CHARACTERISTICS

DESCRIPTION

TECHNICAL FIELD

The present invention falls within the scope of the production of heat exchangers, particularly, but not exclusively, for the petrochemical sector. In particular, the invention relates to a heat exchanger tube of the two-component type, that is, formed by at least two components. The heat exchanger tube has improved heat conductivity features. The invention also relates to a heat exchanger comprising a plurality of heat exchanger tubes according to the invention and to a method for producing a heat exchanger tube.

BACKGROUND ART

As is well known, heat exchangers are used whenever there is a need to transfer heat from a high-temperature fluid to a low-temperature fluid. In particular, heat exchangers comprising a plurality of finned heat exchange elements are used in a wide range of plants (e.g., in the petrochemical, energy, manufacturing and production sectors in general).

Among the various types of exchangers known on the market, those formed of bundles of heat exchanger tubes of the two-component type are considered. In particular, the term "two- component" is meant to indicate that the tube comprises at least two components: an inner (or base) component, destined for a first fluid to pass through, and an outer component destined for a second fluid to flow over.

Typically, the base component is made of a conductive metallic material with high mechanical strength (usually steel), while the outer component is made of a metallic material with high thermal conductivity (usually aluminium, copper or its alloys). In a known embodiment thereof, the two components are formed by two coaxial tubular bodies with a cylindrical cross section.

Within the field of two-component heat exchanger tubes, those with radial fins, usually known as “ finned tubes’ are identified. In a first known embodiment, described for example in the granted patent IT0001349756, the two components of the heat exchanger tube both have a tubular configuration and are coaxially connected. In particular, the base component defines a longitudinal cavity destined for a first fluid to pass through, usually at high temperature. The outer component is instead fitted on the base component, i.e., so that the outermost surface of the inner component is connected to and in contact with the innermost surface of the outer component.

The outer component comprises a shaped portion defining, in one piece, the aforesaid fins. These fins have a circular profile if observed in a section plane orthogonal to the axis around which the two elements extend. Instead, if considered in a plane containing the axis of the exchanger tube, they define a continuous spiral coaxial with said longitudinal axis. In particular, the fins are produced through an expansion and plastic deformation operation carried out with appropriate forming means. A heat exchanger tube of this type is usually also indicated with the term "extruded" and the operating temperatures can be even higher than 250°.

In another known embodiment, the exchanger tube differs from the " extruded " one described above due to a different configuration of the outer component, while the inner one is always tubular in shape. In fact, in this case the outer component is defined by a strip of thermally conductive material that is spirally connected in a continuous manner around the outer surface of the base component. As a result of the spiral arrangement, the body of the strip defines the fins, which are also in this case circular in shape when observed in a plane transverse to the axis of the tube. Tubes based on this construction principle are also normally referred to as " applied fin tubes" .

More precisely, the strip is connected at one of its edge surfaces to the outer surface of the base component. Depending on how this connection is made, the heat exchanger tubes take different names. In this regard, Figure 2 shows an embodiment commonly indicated with the term "L finned tube ", in which the edge portion of the strip defining the fins is folded through 90°, to give the fins an L-shaped profile, if considered in a longitudinal section plane. In particular, for each fin, the edge portion coincides with the foot portion of the fin, while the body of the fin is defined by the remaining part of the strip.

The edge portion of the strip is connected to the outer surface of the base component typically by mechanical upsetting or welding. The extension of the edge portion identifies the pitch of the spiral, i.e., the longitudinal distance, between one fin and the other.

In another embodiment, shown in Figure 3 and known in the field by the term "KL finned tube" , the edge portion of the fin is folded in a manner similar to that provided for an "L finned tube " described above. In this case, however, in order to facilitate connection, the outer surface of the component is knurled before connection of the strip. Following connection, the edge portion of the fin is also knurled or in any case upset in order to increase the adhesion against the surface of the base component.

In a further known embodiment, shown in Figure 4 and known with the term "LL finned tube ", the edge portion of the strip, as well as being folded through 90° with respect to the body as in the previous cases, is shaped so as to define a first region and a second region, on different planes, respectively adjacent to and distal from the body of the strip. In this case, the edge portion is fixed so that, for each fin, the second region is in contact with the outer surface of the base component, while the first region overlaps a second region of an adjacent fin. Therefore, in a longitudinal sectional view such as that of Figure 4, for each fin, the edge portion is connected to the inner surface of the base component and simultaneously connected to and overlapping a part of the foot portion of an adjacent fin.

Figure 5 refers to a further embodiment, wherein the edge portion is inserted into a spiral groove previously formed on the outer surface of the base component. In this embodiment, normally known with the term "G embedded finned tube ", after insertion in the spiral groove, the edges of this groove are upset, by means of a suitable tool, against the opposite sides of the edge portion, so as to ensure mechanical fixing of the strip.

In general, regardless of their specific configuration (L, LL; KL, G embedded, extruded), heat exchanger tubes of the types described above, and others related to them, are used in bundles within heat exchangers, typically coolers, of large dimensions. Extruded tubes, for example, are used in air coolers destined for the petrochemical industry with operating temperatures of up to 280 °C. In the case of bundles of "embedded" G-tubes, the operating temperatures can be even higher, up to 450 °C. In any case, in these coolers, a high-temperature liquid passes through the base component of the exchanger tube and air, normally forced through a blower or other equivalent means, flow over the fins defined by the outer component (in the form of a tube or applied strip).

