DESCRIPTION

TECHNICAL FIELD

[0001] The present disclosure concerns heat exchangers. Specifically, the present disclosure relates to two-phase heat exchangers, wherein at least a first two-phase fluid stream containing a liquid phase and a vapor phase flows in heat exchange with a second stream.

BACKGROUND ART

[0002] Two-phase heat exchangers are commonly used in several industrial sectors. For instance, two-phase heat exchangers are used in refrigerant circuits to evaporate and/or to condense fluid streams.

[0003] Refrigeration circuits are used for example in the oil and gas industry for the liquefaction of natural gas. A stream of compressed refrigerant is chilled and condensed in heat exchange with a stream of expanded, partly liquefied and evaporating two-phase refrigerant in a heat exchanger.

[0004] High performances are achieved with wound coil heat exchangers. However, this kind of heat exchangers is not free of drawbacks. In particular, they are very complex and expensive. The number of suppliers is small, due to the complexity of the underlying manufacturing technology.

[0005] As an alternative to wound coil heat exchangers, plate fin heat exchangers have been developed, which have a simpler and less expensive structure. However, this kind of heat exchangers do not allow downward evaporation flow, i.e. they do not allow a two-phase evaporating fluid stream to flow in a top-to-bottom direction across the heat exchanger. The reason for such limitation is a maldistribution of liquid and vapor, which would result in uneven distribution of vapor and liquid flow in the various sections of the heat exchanger and therefore lead to inefficient heat exchange.

[0006] On the other hand, downward evaporation would be beneficial in terms of overall efficiency of the compression, condensation, evaporation cycle of a refrigeration circuit, for instance, since a reduced pressure drop would occur in the evaporation stream, in that gravity would facilitate the downwards flow.

[0007] Measures aimed at solving the above problems and allowing a top-to-bottom stream of the evaporating fluid though a fin plate heat exchanger would therefore be welcomed in the art.

SUMMARY

[0008] According to one aspect, a plate fin heat exchanger is disclosed herein, which comprises a core having a top and a bottom. The core comprises corrugated heat transfer fins and parting sheets arranged according to an alternate layout, with a parting sheet separating adjacent corrugated heat transfer fins. The corrugated heat transfer fins and parting sheets form heat-releasing fluid ducts fluidly connecting a heat-releasing fluid inlet header at the bottom of the core and a heat-releasing fluid outlet header at the top of the core. The heat-releasing fluid can be a condensing fluid, i.e. a two- phase fluid, the vapor phase whereof condenses while flowing through the heat exchanger. The corrugated heat transfer fins and parting sheets further form evaporating fluid ducts fluidly connecting an evaporating fluid inlet header at the top of the core and an evaporating fluid outlet header at the bottom of the core.;

[0009] A vapor-liquid distributor between the evaporating fluid inlet header and the core ensures uniform distribution of the liquid and vapor phases through the evaporating fluid ducts, facilitating a uniform flow in the downward direction and efficient heat exchange between the evaporating downwardly flowing fluid and the heat-releasing upwardly flowing fluid.

[0010] The vapor-liquid distributor comprises an inlet plenum and a plurality of evaporating fluid receiving chambers. The evaporating fluid receiving chambers can be horizontally arranged side-by-side in a direction orthogonal to the corrugated heat transfer fins and parting sheets of the core. Each evaporating fluid receiving chamber can be fluidly coupled to the inlet plenum through a nozzle arrangement. Each nozzle arrangement comprises a first nozzle and a second nozzle; wherein the first nozzle and the second nozzle are distanced from one another in a vertical direction. A fin plate can be positioned in each evaporating fluid receiving chamber, between the first nozzle and the second nozzle, the fin plate forming vertically extending flow channels. [0011] In some embodiments, each evaporating fluid receiving chamber is fluidly coupled to a respective non-pass layer. Each non-pass layer can include: a first parting sheet; a second parting sheet; an inflow distribution fin arrangement between the first parting sheet and the second parting sheet, forming fluid ducts which extend opposite the nozzle arrangement and adapted to receive the evaporating fluid from the nozzle arrangement and distribute the evaporating fluid towards apertures in the first parting sheet and second parting sheet. Moreover, each non-pass layer is fluidly coupled through said apertures in the parting sheets with at least one pass layer adapted to receive evaporating fluid flowing through the apertures of at least one parting sheet of the adjacent non-pass layers. Each pass layer has a fluid connection towards a set of co-planar evaporating fluid ducts of the heat exchanger core.

