EP0278961B1 - Countercurrent heat-exchanger with helical bank of tubes - Google Patents

Abstract

A countercurrent heat-exchanger has several helical banks of tubes (1A, 1B) where a primary fluid flows, and a secondary fluid flows in the opposite direction in helical channels (2A, 2B) formed between the coils of the banks of tubes (1A, 1B). Each bank of tubes (1A, 1B) is composed of ten helical tubes linearly arranged side by side that form the helical channels (2A, 2B) for the secondary fluid between the central tube (9) and the jacket tube (10). The helical tubes are linked at both ends of each bank of tubes (1A, 1B) to one joining chamber (5A, 5B; 6A, 6B) composed of a holed joining plate (16) and of a lid (17). The helical banks of tubes rest freely on helically arranged supporting arms (20) fixed on the central tube (9), distributed on several radial planes and extending up to the jacket tube (10). Strap retainers (21) link the supporting arms (20) on the same radial plane. The helical banks of tubes can be attached for cleaning, and be removed from the jacket tube (10) together with their joining chambers (5A, 5B; 6A, 6B), the closing lid (13), the central tube (9), the primary inlet (3) and the primary outlet (8).

Description

The present invention relates to a counterflow heat exchanger with at least one coil tube bundle and a coil flow channel for the flow of a primary fluid and a secondary fluid in counterflow, the coil tubes at the ends of each tube bundle being connected to a central distributor or central collector for the primary fluid and each tube bundle consisting of coil tubes are wound in a corresponding helical surface with a constant pitch around a common longitudinal axis and are strung together without gaps to form a closed helical flow channel between a core tube and a jacket tube.

The prior art relating to heat exchangers of this type can be explained, for example, by means of the following patent publications: GB-A-791843, FR-A-2482717 and FR-A-2214093.

GB-A-791843 describes a heat exchanger of this type with two tube bundles each consisting of three spiral tubes or one tube bundle consisting of four spiral tubes, which are connected radially to a distribution box and parallel to the longitudinal axis to a collecting box. In the description it is mentioned that the helical tubes are almost in contact, do not have to be in contact with one another, do not form completely tight partition walls and delimit a not completely sealed helical channel. The arrangement described here is unlikely to be intended or suitable for a heat exchanger with a large number of spiral tubes and tube bundles.

Known heat exchangers of the type mentioned at the outset generally have a small number of helical tubes and tube bundles. Connecting the hard-to-reach ends of the helical tubes that are lined up usually requires a significant bending of the tube ends from the corresponding helical surface in order to connect them to a conventional distributor or collector (e.g. by welding or soldering), is intrinsically complicated and becomes significant as the number of tubes increases difficult. Known heat exchangers with a small number of spiral tubes and a correspondingly limited heat exchange surface have a limited range of applications.

In a countercurrent heat exchanger of the type mentioned, the helical tubes are strung together to form practically closed helical surfaces without gaps, in order to form closed helical channels and to ensure operation in the countercurrent flow with optimum efficiency.

The production of such heat exchangers was previously possible at best with a small number of spiral tubes and becomes particularly problematic with an increasing number of tubes in that the connection of the adjacent spiral tubes becomes particularly difficult due to the inaccessibility of the tube ends and is not possible with conventional connections.

The problems in this regard can be explained, among other things, by the fact that coiled tubing cannot be shaped so precisely that they can be strung together without causing tension. When round tubes are touched along the side of a spiral line, tensions have the effect that, in the case of low interference, one spiral tube can slide off the other. The convex tube walls that press against each other are thus in an unstable equilibrium, so that a small deflecting force can bring unsecured spiral tubes out of their correct position.

On the one hand, it is particularly difficult to bend rigid pipes into coils that lie exactly against one another and to connect them in a safe manner to a conventional distributor or collector.

Flexible pipes, on the other hand, are much easier to wind, but must be secured in their desired position in the tube bundle in order to achieve stable spiral tube bundles.