It is known that in order to perform their function effectively, these cooling devices require a large number of heat exchanger tubes. To give an example, in a medium sized exchanger there are typically several bundles of heat exchanger tubes, the number of which typically varies between 70 and 400 tubes per single bundle. The bundles can be arranged in series or parallel, or even operate individually, i.e., independently of the other bundles. In these devices, the length of the tubes is typically between 2.5 and 18 metres, regardless of their configuration. The heat exchange capacity, i.e., the thermal conductivity, of each tube is a determining factor, not only in terms of general efficiency, but also with regard to the construction costs and the final overall size of the cooling device, as well as all the related aspects (quantity and cost of the material used, installation and transport costs, costs of the foundations and in general of the structures necessary for installation in the system that includes the cooling device, difficulties in the design and division of the spaces of the plant itself).

There is therefore a need to provide high-performance exchanger tubes and at the same time to improve the thermal conductivity of the individual exchanger tubes, in the configurations already known (such as those described above). This with the aim not only to improve the performance, without any increase in size, of a cooling device, but also to reduce, without any decrease in performance, the size of the device, eliminating or at least attenuating the other disadvantages related to size itself.

Despite the fact that this need has been felt for many years, the solutions proposed have not so far produced acceptable results or in any case results that represent a significant step forward in the sector. In the aforesaid patent TG0001349756, for example, a solution was proposed to improve heat exchange between the two elements forming an extruded tube. In particular, raised portions are provided on the outermost surface of the inner component, which are anchored to the outer component as a result of the forces generated during its deformation to produce the fins.

Other solutions proposed in the sector aim to improve the performance of the heat exchanger tube by combining and/or choosing better performing materials. In particular, some proposed solutions concern particular geometries and/or configurations of the fins. In this regard, shaped fins have been proposed, for example bored, cut, made of two materials (for example partly in copper and partly in another conductive material). Other solutions involve improving the conductivity of the exchanger tube components by machining the innermost surface of the base component, for example a helical rifling adapted to increase turbulence.

However, these solutions are limited by the times and costs required to produce them and/or the raw material costs required for their implementation. On the whole, there is the need for a new technical solution that allows the performance of heat exchanger tubes to be greatly increased without upsetting the production process underlying their manufacture.

SUMMARY The main aim of the present invention is to provide a solution to overcome or at least mitigate the above-mentioned problems. Within this aim, a first object of the present invention is to provide a heat exchanger tube of the two-component type with improved performance, in terms of thermal conductivity, with respect to exchanger tubes of known type of the same type. A further object is to provide a heat exchanger tube in which the higher performance in terms of conductivity can be obtained without significantly increasing the process costs compared to the present ones. A further object is to provide an exchanger tube that is reliable and easy to manufacture at competitive costs.

The Applicants have found that the aim and the objects set forth above can be achieved by providing a conductive interface layer in the region, or regions, where the connection between the two constituent elements of the exchanger tube is produced. In fact, measurements and microscopic analysis carried out in this region, or in these regions, have revealed that between the surfaces of the two elements (base and outer) there is a gap (in the order of microns) determined by the morphology and by the finish of the surfaces themselves. This gap inevitably limits the heat exchange between the two elements of the tube since, due to the lack of continuity, the transmission of heat from the base component to the outer one does not occur by conduction, but by convention and/or radiation. Regardless of its specific configuration (L, LL, KL, G, etc.), in the case of an "embedded" exchanger tube, the critical region is found between the foot portion of the fins and the outer surface of the base component, while in an " extruded " tube, the microscopic gap between the inner surface of the outer tube and the outer surface of the base component affects the maximum thermal power that can be dissipated.

The idea underlying the present invention is therefore to provide a highly conductive interface formed by a layer comprising graphene in pure form or in the form of a derivative, wherein this layer eliminates or at least greatly limits the above-mentioned microscopic gap. More precisely, the Applicant has found that the intended aim and objects can be achieved by a two-component heat exchanger tube comprising:

- at least one inner component made of metallic material of tubular shape comprising at least one outermost surface and at least one innermost surface, wherein the latter defines a longitudinal cavity for the passage of a first fluid;

- at least one outer component made of metallic material comprising a base surface at which it is mechanically connected to said first component, wherein said outer component is adapted for a second fluid to flow over and wherein said base surface extends around the outermost surface of the inner component. The heat exchanger tube according to the invention is characterized in that a layer comprising graphene in pure form or in derivative form is provided between the outermost surface of the inner component and the base surface of said outer component.

Advantageously, the layer of graphene acts as a thermal bridge between the two components forming the heat exchanger tube, greatly increasing the thermal conductivity between them. During the manufacturing process of the exchanger tube, graphene in pure form or in derivative form may be applied to the base surface of the outermost component and/or to the outermost surface of the inner component so as to give rise to said layer following connection of the two components. At the end of the manufacturing process, said layer is formed of only graphene in pure form or in derivative form.

In accordance with a preferred embodiment, the outer component is configured to define at least one heat exchange fin, adapted for said second fluid to flow over, which extends around the inner component.

In accordance with a possible embodiment, the outer component is configured to define a plurality of fins, which extend around the base component continuously according to a spiral profile, considered in a longitudinal section plane containing a longitudinal axis of said inner component. Said fins have a circular shape considered on a transverse plane orthogonal to said longitudinal axis.

In a possible variant, the outer component is defined by a tubular body defining a cylindrical cavity in which the inner tubular component is housed; in this variant, the base surface of said outer component delimits said cylindrical cavity.

