EVAPORATOR

Abstract

The present invention is a cross-flow evaporator adapted to generate vapor from the heat of the exhaust gases from an internal combustion engine. The evaporator is constituted, among other elements, by two plates spaced from one another which contain chambers. The heat exchange tubes alternately communicate the chambers of both plates, establishing a specific path for the fluid intended to change phase. The tubes extending between the chambers of the two plates are arranged transverse to the flow of the hot gas. This evaporator is suitable for heat recovery systems using a Rankine cycle, making use of the heat from the exhaust gases.

The invention is characterized by a special configuration of the walls which prevents the crack failure or damage caused as a result of the differential expansion between the exchange tubes and said walls.

Claims

1. An evaporator for the evaporation of a first fluid by means of the heat provided by a second fluid, the second fluid being a hot gas, wherein said evaporator comprises: a first plate (1) and a second plate (2) facing one another and arranged spaced from one another, defining an inner face, the face facing the other plate, and an outer face opposite the inner face; wherein each of the plates (1, 2) comprises a plurality of chambers (1.1, 2.1); an intake manifold (4) of the first fluid and an exhaust manifold (5) of the first fluid situated in fluid communication with one another and with at least one different chamber (1.1, 2.1) of any of the plates (1, 2); a plurality of heat exchange tubes (3) wherein each of the heat exchange tubes (3) extends between a chamber (1.1) of the first plate (1) and a chamber (2.1) of the second plate (2); wherein each chamber (1.1, 2.1) of one plate (1, 2) is in fluid communication with two or more chambers (1.1, 2.1) of the other plate (1, 2) by means of at least two heat exchange tubes (3), except the chambers (1.1, 2.1) in fluid communication with the intake manifold (4) or the exhaust manifold (5); there being for each of the heat exchange tubes (3) a path of fluid communication from the intake manifold (4) to the exhaust manifold (5) passing through the inside of said heat exchange tube (3); two first side walls (6) extending between the first plate (1) and the second plate (2) housing the plurality of heat exchange tubes (3) and establishing between both a space for the passage of the second fluid, wherein the second fluid enters through an inlet (I2) and exits through an outlet (O2); characterized in that the first side walls (6) are elastically deformable, which allows compensating the differential expansion between the heat exchange tubes (3) and said first side walls (6).

2. The evaporator according to claim 1, wherein the tubes (3) are elastically deformable according to their longitudinal direction.

3. The evaporator according to claim 1, wherein said evaporator additionally comprises second side walls (7), situated between the first plate (1) and the second plate (2), these second side walls (7) being spaced from the first side walls (6), wherein the second side walls (7) are elastically deformable and are arranged internally with respect to the first side walls (6).

4. The evaporator according to claim 3, wherein the first side walls (6), the second side walls (7), or both, are elastically deformable by means of one or more crimps or corrugations (6.1, 7.1).

5. The evaporator according to claim 4, wherein the crimps (6.1, 7.1) have a main direction according to the longitudinal direction established between the inlet (I2) and the outlet (O2) of the second fluid.

6. The evaporator according to claim 4, wherein the crimps (6.1, 7.1) have a sinusoidal path.

7. The evaporator according to claim 3, wherein the stiffness constant of the elastically deformable second side walls (7) is less than the stiffness constant of the elastically deformable first side walls (6).

8. The evaporator according to claim 1, wherein the inlet (I2), the outlet (O2), or both, have a manifold (8, 9).

9. The evaporator according to claim 3, wherein: a. the second side walls (7) are prolonged inside one or more intake/exhaust manifolds of the second fluid (8, 9); and, b. at least one prolongation of the second side walls (7) inside the manifold (8, 9) is spaced from said manifold (8, 9).

10. The evaporator according to claim 3, wherein between the first side walls (6) and the second side walls (7) there is a chamber that is in fluid communication with the intake manifold (4) of the first fluid such that the entrance of the first fluid in the evaporator is carried out by means of previous passage through the chamber formed between the first and second side walls (6, 7).

11. The evaporator according to claim 1, comprising: either a first shield plate (11) located in the passage space of the second fluid, spaced from the first plate (1), or a second shield plate (11) located in the passage space of the second fluid, spaced from the second plate (2); or, or both the first and second shield plates (11); wherein the shield plates (11) have multiple of perforations for the passage of the heat exchange tubes (3) leaving a chamber between said shield plates (11) and their corresponding plates (1, 2) for protecting the welds between the exchange tubes (3) and said plates (1, 2).

