HEAT TRANSFER PLATE

Abstract

A heat transfer plate includes a heat transfer area provided with a heat transfer pattern comprising elongate alternately arranged heat transfer ridges and valleys, a respective top portion of the ridges extending in a top plane and a respective bottom portion of the valleys extending in a bottom plane. The heat transfer ridges comprise ridge contact areas within which the ridges are arranged to abut an adjacent first heat transfer plate. Within at least half of the heat transfer area, the top portions of the ridges have a first width w1, and the bottom portions of the valleys have a second width w2, w1≠w2. The top portion of a number of first heat transfer ridges of the heat transfer ridges, within a respective first ridge contact area of the ridge contact areas, has a third width w3, wherein, if w1>w2 then w3<w1, and, if w1<w2 then w3>w1.

Claims

1. A heat transfer plate for a plate heat exchanger, the heat transfer plate having a transverse center axis and comprising a first distribution area, a heat transfer area and a second distribution area arranged in succession along a longitudinal center axis of the heat transfer plate extending perpendicular to a transverse center axis of the heat transfer plate, the heat transfer area being provided with a heat transfer pattern differing from a pattern within the first and second distribution areas, the first distribution area adjoining the heat transfer area along an upper borderline-(44), and the second distribution area adjoining the heat transfer area along a lower borderline, wherein the heat transfer pattern comprises elongate alternately arranged heat transfer ridges and heat transfer valleys extending obliquely in relation to the transverse center axis of the heat transfer plate, a respective top portion of the heat transfer ridges extending in a top plane and a respective bottom portion (42)-of the heat transfer valleys extending in a bottom plane, which top and bottom planes are parallel to each other, a center plane extending half-way between, and parallel to, the top and bottom planes defining a border between the heat transfer ridges and the heat transfer valleys,wherein the heat transfer ridges comprise ridge contact areas within which the heat transfer ridges are arranged to abut an adjacent first heat transfer plate in the plate heat exchanger, and the heat transfer valleys comprise valley contact areas within which the heat transfer valleys are arranged to abut an adjacent second heat transfer plate in the plate heat exchanger, wherein, within at least half of the heat transfer area, the top portions of the heat transfer ridges have a first width w1, and the bottom portions of the heat transfer valleys have a second width w2, a width of the top and bottom portions being measured perpendicular to a longitudinal extension of the heat transfer ridges and heat transfer valleys, and w1≠w2, the top portion of a number of first heat transfer ridges of the heat transfer ridges, within a respective first ridge contact area of the ridge contact areas, having a third width w3, wherein, if w1>w2 then w3<w1, and, if w1<w2 then w3>w1.

2. A heat transfer plate according to claim 1, wherein, if w1>w2 then w3≥w2, and, if w1 <w2 then w3≤w2.

3. A heat transfer plate according to claim 1, wherein w1>w2, and wherein the bottom portion (42)-of a number of first heat transfer valleys of the heat transfer valleys, within a respective first valley contact area of the valley contact areas, has a fourth width w4, w2<w4.

4. A heat transfer plate according to claim 3, wherein w4≤w3.

5. A heat transfer plate according to claim 3, wherein, with reference to a cross section through, and perpendicular to the longitudinal extension of, the heat transfer ridges and heat transfer valleys, the first heat transfer ridges, within the first ridge contact areas, and the first heat transfer valleys, within the first valley contact areas, are symmetrical with respect to said center plane.

6. A heat transfer plate according to claim 3, wherein each of the first heat transfer valleys extend from one of said upper and lower borderlines.

7. A heat transfer plate according to claim 3, wherein, for each of the first heat transfer valleys, the first valley contact area is the valley contact area arranged closest to said one of said upper and lower borderlines.

8. A heat transfer plate according to claim 3, wherein the first valley contact areas are comprised in a respective end portion of the first heat transfer valleys, which end portion extends from said one of said upper and lower borderlines and has a constant width within the bottom portion.