In another possible embodiment, the heat exchanger tube comprises a plurality of outer components each comprising a collar defining an inner surface at which it is connected to the outer surface of said inner component, each outer component defining a fin extending from said collar surrounding it. These outer components are connected to the inner component so as to be side by side longitudinally. For each of them, a layer of graphene, in pure or derivative form, is provided between the inner surface of the collar and the outermost surface of the inner component.

According to a possible embodiment, the second component is defined by a strip made of metallic material mechanically applied to the outermost surface of the inner component, at said base surface which is defined by an edge portion of said strip. In this case, the layer comprising graphene in pure form or in derivative form remains arranged between the outermost surface of said inner component and said base surface defined by said edge portion.

In a possible variant, said edge portion is a longitudinal portion folded with respect to the strip body, so that said fins, generated following the spiral application of said strip to said inner component, have a substantially L-shaped conformation, considered in a longitudinal section plane containing the longitudinal axis of the inner component; for each fin, considered on said section plane, a foot portion and a body portion are identified, where said foot portion is defined by a stretch of the edge portion of the strip. In this variant, the layer comprising graphene is provided between at least one first side of the foot portion, facing the inner component, and the outermost surface of the same inner component.

In a further possible variant, for each of the fins, considered in the longitudinal section plane indicated above, the foot portion comprises a first region and a second region, wherein the second region is between the first region and the body portion. These regions are configured to be " offset " so that an inner side of the first region and an inner side of the second region are respectively adjacent to and distal from the outermost surface of the inner component. Following spiral wrapping of the strip around the inner component, the second region of the foot portion overlaps the first region of an adjacent fin. In this variant, the layer of graphene is provided between the outer surface of the base component and the inner side of the first region of the foot portion of each fin.

Preferably, a further layer of graphene, in pure or derivative form, is provided between the overlapping regions of two adjacent fins.

In accordance with another embodiment, the edge portion of the strip is inserted into a predefined spiral groove on the outer surface of the inner component; in this case, the layer of graphene is defined at least between the surfaces of said spiral groove and the edge portion of said strip inserted therein.

According to a further embodiment, the body of said strip is folded on itself so that at least two portions thereof are facing each other defining a space inside which a further layer of graphene in pure form or in derivative form is provided.

Within this embodiment, according to a first possible variant, the body of the strip is folded so that said two portions are facing each other according to a U-shaped configuration, where said U is facing the outer surface of the base component. According to another possible variant, the body portion is folded in such a way that said two portions are facing each other and connected in such a way that said further layer is completely surrounded by the body of the strip.

According to a further possible variant, the body portion of the strip is folded in such a way that said fins, defined following application of said strip on said inner component, have a substantially "tuning fork" configuration for which a base part and a head part are identified, wherein each part is defined by two mutually facing portions of said strip, wherein said further layer of graphene is defined between the two portions defining the base part.

LIST OF FIGURES

Further features and advantages of the invention will become more evident by examining the following detailed description of some preferred, but not exclusive, embodiments of the heat exchanger tube according to the invention, illustrated by way of non-limited example, with the aid of the accompanying drawings, wherein:

- Figures 1 to 5 refer to known embodiments of exchanger tubes of the two-component type with fins;

- Figures 6 to 15 each show a possible embodiment of a heat exchanger tube according to the present invention.

The same reference numerals and letters in the figures identify the same elements or components.

DETAILED DESCRIPTION

With reference to the aforementioned figures, the present invention therefore relates to a heat exchanger tube generically indicated with the reference numeral 1. The heat exchanger tube 1 will hereinafter also be referred to with the expression "heat exchanger tube 1" or more simply "tube 1". The heat exchanger tube 1 is destined for the production of a heat exchanger device, for example a liquid-air type cooler, preferably operating in a temperature range between 100 and 500 °C.

In any case, the heat exchanger tube 1 according to the invention is of the two-component type, i.e., comprising at least two components (or elements) connected to each other, which define its structure. In particular, the tube 1 comprises at least one inner component 10 (hereinafter also referred to with the expression "base component 10") having a tubular shape and made of a metallic material. The " tubular " shape comprises an outermost surface 11 and at least one innermost surface 12; the latter defines a longitudinal cavity for the passage of a first fluid, preferably a high temperature fluid.

In accordance with a preferred embodiment, visible in the attached figures, the two surfaces 11, 12 are cylindrical and therefore the base component 10 is a hollow cylinder with a rectilinear longitudinal axis 100.

However, the term " tubular " is not limited to this configuration. In fact, the base component 10 may have a cross-section, i.e. orthogonal to the longitudinal axis 100, other than cylindrical, for example rectangular, elliptical or other. At the same time, the shape of the outermost surface 11 may also differ from the shape of the innermost surface 12.

The exchanger tube 1 comprises at least one outer component 20 comprising a body made of a metallic material defining at least one base surface 2 IB at which said body is connected to the base component 10. For the purposes of the present invention, the outer component 20 according to the invention extends around said base component 10. More precisely, the base surface 2 IB of the outer component 20 surrounds the base component 10, where this condition is considered in a transverse plane substantially orthogonal to the longitudinal axis 100 of the base component 10.

In any case, at said base surface 2 IB the body made of metallic material of the outer component 20 is mechanically connected to the outermost surface 11 of the base component 10. With the term " mechanically " is meant that the outer component 20 is connected to the base component 10 exclusively through mechanical operations/machining (for example hot deformation, cold deformation, upsetting, etc.) without the use of filler material (for example glues, bonding substances, adhesive resins) to determine the adhesion between the two components.

