FR2954479A1 - HEAT EXCHANGER TUBE, METHOD FOR MANUFACTURING SAME, AND HEAT EXCHANGER COMPRISING SUCH TUBES - Google Patents

Abstract

This tube (1) comprises a tubular base body (10), an intermediate casing (20) placed at the periphery of the body, and fins (30) wound spirally around the casing. The envelope and / or the fins comprise (s) a zone of mechanical deformation (Z), ensuring their mutual bonding, which guarantees a good mechanical strength, good thermal conduction properties and limits the corrosion problems of the basic body

Description

The invention relates to a tube for a heat exchanger, to a method of manufacturing the same, and to a heat exchanger comprising a plurality of such tubes. The invention relates more particularly to the technical field of tube heat exchangers using air as a secondary exchange fluid, such as equipment of the air-refrigerant type, air-condenser, air-heater or aero-evaporator. The latter are used respectively for the cooling, condensation, heating and evaporation of a fluid, in particular in refining processes, gas treatment and compression stations, gas liquefaction units, coal and gas synthesis, power generation facilities, regasification units, or other fluid processing facilities. In general, such equipment comprises a main heat exchanger provided with a bundle of tubes, each of which comprises in particular a basic tubular body, as well as external fins. It is also provided distribution manifolds and distribution of the fluid between the tubes. A first fluid to be cooled, condensed, heated or evaporated circulates inside the tubular body. The heat treatment of this fluid is performed at the outer fins, by heat exchange with a second fluid flowing to the periphery of each tube, including ambient air. For this, a circulation or forced ventilation of ambient air is provided by fans positioned either below (what is called a forced draft) or above (so-called induced draft) tubes exchanger . The present invention is more particularly concerned with the technical problem of the joining of the basic tubular body with respect to the external exchange fins. A first known solution consists in directly winding, in a helical form, an aluminum strip around the base body, so as to form the fins. This first state of the art may be called "coiled fins". Alternatively, the fins may be embedded in a groove made in the base body, or may be fixed around the body after folding the foot of the fin in an L shape, in order to increase the surface area. contact between the body and the fin. In the latter case, the foot of the fin can also be knurled to strengthen the holding on the base body. This solution, said flanged fins, however, has certain disadvantages. Thus, the protection against external corrosion of this type of tube is not satisfactory and, when used in a marine or industrial environment with high humidity, the base body may be subject to significant corrosion, since 'outside. Another known type of assembly is the so-called extruded fin tube, in which a base tube covered with an aluminum peripheral tube is used.

The fins are helically formed in aluminum, using a series of rotating discs. This solution offers the advantage of protecting the base tube against external corrosion. On the other hand, it has certain disadvantages, related first of all to the need for recovery of the ends to obtain complete coverage. Moreover, the manufacturing processes used are relatively difficult to control. In addition, it is necessary to control the contact between the two tubes, which requires the use of specific tools that slow down the manufacturing. Finally, a final disadvantage is that the amount of aluminum required for the manufacture of this type of tube is almost twice as high as that required to produce the tubes with coiled fins, while the thermal performance is slightly lower. Another way of bringing the fins to the tubular body is to cut the fins in a strip and then insert them around the tube. The main problem lies in the creation of a game, at the junction between the tube and the fin, which is not conducive to heat exchange. To reduce this clearance, the tubular body can be expanded when its thickness is low and the material used is easily deformable. There are also treatments that can be carried out after manufacture, such as galvanizing if the tubes and fins are made of steel. In the case of aluminum fins, it is very difficult to get a good contact between the tube and the fin.