The production of compact countercurrent heat exchangers with as large a number of spiral tubes as possible would be particularly advantageous in order to achieve very large heat exchange surfaces with an optimal efficiency and thus to enable a considerable expansion of the application range of such heat exchangers.

For certain applications, the use of corrosion-resistant materials is also particularly desirable or necessary, and plastic pipes could be particularly suitable for this purpose.

The object of the invention is to provide a heat exchanger of the type mentioned at the outset, which can have a larger number of spiral tubes and can also be produced simply and inexpensively.

This object is achieved according to the invention in that the helical tubes are connected at the ends of each tube bundle to an auxiliary distributor or auxiliary collector which consists of a perforated connection plate which is perpendicular to the corresponding spiral surface and a removable cover for connection to the central distributor or central collector for the primary fluid and is arranged between the core tube and the jacket tube in such a way that the ends of the spiral tubes are connected to the auxiliary distributor or auxiliary collector without substantial deviation from the corresponding spiral surface. This perforated connection plate of each auxiliary distributor or auxiliary collector is in each case provided with staggered bores, the ends of the adjoining helical tubes being accommodated in corresponding staggered bores of the connection plate without substantial deviation from the corresponding helical surface and being firmly connected to the latter.

The terminal plate each he ^f indungsgemäss The auxiliary manifold or auxiliary collector provided is provided with two rows of staggered bores, which run parallel to the corresponding helical surface at a small distance on both sides thereof, the ends of the helical tubes alternately being slightly bent on both sides of this helical surface, then running parallel to this helical surface and are alternately connected to corresponding holes in the two rows.

According to a preferred embodiment of the invention, the heat exchanger is characterized in that each tube bundle consists of flexible helical tubes which rest freely on support arms, these support arms being firmly connected to the core tube and being distributed in the corresponding helix area around the core tube, so that the helical tubes are supported against each other in an immovable position.

The flexible spiral tubes can advantageously be curved and supported in opposite axial directions by the support arms in the corresponding spiral surface.

The spiral tubes and the auxiliary distributors or auxiliary collectors according to the invention can advantageously be made of any suitable plastics, for example Teflon. In this case, the ends of the helical tubes can easily be tightly connected in the corresponding bores of the connection plate by means of a fusion connection. All parts of the heat exchanger can preferably consist of the same plastics, or at least be covered with them, in order to achieve the highest possible resistance of the entire heat exchanger to chemical attacks and thereby to achieve a maximum service life.

The support arms are advantageously provided with teeth for receiving the helical tubes and profiled for stiffening.

These support arms are also advantageously inclined with respect to the common longitudinal axis, preferably alternately in opposite axial directions.

The support arms offset in the corresponding helical surface in the axial direction and in the circumferential direction, which are attached on one side to the core tube and on which all the helical tubes of a tube bundle lie freely and are evenly supported, enable the helical configuration of the entire tube bundle to be maintained.

The support arms perform various functions with regard to the construction of the spiral tube bundles on the core tube, which can be explained as follows. When winding flexible pipes made of plastic or soft metal, the pipes are each tensioned as a result of the required tensile force so that the pipe coils formed one after the other come to lie close together. This tensile force hugs the first or innermost tube coil on the core tube and each additional tube coil on the previous one. This tensile force exerts a radial force on the pipes, which can be broken down into two components, one of which is parallel and the other is directed transversely to the longitudinal axis of the support arm. The component directed parallel to the support arm presses the pipe helix that arises in each case towards the inner, previous coil, and the transverse component presses the pipe helix against the support arm. From a static point of view, each support arm acts as a beam clamped on one side (on the core tube).

It is known that the maximum bending moment of a beam clamped on one side, which lies freely on the other end, is several times smaller than that of the cantilever beam clamped on one side.

If the support arms are to have a relatively large length or range in order to support a correspondingly large number of coils, the outer ends of the support arms can be held by lateral tensioning straps, so that the support arms are supported by these straps and thus stiffened, and that their overall height can be kept correspondingly small.

According to an advantageous embodiment, the support arms are distributed in different radial planes and are connected to one another at their free ends by tensioning straps in each radial plane.

