EP2032928B1 - Hollow platelet heat exchangers - Google Patents

Abstract

One of these heat exchangers (76) consists of a stack of thin-metal walled hollow platelets (7S1-J5), 12 cm long and 5 wide. Each of these walls has a central region stiffened by alternating bosses with steep slopes, situated between two connection regions. Each wall is made by pressing then cutting an appropriate sheet of metal (aluminium 0.3 mm thick). The edges of the two fin walls form steps, symmetrically welded, the height of each step determining the internal half-thickness of a fin. Each platelet connection region ends in a narrow mouth with a cross section that has the same surface area as the embossed central region, and is welded to the edges of a slot made in an external manifold (80-82). The thickness of the internal channel of a platelet is about 0.4 mm when the fluid concerned is a liquid (water) and that of the spaces between the platelets is 7 mm when the other fluid is a gas (air). By hot pressing or thermoforming, sheets of glass or polymer may also be used but the performance is not as good. A radiator can be made of several exchangers mounted in parallel on each side of two flat main manifolds. Applications: any heat exchangers with high volumetric conduction, low weight and low pumping and ventilating power.

Description

The invention relates primarily to a heat exchanger, consisting of a stack of hollow plates, which has very high performance, that is to say a very large volume conductance associated with a reduced frontal area, a need for low power mechanical means for the propulsion of the fluids concerned and the possibility of treating liquid and / or gaseous fluids, at differential pressures and relatively high temperatures.

The invention also relates, secondly, heat exchangers similar to the previous, generally less powerful than him but may be better suited to certain particular applications.

Hollow-plate heat exchangers have a much higher performance than full-metal finned heat exchangers. Indeed, for the same volume conductance, in such a liquid / gas heat exchanger, the gap between contiguous hollow plates is much greater than that between full fins. In this way, the weight of the former, their size, their frontal surface and the power consumed (pumping liquid (s) and / or gas ventilation), are significantly lower than those of the latter. And yet, solid metal fin heat exchangers remain of universal use in many fields. Under these conditions, when the heat engines are equipped with usual water / air radiators, the frontal surface (master torque) of these radiators measures about 0.3 dm ² per kW to be evacuated, whereas their implementation consumes a mechanical power ( ventilation and pumping) which equals up to 10% of the thermal power to dissipate, or more if the temperature differences are small. This shows the interest of heat exchangers with hollow plates.

Heat exchangers, constituted by a one-piece stack of hollow wafers made of polymer, glass or metal, are described in the European patent. EP 1 579 163 B1 , granted to TET. The method for producing one of these exchangers is to manufacture, by thermo-blowing a polymer parison, an accordion-shaped blank, provided with biconvex bellows, embossed walls by alternating bosses with steep slopes, then to perform a controlled compression. As a result of this compression, these bellows take the definitive form of a one-piece stack rigid hollow inserts, with a thin internal channel, connected to two internal collectors. Such monobloc polymer heat exchangers provide completely satisfactory results for many applications, as long as the desired volume conductance remains average (at most 20 W / ° C / dm ³ ) and the treated fluids are at moderate differential pressure. (at most 0.1 MPa) and at low temperature (<100 ° C). Indeed, in many particular cases, their advantages of weight, cost, size and power consumed (3 to 5% of the thermal power to be evacuated) largely compensate for these limited performances, especially when the initial temperature difference between the two fluids concerned is relatively low (<60 ° C).

This monobloc heat exchanger, formed of hollow wafers with corrugated walls of polymer, is of multiple interest. Its walls conciliate a certain stiffness and a certain finesse, which are two antinomic characters, so that its weight, its cost, its size are small. Its thin internal channel makes it possible, despite a laminar flow of the coolant, to obtain a good thermal conductance between this liquid and the wall of the hollow wafer. On the other hand, its embossed walls generate a relatively large turbulence in the flow of air between platelets, which makes it possible to substantially increase the distance between them. This considerably reduces the energy required to propel air between these pads. In addition, this significant turbulence of the air circulating between the plates increases the apparent thermal conductivity of this air and therefore the overall thermal conductance of the exchanger.

But experience has shown that this two-step technique, thermo-blow and controlled compression biconvex bellows a polymer blank, stum on limited results, as soon as we seek to increase the level of performance sought and including the volume conductance of the heat exchanger thus produced. Indeed, with this technique, it is impossible to completely control the two-step manufacturing process of a one-piece stack of hollow wafers, as regards the thicknesses of the internal channel and those of the wafer walls, although these thicknesses are determining parameters for the value of the volume conductance of the exchanger. In practice, this results, for the inner channel of the hollow plates, by a thickness having an average value of about two millimeters, with a dispersion of at least thirty percent. For those whom it concerns the thickness of their walls, the average value is of the order of a millimeter and the dispersion of about fifty percent, this dispersion being essentially due to the irregular thinning of the wall during the thermo-blow of the blank .

In addition to this performance limitation attributable to these thickness problems, it should be noted that the presence of internal collectors stacked hollow plates adds another aspect to this limitation: the creation of a central channel, common to all these hollow plates which allows a rapid direct flow of liquid between these two collectors. As a result, this relatively large central channel hardly contributes to the heat exchange sought.