Another type of assembly provides for brazing the fins on the tubular body, which is made of steel. This method makes it possible to obtain a tube whose thermal properties are interesting and which has a notable protection against external corrosion. However, the manufacturing costs involved in this type of assembly are significantly higher than those corresponding to the processes presented above. In addition, during the brazing step, the base body undergoes a heat treatment because of the temperatures to achieve for the melting of aluminum alloys, which can alter its quality. Finally, US-B-7,093,650 relates to a heat exchanger tube comprising, in addition to the body and the fins, an intermediate layer made of resin, covering the base tube and around which are wound the fins. The use of this resin protects the base body against external corrosion phenomena. The disadvantages of this type of assembly are, first of all, related to the addition of a thermal resistance by the resin which is not good heat conductor. On the other hand, these heat exchangers can not be used at temperatures above about 150 ° C. In fact, the resins used either do not resist these temperature ranges or prevent the expansion of the metals at these temperatures. The invention aims to remedy the various disadvantages of the prior art, mentioned above. It aims in particular to provide a heat exchanger tube which, while relatively economical, is not substantially subject to the corrosion phenomenon and has good properties of thermal conduction and mechanical strength. For this purpose, the subject of the invention is a tube for a heat exchanger, comprising a basic tubular body, an intermediate casing placed on the periphery of the body, and fins wound spirally around the casing, characterized in that that the envelope and / or the fins comprises (s) a zone of mechanical deformation, ensuring their mutual bonding. A heat exchanger tube according to the invention may advantageously have the following characteristics: the zone of mechanical deformation is a crimping zone; the envelope is hollowed out with at least one receiving groove of one end of a fin, the zone of mechanical deformation being provided in the vicinity of at least one edge, in particular of a lateral edge, of said groove ; the intermediate envelope and the fins are made of the same material, in particular aluminum or aluminum alloy, or else copper. The invention also relates to a method for manufacturing a tube for heat exchanger, this tube comprising a tubular base body, an intermediate casing placed on the periphery of the body, and fins spirally wound around the casing, characterized in that mutually positions the casing and the fins in the configuration they must adopt, and mechanically deforms the casing and / or the fins to ensure their mutual bonding. A method of manufacturing a heat exchanger tube according to the invention may advantageously have the following characteristics: the base body and the casing are made separately and the base body is introduced into the internal volume of the body; the envelope; a base body is provided whose external dimensions, in particular the diameter, are smaller than the internal dimensions of the envelope, the base body is introduced into the interior volume of the envelope, and a magnetic field is applied to this body and this envelope, so as to secure them mutually; a basic body is provided whose external dimensions, in particular the diameter, are greater than or equal to the internal dimensions of the envelope, a stress is imposed so as to modify the radial dimensions of the body and / or the envelope; , in order to introduce the base body into the interior volume of the envelope, and said stress is removed, so that the radial surfaces facing the body and the envelope come into mutual contact; a thermal stress is imposed; a basic body is available whose external dimensions, in particular the diameter, are smaller than the internal dimensions of the envelope, the base body is introduced into the interior volume of the envelope, and the envelope is mechanically deformed; , in particular by crimping, so as to secure it to the basic body. The invention finally relates to a heat exchanger comprising several tubes as above. The present invention will be better understood and other advantages will appear on reading the detailed description of an embodiment, taken by way of non-limiting example and illustrated by the appended drawings, in which: FIG. longitudinal sectional view illustrating a heat exchanger according to the invention; Figures 2 and 3 are longitudinal sectional views, illustrating more specifically the joining of the various components of the exchanger according to the invention; and FIG. 4 is a graph illustrating, in a comparative manner, the amount of material used for an exchanger according to the invention, as well as for two exchangers of the prior art. In Figure 1, there is shown a tube 1 belonging to a heat exchanger. The latter comprises, in the usual way, several of these tubes 25 arranged in a bundle, in a number typically between 50 and 300. The exchanger further comprises an inlet and an outlet of a first fluid, intended to circulate in the volume. inside each of the tubes. In addition, a second fluid, generally ambient air, is circulated transversely to the tubes, by means of fans, to enter into heat exchange with the aforementioned first fluid. The various mechanical elements mentioned above are conventional, so that they are not illustrated in the figures and are briefly presented in the description. The tube 1 comprises a tubular base body 10, an intermediate casing 20, and peripheral fins 30.

