Tube for heat exchange

Abstract

The present invention relates to a device for heat exchange between a hot gas and a liquid coolant. The tube has a flat configuration, with intermediate channels formed by a set of fins and two lateral channels with a larger hydraulic diameter. The invention is characterized by a specific way of reducing the passage section in order to prevent a by-pass effect in the tube so that gas flow is directed mainly through the set of fins.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. EP24382943.9, filed Sep. 2, 2024. The applications are herein incorporated by reference in their entireties, including without limitation, the specification, claims, and abstract, as well as any figures, tables, appendices, or drawings thereof.OBJECT OF THE INVENTION

[0002] The present invention relates to a device for heat exchange between a hot gas and a liquid coolant. The tube has a flat configuration, with intermediate channels formed by a set of fins and two lateral channels with a larger hydraulic diameter.

[0003] The invention is characterized by a specific way of reducing the passage section in order to prevent a by-pass effect in the tube so that gas flow is directed mainly through the set of fins.

[0004] The present invention has a significant environmental impact, helping to reduce nitrogen oxide emissions.BACKGROUND

[0005] One of the most intensely developed fields of the art is the field of heat exchangers, particularly hot gas and liquid coolant heat exchangers. The application of heat exchangers of this type are of particular interest in exhaust gas recirculation systems (or EGR) in internal combustion engines.

[0006] Exhaust gasses are gasses at very high temperature, around 600° C., which have no oxygen or a very small amount of oxygen. In EGR systems, this gas is used for mixing with intake air, thereby reducing the oxygen available in the mixture of oxidizing agent entering the engine cylinders. A reduced amount of oxygen in the intake considerably reduces the formation of nitrogen oxides, where oxides of this type are very harmful to health.

[0007] The recirculated exhaust gas introduced into the intake must first be cooled, since the introduction of hot gas into the intake strongly affects the performance of the internal combustion engine. A high temperature implies a low gas density and, therefore, less cylinder filling. Engine power is directly proportional to the degree of cylinder filling.

[0008] The cooling function of the recirculated gas is carried out in a heat exchanger that reduces its temperature by removing heat from the gas by means of a liquid coolant. Another significant problem to be solved is the space occupied by this device since the space in the engine compartment is limited.

[0009] Reduction in the size of the heat exchanger is achieved with highly efficient tubes for heat exchange between the hot gas and the liquid coolant.

[0010] One of the most efficient configurations is that formed by flat tubes inside which there is a set of fins. The flat tube configuration shows mainly two main flat walls extending longitudinally and connected laterally by a curved section. According to a cross-section, there are two straight segments connected by two arc-shaped segments on both sides.

[0011] The dissipating fins located in the central part connect one flat wall to another, establishing a set of internal channels intended for the passage of hot gas. The hot gas gives off its heat to the fins, which in turn transfer said heat to the flat walls of the tube.

[0012] The configuration of the tube, closed by the curved side segments, results in the two lateral channels having a hydraulic diameter larger than the hydraulic diameter of the dissipating fins. The hydraulic diameter of a channel or conduit is defined as the amount Dh-4 A / p, where A is the cross-section area of the channel or conduit and p is the perimeter of said cross-section. In this way, the hydraulic diameter can be measured not only in a channel or conduit with a circular section but also in a channel or conduit with any perimeter shape.

[0013] Of particular interest is the section with a convex perimeter shape, that is, sections that verify that, given any two distinct points of the perimeter, the points of the straight line connecting them are all points inside the section.

[0014] Since the hydraulic diameter of the lateral channels is larger than the hydraulic diameter of the channels of the dissipating fins, their resistance to the passage of the hot gas flow is lower, giving rise to two preferred paths for the gas, the paths formed by the two side channels.

[0015] If a significant part of the total gas flow passes through the lateral channels, this hot gas is not cooled with the same efficiency as the gas passing through the channels of the set of fins. Another effect caused by the passage of hot gas through the lateral channels is a pressure drop, and therefore a reduced speed of the gas through the channels of the set of fins. A reduced speed of the hot gas, since it is a gas coming from the combustion chamber, causes a progressive deposition of particles that gradually reduce the section and hinder heat transfer to the fin. This process is known as fouling. That is, the reduction in speed in the central channels causes a gradual reduction in heat exchanger performance and increased fouling because the speed is not sufficient to sweep away the deposited particles or prevent their deposition.