High performance cooling devices for various applications are described in the German application DE 102 18 274 and the published international application WO 2006/010822 , filed by TET. In the known devices of the international application, the radiators are heat exchangers made according to the method of the European patent of TET. For a particular application (the cooling of the exhaust gases of a diesel engine with a view to recycling them), it is provided in this application to use a single-block heat exchanger with metal hollow plates, capable of withstanding a differential pressure. and a temperature much higher than those to which a polymer monobloc exchanger can be subjected. For this purpose, the metal accordion blank of this heat exchanger had to be manufactured by hydroforming. This known technique seems promising in the field of monoblock heat exchangers with hollow metal plates but, for the moment, it has not yet been properly implemented and, in addition, it is itself limited as to its theoretical efficiency. . Indeed, as the thermal resistivity of the cooling liquids, water or oil, is high, the thermal resistance of the liquid layer, in laminar flow in such hollow plates, is inevitably important, given an average thickness of at least 2 mm. This removes a lot of interest in the low thermal resistance that would be provided by the metal walls envisaged.

Consequently, another way of producing metal heat exchangers had to be developed for several particular applications, in particular for the one originally planned and, more generally, for any device involving the availability of very high performance heat exchangers. For this purpose, these new metal exchangers must have weight, bulk, front surface and mechanical power consumed, as small as those of exchangers monoblocks referred to above. And this, while having a much higher volume conductance (at least 100 W / ° C / dm ³ , for example) and, above all, the ability to properly operate at differential pressures and high temperatures, for example 1 MPa and 600 ° C. And, derived from these first metal exchangers, other less efficient polymer or glass are also possible, which relate to specific applications, particularly those using corrosive fluids.

To do this, unlike monoblock metal heat exchangers, initially designed for cooling the exhaust gases of diesel engines, the new heat exchangers, in particular designed for this particular use, must be equipped with metal hollow plates, provided with an internal channel as fine and precise as possible and walls both rigid and very thin. As for the general characteristics of such a heat exchanger, they will obviously be totally different from those of the previous ones. They will be borrowed from a heavy and bulky heat exchange device, developed for the cooling of electrical transformers of distribution networks, described in the patents US 3,153,447 of 1964 and US 3,849,851 of 1974 . This device consists of large hollow-walled metal plates welded to two external collectors, adapted to be vertically arranged and cooled by air circulating by natural convection.

The first object of the invention is a high performance heat exchanger, formed of hollow plates with thin metal walls stiffened by an appropriate embossing, having both weight, compactness and reduced frontal area, low mechanical power consumption and very high volumetric conductance. , while being well adapted to a reliable industrialization easily controllable and, furthermore, capable of treating liquid and / or gaseous fluids, at high temperatures and / or differential pressures.

The second subject of the invention relates to improved heat exchangers, similar to the previous one, which are less efficient than it, but better adapted to particular specific applications, different from those of this previous one, comprising a stack of hollow wafers, with thin polymer walls. or glass, stiffened by an appropriate embossing.

The third object of the invention is a compact radiator with a reduced frontal surface, made from these improved heat exchangers, having a high thermal conductance and requiring very low pumping and ventilation powers.

• des plaquettes métalliques creuses, à canal interne mince, sont empilées à pas constant et raccordées à des collecteurs externes ;
• ces plaquettes comportent une zone centrale gaufrée, située entre deux zones de raccordement dotées d'embouchures étroites à surface sensiblement égale à celle d'une section transversale de la zone centrale ;
• les parois de ces plaquettes ont été réalisées par emboutissage et découpe d'une feuille de métal;
• les bords latéraux des deux parois d'une plaquette creuse sont soudés ;
• l'écart entre les facettes en regard est uniforme, très étroit, exactement connu et pratiquement constant, dans la plage des pressions différentielles prévues ;
• les espaces de séparation des plaquettes sont relativement étroits;

est caractérisé en ce que :

• les parois de chaque plaquette creuse sont à la fois rigides et très fines, leur zone centrale gaufrée présentant une ou plusieurs suites de bossages alternatifs alignés, dotés de facettes écrouies à fortes pentes, créant un nombre important d'arêtes vives, orientées dans des directions obliques ou perpendiculaires à l'alignement des bossages.

According to the invention, a heat exchanger with reduced weight and space requirement and with a very high volume conductance, suitable for treating fluids with high differential pressures and high temperatures, in which:

• thin-channel, hollow metal plates are stacked at constant pitch and connected to external collectors;
• these plates comprise a central embossed area, located between two connection areas with narrow mouths with a surface substantially equal to that of a cross section of the central zone;
• the walls of these plates were made by stamping and cutting a sheet of metal;
• the lateral edges of the two walls of a hollow plate are welded;
• the gap between the opposing facets is uniform, very narrow, exactly known and practically constant, in the range of expected differential pressures;
• the separation spaces of the platelets are relatively narrow;

is characterized in that

• the walls of each hollow wafer are both rigid and very thin, their embossed central zone having one or more aligned alternating bosses series, with hardened facets with steep slopes, creating a large number of sharp edges, oriented in directions oblique or perpendicular to the alignment of the bosses.

Before commenting on the interest of these new provisions, it should be noted that in the US patents concerned, the thickness of the walls of the plates does not need to be thin and their rigidity is not a particular problem, so that the embossing of the central zone of these walls is not the solution to a problem of stiffness which, in this case, practically does not exist. Indeed, an adequate thickness of walls made of a conventional metal provides without difficulty. It is only a question of increasing the heat exchange surface of the plates without increasing their dimensions. This is done by longitudinal undulations that result from relatively small depressions, made at constant pitch in the walls. The particular profile of these ripples is represented: it is commonplace and can hardly be characterized by any originality, this aspect of things having no interest in this type of exchangers. On the other hand, because of these corrugations, the internal channel of the hollow plates has an undulating thickness which varies symmetrically about a relatively large average value. And the walls of this internal channel do not have facets sloping facing.

