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 chambers by means of caps that allow the evacuation-of the gases generated during a brazing welding in the manufacturing process.

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, wherein each plate has a first face and a second face, wherein the first face of the first plate faces the first face of the second plate; wherein each of the plates has a length and a width and the length is along a longitudinal direction X-X, wherein the first plate (1) comprises a plurality of cavities and the second plate (2) comprises a plurality of cavities, wherein each cavity is open through the second face of their respective plates, said cavities being defined by inner walls (1.1.1, 2.1.1); wherein at least one of said first and second plates is formed by stacking a plurality of flat elemental plates, the plurality of elemental plates including a first elemental plate having perforations to allow for the passage of heat exchange tubes and a second elemental plate having perforations including said inner walls and defining said cavities, the first elemental plate and the second elemental plate being attached to one another; an intake manifold (4) of the first fluid and an exhaust manifold (5) of the first fluid; a plurality of heat exchange tubes (3) wherein each of the heat exchange tubes (3) extends between one of the cavities of the first plate (1) and one of the cavities of the second plate (2), wherein each cavity of the first plate (1) is in fluid communication with two cavities of the second plate (2) via the heat exchange tubes (3), and each cavity of the second plate (2) is in fluid communication with two cavities of the first plate (1) via the heat exchange tubes (3), with the exception of one of the cavities of the first plate (1) which is in fluid communication with the intake manifold (4) and only one cavity of the second plate (2) via the heat exchange tubes (3) and one of the cavities of the second plate (2) which is in fluid communication with the exhaust manifold (5) and only one cavity of the first plate (1) via the heat exchange tubes (3); there being a path of fluid communication from the intake manifold (4) to the exhaust manifold (5) passing through the interior of said heat exchange tubes (3) and the cavities of the first and second plates; two 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 the two side walls and the first and second plate a space for the passage of the second fluid, wherein the second fluid enters through an inlet (I2) and exits through an outlet (O2) along the longitudinal direction X-X; and wherein each cavity that is not associated with the manifolds (4, 5) is closed by means of a dedicated cap (7) to define a plurality of chambers (1.1, 2.1) in the first and second plates, wherein each cap (7) has cap walls (7.1) such that following insertion of each of the dedicated caps into the corresponding cavity, the cap walls (7.1) are attached to the inner walls of said cavity.

2. The evaporator according to claim 1, wherein the second elemental plate (1.3, 2.3) is a composite plate comprising a plurality of plates stacked on one another.

3. The evaporator according to claim 1, wherein the chambers (1.1) of the first plate (1) are offset relative to the chambers (2.1) of the second plate (2) along the longitudinal direction X-X.

4. The evaporator according to claim 3, wherein the offset comprises a consecutive overlap of chambers (1.1) of the first plate (1) relative to chambers (2.1) of the second plate (2) according to a projection perpendicular to the longitudinal direction X-X.

5. The evaporator according to claim 1, wherein the inner walls (1.1.1, 2.1.1) and the cap walls (7.1) of the cap (7) are parallel to one another.

6. The evaporator according to claim 1, wherein at least one of the caps (7) is dome-shaped (7.4) having a semicircular section.

7. The evaporator according to claim 1, wherein at least the first plate (1), the second plate (2) and the heat exchange tubes (3) are welded by means of brazing.

8. The evaporator according to claim 1, wherein at least one of the caps is welded to the corresponding plate by means of brazing.

9. The evaporator according to claim 1, wherein at least one of the caps (7) has a ventilation opening (7.2).

10. The evaporator according to claim 9, wherein the cap(s) having a ventilation opening (7.2) further comprise a weld point or a weld bead or a plug in said ventilation opening (7.2).

11. The evaporator according to claim 1, wherein at least one of the caps (7) comprises outer projections (7.3) adapted to act as a stop when said at least one cap (7) is inserted into its corresponding cavity.

12. The evaporator according to claim 1, wherein at least one of the caps (7) comprises outer projections (7.4) adapted to increase friction with the inner walls (1.1.1, 2.1.1) of the corresponding cavity, and/or to abut with opposing projections located on the inner walls (1.1.1, 2.1.1) of the corresponding cavity.

