Plates with corrugated flow profiles for a plate-type heat exchanger

Abstract

A plate group for a plate-type heat exchanger device. The plate group includes a first plate (30a) and a second plate (31a), which extend in first and second directions and are displaced from each other in a third direction to enclose a first fluid channel for a flow of first heat exchanger fluid (28) along the first direction. The first and second plates are provided with respective first and second corrugated profiles (60a, 61a). The first corrugated profile (60a) defines a first succession of height variations in the third direction, and the second corrugated profile (61a) defines a second succession of height variations in the third direction that is essentially congruent but mirror-symmetric to the first succession such that the first and second corrugated profiles bound a first sequence of asymmetric venturi-shaped units inside the first fluid channel.

Description

Plates with Corrugated Flow Profiles for a Plate-type Heat ExchangerTechnical Field

[0001] The invention relates to a plate-type heat exchanger device and to a group of heat exchanger plates for such a heat exchanger device.Background Art

[0002] "Heat exchange" refers to the transfer of thermal energy between fluids, either liquids or gasses, which are flowing along each other and are in thermal contact via thermally conductive structures. Fluid-to-fluid recuperative heat exchangers are configured to recoup thermal energy from a first fluid flow by passing this fluid along a second fluid flow that remains separate from the first fluid. The heat exchanger (HE) defines first HE channels for conveying the first fluid, and second HE channels for conveying the second fluid separate from the first fluid.

[0003] Conventional plate-type heat exchangers are manufactured by stacking several HE plates into a configuration that defines flow channels in-between the plates. Typically, the channels are arranged as interleaved channel groups in-between the plates, in a way so that two HE working fluids, one relatively hot and the other relatively cold, may be conveyed through these interleaved channel groups. The HE plates form material barriers between the first and second channels and are adapted to transfer thermal energy between the first and second fluids when they pass through the channels. The heat transfer capacity of a HE device depends on the rate of heat transfer between either one of the HE working fluids and the plate structure. Another factor of relevance for the commercial efficiency of the HE device is the flow resistance that the working fluids experience when passing through the channels.

[0004] Patent document FR2547905 A1 describes a counter-flow heat exchanger device with plates provided with sinusoidally undulated corrugations wherein the crests and troughs line up in a mirror-symmetric arrangement to increase the heat transfer coefficient. A disadvantage of this known HE device is that the induced turbulence in the fluid flow yields an increased flow resistance and a corresponding substantial pressure drop in the flow across the channel.

[0005] It would be desirable to obtain a plate-type heat exchanger assembly that yields an improved high heat transfer efficiency, and possibly an improved mechanical rigidity.Summary of Invention

[0006] Therefore, according to a first aspect, there is provided a plate group for a plate-type heat exchanger (HE) device in accordance with claim 1 . The plate group includes a first HE plate and a second HE plate. Each respective HE plate extends with its plate surface generally in first and second directions. The first and second HE plates are placed at a distance from each other in a third direction to enclose a first fluid channel, which is adapted to convey a first flow of first HE fluid along the first direction. The first HE plate is provided with a first corrugated profile and the second HE plate is provided with a second corrugated profile. The first corrugated profile definesa first succession of height variations in the third direction, and the second corrugated profile defines a second succession of height variations in the third direction. The second succession may be is essentially congruent but mirror-symmetric to the first succession. The first and second corrugated profiles jointly bound a first sequence of asymmetric venturi-shaped units inside the first fluid channel.

[0007] Providing a HE plate group with at least one sequence of asymmetric multi-venturi- shaped corrugation profiles yields a (desirable) increase of the heat transfer coefficient - in particular for a flow characterized by a low Reynolds number in a range 2000 < Re < 8000 and a non-cavitating mode of operation - at the expense of a relatively small (undesirable) increase of pressure drop across the channel. On the one hand, the converging parts of the multi-venturi sequence trigger disturbances in the boundary layer of the fluid flow through the channel to prevent stratification of the fluid flow and allow a larger portion of the flow to be brought into thermal contact with the channel wall and thus to increase the rate of heat transfer to the channel wall. On the other hand, the diverging parts of the multi-venturi sequence allow the friction factor to remain relatively low because the fluid flow does not significantly separate from the plate surfaces while the cross-sectional channel area changes.

[0008] For example, for a flat-plate channel operating in the transitional range from laminar to turbulent with a Reynolds number of Re=3000, the heat transfer may be described by a Nusselt number of Nu=10 and the pressure drop may be described by a Darcy friction factor of f=0.045. A similar channel constructed using corrugated plates according to the present invention may be described by a doubling of the Nusselt number (Nu=20) at the expense of an increase in the friction factor of only 1 / 3 (to f=0.06), yielding a more economical design of the heat exchanger.

[0009] Each of the first and second successions of height variations present in the first and second corrugated profiles may form at least one series of mutually alternating crest lines and trough lines. These lines may extend across the plate with a component in the second direction and alongside each other. The term “line” as used in “crest line” and “trough line” broadly refers herein not only to straight lines that extend in a strictly linear fashion between two points in 3- dimensional Euclidian space, but also to curved lines that can be expressed as a contiguous set of 3D points described by three coordinate-functions that all depend on one input parameter (i.e. a “parametric curve”). The macroscopic shape of the plates and the possible curvature of the crest and trough lines across the plates may be varied to obtain a plate group with a determined heat transfer performance and mechanical stiffness.

[0010] According to an embodiment, the plate group includes a third HE plate, which also extends predominantly along the first and second directions and is provided with a third corrugated profile. The third HE plate is positioned at a distance of the second HE plate in the third direction but on a side of the second HE plate opposite to the first HE plate, to enclose a second fluid channel for a second flow of second HE fluid. The third corrugated profile defines a third succession of height variations in the third direction. The third succession may be is essentially congruent to the first succession and mirror-symmetric relative to the secondsuccession. The second and third corrugated profiles jointly bound a second sequence of asymmetric venturi-shaped units inside the second fluid channel.

[0011] By alternatingly stacking several (essentially) congruent plates with similar asymmetric corrugation profiles in mirror-symmetric orientations, a HE plate stack may be obtained which defines a plurality of interleaved channels with multi-venturi profiles for each fluid flow, while requiring relatively little manufacturing effort.

[0012] In embodiments, a respective unit in the first sequence of asymmetric venturi-shaped units includes a converging channel portion and a diverging channel portion. In the converging channel portion, a height of the first fluid channel may reduce monotonically from a maximum height value D1 to a minimum height value D2. In the diverging channel portion, the height of the first fluid channel may increase monotonically from the minimum height value back towards the maximum heigh value. A length L1 of the converging channel portion along the first direction may be smaller than a further length L3 of the diverging channel portion. Each of the venturi-shaped units may thus have mirror symmetry relative to the third direction but may be symmetric with respect to the first direction, in that the converging section is shorter than the diverging section. For example, a ratio of the further length to the length may be in a range 3 < L3 / L1 < 8, to obtain a good balance between increased heat transfer coefficient and pressure drop.

[0013] According to embodiments, each of the first corrugated profile and the second corrugated profile forms at least one series of crest lines and trough lines. The crest lines and trough lines may be curved to form arcs about nominal axes. These axes may extend perpendicular to the second direction and result in locally anticlastic curvature of the respective first or second HE plate. The arcs may for instance curve towards positive or negative first direction around nominal axes that are substantially parallel with the third direction while extending along respective HE plates that have macroscopically flat plate shapes (i.e. a flat mean plate shape in lowest order approximation). Alternatively, the arcs may for instance extend along HE plates that are macroscopically curved towards the third direction around nominal axes that are substantially parallel with the first direction.

[0014] The terms “anticlastic surface” and “anticlastically curved (surface)” refer to a surface that is curved in multiple directions away from a nominal tangent plane of that surface, having multiple centres of curvature that are located on opposing sides of the surface, such as a dualcurved saddle shape. By contrast, a “synclastic surface” is also curved in multiple directions but has its centres of curvature located on the same side of the surface. The term “locally anticlastically curved” is used herein to refer to a small-scale multi-curvature that forms a small perturbation to the general shape of the surface, and for which the locally defined centres of curvature may vary as function of position along the surface.

[0015] By augmenting the HE plates with multi-venturi corrugated profiles having arc-shaped crest and trough lines, small-scale anti-clastic plate deformations are introduced into the plate geometry which increase the bending stiffness of the plates as compared to flat plates.

[0016] In a further embodiment, each of the first and second plates is predominantly monoclastically curved about a respective nominal axis that extends parallel with the first direction. The nominal axes of distinct HE plates may then be arranged mutually parallel in a mid- sagittal plane of the plate group.

[0017] The terms “monoclastic surface” and “monoclastically curved (surface)” refer herein to a surface that is curved in only one direction away from a nominal tangent plane of that surface, having an axis of non-zero curvature in one direction but for which the curvature in the other direction is zero, such as in a semi-circular or parabolic cylindrical sheet. The term “predominantly monoclastically curved” is used herein to refer to a macroscopic curvature of the surface as a whole, whereas the surface may still include anticlastic shape perturbations at a local level. A predominantly monoclastically curved HE plate (i.e. a single-direction curved mean plate shape in lowest order approximation) with at least one more multi-venturi profile has increased stiffness against determined plate stress distributions that may arise during operation of the HE device, as compared to flat HE plates.

[0018] In yet a further embodiment, the venturi-shaped units have unit lengths (Lu) along the first direction, and the monoclastic curvatures of the first and second HE plates are substantially (semi-)cylindrical curvatures that may be described with nominal axes that are located at respective radii of curvature (Rp) away from the corresponding HE plate and towards the positive or negative third direction. In this case, the radii of curvature may be at least one order of magnitude larger than the unit lengths (i.e. Rp > 10- Lu).

[0019] Setting the radii of plate curvature at least one order of magnitude larger than the venturi unit lengths facilitates HE design procedures in which flow effects are modelling / estimated based on flat-plate multi-venturi geometries while treating the plate curvature as a perturbation.

[0020] In an alternative further embodiment, the first and second HE plates are predominantly flat, and the crest lines and trough lines of the first and second corrugated profiles are curved to form arcs along respective nominal mean planes of corresponding HE plates. These arcs may be curved about respective nominal axes that extend substantially parallel with the third direction and are arranged mutually parallel in a mid-sagittal plane of the plate group.

[0021] Providing a flat HE plate with multi-venturi corrugations that are curved along the plate increases bending stiffness compared to flat plates. Furthermore, by tailoring the along-plane curvature of the crests and troughs to the intended operational conditions of the HE plates, undesired edge effects in the fluid flows along the sides of the fluid channels may be mitigated.

