Heat Exchanger and Method of Cooling a Flow of Heated Air

Abstract

A heat exchanger, particularly a charge-air cooler, in which heated air is cooled by a cooling fluid, is constructed from stacked pairs of plates with air flow passages arranged between adjacent ones of the plate pairs. Each of the pairs of plates includes an inlet and an outlet for the cooling fluid flow arranged within an inlet and outlet region and aligned with the direction of the air flow through the heat exchanger. A flow barrier formed by beads of the plates is arranged between the inlet and outlet region and a heat exchange section of the plate pair. A flow of cooling fluid is directed through a coolant flow path extending through the plate pair between the cooling fluid inlet and the cooling fluid outlet, with the cooling fluid flow path having a first portion along one longitudinal edge of the plates, a second portion along an opposing longitudinal edge of the plates, and a third portion extending through the heat exchange section between the first and second portions. The flow of cooling fluid through the third portion is in a direction counter to the flow of air.

Claims

1. A heat exchanger comprising: a plurality of stacked plate pairs having air flow passages arranged between adjacent ones of the plurality of stacked plate pairs, the air flow passages extending between a set of first longitudinal edges of the stacked plate pairs and an opposing set of second longitudinal edges of the stacked plate pairs to define an air flow direction through the heat exchanger perpendicular to the first and second longitudinal edges; an inlet and outlet region for cooling fluid, each of the plurality of stacked plate pairs having an inlet for cooling fluid and an outlet for cooling fluid arranged within the inlet and outlet region and aligned with the air flow direction; a plurality of corrugated internal fins, each being located within one of the plurality of stacked plate pairs and having a low pressure drop direction aligned with the direction of the longitudinal edges and a high pressure drop direction aligned with the air flow direction; a plurality of flow barriers constructed by beads of the plate pairs, said plurality of flow barriers arranged between the inlet and outlet region for the cooling fluid and the plurality of corrugated internal fins; and a plurality of cooling fluid flow paths, each of the cooling fluid flow paths extending through one of the plurality of stacked plate pairs between the inlet for cooling fluid and the outlet for cooling fluid and including a first portion extending between one of the plurality of corrugated internal fins and one of the set of first longitudinal edges, a second portion extending between that one of the plurality of corrugated internal fins and one of the set of second longitudinal edges, and a third portion extending through that one of the plurality of corrugated internal fins in the high pressure drop direction to provide fluid communication between the first portion and the second portion, wherein the direction of cooling fluid flow along the third portion is counter to the air flow direction.

2. The heat exchanger of claim 1, wherein each of the cooling fluid flow paths further includes a fourth portion located within the inlet and outlet region and extending from the inlet for cooling fluid and the first portion, and a fifth portion located within the inlet and outlet region and extending from the second portion to the outlet.

3. The heat exchanger of claim 1, wherein the inlet and outlet region for cooling fluid is at least partially bounded by lateral edges of the plate pairs perpendicular to the longitudinal edges of the plate pairs.

4. The heat exchanger of claim 1, wherein each one of the cooling fluid flow paths further includes a fourth portion arranged between that one of the plurality of corrugated internal fins and a lateral edge of the plate pairs perpendicular to the longitudinal edges of the plate pairs, the fourth portion being fluidly connected to the first portion such that cooling fluid directed along the cooling fluid flow path flows through either the third portion or the fourth portion.

5. The heat exchanger of claim 4 wherein the plurality of flow barriers is a first plurality of flow barriers, further comprising a second plurality of flow barriers constructed by beads of the plate pairs, the second plurality of flow barriers at least partially bounding the fourth portions of the plurality of cooling fluid flow paths.

6. The heat exchanger of claim 5, wherein each one of the plurality of corrugated internal fins is arranged between one of the first plurality of flow barriers and one of the second plurality of flow barriers.

7. The heat exchanger of claim 4, wherein each one of the cooling fluid flow paths further includes a fifth portion fluidly connected to the fourth portion to receive flow therefrom, the fifth portion being arranged between the second portion and one of the set of second longitudinal edges.

8. The heat exchanger of claim 7, further comprising a third plurality of flow barriers constructed by beads of the plate pairs, the second portions of the cooling fluid flow paths being separated from the fourth portions of the cooling fluid flow paths by the third plurality of flow barriers.

