EP1579163A1

EP1579163A1 - Heat exchanger, methods and means for making same

Info

Publication number: EP1579163A1
Application number: EP03813175A
Authority: EP
Inventors: Jean-Paul Domen
Original assignee: Technologies de l'Echange Thermique
Current assignee: Technologies de l'Echange Thermique
Priority date: 2002-12-13
Filing date: 2003-12-12
Publication date: 2005-09-28
Anticipated expiration: 2023-12-12
Also published as: ATE356328T1; DE60312386D1; FR2848653B1; MXPA05006251A; EA007134B1; FR2848653A1; BR0316761A; JP2006509637A; ES2283880T3; EA200500971A1; AU2003300586B2; CA2509777A1; DE60312386T2; CN1720422A; KR20050085611A; WO2004055462B1; AU2003300586A1; WO2004055462A1; CN100575851C; EP1579163B1

Abstract

The cross section of the single extended piece is shaped like a fish spine, with oblique hollow fishbones (12-14), forming parallel symmetrical pairs from a common central channel (16). The internal thickness of the fishbones is very small, as is the space between them and the thickness of the central channel. Each symmetrical pair of longitudinal fishbones forms one modular pipe of the piece The common central channel is in all the planes of symmetry of the stack of longitudinal fishbones in the piece. These symmetrical pairs contain rectilinear central elements to connect the ends together by two hollow connectors each formed from two returnable surfaces. The axes of the stack of connectors are the same as those for the two feed collectors for each modular pipe and one end of each collector ends by one of the two connection pipes of the piece. Outline of a modular heat exchanger as described above, with a stack of biconvex vents like an accordeon. Multiple exchanger modules can be installed in an envelope made of two half-shells which completely enclose the enchangers whilst controlling the spaces between them. Each half-shell encloses a longitudinal half of an exchanger or the assembly of several exchangers and has a half-tube connector at each end. The edges of the half-shells are welded together and the half-connectors are welded to the connections of the exchanger(s). ALSO CLAIMED is a mould for fabricating the rough exchanger and a method for fabricating the exchanger, as well as a method for fabricating the rough exchanger in metal and a method for finishing it, together with a machine-tool making the exchanger from a mould.

Description

HEAT EXCHANGER

METHODS AND MEANS FOR MANUFACTURING THIS EXCHANGER

The invention relates to a heat exchanger, of an entirely new type, as well as to its methods and to its manufacturing means.

Heat exchangers between two fluids are used wherever there is a need to recover or evacuate heat, without mixing the fluid that transports it with the fluid that evacuates it. In heat exchangers, at least one of the two fluids is confined, that is to say forced in its entirety to circulate in a limited space, while the other may be only partially or not at all . This is the case, for example, of hot water central heating radiators, depending on whether or not they are partially enclosed. This is also the case for the heat exchanger of a heat pump, traversed by a cold gas and immersed in a watercourse. When the two fluids concerned must be confined, in particular to be able to be recovered and recycled, the heat exchanger to be used must then include one or more internal active parts, surrounded by an external part or envelope, all provided with connection pipes, the part external being generally insulated.

There are several operating modes for heat exchangers: counter-current, co-current and cross-current. The advantage of an exchanger, operating against the current, is that it makes it possible to transfer, from the hot fluid to the cold fluid, practically all the temperature difference which exists between them. The co-current exchanger only achieves an intermediate temperature between those of the two fluids. As for the cross-current exchanger, its structure being different from that of the previous ones, it is less efficient than that against the current but nevertheless well suited to particular uses (usual automobile radiators, for example).

The heat exchangers must all, in order to have maximum efficiency, have the following characteristics: have (1) active surfaces, that is to say participating directly in the heat exchange, as large as possible, (2) thicknesses passage for the two fluids, both weak and substantially constant along the active surfaces, so that practically the entire mass of the confined fluid (s) takes part in the exchange, and (3) a large total passage section for the or confined fluids, proportional to the thermal power to be exchanged, in order to minimize pressure losses.

In many industrial applications, the active walls of the countercurrent heat exchangers used are made of a metal which is a good heat conductor, suitable for the fluids concerned. Stainless steel of a particular type, therefore expensive, is, for example, necessary in the case where one of the two fluids is relatively corrosive (water of sea, for example). Several metal models of heat exchangers between two confined fluids circulating against the current exist on the market. They are, for the most part, constituted by a stack of large rectangular plates, separated from each other by tight seals, and by connection chambers allowing each of the faces of these plates to be in contact with a fluid. different. To be in agreement with the characteristics of all the heat exchangers referred to above, this type of device is necessarily heavy and bulky in three dimensions. In order to reduce losses, its optimal shape approaches the cube. These two disadvantages are added to that of their high manufacturing cost, which results from the number of operations to be carried out, proportional to the number of plates to be assembled. In the case of a heat exchanger for corrosive fluids, the relatively high price of the metal used must also be taken into account.

Plastic counter-current heat exchangers are also used, for the qualities of inalterability of this material, which allow them to withstand most of the corrosive fluids without damage. To this first advantage, there is their lower weight and lower raw material cost. Together, these advantages largely compensate for the deficit in thermal conductivity of plastic materials and the fact that the maximum temperature of the fluids concerned must generally be less than 100 or 120 ° C. Until now, it is common to make plastic heat exchangers between two confined fluids circulating against the current, by means of a bundle of relatively small, small diameter pipes, installed in staggered rows in a large diameter pipe. The fluids inside and outside the small pipes flow in reverse. The advantage of small diameter pipes is, of course, to best increase the active exchange surfaces for a given section of the large pipe and to decrease the maximum thicknesses of fluid surrounding these small pipes, which improves the exchanges between the inside and outside of these pipes. But this type of heat exchanger has a major drawback which comes from the fact that it is necessary to make a sealed connection at the two ends of each pipe and, moreover, to ensure that the bundle formed is, over its entire length, regularly arranged. inside the big pipe. This is so that all the walls of the interior pipes are surrounded by the same reduced thickness of fluid, so that the heat exchange can take place in the best conditions. This assembly operation is also relatively expensive, because of the large number of meticulous assembly and welding operations that it involves.

