HEAT TRANSFER PLATE, GASKET AND CASSETTE

Abstract

 A heat transfer plate (8), a gasket (84) and a plate cassette (108) are provided. The heat transfer plate (8) comprises an upper end portion (18), a center portion (34) and a lower end portion (26). The upper end portion (18) comprises a first and a second porthole (20, 22) and an upper distribution area (24) and the lower end portion (26) comprises a third and a fourth porthole (18, 20) and a lower distribution area (32). The heat transfer plate (8) further comprises a front gasket groove (52). An upper groove portion (62) of the front gasket groove (52) extends between the second porthole (22) and the upper distribution area (24) and a lower groove portion (64) of the front gasket groove (52) extends between the fourth porthole (30) and the lower distribution area (32). The heat transfer plate (8) is characterized in that a depth of the front gasket groove (52), within the upper and lower groove portions (62, 64), increases, from a first smallest depth (ds1) to a first largest depth (dl1), along a longitudinal extension of the upper and lower groove portions (62, 64) so as to be the first largest depth (dl1) at a largest distance from a longitudinal center axis (LP) of the heat transfer plate (8). The gasket (84) is designed to fit in the front gasket groove (52).

Description

Technical Field

[0001] The invention relates to a heat transfer plate, a gasket for such a heat transfer plate and a cassette comprising such heat transfer plates.

Background Art

[0002] Plate heat exchangers, PHEs, typically comprises 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.

[0003] In one type of well-known PHEs, the so called semi-welded PHEs, the heat transfer plates are typically "flipped" in relation to each other and welded in pairs to form tight cassettes, and gaskets are arranged between the cassettes. The end plates, and therefore the cassettes, are pressed towards each other by some kind of tightening means whereby the gaskets seal between the cassettes. 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, one fluid in the cassettes and the other fluid between the cassettes, 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.

[0004] Typically, the heat transfer plates each comprise two end portions and an intermediate heat transfer portion. The end portions comprise the inlet and outlet port holes and distribution areas pressed with a distribution pattern. Similarly, the heat transfer portion comprises a heat transfer area pressed with a heat transfer pattern. The main task of the distribution areas of the heat transfer plates is to spread a fluid entering the channel across the width of the heat transfer plates before the fluid reaches the heat transfer areas, and to collect the fluid and guide it out of the channel after it has passed the heat transfer areas. On the contrary, the main task of the heat transfer area is heat transfer.

[0005] The design of the different areas of the heat transfer plates is typically optimized to the main tasks of the different areas. Since the distribution areas and the heat transfer area have different main tasks, the distribution pattern normally differs from the heat transfer pattern. The distribution pattern may be such that it offers a relatively weak flow resistance and low pressure drop which is typically associated with a more "open" distribution pattern design. An example of such a pattern is the so-called chocolate pattern. The heat transfer pattern may be such that it offers a relatively strong flow resistance and high pressure drop which is typically associated with a more "dense" heat transfer pattern design, such as a so-called herringbone pattern.

[0006] Even if the conventional distribution patterns are optimized for effective fluid spreading and collecting, it may still be difficult to achieve a desired, which often is an even, flow distribution across the heat transfer plate. One reason for this may be that the distance between the portholes and the heat transfer portion typically varies depending on the fluid flow path across the distribution areas. Taking, as an example, a rectangular heat transfer plate having a rectangular heat transfer portion and the portholes arranged at the four plate corners, a fluid flow path from a specific one of the upper portholes to the "diagonally" arranged one of the upper corners of the heat transfer portion will be considerably longer than a fluid flow path from the specific upper porthole to the other one of the upper corners of the heat transfer portion. Typically, longer fluid flow paths are associated with a higher pressure drop and a stronger flow resistance than shorter fluid flow paths, and vice versa. Consequently, the fluid flow along the shorter fluid flow paths will be larger than the fluid flow along the longer fluid flow paths which will result in an uneven fluid flow across the heat transfer area of the heat transfer plates. In turn, this will lead to an impaired heat transfer capacity of the heat transfer plates and, consequently, the complete PHE.

SUMMARY

[0007] An object of the present invention is to provide a heat transfer plate, a gasket and a cassette which at least partly solve the above discussed problem of prior art. The basic concept of the invention is to vary a press depth of the heat transfer plate, and a thickness of the gasket, to promote a desired fluid distribution across the distribution areas, and thus the heat transfer area, of the heat transfer plate. The heat transfer plate, which is also referred to herein as just "plate", the gasket and the cassette for achieving the object above are defined in the appended claims and discussed below.

[0008] A heat transfer plate according to the present invention is corrugated so as to extend in and between parallel imaginary separated upper and lower planes. It comprises an upper end portion, a center portion and a lower end portion arranged in succession along a longitudinal center axis of the heat transfer plate. The upper end portion comprises a first and a second porthole and an upper distribution area provided with an upper distribution pattern. The lower end portion comprises a third and a fourth porthole and a lower distribution area provided with a lower distribution pattern. The center portion comprises a heat transfer area provided with a heat transfer pattern differing from the upper and lower distribution patterns. The heat transfer plate further comprises, on a front side thereof, a front gasket groove. The front gasket groove includes an annular groove part, an upper ring groove part and a lower ring groove part. The annular groove part extends around the center portion, the upper and lower distribution areas and the first and third portholes. The upper ring groove part encloses the second porthole and the lower ring groove part encloses the fourth porthole. A upper groove portion of the front gasket groove extends between the second porthole and the upper distribution area and a lower groove portion of the front gasket groove extends between the fourth porthole and the lower distribution area. The heat transfer plate is characterized in that a depth of the front gasket groove, within the upper and lower groove portions, increases, from a first smallest depth to a first largest depth, along a longitudinal extension of the upper and lower groove portions so as to be the first largest depth at a largest distance from the longitudinal center axis of the heat transfer plate. Further, the front gasket groove has a center depth at a respective center of the upper and lower groove portions.