According to the first provision of the invention, it is first of all very thin-walled plates (for example, 0.15 mm for some steels) to which their hardening, obtained "as a bonus" on the occasion of a standard stamping (cold), gives a hardness and an elastic limit particularly large: each facet of these hollows and bumps acts as a stiff lamella and, in addition, each sharp edge behaves like a beam in which these lamellae are recessed. These slats can therefore take only a very limited arrow, under the action of differential pressures applied. In particular, when the overpressure is external, this arrow always remains substantially less than half the internal thickness of the hollow plates, which thickness, measured between the facets of the bosses, is by construction exactly known and particularly reduced (0.3 mm, for example). This avoids any contact between opposite facet walls so that the heat exchange function between the two fluids is always correctly ensured.

Under these conditions, each hollow bossed plate according to the invention owes its remarkable primary stiffness to the fact that the metal constituting its walls is hardened and that, in addition, its alternating bosses significantly increase the moment of inertia. These very thin doubly stiff strips are then able to perfectly play a role of effective heat exchanger between the two fluids that circulate along their two faces, even if there is a high differential pressure between these fluids. The immediate characteristics of these embossed alternating bosses, which must ensure this stiffness, define the base of the invention. They result in hardened facets with steep slopes, generated by significant local elongations of the initial flat sheet, which thus create many very thin and very stiff slats, all edges of which are embedded in beams constituted by the sharp edges of the bosses. .

The sharp edges of the dihedrons, formed between them by these strongly sloping facets, have a second known effect, that of increasing the thermal conductivity. Apparent air: obliquely and / or perpendicularly perpendicular to the direction of flow of this air, the effect of which is to cause significant turbulence in the generally high velocity air currents passing through the relatively narrow spaces platelet separation. This provision would make no sense in the case of the vertically arranged corrugated plates of the US patents concerned, whose separation spaces to unspecified dimensions are traversed by slow air currents circulating by natural convection.

If now, to conclude this argument, we refer to the European patent of TET, we can note that all the causes of the performance limitations listed above are removed in this new heat exchanger and replaced by their opposites: the walls and the internal channel have very fine, precise, well known thicknesses and, as will be specified below, the central channel may disappear. On the other hand, all the positive-effect characteristics relating to the embossed walls of the hollow plates of the monobloc polymer heat exchanger described in this European patent are maintained. To these characteristics, are added those resulting from the hardening of the metal sheets used. And thanks to their combination with the advantages of the exchanger described in the US patents and the use (a priori badly come, in the context of the high differential pressures provided) of very thin walls and the creation of a internal channel particularly narrow, a new and unobvious heat exchanger is realized. And this new exchanger has consequently a performance that transcends very strongly those already very efficient monobloc heat exchangers polymer, according to the European patent TET.

• chaque plaquette creuse comporte au moins deux alignements de bossages alternatifs ;
• deux alignements contigus sont séparés par une cloison rectiligne étroite, formée par deux reliefs internes emboutis, assemblés par soudure;
• la hauteur de ces reliefs égale à la moitié de la valeur de l'épaisseur interne des plaquettes, au niveau des crêtes de leurs bossages.

According to particular characteristics, complementary to the main characteristics above,

• each hollow wafer has at least two alignments of alternating bosses;
• two contiguous alignments are separated by a narrow rectilinear partition, formed by two embossed internal reliefs, assembled by welding;
• the height of these reliefs equal to half the value of the internal thickness of the plates, at the level of the peaks of their bosses.

With these latter provisions, taken from a possibility provided in the US patents concerned to improve the rigidity of the plates when they are large (m ² ), two particularly interesting results are obtained for the heat exchanger according to the invention. Firstly, under the action of a relatively high internal overpressure, applied to the hollow plates of such a heat exchanger, the internal rectilinear partition maintains the internal thickness of the embossed central zones at a value practically independent of the differential pressure. suffered by thin walls of platelets. This has the result of allowing these hollow plates, with very thin walls stiffened by an appropriate embossing, to withstand without damage a relatively high internal pressure. In fact, in the absence of such welded internal reliefs, the contiguous alignments of alternating bosses with high stiffness would be separated by a flexible hinge zone. In response to such an overpressure, this would cause a slight swelling of the wafers causing a significant decrease in heat exchange in their separation spaces or even a rapid deterioration of these wafers. However, thanks to such a partition formed by these two welded internal reliefs, it is not necessary to systematically increase the thickness of the very thin walls of the hollow plates to be able to cope with a high transient internal pressure. This allows for lighter and less expensive heat exchangers.

The second advantage of these welded internal reliefs results in a greater efficiency of the heat exchange sought. In fact, this internal partition thus formed between two contiguous alignments of alternating bosses constitutes a barrier for the flow of liquid entering the hollow wafer. Each barrier has the first effect of preventing a large direct flow between the two external collectors, along a smooth wall of small area and therefore not very effective for the desired heat exchange, especially since this surface is not swept by a strong current of air since it is in the wake of the upstream collector. On the other hand, this barrier has the second effect of directing the incoming current towards the two alignments of alternating bosses with high heat exchange efficiency and thus maximizing the heat exchange effected.

Note that these two advantages are of little interest for the heat exchanger with large hollow plates, relatively thick walls, described in the US patents concerned. Indeed, in this exchanger, the maximum differential pressure, which appears at the foot of the large vertical plates, is the relatively low hydrostatic pressure generated by the cooling oil. What does not concern the heat exchanger according to the invention, which can obviously be installed in any interesting position and especially be able to operate with very high differential pressures. In addition, as this oil flows from top to bottom by natural convection in hollow plates much wider than the external collectors, its low upstream dynamic pressure, due to a reduced speed of circulation, it avoids much can privilege a rapid direct course from one collector to another.