In the case of certain heat exchange devices between a confined fluid and the outside air, incorporated in refrigerators and / or freezers, such as those described in the European patent application published under the number EP 1 122505 A1, 08 August 2001, the elementary heat exchangers which constitute them are metallic and formed by two corrugated rectangular plates and / or provided with bosses. These plates have two connection rings installed in two opposite corners and they are symmetrically mounted one on the other, so as to be able to constitute hollow and flat elements, provided with a diametrically opposite inlet and outlet. The peripheral edges of each pair of plates and rings are welded to each other, in a continuous manner, and the contact zones of the bosses or the contact lines of the tops of the corrugations, welded by relatively spaced points. To reduce the cost of assembling several such hollow and flat elementary heat exchangers of this kind, automatic methods have been developed, in particular that described in US Pat. No. 4,860,421 of August 29, 1989.

The first object of the invention is a method for manufacturing an elementary heat exchanger, of an entirely new type, the specifications of which are as follows: to be in one piece, that is to say without assembly or welding, and to be highly efficient , limited dimensions, reduced weight, low production cost and, generally, intrinsic inalterability, with regard to corrosive fluids.

The second object of the invention is such an elementary heat exchanger, comprising a single compact active part.

The third object of the invention relates to such an elementary heat exchanger, easy to manufacture using machine tools and standard equipment for automatic production in the industry.

The fourth object of the invention is a draft of this elementary heat exchanger, which a simple operation can transform into an active part of this exchanger.

The fifth object of the invention is a particular mold, suitable for the manufacture of such a blank of the active part of this elementary heat exchanger.

According to the invention, a method for manufacturing a one-piece elementary heat exchanger, with high efficiency, limited dimensions, reduced weight, low production cost and, generally, intrinsic unalterability, is characterized in that it comprises the following steps:

- Produce in a mold, by heat blowing or hydroforming, a blank of a suitable material, consisting of a stack of generally biconvex bellows, relatively deep compared to the transverse dimension of the blank and comparable to those of an accordion, said bellows comprising elongated central parts, provided with end fittings, flanks, ridges and bottoms respectively having shapes adapted so that these flanks have a much greater stiffness than those of the bottoms and crests, said stack being of its side provided with two connection pipes, centered on the stacking axes of said end fittings;

the constituent elements of this blank being at appropriate temperatures, flexibility and elasticities, applying internal depression and / or external compression forces thereto, parallel to the stacking axis of the bellows, then release and / or stop these depression and / or compression forces, when the compressed part thus produced becomes a stack of pairs of hollow plates, communicating and generally symmetrical, with internal thickness and small, substantially constant spacing; - If necessary, after the part thus produced has cooled, surround it with a member, ensuring tightening, in order to maintain the gaps between the walls of the pairs of plates at their initial values.

According to a particular characteristic of this process, the mold to be used for its implementation comprises flared grooves, with ridges and rectilinear bottoms, narrow and parallel, the sides of these grooves are embossed, the bumps of a side facing the hollows the other.

According to two characteristics complementary to the previous one, the mean planes of the embossed sides of the mold form angles of 20 to 30 ° with their plane of symmetry and their end fittings have profiles of reversible surfaces.

According to the invention, a single-piece elementary heat exchanger with high efficiency, limited dimensions, reduced weight, low production cost and, generally, intrinsic unalterability, is characterized in that:

- It consists of a single active part, without assembly or welding, formed by a stack of pairs of elongated, hollow, communicating and generally symmetrical plates; - The internal faces of the walls of each hollow plate, as well as the external faces of the walls of two contiguous hollow plates, are at all points separated from each other by narrow, substantially constant spaces;

- These pairs of hollow plates constitute the elementary conduits of the active part which comprise central parts, the two ends of which are connected to each other, by two hollow connections;

- Each elementary conduit of the active part has two supply manifolds, the axes of which coincide with the stacking axes of the end fittings;

- one end of each collector ends in a connection tube for the active part. According to a particular characteristic of this heat exchanger, the walls of the pairs of hollow plates are embossed and generally symmetrical, while their mean longitudinal planes are perpendicular to their plane of symmetry.

According to another particular characteristic of this elementary heat exchanger, the walls of the pairs of hollow plates are embossed and generally symmetrical, while their mean longitudinal planes together form dihedrons from 120 to 160 ° and their hollow end connections have been made. from returnable surfaces. Thanks to these arrangements, several types of elementary heat exchangers can be produced using known techniques, satisfying the specifications set out above. To do this, we will use thermal blowing or hydroforming techniques. Heat blowing is the hot forming, under strong pneumatic pressure, of polymers or glass. This technique is used for the manufacture of containers, flasks and bottles of all kinds, with relatively complex shapes. Hydroforming is cold stamping, under very high hydraulic pressure, of metal tubes or plates. This technique is used in many industries, to produce hollow parts or components with complex shapes. Specialists in heat blowing know from experience that the containers, produced by this technique, cannot have walls of constant thickness, since these containers have relatively narrow and deep hollow parts. In the case of the present invention, during a heat-blowing operation, the elements of the parison slice (the hollow pasty mass of glass or of polymer to be shaped, in glassmaking language), lying between the outer edges of two contiguous parallel ridges of the flared grooves of the mold used for the manufacture of a bellows blank, have different spells according to their position relative to these ridges. Along the crests of the mold, the bottoms of the bellows of the blank are formed and the thickness of these bottoms is substantially that of the parison. Along the sides of the mold, the initially flat parison slice, between the interior edges of the mold ridges, swells and, gradually decreasing in thickness, is applied to the sides of the mold grooves. At the end, if everything has been planned so that everything goes well, it becomes relatively thin or very thin and it is applied to the bottom of the groove, to form the crest of the blank, otherwise this crest is perforated and the draft completed, unusable. In the case of good manufacturing conditions, the thickness of the bottoms of the bellows of such a blank is greater than the average thickness of their sides and much greater than the thickness of their ridges. The ratio between the thicknesses of the bottoms and the crests of the bellows depends on the ratio between the width of the parison slice between two crests of the mold grooves and twice their depth or even the sine of the half-angle of the dihedron formed by the medium shots of the sides of the grooves. Below a minimum value of this half-angle, the crests of the bellows cannot be completely formed. The optimum value for this half-angle is between 20 and 30 °, the minimum being imposed by the minimum angle of correct formation of the ridges of the thermofoated part and the maximum by the maximum angle of reversal of the surfaces of the fittings. bellows end. The above considerations apply without much change to the hydroforming operations of metal gobs.

In a first case of implementation of the method according to the invention, using a polymer or a metal which is relatively flexible and cold elastic, (polyethylene or brass, for example) it is simple, thanks to the known techniques of heat blowing and hydroforming, to manufacture a blank according to the invention, which comprises bellows with embossed flanks whose mean longitudinal planes form dihedrons having too large a half angle , 45 ° for example, which prevents any overturning of their end fittings. Then, as the crests and the bottoms of the bellows are much less stiff than the flanks, it is easy (1) to cold crush this blank, to give it the form of a stack of pairs of hollow plates, generally symmetrical and communicating, having internal thicknesses and small and substantially constant spacings and average longitudinal planes perpendicular to their plane of symmetry and (2) to keep this initial shape by means of an appropriate member ensuring the maintenance by tightening.

