HEAT EXCHANGING ELEMENT AND METHOD FOR THE MANUFACTURE THEREOF

Abstract: One embodiment of a heat-exchanger element includes a metal layer (1) and at least one metal conduit (2) which lies against and is fused together with the metal layer and which extends between two mutually opposing outer edges of the element so that the metal layer will form heat-transporting flanges on both sides of the conduit. The conduit is fused with the metal layer so that the conduit will have a free-laid surface which faces away from the metal layer. Another embodiment of the element includes two metal layers and at least one metal conduit which is placed between and lies against and is fused with the metal layers and extends between two mutually opposing edges of the element so that the metal layers form heat-transporting flanges on both sides of the conduit. At least one metal layer has a groove in which part of the conduit is inserted. The invention also relates to methods of manufacturing such elements.

Description: HEAT EXCHANGING ELEMENT AND METHOD FOR THE MANUFACTURE THEREO DESCRIPTION Technical Field The present invention relates to a heat-exchanger ele¬ ment comprising one or two metal layers and at least one metal conduit which extends between two mutually oppos- ing outer edges of the element and lies against and is fused together with the metal layer or layers, so that the metal layer or layers will form heat-transporting flanges on opposite sides of the conduit. The heat- exchanger element is particularly intended for use as an absorber in solar energy devices, but may also be used for other purposes, such as radiators in domestic heat¬ ing systems or in other air-water heat-exchanging appli¬ cations. Background Art A heat-exchanger element which consists of two aluminium bands which are cold-fused with a copper conduit placed therebetween is known from Swedish published specifica- tion 423,150 and Danish published specification 155,298. One advantage of such a heat-exchanger element lies in the small thermal mass of the element, which is due to the use of thin aluminium bands and also to the high resistance of said elements to corrosion, which in turn is due to the fact that the conduit through which the hot medium flows is made of copper. In manufacture, the copper conduit can be given the wall thickness required to resist the pressure and the corrosive effect generat¬ ed by the heat-carrying medium. Although a heat-exchang- ing element of this kind will normally function satis¬ factorily, the fact that grooved rolls must be used in order to compensate for the wall thickness of the copper conduit, axial guiding of the rolls and also guiding of the flattened copper conduit into the roll grooves is highly demanding. When guiding of the rolls and the flattened copper conduit is deficient in some respect, the conduit will creep out of the grooves on the flat or smooth part of the rolls, and the copper conduit will crack as a result of being excessively reduced. The manufacture of heat-exchanger elements in accordance with the Swedish and the Danish patent specifications incurs high investment costs in the construction of the rolling mill and results in a low roll speed in produc¬ tion, since it is necessary to continuously check the guidance between the grooves of the rolls and the copper conduit through the roll grooves. Furthermore, there is a risk that the manufactured heat-exchanger element will have a poor quality, which is first manifested after the element has been finally installed or fitted on the premises of the customer. As before mentioned, the heat-exchanger elements accord¬ ing to the Swedish published specification 423,150 and the Danish published specification 155,298 are comprised of two metal layers located on opposite sides of the conduit. Thus, two metal bands must be handled and guided during their passage through the rolls, which is a time-consuming and relatively complicated procedure. Furthermore, it is necessary to mechanically work both metal layers in order to enable collecting pipes to be connected to the conduit enclosed between the metal layers. JPA 59-60194 relates to a heat-exchanging element which corresponds to the element taught by the aforedescribed Swedish published specification, this known element also having conduit ends which project outwardly from the two metal layers. USA 2,828,533 teaches a method of fusing metal layers and metal conduits together with the aid of smooth rolls, so as to form a heat-exchanger element. Subse¬ quent to this fusion operation, the element has a uni¬ form thickness over the whole of its extension. This is achieved by reducing the layer thickness in the region of the conduit to a greater extent than in the