Heat exchanger with recesses to avoid stagnant medium

Abstract

A brazed plate heat exchanger comprising an end plate 11 and a stack of heat exchanger plates 12, 12a, 12b provided with a pattern including ridges R and grooves G that form contact points 16 between adjacent heat exchanger plates, the heat exchanger plates forming inter-plate flow paths through which a medium exchanges heat on the heat exchanger plates, the heat exchanger plates further provided with port openings O1-O4 in selective fluid communication with the flow paths, the port openings being surrounded by port opening areas 13 that seal against corresponding port opening areas of adjacent heat exchanger plates, the adjacent heat exchanger plates being brazed at the contact points. The end plates are connected by brazing joints, and the end plates have port openings and flat areas 14 around the port openings in a common plane, and recesses 15 are formed in multiple protrusions R of the heat exchanger plates in areas overlapping with any of the flat areas of the end plates, and the recesses in the heat exchanger plates adjacent to the end plates connect the flow paths formed between the end plate and the adjacent heat exchanger plates with adjacent flow paths to allow the flow of medium therebetween, and the brazing joints connecting the adjacent heat exchanger plates are arranged between the port opening area and at least one recess.

Description

[Technical Field]

[0001] The present invention relates to a heat exchanger with indentations to avoid stagnant media. More specifically, the present invention relates to a brazed plate heat exchanger including an end plate and a stack of heat exchanger plates having a pattern including ridges and grooves adapted to form contact points between adjacent heat exchanger plates and allow the heat exchanger plates to form inter-plate flow channels through which a media exchanges heat on the heat exchanger plates. The heat exchanger plates further have port openings formed therein that selectively fluidly communicate with the flow channels, and the port openings are surrounded by port opening areas that seal against corresponding port opening areas of adjacent heat exchanger plates. The adjacent heat exchanger plates are connected at the contact points by brazed joints. The end plate has port openings and flat areas around the port openings in a common plane. Indentations are formed in the multiple ridges of the heat exchanger plate in areas overlapping the flat areas of the end plate, and the indentations in the heat exchanger plate adjacent to the end plate connect the flow channels formed between the end plate and the adjacent heat exchanger plate with adjacent flow channels, allowing a media to flow therebetween. [Background technology]

[0002] When exchanging heat between different media in any type of heat exchanger, it is generally preferable to avoid stagnant media, i.e., media that is stationary and not moving through a general flow path. Stagnant media is troublesome for many reasons, including damaging the heat exchanger because bacteria or microorganisms can grow in the stagnant areas, causing the media to stop moving. Furthermore, it can hinder the general efficiency of the heat exchanger. In the case of brazed plate heat exchangers, which contain a pressed pattern of ridges and grooves that maintain the heat exchanger plates at a distance from each other, the area historically critical to the formation of stagnant media is between the end plates, which have flat areas near the port openings, and the adjacent heat exchanger plate, which creates a dead-end flow path between the end plates where the media is prone to stagnation.

[0003] The '699 patent solves the problem of stagnant media in the space between the flat area of the end plate and the adjacent heat exchanger plate by providing a distribution channel between the flow passage and the adjacent flow passage (which would otherwise be a dead-end flow passage). The distribution channel allows flow (which would otherwise be "still" in the dead-end flow passage). The distribution channel in the '699 patent is located directly adjacent to the port opening area, i.e., at the very rear end of the ridge. While the solution disclosed in this patent is effective in avoiding stagnant media, it has some drawbacks in terms of strength.

[0004] Therefore, the prior art heat exchangers are weak and cannot withstand high pressures. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 0857288 Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide a brazed plate heat exchanger that reduces the risk of stagnant media and improves the strength of the heat exchanger by increasing the number of contact points between the ridges and grooves of adjacent plates around the port opening area. [Means for solving the problem]

[0007] The present invention provides 1. A brazed plate heat exchanger comprising: end plates; and a stack of heat exchanger plates having a pattern including ridges and grooves adapted to form contact points between adjacent heat exchanger plates such that the heat exchanger plates form inter-plate flow paths through which a medium exchanges heat on the heat exchanger plates, the heat exchanger plates further having port openings in selective fluid communication with the flow paths, the port openings being surrounded by port opening areas that seal against corresponding port opening areas of adjacent heat exchanger plates, the adjacent heat exchanger plates being connected by brazed joints at the contact points, the end plates The plate has port openings and flat areas around the port openings in a common plane, and recesses are formed in the multiple protrusions of the heat exchanger plate in areas overlapping with any of the flat areas of the end plates, and the recesses in the heat exchanger plate adjacent to the end plate connect the flow passages formed between the end plate and the adjacent heat exchanger plate with adjacent flow passages to enable the flow of a medium therebetween, and the brazed joint connecting the adjacent heat exchanger plates is located between the port opening area and at least one recess.