In a second case of implementation of the method according to the invention, by molding a blank, of shape identical to that of the previous one, in glass or in a flexible polymer when hot and relatively stiff when cold (polypropylene, for example), then by proceeding with hot, appropriate crushing of this blank to give it the desired shape and then allowing the part thus produced to cool, in an adequate template, the shape given to this part is stable and final. Any member capable of maintaining it by clamping then becomes completely useless.

In these first and second cases, thanks to the particular characteristic of the process defined above, the sides of the bellows of the blank produced are embossed. Because of this embossing, (an alternating succession of hollows and bumps, in the form of four-slope roofs, for example) the moment of inertia of the walls with respect to their mean plane increases enormously and, consequently, the stiffness of the bellows flanks becomes very large (> 100) compared to those of their bottoms, although the thickness of these is, in the case of heat blowing, much greater than the average thickness of the flanks of the bellows. Consequently, in these two cases, the ridges and the bottoms of the bellows behave in relatively flexible hinges in the first case and very flexible in the second. Indeed, the ratio between the stiffness of the embossed flanks and that of the relatively thick bottoms of the bellows of the blank increases rapidly soon after it leaves the mold since the relatively thin flanks cool much faster than the relatively thick bottoms. In both cases, the significant stiffness of the embossed walls of the hollow plates prevents any subsequent deformation of their stack.

In a third case of implementation of the method according to the invention, the mean planes of the relatively deep embossed flanks of the bellows form dihedrons of approximately 50 ° and their end connections are returnable surfaces. Under these conditions, by preserving the material of the blank of the second case referred to above, under the action of internal depression and / or external compression forces applied to this blank, the convex surfaces of its half-bellows subjected to this force tilts and becomes concave and they remain so, thanks to the stable reversal of the sides of the end fittings of these half-bellows. Despite the cambering force generated by the inversion of these end fittings, any subsequent curvature of the mean longitudinal planes of these particularly stiff embossed plates is prohibited. It will be noted, in this third case of implementation of the method according to the invention, that the reversal of the bellows of the blank really only concerns the end fittings of these bellows, since their central parts undergo only a simple fold, but the inversion of these end fittings ensures the maintenance and stability of these folds. Such an inversion is stable in that the end connections of the central parts of the bellows are returnable surfaces, semi-truncated cones, for example. These surfaces have such a property because the depth of the bellows and their end fittings is sufficiently large compared to the transverse dimension of the blank. Such an arrangement is necessary since the second mandatory characteristic of a reversible surface, the first being, in the case of a truncated cone, a half-angle at the top less than about 60 °. It is known in fact that the reversal of a reversible surface comprises a short buckling phase between the two stable states of this surface. Such a transition buckling can only exist in the case where the sides of the bellows are at the same time, not too far apart from each other and, relatively deep with respect to the transverse dimension of the blank, taking into account the thickness of their wall and of the Young's modulus of the material used. As an indication, the depth of the bellows may, for example, taking into account these two parameters, vary from 95 to 50% of the radius of frustoconical end fittings. Finally, it will be noted that, in the case of an accordion, this relative dimension of the bellows is, in general, only 10 to 15%, which has the effect of making it possible to fold and deploy their end fittings effortlessly , in the absence of any bistable phenomenon.

According to the invention, a heat exchanger between two confined fluids, which comprises in one envelope one or more of these elementary exchangers, is characterized in that;

the casing is formed by two half-shells which completely and tightly surround this or these elementary exchangers, by marrying the overall exterior shape or shapes, while providing narrow spaces for them and keeping contact with the external central lines of their two hollow end plates;

- Each half-shell envelopes a longitudinal half of an elementary exchanger or of the assembly formed by several exchangers and comprises, at each of its ends, one or more connection half-pipes, and at its bottom, one or more openings of fixation ; - The edges of these half-shells and these half-tubes are fixed to each other in a sealed manner, and the edge or edges of this or these openings, similarly fixed to one of the two connection tubes of this exchanger or of each of these exchangers.

According to the invention, the mold for manufacturing a blank for the active part of the elementary heat exchanger, defined above, comprises two metal jaws, in the form of parallelepipedic blocks, symmetrical with respect to their joint plane;

- in each of these blocks, are hollowed out relatively long flared grooves, with crests and narrow and parallel rectilinear bottoms, the two flanks of which are embossed, hollow and bumps of one facing the bumps and hollows of the other, - The crests of the groove separation bosses are parallel to the joint plane and they have, with respect to this plane, a difference greater than their own width;

the angles formed with their plane of symmetry by the mean longitudinal planes of the embossed sides of each of the mold grooves are greater than a minimum angle imposed for the conditions for correct molding of the blank and, preferably, less than the maximum angle turning the end fittings of the blank to be produced, this maximum angle being imposed by the breaking limit of the material used;

the ends of the sides and of the bottoms of the grooves meet to form two symmetrical surfaces, if necessary, with a reversible profile, such as half-truncated cones, which end at the joint plane of the mold, the two stacking axes of these two surfaces being located in this joint plane;

- these two stacking axes being those of future supply manifolds for the elementary conduits of said active part, coaxial cylinder portions are cut in each of the bosses separating two contiguous grooves, in order to delimit these collectors;

- At one end of each of these axes is arranged a semi-cylindrical cavity, intended to mold half of one of the two connecting pipes of an elementary exchanger;

- one of these semi-cylindrical cavities opens onto the outside.

A process for manufacturing by heat blowing a glass or polymer blank of the active part of the elementary heat exchanger according to the invention, defined above, comprises the following steps:

- using an extruder, make a relatively flat hollow parison with the chosen material;

- Introduce this parison between the two jaws of the mold defined above;

- close the mold jaws and, on this occasion, seal the upper and lower ends of the parison in place;

- insert a nozzle into the open cavity of the mold jaws and make it perforate the parison; - apply a short time, inside the parison, a high pneumatic pressure, so as to produce hot by heat blowing a blank of the active part, which reproduces the grooves of the mold and resembles the biconvex bellows of an accordion;

- remove the nozzle, open the mold jaws and remove the blank. A process for manufacturing, by hydroforming, a metal blank of the active part of the elementary heat exchanger according to the invention, defined above, comprises the following steps:

- Introduce a flattened metal tube of appropriate length, between the two jaws of a mold with high mechanical resistance, of the type defined above, then close these jaws and, on this occasion, seal the ends of the tube in place;

- Insert a nozzle in the open cavity of the mold, so that it is engaged in a sealed manner in this tube;

- apply for a very short time, inside the tube, a high hydraulic pressure, adapted to press the metal on the walls of the mold, in order to cold produce a blank with thin walls of the active part, which reproduces the grooves of the molds and resembles the biconvex bellows of an accordion;

- remove the nozzle, open the mold jaws and remove the blank.

