Heat exchanger device for EGR systems

Abstract

The present invention relates to a heat exchanger device for EGR (“Exhaust Gas Recirculation”) systems, with a constructive solution which minimizes thermal fatigue when boiling occurs. The invention is characterized by a specific configuration of the inner space of the shell divided into a first exchange sub-space and a second degassing space communicated with one another, and wherein the inlet and outlet ports are located at the end where the cold baffle is located.

Claims

1. A heat exchanger device for EGR systems, wherein in the operative mode the heat exchanger is configured for transferring heat from a first fluid, a hot gas, to a second fluid, a liquid coolant, wherein the exchanger comprises: a first baffle; a second baffle; a tube bundle with a first inner space for the passage of the first fluid, the hot gas, extending along a longitudinal direction X-X′ between the first baffle and the second baffle, wherein a first end of the tube bundle is attached to the first baffle and a second end of the tube bundle, opposite the first end, is attached to the second baffle, and wherein the first end of the tube bundle is configured for receiving the hot gas and the second end of the tube bundle is configured for the exit of the cooled gas; a shell housing the tube bundle, establishing a second space between the tube bundle and said shell for the passage of a liquid coolant which, in the operative mode, covers the tubes of the tube bundle; a first inlet port for the entry of the liquid coolant to the second space of the inside of the shell; a second outlet port for the exit of the liquid coolant from the second space of the inside of the shell; wherein the first inlet port and the second outlet port are located at the end of the second space, according to the longitudinal direction X-X′, corresponding to the second baffle; the shell houses a separator extending according to the longitudinal direction X-X′, dividing the second space into a first heat exchange sub-space wherein the tube bundle is housed and a second degassing sub-space; the first inlet port is in fluid communication with the first sub-space and the second outlet port is in fluid communication with the second sub-space, wherein the first sub-space and the second sub-space are in fluid communication through at least one opening located, according to the longitudinal direction X-X′, at the end corresponding to the first baffle, and wherein in the operative mode the flow of the second fluid in the first sub-space is in counter-current with respect to the flow of the first fluid.

2. The heat exchanger device according to claim 1, wherein said heat exchanger is configured for operating in a position such that the longitudinal direction X-X′ is in an inclination in the range [−40°, 90°), the horizontal direction being 0° and perpendicular to the direction defined by the direction of gravity, wherein: for positive angles of inclination, the first baffle is in a higher position than the second baffle according to the direction of gravity, and, for angles of inclination strictly smaller than 90°, the second sub-space is located in an upper position with respect to the first sub-space according to the direction of gravity.

3. The heat exchanger device according to claim 1, wherein the second sub-space is configured for directing the coolant fluid, together with the bubbles generated by boiling in the first sub-space, from the end of the first baffle to the second outlet port.

4. The heat exchanger device according to claim 1, wherein the separator comprises one or more openings along the longitudinal direction X-X′.

5. The heat exchanger device according to claim 1, wherein the separator is only attached to the shell.

6. The heat exchanger device according to claim 1, wherein the separator is spaced from the first baffle, the second baffle, or both baffles.

7. The heat exchanger device according to claim 1, wherein the following conditions are verified:
S.sub.p≤S.sub.d≤S.sub.h wherein S.sub.p is the cross-section of the outlet port, S.sub.d is the cross-section of the second degassing sub-space, and S.sub.h is the cross-section of the first exchange sub-space.

8. The heat exchanger device according to claim 7, wherein one or both the inequalities is a strict inequality: “<”.

9. The heat exchanger device according to claim 1, wherein the separator has at least one tab oriented towards the first sub-space for the purpose of accelerating the coolant fluid.

10. The heat exchanger device according to claim 9, wherein at least one of the at least one tab is located between two tubes of the tube bundle.

11. The heat exchanger device according to claim 9, wherein the at least one tab is a plurality of tabs, wherein said plurality of tabs are positioned such that they define a plane parallel to the first baffle.

12. The heat exchanger device according to claim 9, wherein the at least one tab is located at the end of the separator.

13. The heat exchanger device according to claim 1, wherein the separator comprises at least one protrusion projected towards the second sub-space to favor the collapse of the bubbles.