• les angles formés par les normales à deux facettes adjacentes des bossages alternatifs mesurent au moins 30°, pour que les arêtes vives de ces facettes puissent être efficaces dans la création de turbulences et être assimilables à des poutrelles dans lesquelles sont encastrées les facettes de ces bossages;
• l'angle maximal des normales à deux facettes adjacentes est limité par les restrictions imposées aux conditions d'emboutissage de la feuille de métal concernée.

According to complementary features of the preceding ones:

• the angles formed by the normal two adjacent facets of the alternating bosses measure at least 30 °, so that the sharp edges of these facets can be effective in creating turbulence and be comparable to beams in which are embedded the facets of these bosses ;
• the maximum angle of the adjacent two-facet normals is limited by the restrictions imposed on the drawing conditions of the metal foil concerned.

According to a complementary feature of the preceding, the facets facing a wafer have parallel walls and the gap separating these walls is constant and of the same order of magnitude as their thickness.

• les bossages alternatifs ont, en propre, deux facettes en forme de trapèze isocèle, possédant une arête longitudinale commune, et, en partage, deux facettes en forme de losange ;
• la grande diagonale des facettes en losange peut mesurer quelques dizaines de fois l'épaisseur de la paroi des plaquettes.

According to complementary features of the preceding ones:

• the alternating bosses have, in their own right, two isosceles trapezoid-shaped facets, having a common longitudinal edge, and, in sharing, two diamond-shaped facets;
• the large diagonal diamond facets can measure a few tens of times the thickness of the wall of platelets.

• les bossages alternatifs ont, en propre, deux facettes en forme de triangle et, en partage, deux facettes en forme d'hexagone, possédant une arête transversale commune ;
• l'écart entre les arêtes transversales des facettes en hexagone peut mesurer quelques dizaines de fois l'épaisseur de la paroi des plaquettes.

According to alternative characteristics to the previous ones:

• the alternating bosses have, in their own right, two facets in the form of a triangle and, in sharing, two facets in the shape of a hexagon, having a common transverse edge;
• the difference between the transverse edges of the facets in hexagon can measure a few tens of times the thickness of the wall of the platelets.

According to a complementary feature of the previous ones, the embossed central zone of each hollow plate is connected to the external collectors by two connection zones provided with lateral edges having a high obliquity and smooth walls comprising portions of conical frustums.

According to a complementary feature of the previous ones, the external collectors have an aerodynamic profile adapted to minimize their drag.

According to a possible complementary feature of the preceding, symmetrical bosses facets appear as cut diamonds and have several secondary facets, with complementary sharp edges.

Thanks to these different arrangements, the volume conductance of the heat exchanger thus produced is particularly high. And this, for several reasons: (1) platelets have metal walls that have negligible thermal resistance, (2) the thermal resistance of the very thin layer of water or oil inside these platelets is low , despite the laminar flow of this layer and the relatively high thermal resistivity of these liquids and (3) the turbulence and the apparent thermal conductivity of the air, which flows between the platelets, increase with the height of the bosses and the total number sharp edges they contain. With at least two alignments each comprising some alternative bosses, with facets inclined at approximately 45 °, an effective compromise is made between the various parameters concerned. Indeed, embossing bosses whose slope facets is less than about 50 ° is a standard operation that poses no problem of realization and a minimum angle of 30 ° between the normal two adjacent facets ensures a good turbulence in the flow of air and a minimum width for each of the alignments of the bosses in the central area of the pads, since the height of these hollows and bumps is fixed. In addition, a minimum angle of 30 ° between the adjacent two-faceted normals gives the edge concerned sufficient stiffness to be comparable to a beam, all of these edges being then comparable to a trellis of beams. .

In addition, with a heat exchanger formed by the stack of a large number of such identical plates, connected to two external collectors, it is possible to considerably reduce the pressure losses of a liquid circulating at constant flow and in laminar flow, which can, if necessary, be relatively fast. In any case, such a stack significantly reduces the power required to pump this liquid. And, in addition to the use of aerodynamic external collectors, despite the relatively large gap separating the plates, their largest dimension, installed parallel to the flow velocity of the two fluids that intersect, significantly reduces the aerodynamic drag of the radiator and / or the power required for its ventilation.

With regard to the metals used for the manufacture of the walls of the hollow wafers according to the invention, it should be noted that they are not very numerous but well known to the stamping specialists and that finally the choice (aluminum or steel, for example) example) will be primarily determined by the mechanical behavior of these metals in the operating temperature range of the heat exchangers that will incorporate these platelets.

1. 1) emboutissage et découpe de parois identiques de plaquettes dans une feuille métallique fine ;
2. 2) retournement tête-bêche d'une paroi ;
3. 3) assemblage de deux parois conjuguées, par soudure de leurs rebords latéraux et des reliefs de leur cloison centrale interne,
4. 4) montage et fixation par soudure de ces plaquettes creuses sur leurs deux collecteurs externes.

Thanks to these various provisions, the industrial manufacture of very high performance heat exchangers, according to the invention, comprises a set of operations perfectly controllable and relatively easy to automate, which leads to an interesting cost price for the mass production of these exchangers. Indeed, these operations are as follows:

1. 1) stamping and cutting identical walls of platelets in a thin metal sheet;
2. 2) turning head to tail of a wall;
3. 3) assembly of two conjugate walls, by welding their lateral edges and reliefs of their internal central partition,
4. 4) mounting and fixing by welding of these hollow plates on their two external collectors.

