Abstract
A heat exchanger for cooling a gas includes a gas inlet, a gas outlet, and a plurality of cooling tubes arranged between the gas inlet and the gas outlet, wherein the cooling tubes of two successive tube rows are arranged offset transversely to a flow direction of the gas. A fin having openings is provided for receiving a corresponding number of the cooling tubes. The fin has slits arranged at a distance from the openings and configured to follow an edge profile of a honeycomb-shaped hexagon, with the slits of each hexagon surrounding a corresponding one of the openings at the distance. Arranged between adjacent ones of the openings is a corresponding one of the slits at a same distance from each of the adjacent openings, with each slit having an end ending at a deformation point of the fin.
Claims
1. A heat exchanger for cooling a gas, said heat exchanger comprising: a gas inlet; a gas outlet; a plurality of cooling tubes arranged between the gas inlet and the gas outlet, wherein the cooling tubes of two successive tube rows are arranged offset transversely to a flow direction of the gas; and a fin having openings for receiving a corresponding number of the cooling tubes and slits having a longitudinal side and opposing ends, with the longitudinal side of the slits being aligned with an edge profile of a honeycomb-shaped hexagon surrounding a corresponding one of the openings at a distance, wherein adjacent ones of the openings are separated by a corresponding slit located between the adjacent openings, with at least one end of each slit terminating at a deformation point of the fin.
2. The heat exchanger of claim 1, wherein the slits have a straight configuration.
3. The heat exchanger of claim 1, wherein the slits have a width which is greater than a minimum width of the deformation point.
4. The heat exchanger of claim 1, wherein the cooling tubes are arranged in groups arranged between the gas inlet and the gas outlet, wherein one of the groups of cooling tubes in adjacent relation to the gas inlet is penetrated by a plurality of said fin.
5. The heat exchanger of claim 4, wherein a plurality of the groups of cooling tubes is penetrated by a plurality of said fin.
6. The heat exchanger of claim 1, wherein the cooling tubes are arranged in groups, with one of the groups of cooling tubes comprising at least two tube rows which are in series in the flow direction of the gas.
7. The heat exchanger of claim 1, wherein the fin has edge sides lying in the flow direction of the gas, with at least one of the edge sides being shaped with a sawtooth profile corresponding to a pattern of the slits.
8. The heat exchanger of claim 7, wherein the edge sides include recesses for formation of the deformation point with those of the slits which are adjacent to the at least one of the edge sides.
9. The heat exchanger of claim 1, wherein the fin has a thickness of less than 0.16 mm.
10. The heat exchanger of claim 1, wherein the fin has a flat configuration.
11. The heat exchanger of claim 1, wherein the fin is formed with embossed features between the openings, said slits arranged outside the embossed features.
12. The heat exchanger of claim 1, wherein mutually opposite pairs of the slits of a hexagon are of equal length, with one pair of mutually opposite slits having a length which is different than a length of the two other pairs of mutually opposite slits of the hexagon.
13. The heat exchanger of claim 12, wherein the slits extending perpendicularly to an edge side of the fin in facing relation to a flow of gas have a length which is longer than a length of the two other pairs of mutually opposite slits of the hexagon.
14. The heat exchanger of claim 1, wherein the slits are all of equal length.
15. The heat exchanger of claim 1, wherein the slits adjoining an edge side of the fin in facing relation to a flow of gas are open toward the edge side.
16. The heat exchanger of claim 1, wherein the deformation point is a center of a star-shaped arrangement of three slits located between three adjacent openings.