9. The heat exchanger of claim 8, wherein each one of the second plurality of flow barriers is joined to one of the third plurality of flow barriers.

10. The heat exchanger of claim 4, wherein the fourth portion is fluidly connected to the second portion.

11. A method of cooling a flow of heated air, comprising: directing a flow of heated air through air flow passages of a heat exchanger in an air flow direction; directing a flow of cooling fluid into the heat exchanger and distributing the flow of cooling fluid among plate pairs of the heat exchanger through cooling fluid inlets of the plate pairs, the air flow passages being arranged between adjacent ones of the plate pairs; within each one of the plate pairs, directing the cooling fluid through a first duct in a direction perpendicular to the air flow direction; within each one of the plate pairs, directing a first portion of the cooling fluid from the first duct through a heat exchange section of the plate pair in a direction counter to the air flow direction; transferring heat from the flow of heated air to the first portion of the cooling fluid as the first portion of the cooling fluid flows through the heat exchange section of the plate pair; within each of the plate pairs, directing a second portion of the cooling fluid from the first duct through a bypass section of the plate pair in a direction counter to the air flow direction, the transfer of heat between the flow of heated air and the second portion of the cooling fluid being inhibited within the bypass section so that the second portion of the cooling fluid exits the bypass section at a lower temperature than the first portion of the cooling fluid exits the heat exchange section; within each of the plate pairs, directing the first portion of the cooling fluid through a second duct in a direction perpendicular to the air flow direction after directing the first portion of the cooling fluid through the heat exchange section of the plate pair; within each of the plate pairs, directing the second portion of the cooling fluid through the second duct in a direction perpendicular to the air flow direction after directing the second portion of the cooling fluid through the bypass section of the plate pair; and removing the flow of cooling fluid from the heat exchanger through cooling fluid outlets of the plate pairs.

12. The method of claim 11, wherein the steps of directing the first portion of the cooling fluid through the second duct and directing the second portion of the cooling fluid through the second duct includes arranging the second portion upstream of the first portion with respect to the air flow direction.

13. The method of claim 11, wherein mixing of the first portion of the cooling fluid flow with the second portion of the cooling flow within the second duct is prevented.

14. The method of claim 11, wherein directing the first portion of the cooling fluid flow through a heat exchange section of the plate pair includes passing the first portion of the cooling fluid flow through a corrugated internal fin arranged within the plate pair.

15. The method of claim 11, wherein directing the first portion of the cooling fluid flow through a heat exchange section of the plate pair includes passing the first portion of the cooling fluid flow through a successively arranged series of flow passages, each of the successively arranged series of flow passages extending in a direction perpendicular to the air flow direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 shows a perspective view of a heat exchanger according to an embodiment of the invention (illustrated without a housing).

[0016] FIG. 2 shows a similarly perspective view with a cover plate on the stack of plate pairs and fins.

[0017] FIG. 3 shows a stack made of plates and fins in which the one plate of the upper plate pair has been removed in order to make the interior of this plate pair visible.

[0018] FIGS. 4 and 5 show two plates which form a plate pair.

[0019] FIG. 6 shows a perspective view of a plate part with an internal fin.

[0020] FIG. 7 shows a view of the heat exchanger in a suitable housing.

[0021] FIGS. 8 and 9 show modified plate configurations.

[0022] FIGS. 10A-10D show a plate of a plate pair according to additional embodiments.

DETAILED DESCRIPTION

[0023] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of including, comprising, or having and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms mounted, connected, supported, and coupled and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, connected and coupled are not restricted to physical or mechanical connections or couplings.

[0024] In the perspective illustration (FIG. 1) of the heat exchanger, which is an indirect air cooler in the exemplary embodiment, the inlet 4 and the outlet 5 are located at the right-hand edges of metallic plates 1, which therefore represent the common edges E here. The inlet 4 is arranged at the end remote from the air inflow side AAir of the heat exchanger. The outlet 5 is, on the other hand, located closer to the inflow side of the charge air which is indicated by three block arrows. The inlet and outlet connectors have the reference symbols 40 and 50. The inlet and outlet cross sections have a circular shape in these embodiments. Instead of charge air, a mixture of charge air and exhaust gas or pure exhaust of an internal combustion engine (not shown) can also be present.

