FR2960288A1 - Nest plate for heat exchanger utilized for e.g. treating corrosive fluids, has set of hollow plates, where connection zones are provided for connecting two individual sections with ends of central zones of hollow plates - Google Patents

Abstract

The plate has a set of hollow plates with constant steps, where the plates are connected with two external collectors. A set of walls of the hollow plates comprises an embossed zone that is provided with one or more alignments of alternative embosses. A mold holds required embosses at central zones of walls of the hollow plates to provide uniform inner thickness to the embossed zone. Two connection zones are provided for connecting two individual sections (22) with ends of the central zones of the plates made of glass of carbon. An independent claim is also included for a heat exchanger comprising connection pipettes.

Description

HEAT EXCHANGERS WITH HOLLOW PLATES OF POLYMER

The invention relates to improvements to one of the heat exchangers described in European Patent No. 2,032,928, filed on 21/12/07 and granted on 09/09/09.

In this European patent, the heat exchanger, concerned by the present invention, consists of hollow polymer wafers, stacked at constant pitch and connected to two external collectors; the walls of these platelets were made by thermoforming and then cutting a sheet; these walls have a relatively large central embossed zone, lateral flanges comprising a step determining the internal half-thickness of this central zone, and zones of connection to the two external collectors; the lateral edges of the two walls of the hollow plates are welded; the embossed central zone has one or more alternating bosses aligned with steep facets, creating a large number of sharp edges, oriented in oblique directions and / or perpendicular to these alignments; - The gap between the facets facing a wafer is uniform and substantially constant, in the range of expected differential pressures.

The hollow wafers of such a polymer heat exchanger have thin walls (of the order of a millimeter), to which the hollows and bumps provide remarkable rigidity. Indeed, each of their facets acts as a stiff lamella and each sharp edge behaves like a beam in which these slats are embedded. These strips can therefore take a very limited arrow, under the action of differential pressures allowed. The internal thickness of these hollow plates, measured between the facets of the bumps or depressions, is by construction exactly known and moderately low (1 to 2 mm). The fluid circulates in laminar flow. The pressure drops are minimized. Any contact between opposite facet walls is avoided. The heat exchange function between the two fluids concerned is always correctly ensured and the energy used for their circulation is reduced. The sharp edges of the dihedrons, formed between them by the steeply sloping facets of these wafers, provide another interesting result, namely that of appreciably increasing (+ 80%) the apparent thermal conductivity of the fluid which circulates between these hollow wafers, stacked to form a heat exchanger. Indeed, these ridges, obliquely and / or perpendicular to the flow direction of the fluids, have the effect of generating significant turbulence in the fluid currents, particularly air, at generally high speed through the spaces 35 separating these stacked wafers. Such a polymer heat exchanger is perfectly satisfactory for many applications, especially for the treatment of corrosive fluids to which it remains indifferent. But it has a limitation of use, because of the reduced differential pressure that it can accept between the two fluids concerned and the temperature ceiling to which it is subject. This makes it banned from use in many industrial fields. In addition and above all, its manufacturing cost is relatively high, although the industrial manufacture of the only hollow wafers, by welding the side edges of their thermoformed walls, is a simple operation. In fact, the industrial assembly, by welding these hollow plates on their external collectors, requires the use of specific machines and relatively long intervention times.

The first object of the invention relates to hollow polymer wafers, intended to be stacked to form heat exchangers between fluids, particularly effective. The second object of the invention relates to such hollow polymer wafers, particularly reduced manufacturing cost. The third object of the invention relates to heat exchangers, formed by such hollow polymer wafers, supporting differential pressures of up to a few bars. The fourth object of the invention relates to heat exchangers, formed by such hollow polymer wafers, adapted to treat fluids at temperatures close to or even higher than the initial melting temperature of the polymer in question.

According to the invention, a hollow wafer, for heat exchanger in which - hollow wafers are stacked at constant pitch and connected to two external collectors; The walls of these hollow plates comprise an embossed central zone having one or more alternating bosses lined up with steep facets, creating a large number of edges, oriented in oblique directions and / or perpendicular to these alignments; the thickness of the gap between the facets opposite a hollow wafer is uniform and substantially constant, within the range of the authorized differential pressures; is characterized in that: - it is manufactured by extrusion - blowing a polymer parison, between the two jaws of a suitable mold, - this suitable mold is adapted (a) to make the central zones of the two walls of the hollow wafer, the desired alternating bosses, (b) imparting to the embossed central zone of the hollow wafer thus formed an inner thickness as uniform as possible and (c) simultaneously shaping two individual sections of external collectors and two zones of connecting these sections to the ends of the central zone of the wafer. Thanks to these provisions, the manufacture of a hollow plate for heat exchanger 35 is performed by a common technique, in particular used for the manufacture of all containers with neck, plastic (cans and bottles). Such a transfer of technology is in itself particularly advantageous because of the substantial reduction in the cost of manufacturing the hollow plates thus produced, but it is also so by the additional possibilities that it brings them. The hollow plates thus manufactured are extracted from their mold in a quasi-definitive form.

