Louvered fins for heat exchanger

Abstract

The invention concerns a louvered fin comprising an assembly of wave stems (123) alternately linked by a wave crest (121) and a wave base (122), and wherein the wave stems (123) are provided with flaps (125) cut out in said wave stems (123) and sloping at angle relative to the main undulating direction (D1). The wave stems (123), crests (121) and bases (122) form, in cross-section relative to the main undulating direction (D1), rectilinear segments, the crests and the bases being mutually parallel.

Description

[0001] The present invention relates to a corrugated fin for a plate and fin heat exchanger.

[0002] There are various types of plate and fin heat exchangers, each tailored to one field of use. In particular, the invention applies advantageously to a heat exchanger of a unit for separating air or H2/CO (hydrogen/carbon monoxide) mixtures by cryogenic distillation.

[0003] This exchanger may be a main heat exchange line or a reboiler/condenser.

[0004] FIG. 1 of the appended figures depicts, in perspective, with partial cutaways, one example of such a heat exchanger, of conventional structure, to which the invention applies.

[0005] The heat exchanger 1 depicted consists of a stack of parallel rectangular plates 2, all identical, between them defining a plurality of passages for fluids to be placed in an indirect heat-exchange relationship. In the example depicted, these passages are, in succession and cyclically, passages 3 for a first fluid, 4 for a second fluid and 5 for a third fluid.

[0006] Each passage 3 to 5 is bordered by closure bars 6 which delimit it, leaving inlet/outlet apertures 7 for the corresponding fluid uncovered. Arranged in each passage are brace corrugations or corrugated fins 8 which at the same time act as heat-exchange fins, as braces between the plates, particularly during the brazing and to prevent any deformation of the plates when fluids under pressure are used, and also serve to guide the flow of the fluids.

[0007] The stack of plates, closure bars and brace corrugations is generally made of aluminum or of an aluminum alloy and is assembled in a single operation by furnace brazing.

[0008] Fluid inlet/outlet boxes 9, of semicylindrical overall shape, are then welded to the exchanger body thus produced in such a way as to sit over the rows of corresponding inlet/outlet apertures, and they are connected to pipes 10 for feeding and discharging the fluids.

[0009] These exchangers pose specific problems due to the high flow rates of fluids to be processed and to the magnitude of the heat exchanges needed in order to produce very high temperature differences between the inlet and outlet side of the exchanger:

[0010] in order to achieve the desired heat exchange and in order to process significant flow rates of fluid, the exchangers of cryogenic type, as described with reference to FIG. 1, have large sizes (are several meters long) and may be made up of several individual bodies as described hereinabove. The volumes of such exchangers are therefore very high;

[0011] the high flow rates and long heat exchange lengths lead to pressure drops which result in high energy consumption at the main compressor.

[0012] In order to reduce the volume of the exchanger and/or the power consumption of the plant, the performance of the heat exchange corrugation fitted into the exchanger in terms of pressure drops is of fundamental importance.

[0013] In this industrial field, use is very conventionally made of brace corrugations 8 of the serrated, straight or perforated straight type.

[0014] The serrated corrugation, which is the most commonly used, is thermally very efficient but in terms of pressure drops, its performance is somewhat penalizing.

[0015] Also known are other heat exchangers used in the automotive industry to produce air conditioning circuit evaporators. These exchangers, the corrugations of which are generally made from aluminum sheet, differ from cryogenic exchangers in that they are small in size, namely measuring a few centimeters (a maximum of about ten), in that they are not subjected to much mechanical stress because they operate at pressures close to atmospheric pressure, and in that they are not subject to the same requirements in terms of pressure drop.

[0016] The corrugations of the exchangers of the type used in the automotive industry are manufactured using wheels, with channels of triangular or sinusoidal section, and limited densities, from thin strip (about 0.1 mm thick).

[0017] In the automotive field, use is particularly made of brace corrugations known as “louvered corrugations”, as depicted in FIG. 2.

[0018] A louvered corrugation has an overall main direction of corrugation D1 defining an overall direction F of flow of the fluid. In the plane P orthogonal to the overall main direction of corrugation D1, the corrugation has a cross section of sinusoidal shape, stretched heightwise. The sinusoid thus defined extends in a direction D2 perpendicular to the direction D1, these two directions being assumed, for the convenience of the description, to be horizontal as has been depicted in FIG. 2.