[0012] In some embodiments, wherein the heat-releasing flid is a condensing fluid, which contains vapor and liquid and which condenses by heat release towards the evaporating fluid in the heat exchanger, each heat-releasing fluid duct can be divided into at least a lower section and an upper section. The lower section and the upper section of each heat-releasing fluid duct can be fluidly coupled to one another through a condensation redistributor arranged therebetween, to achieve a more uniform distribution of the two-phase condensing fluid throughout the heat exchanger, avoiding concentration of liquid phase in some ducts and concentration of vapor phase in other.

[0013] Further features and embodiments of the heat exchanger according to the present disclosure are set forth in the attached claims and will be described in greater detail below, reference being made to the enclosed drawings.

[0014] In the present disclosure “vertical” means a direction parallel to the direction of the force of gravity and “horizontal” means a direction orthogonal to the direction of the force of gravity. In the present description and attached claims definitions of orientations, positions and directions, such as “vertical”, “horizontal”, “top”, “bottom” and the like are referred to the heat exchanger in the operating position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Reference is now made briefly to the accompanying drawings, in which:

Fig. l is an axonometric view of a heat exchanger according to the present disclosure in one embodiment; Fig.2 is a sectional view according to a vertical plane passing through evaporating fluid ducts formed by one of the corrugated heat transfer fins of the core;

Fig.3 is a sectional view according to a vertical plane passing through the condensing fluid ducts formed by another of the corrugated heat transfer fins of the core;

Fig.4 is a sectional view according to line IV-IV of Fig.3;

Fig.5 is a sectional view according to a vertical plane of the non-pass layer of the evaporating fluid inlet header and vapor-liquid distributor associated therewith;

Fig.6 is a sectional view according to line VI- VI of Fig.5;

Fig.7 is a sectional view according to a vertical plane of the pass layer of the vapor-liquid distributor;

Figs. 8, 9, 10 and 11 are side views of components forming the vapor-liquid distributor;

Fig.12 is a sectional view of the condensation redistributor;

Fig.13 is an axonometric view of a portion of the condensation redistributor; and Figs. 14, 15 and 16 are side views of components of the condensation redistributor.

DETAILED DESCRIPTION

[0016] In the following description, reference will be made to a heat exchanger which is designed for exchanging heat between a flow of two-phase evaporating fluid and a flow of a two-phase condensing fluid, wherein the condensing fluid is a heatreleasing fluid, i.e., releases heat; the evaporating fluid absorbs heat released by the heat-releasing fluid. Both fluids undergo a phase change when flowing through the heat exchanger. Nevertheless, some features disclosed herein, specifically those regarding the evaporating fluid section of the heat exchanger, can be used also in a heat exchanger in which a two-phase evaporating fluid is in heat exchange with a heatreleasing fluid, which does not undergo a change of phase while flowing through the heat exchanger, for instance a liquid.

[0017] Turning now the exemplary embodiment shown in the drawings, a general overview of the structure of a plate fin heat exchanger 1 according to the present disclosure is shown in Figs. 1, 2, 3 and 4.

[0018] Fig. 1 illustrates an axonometric view of the plate fin heat exchanger 1. The plate fin heat exchanger 1 comprises a core 3 having a top 3 A and a bottom 3B. In the core, sequentially arranged corrugated heat transfer fins, distributor fins and parting sheets are arranged to provide:

- descending flow ducts or passages, for an evaporating fluid, also referred to as evaporating fluid ducts, and

- ascending flow ducts or passages for a heat-releasing fluid, in the particular embodiment disclosed herein a two-phase condensing fluid, also referred to as condensing fluid ducts.

