EP3161402B1 - Heat exchanger - Google Patents

Description

Technical field

The invention relates to a heat exchanger for an exhaust system of a motor vehicle, with a housing and with a plurality of tubes through which an exhaust gas can flow and around which a coolant can flow, the tubes being arranged within the housing and the housing having a coolant inlet and a coolant outlet The exhaust gas and the coolant can flow in countercurrent to one another through the heat exchanger, the internal volume of the housing being divided into a first flow path and a second flow path, and the tubes being arranged within the second flow path, the first flow path being a bypass to the second Forms flow path.

State of the art

Heat exchangers are used in motor vehicles to cool exhaust gas coming from the internal combustion engine. For this purpose, a heat transfer is generated between the exhaust gas flowing in an exhaust gas line and a coolant in order to transfer heat from the exhaust gas to the coolant.

The cooled exhaust gas can be returned to the internal combustion engine as part of a so-called exhaust gas recirculation. By adding chilled Exhaust gas to the fresh air, which is fed into the combustion chamber for combustion, can reduce the pollutant emissions of the internal combustion engine.

A design known in the prior art is a tube bundle heat exchanger. The exhaust gas is guided in this through a plurality of tubes which are arranged within a housing and around which a coolant flows.

From the DE 10 2008 038 629 A1 a heat exchanger according to the preamble of claim 1 is known.

The devices which are known from the prior art can be flowed through in such a way that the exhaust gas and the coolant flow essentially in the same direction (direct current) or in such a way that the exhaust gas and the coolant flow in opposite directions (counterflow). From the DE 10 2006 005 246 A1 a heat exchanger for an exhaust gas line is known, which can be used both for a flow in cocurrent and for a flow in counterflow.

A disadvantage of the devices in the prior art is in particular that overheating can occur on the inflow side of the exhaust gas into the heat exchanger, which leads to boiling of the coolant within the heat exchanger. Boiling the coolant can cause damage to the coolant circuit and strong boiling lowers the overall thermodynamic efficiency.

From the DE 10 2009 034 723 A1 a heat exchanger is known which provides two fluid inlets for the coolant and one fluid outlet for the coolant. The coolant distribution on the inflow side of the exhaust gas can be improved by the additional fluid inlet, as a result of which the boiling of the coolant can be counteracted.

A disadvantage of this heat exchanger is that additional fluid connections have to be provided, as a result of which the structure of the heat exchanger becomes more complex and a larger installation space is required.

Presentation of the invention, task, solution, advantages

It is therefore the object of the present invention to provide a heat exchanger which effectively reduces or completely avoids the boiling of the coolant on the inflow side of the exhaust gas.

The object with regard to the heat exchanger is achieved by a heat exchanger with the features of claim 1.

An embodiment of the invention relates to a heat exchanger for an exhaust system of a motor vehicle with a housing and with a plurality of tubes through which an exhaust gas can flow and around which a coolant can flow, the tubes being arranged within the housing and the housing having a coolant inlet and a Has coolant outlet, the exhaust gas and the coolant being able to flow in countercurrent to one another through the heat exchanger, the internal volume of the housing being divided into a first flow path and a second flow path and the tubes being arranged within the second flow path, the first flow path being a bypass for forms the second flow path, the cross-sectional area of the first flow path between 15% and 65%, preferably between 30% and 50%, of the total cross-sectional area of the housing through which the coolant flows, the total of the coolant du Flowed cross-sectional area of the housing is formed by the cross-sectional area of the first flow path and the cross-sectional area of the second flow path minus the cross-sectional area occupied by the tubes.

A bypass for the coolant is particularly advantageous in order to be able to direct the coolant within the housing to the side on which the exhaust gas enters the pipes. The exhaust gas has the highest temperature level on the inflow side of the exhaust gas, as a result of which the coolant is strongly heated in this area. In extreme cases, the boiling point of the coolant, so-called film boiling, can occur in this area, which can damage the coolant circuit and the overall cooling capacity is reduced. The bypass advantageously leads coolant directly from the coolant inlet to the inflow side of the exhaust gas without first absorbing a significant amount of heat.

