles in which these tubes are installed can have conical or wedge-shaped extensions at the inflow end. This measure is particularly recommended when using U-shaped strands on the side of the U-shaped connection of the legs. However, it is not a requirement. Where this appears advantageous, such extensions can also be attached to the outflow side of the tube bundles.

The material from which the strands according to the invention are made depends on the conditions of use, especially on the medium to which the strands are exposed and on the intended operating temperature. The expert selects the appropriate material in each case based on his knowledge. Some of the materials that can be considered are, by way of example and without any limitation: metal, plastic, rubber, wood, ceramic, carbon. Of the plastics, polypropylene (PP) or polyvinyl chloride (PVC) are preferred for media that are less aggressive. In more aggressive media and at higher application temperatures, strands made of fluorine-containing polymers such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-perfluoropropylene copolymer (FEP) or copolymers of tetrafluoroethylene with

Perfluoroalkyl vinyl ether (PFA) is used. The range of carbon materials is not limited to non-graphitic and graphitic carbon. Parts made of carbon fiber-reinforced carbon or carbon fiber-reinforced plastic can also be used.

The outer diameter of the strand is preferably one third to eight tenths of the inner diameter of the heat exchanger tube surrounding it. These dimensional ratios have proven to be effective in heat exchangers for aggressive chemical media, in which the exchanger tubes are made of graphite and the strands are made of plastic. However, the invention is not limited to these dimensional ratios. If necessary, deviations can be made from them.

In cases where the strand must be arranged in a stable position within the pipe, it is recommended that the strand be supported in places on the smooth inner wall of the pipe. In general, this can be achieved by supporting the strand on the inner wall of the exchanger pipe using known means such as webs. When selecting and arranging the support elements, care should only be taken to ensure that the flow in the annular gap is not significantly impaired. According to a preferred procedure, support is achieved when the strand passes through the pipe in a spiral shape. This spiral shape is created with flexible material by twisting the strand, for example in the form of a corrugated pipe, around its axis when inserting it into the pipe or by locking it after insertion at the opposite end of the pipe or tube base, then twisting it, compressing it slightly and then inserting it at the other end of the pipe or tube base.

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tube sheet is also determined. In this way, the strand is supported on the inner surface of the tube.

In the following, the effectiveness of the invention is demonstrated by an embodiment:

All heat exchanger tubes of an industrially applicable partial pressure condenser equipped with fluid-tight graphite tubes, 32 mm outer diameter and 22 mm inner diameter were equipped with commercially available corrugated tubes made of polytetrafluoroethylene bent in a U-shape as shown in Fig. 2, the largest diameter of which, measured at the corrugation, was 16 mm and the smallest diameter of which, measured at the outer wall of the tube, i.e. at the bottom of the corrugation, was 14 mm. The heat transfer performance of the partial pressure condenser was measured under the same product and with the same coolant (water), once without built-in turbulence-generating strands and once with such strands:

Operating conditions/measurement results:

- Test without strands in the pipes, product mass flow: 6066 kg/h

Temperature of the product at the device inlet: 123.75 "C Temperature of the product at the device outlet: 37.4 "C Mass flow of cooling water: 147 m ³ /n Temperature of the cooling water at the device inlet: 21 "C Temperature of the cooling water at the device outlet: 26 °C

- Test with strands in the pipes: Mass flow product: 11058 kg/h

Temperature of the product at the device inlet: 123.60 ⁰ C Temperature of the product at the device outlet: 39 ⁰ C

Cooling water mass flow: 51

Temperature of cooling water at the device inlet: 20 ⁰ C Temperature of cooling water at the device outlet: 39 "C

A comparison of the amounts of heat transferred per unit of time in the two tests shows that 1.32 times more heat was transferred with the solution according to the invention than with the apparatus without strands in the heat exchanger tubes. The increase in heat transfer performance is achieved with a cooling water quantity reduced to approx. 1/3 and an increase in product throughput by almost double.

The invention is further explained by way of example in the following figures using schematic representations.

Show it:

Fig. 1: A partial longitudinal section through a tube bundle heat exchanger which shows a tube arrangement according to the invention.

Fig. 2: A partial longitudinal section through a tube bundle heat exchanger, with a U-shaped strand inserted into adjacent heat exchanger tubes.

Fig. 3: A top view of the front side of a head plate of the tube bundle of a heat exchanger, whose exchanger tubes are equipped with U-shaped strands.

Fig. 4: A partial longitudinal section through the tube bundle of a heat exchanger at the location of an exchanger tube with a filled hollow strand.

Figs. 5, 6 and 7:

Various embodiments of strands according to the invention.

Fig. 8, 8a, 8b, 8c:

A heat exchanger tube in which a strand is attached and fixed along a helical line to the tube wall.