[0019] The condensing fluid ducts and evaporating fluid ducts will be described in greater detail below.

[0020] The heat exchanger 1 further comprises an evaporating fluid inlet header 5 at the top 3 A of the core 3 and an evaporating fluid outlet header 7 at the bottom 3B of the core 3. An evaporating fluid enters the heat exchanger 1 at the top thereof through the evaporating fluid inlet header 5 and exits the heat exchanger 1 at the bottom thereof through the evaporating fluid outlet header 7. Therefore, the evaporating fluid flows in a downwards direction from the top 3 A to the bottom 3B of the core 3. Arrow Fef generally indicates the direction of flow of the evaporating fluid.

[0021] While flowing through the core 3 of the heat exchanger 1 from the top 3 A to the bottom 3B, the evaporating fluid receives heat from a condensing fluid, which streams in counterflow, from the bottom 3B towards the top 3 A of the core 3. The condensing fluid enters the heat exchanger 1 through a condensing fluid inlet header 9 at the bottom 3B of the core 3 and exits the heat exchanger 1 through a condensing fluid outlet header 11 at the top 3 A of the core 3. Therefore, the condensing fluid flows in an upwards direction broadly according to arrow Fcf.

[0022] With continuing reference to Fig. 1, Figs.2, 3 and 4 show some more details of the structure of the core 3 . Specifically, as shown in Fig. 4, the core 3 comprises a layered structure including parting sheets 15 and corrugated heat transfer fins 17, 19 arranged in an alternate manner. Specifically, each corrugated heat transfer fin 17 is sandwiched between two parting sheets 15, to form evaporating fluid ducts 21. Each corrugated heat transfer fin 17 forms a plurality of co-planar evaporation fluid ducts. Each corrugated heat transfer fin 19 is in turn sandwiched between two parting sheets plurality of co-planar condensing fluid ducts.

[0023] Side bars sealingly close the ducts formed by the corrugated plate fins and parting sheets.

[0024] Fig.2 illustrates a sectional view according to line II-II in Fig.4 of one layer featuring a set of co-planar evaporating fluid ducts 21 and relevant corrugated heat transfer fin 17. The evaporating fluid ducts 21 are fluidly coupled to the evaporating fluid inlet header 5 through a vapor-liquid distributor 27 and distribution fins 29. The evaporating fluid ducts 21 are further fluidly coupled to the evaporating fluid outlet header 7 through distribution fins 31. The distribution fins 29, 31 as well as the heat transfer fins 17, 19 can be formed by respective corrugated metal sheets.

[0025] In the exemplary embodiment shown in the attached drawings, the evaporating fluid inlet header 5 and the evaporating fluid outlet header 7 are arranged in a central position with respect to the core 3, but in other embodiments the evaporating fluid inlet and outlet headers 5, 7 can be arranged on a side of the core 3. The shape and orientation of the distribution fins 29, 31 will depend upon the position of the evaporating fluid inlet and outlet headers 5, 7.

[0026] Fig.3 illustrates a sectional view according to line III-III in Fig.4 of one layer featuring a set of co-planar condensing fluid ducts 23 and relevant corrugated heat transfer fin 19. The condensing fluid ducts 23 are fluidly coupled to the condensing fluid inlet header 9 through distribution fins 35 and are further fluidly coupled to the condensing fluid outlet header 11 through distribution fins 37.

[0027] In the embodiment of Fig.3, the condensing fluid ducts 23 are actually divided into a lower section and an upper section. More specifically, each condensing fluid duct 23 is divided into a lower section 23 A of the condensing fluid duct and an upper section 23B of the condensing fluid duct 23. The lower section 23 A of co-planar condensing fluid ducts 23 are formed by corrugated heat transfer fins 19 A, while the upper section 23B of co-planar condensing fluid ducts 23 are formed by corrugated heat transfer fins 19B. The lower sections 23 A of the condensing fluid ducts 23 are fluidly coupled to the condensing fluid inlet header 9 through distribution fins 39, while the upper sections 23B of the condensing fluid ducts are fluidly coupled to the condensing fluid outlet header 11 through distribution fins 41.