[0022] In yet a further embodiment, the venturi-shaped units have unit lengths (Lu) along the first direction, and the nominal axes associated with the curvatures of the crest lines and trough lines are located at respective radii of curvature (Rvi, Rvj) away from the corresponding crest line or trough line and towards the positive or negative first direction. Also in this case, the radii of curvature may be at least one order of magnitude larger than the unit lengths (i.e. Rvi, Rvj > 10 Lu).

[0023] Setting the radii of crest / trough line curvature at least one order of magnitude larger than the venturi unit lengths facilitates HE design procedures in which flow effects are modelling / estimated based on flat-plate straight-line multi-venturi geometries, while treating the line curvature as perturbation.

[0024] According to embodiments, the first HE plate includes two (i.e. at least two, including i.a. exactly two, or three, or four, or more) first corrugated profile portions and a (i.e. at least one, including i.a. exactly one, or two, or three, or more) first flat plate portion, and the second HE plate includes two (i.e. at least two, including i.a. exactly two, or three, or four, or more) second corrugated profile portions and a (i.e. at least one, including i.a. exactly one, or two, or three, or more) second flat plate portion. A respective one of the at least one first flat plate portion may extend in the first direction and interconnect a corresponding pair of the at least two first corrugated profile portions. A respective one of the at least one second flat plate portion may extend in the first direction and interconnect a corresponding pair of the at least two second corrugated profile portions. The at least two second corrugated profile portions and at least one flat plate portion may be essentially congruent but mirror-symmetrically positioned relative to the at least two first corrugated profile portions and at least one flat plate portion. The first and second flat plate portions jointly bound at least one straight channel section inside the first fluid channel with a first channel height along the third direction that is essentially constant. Similar flat plate portions interconnecting corrugated profile portions may be included in the third HE plate and / or in further HE plates that may belong to the plate group.

[0025] When the HE fluid flows through a channel portion with the venturi-shaped profile, the intensity of turbulence in the flow is expected to increase. By providing the flat plate portions and corresponding straight channel section in-between venturi profile portions, the turbulence intensity in the fluid flow is given the opportunity to drop back to a value that approaches a typical turbulence intensity for a flat-plate HE channel. Depending on the length of the HE plates, multiple (e.g. two, three, or more, or even several tens of) corrugated profile portions interrupted by flat plate portions may be present in each respective HE plate.

[0026] In a further embodiment, the first and second HE plates are spaced apart at a mean inter-plate distance (Dp) along the third direction, and each of the first and second flat plate portions has a length (Lf) along the first direction and extending in-between the corresponding first or second sequences of height variations. This length may be smaller than twenty times the mean inter-plate distance (i.e. L2 < Lf < 20 Dp). In case a throat section and / or a widest section of a venturi-unit have non-zero lengths (L2, L4 > 0), the length (Lf) of the flat plate portions is preferably larger than both the section lengths (L2, L4 < Lf).

[0027] The length (Lf) of the flat plate portions and straight channel section may be chosen in a range from zero to at most ten times a hydraulic diameter of the straight channel section, to obtain an optimal trade-off between a relatively large increased heat transfer coefficient and a relatively small increase in pressure drop. In the straight channel section, increased heat transfer coefficients may be obtained as the flow is still turbulent due to the upstream sequence of Venturiunits, but the friction factor assumes a very low value of a flat plate and thus requires only little additional driving pressure difference as compensation. Inside the straight channel section, the increased turbulence is expected to have decayed to an insignificant level after approximately ten hydraulic diameters, so that further increase of the flat plate portion length will lead to diminishing returns in heat transfer vs. pressure drop efficiency.

[0028] According to embodiments, both the first and second plates are provided with embossments that are formed as local depressions and / or protrusions relative to the surrounding plate surface. The embossments may have an elongated shape associated with an elongation axis that extends substantially parallel with a nominal mean plane of the plate. The elongated shape may for instance be a semi-ellipsoid shape, a semi-spindle shape, or a semi-capsule shape. Respective embossments on the first HE plate may be arranged in pairs with respective embossments on the second HE plate, and may be mutually abutting in the third direction and with corresponding elongation axes rotated at different angles about local axes along the third direction.

[0029] Using known embossment techniques to form locally raised and lowered areas in the first and second HE plates provides an efficient way to form structures for maintaining the plates at determined distances. Forming the embossments with elongated shapes and mutually rotated elongation axes for two abutting embossments on adjacent first and second HE plates reduces the probability that these embossments are inadvertently misaligned in transverse directions.

[0030] In embodiments, the plate group may further include one or more plate spacers inside the first fluid channel and / or inside the second fluid channel. The spacers are adapted to abut both the first HE plate and the second HE plate. A respective plate spacer may be formed by a strip of material that is helically twisted over at least 180° about its longitudinal centreline. The twisted shape may be described by a periodically varying twist rate (d0 / dx), which may have a spatial period that is substantially identical to a length (Lu) of a venturi-shaped unit.

[0031] The material of the strip is sufficiently strong to maintain a defined distance between the first and second HE plates. Positioning one or more twisted tape spacers in-between the plates may efficiently be used for keeping the channel height fixed. The term “twisted tape” refers herein to a helical shape that can be obtained from continuously twisting two opposite lateral edges of an initially generally rectangular elongated strip of material in the same angular direction about a longitudinal centreline, so as to obtain a chiral (helical) shape. Providing the twisted tape spacer with a non-uniform twist rate that matches the spatial periodicity of the multi-venturi plate profile allows the vertical portion of the twisted tape spacer to abut the plates near the widest section of the venturi profile while allowing the horizontal portion to pass unhindered through the throat section, thus yielding a turbulating spacer that is easy to place and stabilize. The twisted tape spacer may be helically twisted over at least 180° about its longitudinal centreline.

[0032] In embodiments, the plate group may further include one or more local plate spacer structures arranged inside the first fluid channel and / or the second fluid channel. Such plate spacers may be formed as local pillar structures, such as poles or pins, which have a round orelliptical or lenticular- or stadium- or aerofoil- or teardrop-shaped cross-section in the first and second directions. The individual spacers may be fixed (for instance by brazing, welding, or gluing) to a surface of at least one of the first and second HE plates, and may extend, predominantly in a normal direction from the plate surface, towards and up to an opposite surface of an adjacent second or first HE plate. Any combinations and distributions of channel spacer structures are contemplated.

[0033] In embodiments, each of the first and second plates defines a central plate region, plate flanges at respective transverse plate edges on opposite sides of the central plate region, and further plate flanges at respective longitudinal plate edges on further opposite sides of the central plate regions. The central plate region may be provided with the corrugated profile associated with the asymmetric venturi-shaped units. The plate flanges may include distal flange portions that are jointly displaced towards a positive or negative third direction away from the central plate region. The further plate flanges may include further distal flange portions that are jointly displaced towards the negative or positive third direction away from the central plate region in opposite direction relative to the plate flanges.

[0034] Providing the HE plates with edge flanges along which the plates may be stacked on top of each other while maintaining a required channel spacing in the central plate region allows a reduction in the amount of material and welding operations needed to manufacture the plate group.

[0035] According to a second aspect, and in accordance with advantages and effects described herein above, there is provided a plate-type HE device, which includes a plurality of plate groups composed of first and second HE plates in accordance with the first aspect. The first and second HE plates enclose a group of first fluid channels and a group of second fluid channels.

[0036] In one group of embodiments of such a HE device, the group of first fluid channels and / or the group of second fluid channels extends in a Z-flow arrangement or in a C-flow arrangement between the respective inlets and outlets, the group of first fluid channels is interleaved in a counterflow arrangement relative to the group of second fluid channels in a central plate region. The C- and Z-flow channel arrangements allow the channels that belong to the same HE fluid to be interleaved in the central plate region with the other channels from the other HE fluid, but to break out of this interleaving to enter or exit the heat exchanger as a noninterleaved group. Counterflow heat exchanger arrangements involve interleaved flow channels in which the distinct fluids flow in opposite directions, and have a relatively high heat exchanging efficiency.

[0037] In another group of device embodiments, the group of first fluid channels and / or the group of second fluid channels extends in a continuous linear arrangement between the respective inlets and outlets, and the group of first fluid channels is interleaved in a counterflow arrangement relative to the group of second fluid channels in a central plate region. A continuous linear arrangement - including uninterrupted linear channels that do not deflect sideways at thechannel inlets or outlets - allows maximizing the lengths of the corrugated profiles with venturishaped units and the counter current flows passing along these profiles.

[0038] In yet another group of device embodiments, the group of first fluid channels is interleaved in a crossflow arrangement relative to the group of second fluid channels in the central plate region.

[0039] Any selection or combination of features discussed for the HE plate group discussed herein may also be present in embodiments of the HE device according to this second aspect.

[0040] According to a third aspect, and in accordance with advantages and effects described herein above with reference to the first and second aspects, there is provided a HE plate adapted for use in a plate group according to the first aspect or a plate-type HE device according to the second aspect. According to an embodiment, the HE plate extends in the first and second directions and is provided with the corrugated profile described above. The corrugated profile may be composed of a plurality of half-venturi-shaped units defining a succession of height variations in a third direction. Each respective half-venturi-shaped unit may include a converging plate portion and a diverging plate portion. In the converging plate portion, a channel-side surface of the HE plate decreases monotonically over an amplitude AD towards the negative third direction. In the diverging plate portion, the channel-side surface of the HE plate increases monotonically over the amplitude AD back towards the positive third direction. A length L1 of the converging plate portion defined along the first direction may be at least three times smaller than a further length L3 of the diverging plate portion along the first direction. Furthermore, a sum L1+L3 of the length and the further length may be at least four times larger than the amplitude.

[0041] Any selection or combination of plate-specific features discussed for HE plate group and the HE device discussed herein may also be present in embodiments of the HE plate according to this third aspect.

[0042] In further aspects of the invention, methods are provided for manufacturing a HE plate, a plate group, and a plate-type HE device in accordance with the previous aspects.Brief Description of Drawings

[0043] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. In the drawings, like numerals designate like elements. Multiple instances of an element may each include separate labels appended to the reference number (for instance “62i” and “62j”). The reference number may be used without an appended label (e.g. “62”) to generally refer to an unspecified instance or to all instances of that element.