9. A heat transfer plate according to claim 3, wherein an absolute position, with respect to the longitudinal and transverse center axes of the heat transfer plate, of a respective one of the first ridge contact areas arranged within an upper right quarter, upper left quarter, lower right quarter, and lower left quarter, respectively, of the heat transfer plate, is at least partly overlapping with an absolute position , with respect to the longitudinal and transverse center axes of the heat transfer plate, of a respective one of the first valley contact areas arranged within a lower left quarter, lower right quarter, upper left quarter and upper right quarter, respectively, of the heat transfer plate.

10. A heat transfer plate according to claim 3, wherein a mirroring, across the transverse center axis of the heat transfer plate , of a position of one of the first valley contact areas arranged within an upper half of the heat transfer plate, is at least partly overlapping with a position one of the first valley contact areas arranged within a lower half of the heat transfer plate.

11. A heat transfer plate according to claim 1, wherein a mirroring, across the transverse center axis of the heat transfer plate, of a position of one of the first ridge contact areas arranged within an upper half of the heat transfer plate, is at least partly overlapping with a position of one of the first ridge contact areas arranged within a lower half of the heat transfer plate.

12. A heat transfer plate according to claim 1, wherein each of the first heat transfer ridges extend from one of said upper and lower borderlines.

13. A heat transfer plate according to claim 1, wherein, for each of the first heat transfer ridges, the first ridge contact area is the ridge contact area arranged closest to said one of said upper and lower borderlines.

14. A heat transfer plate according to claim 1, wherein the first ridge contact areas are comprised in a respective end portion of the first heat transfer ridges which end portion extends from said one of said upper and lower borderlines and has a constant width within the top portion.

15. A heat transfer plate according to claim 1, wherein the upper and lower borderlines are non-straight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The invention will now be described in more detail with reference to the appended schematic drawings, in which

[0042] FIG. 1a schematically illustrates channels formed between prior art heat transfer plates when stacked in a first way,

[0043] FIG. 1b schematically illustrates channels formed between the heat transfer plates of FIG. 1a when stacked in a second way,

[0044] FIG. 2 is a schematic side view of a plate heat exchanger

[0045] FIG. 3 is a schematic plan view of a heat transfer plate according to the invention,

[0046] FIG. 4 schematically illustrates a general cross section of a heat transfer pattern of the heat transfer plate of FIG. 3,

[0047] FIG. 5 schematically illustrates a local cross section of a heat transfer pattern of the heat transfer plate of FIG. 3,

[0048] FIG. 6a schematically illustrates channels formed between heat transfer plates according to the invention, within a larger heat transfer area portion, when stacked in a first way,

[0049] FIG. 6b schematically illustrates channels formed between heat transfer plates according to the invention, within a smaller heat transfer area portion, when stacked in the first way,

[0050] FIG. 7a schematically illustrates channels formed between heat transfer plates according to the invention, within a larger heat transfer area portion, when stacked in a second way,

[0051] FIG. 7b schematically illustrates channels formed between heat transfer plates according to the invention, within a smaller heat transfer area portion, when stacked in the second way,

[0052] FIG. 8 schematically illustrates locations of ridge and valley contact areas when the heat transfer plate of FIG. 3 is arranged between two other heat transfer plates according to FIG. 3 in a plate pack, and

[0053] FIG. 9 schematically illustrates locations of first ridge and valley contact areas of the heat transfer plate of FIG. 3.

DETAILED DESCRIPTION

[0054] With reference to FIG. 2, a gasketed plate heat exchanger 2 is shown. It comprises a first end plate 4, a second end plate 6 and a number of heat transfer plates, one of them denoted 8, arranged in a plate pack 10 between the first and second end plates 4 and 6, respectively. The heat transfer plates are all of the same type and “rotated” in relation to each other.