neighbo¬ uring regions. As a result of this greater reduction in layer thickness, the layer, or layers, and the conduit are extended to different extents in the direction in which they are fed through the rolls, causing the ele- ment to rupture at the interface or junction between layer and conduit. JPA 58-32535 teaches a heat-exchanger element comprising a metal layer which is formed partially around a conduit and connected thereto by adhesion. Summary of the Invention An object of the present invention is to avoid at least partially the drawbacks of earlier known heat-exchanger elements and also to avoid the drawbacks of methods for their manufacture. These objects are fulfilled by means of the present invention, which is characterized by the features set forth in the characterizing clauses of the following Claims. Brief Description of the Drawings Figure 1 is a cross-sectional view of a first embodiment of an inventive heat-exchanger element, and also illus¬ trates a roll pair in which the element is manufactured; Figure 2 is a cross-sectional view of a second e bodi- ment of an inventive element, and also shows a roll pair for manufacturing the element; Figure 3 is a cross-sectional view of a slightly modi¬ fied embodiment of the element illustrated in Figure 2, and also illustrates a roll pair for manufacturing the element; Figure 4 is a cross-sectional view of the element shown in Figure 2 or 3 subsequent to manufacture and after inflating the conduit; Figure 5 is a cross-sectional view of a third embodiment of the inventive element, and also illustrates a roll pair for the manufacture of said element; and Figure 6 is a schematic illustration from above of the element shown in Figure 4 connected to a collecting pipe. Figures 1, 3 and 5 illustrate rolling of different heat- exchanger elements, while Figure 4 illustrates a com¬ pleted element. All of the elements illustrated are comprised of at least one metal layer, such as an alu¬ minium layer, and at least one metal conduit, such as a copper conduit. It will be understood, however, that other materials may be used, such as copper for the metal layer and aluminium for the conduit. The conduit extends between two mutually opposing outer edges of the element, so that the metal layer or layers will form heat-transporting flanges having a wide surface area and a small wall thickness on opposite sides of the conduit. Prior to rolling, the conduit is flattened and then subjected to a recrystallizing annealing process to return the conduit to the same ductile state as that possessed by the conduit prior to being flattened. Before rolling is commenced, those surfaces on the metal layer, or layers, and the flattened and annealed conduit that are to be mutually joined are brushed mechanically. Furthermore, before rolling and brushing of said surfac- es is commenced, the metal layer or layers of some of the embodiments are grooved, as will be described here- below. Figure 1 illustrates a metal band 1 provided with a groove la, a flattened conduit 2, and two rolls VI and V2. The groove la extends in the direction of the longi¬ tudinal axis of the band 1 and has a depth corresponding generally to half the thickness of the band. The groove la has been formed conveniently by cutting the metal band mechanically with a high speed miller or some corresponding machine. The width of the flattened con¬ duit 2 is slightly smaller than the width of the groove la and the thickness of the conduit is generally equal to the depth of the groove la. The wall thickness of the conduit 2 is smaller than the thickness of the metal band. The rolls VI and V2 are smooth, or planar, and are spaced apart at a distance which is so much smaller than the thickness of the metal band as to achieve a total reduction in the thickness of the rolled metal band of at least about 65%, thereby ensuring satisfactory metal¬ lurgical connection (fusion) between band and conduit. Prior to rolling, the flattened conduit 2 and the metal band 1 are brought together in front of the rolls VI and V2, whereafter the band 1 with the conduit guided in the groove la is passed through the rolls in a conventional manner, therewith obviating the need for separate axial guiding of the rolls. When rolling the band, all parts of the band 1 must be extended equally over the full width of the band, since otherwise the band will not be flat or may be torn off. In the illustrated case, the rolled composite, i.e. the band 1 and the flattened conduit 2, has the same thickness over the whole of its width because of the groove in the band, and the rolling operation can therefore be considered to be a conven- tional band rolling operation with smooth rolls. After having passed through the roll