13. The evaporator according to claim 1, wherein each cap has a longitudinal extent in a direction transverse to the longitudinal direction X-X.

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

15. The evaporator according to claim 1, wherein each of the chambers has a longitudinal extent in a direction transverse to the longitudinal direction X-X.

Description

DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) 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.

(3) FIG. 2 shows a schematic section view of another embodiment of the invention that allows seeing 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. In this embodiment, unlike the preceding embodiment, the exhaust manifold of the first fluid is formed in the opposite plate.

(4) FIG. 3A shows a detail of a schematic section of another embodiment that allows seeing a constructive feature of the plate, manufactured by means of stacking of die-cut plates, in which the chambers are configured.

(5) 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.

(6) FIG. 4 shows a perspective view of one of the plates according to another embodiment, in which the chambers are configured.

(7) FIG. 5 shows a top view of another embodiment of the cap seen from its outer portion.

(8) FIGS. 6A, 6B and 6C show section views of different examples of caps. FIG. 6A shows a section view of a cap with a ventilation opening, where the section passes through said opening. FIGS. 6B and 6C show section views of caps without the ventilation opening and with outer projections with various functions.

DETAILED DESCRIPTION OF THE INVENTION

(9) According to the first inventive-aspect, 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.

(10) 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 results in 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.

(11) 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.

(12) As shown in FIGS. 1 and 2, according to embodiments of the invention, the evaporator is formed by two plates (1, 2) of rectangular configuration, 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 figures.

(13) 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 limit a prismatic-shaped internal volume with essentially rectangular bases. These side walls (6) are the walls depicted as being vertical in FIG. 1.

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) 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 another through the exchange tubes (3).

(19) 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.

(20) 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.

(21) 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 overlapping, overlap being understood as that obtained by means of a projection according to the direction perpendicular to any of the main 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).

(22) 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).

(23) 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).

(24) In the embodiment of FIG. 2, 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 FIG. 2, the heat exchange tubes (3) are depicted as being parallel and in FIG. 4, the holes that receive the exchange tubes (3) are offset, leaving a staggered distribution.

(25) Each of the slots is closed with a cap (7), configuring the corresponding chamber (1.1, 2.1) therein. According to one embodiment, the caps (7) are obtained in a single part by machining, whereas in the examples shown in FIGS. 2, 3A, 5, 6A, 6B and 6C, the caps are configured from a stamped and die-cut metal sheet.

(26) 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.

(27) In this particular example, to limit the thickness of the plate to be die-cut, two identical die-cut plates have been 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).

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

(29) 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, the inner walls of the slots (1.1.1, 2.1.1) are perpendicular to the main plane of the plate (1, 2).

(30) When the caps (7) are manufactured by means of die-cutting and stamping the side walls of the caps (7) are parallel to one another and are tightly fit against walls of the chambers (1.1, 2.1). The attachment by means of brazing of the caps through these walls arranged perpendicular to the caps (1, 2) has the advantage that the internal pressure when the evaporator is in the operative mode applies a force on the inner side of the cap (7), with a resultant force that tends to remove the cap. This resultant force is parallel to the surfaces attached by brazing, and the stresses generated are shear stresses. Welding by brazing is suitable for absorbing these shear stresses, increasing the service life of the evaporator.

(31) The caps (7) are elongated and configured according to a main direction. FIG. 5 shows a top view of a plug (7), with the described vertical walls even though they are not seen in this top view, and an elongated configuration with rounded ends. The elongated configuration extends according to a main direction which, in this figure, is identified by means of a discontinuous line. This cap (7) is suitable for closing the open cavities seen in FIG. 4, giving rise to the chambers (1.1, 2.1).