[0008] By providing the depressions, raised cross-channels are formed for the flow of media and prevent stagnant media from being present in what would otherwise be dead-end channels in the space between an end plate and an adjacent heat exchanger plate, such as the first or last plate in the stack. Furthermore, it was surprisingly discovered that by positioning the depressions a short distance from the rearmost ends of the channels, i.e., away from the port opening areas closest to the depressions, space is provided for the contact points and therefore the brazed joints, while still preventing stagnant media in the channels. Therefore, it was discovered that good media flow is achieved even when brazed joints are located between the depressions and the port opening areas. The brazed joints between the port opening areas and at least some of the depressions result in a stronger heat exchanger. Furthermore, the pressure areas around the ports are reduced because the contact points are closer to the port opening areas. Additional contact points are achieved. Furthermore, the contact points are closer to the port openings. For example, the distance between the port opening and the first row of contact points can be shorter than in the prior art, resulting in a smaller area around the port opening exposed to medium pressure, and a higher density of contact points in the immediate vicinity of the port opening, resulting in a stronger heat exchanger and preventing stagnant medium in dead-end flow paths.

[0009] The end plate may be a conventional end plate having a flat area around the port opening, e.g., at the end of a rectangular end plate. The port opening and the flat area of the end plate are disposed in a common plane. The end plate may be a front end plate or a back end plate. The flat area of the end plate may be adapted to connect to a hydroblock or similar conventional fitting. The end plate may have a ridge and groove pattern in the center portion.

[0010] The contact points can be located on the ridges on either side of a recess or recesses that connect a flow path with an adjacent flow path (which would otherwise form a dead-end flow path together with the end plate). Thus, a very strong heat exchanger can be obtained while preventing stagnant medium. Therefore, the heat exchanger plates can be connected to each other by multiple rows of brazed joints, and the recess or recesses can be located between the first and second rows of brazed joints, counting from the port opening area closest to the recess.

[0011] The present invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic exploded view of a heat exchanger according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic front view of the heat exchanger plate of FIG. [Figure 3] FIG. 3 is a schematic front view of the heat exchanger plate of FIG. 2, showing imaginary contact points between the shown plate and a further heat exchanger plate. [Figure 4] FIG. 4 is a schematic exploded view of a heat exchanger according to a second embodiment of the present invention. [Figure 5] FIG. 5 is a schematic front view of the heat exchanger plate of FIG. [Figure 6] FIG. 6 is a schematic front view of the heat exchanger plate of FIG. 5, showing imaginary contact points between the shown plate and a further heat exchanger plate. [Figure 7] FIG. 7 is a schematic front view of a heat exchanger plate according to a third embodiment. [Figure 8] FIG. 8 is a schematic front view of the heat exchanger plate of FIG. 7, showing imaginary contact points between the shown plate and a further heat exchanger plate. [Figure 9] FIG. 9 is a schematic front view of a heat exchanger plate according to another embodiment of the present invention, showing one type of plate. [Figure 10]FIG. 10 is a schematic front view of a heat exchanger plate according to another embodiment of the present invention, showing another type of interleaved plate. [Figure 11] FIG. 11 is a schematic perspective view of a portion of the heat exchanger plate of FIG. 9, showing imaginary contact points in both directions between the shown plate and a further heat exchanger plate. DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to Figure 1, there is shown a schematic diagram of a heat exchanger 10 according to one embodiment of the present invention. The heat exchanger 10 includes an end plate 11 and a plurality of heat exchanger plates 12 stacked in a stack to form the heat exchanger 10. In the embodiment of Figure 1, the heat exchanger plates 12 are identical.