[0009] The annular groove part of the front gasket groove need not be circular but may have any form suitable for the heat transfer plate. Similarly, the upper and lower ring groove parts of the front gasket groove need not be circular but may have any form suitable for the heat transfer plate, and especially the portholes thereof.

[0010] The depth of the front gasket groove is measured perpendicular to the imaginary upper and lower planes defining the extension of the heat transfer plate.

[0011] The front gasket groove is arranged to accomodate a gasket for sealing, and definition of a front fluid channel, between the heat transfer plate and an overlaying suitably designed heat transfer plate, possibly another heat transfer plate according to the present invention. The front fluid channel allows a fluid flow between the first and the third porthole. The heat transfer plate is further arranged to cooperate with an underlaying suitably designed heat transfer plate, possibly yet another heat transfer plate according to the present invention, for definition of a back fluid channel allowing a fluid flow between the second and the fourth porthole, i.e. a fluid flow through passages defined by a backside of the upper and lower groove portions of the front gasket groove. Since the front gasket groove, within the upper and lower groove portions, has a varying depth and is the deepest at the largest distance from the longitudinal center axis of the heat transfer plate, these passages may have a varying depth and be the most shallow at the largest distance from the longitudinal center axis of the heat transfer plate. Thus, the heat transfer plate will allow a relatively small fluid flow through these passages at the largest distance from, and a larger fluid flow through these passages closer to, the longitudinal center axis of the heat transfer plate. A desired flow distribution across the heat transfer plate and a more efficient heat transfer may thereby be achieved.

[0012] The depth of the front gasket groove may be gradually increasing along the longitudinal extension of the upper and lower groove portions of the front gasket groove so as to allow for a gradually varying fluid flow on the backside of the upper and lower groove portions of the front gasket groove. For example, the gradual increase may be step-wise or wavelike. As another example, the depth of the front gasket groove may be linearly increasing along the longitudinal extension of the upper and lower groove portions of the front gasket groove so as to allow for a linearly varying fluid flow on the backside of the upper and lower groove portions of the front gasket groove.

[0013] According to one embodiment the front gasket groove of the heat transfer plate has, along more than half of its longitudinal extension, a nominal depth, which is essentially equal to a distance between the imaginary upper and lower planes, wherein said first smallest depth < said first largest depth < said nominal depth. Where the front gasket groove has the nominal depth its bottom extends in the imaginay lower plane, i.e. in so called bottom plane. This embodiment may facilitate permanent bonding of the heat transfer plate and an underlaying suitably designed heat transfer plate, possibly another heat transfer plate according to the present invention, into a cassette.

[0014] The heat transfer plate may be so constructed that said first smallest depth of the upper and lower groove portions of the front gasket groove is essentially equal to said center depth - a max depth deviation from said center depth, and said first largest depth of the upper and lower groove portions of the front gasket groove is essentially equal to said center depth + said max depth deviation from said center depth. This construction means that the first smallest depth and the first largest depth deviate equally from the center depth wich may enable a mechanically straightforward design of the heat transfer plate.

[0015] The heat transfer plate may be so designed that the center depth, i.e. the depth of the front gasket groove at the respective center of the upper and lower groove portions, is essentially equal to half the distance between the imaginary upper and lower planes. Where the front gasket groove has the center depth its bottom extends in so called half plane.

[0016] Said upper groove portion of the front gasket groove may be comprised in an upper diagonal portion of the annular groove part of the front gasket groove, which upper diagonal portion extends between the upper ring groove part of the front gasket groove and the upper distribution area. Further, said lower groove portion of the front gasket groove may be comprised in a lower diagonal portion of the annular groove part of the front gasket groove, which lower diagonal portion extends between the lower ring groove part of the front gasket groove and the lower distribution area.

[0017] In addition to the above, the heat transfer plate may be such that a depth of the front gasket groove, within an inner portion of the upper ring groove part of the front gasket groove, which inner portion extends between the second porthole and the upper diagonal portion of the annular groove part, and within an inner portion of the lower ring groove part of the front gasket groove, which inner portion extends between the fourth porthole and the lower diagonal portion of the annular groove part, increases, from a second smallest depth to a second largest depth, along a longitudinal extension of the inner portions of the upper and lower ring groove parts so as to be the second largest depth at a largest distance from the longitudinal center axis of the heat transfer plate. Thus, the depth of the front gasket groove may be varying along the upper and lower diagonal portions of the annular groove part, as well as along the inner portions of the upper and lower ring groove parts, of the front gasket groove. Such a design may make it easier to obtain the desired flow distribution across the heat transfer plate.

[0018] The first and second smallest depths may, or may not, be the same. Similarily, the first and second largest depths may, or may not, be the same.

[0019] Alternatively, said upper groove portion of the front gasket groove may be comprised in an inner portion of the upper ring groove part of the front gasket groove, which inner portion extends between the second porthole and the annular groove part or the upper distribution area. Further, said lower groove portion of the front gasket groove may be comprised in an inner portion of the lower ring groove part of the front gasket groove, which inner portion extends between the fourth porthole and the annular part or the lower distribution area.