12. The evaporator according to claim 3, wherein the second side walls (7) and the shield plate or plates (11) are configured as a single part.

13. The evaporator according to claim 3, wherein there are thermal insulation means in the chamber (10) situated between the first side walls (6) and the second side walls (7).

14. The evaporator according to claim 3, wherein either the first side walls (6), the second side walls (7), or both (6, 7), extend along the outer side of the first plate (1) and along the outer side of the second plate (2), being attached to one another, configuring a shell.

15. The evaporator according to claim 14, wherein either the first side walls (6), the second side walls (7) or both, are configured in the form of two U-shaped halves attached to one another.

16. The evaporator according to claim 1, wherein the first plate (1), the second plate (2), or both (1, 2), allow bending according to the direction perpendicular to the longitudinal direction established between the inlet (I2) and the outlet (O2) of the second fluid.

17. A heat recovery system for internal combustion vehicles comprising an evaporator according to claim 1.

Description

DESCRIPTION OF THE DRAWINGS

[0063] These and other features and advantages of the invention will be better understood based on the following detailed description of a preferred embodiment, given solely by way of illustrative, non-limiting example in reference to the attached drawings.

[0064] FIG. 1 shows a perspective view of an embodiment of the invention. In this figure, some heat exchange tubes have been intentionally removed from the inside for greater clarity.

[0065] FIG. 2 shows a schematic section view of another embodiment of the invention that allows observing the inside of the evaporator, of the two plates and of some of the chambers, as well as the exchange tubes going from one plate to the other.

[0066] FIG. 3A shows a detail of a schematic section of another embodiment that allows observing a constructive detail of the plate, manufactured by means of stacking of die-cut plates, in which the chambers are configured.

[0067] FIG. 3B shows a top view of an embodiment of one of the die-cut metal sheets giving rise to one of the main plates of the evaporator.

[0068] FIG. 4 shows a perspective view of one of the plates according to another embodiment, in which the chambers are configured.

[0069] FIG. 5 shows a cross section with respect to the longitudinal direction X-X defined by the direction of the flow of the second fluid of one embodiment with first walls situated on the outside and second walls situated on the inside.

[0070] FIG. 6 shows a perspective view of an embodiment of an elastically deformable wall.

DETAILED DESCRIPTION OF THE INVENTION

[0071] According to the first aspect of the invention, the present invention relates to an evaporator intended for transferring the heat from a hot gas to a liquid, which raises its temperature, changes phase and exits as superheated vapor.

[0072] In the embodiments, the hot gas, the one identified as second fluid, is the exhaust gas of an internal combustion engine. In these embodiments, the first fluid is ethanol. Ethanol enters in liquid phase inside the evaporator. The transfer of heat from the second fluid to the first fluid leads to a first step where the temperature of the first fluid raises until reaching the boiling temperature; in a second step it changes phase, maintaining the temperature about equal to the boiling temperature; and in a third step, in the vapor phase the temperature further increases.

[0073] In this embodiment, the superheated ethanol vapor is used in a Rankine cycle to generate mechanical energy recovering part of the heat from the exhaust gases of the internal combustion engine.

[0074] As shown in FIGS. 1 and 2, according to embodiments of the invention, the evaporator is formed by two rectangular plates (1, 2), with two longer sides and two shorter sides, spaced from and parallel to one another. In the figures, the parallel plates (1, 2) are depicted as being horizontal up and down according to the orientation of the drawings.

[0075] The longer sides of the plates (1, 2) are connected by means of respective side walls (6) in the form of a flat plate that limits a prismatic-shaped internal volume with essentially rectangular bases. These side walls (6) are the walls depicted as being vertical in FIG. 1.

[0076] The shorter sides of the plates correspond to the ends of the evaporator where the inlet (I.sub.2) for the second fluid is located, and the outlet (O.sub.2) is located at the opposite end. The direction of the second fluid establishes a longitudinal direction identified as X-X in FIG. 2.