[0016] This problem has been identified in the prior art and an attempt has been made to avoid it at the inlet end of the pipe by adding an additional piece. There are two solutions known in the prior art, either including a plate that covers the inlet of the lateral channels or inserting an element also into the lateral channels that prevents or limits the passage of hot gas in the lateral channels.

[0017] In either case, it is necessary to design and manufacture an additional piece as well as include manufacturing steps that position and secure these gas passage limiting pieces.

[0018] Patent application No. EP2372287 A1 describing the use of a plate located at the end of the exchanger intended for covering at least partially the lateral channels, reducing the passage section, is known.

[0019] Patent application No. EP3135895 A1 describing the use of plugs intended to be inserted at least partially into the lateral channels, reducing the passage section, is known.

[0020] Patent application No. EP3726176 A1 describing the use of a clip intended to be inserted at least partially into the lateral channels, reducing the passage section, is known.

[0021] The prior art does not show how to solve the problem of reconfiguring the tube to avoid the use of additional pieces that prevent the reduction of the speed of the gas in the channels of the set of dissipating fins housed in the tube. The present invention solves the identified problems without having to manufacture and add an additional piece to the tube.SUMMARY

[0022] A first aspect of the invention relates to a tube suitable for heat exchange between a hot gas and a liquid coolant, and more preferably, a tube adapted for heat exchange between a hot gas and a liquid coolant.

[0023] According to a first aspect of the invention, the tube is as follows:

[0024] the tube has a flat configuration, configured by means of two essentially parallel flat walls extending along a longitudinal direction and joined on both sides by means of a curved wall segment;

[0025] the tube comprises a set of fins housed inside the tube extending from the inner surface of one flat wall to the inner surface of the other flat wall;

[0026] the set of fins comprises a plurality of internal channels and a lateral channel on each side, the lateral channel being the one formed between the group of fins and the curved wall segment;

[0027] the hydraulic diameter of the lateral channels is larger than the hydraulic diameter of the internal channels, wherein the hydraulic diameter is D_h=4 AVp, where A is the cross-section area of the channel and p is the perimeter of said cross-section, and

[0028] wherein at least one curved wall segment comprises a deformed portion, with a configuration of the deformed portion penetrating into the lateral channel reducing the section thereof.

[0029] The flat tube comprises two essentially parallel flat walls, “essentially” being understood as the possibility of having certain manufacturing deviations. These flat walls are spaced from one another to leave the set of fins interposed in order to transfer the heat from the hot gas to the flat walls. That is, in an operative mode, the hot gas is in contact with the flat tube and, to a greater extent, with the fins.

[0030] The hot gas gives off heat to the fins by convection and the fins in turn transfer the heat to the tube by conduction since the fins and tube are in contact with one another or they are both attached together by welding, preferably by brazing. The result is an efficient heat transfer from the hot gas to the tube. In an operative mode, the tube is bathed externally in a liquid coolant which removes from the tube heat coming from the hot gas.

[0031] According to a preferred example, the flat walls extend in the form of two rectangular plates joined on both sides by means of a curved wall segment. This curved wall segment forms a channel with a hydraulic diameter larger than the hydraulic diameter of the internal channels existing between dissipating fins. It is considered that the tube has a flat configuration because the area of the flat walls is larger than the area of the curved wall segment.

[0032] The hot gas entering the tube having a flat configuration runs into two types of channels, the channels formed by the set of fins and the two lateral channels where these lateral channels have a hydraulic diameter larger than the hydraulic diameter of the intermediate channels located between the fins of the set of fins.

[0033] Larger hydraulic diameter provides a lower hydraulic resistance to the passage of hot gas, so it gives rise to a preferred path or by-pass which reduces the speed of passage through the channels through the fins. However, the lower hydraulic resistance of the lateral channels is increased by means of a deformed portion of the curved wall segment having a configuration penetrating into the lateral channel in order to reduce the section thereof.

