EP0015915B1 - Device for heat exchange and manufacturing process thereof - Google Patents

Abstract

The devices (1) for heat exchange intended for a temperature range of 0-200 C comprise pipes (3) which form windings or coils. The adjacent pipes are jointed together by means of a metal coasting so as to form a tight wall (4). A heat exchanger liquid, preferably water, circulates through the pipes (3). To increase the heat exchanging surface, the wall (4), which is in contact with a gas, comprises heat conductive grooves (5).

Description

The invention relates to a heat exchanger system with at least two heat exchanger elements, each of which has at least one tube bent in one plane or in a cylinder surface for a first medium involved in the heat transfer, with adjacent sections of the tube or the tubes in each case forming a sealed heat exchanger element heat transfer wall are connected.

In a known heat exchanger system of this type (DE-A-2237430). which is to serve in particular as a steam generator in nuclear power plants, the adjacent pipe sections for forming the dense wall are welded to one another directly or via webs in order to avoid pipe vibrations and to facilitate the suspension of the heat exchanger elements. These advantages come into their own especially at high temperatures.

If such a heat transfer system is to be operated at moderate temperatures in the range of 0-200 ° C, it is relatively expensive, in particular if the second medium covering the wall has a relatively poor heat transfer and possible corrosive properties.

The invention is based on the object, starting from the heat exchanger system according to DE-A-22 37 430, to provide a heat exchanger system which can be operated at moderate temperatures in the range from 0 to 200.degree. C. and which enables a compact construction which is on the side of the second medium has a very large heat transfer surface and thus ensures a large heat transfer and which is inexpensive to produce.

According to the invention, this object is achieved in that the wall is formed by a metallic cast body that tightly envelops the sections of the tube or tubes, the heat-conducting projections, the surface of which is a multiple of the tube inner surface that they account for, preferably ribs that run approximately parallel to one another , and that at least two heat exchanger elements are arranged relative to one another in such a way that at least one closed channel, into which the projections protrude, is formed for a second medium involved in the heat transfer. This design results in a smaller, more compact heat exchanger system, which has the additional advantage that, in the case of corrosive properties of the second medium, the pipe material is protected from corrosion attacks by the cast body. This also ensures that the two media always remain separate.

From GB-A-987739 it is known to connect two parallel steel pipes to one another by means of a cast body, the casting mold being designed in such a way that casting fins extending transversely to the pipes are formed during casting. The heat exchanger elements thus formed are e.g. used as an economizer in steam generators, the steel pipes being protected against corrosion by the cast body. The cast body obviously has no supporting function here.

FR-A-1 031 374 describes a heat exchanger intended for a hot gas piston engine, in which a plurality of pipes through which liquid flows and each bent into a loop are distributed in a circular ring, each pipe loop lying in a radial plane of the ring. All pipes are enclosed in a uniform cast body that has slit-shaped channels that run parallel to the pipe loops and are open on the inside of the circular ring without projections. The channels are closed by a special sleeve that lies against the inner circumference of the circular ring. This known heat exchanger takes up a lot of space and is expensive to manufacture.

Since there are no heat exchanger elements consisting of a tube and a cast body encasing this, which would have to be brought together to form a heat exchanger system, the known heat exchanger could not be a model for the invention, because its design is closely related to the requirements of a hot gas piston engine.

If the heat exchanger system is to have the shape of a cuboid, this is best achieved by the tube or tubes of each heat exchanger element running in a serpentine or meandering manner in a single plane. If the supply and discharge lines have circular or annular connection cross sections, the heat exchanger elements are expediently designed in such a way that the pipe or the pipes run along helical lines on a single, fictitious pipe cylinder. Such a design also has particular advantages if the second medium has a pressure which differs greatly from the atmospheric pressure, because then each heat exchanger element forms a load-bearing wall with its cast body because of the coiled tube. If a high flow velocity is provided to improve the heat transfer on the side of the second medium, it can be advantageous in the case of a circular cylindrical design of the heat exchanger elements to design the projections as radially projecting ribs which run essentially in the axial direction of the tubular cylinder. In this way, the total pressure drop can be kept relatively small.

If, on the other hand, the volume flow of the second medium is relatively small, and for example for reasons of pollution, the flow cross sections for the second medium cannot be arbitrary reduce, the projections are advantageously designed as radially projecting ribs, essentially extending along helical lines.