14. The heat exchanger device comprising a plurality of protrusions according to claim 13, wherein said plurality of protrusions have a labyrinth configuration to prolong the flow path in the second sub-space.

15. An EGR system comprising a heat exchanger device according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features and advantages of the invention will become more apparent based on the following detailed description of a preferred embodiment, given solely by way of non-limiting illustrative example in reference to the attached figures.

(2) FIG. 1 schematically shows a longitudinal section of a first embodiment.

(3) FIG. 2 schematically shows a longitudinal section of a second embodiment.

(4) FIG. 3 schematically shows a longitudinal section of a third embodiment.

(5) FIG. 4 schematically shows a cross-section of a fourth embodiment, wherein the heat exchanger has a circular cross-section.

(6) FIG. 5 schematically shows a cross-section of a fifth embodiment, wherein the heat exchanger has a rectangular cross-section.

(7) FIG. 6 schematically shows, according to a longitudinal section, a sixth embodiment based on the preceding embodiment with a shell having a rectangular section.

(8) FIG. 7 schematically shows another embodiment of the separator shown with a pre-configuration before being bent to form flow deflectors.

DETAILED DESCRIPTION

(9) According to the first inventive aspect, the present invention relates to a device for heat exchange in EGR systems wherein the temperature of a portion of the hot gas, identified as first fluid, coming from the combustion chamber, must be reduced in order to be able to be reintroduced into the intake, thereby reducing the nitrogen oxide content in the exhaust.

(10) The described heat exchange device has said purpose, wherein heat from the first fluid is given off to a second fluid, the liquid coolant.

(11) The described embodiments solve the problems already identified as being caused by the boiling of the liquid coolant which is in contact with the hotter surfaces where heat exchange occurs, particularly in the baffle directly receiving the hot gas.

(12) FIG. 1 is a schematic figure of a first embodiment of the invention depicting a longitudinal section of the heat exchanger according to this first example.

(13) The heat exchanger comprises a hot gas inlet, wherein in this embodiment the inlet is configured by means of an inlet manifold (C1) located on the right-hand side of the drawing. The flow of the hot gas is depicted by a large, hollow arrow. According to other embodiments, the coupling of the heat exchanger with other devices located upstream of the gas flow, such as a filter or a catalytic converter, can be direct coupling without using a manifold.

(14) After traversing the heat exchanger giving off part of its heat, the cooled gas exits through an outlet manifold (C2) located on the left-hand side of the same drawing. The flow of the cooled gas is also depicted with a large, hollow arrow. Likewise, according to other embodiments the coupling with other elements located downstream of the gas flow can be direct coupling without using a manifold.

(15) The direction of advancement of the gas from the inlet manifold (C1) to the outlet manifold (C2) defines a longitudinal direction X-X′.

(16) There is located between the inlet manifold (C1) and the outlet manifold (C2) the region where heat exchange is established, limited between a first baffle (1), the baffle which will be identified as the hot baffle as it is the one which directly receives the hot gas, and a second baffle (2), the baffle which will be identified as the cold baffle as it is located where gas that has been cooled exits.

(17) The exchange region also comprises a tube bundle (3) responsible for heat exchange between the first fluid and the second fluid. The tube bundle (3) extends between the first baffle (1) and the second baffle (2), wherein a first end (3.1) of the tube bundle (3) is attached to the first baffle (1) and a second end (3.2) of the tube bundle (3), opposite the first end (3.1), is attached to the second baffle (2), and wherein the first end (3.1) of the tube bundle (3) is configured for receiving the hot gas and the second end (3.2) of the tube bundle is configured for the exit of the cooled gas. The tube bundle (3) also defines two spaces, a first inner space (E1) for the passage of the first fluid, the hot gas, and a second outer space (E2) through which the second fluid, the liquid coolant, circulates.

(18) The tube bundle (3) is housed in a shell (4) which closes the second space (E2) outside the tubes of the tube bundle (3).

