Patent Publication Number: US-2020278158-A1

Title: Heat transfer plate and a plate pack for a heat exchanger comprising a plurality of such heat transfer plates

Description:
TECHNICAL FIELD 
     The invention relates to a heat transfer plate and its design. The invention also relates to a plate pack for a heat exchanger comprising a plurality of such heat transfer plates. 
     BACKGROUND ART 
     Plate heat exchangers, PHEs, typically consist of two end plates in between which a number of heat transfer plates are arranged in a stack or pack. The heat transfer plates of a PHE may be of the same or different types and they may be stacked in different ways. In some PHEs, the heat transfer plates are stacked with the front side and the back side of one heat transfer plate facing the back side and the front side, respectively, of other heat transfer plates, and every other heat transfer plate turned upside down in relation to the rest of the heat transfer plates. Typically, this is referred to as the heat transfer plates being “rotated” in relation to each other. In other PHEs, the heat transfer plates are stacked with the front side and the back side of one heat transfer plate facing the front side and back side, respectively, of other heat transfer plates, and every other heat transfer plate turned upside down in relation to the rest of the heat transfer plates. Typically, this is referred to as the heat transfer plates being “flipped” in relation to each other. 
     In one type of well-known PHEs, the so called gasketed PHEs, gaskets are arranged between the heat transfer plates. The end plates, and therefore the heat transfer plates, are pressed towards each other by some kind of tightening means, whereby the gaskets seal between the heat transfer plates. Parallel flow channels are formed between the heat transfer plates, one channel between each pair of adjacent heat transfer plates. Two fluids of initially different temperatures, which are fed to/from the PHE through inlets/outlets, can flow alternately through every second channel for transferring heat from one fluid to the other, which fluids enter/exit the channels through inlet/outlet port holes in the heat transfer plates communicating with the inlets/outlets of the PHE. 
     The end plates of a gasketed PHE are often referred to as frame plate and pressure plate. The frame plate is often fixed to a support surface such as the floor while the pressure plate is movable in relation to the frame plate. Often, an upper carrying bar for carrying the heat transfer plates, and possibly also the pressure plate, is fastened to the frame plate and extends from an upper part thereof, past the pressure plate and to a support column. Similarly, a lower guiding bar for guiding the heat transfer plates, and possibly also the pressure plate, is fastened to the frame plate and extends from a lower part thereof, on a distance from the ground, past the pressure plate and to the support column. 
     For a PHE to work properly, it is important that the heat transfer plates are aligned with each other in the stack since non-aligned heat transfer plates may result in a leaking PHE. Although the carrying and guiding bars of a heat exchanger may provide alignment of, by engagement with, the heat transfer plates, this alignment may be insufficient. Also, some PHEs may lack a carrying bar and/or a guiding bar. In view thereof, some heat transfer plates are provided with guiding sections wherein a guiding section of one heat transfer plate is arranged to engage with a guiding section of another heat transfer plate for alignment of the heat transfer plates. WO 2010/064975 discloses such heat transfer plates arranged in a stack wherein every other heat transfer plate is “rotated” in relation to the other heat transfer plates. Although WO 2010/064975 discloses a guiding solution that works very well, it is limited to alignment of heat transfer plates “rotated” in relation to each other. 
     SUMMARY 
     An object of the present invention is to provide a heat transfer plate which solves the above mentioned problem. The basic concept of the invention is to provide the heat transfer plate with a guiding solution which is more flexible than known solutions in that it enables alignment of the heat transfer plate and another heat transfer plate irrespective of whether the two heat transfer plates are “rotated” or “flipped” in relation to each other. Another object of the present invention is to provide a plate pack for a heat exchanger comprising a first, a second and a third such heat transfer plate. The heat transfer plate and the plate pack for achieving the objects above are defined in the appended claims and discussed below. 
     A heat transfer plate according to the present invention has opposing first and second sides, an outer edge and a central extension plane and includes an edge portion comprising corrugations. The corrugations extend between first and second planes which are parallel to the central extension plane, and the central extension plane is arranged between the first and second planes. The corrugations are arranged, at the first side of the heat transfer plate, to abut a first adjacent heat transfer plate, and at the second side of the heat transfer plate, to abut a second adjacent heat transfer plate, when the heat transfer plate is arranged in a plate heat exchanger. Longitudinal and transverse centre axes of the heat transfer plate extending parallel to the central extension plane and perpendicular to each other, define a first, a second, a third and a fourth plate area. The first and second plate areas are arranged on the same side of the transverse centre axis and the first and the third plate areas are arranged on the same side of the longitudinal centre axis. The first, third and fourth plate areas comprise a first, third and fourth guiding section, respectively. The heat transfer plate is characterized in that the first and fourth guiding sections each comprise, as seen from the first side of the heat transfer plate, a male projection projecting beyond the first plane and arranged to engage with the first adjacent heat transfer plate for alignment of the heat transfer plate and the first adjacent heat transfer plate, and, as seen from the second side of the heat transfer plate, a female recess arranged to engage with the second adjacent heat transfer plate for alignment of the heat transfer plate and the second adjacent heat transfer plate. Further, the third guiding section comprises, as seen from the second side of the heat transfer plate, a male projection projecting beyond the second plane and arranged to engage with the second adjacent heat transfer plate for alignment of the heat transfer plate and the second adjacent heat transfer plate, and, as seen from the first side of the heat transfer plate, a female recess arranged to engage with the first adjacent heat transfer plate for alignment of the heat transfer plate and the first adjacent heat transfer plate. 
     The first and second sides of the heat transfer plate may also be referred to as front and back side. 
     The central extension plane may be arranged half way between the first and second planes. 
     The longitudinal centre axis may extend along opposing long sides of the heat transfer plate, while the transverse centre axis may extend along opposing short sides of the heat transfer plate. 
