Patent Application
20080251242
The present invention relates to heat exchangers, especially for cooling exhaust gases, and to a modular heat exchanger system.
Current diesel engines are normally equipped with exhaust gas recirculation coolers in order to satisfy the increasingly stringent demands placed on exhaust gas purification. The cooling of the exhaust gas and resupplying of the cooled exhaust gas reduces the combustion temperature and leads to decreased NOX emissions.
DE 102 30 852 A1 discloses a heat exchanger with a first collecting vessel and with a second collecting vessel for a first medium, the two collecting vessels each having a first media connection for the first medium and being interconnected in a communicating manner via at least one heat exchanger element, and with a housing which accommodates the heat exchanger element, guides a second medium in the inside and has second media connections for the second medium. The housing accommodates, in the interior thereof, at least one collecting vessel, preferably both collecting vessels, so that they are located, at least in part, at a distance from the housing inner wall at least in certain regions.
DE 100 61 949 A1 further discloses a heat exchanger having a core region for carrying out an exchange of heat between a first fluid and a second fluid, the core region having a large number of tubes which form in the inside first passageways through which the first fluid flows, the tubes being arranged to form a plurality of spaces between adjacent tubes through which the second medium flows, and a large number of ribs which are each arranged in each space between adjacent tubes to divide each space into a plurality of space parts which are interconnected via openings provided in each rib; and a core housing in which the core region is accommodated and which forms a second passageway having the plurality of spaces, the two ends of each tube being separated from the inner wall surface of the core housing in the width direction at right angles to the longitudinal direction of the tubes, so as to form predetermined free spaces from the inner wall surface of the core housing, and the predetermined free spaces being provided in such a way that they are interconnected along the entire surface region of the tubes in the lamination direction of the tube.
Exhaust gas coolers are generally laser-welded or soldered based on Ni and have ribs on the gas side. In this case, ribs are normally encased in tubes and subsequently soldered in a housing. Other known designs provide for disks to be soldered to one another.
Most applications generally provide for gas to flow axially through a set of disks, the coolant being supplied or removed from above via the cover plate. Nevertheless, this design has the problem that the housing can generally become very warm, as the housing is not cooled.
Starting herefrom, the invention is based on the object of improving a heat exchanger, especially for cooling exhaust gases, and a modular heat exchanger system.
According to the invention, the object is achieved by a heat exchanger as claimed in claim 1, especially for cooling exhaust gases, with at least one first flow channel of a first medium, especially a gas, with at least one second flow channel of an at least second medium, especially a cooling medium, with at least one first disk, with at least one second disk, the first disk and the second disk being interconnected and forming the first flow channel of the first medium, with at least one housing element, especially a first housing element and a second housing element forming, together with the first disk and with the second disk, the second flow channel of the second medium, wherein the first housing element can be cooled by the second medium.
The first flow channel leads via entry openings in the [ . . . ] for the first medium, which [ . . . ] especially hot exhaust gas having a temperature of from 200° C. to 800° C., through pairs of disks which are each formed by two disks, to an exit opening. The second flow channel of a second medium, especially a cooling medium, in particular a liquid cooling medium such as water, leads through at least one exit and through at least one housing element, including in particular a second housing element, and through the opening, owing to a setting-apart of adjacent pairs of disks and disk edge surfaces, to an exit in a second housing element. A respective first disk is connected to a second disk, especially with a material fit such as soldering, welding, bonding. The first disks, the second disks and the housing element surround the second flow channels. The first housing element is cooled by the second medium, especially cooling medium such as liquid coolant, cooling water, air, refrigerant, especially of an air conditioning system. This reduces thermal stresses. The heat exchanger, especially the exhaust gas heat exchanger, is much more durable. The housing element can be made of a material which is not heat-resistant and would be destroyed in particular at temperatures of greater than 200° C., especially at temperatures of greater than 400° C. In particular, the plastics material or aluminum housing element can be manufactured cost-effectively, thus considerably reducing the manufacturing costs.
In an advantageous embodiment, the heat exchanger has a first housing element around substantially all of which the second medium, especially cooling medium, is able to flow and which particularly advantageously cools the housing element, so almost no thermal stresses occur or thermal stresses are advantageously reduced and the durability is substantially increased and the material costs are particularly advantageously lowered.