(19) This same FIG. 1 shows this second space (E2) outside the tube bundle (3). It is in turn sub-divided into two sub-spaces by means of a separator (7) extending according to the longitudinal direction X-X′: a first heat exchange sub-space (E2.1) in which the tube bundle (3) is housed, and a second sub-space (E2.2) which is identified as a degassing space in this description.

(20) The same drawing depicts the direction of gravity ({right arrow over (g)}) by means of an arrow vertically oriented according to the orientation of the drawing. The longitudinal direction in this embodiment is therefore horizontal with respect to the direction of gravity.

(21) Following the reference of gravity, the first heat exchange sub-space (E2.1) is located in the lower part and the second degassing sub-space (E2.2) is located in the upper part. In all the examples described in the description, the second sub-space (E2.2) being above the first sub-space (E2.1) according to the direction established by the action of gravity is considered a preferred feature. The action of gravity is relevant. Bubbles are always generated on a surface where heat is being given off to the liquid coolant and this point reaches temperature and pressure conditions such that they give rise to boiling.

(22) The surfaces where heat is given off to the liquid coolant are: the outer surfaces of the tubes of the tube bundle (3), the surface of the first baffle (1) in contact with the liquid coolant, and to a lesser extent, the surface of the second baffle (2) in contact with the liquid coolant if the required temperature and pressure conditions arise.

(23) Boiling occurs mainly on the first two surfaces. The generated bubbles tend to move up by flotation, hence the first heat exchange sub-space (E2.1) has been located in the lower part and the second degassing sub-space (E2.2) in the upper part according to the direction of gravity ({right arrow over (g)}).

(24) The entry of the liquid coolant occurs through a first inlet port (5) located on the side depicted on the left-hand side in FIG. 1, the side corresponding to the end where the second baffle (2) or cold baffle is located. The liquid coolant covers the tubes of the tube bundle (3), removing heat. The flow of the liquid coolant initially shows a flow distribution at the inlet thereof that tends to occupy all the available space according to the cross-section, and it then moves in counter-current according to the longitudinal direction X-X′ to the first baffle (1), the hot baffle.

(25) It has been proven by means of numerical simulation that the liquid coolant shows a more uniform temperature distribution in the specific configuration being described than a co-current configuration, such that the greater temperature uniformity minimizes the appearance of points that stand out with a higher temperature than the rest of the points located nearby, preventing the appearance of preferred points where bubbles are generated due to boiling.

(26) Likewise, when the liquid coolant reaches the first baffle (1), there is established a transverse flow, understood as being perpendicular to the longitudinal direction X-X′, which keeps to the surface of the first baffle (1) until exiting through an opening (7.1) communicating the first heat exchange sub-space (E2.1) in the lower part and the second degassing sub-space (E2.2) of the upper part, minimizing the presence of stagnation areas.

(27) In the preferred embodiment, the opening (7.1) is configured by a separation between the separator (7) and the first baffle (1), giving rise to a flow which keeps to said first baffle (1) as much as possible.

(28) Stagnation areas are areas with zero or almost zero flow speed. Stagnation areas where liquid coolant are present and which are limited by surfaces where heat is given off from the hot gas to the liquid coolant are areas where the liquid coolant is constantly receiving heat with an increase in temperature, so boiling is inevitable. Furthermore, since there are no transport mechanisms in the fluid, the vapor generated by boiling is not removed either, giving rise to large spaces with vapor instead of liquid. If this space occupied by the vapor also corresponds to the surface where heat is given off, the heat transfer rate decreases and the temperature in the material where the surface is located is increased even more, drastically increasing thermal stresses.

(29) With the described configuration, it has been verified that there are no stagnation areas, and the bubbles which are generated on the surface of the first baffle (1) move up both by flotation and by convection of the transverse flow to the opening (7.1), and all these bubbles are therefore evacuated.

(30) The bubbles evacuated through the opening (7.1) are transported through the second sub-space (E2.2) where there are no heat exchange surfaces, so it is observed that the size of the bubbles decrease significantly or the bubbles disappear altogether. Hence, this second sub-space (E2.2) has been identified as a degassing space in the description.

(31) Finally, the liquid coolant flow reaches the second outlet port (6).