[0077] Each of the plates (1, 2) has a plurality of chambers (1.1, 2.1). Exchange tubes (3) extend from one chamber (1.1, 2.1) of a plate (1, 2) to another chamber (1.1, 2.1) of the other plate (1, 2). The heat exchange tubes (3) are arranged transverse to the flow of the second fluid; i.e., transverse to the longitudinal direction X-X.

[0078] Each chamber (1.1, 2.1) has exchange tubes (3) such that it is in fluid communication with two or more chambers (1.1, 2.1) of the other plate (1, 2). The chamber receives the first fluid through the exchange tubes (3) coming from a chamber (1.1, 2.1) of the other plate (1, 2) and the fluid exits towards the other chamber of the other plate (1, 2) through the other exchange tubes (3) connecting them.

[0079] FIG. 2 schematically depicts this condition by offsetting the chambers (1.1) of the first plate (1) and the chambers (2.1) of the second plate (2) according to the longitudinal direction X-X.

[0080] By means of this connection of the chambers (1.1, 2.1), the first fluid passes through the chambers sequentially, crossing from one plate (1, 2) to the other through the exchange tubes (3).

[0081] According to the section view depicted in FIG. 2, the flow of the first fluid follows a zigzag path, alternating between the first plate (1) and the second plate (2), moving from left to right. Nevertheless, there can be additional chambers (1.1, 2.1) according to the transverse direction which are prolonged according to the direction perpendicular to the plane of the paper, as depicted in FIG. 2, such that the path can also alternate between the first plate (1) and the second plate (2), following a zigzag path, before passing to the next chamber (1.1, 2.1) according to the direction X-X.

[0082] Another option that allows increasing the volume of flow that is conveyed is to use two or more rows of tubes in the communication between two chambers.

[0083] The heat exchange tubes (3) are distributed inside the prismatic volume defined by the plates (1, 2) and the side walls (6) with an orientation transverse to the direction of the main flow of the second fluid. The path followed by the first fluid in the path, alternating between the first plate (1) and the second plate (2), will depend on how the chambers (1.1, 2.1) of both plates (1, 2) are overlapped, overlap being understood as that obtained by means of a projection according to the direction perpendicular to any of the mid-planes of the plates (1, 2). The chambers (1.1, 2.1) between which the passage of the first fluid in the first plate (1) and in the second plate (2) is alternated are shown as being consecutively overlapped according to a projection in the direction perpendicular to both plates (1, 2).

[0084] Said FIG. 2 shows a first chamber (1.1) of the first plate (1) in fluid communication with an intake manifold (4). The path of the first fluid ends in a last chamber (2.1) of the second plate (2) in fluid communication with a second outlet manifold (5).

[0085] In the example shown in FIG. 1 the inlet manifold (4) and outlet manifold (5) are in the same plate (1), whereas in the example shown in FIG. 2 they are in different plates (1, 2).

[0086] In the embodiment of FIGS. 2 and 5, the plates (1, 2) have chambers (1.1, 2.1) configured by means of machining. The machining of the chambers (1.1, 2.1) gives rise to slots such as those shown in FIG. 4. In FIGS. 2 and 5, the heat exchange tubes (3) are depicted as being parallel and in FIG. 4, the perforations that receive the exchange tubes (3) are offset, leaving a staggered distribution.

[0087] Each of the slots is closed with an upper metal sheet configuring each of the chambers (1.1, 2.1) therein from the slots.

[0088] The detail of FIG. 3A shows an alternative way of configuring the main plates (1, 2) of the evaporator. Each of the main plates (1, 2) is in turn formed by a first elemental plate (1.2, 2.2) having perforations to allow for the passage of the ends of the heat exchange tubes (3), and a second elemental, die-cut plate (1.3, 2.3) with perforations to configure the chambers (1.1, 2.1), the first elemental plate (1.2, 2.2) and the second elemental plate (1.3, 2.3) being attached to one another.

[0089] In this particular example, to limit the thickness of the plate to be die-cut, two identical die-cut plates are used, and once stacked form the second elemental plate (1.3, 2.3). The desired thickness, or in other words, the height of the chamber (1.1, 2.1) formed by the perforations, can be obtained by stacking a plurality of plates (1.3, 2.3).

[0090] FIG. 3B shows a second die-cut plate (1.3, 2.3) with the perforations giving rise to the chambers (1.1, 2.1).