The base body 10 is hollow, so as to ensure the passage of the aforementioned first fluid. It is made of any suitable metallic material, such as for example a grade of steel, such as carbon steel or stainless steel, duplex, incolloy, inconel, titanium or even copper. Advantageously, the body 10 has an outside diameter of between 10 and 60 mm. The intermediate sheath 20, forming a sheath, is disposed at the periphery of the base body 10. This envelope is hollowed out with a groove 22, extending at its outer periphery in a spiral shape, in particular of a helix.

In a manner known per se, the peripheral fins 30 may have a flat surface, or be provided with disrupters for improving the heat exchange performance. In addition, the inner radial end 32 of these fins is embedded in the groove 22 above, as will be explained in more detail in the following.

Advantageously, the casing 20 and the fins 30 are made of the same material. As a purely indicative example, mention may be made in particular of aluminum or an aluminum alloy, or even copper. In addition, the body 10 and the envelope 20 may have different profiles. Thus, they can both be cylindrical, of circular section, but also in a variant of oblong, oval, elliptical or flattened section. A method of manufacturing the tube 1, described above, will now be explained in more detail in the following. This method comprises two main steps, namely on the one hand the mutual attachment of the base body 10 with respect to the casing 20 and, on the other hand, the mutual attachment of the casing with respect to the fins 30.

The body 10 and the envelope 20 are made separately, by any appropriate process. Two alternative methods can then be implemented. These two elements can first be formed so that, under the normal conditions of use of the tube 1, the outside diameter of the body is smaller than the inside diameter of the envelope. In this case, the body is inserted inside the envelope, thanks to this difference in diameters. Then, in order to guarantee a satisfactory quality of contact between these two elements, to limit thermal losses, it is possible to carry out a crimping operation of the envelope around the base body. For this purpose, it is possible to use a magnetic field, the properties of which allow the casing 20 to be crimped onto the body 10, by non-reversible material movement and without intermediate play. In this case, this step is advantageously carried out before the step of securing the envelope and the fins, described below.

Alternatively, it is also possible to deform the envelope by any suitable tool, such as for example wheels, in which case this step is advantageously carried out after the step of securing the envelope and the fins. According to an alternative, the body and the envelope can be formed so that, under the normal conditions of use of the tube 1, the outside diameter of the body is smaller than the inside diameter of the envelope. It is then a question of applying a stress, in particular a thermal stress, to at least one of these elements, in order to modify its radial dimensions. Thus, the envelope is expanded by heating it and / or the body is contracted by cooling it, then the body is introduced into the envelope, operation now made possible. Finally, it removes the thermal stress, so that the peripheral walls facing the envelope and the body come closer, without interlayers. These steps of placing in thermal stress and introduction are advantageously implemented before the joining of the envelope and the fins, described below.

This joining is illustrated with reference to Figures 2 and 3. In Figure 2, there is the groove 22 for receiving the fins, which advantageously has a depth of between 0.2 and 0.5 mm. The transverse dimension, or width, of this groove is slightly greater than that of the inner end 32 of the fins, to form a game facilitating the insertion of the latter. Then, the constituent strip of the fins is inserted in the groove 22. The fins and the envelope are positioned in the final configuration they must adopt, once the tube 1 made. The lateral edges 24 of this groove are then mechanically deformed according to an action indicated by the arrows F in FIG. 3, which makes it possible to mutually fasten the fins and the envelope. There is thus a zone Z of mechanical deformation, shown in dotted lines, at the walls facing the fin and the envelope.

This deformation is for example made by crimping, which is implemented in a manner known per se. Alternatively, in addition or alternatively to the deformation of the edge of the groove, it is also possible to deform the end 32 of the fin 30, to secure the latter relative to the envelope.