[0034] Section reduction increases the hydraulic resistance to be at least the hydraulic resistance of the internal channels through the fins, and more preferably to be greater than the hydraulic resistance of the internal channels through the fins.

[0035] In a preferred example of the invention, the deformed portion of the curved wall segment establishes the closure of the passage of the lateral channel except for an opening established between the deformed portion and the set of dissipating fins and with a spacing given by a separation tolerance between 1 and 5 tenths of a millimeter, more preferably between 1 and 4 tenths of a millimeter, and more preferably between 1 and 3 tenths of a millimeter, and more preferably between 1 and 2 tenths of a millimeter.

[0036] According to an embodiment applied to the embodiments described above, the deformed segment is spaced from both ends according to the longitudinal direction.

[0037] According to this embodiment, the deformed segment locally affects the curved wall segment but said deformation is spaced from the end of the tube which is intended for connecting with a baffle or with a manifold. In this way, these connections of the ends of the tube are not affected by the deformation and maintain the tolerances, preventing construction and assembly problems.

[0038] According to an embodiment applied to the embodiments described above, the set of fins is formed by a sheet corrugated by stamping, with the direction of the corrugation being in accordance with a direction perpendicular to the longitudinal direction and parallel to the flat walls.

[0039] This embodiment uses a stamped sheet which is configured with a shape which, according to a cross-section with respect to the longitudinal direction, shows a corrugated profile, alternating segments intended to be attached to one of the flat walls and segments intended to be attached to the other flat wall, leaving between both segments a wall that configures a surface which, in an operative mode, is exposed to the hot gas. Between both walls extending between the segments attached to the flat walls, the fins, internal channels are formed between the fins.

[0040] Manufacturing by means of a single stamped sheet allows forming a piece which is inserted into the tube formed by the two spaced flat walls and the curved wall segments. Once the stamped sheet is positioned inside the tube, attachment between the stamped sheet and the tube is performed, preferably by means of brazing.

[0041] One embodiment of this example is by using sheets formed by metals with two melting temperatures, the material with a lower melting temperature being located on the outer face that comes into contact with the surface to be attached and the material with a higher melting temperature being located in the center in order to maintain structural integrity when the temperature to which the assembly is subjected is a temperature between both melting temperatures.

[0042] According to an embodiment applied to the embodiment described above, the corrugated sheet additionally shows a second corrugation according to the longitudinal direction.

[0043] According to this embodiment, the stamped sheet shows two corrugations, a first transverse corrugation and a second longitudinal corrugation. The transverse corrugation is the one seen according to a cross-section with respect to the longitudinal direction and it is the one that allows forming the fins extending between one flat wall and another flat wall, in turn forming the internal channels between the fins.

[0044] The second corrugation, the longitudinal corrugation, is the one which establishes the sinusoidal trajectory of the internal channels between the fins. The shape of the longitudinal corrugation is such that each internal channel, particularly those located closest to the side curved wall segments, along the trajectory thereof, is arranged spaced apart from and close to the wall in the side curved segment.

[0045] According to an embodiment applied to the embodiment described above, the position of the deformed portion according to the longitudinal direction is at a point of minimum distance between the corrugation and the inner wall of a curved wall segment.

[0046] According to the example described above, the second corrugation, the longitudinal corrugation, establishes a condition of being arranged in an alternating manner spaced apart from and close to the wall in the side curved segment. According to this embodiment, the deformed portion is positioned longitudinally in a position coinciding with the closest place, establishing a greater constriction of the lateral channel.

[0047] This condition shows how, an embodiment including more than one deformed portion, for example, close to both ends of the tube and also in both channels, can be located at points according to the longitudinal direction that does not involve a condition of symmetry according to a central longitudinal axis of the tube.

[0048] According to an embodiment applied to the embodiments described above, the deformed portion is spaced from the set of fins.

[0049] According to this embodiment, there is no contact between the fins and the deformed portion, preventing deformations or damage to the fins. Although there is no contact, the passage of hot gas through this separate region is minimal and it maintains a hydraulic resistance higher than that of the internal channels located between the fins of the set of fins.