[0020] The heat transfer plate may be so designed that the first and third portholes are arranged on one side of the longitudinal center axis of the heat transfer plate, and the second and fourth portholes are arranged on another opposite side of the longitudinal center axis. Thereby, the heat transfer plate may be suitable for use in a plate heat exchanger of so-called parallel flow type. Such a parallel-flow heat exchanger may comprise only one plate type. If instead the first and fourth portholes had been arranged on one and the same side, and the second and third porthole had been arranged on the same and the other side, of the longitudinal center axis, the plate could have been suitable for use in a plate heat exchanger of so-called diagonal flow type. Such a diagonal flow heat exchanger may typically comprise more than one plate type.

[0021] The heat transfer plate may be so designed that the upper groove portion of the front gasket groove is a mirroring, parallel to a transverse center axis of the heat transfer plate, of the lower groove portion of the front gasket groove. This may enable a plate pack containing only heat transfer plates according to the present invention.

[0022] A gasket according to the present invention is for a heat transfer plate comprising an upper end portion, a center portion and a lower end portion arranged in succession along a longitudinal center axis of the heat transfer plate. The upper end portion comprises a first and a second porthole and an upper distribution area, the lower end portion comprises a third and a fourth porthole and a lower distribution area, and the center portion comprises a heat transfer area. The gasket comprises an annular gasket part arranged to extend around the center portion, the upper and lower distribution areas, and the first and third portholes of the heat transfer plate. The gasket further comprises an upper ring gasket part arranged to enclose the second porthole of the heat transfer plate, and a lower ring gasket part arranged to enclose the fourth porthole of the heat transfer plate. An upper gasket portion of the gasket is arranged to extend between the second porthole and the upper distribution area of the heat transfer plate, and a lower gasket portion of the gasket is arranged to extend between the fourth porthole and the lower distribution area of the heat transfer plate. The gasket is characterized in that a thickness of the gasket, within the upper and lower gasket portions, increases, from a first smallest thickness to a first largest thickness, along a longitudinal extension of the upper and lower gasket portions so as to be the first largest thickness at a largest distance from a longitudinal center axis of the gasket. The gasket has a center thickness at a respective center of the upper and lower gasket portions.

[0023] The thickness may be gradually increasing along the longitudinal extension of the upper and lower gasket portions of the gasket.

[0024] The thickness may be linearly increasing along the longitudinal extension of the upper and lower gasket portions of the gasket.

[0025] The gasket may, along more than half of its longitudinal extension, have a nominal thickness, wherein said first smallest thickness < said first largest thickness < said nominal thickness.

[0026] Said first smallest thickness may be essentially equal to said center thickness - a max thickness deviation, and said first largest thickness may be essentially equal to said center thickness + said max thickness deviation.

[0027] Said center thickness may be essentially equal to half a maximum thickness of the gasket.

[0028] Said upper gasket portion of the gasket may be comprised in an upper diagonal portion of the annular gasket part of the gasket, which upper diagonal portion extends on an inside of the upper ring gasket part of the gasket. Said lower gasket portion of the gasket may be comprised in a lower diagonal portion of the annular gasket part of the gasket, which lower diagonal portion extends on an inside of the lower ring gasket part of the gasket.

[0029] In addition to the above, the gasket may be so designed that a thickness of the gasket, within an inner portion of the upper ring gasket part of the gasket, which inner portion extends between an outer portion of the upper ring gasket part of the gasket and the upper diagonal portion, and within an inner portion of the lower ring gasket part of the gasket, which inner portion extends between an outer portion of the lower ring gasket part of the gasket and the lower diagonal portion, increases, from a second smallest thickness to a second largest thickness, along a longitudinal extension of the inner portions of the upper and lower ring gasket parts so as to be the second largest thickness at a largest distance from the longitudinal center axis of the gasket.

[0030] Alternatively, said upper gasket portion of the gasket may be comprised in an inner portion of the upper ring gasket part of the gasket, which inner portion extends between an outer portion of the upper ring gasket part of the gasket and an upper diagonal portion of the annular gasket part of the gasket, which upper diagonal portion extends on an inside of the upper ring gasket part of the gasket. Further, said lower gasket portion of the gasket may be comprised in an inner portion of the lower ring gasket part of the gasket, which inner portion extends between an outer portion of the lower ring gasket part of the gasket and a lower diagonal portion of the annular gasket part of the gasket, which lower diagonal portion extends on an inside of the lower ring gasket part of the gasket.

[0031] The gasket may be such that the upper and lower ring gasket parts of the gasket are arranged on one and the same side of the longitudinal center axis of the gasket.

[0032] The upper gasket portion of the gasket may be a mirroring, parallel to a transverse center axis of the gasket, of the lower gasket portion of the gasket.

[0033] The above different embodiments of the gasket according to the invention correspond to the above different embodiments of the heat transfer plate according to the invention. Thus, the advantages of the above different embodiments of the heat transfer plate are transferable to the above different embodiments of the gasket.

[0034] A cassette according to the invention comprises two permanently joined heat transfer plates as described above, wherein a back side side of one of the heat transfer plates faces a back side of another one of the heat transfer plates, and said another one of the heat transfer plates is turned upside down in relation to said one of the heat transfer plates.

[0035] It should be stressed that the advantages of most, if not all, of the above discussed features of the inventive heat transfer plate appear when the heat transfer plate is combined with other suitably constructed heat transfer plates and suitably designed gaskets in a plate heat exchanger.

[0036] 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

[0037] The invention will now be described in more detail with reference to the appended schematic drawings, in which

Fig. 1 is a schematic front view of a semi-welded plate heat exchanger,

Fig. 2 is a schematic side view of the plate heat exchanger in Fig. 1,

Fig. 3 is a schematic plan view of a heat transfer plate illustrating a front thereof, and a gasket,

Fig. 4 is a schematic plan view of the heat transfer plate in Fig. 3 illustrating a back thereof, and a schematic plan view of a pile of three adjacent heat transfer plates in a plate pack and the gasket in Fig. 3,

Fig. 5 illustrates abutting outer edge parts of the three heat transfer plates of the pile in Fig. 4, as seen from the outside of the plate pack, and

Fig. 6 is a schematic cross section of the plates and the gasket in Fig. 4, taken along line A, B, C or D.