[0025] An advantage of the invention worth mentioning is that the inlet 4 and the outlet 5 can be located on opposite edges which would then constitute the common edges E, without changing the throughflow, as a result of which structural restrictions can be coped with better than hitherto. In the exemplary embodiment shown, these edges E are the lateral edges of the plates 1. Two parallel longitudinal edges of the plates 1 are located approximately perpendicularly on the lateral edges, wherein the terms are used merely to differentiate between the edges, but do not in any case mean that the longitudinal edges, as shown in the exemplary embodiment, are longer than the lateral edges. The edges can all have the same length. The lateral edges can also be longer than the longitudinal edges. The fact that the edges in the exemplary embodiment shown are straight and therefore approximately rectangular plates 1 are present is also not an important precondition for solving the stated problem. The edges can also be arcuate or embodied in some other way which deviates from a straight line.

[0026] In the exemplary embodiment shown, the plates 1 have a cutout 8 at the common edge E which is the right-hand lateral edge in FIG. 1. The depth of the cutout 8 is somewhat smaller than the depth of the inlet and outlet region 10. The position of the inlets and outlets 4, 5 is situated approximately in the center between the central longitudinal axis 15 of the plates 1 and their longitudinal edges. The inlet-side flow paths 11 extend from the inlets to the first ducts 12, which are arranged in the inner edge region of the one longitudinal edge in the plate pairs 1a, 1b. In the inner edge region of the other longitudinal edge there is the at least one second duct 13 which leads to the outlet-side flow path 11 and further to the outlet 5.

[0027] In the exemplary embodiment shown, the ducts 12, 13 have the same cross section throughout. The ducts 12, 13 have a low flow resistance, that is to say at least a partial cross section of the ducts 12, 13 does not have flow impediments or the like. Since, as mentioned, approximately rectangular plates are present in the exemplary embodiment shown, the flow paths 11 and the ducts 12, 13 are also located approximately perpendicularly with respect to one another.

[0028] In some embodiments (not shown), the inlets and outlets 4, 5 are also arranged at a common edge E but in the vicinity of the corners of the plates 1 here, with the result that the lengths of the flow paths 11 becomes virtually zero. In other words, fluid can enter virtually directly into the first ducts 12 and virtually directly enter the outlets 5 from the second ducts 13. There would also be no reason, in at least some embodiments, not to arrange the inlets 4 in the corners and merely to position the outlets 5 approximately as shown, or vice versa. As a result, only significantly pronounced outlet-side flow paths 11 would be present in such embodiments while the length of the inlet-side flow paths 11 would approach zero, that is to say would be virtually invisible. The designer therefore has multiple options available for adapting the heat exchanger to restrictions forced on him by the installation location, without having to accept a loss of power.

[0029] The flow paths 11 can be implemented by construction of beads in the plates 1 forming the pairs, as is apparent from the illustrations according to FIGS. 4 and 5. Instead of beads, rods which are inserted and soldered in the plate pairs can also be provided. In the exemplary embodiment shown, the beads or the rods form the flow barriers 6 mentioned above. These figures show plan views of the two plates 1 which form a plate pair 1a, 1b, with an internal fin 14 which is inserted therein, but is not illustrated in detail here.

[0030] The plate 1b shown in FIG. 5 is rotated through 180 about its longitudinal axis 15 and is positioned on the plate 1a in FIG. 4. The two beads come to bear one against the other in the plate pair 1a, 1b and are connected later. They accordingly have a height which is approximately half as large as the distance between the two plates 1 which form the plate pair 1a, 1b. The height of the internal fin 14 must correspond to this distance. In addition, the plates 1a and 1b come to bear one against the other with their edges and are connected to one another in a sealed fashion. In the exemplary embodiment they are bent-over edges.

[0031] Various other edge configurations are known from the prior art. These can alternatively be provided.

[0032] The inlet and outlet openings 4, 5 of the plate pair 1a, 1b are provided with collars 41, 51 which protrude upward at the upper plate 1a and downward at the lower plate 1b. The connection to the adjacent plate pairs 1a, 1b takes place at these collars. Sealing rings which are located between the plate pairs and connect the latter are also an alternative to such collars 41, 51. In embodiments which are not shown just one of the plates 1 has a bead whose height has to be correspondingly larger, that is to say which should correspond to the height of the internal fin 14. Of course, the entire stack, that is to say the plate pairs and the fins 2 located therebetween, are connected to one another, preferably connected metallically, for example soldered in a soldering oven. The soldered-in internal fin 14 through which the fluid flows is located within each plate pair 1a, 1b.