[0014] The heat exchanger plates 12 are made from sheet metal and are provided with a pattern of ridges R and grooves G so that, when the plates are stacked to form the heat exchanger 10, interplate flow passages through which fluids exchange heat are formed between the plates. Contact points are established between at least some of the intersecting ridges and grooves of adjacent plates 12, forming the interplate flow passages through which fluids exchange heat. The pattern in the embodiment of FIGS. 1-3 is a herringbone pattern. However, the pattern may also be in the form of diagonally extending straight lines, as described below. The pattern of ridges R and grooves G is a corrugated pattern having a corrugation depth. The pattern is a pressed pattern. The pattern is adapted to maintain the plates 12 at a distance from each other except at the contact points, creating spaces between adjacent heat exchanger plates and flow passages.

[0015] In the embodiment shown, to provide a seal along the circumference of the heat exchanger 10, each heat exchanger plate 12 is surrounded by a skirt S that extends approximately perpendicular to the plane of the heat exchanger plate 12 and is adapted to contact the skirt of an adjacent plate 12.

[0016] Port openings O1-O4 are arranged on the heat exchanger plate 12 to allow heat-exchanging fluid to enter and exit the inter-plate flow passages. In the illustrated embodiment, four port openings O1-O4 are arranged on the end plate 11 and the heat exchanger plate 12. Some port openings are not shown in FIG. 1 , but this is understood by those skilled in the art and does not affect the disclosure of the present invention. Port opening areas 13 surrounding the port openings O1-O4 are provided at different heights, i.e., different levels, to achieve selective communication between the port openings and the inter-plate flow passages. For example, the port opening areas 13 are flat. The port opening areas 13 are arranged to seal against corresponding port opening areas 13 on the adjacent heat exchanger plate 12. For example, the port openings O1-O4 and the port opening areas 13 are arranged in a conventional manner.

[0017] In the heat exchanger 10 of FIG. 1 , the port opening region 13 is arranged such that the first port opening O1 and the second port opening O2 are in fluid communication with each other through interplate channels, and the third port opening O3 and the fourth port opening O4 are in fluid communication with each other through adjacent interplate channels. In the illustrated embodiment, the heat exchanger plates 12 are rectangular with rounded corners, and the port openings O1-O4 are located near the corners. Alternatively, the heat exchanger plates 12 may be square with rounded corners, for example. Alternatively, the heat exchanger plates 12 may be arranged in a circular, elliptical, or other suitable shape, with the large port openings O1-O4 distributed in an appropriate manner. In the illustrated embodiment, four port openings O1-O4 are formed in each heat exchanger plate 12. Alternatively, the heat exchanger plates 12 may be formed with another number of ports, such as six, eight, or ten. In the embodiment of FIG. 1, the heat exchanger plates 12 are identical, with the plates 12 rotated 180 degrees in their plane relative to every other adjacent heat exchanger plate 12 .

[0018] The end plate 11 of FIG. 1 is formed with a flat region 14 having port openings O1-O4. The port openings O1-O4 of the end plate 11 are aligned with the port openings of the heat exchanger plate 12 in a conventional manner. For example, the end plate 11 includes a first end with a first flat region and adjacent port openings O1 and O3, and a second end with a second flat region and adjacent port openings O2 and O4. For example, the end plate 11 is a conventional end plate. In the illustrated embodiment, the end plate 11 includes a central portion having a pattern of ridges (R) and grooves (G) similar to that of the heat exchanger plate 12. The end portions do not have the ridge and groove pattern. Instead, the end portions are formed with flat regions 14 around at least the port openings O1-O4. The port openings O1-O4 and the flat region 14 are disposed in a common plane. Thus, the flat areas 14 of the end plate 11 form flow channels with the grooves (G) of an adjacent heat exchanger plate 12, such as the first heat exchanger plate in the stack of heat exchanger plates. The flat areas 14 form flow channels with the adjacent heat exchanger plate 12 near the port opening areas 13 of the adjacent heat exchanger plate 12.