In an advantageous embodiment, the temperature of the first medium, especially of the exhaust gas of an internal combustion engine, prior to entering the heat exchanger is higher than the temperature of the second medium, especially of the cooling medium, prior to entering the heat exchanger. Despite a high temperature of the uncooled exhaust gas, almost no thermal stresses occur on the housing element which can particularly advantageously be made of an inexpensive material.
In an advantageous embodiment, the first housing element is made of a first material, especially aluminum or plastics material, and the second housing element is made of another second material, especially steel. In a particularly advantageous manner, both housing elements are particularly advantageously cooled by the cooling medium. The first material, aluminum, plastics material, etc., is particularly advantageously inexpensive and leads advantageously to a saving in weight and a lower overall space requirement.
In an advantageous embodiment, the second housing element has at least one housing opening, especially a first housing opening for an entry of the first medium into the first flow channel, especially a second housing opening for an exit of the first medium from the first flow channel, especially a third housing opening for an entry of the second medium into the second flow channel and especially a fourth housing opening for the exit of the first medium from the second flow channel.
In an advantageous embodiment, the first housing element and the second housing element can be opened in at least one stacking direction of the first disks and the second disks. The disks and pairs of disks can be mounted and manufactured particularly advantageously.
In an advantageous embodiment, the first housing element and the second housing element are interconnected or interconnectable with a material fit, especially by soldering, welding, bonding, etc., and/or interconnected or interconnectable with a form fit, especially by screwing, clipping, or by deformation such as folding, crimping, bordering, etc.
In an advantageous embodiment, the first housing element and the second housing element are particularly advantageously sealed relative to one another using a sealing element, especially an O-ring, a square ring, a film seal, etc.
In an advantageous embodiment, the first disk and/or the second disk has projections, especially turbulence-generating elements between adjacent disks and/or pairs of disks, thus particularly advantageously improving the transfer of heat between the first medium and the second medium.
In an advantageous embodiment, the first disks and/or the second disks each have at disk ends at least one cup, as a result of which adjacent pairs of disks are particularly advantageously interconnected and the first medium can flow particularly advantageously.
In an advantageous embodiment, the cups each have at least one cup opening, especially for the passage of the first cooling medium.
In an advantageous embodiment, a respective first disk and a respective second disk form a pair of disks and are interconnected particularly advantageously with a material fit, especially by soldering, welding, bonding, etc., and form a pair of disks.
In an advantageous embodiment, a plurality of pairs of disks can particularly advantageously be stacked on one another and are interconnected at cup opening edges with a material fit, especially by soldering, welding, bonding, etc.
In an advantageous embodiment, the pairs of disks form the first flow channels for the first medium, especially for exhaust gas to be cooled, the exhaust gas to be cooled flowing particularly advantageously within a number of pairs of disks.
In an advantageous embodiment, two adjacent pairs of disks are arranged set apart from one another. This forms the second flow channels of the second medium, especially cooling medium, particularly advantageously between adjacent pairs of disks.
In an advantageous embodiment, the second flow channels of the second medium, especially cooling medium, are formed between the first housing element and a disk pair edge surface. The disk pair edge surface is in particular the outer surface of the outside of the interconnected pairs of disks of the first and second disks.
In an advantageous embodiment, third flow channels of a third medium are formed next to the second flow channels, thus allowing the exhaust gas particularly advantageously to be cooled in two successive cooling stages.
In an advantageous embodiment, the third flow channels of the third medium are particularly advantageously formed between the first housing element and the disk pair edge surfaces.
In an advantageous embodiment, the third flow channels are separated from the second flow channels, especially by at least one partition element. In this way, the at least two cooling circuits are particularly advantageously separated and the first housing element is particularly advantageously cooled, as a result of which thermal stresses are particularly advantageously reduced and the durability of the heat exchanger is particularly advantageously increased, and the manufacturing costs are particularly advantageously reduced.
In an advantageous embodiment, the second medium, especially cooling medium, of a high-temperature cooling circuit is able to flow through the second flow channels and a third medium, especially cooling medium, of a low-temperature cooling circuit is able to flow through the third flow channels.