     The edge portion may be an outer peripheral edge portion of the heat transfer plate or an inner edge portion such as an edge portion defining a port hole of the heat transfer plate. Further, the complete edge portion, or only one or more portions thereof, may comprise corrugations. The corrugations may be evenly or unevenly distributed along the edge portion, and they may, or may not, all look the same. The edge portion may comprise further corrugations extending within or outside the first and second planes. 
     The corrugations define ridges and valleys which may give the edge portion a wave-like design. As seen from the first side of the plate, when the heat transfer plate is arranged in a plate heat exchanger, the ridges are arranged to abut the first adjacent plate while the valleys are arranged to abut the second adjacent heat transfer plate. 
     The heat transfer plate may be essentially rectangular, and the longitudinal and transverse centre axes essentially perpendicular to each other so as to define four essentially rectangular plate areas. 
     “As seen from the first side of the heat transfer plate” means when the first side of the heat transfer plate is viewed at a distance. Similarly, “as seen from the second side of the heat transfer plate” means when the second side of the heat transfer plate is viewed at a distance. 
     The heat transfer plate and the first and second adjacent heat transfer plates may all be of the same type. Alternatively, the heat transfer plate and the first and second adjacent heat transfer plates may be of different types. For example, the heat transfer plate and the first and second adjacent heat transfer plates may all comprise guiding sections as defined in the claims but otherwise be differently designed. 
     The above configuration of the guiding sections may enable alignment of the heat transfer plate and an adjacent heat transfer plate irrespective of whether the adjacent heat transfer plate is rotated or flipped with respect to the heat transfer plate. Further, alignment of the heat transfer plate and the adjacent heat transfer plate by means of at least two of the guiding sections of the heat transfer plate may be enabled, which improves the alignment. Moreover, alignment of the heat transfer plate and two adjacent heat transfer plates, e.g. the first and second adjacent heat transfer plates referred to above, by means of each of said at least two of the guiding sections of the heat transfer plate may be enabled, which improves the alignment. The alignment enablement is naturally dependent on the design of the adjacent heat transfer plate(s). 
     The second plate area may comprise a second guiding section comprising, as seen from the second side of the heat transfer plate, a male projection projecting beyond the second plane and arranged to engage with the second adjacent heat transfer plate for alignment of the heat transfer plate and the second adjacent heat transfer plate, and, as seen from the first side of the heat transfer plate, a female recess arranged to engage with the first adjacent heat transfer plate for alignment of the heat transfer plate and the first adjacent heat transfer plate. Thereby, alignment of the heat transfer plate and the adjacent heat transfer plate by means of all of the guiding sections of the heat transfer plate may be enabled, which improves the alignment. Moreover, alignment of the heat transfer plate and two adjacent heat transfer plates, e.g. the first and second adjacent heat transfer plates referred to above, by means of each of all the guiding sections of the heat transfer plate may be enabled, which improves the alignment. Again, the alignment enablement is naturally dependent on the design of the adjacent heat transfer plate(s). 
     A respective top of the male projections of the first and second guiding sections may extend from a distance ML 1  to a distance ML 2  from the transverse centre axis and from a distance MW 1  to a distance MW 2  from the longitudinal centre axis, and a respective opening or root of the female recesses of the third and fourth guiding sections may extend from a distance FL 1  to a distance FL 2  from the transverse centre axis and from a distance FW 1  to a distance FW 2  from the longitudinal centre axis, wherein FL 1 &lt;ML 1 &lt;ML 2 &lt;FL 2  and FW 1 &lt;MW 1 &lt;MW 2 &lt;FW 2 . Further, (each of) the male projections of the first and second guiding sections may fit into (each of) the female recesses of the third and fourth guiding sections. By “fit” is meant that the male projections at least partly could be received in the female recesses. For example, the male projections could have outer circumferences which are smaller than inner circumferences of the female recesses and/or outer surfaces of the male projections could define volumes which are smaller than volumes defined by inner surfaces of the female recesses. Naturally, reception of the male projections of a heat transfer plate in the female recesses of the same heat transfer plate is not relevant and impossible without deforming or cutting the heat transfer plate. However, this embodiment may enable alignment of the heat transfer plate and first and second adjacent heat transfer plates of the same type as the heat transfer plate, or at least comprising guiding sections as above defined, by insertion of the male projections of the first and second guiding sections of the heat transfer plate in the female recesses of the third and fourth guiding sections of the first and second adjacent heat transfer plates, and reception, of the male projections of the first and second guiding sections of the first and second adjacent heat transfer plates, by the female recesses of the third and fourth guiding sections of the heat transfer plate. 
     A respective top of the male projections of the third and fourth guiding sections may extend from a distance ML 3  to a distance ML 4  from the transverse centre axis and from a distance MW 3  to a distance MW 4  from the longitudinal centre axis, and a respective opening or root of the female recesses of the first and second guiding sections may extend from a distance FL 3  to a distance FL 4  from the transverse centre axis and from a distance FW 3  to a distance FW 4  from the longitudinal centre axis, wherein FL 3 &lt;ML 3 &lt;ML 4 &lt;FL 4  and FW 3 &lt;MW 3 &lt;MW 4 &lt;FW 4 . Further, (each of) the male projections of the third and fourth guiding sections may fit into (each of) the female recesses of the first and second guiding sections. The meaning of “fit” is as defined above. This embodiment may enable alignment of the heat transfer plate and first and second adjacent heat transfer plates of the same type as the heat transfer plate, or at least comprising guiding sections as above defined, by insertion of the male projections of the third and fourth guiding sections of the heat transfer plate in the female recesses of the first and second guiding sections of the first and second adjacent heat transfer plates, and reception, of the male projections of the third and fourth guiding sections of the first and second adjacent heat transfer plates, by the female recesses of the first and second guiding sections of the heat transfer plate. 
     The first and fourth guiding sections may each comprise a first plane portion extending between the outer edge of the heat transfer plate and the male projection, or even surrounding the male projection, and extending parallel to the central extension plane. Further, the second and third guiding sections may each comprise a second plane portion extending between the outer edge of the heat transfer plate and the male projection, or even surrounding the male projection, and extending parallel to the central extension plane. This embodiment excludes arrangement of the male projections immediately at an outer edge portion of the heat transfer plate which may improve the stability of the guiding sections. 