[0044] Figure 1 a schematically shows a perspective view of counter-current plate-type heat exchanger device, according to an embodiment;

[0045] Figure 1 b schematically shows a side view of the heat exchanger device from figure 1 a;

[0046] Figure 1c schematically shows an exploded perspective view of a plate core in the heat exchanger device from figure 1 a;

[0047] Figure 2a schematically shows a cross-sectional side view of a plate group in a countercurrent heat exchanger, according to an embodiment;

[0048] Figure 2b schematically shows a cross-sectional side view of venturi-shaped unts in the plate group from figure 2a;

[0049] Figure 3a schematically shows an exploded perspective view of a plate group, according to another embodiment;

[0050] Figure 3b schematically shows a top view of a heat exchanger plate and a frontal view of a plate group from figure 3a;

[0051] Figure 4a schematically shows an exploded perspective view of a plate group, according to yet another embodiment;

[0052] Figure 4b schematically shows a top view of a heat exchanger plate and a frontal view of a plate group from figure 4a;

[0053] Figure 5a schematically shows an exploded perspective view of a plate group in a cross-current heat exchanger, according to another embodiment;

[0054] Figure 5b schematically shows a cross-sectional view of the plate group from figure 5a;

[0055] Figure 6a schematically shows a perspective view of a heat exchanger plate with spacers, according to an embodiment, and

[0056] Figure 6b schematically shows a cross-sectional side view of a plate group in a countercurrent heat exchanger including a spacer from figure 6a.

[0057] The figures are meant for illustrative purposes only, and do not serve as restriction of the scope or the protection as laid down by the claims.Description of Embodiments

[0058] The following is a description of certain embodiments of the invention given by way of example only and with reference to the figures. In these examples, the X-, Y-, and Z-directions are associated with a Cartesian coordinate system. The X-direction may be referred to as “longitudinal direction”, which in examples may correspond to co- or counter-flow direction of fluids through channels in medial plate regions of exemplary heat exchanger devices. The Z- direction may be referred to as “plate-interspacing” direction, which is associated with the gaps between the heat exchanger plates. The Y-direction represents a remaining direction that is transverse to both X- and Z-directions. In examples that include macroscopically flat plates and fluid channels, the Y-direction corresponds to the widest transverse dimension of the fluid channels. In the following description of examples, a direction will not be indicated with a sign (e.g. X-direction) when both positive and negative directions are referred to (e.g. ±X-direction) or if the distinction is immaterial. A positive or negative heading will be specifically indicated (e.g. +X or -X-direction) if this heading is of interest.

[0059] Figure 1a schematically shows a perspective view of an assembled heat exchanger (HE) device 10 according to a first embodiment, which in this example is a counter-current platetype fluid-to-fluid recuperative HE device 10. In this counter-current channel configuration, thefirst and second heat exchanger fluids traverse a central region of the HE device 10 in opposite +X- and -X-directions.

[0060] The HE device 10 comprises a plate core 22 that is mounted inside a frame 12. The frame 12 is composed of end panels 14, 15 and connection members 16, which jointly enclose a receiving space that is occupied by the plate core 22. The end panels 14, 15 may be structurally reinforced plates, which in the illustrated example extend generally in X- and Y- directions, and are adapted to enclose and protect the plate core 22 from both sides along a third direction Z. Each of the connection members 16 mechanically connects the first end panel 14 with the second end panel 15, at respective end panel connection regions. In this example, each connection member 16 is formed as a rigid beam that is fixed at its opposite distal ends to respective distal corners of the end panels 14, 15.

[0061] The exemplary HE device 10 is adapted to receive a fluid stream 28 via a plurality of first inlet apertures 24, and a second fluid stream 29 via a plurality of second inlet apertures 25, and to guide these fluid streams 28, 29 via separate channels through the plate core 22. The fluid streams 28, 29 have different temperatures and possibly different compositions The device 10 is configured to recuperate heat from one fluid and to transfer this heat to the other fluid. In this example, the first fluid 28 is the hotter fluid and the second fluid 29 is relatively colder. The initially hotter first fluid 28 cools down while flowing from the first inlet apertures 24 through the first channels 38 towards first outlet apertures 26. By contrast, the initially colder second fluid 29 is heated by receiving part of the thermal energy from the first fluid 28, while the second fluid 29 flows from the second inlet apertures 26 through the second channels 39 and towards second outlet apertures 27. The recuperated thermal energy may be transported by the second fluid 29 to be utilized elsewhere e.g. for pre-heating. In various industrial applications, the temperatures and compositions of the fluids that make up the first and second fluid flows 28, 29 differ to such an extent that mixing of these fluids should be avoided. The first channels 38 are therefore fluidly separated from the second channels 39.

[0062] First and second inlet and outlet headers (not shown) are coupled at opposite short end faces and near the flanking plate 20 of the HE device 10, to supply and discharge the first and second fluids 28, 29 to and from the first and second channel inlet and outlet apertures 24-27, respectively. Preferred connections of the apertures 24-27 fluid supply and discharge headers will be determined by desired operating conditions of the device 10 via known methods.

[0063] Figure 1 b schematically shows a side view of the exemplary HE device 10 and illustrates that the first channels 38 form a parallel array of fluid conduits and that the second channels 39 form another parallel array of fluid conduits. Except from the outermost channels in Z-directions, each first channel 38 is directly enclosed by two second channels 39, and each second channel 39 is directly enclosed by two first channels 38. The first channels 38 and second channels 39 thus extend one above the other through the plate core 22, thereby forming an interleaved sequence of channels.

[0064] Figure 1 c schematically shows a partially exploded view of the plate core 22 in the HE device 10 from figure 1 a. This exemplary plate core 22 is formed by several first and second plates 30, 31 , which are stacked in an alternating arrangement along the Z-direction. Figure 1 c schematically depicts a stack of four first plates 30 and four second plates 31 . Plate cores 22 according to the present invention are not considered limited to these specific numbers, but may be composed of different numbers of plates.

[0065] The plates 30, 31 in figure 1 c are arranged mutually parallel, each plate with its macroscopic surface shape extending predominantly along the X- and Y-directions. The HE plates 30, 31 are mutually spaced in the Z-direction, to define the first channels 38 for conveying a first working fluid 28 and the second channels 39 for conveying a second working fluid 29. In this example, spacer bars 50, 51 are provided in-between the plates 30, 31 and along the plate edges 42, 44, 46, 48, to maintain the channels 38, 39 at determined heights.

[0066] In figure 1 c, two top-most plates 30a, 31 a are displaced towards the positive Z-direction relative to remainder of the plate core 22 merely to illustrate geometric details of plate regions. In the example, the plates 30, 31 have continuous translational symmetry along the Y-direction, implying that the XZ-cross-sectional shape of the HE plates remains substantially the same at different Y-positions.

[0067] The HE plates 30, 31 are made of mechanically rigid and thermally conductive material, and are adapted to transfer thermal energy from the first fluid 28 to the second fluid 29. The HE plates may be individually formed as continuous unitary structures without through holes, and may for instance be manufactured by known methods such as extrusion, casting, or by folding and / or pressing an initially flat and quadrilateral (e.g. rectangular) plate blank. The plates 30, 31 may consist essentially of a metal, a metal alloy (e.g. steel), a ceramic, a glass, or a graphite / polymer composite. Plates formed from such materials can be made thermally and mechanically stable, and are able to withstand high temperatures and pressures. Alternatively, the plates may consist essentially of metal (alloy) coated one or more surfaces with an enamel material, for instance a vitreous enamel (i.e. glass) layer. Ceramics, full-glass, enamelled, and graphite / polymer composite plate materials allow the HE assembly to operate in hostile environments in which at least one of the fluids is corrosive.

[0068] The geometry of each respective first plate 30 may be subdivided into a first proximal region 52, a first medial region 54, and a first distal region 56. Similarly, the plate geometry of each second plate 31 may be subdivided into a second proximal plate region 53, a second medial plate region 55, and a second distal plate region 57. The non-limiting terms “proximal” and “distal” merely indicate that these plate regions are located on opposite sides of their corresponding medial plate region, and relative to the viewpoint presented in figure 1 c.

[0069] The first and second proximal plate regions 52, 53 are located at corresponding transverse plate edges 42, 43, and have substantially flat upper and lower plate surfaces. The first and second distal plate regions 56, 57 are located at opposite transverse plate edges 44, 45,and have substantially flat upper and lower plate surfaces. The second fluid 29 enters and exits the second channels 39 via the apertures 25, 27 defined at these transverse plate edges 42-45.

[0070] Groups of guiding strips 58 are provided in the entrance and exit regions of the second channels 38. Each respective guiding strip 58 forms a smooth and continuous arc, and the strips 58 in each group are arranged to smoothly guide the first fluid 28 along a 90°-curve from the initial supply flow along the -Y-direction at the inlet aperture 24, to the counter-flow direction along the -X-direction inside the channel 38, and then back to the final discharge flow along the +Y- direction at the outlet aperture 26. The strips 58 thus guide the second fluid flows in a C-shaped path through the plate core 22. Near the respective inlet and outlet apertures 24 and 27 or 25 and 26, the hot and cold fluid flows cross each other at about 90°. Arrow symbols in figures 1a-1c schematically indicate macroscopic directions of flows of the first and second fluids 28, 29 through the channels 38, 39 of the HE device 10. In this example, the flow paths of the first fluid28 extend linearly in the longitudinal direction X, whereas the flow paths of the second fluid 29 curve in C-shapes along the longitudinal and transverse directions X, Y. In other embodiments, the first channels and / or second channels may be entirely linear, or may resemble Z-shapes, or serpentine shapes, or various other shapes.

[0071] At the medial plate regions 54, 55 of the plate core 22, the first and second fluids 28,29 flow in counter-current fashion through the channels 38, 39. Each medial plate region 54, 55 includes a corrugated profile 60, 61 with a repeating sequence of venturi-shaped corrugations. The term “corrugated” refers herein to rows of folds or undulations in a plate region that resemble a series of waves when seen from a cross-sectional side view. This term "corrugated" may refer in a strict manner to a succession of height variations forming parallel rows of folds or waves that extend in linear trajectories across the entire plate, or may refer in a broader manner to a succession of height variations forming locally parallel rows of folds or waves that extend in curved trajectories across the plate. Each first corrugated plate profile 60a defines a first succession of height variations in the Z-direction. Similarly, each second corrugated plate profile 61a defines a second succession of height variations in the Z-direction, this second succession being essentially congruent to the height variations in the first profile 60a but mirrored in the Z- direction. The term “essentially congruent” indicates in this context that the corrugated profiles of distinct plates are geometrically identical at a macroscopic scale, so that the two plates can be made almost entirely coinciding by appropriate translation and rotation of one plate towards the other. At smaller scale, however, the corrugated profiles may still include local shape perturbations, such as embossments, which cause the geometries of the plates to deviate from being strictly congruent.

[0072] Two vertically adjacent plates 30a, 31a are placed with their first and second corrugated profiles 60a, 61a mutually aligned along the X- and Y-directions, and in a mirror-symmetric pose at a mutual distance relative to the Z-direction such that the first and second height variations jointly bound a first fluid channel 38a. Part of this first channel 38a forms a first sequence of asymmetric venturi-shaped units. Another first plate 30b with a corrugated profile 60b is placed ata distance below the second plate 31 a, such that the second plate 30b and further first plate 30b together bound a second fluid channel 39a. The corrugated profiles 61 a, 60b of these plates 30b, 31a form a second sequence of asymmetric venturi-shaped units. This sequence of plates and channels is repeated by alternatingly stacking multiple first and second plates 30, 31 in mirrored orientations above each other.