• il comprend deux groupes identiques d'échangeurs thermiques métalliques à plaquettes creuses, associés à deux collecteurs principaux amont et aval, à épaisseur réduite, dotés de faces planes en forme de trapèzes rectangles, légèrement écartés l'un de l'autre et disposés de manière que leurs coins carrés soient opposés;
• les collecteurs individuels amont et aval des échangeurs de chaque groupe sont respectivement raccordés, à intervalle constant peu supérieur à la largeur de la zone centrale des échangeurs, aux deux faces de ces deux collecteurs principaux amont et aval.

According to the invention, a compact radiator with a very high volume conductance is characterized in that:

• it comprises two identical groups of metal heat exchangers with hollow plates, associated with two main heads upstream and downstream, reduced thickness, with flat faces in the form of trapezoid rectangles, slightly spaced apart from each other and arranged so that their square corners are opposite;
• the individual headers upstream and downstream of the exchangers of each group are respectively connected, at a constant interval little greater than the width of the central zone of the exchangers, to the two faces of these two main headstream upstream and downstream collectors.

Thanks to these arrangements, it is possible to construct a radiator with a very high volume conductance which has a master torque as low as possible (up to 0.10 dm ² per cubic meter). kW to evacuate). It is indeed possible to easily assemble on either side of the two flat head collectors, a large number of heat exchangers themselves formed by a large number of metal hollow plates stacked according to the invention. This compact radiator also requires particularly low pumping and ventilating powers, about five times lower than the powers required by solid finned radiators having the same thermal conductance.

• la figure 1 est une vue de dessus d'une première paroi gaufrée de plaquette creuse selon l'invention ;
• la figure 2A est une vue de dessus d'une seconde paroi gaufrée de plaquette creuse selon l'invention et les figures 2B et 2C, des vues de facettes particulières de cette paroi ;
• la figure 3 est une section longitudinale des bossages alternatifs de cette première paroi;
• la figure 4 est une section longitudinale d'une extrémité de plaquette creuse, soudée à un collecteur ;
• la figure 5 est une perspective cavalière d'un échangeur thermique à quinze plaquettes creuses ;
• la figure 6 est une vue de dessus d'un radiateur, selon l'invention, construit au moyen de ces échangeurs thermiques.

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:

• the figure 1 is a top view of a first embossed hollow plate wall according to the invention;
• the Figure 2A is a top view of a second embossed wall of hollow wafer according to the invention and the Figures 2B and 2C views of particular facets of this wall;
• the figure 3 is a longitudinal section of the alternative bosses of this first wall;
• the figure 4 is a longitudinal section of a hollow wafer end, welded to a collector;
• the figure 5 is a cavalier perspective of a heat exchanger with fifteen hollow plates;
• the figure 6 is a top view of a radiator, according to the invention, constructed by means of these heat exchangers.

According to figure 1 , there is shown a first embodiment of a thin metal wall 10 of a hollow wafer. This wall has been stamped and then cut so as to have a central embossed zone 13, disposed between two connection zones. By way of example, this wall is made of aluminum and has a thickness of 0.3 mm and its embossed central zone is 60 mm wide and 76 mm long. This central zone 13 is formed by two identical, contiguous alignments 12 and 14 of alternating bosses, separated by a narrow rectilinear zone 16, 4 mm wide. The two connection areas 18 and 20 have smooth walls. Each alignment comprises two identical alternating bosses, formed of bumps and valleys, that is, for the alignments 12-14, four bumps 22 _1-2 and 24 _1-2 , on the one hand, and four recesses 22 ' _1-2 and 24 ' _1-2 , on the other hand, the latter being represented in gray. Each bump 22 _1-2 -24 _1-2 or each recess 22 ' _1-2 -24' _1-2 has the form of a roof with four slopes having four sharp edges steeply inclined, or for each alternating boss of the alignment 12: (1) own, two symmetrical trapezoids 26 _{1 -2} and 28 _1-2 for the bumps, and 26 ' _1-2 and 28' _1-2 for the hollows, all with a large base of 19 mm, (2) shared with the adjoining boss of the same alignment, two isosceles triangles _1-2 and 32 _1-2 for the bumps, and 30 ' _1-2 and 32' _1-2 for the depressions, all with a base of 28 mm, (3) a longitudinal crest 34 _1-2 for the bumps and 34 ' _1-2 for the hollows, all 5 mm long, and (4) the same height of 5 mm. It will be noted that the two pairs of isosceles triangles 30 ₂ -30 ' ₁ and 30' ₂ -32 ₁ of the alignment 12 (and likewise at 14), which belong to two consecutive alternations of the alternating boss, form two plane diamonds.

In the center of the narrow rectilinear zone 16, which divides in two the embossed central zone 13 of the wall 10 shown, is made by stamping an internal relief 36 of 2 mm wide, with symmetrical flanks as steep as the laser technology allows. stamping. Such a relief 36 has a height equal to half of the maximum distance separating the ridges of the bosses of the two walls of the formed hollow plate (ie 0.2 mm, as will be specified below). Two lines 38-40 separate the parallel outer edges of the two alternate boss lobes 12-14 from a hollow wafer wall, the pair of parallel outer flanges 42-44, which form a part of the two-wall joint plane. wafer. The lines 38-40 and the flanges 42-44 are 1 mm wide and form a small step of 0.2 mm high, which determines half of the internal thickness of a plate at the peaks of its bosses. These two flat lines 38-40 end at the two flat portions 46-48 of the two connection areas 18-20 of the wall 10 and these two parallel flanges 42-44 end with the two pairs of oblique outer flanges 50 ₁ -50 ₂ and 52 ₁ -52 ₂ of these same connection areas; they form the other part of the joint plane of the walls of the wafer. Each flange 50 ₁ - ₂ or 52 ₁ - ₂ forms an angle of 60 ° with the longitudinal line of symmetry of the wall 10. The end of each connection zone 18-20 comprises a portion of almost flat truncated cone 54- 56, 87.5 ° half-angle at the top. This frustoconical portion is delimited by two pairs of circular arcs 58 ₁ - ₂ and 60 ₁ - ₂ , the latter pair being 8 mm long. And their ends are connected to each other by two steps of 1.5 mm high, so that the surface of each of the mouths upstream or downstream, thus arranged for a hollow plate, measure 24 mm ² , substantially the cross-sectional area of the inner space of the embossed central zone 13 of the wafer.