Such tensioning straps are thus advantageously arranged in such a way that on the one hand they keep the distances between the superimposed support arms constant, so that the height or the cross section of the spiral flow channels is kept the same everywhere. On the other hand, the tensioning straps secure the outermost windings, which can be particularly important when moving the spiral tube bundle arrangement relative to the jacket tube.

In order to improve the heat exchange, the heat exchanger according to the invention, in particular when using metallic helical tubes, can be rotatably mounted about its common longitudinal axis and connected to a drive which is designed such that it can set the heat exchanger in an oscillating rotary movement.

The heat transfer in the countercurrent heat exchanger according to the invention with helical tube bundles is increased here in that the entire heat exchanger is rotated back and forth in a constant sequence about its longitudinal axis. The heat transfer between a flowing fluid and a pipe wall is known to be greatest in the start-up section, and depending on the flow conditions in the start-up section it can be many times greater than after a certain section through which flow passes. This phenomenon is exploited here in that the heat exchanger can be rotated back and forth around its longitudinal axis. As a result, the additional speeds of the two liquids with respect to the pipe wall, which overlap the basic currents, constantly swell up and down both in the pipes and outside. Are the additional relative speeds and the basic flow within the same order of magnitude are thereby repeatedly brought about in time with the oscillating rotary movement, hydrodynamic starting conditions which lead to an increase in the heat transfer on the inside and outside of the tube wall.

• Fig. 1 einen schematischen Längschnitt einer Ausführung des Wärmeaustauschers.
• Fig. 2 einen Querschnitt einer Anschlusskammer der Ausführung gemäss Fig. 1.
• Fig. 3 einen Querschnitt einer weiteren Ausführung mit vier Rohrbündeln und Stützarmen.
• Fig. 4 eine teilweise perspektivische Ansicht von Stützarmen auf einem Kernrohr.
• Fig. 5 die Abwicklung eines gemäss Fig. 4 abgestützten Wendelrohrs.
• Fig. 6 einen teilweisen Längschnitt eines mit Spannbändern versehenen Ausführung des Wärmeaustauschers gemäss Fig. 3.
• Fig. 7 eine teilweise perspektivische Ansicht eines Spannbands der Ausführung gemäss Fig. 6.
• Fig. 8 einen teilweisen Längschnitt einer weiteren Ausführung des Wärmeaustauschers mit einer Variante der Stützarme und Spannbänder.

Embodiments of the invention are explained in more detail with reference to the drawing. In it show:

• Fig. 1 is a schematic longitudinal section of an embodiment of the heat exchanger.
• 2 shows a cross section of a connection chamber of the embodiment according to FIG. 1.
• Fig. 3 shows a cross section of a further embodiment with four tube bundles and support arms.
• Fig. 4 is a partial perspective view of support arms on a core tube.
• 5 shows the development of a helical tube supported according to FIG. 4.
• 6 shows a partial longitudinal section of an embodiment of the heat exchanger according to FIG. 3 provided with tensioning straps.
• 7 is a partial perspective view of a strap of the embodiment according to FIG. 6.
• Fig. 8 is a partial longitudinal section of another embodiment of the heat exchanger with a variant of the support arms and straps.

1 shows an embodiment of the heat exchanger with two spiral tube bundles 1A, 1B for the flow of a primary fluid in countercurrent flow with a secondary fluid which flows through two corresponding spiral flow channels 2A, 2B, which are formed between the two parallel spiral tube bundles 1A and 1B.

As indicated by arrows at the top in FIG. 1, the primary fluid is fed from a primary inlet 3 via a central distributor 4 and two auxiliary distributors 5A, 5B to the upper end of the spiral tube bundles 1A, 1B and at its lower end via two auxiliary collectors 6A, 6B, one Central collector 7 and an upper primary outlet 8 discharged.

The auxiliary distributors 5A, 5B and the auxiliary collectors 6A, 6B consist of a two-part connection chamber and are referred to below as the connection chamber.