The coolant and the exhaust gas preferably flow in countercurrent to one another, thereby maximizing the possible heat transfer between the exhaust gas and the coolant. Accordingly, the coolant flowing through the second flow path already flows into heat transfer with the exhaust gas by flowing around the tubes before it arrives at the inflow side of the exhaust gas. The heat absorption capacity is therefore less than with the coolant, which flows through the bypass or the first flow path directly to the inflow side of the exhaust gas. In the following, the terms bypass and first flow path are used synonymously.

There are advantageously two cross-sectional areas for the coolant, the ratio of which has a significant influence on the pressure loss which arises and on the quantity of coolant required to achieve a specific cooling capacity. The first cross-sectional area is the cross-sectional area of the bypass (A _B ) or of the first flow path, while the second cross-sectional area is given by the total cross-sectional area (A _T ) through which the coolant flows, within which the cross-sectional area of the first flow path and that of the second flow path count minus the cross-sectional area occupied by the pipes.

The ratio of the cross-sectional area A _B to the cross-sectional area A _{T is} preferably between 15% and 65%, particularly preferably between 30% and 50%. It has been found that different heat exchangers which have a ratio of the cross-sectional areas in this area have a particularly low coolant requirement in order to achieve a predetermined cooling capacity. Furthermore, the pressure loss of the coolant within the housing is particularly low in such a size range of the cross-sectional areas.

A heat exchanger with the features of claim 1 is therefore particularly suitable in order to generate a maximum cooling capacity with minimal pressure loss. Heat exchangers with these features thus have a particularly favorable cooling characteristic.

In addition, it is advantageous if the tubes have a rectangular cross section, the width of the cross section in each case between 13 mm and 17 mm and the height between 4 mm and 5 mm.

A rectangular cross section of the tubes is particularly advantageous in connection with a likewise rectangular housing cross section. In such an arrangement, the tubes can be easily spaced from one another and from the housing, so that suitable gaps are created between the tubes and the housing in order to ensure a sufficient flow of the coolant.

The tubes particularly preferably have a rectangular cross section, which has a width between 13 mm and 17 mm and a height between 4 mm and 5 mm. Pipes of this dimension are advantageous because they have a very good ratio of the cross-section that can be flowed through to the outer surface, which is particularly advantageous for applications in an exhaust system of a motor vehicle in order to achieve maximum cooling performance. In particular, the exhaust gas temperatures of several hundred degrees Celsius that are usually to be expected, the usually prevailing coolant temperature and the exhaust gas temperature to be reached after cooling are decisive variables for the design of the heat exchanger.

It is also preferable if the tubes are arranged at a distance from one another such that the central axes of the tubes are spaced apart from one another in width by 14.5 mm to 18.5 mm and are spaced apart from one another in height by 5.5 mm.

An arrangement with a division in the width of 14.5 mm to 18.5 mm and with a division in the height of 5.5 mm to 6.5 mm is particularly advantageous in order to ensure adequate gaps between given tube sizes, as described above to reach the neighboring tubes. The gap size must be large enough to avoid congestion or the generation of excessive pressure loss.

It is also advantageous if the first flow path is thermally insulated from the second flow path and / or the housing and / or the pipes and / or the coolant flowing around the pipes.

Thermal insulation is particularly advantageous since it leads to the coolant flowing through the bypass or the first flow path being thermally decoupled from the coolant in the second flow path and in particular from the exhaust gas in the pipes. Therefore, the coolant after flowing out of the bypass into the second flow path in the region of the exhaust gas inflow side has a particularly large heat absorption capacity, as a result of which a particularly large cooling effect can be generated and the boiling of the coolant can be effectively prevented.

It is also expedient if the coolant inlet and the inflow side of the exhaust gas are arranged at opposite end regions of the housing in the main direction of extension of the pipes.

The arrangement of the coolant inlet and the inflow side of the exhaust gas at opposite end regions allows the heat exchanger to flow through in countercurrent. This is particularly advantageous in order to be able to achieve the greatest possible heat transfer within the heat exchanger.

In addition, it is advantageous if the tubes have turbulence-generating means on their inner surface and / or on their outer surface.