(32) FIGS. 6A, 6B and 6C show sections according to a plane transverse to the main direction of the cap (7). According to this cross-section, the vertical walls are prolonged by means of a semicircumferential arc giving rise to a configuration of the caps (7) with elongated dome-shape. This appearance is clearly shown in FIG. 1, in the upper portion of the evaporator, where a plurality of caps (7) are distributed parallel to one another and transverse with respect to the main direction of the evaporator X-X. This distribution corresponds to the distribution of chambers (1.1, 2.1) shown in FIG. 4.

(33) In the operative mode, the phase change of the first fluid increases its specific volume, and since it is confined, pressure increases inside the chambers (1.1, 2.1) and also inside the caps (7). The semicircumferential arc shape allows the cap to support the pressure without generating bending stresses in the portions of the surface that are not attached by welding. This condition, the absence of bending stresses, allows using minimal thickness in the caps (7).

(34) The transverse arrangement of the chambers (1.1, 2.1) with respect to the longitudinal direction of the evaporator makes bending of the plate according to a direction parallel to the main plane of the plate and transverse to the longitudinal direction X-X easier. Although FIG. 4 does not show the longitudinal direction X-X, it is the direction that corresponds to the direction of any of the longer sides of the plate (1, 2).

(35) The distribution of the chambers (1.1, 2.1) in the first and second plate (1, 2) corresponds to a direction of movement of the flow of the first fluid according to the longitudinal direction. The temperature of this fluid is lower at the inlet that at the outlet such that the differential expansion of the heat exchange tubes (3) makes the plates (1, 2) be forced to bending. The transverse arrangement of the caps (7) makes elastic deformation of the plates in response to the stresses imposed by these differential expansions easier.

(36) The manufacturing of the evaporator is performed with an assembly of all its components incorporating brazing paste in all those places where welding is required. The sinuous path imposed by the heat exchange tubes (3), alternating the fluid connection of chambers (1.1) of the first plate and chambers (2.2) of the second plate (2.2), complicates both the entrance of the reducing atmosphere of the furnace and the exit of the volatile elements that are generated in the furnace by the evaporation of part of the components of the brazing paste and the internal oxygen.

(37) The caps (7) allow being subsequently included in at least one of the chambers (1.1, 2.1). The subsequent inclusion requires a second welding operation that does not necessarily have to be by brazing.

(38) FIG. 5 shows a ventilation opening (7.2). With this ventilation opening (7.2), it is possible to include all the caps (7) in the chambers (1.1, 2.1) before the evaporator passes through the furnace to achieve welding by brazing. The volatile elements exit through the openings (7.2), preventing the increase in internal pressure.

(39) Once the caps (7) are welded, the openings are closed with either a weld point or a weld bead or with a plug, assuring tightness of the chamber (1.1, 2.1) closed by the cap (7).

(40) As indicated above, FIG. 6A shows the cross-section of a cap (7) with a ventilation opening (7.2) in the upper portion thereof.

(41) FIG. 6B shows a section of the cap (7) with an outer projection (7.3) configured to act as a stop on the outer surface of the plate (1, 2). One way of achieving this outer projection (7.3) is by means of punches or projections existing in stamping tools.

(42) FIG. 6C again shows a cap (7) with outer projections (7.4). The configuration of the outer projections (7.3) of FIG. 6B shows a wedge shape favoring support on the outer surface of the plate (1, 2) to act as a stop.

(43) In this FIG. 6C, the orientation of the outer projections (7.4) is opposite and the form of wedge allows the entrance in the slot of the plate (1, 2) giving rise to the chamber (1.1, 2.1) but imposes a friction force against the vertical wall of said slot. Such projections (7.4) favor retaining the cap (7) by friction inside the slot, giving rise to the chamber (1.1, 2.1) when it is closed by means of said cap (7).

(44) The edge defined between the vertical wall of the slot and the outer surface of the plate (1, 2) can have a perimetral projection (not shown in the figure). This recess allows a projection (7.4) like the one shown in FIG. 6C, with wedge shape directed towards the base of the cap (7), to make the entrance in the slot easier; overcoming the perimetral projection of the edge of the slot but, once it is overcome, to prevent the exit thereof. This projection thus configured assures that the caps (7) inserted during the assembly process do not come out until they are welded in the brazing furnace.