[0028] In some embodiments, the cross-sectional area of each condensing duct 23 can vary from the bottom towards the top of the heat exchanger, to balance the variation of volumetric flow through the core 3. As a matter of fact, if the heat-releasing fluid flowing through the fluid ducts 23 is a two-phase condensing fluid, the volumetric flowrate thereof reduces from bottom to top, due to the condensation of vapor phase into liquid phase. To balance the reduction of volumetric flow and prevent an excessive reduction of the flow speed, the cross-sectional area of each condensing duct 23 can reduce from bottom to top. Such reduction can be achieved, for instance, by using different metal sheets to form the corrugated heat transfer fins 19 A, 19B. For instance the thickness of the metal sheet can increase from bottom to top, such that the free cross-sectional area of the ducts 23 reduces stepwise when moving from a thinner to a thicker metal sheet.

[0029] The lower section 23 A and the upper section 23B of the condensing fluid ducts 23 are in fluid communication with one another through a condensation redistributor 45, which will be described in greater detail later on. The condensation redistributor 45 is fluidly coupled to the lower sections 23 A of the condensing fluid ducts 23 through distribution fins 47 and to the upper sections 23B of the condensing fluid ducts 23 through distribution fins 49.

[0030] With continuing reference to Figs 1, 2, 3 and 4, Figs. 5 to 7 illustrate the structure and operation of the vapor-liquid distributor 27 in greater detail.

[0031] The vapor-liquid distributor 27 comprises a sequence of parting sheets and side bars, defining alternately arranged layers, which will be referred to herein as “pass layers” and “non-pass layers”. The pass layers and the non-pass layers are fluidly coupled to the evaporating fluid inlet header 5, and to the evaporating fluid inlet header 5 such that the evaporating fluid inlet header 5 is fluidly coupled to the evaporating fluid ducts 21 of the core 3, as will be described in more detail below.

[0032] More specifically, the evaporating fluid inlet header 5 includes an inlet plenum 51, which in the embodiment shown has a semi-cylindrical shape and is fluidly coupled to an inlet duct 53 (Fig.5), wherethrough the evaporating two-phase fluid enters the plate fin heat exchanger 1. [0033] The semi-cylindrical inlet plenum 51 extends horizontally, parallel to the core 3 of the heat exchanger 1 in a direction orthogonal to the heat corrugated heat transfer fins 17, 19 and to the parting sheets 15. Pairs of nozzles 55, 57 of the vapor-liquid distributor 27 are arranged along the longitudinal extension of the semi-cylindrical inlet plenum 51.

[0034] More specifically, in the illustrated embodiment each pair of nozzles comprises an upper nozzle 55 and a lower nozzle 57. The nozzles 55, 57 of each pair of nozzles can be aligned vertically one above the other. In some embodiments, the two nozzles 55, 57 of each pair converge one towards the other, as shown by center lines 55A, 57A thereof. Each pair of nozzles 55, 57 opens in a respective evaporating fluid receiving chamber 59. Each evaporating fluid receiving chamber 59, except the first and the last ones at the two ends of the inlet plenum 51 (see Fig.6), are formed between a first parting sheet 61 and a second parting sheet 63. A parting sheet 61 is shown in Fig.9 and a parting sheet 63 is shown in 8.

[0035] Each parting sheet 61, 63 comprises a set of upper apertures 65 and a set of lower apertures 67. The upper apertures 65 of each parting sheet 61, 63 are aligned along aline LI, which can be inclined downwards with respect to a horizontal direction and moving away from the inlet plenum 51. The lower apertures 67 are aligned along a line L2, which can be horizontal, parallel to a bottom of the evaporating fluid receiving chambers 59.