A heat exchanger has a first housing element which is an integral part of at least one other component, especially a water jacket, a cylinder head of an internal combustion engine, a water tank of a coolant cooler, etc. The heat exchanger can in this way be integrated into an existing component, thus significantly reducing in particular the overall space, especially in the front region of a vehicle.
A heat exchanger has a second housing element but no first housing element. The heat exchanger is used in particular for cooling exhaust gases, with at least one first flow channel of a first medium, especially a gas, with at least one second flow channel of an at least second medium, especially a cooling medium, with at least one first disk, with at least one second disk, the first disk and the second disk being interconnected and forming the first flow channel of the first medium, with at least one second housing element.
A modular heat exchanger system has at least one heat exchanger, especially for cooling exhaust gases, with at least one first flow channel of a first medium, especially a gas, with at least one second flow channel of an at least second medium, especially a cooling medium, with at least one first disk, with at least one second disk, the first disk and the second disk being interconnected and forming the first flow channel of the first medium, with at least one housing element, especially a first housing element and a second housing element forming, together with the first disk and the second disk, the second flow channel of the second medium, wherein the first housing element can be cooled by the second medium.
In a further advantageous embodiment, the cooler consists of a set of disks. The set of disks consists of pairs of disks which form a flow channel for a first medium and have turbulence-generating structures, especially turbulence inserts. The turbulence inserts can be formed either by impressions in the disks or preferably by a soldered-in turbulence metal sheet. The gaps between two disks form channels for a second medium. Each two adjacent pairs of disks are at both ends in flow connection with the adjacent pairs of disks via lateral openings which can be arranged in a dome or cups projecting out of a disk or out of both disks in order to bridge the gap between the pairs of disks. The pairs of disks are formed in particular from two identical disks. The gaps between the disks can each be supported relative to one another by knobs, dimples or inserted elements such as, for example, metal sheets, ribs, support elements. The supporting elements can be welded, soldered or bonded to one another or held by a form fit. Knobs or dimples are impressed into the disk material. They can also project as elongate beads to improve the flow distribution of the second medium in the flow channel.
In a further embodiment, the first medium will be a medium to be cooled and especially a hard medium, conventionally a hot gas such as exhaust gas or compressed charge air, and the second medium will be a liquid cooling medium such as coolant of an internal combustion engine or, in future applications, coolant of a cold circuit. The coolant can be guided parallel or counter to the main flow direction of the first medium (coflow or counterflow). The design is particularly suitable for counterflow connection, which is preferable in terms of thermodynamics, as it is distinguished by a particularly low risk of boiling in the coolant, because suitable guidance of the coolant allows dead water zones to be substantially prevented.
In a further embodiment, the flow channel for the second medium can be divided into two portions which are supplied with coolant from differing cooling circuits, in particular one circuit with warmer coolant at the entry end of the first medium and one low-temperature cooling circuit at the exit end of the first medium to increase the cooling power. The circuits can be separated, for example, by a transverse bead which is impressed into the disks, the channel remaining laterally free being blocked with sufficient tightness by a component (a type of grid) which is form-fitted to the pair of disks. Grids of this type can also be configured in such a way that no transverse beads are required in the disks; instead, the channel is blocked by at least two grids which are inserted into the bundle of disks on the opposing sides. These grids can, however, again be positioned by means of beads or knobs, especially during a soldering process or if no rigid connection to the bundle of disks is produced.
In a further embodiment, the channel for the second medium can be formed outwardly by a housing jacket or by a cavity, through which coolant flows, in another component, for example in the water jacket or cylinder head of the engine unit, in the water tank of a coolant cooler (in-tank) or in a combination housing through which coolant flows and into which a plurality of heat transfer means are integrated and combined to form a module.