In any case, the outer component 20 is configured for a second fluid to flow over, preferably at a low temperature, i.e., at a temperature lower than that of the fluid passing through the cavity of the basic component 10. Preferably, in fact, the heat transmission produced by the exchanger tube 1 takes place from the first fluid towards the second fluid. However, the possibility of the second fluid having a higher temperature than the first fluid, so that the heat transfer takes place from the outer component 20 towards the inner component 10, also falls within the scope of the present invention. In any case, within the scope of the present invention, the exchanger tube 1 and the two components 10, 20 of which it is formed are configured, in terms of materials and structure, in such a way as to allow the tube to be used, individually or in a bundle with other exchanger tubes, for example to produce a cooler with operating temperatures between 100 °C and 500 °C.

According to a preferred embodiment, the body of the outer component 20 is configured so as to define at least one heat exchange fin, which extends around the base component 10, over which the second fluid flows, preferably at a low temperature, i.e., at a temperature lower than that of the fluid passing through the cavity of the base component 10. Preferably, the outer component 20 configures a plurality of fins 25 which are placed side by side in a longitudinal direction, i.e., according to a direction parallel to the longitudinal axis 100 of the base component 10.

In any case, according to the present invention a layer 5 comprising graphene in pure form or in derivative form is provided at least between the base surface 2 IB of the outer component 20 and the outermost surface 11 of the base component 10. This layer essentially forms a highly conductive interface between the two elements forming the tube 1, since graphene has a very high thermal conductivity index, between 1000 W/mK and 5000 W/mK. Through the layer comprising graphene, a thermal bridge is formed, which greatly increases the heat transmission by conduction between the two components of the exchanger tube 1.

Preferably, graphene present in the aforesaid layer is in pure form, also called "pristine". Alternatively, it may be present in the form of a derivative, mainly as graphene oxide (or "GO"). In this regard, in a possible mode of use thereof, graphene can also be functionalised with other atoms or groups of atoms in addition to oxygen. Where graphene is present in the form of a derivative, carbon preferably constitutes at least 90% by weight of the derivative, even more preferably at least 95% by weight.

According to an embodiment visible in the figures, the outer component 20 is configured to define a plurality of fins 25, which extend around the base component 10 in a continuous manner according to a spiral profile, considered in a longitudinal section plane containing the longitudinal axis 100 of the tube 1. These fins 25 have a circular shape considered in a transverse plane, orthogonal to said longitudinal axis 100. With respect to said transverse plane, the fins 25 therefore extend around the base component 10 so that they are coaxial to the inner component 10. Figure 6 refers to a first embodiment of an exchanger tube 1 according to the present invention, whose structure is substantially related to that of an "extruded" type tube. In particular, the base component 10 is formed by a cylindrical body made of a metallic material, preferably steel. The outer component 20 is also defined by a tubular body defining a cylindrical cavity, in which the cylindrical body defining the base component 10 is housed. More precisely, in this embodiment, the base surface 2 IB of the outer component 20 is cylindrical and coincides with the innermost surface of the outer component 20 delimiting the cylindrical cavity housing the base component 10. Therefore, according to the present invention, the layer 5 comprising graphene is provided between the inner cylindrical surface (base surface 2 IB) of the outer component 20 and the outer cylindrical surface 11 of the base component 10.

In Figure 6, the layer 5 of graphene extends for a length lower than the longitudinal extension of the exchanger tube 1. In any case, the layer 5 of graphene preferably extends along the entire length of the exchanger tube 1, length measured parallel to its longitudinal axis 100. The tubular body defining the outer component 20 is coaxial to the inner body 10 and surrounds it. Therefore, the layer 5 comprising graphene is substantially a cylindrical layer arranged between the two cylindrical surfaces (11, 21B) of the inner component 10 and of the outer component 20 respectively.

Again with reference to Figure 6, the outer component 20 is defined by a body made of metallic material with high thermal conductivity and easily deformable. In this regard, preferred materials for the outer component 20 are aluminium, copper or alloys thereof. In any case, the outer component 20 comprises a plurality of fins 25 which extend around the base component

10 in a continuous manner according to a spiral profile, considered in a longitudinal section plane containing the longitudinal axis 100 of the tube 1. Instead, said fins 25 have a circular shape considered in a transverse plane, orthogonal to said longitudinal axis 100.

A possible embodiment of a method for producing the exchanger tube of Figure 6 is described below. In particular, the method comprises the steps of:

(a) providing a first tubular body, preferably made of a metal material having high mechanical strength, defining the base component 10 and providing a second tubular body, made of a material having a high thermal conductivity index, defining the outer component 20;

(b) applying a layer comprising graphene in pure or derivative form to the outermost surface

11 of the basic component 10 and/or to the base surface 2 IB of the outer component 20;

(c) inserting the base component 10 inside the outer component 20; d) hot or cold deforming the second component 20 so as to make said fins 25, wherein this deformation is implemented through the action of forming means generating a pressure on said outer component 20 as a result of which the base surface 2 IB thereof adheres to the outermost surface 11 of the base component 10.

According to the invention, the connection between the two components 10, 20, in particular between the base surface 2 IB of the outer component 20 and the outermost surface 11 of the inner component 10, is produced only as a result of the hot or cold mechanical deformation generated by the forming means. Following this deformation, the layer 5 comprising graphene remains between the two surfaces (11,21B) indicated above so as to eliminate or at least considerably limit the microscopic gap that would remain even following this connection.