For all these hollow plates, except the first of a heat exchanger, it is sufficient to remove the caps formed by the parison at the ends of the individual sections of the external collectors. To pass from a batch of such hollow polymer wafers to a heat exchanger, immediately usable, it will be sufficient to have, by a specific machine, welded stacks of the two individual sections of external collectors, having circular edges previously brought to their surface. melting temperature by appropriate heating. The open ends of the external collectors of such a heat exchanger are, finally, respectively provided with connectors, cranked or straight, welded in the same way as the collector sections. The length of the individual sections of external collectors determines the width of the gap between the bosses belonging to two contiguous wafers, stacked to form a heat exchanger. From a standard manufacturing height, it is easy to weld an intermediate ring to each section to obtain any particular separation between the bosses of two neighboring plates. As for the appropriate mold, it consists of two symmetrical jaws of relatively simple design.

According to complementary features of such a hollow wafer, the facets of its alternative bosses are in the form of trapezes and isosceles triangles, assembled to form alignments of hollows and bumps, in the form of roofs with four slopes, provided with slightly flattened edges; each of these facets comprises at least one rectilinear nip, parallel to the flow direction of the fluids, for dividing the surfaces of these facets into at least two parts so that, in a heat exchanger in operation, the maximum deflection of these parts facets is reduced to a value substantially less than the thickness of the internal or external channel they delimit; - These pinches are constituted by sets of internal reliefs, welded at the time of closure of the mold around the parison; two contiguous alignments of bosses are separated by a continuous pinch. Due to the slight leveling of the joining ridges of the facets, the thicknesses of the walls of the hollow plates are uniform even along these ridges. This prevents the formation of mechanically weak areas in the wafer walls and thus allows them to operate at relatively high pressures. Thanks to the parallel nips in the flow direction of the fluids, arranged in the facets of the bosses, the ratio between a differential pressure and the flexural stresses it causes in the material of the walls of the exchanger is considerably lower ( of the order of 4 times) than in the absence of these pinches. In this way, a heat exchanger made of a given material, the limiting stress of use is known, can withstand a differential pressure four times stronger with the nips than without them.

The dimensions of these wafers can vary widely, depending on the intended applications: a length of 5 to about 100 cm and a width of 3 to about 60 cm, or more if the machines used for the extrusion blow molding operation allow it . As for the thickness of the polymer walls, it is in practice limited to a range of 1 to 3 mm, in order to be able to provide satisfactory thermal conductances and for reasons of weight and cost. The number of alternate bosses alignments of the embossed central zone of a wafer can range from unity to several tens. It is substantially the same for the number of bosses in an alignment. As for the width, length and height of a boss, they depend on the specifications of the heat exchanger to be produced and, as a first step, on the differential pressure of the fluids concerned: the greater this pressure is, the smaller these dimensions will be. and vice versa. In all cases, the height of a boss will be a fraction of its width. The thickness adopted for the walls of the plates may increase somewhat with their dimensions and with the differential pressure they must withstand, but this wall thickness depends mainly on the number of parallel pinches, arranged on each facet of the bosses. For large bosses (typically> 2 dm2), this number will generally be greater than 2 and for small bosses (typically <20 cm2), it may be zero. In each particular case, a simple modeling makes it possible to optimize the combination, thickness of the walls and number of nips per facet, to optimize the arrow. The internal thickness to be given to these hollow wafers varies with the nature of the fluid circulating inside, this internal thickness being generally lower for liquids than for gases. The range of these internal thicknesses generally ranges from a little less than a millimeter to a few centimeters. It is the same for the gaps between the stacked plates of a heat exchanger.