[0091] In the described examples, whether the slots are formed by a machining operation on the plate (1, 2) or are obtained by stacking second die-cut plates (1.3, 2.3), the inner walls (1.1.1, 2.1.1) of the slots are perpendicular to the main plane of the plate (1, 2). Nevertheless, other methods for producing a slot do not have to give rise to vertical walls.

[0092] FIG. 5 shows a section of the evaporator perpendicular to direction X-X established by the flow of the second fluid and according to one embodiment.

[0093] According to the section and according to the position shown in FIG. 5, the first plate (1) is arranged at the top and the second plate (2) is arranged at the bottom. The section coincides with chambers (1.1, 2.1) which, in both the upper plate (1) and lower plate (2), extend along the entire width.

[0094] If the section were to be established at a point closer to the inlet of the first fluid, this same section could present a larger number of chambers (1.1, 2.1) such that there is also an exchange between both plates (1, 2) according to a transverse path. This transverse path would be contained in the plane corresponding to the section.

[0095] The heat exchange tubes (3) are subjected to the heat of the hot gas on the outer surface thereof and to the first fluid, ethanol, with a lower temperature, on the inner surface thereof. Particularly in the first step, the temperature of the tubes is below the boiling temperature for ethanol. At the end of the evaporator, the tubes are at temperatures close to the inlet temperature of the hot gas because the ethanol is overheated. This temperature gradient gives rise to a progressive expansion from one end of the evaporator to the opposite end.

[0096] The plates (1, 2) are linked through both the heat exchange tubes (3) and the walls (6). According to the example shown in FIG. 1, the walls (6) are in contact with the hot gas.

[0097] The larger spacing between plates (1, 2) and the fact that this spacing is larger at one end than at the other generates stress in the walls (6). This stress can give rise to excessive values causing damage to, or even the crack failure of, the evaporator.

[0098] The invention establishes as a condition that the walls (6) must be elastically deformable, such that the stress generated by the greater difference in thermal expansion with the exchange tubes is compensated with the elastic deformation of the walls (6). A particular way of achieving the walls (6) to be elastically deformable is by using plates with one or more crimps or corrugations (6.1) according to the direction transverse to the direction in which they are desired to be elastically deformable.

[0099] A particular configuration of the crimps (6.1) is sinusoidal. The advantage of such crimps (6.1) is that the two main directions of the plane containing the plate in the path of the crimp along the sinusoid are combined, and greater stiffness against bending is maintained while providing the capacity of being elastically deformable with respect to tension in the direction transverse to the main axis of the sinusoid.

[0100] In order to compensate for the progressive expansion of the heat exchange tubes (3) according to longitudinal direction X-X in which the hot gas flows, according to one embodiment the crimps (6.1) extend according to said longitudinal direction X-X whether they are longitudinal or sinusoidal.

[0101] According to another embodiment, the heat exchange tubes (3) are also elastically deformable. One way of getting them to be elastically deformable is by means of a helical corrugation.

[0102] Compression of the heat exchange tubes (3) reduces the gap between plates as a result of expansion and further reduces stresses to a greater extent.

[0103] The expansion occurring on the walls (6) is caused primarily by the fact that they are in direct contact with the hot gas. According to the embodiment shown in FIG. 5, the evaporator comprises second walls (7), situated on the inside and spaced from the first walls (6). Now these inner second walls (7) are the ones in direct contact with the hot gas. The second walls also extend between the first plate (1) and the second plate (2). These second walls are elastically deformable such that the expansion caused as a result of the hot gas is compensated for with their capacity for being elastically deformed.

[0104] In the graphical depiction, a corrugated line has been used to show that it has a corrugated configuration (7.1), which is what provides said second walls with their elastically deformable behavior.

[0105] In this embodiment elastically deformable first walls (6) and elastically deformable second walls (7) have been selected, where the stiffness of the first walls (6) is greater than the stiffness of the second walls (7). With this configuration, the inner walls demarcate the flow of the hot gas and do not increase stresses due to the more notable effects of expansion, and the first walls (6) provide the necessary stiffness to the entire assembly without generating stresses that generate fractures because they are also elastically deformable.

