US20110000657A1

US20110000657A1 - Extruded tube for a heat exchanger

Info

Publication number: US20110000657A1
Application number: US12/834,259
Authority: US
Inventors: Jens Ruckwied; Ulrich Maucher; Peter Geskes
Original assignee: Behr GmbH and Co KG
Current assignee: Mahle Behr GmbH and Co KG
Priority date: 2008-01-10
Filing date: 2010-07-12
Publication date: 2011-01-06
Also published as: JP2011509393A; EP2242979A1; CN101910774A; KR20100106434A; WO2009086894A1; DE102008062704A1; EP2242979B1

Abstract

An extruded tube for a heat exchanger is provided that includes two at least approximately parallel outer side walls that extend in a longitudinal direction and a transverse direction of the extruded tube and that are connected by two outer narrow sides in a vertical direction of the extruded tube, wherein at least one continuous web extends between the side walls in the longitudinal direction and in the vertical direction and separates at least two ducts of the extruded tube, and wherein at least one of the outer side walls has embossings that serve to form both bulged portions that project into the ducts of the side walls and also bulged portions that extend substantially in the transverse direction of the web, wherein the bulged portions of the at least one web have a controlled orientation with respect to the transverse direction.

Description

This nonprovisional application is a continuation of International Application No. PCT/EP2008/010829, which was filed on Dec. 18, 2008, and which claims priority to German Patent Application No. DE 10 2008 003 737, which was filed in Germany on Jan. 10, 2008, and which are both herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an extruded tube for a heat exchanger and to a heat exchanger with an extruded tube of the invention, as well as to a method for producing an extruded tube of the invention.
2. Description of the Background Art
U.S. Pat. No. 3,596,495 A describes tubes that can be produced by extrusion and drawing for a heat exchanger, in which according to an exemplary embodiment several chambers are separated by internal webs. Moreover, the chambers are deformed by externally introduced depressions both in the area of the side walls and in the areas of the webs in order to produce turbulences for a fluid flowing therethrough.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an extruded tube for a heat exchanger in which an especially high heat transfer is achieved with a proportionally low pressure drop across the extruded tube.
In an embodiment, a specific precise shaping of the channel can be achieved by the controlled orientation of the bulges in the web not only in the vertical direction but also in the transverse direction. In contrast, according to the aforementioned state of the art, only an uncontrolled narrowing of the channels by bulging of the web, random with respect to the orientation, is possible in the transverse direction.
It is provided in an embodiment that at least one of the channels of the extruded tube in the longitudinal direction has a regular, wave-shaped course in regard to the transverse direction. In this way, on the one hand, the turbulences and heat transfer are increased and, on the other, narrow areas are avoided, which can cause too great a pressure drop and possibly blockage by accumulation of fluid or substances precipitated from the fluid. Especially preferably, in this case, a distance in the transverse direction between two neighboring webs is substantially constant.
In an embodiment, in the interest of simple and reliable fabrication, at least one of the impressions can have an elongated form, whereby a majority of webs are overlapped and bulged by the same impression. The elongated impression can have an orientation angle to the transverse direction, so that bulges, formed by the same impression of side walls and webs, are not located at the same height in the longitudinal direction of the tube. An orientation angle of this type is advantageously approximately between 0° and 45°, preferably approximately between 20° and 45°, and especially preferably approximately between 28° and 42°.
In an embodiment, the elongated impression has an orientation parallel to the webs and/or is arranged above the webs or only slightly offset to the webs. Especially advantageously, the impression has a length that is 1.1- to 3.25-fold, particularly 1.35- to 2.45-fold, particularly 1.62- to 2.16-fold of the channel width. As a result, possibly a force acting uniformly in sections, and thus a marked bulging of the web, are assured, because optionally flowing of the material under the embossing surface that is only local due to the surface pressure because of an embossing, made only punctiform or limited in length, and thereby an undesirable reduction in wall thickness are reduced or avoided.
Alternatively or in addition, it can be provided that at least one of the impressions coincides substantially only with the at least one web. In this case, another impression cannot coincide with a web. In this way, impressions for bulging out the side walls and impressions for bulging out the webs can be placed as desired spatially separated from one another, so that there are especially broad design options for the shaping of the channels. This type of isolated impression of a side wall can have in particular an orientation opposite to the transverse direction. An orientation angle of these impressions relative to the transverse direction can be advantageously approximately between 0° and 45°, preferably approximately between 25° and 45°, and especially preferably approximately between 30° and 40°.
For an especially effective generation of turbulence, at least one of the impressions can be made winglet-shaped. In optimized form, the winglet-shaped impression in this regard has a length-to-width ratio of between 2 and 5, preferably between 2.3 and 4, and especially preferably between 2.5 and 3.2. According to an advantageous variant, the winglet-shaped impression has a length-to-width ratio of between 1.2 and 5, preferably between 1.5 and 3, and especially preferably between 1.8 and 2.5.
It became evident that too long impressions can also lead to a flat deformation of the side walls or can cause the short side walls to bulge. This disadvantageously changes the outer dimension of the extruded tube and worsens the coolant flow; similarly, buckling of the side wall and blockage or reduction of the channel cross section and thereby an increased pressure loss can occur during deformation processes of the extruded tube in the area of the impression.
It is advantageously provided in general that the orientations of at least a few bulges of neighboring webs, which are substantially at the same height in the longitudinal direction, are the same. As a result, a largely constant cross section of the channel at least in regard to the transverse direction is made possible, so that the risk of blockage by deposits, for example, during use for exhaust gas cooling, is low. Alternatively, depending on the requirements; it can also be provided that the orientations of at least a few bulges of neighboring webs, which are substantially at the same height in the longitudinal direction, are opposite. As a result, narrow areas of the tubes can be formed in a controlled manner, which can produce an especially great turbulence. This can be advantageous when the risk of blockage by deposits is low, for example, in the case of charge air coolers, coolant coolers, and exhaust gas coolers for low-pressure EGR [exhaust gas recirculation] or high-pressure EGR coolers in the case of moderate soot and/or HC emissions.
In an embodiment, in the longitudinal direction of a channel, bulging of one of the side walls and bulging of the web are provided alternately one behind the other to produce a uniform turbulence in all spatial directions. Bulging of the web in a first orientation in the transverse direction occurs in the longitudinal direction of a channel in an especially advantageous manner, then bulging of one of the two side walls, followed by bulging of the web in the other orientation, and then bulging of the other side wall. In this way, a screw-like course of the channel is created which advantageously gives the fluid stream a twist. Several such sections with particularly different twist directions can be provided over the length of the extruded tube.
Another embodiment provides that the bulging of the webs and/or the channel walls is designed alternately in the opposite direction, so that an alternating acceleration and deceleration of the flow result.
In another embodiment, in the longitudinal direction of a channel, bulges of two webs bounding the channel have bulges directed toward one another and lying at the same height, so that the channel width is reduced by the bulges. As a result, acceleration of the flow at this narrow area can be achieved. Alternatively or in addition, it is provided that in the longitudinal direction of a channel, bulges of two webs bounding the channel have bulges directed away from one another and lying at the same height, so that the channel width is increased by the bulges. As a result, deceleration of the flow at this area can be achieved. As previously noted, in a preferred embodiment, an alternate widening and narrowing of the channels can also be provided.
In an embodiment, it is provided that the bulging of the web is formed both by an impression of the first side and also an at least partially coinciding impression of the second side. As a result, an especially marked bulging of the web with only a small bulging of the side walls can be achieved. In a first variant, the orientation of the bulging thereby is opposite to the coinciding impressions. In an alternative or additional second variant the orientation of the bulging is aligned relative to the coinciding impressions.
In a simple realization of an extruded tube of the invention, the controlled oriented bulging of the web occurs by means of an embossing tool inclined relative to the side walls. In this way, during embossing a force oriented in the transverse direction is exerted on the web, so that the direction of its bulging or buckling is predefined. In an alternative or additional solution, the controlled oriented bulging of the web occurs by means of an embossing tool acting eccentrically relative to the web. In particular, the embossing tool in the transverse direction in this case can only be as broad as the web, and the deviation of the embossing center from the web middle relatively small, so that, on the one hand, a controlled directed bulging of the web occurs and, on the other, the side wall, adjacent to the web, is bulged out as little as possible in the vertical direction.
In order to be able to mount the extruded tube of the invention simply and sealingly in a bottom of a heat exchanger, an end area of the extruded tube is preferably not provided with bulges. A distance of a tube end to a first embossing in this case is advantageously approximately between 2 mm and 15 mm, especially preferably approximately between 4 mm and 8 mm. In an alternative exemplary embodiment, a distance of a tube end to a first embossing is advantageously approximately between 4 mm and 20 mm, especially preferably approximately between 6 mm and 12 mm.
In an embodiment of the invention, an extruded tube has a curved area, so that the heat exchanger can be, for example, a U-flow heat exchanger or in general adapted by the bending of the tube to a predefined space. To avoid an excessive channel narrowing within the curved region, the bulges there expediently have an at least reduced depth. Especially preferably, in this case, no bulges are arranged in the curved region at least in sections.
In an embodiment, the tube material can be a material that is mad of, for example, aluminum alloys, AlMn alloy, AlMg alloy, and AlMgSi alloy. Such light metal alloys can be extruded especially well and shaped with the impressions of the invention. It became evident that extruded tubes made of such alloys when used as exhaust gas coolers have a good corrosion resistance to aggressive condensate.
In the case of an optimized geometry of the extruded tube, a depth of the impressions is less than about 75%, preferably less than about 45%, and especially preferably less than about 30% of an inside tube diameter in the vertical direction.
Furthermore, tests have shown that in the longitudinal direction a distance between an impression of the tube bottom side to a next impression of the tube top side is advantageously no more than 10-fold, preferably no more than 6-fold, and especially preferably no more than 3.5-fold of an inside tube diameter in the vertical direction. In addition, an optimized realization has the property that in the longitudinal direction a distance between an impression for bulging of a side wall to a next impression for bulging of a web is no more than 8-fold, preferably no more than 6-fold, and especially preferably no more than 3-fold of an inside tube diameter in the vertical direction.
In case of impressions overlapping several webs in the transverse direction, a length of the impression in the transverse direction optimally is approximately between 25% and 100%, preferably between 35% and 90%, and especially preferably between 45% and 80% of a width of the extruded tube in the transverse direction.