(32) It must be pointed out that the most common tests evaluating the extent at which the heat exchanger is exposed to boiling phenomena carry out measurements in the outlet port (6) so, even though bubbles are generated, it is important for these bubbles to decrease or even collapse before the exit thereof, improving the overall behavior of the heat exchanger with respect to boiling.

(33) Embodiments in which the longitudinal direction X-X′ has a specific angle of inclination with respect to the horizontal direction are also considered. In the embodiment shown in FIG. 1, the angle of inclination is zero. Nevertheless, those embodiments in which the angle of inclination is in the range [0, 90), i.e., without reaching 90 degrees, are also considered.

(34) The angle of inclination is considered positive when the position of the first baffle (1) is raised with respect to the second baffle (2).

(35) In an inclined position with a positive inclination, some points of the first exchange sub-space (E2.1) are located above some points of the second degassing sub-space (E2.2); nevertheless, the described effects continue to be observed since the opening (7.1) communicating both sub-spaces (E2.1, E2.2) is shown at the higher point, allowing the passage of bubbles.

(36) Furthermore, although some points of the first exchange sub-space (E2.1) are located above some points of the second degassing sub-space (E2.2), the center of masses of the volume defined by the first exchange sub-space (E2.1) is located below the center of masses of the volume defined by second degassing sub-space (E2.2). In other words, the first exchange sub-space (E2.1) is still considered as being below the second degassing sub-space (E2.2).

(37) Likewise, those embodiments of the invention in which the angle of inclination is negative, specifically in the range [−40,0), are considered. It has been experimentally verified that in common operative conditions, although the position of the opening (7.1) communicating the first sub-space (E2.1) and the second sub-space (E2.2) is located at a lower point with respect to the rest of the points of the separator (7), the bubbles are entrained by the main flow although the bubbles will tend to float in counter-current when they reach the separator (7).

(38) The same occurs when the angle is positive, the bubbles' tendency to float and therefore to move in the direction contrary to gravity can give rise to a backward movement component in the second sub-space (E2.2), nevertheless the flow speed overcomes this tendency and this is achieved to a greater extent in the second degassing sub-space (E2.2) with positive angles as the cross-section in this second sub-space (E2.2) is smaller than the cross-section in the first sub-space (E2.1), and therefore the flow speeds of the liquid coolant are greater.

(39) FIG. 1 also shows the separator (7) with an additional opening (7.2) along the longitudinal direction X-X′ that is different from the main opening (7.1) communicating the first exchange sub-space (E2.1) and the second degassing sub-space (E2.2).

(40) FIG. 2 shows another embodiment of the invention in which all the elements coincide with the first embodiment, with the exception that in this embodiment there is a plurality of additional openings (7.2) along the longitudinal direction X-X′.

(41) This plurality of openings (7.2) allow the exit of the bubbles generated along the exchange tube bundle (3) given that these bubbles move up and find the passage towards the second degassing sub-space (E2.2) without having to run along the entire path to the first baffle (1) in order to exit through the main opening (7.1) located in this first baffle (1).

(42) The amount of bubbles that accumulate to exit through this first main opening (7.1) is therefore also reduced. It has been verified that with additional openings (7.2) the second degassing sub-space (E2.2) still maintains a flow directed to the second outlet port (6) where the bubbles have a reduced size or collapse.

(43) There is a possibility that a stagnation area may appear in the second degassing sub-space (E2.2), at its end in contact with the second outlet port (6). FIG. 3 shows a third embodiment in which an additional opening (7.2) has been added by means of distancing the separator (7) and the second baffle (2), allowing the passage of a small liquid coolant flow intended for preventing the appearance of stagnation or recirculation areas.

(44) The same FIG. 3 is used to describe another embodiment which allows breaking the vapor bubbles before they exit the heat exchanger and which is applicable to any of the examples described up until now and below.

(45) According to this embodiment, the second sub-space (E2.2) houses a porous element (8) which, although it allows the passage of the liquid coolant, forms narrow channels that either cause gas bubbles to break into other smaller bubbles or even to collapse, causing them to disappear.