According to a first particular embodiment of these hollow plates, in the rows of alternating bosses of the embossed central zone, the end facets are flattened isosceles triangles, the lateral facets are trapeziums and the facets of the plate, between two ridges of alternating bosses, are rhombuses; each of these triangles and each of these lozenges, formed by two coplanar triangles, comprises two pinches dividing it into three parts of substantially equal surfaces; each trapezium comprises a nip substantially located at one-third of its height, starting from its large base; . According to a second particular embodiment of hollow plates, in the alternating bosses alignments of the embossed central zone, the end facets are trapeziums, the lateral facets are flattened isosceles triangles and the connecting facets between two ridges. alternate bosses are hexagons; each of these triangles has a nip substantially located one-third of its height, from its long side; each trapezium or hexagon, formed by two coplanar trapezoids, comprises two pinches dividing it into three parts of substantially equal surfaces.

According to a particular feature of this hollow wafer, the polymer used is loaded with suitable fibers, in particular glass or carbon; Thanks to these various arrangements, the walls of the facets of the hollow plates of a heat exchanger are capable of withstanding a relatively large differential pressure, for example a few bars, when the polymer used is loaded with glass or carbon fibers. This is the result of parallel welded nips at optimized locations of the isosceles triangles and trapezoids (determined by modeling the stresses on the facets of the hollow plates). The calculation shows that in the case of bosses of average dimensions (10> S> 100 cm), a small number (1 or 2) of parallel pinches, arranged in its trapezoid and triangular facets, divides by 10 the maximum arrow. male of these facets, which would result from their absence.

According to complementary features of the previous ones, the two individual sections of external collectors of a hollow wafer are constituted by two pairs of polymer inserts incorporated in the ends of the wafer; these inserts are provided with a central opening, with circular or oblong periphery, and with several grooves of the same section, arranged in the part of this periphery directed towards the inside of the wafer; these two pairs of inserts, previously heated to a temperature slightly lower than their melting temperature, were installed in housings made in the two jaws of the mold and were welded to the hollow wafer, by intimate contact with the melt parison, due to the pressure of the air injected inside; - The ducts, with identical sections, resulting from the parison welded to the walls of the grooves of each pair of inserts, open on passages arranged between equidistant oblique nips, made in a connection area of the central zone of the wafer. one of its two sections of collectors. Thanks to the two pairs of inserts assembled to form the two sections of external collectors, there is a solution with several advantages. First, it gives the individual sections of collectors of each hollow wafer, rigidity and flatness sufficient to allow them to be stacked at constant pitch. Then, the conduits of these inserts and the oblique nips of the connection areas all cooperate to ensure a balanced distribution of fluid flow rates inside the hollow wafer. Conversely, a grouping of these substantially identical shared flows occurs at the output. The circular periphery inserts are particularly suitable for hollow plates having a small number (<3) of bossed channels. As for oblong periphery inserts, they become practically indispensable for hollow inserts with a large number of bossed channels (> 5).

According to another complementary feature of the invention, a heat exchanger formed by the stack of these hollow polymer wafers has been subjected to crosslinking, in particular by exposure to ionizing radiation.

Thanks to these provisions, the temperature of the fluids that can be treated by such a heat exchanger is considerably increased, up to exceeding the melting temperature of the non-crosslinked polymer. Consequently, the possible increase in the temperature of the treated fluids, due to the crosslinking of the polymer used, and that of the differential pressure of these same fluids, due to the loading of the appropriate fibers of this same polymer, open to the heat exchangers according to the invention of the possibilities of new applications particularly interesting in many fields of the industry.

The features and advantages of the invention will emerge more precisely from the following description of a non-limiting embodiment of the invention, with reference to the appended drawings, in which: FIG. A, a front view of a first hollow plate according to the invention; at B, a longitudinal section of an alignment of bosses of two of these first hollow plates; in C, a cross section of the central embossed areas of two of these first hollow plates juxtaposed; in D, a profile view of this first hollow plate; - Figure 2 shows: in A, a front view of a collector section insert, circular contour; in B, a sectional view of this insert; at C, a front view of the end of a large hollow wafer, having a neck-reader section with oblong contour; - Figure 3 shows the front view of a second hollow plate according to the invention; - Figure 4 shows a perspective view of a heat exchanger formed by the assembly of these hollow plates.