According to a preferred embodiment, before step b), the method comprises the step of cleaning the outermost surface 11 of the base component 10 and/or the base surface 2 IB of the outer component 20. This step is implemented to minimize the presence of impurities that could reduce the efficiency of graphene. In a first embodiment, this cleaning is carried out by means of a mechanical action (for example by sanding, brushing, conventional sandblasting, carbon dioxide blasting). Alternatively, chemical means such as chemical worms, solvents or reagents may be used.

In a preferred embodiment of the above method, in step b) graphene is applied dispersed in a liquid such as water or an organic solvent. Preferably, the application of this dispersion on the selected surfaces (the outermost surface 11 of the base component 10 and/or the base surface 2 IB of the outer component 20) is carried out by means of a mechanical deposition technique, which may be, for example, coating, spraying, application through an impregnated pad, painting, immersion deposition or glazing or other equivalent deposition techniques carried out with mechanical means.

In an alternative embodiment, still falling within the scope of the present invention, graphene dispersed in liquid may also be applied by a chemical (e.g., PVD, CVD, ALD or PLD deposition) or electrochemical/electrophoretic (using galvanic means and/or currents between anode and cathode) deposition technique.

Regardless of the manner with which the graphene dispersion is applied, in step d), the plastic deformation implemented on the outer component 20 leads to an increase in the temperature of the two components 10 and 20 following which the liquid or solvent of the above-mentioned dispersion evaporates. Therefore, at the end of the manufacturing method, the conductive interface between the two components 10,20 is formed by graphene alone in pure form or in derivative form, as appropriate.

In a possible embodiment, still falling within the scope of the present invention, the liquid in which graphene is dispersed could be evaporated before inserting the base component 10 into the outer component 20.

In a further embodiment, graphene could be applied to the surfaces of interest in powder state, i.e. without being dispersed in liquid, solvent or an organic matrix. In this regard, powdered graphene could be applied by scattering, using magnetic and/or electrostatic fields. For the same purpose, a galvanic technique comprising depositing a compatible base on the surfaces to be coated with graphene and conveying the latter through electric currents could be used. A further technique that could be used to deposit graphene powder could be plasma spray or cold plasma.

According to a preferred embodiment of the method described above, the base component 10 is mounted on a spindle which remains inside it during execution of step c). In particular, within the context of step c) the spindle is rotated so as to rotate the base component 10. Therefore, the latter is rotated during its insertion inside the second component 20, which instead remains stationary during this step.

In this regard, the spindle is preferably inserted into the basic component 10 before the application of the graphene layer on the outermost surface 11 of the base component 10 and/or on the base surface 2 IB of the outer component 20. In an alternative embodiment, the spindle could be inserted into the base component 10 after application of the graphene layer to the relevant surface(s).

In an alternative embodiment, the base component 10 is pushed and is rotated through an external wheel system without using a spindle.

Referring again to step c), the base component 10 is inserted into the outer component 20 according to a first insertion direction. At the end of this insertion, the assembly of the two components 10,20 is moved in a second direction, opposite the first one, so as to be subjected to the action of the forming means.

In this regard, according to a possible embodiment of the manufacturing method, in step d) the forming means have a configuration substantially referable to that described in document US 2779223. In substance, they comprise a group formed by three blade tool units arranged in positions angularly equally spaced apart by 120° around the longitudinal axis 100 of the exchanger tube 1. During the movement in said second direction, the tool units act on the outer component 20, pressing it against the base component 10 and deforming its outer surface so as to define the fins 25, which have the configuration indicated above.

The manufacturing method described above could also be implemented in-line. In this case, the assembly of the components 10, 20 would be fed in the same direction of movement already followed previously by the base component 10 to be inserted into the outer component 20.

In a possible embodiment of the manufacturing method, step d) comprises the use of lubricant containing graphite (also of the intercalated or expandable type), which is deposited on the outer surface of the outer component 20 during the action of the forming means and/or on the fins 25 produced following the action of said forming means. Advantageously, the high temperatures and shear stresses, which are generated on the surfaces on which the forming means act, allow an in-situ conversion, on these surfaces, of graphite into graphene, with a further increase in the thermal conductivity of the exchanger tube.

In any event, also in this case, at the end of each of the production processes described above, the conductive interface between the two components 10, 20 is formed only by graphene in pure form or in derivative form, as appropriate.

In a further possible embodiment of the manufacturing method, at the end of step d), a further layer of graphene is applied to one or more regions of the outer component 20 to increase the conductivity of its outer surface. This further layer, for example, could be applied onto one or more regions of the surface of the fins 25, for example in proximity of the ends of the fins and/or in proximity of the foot of these fins.

This further layer may be applied according to any one of the techniques above indicated with reference to the layer of graphene provided between the two components 10, 20. In a possible embodiment, for example, the application of said further graphene layer could take place by painting the fins 25 in the regions of interest. This painting could involve the entire surface of the outer component 20 as well as any end portions of the base component 10 not covered by the outer component 20.

In a possible embodiment thereof, the manufacturing method could also comprise the further step of making incisions on the fins 25 to increase turbulence and thus heat exchange with the fluid flowing over them. In this regard, such incisions could be made with the technique known in the art with the term " serrated " whereby the incisions are made by means of blades acting on the top of the fins in a direction parallel to the longitudinal axis 100 of the tube 1. The incisions defined with this technique appear to be substantially radial on a plane of observation substantially orthogonal to said longitudinal axis 100.