As can be seen from FIG. 1, the tube bundles 1A, 1B with their corresponding connection chambers 5A, 5B and 6A, 6B are arranged in a closed annular space between a core tube 9 and a coaxial jacket tube 10 with a common longitudinal axis of the heat exchanger. As shown schematically in FIG. 1, each tube bundle 1A, 1B consists of ten helical tubes which are wound around the common longitudinal axis in a corresponding helical plane with a constant pitch and are closely lined up between the core tube 9 and the jacket tube 10.

The heat exchanger housing consists of the casing tube 10 with an outer flange 11, a bottom 12 and an end cover 13, which here consists of one piece with the core tube 9 and is tightly connected to the outer flange 11. Together with the core tube 9, the casing tube 10 and the base 12, this closing cover 13 forms the closed annular space which encloses the tube bundles 1A, 1B with their four connection chambers 5A, 5B, 6A, 6B, a secondary inlet 14 in the base 12 supplying a secondary fluid , which flows through the spiral flow channels 2A, 2B upwards and is discharged through a lateral secondary outlet 15 at the upper end of the casing tube 10.

The structure of the connection chambers 5A, 5B and 6A, 6B is shown in cross-section in FIG. 2 and consists of a perforated connection plate 16 and a removable cover 17 attached thereon with a pipe section 18 which connects the connection chamber to the corresponding central distributor arranged in the core tube 9 4 or central collector 7 connects.

The connection plate 16 of the connection chambers 5A, 5B, 6A, 6B is arranged perpendicular to the corresponding spiral plane and is provided with bores which are offset in two rows to accommodate the ends of the spiral pipes and which run parallel to the spiral plane at a short distance. The ends of the helical tubes lined up in a row are received in the corresponding offset bores of the two rows in the connection plate 16, tightly connected to it and thus connected in parallel to the corresponding connection chamber 5A, 5B or 6A, 6B.

The lid 17 is attached to the connection plate 16 in any suitable way, e.g. tightly connected with screws and sealants.

To connect to the provided connection chambers, the ends of the helical tubes only have to be bent slightly in order to be inserted and fastened alternately in rows of corresponding bores arranged offset in two adjacent planes parallel to the corresponding helical plane in the perforated connection plate 16.

This special arrangement of the connection chambers offers decisive advantages over known pipe connections, which require a significant bending of the pipe ends in order to connect them tightly with a conventional connection plate or the like. The arrangement of the connection chambers thus bypasses the important problems when connecting the tube bundles in a very simple manner, whereby the complicated bending for connecting numerous inaccessible adjacent tubes and any impairment of their strength due to their deformation when bending with an insufficient bending radius are simply avoided.

After loosening the end cover 13 from the outer flange 11, the entire insert, consisting of the end cover 13 with the core tube 9 and the tube bundles 1A, 1B with the connection chambers 5A, 5B and 6A, 6B, the primary inlet 3, the central distributor 4 and the central collector 7 with the primary outlet 8 are pulled out of the jacket tube 10 as a whole.

Thanks to this special arrangement of the spiral tube bundles 1A, 1B with the connection chambers 5A, 5B and 6A, 6B on the core tube 9, the tube bundles can thus be exposed in a particularly simple manner and by suitable means, e.g. with liquid jets or brushes that are inserted laterally, can be cleaned quickly and effectively as required.

This represents a particularly important advantage of the heat exchanger arrangement in that an effective cleaning of the spiral tube bundle is essential in many applications, in particular if the secondary fluid forms a coating on the outer surface of the spiral tubes, which affects the heat exchange more or less quickly.

The embodiment of the heat exchanger described above comprises two helical tube bundles, the number of which can be increased slightly.

In contrast to known heat exchangers of the same type, however, both the number of adjacent spiral tubes of the tube bundle and the number of tube bundles can be increased without any particular difficulty by appropriately equipping the heat exchanger with the connection chambers required in each case.

It is also possible to arrange the connection chambers in several transverse planes as the number of tube bundles increases. with respect to the common longitudinal axis so that any number of tube bundles with the same pitch at both ends thereof can be equipped according to the invention with auxiliary distributors and auxiliary collectors between the core tube and the jacket tube.