[0050] This condition also allows compensating for positional and shape tolerances of the fins with respect to the deformation on the wall in the side curved segment.

[0051] According to an embodiment applied to the embodiments described above, the deformed portion shows, according to a projection in a plane parallel to the flat walls, an arc configuration, wherein the arc has a minimum ratio between the radius of curvature and thickness is in the range [13-20], more preferably in the range [14-19], more preferably in the range [15, 18], more preferably in the range [16-17.5] and more preferably in the range [16.1-17.2].

[0052] In reality, the deformed portion causes several types of deformation. According to the projection in a plane parallel to the flat walls, the deformation is an arc-shaped indentation that penetrates into the lateral channel with a first radius of curvature having its center outside the tube. This is the main deformation, however, the transition between the arc and the wall in the side curved segment without deformation has a second radius of curvature in the same parallel plane and with the center inside the tube. In this case, the minimum ratio between this second radius of curvature and the thickness is in the range [0.9-3.1], more preferably in the range [1-3], and more preferably in the range [1.25-2.75].

[0053] According to a preferred example, the deformed surface also shows a curvature according to a plane of section which is perpendicular to the longitudinal direction X-X′ and passes through the center of the deformed arc. This curvature is characterized by means of a third radius of curvature with a center outside the tube. In this case, the minimum ratio between this third radius of curvature and the minimum thickness is in the range [0.7-2.3], more preferably in the range [0.9-2.1], and more preferably in the range [1-2].

[0054] In the three radius it is indicated that the ratio in the identified ranges is the minimum given that the curvature may vary. The use of the minimum ratio corresponds to a minimum radius for a constant thickness and is the point where the deformation was greater, and therefore where it is more likely for cracks to appear, for example.

[0055] A second aspect of the invention relates to a method of manufacturing the tube and is defined by the following steps:

[0056] providing a tube having a flat configuration, configured by means of two essentially parallel flat walls extending along a longitudinal direction and joined on both sides by means of a curved wall segment;

[0057] inserting into the tube a set of fins leaving a lateral channel between the set of fins and each curved wall segment;

[0058] pressing the curved wall segment in a region of its outer surface causing a deformed portion which narrows the section of the lateral channel;

[0059] attaching the set of fins to the tube, preferably by brazing.

[0060] According to this second aspect of the invention, the method provides the tube having a flat configuration inside which a set of fins can be housed by insertion.

[0061] Preferably, the set of fins is formed by a single sheet metal element configured by stamping. The folded configuration is formed by means of a corrugation, giving rise to fins with a corrugated cross-section. A preferred example uses a square wave corrugation which allows generating top and bottom surface segments that favor attachment with the inner surface of the flat tube.

[0062] According to another example applicable to the foregoing, the set of fins also shows a second longitudinal corrugation which causes a sinusoidal flow.

[0063] Also preferably, the set of fins has a material on their surfaces with a melting point lower than the melting point of the central part, allowing subsequent attachment by brazing without having to add any brazing paste.

[0064] The insertion preferably leaves the set of fins centered in the flat tube and according to the transverse direction (transverse being understood as the direction perpendicular to the longitudinal direction and extending parallel to the planes defined by the tube) and leaves a channel between the set of fins and each curved wall segment.

[0065] The set of fins inserted into the tube preferably maintains its position inside the tube by friction before the definitive fixing thereof, preferably by means of brazing. Once the set of fins is fixed inside the tube, it is when deformation by pressure is caused on the sides of the tube, in the curved wall segments, causing recesses which reduce the passage section of the lateral channels existing between the group of fins and the curved wall segment.

[0066] According to one embodiment, the deformation force to cause the recesses is carried out with protrusions acting laterally with a calibrated displacement according to the degree of deformation required.

[0067] Once the tube has been deformed, the set of fins and the tube are attached, for example, by passing the assembly through a furnace for brazing same.BRIEF DESCRIPTION OF THE DRAWINGS

[0068] These and other features and advantages of the invention will become more apparent based on the following detailed description of a preferred embodiment, given only by way of illustrative and non-limiting example, in reference to the attached figures.