[0106] Between the first walls (6) and the second walls (7) there is a chamber (10) that can contain insulating means, preventing heat from seeping out reducing the heat recovery capacity of the device.

[0107] Air, a coolant, ethanol, or even vacuum are considered among the insulating means.

[0108] According to another embodiment, when the first fluid, in this case ethanol, is in liquid phase it is made to pass through the chamber (10) formed between the first walls (6) and the second walls (7). This liquid cools both walls (6, 7), and in particular the second walls (7) which are at a higher temperature as they are in direct contact with the hot gas.

[0109] As an additional effect, the temperature of the first fluid increases. The passage through the chamber (10) is carried out before introducing the first fluid in the inlet into the manifold (4) communicating with the first chamber (1.1) of the first plate (1). The first fluid therefore has a temperature closer to the boiling temperature, and the energy required for the first step as well as the total length of the heat exchanger are reduced.

[0110] According to the embodiment shown in FIGS. 2, 3A and 5, the evaporator includes two shield plates (11). The first plate (1) has a shield plate (11) spaced from said first plate (1) as shown on the top part of the evaporator, and the second plate (2) has a shield plate (11) also spaced from the second plate (2).

[0111] The space between the first plate (1) and its shield plate (11), or the space between the second plate (2) and its shield plate (11), forms a chamber protecting the welds between the exchange tubes (3) and the main plates (1, 2).

[0112] The shield plates (11) have perforations to allow the passage of the exchange tubes (3). The perforations of the shield plates (11) allow the passage therethrough, but the shield plates (11) are not necessarily attached to the exchange tubes (3). As they are not attached to the exchange tubes (3), there is no damage to the welds, nor are they affected by the expansion of the exchange tubes (3).

[0113] FIG. 5 shows the second walls (7), independent of the shield plates (11). According to another embodiment, both are configured from one and the same plate.

[0114] According to another embodiment, the second internal walls (7) are prolonged inside the intake manifold (8) of the second fluid, inside the exhaust manifold (9) of the second fluid, or inside both. This prolongation is spaced from the corresponding manifold (8, 9) forming a chamber offering protection from direct contact with the hot gas.

[0115] FIG. 6 shows an embodiment of a side wall (6, 7), with the prolongations for the manifolds (8, 9). The use of two symmetrical parts as shown, facing one another, establishes the walls on both sides of the evaporator, as well as the chambers for protecting the manifolds (8, 9). This side wall (6, 7) shows a corrugation that is prolonged along the longitudinal direction X-X so that the side wall (6, 7) is elastically deformable at least in the direction joining the first plate (1) and the second plate (2).

[0116] The configuration of the first inner-walls (6) and of the second inner walls (7) can differ in dimensions of the parts thereof so that the walls (6) and other walls (7) can be arranged parallel, can maintain the surfaces inside the intake manifold (8) and exhaust manifold (9) forming inner chambers in both cases, and it can also differ in the corrugation or crimps (6.1, 7.1) providing the elastically deformable behavior to determine the degree of stiffness thereof.

[0117] Once the two parts are attached as shown in FIG. 6, the upper edge is configured for being adapted to the periphery of the first plate (1) and the lower edge is configured for being adapted to the periphery of the second plate (2).

[0118] Therefore, each of the parts shows a U-shaped configuration where the arms of the U are the prolongations housed inside the manifolds (8, 9) of the second fluid. Once they are attached to one another, they give rise to the walls (6, 7) of the evaporator.

[0119] At the beginning of the description it was indicated that expansion of the exchange tubes (3) is greater at one end of the evaporator than at the other end. In the general case, given that the three steps are identified in the evaporator, the increase in temperature is not linear, nor is the degree of expansion of the exchange tubes (3) according to the longitudinal direction X-X according to the forward movement direction of the flow of the second fluid.

[0120] According to another embodiment, the first plate (1), the second plate (2) or both (1, 2) are elastically deformable, allowing bending according to an axis parallel to such plates and perpendicular to longitudinal direction X-X.

[0121] The property of being elastically deformable according to this direction, according to the described embodiments, is achieved by configuring the chambers (1.1, 2.1) of the plates according to the transverse direction with respect to the larger sides of the plate (1, 2) and by choosing the means for closing the chambers on the outer face, facilitating said elastic deformation.