DE102009041406B3 - Heat exchanger for use as evaporator in energy recovery plant of motor vehicle, has smaller flat tube arranged in larger flat tube, where broad sides of walls of larger flat tube lie against each other, when tubes are coaxially arranged - Google Patents

Abstract

The exchanger has an extruded smaller flat tube (10) arranged in a larger flat tube (20). Flow channels (1, 2) are provided for flow of two fluids i.e. water. One of the flow channels (1) is provided in an inner side of the smaller flat tube. The other flow channel (2) completely surrounds the former flow channel. Broad sides (21) of tubular walls of the larger flat tube lie against each other, when the tubes are arranged in a coaxial manner. The tubular walls of the larger flat tube and the smaller flat tube are deformed from sheet metal strips. A tubular base is arranged at tubular ends.

Description

The invention relates to heat exchangers with coaxially arranged flat tubes which form a tube stack, comprising a smaller flat tube, which is arranged in a larger flat tube and with flow channels for at least two fluid streams, wherein a first flow channel is formed in the interior of the smaller flat tube and a second flow channel completely or substantially encloses the first flow channel.

A heat exchanger of this type is known. In this known heat exchanger, the tube walls of the coaxially arranged flat tubes abut each other, so that the heat is exchanged via the connected walls. This form of heat exchange could not be considered very efficient.

From the WO 2005/033603 A2 . 7 , another heat exchanger is known, which consists of coaxially arranged flat tubes, wherein a first flow channel is formed in the interior of the smaller flat tube and a second flow channel between the coaxially arranged tubes. Of this prior art, which is characterized by flat coaxial tubes, which naturally have two opposite broad sides and two opposite narrow sides connecting the broad sides, the invention described below proceeds. The tubes of this prior art are designed as extruded profile tubes, which is why such heat exchangers are quite difficult to build. In addition, in the cited document a single coaxial flat tube - so two nested flat tubes - forms the entire heat exchanger. Furthermore, no turbulence generating structures are present in the flow channels, which is why the heat exchange performance can not reach the desired level.

From the DE 697 20 909 T2 is a heat exchanger and its manufacturing method known. It is an oil cooler that has coaxial tubes. The coaxial tubes are formed as flat tubes, which are manufactured and connected in a certain way in order to improve the durability of the tube formation. The oil cooler is arranged in the collecting tank of a radiator.

From the DE 10 2007 010 969 A1 Finally, an air conditioner with a heat exchanger is known in which a refrigerant circuit and a refrigerant circuit are integrated. The heat exchanger is also flowed through by cooling air. Therefore, corrugated fins have been placed between the flat tubes. The heat exchanger also has a tube-in-tube arrangement.

The object of the invention is to provide compact, relatively lightweight and more efficient heat exchangers.

The solution according to the invention is carried out with a heat exchanger having the features of claim 1.

According to a significant aspect of the invention, it is provided that the coaxially arranged tubes bear against one another with the broad sides of the tube walls of the larger flat tubes or with parts thereof. Since the coaxial tubes form a tube stack, a comparatively compact heat exchanger is created comparatively. The proposed construction allows as an option to connect the second flow channels via the tube walls of the larger coaxial tubes in order to achieve a fluid exchange, which has certain advantages for certain applications. Furthermore, as a result of the fact that the tube walls consist of one or more deformed sheet-metal strips, a considerably lighter and more compact heat exchanger is provided than for example heat exchangers which have extruded tubes or tube walls. A significant performance advantage compared to heat exchangers with extruded tubes results from the fact that the flow channels of the coaxial tubes are preferably equipped with turbulence generating structures, fins or the like. Alternatively, the possibility is provided to replace the slats by punctiform deformations of the tube walls, which can also provide turbulence in the fluids.

The invention provides a highly efficient heat exchanger, which can be used as a preferred evaporator in an exhaust gas energy recovery system in motor vehicles. Other heat exchanger applications are also available.

Other features will be apparent from the dependent claims, which are to be considered as individually listed at this point. In addition, these and other features and advantages thereof will become apparent from the following description of embodiments with reference to the accompanying drawings.

The 1 shows manufacturing steps of a coaxial flat tube.

The 2 shows a perspective view of a proposed heat exchanger, comprising a tube stack, formed from coaxial tubes after 1 ,

The 3 shows an enlargement of one end of the tube stack.

The 4 shows a pipe stack.

The 5 . 6 and 7 show the production of various coaxial tubes.