     Similarly, the first and fourth guiding sections may each comprise a second plane portion extending between the outer edge of the heat transfer plate and the female recess, or even surrounding the female recess, and extending parallel to the central extension plane, and the second and third guiding sections may each comprise a first plane portion extending between the outer edge of the heat transfer plate and the female recess, or even surrounding the female recess, and extending parallel to the central extension plane. This embodiment excludes arrangement of the female recesses immediately at an outer edge portion of the heat transfer plate which may improve the stability of the guiding sections. 
     The first and second plane portions referred to above may extend in different planes. For example, they may extend in the first and the second plane, respectively, of the heat transfer plate. The first and second plane portions may then be arranged to abut the first and the second adjacent heat transfer plate, respectively, which may improve the stability of the guiding sections. 
     Each of the first plane portions of the first, second, third and fourth guiding sections may “branch” towards the outer edge of the heat transfer plate so as to define and at least partly enclose a respective third plane portion extending in the second plane. 
     The heat transfer plate may be such that, as seen from the first side of the heat transfer plate, two reinforcement recesses, in relation to the first plane portions, are arranged on opposite sides of each of the first plane portions, and two reinforcement projections, in relation to the second plane portions, are arranged on opposite sides of each of the second plane portions. The reinforcement recesses and projections may be arranged in succession along the outer edge of the heat transfer plate. As implied by the names, the reinforcement recesses and projections are arranged to reinforce and stiffen the heat transfer plate so as to reduce the risk of deformation of the guiding sections of the heat transfer plate when this engages with the first and second adjacent heat transfer plates, which could affect the alignment of the three heat transfer plates negatively. Bottoms of the reinforcement recesses may extend in the second plane while tops of the reinforcement projections may extend in the first plane. The reinforcement recesses and projections may then be arranged to abut the first and the second adjacent heat transfer plate, respectively, which may improve the stability of the guiding sections. For example, one or more of the reinforcement recesses and projections could comprise a respective one of the corrugations of the edge portion of the heat transfer plates. 
     The first, second, third and fourth guiding sections may be arranged at a respective one of four corners of the heat transfer plate. Then, the guiding sections may be arranged as far from each other as is possible and suitable which may result in an optimized alignment between the heat transfer plate and the first and second adjacent heat transfer plates. 
     The heat transfer plate may comprise two opposing long sides extending parallel to the longitudinal centre axis and two opposing short sides extending parallel to the transverse centre axis. Within each of the first, second, third and fourth guiding sections, the female recess and the male projection may be arranged on opposite sides of an imaginary straight line extending with an angle of 45 degrees in relation to one of the long sides and one of the short sides of the heat transfer plate. This may result in an optimized alignment between the heat transfer plate and the first and second adjacent heat transfer plates. 
     The heat transfer plate may be so designed that a depth of the female recesses of the third and fourth guiding sections is a ≥height of the male projections of the first and second guiding sections, and a depth of the female recesses of the first and second guiding sections is a ≥height of the male projections of the third and fourth guiding sections. Such an embodiment may enable that the complete male projections of the heat transfer plate may be received in recesses of first and second adjacent heat transfer plates of the same type as the heat transfer plate, or at least comprising guiding sections as above defined, and that the female recesses of the heat transfer plate completely may receive male projections of the first and second adjacent heat transfer plates. In turn, this enables an optimized alignment of the heat transfer plate and the first and second adjacent heat transfer plates. 
     At least one of the male projections of the first and second guiding sections and at least one of the female recesses of the third and fourth guiding sections may have an at least partly uniform cross section parallel to the central extension plane. Similarly, at least one of the female recesses of the first and second guiding sections and at least one of the male projections of the third and fourth guiding sections may have an at least partly uniform cross section parallel to the central extension plane. Thereby, a good fit between the male projections and the female recesses of the heat transfer plate and first and second adjacent heat transfer plates of the same type as the heat transfer plate, or at least comprising guiding sections as above defined, may be enabled. 
     At least one of the male projections of the first and second guiding sections and at least one of the female recesses of the third and fourth guiding sections may have a cross section parallel to the central extension plane comprising two perpendicular portions, i.e. two portions that are perpendicular to each other, each. Similarly, at least one of the female recesses of the first and second guiding sections and at least one of the male projections of the third and fourth guiding sections may have a cross section parallel to the central extension plane comprising two perpendicular portions each. Thereby, alignment, in two perpendicular directions, i.e. optimum alignment, of the heat transfer plate and first and second adjacent heat transfer plates of the same type as the heat transfer plate, or at least comprising guiding sections as above defined, may be enabled. 
     A plate pack for a heat exchanger according to the invention comprises a first, a second and a third heat transfer plate as described above, which heat transfer plates may or may not be similar. The second heat transfer plate is arranged between the first and third heat transfer plates. When the first and second sides of the second heat transfer plate abut the second side of the first heat transfer plate and the first side of the third heat transfer plate, respectively, and the second heat transfer plate is rotated 180 degrees in relation to the first and third heat transfer plates about an axis extending parallel to a normal of the central extension plane, and through a cross point between the longitudinal and transverse centre axes, of the second heat transfer plate, i.e. when the heat transfer plates are rotated in relation to each other with the above definition,
         the male projections of the first and fourth guiding sections of the second heat transfer plate are received in the female recesses of the fourth and first guiding sections, respectively, of the first heat transfer plate,   the male projections of the second and third guiding portions of the first heat transfer plate are received in the female recesses of the third and second guiding sections, respectively, of the second heat transfer plate,   the male projections of the fourth and first guiding sections of the third heat transfer plate are received in the female recesses of the first and fourth guiding sections, respectively, of the second heat transfer plate, and   the male projections of the second and third guiding portions of the second heat transfer plate are received in the female recesses of the third and second guiding sections, respectively, of the third heat transfer plate.       