In case of an impression bounded only between two webs, their length in the transverse direction is approximately between 25% and 130%, preferably between 35% and 95%, and especially preferably between 45% and 75% of a width of the channel, bounded by the webs, in the transverse direction.
To improve the heat transfer, it is advantageous in general for a fin element to be arranged from the outside on at least one of the side walls, particularly by means of a material connection. This can be in particular planar soldering. To assure as uniform a heat transfer as possible between fins and extruded tubes, it is advantageous that a repeat unit of the impressions in the longitudinal direction and a repeat unit of the fins of the fin element are not integer multiples of one another. As a result, unfavorable regular overlappings of contact areas of the fins with impressed areas of the tube surface can be avoided.
For further improvement of heat transfer, in an extruded tube of the invention at least one half-web can project from one of the side walls into one of the channels.
In an optimized embodiment, a hydraulic diameter, defined as four times the ratio of the area of the flow-through cross section to a perimeter wettable by the first fluid, is provided within a range between 1.2 mm and 6 mm.
Preferred ranges for the hydraulic diameter are particularly between about 2 mm and about 5 mm, especially preferably between 3.0 mm and 3.4 mm, particularly preferably between 3.1 mm and 3.3 mm, and particularly about 3.2 mm.
In general and particularly for structural designs of high-pressure heat exchangers, it was found that the hydraulic diameter (dh) is advantageously between about 2.5 mm and 4 mm, particularly preferably between about 2.8 mm and 3.8 mm.
In general and particularly for structural designs of low-pressure heat exchangers, it was found that the hydraulic diameter (dh) is advantageously within a range between 2 mm and 3.5 mm, particularly preferably between 2.5 mm and 3.5 mm.
To optimize the weight and quantity of material, a ratio of the hydraulic diameter (dh) and a channel cover thickness (s) is advantageously within a range between 0.8 and 8, preferably within a range between 1.2 and 6, and especially preferably within a range between 1.4 and 6. For the same reason, a ratio of a web thickness (d) and a channel cover thickness (s) is preferably less than 1.0.
A ratio of a perimeter of the extruded tube and the perimeter wettable by the first fluid is within a range between 0.1 and 0.9, particularly between 0.1 and 0.5, whereby the last range named is especially suitable for exhaust gas coolers.
In the optimized structural design of an exemplary embodiment, a ratio of a distance (e) between two, particularly opposite partial webs and/or partial webs offset with respect to one another to a height (b) of the tube cross section is within a range below 0.8, particularly within a range between 0.3 and 0.7. A ratio of a distance (a3) of a first partial web to a full web to a distance (a4) of a second partial web to the full web with a suitable structural design is preferably within a range between 0.5 and 1.0, particularly preferably within a range between 0.6 and 0.8.
In general, to increase the lifetime and particularly during involvement of a fluid with corrosive properties, such as, for example, exhaust gas, it can be provided that at least one web and/or the channel cover, preferably the inner surface of the channel cover, have corrosion protection, preferably in the form a zinc coating and/or paint.
Depending on requirements, a cross section of the extruded tube can advantageously be formed, for example, rectangular, oval, or semi-oval.
In an especially suitable structural design of an extruded tube for use in a heat exchanger, a number of 2 to 20, preferably 5 to 15, especially preferably 7 to 12, especially preferably 8 to 11, and particularly preferably 9 webs are arranged next to one another across a tube cross section.
The object of the invention is achieved, by a heat exchanger with an extruded tube of the invention. In this regard, a first fluid, which exchanges heat with a fluid flowing outside around the tube, is conveyed in the extruded tube. Such heat exchangers are widely used particularly in motor vehicles, whereby here, because of the high weight and space requirements, optimization of the exchanger performance by the impressions of the invention is particularly advantageous.
In an embodiment, in this case, air flows around the extruded tube. In an alternative embodiment, a cooling fluid can also flow around the extruded tube, for example, in the case of an indirect exhaust gas cooler of a motor vehicle.
The heat exchanger of the invention can be an exhaust gas cooler for cooling a recirculated exhaust gas stream, but also a charge air cooler of a combustion engine, an oil cooler, or also a coolant cooler. These heat exchangers are used especially preferably in a motor vehicle.
The object of the invention is also achieved for a manufacturing method for the extruded tube. Expediently, the extruded profiles are first shaped by a known extrusion process depending on the type of a generally prismatic base body and then the impressions are introduced. This can occur in a step, directly following the extrusion, particularly also in the case of a still warm profile, or also in a completely separate step on a cooled and/or temporarily stored profile strip.
In an advantageous detail design, the impression occurs by means of an embossing roller. Alternatively or in addition, however, it can also occur by means of a press die.
In an embodiment, to optimize the manufacturing cost, a step, following the impression, of separating the extruded tube from an endless or quasi-endless profile strip is provided. This can occur, for example, by a sawing process. In an especially advantageous detail design, the separation occurs by a tear-off process, however, particularly after a preceding scoring. In this way, the occurrence of chips during the separation can be largely avoided.
According to an embodiment, the orientations of at least a few bulges of neighboring webs, which are substantially at the same height in the longitudinal direction, are opposite, whereby preferably in the longitudinal direction of a channel, bulging of one of the side walls and bulging of the web are provided alternately one behind the other, whereby preferably a first bulging of the web in a first orientation in the transverse direction occurs in the longitudinal direction of a channel, then bulging of one of the two side walls, followed by bulging of the web in the other orientation in each case, and then bulging of the other side wall in each case, whereby preferably in the longitudinal direction of a channel, bulges of two webs, bounding the channel, have bulges directed toward one another and lying at the same height, so that the channel width is reduced by the bulges, whereby preferably in the longitudinal direction of a channel bulges of two webs, bounding the channel, have bulges directed away from one another and lying at the same height, so that the channel width is increased by the bulges, whereby preferably the bulging of the web is formed both by an impression of the first side and also an at least partially coinciding impression of the second side, whereby especially preferably the orientation of the bulging in regard to the coinciding impressions is in the opposite or same direction.
According to an embodiment, the controlled oriented bulging of the web occurs by means of an embossing tool inclined relative to the side walls, whereby preferably the controlled oriented bulging of the web occurs by means of an embossing tool acting eccentrically relative to the web, whereby preferably an end region of the extruded tube is not provided with bulges, whereby preferably a distance of a tube end to a first embossing is approximately between 2 mm and 15 mm, particularly approximately between 4 mm and 8 mm.
According to an embodiment, the extruded tube has a curved region, whereby preferably in the curved region there is an at least reduced depth of the bulges, whereby preferably no bulges are arranged in the curved region at least in sections, whereby the tube material is made of a material, such as, aluminum alloys, AlMn alloy, AlMg alloy, and AlMgSi alloy, whereby preferably a depth of the impressions is less than about 75%, particularly less than about 45%, and particularly less than about 30% of an inside tube diameter in the vertical direction, whereby preferably in the longitudinal direction a distance between an impression of the one side wall to a next impression of the other side wall is no more than 10-fold, particularly no more than 6-fold, and particularly no more than 3.5-fold of an inside tube diameter in the vertical direction, whereby preferably in the longitudinal direction a distance between an impression for bulging of a side wall to a next impression for bulging of a web is no more than 8-fold, particularly no more than 6-fold, and particularly no more than 3-fold of an inside tube diameter in the vertical direction, whereby preferably a length of the impression, overlapping several webs, in the transverse direction is approximately between 25% and 100%, particularly between 35% and 90%, and particularly between 45% and 80% of a width of the extruded tube in the transverse direction, whereby preferably a length of an impression arranged between two webs in the transverse direction is approximately between 25% and 130%, particularly between 35% and 95%, and particularly between 45% and 75% of a width of the channel, bounded by the webs, in the transverse direction.
According to an embodiment, a fin element is arranged from the outside on at least one of the side walls, particularly by means of a material connection, whereby preferably a repeat unit of the impressions in the longitudinal direction and a repeat unit of fins of the fin element are not integer multiples of each other, whereby preferably at least one half-web projects from one of the side walls into one of the channels.
According to an embodiment, a hydraulic diameter, defined as four times the ratio of the area of the flow-through cross section to a perimeter wettable by the first fluid, is within a range between 1.2 mm and 6 mm, whereby preferably the hydraulic diameter is between about 2 mm and about 5 mm, particularly between 3.0 mm and 3.4 mm, particularly between 3.1 mm and 3.3 mm, and particularly about 3.2 mm, whereby preferably the hydraulic diameter is between about 2.5 mm and 4 mm, particularly between about 2.8 mm and 3.8 mm, particularly for a high-pressure heat exchanger, whereby preferably the hydraulic diameter is within a range between 2 mm and 3.5 mm, particularly between 2.5 mm and 3.5 mm, particularly for a low-pressure heat exchanger, whereby preferably a ratio of the hydraulic diameter and a channel cover thickness is within a range between 0.8 and 9, particularly within a range between 1.2 and 6, particularly within a range between 1.4 and 6, whereby preferably a ratio of a web thickness and a channel cover thickness is less than 1.0, whereby preferably a ratio of an outer perimeter of the extruded tube and the perimeter wettable by the first fluid is within a range between 0.1 and 0.9, particularly between 0.1 and 0.5, whereby preferably a ratio of a distance between two, particularly opposite partial webs and/or partial webs offset with respect to one another to a height of the tube cross section is within a range below 0.8, particularly within a range between 0.3 and 0.7, whereby preferably a ratio of a distance of a first partial web to a full web to a distance of a second partial web to the full web is within a range between 0.5 and 1.0, particularly within a range between 0.6 and 0.8.
According to an embodiment, at least one web and/or the channel cover, preferably the inner surface of the channel cover, have corrosion protection, preferably in the form of a zinc coating and/or paint, whereby preferably a cross section of the extruded tube is formed rectangular, oval, or semi-oval, whereby preferably a number of 2 to 20, particularly 5 to 15, particularly 7 to 12, particularly 8 to 11, particularly 9 webs are arranged next to one another across a tube cross section.
According to an embodiment, air flows around the extruded tube of the heat exchanger, whereby preferably cooling fluid flows around the extruded tube, whereby preferably the heat exchanger is an exhaust gas cooler for cooling a recirculated exhaust gas stream, a charge air cooler, an oil cooler, or a coolant cooler.
According to an embodiment of the method, the impression occurs by means of an embossing roller, whereby preferably the impression occurs by means of an press die, whereby preferably the impression is followed by a step of separating the extruded tube from an endless or quasi-endless profile string, whereby preferably the separation occurs by means of a sawing process or by a tear-off process, particularly after a preceding scoring.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