The 8th shows another pipe stack.

The 9 shows variants of the tube stack formation.

The 10 shows further variants of the tube stack formation.

The 11 and 12 show one end of the heat exchanger with a tubesheet.

The 13 shows an alternative pipe design.

The heat exchanger of the embodiment is an evaporator, which is included in an energy recovery system of a motor vehicle. In the evaporator are the exhaust gases of the motor vehicle engine and a liquid to be evaporated, such as water or the like, in the heat exchange. The water to be evaporated flows through the second flow channels visible in the sections 2 that the first flow channels 1 completely include. The first flow channels 1 that are inside the smaller flat tubes 10 are located, are flowed through by the exhaust gases. Like from the 2 and 3 can be recognized, are - based on their cross section - smaller tubes 10 a little longer than the larger pipes 20 so that they have a projection on both ends 7 own, 3 ). At the ends are not shown collection boxes for the exhaust gas, the tube plates 15 are fixed ( 11 and 12 ). The water can be side of the tube sheets 15 at the entrance 16 enter, via water channels 3 into the flow channels 2 enter the coaxial tubes and exit at the opposite end of the tubes as steam. The tube sheets 15 can be made from two plates 15 which are joined flat and in which the water channels 3 are included. Only one plate 15 was in the 11 and 12 shown so that the water channels 3 are visible.

The 1 shows a top-to-bottom sequence of the manufacturing steps of the coaxial flat tubes 10 . 20 , In the preferred embodiment shown are both the smaller 10 also the larger flat tubes 20 Made of metal strips. In an embodiment not shown, the smaller flat tubes could 10 also be of the extruded type. The metal strips are those made of a suitable stainless steel. Also in the first and second flow channels 1 . 2 located turbulence generating organs 5 (hereafter: slats 5 ) are made of stainless steel and usually have different geometries. The pipe stack 30 the heat exchanger is preferably soldered, which is why corresponding soldering requirements, such as the insertion of Lotfolien, degreasing, etc. are carried out, which is not particularly addressed here.

The pipe wall of the smaller flat pipes 10 is made of a deformed sheet metal strip attached to an in 1 invisible longitudinal seam was welded. In these smaller flat tubes 10 becomes a lamella 5 used. Then, in the embodiment shown to form the coaxial tubes 10 . 20 two more slats 5 around the smaller pipes 10 placed, after which the pipe wall of the larger pipes 20 , here also from two metal strips, is formed. The two metal strips can also work together with the lamellae 5 around the smaller pipes 10 be placed ( 5 and 6 ). The width of the metal strips is set so that in both broadsides 21 the pipe wall of the big flat pipes 20 one longitudinal gap each 22 remains, which is extremely advantageous both in terms of manufacturability but can also come into play as a functional advantage of the heat exchanger. With regard to production, the longitudinal gaps allow 22 allow certain manufacturing tolerances that would otherwise not be possible. With regard to the function of the heat exchanger allow the longitudinal column 22 a fluid exchange in the second flow channels 2 in which, as mentioned above, the evaporation takes place. If the fluid exchange does not take place, the longitudinal gaps 22 by means of a sheet metal strip 23 be closed. The longitudinal column 22 in the outer tubes of the tube stack 30 are in any case closed by means of a strip.

Another advantageous alternative according to 7 provides for the production of the pipe wall from a single sheet metal strip. This alternative embodiment has only a longitudinal gap in one of the broad sides of each coaxial tube. The tubes can then be arranged in the tube stack either so that the tube gaps a flow connection of the second flow channels 2 each two adjacent pipe gaps are approximately congruent to each other or are arranged so that no flow connection is possible. In each case, the longitudinal gap is closed by the tube wall of the coaxial tube adjacent in the tube stack.

In the embodiments described so far, it is considered advantageous defined pipe contact surfaces 25 in the broad sides of the pipe wall of the larger flat pipes 20 to create. This is done by means of two longitudinal beads 26 in the the pipe wall of the larger pipes 20 forming sheet metal strip shown. In the pipe stack then lie the longitudinal beads 26 of a coaxial tube on just such a coaxial tube and allow there a well-defined solder joint. The longitudinal beads 26 In any case, parts of the broadsides 21 In other versions ( 8th ) is dispensed with such longitudinal beads. For that are the broadsides 21 The larger flat tubes have been provided with a suitable roughness or with surface structures that allow defined solder joints. It can be seen that the embodiment without longitudinal corrugations is more advantageous in terms of the compactness of the heat exchanger, although the longitudinal corrugations must be only a few tenths of a millimeter in size.

