Patent Application
20140041832
The present invention relates to a device for reducing the vibrations of a tube bundle of a heat exchanger inside its shell, wherein this device allows a secure and quick insertion after the bundle has been manufactured. This easy insertion after manufacturing the bundle allows the high temperatures to which the bundle is subjected for the attachment by means of brazing to not affect the properties of the device, particularly the elasticity achieved by means of tempering, for example.
The heat exchangers designed for high fluid flow rates, for example those used in “EGR” (Exhaust Gas Recirculation) systems for reducing nitrogen oxide (NOx emissions in internal combustion engines, are devices with important masses.
The usual configuration is that of arranging a shell housing a tube bundle, which tubes form a packing. Inside the shell there circulates a first fluid, the liquid coolant, which removes heat from the tube bundle, through which tubes there circulates a second fluid, the gas to be cooled.
The tube bundle has a longitudinal shape and its mass is important. When this exchanger is subjected to external excitations as occurs in a vehicle, the bundle has a dynamic behavior which is characterized by the fundamental modes of vibration. The most relevant is the first fundamental mode of vibration and is associated with the lowest fundamental frequency. The shifts due to deformation in the antinodes of the wave associated with the mode of vibration can be high, giving rise to significant deformations which are the cause of fatigue of materials, mechanical interferences and therefore the source of breakages and noise.
In particular, truck exchangers are very long, being able to reach lengths of over 300 mm with bundles having natural frequencies of around 200 Hz, which are within the range of the engine. This type of bundles or also referred to as batteries can weigh between 5 and 11 kilograms, giving rise to very resistant supports.
The usual way of manufacturing these bundles is by means of brazing. The pipes, attachment parts and supports are assembled by interposing in the attachment surfaces brazing paste containing alloys which melt below the melting point of the component parts. The assembly thus attached is introduced in a furnace causing the melting of the brazing paste but not that of the metal of the parts to be attached. Nevertheless, although these parts do not reach a melting temperature, the temperatures of the furnace can be around 1100° C., which is sufficient to soften them. For example, a steel with martensitic structures obtained by means of tempering to achieve certain elastic properties would disappear after passing through the brazing furnace.
The bundle is formed by pipes, the natural frequency of which depends on the length thereof, the latter being reduced as said pipes are made longer. When the natural frequency of the pipes is very low and is close to the first harmonics caused by the engine, the bundle can enter into resonance and a breakage due to vibrations can occur. To prevent the problems of vibrations of the bundle of the exchanger inside the shell, support points between the bundle and the shell different from the ends are established, such that the pipes forming the bundle work as if they were shorter than they actually are, and therefore they have a higher natural frequency, far from the frequencies at which the engine vibrates. These intermediate support points therefore define new nodes which change the dynamic behavior of the bundle due to vibration.
It is convenient for these support points between the bundle and the shell to be elastic, therefore if elastic parts are incorporated for this purpose they must be installed after passing through the furnace because otherwise their elastic properties would be destroyed and any deformation that they experience would be permanent.
The solution proposed in the European patent with publication number EP1870656A2 is known. This patent application describes elastic clips which can be installed after the bundle has passed through the furnace.
The clips described are installed in one of the faces of the tube bundle, either because an anchor receiving the elastic element has previously been fixed on the bundle (in the furnace for example), or the part which keeps the tubes attached at certain points of the length of the bundle is used. This part is usually referred to as baffle.
When this part is used, holes are made which admit a flat bar from which a wedge- or harpoon-shaped element emerges. This configuration allows the insertion by sliding the elastic support in a direction parallel to the main longitudinal direction of the bundle and transverse to the part. To be removed, it is necessary to press the flexible wedge- or harpoon-shaped section and force the exit.
All the proposed solutions require the insertion in each of the faces of the bundle in an independent manner and although the anchor prevents the exit thereof it does not assure an attachment without vibrations. The wedge or harpoon recovers its position after the insertion if it has a certain clearance. This clearance is maintained after the insertion and can give rise to unwanted vibrations.
The present invention proposes a simpler alternative solution which allows its installation once the bundle has already passed through the furnace, drastically reduces the installation time and also allows its removal for its replacement in a quick manner.
The present invention relates to a device which can be installed in a heat exchanger, preferably in an exchanger belonging to an EGR system for cooling the exhaust gases of a internal combustion engine, which is arranged in the tube bundle or battery, which tubes are housed in the shell such that an elastic support of the bundle is established on the inner surface of the shell. The special configuration of this device allows solving the problems described above.