Turbulence-generating means, such as winglets or ribs, are particularly advantageous in order to produce a swirling of the exhaust gas and / or the coolant. A greater heat transfer can be achieved in turbulent flows than in laminar flows. In addition, congestion of the coolant and the resulting high temperature areas can be reduced or avoided entirely.

Another preferred exemplary embodiment is characterized in that the inflow direction and / or the outflow direction of the coolant each form a normal to the main flow direction of the tubes.

Such an arrangement of the coolant inlet and the coolant outlet is particularly preferred in order to obtain the most compact possible design. Furthermore, it is advantageous since, in particular, an advantageous distribution of the coolant over the entire cross section of the housing can be achieved by an inflow direction of the coolant, which is oriented as a normal to the main flow direction of the tubes. The direction of expansion of the coolant here is a direct extension of the inflow direction, as a result of which the coolant does not have to undergo any or only insignificant deflections in order to be completely distributed over the cross section of the housing.

Furthermore, it is particularly advantageous if the first flow path is formed on one of the inner surfaces of the housing and is separated from the second flow path by a wall.

An arrangement of the first flow path or the bypass on one of the inner surfaces of the housing is advantageous in order to carry out the bypass spatially separate from the pipes running through the housing. This serves to simplify the flow guidance and further reduces the heat transfer from the pipes or the exhaust gas flowing therein to the coolant in the bypass.

It is also preferable if the wall has one or more openings, each of which forms a coolant transfer between the first flow path and the second flow path.

The coolant can preferably pass from the second flow path into the first flow path or from the first flow path into the second flow path through openings in the wall delimiting the bypass. In this way, the coolant can be easily exchanged between the two flow paths. The openings are preferably arranged in the region of the coolant inlet and the coolant outlet.

It is also advantageous if the channel has a shorter extension along the main direction of extension of the tubes than the interior of the housing, the open end regions of the channel opening freely into the interior volume of the housing.

A shorter extension of the channel compared to the interior of the housing can ensure that the open end regions of the channel do not abut the walls delimiting the interior volume of the housing, which could make it difficult to transfer fluid from the second flow path into the bypass. As an alternative to the end regions which open out freely into the inner volume, the channel can also have openings which allow fluid to pass between the flow paths.

Furthermore, it is expedient if the coolant can flow from the coolant inlet through the first flow path into the second flow path and / or if the coolant can flow from the first flow path through the second flow path to the coolant outlet.

Depending on the position of the coolant inlet relative to the bypass, the coolant can either flow directly from the coolant inlet into the second flow path and from there through the opening into the bypass or directly from the coolant inlet into the bypass and through the opening into the second flow path. The coolant outlet is preferably arranged on the side of the housing opposite the bypass in order to ensure that the coolant in each case flows out of the bypass through the opening into the second flow path before it flows out of the coolant outlet. In this way, the additional cooling of the exhaust gas inflow side, which is arranged on the end region of the heat exchanger which also has the coolant outlet, is ensured.

It is also advantageous if the tubes are received at the end in tube plates which limit the area of the housing through which the coolant can flow in a direction along the main direction of flow of the tubes.

Tube plates are advantageous in order to form a receptacle for the tubes and also to limit the area in the housing through which the coolant flows. Diffusers or other elements can be connected to the tube sheets, which are preferably connected to the housing in a fluid-tight manner, which in particular promote the supply and discharge of the exhaust gas into the tubes and out of the tubes.

Advantageous developments of the present invention are described in the subclaims and in the following description of the figures.

Brief description of the drawings

Fig. 1

zwei Schnittansichten eines Wärmeübertragers, wie er aus dem Stand der Technik bekannt ist,

Fig. 2

zwei Schnittansichten eines alternativ ausgestalteten Wärmeübertragers, wie er aus dem Stand der Technik bekannt ist,

Fig. 3

zwei Schnittansichten eines Wärmeübertragers, wobei im Inneren des Gehäuses ein Bypass zum Hauptströmungsweg des Kühlmittels angeordnet ist,

Fig. 4

zwei Schnittansichten eines Wärmeübertragers gemäß Figur 3, wobei der Kühlmitteleinlass auf der gleichen Seite des Gehäuses angeordnet ist, wie der Kühlmittelauslass,