[0055] The heat transfer plates are separated from each other by gaskets (not shown). The heat transfer plates together with the gaskets form parallel channels arranged to alternately receive two fluids or media for transferring heat from one fluid or medium to the other. To this end, a first fluid is arranged to flow in every second channel and a second fluid is arranged to flow in the remaining channels. The first fluid enters and exits the plate heat exchanger 2 through an inlet 12 and an outlet 14, respectively. Similarly, the second fluid enters and exits the plate heat exchanger 2 through an inlet and an outlet (not visible in the figures), respectively. For the channels to be leak proof, the heat transfer plates must be pressed against each other whereby the gaskets seal between the heat transfer plates. To this end, the plate heat exchanger 2 comprises a number of tightening means 16 arranged to press the first and second end plates 4 and 6, respectively, towards each other.

[0056] The design and function of gasketed plate heat exchangers are well-known and will not be described in detail herein.

[0057] The heat transfer plate 8 will now be further described with reference to FIGS. 3, 4 and 5 which illustrate the complete heat transfer plate and cross sections of the heat transfer plate. The heat transfer plate 8 is an essentially rectangular sheet of stainless steel pressed, in a conventional manner, in a pressing tool, to be given a desired structure. It defines a top plane T, a bottom plane B and a center plane C (see also FIG. 2) which are parallel to each other and to the figure plane of FIG. 3. The center plane C extends half way between the top and bottom planes, T and B, respectively. Further, the heat transfer plate has a longitudinal centre axis I and a transverse centre axis t dividing the heat transfer plate 8 into upper right and left quarters a and b, and lower right and left quarters c and d.

[0058] The heat transfer plate 8 comprises a first end area 18, a second end area 20 and a heat transfer area 22 arranged there between. In turn, the first end area 18 comprises an inlet port hole 24 for the first fluid and an outlet port hole 26 for the second fluid arranged for communication with the inlet 12 for the first fluid and the outlet for the second fluid, respectively, of the plate heat exchanger 2. Further, the first end area 18 comprises a first distribution area 28 provided with a distribution pattern in the form of a so-called chocolate pattern. Similarly, in turn, the second end area 20 comprises an outlet port hole 30 for the first fluid and an inlet port hole 32 for the second fluid arranged for communication with the outlet 14 of the first fluid and the inlet of the second fluid, respectively, of the plate heat exchanger 2. Further, the second end area 20 comprises a second distribution area 34 provided with a distribution pattern in the form of a so-called chocolate pattern. The structures of the first and second end areas are the same but mirror inverted with respect to the transverse centre axis t.

[0059] The heat transfer plate 8 further comprises an outer edge portion 35 extending around the first and second end areas 18 and 20, respectively, and the heat transfer area 22. The outer edge portion 35 comprises corrugations extending between and in the top and bottom planes T and B to define edge ridges 37 and edge valleys 39. The heat transfer plate 8 further comprises a gasket groove 41 arranged to receive a gasket. Along two opposing long sides 43 and 45 of the heat transfer area 22 the gasket groove 41 borders on, or limits, the heat transfer area 22 and extends between the heat transfer area 22 and the outer edge portion 35. The design of gasket grooves of gasketed plate heat exchangers is well-known and will not be described in detail herein.

[0060] The heat transfer area 22 is provided with a heat transfer pattern in the form of a so-called herringbone pattern. It comprises alternately arranged straight elongate heat transfer ridges 36 and heat transfer valleys 38, hereinafter also referred to just ridges and valleys, in relation to the center plane C which defines the transition between the ridges and valleys. The ridges and valleys 36 and 38 extend obliquely in relation to the transverse centre axis t and form V-shaped corrugations, the apices of which are arranged along the longitudinal centre axis l of the heat transfer plate 8. With reference to FIGS. 4 and 5, a respective top portion 40 of the ridges 36 extends in the top plane T, while a respective bottom portion 42 of the valleys 38 extends in the bottom plane B. The heat transfer area 22 adjoins the first and second distribution areas 28 and 34, respectively, along upper and lower borderlines 44 and 46, respectively (FIG. 3).