If the tube bundles of the heat exchanger consist of tubes with low rigidity, e.g. made of plastic tubes or soft metal tubes, the tube bundles made of flexible tubes are supported by staggered support arms, as shown in FIGS. 3 to 7.

The heat exchanger shown in cross-section in FIG. 3 essentially corresponds to the arrangement described in accordance with FIGS. 1, 2, parts of the same type being identified in all figures with the same reference symbols.

3, however, has four spiral tube bundles 1A to 1D, each with four corresponding auxiliary distributors and auxiliary collectors, each of which corresponds to the described connection chamber according to FIG. 2.

3 shows the four spiral tube bundles 1A to 1D with the four auxiliary distributors or connection chambers 5A to 5D, as well as support arms 20 and tensioning straps 21.

3 to 8, the heat exchanger is equipped with a plurality of support arms 20, each of which supports a coil tube bundle, is fastened to the core tube 9 and is distributed in the coil planes corresponding to the tube bundles, the coil tubes abutting against these support arms 20 and are supported.

It can also be seen from FIGS. 3 and 6 that these support arms 20 extend radially outward from the core tube 9 to the inside of the jacket tube 10, wherein they are held at their free outer end by tensioning straps 21.

The support arms 20 are distributed in different radial planes, so that they are each aligned in corresponding rows parallel to the common longitudinal axis, as can be seen in particular from FIG. 6, the axial distance between the support arms in each row corresponding to the distance between the adjacent turns of the tube bundle and thus determines the axial height of each spiral flow channel.

Fig. 4 shows, for simplification of the drawing, only two helical tube sections and two support arms 20 fastened to the core tube 9, which are arranged in the corresponding helical plane and are slightly inclined outward in opposite directions with respect to the perpendicular to the longitudinal axis. The helical tubes alternately lie freely on opposite sides of the successively arranged support arms 20 and are thereby alternately slightly curved in opposite axial directions.

5 shows the development of a helical tube which is supported in this way by the support arms 20 and is alternately slightly bent. The spiral tubes are braced on the support arms 20 by such a wave-like arrangement and are thus held in their position on each support arm.

6 and 7 show in particular an embodiment of the tensioning straps 21 for holding the support arms 20 at their free ends in the same radial plane and with the required distance, which determines the axial height of the spiral flow channels. These straps 21 each consist of a longitudinal band with a smooth outside, have approximately the same width as the support arms 20 and are folded at regular intervals, which correspond to the required axial height of the spiral flow channels.

These folded tensioning straps 21 thus have a series of parallel inward support surfaces 22 for supporting the corresponding support arms 20, each of which is provided with an incision 23 at its free end. The position of the support arms 20 is secured here with a snap connection, which consists of the incision 23 at the end of each support arm 20 and a corresponding barb 24 which protrudes from the support surface 22 and is provided for hooking into the incision 23. Fig. 7 essentially shows the shape of the tensioning strap 21 and its interaction with a support arm 20. The tensioning straps 21 shown here can e.g. are made from metal strips of 0.2 mm thickness, which due to their folded shape have a high rigidity.

As can be seen from FIGS. 6 and 7, the helical tubes are arranged adjacent to one another on the support arms 20, the outermost windings each being secured in their position at the end of the support arms 20 in that the Barbs 24 of the straps 21 are adapted to be received in the corresponding incisions 23 at the ends of the support arms 20.

The straps 21 secure both the required outer radius of the tube bundle and their exact adaptation to the inner diameter of the casing tube 10, thereby ensuring the required sealing of the spiral flow channels and their constant axial height on the circumference of the tube bundle.

These lateral straps 21 are also used to absorb forces that may act on the outermost pipe windings due to an axial movement of the jacket tube 10 with respect to the tube bundle, especially when the jacket tube is removed for cleaning the tube bundle.

The arrangement of the tensioning straps 20 shown in FIGS. 6 and 7 does not result in a significant reduction in the flow cross-section of the helical flow channels and the outer surface of the helical tube bundle.