Fig. 5

ein Diagramm, welches auf der X-Achse das Verhältnis der Querschnittsfläche des Bypasses im Verhältnis zu der gesamten vom Kühlmittel durchströmten Querschnittsfläche des Wärmeübertragers darstellt und auf der Y-Achse die prozentuale Reduktion des Kühlmittelbedarfs, und

Fig. 6

ein Diagramm, welches auf der X-Achse das Verhältnis der Querschnittsfläche des Bypasses im Verhältnis zu der gesamten vom Kühlmittel durchströmten Querschnittsfläche des Wärmeübertragers darstellt, wobei auf der Y-Achse der jeweils entstehende Druckverlust aufgetragen ist.

The invention is explained in detail below using exemplary embodiments with reference to the drawings. The drawings show:

Fig. 1

two sectional views of a heat exchanger, as is known from the prior art,

Fig. 2

two sectional views of an alternatively designed heat exchanger, as is known from the prior art,

Fig. 3

two sectional views of a heat exchanger, a bypass to the main flow path of the coolant being arranged in the interior of the housing,

Fig. 4

two sectional views of a heat exchanger according to Figure 3 , wherein the coolant inlet is arranged on the same side of the housing as the coolant outlet,

Fig. 5

a diagram which shows on the X-axis the ratio of the cross-sectional area of the bypass in relation to the total cross-sectional area of the heat exchanger through which the coolant flows and on the Y-axis the percentage reduction in the coolant requirement, and

Fig. 6

a diagram showing the ratio of the cross-sectional area of the bypass in relation to the total cross-sectional area of the heat exchanger through which the coolant flows, the pressure loss occurring in each case being plotted on the Y axis.

Preferred embodiment of the invention

The following Figures 1 to 4 each show two views of a heat exchanger. A view is shown in the left part of the figures, in which the tubes are aligned as surface normal to the plane of the drawing. The viewer's gaze is directed along the main direction of extension of the pipes. In the right part of the figures, a longitudinal section through the heat exchanger is shown.

The Figure 1 shows a heat exchanger 1, which has a housing 2. A plurality of tubes 3 run through the housing 2. The tubes 3 project beyond the housing 2 on the left and right and are preferably received at the end by tube plates which close off the housing 2 to the left and right.

Exhaust gas can flow through the tubes 3. Reference number 4 denotes the inflow side from which exhaust gas can flow into the pipes. At the right end region of the tubes 3, the outflow side is identified by the reference number 7. In alternative configurations, additional diffusers can be arranged on the inflow side and the outflow side, which supports the inflow of the exhaust gas into the tubes and the outflow of the exhaust gas out of the tubes.

The housing 2 has a coolant inlet 5 on the wall on the right. This can be formed, for example, by an opening in the housing wall or by a connection piece. A coolant can flow into the housing 2 through the coolant inlet 5. At the left end on the lower housing wall, a coolant outlet 6 is arranged, through which the coolant can flow out of the housing 2. The coolant inlet 5 flows through the housing 2 from the right side to the left side to the coolant outlet 6 with coolant. The coolant flows around the tubes 3 while the exhaust gas flows through them.

The flow path for the coolant inside the housing 2 is identified by reference number 8.

In the left part of the Figure 1 It can be seen that the coolant flows into the housing 2 from above through the coolant inlet 5 and flows out of the housing 2 through the coolant outlet 6 downwards. The main flow direction of the exhaust gas in the tubes 3 and the main flow direction of the coolant in the flow path 8 within the housing are designed in opposite directions to one another in the so-called counterflow.

The tubes 3 are arranged one above the other in three rows of three, wherein there are gaps between the tubes 3 and the inner walls of the housing 2, through which the coolant can flow. The number and arrangement of the pipes is exemplary and can be varied as desired in alternative designs.

The Figure 1 and the following Figure 2 represent heat exchangers as are known from the prior art.

Figure 2 shows a heat exchanger 1, as already in Figure 1 was shown. In contrast to Figure 1 the coolant inlet 9 is not arranged on the upper outer wall of the housing 2 but, like the coolant outlet 6, also on the lower outer wall. This is also in the left part of the Figure 2 to recognize.