[0061] As will be further discussed below, in the plate heat exchanger 2 the heat transfer plate 8 is arranged to be positioned between a first heat transfer plate 48 and a second heat transfer plate 50, as is illustrated in FIGS. 6a and 6b. Arranged like that, the corrugated outer edge portion 35 of the heat transfer plate 8 will abut the corrugated outer edge portions of heat transfer plates 48 and 50. Further, the heat transfer pattern of the heat transfer plate 8 will cross the heat transfer patterns of the heat transfer plates 48 and 50, as is schematically illustrated, for an upper left portion of the heat transfer area 22 of the heat transfer plate 8, in FIG. 8. More particularly, since the plates are “rotated” in relation to each other, the ridges 36 (illustrated by thicker solid lines) of the heat transfer plate 8 will, in ridge contact areas 52 (some of which are illustrated by circles drown with thicker lines), cross and abut the valleys (illustrated by thinner dashed lines) of the first heat transfer plate 48. Further, the valleys 38 (illustrated by thinner solid lines) of the heat transfer plate 8 will, in valley contact areas 54 (some of which are illustrated by circles drown with thinner lines), cross and abut the ridges (illustrated by thicker dashed lines) of the second heat transfer plate 50.

[0062] All the ridges and valleys 36 and 38, except for the ridges and valleys extending from the upper and lower borderlines 44 and 46, have essentially constant cross sections along their lengths, which cross sections are illustrated in FIG. 4. In these cross sections, the top portions 40 of the ridges 36 have a first width w1, while the bottom portions 42 of the valleys 38 have a second width w2, a width of the top and bottom portions 40 and 42 being measured perpendicular to a longitudinal extension of the ridges and valleys 36 and 38. w1 is larger than w2, meaning that the top portions 40 are wider than the bottom portions 42.

[0063] The heat transfer ridges 36 and the heat transfer valleys 38 extending from the upper and lower borderlines 44 and 46 have cross sections varying along their lenghts. The ridges and valleys 36 and 38 extending from the upper and lower borderlines 44 and 46 have cross sections as illustrated in FIG. 5 within upper and lower strips 56 and 58, respectively, of the heat transfer area 22 (FIG. 3), i.e. within a respective end portion 36′ and 38′ extending from the upper and lower borderlines 44 and 46 (illustrated in FIG. 8 for the upper borderline 44). The upper strip 56 extends along and immediately adjacent the upper borderline 44 with a uniform width, while the lower strip 58 extends along and immediately adjacent the lower borderline 46 with the same uniform width, as is illustrated, for the upper strip 56, by the dashed line extending parallel to the upper borderline 44, in FIG. 8. Within the upper and lower strips 56 and 58, the top portions 40 of the ridges 36 have a third width w3 and the bottom portions 42 of the valleys 38 have a fourth width w4, w3<w1 and w2<w4. Here w3=w4 which means that the top portions and bottom portions are of equal width within the upper and lower strips 56 and 58. Further, within the upper and lower strips 56 and 58, the ridges 36 and the valleys 38 are symmetrical with respect to the center axis C. Thus, within the upper and lower strips 56 and 58, the ridges and valleys 36 and 38 have a locally decreased top portion width and a locally increased bottom portion width, respectively. Outside the upper and lower strips 56 and 58, the ridges and valleys 36 and 38 extending from the upper and lower borderlines 44 and 46 have cross sections as illustrated in FIG. 4, i.e. a top portion width which exceeds the bottom portion width.

[0064] Accordingly, the upper and lower strips 56 and 58 of the heat transfer area 22 are provided with a symmetric heat transfer pattern while the rest of the heat transfer area is provided with a general asymmetric heat transfer pattern.

[0065] With reference to FIGS. 3 and 8, at least some (here, all but possibly the outermost ones) of the heat transfer ridges 36 extending from the upper and lower borderlines 44 and 46 comprise a ridge contact area 52 arranged within the upper and lower strips 56 and 58. Herein, these heat transfer ridges and ridge contact areas are referred to as first heat transfer ridges or just first ridges 36a, and first ridge contact areas 52a. Similarly, at least some (here, all but possibly the outermost ones) of the heat transfer valleys 38 extending from the upper and lower borderlines 44 and 46 comprise a valley contact area 54 arranged within the upper and lower strips 56 and 58. Herein, these heat transfer valleys and valley contact areas are referred to as first heat transfer valleys or just first valleys 38a, and first valley contact areas 54a.