FIG. 1 shows a schematic illustration of an extruded tube for the definition of the individual spatial axes.

FIG. 2 shows a first exemplary embodiment of an extruded tube of the invention with overall nine variations 2.1 to 2.9.

FIG. 3 shows an illustration of embossing processes for manufacturing an extruded tube according to FIG. 2.

FIG. 4 shows a spatial illustration of an extruded tube according to the first exemplary embodiment.

FIG. 5 shows a detail from the extruded tube of FIG. 4.

FIG. 6 shows a second exemplary embodiment of an extruded tube of the invention with 10 variations 6.1 to 6.10.

FIG. 6 a shows additional variations 6.11 to 6.17 of the second exemplary embodiment.

FIG. 7 shows stereoscopic views of two embossing rollers for the production of an extruded tube according to the invention.

FIG. 8 shows an illustration, based on measurements and calculations, of a preferred selection of a hydraulic diameter in regard to the ratio of the perimeter wettable by the first fluid and an outer perimeter of the extruded tube.

FIG. 9A and FIG. 9B show two variations of a preferred embodiment of a cross section of an extruded tube having an extruded channel cover and webs extruded with the channel cover.

FIG. 10A and FIG. 10B show two variations of another embodiment, as in FIG. 9A and FIG. 9B, with partial webs.

FIG. 11A and FIG. 11B show two variations of another embodiment, as in FIG. 9A and FIG. 9B, with partial webs.

FIG. 12 shows another embodiment of a cross section of an extruded tube with partial webs.

FIG. 13 shows another embodiment of a cross section of an extruded tube with partial webs.