In order to keep the temperature difference on the cast material of the heat exchanger as small and uniform as possible, the protrusions can preferably be formed as turns in the case of pipes wound according to helical lines, which rise in the opposite sense to the turns of the pipes. A significant improvement in the heat transfer on the side of the second medium can be achieved in that the projections have a tree-like branched cross section, the passage area for the heat flow decreasing with increasing distance from the base of the projection.

The heat exchangers can be produced in a particularly simple manner by a method according to the invention in that the tube of each heat exchanger element is bent and placed in a casting mold, the mold is poured out with a metal and the projections are machined out of the cast body, and that at least two heat exchanger elements are added be connected to a heat exchanger system.

In order to reduce the machining work, it can be expedient according to another method that the tube of each heat exchanger element is bent and placed in a casting mold, that the mold is poured out with a metal and the casting body is machined in such a way that recesses for anchoring the rib-like parts forming the projections Parts are created which are caulked, soldered or welded into these recesses and that at least two heat exchanger elements are connected to form a heat exchanger system.

In the mass production of heat exchangers, savings can be achieved by a further process in that the tube of each heat exchanger element is bent and inserted together with the rib-like parts forming the projections into the casting mold, which is poured out with metal in such a way that the rib-like parts exclusively with their Foot are enclosed in the cast body, and that at least two heat exchanger elements are connected to form a heat exchanger system.

The invention will now be explained in more detail using some exemplary embodiments shown schematically in the drawing.

Figure 1 shows a longitudinal section through a box-shaped heat exchanger system with several flat heat exchanger elements.

Figure 2 shows a cross section 11-11 through the heat exchanger system of FIG. 1.

Figure 3 is a cross section through a heat exchanger system with two concentrically arranged, circular cylindrical heat exchanger elements.

FIG. 4 shows, on an enlarged scale, a longitudinal section IV-IV of the heat transfer system according to FIG. 3.

FIG. 5 is, analogously to FIG. 3, a cross section through a modified heat exchanger system with two concentrically arranged heat exchanger elements.

FIG. 6 shows a longitudinal section of a variant of FIG. 5.

FIG. 7 shows a longitudinal section through a heat exchanger system with a plurality of heat exchanger elements, in each of which a tube is arranged after a spiral.

FIG. 8 is a horizontal section through a heat transfer element in the levels VIII _1, VII ₂ and Vii1 ₃ of FIG. 7.

Figure 9 illustrates the cross section through two ribs with branches.

Figure 10 shows a cross section of another embodiment of branched ribs and their mutual arrangement.

Figures 11 and 12 each represent a cross section through further branched ribs.

FIG. 13 shows a cross section through part of a circular cylindrical heat exchanger element with simple ribs which run along helical lines.

Figure 14 shows the development of a cylinder with helical, interrupted ribs.

In the exemplary embodiment according to FIGS. 1 and 2, several flat heat exchanger elements 1, of which only two are shown in FIG. 2, are combined to form a box-shaped heat exchanger system 2. Each of the heat exchanger elements consists of a tube 3 which is bent back and forth in a vertical plane. The adjacent sections of each tube 3 are each cast with an aluminum body 4, the two side faces of which have cast-in projections 5 in the form of ribs and are parallel to the bending plane. The outermost ribs 5 'of each element 1 are somewhat longer than the other ribs and are each connected by a weld 6 to an abutting rib 5' of an adjacent heat exchanger element, as a result of which the aforementioned box shape and channels closed between these elements are created. In the case of the heat exchanger elements located at the two ends of the heat exchanger system 2, an end plate 8 is welded on the free side, which extends over the entire outer ribbed surface of the respective heat exchanger element. At the upper end of each end plate 8 there is a funnel wall 9 and two funnel surfaces 10 and 11 are welded onto the two transverse edges of the heat exchanger elements which are formed by the upper ends of the ribs 5 '. A discharge line for the second medium is connected to the funnel thus formed, which is not apparent from the drawing. An identical funnel with a feed line for the second medium is located at the lower end of the heat exchanger system 2.