The partial longitudinal section according to Fig. 1 shows a tube 1 of the tube bundle of a tube bundle heat exchanger, the parts of which come into contact with the product, with the exception of the strand inserted into the tubes 1, are made of tantalum.

The tantalum tube 1, which is smooth on its surface due to the manufacturing process, is welded into the upper tube plate 2 and lower tube plate 3 of the tube bundle, which are only shown in outline. The extruded body 4 is a tube made of FEP in the form of a tube that is closed at its upper end 5 by squeezing and/or welding and has a thread-like profile 6 on its outer surface. The extruded body 4 is open at its lower end 9. The extruded body 4, which causes the turbulence and reduces the fluid-accessible internal cross section 7 of the heat exchanger tube 1, is held both at the upper tube plate and at the lower tube plate 3 of the tube bundle by means of a pin 8, 8 ¹ guided through the extruded body 4, which is supported on the upper 2 and the lower tube plate 3. It is possible to hold the extruded body 4 under a certain longitudinal tension by means of these locking devices 8, 8 ¹ in order to adapt it to elements that disrupt the flow during operation.

To prevent back and forth movements. Fig. 1a, which shows a view of the upper part of Fig. 1 rotated by 90°, shows that the locking of the strand 4 is effected by a pin 8. The fluid passing through the heat exchanger flows from bottom to top through the heat exchanger, as the arrows in Figs. 1 and 1a indicate. According to a preferred embodiment, the largest external diameter a of the strand 4 is 1/3 to 8/10 of the internal diameter b of the heat exchanger tube 1.

Fig. 2 shows a variant of the invention in which the legs 10, 10' of a U-shaped corrugated pipe 11 are located in adjacent pipes 1, 1' of a heat exchanger. The elevations 12 and depressions 12' on the surface of the strand 4, which cause the turbulence in the flow in the pipes 1, run in a spiral shape. The parts of the heat exchanger that come into contact with the product, of which only the upper tube plate 2 and two pipes 1, 1» of the tube bundle are shown in detail here, consist of graphite impregnated with a synthetic resin, with the exception of the strand bodies 4. The graphite tubes 1, 1· are glued 16 into the upper tube plate 2 and into the lower tube plate of the tube bundle (not shown). The threaded pipes forming the strand bodies 4 are made of polypropylene. In the heat exchanger, which is only partially shown here, the product flow runs from top to bottom through the tubes 1, 1·, as the arrows indicate. On the inlet side 15, 15' of the product flow into the tubes 1, ¹ · there is a cross-section 14, 14' which widens, for example conically, against the direction of flow in order to facilitate the flow of the product fluid into the tubes 1, ^1· . The figure shows that the strands 4 in this arrangement in the heat exchanger tubes 1, ^1·

are always closed at their upper end, the inflow side 15, 15' into the exchanger tubes 1, 1'. No product can enter them. At their lower end, not visible here, the strands 4 can be either open or closed. They can also be fixed or not, for example, at the lower tube sheet. It is easy to see that the U-shaped design also offers considerable advantages during assembly.

In the plan view shown in Fig. 3 of the upper tube sheet 2 of a tube bundle of a heat exchanger according to the invention, in which the tubes 1 are equipped with U-shaped strands 4, the inflow openings 15, 15' of the heat exchanger tubes 1 and the U-shaped ends of the strands 4, each extending over two adjacent tubes 1, ¹¹ , can be seen. The tube ¹¹¹ is a plugged blind tube. However, it could also be provided with a corrugated tube 4 according to Fig. 1.

In Fig. 4, the upper 2 and lower tube plate 3 of a tube bundle are shown, into which (2, 3) an exchanger tube 1 is glued (16). The parts of the exchanger that come into contact with the product, with the exception of the extruded body 4, are again made of fluid-tight graphite. The tubular extruded body 4, which is closed at its upper 5 and lower 9 ends, consists of a rubber-like copolymer of vinylidene fluoride with hexafluoropropylene, which is commercially available under the brand ^iton. Its surface has a large number of knobs 13 in order to produce the desired turbulence in the flow in the tube 1. The extruded body 4 is suspended at its upper end 5 by a welded-in PTFE pin 8 that passes through it on the top of the upper tube plate 2 of the tube bundle. In its lower part, the extruded body 4 contains a specific gravity

Mass 17, for example silicon dioxide, barite or chips of a corrosion-resistant alloy bonded with a synthetic resin, in order to tighten it and to protect it against undesirable and uncontrollable movements in the flow. The interior of the strand 4 could also be foamed with a plastic 19 in addition to or without the weighting filling in order to give the strand longitudinal rigidity.

Figures 5, 6 and 7 show some further examples of embodiments of strands according to the invention.

Fig. 5 shows a section of a heat exchanger tube 1, which contains a hollow strand 4 in the form of a corrugated tube, on the surface of which elevations 12 and depressions 12' are arranged in alternating sequence, which run concentrically around the longitudinal axis of the tube.