[0019] When the heat exchanger plate 12 and the end plate 11 are attached to form part of the plate heat exchanger 10, the two port opening areas 13 come into contact with the flat area 14 of the end plate 11. Also, the ridge R of the heat exchanger plate 12 comes into contact with the flat area 14 of the end plate 11. Therefore, flow paths are formed between the flat area 14 at the end of the end plate 11 and the adjacent heat exchanger plate 12. The flow paths are formed in the areas between adjacent port openings of the heat exchanger plate 12. For example, flow paths are formed between the flat area 14 and the adjacent heat exchanger plate 12 by grooves G connected to the first port opening O1, and some grooves (G) end when the grooves G reach the port opening area 13 around the adjacent third port opening O3.

[0020] Referring again to FIG. 2 , the heat exchanger plate 12 is formed with indentations 15. The indentations 15 are positioned to provide trans-ridge flow channels. The indentations 15 are positioned on the ridges R of the heat exchanger plate 12, with at least some of the ridges having at least one indentation 15 formed therein. At least some of the indentations 15 are positioned near the port openings O3 and O4 to connect the grooves G that form flow channels with the flat regions 14 to adjacent grooves G, preventing stagnant medium in the flow channels between the heat exchanger plate 12 and the flat regions 14 of the end plates 11. By providing the indentations 15, dead-end flow channels bounded by the ridges R and the flat edges 14 of the end plates 11 are avoided. The indentations 15 are positioned to a depth corresponding to at least 5% of the depth of the corrugations of the heat exchanger plate 12. For example, the depth of the indentations 15 is less than 80% of the depth of the corrugations. For example, the depth of the depressions 15 is 20 to 80%, 40 to 80%, 50 to 80%, 50 to 60%, or 50% of the depth of the corrugations.

[0021] Referring to FIG. 3 , contact points 16 between a heat exchanger plate 12 and an additional heat exchanger plate are shown schematically. Typically, brazed joints are disposed at the contact points 16, and the contact points 16 correspond to the brazed joints. For example, each contact point 16 between adjacent heat exchanger plates 12 corresponds to a brazed joint. In FIG. 3 , the contact points 16 are shown on the rear surface of the heat exchanger plate 12, and contact points 16 on the front surface of an adjacent heat exchanger plate are located at corresponding locations on the protrusions R, such as some locations shown schematically by squares near the third port opening O3 in FIG. 3 , as will be understood by those skilled in the art. As shown in FIG. 3 , at least some of the recesses 15 are positioned at a distance from the port opening regions 13 of the third port opening O3 and the fourth port opening O4, leaving space for the brazed joints between the recesses 15 and the port openings O3 and O4. Therefore, the brazed joints connecting the heat exchanger plates to the adjacent ones are arranged between the port opening region 13 and at least one recess 15. The recesses 15 are formed in the regions where the plurality of ridges R of the heat exchanger plate 12 overlap with the flat region 14 of the end plate 11. The recesses 15 of the heat exchanger plate 12 adjacent to the end plate 11 connect the flow passages formed between the flat region 14 of the end plate 11 and the adjacent heat exchanger plate 12 with the adjacent flow passages, allowing the medium to flow therebetween and preventing stagnant medium therein. At the same time, the brazed joints connecting the adjacent heat exchanger plates 12 in the region overlapping with the flat region 14 of the end plate 11 are arranged between the port opening region 13 and at least one recess 15, or a plurality of recesses 15, or all of the recesses 15.

[0022] In the embodiment of FIGS. 1-3, the recesses 15 of the heat exchanger plate 12 are not all positioned immediately adjacent to the port openings O3 and O4. For example, every other recess 15 is positioned a significant distance from the port openings O3 and O4. For example, at least one recess 15 or multiple recesses 15 are positioned a distance from the nearest port opening region 13 corresponding to a brazed joint, and a recess 15 is positioned directly adjacent to the brazed joint between the recess 15 and the port opening region 13. For example, more recesses 15 are positioned near the port opening region 13 surrounding the fourth port O4 than near the port opening region 13 surrounding the third port opening O3.

[0023] 4-6, a second embodiment of a heat exchanger 10 is shown in which the end plates 11 are similar to those described above with reference to FIG. 1. Also, in FIG. 4, some port openings have been omitted, as would be understood by one skilled in the art. In the embodiment of FIGS. 4-6, the heat exchanger plates 12 are identical and are provided with a herringbone pattern of ridges R and grooves G, with every other heat exchanger plate 12 rotated 180 degrees in its plane.