(46) The porous element (8) preferably covers the entire passage section of the second sub-space (E2.2) to force all the liquid coolant flow and bubbles to go through said porous element (8).

(47) The porous element (8) must be interpreted in a broad manner as any material which allows passage through narrow fluid passage channels or paths. The materials suitable for allowing the passage of fluid and causing the bubbles to break or collapse include, among others: porous materials with their pores communicated with one another; compact fibers; meshes and/or specifically metallic meshes; metallic bands that are partially wound forming a ball and compacted into a bundle; a combination of any of the foregoing.

(48) According to another embodiment, the second sub-space (E2.2) comprises a plurality of porous elements distributed consecutively along the longitudinal direction.

(49) FIG. 4 schematically shows a cross-section according to a fourth embodiment in which said cross-section is located close to the first baffle (1) to enable observing the inner spaces and the second baffle (2) where the inlet port (1) and the outlet port (2) are located.

(50) This section does not allow observing the main opening (7.1) allowing the passage of the liquid coolant from the first exchange sub-space (E2.1) to the second degassing sub-space (E2.2) as it corresponds to the section that is eliminated to enable observing the inside of the heat exchanger.

(51) This embodiment uses a shell (4) having a circular section and the separator (7) is formed by a bent sheet defining a first heat exchange sub-space (E2.1) in the lower part and a second degassing sub-space (E2.2) in the upper part. In this embodiment, the tubes of the tube bundle (3) are planar tubes vertically oriented to favor the upward movement of the bubbles generated on the exchange surfaces, being removed from the space between tubes (3) where heat exchange occurs.

(52) In this embodiment, the separator (7) is only attached to the shell (4) and not to the first baffle (1) or the second baffle (2). The attachment with the shell (4) is established in two attachment segments (7.4), one in the upper part and another in the lower part on both sides.

(53) The attachment of the part giving rise to the separator (7) has a first attachment segment (7.4) in the upper part and a second attachment segment (7.4) in the lower part, always according to the direction of gravity ({right arrow over (g)}), given that between both attachment segments (7.4) there is a segment (7.5) spaced from the shell (4) and kept to the tube bundle (3) to reduce the volume through which the liquid coolant passes outside the tube bundle (3), because otherwise, a preferred path with less resistance to the passage of the liquid coolant than that shown in the inside of the tube bundle (3) would be established, resulting in a greater liquid coolant flow speed in the inside of said tube bundle (3).

(54) This same FIG. 4 shows a reduction in the passage section by means of a step (7.3) configured in the separator (7). It has been verified that the optimum conditions so as to not penalize pressure drop in the outlet flow are as follows:
S.sub.p≤S.sub.d≤S.sub.h where S.sub.p is the cross-section of the outlet port (6), S.sub.d is the cross-section of the second degassing sub-space (E2.2), and S.sub.h is the cross-section of the first exchange sub-space (E2.1).

(55) It has been observed that the behavior of the heat exchanger with respect to pressure drop is better when one or both the inequalities are strict: “<”.

(56) When the outlet port (6), the second degassing sub-space (E2.2), or the first exchange sub-space (E2.1) have a variable section along the path of the fluid in the operative mode, then the value of the section is measured where said section is maximum. For example, if there is a stepping which changes the section in a segment, then the larger section is taken. The same occurs if a specific segment has projections, in this case the section to be measured will be the section taken without the projections.

(57) FIG. 5 schematically shows, in a cross-section, a fifth embodiment in which said cross-section is of an essentially rectangular configuration. In this embodiment, the shell is configured with a rectangular section and allows all the tubes of the tube bundle (3) to have the same dimensions and to be equally distributed in the first heat exchange space (E2.1).

(58) In this embodiment, the separator (7) is a planar plate dividing the first sub-space (E2.1) where the tube bundle (3) is housed and the second degassing sub-space (E2.2).

(59) According to this embodiment, the two sides of the separator (7) extend into two perpendicular strips constituting respective attachment segments (7.4) which are supported on the inner wall of the shell (4) such that the separator (7) is attached to said wall by welding.