[0073] From a viewpoint located above each first plate 30, the upper surface of the medial plate region 54 forms a repeating series of crest lines 76 and trough lines 77, which extend mutually parallel in the Y-direction across the plate 30. A similar repetitive series of parallel crest lines and trough lines is formed in the medial plate region 55 of each second plate 31 , although the relative directions of the crests and troughs are reversed due to the mirror-symmetrical poses of the second plates 31 .

[0074] Figure 2a schematically presents a cross-sectional side view of an exemplary plate group 32, illustrating the corrugated profiles 60, 61 in the medial plate regions 54, 55 from figure 1c. The interleaved channels 38, 39 and counter-current operation are illustrated by arrows indicating first and second flow directions 40, 41 of corresponding fluids 28, 29.

[0075] Two first plates 30a, 30b and two second plates 31a, 31 b are shown, which extend with their nominal mean planes Sp along the X- and Y-directions. The first and second plates 30, 31 are spaced relative to each other in the Z-direction, such that the (periodically varying) gap enclosed between each plate pair forms a fluid channel. A lower surface 36 of a first plate 30 and an upper surface 35 of an adjacent second plate 31 form the upper and lower boundaries of a first fluid channel 38. Similarly, the lower surface 37 of a second plate 31 and an upper surface 34 of a lower-situated first plate 30 form the upper and lower boundaries of a second fluid channel 39. The non-limiting terms “upper” and “lower” are used in a non-limiting manner to indicate position with respect to the view presented in Figure 2a, and will change when the orientation of the device 10 changes with respect to the Z-direction.

[0076] The first fluid channels 38 allow the first fluid 28 to flow 40 in the negative X-direction along the extent of the medial plate regions 54, 55, whereas the second fluid channels 39 allow the second fluid 29 to flow 41 in the positive X-direction along the medial plate regions 54, 55 . These positive and negative directions ±X describe the flows at macroscopic level i.e. a zeroth order approximation that does not yet include the effect of the corrugated profiles 60, 61 . The mean plane Sp of each respective HE plate 30, 31 is a nominal plane that extends in the X- and Y-directions through the arithmetic mean value of the plate deflections in the Z-direction. The mean planes Sp of two adjacent plates 30, 31 are spaced at an inter-plate distance Dp along the Z-direction. In this example, the average distance Dp has a value in a range of about 4 millimetres to 20 millimetres (endpoints included).

[0077] At the corrugated profile 60 (or 61) in the medial plate region 54 (or 55), both surfaces 34 and 36 (or 35 and 37) of the same plate 30 (or 31) jointly deflect away from the mean plane Sp in an undulating manner towards both Z-directions. A repeating pattern is thereby formed, in which each plate deflection in the positive Z-direction is followed by another plate deflection ofequal magnitude in the negative Z-direction, and vice versa. As a result of the shape congruence and mirror-symmetric positioning of the plates 30, 31 , the channel 38 (or 39) defined between mutually facing plate surfaces 36 and 35 (or 37 and 34) of two enclosing plates 30, 31 forms a sequence of venturi-shaped units 62 (or 63) with a repetitive pattern of constrictions and dilations of the channel 38 (or 39). The local inter-plate distance in the Z-direction thereby oscillates - i.e. alternatingly increases and reduces - about the mean inter-plate distance Dp. The recurring local narrowing and widening of the fluid channels 38 imparts a pulsating effect on the first fluid 28 flowing inside these channels 38 (Bernoulli's principle).

[0078] In this example, the venturi-shaped units 62i, 62j for the first channel 38 form a sequence of identical shapes with unit lengths Lu along the X-direction. The index labels i, j are used herein to distinguish between venturi-shaped units at different positions along the X- direction, whereas the index labels a, b, c, d are used to distinguish between plates at different levels along the Z-direction. The unit length Lu may for instance have a value in a range of 8 millimetres to 180 millimetres (endpoints included).

[0079] In figure 2a, the corrugated profiles 61 of the second plates 31 are essentially congruent to the corrugated profiles 60 of the first plates 30, but the second plates 31 are mirrored in the Z- direction with respect to their individual mean planes Sp. In this example, the plates 31 , 30 bounding the second channel 39 are placed at an inter-plate distance that is essentially identical to the mean inter-plate distance Dp for the first channel 38. The resulting venturi-shaped units 63 for the second channel 39 are congruent to the venturi-shaped units 62 of the first channel 38, but are mirrored and shifted over a length L1+L2 relative to the X-direction (see figure 2b).

[0080] Figure 2b illustrates geometrical properties of a venturi unit 62 in the exemplary multiventuri channels from figure 2a. The venturi unit 62 may be described by differently oriented portions of the plates 30, 31 within each unit 62, and / or described by the sections of the channel bound by these place portions. Within one unit 62, the first channel 38 defines a converging channel section 64, a throat section 65, a diverging channel section 66, and a widest section 67. The converging channel section 64 is bounded by two converging plate portions 68, 69 of the corresponding first and second plates 30, 31 . The throat section 65 is bounded by two transition portions 70, 71 of the corresponding plates 30, 31 , and the diverging channel section 66 is bounded by two diverging plate portions 72, 73 of the corresponding plates 30, 31 . The unit 62 continues at its trailing end into a next venturi-shaped unit. Here, the first and second plates 30, 31 define two further transition portions 74, 75, which jointly bound the widest channel section 67, and which smoothly interconnect the diverging plate portions 72, 73 with the converging plate portions 68, 69 of a next venturi-shaped unit.

[0081] At the converging plate portions 68 and 69, each plate surface 36 and 35 moves monotonically inwards into the channel 38 as function of increasing position downstream along the length of the converging channel section 64. Consequently, the height of the first fluid channel 38 decreases in a monotonic fashion from the maximum first channel height D1 at a leading opening of the unit 62 to the minimum first channel height D2 in the throat section 65. When thefirst fluid 28 passes through the converging channel section 64, the channel contracts in the Z- direction, which causes the YZ-cross-sectional area to decrease in a smooth monotonic fashion.

[0082] An inwards tilt of the converging plate portion 68 away from the X-direction (parallel with the midplane Sp) and towards the negative Z-direction may be described by a convergence angle a. Because of the mirror symmetry in Z-direction, a local slope of the converging plate portion 69 of the second plate 31 away from the X-direction and towards the positive Z-direction may be described by the opposite angle -a. Preferably, the magnitude of the angle a is in a range of 30° < a < 60°?

[0083] The throat section 65 interconnects the converging channel section 64 with the diverging channel section 66 and marks the position in the unit 62 where a vertical distance between the first lower plate surface 36 and the second upper plate surface 35, referred to as the “local channel gap”, assumes a minimal value D2. When the first fluid 28 flows through the throat section 65, the decreasing YZ-cross-sectional channel area causes the flow 40 to accelerate, which is accompanied by a pressure drop in the fluid 28. This phenomenon is called the Venturi effect.

[0084] The transition portion 70 interconnects the converging plate portion 68 with the diverging plate portion 72 of this unit 62. At this location 70, the first plate 30 forms a concave upwards fold. As the plate 30 has translational symmetry along the Y-direction, the fold continues into the page of figure 2b. From a viewpoint located above the plate 30, the first upper plate surface 34 forms a trough line 77 along the Y-direction. A similar trough line is present in the second plate 31 at its transition portion 71 , but now from a viewpoint below the plate 31 . From a viewpoint inside the channel 38, the first lower surface 36 of the first plate 30 and the second upper surface 35 of the second plate 31 form further crest lines at the transition portions 70, 71 .

[0085] At the diverging plate portions 72 and 73, each of the plate surfaces 36 and 35 moves monotonically outwards relative to the centre of the channel 38 as function of increasing position downstream along the length of the diverging channel section 66. Consequently, the height of the first fluid channel 38 increases in a monotonic fashion from the minimum first height D2 at the throat section 65 back to the maximum first height D1 at the widest channel section 67. When the first fluid 28 passes through the diverging channel section 66, the channel dilates in the Z- direction, which causes the YZ-cross-sectional area to increase again in a smooth and monotonic fashion.

[0086] An outwards tilt of the diverging plate portion 72 in the positive Z-direction and back towards the mean plane Sp may be described by a divergence angle p. Similarly, a tilt of the diverging plate portion 73 in the negative Z-direction back towards the mean plane Sp may be described by an opposite angle -p. Preferably, the magnitude of this divergence angle p is in a range of +1 ° < p < +15°. Maintaining a small non-zero angle p ensures that the plate curvature remains smooth and that the deflections of the fluid flow 40a in ±Z-directions away from the X- direction remain small. This prevents the flow 40a from separating from the plate walls 35a, 36a, and lowers the probability that the flow 40a forms a local jet stream. The flow 40a may maintain amore laminar character when it enters the leading opening of the subsequent venturi-shaped unit 62j, thus allowing the flow resistance and pressure drop for the first flow 40a inside the first channel 38a to remain low.

[0087] The further transition portion 74 interconnects the diverging plate portion 72 with a converging plate portion of a next venturi-shaped unit 62. Here, the first plate 30 forms a concave downwards fold. From a viewpoint located above the plate 30, the first upper plate surface 34 forms a crest line 76 along the Y-direction. A similar crest line is present in the second plate 31 at its further transition portion 75, but now from a viewpoint below the plate 31 . From a viewpoint inside the channel 38, the lower surface 36 of the first plate 30 and the upper surface 35 of the second plate 31 form further trough lines at the further transition portions 74, 75.

[0088] In this example, each of the venturi-shaped units 62, 63 has mirror symmetry relative to the Z-direction and continuous translational symmetry relative to the Y-direction. However, each venturi-shaped unit 62 (or 63) is asymmetric with respect to the X-direction, in that the converging section 64 is considerably shorter than the diverging section 66. Viewed along the X-direction, the converging channel section 64 has a length L1 , the throat section 65 has a length L2, the diverging channel section 66 has a length L3, and the widest section 67 has a length L4. The four sections lengths L1 to L4 add up to the total length Lu of the venturi unit 62.

[0089] Furthermore, the length L1 of the converging section 64 is smaller - for instance in the example of Figure 2b about 6 times smaller - than the length L3 of the diverging section 66. The (absolute) rate of narrowing of the converging section 64 is larger, preferably at least 4 times larger, than the (absolute) rate of widening of the diverging section 66. In this example, the lengths L2 and L4 of the throat section 65 and widest section 67 are negligeable (L2, L4 = 0), whereas the length L3 is larger than the length L1 . The length L3 may for instance have a value in a range 3 < L3 / L1 < 8. This range implies that the throat section 65 lies at a longitudinal distance 1 / 9 Lu < L1 < YrLu downstream of a leading opening of the converging section 64 where the height D1 of the channel 38a is a maximum, and lies at a longitudinal distance 8 / 9 Lu > L3 > % Lu upstream of a trailing opening of the diverging section 66 where the height D1 of the channel 38a is again a maximum.