In other possible embodiments, the fins 25 could also be bored or punched, optionally in combination or not with incisions such as those described above or of other type.

Figures 7 to 13 refer to further possible embodiments of a heat exchanger tube according to the invention. In particular, these embodiments are of the "applied fin" type, i.e., in which the fins are defined following the spiral application, on the outermost surface 11 of the base component 10, of the second component 20, which for this purpose is defined in the form of a strip of conductive metallic material, preferably an aluminium or copper strip. With reference to Figures 7 to 10, hereinafter the expression " strip 20" will be used to indicate the " second component 20" . The strip 20 is mechanically applied to the outermost surface 11 of the base component 10. Therefore, the strip 20 extends around the first component 20, so that each fin defined thereby surrounds the base component 10 thereby resulting coaxial thereto.

Also in this case, regardless of the manufacturing process with which the strip 20 is mechanically applied to the base component 10, the conductive interface between the two components 10,20 is formed by graphene alone in pure form or in derivative form, as appropriate.

Specifically, Figure 7 refers to an embodiment relating to an exchanger tube of the "L finned" type. In particular, the strip 20 is mechanically applied, at an edge portion 3 IB thereof, to the outermost surface 11 of the base component 10.

Again with reference to Figure 7, this edge portion 3 IB is defined by the folding of an edge of the strip 20, so that the fins 25, generated following the spiral application of the strip 20, have a substantially L-shaped configuration, considered in a longitudinal section plane containing the longitudinal axis of the exchanger tube 1.

Considering the fins 25 in a longitudinal section view, as in Figure 7, a foot portion 4 IB and a body portion 41C are identified for each fin 25. The foot portion 4 IB of each fin 25 is therefore defined by at least one stretch of the edge portion 3 IB of the strip, while the body portion 41C is defined by the body of the strip 20 with respect to which the edge portion 3 IB is folded.

For each fin 25, a first side LI facing the outermost surface 11 of the base component 10 and a second side L2 opposite the first side LI are identified on the foot portion 41B. In this embodiment, the layer 5 comprising graphene is provided between the first side LI of the foot portion 4 IB and the outer surface 11 of the base component 10. It is evident that, according to the present invention, the first side LI essentially defines the base surface of the second component 20 at which it is connected to the outermost surface 11 of the first component 10.

A possible manufacturing method of the heat exchanger tube of Figure 7 is described below, which in substance comprises the steps of: al) providing a first tubular body made of metallic material, preferably with high mechanical strength, defining the base component 10; a2) providing a strip made of metallic material, preferably with a high thermal conductivity index, defining the outer component 20; a3) folding an edge portion 3 IB of the strip for the whole of its length according to an L-shaped configuration; a4) applying a layer comprising graphene in pure or derivative form to the outermost surface 11 of the base component 10 and/or to a first side LI (base surface of the second component 20) of the edge portion 3 IB destined to be mechanically connected to the outermost surface 11 of the base component 10 a5) mechanically connecting, according to a spiral winding, the edge portion 3 IB of the strip 20 to said outer surface 11 of the base component 10 so that said layer 5 comprising graphene is located between said first side LI of said edge portion 3 IB and said outermost surface 11 of the base component 10.

In accordance with a preferred embodiment, the mechanical connection of the edge portion 3 IB takes place by means of an upsetting thereof against the outer surface of the base component 10. Said connection could also be carried out by means of autogenous spot welding or in any case by any other technique suitable for the purpose that does not require filler material.

In any case, according to the invention, at the end of mechanical connection of the strip 20 to the base component 10, the layer 5 forms a conductive interface between the two components 10, 20 formed by graphene alone or by graphene in derivative form.

Figure 8 shows another possible embodiment of an exchanger tube according to the invention relating to an exchanger tube of the "KL finned" type. Similarly to what is shown in Figure 7, also in this case the strip 20 is connected to the outer surface 11 of the base component 10 by means of an edge portion thereof 31 folded with respect to the body of the strip 20 so that, following spiral winding, the fins 25 have a substantially L-shaped configuration. Therefore, also in this case the layer comprising graphene in pure or derivative form is provided between a first side LI (base surface) of the edge portion 3 IB and the outer surface 11 of the base component 10.

In fact, the embodiment of Figure 8 differs from that of Figure 9 in the manufacturing method, which provides for knurling the outermost surface 11 of the base component 10 before applying the layer 5 comprising graphene thereon and in any case before applying the strip 20 defining the fins 25.

In any case, the edge portion 3 IB of the strip 20, i.e. the foot portion 41B of the fins 25, is pressed against the outer surface 11 of the base component 10, possibly also by means of knurling, until the two parts are firmly fixed. Therefore, in accordance with the objects of the invention, the connection between the two components 10, 20 is in any case produced through a mechanical operation.

Therefore, with respect to the manufacturing method described above comprising steps al) - a5), for producing the exchanger tube 1 of Figure 8, before step a5), the step of knurling the outermost surface 11 of the base component 10 is also included. Preferably, following step a5), the further step of knurling the edge portion 3 IB on the side opposite the one (first side LI) in contact with the layer 5 of graphene is also included.