[0069] FIG. 1 This figure shows a perspective view of an embodiment of the exchange tube.

[0070] FIG. 2 This figure shows a front view of the same embodiment seen from one of the ends of the tube. The right side of the view includes a rectangle in a dashed line which identifies the area that has been enlarged in the lower part of the figure in order to identify the third radius of curvature.

[0071] FIG. 3A This figure shows a top view of the same embodiment in order to allow seeing the deformed portions and the passage restriction imposed on the lateral channels. It has been included on the left side, on one of the deformations, a rectangle in a dashed line which identifies the area that has been enlarged in the upper part of the figure in order to identify the first and second radius of curvature.

[0072] FIG. 3B This figure shows the same view as that of FIG. 3A but sectioned through a midplane in order to allow seeing the inner structure of the tube and the fins.

[0073] FIG. 4 This figure shows a perspective view of the same section as that of FIG. 3B in order to observe the configuration of the fins.DETAILED DESCRIPTION

[0074] According to the first inventive aspect, the present invention relates to a tube for heat exchange between a hot gas, preferably the exhaust gas coming from the combustion chamber of an internal combustion engine, and a liquid coolant. The use of this heat exchange tube allows the temperature of the exhaust gases from an internal combustion engine to be reduced, allowing use thereof as recirculated gas in EGR systems.

[0075] Now in reference to FIG. 1, according to a preferred example, the tube (1) is a flat tube such as the one shown in a perspective view.

[0076] The tube (1) is said to be flat because it is delimited by two flat main walls (1.1) arranged parallel to one another. According to the described example, the sides are joined by curved wall segments (1.2), in this example in the form of semicylindrical segments, allowing continuity to be established in the slope of the wall of the tube (1) without edges that cause stress concentrations.

[0077] FIG. 1 shows a portion of the tube (1) according to a longitudinal direction (X-X′) where one of the ends is shown in foreground.

[0078] As shown in FIG. 2 which allows seeing the inside of the tube (1) through the opening of the end, a set of fins (1.3) intended for increasing heat exchange between the inside of the tube (1) and the outside is arranged therein.

[0079] This end in FIG. 1 does not show the set of fins (1.3) since they are set back a distance d, with distance d being identified in FIG. 3B. This aspect will be described below.

[0080] Hot gas passes through the inside of the tube (1). The hot gas gives off its heat to the walls (1.1, 1.2) of the tube (1) because the hot gas is either in direct contact with the inner surface of the walls (1.1, 1.2) or in indirect contact through the set of fins (1.3).

[0081] When heat is given off through the fins of the set of fins (1.3), the hot gas gives off heat to the fin by convection and the fin transfers the heat by conduction to the inner surface portion of the wall of the tube (1) with which it is in contact. Finally, the outside of the tube (1) is dipped in a liquid coolant which removes the heat through the outer surface by convection.

[0082] In this embodiment, the set of fins (1.3) is spaced from the end, leaving a free portion d without fins (1.3) at the end of the tube (1). This free portion allows, for example, attaching the tubes (1) to a baffle to form a bundle of tubes (1), forming a heat exchanger without the set of fins (1.3) interfering in the attachment of the tube (1) to other elements such as the baffles or other structures located at the inlet.

[0083] FIG. 2 shows a section of the tube (1) according to a cross-section with respect to the longitudinal direction (X-X′). There can be seen in the central area of the tube (1) straight segments, oriented horizontally according to how they are shown in the figure, resulting from the cross-section with the flat walls (1.1) that are arranged parallel to and spaced from one another. The set of fins (1.3) extends from one flat wall (1.1) to the other flat wall (1.1) and, also following the orientation of the figure, the fins (1.3) are prolonged vertically from the lower flat wall (1.1) to the upper flat wall (1.1).

[0084] The sides of the tube (1) show arc-shaped semi-circumference segments resulting from sectioning the cylindrical segments which connect both flat walls (1.1). This section shows how the hydraulic diameter defined between two consecutive fins is smaller than the hydraulic diameter defined by the lateral channel, i.e., the one formed between the curved wall segment (1.2) and the fin (1.3) closest to said curved wall (1.2).