DETAILED DESCRIPTION

According to the illustration according to FIG. 1, the invention relates to extruded tubes, which extend at least in sections in a longitudinal direction designated by z. The extruded tubes have a longitudinal extension transverse to the longitudinal direction, whereby they are formed particularly as flat tubes. A transverse direction within the meaning of claim 1 is designated as the y direction in FIG. 1, whereby the (long) side walls 1, 2 of the extruded tube extend substantially in this direction. A vertical direction is designated by x in FIG. 1 and extends perpendicular to the longitudinal direction and to the transverse direction. The side walls 1, 2 need not necessarily extend straight in cross section but can also be curved and in this sense are oriented only “substantially” in the transverse direction or “at least nearly parallel.”
The side walls 1, 2 are connected together to form a closed flat tube via shorter, curved, narrow sides 3, 4 running substantially in the vertical direction.
Within the flat tube, the side walls are connected via at least one web, in the shown exemplary embodiments in each case via several continuous webs 5, 79, 89 with separation of separate channels 6 from one another. Apart from these continuous webs or full webs 5, 79, 89, partial webs 5′, 79′, 89′ can optionally also be provided (see, for instance, FIG. 4 or also FIG. 10A to FIG. 11B), which project into channels 6 like fins to increase the contact area between the channel wall and the fluid.
To optimize the turbulences of the flowing fluid, the extruded tubes are provided with impressions 7, which form local bulges relative to the longitudinal direction, which project into channels 6 and influence the fluid flow. In this case, this can refer to bulges in side walls 1, 2, which protrude accordingly in the vertical direction, or also bulges or bucklings of the continuous webs 5, 79, 89, which project accordingly in the transverse direction. Such bulges of the webs are achieved in that an impression is carried out at least partially coinciding with the attachment area of the web to the side wall.
It is achieved by suitable measures in this case that the orientation of the bulging of the web is predefined in a controlled manner in the transverse direction and does not occur arbitrarily or randomly. To achieve this, two different approaches can be taken during the production of the impressions:
On the one hand, a press die 8 (see FIG. 3) or an embossing roller 9′ as well (see FIG. 7) has an inclined embossing edge 8 a, 10′. FIG. 3 under A shows a simple embossing of an extruded tube by means of a smooth and not inclined embossing edge, overlapping most of the extruded tube in the transverse direction, by means of which webs 5 are bulged out in an uncontrolled manner toward the left or right. Under B, the embossing edge, in contrast, is provided with an angle alpha of a few degrees, typically no more than 10 degrees, relative to the side surface 1. As a result, all of webs 5 in example B are bulged out toward the right in a controlled manner, because the forces during embossing act asymmetrically in the region of the web attachments.
On the other hand, control of the bulging direction can also be achieved for punctiform impressions. To this end, in Example C of FIG. 3, a toothed embossing edge 8 b is shown, which acts on the extruded tube only with small local projections or in a point-like manner. The points of action are thereby localized substantially over webs 5, but slightly off-center. As a result, a buckling of webs 5 is also achieved in a predefined orientation relative to the transverse direction. The direction of the bulging of webs 5 in Example C would also be to the right, because the embossing points act somewhat to the left of the center of webs 5.
An option that is an alternative or an addition to press dies 8 of a substantially punctiform embossing with local projections is given by embossing roller 9, shown in FIG. 7, with punctiform local projections 10. Embossing roller 9′, also shown in FIG. 7, in contrast, has elongated projections 10′, which extend over at least one entire channel width or also over the substantially entire width of the extrusion profile. Embodiments such as those in FIG. 4, for example, can be produced with this type of roller 9′, whereby embodiments such as those shown in FIG. 6 and FIG. 6 a can be produced with the local projections of embossing roller 9. In principle, both types of projections 10, 10′ can also be provided together on the same embossing roller.
A first exemplary embodiment according to FIG. 2 and a second exemplary embodiment according to FIG. 6 with several variations in each case are substantially shown in the present case. The first exemplary embodiment according to FIG. 6 deals with impressions of the first type with smooth, inclined embossing edges, which in each case at the same time overlap more than one web 5 of the extruded tube and thereby also at the same time bulge the side walls between the webs inwardly. Expediently, the embossing edges or impressions are arranged in this case at an orientation angle relative to the transverse direction. As a result, the bulges, caused by the same impression, of neighboring webs are offset in the longitudinal direction to one another, so that in a simple manner a wave-shaped modulation of channels 6 is achieved with a channel wall distance, largely constant in the transverse direction. This type of orientation angle in a typical embodiment is about 35° and is present in Examples 2.3 to 2.9. Such impressions with an angled course to the transverse direction are especially highly suitable for combining with a cooling fin (not shown) soldered in a planar manner to the extruded tube, because a disadvantageous overlapping of impressions and fins with the result of areas of poor heat removal is avoided.
In general, in Examples 2.1 to 2.9 impressions of the top side are shown as solid lines and impressions of the bottom side, which are not visible in the top view, as dashed lines. The controlled bulging direction of the webs is depicted in each case as a direction arrow within the impressions.
The impressions are expediently made in both side surfaces 1, 2. These opposite impressions can be arranged coinciding (e.g., FIG. 2, Examples 2.2 and 2.4) or offset in an alternating manner (e.g., 2.1, 2.3). The orientation angle of the impressions can vary and in particular alternate as in Examples 2.5, 2.8, and 2.9. Several impressions, shorter in the transverse direction, with varying orientation angles can also be provided over the width of the extruded tube; see, for instance, Examples 2.6 to 2.9.
In some of the described examples, for example, in case 2.1, 2.3, or 2.7, the bulging directions of the webs by impressions from above are opposed by those of the impressions from below alternating in the longitudinal direction, to achieve turbulence generation as great as possible with a moderate increase in pressure loss.
In the second exemplary embodiment according to FIG. 6, these are largely local impressions of the second type. In contrast to the first case according to FIG. 2, hereby an embossing is not made over the entire tube width but only locally limited. This has the advantage that the buckling of the tube webs and the constriction of the channel height in the vertical direction can occur separately one after the other. Thus, there is additional design flexibility, which is very helpful particularly in view of the generation of spin flow in the channels. In this way, even more complex 3-dimensional swirling and flow conditions can be generated than in the first case.
Advantageously, the impressions are made in the longitudinal direction alternately in the form that in the longitudinal flow direction after embossing of the tube webs, an embossing of the tube wall occurs and then again a shaping of the tube webs, etc. The embossments can be made in addition alternately in both side walls 1, 2, specifically particularly in the form that in the longitudinal direction after the buckling of a web 5 in the one direction by an impression 7 on the upper side wall 1 an impressing of the lower side wall 2 occurs, in the longitudinal direction then the buckling of a web 5 in the other orientation direction by an impression 7 on the lower side wall 2, and in the longitudinal direction then an impression 7 of the upper side wall 1. Afterwards, the embossing of the webs by means of bulging of a web 5 in the first direction by impression on the top side wall 1, etc., repeats cyclically. Any other combinations and sequences of the impressions in the flow direction are also conceivable, however; see the exemplary illustrations 6.1 to 6.17 in FIGS. 6 and 6 a. In the illustrations, the impressions that bulge out because of the spatial overlapping of a web 5 have a direction arrow. A deviation from the central position is not shown in the drawings for the sake of clarity. Basically, only a small control deviation of the press die from the central position over a web 5 is necessary to predefine the bulging direction of the web.
To be able to achieve the greatest and most uniform bulging of the webs possible, these can also be bulged out on both sides from the top and bottom side, as shown in FIG. 6 a, Examples 6.11 to 6.13. In this case, the impressions of the side walls acting on the webs in each case overlap at least partially, so that the web is largely bulged out at the same location from both side walls. The direction of the bulging relative to the overlapping impressions in this case can be in the same direction (see, for instance, 6.11 and 6.13) or in the opposite direction as well (see 6.12).
The embossing of the tube webs and the tube walls, on the one hand, causes a reduction in the hydraulic diameter and thereby an increase in tube performance in regard to heat transfer, but, on the other, also a directed flow deflection both in the y-z plane and also in the x-z plane.
FIG. 6 shows advantageous impressions by way of example in a tube with three intermediate webs 5. The impression of the top side wall 1 in each case is shown using a solid line and the impression of the bottom side wall 2 using a dashed line. The direction of the web buckling is indicated in each case with an arrow. Depending on the requirements, the impressions in the x-, y-, and z-direction can be made round, oval, elongated oval, rectangular, or also in another form. The impressions are carried out alternately as previously described. The deformation of the channel tube wall at a location can be carried out by one or two embossings per channel (see, for instance, Examples 6.4, 6.5, 6.9, and 6.10). However, in special cases, particularly in very broad channels, this can be also done by more than two impressions at one location.