[0090] In the example of figure 2b, a thickness d of the first plate 30 is essentially uniform across the plate 30 and has a value of in a range of 0.4 to 2.0 millimetres. This thickness d is defined as a shortest perpendicular distance between the upper and lower surfaces 34 and 36 of the plate 30. This thickness d is substantially identical to the thickness d of the second plate 31 , defined as a shortest perpendicular distance between the upper and lower surfaces 35 and 37 of plate 31 .

[0091] The total magnitude of the bi-directional plate deflections, occurring in the upwards and downwards concave folds of one plate, may be described by a crest-to-crest amplitude AD. For the first plate 30, this deflection amplitude AD is defined as the distance between the highest (i.e. outermost) position of the upper surface 34 and the lowest (i.e. innermost) position of the lower surface 36 in Z-direction and relative to the channel 38. Similarly, for the second plate 31 , thisdeflection amplitude AD is defined as the distance between the highest position of the upper surface 35 and the lowest position of the lower surface 37 in Z-direction and relative to the channel 38. It follows implicitly from figure 2b that the mean inter-plate distance Dp is the sum of the minimum channel gap D2 and the crest-to-crest amplitude AD (i.e. Dp = D2 + AD). Preferably, a ratio of the amplitude AD to the mean inter-plate distance Dp is in a range of 0.1 < AD / Dp < 0.5, implying that the deflection magnitude of the venturi-shaped corrugations is between 10% and 50% of the mean plate distance Dp. In an example, the amplitude AD may for instance be about 20 millimetres and the mean inter-plate distance Dp may be about 100 millimetres, yielding a ratio AD / Dp of approximately 0.2.

[0092] At the concave upwards and downwards folds located at respective transition portions 70, 71 , 74, 75, the plate surfaces 34-37 curve relatively rapidly but smoothly. The local plate curvature at the concave upwards folds at transition portions 70 may be described by a curvature radius r1 , and the local plate curvature at the concave downwards folds at transition portions 74 may be described by a curvature radius r2. Preferred, the radii of curvature are in a range of 2 < r1 , r2 < 8 millimetres. In the example shown in Figure 2b, both r1 and r2 have a value in a range of 4 to 5 millimetres and approximately equal to 1 AD.

[0093] Figures 3a and 3b illustrate another embodiment of a plate group 132 for a HE device, which partly resembles the plate group 32 from figure 2a but is composed of curved first and second HE plates 130, 131. Elements from figures 1a-2b may also be included in the embodiment of figures 3a-3b, although not all elements are explicitly discussed or indicated. Similar elements are designated with similar reference numbers but with a leading numeral 100 to distinguish the embodiments.

[0094] Figure 3a schematically shows an exploded view of the plate group 132, in which all plates 130, 131 have downwards convex shapes with similar curvatures and mutually parallel axes of curvature. Each respective first plate 130 is predominantly monoclastically curved with its longitudinal plate edges 146, 148 displaced towards the negative Z-direction and about a respective curvature axis Ax that extends parallel with the X-direction. Similarly, each second plate 131 is predominantly monoclastically curved with its longitudinal plate edges 147, 149 towards the negative Z-direction and about a respective nominal axis of curvature Ax’ that also extends parallel with the X-direction. All axes Ax, Ax’ are arranged mutually parallel and lie in a mid-sagittal plane Sm of the plate group 132, which intersects the longitudinal midline of each plate 130, 131.

[0095] In this case, the medial plate region of the first plate 130 includes two distinct corrugated profiles 160a1 , 160a2, which are interconnected by a flat intermediate plate portion 178a. Similarly, the medial plate region of the second plate 131 includes two distinct corrugated profiles 161 a1 , 161 a2, which are interconnected by another flat intermediate plate portion 179a.

[0096] In this example, the semi-venturi units in the corrugated profiles 160, 161 have unit lengths Lu along the X-direction. Each curved plate 130 or 131 has its axis of curvature Ax, Ax’ located below the corresponding plate 130, 131 , at a distance in the negative Z-directioncorresponding to a radius of curvature Rp, Rp’ that is essentially identical for all plates. The plates 130, 131 are interspaced by mean inter-plate distances Dp, which in this plate arrangement is defined in the Z-direction along the mid-sagittal plane Sm and has essentially equal values for all plates. The essentially identical radii Rp for all plates 130, 131 imply that the axes Ax of adjacent plates lie at regular spacings Dp below each other. In this example, the radii Rp are at least one order of magnitude larger than the lengths Lu of the semi-venturi units in the corrugated profiles 160, 161 (i.e. Rp > 10 Lu).

[0097] The local vertical extrema in the corrugated profiles 160, 161 form series of crest lines 176a and trough lines 177a. Due to the curvature of the plates 130, 131 , the crest and trough lines 176a, 177a are also curved towards the negative Z-direction into arcuate shapes that have the same axis Ax and radius Rp of curvature as the corresponding plate. At the trough lines 177 of the first plate 130, the plate locally curves in concave upward direction in an XZ-plane but simultaneously curves in concave downward direction in an YZ-plane, resulting in a locally anticlastic curvature 180 (see inset figure). The resulting curved plate arrangement has an improved resistance against undesired bending of the plate core associated with sagging and / or thermal deformations during operation.

[0098] Figures 4a and 4b illustrate yet another embodiment of a plate group 232 for a HE device. Similar elements as in the plate groups from figures 1a-2b may be included in the plate group 232 of figures 4a-b, although not all elements are explicitly discussed or indicated. Similar elements are designated with similar reference numbers but with a leading numeral 200 to distinguish the embodiments.

[0099] Figure 4a schematically shows an exploded view of the plate group 232, which is composed of first and second HE plates 230, 231 , which are macroscopically flat in the sense that their nominal mean planes Sp are flat as in figure 1 c.

[0100] The local vertical extrema in the corrugated profiles 260, 261 form series of crest lines 276a and trough lines 277a with curved shapes that in this case extend in XY-directions along the mean plane Sp of the corresponding plate 230 or 231 . The arcs curve around respective nominal axes Azi, Azj that extend mutually parallel along the Z-direction and in a mid-sagittal plane Sm that intersects the longitudinal midline of each plate 230, 231 .

[0101] In this example, the medial plate region of the first plate 230 includes two distinct corrugated profiles 260a1 , 260a2, which are interconnected by a flat intermediate plate portion 278a. The medial plate region of the second plate 231 includes two distinct corrugated profiles 261 a1 , 261 a2, which are interconnected by another flat intermediate plate portion 279a. The semi-venturi units in the profiles 260, 261 have unit lengths Lu defined along the X-direction.

[0102] The nominal axes Azi, Azj associated with the curvatures of the crest and trough lines 276, 277 are located at respective associated radii of curvature Rvi, Rvj at distances in the X- direction away from the corresponding crest or trough line 276 or 277. The radii Rvi, Rvj are at least one order of magnitude larger than the unit lengths (i.e. Rvi, Rvj > 10 Lu). In this example, the radii Rv are essentially identical for all arcuate crest and trough lines of corresponding semi-venturi units 262. This implies that the axes Az of longitudinally adjacent semi-venturi units 262 also lie at regular spacings Lu in the X-direction away from each other.

[0103] Due to the additional curvature of the crest and trough lines 276, 277 towards the positive X-direction into arc shapes, the plate locally curves in concave upward direction in an XZ- plane as well as in a concave longitudinal direction in an XY-plane, resulting in a locally anticlastic curvature 280 (shown in the inset figure).

[0104] The first and second HE plates 230, 231 are spaced apart at a mean inter-plate distance Dp along the Z-direction. Each of the first and second flat plate portions 278, 279 has a length Lf defined along the X-direction and extending in-between the corresponding first or second successions of height variations 260a1 , 260z2; 261 a1 , 261 a2. This length Lf is smaller than twenty times the mean inter-plate distance (i.e. Lf < 20 Dp).

[0105] In this example, flat plate portions (e.g. medial portion 278) of the first HE plate 230 include embossments 282, and flat plate portions (e.g. medial portion 279) of the second HE plate 231 include similar embossments 283. Each respective embossment 282, 283 is formed as a local semi-capsule-shaped protuberance in the plate surface that keep the continuity of the plate intact and does not create an opening to a fluid channel above or below. Each respective embossment 282, 283 curves in positive or negative Z-direction away from the macroscopic plate surface, to form a spacer structure for locally holding the adjacent plate at a determined distance and thus keeping the mean inter-plate distance Dp as constant as possible under varying temperature and differential pressure conditions inside the channels. In this example, the long axes Ac of the semi-capsule-shapes of the first embossments 282 are rotated from the X- direction towards the negative Y-direction. By contrast, the long axes Ac of the semi-capsule- shapes of the second embossments 283 are rotated from the X-direction towards the positive Y- direction to relax transverse alignment tolerances between the abutting first and second embossments.

[0106] Figures 5a-5b illustrate another embodiment of a plate group 332, which is configured for cross-current operation, and which includes HE plates 330, 331 provided with folded edge flanges for improved mechanical connection and channel definition. Features in the plate groups that have already been described above with reference to the embodiments in figures 1a-4b may also be present in the plate group 332 shown in figures 5a-5b and will not all be discussed here again. For the discussion with reference to figures 5a-5b, like features are designated with similar reference numerals preceded by 300 to distinguish the embodiments.

[0107] Figure 5a shows four plates 330, 331 of the late group 332 in a partially exploded view. Each of the first and second plates 330, 331 is composed of a plurality of interconnected plate portions, each portion having a distinct orientation and location on the plate. Such plate geometries may for instance be formed by pressing or folding an initially flat and quadrilateral plate blank, or casting.

[0108] The first HE plate 330 (and similarly the second HE plate 331) includes a central region 354 (or 355 for the second plate 331), and a folded plate flange along each of its four plate edges342, 344, 346, 348 (or 343, 345, 347, 349). The periphery of the first plate 330 is formed by first transverse plate edges 342, 344 that extend along the Y-direction and are located on opposite sides of the central region 354 viewed along the X-direction, and by first longitudinal plate edges 346, 348 that extend along the X-direction and are located on opposite sides of the central region 354 viewed along the Y-direction. In a similar way, the periphery of the second plate 331 is formed by second transverse plate edges 343, 345 that extend along the Y-direction and are located on opposite sides of the central region 355 viewed along the X-direction, and by second longitudinal plate edges 347, 349 that extend along the X-direction and are located on opposite sides of the central region 355 viewed along the Y-direction.