     Further, when the first and second sides of the second heat transfer plate abut the first side of the first heat transfer plate and the second side of the third heat transfer plate, respectively, and the second heat transfer plate is rotated 180 degrees in relation to the first and third heat transfer plates about an axis coinciding with the transverse centre axis of the second heat transfer plate, i.e. when the heat transfer plates are flipped in relation to each other with the above definition,
         the male projections of the first and fourth guiding sections of the second heat transfer plate are received in the female recesses of the third and second guiding sections, respectively, of the first heat transfer plate,   the male projections of the first and fourth guiding sections of the first heat transfer plate are received in the female recesses of the third and second guiding sections, respectively, of the second heat transfer plate,   the male projections of the second and third guiding sections of the third heat transfer plate are received in the female recesses of the fourth and first guiding sections, respectively, of the second heat transfer plate, and   the male projections of the second and third guiding sections of the second heat transfer plate are received in the female recesses of the fourth and first guiding sections, respectively, of the third heat transfer plate.       

     Still other objectives, features, aspects and advantages of the invention will appear from the following detailed description as well as from the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail with reference to the appended schematic drawings, in which 
         FIG. 1  is a schematic plan view of a heat transfer plate and a plate pack for a heat exchanger according to the invention, 
         FIG. 2 a    is a schematic plan view of an upper left corner portion of the heat transfer plate of  FIG. 1  comprising a first guiding section, 
         FIG. 2 b    is a schematic plan view of an upper right corner portion of the heat transfer plate of  FIG. 1  comprising a second guiding section, 
         FIG. 2 c    is a schematic plan view of an lower left corner portion of the heat transfer plate of  FIG. 1  comprising a third guiding section, 
         FIG. 2 d    is a schematic plan view of an lower right corner portion of the heat transfer plate of  FIG. 1  comprising a fourth guiding section, 
         FIG. 3 a    schematically illustrates a cross section A-A of the portion of  FIG. 2   a,    
         FIG. 3 b    schematically illustrates a cross section B-B of the portion of  FIG. 2   b,    
         FIG. 3 c    schematically illustrates a cross section C-C of the portion of  FIG. 2   c,    
         FIG. 3 d    schematically illustrates a cross section D-D of the portion of  FIG. 2   d,    
         FIG. 3 e    schematically illustrates a cross section E-E of the portion of  FIG. 2   d,    
         FIG. 3 f    schematically illustrates a cross section F-F of the portion of  FIG. 2   d,    
         FIG. 3 g    schematically illustrates a cross section G-G of the portion of  FIG. 2   d,    
         FIG. 4 a    schematically illustrates a cross section X-X of a portion of the plate pack of  FIG. 1 , with heat transfer plates rotated in relation to each other, 
         FIG. 4 b    schematically illustrates a cross section Y-Y of a portion of the plate pack of  FIG. 1 , with heat transfer plates rotated in relation to each other, 
         FIG. 4 c    schematically illustrates a cross section Z-Z of a portion of the plate pack of  FIG. 1 , with heat transfer plates rotated in relation to each other, 
         FIG. 4 d    schematically illustrates a cross section Q-Q of a portion of the plate pack of  FIG. 1 , with heat transfer plates rotated in relation to each other, 
         FIG. 5 a    schematically illustrates a cross section of a portion of a plate pack corresponding to cross section X-X, with heat transfer plates flipped in relation to each other, 
         FIG. 5 b    schematically illustrates a cross section of a portion of a plate pack corresponding to cross section Y-Y, with heat transfer plates flipped in relation to each other, 
         FIG. 5 c    schematically illustrates a cross section of a portion of a plate pack corresponding to cross section Z-Z, with heat transfer plates flipped in relation to each other, 
         FIG. 5 d    schematically illustrates a cross section of a portion of a plate pack corresponding to cross section Q-Q, with heat transfer plates flipped in relation to each other, 
         FIG. 6  schematically illustrates a cross section of the plate pack portion of  FIGS. 4 a -4 d    as well as the plate pack portion of  FIGS. 5 a -5 d    parallel to a respective longitudinal centre axis, and through a respective outer edge portion, of the heat transfer plates, and 
         FIG. 7  schematically illustrates an alternative cross section of a female recess or a male projection of the guiding sections. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a plate pack  2  for a gasketed plate heat exchanger comprising a plurality of heat transfer plates is shown. All of the heat transfer plates are of the same type. In  FIGS. 4 a   - 4   d,  which will be further discussed below, a first, a second and a third heat transfer plate  4   a,    4   b  and  4   c,  respectively, of this plurality of heat transfer plates are illustrated. The first heat transfer plate  4   a  is also visible in  FIG. 1 . The design and function of a gasketed plate heat exchanger are well known and were discussed by way of introduction and, therefore, no further description is given here. 
     The heat transfer plate  4   a  will now be further described with reference to  FIGS. 1, 2   a - 2   d  and  3   a - 3   g  which illustrate the heat transfer plate and portions and cross sections of the heat transfer plate, respectively. The heat transfer plate  4   a  is an essentially rectangular sheet of stainless steel having opposing first and second sides  6  and  8 , respectively, which also may be referred to as front and back sides. In  FIG. 1 , only the first side  6  is visible. The heat transfer plate  4   a  comprises two opposing long sides  10  and two opposing short sides  12 . 
     The heat transfer plate further has a longitudinal centre axis  20  extending parallel to, and half way between, the long sides  10 , and a transverse centre axis  22  extending parallel to, and half way between, the short sides  12 , and thus perpendicular to the longitudinal centre axis  20  ( FIG. 1 ). The longitudinal and transverse centre axes divide the heat transfer plate  4   a  into four equally large first, second, third and four plate areas,  24 ,  26 ,  28  and  30 , respectively. The first and second plate areas  24  and  26  are arranged on the same side of the transverse centre axis  22  while the first and the third plate areas  24  and  28  are arranged on the same side of the longitudinal centre axis  20 . 