[0036] Preferably, the upper and lower apertures 65, 67 are paired, in the sense that to each upper aperture 65 corresponds a lower aperture 67, which is vertically aligned with the upper aperture 65.

[0037] The first and last evaporating fluid receiving chambers 59 are formed between one parting sheet 61 or 63 and a cap sheet or external wall 71, as shown in Fig.6.

[0038] Fig.6 shows a small number of evaporating fluid receiving chambers 59. However, it shall be understood that the number of evaporating fluid receiving chamber can be much larger than the one shown, depending on the width of the heat exchanger. In some embodiments, more than one evaporating fluid inlet header 5 and more than one vapor-liquid distributor 27 can be provided for the same heat exchanger 1. [0039] Between sequentially arranged parting sheets 61, 63, pass layers 81 and nonpass layers 82 are alternatingly arranged, with one pass layer 81 sandwiched between two non-pass layers 82, and vice-versa. A pass layer 81 is a layer wherefrom the evaporating two-phase fluid injected by the nozzles 55, 57 can pass to the core 3 of the heat exchanger through distribution fins 29. A non-pass layer 82 is a layer wherefrom the two-phase evaporating fluid cannot flow directly into the core 3 of the heat exchanger 1. For that purpose, the non-pass layer 82 is closed at the bottom by a respective side bar 84, as shown in Figs 5 and 10. From each non-pass layer, the two-phase fluid is forced to flow through apertures 65 and 67 into the neighboring pass layers as described in more detail below.

[0040] More specifically, each pass layer 81 is coplanar to a corresponding set of mutually co-planar evaporating fluid ducts 21, formed by a respective corrugated heat transfer fin, and is fluidly coupled to said co-planar evaporating fluid ducts 21. Each non-pass layer 83 is coplanar to a corresponding set of mutually co-planar condensing fluid ducts, and more specifically to a set of co-planar condensing fluid ducts 23B of the upper section. However, no fluid connection is provided between the non-pass layers and the condensing fluid ducts 23 A, while the non-pass layers are fluidly coupled to adj cent pass layers as will be described in greater detail below.

[0041] In detail, each non-pass layer 82 is formed between a pair of adjacent parting sheets 61, 63 and a first frame made of side bars 75 arranged as shown in Fig.10, which surround a volume 76. The non-pass layer 82 is open towards the evaporating fluid receiving chamber 59, such that evaporating two-phase fluid can flow from the evaporating fluid receiving chamber into the non-pass layers.

[0042] Each pass layer 81 is formed between a pair of adjacent parting sheets 61, 63 and a second frame made of side bars 77 arranged as shown in Fig.11, which surrounds a volume 78. The volume 78 is open at the bottom and evaporating two-phase fluid entering the pass layer 81 is free to flow into the distribution fins 29 and therefrom into a corresponding set of coplanar evaporating fluid ducts 21 formed in the core 3.

[0043] Fig.5 illustrates a sectional view of a non-pass layer along a vertical plane parallel to the parting sheets 61, 73 and Fig.7 illustrates a sectional view of a pass layer 81 along a vertical plane parallel to the parting sheets 61, 63. [0044] To improve the fluid flow in each evaporating fluid receiving chamber 59, a respective plate fin 85 is located in the evaporating fluid receiving chamber 59, to form flow channels or ducts extending in a vertical direction. These ducts guide vapor generated by the expansion of fluid phase through the lower nozzle 57 towards the upper part of the fluid receiving chamber 59.

[0045] Moreover, in each non-pass layer 82, between the adjacent parting sheets 61, 63, an inflow distribution fin arrangement is placed, which facilitates the distribution of vapor and liquid towards the upper apertures 65 and towards the lower apertures 67, respectively.