[0109] The central region 354 (or 355) forms the main heat transfer area and defines a corrugated profile 360 (361) with a repeating sequence of venturi-shaped corrugations and linear crest and trough lines along the Y-direction similar to figures 1c-2b. Figure 5a shows sharply cornered transitions between the boundary of the corrugated profiles 360, 361 and the folded flanges along the longitudinal plate edges 346-349, which may for instance be forming when the plate made with casting techniques. It will be understood that the transitions may be made smoother in case the plates are formed by folding and pressing an initially flat plate blank.

[0110] Folded flanges are provided along the first transverse edges 342, 344 of the first plate 330. These flanges are each composed of an oblique flange portion that is folded towards the negative Z-direction at a non-zero slant angle from the central region 354, and a distal flange portion that is folded back towards the X-direction from the oblique flange portion to be essentially parallel to the nominal mean plane Sp of the central region 354. Further folded flanges are provided along first longitudinal edges 346, 348 of the first plate 330. These further flanges are each composed of a further oblique flange portion that is folded towards the positive Z-direction at a further non-zero slant angle from the central region 354, and a further distal flange portion that is folded back towards the Y-direction from the further oblique flange portion to be essentially parallel to the mean plane Sp of the central region 354. In the example of figure 5a, the flanges along the transverse edges 342, 344 are folded towards a negative Z-direction, whereas the the further flanges along the longitudinal edges 346, 348 are folded in an opposite manner towards the positive Z-direction.

[0111] The shape of each of the second plates 331 is substantially identical the shape of the first plates 330, but the second plates 331 are arranged in mirror-symmetric positions relative to the first plates 330. A respective first plate 330 is placed on top of a second plate 331 , with respective pairs of distal flange portions of their transverse edges 342-345 in abutting arrangement. The vertical space between the central plate regions 354 and 355 thereby forms a first fluid channel 338. By contrast, a respective second plate 331 is placed on top of a next first plate 330, with respective pairs of distal flange portions of their longitudinal edges 346-349 in abutting arrangement. The vertical space between the central plate regions 355 and 354 thereby forms a second fluid channels 339. The plates 330 and 331 may for instance be fixed to each other by welding abutting distal flange portions. Further details of the plate edge geometry andmethods of manufacturing are presented in patent document US10054374B2, which is hereby incorporated by reference in its entirety.[001 12] Figure 5b schematically presents a side view of the exemplary plate group 332, viewed in a cross-section along an XZ-plane through the medial plate regions 354, 355. The shapes of the corrugated profiles in the medial plate regions 354, 355 are substantially identical to figure 2a. The plate group 332 defines first fluid channels 338 for conveying the first fluid 340 generally along the Y-direction (indicated by the flow direction arrow 341 a), and second fluid channels 339 for conveying the second fluid 341 generally along the X-direction (indicated by the (^-symbols representing the first flow direction 340).[001 13] Figures 6a-6b schematically illustrate an exemplary plate group 432 that is composed of multiple heat exchanger plates 430, 431 (only three are shown), and which includes plate spacers 482 for holding the plates 430, 431 at a determined mean inter-plate distance Dp in the Z- direction. Features in the plate groups that have already been described above with reference to figures 1 a-5b may also be present in the plate group 432 in figures 6a-6b. Like features are designated with similar reference numerals preceded by 400 to distinguish the embodiments. [001 14] Each respective plate spacer 482 is composed of a strip of rigid and self-supporting material, which is formed as a helically twisted surface with a nominal centreline As extending through a midline along the longest dimension of the spacer. At each distinct axial position along the nominal centreline As, which in this case is parallel to the X-direction, a transverse cross- sectional shape of the spacer 482 in a local YZ-plane may resemble a thin rectangle that is centred on the centreline As and is rotated over a local angle 0 about this centreline As relative to an orientation 0O= 0° of the strip at a reference axial position, for instance relative to a vertical orientation of a leading edge of the spacer. The cross-sectional shapes of the spacer at distinct axial positions along the centreline As may be mutually congruent, but may have different orientations i.e. different values for the local angle 0(x). In particular, the local angle 0(x) may continuously and monotonically increase or decrease as function of increasing axial position along the centreline As. Due to the resulting helical shape, the strip spacer 482 is referred to as a “twisted tape spacer”.[001 15] Figure 6a shows a first HE plate 430 with a corrugated profile that resembles the plate shape from figure 1 c. The profile includes multiple unit cells, each unit composed of a converging plate portion 468, a diverging plate portion 472, and transition portions 470, 474 interconnecting the converging and diverging portions 468, 472. The upper plate surface 434 supports two plate spacers 482a, 482b, which are placed next to each other in the Y-direction, and which have respective centrelines As oriented mutually parallel and along the X-direction. The first spacer 482a is twisted five times over 180° about its centreline Asa and extends over five consecutive unit lengths Lu of the plate 430. The second spacer 482b is twisted one time over 180° about its longitudinal centreline Asb and extends over one unit length Lu of the plate 430.[001 16] Figure 6b illustrates a cross-sectional side view of the exemplary plate group 432, showing the first twisted tape spacer 482a located within the second fluid channel 439. Thenominal centreline As extends substantially along the X-direction, and each full (i.e. 360°) helical twist of the spacer 482a covers a unit spacer length Ls that is substantially identical to two times the length Lu of a Venturi unit cell 463 defined by the corrugated profiles of the second and first plates 431a, 430b. Alternatively or in addition, similar twisted tape spacers 482 with a twist profile that is reversed along the X-direction may be provided within the first fluid channels 438.

[0117] The twisting speed of the spacer 482 may be described by a twist rate function d0 / dx defined as a local infinitesimal change d0 of the twist angle 0 resulting from an infinitesimal change of axial position dx along the centreline As. In general, the local twist rate function d0 / dx may also change as function of position along the centreline As. The inset graph in figure 6b illustrates that the function d0 / dx varies periodically in this example, with a spatial period that may be substantially identical to a length Lu of a single Venturi unit cell 463. In this example, the twist angle 0 of the spacer 482 sweeps through 180° i.e. half a twist while covering the length Lu of a venturi unit 463 (this implies j(d0 / dx)dx = 180° integrated across a unit length Lu). In other embodiments, the twist angle 0 may sweep through an positive integer multiple N of 180° across the length Lu of one venturi unit 463 (i.e. j(d0 / dx)dx = N 180° across Lu, with N = 2, 3, 4, ...).

[0118] Across one spacer unit length Ls, the spacer 482 defines, in sequence, a first fast twisting portion 484 that aligns with a converging channel section 464i, a first slow twisting portion 485 that aligns with a diverging channel section 466i, a second fast twisting portion 486 that aligns with a next converging channel section 464j, and a second slow twisting portion 487 that aligns with a next diverging channel section 466j. At the throat sections where a height of the second channel 439 becomes minimal, a respective fast twisting portion 484, 486 continues into its corresponding slow twisting portion 485, 487. The YZ-cross-sectional shapes of the spacer 482 at the throat sections 465 may be oriented predominantly transverse towards the Y- directions, corresponding with 0 = ±90°. The inset graph further illustrates that the values for d0 / dx are relatively high throughout each of the fast twisting portions 484, 486, but comparatively lower throughout each of the slow twisting portions 485, 487.

[0119] The exemplary Venturi-units shown in figures 2a-b includes throat sections 65 and widest sections 67 with almost vanishing lengths (L2 and L4 almost 0). In alternative embodiments, either the throat section 65 or the widest section 67, or both, may extend with flat plate surface portions generally in the X-direction (i.e. with corresponding constant channel widths D2 and D1 , respectively) over a finite length (i.e. L2, L4 > 0). For instance, the length L2 may be in a range 0 < L2 < 100 millimetres and the length L4 may be in a range 0 < L2 < 100 millimetres.

[0120] The present invention may be embodied in other specific forms. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to the person skilled in the art that alternative embodiments of the invention can be conceived and reduced to practice. All changes which comewithin the meaning and range of equivalency of the claims are to be embraced within their scope, to the extent permitted by applicable national laws and / or intergovernmental agreements.

[0121] In the examples shown in the figures, the HE plates were formed with generally quadrilateral peripheral shapes, which are relatively easy to produce. In alternative embodiments, the HE plates may be formed with different polygonal peripheral shapes, such as hexagonal peripheral shapes, to facilitate optimizing the positioning and construction of fluid supply and discharge headers and conduits. Alternative embodiments composed of HE plates with curved or partly polygonal partly curved peripheral shapes may also be conceived.

[0122] In the described embodiments, the first and second HE plates enclose a group of first fluid channels and a group of second fluid channels. Various channel and fluid flow configurations are contemplated and fall within the present scope, such as one or both of the first and second channel groups in a Z-flow arrangement or in a C-flow arrangement or in a direct linear arrangement between respective channel inlets and outlets. In addition, the group of first fluid channels may be interleaved in a counterflow or a crossflow arrangement relative to the group of second fluid channels in a central plate region.

[0123] In examples shown in figures 1c, 3a, and 4a, the HE plates included predominantly flat proximal and distal plate regions (figures 1c, 3a 4a), and possibly also intermediate flat plate portions (figures 3a, 4a), In alternative embodiments, any or all of such flat plate parts may be absent. For instance, HE plates and plate groups are conceivable that include a corrugated multiventuri profile which extends uninterruptedly along the entire length(s) of the HE plate(s) i.e. from the leading transverse plate edge(s) to the trailing transverse plate edge(s).

[0124] Channel spacer structures may be provided in-between the HE plates in any of the described plate geometries, which serve as structural supports that keep the HE plates at substantially constant distances when subjected to differential pressures and temperatures arising between and across the fluid channels during operation. Such spacer structures may be formed either as local embossments in the plates (e.g. semi-circular, -ellipsoid, -spindle, -capsule, or polyhedral local dimples and / or protrusions of the plate surface), or as local spacer structures (e.g. poles, pins, or pillar-like structures with round or elliptical or lenticular or stadium or teardrop or other horizontal cross-sectional shapes) or elongated spacer structures (e.g. bars, strips, or beam structures with a polygonal or I- or H- or T-shaped vertical cross-section) that are placed on or fixed to the plate surface (e.g. by brazing, welding, or gluing) and extend with a predominant component in a normal direction from the plate surface. Any combinations and distributions of channel spacer structures are contemplated.