[0066] As is clear from the figures, the upper and lower borderlines 44 and 46 defining the extension of the first and second distribution areas 28 and 34 and the heat transfer area 22 are curved and outwards bulging towards the transverse center axis t of the heat transfer plate 8 to improve the strength and the flow distribution capacity of the heat transfer plate 8. Because of this borderline curvature, the distance between adjacent ridge and valley contact areas 52 and 54 close to the upper and lower border lines 44 and 46 may be longer than if the upper and lower border lines instead had been straight. A longer distance between adjacent contact areas may result in an increased risk of plate deformation when the heat transfer plate 8 is arranged between the first and second heat transfer plates 48 and 50 in the plate pack 10 in the plate heat exchanger 2, especially during operation of the heat exchanger. Further, another factor that may increase the risk of plate deformation is an asymmetric heat transfer pattern comprising ridges and valley having top and bottom portions, respectively, of different widths. With such an asymmetric heat transfer pattern, the deformation risk is the highest when the heat transfer plates are “rotated” in relation to each other in the plate pack in which case the ridge top portions and valley bottom portions of one heat transfer plate abut the valley bottom portions and ride top portions of the adjacent heat transfer plates. According to the present invention the difference between the ridge top portion width and valley bottom portion width is reduced, or even erased, locally, close to the upper and lower borderlines where the risk of plate deformation is the highest, which reduces the risk of plate deformation. Thereby, the strength of the heat transfer plate is improved while the heat transfer plate maintains its asymmetric properties across most of the heat transfer area, and its overall asymmetric characteristics. The upper and lower strips within which the heat transfer pattern is locally changed are made sufficiently wide to comprise at least one ridge contact area for at least a majority of the ridges extending from the upper and lower borderlines, and at least one valley contact area for at least a majority of the valleys extending from the upper and lower borderlines. At the same time, the upper and lower strips within which the heat transfer pattern is locally changed are made narrow enough so as to have an insignificant effect on the asymmetric characteristics of the heat transfer pattern.

[0067] In the plate pack 10 of the heat exchanger 2, the first and second heat transfer plates 48 and 50 are arranged “rotated” in relation to the heat transfer plate 8. Consequently, the ridges 36 within the upper right and left quarters a and b, and the lower right and left quarters c and d, of the heat transfer plate 8 abut, within the ridge contact areas 52, the valleys within the lower left and right quarters and the upper left and right quarters, respectively, within the valley contact areas, of the heat transfer plate 48. Further, the valleys 38 within the upper right and left quarters a and b, and the lower right and left quarters c and d, of the heat transfer plate 8 abut, within the valley contact areas 54, the ridges within the lower left and right quarters and the upper left and right quarters, respectively, within the ridge contact areas, of the heat transfer plate 50. In the plate pack 10, the upper strip 56 of the plate 8 is arranged between the lower strips of the plates 48 and 50, while the lower strip 58 of the plate 8 is arranged between the upper strips of the plates 48 and 50. The plate portions of locally changed cross section should abut each other, i.e. the first ridge and valley contact areas of the heat transfer plate 8 should abut the first valley and ridge contact areas of the heat transfer plates 48 and 50. To this end, since the plates 8, 48 and 50 look the same, with respect to the longitudinal and transverse center axes l, t, an absolute position of the first ridge contact areas 52a within the upper right quarter a, upper left quarter b, lower right quarter c, and lower left quarter d, respectively, of the heat transfer plate 8, is at least partly overlapping with an absolute position of the first valley contact areas 54a arranged within the lower left quarter d, lower right quarter c, upper left quarter b and upper right quarter a, respectively, of the heat transfer plate 8. This is illustrated in FIG. 9 for first ridge contact areas 52a1, 52a2, 52a3 and 52a4 which are arranged on the same distances (pt1, pl1 ), (pt2, pl2), (pt3, pl3) and (pt4, pl4) from the longitudinal and transverse center axes l and t as first valley contact areas 54a1, 54a2, 54a3 and 54a4.

