Patent Publication Number: US-2002005280-A1

Title: Plate heat exchanger

Description:
[0001] This invention relates to a plate heat exchanger including a plate stack through which the heat-exchanging media preferably pass in a mutual counterflow pattern and whose individual plates are provided with embossments, with neighboring plates directly supporting one another.  
       [0002] EP 0 658 735 B1 describes a plate-type crossflow heat exchanger whose individual plates are paired up in a manner that the plates of a pair face each other in mirror-image fashion. An undulating channel extending between the individual plates of a plate pair constitutes the path for one of the two heat exchanging media. The other medium travels in the crossflow direction through tubular-profile channels between the individual plates separating neigboring plate pairs.  
       [0003] To produce the undulating flow pattern for the first medium and the straight tubular flow pattern for the other medium the plates are provided with several parallel rows of sectional trough-shaped embossments extending in the flow direction of the second medium. The sectional embossments of neighboring rows in the plate are mutually offset in the longitudinal direction, creating between adjoining plates flat-surfaced supports in the form of essentially rhomboid support zones which are evenly distributed over the entire surface of the plates. The usefulness of this type of plate heat exchanger is limited to crossflow operation. Because the channels have too small a cross section, any other mode of operation, for instance in a counterflow pattern, is rendered impossible.  
       [0004] It is the objective of this invention to introduce a plate heat exchanger which permits counterflow operation, which offers a high pressure load capacity with respect to both media and which can be manufactured cost-effectively in terms of materials and assembly labor.  
       [0005] As the solution for achieving this objective with a plate heat exchanger of the type first above mentioned the invention proposes to provide the plates with parallel rows of trough-shaped sectional embossments which are located on the same side of all plates and which are equidistant from one another, with the rows of consecutive plates superpositioned over one another.  
       [0006] A plate heat exchanger of this type offers sufficiently large channel diameters for both media in a counterflow operation. This plate heat exchanger also features high compressive load resistance with respect to both media in the heat exchange, and it can be produced cost-effectively in terms of materials and labor.  
       [0007] The sectional embossments of consecutive plates preferably extend in a mutually offset arrangement in the direction of the rows. This offset should preferably correspond to half the length of a sectional embossment.  
       [0008] In an enhanced design variation the sectional embossments of the neighboring rows of a plate are mutually offset in the direction of the rows. This offset should again preferably correspond to half the length of a sectional embossment.  
       [0009] In another design variation of the plate heat exchanger according to this invention, the plates making up the plate stack are rectangular, with the intake and the outflow of the first heat-exchange medium taking place on the two short sides of the plates while the intake of the second heat-exchange medium takes place at one end and its outflow at the other end on the long sides of the plates. The rows composed of the sectional embossments preferably extend parallel to the short sides of the plates.  
       [0010] In the attached drawings which show examples of this invention  
       [0011]FIG. 1 is a schematic illustration of two plate heat exchangers serving as recuperators for gas turbines;  
       [0012]FIG. 2 represents the plate heat exchangers serving as recuperators with a functional pattern differing from that in FIG. 1;  
       [0013]FIG. 3 represents the plate heat exchangers serving as recuperators with a functional pattern differing from that in FIG. 1 and FIG. 2;  
       [0014]FIG. 4 is a perspective view of a plate heat exchanger composed of a stack of ten plates; and  
       [0015]FIG. 5 is an enlarged perspective view of the plates in the plate stack. 
     
    
    