[0019] The corrugation has corrugation crests 21, defined by the crests of the sinusoid, and corrugation troughs 22, defined by the troughs of the sinusoid. The crests 21 and the troughs 22 alternately connect corrugation legs 23 each having a vertical mean plane perpendicular to the direction D2.

[0020] Two consecutive corrugation legs 23 between them define a fluid passage with respect to the overall direction F of flow.

[0021] Cut from each corrugation leg 23 is a series of flaps 25, which are mutually parallel and inclined with respect to the vertical mean plane and to the overall main direction of corrugation D1. The flaps 25 define openings constituting secondary passages for the fluid, in a mainly transverse direction, from one channel to an adjacent channel. These flaps extend over just part of the height of the corrugation leg.

[0022] Louvered, triangular or sinusoidal corrugations of the type described hereinabove have hitherto not been used in industrial-scale plate heat exchangers for the following reasons.

[0023] Firstly, the corrugation crests and troughs, whether the corrugation be triangular or sinusoidal, offer brazing lines only on the dividing plates, and therefore offer only very small surface area for mechanical connection to the plates. Such fin geometries are therefore not suited to the high pressures used in industrial exchangers, which are conventionally between 6 and 10 bar, and sometimes reach as high as 80 bar.

[0024] Secondly, the shape of the louvered corrugations used in the automotive industry is closely connected to the method of manufacture using the wheel, which is particularly suited to high manufacturing throughputs. Other corrugation shapes can be obtained only with great difficulty using such a method of manufacture involving the wheel. With such a method of manufacture, the cutting of the flaps can be done correctly only over part of the height of the corrugation legs. This cutting-out is not enough to achieve the level of heat exchange performance required in industrial exchangers.

[0025] Thirdly, the conventional method of manufacture of louvered corrugations, that is to say using the wheel, may prove difficult to adapt to significant strip thicknesses, of the order of 0.2 to 0.5 mm, as used in industrial exchangers in order to withstand the mechanical stresses on the fins.

[0026] The object of the invention is therefore to propose a fin of the louvered type, whose performance in terms of pressure drop is better in particular than the serrated corrugation, and which can be used in industrial exchangers, particularly plate and fin heat exchangers of a unit for separating air or H2/CO mixtures by cryogenic distillation, whether this be in the main heat exchange line or in a reboiler/condenser.

[0027] To this end, the subject of the invention is a corrugated fin for a plate and fin heat exchanger, of the type with louvers defining an overall main direction of corrugation, comprising a set of corrugation legs alternately connected by a corrugation crest and by a corrugation trough, the legs being provided with flaps cut from said corrugation legs and inclined at an angle with respect to the main direction of corrugation, characterized in that the corrugation legs, the corrugation crests and the corrugation troughs form, in cross section with respect to the main direction of corrugation, straight segments, the crests and the troughs being mutually parallel.

[0028] Thus, the fin offers a brazing area that allows it to be used in exchangers of the aforementioned type.

[0029] According to other features of the invention, taken alone or in any technically conceivable combination:

[0030] the corrugation legs are all mutually parallel and perpendicular to the corrugation troughs, so that the fin has a square wave-shaped corrugation;

[0031] each flap is cut along the direction of the straight segment defined by the corrugation leg over substantially the entire length of said segment; and

[0032] the fin has a substantially uniform wall thickness of between 0.2 and 0.5 mm.

[0033] One significant difficulty in the design of the corrugated fins lies in obtaining an optimum compromise between performance in terms of pressure drop and performance in terms of the thermal efficiency of the corrugation. The problem is that, when producing such fins, one is looking for effects of turbulence and remixing of the fluid within the passage channels, so as to increase the local temperature difference between the fluid and the wall, and thus encourage heat exchange. However, it is essential to keep control over these effects of turbulence and of remixing of the fluid, so as to limit the pressure drops generated by the fin. It is essential, particularly in industrial plants, for example plants for separating air or H2/CO mixtures by cryogenic distillation, to limit the power consumption needed to set the fluid in motion in the heat exchangers.