The 9 and 10 show four different ways of forming the tube stack 30 , Shown are only the outer tube shells of the coaxial tubes. The representation a) shows pipes with one-piece, outer pipe shells and without fluid exchange in the pipe stack 30 , The representation b) shows a tube stack 30 in which a fluid exchange between pairs of coaxial tubes is possible. The illustrations c) and d) differ from the illustrations a) and b) in that two-part outer pipe shells were provided. As shown in c), there is no fluid exchange between the flow channels 2 the pipes of the raw pile 30 possible. In the representation d), however, the fluid exchange is possible, that means there are all flow channels 2 the pipes in fluidic connection. In the 9 the tubes of the tube stack have the described pipe contact surfaces 25 in the form of longitudinal beads 26 in the outer pipe shells.

The 10 is different from the 9 in that the outer pipe shells of the pipes full-surface contact surfaces 26 have.

In the embodiment according to 13 an alternative design of the tube is shown. It was on the longitudinal column 22 and thus on the possible fluid exchange in the tube stack 30 waived. The two outer pipe shells form an overlapping solder seam at their longitudinal edges 8th , This embodiment is advantageous in terms of manufacturing tolerances. The width of the overlap allows for certain tolerances.

Claims (17)

Heat exchanger with coaxially arranged flat tubes ( 10 . 20 ) forming a tube stack comprising a smaller flat tube ( 10 ), which in a larger flat tube ( 20 ) and with flow channels ( 1 . 2 ) for at least two fluids, wherein a first flow channel ( 1 ) inside the smaller flat tube ( 10 ) is formed and a second flow channel ( 2 ) the first flow channel ( 1 ) completely or largely surrounds, wherein the coaxial tubes with the broad sides ( 21 ) of the tube walls of the larger flat tubes ( 20 ) or with parts thereof abut each other. Heat exchanger according to claim 1, characterized in that at least some of the second flow channels ( 2 ) in the tube stack ( 30 ) arranged coaxial pipes are fluidically connected. Heat exchanger according to claim 2, characterized in that the fluidic connection of the second flow channels ( 2 ) takes place over the pipe walls lying in the pipe stack. Heat exchanger according to claim 1, characterized in that the second flow channels ( 2 ) in the tube stack ( 30 ) are fluidically separated from each other. Heat exchanger according to one of the preceding claims, characterized in that the pipe walls with mating pipe contact surfaces ( 25 ) are equipped. Heat exchanger according to claim 5, characterized in that these pipe abutment surfaces have a rough or specially contoured surface structure which allows a good solder joint. Heat exchanger according to claim 5, characterized in that the pipe abutment surfaces ( 25 ), for example, as two defined longitudinal beads ( 26 ) of the tube walls are formed. Heat exchanger according to one of the preceding claims, characterized in that the tube walls of the coaxial flat tubes ( 10 . 20 ) are formed from sheet metal strips. Heat exchanger according to claims 1-6, characterized in that the smaller flat tube ( 10 ) is an extruded tube and the larger flat tube ( 20 ) can be produced from at least one metal strip. Heat exchanger according to one of the preceding claims, characterized in that each tube wall of the larger flat tubes ( 20 ) consists of one or two deformed metal strips. Heat exchanger according to one of the preceding claims, characterized in that the sheet metal strip is dimensioned so that after the formation of the tube wall an open longitudinal gap ( 22 ) is present in the pipe wall. Heat exchanger according to one of the preceding claims, characterized in that the open longitudinal gaps the fluidic Allow connection of the second flow channels in the pipe stack. Heat exchanger according to claim 1, characterized in that in the flow channels ( 1 . 2 ) at least one turbulence-producing organ ( 5 ) is arranged. Heat exchanger according to one of the preceding claims, characterized in that the smaller flat tubes ( 10 ) are longer than the larger flat tubes ( 20 ). Heat exchanger according to one of the preceding claims, characterized in that preferably at both pipe ends, the smaller flat tubes ( 10 ) a supernatant ( 7 ) to the larger flat tubes ( 20 ) exhibit. Heat exchanger according to one of the preceding claims, characterized in that a tube plate is arranged at the tube ends. Heat exchanger according to one of the preceding claims, characterized in that the tube sheet a collection box connection for the first flow channels ( 10 ) and an inlet / outlet for the second flow channels ( 20 ) having.

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