[0033] Since the aforementioned internal fin 14 can have a smaller dimension than the plate 1 in which it is inserted owing to construction of the ducts 12, 13, the position of the internal fin 14 is indeterminate, which is disadvantageous. A correct position of the internal fin 14 within the plate 1 can be implemented by virtue of the fact that inwardly protruding knobs or similar shaped elements 16 are formed in the corners of the plates 1 and serve as a stop for the internal fin 14. As a result, the preassembly of the heat exchanger improves. With this measure it is also possible to prevent an undesired bypass for the fluid, or at least largely suppress it. However, in some embodiments such a bypass may be desirable, as described in greater detail hereafter.

[0034] In FIGS. 3, 4 and 5, the inlet and outlet region which has already been mentioned is provided with the reference symbol 10. It makes up approximately 12% of the entire heat-exchanging area here. Since this region for exchanging heat cannot contribute very much, the aim is to make it as small as possible. In FIG. 3, two arrows indicate that the corrugated internal fin 14 is preferably inserted into the plate pair 1a, 1b in such a way that when there is a flow through them in the longitudinal direction a significantly lower pressure loss dp occurs than when there is a throughflow in the lateral direction. The fluid is forced by the special design to take the path in the lateral direction and accordingly to flow though the plate pairs 1a, 1b in countercurrent with respect to the direction of the flow of air.

[0035] The heat exchanger thereby provides multiple cooling fluid flow paths extending hydraulically in parallel with one another between the inlet 4 for the cooling fluid and the outlet 5 for the cooling fluid, with each one of the multiple cooling fluid flow paths extending through one of the plate pairs 1a, 1b. Each such cooling fluid flow path includes a first portion 12 extending between one of the internal fins 14 and a longitudinal edge of the pair, and a second portion 13 extending between that one of the internal fins 14 and the opposing longitudinal edge of the plate pair. A third portion of the cooling fluid flow path extends through the internal fin in the high pressure drop direction to provide fluid communication between the first portion 12 and the second portion 13. Preferably, the direction of the cooling fluid flow along that third portion of the cooling fluid flow path is counter to the direction of the heated air flow. In some, but not all, embodiments the cooling fluid flow path also includes a portion 11 located within the inlet and outlet region and extending from the inlet 4 for the cooling fluid to the first portion 12, as well as another portion 11 located within the inlet and outlet region and extending from the second portion 13 to the outlet 5 for the cooling fluid.

[0036] FIG. 6 shows, in a section, a perspective view of the corrugated internal fin 14 which is located in the plate 1. Some details of the corrugated internal fin 14 can be seen. The direction in which the corrugation runs in the heat exchanger is the lateral direction thereof, that is to say the direction of the significantly higher pressure loss dp. In the corrugation edges 17 there are breakthroughs or cutouts 18 offset alternately to the left and to the right when viewed in the direction of said corrugation edge 17. The width of the ducts 12, 13 is determined by the distal end of the flow barrier 6 and the longitudinal edge of the plate. As is also shown by FIG. 6, a narrow strip of the duct 12 is completely free.

[0037] In embodiments according to the invention (not shown) the entire duct 12, 13 is of free design. In other embodiments (not shown) the longitudinal edge of the internal fin 14 extends directly to the longitudinal edge of the plates 1, with the result that the entire duct cross section is occupied by a section of the internal fin 14. The function of the ducts 12, 13 is retained because the aforementioned section points in the direction of the low pressure loss dp which corresponds to the direction of the duct. There is also the possibility of covering the cross section of the one duct completely with part of the internal fin 14 and leaving the other duct completely free.

