Abstract:
The heat exchanger comprises metal plates ( 6, 7 ) which have been press-formed and assembled in pairs by welding two opposite sides to make modular elements ( 2 ) that are stacked and which define two independent circuits for a first and a second fluid. The two metal plates ( 6, 7 ) of the modular element ( 2 ) are set flatly against each other over a predefined width (L) and are joined by solder ( 12 ) along this width and meant to ensure the mechanical cohesion of the assembly and by another solder ( 13 ) performed along the external edges of the plates and ensuring their sealing. The ends of the plates ( 6, 7 ) are welded to opposite connection partitions forming an exchange block which is itself mounted on four corner posts of the heat exchanger body.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to a heat exchanger with welded heat-exchange plates, in order to achieve an exchange of heat between a first fluid and a second fluid. 
       BRIEF DESCRIPTION OF RELATED ART 
       [0002]    Already known, notably through European patent No. EP 0639258 B1 from the same inventor, is a heat exchanger with welded heat-exchange plates, of compact structure, bearing the commercial name “HEATEX” (registered trademark), comprising previously swaged metal plates, assembled by twos by welding on two opposite sides, and thereby forming stacked modular elements defining two independent circuits respectively for a first fluid and for a second fluid. All the plates, thus joined, form a heat-exchange block of rectangular horizontal section, hence generally parallelepipedal, which is assembled to four posts or corner uprights belonging to the frame of the heat exchanger. The open ends of the stacked modular elements are welded by being placed alongside one another on the edge of openings made in the opposite vertical connecting walls of the heat-exchange block. The heat exchanger is closed by four side doors screwed onto the uprights of the frame and easily removable for maintenance. 
         [0003]    In particular, European patent No. EP 0639258 B1 offers a solution which removes the stresses of differential expansion, between the heat-exchange block constituted by all the stacked plates, on the one hand, and the frame on the other hand, thanks to “corner gutters” that are secured to the aforementioned connecting walls, and that partially surround the uprights of the frame, with the possibility of relative sliding. 
         [0004]    Thanks to these arrangements, the heat exchanger according to European patent No. EP 0639258 B1 has advantageous features, in terms of behavior at temperature, relative to the prior embodiments, also known, of heat exchangers with welded plates, such as those described in European patent applications EP 0165179 A and EP 0186592 A. 
         [0005]    However, the heat exchanger with welded heat-exchange plates according to European patent No. EP 0639258 B1 still poses certain problems, and therefore remains perfectable, for uses under considerable thermomechanical stresses. 
         [0006]    In particular, when the heat-exchange block is set at temperature, because of the temperature gradient that prevails in service, the heat-exchange plates tend to expand lengthwise, in a direction perpendicular to the connecting walls situated at their ends. The corresponding expansion stress is calculated by the ratio F/S, F being the expansion force and S the section of the weld withstanding this stress. 
         [0007]    When the expansion is considerable, the stress is also and this may result in a breakage of the welds connecting the two plates associated in a modular element, a breakage which occurs notably level with the zone where the heat-exchange plates and the adjacent connecting wall are alongside. 
         [0008]    It is therefore appropriate to reduce the level of stresses at this location, in order to bring it to a value below the breaking threshold, by a reduction of the expansion force and/or by an increase of the weld section. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The invention provides enhancements to the heat exchanger with welded plates, as described in European patent No. EP 0639258 B1, for the purpose of enhancing its behavior at temperature, and notably to prevent the risk of breakage under the effect of the expansion stresses. 
         [0010]    Accordingly, the essential subject of the invention is a heat exchanger with welded heat-exchange plates, of the type considered above, that is to say comprising previously swaged metal plates assembled in twos by welding on two opposite sides in order to form stacked modular elements defining two independent circuits respectively for a first fluid and for a second fluid, the ends of the heat-exchange plates being welded by being placed alongside one another on the edge of openings made in the opposite connecting walls, perpendicular to said plates, in order to form an overall parallelepipedal heat-exchange block which is assembled to four posts or corner uprights belonging to the frame of the heat exchanger, this exchanger being characterized in that, on their sides to be assembled, the two swaged metal plates constituting each modular element are on each side pressed flat against one another over a predefined width, are joined together by a first weld made in this width and providing the mechanical cohesion of the assembly, and are also joined together along their outer edges by a second weld providing the seal. 