[0068] FIGS. 6a and 6b illustrate what it looks like inside the plate pack 10 of the plate heat exchanger 2 within (FIG. 6b) and outside of (FIG. 6a) the upper and lower strips of the heat transfer areas of the heat transfer plates 8, 48 and 50. It should be said that FIGS. 6a and 6b are simplified for reasons of clarity and do not depict true cross sections of the plate pack, since the ridges and valleys of different plates extend obliquely in relation to each other and not in parallel as is indicated by the figures. As previously said, within the heat transfer area 22, the top portions 40 of the ridges 36 and the bottom portions 42 of the valleys 38 of the plate 8 abut the bottom portion of the valleys and the top portion of the ridges of the plates 48 and 50, respectively. With reference to FIG. 6a, outside the upper and lower strips, the top portion of the ridges of the plates are wider than the bottom portion of the valleys of the plates. With reference to FIG. 6b, within the upper and lower strips, the top portion of the ridges of the plates and the bottom portion of the valleys of the plates are equally wide so as to reduce the risk of plate deformation where it is most likely to occur. The plates 8 and 48 form a channel of volume V1 and the plates 8 and 50 form a channel of volume V2, wherein V1 equals V2.

[0069] Instead of being “rotated” in relation to each other, the plates in the plate pack can be “flipped” in relation to each other, as is illustrated in FIGS. 7a and 7b. Arranged like that, the heat transfer pattern of the heat transfer plate 8 will cross the heat transfer patterns of the heat transfer plates 48 and 50, as is schematically illustrated, for an upper left portion of the heat transfer area 22 of the heat transfer plate 8, in FIG. 8. More particularly, since the plates are “flipped” in relation to each other, the ridges 36 (illustrated by thicker solid lines) of the heat transfer plate 8 will, in ridge contact areas 62 (some of which are illustrated by squares drown with thicker lines), cross and abut the ridges (illustrated by thicker dashed lines) of the first heat transfer plate 48. Further, the valleys 38 (illustrated by thinner solid lines) of the heat transfer plate 8 will, in valley contact areas 64 (some of which are illustrated by squares drown with thinner lines), cross and abut the valleys (illustrated by thinner dashed lines) of the second heat transfer plate 50.

[0070] Clearly, the location of the ridge contact areas and valley contact areas of the heat transfer plate 8 is dependent on whether the heat transfer plate is arranged to be “rotated” or “flipped” in relation to the other plates in a plate pack.

[0071] With reference to FIGS. 3 and 8, at least some (here, all but possibly the outermost ones) of the heat transfer ridges 36 extending from the upper and lower borderlines 44 and 46 comprise a ridge contact area 62 arranged within the upper and lower strips 56 and 58. Herein, these heat transfer ridges and ridge contact areas are referred to as first heat transfer ridges or just first ridges 36b, and first ridge contact areas 62b. Similarly, at least some (here, all but possibly the outermost ones) of the heat transfer valleys 38 extending from the upper and lower borderlines 44 and 46 comprise a valley contact area 64 arranged within the upper and lower strips 56 and 58. Herein, these heat transfer valleys and valley contact areas are referred to as first heat transfer valleys or just first valleys 38b, and first valley contact areas 64b.