In FIG. 6.3, impressions of the side walls 1, 2 are shown between webs 5, which are oriented in a defined orientation angle to the transverse direction. The orientation angle of the impression relative to one of the axes z or y in the present case is approximately between 30° and 40°. Any other combinations between the deflection direction and impression sequence also beyond the depicted variants are conceivable.
Examples 6.4, 6.5, 6.9, and 6.10 show variants with winglet-like impressions, i.e., elongated and preferably angled to one another, between webs 5. Depending on the requirements, any combinations of winglets beyond the depicted embodiments both relative to position and orientation to one another, as well as to the direction of the webs, are conceivable. For the impressions in the form of winglets, it became evident that an orientation angle of the impression relative to one of the axes z or y is especially preferable between about 28° and 42°.
To be able to increase the turbulence still further, it can also be provided apart from the shown variants, particularly for very broad channels, to impress more than one winglet per channel in the transverse direction.
The shape of the winglet is selected so that the ratio of its length to its width is a multiple, particularly about 1.8-fold to 2.5-fold or about 2.5-fold to 3.2-fold.
Impressions between webs 5 in winglet form have the advantage over more simply shaped impressions that with this type of flow guidance an even greater heat transfer performance can be achieved, because the flow experiences a still greater directed deflection with considerably greater swirling.
It applies to both exemplary embodiments according to FIG. 2 and FIG. 6 that during use of highly contaminated fluids, such as, e.g., exhaust gas from a combustion engine, with the narrowing of channels 6 the risk of blockage due to accumulation of components from the gas phase, particularly soot and/or unburned hydrocarbons, increases. Therefore, in this case, the bulges of webs 5 are designed so that they bulge out in the transverse direction always in the same orientation, so that the free channel distance between neighboring webs 5 does not change or changes only slightly. In the longitudinal direction, the webs therefore have a parallel wave shape to one another in regard to the transverse direction.
Depending on the use, however, it can also be advantageous to lay out webs 5 so that the orientations of the bulges of neighboring webs 5 are precisely in the opposite direction to one another, to alternately narrow channel 6 as much as possible and then again to widen it as greatly as possible. An example of such an arrangement is shown in FIG. 6 a, Example 6.13. This alternate narrowing and widening of the channel cross section makes possible an additional increase in performance for applications, in which deposits are not critical, such as charge air coolers, coolant coolers, oil coolers, or exhaust gas coolers for low-pressure EGR applications or high-pressure EGR applications with moderate soot and/or HC emissions. Depending on the requirements, in this case, the appropriate compromise with a drop in pressure resulting from the swirling and narrowing must always be considered.
In FIG. 6 a, Examples 6.14 and 6.15, another option is shown to allow the side wall and also the web/neighboring webs to buckle with only one impression in that the die in addition to the channel width also covers another part or more than this part of the neighboring web(s). Apart from the variants shown in FIGS. 6.14 and 6.15, all already mentioned combinations of web bucklings for a channel impression direction are also conceivable here.
For dimensional stability of the outer dimensions of the extruded tube, it is advantageous not to bulge out the closing narrow sides 3, 4 with use of impressions. In this case, in both lateral outer channels, however, only a wave-shaped bulging of the web, arranged closer to the tube middle, occurs whereas the outer wall remains undeformed. Depending on the application, it is therefore advantageous to provide outer channels with a larger or smaller flow cross section, in order to minimize in the first case the risk of blocking of the gas channel by the greater narrowing of the distance between web 5 and the outer narrow side 3, 4 in the area of the bulge, or in the second case to achieve a similarly high turbulence in outer channel 6 as well as in the inner channels. If no special requirements are made for the outside dimension of the extruded tube, it can naturally be expedient to provide the narrow sides 3, 4 as well with impressions and to bulge them out in the transverse direction.
Joining the extruded tube in a bottom and for configuring the tube ends:
To join the extruded tube in a tube bottom, it is advantageous not to emboss the embossments in the end regions, so that a defined insertion of the extruded tube with a circumferentially constant gap in the bottom is possible and thereby good joining of the extruded tube-bottom connection is assured. Another reason is that a defined widening of the extruded tube for fixing the extruded tube and bottom via a common contact surface remains possible.
The required distance of the profile end to the first embossing depends in particular on the depth of the impressions. The distance is to be selected so that no or only a very minor deformation of the original tube geometry occurs in the area of the joint. In typical cases of heat exchangers dimensioned for use in motor vehicles, this means a distance between 2-15 mm, particularly 4-8 mm. In special cases, this dimension can also exceed these distances.
Bending of the embossed extruded tubes:
A great advantage of the extruded tube heat exchanger compared with other exchanger tubes, e.g., stainless steel tubes, is the very great design flexibility, particularly because of the option of bending the extruded tube.
For bending the extruded tube, it is particularly advantageous when impressions are not used in the area of the bending, to prevent too great a deformation and perhaps even closing of individual channels. Alternatively, in the bending area, the impression depth only can be reduced or, for example, only embossing of the webs or only narrowing of the channel walls can be provided. In the manufacturing process, the embossing of the tubes occurs first and then the bending into the desired form.
Manufacturing method:
The manufacturing of the impressions can occur advantageously in two alternative or also cumulative ways: the extruded tube is embossed by means of at least one tool roller [roller-shaped tool]. Such a roller 9 is pictured by way of example in FIG. 7. Advantageously, at least two counterrotating tool rollers are used, by which in one work step both the top side wall 1 and the bottom side wall 2 are embossed; and/or the extruded tube is embossed by a die set or various single press dies.
For both types of fabrication, the impression can be created both in a single stage and multistage manner via several embossing rollers or die sets provided one after another in the fabrication direction.
To prevent bending of the extruded tube during the fabrication process, the extruded tube is held in position by means of at least one holding function before and/or after the embossing step. It is assured by a lateral roller guidance that the extruded tube does not shift in the transverse direction during the embossing process. If this holding function can prevent the warping of the extruded tube only partially, this can be corrected by a subsequent work step via stretching or resizing of the extruded tube via another set of rollers or a press.
The embossing by means of rollers has the advantage that the method can be carried out with a continuous feed motion of the extruded tube, whereas timing of the feed motion is generally necessary for fabrication by means of die sets.
In order to be able to join the extruded tube optimally in the bottom later, it is important that there are no embossments and/or a change in cross section of the extruded tube in the area of the profile separation. This can be achieved in several ways: the distance of the impressions is so great that separation of the extruded tube is possible; and/or embossments are omitted at the separation point.
The latter can be provided for the embossment by means of rollers, for example, by a suitable geometry of the embossing rollers. In this case, the roller circumference is always an integer multiple of the later profile length. Another possibility for providing a sufficiently broad sawing or joining area is to make the provision of the roller variable, so that depending on the provision of the rollers embossments are or are not shaped.
Another advantage of the fabrication by means of rollers is that different profile variants can be produced by an exchange of rollers in a very simple way with the same production line.
Besides an exchange of embossing rollers, alternatively, also only one embossing roller can be used in which the raised areas for embossing are placed such that they are exchangeable. In this case, the work is done with a basic roller in which variable embossing sets can be used. Alternatively, it is also conceivable for this purpose to pull onto a basic roller without or with a few embossments an additional sheathing body, which provides the desired embossing arrangement. In both cases, work is done with only one basic roller body.
For embossing the extruded profile by means of die sets, optionally to achieve a large sawing region the dies must be totally or partially discontinued in the sawing and joining region, so that no or only very faint embossments are produced.
The production sequence for the embossed extruded tube is therefore described as follows:
(1) The extruded tubes are provided either in a prefabricated length minus the fabrication-related stretching during the embossing process, or as bar material with a multiple of the later tube length, or as continuous material in a coil shape for the embossing process.
(2) Embossing of the extruded tubes by means of rollers or die set
(3) Correction of possible bending by means of extension and/or standardizing rollers/press
(4) Possibly separation of the extruded tubes
(5) Possibly bending of the extruded tubes
(6) Cleaning of the extruded tubes.
The sequence of these steps is selected so that they can be linked very simply to one another to create a production line that is very simple and cost-effective to realize.
Separation of the extruded tubes:
The separation occurs preferably by means of a saw running concurrently during the embossing process, but can also occur in a separate sawing process following the embossing process. Alternatively, the separation of the extruded tubes can also occur by means of scoring and subsequent tearing off of the tubes. This has the advantage that no chips arise and no additional saw lubricant is required. As a result, depending on the application, a subsequent cleaning step may be totally or partially omitted.
Material:
In principle, the embossed extruded tubes can be produced with any extrudable material. All extrudable aluminum alloys, particularly Al alloys, especially AlMn alloys, AlMg alloys, and AlMgSi alloys, are advantageous for the application pursued here of heat exchangers, such as exhaust gas coolers, oil coolers, coolant coolers, and charge air coolers.
If the extruded tube is used in a corrosion-critical application, e.g., as a gas-conducting extruded tube of an exhaust gas cooler or a low-pressure charge air cooler, corrosion studies have shown that an especially high corrosion resistance can be achieved in that reducing contaminations in the extruded tube material are present in the following percentages by weight:
Silicon: Si<1%, particularly Si<0.6%, especially Si<0.15%
Iron: Fe<1.2%, particularly Fe<0.7%, especially Fe<0.35%
Copper: Cu<0.5%, particularly Cu<0.2%, especially Cu<0.1%
Chromium: Cr<0.5%, particularly 0.05%<Cr<0.25%, especially 0.1%<Cr<0.25%
Magnesium: 0.02%<Mg<0.5%, particularly 0.05%<Mg<0.3%
Zinc: Zn<0.5%, particularly 0.05%<Zn<0.3%
Titanium: Ti<0.5%, particularly 0.05%<Ti<0.25%
An especially high corrosion resistance of these extruded tubes can be achieved in general when the grain sizes measured in the extrusion direction are <250 μm, particularly <100 μm, especially <50 μm.
Impression depth:
The specific depth of the impression depends greatly on the application. It became evident, however, that especially from the standpoint of thinning of the material and the pressure loss generated by the impression, an impression depth less than 75% of the clear tube height b, particularly less than 45%, especially less than 30%, has proven advantageous.
Distance of the impressions:
The distance of the impressions to one another also greatly depends on the application. An especially advantageous range could also be found for this, however:
(1) In the longitudinal direction based on embossments of the one side wall 1 to those of the other side wall 2 between 0-fold and 10-fold of the clear tube height b, particularly between 0-fold and 6-fold of the clear tube height b, especially between 0-fold and 3.5-fold of the clear tube height b.
(2) In the longitudinal direction based on embossments which are used to reduce the channel height to embossments which are used to bulge out the webs on the one side wall between 0-fold and 8-fold of the clear tube height b, particularly between 0-fold and 6-fold of the clear tube height b, especially between 0-fold and 3-fold of the clear tube height b.
Length of the impressions:
The length of the impressions also depends greatly on the application. For this purpose, however, an especially advantageous range, associated with the tube width or channel width, could also be found:
The length of the impression in case of the exemplary embodiment according to FIG. 2 should be between 100% and 25% of the tube width, particularly between 90% and 35%, especially within the range between 80% and 45% of the tube width.
The length of the impression in case of the exemplary embodiment according to FIG. 6 should be between 130% and 25% of the channel width, particularly between 90% and 35%, especially within the range of 75% and 45% of the channel width.
The length of the impression in the case of an exemplary embodiment that is not shown is between 325% and 25% of the channel width, particularly between 250% and 35%, especially within the range of 215% and 45% of the channel width.
Soldering of an outer fin, e.g., for coolant coolers, charge air coolers:
If an additional outer fin is attached to the embossed extruded tube, for instance, in a cross-flow cooler, care must be taken that the impressions in the transverse direction are not arranged aligned but rather slightly offset, to assure the best possible soldering of the outer fin. The arrangements of impressions, shown in FIGS. 2.3-2.9 and FIGS. 6.6-6.10, are especially suitable for this. For the arrangements of impressions shown in FIGS. 6.6-6.10, the distances of similar impressions in channels neighboring each other in the longitudinal direction are realized advantageously so that these are not an integer multiple of the fin density but rather either smaller or greater, particularly advantageously within the range of k/3 to n/3 of the fin depth, for k=1, 4, 7, 10, . . . and n=2, 5, 8, 11, . . . , so that the best possible soldering of the outer fin results.
Exemplary embodiments of extruded tube cross sections that are not impressed:
A hydraulic diameter within a range between 2 mm and 5 mm has proven especially preferable for realizing the concept of the invention. The size of said range realizes particularly advantageously—as explained in detail with use of FIG. 8—a balance between the tendency to realize as good a heat transfer as possible in an extruded tube, on the one hand, and the tendency, on the other, to reduce a pressure loss, or to realize an acceptable pressure loss while nevertheless realizing good heat transfer. In this connection, a hydraulic diameter within the range between 3 mm and 3.4 mm, in particular between 3.1 mm and 3.3 mm, has proven to be further particularly preferable. In particular in regard to the latter range of a hydraulic diameter between 3.1 mm and 3.3 mm, it became evident that a hydraulic diameter of approximately 3.2 mm is especially expedient. Although it is fundamentally not possible to prevent fouling of the extruded tube or the heat exchanger tube within the stated range either, tests have shown, however, that in said range, fouling stabilizes in such a way that a decline in performance is also kept at a relatively low level. Whereas it is to be expected in ranges of the hydraulic diameter outside the aforementioned ranges that an extruded tube will become increasingly fouled with an increase in pressure loss the longer it is operated, in the case of the aforementioned preferred ranges of a hydraulic diameter of demonstrated dimensions, it is to be assumed that a pressure loss stabilizes at a relatively low level. A possible suboptimal heat-transfer performance of a heat exchanger is not reduced further with continued heat exchanger operation. In the case of a hydraulic diameter outside the aforementioned ranges, in contrast, a disproportionate increase in pressure loss and ultimately in the worst case blockage of the channels occur during further operation of the flow channel.
An extruded tube according to the concept of the invention can be used advantageously both within the context of high-pressure exhaust gas recirculation and within the context of low-pressure exhaust gas recirculation. Furthermore, an application for charge air cooling or coolant cooling is also possible. In all fields of application, in particular those stated above or the like, an increase in the number of webs to improve heat transfer is avoided according to the concept of the invention by selecting the hydraulic diameter within a range between 1.2 mm and 6 mm. However, tests have shown that a selection, optimized for low-pressure exhaust gas recirculation, high-pressure exhaust gas recirculation, or charge air cooling, of a range for the hydraulic diameter can be different. In the case of high-pressure exhaust gas recirculation, as has been found, both the increase in pressure loss and the increased risk of blockage or significant fouling of a channel by soot particles or the like are relatively critical. For a high-pressure heat exchanger, a range of a hydraulic diameter between 2.5 mm and 4 mm, particularly between 2.8 mm and 3.8 mm, has proven particularly advantageous.
In a low-pressure exhaust gas recirculation concept, there is no or only a very low soot entry, so that in this case smaller hydraulic diameters than in high-pressure EGR coolers can also be used advantageously. For a low-pressure heat exchanger, a range of a hydraulic diameter between 2 mm and 3.5 mm, in particular between 2.5 mm and 3.5 mm, has proven especially advantageous.
It has proven particularly advantageous, especially to increase corrosion resistance, to select a ratio of a web thickness and a channel cover thickness below the value of 1.0. In other words, to increase the corrosion resistance, it is advantageous to provide the channel cover with a greater wall thickness than a web. This is advantageous in particular in regard to the design of an extruded tube in which at least the channel cover is produced based on an aluminum material.
Furthermore, it has proven to be fundamentally relevant to optimize a channel cover thickness in such a way that, on the one hand, a corrosion resistance, in particular in the case of an extruded tube based on an aluminum material, is sufficiently assured and, on the other, a sufficient number of extruded tubes are provided in the available installation space of a heat exchanger. Installation space for a heat exchanger in an engine is usually rather limited, so that it is basically within the scope of an improvement to provide as many extruded tubes as possible in a heat exchanger, and therefore to design a channel cover thickness not to be too thick. According to a particularly preferred refinement of the invention, a ratio of the hydraulic diameter and a channel cover thickness within a range between 0.8 and 9 has proven to be particularly advantageous. Said range has proven to be particularly expedient in particular in an extruded tube based on an aluminum material, in particular in an extruded tube in which at least the channel cover is based on an aluminum material. Also advantageous is a range between 1.2 and 6.0, in particular a range between 1.4 and 6, with regard to the design of the channel cover thickness (installation space requirement, corrosion resistance) and the hydraulic diameter (heat transfer, pressure loss).
The concept of the invention and/or one or more of the aforementioned refinements individually or in combination have proven particularly advantageous for dimensions of an extruded tube that realize a ratio of an outer perimeter of the extruded tube and the perimeter wettable by the first fluid within a range between 0.1 and 0.9, particularly between 0.1 and 0.5 for an exhaust gas cooler. The tests carried out in this regard have shown that within the range of the specified dimensions, the behavior of an extruded tube is particularly advantageous in regard to the above-explained problem.