The invention achieves the previously mentioned objectives. The invention firstly ensures the protection of the base body vis-à-vis external corrosion, which is not allowed by the tubes comprising coiled-type fins, as presented in the preamble. In addition if the base body is made of a noble material, the extra thickness that it is essential to provide in the material of this body, to achieve embedded type fins is no longer necessary thanks to the invention. The advantage of the invention, vis-à-vis a tube with extruded fins lies in particular thermal performance. Indeed, at the junction between the casing and the fin, the thickness of the latter is lower in the invention, since the fin is reported. Therefore the surface, which is at the highest temperature and is directly in contact with the air, is more important thanks to the invention. Finally, the invention makes it possible to reduce the amount of aluminum used to manufacture the fins. In this regard, Figure 4 shows the amounts of aluminum used for the manufacture of different tubes. The curve in solid lines is relative to a tube according to the invention. In this case, the quantity Q of aluminum, which corresponds to the mass of the envelope and the fins, increases continuously with the thickness E of this envelope. The lower curve in phantom is related to a tube finned coiled, the amount of aluminum corresponding only to the mass of the fins. Finally, the upper curve in dashed lines is relative to a tube with extruded fins, the amount of aluminum corresponding to the mass of the peripheral tube and fins integrally with it. For these two other curves, this quantity Q does not vary with the thickness E. FIG. 4 clearly shows the interest of the invention in economic terms, in particular for thicknesses E up to 2.5 mm. It should be noted that the present comparison only relates to the quantities of aluminum. Thus, for the tube with coiled fins (curve in phantom), it is necessary to take into account the extra thickness needed to embed the strip in the base tube. Under these conditions, the amount of total material required to produce this type of tube is greater than that used in the invention. The invention also has specific advantages in comparison with the solution presented in US Pat. No. 7,093,650. Indeed, the mutual bonding of the casing and the fins in the invention guarantees a better mechanical strength than in this prior art, for which this connection is implemented by adhesion. Furthermore, the tube for heat exchanger according to the invention can be used at high temperatures, of the order of 400 ° C. Finally, the tube of the invention allows a very satisfactory discharge of heat from the base body towards the fins, in particular when the casing is crimped around the base body.

Claims (11)

REVENDICATIONS1. Tube (1) for a heat exchanger, comprising a basic tubular body (10), an intermediate casing (20) located at the periphery of the body, and fins (30) wound spirally around the casing, characterized in that the envelope (20) and / or the fins (30) comprise (nt) a zone of mechanical deformation (Z), ensuring their mutual joining. 2. Tube for heat exchanger according to claim 1, wherein the zone 10 of mechanical deformation (Z) is a crimping zone. 3. tube for heat exchanger according to claim 1 or 2, wherein the casing (20) is hollowed out with at least one groove (22) for receiving an end (32) of a fin (30), the zone of mechanical deformation (Z) being provided in the vicinity of at least one edge, in particular of a lateral edge (24), of said groove (22). 4. Tube for heat exchanger according to one of the preceding claims, wherein the intermediate casing (20) and the fins (30) are made of the same material, in particular aluminum or aluminum alloy, or in copper. 5. A method of manufacturing a tube (1) for heat exchanger, this tube comprising a tubular base body (10), an intermediate casing (20) placed at the periphery of the body, and fins (30). wound in a spiral around the casing, characterized in that the casing (20) and the fins (30) are mutually positioned in the configuration to be adopted, and the casing and / or the fins are mechanically deformed to ensure their mutual solidarity. 6. Method according to the preceding claim, wherein the base body (10) and the casing (20) are made separately and the base body is introduced into the interior volume of the casing. 7. The method of claim 6, wherein there is a base body whose outer dimensions, including the diameter, are smaller than the inner dimensions of the casing, the base body is introduced into the interior volume of the body. envelope, and a magnetic field is applied to this body and to this envelope, so as to mutually secure. 8. The method of claim 6, wherein there is a base body whose outer dimensions, including the diameter, are greater than or equal to the inner dimensions of the envelope, is imposed a constraint so as to change the radial dimensions of the body and / or the envelope, in order to introduce the base body into the interior volume of the envelope, and the said stress is eliminated, so that the radial surfaces facing the body and the envelope come into mutual contact. 9. Process according to the preceding claim, in which a thermal stress is imposed. 10. The method of claim 6, wherein there is a base body whose outer dimensions, including the diameter, are smaller than the inner dimensions of the casing, the base body is introduced into the inner volume of the casing. envelope, and the envelope is mechanically deformed, in particular by crimping, so as to secure it to the base body. 11. Heat exchanger comprising several tubes (2) according to any one of claims 1 to 4.