Description
BRIEF DESCRIPTION OF THE DRAWING
(1) The invention is explained below by means of an illustrative embodiment, which is illustrated schematically in the drawings. In the drawings;
(2) FIG. 1 shows a fin of a heat exchanger in plan view;
(3) FIG. 2 shows the fin of FIG. 1 in perspective illustration;
(4) FIG. 3 shows a predetermined breaking region between three slits in an enlarged illustration;
(5) FIG. 4 shows a perspective illustration of a heat exchanger insert for cooling hot gases;
(6) FIG. 5 shows the heat exchanger insert of FIG. 4 partially in section;
(7) FIG. 6 shows the heat exchanger insert of FIG. 4 partially in section in another perspective view viewed in the direction of the hot gas inlet;
(8) FIG. 7 shows another embodiment of a fin of a heat exchanger in plan view;
(9) FIG. 8 shows another embodiment of a fin of a heat exchanger in plan view; and
(10) FIG. 9 shows another embodiment of a fin of a heat exchanger n plan view.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(11) FIG. 1 shows a fin 1 of a heat exchanger, not illustrated specifically, for cooling gases. FIG. 2 shows said fin 1 in a perspective illustration. A plurality of cooling tubes penetrates said fins 1 in a manner not illustrated specifically. The fins 1 are mounted in a stacked arrangement (FIG. 6). Circular openings 2 in the fins 1 accommodate the cooling tubes 13 (FIG. 5). The openings 2 each have a collar 3, which faces downward in the plane of the image in FIG. 2. The collar 3 simultaneously determines the spacing between two successive stacked fins 1. A plurality of such fins 1 or lamellae arranged one above the other, with the cooling tubes 13 arranged therein, forms a group 14-17 (FIG. 4). An individual group 14-17 can also be referred to as a heat exchanger assembly. In the installed situation within the heat exchanger 10, an assembly of this kind is referred to as the first stage, second stage etc., depending on its position in the flow path. The individual assemblies or groups 14-17 can be arranged spaced apart. According to the invention, it is envisaged that at least one of these groups 14-17 of cooling tubes 13, in combination with said fins 1, is arranged within the heat exchanger 10 according to the invention, In particular, it is the group 14 which is closest to the gas inlet 11 (FIG. 4).
(12) The perspective illustration in FIG. 2 shows that, apart from the collars 3, said fin 1 is flat. This is a fin 1 which is produced from a sheet-metal blank. Owing to use in heat exchangers 10 in an aggressive environment, the fins 1 are made of stainless steel. The steel preferably has a high elasticity with a uniform thickness, It is preferably 0.12 mm. One suitable material is X2CrTi12 with the material number 1.4512. This material has a tensile strength Rm of 380 to 560 N/mm.sup.2. The proof stress Rp02 is about 280 to 290 N/mm. In practice, the elongation A 80% reaches values over 25%. In particular, the elongation is 30% and, in particular, is over 34%. Other conventional materials are the materials 1.4404 (austenitic high-grade steel) or 1.4521 (ferritic high-grade steel).
(13) The special feature of the structure according to the invention of the heat exchanger 10 is the geometry of the fins 1. Next to the openings 2 for the cooling tubes 13, the fins 1 have regularly arranged slits 4. The slits 4 have the shape of elongate holes with fully rounded ends. All the slits 4 are straight, of the same length and of uniform width. They are arranged in a polygonal shape, more specifically in this case in a hexagon shape or honeycomb shape. The polygon shape described is a regular hexagon. There is one slit 4 between every two adjacent cooling tubes 13 or openings 2. The cooling tubes 13 or openings 2 are arranged in series in rows R1, R2, R3. The rows R1, R2, R3 etc. are each arranged offset transversely to the preceding row. As a result, there is an opening 2 or cooling tube 13 in each cell bounded by the six straight slits 4. The slits 4 have a length L1 The length L1 is slightly less than the diameter D1 of the circular opening 2. In this illustrative embodiment, the length L1 is 7.5 mm in comparison with the diameter D1 of 8 mm. The width B1 of the slits 4 is 1.5 mm. The ratio of the length L1 to the width B1 of the slits 4 is therefore 5:1. All the adjacent slits are at an angle W of 120° to one another.