In a further advantageous embodiment of the heat transfer means with its own housing jacket, use is made of an at least two-part housing jacket which opens substantially in the stacking direction of the bundle of disks. A lid or cover plate, which closes off the bundle of disks at the top, and a trough, into which the bundle of disks is inserted, constitute the basic components of the housing jacket. The lid and trough are in a particularly beneficial embodiment peripherally interconnected, especially soldered. The connections for the second medium are located at the opposing ends of the housing and can be arranged in any desired arrangement in one of the parts of the housing. Further connections are provided in the center of the cooler to integrate a plurality of cooling circuits. The connections for the first medium can be located, on the one hand, on the same side of the heat transfer means, i.e. for example both in the lid or both in the housing trough. Furthermore, also possible is a diagonal throughflow in which either the entry or the exit is located in the lid and the other connection in the housing trough. Finally, guiding the first medium in a U-flow is also possible. In this case, not all pairs of disks are in flow connection at the entry for the first medium; instead, this connection is prevented at one point between two specific pairs of disks in that between these pairs either the lateral connecting openings are not formed or there is inserted an additional metal sheet which obstructs the connection and uncouples the pairs of disks located at the entry from the pairs of disks located further below. The first medium flows through the cooler in the disks, which are interconnected below the entry up to the break, in the longitudinal direction of the heat exchanger. At the other end, all pairs of disks are interconnected and the first medium flows into the pairs of disks which are uncoupled at the entry end and flows back to the entry end where it leaves the heat transfer means, on the side opposing the entry, through an exit. The housing must withstand the pressure of the second medium. In the direction perpendicular to the stacking direction of the heat transfer means, the housing is not soldered to the bundle of disks. It may be beneficial to increase the pressure stability of this side by means of impressed beads in the housing.
In a further advantageous configuration, the disks are particularly advantageously prevented from moving transversely to the stacking direction during the soldering process. The disks can at certain points be form-fitted to the housing contour.
Furthermore, it may be advantageous if respective pairs of disks with a turbulence insert are preproduced in a first joining step to form channels for the first medium. These pairs of disks can be interconnected by means of a form-fitting embodiment with or without compression, by means of a clamping or crimping connection, the connection basically being a folded connection, by means of weld points or adhesive points or the like. This procedure can greatly simplify the encasing process (stacking of the individual parts, especially the disks) and the process safety of the joining process as a whole can be increased.
Embodiments without an independent housing jacket of the heat exchanger are also particularly advantageous. In this case, the bundle of disks is closed off at the top by a cover plate into which the entry and exit for the first medium are integrated. At the bottom there is generally a base plate. Fastening at the site of installation is carried out by means of a tight joint between the cover plate and the component forming the cavity through which coolant flows, for example via a screw connection, crimping or bordering connection, clamping connection, the seal generally being produced by means of a sealing element, for example an O-ring. This type of linking can also be utilized to embody an independent cooler housing jacket in that, for example, a cover plate made of a steel or aluminum material is connected in the aforementioned manner to a water-guiding plastics material housing. For connection, use may in this case be made, for example, of a bordering connection or a screw connection with injected threaded sockets in a plastics material component and slots in the cover plate. Furthermore, the screwing can be carried out by means of through-holes in the housing and screwing in the cover plate (threads in passages, self-tapping screws in a smooth passage, threaded bushes).
In a further advantageous embodiment, the flow channel for the second medium (housing or cavity in another component) is advantageously configured in such a way that it extends in the region in which the channel cross section is markedly restricted by the dome at the disk ends and subsequently tapers toward the center of the heat transfer means, thus urging the 2nd medium into the channels between the pairs of disks. The distribution of the second medium can thus be significantly improved. A likewise highly beneficial possibility for achieving optimum distribution of the 2nd medium is the funnel-shaped configuration of the transition of the disks from the domes to the channel for the 1st medium. In this way too, the 2nd medium is urged into the channels between the pairs of disks.