         [0011]    Therefore, the invention replaces the usual “edge-to-edge” assembly of the two swaged plates with a particular configuration consisting in carrying out a “dimpling” of one of the plates and even of both plates, so that both plates are juxtaposed over a predefined width, preferably at least equal to fifteen millimeters, allowing the achievement of a double weld. 
         [0012]    The first weld, which is a spot weld or a laser weld or an electrode wheel weld, ensures the mechanical cohesion of the assembly, that is to say its resistance to pressure. The second weld, which is advantageously a weld of the “TIG” or “plasma” type, for its part simply ensures the seal. The total weld section is therefore greatly increased, making the assembly of the plates much stronger. 
         [0013]    According to another aspect of the present invention, each post or corner upright of the frame of the heat exchanger with welded heat-exchange plates has a beveled inner edge, the adjacent connecting wall being connected to the post or corner upright in the region of this beveled edge. 
         [0014]    Therefore, when the heat-exchange plates tend to expand, they may take with them the connecting walls which then comprise a possibility of additional deformation, by bending in the space released by the beveled edges of the posts or corner uprights. The expansion stress is therefore absorbed largely by the bending, now made possible, of the connecting wall. 
         [0015]    According to an advantageous additional arrangement, each connecting wall comprises, in its two lateral zones, bellows-like conformations for its connection to the post or corner upright, in the region of the beveled edge. The bellows-like conformations, which may each consist simply of two inverted folds together forming a sort of sinewave, facilitate, as required, an expansion along an axis perpendicular to the direction of longitudinal expansion of the heat-exchange plates. As is easy to understand, the beveled edges of the posts or uprights offer a free space used here not only for the bending of the connecting walls, but also for the housing and the deformation of the bellows-like conformations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    In any case, the invention will be better understood with the aid of the following description, with reference to the appended schematic drawings representing, as an example, one embodiment of this heat exchanger with welded heat-exchange plates. 
           [0017]      FIG. 1  is a partial and very schematic view, in exploded perspective, showing the general principle of assembling a heat exchanger of the type covered by the present invention; 
           [0018]      FIG. 2  is a view in cross section illustrating the current method of assembling the plates of such an exchanger, on one of their sides; 
           [0019]      FIG. 3  is a view in section similar to  FIG. 2 , but illustrating the method of assembly according to the present invention; 
           [0020]      FIG. 4  is a view in section passing through one of the corner zones of such an exchanger, and illustrating the current method of connection between a connecting wall and a post or corner upright; 
           [0021]      FIG. 5  is a view in section similar to  FIG. 4 , but illustrating the method of connection according to the present invention; 
           [0022]      FIG. 6  is a view in horizontal section of a heat exchanger according to the present invention; 
           [0023]      FIG. 7  is a view in perspective showing a detail of the bottom portion of the heat exchanger of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    With reference to  FIG. 1 , a heat exchanger with welded heat-exchange plates comprises a series of modular elements  2 , of generally square or rectangular shape, that are stacked and all assembled between two opposite connecting walls  3 , of rectangular shape, perpendicular to the modular elements  2 . 
         [0025]    These modular elements  2  have a very elongated section, and their ends are welded, by being placed alongside, on the edges of parallel openings  4  arranged in the connecting walls  3 . 
         [0026]    These connecting walls  3  are themselves assembled, along their longitudinal edges (vertical in this instance), to posts or corner uprights  5 , that are four in number. The bottom and top ends of the posts or corner uprights  5  are assembled, respectively, to a bottom support and a top support, not shown in  FIG. 1 , to form a complete frame, of generally parallelepipedal shape. 
         [0027]    Inside this frame, which is closed on its lateral faces by doors not shown, all of the modular elements  2  form a heat-exchange block, itself of generally parallelepipedal shape, which defines two independent fluid circuits, namely a first fluid circuit consisting of the modular elements  2 , and a second fluid circuit resulting from the free spaces situated between these modular elements  2 . Inlet and outlet hoses, for the two fluid circuits thus formed, are also provided. 
         [0028]    For a more detailed description of this type of heat exchanger, reference is made to the aforementioned European patent No. EP 0 639 258 B1. 
         [0029]    With reference to  FIGS. 2 and 3 , each modular element  2  results from the assembly, on two opposite sides, of two metal plates  6  and  7  with at least one of them being previously swaged. 
         [0030]    More particularly,  FIG. 2  illustrates the current method of assembling the two plates  6  and  7 , on one of the sides (the other side being made in a symmetrical manner). The two plates  6  and  7  are in this instance each folded at 45°, one in the direction of the other, and a single longitudinal weld  8 , of the “TIG” type, joins these two plates  6  and  7  along their edges, brought one against the other. 
         [0031]    Still considering one side of the modular element  2 , the welded assembly of the end of the latter to the connecting wall is carried out, in the illustrated example (for plates of a thickness of 1.5 mm), over a section of 2×2.8 mm×1.5 mm, or 8.4 mm 2 , and this welded assembly has a concentration of stresses at a point, level with the longitudinal weld  8 . 
         [0032]      FIG. 3  illustrates the solution proposed here by the present invention. One of the plates  6  in this instance remains flat in the region of the side of the modular element  2 , while the other plate  7  is made with a “dimpling”, that is to say that it has a first fold  9 , for example at 45°, followed by a second fold  10  for example at 45° but in the direction opposite to the previous one, leading to the formation of a lateral band  11  of width L, parallel to the main plane of the plate  7  in question. 
         [0033]    By this lateral band  11 , of width L, the plate  7  is pressed flat against the lateral region of the plate  6 . The two plates  6  and  7  are then joined to one another, in the width L, by a first weld  12  which may be a spot weld or a laser weld or an electrode wheel weld, ensuring the mechanical strength of the assembly. 
         [0034]    The two plates  6  and  7  are also joined to one another, along their outer edges, by a second weld  13  which is notably a weld of the “TIG” type, by which in this instance simply the seal is ensured. 
         [0035]    Advantageously, the two plates  6  and  7  are therefore juxtaposed in the lateral region of the modular element  2 , over a width L equal to at least fifteen millimeters. 
         [0036]    Supposing that this width L is strictly equal to 15 mm, and everything else remaining equal, the embodiment according to the invention achieves, at the assembly of the end of the modular element  2  to the connecting wall, a weld section equal to: [(2×15)+5.6+4]×1.5 or 59.4 mm 2 , instead of the 8.4 mm 2  obtained with the current method of assembly. The mechanically strong weld section is therefore multiplied by more than 7, in other words increased by more than 600%. 
         [0037]      FIG. 4  represents, in horizontal section, one of the corner zones of a heat exchanger, showing a portion of a modular element  2  assembled to a connecting wall  3 , and a post or corner upright  5  belonging to the frame of the heat exchanger. More particularly, this  FIG. 4  illustrates the current method of connection between the connecting wall  3  and the post or corner upright  5 , the latter having a usual square section. In this case, the connection has a rigidity at the two points P 1  and P 2 , a rigidity which opposes the free longitudinal expansion of the heat-exchange plates, in the direction of the arrow F. 
         [0038]      FIG. 5  illustrates the solution proposed here by the present invention. The latter consists in beveling the inner edge of the post or corner upright  5 . More particularly, a 45° cut of the two adjacent faces  14  and  15  of the post or upright  5  is made over a width of at least ten millimeters, so as to form a bevel  16  which itself releases a free space  17  of triangular section. 
         [0039]    Therefore, when the modular element  2  tends to expand, in the direction of the arrow F, it may carry with it the adjacent connecting wall  3 , which can bend by entering the free space  17 , the first point of rigidity P 1  being removed. The expansion stress is therefore largely absorbed by the bending of the connecting wall  3 . 
         [0040]    In addition, as also shown in  FIG. 5 , the connecting wall  3  is connected to the post or corner upright  5 , in each lateral zone, by a bellows-like conformation, resulting from two inverted folds  18  and  19 , giving this wall  3  locally (seen in horizontal section) a sinewave appearance. This bellows-like conformation introduces an additional zone of flexibility, making it easier, if necessary, for the heat-exchange block to expand along an axis perpendicular to the direction of the arrow F. 
         [0041]      FIG. 6 , and  FIG. 7  which represents a detail thereof, also illustrate additional arrangements provided at the base and the top of the heat exchanger, to allow the expansion of the heat-exchange block on two opposite sides. The bottom support of the frame in this instance being marked  20 , each connecting wall  3  has, at its base, a portion  21  deprived of openings  4  and folded to the horizontal above the bottom support  20 , to which it is attached. On the portion  21  a longitudinal fold  22  is formed which makes it possible to absorb the expansion at this location. Naturally, similar arrangements are provided in the top portion of the heat exchanger. 
         [0042]    It should be noted that the heat exchanger described above may be produced equally with swaged plates provided with a network of bosses, or dishes, or with swaged plates having parallel ribs or grooves, or else with smooth plates provided with fitted mounting blocks, according to all configurations known per se. These heat-exchange plates may consist of simple metal sheets, for example made of stainless steel. In particular applications, they may also be metal sheets called “sandwich” metal sheets, made on one face with a stainless steel support layer, sufficiently thick to ensure resistance to the pressure, and on the other face by a thin layer made of precious metal or alloy, particularly nickel-based, tantalum-based or zirconium-based. It will be noted that the arrangements of the present invention are particularly suitable for assembling such “sandwich” metal sheets together. Specifically, with the usual technique, during the edge-to-edge welding of such metal sheets, there is a certain risk of a rise of ferrite in the melted metal core, by migration effect. The risk of corrosion is then considerable, the weld produced not having the characteristics of the precious metal. On the other hand, by, in this instance, applying the technique of the present invention, as illustrated by  FIG. 3 , with the use of metal sheets  6  and  7  of the “sandwich” type, the layer of precious metal protrudes from the stainless steel support layer, and it is possible to produce on the one hand the spot weld  12  ensuring the cohesion of the assembly, and on the other hand the sealing weld  13  of the “TIG” type, only by overlap between the two layers of precious metal or alloy which protrude from the respective stainless steel support layers. 
         [0043]    Heat exchangers with welded heat-exchange plates, produced according to the invention, may find industrial applications in varied fields: the chemical and pharmaceutical industry, the agribusiness industry, heating installations, etc. 
         [0044]    It goes without saying, and as emerges from the foregoing, that the invention is not limited solely to the embodiment of a heat exchanger that has been described above, as an example; on the contrary it embraces all the embodiment and application variants observing the same principles. In this way, in particular, a user would not depart from the context of the invention:
       by producing the heat-exchange plates in all shapes and dimensions, in particular with generally square or rectangular shapes and made of all weldable materials;   by producing the welds of these plates by using all appropriate methods, whether they be the first weld or the second weld, for example by producing the second weld with a “plasma” method;   by modifying the connection of the connecting walls with the uprights or posts of the frame, the connecting walls not necessarily being welded to the frame, but also being able to be welded to intermediate parts, themselves applied about a post, which notably travel over the beveled edge and the faces adjacent the bevel and which may protrude over the next faces;   by using the heat exchanger not in a vertical position, but in a horizontal position, according to the envisaged application, the words “upright” and “post” in this instance having a purely structural meaning but not implying a vertical orientation.