According to FIG. 1, at A, the front view of a first hollow plate 12 according to the invention is shown, and at B, the section of this plate along a line BB. For example, the hollow plate 12 has a generally rectangular shape and measures 300 mm between its parallel edges 14-16 and 200 mm between its side edges 18-20, with 360 mm between the extreme edges of its two sections of external collectors 22-24. The embossed central zone of this hollow plate 12 comprises two identical identical alignments 26-28 of alternating bosses, separated by a rectilinear central nip 30, 2 mm wide, constituted by the welding of the contiguous ends of two internal reliefs arranged in the parison, during his casting. According to the front view A, the section B and the profile view D, each alignment 26-28 of bos- sages subsequently comprises seven alternations, four hollow 321.4 and three bumps 325.7, the hollows being represented in gray on the front view A and the section B. The thickness of the embossed walls 13a-b of the hollow plate 12, seen in section B, is 1 mm and its internal thickness 12c is 2 mm. According to the view A of FIG. 1, each recess and bump is in the form of a four-pitched roof with four oblique, strongly inclined edges and four facets constituted by (1) two symmetrical trapezes 341.2 for the recesses and 361.2 for the bosses. , all with a large base of 40 mm, (2) between the crests of two contiguous bosses, a connecting diamond formed by two isosceles flattened coplanar triangles, respectively referenced 381.2 for the hollows and 401.2 for the bumps, all with a large side 90 mm, (3) a slightly flattened longitudinal ridge 42, between two symmetrical trapezes, for the hollows and 44 for the bumps, these two peaks being 15 mm long, and (4) the same height of 14 mm. The lateral edges 18-20 of the wafer 12 are separated from the large bases of the trapeziums 34-36 by a welded-walled edge 19, 5 mm wide, followed by two connecting ramps 21 with the inside of the wafer. The lateral edges of the corners, the quasi rectangle formed by the wafer 12, are cut to form hooks 23 allowing easy suspension of the wafer. At these four corners, each of the connecting ramps 21 bypasses a flexible external relief 25 of one of the walls of the wafer 12. In a heat exchanger, the gap between two vertices facing these external reliefs 25 is very small. slightly greater than the assembly pitch of the hollow wafers. This improves the mechanical strength of this exchanger. The hollows of this plate 12 are shown in gray.

In each of the trapezoids 34-36, there is a nip 46 for the hollows and 48 for the bumps. These nips 46-48, similar to the central pinch (2 mm wide), almost connect the steep edges of these trapezoids, are parallel to their bases and are located substantially one third of their height, from their large base. In each of the flattened isosceles triangles 38-40 and in the plane diamonds, shared between a hollow and a hump, that these triangles form, are practiced two pinches 50-52, parallel and similar to the preceding ones 46-48. These nips 50-52 connect almost two sides of these triangles and rhombs and they are arranged so as to arrange three substantially equal surfaces. The view C of FIG. 1, along the cross-sectional line CC of two hollow plates 121-122, juxtaposed in a heat exchanger, shows the internal thickness 13c (2 mm) of these plates, the thickness of their walls 13a. -b (1 mm), the nips 48 made in the four trapezoids 36 of two bumps belonging to the two rows 26-28, and the gap 54, 6 mm wide, which separates these two plates 121.2 juxtaposed. According to the view A of FIG. 1, each of the outer collector sections 22-24 of the hollow plate 12 incorporates a pair of circular inserts 58-60 which, after having been welded to the external faces of the walls of this plate, have a final internal diameter of 30 mm. Each pair of inserts is divided into two semi-circular parts, respectively external and internal to the hollow wafer 12. The inner portion has lateral radial ducts 62a-b and central 63a-b. The lateral ducts 62a-b open out in front and along oblique nips 64a-b and 66a-b, arranged in the two connecting zones 68-70 of these sections 22-24 and the isosceles triangular ends 38 of the central zone. embossed hollow plate 12. The central ducts 63a-b open on either side of the central nip 30. According to the profile view D, the recesses 321.4 and alternating bumps 325_7 of a wafer 12 appear on each side of its rectilinear central portion 56, which has at its two ends the inserts 58-60 which form the individual sections 22-24 of the external collectors of this wafer. The thickness of this central portion 56 is 4 mm and that of these collector sections 22-24, 10 mm, the latter thickness being the assembly pitch of the hollow plates 12, stacked in a heat exchanger. Furthermore, the profile view D shows that, from each section of collector, formed by the assembly of the inserts 58-60, spring the overhanging edge 19 of the walls of the plate 12, welded between these inserts.