In a further advantageous embodiment, an uncooled bypass channel, for example in the form of one or more pairs of disks, can be provided in the cooler. Air gap insulation of the bypass channel is preferably utilized to achieve the substantially uncooled conveyance of the first medium (in particular recirculated exhaust gas of an internal combustion engine). Exemplary embodiments of air gap-insulated bypass tubes:
outer casing soldered from half-shells, a tube with support knobs inserted on the inside;
outer and inner casings soldered from half-shells;
soldered to the lid or cover disk is a further metal sheet forming, together with the lid/cover disk, a channel which is used as the bypass channel (non-air gap-insulated);
on the side of the cover metal sheet lid facing the bundle of disks, a further metal sheet is soldered on and an additional gas channel formed (non-air gap-insulated);
a bypass tube, which can be in one piece or two pieces, is soldered to the lid/cover disk, beads or knobs preventing planar abutment in the bypass channel and/or in the cover sheet/lid;
on entry or exit of gas in the housing trough, the bypass can be formed with additional metal sheets or tubes in the same ways as described for the lid/cover plate;
on entry or exit of gas in the lid/cover plate and the other gas connection in the housing trough, the bypass can be attached to one of the two parts and the bypass can also include the transverse connection between the pairs of disks;
in the U-flow, a bypass solution can be provided as a result of the fact that the uncoupling is configured so as to be able to switch between the pairs of disks on the entry side and on the opposing side, for example by means of a rotary slide which releases the direct path from the entry to the exit in the event of a bypass and breaks off the passage in normal cooler mode, so the cooler is flowed through in a U-flow.
In a further advantageous embodiment, the bypass valve used is a conventional, external valve with separate feed lines to the bypass and to the heat-transferring flow channels. However, use may also be made of flaps or valves which are integrated into the entry nozzle or exit nozzle. These may, in particular, also be configured as a flap or rotary slide. Particularly advantageous is the embodiment of the bypass flap as a combination valve in which, in addition to switching between bypass and normal cooler mode, both paths can also be completely obstructed and the amount of recirculated exhaust gas can thus be regulated.
In a further advantageous embodiment, especially in an embodiment without a housing, a heat transfer means is used in the crossflow between the first and the second medium. Heat exchangers of this type could preferably be used in the cooling module of a motor vehicle. In this case, the medium to be cooled would be guided as the first medium through the heat exchanger and cooling air is used as the second medium. A heat transfer means of this type can be fastened using the cover plate or the base plate within a cooling module or in each case to other components of the cooling module; however, it can also have its own frame which, on the one hand, includes the cover plate and base plate while still establishing a connection between the cover plate and base plate and thus ensuring rigidification of the heat exchanger. The connection between the cover plate and base plate can be provided either by additional components connected to the cover plate and base plate or by means of suitable configuration of the cover plate and base plate, for example as U-shaped components which open in opposition to one another and jointly form the frame. This frame can additionally be connected to the individual pairs of disks. This increases, in particular, the vibration strength of the component. The connection can be produced by a form fit, although it can also be provided, in particular, by a tight soldered joint. The heat transfer means is then fastened to the frame and/or via the connections for the first medium. Instead of arranging the heat transfer means in a cooling module, it can also be fastened in the chassis, i.e. in particular to the frame of a motor vehicle, in exceptional cases so as to be secured to the engine. Preferably, a component of this type can be used as a direct exhaust gas cooler. However, applications as a charge air cooler, coolant cooler, oil cooler, condenser, etc. are also beneficial.
Further advantageous configurations emerge from the sub-claims and from the drawings.
Exemplary embodiments are illustrated in the drawings and will be described hereinafter in greater detail. In the drawings:
a is a plan view of a further exemplary embodiment of the heat exchanger with a shaped formation in the entry or exit region of the housing element;
b is an isometric representation of a further exemplary embodiment of the heat exchanger with a shaped formation in the entry or exit region of the housing element;
a is a plan view and
In the heat exchanger 60, the cooling medium 17 is optimally distributed in the entry region by means of a shaped formation 61, which is in particular formed as a bulge, in the housing element 6, 7 over the entire width of the pair of disks. The entry region of the first medium is thus cooled over its entire circumference.
The heat exchanger 70 is shown in a sectional view. The heat exchanger is formed as what is known as a U-flow embodiment. In this case, the cooling medium 15, 17 is conveyed axially, whereas the first medium flows through the heat exchanger in a U-shaped manner. This is achieved by inserting a separating metal sheet 71 between two pairs of disks. The separating metal sheet has no opening in the region of the entry/exit of the first medium (cup region). Conversely, on the opposite side, a suitable opening is present in the cup region, so the first medium can flow from the upper half of the cooler into the lower half. In this case, the position of the separating metal sheet 71 is arranged in other embodiments (not shown) above or below the center, so either above/below the separating metal sheet the same number of pairs of disks are present or the pairs of disks are non-uniformly distributed.