(14) The distance between the central longitudinal axis MLA of a slit 4 from a central point M of an opening 2 is denoted by D2 in FIG. 1. This distance D2 corresponds to the diameter D1 of the openings 2. A slit 4 is always located precisely in the center between two of the openings 2. All the openings 2 are located centrally in the individual cells formed by the slits 4. FIG. 1 furthermore shows that edge sides 5, 6 lying in the flow direction (arrow P) of the gas have a sawtooth profile. To produce the fins 1 a relatively large sheet metal blank was divided up, more specifically in the region of deformation points 7. These deformation points 7 are always bounded by a slit 4 facing in the flow direction P. Apart from the edge skies 5, 6, the deformation points 7 are located where in each case the ends of three slits 4 offset by 120° relative to one another are adjacent. The deformation points 7 are located at vertices of the polygon. In respect of the edge sides 5, 6, these are merely the slits 4 extending parallel to the flow direction P. Since these deformation points 7 at the edges are subject to particularly high thermal loads, it is envisaged that the deformation points created here are not more resistant than those that are arranged between the slits 4 arranged in a star shape.
(15) There are therefore circular-arc-shaped recesses 8 of diameter D3 at the ends of the slits 4 which face the edge sides 5, 6. The recess 8 can be produced very easily by using a stamping tool that removes the actual core region of the deformation point 7.
(16) FIG. 3 shows the deformation point 7 in an enlarged illustration. The boundaries of the deformation point 7 are indicated by the dashed line. The lines delimit the region in which the highest material stresses occur. From a design point of view, the three slits 4 delimit between them an incircle 9 enclosed by the star-shaped region of the deformation point 7. If the incircle 9 is removed by a stamping tool that is moved slightly upward in the plane of the image in FIG. 3, the stamping tool engages in the two upper slits 4. The stamping tool for removing the deformation point 7 and hence for separating the sheets preferably has a somewhat larger diameter. In this example, the width 81 of the slits 4 is equal to the diameter D4 of the rounded ends of the slits 4. The central region 9 also has this diameter D4. This is 1.5 mm, for example. In the case of a somewhat larger stamping tool with a diameter of 2 mm, for example, the recess 8 with the diameter D3 is obtained, which is then likewise 2 mm. To ensure that the fin 1 still has a deformation point 7 in the region of the recess 8, the recess 8 is positioned in such a way that a width B2 (FIG. 1) remains. In this illustrative embodiment, B2 is about one third of the width of the slit 4, i.e. about 0.5 mm.
(17) In principle, the deformation point 7 is narrower at its narrowest point B3 (FIG. 3) than the width B1 of the slits 4.
(18) Variations within the scope of the invention are possible by modifying the length L1 of the individual slits 4. Longer slits 4 result in smaller deformation points 7 and increase the elasticity of the fin 1. Shorter slits 4 would increase the stiffness of the fin 1.
(19) FIG. 4 shows a heat exchanger 1 for cooling hot gases. The illustrated heat exchanger has a gas inlet 11 and a gas outlet 12 at a distance from the gas inlet 11. A multiplicity of parallel cooling tubes 13 is arranged between the gas inlet 11 and the gas outlet 12. The cooling tubes 13 are surrounded by the fins 1 as explained above.
(20) FIG. 4 shows that the heat exchanger 10 has a plurality of groups 14-17 arranged in series. The hot gas to be cooled flows successively through the groups 14-17. The cooling water which flows through the cooling tubes 13 is deflected between two successive groups 14-17. For this purpose, there are baffles 19-22 outside a housing 18 surrounding the cooling tubes 13 and the fins 1. The heat exchanger 10 illustrated is inserted into another housing (not illustrated specifically). Cooling water is fed to the first group 14 from above in the plane of the image, for example. The cooling water then flows through the cooling tubes 13 from the top down and emerges underneath the first group 14. Between the two baffles 19, 20, the cooling water flows around the first group 14 and the subsequent second group 15 on the outside and, above the second group 15, flows back into the cooling tubes 13 from above at that location. This process is repeated until the last group 17. All the baffles 19-22 are configured in an identical way. They can be surrounded by elastomeric seals in order to effect sealing relative to the surrounding further housing and to avoid bypass flows of the cooling water.