Fig. 6 is intended to illustrate a strand 4 which has the shape of a strip twisted into the form of a snail and which consists, for example, of polyvinyl chloride or a sheet of stainless steel.

Fig. 7 shows a strand insert 4 which, similar to a string of pearls, consists of geometric bodies, preferably round bodies, which are arranged one behind the other in the longitudinal direction. In the present case, balls made of non-graphitic carbon are held one behind the other by means of a strand made of carbon fibers and arranged in a heat exchanger tube 1 made of apparatus construction graphite.

Fig. 8 shows in conjunction with Figures 8a, 8b and 8c a possibility of inserting a strand 4 made of a sufficiently flexible material in the heat exchanger surrounding it.

tube 1 to keep it in a stable position. The support is achieved here by twisting the strand 4 around its longitudinal axis after it has been inserted into the exchanger tube 1 and, if necessary, after the strand 4 has been secured at the lower end of the tube 1, with slight compression, in such a way that it takes on the shape of a spiral and lies along a spiral-shaped contact line on the inner wall 18 of the exchanger tube 1 and is thus supported against movements possibly caused by the flow. Of course, the strand 4 twisted in this way must be secured against turning back at its upper and lower ends (not shown) in the exchanger tube 1 or at the upper and lower tube bottoms of the tube bundle (also not shown).

List of reference symbols

1, 1', 1" tubes of the tube bundle of a heat exchanger

2 upper tube sheet/head plate of the tube bundle

3 lower tube sheet of the tube bundle

4 strand bodies/strand

5 upper end of the strand body (4)

6 thread-like profile of the extruded body (4)

7 Internal cross-section of the pipe (1)

8, 8 ¹ pins for holding the strand (4) 9 lower end of the strand body (4)

10, 10· Legs of the U-shaped corrugated pipe

11 U-shaped corrugated pipe

12 surveys J

V on the surface of the corrugated pipe 12' recesses j

13 studs on strand body (4)

14, 14' expanding cross section

15, 15' Inlet side of the heat exchanger tubes

16 Bonding the graphite tubes into a tube sheet of the tube bundle

17 specific gravity filling in the strand body (4)

18 Inner wall of the pipe (1)

19 Filling in (4) made of foamed plastic

Claims (12)

P rotective claims 1. Tube for tube bundles of heat exchangers with elements located inside the tube that generate turbulence in the flow in the tube, characterized in that the inner wall of the pipe (1) is free of elevations and depressions that affect the fluid flow in the pipe (1) and in the interior of the tube (1) there is a strand (4) whose outer surface is provided with profiles (6, 12, 12', 13) that generate turbulence in the fluid flow and that between the outer circumference (a) of this strand (4) and the inner surface (18) of the heat exchanger tube (1) there is a space for a fluid to flow through the heat exchanger tube (1). 2. Pipe (1) according to claim 1,
characterized in that the strand (4) is designed as a corrugated pipe closed on at least one side. 3. Pipe (1) according to claim 1 or 2, characterized in that the strand (4) has a U-shape (11), the legs (10, 10') of the U of the strand (4) are located in two adjacent tubes (1, ¹ ) of a heat exchanger and the bend of the U connecting the legs (10, 10') is arranged outside the tubes (1). 4. Pipe (1) according to one of claims 1 to 3, characterized in that the strand (4) consists of a material from the group thermoplastic, thermosetting plastic, elastomer, carbon, carbon fiber reinforced carbon, carbon fiber reinforced plastic, ceramic, metal, wood. 5. Pipe (l) according to one of claims 1 to 3, characterized in that the strand (4) consists of a material from the group polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride. 6. Pipe (1) according to one of claims 1 to 5, characterized in that the pipe (1) has, at at least one of its ends or at the holes aligned with the pipe (1) in the upper (2) and/or lower tube plate (3) of the tube bundle, a cross-section (14, 14") which widens outwards and increases the flow cross-section. 7. Pipe (l) according to one of claims 1 to 6, characterized in that the largest external diameter (a) of the strand (4) is 1/3 to 8/10 of the internal diameter (b) of the heat exchanger tube (1). 8. Pipe (1) according to one of claims 1 to 7, characterized in that the strand (4) is supported on the pipe inner wall (18). 9. Pipe (1) according to one of claims 1 to 8, characterized in that the strand (4) passes through the pipe (1) in a spiral shape. 10. Pipe (1) according to one of claims 1 to 9, characterized in that when using a hollow strand (4), the hollow space of the strand (4) is at least partially filled. 11. Pipe (1) according to claim 10, characterized in that the cavity of the strand (4) is filled with at least one solidified mass. 12. Pipe (1) according to one of claims 1 to 11, characterized in that the pipe (1) consists of graphite.