According to Figure 2A , is shown a thin metal wall 11, stamped then cut, which constitutes a second embodiment of a hollow wafer wall according to the invention. This wall 11 differs from the previous wall 10 only by its embossed central zone, which has only one alignment of bosses 15 wide by 26 mm, and by the shape of its alternating bosses. This unique alignment comprises three bumps 22b _1-3 and three recesses 22'b _1-3 , the latter being represented in gray. Each boss 22b _1-3 and each recess 22'b _1-3 has the shape of a roof with four steeply inclined slopes. For the three alternative bosses of the alignment 15 this gives for each: (1) in one's own, pairs of symmetrical lateral triangles 25b _1-2 , 27b _1-2 , 29b _1-2 for the bumps, and likewise 25 ' b _1-2 , 27'b _1-2 , 29'b _1-2 for the hollows, all with a large base of 14 mm, and (2) shared with the contiguous boss, central hexagons 31 _1-5 , all with a transverse ridge 18 mm long, and the same height of 5 mm.

According to Figures 2B and 2C , are represented, as variants of the facets of the bosses of the figures 1 and 2A , two of the main facets of the Figure 2A presenting secondary facets. The Figure 2B has a lateral triangle facet 25, having three secondary facets 37 _1-3 forming a relatively flat trihedron with three sharp edges, provided with a diamond tip 39, located at the center of gravity of this triangle. The Figure 2C has a longitudinal facet in hexagon 31, having six triangles with coplanar sides 41 _1-6 , provided with a central diamond tip 43 _1-6 , similar to that 39 of the Figure 2B . The height of these tips is determined by the limitations of stamping technology of metal sheets.

The figures 1 and 2A illustrate two possible forms that can take the bosses of the embossed walls of the hollow plates according to the invention. And the Figures 2B and 2C illustrate the possible variants that the main facets of these bosses can experience, in order to improve their ability to produce turbulence in the air currents between platelets.

The figure 3 represents an enlargement of a longitudinal section along an axis AA '(see fig.1 ) of one end of a portion of a hollow wafer before it is connected to a collector. This wafer is the result of the welding of the two walls 10a and 10b, this wall 10b being the wall 10a turned upside down, about the transverse axis of symmetry BB '(see fig.1 ). This AA 'cut is made along the crests 35 ₂ and 35 ' ₂ of the alternating boss formed by the boss 24 ₂ and the hollow 24' ₂ of the alignment 14 and it passes through the connection zone 18 of the wall 10a of this wafer. The figure 4 represents an enlargement of a section of this same end of plate, carried out along the longitudinal line of symmetry CC '(see fig.1 ) alignments 12 and 14 of alternating bosses and connection areas 18 and 20 of the wall 10a.

On the figure 3 , the bumps and depressions of the first embodiment of the lower wall 10b and the upper wall 10a of a plate are reversed, so that the references 24 ₂ and 24 ' ₂ of the top wall 10a, seen in profile on this figure 3 , respectively appear as a hollow and a bump. In this hollow is nested the boss 24 ' ₁ and in this bump, the hollow 24 ₁ of the wall 10b defined above. The thickness of the portion 62 of the internal channel of a hollow wafer, located between the nested crests 34 ₁ -35 ' ₂ or 34' ₁ -35 ₂ of the embossed zone of this wafer, is 0.4 mm and that of the portion 64 of this internal channel, located between the slopes at 45 ° of the rising or falling flanks of these bosses, is 0.28 mm. The thickness of the inner channel 66, between the planar portions of the connection areas 18 and 20, is 0.4 mm.

According to figure 3 , the right part of the section along the line AA 'represents (1) the beginning 68 of the progressive separation of the walls of the two conical sections opposite 54-56 of the walls 10a-10b, which terminate these two connection zones (2) the two symmetrical steps of these walls which start with the circles 58 ₂ and 58 ₁ and (3) the two symmetrical external flanges 52 ₂ and 50 ₁ which define the joint plane of the walls 10a and 10b.

According to figure 4 , the section shown is made along the longitudinal axis of symmetry CC 'of a hollow wafer end engaged and welded by a weld bead 70, in the edges and ends of a slot 72, in the form of 120 ° arc of circle formed in the connecting shell 74 of an external collector 75, formed by two elongate shells, welded to one another. The section shown shows two parallel sections 16a and 16b of the narrow central zones of the walls 10a and 10b, separated by a gap 66 of 0.4 mm and two other divergent sections 54 and 56 corresponding to the conical sections facing the connecting zones of the two walls 10a and 10b of the hollow wafer. The difference between the extreme edges of these two divergent sections is 3 mm and the length of arches 60 ₂ and 60 ₁ (see fig.1 ) of 120 °, 8 mm. In this way, the extent of the straight sections of the internal channel with embossed walls and that of the openings of the ends of the fin are substantially equal.