FIG. 2 shows, at A, a ring insert 58, intended to be assembled in pairs, in order to form an individual section 22-24 of external collector of a hollow wafer 12. Before the introduction of these two pairs of inserts 58 in the jaws of the mold of these hollow wafers, their diameters, external and internal, are 56 and 32 mm. Each insert 58 has a circular central opening 72 and is divided into two semi-circular parts, 74 and 76, respectively external and internal to the hollow wafer 12. The inner semi-circular portion 76 comprises two pairs of radial grooves, lateral 78a b and central 80a-b and three partition walls 82, 84, 86 between these grooves, the central partition 84 having a lug 85 allowing perfect placement of each insert 58 in a jaw of the wafer manufacturing mold. In B, in this figure 2 is shown a sectional view of the insert 58, in which the central opening 72 appears, as well as the lateral groove 78b and the central groove 80b. On the outer face of this insert 58, there appears a circular relief 88, intended to be welded to an identical circular relief of the collector section of the contiguous hollow plate.

During the manufacture of a hollow wafer, the walls of the parison, subjected to the internal pressure of the air blown, marry the internal faces of the jaws of the mold, weld locally between them and the inserts, arrange the internal volume of the wafer and create the internal pinches of the facets of the bosses. These results are obtained by the action of the reliefs, machined on the internal faces of the jaws of the mold.

In Figure 2, is shown (transparent) C, the front view of the end 61 of a large hollow plate, according to the invention, with a different collector section of the previous. In a border 57, formed by the welded walls of the parison, this end 61 is locally clamped between two inserts, welded to the parison. These inserts have an oblong central opening 73, with a similar periphery, comprising two parts, one rounded 75, external to the wafer, and the other, elongated internal 77. This inner portion 77 comprises twelve con-ducts 791.12 of the same section, regularly distributed and separated from each other by eleven partitions 831.11. Eleven oblique pinches 811.11, substantially parallel and equidistant, follow these eleven partitions 831.11 and are arranged in the connection zone of this insert with the central zone of a large hollow plate.

This exchanger 122 is a compact block in the form of a parallelepiped of 12 dm3, having a thermal conductance between water and air of 200 W 1 ° C and 400 W / ° C between water and water. 'water. After crosslinking the polymer used, this heat exchanger can process fluids at high temperatures (150 ° C for HDPE polyethylene and 400 ° C for a polyamide) significantly larger than the melting temperature before crosslinking. Several techniques are available for effecting this crosslinking, in particular ionizing radiation. Thanks to the parallel nips 48-50 formed in the facets of the bosses of the hollow plates, the differential pressure allowed for the heat exchanger 122 having walls 1 mm thick, is about 3 bars, when the polymer used for the parison is loaded with fiberglass or carbon. But these maximum possible values of temperature and differential pressure can not be simultaneous. And compromises will be necessary in each particular case. Under these conditions, the industrial applications of a heat exchanger according to the invention go out. however, particularly extensive: condensation of steam in a distiller, recovery of smoke energy or hot water discharged, cooling of recycled water, heat engines or exhaust gases for the EGR of diesel engines. Indeed, thanks to their relatively thin walls, the hollow polymer wafers according to the invention have a reduced weight, which minimizes the cost of the heat exchangers that incorporate them. In addition, since the polymers used are indifferent to corrosive fluids, the heat exchangers according to the invention are authorized for use in fields hitherto reserved for heat exchangers of titanium or various relatively expensive alloys. In practice, the heat exchangers according to the invention may, for certain particular applications, be assembled in series and in parallel to form assemblies having thermal conductances of several tens or hundreds of kilowatts per degree.

The invention is limited neither to the hollow plates 12 and 92 described nor to the heat exchanger 122 which incorporates them. Indeed, when these hollow wafers have dimensions significantly greater than those of these two wafers, described by way of non-limiting examples, the number of bosses alignments increases, as the number of bosses in each alignment. Moreover, the dimensions of these bosses can be modified as a function of the differential pressures to be borne, and more generally of the specifications of the exchanger to be produced. However, when the platelet dimensions are significantly lower than those of the two pads 12-92 described, the height of these bosses decreases accordingly. On the other hand, when the platelets are small or medium (typically <20 dm2), the internal platelet thickness and / or the distance between two contiguous platelets are small (typically <2 mm), the fluid flows are laminar. and the efficiency of the heat exchange performed is, however, large. On the other hand, when these platelets are large (typically> 50 dm2), these thicknesses and / or these differences can be large (typically> 2 cm). In this case, the Reynolds number, which derives from these dimensions and fluid velocities that pass through the exchanger, is such that the flows are turbulent.