The rest of the structure of the heat exchanger 1 Figure 2 agrees with the structure of the heat exchanger 1 Figure 1 match. Identical reference numerals have been used for identical elements.

Figure 3 shows a view of a heat exchanger 20. Similar to the heat exchanger 1 of FIG Figure 1 a coolant inlet 5 is arranged on the right end region on the upper outer wall of the housing 2 and a coolant outlet 6 is arranged on the lower outer wall on the left end region. The housing 2 has a first flow path 22 on the inside and a second flow path 21.

The tubes 3 are arranged in the second flow path 21. The first flow path 22 can, as in FIGS Figures 3 and 4 shown, be formed by a channel 23 which is arranged above the tubes 3 within the housing 2 and creates a spatial separation of the first flow path 22 from the second flow path 21. Alternatively, the first flow path can also be separated from the second flow path, for example, by a wall that runs between two opposite inner surfaces of the housing.

In the Figure 3 a free space 24 is formed between the channel 23 and the housing 2 at the right end region of the housing 2 and a free space 25 is formed at the left end region. Coolants can flow between the first flow path 22 and the second flow path 21 through these free spaces 24, 25, which are formed by spacing the channel end from the housing inner wall.

In an alternative embodiment, the channel, which delimits the first flow path, can also extend over the entire length of the housing. The channel then advantageously has openings in one of its walls, which allow the fluid to flow over between the flow paths. Furthermore, fluid communication of the channel with the coolant inlet and the coolant outlet can also be generated through openings in the walls.

Figure 3 shows that the coolant flows along the coolant inlet 5 into the housing 2 and there flows vertically down into the second flow path 21 and also flows into the first flow path 22. The coolant in the second flow path 21 flows around the pipes 3, whereby a heat transfer between the exhaust gas flowing in the pipes 3 and the coolant is generated. The coolant in the first flow path 22, on the other hand, flows essentially thermally decoupled to the left within the first flow path 22, which functions as a bypass, and exits the channel 23 at the end there. The coolant from the first flow path 22 and the second flow path 21 finally flows downward in a direction transverse to the main flow direction of the tubes 3 and out of the housing 2 through the coolant outlet 6.

The coolant in the first flow path 22 is thus passed directly to the inflow side 4 of the pipes 3 and absorbs the heat of the exhaust gas there. Since the coolant flowing through the first flow path 22 has a higher heat absorption capacity than the coolant which has already flowed along the tubes 3 through the second flow path 21, particularly good cooling can be achieved on the inflow side 4 of the exhaust gas.

In the left part of the Figure 3 the rectangular cross section of the channel 23, which forms the bypass for the coolant, can be seen. The channel 23 is arranged above the tubes 3 at a distance from the tubes 3 in the housing 2. Furthermore, the division of the housing 2 into the first flow path 22 and the second flow path 21 can be seen.

The cross-sectional area of the channel 23 or the first flow path 22 is denoted by A _B. The entire inner cross-sectional area of the housing 2, through which the coolant flows, is referred to as _AT . The cross-sectional area _AT is formed by the cross-sectional area of the first flow path 22 and the second flow path 21 minus the cross-sectional area of the tube 3. The ratio of A _B to A _T is preferably between 15% and 65%. It is particularly preferably between 30% and 50%. The advantages of such a relationship are shown in the following Figure 5 explained in more detail.

Figure 4 shows an alternative embodiment of the heat exchanger 20, wherein the coolant inlet 9 and the coolant outlet 6 are arranged on the lower outer wall of the housing 2. The heat exchanger 20 the Figure 4 is analogous to the Figure 2 executed, wherein a channel 23 is also arranged as a bypass for the coolant in the interior of the housing 2.

The different arrangement of the coolant inlet 9 also influences the flow through the flow paths 22, 21. In Figure 4 The coolant flows through the coolant inlet 9 from below into the second flow path 21 and there on the one hand to the left and on the other hand further upwards and through the free space 24 into the first flow path 22. At the end of the channel 23, the coolant flows in the region of the inflow side 4 through the Free space 25 to the tubes 3, whereby a strong cooling of the tubes 3 can be generated. The coolant finally flows out of the housing 2 via the coolant outlet 6.