According to figure 5 , an elemental heat exchanger 76 is shown which comprises fifteen thin hollow metal fins 78 _1-15 with embossed walls. The ends of these hollow plates are engaged and welded as indicated above in slots with circular edges, having 3.5 mm wide and a pitch of 8 mm, made in the walls of the external collectors 80-82, aerodynamic profile. To allow the easy realization of such welds, the collectors 80-82 are constituted by two elongate shells, with a U-shaped cross-section, welded to one another along a line 83. They are made from metal strips cut from sheets identical to those used for the manufacture of the stamped walls of the wafers. Slots of width, length and not suitable are practiced in half of these strips, then the two types of strips thus prepared are transformed into frontal closing and connecting shells 75, by means of two conjugated templates, with raised profiles and hollow. Then, the mouths of the various hollow plates are welded to the slots of the connecting shells. Then, two frontal closure shells are in turn welded to the two previous ones and one of their ends is closed, to constitute both the two profiled external collectors and the exchanger itself.

According to figure 6 is shown the top view of a compact radiator 81. On either side of two flat head collectors 84-86, shaped trapezoidal rectangles arranged upside down, can be connected in parallel six identical heat exchangers 76 _{1 -6} , so as to constitute a compact radiator with appropriate overall thermal conductance. These flat collectors 84-86 have parallel sides 88 _1-2 and 90 _1-2 and a thickness substantially equal to the maximum dimension of the straight sections of the external collectors 80 _1-2 . Two adjacent exchangers are mounted so that the side edges of their pads are substantially contiguous or slightly interposed. In the first case, the feet of the upstream 80 1 _-6 and downstream 82 _1-6 external manifolds are engaged to the same depth in appropriate circular openings, 94 _1-6 and 96 _1-6 , at constant intervals along the 92-93 long sides of the main headers 84-86 and then they are welded. In the second case, the sink depths of the collectors are different for the even and odd-numbered exchangers. The length of the largest 88 ₂ - 90 ₂ of the parallel sides of the two main manifolds 84-86 is determined by the number of heat exchangers 76 to be mounted. The short sides of the two main manifolds 84-86 have lengths determined by the spacing of the outer collectors 80-82 and by the gap 100 (typically 5 mm) which separates their oblique sides.

Such an assembly of heat exchangers formed by stacks of thin hollow metal plates with very thin walls stiffened by embossing makes it possible to form a compact radiator which is particularly useful for cooling high power thermal engines (> 100 kW). They have in fact a very low torque master, a very high thermal conductance, reduced pumping and ventilation powers, limited space and weight. It is also suitable for the treatment of exhaust gases of diesel engines, used cooled to improve the low-speed operation of these engines. More generally, any heat exchange between two fluids, in particular between a liquid and a gas, having a high temperature and / or differential pressure (up to about 600 ° C. and 1 MPa) can be effectively achieved by means of such a device. compact metal set.

The invention is not limited to the examples described. The length and width of the hollow wafers may be significantly larger than those illustrated in FIG. figure 1 and measure several decimetres. It is the same for the number of alternative bosses in each alignment and the number of alignments in each plate. The maximum dimensions of a wafer are in practice determined by those of the plate of the stamping press available. As for the number of hollow plates in a heat exchanger, it can go up to a few tens. It is the same for the total number of exchangers assembled in a compact radiator.

Note also that it is possible to manufacture a hollow wafer according to the invention using two similar embossed walls similar but not identical because of their different side edges. Instead of two identical walls, with side edges with a small step defining the half thickness of the inner channel of the central zone, there will be a wall whose edges have a step twice as high as the previous one and another wall without any step . This will require the use of two different pairs of stamping molds but will be of little economic importance when production is important.

The figures above illustrate hollow plates for liquid / gas heat exchanger. And, in these metal plates, with a very narrow internal channel (0.3 mm), the liquid flows. In the case of a gas / gas heat exchanger, the thickness of this internal channel is obviously much larger (typically> 1 mm) and the gap between platelets is generally reduced compared to that of the exchanger shown. This is so that the mass flow rates and velocities of the two gases are comparable on each side of the walls of the hollow plates.

Moreover, for particular applications, particularly in chemistry and in any field where corrosive fluids are concerned, it is often desirable and sometimes necessary to have glass heat exchangers with high performance and better than any other, perfectly adapted to their conditions of use. For this purpose, these glass heat exchangers will have high volumetric conductances, but however halfway to those indicated above for hollow-plate exchangers either monoblock polymer or metal of the type according to the invention (20 or 100 W / ° C / dm ³ ). With regard to the maximum temperatures and differential pressures that may be applied to these glass heat exchangers, they will be lower than those that support the metal heat exchangers according to the present invention and higher than those for the polymer monoblock exchangers according to the patent TET. For this type of application, it may also be advantageous to have polymer heat exchangers having a volume conductance of about 50% greater than that of these monobloc exchangers, while maintaining their ranges of differential pressures and temperatures. .

To do this, we can adopt and adapt the new technology of metal heat exchangers according to the invention and, instead of a metal sheet, simply use a glass sheet or polymer and treat it by hot stamping or by thermoforming. The manufacturing processes used in these two techniques for shaping a sheet are close to one another: the first uses a mechanical pressure and two conjugate molds comprising recesses and / or reliefs, and the second, a pneumatic pressure and a single mold with recesses and / or reliefs; And both use proper heating. But, no hardening is produced.

The thicknesses of the walls and internal channels of such a heat exchanger with hollow wafers of glass or polymer, embossed walls and external collectors, will inevitably be increased, in agreement with the mechanical characteristics particular types of glass or polymer used. Their performance derives directly from this, as explained above.