The tubes 3 emerge laterally from the top and bottom of the heat transfer system 2 and end Flanges 13. The flanges 13 are connected to flanges of pipe sockets 14, the upper of which open into a distributor 15 and the lower, not shown in the drawing, into a collector. The distributor 15 and the collector are divided by bellows 17 because of the thermal expansion differences between them on the one hand and the cast aluminum body 4 on the other.

In operation, the channels between the two end plates 8 and their adjacent heat exchanger elements 1 and the channels between adjacent heat exchanger elements 1 are flowed through from bottom to top by the second, heat-emitting, gaseous medium. Water flows through the pipes 3 as the first medium from top to bottom, which comes from the distributor 15 and reaches the collector (not shown). The large heat transfer surface formed by the fins 5 compensates for the relatively poor heat transfer coefficient of the gas, so that the temperature difference between the heat-emitting gas and the heat-absorbing surface of the fins 5 remains relatively small. The fins 5 are wedge-shaped, so that the increased heat flow in the region of the fin nozzle can flow to the pipe 3 with a relatively low temperature drop. Since the water flowing in the pipe 3 ensures good heat transfer, there are also no high temperature differences on the water side.

In the exemplary embodiment according to FIGS. 3 and 4, tubes 3a and 3b are wound according to helical lines. Each tube coil formed in this way is encased by an aluminum body 4a or 4b and forms a circular cylindrical heat exchanger element 1a or 1b. The heat exchanger element 1 a has radial longitudinal ribs 5 on its inside, while its outside is smooth. In addition to the normal fins 5, the heat exchanger element 1b has a greatly widened fin 23, in which a pipe section 24 connected to the upper end of the coiled tubing runs downwards in an axially parallel manner. Below the heat exchanger system, the pipe section 24 leads outwards, piercing a funnel wall (not shown).

In operation, a gas flows through the highly jagged ring channel delimited by the surfaces of the ribs 5 between the two heat exchanger elements 1a and 1b, while a liquid flows through the two tubes 3a and 3b, which are preferably connected in parallel. 5, ribs 5 are also arranged on the inside of the heat exchanger element 1b. The flow channel for the gas is delimited on the inside by a circular-cylindrical displacer 25. Likewise, the heat exchanger element 1 a could also be provided with ribs on the outside and surrounded by a circular cylindrical jacket. The exemplary embodiment according to FIG. 6 differs from that according to FIG. 5 in that the inner heat exchanger element 1b has two coils 3c and 3d, both of which open at their upper end into a common collecting tube 26, which is surrounded by an aluminum cast body 27, through the wall of a funnel 28 leads and finally ends outdoors with a flange 29. The upper end of the tube coil 3a leaves the heat exchanger element 1a outside the funnel 28 and is provided with a flange 29 '.

In the exemplary embodiment according to FIGS. 7 and 8, five heat exchanger elements are designed as circular, cast disks 4f to 4k and are arranged coaxially one above the other, within which tubes 3f ... 3k which are bent according to spirals run. The fins 5 are each perpendicular to the plane of the tubes and are bent according to involutes.

The heat exchanger elements are surrounded on the outside by a cylindrical jacket 130, which is tightly connected to the cast bodies 4f, 4h and 4k by flat ring plates 31, 32 and 33.

On the inside of the heat exchanger elements, two shut-off disks 35 and 36 are arranged in the bore of the cast bodies 4g and 4i.

On the second uppermost cast body 4g (FIG. 8), the involute-shaped ribs 5, if they are followed in the counter-clockwise direction, on the top of the element (section VIII ₁ ) from the outside inwards and on the underside from the inside out (section VIII ₃ ). The uppermost cast body 4f has ribs only on its underside, which run like those on the top of the adjacent pane 4g. The cast body 4i is designed in the same way as 4g, while the intermediate cast body 4h has ribs that run in reverse: on the top, always referring to the counterclockwise direction, they lead from the inside to the outside and on the bottom from the outside to the inside. The lowermost cast body 4k only carries ribs on its upper side, which run from the inside to the outside.

This rib arrangement ensures that the gaseous medium, which enters the stack of heat exchanger elements centrally from below through the inlet 50 of the heat exchanger system, flows outward in the channel between the mutually facing ribs 5 of the cast bodies 4i and 4k, through the lower one Annulus 42 between the cast body 4i and the jacket 30, rotating further in the counterclockwise direction, rises and flows inward in the counterclockwise direction through the channel between the cast bodies 4h and 4i. Continuously rotating in the same direction, it flows outwards into the upper annular space 42 'in the channel between the cast bodies 4g and 4h and finally, flowing inward via the channel between the cast bodies 4f and 4g, reaches the outlet opening 51 of the heat transfer system.