(21) FIG. 5 shows a perspective illustration of the heat exchanger 10 partially in section. The first group 14 is illustrated without the upper tube sheet 23 shown in FIG. 4, leaving the view of the individual cooling tubes 13 and the fins 1 free. From the direction of view in FIG. 6 of said first group 14, it can be seen that the fins 1 are arranged in an arrangement stacked close together one above the other. Via an inflow funnel 24 which increases in size in the flow direction, the gas flow supplied is guided as uniformly as possible onto the inflow area formed by the fins 1. The gas flow flows through between the adjacent fins 1 and, in the process, flows around the cooling tubes 13. This process is repeated from the first until the last group 14-17. From the illustration in FIG. 5, it can be seen that fins 1 of the subsequent group 15 are arranged at a certain distance from the fins 1 of the first group 14. The individual cooling tubes 13, which are arranged in mutually offset rows, together with the respective fins 1 stacked one above the other, form the respective group 14-17 of the heat exchanger 10. A certain spacing between the groups 14-17 is required since space is needed for the baffles 19-22 for diversion of the cooling water. In the region of the baffles 19-22, on the upper side of the individual groups 14-17, one row of cooling tubes 13 is as it were missing, and therefore the groups 14-17 are arranged at a distance from one another.
(22) FIGS. 7 to 9 show three further illustrative embodiments of fins for said heat exchangers. For these illustrative embodiments, the same reference signs are used for the components of substantially identical construction as for the illustrative embodiment in FIGS. 1 to 3.
(23) The illustrative embodiment in FIG. 7 differs from that in FIG. 1 in width and length. Whereas, in the case of the illustrative embodiment in FIG. 1 a total of six tube rows is arranged in series, there are only four and also only a maximum of four cooling tubes across the width in the illustrative embodiment in FIG. 7. The arrangement and shape of the slits 4 and of the deformation points and openings 2 are identical, however.
(24) Whereas the illustrative embodiment in FIG. 1 shows additional recesses at the deformation points in the edge region on the edge side 5 facing the flow and on the opposite edge side 6, these are not present in the illustrative embodiment in FIG. 7. The edge sides 5 and 6 are as it were rounded. The recesses, which lead to pointed projections in the example in FIG. 1, have been smoothed, with the result that the profile of the edge sides 5, 6 no longer has any sharp jumps or bends in the profile.
(25) The illustrative embodiment in FIG. 8 represents an alternative to this. There, the illustrated fin 1 is provided with additional recesses 25 in the region of its edge side 5 facing the flow. They are arranged where those slits 4 which extend in the flow direction according to the arrow P and thus parallel to the flow direction or perpendicularly to the edge side 5 end. The sawtooth profile of the edge side 5 is interrupted by the additional recesses 25 in the region of the slits 4. The slits 4 open via the recesses 25 into the edge side 5 with the sawtooth profile. The recesses 25 are produced by stamping out the end regions of the slits 4 facing the edge side 5. As a result, the deformation point denoted by 7 in FIG. 1 is omitted and is replaced by a circular recess 25. The diameter of the recess 25 is larger than the width B1 of the slit 4. The diameter is approximately twice as large as the width B1. Concave enlargements of the inlet region of the slit 4 are thereby obtained at the transition from the edge side 5 facing the flow to the slit 4. These enlarged recesses 25 have the effect that the thermally induced stresses in the inflow region of the fin 1 are significantly further reduced, particularly because it is here that the highest temperatures prevail and therefore that material fatigue can occur earlier than on the opposite edge side 5 facing away from the flow.