Detailed description

[0038] Figs. 1 and 2 show a semi-welded gasketed plate heat exchanger 2 as described by way of introduction. It comprises a frame plate 4, a pressure plate 6, a pack of heat transfer plates 8, fluid inlets 9, fluid outlets 10 and tightening means 12.

[0039] The heat transfer plates 8, hereinafter also referred to as just "plates", are all similar. One of them, denoted 8a, is illustrated in further detail in Figs. 3 and 4. The plate 8a is an essentially rectangular sheet of stainless steel having a front side 14 (illustrated in Fig. 3) and an opposing back side 16 (illustrated in Fig. 4). The plate 8a comprises an upper end portion 18, which in turn comprises a first porthole 20, a second porthole 22 and an upper distribution area 24, and a lower end portion 26, which in turn comprises a third porthole 28, a fourth porthole 30 and a lower distribution area 32. The plate 8a further comprises a center portion 34, which in turn comprises a heat transfer area 36, and an outer edge portion 38 extending around the upper and lower end portions 18 and 26 and the center portion 34. The upper end portion 18 adjoins the center portion 34 along an upper borderline 40 while the lower end portion 26 adjoins the center portion 34 along a lower borderline 42. The upper end portion 18, the center portion 34 and the lower end portion 26 are arranged in succession along a respective longitudinal center axis LP of the plate 8a, which extends perpendicular to a respective transverse center axis TP of the plate 8a. The first and third portholes 20 and 28 are arranged on one and the same side of the longitudinal center axis LP, while the second and fourth portholes 22 and 30 are arranged on one and the other side of the longitudinal center axis LP. The upper end portion 18 is a mirroring, parallell to the respective transverse center axis TP of the of the heat transfer plate 8a, of the lower end portion 26.

[0040] The heat transfer plate 8a is pressed, in a conventional manner, in a pressing tool, to be given a desired structure, such as different corrugation patterns within different portions of the heat transfer plate. As was discussed by way of introduction, the corrugation patterns are optimized for the specific functions of the respective plate portions. Accordingly, the upper and lower distribution areas 24 and 32 are provided with a distribution pattern of chocolate type while the heat transfer area 36 is provided with a heat transfer pattern of herringbone type. Further, the outer edge portion 38 comprises corrugations 44 which make the outer edge portion stiffer and, thus, the heat transfer plate 8a more resistant to deformation. Further, the corrugations 44 form a support structure in that they are arranged to abut corrugations of the adjacent heat transfer plates in the plate pack of the heat exchanger 2. With reference to Fig. 5, the corrugations 44 extend between and in imaginary lower and upper planes 46 and 48, which are parallel to the figure plane of Figs. 3 and 4. A center plane 50 extends half way between the first and second planes 46 and 48.

[0041] With reference to Fig. 3, pressed into the front side 14 of the heat transfer plate 8a is also a front gasket groove 52. The front gasket groove 52 comprises an annular groove part 54, an upper ring groove part 56 and a lower ring groove part 58. The annular groove part 54 encloses the center portion 34, the upper and lower distribution areas 24 and 32 and the first and third portholes 20 and 28. The upper ring groove part 56 encloses the second porthole 22, while the lower ring groove part 58 encloses the fourth porthole 30. An upper half of the front gasket groove 52 is a mirroring, parallell to the transverse center axis TP of the of the heat transfer plate 8a, of a lower half of the front gasket groove 52.

[0042] With reference to Figs. 3, and also Fig. 6 which illustrates a local cross section of the front gasket groove 52, a bottom 60 of the annular groove part 54 extends in the imaginary lower plane 46 along its complete extension except for within upper and lower groove portions 62 and 64 of the annular groove part 54. The upper groove portion 62 is formed by an upper diagonal portion 66 of the annular groove part 54 extending between the upper distribution area 24 and a right upper adiabatic area 68 of the heat transfer plate 8a extending on an inside of the second porthole 22. The lower groove portion 64 is formed by a lower diagonal portion 70 of the annular groove part 54 extending between the lower distribution area 32 and a right lower adiabatic area 72 of the heat transfer plate 8a extending on an inside of the fourth porthole 30. The borders of the upper and lower diagonal portions 66 and 70 are illustrated by broken lines in Fig. 3.

[0043] Further, bottoms 74 and 76 (Fig. 6) of the upper and lower ring groove parts 56 and 58 extend in the imaginary lower plane 46 along their complete extension except for within a respective inner portion 78 and 80 of the upper and lower ring groove parts 56 and 58. The inner portion 78 of the upper ring groove part 56 extends between the second porthole 22 and the right upper adiabatic area 68 of the heat transfer plate 8a. The inner portion 80 of the lower ring groove part 58 extends between the fourth porthole 30 and the right lower adiabatic area 72 of the heat transfer plate 8a. The borders of the inner portions 78 and 80 are illustrated by broken lines in Fig. 3.

[0044] Thus, with reference to Fig. 6, outside the upper and lower diagonal portions 66 and 70 of the annular groove part 54, and the inner portions 78 and 80 of the upper and lower ring groove parts 56 and 58, the front gasket groove 52 has a nominal depth dn which is equal a distance between the imaginary lower and upper planes 46 and 48.