     The heat transfer plate  4   a  comprises four port holes  32  arranged at a respective one of four corners  34 ,  36 ,  38  and  40  of the heat transfer plate, and recesses  42  extending from a respective one of the short sides  12  of the heat transfer plate  4   a  and arranged to receive carrying and guiding bars of the plate heat exchanger. 
     The heat transfer plate  4   a  is pressed, in a conventional manner, in a pressing tool, to be given a desired structure, more particularly different corrugation patterns within different portions of the heat transfer plate. The corrugation patterns are optimized for the specific functions of the respective plate portions. Accordingly, the heat transfer plate  4   a  comprises two distribution areas  44  which each is provided with a distribution pattern adapted for optimized fluid distribution across the heat transfer plate. Further, the heat transfer plate  4   a  comprises a heat transfer area  46  arranged between the distribution areas  44  and provided with a heat transfer pattern adapted for optimized heat transfer between two fluids flowing on opposite sides of the heat transfer plate. Moreover, the heat transfer plate  4   a  comprises inner edge portions  48  surrounding the port holes  32  and an outer edge portion  50  extending along an outer edge  51  of the heat transfer plate  4   a.  The inner and outer edge portions  48  and  50  comprises corrugations  52  which make the inner and outer edge portions stiffer and, thus, the heat transfer plate  4   a  more resistant to deformation. Further, the corrugations  52  form a support structure in that they are arranged to abut adjacent heat transfer plates when the heat transfer plate  4   a  is arranged in the plate heat exchanger. Depending on the design of the distribution and heat transfer patterns, the heat transfer plate  4   a  may also be arranged to abut adjacent heat transfer plates within the distribution and heat transfer areas  44  and  46 , respectively, when the heat transfer plate is arranged in the plate heat exchanger. However, this is not further discussed herein. Also, the heat transfer plate  4   a  comprises a groove  53  arranged to receive a gasket. 
     With reference especially to  FIGS. 2 d , 3 e  and 3 f   , the corrugations  52  extend within and between a first plane  54  and a second plane  56 , which are parallel to a central extension plane  58  and to the figure plane of  FIG. 1 . The central extension plane  58  extends half way between the first and second planes  54  and  56 , respectively, and a bottom of the groove  53  extends in the central extension plane, i.e. in so called half plane. 
     The first, second, third and fourth plate areas  24 ,  26 ,  28  and  30  comprise a first, second, third and fourth guiding section  60 ,  62 ,  64  and  66 , respectively, arranged at a respective one of the four corners  34 ,  36 ,  38  and  40  of the heat transfer plate  4   a.  With reference especially to  FIGS. 2 a , 3 a , 2 d , 3 d  and 3 f   , the first and fourth guiding sections  60  and  66  comprise, as seen from the first side  6  of the heat transfer plate  4   a,  a respective male projection  68  and  70 . The male projections  68  and  70  project from a respective first plane portion  72  and  74  of the first and fourth guiding sections  60  and  66  surrounding the respective male projections  68  and  70  and extending in the first plane  54 . Thus, the male projections  68  and  70  project from the first plane  54 , to a third plane  76  arranged on the opposite side of the first plane  54  than the central extension plane  58 . Further, the first and fourth guiding sections  60  and  66  comprise, as seen from the second side  8  of the heat transfer plate  4   a,  a respective female recess  78  and  80 . The female recesses  78  and  80  extend from a respective second plane portion  82  and  84  of the first and fourth guiding sections  60  and  66  surrounding the respective female recesses  78  and  80  and extending in the second plane  56 . Thus, the female recesses  78  and  80  extend from the second plane  56 , to a fourth plane  86  arranged on the same side of the central extension plane  58  as the first plane  54 . 
     Similarly, with reference especially to  FIGS. 2 b , 3 b , 2 c  and 3 c    the second and third guiding sections  62  and  64  comprise, as seen from the second side  8  of the heat transfer plate  4   a,  a respective male projection  88  and  90 . The male projections  88  and  90  project from a respective second plane portion  92  and  94  of the second and third guiding sections  62  and  64  surrounding the respective male projections  88  and  90  and extending in the second plane  56 . Thus, the male projections  88  and  90  projects from the second plane  56 , to a fifth plane  96  arranged on the opposite side of the second plane  56  than the central extension plane  58 . Further, the second and third guiding sections  62  and  64  comprise, as seen from the first side  6  of the heat transfer plate  4   a,  a respective female recess  98  and  100 . The female recesses  98  and  100  extend from a respective first plane portion  102  and  104  of the second and third guiding sections  62  and  64  surrounding the respective female recesses  98  and  100  and extending in the first plane  54 . Thus, the female recesses  102  and  104  extends from the first plane  54 , to a sixth plane  106  arranged on the same side of the central extension plane  58  as the second plane  56 . 
     Naturally, the male projections as seen from one side of the heat transfer plate forms female recesses as seen from the other side of the plate, and vice versa. 
     Thus, as is clear from  FIGS. 2 a , 2 b , 2 c  and 2 d   , each of the first, second, third and fourth guiding sections  60 ,  62 ,  64  and  66  comprises a male projection and a female recess. Within each of the first, second, third and fourth guiding sections, the female recess and the male projection are arranged on opposite sides of an imaginary straight line  108  extending from the respective one of the corners  34 ,  36 ,  38  and  40  with an angle of 45 degrees in relation to the long side and the short side defining the respective one of the corners. 
     The male projections  68 ,  70 ,  88  and  90  and the female recesses  78 ,  80 ,  98  and  100  all have, parallel to the central extension plane  58 , an essentially uniform rectangular cross section, with a cross section of the female recesses being larger than the cross section of the male projections. All the female recesses have essentially the same cross section while all the male projections have essentially the same cross section. Thus, the male projections fit into the female recesses. Further, all the female recesses have essentially the same depth d while all the male projections have essentially the same height h, and d is essentially equal to h. The depth d and height h of the female recess  78  and the male projection  68  of the first guiding section  60  is illustrated in  FIG. 2   a.    