Thanks to all of these provisions, the objects of the invention are fully realized, namely heat exchangers, adapted to operate against the current, conforming to the three characteristics and to the specifications referred to above. It will be noted more particularly that the one-piece heat exchangers according to the invention have a limited production cost, mainly due to the total absence of assembly and welding operations for the active part. This absence of welds is also a particularly appreciable characteristic in all areas of the industry which experience vibrations.

The efficiency of the heat exchangers according to the invention depends on the thermal conductivity and therefore on the thickness of the walls of their active part. This thickness is a function, on the one hand, of the thickness of the parison or of the metal tube referred to above and, on the other hand, of the ratio of their circumference and of the perimeter of the cross section of the blank. The same mold makes it possible to produce blanks the thickness of the walls of which can, in general, vary from a single to a double.

The large exchange surface necessary for any heat exchanger is easily obtained in the context of the invention since the hollow plates of the active part can be numerous (up to 30, for example) and relatively long (from 50 to 150 cm , for example). This compensates for the relatively limited individual width of these plates, when the average thickness of their walls is small. Indeed, any notable differential pressure, affecting hollow plates with thin walls, causes their deformation, more or less important according to their width, and therefore either a crushing of their separation spaces and an increase in their internal thickness, or the opposite. Either of these deformations would cause a reduction in the heat exchange achieved. These deformations are however very reduced with hollow plates with embossed walls. The great stiffness of thin embossed walls allows plate widths up to 125 mm.

When using glass to manufacture the active part of the exchanger, the negative effects of such a differential pressure can however be fairly easily compensated, if the hollow plates are given a relatively greater width than that indicated more high, while increasing the thickness of the embossed walls of these plates. As glass has a thermal conductivity twice that of water, this double increase easily becomes possible for many applications. It will be noted that the resistance to relative overpressure of the active part of a heat exchanger provided with a casing is important (two to three bars, for walls of active part of 0.5 mm). On the other hand, any pressure inside the envelope that would be too much higher (beyond 100 millibars, for example) than that inside the active part would cause this part to be crushed. This particular case of using a heat exchanger according to the invention is therefore to be avoided.

The respective small thicknesses of passage of the fluids in the exchanger are determined by the internal thickness of the hollow plates and by that of their separation spaces, these two thicknesses being substantially equal when the two fluids concerned are of the same type. On the other hand, when one is a gas and the other a liquid, their mass flow rates and their respective calorific capacities will be taken into account to best determine the thicknesses of the passages to be produced.

The total cross-section of the fluid confined in the exchanger is the product of the section of each elementary duct, formed by each pair of hollow plates of the active part, by the number of these plates. The cross-sectional area of an elementary duct is limited for the reasons explained above, but the number of hollow plates can be relatively large. In addition, when the thermal power to be exchanged is high, it is easy to mount in parallel several heat exchangers, whether or not provided with casings or else, to install several elementary heat exchangers in parallel in a single casing.

As regards the reduced size of a heat exchanger according to the invention, it follows from the fact that, despite a possible long length, the two dimensions of the cross section of its envelope are relatively small and close to one of the other when there is only one active part.

As for its low weight, it follows from the fact that the polymer used (polypropylene, for example) has a relatively low density and that the walls of the part active and its envelope, which together constitute the device, have a priori limited thicknesses. In the case of active metal parts (stainless steel or titanium, for example), the thickness of the walls may remain low due to the high mechanical strength of the metal, which compensates for the greater density and allows the assembly to keep a reduced weight. Such a property will be less characterized in the case of glass.

It will be noted here that good resistance to corrosive fluids is an intrinsic property of most polymers capable of being used for the manufacture of the parts making up the heat exchanger according to the invention. It is obviously the same for glass and special metals, provided for this purpose. As for the reduced manufacturing price of the device, it follows (1) from the fact that, in the case of a heat exchanger for two confined fluids, which comprises only one single active piece, it comprises at most three easy parts to manufacture and assemble, (2) the small number of automatic operations to be carried out for this purpose and (3) the amortization, over a very large number of units, of the generally high price of molds. As for the automatic equipment for implementing the manufacturing processes, it should be noted that they are common in workshops for the manufacture of containers of all shapes, in plastic, glass or metal, and that the arrangements and the additions to be made thereto according to the invention, are within the reach of any professional of the trade concerned.

It will be noted that the use of an adequate polymer, and in particular polypropylene, ABS OR polycarbonate, for the manufacture of the elementary heat exchangers according to the invention, will be the most general case. This will be the case for radiators for heating and, more generally, for air conditioning the interior of automobiles, which will include an elementary heat exchanger and its casing. In these radiators, the engine cooling water or the refrigerant will circulate in the active part and, against the current all around this part, a forced air flow. Another example, comparable to the previous one, is that of condensation heat exchangers, used in dishwashers and dryers. Another particular example is that of hot water central heating radiators which, in general, will use several bare elementary heat exchangers (without casing), installed in parallel. The same will apply to heat exchangers for heat pumps, installed in a stream of water. The elementary glass exchangers will meet the needs of many chemical laboratories. As for those made of an appropriate metal, they will satisfy the wishes of certain high-tech industries which deal with corrosive fluids at high temperature. It will be noted that heat exchangers with reduced dimensions make it possible to satisfy manufacturers of electronic equipment who wish to have more efficient means for cooling certain components of their devices and in particular microprocessors and power transistors. The characteristics and advantages of the invention will emerge more precisely from the following descriptions of embodiments, given by way of nonlimiting examples, illustrated by the drawings below in which:

- Figure 1 shows on the right in Al, a longitudinal section along the plane 17 of Figures 2 and 3, below, (simplified section) of an elementary heat exchanger according to the invention, in the center, a simplified longitudinal section Bl of the blank of this exchanger and, on the left, a real front view C1 of this blank or of this exchanger (the simplified illustrations A1 and B1 include an erasure of the embossings);

- Figure 2 shows real cross sections A2, B2 and C2 of two elementary heat exchangers according to the invention, made along the cutting axis CC which passes along the midline between a hollow and a bump in the embossing of the walls the exchanger shown in Cl;

- Figure 3 shows real cross-sections offset A3, B3 and C3 of two elementary heat exchangers according to the invention, made along the offset cutting axes AA 'and BB', which respectively pass through a hollow and an embossing bump exchanger walls shown in Cl;

- Figure 4 shows a simplified perspective view of the block constituting the half-mold for manufacturing the blank of the active part of the elementary heat exchanger according to the invention; - Figure 5 shows in simplified perspective half of each of the two half-shells of the casing of an elementary heat exchanger according to the invention.