[0045] Within the upper and lower diagonal portions 66 and 70 and the inner portions 78 and 80 the front gasket groove 52 has a varying depth. More particularly, at a respective center of the upper and lower diagonal portions 66 and 70 and the inner portions 78 and 80 the front gasket groove 52 has a center depth dc which is equal to half the distance between the imaginary lower and upper planes 46 and 48.

[0046] Further, within the upper and lower diagonal portions 66 and 70 and along a respective longitudinal extension thereof, the depth of the front gasket groove 52 is gradually and linearly increasing in a direction away from the longitudinal center axis LP of the heat transfer plate 8a from the center depth dc at the respective center of the upper and lower diagonal portions 66 and 70 to a first largest depth dl1 at a largest distance from the longitudinal center axis LP of the heat transfer plate 8a, while the depth of the front gasket groove 52 is gradually and linearly decreasing in a direction towards the longitudinal center axis LP of the heat transfer plate 8a, from the center depth dc at the respective center of the upper and lower diagonal portions 66 and 70 to a first smallest depth ds1 at a smallest distance from the longitudinal center axis LP of the heat transfer plate 8a. Both the first smallest depth ds1 and the first largest depth dl1 is smaller than the nominal depth dn since the bottom 60 of the annular groove part 54 extends above the imaginary lower plane 46 within the upper and lower diagonal portions 66 and 70. The first largest depth dl1 and the first smallest depth ds1 deviate equally from the center depth dc, i.e. dl1+Df1=ds1-Df1=dc, where Df1 is a max depth deviation from the center depth dc.

[0047] Further, within the inner portions 78 and 80 and along a respective longitudinal extension thereof, the depth of the front gasket groove 52 is gradually and linearly increasing in a direction away from the longitudinal center axis LP of the heat transfer plate 8a from the center depth dc at the respective center of the inner portions 78 and 80 to a second largest depth dl2, which here equals dl1, at a largest distance from the longitudinal center axis LP of the heat transfer plate 8a, while the depth of the front gasket groove 52 is gradually and linearly decreasing in a direction towards the longitudinal center axis LP of the heat transfer plate 8a, from the center depth dc at the respective center of the inner portions 78 and 80 to a second smallest depth ds2, which here equals ds1, at a smallest distance from the longitudinal center axis LP of the heat transfer plate 8a. Both the second smallest depth ds2 and the second largest depth dl2s is smaller than the nominal depth dn since the bottoms 74 and 76 of the upper and lower ring groove parts 56 and 58 extend above the imaginary lower plane 46 within the inner portions 78 and 80. The second largest depth dl2 and the second smallest depth ds2 deviate equally from the center depth dc, i.e. dl2+Df2=ds2-Df2=dc, where Df2 is a max depth deviation from the center depth dc. Obviously, here Df2 equals Df1.

[0048] With reference to Fig. 4, the plate 8a further comprises, on the back side 16 thereof, a welding trail 82 (illustrated with broken lines). Within the center portion 34, the welding trail 82 is defined by a backside of the bottom 60 of the annular groove part 54 of the front gasket groove 52. This means that the welding trail 82 and the front gasket groove 52 are aligned within the center portion 34 of the heat transfer plate 8a. Within the upper end portion 18 the welding trail 82 encloses the upper distribution area 24 and the second porthole 22; it also encloses the first porthole 20 separately. Within the lower end portion 26 the welding trail 82 encloses the lower distribution area 32 and the fourth porthole 30; it also encloses the third porthole 28 separately. Along the complete welding trail 82 the heat transfer plate 8a extends in the imaginary lower plane 46.

[0049] A rubber gasket 84 is illustrated in Fig. 3. It comprises an annular gasket part 86, an upper ring gasket part 88 and a lower ring gasket part 90. The annular gasket part 86 is arranged to enclose the center portion 34, the upper and lower distribution areas 24 and 32 and the first and third portholes 20 and 28. The upper ring gasket part 88 is arranged to enclose the second porthole 22, while the lower ring gasket part 90 is arranged to enclose the fourth porthole 30. An upper half of the gasket 84 is a mirroring, parallel to a transverse center axis TG of the gasket 84, of a lower half of the gasket 84.

[0050] With reference to Figs. 3 and 6, a thickness of the annular gasket part 86 is essentially equal to a nominal thickness tn, which in turn is equal to the double nominal gasket groove depth dn, along its complete extension except for within upper and lower gasket portions 92 and 94 of the annular gasket part 86. The upper gasket portion 92 is formed by an upper diagonal portion 96 of the annular gasket part 86 extending on an inside of the upper ring gasket part 88. The lower gasket portion 94 is formed by a lower diagonal portion 98 of the annular gasket part 86 extending on an inside of the lower ring gasket part 90. The borders of the upper and lower diagonal portions 96 and 98 are illustrated by broken lines in Fig. 3.

[0051] Further, a thickness of the upper and lower ring gasket parts 88 and 90 is essentially equal to the nominal gasket thickness tn along their complete extension except for within a respective inner portion 100 and 102 of the upper and lower ring gasket parts 88 and 90. The inner portion 100 of the upper ring gasket part 88 extends between an outer portion 104 of the upper ring gasket part 88 and the upper diagonal portion 96 of the annular gasket part 86. The inner portion 102 of the lower ring gasket part 90 extends between an outer portion 106 of the lower ring gasket part 90 and the lower diagonal portion 98 of the annular gasket part 86. The borders of the inner portions 100 and 102 are illustrated by broken lines in Fig. 3.

[0052] Thus, outside the upper and lower diagonal portions 96 and 98 of the annular gasket part 86, and the inner portions 100 and 102 of the upper and lower ring gasket parts 88 and 90, the gasket 84 has the nominal gasket thickness tn, which is essentially equal to the double nominal depth dn of the front gasket groove 52.