[0038] As is also the case in known heat exchangers, the compressed charge air AAir to be cooled flows through an opening into a housing 3 in which the aforementioned stack made of plate pairs 1a, 1b and fins 2 (not illustrated in more detail) are located (FIG. 7). The housing 3 can be the intake manifold of an internal combustion engine. According to the proposal, the charge air then flows through the corrugated fins 2 in countercurrent with respect to the fluid flowing in the plate pairs, and in the process it is cooled extremely efficiently. The direction of flow of the charge air is, also according to the proposal, provided in the direction of the common edge E at which the inlet 4 and the outlet 5 for the fluid are located, or in the exemplary embodiment in the direction of the lateral edges of the plates 1. As a result, the cooled charge air leaves the heat exchanger through another opening in the housing 3 in order to be available for charging the internal combustion engine (not shown). The protruding edge 9.1, of the cover plate 9 which can be seen in FIG. 2 and which terminates the stack and is connected metallically thereto, for example, can be used in a known fashion to attach the plate stack in the housing 3 and therefore serves as a closure of an assembly opening in the housing 3.

[0039] FIG. 8 shows a plate 1 with elongate holes as inlets and outlets 4, 5. The flow paths 11 have been virtually integrated into the elongate holes since there to a certain extent a flow guide is formed in the direction of the common edge E, as is also the case with the flow paths of the other exemplary embodiments. In embodiments which are not shown, the inlets and outlet 4, 5 have other different hole shapes. These may also include hole shapes which are configured asymmetrically. FIG. 9 in turn shows round plate holes 4, 5 but modified flow barriers 6.

[0040] FIGS. 10A-10D show several variations of a plate 1 of another embodiment, wherein a bypass channel 21 is incorporated into each one of the plate pairs 1a, 1b. As can be seen in FIG. 10A, the bypass 21 allows a portion of the cooling fluid passing through the plate pair 1a, 1b between the cooling fluid inlet 4 and the cooling fluid outlet 5 to bypass the corrugated internal fin 14 along a lateral edge of the plates 1. A flow barrier 18 is provided in order to provide a fluid separation between the heat transfer region, characterized for example by the corrugated internal fin 14, and the bypass channel 21. The flow barrier 18 can be constructed in a similar fashion as the flow barrier 6, such as by beads formed into the plates 1.

[0041] In such an embodiment, the cooling fluid flow path through the plate pair 1a, 1b is thereby modified to add a fourth portion (characterized by the bypass channel 21) arranged between the internal fin 14 and a lateral edge of the plates 1. The fourth portion 21 is fluidly connected to the first portion 12 of the cooling fluid flow path, so that the cooling fluid flowing along the cooling fluid flow path is directed through either the third portion or the fourth portion.

[0042] Heat transfer between the charge air and that portion of the cooling fluid which passes through the bypass channel 21 is intentionally inhibited, for example through the absence of any heat transfer enhancing features within the bypass channel 21, so that the portion of the cooling fluid passing through the bypass channel 21 is essentially unchanged in temperature. Alternatively or in addition, the transfer of heat between the charge air and the portion of the cooling fluid passing through the bypass channel 21 can be inhibited by blocking or impeding the flow of charge air through those portion of the air flow passages directly adjacent the bypass channel 21, for example by way of formed features of the edges of the plates 1. The bypass section 21 thereby allows a portion of the cooling fluid to bypass the heat exchange section of the plate pair 1a, 1b, characterized by that section of the plate pair that is occupied by the corrugated internal fin 14.

[0043] As seen in FIG. 10A, the bypass channel 21 can be fluidly connected to the channel 13 so that the portion of the cooling fluid passing through the bypass channel 21 can discharge directly into the channel 13. The momentum of the cooling fluid passing through the bypass channel 21 will cause it to be directed towards the longitudinal plate edge of the channel 13. This has the beneficial effect of allowing the relatively unheated cooling fluid to cool the leading edges of the plates 1 onto which the heated charge air directly impinges. The inventors have found that such a cooling effect helps to reduce the metal temperature of these leading plate edges, thereby avoiding an undesirable boiling of the cooling fluid which might otherwise result.

[0044] In the alternate plate design of FIG. 10B, the channel 13 is divided into a first portion 13a and a second portion 13b by another flow barrier 19. The flow barrier 19 can be, but need not necessarily be, joined to the flow barrier 18. The flow barrier 19 maintains the separation within the flow channel 13 of the portion of the cooling fluid that passed through the bypass channel 21 and the portion of the cooling fluid that passed through the heat exchange section 14. As a result, the cooling effect on the leading edges of the plates 1 can be enhanced, and the risk of cooling fluid boiling can be further reduced. The flow channel portion 13b thereby defines a fifth portion of the cooling fluid flow channels that is connected in series to the fourth portion defined by the bypass channel 21.