- Figure 6 shows the front view of the embossed wall of a hollow plate of a one-piece heat exchanger or one of the embossed sides of the mold concerned;

- Figure 7 shows the sectional view of two contiguous hollow plates with embossed walls of such an exchanger.

Figures 1, 2 and 3 relate to two embodiments of an elementary heat exchanger according to the invention. For one, the average longitudinal planes of the pairs of elongated hollow plates of these exchangers together form dihedrons of 150 ° (sections A2 and A3) and, for the other, they are perpendicular to their plane of symmetry (sections B2 and B3). In the first case, the exchanger was produced by compression and inversion of the bellows and end fittings of an accordion-shaped blank and, in the second, by symmetrical compression of these bellows and these fittings.

View C1 shows the embossing of the end walls of an elementary heat exchanger or a blank of this exchanger. This embossing is formed by an alternating succession of recesses 120 and bumps 122, in the form of roofs with four slopes (described in detail in FIG. 6). Three offset cross-sectional planes are used to be able to describe the geometric consequences of this embossing: the half-planes AA 'and BB' through respectively a bump 122 and a recess 120 of the wall of a plate and the plane CC, along the line of separation of the recesses and the bumps of a pair of plates.

According to Figure 2, the cross section A2 shows the cross section 10, along the section plane CC, of the active part of a small exchanger and those 11 a-b of the two half-shells of its envelope. Section 10 of the active part has the shape of a fish spine, provided with seven pairs of hollow edges 12 a-b, oblique and parallel to each other. The internal cavity 14 of each edge 12 ab is narrow (2 mm, for example) and the two generally symmetrical edges of a pair communicate with each other by a common channel 16, having substantially the same width as the internal thickness of the cavity 14. The walls of these edges 12 ab are made of polymer, endowed with good mechanical stability up to at least 100 ° C. (polypropylene, for example) and they have 0.5 mm of average thickness and a width 25 mm. The distance 18 between two contiguous edges is approximately equal to the internal thickness of the cavity 14. The distance between the outer walls 13-15, of the two extreme edges of the cross section 10, is 35 mm. The simplified longitudinal section A1 (embossing erased) of an active part 20, along the offset cutting plane 17 of section A2 reveals seven elementary conduits, constituted by seven pairs of elongated generally symmetrical hollow edges 22, arranged like those 12 ab of cross section A2. These generally symmetrical elongated edges 22 share the common central channel 16, which occupies the entire plane of symmetry of the exchanger. The elongated edges 22 include rectilinear central parts 23, the ends of which are connected together by half-trunks of cones 24 and 26 with hollow walls. The centers of these two series of half-truncated cones are aligned on two axes 25 and 27, both parallel to each other, perpendicular to the outer edges of the hollow plates 22, and located in their longitudinal plane of symmetry. These axes 25-27 are those of the two supply manifolds of each of the elementary conduits, constituted by each pair of hollow plates 22. These collectors open onto the two connecting pipes 28-30 of the active part 20, which are shown, arranged in opposite directions and provided with fixing shoulders 29-31 (see sections Al and Cl). The distance between the pipes 28-30 can be large (up to 150 cm) but, in practice, it depends on the possibilities of the machines available for manufacturing the blanks of the active parts of the elementary exchangers.

The cross section B2 is produced along the section plane CC of an active part of a heat exchanger whose mean longitudinal planes of the embossed hollow edges are perpendicular to their plane of global symmetry. The same references are used for Figures A2 and B2. The only difference between the hollow edges 12 a-b of the two figures relates to the orientations of their mean planes with respect to their overall plane of symmetry.

The longitudinal section Bl of the simplified blank 32 (erased embossings) of the active part 20 and its cross section C2 along the cutting plane CC, show that this blank 32 has the form of a stack of generally biconvex bellows 34, the sides 33 ab and 35 ab of which are comparable to those of an accordion. In sections B1 and C2, the bellows shown are, for convenience, only four in number. According to section C2, the opposite ridges 36a and 36b of each bellows are both level, thin (0.3 mm for example) and wide (2 mm, for example) the distance separating these ridges being about 50 mm, in the case of the example used. The bottoms 38a-b of these bellows are flat and have the same width (2 mm) but a significantly greater thickness (1.2 mm, for example). In the case of the small-sized exchanger chosen by way of example, the base of each bellows 34 measures approximately 17 mm with a depth of 25 mm. These dimensions allowed good penetration of the parison section concerned to the bottom of the grooves of the mold used for the manufacture of this blank. Under these conditions, the angle at the apex formed by the mean planes of its flanks 33a-b and 35a-b is approximately 50 °, or 25 ° for the half-angle formed by these mean planes and their plane of transverse symmetry. and 10 or 40 °, for those of the flat facets of the hollows and the embossing bumps. These latter half angles are greater than the minimum clearance angle of any molded part.

According to the actual front view C1 and the simplified longitudinal section Bl, the ends 40 and 42 of each bellows 34 of the blank 32 have the shape of portions of half-truncated cones. The centers of these frustoconical portions are aligned on the axes 25-27 of the blanks of the future supply manifolds 44-46, which are, for example, 16 mm in diameter and end at the connection pipes 28 and 30, shown in Al and Cl. The longitudinal dimension of the bellows 34 is, of course, that indicated for the edges 22 of section A1. The convex junctions of the sides 37a-b and 39a-b of the two external half-bellows of the blank 32, include longitudinal bosses 41-43, intended to serve as support for the centers of the convex and concave walls of the envelope of the active part 20 (see in A2, the straight section lla-b of this envelope). The distance between the support bosses 41-43 is for example 130 mm, for the blank 32 with seven bellows mentioned above.