8 shows an embodiment with helical tube bundles 1A, 1B, 1C, which bear on both sides on double-flange support arms 120 with crossbars 121.

In this case, each tensioning strap according to FIG. 8 consists of a flat longitudinal strap 122 and is connected to the outermost web of the support arm 120 by suitable fastening means, e.g. inward protruding locking pins which snap into corresponding openings in the outermost web of the double-flanged support arm 120 in order to act as a snap lock.

The side straps can also have any other suitable shape to achieve interaction with the support arms.

The embodiment according to FIG. 8 is particularly suitable for applications which require the heat exchanger to be made of plastic in order to ensure sufficient resistance to corrosive media.

Claims (12)

1. Countercurrent heat exchanger with at least one helical tube bundle (1A, 1 B) and a helical flow channel (2A, 2B) for countercurrent flow of a primary fluid and a secondary fluid, the helical tubes being respectively connected at the ends of each tube bundle to a central distributor (4) and a central collector (7) for the primary fluid and each tube bundle consisting of helical tubes coiled in a corresponding helical surface with constant pitch around a common longitudinal axis and arrayed side by side without interruption so as to form a closed helical flow channel between a core tube (9) and a tubular shell (10), characterized in that:

(a) the helical tubes are connected at the ends of each tube bundle (1A, 1B) to an auxiliary distributor (5A, 5B) or an auxiliary collector (6A, 6B) which is composed of a perforated connecting plate (16) and a removable cover (17) for connection to the central distributor (4) or the central collector (7) for the primary fluid and is arranged between the core tube (9) and the tubular shell (10) in such a manner that the ends of the helical tubes are connected to the auxiliary distributor (5A, 5B) or the auxiliary collector (6A, 6B) without substantial deviation thereof from the corresponding helical surface; and

(b) the perforated connecting plate (16) of each auxiliary distributor (5A, 5B) or auxiliary collector (6A, 6B) is provided with holes in staggered arrangement, the ends of contiguous helical tubes being respectively mounted in corresponding staggered holes of the connecting plate (16) and solidly connected thereto without substantially deviating from the corresponding helical surface.

2. Heat exchanger according to claim 1, characterized in that the connecting plate (16) of each auxiliary distributor or auxiliary collector is provided with two rows of holes in staggered arrangement, which extend parallel to the corresponding helical surface at a short distance on either side thereof, the ends of the helical tubes being alternately slightly bent aside on either side of said helical surface, then extending parallel to said helical surface and being alternately connected in corresponding holes of both rows.

3. Heat exchanger according to claim 1, characterized In that each tube bundle (1A to 1D) is composed of flexible helical tubes which rest freely upon brackets (20), these brackets being solidly attached to the core tube (9) and distributed in the corresponding helical surface around the core tube (9) In such a manner that the helical tubes are immovably supported against each other.

4. Heat exchanger according to claim 3, characterized in that the flexible helical tubes are alternately bent and supported in opposite axial directions by the brackets (20).

5. Heat exchanger according to claim 3, characterized in that the brackets (20) are provided with toothing adapted to receive the helical tubes.

6. Heat exchanger according to claim 3, characterized in that the brackets (20) are toothed for reinforcement.

7. Heat exchanger according to claim 3, characterized in that the brackets (20) are inclined with respect to the common longitudinal axis.

8. Heat exchanger according to claim 7, characterized in that the brackets (20) are alternately inclined in opposite axial directions.

9. Heat exchanger according to claim 3, characterized in that the helical tubes are made of a plastic material.

10. Heat exchanger according to claim 9, characterized in that the auxiliary distributor and the auxiliary collector consist essentially of a plastic material, the ends of the helical tubes being incorporated by fusion bonding in the respective holes of the connecting plate (16).

11. Heat exchanger according to claim 1, characterized in that the entire heat exchanger is mounted for rotation around the common longitudinal axis and is arranged so that it may be subjected to an oscillating movement by drive means.

12. Heat exchanger according to claim 1, characterized in that the brackets are distributed in several radial planes and are mutually connected at their free end with straps (21) in each radial plane.

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