Figure 9 refers to a third embodiment of an exchanger tube according to the invention relating to an “LL finned” type exchanger tube. Also in this case, the strip 20 is connected to the outer surface 11 of the base component 10 by means of an edge portion thereof 31 folded with respect to the body of the strip 20 according to an L-shaped configuration. Differently from the embodiment described in Figure 9, in this case, for the edge portion 31, a first region 31-1 and a second region 31-2 are identified, where said second region 31-2 is included between the first region 31-2 and the body of the strip 20. In particular, the two regions 31-1, 31-2, although connected, are " offset " so that the inner side (i.e. the side facing the base component 10) of the first region 31-1 is substantially adjacent to the outer surface 11 of the base component 10, while the inner side of the second region 31-2 is spaced apart therefrom.

As shown in Fig. 9, following spiral winding around the base component 10, the two regions 31-1, 31-2 indicated above are recognised in the foot portion 41B of each fin 25 considered in a longitudinal section plane. More precisely, for each fin 25, the second region 31-2 of the foot portion 4 IB is overlapped to the first region 31-1 of an adjacent fin.

In this embodiment, at least one first layer 5 comprising graphene is provided between the outermost surface 11 of the base component 10 and the inner side (indicated with LI*) of the first region 31-1 of the foot portion 41B. Therefore, in this embodiment, the base surface of the second component 20 is identified in said inner side LI* of the first region 31-1 of said foot portion 41B.

Preferably, a second layer 51 of graphene is provided between the overlapping regions of two adjacent fins.

With respect to the manufacturing method described above comprising steps al) -a5), in the case of manufacturing the tube 1 of Figure 9, the method comprises shaping the edge portion 3 IB of the strip 20 so as to configure the two regions 31-1, 31-2 defined above. This shaping could be carried out in the context of above indicated step a3) or alternatively before or after step a3). Preferably, in the context of step a4) graphene in pure form or in the form of a derivative is applied to the entire inner side of the edge portion 31 of the strip 20 so as to define said first layer 5 between the outer surface 11 of the base component 10 and the inner side of the first region 31-1 of the edge portion 31 and said second layer 51 between the overlapping regions of two adjacent fins, considered in a longitudinal section plane.

Figure 10 relates to a further embodiment of the tube according to the invention, relating to a "G embedded" tube. In this case, the edge portion 3 IB of the strip 20 is not folded, but inserted into a predefined spiral groove on the outer surface 11 of the base component 10. In a preferred embodiment, graphene in pure form or in derivative form is deposited in the groove before carrying out this insertion. Once the strip 20 has been inserted into the groove, the groove edges are pressed/upset against the two opposite sides of the strip 20 thereby fixing the latter to the base component 10. In a possible embodiment, graphene in pure form or in derivative form is previously applied also to the strip 20, at least on its edge portion 31.

In any case, following fixing the strip 20, a layer 5 comprising graphene is defined at the interface between the spiral cavity defined on the outer surface 11 of the base component and the edge portion 31 of the strip 20 inserted therein. In this embodiment, the sides of the edge portion 31 of the second component 20 inserted into the spiral groove practically form the base surface at which the second component 20 is mechanically connected to the inner component 10

A manufacturing method of the heat exchanger tube 1 of Figure 10 is described below. This method comprises the steps of: bl) providing a first tubular body made of metallic material, preferably with high mechanical strength, defining the base component 10; b2) providing a strip 20 made of metallic material, preferably with a high thermal conductivity index, defining said outer component 20; b3) forming a spiral groove on the outer surface 11 of the base component 10; b4) depositing graphene, in pure form or in the form of derivative, in said spiral groove and/or at the sides of an edge portion 3 IB of the strip 20 destined to be connected to said outer surface 11 of said base component 10; b5) mechanically connecting said strip 20 to said outer surface 11 of said base component 10 by inserting the edge portion 3 IB into said spiral groove and upsetting/pressing, following said insertion, the edges of the groove against the opposite surfaces of said strip 20 thereby blocking it in the spiral groove.

According to a preferred embodiment, before step b5) the strip 20 is preformed so as to impart thereto a circular shape suitable for connection to the outermost surface 11 of the base component 10. Preforming of the strip 20 may be carried out before or after the deposition of graphene, i.e. before or after the execution of step b4).

In the context of step b3), the spiral groove is formed by means of a suitable tool acting on the outer surface 11 while the base component 10 is rotated about its longitudinal axis 100. In the context of step b5), the base component 10 is advanced along a movement direction while always keeping it in rotation. The strip 20 is placed around the base component 10 and is inserted into the spiral groove after having taken it to the same tangential speed. Immediately afterwards, the edges of the groove are pressed/upset so that the strip 20 is firmly fixed.

Figures 11, 12 and 13 refer to further possible embodiments of an exchanger tube 1 with applied fins. In particular, with respect to the embodiments shown in Figures 7 to 10, in this case the body of the strip 20 is folded over itself so as to define a space between at least two portions that are facing each other following this folding. Within this space, a layer 55 of graphene in pure form or in derivative form is provided. Preferably, folding of the strip 20 and depositing of graphene in said space are operations carried out before fixing the strip 20 on the outer surface 11 of the base component 10.

In this regard, for each of the embodiments shown in Figures 11, 12 and 13, the strip 20 could be applied according to one of the principles described above commenting the embodiments shown in Figures 7 to 10. In the embodiment shown in Figure 11, the body of the strip 20 is fixed to the outermost surface 11 of the base component 10 according to the same principle described above commenting Figure 10. The body of the strip 20 is instead folded over itself so that for each fin 25, considered in a longitudinal section plane, two portions 25-1, 25-2 are facing each other according to a U- shaped configuration, where this U is facing the outermost surface 11 of the base component 10. In this space, said further layer 55 of graphene is provided. In this respect, in accordance with a possible embodiment, graphene can be applied, before folding the strip 20, onto one or both surfaces of the portions 25-1, 25-2 which will then be facing each other after folding this strip.