FIG. 3 represents the cross sections A3 and B3 of the two preceding elementary heat exchangers, produced according to the offset half-planes of cut AA 'and BB' from the front view Cl, which respectively pass through a hollow and a bump in the embossing of the walls plates of these exchangers. Likewise, the two transverse half-sections, represented in C3, are those of a blank with embossed walls, produced according to these same half-sectional planes. The references on the sections of Figures 2 and 3 are identical. The walls of the plates of an exchanger and those of the bellows of a blank represented on sections A3, B3 and C3 (half-sectional planes AA 'and BB') are distinguished from those represented in A2, B2 and C2 by the fact that, instead of appearing rectilinear like the latter (section plane CC), the walls of the edges 12a and those 33a and 39a of the bellows 34 of Figure 3 show a hollow fold and the walls of the edges 12b and those 33b and 39b of these bellows, a bend in bump.

FIG. 4 represents a simplified perspective view (erasures erased) of one of the jaws 52, in the form of a thick parallelepiped block 54, of the mold 50 for manufacturing the blank 32. In the case of a polymer or glass blank , the block 54 may be made of aluminum and, in the case where this blank must be made of metal, this block may be made of steel with high mechanical strength. The upper face 56 of the block 54, which constitutes the joint plane of the mold, comprises a relatively large number of flared, elongated, contiguous grooves 62. These grooves 62 comprise a generally rectilinear central part 64, having a medium cross section in the form of isosceles trapezoid. The rectilinear bottom 66 of each groove 62 is narrow and corresponds to the small base of the trapezoid. The sides 68a-b of these grooves 62 are identical to the sides 33a-35a of the blank 32. The rectilinear ridges 70 of the separation bosses of these grooves 62 have widths identical to those of the bottoms 38a-b of the bellows 34 of Figure 2 (view C2). As for the bottoms 66 of the grooves 62, their width is that of the internal thickness of the edges plus twice the thickness of their walls, ie 3 mm, in the case of the example presented. Symmetrical portions of truncated cones 67 a-b and 69a-b (portions greater than a quarter) constitute extensions of the oblique flanks 68a-b of the flared grooves 62 which meet and end at the joint plane 56 of the mold. The ends of the narrow rectilinear bottoms 66 of the grooves 62 are extended by quarter cylinders 65 ab which end at the joint plane 56. Portions of cylindrical surfaces 72 and 74, of 16 mm in diameter, for example, cut in the bosses of separation of the grooves 62, starting from the portions of truncated cones 67 ab and 69a-b, constitute mold parts, which will generate the edges of the blanks of the supply manifolds 44 and 46, shown in view Bl of FIG. 1 The centers of these portions of cylindrical surfaces 72-74 are aligned on the axes 25-27 of two half-cavities 76 and 78, (12 mm in diameter, for example), provided with half-shoulders 77-79. These half-cavities 76-78 are hollowed out in the upper face of the block 54 and they will generate the connecting pipes 28-30 of the blank 32 and their shoulders 29-31. These axes 25-27 are mutually parallel, perpendicular to the ridges 70 of the separation bosses of the grooves 62 and located in the joint plane 56 of the mold. The half-cavity 76 is open to the outside.

FIG. 5 shows in perspective, in A5 and B5, the simplified partial views (embossing erased) of two half-shells 80 and 82 which, assembled and welded, constitute the casing 81 of the elementary heat exchanger, according to the invention . These two half-shells were manufactured using standard techniques in the industry (thermoforming of a polymer sheet or stamping of a metal sheet). Each of these half-shells 80-82 is intended to wrap a longitudinal half of the active part 20 of the elementary exchanger and to form the halves of the two connecting pipes 94 and 110 of the casing 81.

The partial view A5 of the half-shell 80 shows a convex outer wall 84, comprising, all around, a narrow continuous flat 85 and, in the middle, a longitudinal boss of the same width 86. This flat and this boss are respectively adapted to establish the reduced distance provided above (for example, 1 mm) from the overall limits of the active part 10, with the exception, however, of the support bosses 41-43 of this active part. At the end of the half-shell 80, appears in relief, the shape 88 of the portion of truncated cone 40 (see view Cl of fig.l) which ensures the connection of the two rectilinear elements of the pair of edges longitudinal convex exterior 13 (see view A2 of fig. 2). In the center of the form 88, appears a circular opening 90, the surround 92 of which is intended to be applied and welded to the shoulder 29 of the connection tube 28 of the active part 20. At the end of the half shell 80, we can see the end part of a connecting half-tube 94 of the casing 81 of the active part 10. The sides 96a-b of the half-shell 80 are all the higher as the number of pairs of longitudinal edges 22 is important. Two flanges 98a-b surround the outer edges of the half-shell 80 (sides 96a-b and half-tubing 94). These edges also appear in A2 in fig. 2.

The partial view B5 of the half-shell 82 shows a concave outer wall 100, comprising all around, a narrow continuous flat 102 and, in the middle, a longitudinal hollow of the same width 104. This flat and this hollow are respectively adapted to establish a reduced gap, similar to that referred to above. At the end of the half-shell 82, there appears in hollow the shape 106 of the portion of truncated cone 42 which ensures the connection of the two rectilinear elements of the pair of external concave longitudinal edges 15 (section A2). In the center of the form 106, a disc 108 appears, situated opposite the opening 90 of the half-shell 80. At the end of the half-shell 82, is arranged the connecting half-pipe 110 of the casing 81. The sides 112 ab of the half-shell 82 have the same height as those 96a-b of the half-shell 80. Two flanges 114 ab surround the outer edges of the half-shell 82. These flanges 114a b are intended to be welded to the edges 98 ab of the half-shell 80. FIG. 6 represents the enlargement of two things, (1) a front view of a longitudinal half of the embossed wall of an elongated hollow plate 22 of a real elementary heat exchanger and (2) a similar front view of the embossed flank of the grooves 62 of a real half-mold, usable for the production of the blanks of this exchanger. In both cases, the embossed walls of the blank or the grooves of the half-mold used for its manufacture comprise an alternating series of recesses 120 and bumps 122, in the form of four-pitched roofs, two in the form of a trapezium 124- 126 and two in the form of isosceles triangles 128-130. The depth of a hollow 120 and the height of a bump 122 are each 2.5 mm by example. The indices b and c, assigned to the references of these four slopes, respectively identify the bumps and the hollows, shown in gray. The half-sectional planes AA 'or BB' referred to above cross in the middle the hollow trapezoids 124c and 126c or the trapezoidal bumps 124b and 126b. The junction lines of the trapezoids 124 and 126 are referenced 121 and 123 depending on whether these trapezoids belong to hollows or bumps. It will be noted that each of two embossed flanks 33-35 of a real blank or those 68 ab of a groove 62 of a real half-mold, comprises an alternating series of hollows and bumps which faces an alternating series bumps and hollows. The dotted lines 129 shown are symbolically used to distinguish the two coplanar slopes 128b and 130c or 130b and 128c which respectively belong to a bump or a trough, each dotted line being the large diagonal of a rhombus. The section plane CC referred to above follows these lines 129. The narrow rectangles 132 and 134, which appear at the two ends of the series of hollows and bumps 120-122 are planar areas connecting the central part (1) of the hollow plates 22 and their end fittings 24-26 in the case of exchangers or (2) grooves 62 of the half-mold with their ends in portions of truncated cones 67 ab and 69 ab. The edges 136 and 138 shown in FIG. 6 are the crest lines 36 or the bottom lines 38 of the blanks 32.