Reference numeral 86 denotes the exit for the third medium. Reference numeral 87 denotes the entry for the third medium. In another exemplary embodiment, the entry 87 and the exit 86 are swapped over.
The heat exchanger 90 has two cooling media circuits. The first cooling circuit is a high-temperature circuit. The second circuit is a low-temperature circuit. The coolant in the high-temperature circuit has a higher temperature than the coolant in the low-temperature circuit. A high- and low-temperature coolant circuit may thus be produced in a heat exchanger. The separating metal sheet 91 is configured as a grid. The separating metal sheet 91 is pushed onto the pairs of disks, especially orthogonally to the longitudinal axis SLA of the disks. Furthermore, the housing element has four openings 92, 93, 94 and 95 for the exit and/or entry of the two cooling media.
Reference numeral 97 denotes the entry for the second cooling medium, in particular of the low-temperature circuit. Reference numeral 96 denotes the exit for the second cooling medium. In another exemplary embodiment, the entry 97 and the exit 96 are swapped over.
In another variation, the heat exchanger 90 is configured as a U-flow cooler, the first and the second cooling medium performing a U-flow, like the exemplary embodiments in
The heat exchanger 100 has a first partial heat exchanger 101 which is cooled using a high-temperature circuit and a second partial heat exchanger 102 which is cooled using a low-temperature circuit. In another variation, the high-temperature circuit and low-temperature circuit are swapped over.
At the entry 103 the second cooling medium, in particular of the low-temperature circuit, enters the partial heat exchanger 102, flows therethrough and leaves the partial heat exchanger through the exit 104. The exit 104 and entry 103 are swapped over in another exemplary embodiment.
The third medium enters the partial heat exchanger 102 via the media entry 105, flows through said partial heat exchanger and leaves it via the media exit 106. In another variation, the media exit 106 and the media entry 107 are swapped over.
The separating plate 107 separates the first partial heat exchanger 102 and the second partial heat exchanger 103, especially in terms of flow.
The heat exchanger 110 does not have any housing and it is, in particular, configured as a crossflow heat exchanger. In this case, the flows between which heat is transferred intersect at least in certain regions. In this case, a cooling rib is located between the pairs of disks 4, 5 forming the flow channels for the first medium. The cooling rib is rigidly connected, for example soldered, bonded, mechanically joined, etc., to the pairs of disks 4, 5, so as to ensure sufficient conduction of heat between the pairs of disks 4, 5 and the rib. The rib 111, especially the corrugated rib, is in this case flowed through by a cooling medium, for example air. The air is moved by means of a cooling medium conveyor L, for example a fan L. In another exemplary embodiment, no rib is provided. In this case, a turbulence-generating structure, which improves the transfer of heat, is impressed into the disks. In another embodiment, the crossflow configuration is configured with a housing. This provides the advantage of allowing this heat transfer means to be attached not only in the front module of the vehicle, i.e. in the front vehicle region which is struck by the headwind, but rather, irrespective thereof, at a suitable location in the vehicle with its own cooling media conveyor.
The rotary slide 123 assumes a bypass position and/or a cooler throughflow position. The rotary slide 123 has at least one recess.
In the bypass position, the bypass is flowed through. In the cooler position, the heat exchanger portion 122 is flowed through. In another embodiment, the bypass 121 and heat exchanger portion are swapped over.
The rotary slide 123 can also assume a position in which both the bypass 121 and the heat exchanger portion are flowed through. The rotary slide rotates through an angle of rotation, especially of 90°, in order to pass from the bypass position into the heat exchanger throughflow position.
The bypass channel 131 is used for the bypassing of medium, so the medium does not flow through the heat exchanger. The insulation, especially air gap insulation, serves to prevent or to reduce the transfer of heat between the bypass channel 131 and the heat exchanger.