In the left part of the Figure 4 the arrangement of the coolant inlet 9 and the coolant outlet 6 on the lower outer wall of the housing 2 can be seen. The Both cross-sectional areas A _B and A _T are as in the previous one Figure 3 educated.

In the Figures 3 and 4 the tubes 3 and the channel 23 have a rectangular cross section. This is particularly advantageous in conjunction with the likewise rectangular cross section of the housing 2 in order to achieve a uniform arrangement of the tubes 3 in the interior of the housing 2. In alternative embodiments, the cross-sectional shapes of the tubes, the channel and the housing can also differ. The in the Figures 3 and 4 The embodiment shown is exemplary and has no restrictive character, in particular with regard to the geometry of the individual elements, the choice of material and the arrangement of the elements relative to one another.

The Figure 5 shows a diagram 30. The ratio between the cross-sectional areas A _B and A _{T is} plotted in percent on the X axis 31. The X axis shows ratios of 0% at the intersection of axes 31, 32 and a maximum of 90%. The Y axis 32 shows the percentage reduction in the coolant requirement to reach a defined exhaust gas temperature. The Y axis 32 shows values of 0% coolant reduction at the intersection of the axes 31, 32 up to a maximum of 35% reduction. In particular, no absolute values are plotted on the Y axis 32, but rather relative values for the individual heat exchangers 33 to 36.

Diagram 30 shows measured values for four different heat exchangers 33, 34, 35 and 36 for different ratios from A _B to A _T. The heat exchangers 33 to 36 are each flowed through in countercurrent. Furthermore, the heat exchangers 33 to 36 can each differ in further geometrical designs. For example, the number of tubes, the cross-section of the tubes, the design of the inner and outer walls of the tubes or the spacing of the tubes from one another can vary.

It can be seen that, in particular with a ratio of A _B to A _T above 15% and below 65%, the percentage reduction in the coolant requirement is increased compared to the ratios of A _B to A _T below 15% and above 65%. The ratio of 15% is marked by the dashed line with the reference number 50. The ratio of 65% is marked with the dashed line with the reference symbol 51.

In particular with a ratio of A _B to A _T in the range from 30% to 50%, the percentage reduction in the coolant requirement is particularly high. The ratio of 30% is marked with the dashed line with the reference symbol 52 and the ratio of 50% with the dashed line with the reference symbol 53. The marking of the ratios 15%, 30%, 50% and 65% applies with the same reference symbol 50 , 52, 53 and 51 also for the following Figure 6 ,

It follows that with a ratio of the cross-sectional areas from A _B to A _T in the range from 30% to 50%, a particularly strong reduction in the coolant requirement for different heat exchangers 33 to 36 can be achieved. This leads to a particularly efficient operation of the respective heat exchangers 33 to 36 with a high thermodynamic efficiency.

The percentage reduction in the coolant requirement for the individual heat exchangers 33 to 36 follows, with increasing ratio between A _B and A _T, a dome-shaped curve that curves upwards in diagram 30. With a low ratio of A _B to A _T below 15%, the coolant reduction is special low and increases towards a ratio between 30% and 50%. The coolant reduction finally decreases again above 50%.

Figure 6 shows a diagram 40, wherein the ratio of A to _{B T} A in percent is plotted on the X-axis 41 and the Y-axis 42 of the pressure loss in percent. Diagram 40 also shows measured values for four heat exchangers 33, 34, 35 and 36. The X axis 41 is analogous to the X axis 31 of the Figure 5 a value range of ratios of 0% at the intersection of the axes 41, 42 and a maximum of 90% at the right end of the X-axis 41. The Y-axis 42 shows the pressure loss occurring at the heat exchanger 33 to 36 as a percentage. The Y axis 42 shows values from 0% pressure loss at the intersection of the axes 41, 42 up to a maximum of 120% pressure loss at the upper end region of the Y-axis 42. In particular, the Y-axis 42 does not show any absolute values, but relative values of the individual heat exchangers as a percentage 33 to 36 to each other.

It can be seen that the pressure loss in a range in which the ratio of A _B to _{AT is} between 15% and 65% is lower than above 65% and below 15%. The range in which the ratio of A _B to A _{T is} between 30% and 50% has the lowest values for the pressure loss.