     As is clear from  FIG. 1  in combination with  FIGS. 2 a , 2 b , 2 c  and 2 d   , an opening  78 ′ and  98 ′ of each of the female recesses  78  and  98  of the first and second guiding sections  60  and  62 , respectively, extends from a distance FL 3  to a distance FL 4  from the transverse centre axis  22 , and from a distance FW 3  to a distance FW 4  from the longitudinal centre axis  20 . Further, a top  90 ′ and  70 ′ of each of the male projections  90  and  70  of the third and fourth guiding sections  64  and  66 , respectively, extends from a distance ML 3  to a distance ML 4  from the transverse centre axis  22 , and from a distance MW 3  to a distance MW 4  from the longitudinal centre axis  20 . FL 3 &lt;ML 3 &lt;ML 4 &lt;FL 4  and FW 3 &lt;MW 3 &lt;MW 4 &lt;FW 4 . Furthermore, a top  68 ′ and  88 ′ of each of the male projections  68  and  88  of the first and second guiding sections  60  and  62 , respectively, extends from a distance ML 1  to a distance ML 2  from the transverse centre axis  22 , and from a distance MW 1  to MW 2  from the longitudinal centre axis  20 . Further, an opening  100 ′ and  80 ′ of each of the female recesses  100  and  80  of the third and fourth guiding sections  64  and  66 , respectively, extends from a distance FL 1  to a distance FL 2  from the transverse centre axis  22 , and from a distance FW 1  to a distance FW 2  from the longitudinal centre axis  20 . FL 1 &lt;ML 1 &lt;ML 2 &lt;FL 2  and FW 1 &lt;MW 1 &lt;MW 2 &lt;FW 2 . 
     With reference especially to  FIGS. 2 a , 2 b , 2 c , 2 d , 3 e , 3 f  and 3 g   , in order to stiffen the corners  34 ,  36 ,  38  and  40  of the heat transfer plate  4   a,  each of the first plane portions  72 ,  102 ,  104  and  74  of the first, second, third and fourth guiding sections  60 ,  62 ,  64  and  66 , respectively, “branches” towards the outer edge  51  of the heat transfer plate  4   a  so as to define and partly enclose a third plane portion  110 ′,  112 ′,  114 ′ and  116 ′, respectively, extending in the second plane  56 . More particularly, the first plane portions  72 ,  102 ,  104  and  74  each comprises a “branch” or sub portion forming a first reinforcement projection  72 ′,  102 ′,  104 ′ and  74 ′ on one side of the respective one of the second plane portions  82 ,  92 ,  94  and  84 . The respective most adjacent one of the corrugations  52  on the other opposing side of the second plane portions  82 ,  92 ,  94  and  84  forms second reinforcement projections  52 A,  52 B,  52 C and  52 D. Each of the third plane portions  110 ′,  112 ′,  114 ′ and  116 ′ forms a bottom of a respective first reinforcement recesses  110 ,  112 ,  114  and  116  arranged on one side of the respective one of the first plane portions  72 ,  102 ,  104  and  74 . The respective most adjacent one of the corrugations  52  on the other opposing side of the first plane portions  72 ,  102 ,  104  and  74  forms second reinforcement recesses  52   a,    52   b,    52   c  and  52   d.    
       FIGS. 4 a -4 d    illustrate cross sections of the first, second and third heat transfer plates  4   a,    4   b  and  4   c  of the plate pack  2  of  FIG. 1 . The second heat transfer plate  4   b  is arranged between the first and third heat transfer plates  4   a  and  4   c.  Further, the second heat transfer plate  4   b  is rotated 180 degrees about an axis perpendicular to, and extending through a cross point between, its transverse and longitudinal centre axes  20  and  22 , in relation to the first and third heat transfer plates  4   a  and  4   c.  Thereby, the first and second sides  6  and  8  of the second heat transfer plate  4   b  abut the second side  8  of the first heat transfer plate  4   a  and the first side  6  of the third heat transfer plate  4   c,  respectively. More particularly, portions of the second heat transfer plate  4   b  extending in the first plane  54  contact opposing portions of the first heat transfer plate  4   a  extending in the second plane  56 , and portions of the second heat transfer plate  4   b  extending in the second plane  56  contact opposing portions of the third heat transfer plate  4   c  extending in the first plane  54 . For example, as schematically illustrated in  FIG. 6  for the outer edge portions of the heat transfer plates  4   a,    4   b  and  4   c,  the corrugations  52  of the inner and outer edge portions  48  and  50  ( FIG. 1 ) of the second heat transfer plate  4   b  abut the corrugations  52  of the inner and outer edge portions  48  and  50  of the first and third heat transfer plates  4   a  and  4   c  at the first side  6  and the second side  8 , respectively, of the second heat transfer plate  4   b.  Further, the first reinforcement projections  72 ′,  102 ′,  104 ′,  74 ′ and the third plane portions  110 ′,  112 ′,  114 ′,  116 ′ of the second heat transfer plate  4   b  partly abut the third plane portions  116 ′,  114 ′,  112 ′,  110 ′ of the first heat transfer plate  4   a  and the first reinforcement projections  74 ′,  104 ′,  102 ′,  72 ′ of the third heat transfer plate  4   c,  respectively. 
     Further, the fourth guiding section  66  of the second heat transfer plate  4   b  engages with the first guiding sections  60  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 4 a   ). More particularly, the male projection  70  of the second heat transfer plate  4   b  is received in the female recess  78  of the first heat transfer plate  4   a  and the first plane portion  74  of the second heat transfer plate  4   b  abuts the second plane portion  82  of the first heat transfer plate  4   a.  Further, the male projection  68  of the third heat transfer plate  4   c  is received in the female recess  80  of the second heat transfer plate  4   b  and the first plane portion  72  of the third heat transfer plate  4   c  abuts the second plane portion  84  of the second heat transfer plate  4   b.    