[0085] A passage opening is distinguished between two consecutive walls of the fins (1.3), and since the fins (1.3) are corrugated according to the longitudinal direction (X-X), the view of FIG. 2 also allows viewing through its cross-section part of the side walls of the fins (1.3) in the corrugated extension thereof.

[0086] According to this embodiment, the set of fins (1.3) shows two corrugations, a first corrugation which is shown through the section of FIG. 2 and corresponds to a square wave profile, and a second corrugation, the corrugation of this section being transverse as it extends along the longitudinal direction (X-X′) following a wavy, for example, sinusoidal, trajectory.

[0087] The first corrugation in the form of square wave allows configuring a surface with flat surfaces at the ends of maximum amplitude of the wave and perpendicular surfaces forming the heat exchange fins. The flat surfaces at the ends of maximum amplitude form surfaces for attachment with the flat walls of the tube (1) that are arranged in parallel and the perpendicular surfaces establish heat exchange surfaces of the fins for heat exchange with the hot gas.

[0088] The flat surfaces of the set of fins (1.3) which are in contact with the flat walls (1.1) are also in contact with a set of localized recesses (1.4) which help to temporarily fix the set of fins (1.3) before passing through the brazing furnace.

[0089] An internal channel (C) is configured between two consecutive perpendicular walls or fins (1.3), and as a result, the set of fins (1.3) configures a plurality of internal channels (Ci). When the localized recesses (1.4) coincide with an internal channel (Ci), they generate surfaces with bulges on the inner surface of the channel which increase turbulence and therefore the degree of convection heat transfer.

[0090] Likewise, the side ends form respective channels (Cl) with a hydraulic diameter larger than the hydraulic diameter of the internal channels (Ci).

[0091] In this embodiment, the set of fins (1.3) is formed by means of a single metal sheet, preferably from a metal that is a good heat conductor, and is stamped to configure the first and second corrugations thereon. This stamped piece configures a single piece that is inserted into the inner tube formed by the flat walls (1.1) and the curved wall segments (1.2). After insertion, it is fixed by brazing.

[0092] FIG. 3A show a top view of the tube (1) in which the curved wall segments (1.2) show four deformed portions (1.2.1) causing a recess which reduces the section of the lateral channel (C1), and therefore also reduces the hydraulic diameter at least in the section where the deformed portion (1.2.1) is located. In this way, the flow that will flow through the lateral channel (Cl) is blocked or restricted significantly by the reduction in passage caused by the deformed portion (1.2.1) such that the flow passing through the internal channels (Ci) is increased.

[0093] This results, in an operative mode, in a greater passage speed of the hot gas through the internal channels (Ci), increasing its effectiveness while preventing fouling at the same time.

[0094] FIG. 3B shows the same top view as that of FIG. 3A with the exception that the inside of the tube (1) and the distribution and shape of the internal channels (C) can be seen by means of a section through a midplane. In particular, this figure shows the sinusoidal corrugated configuration along the longitudinal direction (X-X′). This same view shows the maximum amplitude of the sine wave of the channels adjacent to the lateral channel, coinciding with the longitudinal position of the deformed portion (1.2.1), allowing the necessary deformation to be minimal and to allow maximally closing or constricting the passage of hot gas through the lateral channel (CQ).

[0095] It can be seen that, although heat exchange occurs in this lateral channel (Cl), it is limited to the reduction or elimination of the passage for the hot gas; however, the benefit of increasing speed through the internal channels (Ci), that are much more efficient in heat exchange for transferring heat to the liquid coolant, is much greater.

[0096] FIG. 4 allows seeing the same FIG. 3A in a perspective view, thus also showing the configuration of the internal channels (Ci). In this case, the internal channels are also sectioned but show a lower U-shaped configuration of the non-sectioned part which corresponds to the first corrugation with a section in the form of a square wave. Likewise, the perspective view of this FIG. 4 shows the larger dimensions of the lateral channels and that they cannot be covered by the fins (1.3), giving rise to a larger hydraulic diameter, and therefore a lower hydraulic resistance that is only increased by the deformed portions (1.2.1).