[0034] Another object of the invention is to propose a louvered fin geometry of the type described hereinabove making it possible to limit the pressure drops induced in the fin and to obtain good heat exchange quality, to an extent that will allow this type of fin to be used in industrial cryogenic exchangers.

[0035] To this end, a fin according to the invention, in which the corrugation legs have a thickness e, a mean transverse separation w with respect to the overall main direction of corrugation, which defines the width of a passage channel and a spacing P, and the flaps have a length ls, is characterized in that the length of the flaps is greater than the spacing.

[0036] According to yet other features of the fin according to the invention:

[0037] the length of the flaps satisfies the following relationship:

[0038] ls≧1.1p;

[0039] the angle of inclination of the flaps lies, in terms of absolute value, strictly between a minimum value and a maximum value which are positive and defined by the following equations:

[0040] sin &agr;min=e/ls

[0041] and 1 tan ⁢   ⁢ α max = p 1 s ;

[0042] the angle of inclination of the flaps is substantially equal, in terms of absolute value, to an angle defined by the equation: 2 tan ⁢   ⁢ α 1 = p 21 s

[0043] and

[0044] the angle of inclination of the flaps meets the condition:

[0045] p≧ls sin|&agr;|+e cos|&agr;|.

[0046] The invention also relates to a method for the continuous manufacture, from a flat product in sheet form, of a louvered corrugated fin for a plate heat exchanger, of the type comprising flaps cut from corrugation legs, particularly a fin as described hereinabove.

[0047] According to the method of the invention, the product is passed step by step through a press tool comprising at least a moving tool part with a reciprocating movement, said tool part in the one same movement corrugating the fin and cutting the flaps.

[0048] According to other features of the method:

[0049] the flat product is held in position upstream of said moving tool part by means of a holding device when said moving tool part is active, and the flat product is released to continue its journey and to extract the formed corrugation from the tool when the moving tool part is inactive,

[0050] the holding device and the moving tool part are driven and synchronized by command and control means.

[0051] The invention also relates to a device for implementing the method described hereinabove.

[0052] This device comprises a press tool, a device for continuously feeding the tool with flat product in sheet form, said tool comprising at least one punch and one die that complement each other, said punch being able to be given a relative translational movement with respect to the die in a direction substantially orthogonal to the surface of the flat product in sheet form.

[0053] It is characterized in that said punch extends in a longitudinal overall direction and has a plurality of planar facets of which at least one is directed in the direction of translation of the punch and said overall direction and at least another, intended to form a flap, is directed in the direction of translation of the punch and a direction inclined with respect to the overall direction.

[0054] According to other features of the device according to the invention:

[0055] the punch comprises, between two consecutive facets, a planar setback in the direction of translation and a direction substantially orthogonal to the overall direction;

[0056] the punch has grooves running in the direction of translation, between a facet and a setback;

[0057] the device comprises a device for holding the flat product in sheet form upstream of the tool allowing the flat product selectively to be fixed with respect to the tool or released to allow it to progress; and

[0058] the device comprises command and control means designed to drive and synchronize the tool and the holding device.

[0059] An exemplary embodiment of the invention will now be described with reference to FIGS. 3 to 8 of the attached drawings, in which:

[0060] FIG. 3 is a perspective view of part of a corrugated fin according to the invention;

[0061] FIG. 4 is an enlarged sectional view on the vertical plane V depicted in FIG. 3;

[0062] FIG. 5 is an enlarged schematic view in section, on the horizontal plane H, of the corrugation depicted in FIG. 3, just three corrugation legs being depicted;

[0063] FIG. 6 is a similar partial depiction, on a larger scale;

[0064] FIG. 7 is a schematic depiction of a device for manufacturing a louvered corrugated fin according to the invention; and

[0065] FIG. 8 combines views from above of a punch, a guide, and outlet, central and inlet braces, respectively, used in the device of FIG. 7.

[0066] FIG. 3 depicts a louvered corrugation according to the invention, which has a main overall direction of corrugation D1, and a cross section (FIG. 4) in the form of a square wave, square waves thus defined running in a direction D2 perpendicular to the direction D1. Here again, for the convenience of the description, these two directions are assumed to be horizontal.

[0067] The term “square wave” here means a succession, in alternation, of horizontal and vertical segments, the horizontal segments being aligned.