     Further, the third guiding section  64  of the second heat transfer plate  4   b  engages with the second guiding sections  62  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 4 b   ). More particularly, the male projection  88  of the first heat transfer plate  4   a  is received in the female recess  100  of the second heat transfer plate  4   b  and the second plane portion  92  of the first heat transfer plate  4   a  abuts the first plane portion  104  of the second heat transfer plate  4   b.  Further, the male projection  90  of the second heat transfer plate  4   b  is received in the female recess  98  of the third heat transfer plate  4   c  and the second plane portion  94  of the second heat transfer plate  4   b  abuts the first plane portion  102  of the third heat transfer plate  4   c.    
     Further, the second guiding section  62  of the second heat transfer plate  4   b  engages with the third guiding sections  64  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 4 c   ). More particularly, the male projection  90  of the first heat transfer plate  4   a  is received in the female recess  98  of the second heat transfer plate  4   b  and the second plane portion  94  of the first heat transfer plate  4   a  abuts the first plane portion  102  of the second heat transfer plate  4   b.  Further, the male projection  88  of the second heat transfer plate  4   b  is received in the female recess  100  of the third heat transfer plate  4   c  and the second plane portion  92  of the second heat transfer plate  4   b  abuts the first plane portion  104  of the third heat transfer plate  4   c.    
     Further, the first guiding section  60  of the second heat transfer plate  4   b  engages with the fourth guiding sections  66  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 4 d   ). More particularly, the male projection  68  of the second heat transfer plate  4   b  is received in the female recess  80  of the first heat transfer plate  4   a  and the first plane portion  72  of the second heat transfer plate  4   b  abuts the second plane portion  84  of the first heat transfer plate  4   a.  Further, the male projection  70  of the third heat transfer plate  4   c  is received in the female recess  78  of the second heat transfer plate  4   b  and the first plane portion  74  of the third heat transfer plate  4   c  abuts the second plane portion  82  of the second heat transfer plate  4   b.    
     Thereby, in the plate pack  2 , the second heat transfer plate  4   b  engages, at all four of its guiding sections  60 ,  62 ,  64  and  66 , with both the first and the third heat transfer plate  4   a,    4   c,  which results in a reliable and effective alignment of the first, second and third heat transfer plates. 
     In the above described plate pack  2 , the heat transfer plates are “rotated” in relation to each other. In an alternative plate pack according to the invention, the heat transfer plates are instead “flipped” in relation to each other. Accordingly, the second heat transfer plate  4   b  is arranged between the first and third heat transfer plates  4   a  and  4   c.  Further, the first and third heat transfer plates  4   a  and  4   b  are both rotated 180 degrees about their respective transverse centre axis  22 , in relation to the second heat transfer plate  4   b.  Thereby, the first and second sides  6  and  8  of the second heat transfer plate  4   b  abut the first side  6  of the first heat transfer plate  4   a  and the second side  8  of the third heat transfer plate  4   c,  respectively. More particularly, portions of the second heat transfer plate  4   b  extending in the first plane  54  contact opposing portions of the first heat transfer plate  4   a  extending in the first plane  54 , and portions of the second heat transfer plate  4   b  extending in the second plane  56  contact opposing portions of the third heat transfer plate  4   c  extending in the second plane  56 . For example, as schematically illustrated in  FIG. 6  for the outer edge portions of the heat transfer plates  4   a,    4   b  and  4   c,  the corrugations  52  of the inner and outer edge portions  48  and  50  ( FIG. 1 ) of the second heat transfer plate  4   b  abut the corrugations  52  of the inner and outer edge portions  48  and  50  of the first and third heat transfer plates  4   a  and  4   c  at the first side  6  and the second side  8 , respectively, of the second heat transfer plate  4   b.  Further, the first reinforcement projections  72 ′,  102 ′,  104 ′,  74 ′ and the third plane portions  110 ′,  112 ′,  114 ′,  116 ′ of the second heat transfer plate  4   b  partly abut first reinforcement projections  104 ′,  74 ′,  72 ′,  102 ′ of the first heat transfer plate  4   a  and the third plane portions  114 ′,  116 ′,  110 ′,  112 ′ of the third heat transfer plate  4   c,  respectively. 
     Further, the third guiding section  64  of the second heat transfer plate  4   b  engages with the first guiding sections  60  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 5 a   ). More particularly, the male projection  68  of the first heat transfer plate  4   a  is received in the female recess  100  of the second heat transfer plate  4   b  and the first plane portion  72  of the first heat transfer plate  4   a  abuts the first plane portion  104  of the second heat transfer plate  4   b.  Further, the male projection  90  of the second heat transfer plate  4   b  is received in the female recess  78  of the third heat transfer plate  4   c  and the second plane portion  94  of the second heat transfer plate  4   b  abuts the second plane portion  82  of the third heat transfer plate  4   c.    
     Further, the fourth guiding section  66  of the second heat transfer plate  4   b  engages with the second guiding sections  62  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 5 b   ). More particularly, the male projection  70  of the second heat transfer plate  4   b  is received in the female recess  98  of the first heat transfer plate  4   a  and the first plane portion  74  of the second heat transfer plate  4   b  abuts the first plane portion  102  of the first heat transfer plate  4   a.  Further, the male projection  88  of the third heat transfer plate  4   c  is received in the female recess  80  of the second heat transfer plate  4   b  and the second plane portion  92  of the third heat transfer plate  4   c  abuts the second plane portion  84  of the second heat transfer plate  4   b.    
     Further, the first guiding section  60  of the second heat transfer plate  4   b  engages with the third guiding sections  64  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 5 c   ). More particularly, the male projection  68  of the second heat transfer plate  4   b  is received in the female recess  100  of the first heat transfer plate  4   a  and the first plane portion  72  of the second heat transfer plate  4   b  abuts the first plane portion  104  of the first heat transfer plate  4   a.  Further, the male projection  90  of the third heat transfer plate  4   c  is received in the female recess  78  of the second heat transfer plate  4   b  and the second plane portion  94  of the third heat transfer plate  4   c  abuts the second plane portion  82  of the second heat transfer plate  4   b.    