[0097] Returning to FIG. 3A, in addition to showing the tube (1) in a top view, a rectangle is shown in discontinuous lines which identify a region that is enlarged in the upper part of the figure. This enlarged area shows the deformed portion (1.2.1) as a recess which, according to this top projection over a plane parallel to the flat walls (1.1), is seen as an arc-shaped segment with a first radius (R1) of curvature with a center outside the tube (1).

[0098] This first radius (R1) can vary along the arc although the value of the minimum radius or, in other words, the value corresponding to the larger curvature is considered a critical value, given that it is the most important value in terms of the deformed material. In this embodiment, this first radius (R1) of curvature, divided by the thickness of the sheet metal used in the wall of the tube (1), is in the range [16.1-17.2].

[0099] FIG. 3A also shows a second radius (R2) located at the ends of the deformation arc described above. That is, it is a second radius (R2), with a center inside the tube (1), also measured in a plane parallel to the flat walls (1.1) and also passing through the center of the tube (1). This second radius (R2) is a radius of transition between the arc-shaped segment and the curved wall segment (1.2) without deformation and it shows a greater curvature, and therefore deformation on the material of the wall of the curved segment (1.2) is greater. In these conditions of greater deformations, there is a risk of cracking. It has been proven that the deformation ensures a deformation without cracking if the ratio between this second radius of curvature (R2) and the thickness e of the sheet metal is in the range [0.9-3.1]. In this embodiment, the ratio is specifically in the range [1.25-2.75].

[0100] Now in reference to FIG. 2, the right-side end of the section of the tube (1) depicts a rectangle in a dashed line which identifies the enlarged area shown in the lower area of the same figure.

[0101] It is in the enlarged area where a third radius (R3) of curvature is distinguished, with the center outside the tube (1), but which depicts the curvature according to a plane of section perpendicular to the longitudinal direction (X-X′) of the tube (1). That is, the section shows a segment that is also arc-shaped, where the ratio between the third radius of curvature (R3) and the thickness, for this embodiment, is in the range [1.25-2.75].

[0102] According to an embodiment of the second aspect of the invention, i.e., the method of manufacturing the tube (1), said tube is formed according to the following steps:

[0103] a tube (1) having a flat configuration, configured by means of two essentially parallel flat walls (1.1) extending along a longitudinal direction (X-X′) and joined on both sides by means of a curved wall segment (1.2), is provided.

[0104] This configuration gives rise to a tube with a flat general configuration wherein the sides are arc-shaped according to a cross-section or perpendicular to the longitudinal direction (X-X′). According to this specific example, the curved wall segments (1.2) laterally flanking the tube are walls approximately in cylindrical section with curvature continuity with the flat walls (1.1).

[0105] Next:

[0106] a set of fins (1.3) is inserted into the tube (1), leaving a lateral channel (Cl) between the set of fins (1.3) and each curved wall segment (1.2).

[0107] With the insertion of the set of fins (1.3), the plurality of central channels which favor heat transfer between hot gas and the flat walls is obtained. This is the configuration that may not cover the channel which is formed on the sides with the curved wall segments (1.2), so these lateral channels are a preferred path for the hot gas given their larger hydraulic diameter compared with the hydraulic radius of the channels forming the set of fins (1.3).

[0108] To minimize or even eliminate these preferred side passages for hot gas, the following step is performed:

[0109] pressing the curved wall segment (1.2) in a region of its outer surface causing a deformed portion (1.2.1) which narrows the section of the lateral channel (CQ).

[0110] The tube thus configured reduces the passage through the lateral channels, at least at one or more longitudinally distributed points. However, the set of fins is preferably kept in place by friction. The tube (1), according to the described examples, has a set of deformation points generated by localized recesses (1.4). In this particular case, these localized recesses (1.4) are those that generate friction and help to retain the set of fins (1.3) before proceeding with an attachment or consolidation step. That is, the next step involves:

[0111] attaching the set of fins (1.3) to the tube (1), preferably by brazing.