[0068] The fin has corrugation crests 121 defined by the crests of the square waves, which are flat and horizontal. It has corrugation troughs 122, defined by the troughs of the square waves, which are also flat and horizontal. The crests 121 and the troughs 122 alternately connect corrugation legs 123 which are planar and vertical, the mean plane of which runs perpendicular to the direction D2.

[0069] Cut from the corrugation legs 123 is a series of flaps 125 which are mutually parallel and inclined with respect to the vertical plane and to the overall direction of corrugation D1. The flaps 125 define openings constituting secondary passages for the fluid, in a mainly transverse direction, from one channel to an adjacent channel.

[0070] As can be seen in FIGS. 3 and 4, the flaps 125 of a corrugation leg are cut over the entire height (or practically over the entire height) of the straight segment defined by the mean plane of the corrugation leg considered in cross section.

[0071] This arrangement makes it possible, by comparison with louvered corrugations in which the flaps are cut over just part of the height, to increase the effect of remixing of the fluid flowing through the fin.

[0072] With reference to FIG. 5, we shall now describe the parameters that characterize the louvered corrugation of the type described hereinabove, and influence its performance in terms of pressure drop and in terms of thermal efficiency.

[0073] FIG. 5 is a schematic view in section, on the horizontal plane (H) of symmetry, of the corrugation depicted in FIG. 3, just three corrugation legs being depicted here.

[0074] The lines denoted by the reference 130 represent the vertical plane of a corrugation leg 123, with respect to which plane the angle of inclination &agr; of the flaps 125 is defined.

[0075] The spacing of the corrugation, corresponding to the separation of two consecutive planes 130, corresponding to two consecutive corrugation legs 23, is denoted by the reference p.

[0076] The thickness e of the walls of the corrugation is assumed to be constant. As a result, the width of the channel defined by two consecutive corrugation legs 123 is equal to w=p−e.

[0077] In the type of application at which the invention is aimed, the thickness e is between 0.2 and 0.5 mm, essentially so as to reach a compromise between the mechanical integrity and the density of the fin.

[0078] Along the corrugation, in the direction of corrugation D1, the flaps 125 are configured in a pattern which repeats with a geometric periodicity characterized by a period Π. This pattern here comprises two groups of six flaps inclined respectively at a positive angle &agr; and at a negative angle &agr;, with, between these two groups, a planar region 132, 134 directed in the direction D1. Two transversely consecutive corrugation legs 123 are identical, and therefore are made up of the same sequence of patterns repeating periodically without a relative offset or shift.

[0079] In the planar regions 132, 134, the corresponding corrugation legs 123 have no openings.

[0080] Reference is now made more specifically to FIG. 6.

[0081] One aspect of the invention relies on the observation that some of the geometric parameters of a louvered corrugation, which are described above, have a significant influence on the thermal performance and pressure drop performance of the fin.

[0082] It has been found that this performance is improved when the length ls of the flaps 25 is greater than the spacing p or even than the mean transverse separation w increased by the thickness e, that is to say when the length ls satisfies the following relationship:

[0083] ls≧p or alternatively ls≧w+e.

[0084] As a preference, a flap length ls will be chosen such that:

[0085] ls≧1.1p,

[0086] and more preferably still:

[0087] ls≧1.2p.

[0088] It is thus possible to produce cryogenic exchangers equipped with exchange corrugations of varying densities corresponding to the various modes of operation of the passages in one and the same heat exchanger, particularly having different pressures according to the passages, these pressures being able to be as high as several tens of bar. For example, it is possible to produce high-density fins for short flap lengths or, alternatively, lower-density fins with longer flap lengths.

[0089] According to another aspect of the invention, optimum fin performance is obtained when the angle of inclination of the flaps &agr; lies strictly between a minimum value &agr;min and a maximum value &agr;max which are positive, defined by the following equations:

[0090] sin &agr;max=e/ls

[0091] and 3 tan ⁢   ⁢ α max = p 1 s

[0092] The first of these conditions |&agr;|>&agr;min gives a strictly positive opening v between two consecutive flaps 125A, 125C on the same corrugation leg, namely it defines an orientation of the flaps excluding contact between the trailing edge of the first flap 125A and the leading edge of the second flap 125C.