[0072] As previously said, if the first and second heat transfer plates 48 and 50 are arranged “flipped” in relation to the heat transfer plate 8, the ridges 36 of the heat transfer plate 8 abut, within the ridge contact areas 62, the ridges, within the ridge contact areas, of the heat transfer plate 48. Further, the valleys 38 of the heat transfer plate 8 abut, within the valley contact areas 64, the valleys, within the valley contact areas, of the heat transfer plate 50. The upper strip 56 of the plate 8 is arranged between the lower strips of the plates 48 and 50, while the lower strip 58 of the plate 8 is arranged between the upper strips of the plates 48 and 50. The plate portions of locally changed cross section should abut each other, i.e. the first ridge and valley contact areas of the heat transfer plate 8 should abut the first ridge and valley contact areas of the heat transfer plates 48 and 50. To this end, since the plates 8, 48 and 50 look the same, a mirroring, across the transverse center axis t of the heat transfer plate 8, of a position of the first valley contact areas 64b arranged within an upper half, i.e. the upper left and right quarters a and b, of the heat transfer plate 8, is at least partly overlapping with a position of the first valley contact areas 64b arranged within a lower half, i.e. the lower left and right quarters c and d, of the heat transfer plate 8. Similarly, a mirroring, across the transverse center axis t of the heat transfer plate 8, of a position of the first ridge contact areas 62b arranged within an upper half, i.e. the upper left and right quarters a and b, of the heat transfer plate 8, is at least partly overlapping with a position of the first ridge contact areas 62b arranged within a lower half, i.e. the lower left and right quarters c and d, of the heat transfer plate 8.

[0073] This is illustrated in FIG. 9 for first ridge contact areas 62bu1 and 62bl1 which are arranged on the same distances (Pt1, Pl1) from the longitudinal and transverse center axes l and t, and first valley contact areas 64bu2 and 64bl2 which are arranged on the same distances (Pt2, Pl2) from the longitudinal and transverse center axes l and t.

[0074] FIGS. 7a and 7b illustrate what it looks like inside a plate pack in which the plates are “flipped” instead of “rotated” in relation to each other, within (FIG. 7b) and outside of (FIG. 7a) the upper and lower strips of the heat transfer areas of the heat transfer plates 8, 48 and 50. Just like FIGS. 6a and 6b, FIGS. 7a and 7b are simplified for reasons of clarity and do not depict true cross sections of the plate pack. As previously said, within the heat transfer area 22, the top portions 40 of the ridges 36 and the bottom portions 42 of the valleys 38 of the plate 8 abut the top portion of the ridges and the bottom portion of the valleys of the plates 48 and 50, respectively. With reference to FIG. 7a, outside the upper and lower strips, the top portion of the ridges of the plates are wider than the bottom portion of the valleys of the plates. With reference to FIG. 7b, within the upper and lower strips, the top portion of the ridges of the plates the bottom portion of the valleys of the plates are equally wide. The plates 8 and 48 form a channel of volume V3 and the plates 8 and 50 form a channel of volume V4, wherein V3<V4.

[0075] Thus, the heat transfer plate 8 has one set of ridge and valley contact areas 52 and 54 for “rotation” arrangement and one set of ridge and valley contact areas 62 and 64 for “flipping” arrangement. The upper and lower strips 56 and 58 are preferably made wide enough such that at least some (here, all but possibly the outermost ones) of the heat transfer ridges 36 extending from the upper and lower borderlines 44 and 46 comprise a ridge contact area 52 and a ridge contact area 62 arranged within the upper and lower strips 56 and 58. These heat transfer ridges are then first ridges 36a as well as first ridges 36b. Similarly, the upper and lower strips 56 and 58 are preferably made wide enough such at least some (here, all but possibly the outermost ones) of the heat transfer valleys 38 extending from the upper and lower borderlines 44 and 46 comprise a valley contact area 54 and a valley contact area 64 arranged within the upper and lower strips 56 and 58. These heat transfer valleys are then first valleys 38a as well as first valleys 38b. At the same time the upper and lower strips 56 and 58 are made as narrow as possible so as to maintain the asymmetric characteristics of the heat transfer plate to the greatest extent possible.