[0053] Within the upper and lower diagonal portions 96 and 98 of the annular gasket part 86, and the inner portions 100 and 102 of the upper and lower ring gasket parts 88 and 90, the gasket 84 has a varying thickness. More particularly, at a respective center of the upper and lower diagonal portions 96 and 98 and the inner portions 100 and 102, the gasket 84 has a center thickness tc which is equal to equal to the nominal depth dn of the front gasket groove 52, i.e. half the nominal gasket thickness tn.

[0054] Further, within the upper and lower diagonal portions 96 and 98 and along a respective longitudinal extension thereof, the thickness of the gasket 84 is gradually and linearly increasing in a direction away from a longitudinal center axis LG (Fig. 3) of the gasket 84 from the center thickness tc at the respective center of the upper and lower diagonal portions 96 and 98 to a first largest thickness tl1 at a largest distance from the longitudinal center axis LG of the gasket 84, while the thickness of the gasket 84 is gradually and linearly decreasing in a direction towards the longitudinal center axis LG of gasket 84, from the center thickness tc at the respective center of the upper and lower diagonal portions 96 and 98 to a first smallest thickness ts1 at a smallest distance from the longitudinal center axis LG of the gasket 84. Both the first smallest thickness ts1 and the first largest thickness tl1 is smaller than the nominal gasket thickness tn. The first largest thickness tl1 and the first smallest thickness ts1 deviate equally from the center thickness tc, i.e. tl1+Dg1=ts1-Dg1=tc, where Dg1 is a max thickness deviation from the center thickness tc.

[0055] Further, within the inner portions 100 and 102 and along a respective longitudinal extension thereof, the thickness of the gasket 84 is gradually and linearly increasing in a direction away from the longitudinal center axis LG of the gasket 84 from the center thickness tc at the respective center of the inner portions 100 and 102 to a second largest thickness tl2, which here equals tl1, at a largest distance from the longitudinal center axis LG of the gasket 84, while the thickness of the gasket 84 is gradually and linearly decreasing in a direction towards the longitudinal center axis LG of the gasket 84, from the center thickness tc at the respective center of the inner portions 100 and 102 to a second smallest thickness ts2, which here equals ts1, at a smallest distance from the longitudinal center axis LG of the gasket. Both the second smallest thickness ts2 and the second largest thickness tl2s is smaller than the nominal gasket thickness tn. The second largest thickness tl2 and the second smallest thickness ts2 deviate equally from the center thickness tc, i.e. tl2+Dg2=ts2-Dg2=dc, where Dg2 is a max depth deviation from the center thickness tc. Obviously, here Dg2 equals Dg1.

[0056] It should be stressed that Fig. 6 is very schematic and simplified. For example, in reality, the heat transfer plates 8 and the gasket 84 will not have the edgy designs illustrated in Fig. 6 but rather a more smooth design with smooth transitions where the groove depth/gasket thickness changes from full to reduced depth/thickness. Further, Fig. 6 illustrates a straight cross section while the cross section in reality is curved. Also, the proportions in Fig. 6 may not be accurate.

[0057] In the plate pack of the plate heat exchanger 2, the plates 8 are arranged "flipped" in relation to each other. Accordingly, with reference to Fig. 5, the plate 8a is arranged between the plate 8b and another similar plate 8c, with the front side 14 of the plate 8a facing the front side 14 of the plate 8b and the back side 16 of the plate 8a facing the back side 16 of the plate 8c. With this arrangement, the first and second portholes 20 and 22 of the plate 8a will be aligned with the third and fourth portholes 28 and 30, respectively, of the plates 8b and 8c. Further, the plates 8 are welded together in pairs, back side 16 to back side 16, to form cassettes 108. Fig. 5 shows part of one of the cassettes 108 comprising the plates 8a and 8c. The plates 8a and 8c are welded together along their respective welding track 82 (illustrated for the plate 8a in Fig. 4).

[0058] In the plate pack of the plate heat exchanger 2, a gasket 84 as described above is arranged between each pair of adjacent cassettes 108. Each of the gaskets 84 is arranged in the opposing front gasket grooves 52 of two adjacent heat transfer plates 8 comprised in two adjacent cassettes 108. Thus, with reference to Figs. 3, 5 and 6, a gasket 84 is arranged between the plates 8a and 8b with the annular gasket part 86 extending in the annular groove parts 54 of the front gasket grooves 52 of the plates 8a and 8b, the upper ring gasket part 88 extending in the upper ring groove part 56 of the front gasket groove 52 of the plate 8a and in the lower ring groove part 58 of the front gasket groove 52 of the plate 8b, and the lower ring gasket part 90 extending in the lower ring groove part 58 of the front gasket groove 52 of the plate 8a and in the upper ring groove part 56 of the front gasket groove 52 of the plate 8b.

[0059] The above described embodiment of the present invention should only be seen as an example. A person skilled in the art realizes that the embodiment discussed can be varied in a number of ways without deviating from the inventive conception.

[0060] As an example, the center depth dc, i.e. the depth of the front gasket groove at the respective center of the upper and lower diagonal portions of the annular groove part, and the inner portions of the upper and lower ring groove parts, need not be equal to half the distance between the imaginary lower and upper planes, but it could be larger or smaller. Consequently, the center thickness tc, i.e. the thickness of the gasket at the respective center of the upper and lower diagonal portions of the annular gasket part, and the inner portions of the upper and lower ring gasket parts, need not be equal to half the nominal gasket thickness tn, but could be larger or smaller.