[0046] In some embodiments, the inflow distribution fin arrangement includes a first inflow distribution fin 91 defining flow ducts extending horizontally from the respective evaporating fluid receiving chamber 59 towards the upper apertures 65 of the first parting sheet 61 and second parting sheet 63. The first inflow distribution fin 91 can be formed by a corrugated metal sheet. The inflow distribution fin arrangement can further include a second inflow distribution fin 93 forming flow ducts extending vertically from the first inflow distribution fin 91 towards the lower apertures 67 of the first parting sheet 61 and second parting sheet 63.

[0047] The inflow distribution fin arrangement of each non-pass layer directs the vapor phase of the evaporating fluid mainly towards the upper apertures 65 through the upper part of the first inflow distribution fin 91 and further directs the liquid phase of the evaporating fluid mainly towards the lower apertures 67 through the lower part of the first inflow distribution fin 91 and the second inflow distribution fin 93.

[0048] The liquid-vapor distributor 27 described so far operates as follows. A two- phase, i.e., liquid-vapor stream of evaporating fluid enters the inlet plenum 51. Vapor phase flows predominantly through each upper nozzle 55 and liquid phase flows predominantly through each lower nozzle 57 into each evaporating fluid receiving chamber 59. A concentrated pressure drop in the vapor and liquid phase occurs through the nozzles 55, 57. The concentrated pressure drop through the nozzles 55, 57 ensures that a substantially uniform flow of two-phase evaporating fluid enters in the vari ous fluid receiving chambers 59.

[0049] The vapor phase entering each evaporating fluid receiving chamber 59, or forming therein by expansion of the liquid phase through nozzles 57, is directed by the upper part of each first inflow distribution fin 91 of each non-pass layer 82 towards the upper apertures 65 provided in the parting sheets 61 and 63. Preferably, each first inflow distribution fin 91 forms one duct for each aperture 65.

[0050] The liquid phase is directed towards the lower apertures 65 by the horizontally oriented ducts formed in the lower part of each first inflow distribution fin 91 and by the vertically oriented ducts formed in the second inflow distribution fins 93.

[0051] Since the bottom of each non-pass layer is closed by the side bar 84, the two- phase stream is forced to flow through the upper and lower apertures 65, 67 into the two neighboring pass layers 81, between which each non-pass layer 82 is sandwiched.

[0052] In each pass layer 81, the liquid and vapor phase from each pair of vertically aligned upper and lower apertures 65, 67 flow in a respective duct formed by a vertical distribution fin 97, which defines vertically oriented downwardly extending ducts for the two-phase evaporating fluid flow. Each duct is fluidly coupled to one upper aperture 65 and one lower aperture 67, such that a balanced distribution of liquid phase and vapor phase is obtained in each pass layer and in each duct. The two-phase flow is then directed through the distribution fins 29 into the vertically and downwardly oriented ducts 21 of the core 3. Evaporated fluid is collected at the bottom of the heat exchanger 1 through the evaporating fluid outlet header 7.

[0053] The above-described vapor-liquid distributor 27 facilitates achieving a uniform distribution of liquid and vapor phase throughout the core 3 of the heat exchanger 1 in a downwardly oriented flow of evaporating fluid.

[0054] The condensing fluid moves from the condensing fluid inlet header 9 arranged at the bottom 3B of the core 3, to the condensing fluid outlet header 11 arranged at the top 3A of the core 3, in a bottom-to-top direction. In some embodiments, to achieve a more uniform distribution of the vapor and liquid phase of the condensing fluid throughout the core 3, a redistributor 45 can be provided between sequentially arranged lower section 23A and the upper section 23B of the condensing fluid ducts 23 as mentioned above.

[0055] The redistributor 45 redistributes the vapor and liquid phase of the condensing fluid flowing from the bottom to the top of the core 3, such that the liquid and vapor fl owrates in all ducts is substantially uniform, thus preventing concentrations of li quid in some ducts and vapor in others, which would negatively affect the effi ciency of the heat exchanger.

[0056] An embodiment of the redistributor 45 is disclosed hereafter, referring specifically to Figs. 12 to 16.

[0057] In some embodiments, the redistributor 45 comprises a redistribution chamber 101 which extends horizontally on a side of the core 3 and through which the lower section 23 A and the upper section 23B of the condensing fluid ducts 23 are put in fluid communication.