nip, the metal band will have a thickness of 0.6-1.4 mm, preferably 0.8 mm, and the conduit 2 will have a wall thickness of 0.1-0.5 mm, preferably 0.2 mm. Figure 2 illustrates a metal band 11, a flattened con¬ duit 12, and two rolls Vll and V12, of which the upper roll Vll has a peripherally extending groove Vila. The distance between the bottom of the groove Vila and the other roll V12 corresponds essentially to the total thickness of the rolled element in the immediate vicini¬ ty of the conduit 12. The width of the groove Vila is slightly larger than the sum of the width of the conduit 12 and twice the thickness of the band 11. The band 11 and the conduit 12 are rolled essentially in the same manner as that described above with reference to Figure 1, although with the difference that because of the presence of the groove Vila, it is necessary to guide the rolls Vll and V12 axially. After having passed through the rolls, the band 11 will have a thickness of about 0.5 mm across its entire width and the conduit 12 will have a wall thickness of about 0.3 mm. Figure 3 illustrates a metal band 21, a flattened con- duit 22 and two rolls V21 and V22. Both of the rolls V21 and V22 are provided with peripheral grooves V21a and V22a respectively. The distance between the bottoms of the grooves V21a and V22a corresponds essentially to the total thickness of the rolled element in the near vicin¬ ity of the conduit. The grooves V21a and V22a have mutually the same width, which is somewhat larger than the sum of the width of the conduit 22 and twice the thickness of the band 21. The band 21 and the conduit 22 are rolled essentially in the same manner as that de¬ scribed above with reference to Figure 2. Figure 4 illustrates a rolled heat-exchanger element according to Figure 2 or 3, subsequent to having dilated the conduit 12, 22 in a conventional manner, by intro¬ ducing a suitable pressurized fluid into the conduit. As shown in Figure 4, the conduit has a free surface 6 which is remote from the metal band 11, 21. The element of this embodiment may be used, for instance, as an absorber in solar energy devices, in which several such elements may be joined together and the conduits thereof connected to collecting pipes in which the heat-carrying liquid circulates. The element may also comprise two or more parallel conduits which are fused to a metal band at one and the same time. The Figure 5 illustration includes two metal bands 3 and 4, a flattened conduit 5 and two smooth rolls V3 and V4. Each of the bands 3 and 4 is provided with a respective groove 3a and 4a extending in the longitudinal direction of the bands. The bottoms of the grooves 3a and 4a are mutually spaced apart at a distance which generally equals the thickness of the flattened conduit 5. The width of each groove 3a and 4a is insignificantly small¬ er than the width of the conduit 5. After having passed through the roll nip, the element will have a uniform thickness across the whole of its width and along the whole of its length, while the bands 3 and 4 will have a thickness of about 0.8 mm and the conduit a wall thick¬ ness of about 0.2 mm. Figure 6 is a view from above of the element shown in Figure 4. The metal band 11 or 21 has, at 24, an elon¬ gated part in which the conduit 12 or 22 is fixedly mounted. An end-part 25 of the conduit 12 or 22 extends beyond the left edge of the band 11 or 21 and is hard- soldered to a collecting pipe 26 forming part of a solar energy device (not shown) . The collecting pipe 26 is provided with a plurality of holes 27 for receiving the conduits of corresponding elements mounted in parallel with the element illustrated in Figure 6. A correspond¬ ing collecting pipe (not shown) can be connected to the other ends of said elements. The end-part 25 of the conduit has been laid free from the metal band 11 or 21, by applying a separating agent onto the metal band or the conduit 12 or 22 in that region where the metal band is to be separated from the conduit prior to rolling said element, thereby prevent¬ ing the conduit and the band from fusing together in this region when passing through the rolls. When cutting the rolled conduit and band to form individual elements, the band, but not the conduit, is further cut to a length corresponding to the length of said end-part. Cutting of solely the band is preferably not carried out until the conduit has been dilated to the form shown in Figure 4. Although the invention has been described and illustrat¬ ed with reference to a number of exemplifying embodi¬ ments thereof, it will be understood that the invention is not restricted to these particular embodiments and that the invention is restricted solely by the scope of the following Claims.