[0061] As another example, the first largest depth and the first smallest depth of the upper and lower diagonal portions of the annular groove part need not deviate equally from the center depth dc. Similarly, the second largest depth and the second smallest depth of the inner portions of the upper and lower ring groove parts need not deviate equally from the center depth dc. Consequently, the first largest thickness and the first smallest thickness of the upper and lower diagonal portions of the annular gasket part need not deviate equally from the center center thickness tc. Similarly, the second largest thickness and the second smallest thickness of the inner portions of the upper and lower ring gasket parts need not deviate equally from the center thickness tc.

[0062] Further, the front gasket groove and the gasket need not have gradually and linearly changing depth and thickness, respectively. As an example, the depth and thickness may instead change intermittently and stepwise.

[0063] The upper and lower diagonal portions of the annular groove and gasket parts need not have the shape depicted in the drawings. For example, instead of being curved, they may be straight. Similarly, the upper and lower ring groove and gasket parts need not have the shape depicted in the drawings. For example, instead of being circular, they may have the shape of a triangle with rounded corners.

[0064] Instead of being arranged on the same side of the longitudinal center axis of the heat transfer plate, the first and third portholes could be arranged on opposite sides of the longitudinal center axis to make the plate suitable for use in a heat exchanger of diagonal flow type instead of a heat exchanger of parallel flow type.

[0065] The borders of the diagonal and inner groove and gasket portions (illustrated by broken lines in Fig. 3) can be moved so as to reposition, reduce or expand the areas within which the groove depth and the gasket thickness are varied.

[0066] Instead of varying the groove depth and gasket thickness along the diagonal and inner portions of the front groove and gasket parts, the groove depth and the gasket thickness could be varied along only the diagonal portions, or only along the inner portions, of the front groove and gasket parts.

[0067] In the above described embodiments, the plates and the gaskets between the cassettes are all similar, but this is not mandatory. As an example, in a plate pack, plates of different types may be combined, such as plates having differently configurated heat transfer patterns.

[0068] 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. Similarly, the gaskets need not be made of rubber.

[0069] The inventive heat transfer plate could be used in connection with other types of plate heat exchangers than semi-welded ones, for example gasketed, welded, brazed and fusion-bonded plate heat exchangers. In connection therewith, the plates in the plate pack could be "rotated" instead of "flipped" in relation to each other. Further, the bottom of the front gasket groove need not extend in the imaginary lower plane outside the upper and lower groove portions of the annular groove part and the inner portions of the upper and lower ring groove parts but could extend in one or more other planes, for example in the center or half plane. Consequently, the thickness of the gasket outside the upper and lower gasket portions of the annular gasket part and the inner portions of the upper and lower ring gasket parts need not be equal to double the distance between the imaginary lower and upper planes of the heat transfer plate.

[0070] The above described gasket 84 is discontinuous so as to comprise an annular gasket part and two separate ring gasket parts. However, in alternative embodiments the gasket could be continuous such that the annular and ring gasket parts are connected and integrally formed.

[0071] The heat transfer plate need not be provided with a heat transfer pattern of herringbone type and distribution patterns of chocolate type but could be provided with other patterns, both symmetric and asymmetric patterns. Further, the heat transfer pattern may have one single design across the complete heat transfer area, and thus lack the bands of deviating pattern extending along the upper and lower borderlines separating the heat transfer area from the distribution areas.

[0072] It should be stressed that the attributes front, back, upper, lower, first, second, third, etc. is used herein just to distinguish between details and not to express any kind of orientation or mutual order between the details.

[0073] 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.

Claims

1. A heat transfer plate (8) being corrugated so as to extend in and between parallel imaginary separated lower and upper planes (46, 48) and comprising an upper end portion (18), a center portion (34) and a lower end portion (26) arranged in succession along a longitudinal center axis (LP) of the heat transfer plate (8), the upper end portion (18) comprising a first and a second porthole (20, 22) and an upper distribution area (24) provided with an upper distribution pattern, the lower end portion (26) comprising a third and a fourth porthole (28, 30) and a lower distribution area (32) provided with a lower distribution pattern, and the center portion (34) comprising a heat transfer area (36) provided with a heat transfer pattern differing from the upper and lower distribution patterns, wherein the heat transfer plate (8) further comprises, on a front side thereof (14), a front gasket groove (52) including an annular groove part (54) extending around the center portion (34), the upper and lower distribution areas (24, 32), and the first and third portholes (20, 28), an upper ring groove part (56) enclosing the second porthole (22) and a lower ring groove part (58) enclosing the fourth porthole (30), an upper groove portion (62) of the front gasket groove (52) extending between the second porthole (22) and the upper distribution area (24) and a lower groove portion (64) of the front gasket groove (52) extending between the fourth porthole (30) and the lower distribution area (32), characterized in that a depth of the front gasket groove (52), within the upper and lower groove portions (62, 64), increases, from a first smallest depth (ds1) to a first largest depth (dl1), along a longitudinal extension of the upper and lower groove portions (62, 64) so as to be the first largest depth (dl1) at a largest distance from the longitudinal center axis (LP) of the heat transfer plate (8), the front gasket groove (52) having a center depth (dc) at a respective center of the upper and lower groove portions (62, 64).

2. A heat transfer plate (8) according to claim 1, wherein the depth is gradually increasing along the longitudinal extension of the upper and lower groove portions (62, 64) of the front gasket groove (52).

3. A heat transfer plate (8) according to any of the preceding claims, wherein the front gasket groove (52) along more than half of its longitudinal extension has a nominal depth (dn) which is essentially equal to a distance between the imaginary lower and upper planes (46, 48), wherein said first smallest depth (ds1) < said first largest depth (dl1) < said nominal depth (dn).