[0125] The present disclosure further relates to the embodiments reflected in the following clauses. c1 . A plate group (32) for a plate-type heat exchanger, HE, device (10), the plate group comprising a first HE plate (30a) and a second HE plate (31a) extending in first and second directions (X, Y) and placed at a distance from each other in a third direction (Z) to enclose a first fluid channel (38a) for a first flow (40a) of first HE fluid (28) along the first direction (X);wherein the first and second HE plates are provided with respective first and second corrugated profiles (60a, 61a), the first corrugated profile (60a) defining a first succession of height variations in the third direction (Z), the second corrugated profile (61a) defining a second succession of height variations in the third direction, the second succession being essentially congruent but mirror-symmetric to the first succession such that the first and second corrugated profiles bound a first sequence of asymmetric venturi-shaped units (62i, 62j) inside the first fluid channel (38a). c2. The plate group (32) according to clause c1 , comprising a third HE plate (30b) extending predominantly along the first and second directions (X, Y) and comprising a third corrugated profile (60b), wherein the third HE plate is located at a side of the second HE plate (61a) opposite to the first HE plate (30a) to enclose a second fluid channel (39a) for a second flow (41a) of second HE fluid (29); wherein the third corrugated profile (60b) defines a third succession of height variations in the third direction (Z), the third succession being essentially congruent to the first succession and arranged mirror-symmetric relative to the second succession such that the second and third corrugated profiles jointly bound a second sequence of asymmetric venturi-shaped units (63i, 63j) inside the second fluid channel (39a). c3. The plate group (32) according to clause c1 or c2, wherein a respective unit (62i) in the first sequence of asymmetric venturi-shaped units (62) comprises: a converging channel portion (64), wherein a height of the first fluid channel (38a) reduces monotonically from a maximum height value (D1) to a minimum height value (D2), and a diverging channel portion (66), wherein the height of the first fluid channel increases monotonically from the minimum height value back towards the maximum height value; and wherein a length (L1) of the converging channel portion (64) along the first direction (X) is smaller than a further length (L3) of the diverging channel portion (66). c4. The plate group (132; 232) according to any one of clauses c1-c3, wherein the first corrugated profile (160; 260) and second corrugated profile (161 ; 261) form series of crest lines (176; 276) and trough lines (177; 277), the crest and trough lines being curved to form arcs about nominal axes (Ax; Azi, Azj), wherein the axes extend substantially perpendicular to the second direction (Y), for instance parallel with the first direction (X) or parallel with the third direction (Z), and result in locally anticlastic curvature (180; 280) of the respective first or second HE plate (130, 131 ; 230, 231). c5. The plate group (132) according to clause c4, wherein each of the first and second HE plates (130, 131) is predominantly monoclastically curved about a respective nominal axis (Ax) that extends parallel with the first direction (X), and wherein the nominal axes of distinct HE plates are arranged mutually parallel in a mid-sagittal plane (Sm) of the plate group. c6. The plate group (132) according to clause c5, wherein the venturi-shaped units (162) have unit lengths (Lu) along the first direction (X), wherein monoclastic curvatures of the first and second HE plates (130, 131) are substantially cylindrical curvatures that are associated withnominal axes (Ax) located at respective radii of curvature (Rp) away from the corresponding HE plate and towards the positive or negative third direction (±Z), and wherein the radii of curvature are at least one order of magnitude larger than the unit lengths (i.e. Rp > 10 Lu). c7. The plate group (232) according to clause c4, wherein the first and second HE plates (230, 231) are predominantly flat, and wherein the crest lines (276) and trough lines (277) of the first and second corrugated profiles (260, 261) are curved to form arcs along respective nominal mean planes (Spa, Spb) of corresponding HE plates, the arcs being curved about respective nominal axes (Azi, Azj) that extend parallel with the third direction (Z) and are arranged mutually parallel in a mid-sagittal plane (Sm) of the plate group. c8. The plate group (232) according to clause c7, wherein the venturi-shaped units (262) have unit lengths (Lu) along the first direction (X), wherein the nominal axes (Azi, Azj) associated with the curvatures of the crest lines (276) and trough lines (277) are located at respective radii of curvature (Rvi, Rvj) away from the corresponding crest line (276) or trough line (277) and towards the positive of negative first direction (±X), and wherein the radii of curvature are at least one order of magnitude larger than the unit lengths (i.e. Rvi, Rvj > 10 Lu). c9. The plate group (132; 232) according to any one of clauses c1-c8, wherein the first HE plate (130) includes two first corrugated profile portions (160a1 , 160a2) and a first flat plate portion (178a), the first flat plate portion extending in the first direction (X) and interconnecting the first corrugated profile portions; wherein the second HE plate (131) includes two second corrugated profile portions (161 a1 , 161 a2) and a second flat plate portion (179a), the second flat plate portion extending in the first direction (X) and interconnecting the second corrugated profile portions; and wherein the second corrugated profile portions and second flat plate portion are essentially congruent but mirror-symmetric to the first corrugated profile portions and the first flat plate portion, and the first and second flat plate portions jointly bound a straight channel section inside the first fluid channel (138) with a first channel height (Dp) that is essentially constant. c10. The plate group (232) according to clause c9, wherein the first and second HE plates (230, 231) are spaced apart at a mean inter-plate distance (Dp) along the third direction (Z), wherein each of the first and second flat plate portions (278, 279) has a length (Lf) defined along the first direction (X) and extending in-between the corresponding first or second successions of height variations (260a1 , 260z2; 261 a1 , 261 a2), and wherein the length (Lf) is smaller than twenty times the mean inter-plate distance (0 < Lf < 20 Dp). c11 . The plate group (232) according to any one of clauses c1-c10, wherein both the first and second plates (230; 231) are provided with embossments (282; 283) that are formed as local depressions and / or protrusions relative to the surrounding plate surface, wherein the embossments have an elongated shape, for instance a semi-ellipsoid, semispindle, or semi-capsule shape, associated with an elongation axis (Ae) that extends substantially parallel with a nominal mean plane (Sp) of the respective plate (230; 231);and wherein the embossments are arranged in pairs that are mutually abutting in the third direction (Z), with their elongation axes (Ae) rotated over different angles about local axes (Ar) along the third direction (Z). c12. The plate group (432) according to any one of clauses c1-c11 , further comprising one or more plate spacers (482) inside the first fluid channel (438a) and / or the second fluid channel (439a), wherein a respective plate spacer (482) is formed by a strip of material that is helically twisted over at least 180° about its longitudinal centreline (As) subject to a periodically varying twist rate (d0 / dx) with a spatial period that is substantially identical to a length (Lu) of a venturi-shaped unit (463). c13. The plate group according to any one of clauses c1-c12, further comprising one or more local plate spacers arranged inside the first fluid channel and / or the second fluid channel, wherein the local plate spacers are formed as pillar structures having round or elliptical or lenticular- or stadium- or aerofoil- or teardrop-shaped cross-sections in the first and second directions (X, Y), and wherein the local plate spacers are mechanically fixed to a surface of the first or second HE plate and extend predominantly in the third direction (Z) up to an opposite surface of the second or first HE plate. c14. The plate group according to any one of clauses c1-c13, wherein each of the first and second plates (330; 331) defines: a central plate region (354; 355) provided with the corrugated profile (360; 361) associated with the asymmetric venturi-shaped units; plate flanges at respective transverse plate edges (342; 343) on opposite sides of the central plate region, and comprising distal flange portions that are jointly displaced towards a positive or negative third direction (±Z) away from the central plate region, and further plate flanges at respective longitudinal plate edges (346; 347) on further opposite sides of the central plate regions, and comprising further distal flange portions that are jointly displaced towards the negative or positive third direction (+Z) away from the central plate region in opposite direction relative to the plate flanges. c15. A plate-type heat exchanger, HE, device (10), comprising a plurality of plate groups (32) composed of first and second HE plates (30, 31) according to any one of clauses c1-c14, wherein: wherein the first and second HE plates (30, 31) enclose a group of first fluid channels (38) and a group of second fluid channels (39); wherein the group of first fluid channels and / or the group of second fluid channels extends in a Z-flow or C-flow arrangement (57, 55, 53) or in a direct linear arrangement (52, 54, 56) between the respective channel inlets and outlets (24, 25, 26. 27); and wherein the group of first fluid channels (38) is interleaved in a counterflow arrangement relative to the group of second fluid channels (39) in a central plate region (54, 55), or wherein the group of first fluid channels (338) is interleaved in a crossflow arrangement relative to the group of second fluid channels (339) in the central plate region (354, 355).c16. A heat exchanger, HE, plate (30) for a plate-type HE device (10), for instance a HE device according to clause c15, wherein the HE plate extends in the first and second directions (X, Y) and is provided with a corrugated profile (60); wherein the corrugated profile is composed of a plurality of half-venturi-shaped units (62) defining a succession of height variations in a third direction (Z), each respective half-venturi- shaped unit (62) comprising a converging plate portion (68) wherein a channel-side surface (36) of the HE plate (30) decreases monotonically over an amplitude (AD) towards the negative third direction (-Z), and a diverging plate portion (72) wherein the channel-side surface (36) of the HE plate increases monotonically over the amplitude (AD) back towards the positive third direction (+Z); wherein a length (L1) of the converging plate portion (68; 69) along the first direction (X) is at least three times smaller than a further length (L3) of the diverging plate portion (72; 73) along the first direction (X); and wherein a sum (L1+L3) of the length (L1) and the further length (L3) is at least four times larger than the amplitude (AD).List of Reference SymbolsSimilar reference numbers used in the description to indicate similar elements but differing only in the hundreds have been omitted but are deemed implicitly included.10 HE device12 frame14 1stend panel15 2ndend panel16 connection member (e.g. corner beam)20 flanking plate22 HE plate core24 1stinlet aperture25 2ndinlet aperture26 1stoutlet aperture27 2ndoutlet aperture28 1stfluid29 2ndfluid30 1stHE plate31 2ndHE plate32 HE plate group34 1stupper plate surface35 2ndupper plate surface36 1stlower plate surface37 2ndlower plate surface38 1stfluid channel39 2ndfluid channel40 1stfluid flow41 2ndfluid flow42 1sttransverse edge43 2ndtransverse edge44 1stopposite transverse edge45 2ndopposite transverse edge46 1stlongitudinal edge47 2ndlongitudinal edge48 1stopposite longitudinal edge49 2ndopposite longitudinal edge50 1stspacer member51 2ndspacer member52 1stproximal plate region53 2ndproximal plate region54 1stmedial plate region55 2ndmedial plate region56 1stdistal plate region57 2nddistal plate region58 guiding member60 1stcorrugated profile61 2ndcorrugated profile62 1stventuri unit cell63 2ndventuri unit cell64 converging channel section65 throat section66 diverging channel section67 widest section68 1stconverging plate portion69 2ndconverging plate portion70 1std-i transition portion71 2ndd-i transition portion72 1stdiverging plate portion73 2nddiverging plate portion74 1sti-d transition portion75 2ndi-d transition portion76 crest line77 trough line160 1stcurved corrugations161 2ndcurved corrugations178 1stflat plate portion179 2ndflat plate portion180 anticlastic curvature182 diagonal elongated dimple / protrusion spacer260 1stin-plane curved corrugations261 2ndin-plane curved corrugations280 anticlastic curvature282 1stspacer283 2ndspacer484 1stfast twist portion485 1stslow twist portion486 2ndfast twist portion487 2ndslow twist portionX 1stdirection (along flow)Y 2nddirection (transverse to flow)Z 3rddirection (vertical)Dp mean inter-plate distanceD1 maximum channel gapD2 minimum channel gapAD deflection amplitude d plate thicknessLu unit lengthL1 converging section lengthL2 throat section lengthL3 diverging section lengthL4 widest section lengthLf flat portion length a convergence angle (approach angle) p divergence angle (diffusion angle; p < a)0 twist angle d0 / dx twist rate r1 1stradius of curvature (d-i transition) r2 2ndradius of curvature (i-d transition)Rv crest / trough us of curvatureRp plate radius of curvatureAe embossment elongation axisAr embossment pan axisAs twisted tape axisAv axis of profile curvatureAx axis of plate curvatureCv centre of curvatureSm mid-sagittal planeSp (nominal) mean plane