Differently from the solution described above, in the one shown in Figure 12, the body of the strip 20 is always folded so as to define, for each fin 25, two mutually facing portions 25-1, 25- 2 that in this case are however connected so that the space defined between them is closed, where this space is always considered in the same longitudinal section plane in which the fins are considered. Graphene in pure or derivative form is provided in this closed space and is therefore completely surrounded by the body of the fin 25.

Also in this case, folding of the body of the strip 20 and application of graphene are operations carried out before the strip 20 to be applied to the base component 10. In this regard, the edge portion 3 IB can be applied according to the principle described for the exchanger tube in Figure 10 or according to one of the principles described for any one of the embodiments in Figures 7 to 10.

In the embodiment shown in Figure 13, considering the fins 25 in a longitudinal section plane, these have a substantially "tuning fork" configuration, in which it is possible to identify a base portion 251 and a head portion 252. The base portion 251 defines the edge portion 31 that is applied to the outer surface 11 of the base component 10, according to any one of the methods described above.

The two portions 251, 252 have a substantially symmetrical configuration with respect to a transverse plane which is orthogonal to the longitudinal axis 100. This configuration is obtained following folding of the strip 20 so that both portions 251, 252 are defined by two facing portions of the strip 20, 251A-251B and 252A-252B respectively. Said further layer 55 of graphene in pure or derivative form is provided between the two strip portions 251A-251B defining the first portion 251. Advantageously, in the embodiments shown in Figures 11 to 13, the presence of said further layer 55 of graphene further increases the conductivity of the fins 25 and therefore the performance of the exchanger tube 1.

Figure 14 relates to a further possible embodiment of a heat exchanger tube according to the invention. In particular, in this case the heat exchanger tube 1 comprises a plurality of outer components 20 each comprising a collar 23 defining an inner surface (i.e. the base surface according to the invention) at which it is connected to the outermost surface 11 of the base component 10. This inner surface of the collar 23 surrounds the outermost surface of the base component 10.

Each outer component 20 defines a fin 25 that extends from said collar 23 surrounding it and thus surrounding the base component 10. The outer components 20 are connected to the base component 10 so as to be side by side longitudinally along a direction of extension of the exchanger tube 1. For each outer component 20, a layer of graphene, in pure form or in derivative form, is provided between the inner surface of the collar 23 and the outer surface 11 of the base component 10.

Also for the embodiment in Figure 14, at the end of the production method of the heat exchanger tube, the layer 5 between the two components 10, 20 is formed of graphene only, in pure form or in derivative form.

In the embodiment of Figure 14, the base component 10 has a circular cross-section. The inner surface defined by the collar 23 is cylindrical and coaxial to the base component 10. This latter, as well as the collar 23, may have a different configuration to that shown in Figure 14.

Again with reference to this latter, the fins 25 defined by the outer components 20 have a square configuration considered according to a plane of observation orthogonal to the longitudinal axis 100 of the tube 1. However, within the scope of the present invention it would also be possible for the fins to have a different configuration, for example circular or elliptical. In this regard, the fins 25 could have incisions formed according to the " serrated " technique indicated above with reference to the possible variant of the solution shown in Figure 6.

With reference to the embodiments shown in Figures 1 to 14, for each of these further layers of graphene in pure form or in derivative form could be applied in one or more regions of the outer component 20 or of the outer components 20, in a manner entirely analogous to that indicated above with reference to the variant of the solution shown in Figure 6. Fig 15 shows a further possible embodiment of a tube 1 in which the outer component 20 does not define fins, having a tubular configuration defining a cylindrical cavity in which the base component 10 is inserted. In this case, the outer component 20 completely surrounds the base component 10. In this embodiment, the layer of graphene, in pure form or in derivative form, is therefore provided between the outermost surface 11 of the base component 10 and the innermost surface (base surface 2 IB) of the outermost component 20. The outermost surface 22 of the outer component 20 is destined for the second fluid to flow over and could be coated, completely or partially, by a further layer of graphene.

Also for the embodiment in Figure 15, at the end of the production method leading to the production of the heat exchanger tube, the layer 5 forms a conductive interface between the two components 10,20, which is formed by graphene only, in pure form or in derivative form, as appropriate.

The present invention therefore also relates to a heat exchanger comprising a plurality of heat exchange elements 1 according to the invention. More precisely, a heat exchanger according to the invention may comprise a plurality of heat exchanger tubes 1 according to any one of the embodiments described and shown in the figures, as well as other possible equivalent embodiments in any case falling within the scope of the present invention.

In a possible embodiment, a heat exchanger according to the invention may comprise one or more bundles of exchanger tubes of the type shown in Figure 10, and one or more bundles of exchanger tubes without fins of the type shown in Figure 15. The tube bundles are arranged so as to operate in series, i.e. so that the exchanger tubes without fins produce a first thermal gradient, i.e. to reduce the thermal gradient required for the exchanger tubes comprising fins.

The technical solutions indicated above allow the aims and objects to be fully achieved. The use of graphene only, in pure form or in derivative form, between the interface surfaces of the two components increases the thermal conductivity of the heat exchanger tubes, thus making it possible to produce, with the same size, heat exchanger devices with higher performance or to reduce, with the same performance, the size of said heat exchanger devices.