[0024] 5, the heat exchanger plate 12 is provided with a plurality of recesses 15 that form trans-ridge channels and connect adjacent grooves G. In the illustrated embodiment, the recesses 15 are located on the ridges R of the heat exchanger plate 12 near the port openings O3, O4 and at a distance from the port openings O3, O4 to connect adjacent grooves G and prevent stagnant medium in the flow channels formed between the flat region 14 and the adjacent heat exchanger plate 12. In the embodiment of FIGS. 4-6, as shown schematically in FIG. 6, all of the ridges R in the region between the first port opening O1 and the third port opening O3 are formed with recesses 15, leaving space for contact points 16, and therefore brazed joints, between the port opening regions 13 of the third port opening O3 and the fourth port opening O4 and each recess 15. Also in Figure 6, contact points 16 are shown schematically between the heat exchanger plate 12 and a further heat exchanger plate behind the shown heat exchanger plate 12, and contact points 16 on the front side towards another heat exchanger plate 12 are at corresponding locations on the protrusions R, as will be understood by those skilled in the art, such as some locations shown schematically by squares near the third port opening O3 in Figure 6. As shown in Figure 6, the recesses 15 are positioned at a distance from the port opening regions 13 of the third port opening O3 and the fourth port opening O4, leaving space for a brazed joint between the recesses 15 and the port openings O3, O4. Thus, the brazed joint is positioned between the port opening region 13 and the recesses 15.

[0025] In the embodiment of FIGS. 4-6, all but one of the dimples 15 at each end of the plate are formed between the contact points 16. Thus, most of the dimples 15 are disposed between the contact points 16. For example, at least four or at least five dimples 15 are disposed near the third port opening O3, and more, such as at least six or seven, are disposed near the fourth port opening O4. In the embodiment of FIGS. 4-6, the dimples 15 near the third port opening O3 are disposed in a straight line in the longitudinal direction of the heat exchanger plate 12, e.g., parallel to the longitudinal centerline of the plate. For example, the dimples 15 form a continuous trans-ridge channel between the first and last dimples 15 in a row of dimples 15. For example, the dimples 15 near the fourth port opening O4 are disposed in a corresponding manner, optionally with additional dimples 15 deviating from the straight line. For example, the heat exchanger plates 12 are connected to one another by multiple rows of contact points 16, and the multiple recesses 15 are located between the first row of contact points 16 and the second row of contact points 16, counting from the nearest port opening area 13. Thus, the recesses 15 are located outside the first row of contact points 16. For example, a row of recesses 15 forming a continuous raised cross-channel is located outside the first row of contact points 16.

[0026] 7 and 8, the heat exchanger plate 12 is formed with a plurality of dimples 15 forming trans-ridge channels in another pattern, the dimples 15 being distributed between the first port opening O1 and the third port opening O3 and between the contact points 16. In the embodiment of FIGS. 7 and 8, more dimples 15 are distributed in a similar pattern over a larger area between the second port opening O2 and the fourth port opening O4. For example, the pattern of dimples 15 is a regular pattern.

[0027] 9 and 10, another embodiment of the present invention is shown, with FIG. 9 showing a first type heat exchanger plate 12a and FIG. 10 showing a second type heat exchanger plate 12b. The first type heat exchanger plates 12a and the second type heat exchanger plates 12b are alternately stacked and provided with end plates 11 to form a heat exchanger 10. The first type heat exchanger plates 12a and the second type heat exchanger plates 12b are provided with patterns of ridges R and grooves G in the form of diagonally extending straight lines. Thus, the heat exchanger 10 in the embodiment of FIGS. 9 and 10 includes two different types of heat exchanger plates 12a and 12b having patterns of ridges R and grooves G that form interplate flow channels, the flow channels being formed in the areas between the port openings O1-O4 between the flat area 14 of the end plate 11 and the adjacent heat exchanger plate 12a, where the adjacent heat exchanger plate 12a is of the first type. At least the first type heat exchanger plates 12a are formed with depressions 15 that form trans-ridge channels to prevent dead-end channels between the flat areas 14 of the end plates and the adjacent heat exchanger plates 12a. In the embodiment of Figures 9 and 10, the depressions 15 are also distributed over a large portion of the first type heat exchanger plates 12a, including the central heat exchange area.