Claims

Claims1 . A plate group (32) for a plate-type heat exchanger device (10), the plate group comprising a first HE plate (30a) and a second HE plate (31a) extending in first and second directions (X, Y) and placed at a distance from each other in a third direction (Z) to enclose a first fluid channel (38a) for a first flow (40a) of first HE fluid (28) along the first direction (X); wherein the first and second HE plates are provided with respective first and second corrugated profiles (60a, 61a), the first corrugated profile (60a) defining a first succession of height variations in the third direction (Z), the second corrugated profile (61a) defining a second succession of height variations in the third direction, such that the first and second corrugated profiles bound a first sequence of asymmetric venturi-shaped units (62i, 62j) inside the first fluid channel (38a).

2. The plate group (32) according to claim 1 , wherein a respective unit (62i) in the first sequence of asymmetric venturi-shaped units (62) comprises a converging channel portion (64) and a diverging channel portion (66), wherein a length (L1) of the converging channel portion (64) is smaller than a further length (L3) of the diverging channel portion (66) along the first direction (X).

3. The plate group (32) according to claim 1 or 2, wherein a height of the first fluid channel (38a) reduces monotonically from a maximum height value (D1) to a minimum height value (D2) in the converging channel portion (64), and wherein the height of the first fluid channel increases monotonically from the minimum height value back towards the maximum height value in the diverging channel portion (66).

4. The plate group (132; 232) according to any one of claims 1-3, wherein the first HE plate (130) includes two first corrugated profile portions (160a1 , 160a2) and a first flat plate portion (178a), the first flat plate portion extending in the first direction (X) and interconnecting the first corrugated profile portions; wherein the second HE plate (131) includes two second corrugated profile portions (161 a1 , 161a2) and a second flat plate portion (179a), the second flat plate portion extending in the first direction (X) and interconnecting the second corrugated profile portions; and wherein the first and second flat plate portions jointly bound a straight channel section inside the first fluid channel (138) with a first channel height (Dp) that is essentially constant.

5. The plate group (132; 232) according to claim 4, wherein the second corrugated profile portions and the second flat plate portion are essentially congruent but mirror-symmetric to the first corrugated profile portions and the first flat plate portion.

6. The plate group (232) according to claim 4 or 5, wherein the first and second HE plates (230, 231) are spaced apart at a mean inter-plate distance (Dp) along the third direction (Z), wherein each of the first and second flat plate portions (278, 279) has a length (Lf) defined along the first direction (X) and extending in-between the corresponding first or second successions of height variations (260a1 , 260z2; 261 a1 , 261 a2), and wherein the length (Lf) is smaller than twenty times the mean inter-plate distance (0 < Lf < 20- Dp).

7. The plate group (32) according to any one of claims 1-6, comprising a third HE plate (30b) extending predominantly along the first and second directions (X, Y) and comprising a third corrugated profile (60b), wherein the third HE plate is located at a side of the second HE plate (61a) opposite to the first HE plate (30a) to enclose a second fluid channel (39a) for a second flow (41a) of second HE fluid (29); wherein the third corrugated profile (60b) defines a third succession of height variations in the third direction (Z), such that the second and third corrugated profiles jointly bound a second sequence of asymmetric venturi-shaped units (63i, 63j) inside the second fluid channel (39a).

8. The plate group (132; 232) according to any one of claims 1-7, wherein the first corrugated profile (160; 260) and second corrugated profile (161 ; 261) form series of crest lines (176; 276) and trough lines (177; 277), the crest and trough lines being curved to form arcs about nominal axes (Ax; Azi, Azj), wherein the axes extend substantially perpendicular to the second direction (Y), for instance parallel with the first direction (X) or parallel with the third direction (Z), and result in locally anticlastic curvature (180; 280) of the respective first or second HE plate (130, 131 ; 230, 231).

9. The plate group (132) according to claim 8, wherein each of the first and second HE plates (130, 131) is predominantly monoclastically curved about a respective nominal axis (Ax) that extends parallel with the first direction (X), and wherein the nominal axes of distinct HE plates are arranged mutually parallel in a mid-sagittal plane (Sm) of the plate group.

10. The plate group (132) according to claim 9, wherein the venturi-shaped units (162) have unit lengths (Lu) along the first direction (X), wherein monoclastic curvatures of the first and second HE plates (130, 131) are substantially cylindrical curvatures that are associated with nominal axes (Ax) located at respective radii of curvature (Rp) away from the corresponding HE plate and towards the positive or negative third direction (±Z), and wherein the radii of curvature are at least one order of magnitude larger than the unit lengths (i.e. Rp > 10 Lu).11 . The plate group (232) according to claim 8, wherein the first and second HE plates (230, 231) are predominantly flat, and wherein the crest lines (276) and trough lines (277) of the firstand second corrugated profiles (260, 261) are curved to form arcs along respective nominal mean planes (Spa, Spb) of corresponding HE plates, the arcs being curved about respective nominal axes (Azi, Azj) that extend parallel with the third direction (Z) and are arranged mutually parallel in a mid-sagittal plane (Sm) of the plate group.

12. The plate group (232) according to claim 11 , wherein the venturi-shaped units (262) have unit lengths (Lu) along the first direction (X), wherein the nominal axes (Azi, Azj) associated with the curvatures of the crest lines (276) and trough lines (277) are located at respective radii of curvature (Rvi, Rvj) away from the corresponding crest line (276) or trough line (277) and towards the positive of negative first direction (±X), and wherein the radii of curvature are at least one order of magnitude larger than the unit lengths (i.e. Rvi, Rvj > 10 Lu).

13. The plate group (232) according to any one of claims 1-12, wherein both the first and second plates (230; 231) are provided with embossments (282; 283) that are formed as local depressions and / or protrusions relative to the surrounding plate surface, wherein the embossments have an elongated shape, for instance a semi-ellipsoid, semispindle, or semi-capsule shape, associated with an elongation axis (Ae) that extends substantially parallel with a nominal mean plane (Sp) of the respective plate (230; 231); and wherein the embossments are arranged in pairs that are mutually abutting in the third direction (Z), with their elongation axes (Ae) rotated over different angles about local axes (Ar) along the third direction (Z).

14. The plate group (432) according to any one of claims 1-13, further comprising one or more plate spacers (482) inside the first fluid channel (438a) and / or the second fluid channel (439a), wherein a respective plate spacer (482) is formed by a strip of material that is helically twisted over at least 180° about its longitudinal centreline (As) subject to a periodically varying twist rate (d0 / dx) with a spatial period that is substantially identical to a length (Lu) of a venturishaped unit (463).

15. The plate group according to any one of claims 1-14, further comprising one or more local plate spacers arranged inside the first fluid channel and / or the second fluid channel, wherein the local plate spacers are formed as pillar structures having round or elliptical or lenticular- or stadium- or aerofoil- or teardrop-shaped cross-sections in the first and second directions (X, Y), and wherein the local plate spacers are mechanically fixed to a surface of the first or second HE plate and extend predominantly in the third direction (Z) up to an opposite surface of the second or first HE plate.

16. The plate group according to any one of claims 1-15, wherein each of the first and second plates (330; 331) defines:a central plate region (354; 355) provided with the corrugated profile (360; 361) associated with the asymmetric venturi-shaped units; plate flanges at respective transverse plate edges (342; 343) on opposite sides of the central plate region, and comprising distal flange portions that are jointly displaced towards a positive or negative third direction (±Z) away from the central plate region, and further plate flanges at respective longitudinal plate edges (346; 347) on further opposite sides of the central plate regions, and comprising further distal flange portions that are jointly displaced towards the negative or positive third direction (+Z) away from the central plate region in opposite direction relative to the plate flanges.

17. A plate-type heat exchanger device (10), comprising a plurality of plate groups (32) composed of first and second HE plates (30, 31) according to any one of claims 1-16; wherein the first and second HE plates (30, 31) enclose a group of first fluid channels (38) and a group of second fluid channels (39); wherein the group of first fluid channels and / or the group of second fluid channels extends in a Z-flow or C-flow arrangement (57, 55, 53) or in a direct linear arrangement (52, 54, 56) between the respective channel inlets and outlets (24, 25, 26. 27).

18. The plate-type heat exchanger device (10) according to claim 17, wherein the group of first fluid channels (38) is interleaved in a counterflow arrangement relative to the group of second fluid channels (39) in a central plate region (54, 55), or wherein the group of first fluid channels(338) is interleaved in a crossflow arrangement relative to the group of second fluid channels(339) in the central plate region (354, 355).

19. A heat exchanger plate (30) for a plate group (32) according to any one of claims 1-16, wherein the HE plate extends in the first and second directions (X, Y) and is provided with a corrugated profile (60); wherein the corrugated profile is composed of a plurality of half-venturi-shaped units (62) defining a succession of height variations in a third direction (Z), each respective half-venturi- shaped unit (62) comprising a converging plate portion (68) wherein a channel-side surface (36) of the HE plate (30) decreases monotonically over an amplitude (AD) towards the negative third direction (-Z), and a diverging plate portion (72) wherein the channel-side surface (36) of the HE plate increases monotonically over the amplitude (AD) back towards the positive third direction (+Z).

20. The heat exchanger plate (30) according to claim 19, wherein a length (L1) of the converging plate portion (68; 69) along the first direction (X) is at least three times smaller than a further length (L3) of the diverging plate portion (72; 73) along the first direction (X);and wherein a sum (L1 +L3) of the length (L1) and the further length (L3) is at least four times larger than the amplitude (AD).

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