[0093] The maximum value &agr;max of the angle &agr; corresponds, for its part, to the angle of alignment of two consecutive flaps 125B, 125C of two consecutive corrugation legs, and the second condition |&agr;|<&agr;max ensures an opening such that the passages in the consecutive corrugation legs are not aligned, and thus generate turbulence.

[0094] As a preference, some fins are centered in the middle of the passage defined by two corresponding fins belonging to a consecutive corrugation leg, by choosing an angle of inclination of the flaps &agr; substantially equal, in terms of absolute value, to an angle &agr;1 defined by the equation 4 tan ⁢   ⁢ α 1 = 1 21 s .

[0095] To ensure optimum circulation of the fluid in the secondary channels formed by the flaps 125, an angle of inclination &agr; is chosen that satisfies the condition

[0096] p≧ls sin|&agr;|+e cos|&agr;|.

[0097] In addition, this condition makes it possible to ensure ease of manufacture of the corrugation and a separation ec between two rows of flaps 125 that is strictly positive.

[0098] The invention is also aimed at a cryogenic plate heat exchanger of the type comprising a stack of parallel plates 2 which define a plurality of fluid-circulation passages 3 to 5 of flat overall shape, closure bars 6 delimiting these passages, and corrugated fins 8 arranged in the passages, characterized in that at least some of the corrugated fins 8 are of the type described hereinabove.

[0099] A device or machine allowing the manufacture of a louvered corrugated fin, particularly a fin of the type described with reference to FIGS. 3 to 6, and particularly a thick-walled fin will now be described with reference to FIG. 7.

[0100] This device comprises a press tool essentially comprising a die 201 and a punch 202 which can be given a relative translational movement.

[0101] For the convenience of the description, it will be assumed that the die 201 is fixed and the punch 202 can move. The punch 202 may be given a reciprocating translational movement assumed to be vertical. The punch 202 and the die 201 have complementary shapes.

[0102] The tool has an inlet 203 and an outlet 204 via which a metal product in sheet form that is to be processed continuously passes.

[0103] The device possesses means, not depicted, for moving along and guiding the metal sheet 205, which allow the metal sheet to be moved regularly step by step through the tool, in a plane assumed to be horizontal.

[0104] The punch 202, by collaborating with the die 201, in regular intervals shapes the metal sheet fed continuously into the tool.

[0105] The device also comprises means 210 for holding the sheet upstream of the inlet 203, allowing the sheet to be selectively fixed with respect to the tool or released to allow it to progress.

[0106] The holding means 210 may for example essentially consist of two clamping jaws situated one on each side of the surface of the sheet 205.

[0107] The device further comprises command and control means 220 able to command the operation of the tool, in this case the movements of the punch 202 and of the holding means 210, in response to measured and/or prerecorded parameters.

[0108] The command and control means for this purpose comprise a sensor 221 sensing the position of the punch 202, and a sensor 222 sensing the position or status of the holding means 210.

[0109] The command and control means 220 also comprise a computer 225 connected to the position sensors 221, 222 so as to receive their respective detection signals S1, S2.

[0110] The computer 225 is also designed to receive other prerecorded parameters Pi and the preprogrammed command laws Li. The computer 225 sends the punch 202 (that is to say its drive member), and the holding means 210, respective command signals C1, C2 formulated on the basis of the detection signals S1, S2, of the prerecorded external parameters Pi and of the command laws Li.

[0111] For simplification purposes, the die 201 has been assumed to be fixed, but it may in reality be moveable, in alternation with the punch 202. In this case, the die 201 is driven by a drive member also receiving a command signal from the computer 225.

[0112] Some of the constituent elements of the die (or fixed part of the tool) 201 and of the punch (or moving part of the tool) 202 will now be described with reference to FIG. 8.

[0113] The die 201 comprises an inlet brace 231, a central brace 232, and an outlet brace 233, while the punch 202 comprises a first punch part 241 (or “first punch”) and a second punch part 242 (or “second punch”).

[0114] Each of these elements 231, 232, 233, 241, 242 is elongate in a horizontal overall direction D.

[0115] The inlet brace 231 and the central brace 232 are arranged parallel to each other so as to define between them a space 245 of a shape that complements the first punch 241. Likewise, the central brace 232 and the outlet brace 233 are arranged parallel to one another and spaced in such a way as to define between them a passage 246 that complements the second punch 242.