In further embodiments of
Despite their passage cross sections, which are in principle smaller than those of other inserts, turbulence inserts with web ribs have a comparatively low tendency to collect deposits. In principle, there was a risk that turbulence inserts with web ribs would lead increasingly to the blockage of individual passage channels owing to the delicate structure of the web ribs. However, this is the case to a surprisingly low extent, especially if the webs of the web ribs are relatively short. A possible explanation of this might be that the turbulent flow, which is present over large parts of the web rib insert, of the exhaust gas reduces deposition of particles, whereas there are formed flows which are ordered in longer, uniform channels and promote the deposition of particles in proximity to the wall owing to the flow speed which is very low at this location.
In a preferred embodiment, the webs of the web ribs have a length which is no more than about 10 mm, preferably no more than about 5 mm and particularly preferably no more than about 3 mm. Depending on the overall space and internal combustion engine in question, specific demands may be placed on the drop in pressure in the exhaust gas heat exchanger. Depending on these demands, one of the aforementioned length ranges may be preferred.
Also preferably, a density of the web ribs transversely to the exhaust gas flow direction is between about 20 web ribs/dm and about 50 web ribs/dm, preferably between about 25 web ribs/dm and 45 web ribs/dm. These web rib densities have proven to be particularly suitable in trials. In particular, the web ribs strike particularly advantageously a good compromise between the risk of blockage and the cooling power.
With regard to the height of the web ribs, it should be borne in mind that, in the case of high heights, there are available only relatively small primary surface areas, i.e. surfaces cooled by coolant, via which all of the heat must be released into the coolant. In the case of relatively small primary surface areas, the risk of boiling then rises in the case of a liquid coolant. In addition, the effectiveness of the inserts decreases as the height of the web ribs increases. A preferred height of the insert or web rib is therefore between about 3.5 mm and about 10 mm, particularly preferably between about 4 mm about 8 mm and especially preferably between about 4.5 mm and about 6 mm.
In a preferred development of the device according to the invention, provision may be made for an oxidation catalyst to be arranged before the plurality of flow channels. A catalyst of this type generally allows the particle sizes, particle densities and the proportions of hydrocarbons in the exhaust gas to be reduced by means of oxidation. Additionally or alternatively, provision may in this case be made for the inserts themselves to be provided with a coating for the catalytic oxidation of the exhaust gas. Especially in conjunction with oxide-catalytic means, the beneficially usable density of the web ribs transversely to the exhaust gas flow direction can be more than about 50 web ribs/dm, especially about 75 web ribs/dm. This would provide a particularly high heat exchanger power for a given overall space without giving rise to the long-term risk of blockage caused by deposits.
In a particularly preferred embodiment, the web ribs have oblique teeth. Oblique-toothed ribs have been found in experiments to be particularly suitable for ensuring long-term stability of the exhaust gas heat exchanger with respect to deposits. In this case, in a preferred embodiment, the angle between the web walls and a main direction of the web ribs is between about 1° and about 45°. In a particularly preferred embodiment the angle is between about 5° nd about 25°, wherein it can in an alternative preferred embodiment also be between about 25° and about 45°. The former value range of from 5° to 25° is particularly suitable in conventional applications which are highly sensitive to losses in pressure, the latter value range being suitable to achieve an optimized power density, especially in applications which are less sensitive to losses in pressure.
Generally, in the optimization of an insert with oblique-toothed web ribs, a correlation may be identified between the angle of the walls and a longitudinal division of the web rib. In this case, in particular, optimum embodiments at small angles can have larger divisions l than optimized embodiments with large angles. Small angles of attack, in particular, can result in embodiments with a moderate loss in pressure. Large angles of attack, in particular, can result in embodiments with optimized power density. The longitudinal division can be larger in the case of small angles of attack in particular; in the case of large angles of attack, the longitudinal division can in particular be smaller in order to obtain optimized embodiments.
In a preferred embodiment, the device is configured as a stacked-disk heat exchanger. This embodiment is particularly expedient both with regard to the width of a flow channel and with regard to the cost-effective production and combinability of a heat exchanger housing with web rib inserts. Alternatively, the device can however also be configured as a tube bundle heat exchanger or as another form of heat exchanger known per se.
It is generally preferable for the insert to be made of a stainless steel, especially an austenitic steel, to prevent corrosion caused by the aggressive exhaust gas.
In a further advantageous configuration aluminum materials can be used, wherein a suitable corrosion prevention means, such as in particular an alloy and/or a coating, can then particularly advantageously be provided.