[0045] FIGS. 10C and 10D depict variations of the plates 1 of FIGS. 10A and 10B, respectively. In the plates 1 of FIGS. 10C and 10D, the corrugated internal fin 14 defining the heat exchange section of the plate pair has been replaced by a successively arranged series of flow passages 22 through which that portion of the cooling fluid flow that is not directed through the bypass channel 21 is directed. The series of flow passages 22 together constitute a heat exchange section 14 of the plate pair. Each of the flow passages 22 extend in a direction that is parallel to the longitudinal edges of the plates 1 between the flow barrier 6 and the flow barrier 18. The cooling fluid is directed through the series of flow passages 22 in a counter-cross-flow direction to the flow of heated air through the heat exchanger. Additional flow barriers 23 are arranged between adjacent ones of the flow channels 22 in order to define the flow channels 22, with the flow barriers 23 alternatingly extending from the flow barrier 6 and from the flow barrier 18. One of those flow barriers 23 also serves to separate the initial one of the flow passages 22 from the duct 12, while another one of those flow barriers 23 also serves to separate the terminal one of the flow passages 22 from the duct 13.

[0046] A heat exchanger built using the plates 1 as described in FIGS. 10A-D can be particular desirable for cooling a flow of heated air (such as for example compressed charge air for an internal combustion engine) using a flow of liquid cooling fluid with high heat exchange efficiency without the increased risk of causing undesirable boiling of the cooling fluid. In at least one embodiment of a method of cooling such a flow of heated air, a flow of heated air Aair (for example, compressed charge air for an internal combustion engine) is directed through the air flow passages of the heat exchanger in an air flow direction. Simultaneously, a flow of cooling fluid is directed into the heat exchanger and is distributed among the plate pairs 1a, 1b of the heat exchanger through coolant inlets 4 of the plate pairs. Within each one of the plates pairs 1a, 1b, the cooling fluid is first directed through a first duct 12 in a direction that is perpendicular to the air flow direction. A first portion of the cooling fluid is then directed from the first duct 12 through a heat exchange section 14, 14. Within the heat exchange section 14, 14, the cooling fluid is directed in a direction that is overall counter to the air flow direction, such as in a counter-flow or a cross-counter-flow direction. Heat is transferred from the flow of heated air to that first portion of the cooling fluid as it flows through the heat exchange section 14, 14. Simultaneously, a second portion of the cooling fluid is directed from the first duct 12 through a bypass section 21 of the plate pair, also in a direction that is counter to the air flow direction. The transfer of heat between the flow of heated air and the second portion of the cooling fluid is inhibited within the bypass section, so that the second portion of the cooling fluid exits the bypass section at a lower temperature than the first portion exits the heat exchange section. The first and the second portions are subsequently directed through a second duct 13 in a direction that is again perpendicular to the air flow direction.

[0047] In some embodiments, such as ones using plates 1 such as are depicted in FIG. 10A and FIG. 10C, the second duct 13 is a single duct through which the first portion of the cooing fluid and the second portion of the cooling fluid both flow. In such an embodiment, some mixing of the first and second portions of the cooling fluid can occur within the second duct 13. In other embodiments, such as for example ones using plates 1 as are depicted in FIG. 10B and FIG. 10D, the first portion of the cooling fluid and the second portion of the cooling fluid are separated within the second duct 13 and mixing of the two portions within that duct 13 is prevented. The first portion of the cooling fluid can be directed through a portion 13a of the second duct 13 while the second portion of the cooling fluid can be directed through a portion 13b of the second duct 13. The portion 13b can advantageously be arranged to be upstream of the portion 13b with respect to the direction of the heated air flow through the heat exchanger, so that the portion of the flow of cooling fluid that passed through the bypass duct 21 (and which is, consequently, at a lower temperature) can sufficiently depress the temperature of the plates surfaces that are directly impacted by the hottest air in order to prevent any boiling of the cooling fluid.

[0048] Various alternatives to the certain features and elements of the present invention are described with reference to specific embodiments of the present invention. With the exception of features, elements, and manners of operation that are mutually exclusive of or are inconsistent with each embodiment described above, it should be noted that the alternative features, elements, and manners of operation described with reference to one particular embodiment are applicable to the other embodiments.

[0049] The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention.