Abstract:
A brazed heat exchanger comprises a number of heat exchanger plates ( 100, 200, 300 ) provided with a pressed pattern of ridges ( 110   a ) and grooves ( 110   b ) arranged such that flow channels for media to exchange heat are formed between neighboring plates ( 100,200,300 ). The plates ( 100,200,300 ) are further provided with port openings ( 120   a - d ) in selective communication with said flow channels and with a circumferential edge formed by skirts ( 130;240; 335 ) of neighboring plates ( 100,200,300 ) overlapping one another. A reinforcement portion ( 140; 250;340 ) extends outside the skirt ( 130;240; 335 ), and comprises a ribbon of sheet metal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a brazed heat exchanger comprising a number heat exchanger plates provided with a pressed pattern of ridges and grooves arranged such that flow channels for media to exchange heat are formed between neighboring plates, the plates further being provided with port openings in communication with said flow channels and with a circumferential edge formed by a skirt which overlaps skirts of neighboring plates. 
       PRIOR ART 
       [0002]    Brazed heat exchangers are used in a large number of heat exchanging applications. Compared to other types of heat exchangers, brazed heat exchanger are cost-efficient and compact. 
         [0003]    Brazed heat exchangers comprise a number of plates provided with a pattern of pressed ridges and grooves arranged such that flow channels for media to exchange heat are formed between neighboring plates as they are stacked onto one another. Port openings are arranged to provide a selective liquid communication with the flow channels. 
         [0004]    Usually, the plates are provided with a skirt extending around the periphery of the plate in an angle slightly offset from the perpendicular direction. The skirts of two neighboring plates will overlap one another and form a brazed edge extending around the plates, which edge seals the flow channels formed by the plates. 
         [0005]    After the plates have been stacked onto one another, with brazing material provided on the surfaces of the plates, the entire heat exchanger is placed in a furnace to be completely brazed together. The pressed patterns of neighboring plates will provide contact points which are brazed together, 
         [0006]    In order for brazed heat exchangers to withstand high pressure, it has hitherto been necessary to enclose the heat exchanger with rigid plates in order for it not to flex or move upwards or downwards. Such rigid plates primarily strengthens the area around the port openings, which is especially susceptible to damage due to high pressure, since the pressure acting on the port hole generates a force that must be transferred from a bottom portion of the port opening to a top portion of the port opening. Without the rigid plates, the entire force must be transferred by brazing points formed between the ridges and grooves of the pressed patterns of the plates. For obvious reasons, the density of such points is low in the area of the port openings. 
         [0007]    Heat exchangers provided with the rigid plates are, however, prone to burst around the edges, i.e. the seal provided by the overlapping skirts. The present invention aims to increase the strength of the edges of brazed heat exchangers. 
         [0008]    Also, a well known problem with the manufacturing technique is that the stack of heat exchanger “shrinks” during the brazing operation. The shrinking is a result of the brazing material melting during the brazing, hence leaving a space enabling the stacked heat exchanger plates to come closer to one another. The shrinking is most severe in the vicinity of the port openings. 
       SUMMARY OF THE INVENTION 
       [0009]    According to the invention, these and other problems are solved or alleviated by a reinforcement portion extending outside at least a part of the skirt, said reinforcement comprising a ribbon of sheet metal. 
         [0010]    In one embodiment of the invention, the reinforcement portion is provided with a pressed pattern comprising upper and lower surfaces. The upper and lower surfaces may be arranged such that an upper surface of the reinforcement portion of a first heat exchanger plate contacts the lower surface of the reinforcement portion of a heat exchanger plate stacked on top of the first heat exchanger. 
         [0011]    In another embodiment of the invention, the upper and lower surfaces may be arranged such that the upper and lower surfaces of neighbouring plates are aligned. 
         [0012]    The reinforcement portion may extend in the plane of the heat exchanger plate. 
         [0013]    In order to get an as strong heat exchanger as possible, the reinforcement portion may extend along the entire periphery of the heat exchanger plates. 
         [0014]    The reinforcement portion may be pressed such that at least a portion of the reinforcement extends in a direction such that the ribbon and the skirt form a V. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the following, the invention will be described with reference to the appended drawings, wherein: 
           [0016]      FIG. 1  is a schematic perspective view of a heat exchanger plate provided with an edge reinforcement according to a first embodiment of the present invention, 
           [0017]      FIG. 2  is a schematic, partly sectioned, perspective view of a heat exchanger plate provided with an edge reinforcement according to a second embodiment of the present invention, 
           [0018]      FIG. 3  is a schematic, partly sectioned, view showing a third embodiment of the present invention, and 
           [0019]      FIG. 4  is a schematic perspective view showing a heat exchanger manufactured from heat exchanger plates according to  FIG. 1 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    In  FIG. 1 , a heat exchanger plate  100  according to a first embodiment of the present invention is shown. The plate  100  extends in a general plane, and is provided with a pressed pattern of ridges  110   a  and groove  110   b . Moreover, the plate  100  is provided with port openings  120   a - d  (only the port openings  120   a  and  120   b  are shown); neighboring openings are provided on different heights; in the shown figure, the port opening  120   b  is provided on a height equal to the height of the ridges  110   a , whereas the port opening  120   a  is provided at the height of the grooves  110   b.    
         [0021]    A skirt  130  is provided in a basically perpendicular direction vis-á-vis the plane P. The skirt  130  surrounds the area provided with the ridges  110   a  and the grooves  120   b  and the port openings  120   a - d ; skirts of neighboring plates are adapted to overlap one another such that a seal between the plates is achieved. At the end of the skirt opposite the pressed pattern and the port openings, a reinforcement portion  140  is provided. The reinforcement portion extends in an outward direction parallel to the general plane P. 
         [0022]    The reinforcement portion  140  of the first embodiment is provided with a pressed pattern comprising upper areas  145  and lower areas  150 . In a first aspect of the present invention, the upper areas  145  of a first plate  100  are arranged to contact lower areas  150  of a neighboring upper plate  100 , whereas the lower areas  150  of the reinforcement portion  140  of the first plate are arranged to contact the upper areas  145  of the reinforcement portion  140  of a neighboring lower plate. 
         [0023]    For manufacturing a plate heat exchanger according to the first embodiment, heat exchanger plates  100  are stacked onto one another to form a stack of heat exchanger plates. A brazing material is provided between the plates. The brazing material may be any suitable brazing material, e.g. copper, tin, lead, silver, or stainless steel mixed with a liquid depressant, e.g. silica, boron, or mixtures thereof. The stainless steel brazing material is especially suitable if heat exchanger plates of stainless steel are used. 
         [0024]    In some cases, it is possible to use identical heat exchanger plates for the entire stack of heat exchanger plates. In such a case, every other heat exchanger plate is rotated 180 degrees compared to its neighboring plates. This rotation results in the port areas  120   a, b  of neighboring plates interacting such that, seen from one port opening, every other flow channel will be open to a port, every other being closed. This manufacturing method is well known by persons skilled in the art of brazed heat exchangers. 
         [0025]    According to the first aspect, the upper areas  145  of the reinforcement portion  140  of a first plate are arranged to contact the lower areas  150  of the reinforcement portion  140  of a neighboring upper plate. This gives, except from the reinforcing effect, also the beneficial effect that shrinking of the heat exchanger plate stack during brazing is significantly reduced, especially in the vicinity of the port openings  120   a - d . A heat exchanger made from heat exchanger plates  100  according to the first aspect is shown in  FIG. 4 . 
         [0026]    According to a second aspect, the upper areas  145  of the reinforcement portion  140  of a first plate are arranged to align with the upper areas  145  of its neighboring plates; the reinforcement portions  140  of neighboring plates will then contact one another along the areas between the upper areas  145  and the lower areas  150 . The second aspect is beneficial in that the connection between the neighboring reinforcement patterns become stronger connected to one another, but the positive effect on the shrinking is smaller as compared to the first aspect. The second aspect will be more thoroughly described below with reference to  FIG. 3   
         [0027]    A second embodiment of the invention, shown in  FIG. 2 , comprises a number of heat exchanger plates  200  provided with a pressed pattern of ridges  210  and grooves  220  arranged to hold the heat exchanger plates on a distance from one another under formation of flow channels for media to exchange heat. The heat exchanger plates are moreover provided with port openings  230  (only one partially shown in  FIG. 2 ). In order to seal off the flow channels, skirts  240  are arranged along edges of the heat exchanger plates, such skirts  240  being arranged such that an upper side of a skirt of a first heat exchanger plate will contact a lower side of a skirt of a second heat exchanger plate stacked upon the first plate. 
         [0028]    On an outside of the skirt  240 , a reinforcement ribbon  250  is provided. The reinforcement ribbon is pressed such that an outer surface  260  extends such that it forms a truncated V with respect to the skirt  240 . 
         [0029]    Preferably, the outer surface  260  of one heat exchanger cooperates with the outer surfaces  260  of neighboring plates the same way as the skirts of neighboring plates do. 
         [0030]    Hence, neither the skirt  240  nor the outer surface  260  may be provided perpendicular to a plane P of the heat exchanger plate  200 ; if this would be the case, it would be impossible to stack heat exchanger plates upon one another. Instead, there must be a certain angle between the skirts and the plane P and the outer surface and the plane P. 
         [0031]    Consequently, the outer surfaces  260  of neighboring plates will contact one another in the same way as the skirts of neighboring plates contact one another. This will, except for the increased strength of the edge, provide an extra insurance against leakage; if the connection between the skirts  240  of neighboring plates will leak, there is still a possibility that the outer surfaces  260  will provide a seal. 
         [0032]    In  FIG. 3 , a heat exchanger  300  according to a third embodiment, equaling the second aspect as described above, of the present invention is shown. The heat exchanger comprises a number of heat exchanger plates  310 , all of which being provided with ridges  320  and grooves  330  to form flow channels for media to exchange heat, port openings (not shown) and a skirt  335  surrounding the heat exchanger plate and providing a seal for the flow channels by contact between skirts  335  of neighboring plates  300 . 
         [0033]    Moreover, the heat exchanger plates  300  according to the third embodiment comprises a reinforcing portion  340 , which resembles the reinforcement area  140  of the heat exchanger plates according to the first embodiment in that it comprises pressed ridges  350  and grooves  360 . However, the ridges and groves of the third embodiment differ from the ridges and grooves of the first embodiment in that the ridges  350  and grooves  360  of one heat exchanger plate of the third embodiment are located to be placed inline with the ridges  350  and grooves  360  of neighboring plates. Consequently, the ridges and grooves of heat exchanger plates of the third embodiment will not touch one another. 
         [0034]    Instead, contact between the reinforcing portions  340  of neighboring heat exchanger plates takes place between walls  370  connecting said ridges and grooves. 
         [0035]    In  FIG. 4 , a heat exchanger HE comprising heat exchanger plates according to the first embodiment is shown. Here, the interaction between the upper areas  145  and the lower areas  150  of the reinforcement portions  140  of neighboring plates is clearly shown. 
         [0036]    In still another embodiment of the invention, the reinforcement portion only extends around the port areas, i.e. not along the long sides of the heat exchanger plates. This embodiment strengthens the ports, and may be reducing shrinking of the heat exchanger plate stack, but provides only a minor increase of the strength of the sides; as mentioned above, the area around the ports is particularly prone to break. 
         [0037]    Persons skilled in the art will realize that there are several modifications possible within the scope of the invention without departing from the same; such as it is defined by the appended claims.