In an advantageous development, the insert is made of aluminum. An aluminum insert has a particularly low weight. Particularly advantageously, the aluminum insert can be formed by means of alloying or coating to prevent corrosion.
Depending on the flow parameters, especially the Reynolds' number, the length of the run-in region of the flow channels, especially tubes and/or pairs of stacked disks, l/s is from approx. 2.5 to 5 and the length of the web ribs must be selected so as to be below this limit value. S denotes the central passage width between two webs and is thus b/2-t, wherein t denotes the thickness of the metal sheet. This results in a required ratio of l/s<4, in particular l/s<2. If there is a high risk of blockage resulting from the critical exhaust gas composition, l/s<1.5, in particular l/s<1, should be selected.
Oblique positioning of the webs gives rise on the twist side to a higher flow speed on the wall, which counteracts the deposition of soot. A further important advantage of oblique-toothed web ribs is that, in cases in which a low density of the web ribs is required in the flow transverse direction to prevent blockages, especially in the case of a disadvantageous exhaust gas composition, sufficient cooler power can be achieved despite the small surface area of the ribs.
The stacked disk heat exchanger according to the invention comprises an outer housing with a lid, there being provided an entry and an exit for the exhaust gas and also an entry and an exit for a liquid coolant. A plurality of disk elements are provided within the housing, each of the disk elements being composed of an upper half and a lower half. By means of turned-up collars, the disk elements are welded to one another and to the housing in such a way that the coolant flows in each case between the two halves of a disk element from the inlet to the outlet. An insert (not shown) with web ribs is arranged in each case between two disk elements, the gap between two disk elements forming a respective flow channel for the exhaust gas. The inserts have not been shown for the sake of clarity. The inserts are made of a stainless steel. To improve the thermal contact between the inserts and the disk elements or the housing, the inserts can be welded or soldered to the aforementioned elements in a planar manner.
In a further embodiment, the turbulence insert is made of a thin sheet metal material into which parallel web ribs are introduced using shaping measures. Each of the web ribs comprises a number of webs which are arranged in succession in the exhaust gas flow direction. Each two webs which are arranged in succession in the exhaust gas flow direction are arranged offset from one another by half a web width transversely to the exhaust gas flow direction, so each web is followed by a cutting edge with a subsequent web. In the present example, the walls are oriented parallel to the direction of flow of the exhaust gas and form an angle of 0° with an axis B of the web ribs or the main direction of flow of the exhaust gas A. A web rib insert of this type is referred to as a straight-toothed web rib.
In a first exemplary embodiment, the length l of a web is about 4 mm. The width b of an individual web rib is defined as the width of the repeating unit of the periodic structure transversely to the main direction of flow of the exhaust gas. The web rib density 2/b is in the present example about 40 web ribs/dm. The width b of a web rib is thus about 5 mm.
The height h of the web ribs corresponds to the distance between two adjacent disk elements of the heat exchanger and is in the present case about 5 mm.
In a further configuration of the web rib insert, the lateral walls of the individual webs are in this case not oriented parallel to the main direction B of the web ribs. Instead, each of the walls of the webs enclose with the main direction B of the web ribs an angle W of about 30°. The further dimensions of the oblique-toothed web rib inserts correspond to the dimensions of the straight-toothed web rib.
A suitable longitudinal division l for corresponding angles of the walls W is provided by suitable embodiments at 10° with longitudinal divisions l of<approx. 10 mm, at 20° with l<approx. 6 mm, at 30° with l<approx. 4 mm and at 45° with l<approx. 2 mm. The minimum longitudinal division l is in the case of all angles approx. 1 mm. The admissible extent of the channel l/s lies substantially within the same limit as for a straight-toothed web rib, wherein s denotes the web distance transversely to the main direction of flow B. Generally speaking, longitudinal divisions l of<1 mm are difficult to establish for reasons relating to production.
The features of the various exemplary embodiments may be combined with one another as desired. The invention can be used also in fields other than those disclosed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 050 686.0 | Oct 2005 | DE | national |
| 10 2006 014 191.1 | Mar 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/009924 | 10/13/2006 | WO | 00 | 4/18/2008 |