[0116] The movements of the punch 202 with respect to the die 201 as defined with reference to FIG. 7, which are reciprocating vertical movements orthogonal to the surface of the sheet 205, correspond to reciprocating integral movements of the punch parts 241, 242 orthogonal to the plane of FIG. 8.

[0117] The first pressing of the metal sheet by the first punch 241 between the braces 231, 232 makes it possible to carry out a first corrugation and flap-cutting step, while the second pressing step performed on the tool part thus formed by means of the second punch 241 and the central 232 and outlet 233 braces allows the corrugation to be given its definitive shape.

[0118] The first punch 241 and the second punch 242 are of substantially identical shapes, while the braces 231, 232, 233 are of complementary shapes, which means that it will be beneficial to describe the shape of just one punch, for example the first punch 241.

[0119] In the example depicted, this first punch 241 is of a shape designed to shape a square wave louvered corrugation. It has a succession of vertical planar facets, of which facets 251 run in the overall longitudinal direction D of the punch. The “straight” facets 251 correspond to the shapes of the corrugation leg sections devoid of flaps. The punch 241 has other planar lateral facets 252 which are facets that are inclined with respect to this main direction D, and are intended to cut out the flaps. Between two consecutive facets, whether these be two inclined facets 252, or an inclined facet 252 and a “straight” facet 251, the punch has a setback 253 in the form of a planar vertical face orthogonal to the overall direction D.

[0120] Between a setback 253 and a facet 251 or 252 there is formed a vertical groove 255 allowing flaps to be cut from the corrugation legs.

[0121] The operation of the device will now be described in greater detail, it being understood that this operation is repeated a great many times at high speed throughout the time that the metal sheet progresses through the tool.

[0122] In the method of manufacture of a corrugated fin by means of the device which has just been described, the following steps are performed, starting from the initial state in which the punch 202 is in a raised position with respect to the die 201, that is to say is in an inactive position or top-dead-center position (any other position of the punch will be termed “active”):

[0123] the progress of the metal sheet 205 is halted by the holding means 210;

[0124] the punch 202 is actuated in vertical translation toward the die 201, carrying the first punch 241 and the second punch 242 along in the same movement so as, in one and the same movement of the punch 202, to corrugate the fin and cut out the flaps;

[0125] the sheet 205 is released from the holding means 210 so as to allow it to progress through the tool and so as to allow the corrugations already formed to be extracted from the tool; and

[0126] the metal sheet 205 is advanced by one step before the aforementioned operations are repeated, in the same order.

[0127] It should be noted that the prerecorded parameters Pi and the command laws Li correspond to the datum geometry of the corrugated fin. These laws and parameters vary according to the type of corrugation to be produced and according to the desired thermal performance of the corrugated fin or according to the desired flow characteristics of the fluid.

[0128] At each moment, the movement of the punch 202 and of the holding means 210 are synchronized by the computer 225 using the signals S1 and S2 supplied by the sensors 221, 222.

[0129] The method and the device which have just been described allow the continuous production of louvered corrugated fins, particularly square wave corrugations, from metal sheet of significant thickness.

[0130] Thus, this method and this device make it possible to produce louvered corrugations that can be used in industrial exchangers, with high manufacturing throughputs comparable with the throughputs in the manufacture of louvered fins used in the automotive industry.

Claims

1. A corrugated fin for a plate and fin heat exchanger, of the type with louvers defining an overall main direction of corrugation (D1), comprising a set of corrugation legs (123) alternately connected by a corrugation crest (121) and by a corrugation trough (122), the corrugation legs (123) being provided with flaps (125) cut from said corrugation legs (123) and inclined at an angle (&agr;) with respect to the main direction of corrugation (D1), characterized in that the corrugation legs (123), the corrugation crests (121) and the corrugation troughs (122) form, in cross section with respect to the main direction of corrugation (D1), straight segments, the crests (121) and the troughs (122) being mutually parallel.

2. The corrugated fin as claimed in claim 1, characterized in that the corrugation legs (123) are all mutually parallel and perpendicular to the corrugation troughs (122), so that the fin has a square wave-shaped corrugation.

3. The corrugated fin as claimed in claim 1 or 2, characterized in that each flap (12) is cut along the direction of the straight segment defined by the corrugation leg (123) over substantially the entire length of said segment.