4. A heat transfer plate (8) according to any of the preceding claims, wherein said upper groove portion (62) of the front gasket groove (52) is comprised in an upper diagonal portion (66) of the annular groove part (54) of the front gasket groove (52), which upper diagonal portion (66) extends between the upper ring groove part (56) of the front gasket groove (52) and the upper distribution area (24), and said lower groove portion (64) of the front gasket groove (52) is comprised in a lower diagonal portion (70) of the annular groove part (54) of the front gasket groove (52), which lower diagonal portion (70) extends between the lower ring groove part (58) of the front gasket groove (52) and the lower distribution area (32).

5. A heat transfer plate (8) according to any of claims 1-3, wherein said upper groove portion (62) of the front gasket groove (52) is comprised in an inner portion (78) of the upper ring groove part (56) of the front gasket groove (52), which inner portion (78) extends between the second porthole (22) and the upper distribution area (24), and said lower groove portion (64) of the front gasket groove (52) is comprised in an inner portion (80) of the lower ring groove part (58) of the front gasket groove (52), which inner portion (80) extends between the fourth porthole (30) and the lower distribution area (32).

6. A heat transfer plate (8) according to any of the preceding claims, wherein the first and third portholes (20, 28) are arranged on one side of the longitudinal center axis (LP) of the heat transfer plate (8) and the second and fourth portholes (22, 30) are arranged on another opposite side of the longitudinal center axis (LP).

7. A heat transfer plate (8) according to any of the preceding claims, wherein the upper groove portion (62) of the front gasket groove (52) is a mirroring, parallel to a transverse center axis (TP) of the heat transfer plate (8), of the lower groove portion (64) of the front gasket groove (52).

8. A gasket (84) for a heat transfer plate (8) comprising an upper end portion (18), a center portion (34) and a lower end portion (26) arranged in succession along a longitudinal center axis (LP) of the heat transfer plate (8), the upper end portion (18) comprising a first and a second porthole (20, 22) and an upper distribution area (24), the lower end portion (26) comprising a third and a fourth porthole (28, 30) and a lower distribution area (32), and the center portion (34) comprising a heat transfer area (36), wherein the gasket (84) comprises an annular gasket part (86) arranged to extend around the center portion (34), the upper and lower distribution areas (24, 32), and the first and third portholes (20, 28) of the heat transfer plate (8), an upper ring gasket part (88) arranged to enclose the second porthole (22) of the heat transfer plate (8), and a lower ring gasket part (90) arranged to enclose the fourth porthole (30) of the heat transfer plate (8), an upper gasket portion (92) of the gasket (84) being arranged to extend between the second porthole (22) and the upper distribution area (24) of the heat transfer plate (8), and a lower gasket portion (94) of the gasket (84) being arranged to extend between the fourth porthole (30) and the lower distribution area (32) of the heat transfer plate (8), characterized in that a thickness of the gasket (84), within the upper and lower gasket portions (92, 94), increases, from a first smallest thickness (ts1) to a first largest thickness (tl1), along a longitudinal extension of the upper and lower gasket portions (92, 94) so as to be the first largest thickness (tl1) at a largest distance from a longitudinal center axis (LG) of the gasket, the gasket having a center thickness (tc) at a respective center of the upper and lower gasket portions (92, 94).

9. A gasket (84) according to claim 8, wherein the thickness is gradually increasing along the longitudinal extension of the upper and lower gasket portions (92, 94) of the gasket (84).

10. A gasket (84) according to any of claims 8-9, wherein the gasket (84) along more than half of its longitudinal extension has a nominal thickness (tn), wherein said first smallest thickness (ts1) < said first largest thickness (tl1) < said nominal thickness (tn).

11. A gasket (84) according to any of the claims 8-10, wherein said upper gasket portion (92) of the gasket (84) is comprised in an upper diagonal portion (96) of the annular gasket part (86) of the gasket (84), which upper diagonal portion (96) extends on an inside of the upper ring gasket part (88) of the gasket (84), and said lower gasket portion (94) of the gasket (84) is comprised in a lower diagonal portion (98) of the annular gasket part (86) of the gasket (84), which lower diagonal portion (98) extends on an inside of the lower ring gasket part (90) of the gasket (84).

12. A gasket (84) according to any of claims 8-10, wherein said upper gasket portion (92) of the gasket (84) is comprised in an inner portion (100) of the upper ring gasket part (88) of the gasket (84), which inner portion (100) extends between an outer portion (104) of the upper ring gasket part (88) of the gasket (84) and an upper diagonal portion (96) of the annular gasket part (86) of the gasket (84), which upper diagonal portion (96) extends on an inside of the upper ring gasket part (88) of the gasket (84), and said lower gasket portion (94) of the gasket (84) is comprised in an inner portion (102) of the lower ring gasket part (90) of the gasket (84), which inner portion (102) extends between an outer portion (106) of the lower ring gasket part (90) of the gasket (84) and a lower diagonal portion (98) of the annular gasket part (86) of the gasket (84), which lower diagonal portion (98) extends on an inside of the lower ring gasket part (90) of the gasket (84).

13. A gasket (84) according to any of claims 8-12, wherein the upper and lower ring gasket parts (88, 90) of the gasket (84) are arranged on one and the same side of the longitudinal center axis (LG) of the gasket.

14. A gasket (84) according to any of claims 8-13, wherein the upper gasket portion (92) of the gasket (84) is a mirroring, parallel to a transverse center axis (TG) of the gasket (84), of the lower gasket portion (94) of the gasket (84).

15. A casette comprising two permanently joined heat transfer plates according to any of claims 1-7, wherein a back side side of one of the heat transfer plates faces a back side of another one of the heat transfer plates, and said another one of the heat transfer plates is turned upside down in relation to said one of the heat transfer plates.

Drawing