(26) The illustrative embodiment in FIG. 9 differs from that in FIGS. 1, 7 and 8 in having slits 4 of different lengths. Those slits 5 which point in the flow direction and thus extend parallel to the flow (arrow P) are longer than the other slits 4 lying opposite one another in pairs. This is still a hexagonal arrangement of slits 4. However, said hexagons are no longer uniform but are stretched in the flow direction P. Attention is drawn to the fact that the spacing of the rows R1, R2, R3 (see FIG. 1) has not changed. Only the proportions of the slits 4 have been changed. Whereas the slits 4 extending in the flow direction are somewhat longer than in the illustrative embodiment in FIGS. 1, 7 and 8, the slits 4 extending diagonally to the flow direction P are somewhat shorter. The angular positions of the individual slits 4 relative to one another have not changed. They are still arranged in a star shape with an angle of 120° relative to one another.
(27) Another difference is that the deformation regions 7 are no longer symmetrical. The longer slit 4 of the three adjoining slits 4 extends as it were somewhat deeper into the deformation point 7. The central point of the deformation point 7 is thereby displaced somewhat out of the central position toward one of the adjacent openings 2. In this case, it is those openings 2 which are arranged in series in the flow direction P. By varying the length of the mutually opposite slits 4 arranged in pairs, it is possible to position the central point of the deformation point 7 in a manner appropriate to requirements. It can also be seen that the width of the slits 4 is greater than a minimum width of the respective deformation point 7.
(28) The edge side 5 facing the flow is partially rounded. Where the slits 4 extending parallel to the flow direction P are arranged, the deformation point 7 that is usually present there is split transversely to the inflow direction. At that location, there is a region of the edge side 5 which is perpendicular to the inflow direction P. The slits 4 adjacent to the edge side 5 are not open to the edge side 5, as in the illustrative embodiment in FIG. 8, but are closed. As an option, it is possible to provide additional recesses, as shown in FIG. 7.
(29) On the opposite edge side 6, which faces away from the flow direction P, there are rounded regions in the region of the openings 2, as also shown in FIG. 7. The slits 4 adjacent to the edge side 6 end in a deformation point 7 which is simultaneously part of the edge side 6. As a difference from the side 5 facing the flow, however, the deformation point 7 is not cut off transversely to the flow direction P but has a concave hollow 26. As a result, the deformation point 7 is of somewhat thicker construction in this region than on the edge side 5 facing the flow, this being noticeable at the horns on the corners of the concave hollow 26. At this location, there is more material than on the edge side 5 facing the flow. In the region of the deformation points 7 at that location, the edge side 5 facing the flow is therefore less stiff in bending than the deformation points 7 on the opposite edge side 6 facing away from the flow. This concept of the different bending stiffnesses of the fin 1 in the relationship between the edge side 5 facing the flow and the edge side 6 facing away from the flow has also been followed in the illustrative embodiment in FIG. 8. In principle, the fin 1 should exhibit more flexible behavior on the inflow side than on the outflow side in order to take account of a temperature gradient in the flow direction within the fin 1.
REFERENCE SIGNS
(30) 1—fin, lamella 2—opening 3—collar 4—slit in 1 5—edge side 6—edge side 7—deformation point 8—recess 9—incircle of 7 10—heat exchanger 11—gas inlet 12—gas outlet 13—cooling tube 14—group of 10 15—group of 10 16—group of 10 17—group of 10 18—housing of 10 19—baffle of 10 20—baffle of 10 21—baffle of 10 22—baffle of 10 23—tube sheet 24—inflow funnel 25—recesses 26—hollow B1—width of 4 B2—width of 7 at 8 B3—minimum width of 7 D1—diameter of 2 D2—distance D3—diameter of 8 D4—diameter at 4 L1—length of 4 M—central point of 4 MLA—central longitudinal axis of 4 P—flow direction R1—tube row R2—tube row R3—tube row W—angle