Claims (11)

1. Heat exchanger (76) with low weight and high bulk conductance, capable of handling fluids at high differential pressure and temperatures, in which:

   - hollow metal plates (78_1-15), with a narrow internal channel, are stacked evenly spaced and connected to external manifolds (80-82);

   - these plates comprise an embossed central zone (13), located between two connecting zones (18-20) provided with narrow openings (60_1-2) with a surface area approximately equal to the area of a cross-section of the central zone;

   - the walls of these plates (78) have been produced by stamping and cutting a metal sheet;

   - the lateral edges (42-44) of the two walls (10-11) of a hollow plate (78) are welded;

   - the gap (64-66) between opposite faces is uniform, very small, exactly known and practically constant, in the range of the envisaged differential pressures;

   - the gaps separating the plates (78_1-15) are relatively narrow,

   characterised in that:

   - the walls (10-11) of each hollow plate (78_1-15) are both rigid and very thin, their embossed central zone (13) having one or more sets (12-14) of aligned alternating bosses (22-22' and 24-24'), provided with steep strain hardened faces (24, 26, 28, 30), creating a large number of sharp edges, orientated obliquely and/or perpendicularly to the alignment of the bosses.
2. Heat exchanger, in which

   - it is made up of glass or polymer hollow plates (78_1-15), with a thin internal channel, stacked with constant spacing and connected to external manifolds (80-82);

   - the walls of these hollow plates (78) have been produced by hot stamping or thermoforming and then cutting from a sheet of glass or polymer;

   - these plates (78) comprise an embossed central zone (13), located between two connecting zones (18, 20) provided with narrow openings (60_1-2) with an area approximately equal to the area of a transverse cross-section of the central zone;

   - the lateral edges (42, 44) of the two walls (10, 11) of a hollow plate (78) are welded;

   - the gap (64, 66) between opposite faces is uniform, small, exactly known and practically constant, in the range of the envisaged differential pressures;

   - the gaps separating the plates (78)are relatively narrow:

   characterised in that:

   - the central zone of the plates has one or more sets (12, 14) of aligned alternating bosses (22, 22' and 24, 24'), provided with steep faces (24, 26, 28, 30), creating a large number of sharp edges, orientated obliquely or perpendicularly to the alignment of the bosses.
3. Heat exchanger according to claim 1 or 2, characterised in that:

   - each hollow plate (78) comprises at least two rows (12-14) of alternating bosses;

   - two adjacent rows are separated by a narrow, straight partition (36), formed by two internal stamped or thermoformed protrusions, assembled by welding;

   - the height of these protrusions is equal to half of the maximum value of the internal thickness of these hollow plates.
4. Heat exchanger according to claim 1 or 2, characterised in that:

   - the angles formed by the normals to two adjacent faces of the alternating bosses measure at least 30°, so that the sharp edges of these faces can be effective in the creation of turbulence and in withstanding the pressure differences between the fluids;

   - the maximum angle of the normals to two adjacent faces is limited by the restrictions imposed on the conditions under which the material in question is stamped or thermoformed.
5. Heat exchanger according to claim 1 or 2, characterised in that:

   - the alternating bosses have, of their own, two lateral faces in the form of an isosceles trapezium (26_1-2, 26'_1-2), having a common longitudinal edge (34₁, 34'₁) and, shared, two central rhomboid faces (30₂-30'₁);

   - the long diagonal of the rhomboid faces can measure several tens of times the thickness of the wall of the plates:
6. Heat exchanger according to claim 1 or 2, characterised in that:

   - the alternating bosses have, of their own, two lateral faces in the form of an isosceles triangle (25b_1-2, 27b_1-2 and 29b_1-2) for the bosses and (25'b_1-2, 27'b_1-2 and 29'b_1-2) for the hollows and, shared, two central hexagonal faces for the bosses (22b_1-3) and for the hollows (22'b_1-3), these hexagonal faces having a common transverse edge;

   - the gap between the transverse edges of the hexagonal faces can measure several tens of times the thickness of the wall of the plates.
7. Heat exchanger according to claim 1 or 2, characterised in that the embossed central zone (13) of each hollow plate is connected to the external manifolds by two connecting zones (18-20) provided with lateral edges having a significant slant and smooth walls comprising portions of truncated cones (54-56).
8. Heat exchanger according to claim 1 or 2, characterised in that the opposite faces of a hollow plate have parallel walls and the gap (64) separating these walls is constant and of the same order of magnitude as their thickness.
9. Heat exchanger according to claim 1 or 2, characterised in that symmetrical boss faces appear to be cut in a diamond pattern (25-31) and comprise several secondary faces (37_1-3 -41_1-5) and are provided with complementary sharp edges.
10. Heat exchanger according to claim 1 or 2, characterised in that:

    - the external manifolds (80-82) of the hollow plates have an aerodynamic profile capable of minimising the drag of the exchanger;

    - each manifold is made up of two elongated shells, one (75) for connection to the plates and the other for front closure, their transverse cross-section is U-shaped and they are fixed to each other by a weld line (83).
11. Compact, light radiator with high or very high thermal conductivity, characterised in that:

    - it comprises two identical groups of heat exchangers (76) with hollow plates (78_1-15) made from metal, glass or polymer, according to claim 5,

    - these two groups are associated with two thin main upstream (84) and downstream (86) manifolds, provided with flat rectangular trapezoid surfaces, slightly separate from each other (100) and arranged so that their square corners are opposite each other;

    - the individual upstream (82_1-6) and downstream (80_1-6) manifolds of the exchangers in each group are connected respectively, at constant intervals slightly larger than the width of the central zone (13) of the exchangers, to two homologous surfaces of the two main upstream and downstream manifolds.

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