[0076] The heat transfer plate 8 comprises a heat transfer area 22 provided with a heat transfer pattern of alternately arranged ridges 36 and valleys 38. Outside the upper and lower strips 56 and 58 of the heat transfer area, the heat transfer pattern is asymmetric in that the top portions 40 of the ridges 36 are wider than the bottom portions 42 of the valleys 38. Within the upper and lower strips the width of the top portions of the ridges is decreased, while the width of the bottom portions of the valleys is increased, to give the top and bottom portions an equal width and make the heat transfer pattern locally symmetric. In alternative embodiments, the top and bottom portion widths within the upper and lower strips need not be equal but may only differ less than outside the upper and lower strips. The top portion width may even be larger than the bottom portion width outside the upper and lower strips, and smaller than the bottom portion width within the upper and lower strips. Further, instead of changing both the top portion width and the bottom portion width within the upper and lower strips 56 and 58, only one of them could be changed. As an example, within the upper and lower strips, the width of the bottom portions of the valleys could be increased while the width of the top portions of the ridges could be maintained. Alternatively, within the upper and lower strips, the width of the top portions of the ridges could be decreased while the width of the bottom portions of the valleys could be maintained. Also here, the top portion width and the bottom portion width, could, but need not, be equal within the upper and lower strips. Further, in case of equal top and bottom portion widths, with reference to a cross section through, and perpendicular to the longitudinal extension of, the heat transfer ridges and heat transfer valleys, also here the ridges and valleys could be symmetrical with reference to the center plane within the upper and lower strips.

[0077] The above described embodiment of the present invention should only be seen as examples. 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.

[0078] As an example, the upper and lower strips within which the heat transfer pattern is locally changed, need not be of uniform width along their extension and/or need not be continuous but could be intermittent. Accordingly, not all heat transfer ridges and heat transfer valleys extending from the upper and lower borderlines must have a locally changed cross section.

[0079] Further, the upper and lower strips within which the heat transfer pattern is locally changed need not border on, but could be separated from, the upper and lower borderlines along part of, or their complete, extension.

[0080] Further, the heat transfer pattern need not even be locally changed close to the upper and lower borderlines but could instead be changed somewhere else within the heat transfer area, for example along the longitudinal center axis of the heat transfer plate, close to the apices of the V-shaped corrugations of the heat transfer pattern or close to longitudinal edges of the heat transfer area.

[0081] The above specified distribution pattern of chocolate type and heat transfer pattern of herring bone type are just exemplary. Naturally, the invention is applicable in connection with other types of patterns. For example, the heat transfer pattern could comprise V-shaped corrugations wherein the apex of each corrugation points from one long side towards another long side of the heat transfer plate. Further, the heat transfer ridges and heat transfer valleys need not have the cross sections illustrated in the figures. As an example, the heat transfer ridges and valleys could form “shoulders” as illustrated in WO2017/167598. It should also be said that the distribution pattern within the distribution areas may be either symmetric or asymmetric.

[0082] The above described plate heat exchanger is of parallel counter flow type, i.e. the inlet and the outlet for each fluid are arranged on the same half of the plate heat exchanger and the fluids flow in opposite directions through the channels between the heat transfer plates. Naturally, the plate heat exchanger could instead be of diagonal flow type and/or a co-flow type.

[0083] The plate heat changer above comprises one plate type only. Naturally, the plate heat exchanger could instead comprise two or more different types of alternately arranged heat transfer plates, for example two types having different heat transfer patterns, such different inclinations of the heat transfer ridges and valleys.

[0084] 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.

[0085] The present invention could be used in connection with other types of plate heat exchangers than gasketed ones, such as all-welded, semi-welded, fusion-bonded and brazed plate heat exchangers.

[0086] The upper and lower borderlines need not be curved but could have other forms. For example, they could be straight or zig-zag shaped.

[0087] The heat transfer area of the heat transfer plate could comprise upper and lower transition bands bordering on the upper and lower border lines and being provided with a different pattern than the rest of the heat transfer area, wherein the upper and lower strips would be comprised in these upper and lower transition bands. Such transition bands could, for example, be designed like the transition areas of the heat transfer plate according to EP2728292.

[0088] It should be stressed that the attributes front, back, upper, lower, first, second, third, upper, lower, etc. is used herein just to distinguish between details and not to express any kind of orientation or mutual order between the details.

[0089] Further, 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.