Heat exchangers which have a ratio of the cross-sectional areas of 15% to 65%, and preferably 30% to 50%, are therefore particularly well suited to achieve a high thermodynamic efficiency with the lowest possible coolant requirement and the lowest possible pressure loss. Heat exchangers of this type are also suitable for generating a high cooling capacity.

The ratio of the cross-sectional areas A _B to A _T determines in particular the dimension of the bypass relative to the entire area through which the coolant flows. Like diagrams 30, 40 of Figures 5 and 6 show, a ratio of A _B to A _T between 30% and 50% is preferably to be achieved in order to achieve the highest possible thermodynamic efficiency with the lowest possible coolant requirement and the lowest possible pressure loss. A low pressure loss is advantageous since the pump power required to deliver the coolant can be lower, which means that the corresponding pump can preferably be dimensioned smaller.

Claims (11)

1. A heat exchanger (20) for an exhaust gas line of a motor vehicle, with a housing (2) and with a plurality of tubes (3) through which an exhaust gas can flow and around which a coolant can flow, wherein the tubes (3) are arranged within the housing (2) and the housing (2) has a coolant inlet (5, 9) and a coolant outlet (6), wherein the exhaust gas and the coolant can flow through the heat exchanger (20) in counter-current with respect to one another, wherein the internal volume of the housing (2) is separated into a first flow path (22) and a second flow path (21) and the tubes (3) are arranged within the second flow path (21), wherein the first flow path (22) forms a bypass to the second flow path (21), characterised in that the cross-sectional area (A_B) of the first flow path (22) is between 15% and 65%, preferably between 30% and 50%, of the total cross-sectional area (A_T) of the housing (2) through which the coolant can flow, wherein the total cross-sectional area (A_T) of the housing (2) through which the coolant flows is formed by the cross-sectional area (A_B) of the first flow path (22) and the cross-sectional area of the second flow path (21) minus the cross-sectional area occupied by the tubes (3).
2. The heat exchanger (20) according to claim 1, characterised in that the tubes (3) have a rectangular cross-section, wherein the width of the cross-section is between 13 mm and 17 mm, respectively, and the height is between 4 mm and 5 mm.
3. The heat exchanger (20) according to one of the preceding claims, characterised in that the tubes (3) are arranged spaced apart from each other in such a manner that the central axes of the tubes (3) are spaced apart from each other by 14.5 mm to 18.5 mm in width and are spaced apart from each other by 5.5 mm to 6.5 mm in height.
4. The heat exchanger (20) according to one of the preceding claims, characterised in that the first flow path (22) is thermally insulated from the second flow path (21) and/or the housing (2) and/or the tubes (3) and or the coolant flowing around the tubes (3) .
5. The heat exchanger (20) according to one of the preceding claims, characterised in that the coolant inlet (5, 9) and the inflow side (4) of the exhaust gas are arranged in the main extension direction of the tubes (3) in opposite end regions of the housing (2) .
6. The heat exchanger (20) according to one of the preceding claims, characterised in that the tubes (3) have turbulence-generating means on their inner face and/or on their outer face.
7. The heat exchanger (20) according to one of the preceding claims, characterised in that the inflow direction and/or the outflow direction of the coolant respectively forms a normal to the main throughflow direction of the tubes (3).
8. The heat exchanger (20) according to one of the preceding claims, characterised in that the first flow path (22) is formed on one of the inner faces of the housing (2) and is separated from the second flow path (21) by a wall or is separated from the second flow path (21) by a channel (23).
9. The heat exchanger (20) according to claim 8, characterised in that the wall has one or more openings which respectively form a coolant crossing between the first flow path (22) and the second flow path (21).
10. The heat exchanger (20) according to claim 8, characterised in that the channel (23) has a shorter extension along the main extension direction of the tubes (3) than the interior of the housing (2), wherein the open end regions of the channel (23) end freely in the internal volume of the housing (2).
11. The heat exchanger (20) according to one of the preceding claims, characterised in that the coolant can flow from the coolant inlet (5, 9) through the first flow path (22) into the second flow path (21) and/or that the coolant can flow out of the first flow path (22) through the second flow path (21) to the coolant outlet (6).

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