[0028] Referring to FIG. 11 , contact points 16, and therefore brazed joints, are shown schematically on a portion of a first type of heat exchanger plate 12a. The contact points 16 are shown on both sides of the plate 12a. Thus, as shown in FIG. 11 , the recesses 15 near the port openings O1-O4, or at least most of them, are located between the contact points 16. Thus, a contact point 16 is formed between the port opening region 13 and the nearest recess 15, which forms a trans-ridge channel connecting adjacent grooves G in the region overlapping the flat region 14, and another contact point 16 is located on the ridge R on the other side of the same recess 15. For example, the contact points 16 between adjacent heat exchanger plates 12 are located immediately before and after the recesses 15 in the region overlapping the flat region 14 of the end plate 11, which connect the channels with adjacent channels. Therefore, the recesses 15 in the heat exchanger plates 12a adjacent to the end plates 11 connect the flow passages formed between the flat areas 14 of the end plates 11 and the adjacent heat exchanger plates 12a with the adjacent flow passages to allow the flow of medium therebetween and prevent stagnant medium therein, and brazed joints are disposed between the adjacent heat exchanger plates 12a, 12b at positions between the port opening areas 13 and the recesses 15 to provide a strong heat exchanger 10.

Claims

1. 1. A brazed plate heat exchanger (10) comprising: an end plate (11); and a stack of heat exchanger plates (12, 12a, 12b) provided with a pattern including ridges (R) and grooves (G) adapted to form contact points (16) between adjacent heat exchanger plates, such that the heat exchanger plates form inter-plate flow channels through which a medium exchanges heat on the heat exchanger plates, the heat exchanger plates further provided with port openings (O1-O4) in selective fluid communication with the flow channels; a brazed plate heat exchanger (10) in which the port openings are surrounded by port opening areas (13) that seal against corresponding port opening areas of adjacent heat exchanger plates, the adjacent heat exchanger plates being connected at the contact points (16) by brazed joints, the end plate (11) being provided with port openings (O1 to O4) on the same plane and flat areas (14) around the port openings, the plurality of protrusions (R) of the heat exchanger plate in an area overlapping with any of the flat areas (14) of the end plate (11) being formed with depressions (15), the depressions (15) of the heat exchanger plate (12, 12a) adjacent to the end plate (11) connecting a flow path formed between the end plate and the adjacent heat exchanger plate (12, 12a) with an adjacent flow path formed between the end plate (11) and the adjacent heat exchanger plate (12, 12a) to enable the flow of a medium therebetween; 1. A brazed plate heat exchanger (10), characterized in that contact points (16) are arranged on the ridges (R) on both sides of at least one of the recesses (15), and brazed joints connecting adjacent heat exchanger plates are arranged on the ridges (R) and on the contact points (16) between the nearest port opening area (13) and at least one of the recesses (15).

2. 2. The brazed heat exchanger of claim 1, wherein the heat exchanger plates are connected to each other by multiple rows of brazed joints, and the multiple recesses (15) are located between the brazed joints in a first row and the brazed joints in a second row, counting from the nearest port opening area (13).

3. 3. The brazed heat exchanger of claim 1 or 2, wherein the brazed joints connecting adjacent heat exchanger plates are located directly adjacent said recesses.

4. 4. The brazed heat exchanger according to claim 1, wherein the heat exchanger plates are formed with recesses (15) that connect at least every other flow passage formed between the end plate (11) and the adjacent heat exchanger plate (12, 12a) with adjacent flow passages, thereby enabling the flow of a medium therebetween.

5. 5. The brazed heat exchanger according to claim 1, wherein the pattern including the ridges (R) and grooves (G) is formed at a depth of the corrugations, and the depressions (15) are formed at a depth corresponding to at least 5% of the depth of the corrugations.

6. 6. The brazed heat exchanger of claim 5, wherein the depth of the depressions is 30-80%, 40-60%, or 50% of the depth of the corrugations.

7. The brazed heat exchanger according to any one of claims 1 to 6, wherein the end plate (11) has a ridge and groove pattern formed in the central portion.

8. Brazed heat exchanger according to any one of claims 1 to 7, wherein the port opening areas (13) of the heat exchanger plates are arranged at different heights.

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