Claims (8)

REVENDICATIONS1. Hollow plate (12 or 92) for a heat exchanger (122) in which - hollow plates are stacked with constant pitch and connected to two external collectors; the walls of these hollow plates comprise an embossed central zone, having one or more alignments (26-28 or 94-96) of alternating bosses, provided with facets (34-36; 38-40; or 100-102; 106) with steep slopes, creating a large number of edges, oriented in oblique directions and / or perpendicular to these alignments; - The thickness (13c) of the gap between the facets facing a hollow wafer is uniform and substantially constant, in the range of the differential pressures allowed; characterized in that: - it is manufactured by extrusion - blowing a polymer parison between the two jaws of a suitable mold; this appropriate mold is adapted (a) to cause the central zones of the two walls of the hollow wafer to be taken, the desired alternating bosses, (b) to give to the embossed central zone of the hollow wafer thus produced an internal thickness as uniform as possible and (c) simultaneously shaping two individual sections (22-24) of external collectors and two connecting areas (68-70) of these sections at the ends of the central area of the wafer. 2. hollow plate (12 or 92) according to claim 1, characterized in that: - the facets of its alternative bosses have the shape of trapeziums (34-36) and isosceles triangles (38-40), assembled to form four-pitched roof-to-slope alignments of hollows and bumps with lightly leveled edges (42); each of these facets comprises at least one rectilinear nip (46-48 and 50-52), parallel to the flow direction of the fluids, for dividing the surfaces of these facets (34-36; 38-40) into at least two parts, so that in a heat exchanger in operation, the maximum deflection of these parts of facets is reduced to a value significantly less than the thickness of the internal channel (13c) or external (54) they delimit; these nips (46-48; 50-52) are constituted by sets of internal reliefs, welded at the moment of closure of the mold around the parison; - two contiguous alignments (26-28) of bosses are separated by a continuous nip (30). 3. hollow wafer (12 or 92) according to claim 2, characterized in that: - in the alignments (26-28) of alternating bosses of the embossed central zone, the end facets are isosceles triangles flattened (381 ), the lateral facets are trapezoids (341) and the connecting facets between the ridges (42) of two bosses are diamonds, - each of these isosceles triangles (381) and each of these bonding lozenges, formed by two coplanar flattened isosceles triangles (382 - 401), comprises two nips (50-52) dividing it into three parts of substantially equal surfaces; - Each trapezium (34-36) comprises a pinch (46-48), located substantially one third of its height, from its large base. 4. hollow wafer (12 or 92) according to claim 2, characterized in that: - in the alignments (94-96) of alternating bosses of the embossed central zone, the end facets are trapeziums (104), the lateral facets are flattened isosceles triangles (100-102) and the connecting facets between the crests of two bosses are hexagons; each of these flattened isosceles triangles (100-102) comprises a pinch (118) located substantially at one-third of its height, starting from its long side; each end trapezium or each connecting hexagon, formed by two coplanar trapezoids (104-106), comprises two nips (114-116) dividing it into three parts of substantially equal surfaces. 5. hollow wafer (12 or 92) according to claim 1, characterized in that: - the two individual sections (22-24) of external collectors of a hollow wafer are constituted by two pairs of polymer inserts (58 or 77-79) incorporated in the ends of the wafer; these inserts are provided with a central opening (72 or 73), with circular or oblong periphery, and with several grooves (78a, b; 80a, b or 791.12) of the same section, arranged in the part (76 or 77) of this periphery directed towards the inside of the wafer (12-92); these two pairs of inserts, previously heated to a temperature slightly lower than their melting temperature, were installed in housings made in the two jaws of the mold and were welded to the hollow wafer, by intimate contact with the melt parison, due to the pressure of the air injected inside; - The ducts, with identical sections, resulting from the parison welded to the walls of the grooves of each pair of inserts, open on passages arranged between equidistant oblique nips, made in a connection area of the central zone of the wafer. one of its two sections of collectors. 6. hollow wafer (12 or 92) according to claim 1, characterized in that the polymer used is loaded with suitable fibers, especially glass or carbon. 35 7. Heat exchanger (90) formed by the stack of a plurality of hollow polymer wafers (12) or (92), according to one or more of the preceding claims, this stack being made by successive welds of the circular edges. (88) individual sections (22-24) of collectors of these plates and by welded additions of two pipettes 13 (124) to the last plate of this exchanger, the collector sections of the first plate of the stack having preserved their manufacturing caps. 8. heat exchanger (90), according to claim 7, having undergone crosslinking, in particular by exposure to ionizing radiation. 15 20 25 30 35