(60) In this same embodiment, a step (7.3) which modifies the section of the second degassing sub-space (E2.2), reducing it before reaching the second outlet port (6), has been included.

(61) In this embodiment, the separator (7) is made of a sheet and includes a plurality of partial U-shaped die-cuttings resulting in a tab (7.6) located in the inside of the “U” and a non-die-cut root (7.6.1) which keeps the tab (7.6) attached to the sheet of the separator (7). After die-cutting, each of the tabs (7.6) is bent in the root (7.6.1) thereof to orient the tab (7.6) perpendicular to the longitudinal direction X-X′ of the heat exchanger.

(62) In this embodiment, each tab (7.6) is positioned such that it is located between two tubes of the tube bundle (3) and the plurality of the tabs (7.6) define a single plane transverse to the longitudinal direction X-X′ of the heat exchanger.

(63) The technical effect of the presence of the plurality of tabs (7.6) is the configuration of a deflecting baffle which accelerates the liquid coolant flow. In this particular example in which the tabs are close to the first baffle (1), the liquid coolant is accelerated in the vicinities of said first baffle (1), improving its cooling.

(64) This specific way of forming the tabs (7.6) by die-cutting the sheet forming the separator (7) simultaneously allows forming longitudinal grooves in the separator (7) which are openings (7.1) that facilitate the exit of the bubbles to the second degassing sub-space (E2.2). In other words, these openings (7.1) formed by the tabs (7.6) may co-exist with other openings (7.1) generated by other means.

(65) The tabs (7.6) described in this embodiment are applicable to other configurations of the exchanger, specifically to the exchanger having a circular section described in the preceding embodiments.

(66) FIG. 6 shows a longitudinal section of a sixth embodiment which also uses tabs (7.6) like those described in the preceding embodiment. This section shows the direction of bending the tab (7.6) after die-cutting the sheet forming the separator (7) in order to form a surface parallel to the first baffle (1).

(67) In this embodiment, in addition to the opening (7.2) generated by bending the tab (7.6), the opening (7.1) located adjacent to the first baffle (1) and the opening (7.1) having smaller dimensions established by means of distancing the wall (7) with the second baffle (2) are also obtained.

(68) This same embodiment shows, in the separator (7), a set of protrusions (7.7) projected towards the second degassing sub-space (E2.2) which allow guiding the liquid coolant flow in this region. Specifically, in this embodiment the set of protrusions (7.7) has been configured like a labyrinth to increase the length the liquid coolant must circulate, favoring bubble size reduction or even causing the bubble to collapse.

(69) Given that the same FIG. 7 is a longitudinal section, it has been depicted therein locations where the three sections also identified in a preceding embodiment have been measured: S.sub.p the cross-section of the outlet port (6), S.sub.d the cross-section of the second degassing sub-space (E2.2), and S.sub.h the cross-section of the first exchange sub-space (E2.1).

(70) FIG. 7 shows another embodiment applicable to any of the described heat exchangers, both in a configuration with a circular section and a rectangular section. In this embodiment, die-cutting configuring both the tab (7.6) and the openings (7.1) in the gaps left by said tabs (7.6) after being bent as described in the preceding embodiment does not have to be carried out.

(71) According to this embodiment, the separator (7) is configured from a sheet wherein the tabs (7.6) are configured according to strips that are prolonged into an end of said sheet. A simple way of configuring these tabs (7.6) is by die-cutting the spaces between tabs (7.6), in this case rectangular parts, at the end of the sheet, leaving the tabs (7.6) as a result.

(72) FIG. 7 shows the result of the sheet after the die-cutting operation and before carrying out the bending operation.

(73) After die-cutting, the tabs (7.6) are bent through the transverse line located in the attachment root (7.6.1) between each tab (7.6) and the main plate of the separator (7), resulting in a configuration in which all the tabs (7.6), in their operative position inside the heat exchanger, are arranged parallel to the first baffle (1) as described in FIG. 7.

(74) This embodiment places the tabs (7.6) at the end of the separator (7) and is easier to manufacture than the embodiment described in the embodiment shown in FIG. 6 since the bends located at this end are simpler and require tools that are also simpler.