In regard to production aspects and the aforementioned problem, an extruded tube is especially expedient in which a web as a full web is arranged in the tube cross section at one end and on the channel cover inner surface at the other end. In particular, a tube cross section may have only full webs. A full web is advantageously made continuous, without openings, between a first channel cover inner surface and a second channel cover inner surface. As is explained by way of example using FIGS. 9A and 9B, this makes it possible to realize an extruded tube with a hydraulic diameter according to the concept of the invention.
Furthermore, an extruded tube has proven advantageous in which a web as a partial web is arranged in the tube cross section only at one end on the channel inner surface and projects freely into the interior space at the other end. As explained by way of example using FIG. 10A and FIG. 10B, as well as FIG. 11A and FIG. 11B, a hydraulic diameter may be realized in an especially advantageous manner by means of an extruded flow channel according to the concept of the invention.
It became evident that advantageously two partial webs can be arranged with opposing end sides at the other end. Alternatively or in combination with the aforementioned arrangement of partial webs, two partial webs can be arranged with end sides offset laterally with respect to one another at the other end. Preferably, a partial web and a full web are arranged alternately next to one another.
It has proven especially advantageous to make dimensions and arrangements of the partial webs as follows. According to an especially preferred refinement, a ratio of a distance between two partial webs, especially two opposite partial webs and/or two partial webs offset with respect to one another, to a height of the tube cross section is within a range below 0.8, particularly within a range between 0.3 and 0.7. Preferably, a ratio of a distance of a first partial web to a full web to a distance of a second partial web to the full web is within a range between 0.5 and 1.0, preferably within a range between 0.6 and 0.8.
FIG. 8 illustrates the ratio of the perimeter wettable by a fluid, such as, e.g., an exhaust gas, and an outer perimeter of the extruded tube as a function of the hydraulic diameter. A preferred ratio results from the above-explained shaded areas of a preferred hydraulic diameter of 2 mm to 5 mm, particularly 2.8 mm to 3.8 mm. It is evident from FIG. 8 that said ratio should lie within the range between 0.1 and 0.5 in order to achieve the improved degrees of exchange and degrees of pressure loss. FIG. 8 in the present case is provided by way of example for an extruded tube profile shown in greater detail in FIG. 10B. A comparable tendency can also be observed in the additional structural designs, described in greater detail hereinafter, of a flow-through cross section in an extruded tube. Thus, FIG. 8 shows the explained ratio for different web distances a, inter alia of FIG. 10B (in the present case for two examples a=2 mm and a=5 mm), and for different values of a ratio, designated here by k, of a distance between two opposite partial webs to a height of a tube cross section. The ratio k, as illustrated in FIG. 8 by arrows, should be within a range below 0.8, preferably within a range between 0.3 and 0.7. In the present case, the ratio k of a distance e between two opposite partial webs to a height b of the tube cross section increases from 0.25 to 0.75 in the direction of the arrow. This analysis applies both to an exhaust gas cooler within the scope of a high-pressure design in an exhaust gas recirculation system and to an exhaust gas cooler within the scope of a low-pressure design in an exhaust gas recirculation system.
Exemplary structural designs of a cross section of different preferred extruded tubes are described hereinafter in FIG. 9A to FIG. 11B. In this case, it should nevertheless be clear that modifications of the same and any desired combination of features of the embodiments specifically described in the figures are possible, and a hydraulic diameter within the range between 1.5 mm and 6 mm, preferably between 2 mm and 5 mm, preferably between 2.8 mm and 3.8 mm, can still be achieved. In particular, the embodiments shown in the following figures each show a modification in which a channel cover thickness and a web thickness d are identical or similar, and show another modification in which a ratio of a web thickness d and a channel cover thickness s is less than 1.0 mm. Accordingly, the wall thicknesses of partial webs or similar dimensions can also be varied and adapted according to the aim to be achieved.
FIG. 9A and FIG. 9B show two modifications of an extruded tube 61, 61′; in this case, the modifications differ in that the cover thickness s in extruded tube 61′, illustrated in FIG. 9B, is thicker than a web thickness d, whereas said thicknesses are substantially identical in extruded tube 61 illustrated in FIG. 9A. Furthermore, the same reference characters are used for identical features.
Flow channel 61, 61′ is formed as an overall extruded profile, therefore, as an extruded channel cover together with the extruded webs. Flow channel 61, 61′ accordingly has a channel cover 63 having an interior space 67 which is surrounded by a channel cover inner surface 65 and in the present case is designed for the heat-exchanging guiding of the first fluid in the form of an exhaust gas. Furthermore, flow channel 61, 61′, in the present case, has a number of five webs 69, which are arranged in inner space 67 on channel cover inner surface 65 and are formed together with channel cover 63, 63′ as an integral extruded profile. A web 69 runs entirely parallel to a flow channel axis, which is perpendicular to the plane of the drawing, continuously along the flow path formed in housing of a heat exchanger. The shown flow-through cross section, transverse to the flow channel axis, is designed for guiding the exhaust gas in interior space 67. The design is carried out on the basis of the hydraulic diameter dh, which is given for the present extruded tube 61, 61′ with reference to the distances a, b at the bottom right in FIG. 9B. The hydraulic diameter arises as four times the ratio of the area of the flow-through cross section to a perimeter wettable by the exhaust gas. The area of the flow-through cross section in the present case is a multiple of the product of a and b. The wettable perimeter in the present case is likewise a multiple of twice the sum of a and b. In this case, a denotes the width of the free cross section of a flow line 74, divided in the flow channel by webs 69, and b denotes the free height of flow line 74.
In said flow channel 63, 63′, and also in the flow channels explained in greater detail hereinafter, a wall thickness s is within the range between 0.2 mm and 2 mm, for corrosion-critical applications preferably within the range between 0.5 mm and 1.4 mm, for corrosion-non-critical applications preferably within the range between 0.3 mm and 0.8 mm. A height b of a flow path 74 or a height of the inner space 67 in the present case is within the range between 2.5 mm and 10 mm, preferably within the range between 4.5 mm and 7.5 mm. A width a of a channel 74 in the transverse direction is within the range between 3 mm and 10 mm, preferably within the range between 4 mm and 6 mm.
FIG. 10A and FIG. 10B show two additional modifications of an especially preferred embodiment of an extruded tube 71, 71′, which—as explained heretofore—differ only in the wall thickness of channel cover 73, 73′ relative to the wall thickness of a web 79. Flow channel 71, 71′ has in addition webs 79 in the form of full webs and partial webs 79′, arranged alternately next to full webs 79. Extruded tube 71, 71′ is in turn formed entirely as an extruded profile, a channel 74 in turn being formed by the distance between two full webs 79. The hydraulic diameter of the flow-through cross section in extruded tubes 71, 71′, shown in FIG. 10A and FIG. 10B, is specified below FIG. 10B. In the present case, two partial webs 79′ are each arranged with opposing end sides 76.
FIG. 11A and FIG. 11B show two further modifications 81, 81′ of an especially preferred embodiment of an extruded tube 81, 81′ in which two partial webs 89′ are arranged with end sides 86 laterally offset with respect to one another. A hydraulic diameter dh for the shown profile is again obtained from the formula shown below FIG. 10B, where a1 is to be replaced by a4.
A ratio of a distance a3 of a first partial web 89′ to a full web 89 to a distance a4 of a second partial web 89′ to the full web 89 is preferably within a range between 0.5 mm and 1.0 mm, preferably within a range between 0.6 mm and 0.8 mm. The distance e between two opposite partial webs 79′ and/or between two partial webs 89′, offset with respect to one another, to a height b of the tube cross section is basically within a range below 0.8 mm, in particular within a range between 0.3 mm and 0.7 mm.
Each extruded tube shown in FIG. 9A to FIG. 11B is provided according to the invention with impressions and bulges according to the explained exemplary embodiments, to optimize the turbulences and heat transfer, as well as the pressure drop, in the specific application.
Particularly for the extruded profiles shown in FIGS. 10A, 10B, 11A, and 11B, apart from the described procedure for impressing the tube wall and the tube web, an embodiment with exclusive buckling of the full and half-webs is also advantageous. Due to the large number of webs and/or the length of the half-webs, an impression of the tube wall can cause the blocking of the flow channel by contacting or almost contacting half-webs. Therefore, depending on the distance e, particularly for the profiles shown in FIGS. 10A, 10B and 11A, 11B, it is often more advantageous to allow only the webs or half-webs to buckle by selective impressions in the vicinity of the web attachments and to impress the tube walls only as little as possible. This applies particularly for e<1/3b.
FIG. 12 and FIG. 13 in each case show additional embodiments 91, 101 of cross sections of extruded tubes as yet without bulges. In each case, partial webs 92, 102 are present, which extend proceeding from webs 5 in the transverse direction into channels 6. In the example of FIG. 12, the partial webs are each arranged at the same height and in the example of FIG. 13 at a different height.
The illustrations according to FIG. 12 and FIG. 13 are according to scale, so that specific dimensional ratios of the drawn dimensions can be derived from them.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.