[0058] The redistribution chamber 101 receives the two-phase flow from the lower sections 23A of the condensing fluid ducts 23 and moves the two-phase flow further towards the upper sections 23B of the condensing fluid ducts 23 after redistributing the liquid and vapor phases, such that a substantially uniform two-phase flow is maintained in all the upper sections 23B of the vertically oriented condensing fluid ducts 23.

[0059] In some embodiments, the redistributor 45 comprises a plurality of alternately arranged non -pass entry layers 103 and pass entry layers 105. A sectional view of a non-pass entry layer according to a vertical plane is shown in Fig.14. A sectional view of a pass entry layer according to a vertical plane is shown in Fig.16.

[0060] Each pass entry layer 105 is co-planar to a set of mutually co-planar ducts of the lower section 23 A formed by a single corrugated heat transfer fin, such that the upwardly flowing two-phase condensing fluid which flows through said ducts 23A enters the pass entry layer. Each non-pass entry layer 103 is co-planar to a set of mutually co-planar descending ducts 21 formed by a respective corrugated heat transfer fin 17. Each non-pass entry layer is fluidly separated from the descending ducts 21 and fluidly coupled to adjacent pass entry layer.

[0061] Pass entry layers 105 and non-pass entry layers 103 are separated from one another by separation plates 107, one of which is shown in a side view in Fig.15. Each separation plate 107 is sandwiched between a pass entry layer 105 and a non-pass entry layer 103. Similarly each non-pass entry layer 103 is sandwiched between two separation plates 107, and each pass-entry layer 105 is sandwiched between two separation plates 107.

[0062] A respective distribution fin 47, already mentioned above in connection with Fig.3, extends in each pass entry layer 105. The distribution fins 47 form inclined flow ducts which convey the two-phase condensing fluid from the lower sections 23A of the condensing fluid ducts 23 into the redistribution chamber 101. The condensing fluid flow is confined between side bars 108, 109 (Fig.16). The side bars 109 separate each distribution fin 47 from the adj cent distribution fin 49, already mentioned above in connection with Fig.3, which conveys the two-phase condensing fluid from the condensation redistributor 45 to the upper sections 23B of the condensing fluid ducts 23, after redistribution of the vapor and liquid phase in the various ducts formed by the distribution fins 49.

[0063] In practice, direct flowing of the two-phase flow from the upwardly oriented distribution fins 47 into the downwardly directed distribution fins 49 is prevented by the side bars 109 and further side bars 111 provided in each pass entry layer 105.

[0064] Each separation plate 107 comprises an overflow edge 107A arranged above the outlet ends of the ducts formed by the distribution fins 47, to cause a liquid phase of the condensing fluid to overflow from each pass entry layer 105 into the adjacent non-pass entry layers 103.

[0065] Each vertical separation plate 107 (see Fig.15) further comprises a plate aperture 107B fluidly coupling the non-pass entry layer 103, on one side of the vertical separation plate 107, with the pass entry layer 105 on the other side of the vertical separation plate 107. The aperture 107B has a lower, preferably horizontal edge 107C and an upper, preferably horizontal edge 107D. In some embodiments, the lower horizontal edge 107C is approximately at the same height as the overflow edge 107A or at a slightly greater height.

[0066] The bottom of each non-pass entry layer 103 is closed by a side bar 110.

[0067] In some embodiments, vapor guiding fins 112 (see Fig.16) are arranged in each pass entry layer 105. Each vapor guiding fin forms inclined ducts extending from an upper part of the redistribution chamber 101 towards the aperture 107B of the respective separation plates 107, to guide a vapor phase of the incoming condensing fluid towards the apertures 107B of each separation plate 107 between which the vapor guiding fin 112 is sandwiched.