FIG. 7 represents the enlarged view in longitudinal section along the median lines 121-123 of the central parts of two contiguous hollow plates 140 and 142 with embossed walls, separated by a spacing 144. According to this centered longitudinal section, the embossing described in FIG. 6 is translated, after controlled crushing of the blank, by the creation of hollow plates 140-142, with walls 146 ab and 148 ab, formed of a series of bumps, such as 150a or 152b, and of hollows such as 152a or 150b, connected together by slopes at around 30 °, such as 154a-b. The distance between two extreme lines 150a and 150b is approximately 5 mm. The internal thickness of a 140-142 hollow plate with embossed walls is substantially constant, of 2 mm for example. The width of the corrugated space 144 which separates them is also substantially constant and of the same order of magnitude as the internal thickness of the plates.

Under these conditions, such an embossing has the effect of giving the moment of inertia of the wall with respect to its mean plane, a value several hundred times greater than that of the same moment of inertia of a plane wall of a half a millimeter thick. The stiffness of the central part of the wall is increased in the same proportions, while that of the ridges and the bottoms of the bellows of the blanks remains very low, which allows these ridges and these bottoms to act as flexible hinges, taking a very small radius of curvature at the time of the controlled crushing of the blank, while the flanks remain generally flat.

Thanks to these provisions, heat exchanger according to the invention appears with the advantages of all of its manufacturing and use characteristics. As for his manufacturing, it should first of all be noted that the molds concerned use standard manufacturing processes and that they will be used in the context of techniques common in industry. The same is true of automatically operating equipment such as extruders, compressors and displacement systems, which are found in all workshops for the manufacture of containers of all shapes, made of polymer or glass, intended to contain the liquids most more diverse. The same is true of equipment, operating at very high water pressure, used for hydroforming metal parts.

From a blank, in the form of a stack of globally biconvex bellows, comparable to those of an accordion, emerging from the molds according to the invention, the transformation of this blank 32 into an active part 20 of the exchanger thermal elementary according to the invention, calls for a new operation in itself, carried out by means of a particular machine tool, adapted for this purpose. This operation constitutes either a symmetrical crushing of the bellows of the blank or an abrupt reversal of the convex half-bellows of this blank, oriented in a first direction, towards their generally symmetrical half-bellows, oriented in a second direction (they were convex and they become and remain concave). In both cases, the operation is carried out by applying to the bellows a compressive force parallel to their stacking axis. This force will be generated by a controlled vacuum applied inside the blank 32 and / or by a convex profile piston, advancing at a controlled speed, associated with a fixed support with concave profile. This piston and this support will have the same longitudinal dimension as the edges of the active part finally produced. In the case where the compression force is generated by a depression, it will be noted that the external omni-directional forces, which will result therefrom, will act in the direction of the easiest movement, namely the stacking axis of the bellows of the blank. . It will be noted that the flip-flops, constituted by the half-bellows of the blank which, in their second stable state, have taken the form of the concave walls of oblique and hollow longitudinal edges, can, by way of demonstration, resume their first state , by the simple application of sufficient pressure inside the finished active part, but on condition however that the walls thereof have retained or regained a minimum flexibility. It is the same for the half-bellows which have undergone a symmetrical crushing.

It is obviously necessary, so that all these operations are possible and take place correctly, that the blank introduced into the particular machine, having to carry out such a crushing or such a reversal, comprises ridges and sufficiently flexible and elastic bottoms. This is so that their breaking limit is relatively high and that the symmetrical reversal or compression of the flanks concerned of the central parts of the bellows and their end fittings can be carried out without the risk of cracks or bursting. In case the passage from the mold to the compression machine the blank would have a relatively long dead time, this blank would cool and, in particular in the case of glass, could see its flexibility lowered below the minimum limit imposed by a good turning or good compression. In this case, the machine in question should, upstream, include means for reheating the blank, in order to restore the flexibility it needs, so that the half-bellows concerned can be returned without damage.

It will be noted that the hollow connections of the ends of the central parts of the generally symmetrical hollow plates of an elementary heat exchanger according to the invention as well as the biconvex connections of its blank, which have been described above, are portions of truncated cones . This type of surface is of course not the only one that can be used. Indeed, any reversible surface (a very flared pyramid, with square base and leveled top, is reversible relative to a reversal plane containing its base, for example) can be used to constitute the biconvex connections of the ends of the central parts of the bellows of the blank according to the invention. With regard to the embossing of the sides of the bellows, it should be noted that four-slope roofs are not the only way of making them, bumps and hollows in the form of caps and bowls, with more or less rounded bottoms, are also possible.

As for the manufacture and the installation of the envelope of the elementary heat exchanger, it will be noted that these operations also call upon techniques which are commonplace in industry. As regards the tight fixing of the half-shells one on the other and on the connecting pipes of the active part, it will obviously be possible to provide seals and flanges adapted to fit together in others and to remain so.

As for the orientations in opposite directions of the connecting tubes of the active part, it is obvious that these different orientations allow better circulation of the fluids inside the internal and external parts, but they can, without major damage, be identical.

As said above, the elementary heat exchanger according to the invention, whether or not surrounded by a sealed envelope, described above, has all the characteristics necessary for this type of device and it meets all the specific specifications concerning him. It is obviously not limited to the embodiments described.