Each of the pipes 3g to 3i initially extends radially from the outside to the associated one Cast body, wherein the radial portion 38 located within the shell 30 is cast with aluminum. In the disc-shaped cast body, each tube 3g to 3i extends as a spiral 40, preferably as an involute with a small radial part, wound up against the inner edge of the cast body. There, each of the tubes 3g to 3i in each case passes into the level of the fins 5 on the underside of the heat exchanger element in question, where it is cast in as an involute tube 41 in a thickened fin 23 'which, like the neighboring fins, runs in an involute manner. At the outer edge of the cast body, each involute tube 41 merges into a radial tube section 43 which penetrates the jacket 30 and is cast with aluminum within the jacket. The tubes 3f and 3k also each have a radial tube section 39, which is, however, located outside the annular spaces 42 and 42 '. At the inner edge of the two cast bodies 4f and 4k, the spiral tubes 3f and 3k are led up and down out of the cast body and set continues as tube 44 or 45. In order to keep the flow losses on the water side small, the changes in direction of the tube are chosen to be as small as possible by the water circling in the same way within a heat exchanger element in the spiral tube 40 as well as in the involute tube 41. Since the direction of the involute tubes 41 changes due to the alternating direction of the successive lower ribs, the directions of rotation of the spiral tubes 40 of successive heat exchanger elements also change. Thus, the spiral tube 40 in the cast bodies 4g and 4i is wound from the outside inwards in the counterclockwise direction, while that of the cast bodies 4h and 4k runs clockwise from the outside inwards.

The arrangement of the involute tubes 41 and of the tube 45 on the underside of the cast bodies 4g to 4i or 4k ensures that the spiral sections 40 of the tubes 3g to 3k can be better drained and that the gas cross sections run evenly. These two advantages have been dispensed with on the uppermost cast body 4f, since the involute tube 44 is led upward. On the other hand, this slightly reduces the weight for the cast aluminum body 4f.

The pipes 3f ... 3k are expediently connected in series, according to the countercurrent principle, which cannot be implemented consistently here. According to an expedient circuit form, the pipe section 39 of the cast body 4f is therefore connected to the involute pipe 41 of the cast body 4g, the involute pipe 44 forming the water inlet. The pipe section 38 of the cast body 4g is connected to the section 38 of the cast body 4h, the involute tube of which is connected to the section of the cast body 4i and finally the involute pipe of the cast body 4i to the section 39 of the lowermost cast body 4k. Practical considerations as well as thermodynamic calculations can also lead to a different circuit.

While simple ribs are always provided in the exemplary embodiments described so far, it may also be expedient to ramify the ribs, as shown in FIGS. 9 to 12. According to FIG. 9, flat grooves 56 are screwed into the cast body 55, which tightly surrounds the tube 3, into each of which a rib 57 is soldered. The ribs 57 have a stem-shaped central rib 58, from each of which four branch ribs 59 branch off.

In an improved form of branched ribs according to FIG. 10, the trunk rib 38 thickens in accordance with the increasing heat flow against the rib foot 54, and the astra ribs 59 are inclined so that the heat flow reaches the rib foot 54 in a shorter way. The astocks 59 are also arranged such that the spaces for the medium flowing around the fins have a hydraulic radius that changes as little as possible.

Ribs according to Fig. 10 are easy to cast, while the extrusion presents difficulties due to the uneven cross-sectional distribution. In this regard, the cross-sectional shapes according to FIGS. 11 and 12, which are assembled by soldering simple angle profiles 60, are more favorable. These can be formed by folding sheet metal or by extrusion. The profiles 60 are preferably joined together with a first, high-melting solder to form a branched rib, which is then soldered into the grooves 56 of the cast body 55 with a second, less high-melting solder.

In the exemplary embodiment according to FIG. 13, a plurality of ribs 61 extend radially inward from a circular cylindrical heat exchanger element 60, the ribs running along helical lines. With this arrangement, the flow path for the second medium becomes longer and at the same time the flow cross-section becomes smaller, which can help to optimize the heat transfer.