The bundle for which this device is intended has a configuration comprising at least one main face and two adjacent side faces and wherein the bundle furthermore has one or more linking parts or “baffles” between tubes, giving rise to a protrusion in the main face and the adjacent side faces.
The tubes configuring the bundle are held by means of a part which is referred to as a linking part or “baffle”. This part maintains a constant attachment between the different tubes if they are subjected to vibration. This part is required to protrude from the packing formed by the assembly of tubes of the bundle both in the main surface and in the adjacent side surfaces. The anchoring of the device will be established in this protruding area.
As has been described in the state of the art, clips are known which are likewise fixed to the linking part but require the presence of holes in which a wedged tab that allows the entrance but not the exit is inserted.
The device of the present invention additionally comprises:
a first section adapted to be arranged on the main face and two second sections adapted to be arranged on the side faces, wherein these second sections emerge from the ends of the first section and are arranged in opposition, such that the first section and the second sections configure a “U”. This first feature of the device defines a mode of linking with the bundle based on the shape that it has. The presence of two arms extending over both side faces will allow the retention when it is installed, the easy insertion during the installation and its extraction when its replacement is necessary.
one or more anchors arranged in each section configured in a “U” shape and oriented towards the inside of the “U” formed by the first section and the second sections, these anchors being adapted to receive the protrusion formed by the linking parts between tubes of the bundle.
The linking part protrudes in the main face and also in the side faces. The device has a “U” shape with a first section intended to be supported on the main face and two second sections intended to be supported in the side faces. Each of these sections in turn has anchors which also have a “U” shape. These anchors cover a portion of the protrusion formed by the linking part.
The insertion of the device towards the bundle makes the anchors achieve said anchoring by making an approach in a different manner. The anchors which are in the first section approach the protrusion formed by the linking part in an opposite manner and move closer until the U-shaped anchor covers a section of the protrusion. The approaching movement is transverse to the protrusion in the main face. On the other hand, the anchors which are in the second section, with the same approaching movement, move parallel to the protrusion of the side faces. They first make contact with the start of the protrusion on the side face housing the protrusion inside the “U” of the anchor; and, until reaching the final position, they slide allowing the protrusion to slide along their interior.
With this configuration of the device it is possible to incorporate supports on the three faces, the main face and the two adjacent side faces, in a single insertion operation.
These anchors, thus configured, allow the insertion and extraction of the device towards and from the bundle and, in turn, the “U” shape limits the movement of the device in the longitudinal direction defined by the tubes of the bundle.
one or more elastic support elements arranged in each section and oriented towards the outside of the “U” formed by the first section and the second sections, these elastic support elements being adapted to be supported on the inside of the casing of the heat exchanger.
Once the device is located in the final position, it solves the problem of establishing the support between the bundle and the casing by arranging elastic support elements on the outside of the “U”.
In the preferred embodiment of the invention, this elastic element is configured by die-cutting and subsequently bending the flat bar which gives rise to all the elements of the device. The elastic properties of the material used are not affected by the high temperatures of the brazing furnace since the device is installed after the bundle is manufactured.
The support between the bundle and the casing define new nodes in the modes of vibration of the bundle, raising the values of the frequency associated with the modes of vibration with lower characteristic frequencies.
both second sections comprise a retaining clip such that both clips operate in opposition to retain the device in the bundle.
Once the device is inserted on the bundle, the presence of a retaining clip on each side retains the device elastically. The first section and the second sections configured in a “U” shape have an elastic behavior. The presence of a clip in each second side section and operating in opposition traps the bundle. In the preferred mode of the invention the clips have the form of a protrusion towards the inside of the main “U” formed by the first section and the second sections. The protrusion towards the inside enters a groove, for example the one formed by two adjacent tubes. It would likewise be possible to arrange the second sections with a greater length and allow the support of the clips in the edge where the side surface ends.
A heat exchanger incorporating at least one device according to claim 9, wherein this exchanger according to claim 9 is incorporated by reference to this description, is also an object of this invention.
These and other features and advantages of the invention will be more clearly shown from the following detailed description of a preferred embodiment, given only by way of an illustrative and non-limiting example, with reference to the attached figures.
a, 2b show the device according to an embodiment according to an elevational and profile view.
This liquid coolant is in contact with the tube bundle (2), through which tubes the gas to be cooled circulates. The hot gas transfers the heat to the liquid coolant through the exchange surface which defines the tubes forming the tube bundle (2).