Claims

1. Method for manufacturing a one-piece elementary heat exchanger, with high efficiency, limited dimensions, reduced weight, low production cost and, generally, intrinsic unalterability, characterized in that it comprises the following stages:

- Achieving in a mold (50), by heat blowing or hydroforming, a blank (32) of a suitable material, consisting of a stack of bellows (34) generally biconvex, relatively deep compared to the transverse dimension of the blank and comparable to those of an accordion, said bellows (34) comprising elongated central parts, provided with end fittings (40-42), sides (33-35), ridges (36) and bottoms (38) having respectively shapes adapted so that these sides (33-35) have a much greater stiffness than those of the bottoms (38) and ridges (36), said stack being on its side provided with two connection pipes 28-30) , centered on the stacking axes (25-27) of said end fittings (40-42); - The components of this blank (32) being at temperatures, flexibility and appropriate elasticities, apply an internal vacuum and / or external compression forces, parallel to the stacking axis of the bellows, then release and / or stop these depression and / or compression forces, when the compressed part (10) thus produced becomes a stack of pairs of hollow plates (12-22), communicating (16) and generally symmetrical, with internal thickness (14) and spacing (18 ) weak, substantially constant;

- If necessary, after the part (10) thus cooled has surrounded it with a member (81), ensuring tightening, in order to maintain the differences between the walls of the pairs of plates (22) at their initial values ).

2. Method for manufacturing an elementary heat exchanger, according to claim 1, characterized in that the mold (50) to be used for its implementation comprises flared grooves (62), with ridges (70) and bottoms (66) rectilinear , narrow and parallel, the sides (68 ab) of these grooves (62) are embossed, the bumps of one side facing the hollows of the other.

3. Method for manufacturing an elementary heat exchanger according to claim 2, characterized in that the mean longitudinal planes of the embossed sides (68 ab) of the mold (50) form angles of 20 to 30 ° with their plane of symmetry and in that that their end fittings (67 ab and 69 ab) have profiles of returnable surfaces.

4. One-piece elementary heat exchanger (20) with high efficiency, limited size, reduced weight, low production cost and, generally, intrinsic unalterability, characterized in that:

- It is constituted by a single active part (10), without assembly or welding, formed by a stack of pairs of elongated plates (22), hollow (14), communicating

(16) and generally symmetrical;

- the internal faces of the walls (12 ab or 150 ab / 152 ab / 154 ab) of each hollow plate (22 or 140-142), as well as the external faces of the walls of two contiguous hollow plates (140-142), are at all points separated from each other by narrow spaces (14 or 144), substantially constant;

- These pairs of hollow plates (22) constitute the elementary conduits of the active part (10) which comprise elongated central parts (23) the two ends of which are connected to each other, by two hollow connections (24-26);

- Each elementary conduit of the active part (10) has two supply manifolds whose axes coincide with the stacking axes (25-27) of the end fittings (24-26);

- one end of each manifold ends in a connection tube (24-26) of the active part (10).

5. Elementary heat exchanger (20) according to claim 4, characterized in that the walls (150 ab / 152 ab / 154 ab) of the pairs of hollow plates (140-142) are embossed and generally symmetrical, however that their longitudinal planes means are perpendicular to their plane of symmetry.

6. Elementary heat exchanger (20) according to claim 4, characterized in that the walls (150 ab / 152 ab / 154 ab) of the pairs of hollow plates (140-142) are embossed and generally symmetrical, while their longitudinal planes means together form dihedrons from 120 to 160 ° and that their end connections (24-26) have been made from returnable surfaces.

7. blank (32), produced by implementing the first step of the method, according to claim l, for manufacturing a one-piece elementary heat exchanger, characterized in that:

- It comprises a seamless stack of generally biconvex bellows (33, 35, 37, 39) comparable to those of an accordion;

- The ends of the central parts of these bellows are provided with symmetrical connections, if applicable, returnable (40-42); - the bellows this stack have level ridges (36 ab) and narrow bottoms (38 ab), the stiffness of these bottoms and ridges are very low compared to that of their sides (33 ab / 35 ab / 37 ab / 39 ab);

- The sides of the bellows and those of the end fittings (40-42) have significant depths, opposite the transverse dimension of the blank (32).

8. A blank (32) according to claim 7, characterized in that, to ensure an appropriate stiffness for the sides (33 ab / 35 ab / 37 ab / 39 ab) of the bellows, each side has an alternating series of hollows (120) and bumps (122), in particular in the form of four-slope roofs, the hollows of one side corresponding to the bumps of the other.

9. Heat exchanger for confined fluids, comprising one or more elementary exchangers (20) according to claim A, installed in an envelope (81), characterized in that: - the envelope (81) is formed by two half-shells ( 80-82) which completely surround this or these exchangers (20), by marrying the overall exterior shape or shapes, while providing narrow spaces for them and by keeping contact with the external central lines (41-43) of their two hollow end plates;

- Each half-shell (80-82) envelops a longitudinal half of a heat exchanger or of the assembly formed by several exchangers (20) and it comprises, at each of its ends, a connection half-pipe (94- 110), and in its bottom, one or more fixing openings (90);

- The edges (98a-b and 114a-b) of these half-shells and these half-pipes are fixed to each other in a sealed manner and the edge (s) (92) of this or these openings (90 ), similarly fixed to one of the two connection pipes (28-30) of this exchanger or of each of these exchangers.

10. Mold (50) for manufacturing a blank (32) of the active part (20) of an elementary heat exchanger, produced according to the method of claim 1, characterized in that:

- It comprises two metal jaws (52), in the form of parallelepipedic blocks (54), symmetrical with respect to their joint plane (56);

- In each of these blocks (54), are hollowed out elongated flared grooves (62), with crests (70) and bottoms (66) rectilinear, narrow and parallel, the sides (68 ab) of which are embossed, hollow and bumps of one facing the bumps and hollows of the other; - The ridges (70) of the groove separation bosses (62) are parallel to the joint plane (56) and they have, with respect to this plane, a difference greater than their own width;

- The angles, formed with their plane of symmetry by the mean longitudinal planes of the sides (68a-b) of each of the grooves (62) of the mold, are greater than a minimum angle, imposed by the conditions of correct molding of the crests of the 'blank, and preferably less than a maximum turning angle, imposed by the breaking limit of the material used;

- The ends of the sides (68a-b) and the bottoms (66) of the grooves (62) meet to form symmetrical surfaces, if necessary, with a reversible profile (67a-b and

69a-b), which lead to the joint plane (56) of the mold, the two stacking axes (25-27) of these surfaces being located in this joint plane;

- these two stacking axes (25-27) being those of future collectors (44-46) supplying the elementary conduits of the active part, cylinder portions (72-74) are cut in each of the bosses separating two contiguous grooves, in order to delimit these collectors;

- one of the two ends of each of these axes (25-27) comprises a semi-cylindrical cavity (76-78), designed to mold half of one of the two pipes (28-30) for connecting the active part (20); - one of these semi-cylindrical cavities (76) opens onto the outside.