In the divided ribs according to FIG. 14, one (70) of the trailing edges 70, 71 is rounded off with a large radius. The consequence of this is that the Coanda effect causes a thin layer of the medium flowing between the ribs to pass through the gap between two successive ribs into the adjacent flow path. This phenomenon can further improve the heat transfer. The ribs which are inclined in FIG. 14 can also run in the axial direction, in which case the interruptions between the ribs can follow a helical line.

The principle shown in FIG. 14 can of course also be applied to the flat heat exchanger elements according to FIG.

Claims (11)

1. A heat-exchanger arrangement comprising at least two heat-exchanger elements (1), at least one of each of which has a tube (3) bent in one plane or a cylindrical surface for a first heat-exchange medium, adjacent sections of the tube or tubes (3) of each heat-exchanger element (1) being connected to form a sealed wall participating in the heat exchange, characterised in that the wall is formed by a metal casting (4) which encloses the sections of the tube or tubes in sealingtight relationship and which has thermally conductive projections (5), the area of which is a multiple of the tube inner surface they occupy, preferably in the form of fins extending substantially parallel to one another, and at least two heat-exchanger elements (1) are so disposed in relation to one another as to from at least one closed duct, into which the projections (5) extend, for a second medium participating in the heat exchange.

2. A heat-exchanger arrangement according to claim 1, characterised in that the castings (4) of two adjacent heat-exchanger elements (1) are interconnected in sealingtight relationship in the region of their periphery.

3. A heat-exchanger arrangement according to claim 1, in which the projections are formed as fins, characterised in that at least one of the fins (23) is thickened and encloses in sealing-tight relationship a length of tube (24) which is disposed adjacent the sections of the tubes (3b) and which acts as a supply or discharge tube.

4. A heat-exchanger arrangement according to claim 1 or 3, characterised in that the heat-exchanger elements (4f to 4k) are constructed as substantially circular and/or circular annular discs in which the tube sections extend as at least one flat spiral and the projections (5) are curved . to an involute pattern.

5. A heat-exchanger arrangement according to claim 4, characterised in that the projections (5) of at least some of the heat-exchanger elements (4g to 4i) extend in the reverse direction on the top to those on the bottom.

. 6. A heat-exchanger arrangement according to claim 4, characterised in that heat-exchanger elements (4f to 4k) are arranged coaxially in the form of circular discs and circular discs alternately, a plurality of series-connected ducts for the second heat-exchange medium being formed between the heat-exchanger elements, and the projections (5) so extend in each case that the second medium does not change its direction of rotation as it flows through successive ducts.

7. A heat-exchanger arrangement according to any one of claims 1 to 6, characterised in that the castings of every other heat-exchanger element (4f, 4h, 4k) are interconnected in sealing-tight relationship in the region of their periphery.

8. A heat-exchanger arrangement according to any one of claims 1 to 7, characterised in that at least some of the projections (57) have a tree-like branched cross-section, the surface for the passage of the thermal flow decreasing with increasing distance from the base of the projection.

9. A method of producing a heat-exchanger arrangement according to any one of claims 1 to 8, characterised in that the tube (3) of each heat-exchanger element (1) is bent and placed in a mould, the mould is filled with a metal and the projections (5) are formed by machining from the casting (4) and at least two heat-exchanger elements (1) are connected to form a heat-exchanger arrangement.

10. A method of producing a heat-exchanger arrangement according to any one of claims 1 to 8, characterised in that the tube (3) of each heat-exchanger element (1) is bent and placed in a mould, the mould is filled with a metal and the casting (4) is so machined as to form recesses (56) for anchoring fin-like parts forming the projections (5), said parts being caulked, soldered or welded into said recesses and at least two heat-exchanger elements (1) produced in this way are connected to form a heat-exchanger arrangement.

11. A method of making a heat-exchanger arrangement according to any one of claims 1 to 8, characterised in that the tube (3) of each heat-exchanger element (1) is bent and is placed, together with fin-like parts forming the projections (5), into a mould which is so filled with metal that the fin-like parts are cast in the casting (4) solely by their feet and at least two heat-exchanger elements (1) are connected to form a heat-exchanger arrangement.

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