This tube bundle (2) also has in turn an inlet and a differentiated outlet for the second fluid, the gas to be cooled. The figure shows the gas outlet manifold (4).
The tube bundle (2) is housed inside the shell (3) such that there is a space between the bundle and the inner surface of the shell (3). The bundle (2) is subjected to vibrations and is deformed along its length depending on the securing at its ends.
This same figure shows a linking part (2.1) keeping the tubes forming the tube bundle (2) secured to one another, at a certain distance. In the example shown in
This linking part (2.1) is shown protruding in the four walls defining the tube bundle (2) with a prismatic shape. Although the support of the device (1) according to this embodiment occurs directly with the surface of the tube bundle (2), the linking part (2.1) allows the retention in the longitudinal direction. The longitudinal direction is considered to be the preferred direction established by the tubes of the bundle (2).
The devices (1) for reducing the vibrations according to a first embodiment are supported in three faces of the prismatic body of the tube bundle (2), a face which will be referred to as the main face (2.2) and two faces which will be referred to as side faces (2.3). These faces (2.2, 2.3) can have recesses or notches in the spaces between tubes, for example. Once the devices (1) are arranged on the tube bundle (2), they offer towards the outside elastic support elements (1.3) intended to be supported in the inner face of the shell (3) when the bundle is introduced inside the shell (3). This support establishes a node for the mode of vibration of the bundle (2) in the longitudinal position of the device (1).
Once installed, the device (1) must allow an easy insertion in the shell (3) and must be securely linked to the bundle (2) to allow the insertion without the device (1) moving longitudinally with respect to the bundle (2).
Secondarily, it is convenient for it to also allow the exit of the bundle (2) to allow maintenance tasks.
Considering
This flat bar shows a first section (1.1) which is extended by means of two second sections (1.2). Once bent, these second sections (1.2) configure a “U” with the second sections (1.2) in opposition. This U-shaped configuration allows embracing the main face (2.2) and the two side faces (2.3) of the bundle (2).
From the flat bars forming the first section (1.1) and from the second sections (1.2), there extend laterally bent flat bars forming towards one side flexible elements (1.3) and towards the other side there extend laterally bent flat bars forming anchors (1.4) and also skids (1.5).
The flexible elements (1.3) are flexible strips due to their greater length and the nature of the material used which is flexible. These flexible elements (1.3) allow the support of the device (1) in the inner face of the shell (3). The support of the flexible elements (1.3) in the inner face of the shell (3) preferably occurs in a place which is projected (according to the direction perpendicular to the support surface of the device (1) on the tube bundle (2)) wherein the support surface rests on the tube bundle (2).
The flexible elements (1.3) have a height with respect to the first or second sections (1.1, 1.2) from which they emerge greater than the distance between the bundle (2) and the inner wall the shell (3) in order to thus be able to maintain an elastic force of distancing between both elements. The wedged shape of the flexible elements (1.3) allows the easy entrance of the bundle (2) inside the shell (3) even despite the fact that this greater height means a mechanical interference.
The ends of the flexible elements (1.3) are in turn bent towards the inside in order to also offer a wedged surface in the direction of the exit of the bundle with respect to the shell (3).
The shape of the anchors (1.4) is a “U” shape, wherein this “U” shape is oriented such that it covers, at the upper part, the protrusion formed by the linking part (2.1) of the tubes of the bundle (2).
Following this same direction of insertion of the device (1) of the invention, the anchor (1.4) seen in the middle of the figure and which corresponds to the second section (1.2) will enter from the right, housing from the beginning the protrusion formed by the linking part (2.1), and will slide to its final position, allowing the passage of the protrusion of the linking part (2.1).
On the side opposite to where the flexible elements (1.3) extend, there extend skids (1.5) with a bend perpendicular to the support surface of the bundle (2) which reduces the transverse clearance of the protrusion formed by the linking part (2.1) inside the anchor (1.4).
The clip (1.6) is configured to coincide with a gap formed between tubes of the bundle (2). The bundle (2) used in this
The anchors (1.4) prevent the longitudinal movement but allow the insertion without needing to drill the linking part (2.1) or insert tabs which recover inside a hole as occurs in the state of the art.
The attachment by means of the clamping in opposition which occurs due to the U-shaped configuration and with the retention of the clip (1.6) prevents the existence of clearances which would be the source of additional vibrations and noise.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11382143.3 | May 2011 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/058618 | 5/10/2012 | WO | 00 | 10/21/2013 |