4. The corrugated fin as claimed in any one of claims 1 to 3, characterized in that the fin has a substantially uniform wall thickness (e) of between 0.2 and 0.5 mm.

5. The corrugated fin as claimed in any one of claims 1 to 4, in which the corrugation legs (123) have a thickness (e), a mean transverse separation (w) with respect to the overall main direction of corrugation (D1), which defines the width of a passage channel and a spacing (p), and the flaps (125) have a length (ls), characterized in that the length (ls) is greater than the spacing (p).

6. The corrugated fin as claimed in claim 5, characterized in that the length (ls) of the flaps satisfies the following relationship:

ls≧1.1p.

7. The corrugated fin as claimed in claim 5 or 6, characterized in that the angle of inclination of the flaps (&agr;) lies, in terms of absolute value, strictly between a minimum value (&agr;min) and a maximum value (&agr;max) which are positive and defined by the following equations:

sin &agr;min=e/ls

and

5 tan ⁢   ⁢ α max = p 1 s

8. The corrugated fin as claimed in any one of claims 5 to 7, characterized in that the angle of inclination (&agr;) of the flaps (25) is substantially equal, in terms of absolute value, to an angle (&agr;1) defined by the equation:

6 tan ⁢   ⁢ α 1 = p 21 s

9. The corrugated fin as claimed in any one of claims 5 to 7, characterized in that the angle of inclination (&agr;) of the flaps (125) meets the condition:

p≧ls sin|&agr;|+e cos|&agr;|.

10. A plate and fin heat exchanger of a unit for separating air or H2/CO mixtures by cryogenic distillation, particularly an exchanger of a main heat exchange line or a reboiler/condenser, of the type comprising a stack of parallel plates (2) which define a plurality of fluid-circulation passages (3 to 5) of flat overall shape, closure bars (6) delimiting these passages, and corrugated fins (8) arranged in the passages, characterized in that at least some of the corrugated fins (8) are as claimed in any one of claims 1 to 9.

11. A method for the continuous manufacture, from a flat product in sheet form, of a louvered corrugated fin for a plate heat exchanger, of the type comprising flaps (25; 125) cut from corrugation legs (23; 123), in which the product (205) is passed step by step through a press tool (201, 202) comprising at least a moving tool part (201) with a reciprocating movement, said tool part (201) in the one same movement corrugating the fin and cutting the flaps.

12. The corrugated fin as claimed in claim 11, characterized in that the flat product (205) is held in position upstream of said moving tool part (201) by means of a holding device (210) when said moving tool part (201) is active, and the flat product (205) is released to continue its journey and to extract the formed corrugation from the tool when the moving tool part (201) is inactive.

13. The corrugated fin as claimed in claim 12, characterized in that the holding device (210) and the moving tool part (201) are driven and synchronized by command and control means (220).

14. A device for implementing the method as claimed in any one of claims 11 to 13, comprising a press tool (201, 202), a device for continuously feeding the tool with flat product in sheet form (205), said tool comprising at least one punch (202) and one die (201) that complement each other, said punch (202) being able to be given a relative translational movement with respect to the die (202) in a direction substantially orthogonal to the surface of the flat product in sheet form (205), characterized in that said punch (202) extends in a longitudinal overall direction (D) and has a plurality of planar facets of which at least one (251) is directed in the direction of translation of the punch and said overall direction (D) and at least another (252), intended to form a flap, is directed in the direction of translation of the punch and a direction inclined with respect to the overall direction (D).

15. The device as claimed in claim 14, characterized in that the punch (202) comprises, between two consecutive facets, a planar setback (253) in the direction of translation and a direction substantially orthogonal to the overall direction (D).

16. The device as claimed in claim 15, characterized in that the punch (202) has grooves (255) running in the direction of translation, between a facet (251, 252) and a setback (253).

17. The device as claimed in claim 16, characterized in that it comprises a device (210) for holding the flat product in sheet form (205) upstream of the tool (201, 202) allowing the flat product selectively to be fixed with respect to the tool or released to allow it to progress.

18. The device as claimed in claim 17, characterized in that it comprises command and control means (220) designed to drive and synchronize the tool (201, 202) and the holding device (210).