[0068] In some embodiments, a liquid guiding fin 115 is arranged in each non-pass entry layer 103. Preferably, the liquid guiding fin 115 is located between the bottom of the non-pass entry layer 103 and the plate aperture 107B. Each liquid guiding fin 115 defines vertically oriented ducts for the liquid phase of the condensing fluid. Each vertically oriented duct has an inlet end at a distance from the bottom of the non-pass entry layer (side bar 110) and an outlet end which can be located flush with the lower edge 107C, or below the lower edge 107C of the aperture 107B of the separation plate 107.

[0069] A vapor guiding fin 117 can be arranged above the aperture 107 in each non- pass layer. The vapor guiding fins 117 can define vapor guiding ducts parallel to the ducts formed by the vapor guiding fin 112 in the pass entry layer 105.

[0070] To prevent the liquid phase of the condensing fluid entering the pass entry layer 105 from flowing directly into the ducts formed by the distribution fins 49, an additional side bar 119 (Figs.14, 16) is located in each non-pass entry layer 103. Each side bar 119 extends vertically along the vertical edge of the corresponding aperture 107B, at least between the lower edge 107C and the upper edge 107D of the aperture 107A. Each side bar 119 is parallel to the side bars 111 located in the pass entry layers 105.

[0071] Fig.12 shows the above-described components of a non-pass entry layer 103 and of an adjacent pass entry layer 105, overlapped to one another, while Fig. 13 illustrates an axonometric view of a pass entry layer 105 and two adjacent non-pass entry layers 103, between which the pass entry layer is sandwiched. One of the two separation plates 107 is partly removed to show the elements behind the separation plate.

[0072] The operation of the redistributor 45 described above is as follows.

[0073] A two-phase condensing fluid raises along the vertically oriented lower sections 23 A of the condensing fluid ducts 23 formed by each corrugated heat transfer fin 19A and is conveyed into the redistribution chamber 101 through the inclined ducts in the pass entry layers 105, which are formed by the distribution fins 47.

[0074] The vapor phase entering the redistribution chamber 101 from the various pass entry layers 105 flows according to arrows V (Fig.13) from the redistribution chamber 101 through the vapor guiding fins 112 and 117 of both the pass entry layers 105 and the non-pass entry layers 103 and through the distribution fins 49 towards the corrugated heat transfer fins 19B forming the upper sections 23B of the condensing fluid ducts 23.

[0075] Conversely, the liquid phase fills the pass entry layers 105 and flows over the overflow edges 107 A of the separation plates 107 into the two adjacent non-pass entry layers 103, between which the pass entry layer 105 of Fig.13 is arranged.

[0076] The liquid collects in each non-pass entry layer 103 and the level thereof raises from the bottom (side bar 110) thereof and no liquid flows towards the upper section of the heat exchanger, until the level of the liquid in the non-pass entry layer reaches the lower edge 107C of the aperture 107B. When the level of the liquid reaches the lower edge 107C, liquid overflows from the non-pass entry layer 103 into the adjacent pass entry layers 150 and from there into the respective distribution fins 49 that convey the liquid phase towards the corrugated hat transfer fins 19B of the upper section.

[0077] All non-pass entry layers are in fluid communication through a bottom aperture 121, which extends parallel to the redistribution chamber 101, i.e. orthogonal to the co-planar fluid ducts 21, 23, see Figs. 12 and 13. Therefore, the level of the liquid is the same in all non-pass layers, such that a uniform flow of liquid phase of the condensing fluid towards the upper section 23B of condensing fluid ducts 23 is obtained through the redistributor 45.

[0078] An unbalanced distribution of liquid and vapor in the lower sections 23 A of the condensing fluid ducts 23 formed by the lower corrugated heat transfer fins 19A is thus reduced or removed by the redistributor 45 and a uniform distribution of liquid and vapor is achieved at the lower ends of the corrugated heat transfer fins 19B forming the upper sections 23B of condensing fluid ducts 23. [0079] If needed more than one redistributor 45 can be provided along the vertical extension of the core 3, and the uprising ducts wherein the condensing fluid flows can be divided in more than two sections.

[0080] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.