     [0016] By way of a first design example, FIG. 1 shows possible deployment modes of a plate heat exchanger serving as a gas-turbine recuperator. The reference number  1  identifies the exit port for the hot turbine gases. These gases reach temperatures for instance as high as 650° C. (1202° F.). The hot gases flow through the two co-symmetrically configured plate heat exchangers  2  in the direction of the longitudinal axis of the latter and exit into a joint discharge channel  3 . In the discharge channel  3  the temperature of the turbine exhaust gases is still about 200° C. (392° F.).  
     [0017] The compressed air fed to the gas turbine travels through the plate heat exchangers  2  in a counterflow direction, for which purpose one end of each plate heat exchanger  2  is provided with an intake channel  4  while the other end features a joint discharge channel  5 . In the intake channel  4  the temperature of the compressed air may be for instance 175° C. (347° F.), in the discharge channel  5  shared by both plate heat exchangers  2  it may be about 600° C. (1112° F.).  
     [0018]FIG. 1 also indicates that the two plate heat exchangers  2  are angled relative to each other in such fashion that the distance A between them in the area of the common discharge channel  5  is greater than at the level of the separate intake channels  4  of the two plate heat exchangers. The reason for this is that, while the first medium, being the hot gas emanating from the turbine, enters and exits strictly on the short sides  6  of the plate heat exchanger, the second heat-exchange medium, being the compressed air, enters and exits respectively on the long sides  7   a ,  7   b  of the plate heat exchanger  2 . This means that the intake channel  4  is located at one end of the long side  7   a  while the discharge channel  5  is located at the other end of the long side  7   b . This could be considered to constitute a partly diagonal flow of the second medium, i.e. the compressed air, through the plate heat exchangers  2 .  
     [0019] In the design example per FIG. 2, the intake channel  4  for the second medium and the discharge channel  5  are located on the same long side  7   b  of the plate heat exchanger  2  while the other long side,  7   a , is completely closed. Both the intake channel  4  and the discharge channel  5  are in the middle between the paired plate heat exchangers  2  and equally serve both plate heat exchangers. In the design example per FIG. 2 as well, the media travel in a counterflow direction, except that in this case the main flow direction of the second medium follows a “C” pattern. The first medium again flows through the plate heat exchangers in a straight line between the exit port  1  of the gas turbine and the discharge channel  3 .  
     [0020] The design example per FIG. 3 differs from that per FIG. 2 by virtue of additional intake channels  4  and discharge channels  5  also on the long side  7   a  of the plate heat exchangers  2  which are again paired. Thus, each long side  7   a ,  7   b  of the two plate heat exchangers  2  features both an intake channel  4  and a discharge channel  5  for the second heat-exchanging medium. The pattern of the counterflow resembles an elongated “X”.  
     [0021] Details of the plate heat exchanger design examples 1 to 3 are described below with reference to FIGS. 4 and 5.  
     [0022]FIG. 4 again illustrates the intake and discharge flow vectors  1 ,  3 ,  4 ,  5  from the gas-turbine exit port  1 , of the discharge channel  3  as well as the intake channel  4  and discharge channel  5  of the air to be heated. It can also be seen that the plate heat exchanger  2  is composed of multiple stacked steel plates each of which is provided with embossments. Embossed plates of this type can be produced by a deep-draw process or by means of an appropriate stamping press. With the exception of the perimeter of the individual plate  8 , all sectional embossments  9  on the plate are identical and are in the form of straight troughs of limited length. In the illustration per FIG. 4 and  5 , the plates  8  are stacked one atop the other in such fashion that the cambered sides of the trough-shaped sectional embossments  9  point upward.  
     [0023] All trough-shaped sectional embossments  9  are rectangular and of the same length L, with the exception of the end sections described further below. Within a row, the consecutive sectional embossments  9  are uniformly spaced apart over the entire plate  8  by a distance a. The sectional embossments  9  are arranged in rows which extend in the direction parallel to the longest dimension of the rectangular sectional embossments  9 . The individual rows on the plate  8  extend parallel to one another and are uniformly spaced apart by a distance τ. In the direction of the rows, the sectional embossments  9  of neighboring rows are offset in relation to one another, the offset V corresponding to half the length of the embossments  9 . Viewed from the top, the array of sectional embossments  9  thus resembles a masonry wall with the bricks staggered on-center.  
     [0024] This offset V results in half-length sectional embossments  9 ′ along the long sides  7   a ,  7   b  of each plate  8 . Accordingly, the embossment rows which start with a full-length embossment  9  alternate with rows beginning with a half-length sectional embossment  9 ′, as is clearly illustrated in FIG. 4. As is especially recognizable in FIG. 5, the rows of trough-shaped sectional embossments  9  and  9 ′ are situated on the same side of each plate  8  in the plate heat exchanger  2 . It follows that all of the embossments  9  protrude in the same direction i.e. either upward or downward depending on the viewing angle. If all plates  8  were identical in shape and positioning, these plates and their sectional embossments would sit in flush, form-fitted fashion one atop the other with no gap in between, eliminating any flow channels between the plates. Therefore, according to this invention, any two juxtapositioned plates will have a mutually different pattern of sectional embossments  9 ,  9 ′ so that by virtue of their arrangement the embossments  9 ,  9 ′ serve as spacers. This is accomplished by mutually offsetting the embossments  9 ,  9 ′ of neighboring plates  8  so as to avoid an exact match. As can be seen in FIG. 5, this offset V between neighboring plates corresponds to half the length of a trough-shaped sectional embossment  9 . However, there is no offset between the individual rows of embossments  9 ,  9 ′ on neighboring plates  8 , meaning that the rows of one plate are situated precisely above the rows of the following plate in the plate stack. The offset V P  is provided only within the row itself. To that end, the individual plates  8  are stacked in such fashion that a plate whose row begins with a full-length sectional embossment  9  is followed by a plate whose row begings with a half-length sectional embossment  9 ′, and vice versa. In terms of their manufacture, one approach would be to produce two different plate models. As a second possibility, all plates could be identical but in the stacking process every other plate is horizontally rotated by 180° and then placed on the plate beneath it, before all plates are firmly connected.  
     [0025] As a result of the above-described configuration and arrangement of the individual plates  8 , the sectional embossments  9 ,  9 ′ cause each such plate to be supported by the next plate in the direction in which the sectional embossments extend. This is due to the contact between the embossments  9 ,  9 ′ of one plate and the points  10  of the next following plate. These contact points  10  are unembossed areas of the base surface of that next following plate which areas are situated between the embossments  9  of a given row and separate the sectional embossments  9  of that row.  
     [0026] For producing the plate heat exchanger  2 , the individual plates  8  are welded together at their short sides  6  and their long sides  7   a ,  7   b , as can be seen in FIG. 4. The assembly is made in in a way as to allow, in alternating fashion, the flow of one and then of the other heat-exchanging media between the plates. Accordingly, if two neighboring plates form the flow channels for the first medium, the next following plates will form the flow channels for the other medium. To provide the short sides  6  with the necessary intake and discharge openings, the short sides  6  of the plates  8  feature contoured end sections  11  whose height corresponds to the height of the embossments  9 . As shown in FIG. 4, the areas of the two long sides  7   a ,  7   b  which contain neither intake channels  4  nor discharge channels  5  are completely closed, thus forcing a counterflow between the two heat-exchanging media.