     Further, the second guiding section  62  of the second heat transfer plate  4   b  engages with the fourth guiding sections  66  of the first and third heat transfer plates  4   a  and  4   c  ( FIG. 5 d   ). More particularly, the male projection  70  of the first heat transfer plate  4   a  is received in the female recess  98  of the second heat transfer plate  4   b  and the first plane portion  74  of the first heat transfer plate  4   a  abuts the first plane portion  102  of the second heat transfer plate  4   b.  Further, the male projection  88  of the second heat transfer plate  4   b  is received in the female recess  80  of the third heat transfer plate  4   c  and the second plane portion  92  of the second heat transfer plate  4   b  abuts the second plane portion  84  of the third heat transfer plate  4   c.    
     Thereby, in the plate pack above, the second heat transfer plate  4   b  engages, at all four of its guiding sections  60 ,  62 ,  64  and  66 , with both the first and the third heat transfer plate  4   a,    4   c,  which results in a reliable and effective alignment of the first, second and third heat transfer plates. 
     Thus, due to the inventive construction of the first, second, third and fourth guiding sections  60 ,  62 ,  64  and  66 , the heat transfer plates  4   a,    4   b  and  4   c  are properly aligned with each other in a plate pack irrespective of whether they are rotated or flipped in relation to each other. Due to the design, and location on the heat transfer plates, of the female recesses and male projections, the actual alignment of the heat transfer plates is performed by means of outer portions of the female recesses and the male projections, i.e. portions of the female recesses and the male projections facing the respective outer edges  51  of the heat transfer plates. Thus, when the heat transfer plates are aligned, the outer portions of the female recesses and the male projections of one heat transfer plate engage with the outer portions of the male projections and the female recesses, respectively, of the adjacent plates. Inner portions of the female recesses and the male projections, i.e. portions of the female recesses and the male projections facing away from the respective outer edges  51  of the heat transfer plates, do not engage with each other. 
     In that the first and second plane portions  72 ,  74 ,  102 ,  104  and  82 ,  84 ,  92  and  94  extend in the first and second planes  54  and  56 , and the depth of the female recesses  78 ,  80 ,  98  and  100  is equal to the height of the male projections  68 ,  70 ,  88  and  90 , the first and second plate portions, just like inside bottom surfaces of the female recesses and outside top surfaces of the male projections, will abut each other in the plate pack and so make the plate pack more stable. 
     The above described embodiments of the present invention should only be seen as an example. A person skilled in the art realizes that the embodiments discussed can be varied and combined in a number of ways without deviating from the inventive conception. 
     For example, the female recesses and the male projections need not have a rectangular cross section. As an example, they may have a round, triangular or pentagonal cross section, such as the cross section illustrated in  FIG. 7 , which defines a right angle and comprises two outer portions  118  and  120  which are perpendicular to each other for optimum heat transfer plate alignment. Since the alignment function resides within the outer portions  118  and  120 , the inner portions can be cut or shortened so as to enable space efficient female recesses and male projections with large alignment capability. 
     Further, the female recesses need not all have the same cross section and the same depth. Similarly, the male projections need not all have the same cross section and the same height. Also, the depth of the female recesses need not be equal to the height of the male projections but could be larger or even smaller. Also, one or more of the first plane portions of the guiding sections may extend in a plane different from the first plane. Similarly, one or more of the second plane portions of the guiding sections may extend in a plane different from the second plane. 
     Also, the alignment function need not reside solely within the outer portions of the female recesses and the male projections but could instead reside solely within the inner portions of the female recesses and the male projections, or within one or more of the outer portions and/or one or more of the inner portions of the female recesses and the male projections. 
     The heat transfer plate need not be rectangular but may have other shapes, such as essentially rectangular with rounded corners instead of right corners, circular or oval. The heat transfer plate need not be made of stainless steel but could be of other materials, such as titanium or aluminium. 
     The guiding sections of the heat transfer plate need not be arranged at a respective corner of the heat transfer plate but could be arranged closer to the longitudinal centre axis and/or closer to the transverse centre axis. Also, within each of the guiding sections, the female recess and the male projection need not be arranged on opposite sides, but could instead be arranged on the same side, of the imaginary straight line  108  illustrated in  FIGS. 2 a , 2 b , 2 c  and 2 d   . Further, the distance between the female recess and the male projection of each of the guiding section could vary. Typically, the female recesses and the male projections are arranged where there is room available on the heat transfer plate, e.g. in the corners and/or at the centre of the short sides, close to the outer edge, of the heat transfer plate. 
     The plate packs described above comprises one plate type only. Naturally, the plate packs could instead comprise two or more different types of alternately arranged heat transfer plates, for example heat transfer plates with different heat transfer patterns and/or guiding sections as long as the heat transfer patterns and/or the guiding sections are compatible with each other. 
     The present invention could be used in connection with other types of plate heat exchangers than gasketed ones, such as brazed, all-welded and semi-welded (heat transfer plates pairwise welded to each other in cassettes, which cassettes are separated by gaskets) plate heat exchangers. The present invention could also be used with plate heat exchangers lacking carrying and guiding bars, i.e. for heat transfer plates lacking recesses for receiving such carrying and guiding bars. 
     The locations of the first, second, central extension, third, fourth, fifth and sixth planes  54 ,  56 ,  58 ,  76 ,  86 ,  96  and  106  need not be as above defined but could vary. As an example, with reference to  FIGS. 3 a , 3 d  and 4 a   , the fourth plane  86  could instead extend between the second plane  56  and the central extension plane  58 , and the third plane  76  could consequently extend closer to the first plane  54 . As another example, the fourth plane  86  could instead extend between the first plane  54  and the third plane  76 , and the third plane  76  could consequently extend farther away from the first plane  54 . 
     It should be stressed that a description of details not relevant to the present invention has been omitted and that the figures are just schematic and not drawn according to scale. It should also be said that some of the figures have been more simplified than others. Therefore, some components may be illustrated in one figure but left out on another figure.