[0112] Once attached by brazing, the tube (1) offers a high efficiency because the hot gas preferably passes through the channels of the set of fins (1.3) and not through the lateral channels originally defined by the curved wall segments (1.2).

[0113] By blocking passage through these lateral channels, the speed of the flow in the channels formed by the set of fins (1.3) is higher and also favors the prompt entrainment of any particle entering the tube (1) so that it does not remain in the tube.

Claims

1. Tube (1) adapted for heat exchange between a hot gas and a liquid coolant wherein:the tube (1) has a flat configuration, configured by means of two essentially parallel flat walls (1.1) extending along a longitudinal direction (X-X′) and joined on both sides by means of a curved wall segment (1.2);the tube (1) comprises a set of fins (1.3) housed inside the tube (1) extending from the inner surface of one flat wall (1.1) to the inner surface of the other flat wall (1.1);the set of fins (1.3) comprises a plurality of internal channels (C) and a lateral channel (Cl) on each side, the lateral channel (Cl) being the one formed between the group of fins (1.3) and the curved wall segment (1.2);the hydraulic diameter (Dh) of the lateral channels (Cl) is larger than the hydraulic diameter (Dh) of the internal channels, wherein the hydraulic diameter is Dh=4 A / p, where A is the cross-section area of the channel and p is the perimeter of said cross-section, andwherein at least one curved wall segment (1.2) comprises a deformed portion (1.2.1), with a configuration of the deformed portion (1.2.1) penetrating into the lateral channel (Cl) reducing the section thereof.

2. Tube (1) according to claim 1, wherein the deformed segment (1.2.1) is spaced from both ends according to the longitudinal direction (X-X′).

3. Tube (1) according to claim 1, wherein the set of fins (1.3) is formed by a sheet corrugated by stamping, with the direction of the corrugation being in accordance with a direction perpendicular to the longitudinal direction (X-X′) and parallel to the flat walls (1.1).

4. Tube (1) according to claim 1, wherein the corrugated sheet additionally shows a second corrugation according to the longitudinal direction (X-X′).

5. Tube (1) according to claim 1, wherein the position of the deformed portion (1.2.1) according to the longitudinal direction (X-X′) is at a point of minimum distance between the corrugation and the inner wall of a curved wall segment (1.2).

6. Tube (1) according to claim 1, wherein the deformed portion (1.2.1) is spaced from the set of fins (1.3).

7. Tube (1) according to claim 1, wherein the deformed portion (1.2.1) shows, according to a projection in a plane parallel to the flat walls (1.1), an arc configuration, wherein the arc has a minimum ratio between the radius of curvature and thickness which is in the range [13-20], more preferably in the range [14-19], more preferably in the range [15, 18], more preferably in the range [16-17.5] and more preferably in the range [16.1-17.2].

8. Tube (1) according to claim 1, wherein the deformed portion (1.2.1) shows, according to a projection in a plane parallel to the flat walls (1.1), an arc configuration, wherein at least one end of the arc, in the transition thereof with the surface of the lateral channel (Cl), has a minimum ratio between the radius of curvature and thickness which is in the range [0.9-3.1], more preferably in the range [1-3] and more preferably in the range [1.25-2.75].

9. Tube (1) according to claim 1, wherein the deformed portion (1.2.1) shows, according to a section by means of a perpendicular plane of section, the longitudinal direction (X-X′) and a central position of the deformed portion (1.2.1), a minimum ratio between the radius of curvature and thickness which is in the range [0.9-3.1], more preferably in the range [1-3] and more preferably in the range [1.25-2.75].

10. Method of manufacturing a tube (1) comprising the following steps:a) providing a tube (1) having a flat configuration, configured by means of two essentially parallel flat walls (1.1) extending along a longitudinal direction (X-X′) and joined on both sides by means of a curved wall segment (1.2);b) inserting into the tube (1) a set of fins (1.3) leaving a lateral channel (Cl) between the set of fins (1.3) and each curved wall segment (1.2);c) pressing the curved wall segment (1.2) in a region of its outer surface causing a deformed portion (1.2.1) which narrows the section of the lateral channel (Cl);d) attaching the set of fins (1.3) to the tube (1), preferably by brazing.

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