Claims: CLAIMS 1. A heat-exchanger element comprising a metal layer (1; 11; 21) and at least one metal conduit (2; 12; 22) which lies against and is fused together with the metal layer and which extends between two mutually opposing outer edges of the element so that the metal layer will form heat-transporting flanges on both sides of the conduit, wherein the conduit (2; 12; 22) is fused with the metal layer in a manner such that said conduit will have an exposed surface (6) which faces away from the metal layer (1; 11; 21), c h a r a c t e r i z e d in that the metal layer (11; 21) has essentially the same thickness at the conduit (12; 22) as at the flanges (Figures 2-4) . 2. A heat-exchanger element according to Claim 1, c h a r a c t e r i z e d in that the element has a total thickness at the conduit (12; 22) which is greater than the thickness of the metal layer (11; 21). 3. A method of producing a heat-exchanger element comprising a metal layer (1; 11; 21) and at least one metal conduit (2; 12; 22) which lies against and is fused together with said metal layer and which extends between two mutually opposing outer edges of the element so that the metal layer forms heat-transporting flanges on opposite sides of the conduit, said method comprising feeding the metal layer (1; 11; 21) and the flattened conduit (2; 12; 22) between two rolls (VI, V2; Vll, V12; V21, V22) with a part of the conduit and one surface of the metal layer lying against one roll (V2; V12; V22) and the other surface of said metal layer lying against the other roll (VI; Vll; V21) while exerting a roll pressure such as to cold-fuse the metal layer to the conduit, c h a r a c t e r i z e d by feeding the conduit (12; 22) and the metal layer (11; 21) between the two- rolls (Vll, V12; V21, V22) of which at least one (Vll; V21, V22) is provided with a peripheral grove (Vila; V21a, V22a) which accommodates at least a part of the conduit and/or a part of the metal layer. 4. A method according to Claim 3, c h a r a c ¬ t e r i z e d by preferably subjecting the conduit (2; 12; 22) to a re-crystallizing annealing process after flat-rolling said conduit; and by brushing the conduit and the metal layer (1; 11; 21) mechanically prior to the rolling process. 5. A method according to Claim 3 or 4, c h a r a c ¬ t e r i z e d by reducing the thickness of the conduit (2; 12; 22) and of the metal layer (1; 11; 21) by at least 65% during passage thereof through the rolls (VI, V2; Vll, V12; V21, V22). 6. A method according to any one of Claims 3-5, c h a r a c t e r i z e d by mechanically forming a groove (la) in the metal layer (1) prior to said rolling process, and by placing the conduit (2) in said groove (la) when feeding the conduit (2) through the smooth- surfaced rolls (VI, V2). 7. A heat-exchanger element which comprises at least one metal layer (1; 3, 4) and at least one metal conduit (2; 5) which lays against and is fused together with the metal layer and which extends between two mutually opposing edges of the element so that the metal layer will form heat-transporting flanges on both sides of the conduit, c h a r a c t e r i z e d in that the metal layer (1; 3, 4) has a prefabricated groove (la; 3a, 4a) in which a part of the conduit (5) is inserted. 8. A heat-exchanger element according to Claim 7, c h a r a c t e r i z e d in that the element is com¬ prised of two metal layers (3, 4) which are provided with mutually opposing grooves (3a, 4a), into which parts of the conduit (5) are inserted. 9. A heat-exchanger element according to Claim 7 or 8, c h a r a c t e r i z e d in that the total thickness of the element at the conduit (2; 5) is essentially the same as the thickness of the element at the flanges. 10. A method of manufacturing a heat-exchanger element which includes at least one metal layer (1; 3, 4) and at least one metal conduit (2; 5) which lies against and is fused together with the metal layer which extends be¬ tween two mutually opposing outer edges of the element so that the metal layer forms heat-transporting flanges on both sides of the conduit, c h a r a c t e r i z e d by forming a groove (la; 3a, 4a) mechanically in said metal layer (1; 3, 4) prior to the rolling process; inserting the conduit (2; 5) into said groove; and thereafter feeding the metal layer and the conduit together through two rolls (V3, V4) at a roll pressure such as to cold-fuse the metal layer and the conduit together. 11. A method according to Claim 10 in which the element has two metal layers (3, 4), c h a r a c t e r i z e d by feeding the conduit (5) lying between said metal layers through rolls (V3, V4) which are either smooth or of which at least one is grooved peripherally. 12. A heat-exchanger element according to any one of Claims 1-2 or 7-9, c h a r a c t e r i z e d in that at least one end (25) of the conduit (12; 22) extends beyond the edge of the metal layer (11; 21) for connection with a collecting pipe (26). 13. A method of manufacturing a heat-exchanger element according to Claim 12 in which the metal layer (11; 21) and the conduit (12; 22) are fed together between two rolls so as to fuse said layer and said conduit togeth¬ er, c h a r a c t e r i z e d by coating the metal layer and/or the conduit with a separating agent in a region at at least one end of the conduit prior to feeding said layer and said conduit through said rolls; and by removing the metal layer from the conduit in the region of the separating agent after fusion of the metal layer with the conduit, so as to expose said end (25).

Inventors: OLSSON GOERAN, OLSSON, GOERAN
Applicants: SOLSAM SUNERGY AB
Application year: 1992
Main classification: B21C37
IPC codes: B21C37, B23P15, F24J2, F28F1