Claims

1. An extruded tube for a heat exchanger, the extruded tube comprising

two at least approximately parallel outer side walls, which extend in a longitudinal direction and a transverse direction of the extruded tube and are connected by two outer narrow sides in a vertical direction of the extruded tube; and

at least one continuous web extending between the side walls in the longitudinal direction and in the vertical direction and separating at least two channels of the extruded tube,

wherein at least one of the outer side walls has impressions that form bulges of the side walls, the bulges projecting into the channels and extending substantially in the transverse direction, and

wherein bulges of the at least one web have a controlled orientation relative to the transverse direction.

2. The extruded tube according to claim 1, wherein at least one of the channels of the extruded tube in the longitudinal direction has a regular, wave-shaped course with respect to the transverse direction.

3. The extruded tube according to claim 1, wherein a distance in the transverse direction between two neighboring webs is substantially constant.

4. The extruded tube according to claim 1, wherein at least one of the impressions has an elongated form, and wherein a majority of webs are overlapped and bulged out by the same impression.

5. The extruded tube according to claim 4, wherein the elongated impression has an orientation angle to the transverse direction.

6. The extruded tube according to claim 5, wherein the orientation angle is approximately between 0° and 45°, in particular approximately between 20° and 45°, or in particular approximately between 28° and 42°.

7. The extruded tube according to claim 1, wherein at least one of the impressions coincides substantially only with the at least one web.

8. The extruded tube according to claim 1, wherein at least one of the impressions does not coincide with a web.

9. The extruded tube according to claim 8, wherein the impression has an orientation opposite to the transverse direction.

10. The extruded tube according to claim 9, wherein an orientation angle of the impression relative to the transverse direction is approximately between 0° and 45°, approximately between 25° and 45°, or approximately between 30° and 40°.

11. The extruded tube according to claim 1, wherein at least one of the impressions is made winglet-shaped, or wherein at least one of the impressions is made as elongated winglets.

12. The extruded tube according to claim 10, wherein the winglet-shaped impression has a length-to-width ratio of between 1.2 and 5, preferably between 2 and 5, especially preferably between 2.5 and 3.2, or preferably between 1.5 and 3, especially preferably between 1.8 and 2.5.

13. The extruded tube according to claim 1, wherein the orientations of at least some bulges of neighboring webs, which are substantially at the same height in the longitudinal direction, are the same.

14. A heat exchanger for a motor vehicle, comprising an extruded tube according to claim 1.

15. A method for producing an extruded tube according to claim 1, the method comprising:

producing the extruded tube by an extrusion process; and

subsequently impressing the impressions in the side walls.