US20090056909A1

US20090056909A1 - Heat exchanger having an internal bypass

Info

Publication number: US20090056909A1
Application number: US11/848,052
Authority: US
Inventors: Catherine R. Braun
Original assignee: Modine Manufacturing Co
Current assignee: Modine Manufacturing Co
Priority date: 2007-08-30
Filing date: 2007-08-30
Publication date: 2009-03-05

Abstract

The present invention provides an exhaust recirculation cooler for transferring heat between engine exhaust and a coolant. The cooler can include a housing having a first end and a second end spaced from the first end, a heat transfer region extending through the housing and including a plurality of tubes positioned along a flow path for the coolant, and an internal bypass extending through the housing between the first end and the second end adjacent to the heat transfer region. Together, at least one of the plurality of tubes and the internal bypass provide an exhaust flow path through the cooler.

Description

FIELD OF THE INVENTION

The present invention relates to heat exchangers and, more particularly, to an exhaust gas waste heat recovery system and a method of operating the same.

SUMMARY

In some embodiments, the present invention provides an exhaust recirculation cooler for transferring heat between engine exhaust and a coolant. The cooler can include a housing having a first end and a second end spaced from the first end, a heat transfer region extending through the housing and including a plurality of tubes positioned along a flow path for the coolant, and an internal bypass extending through the housing between the first end and the second end adjacent to the heat transfer region. Together, at least one of the plurality of tubes and the internal bypass can provide an exhaust flow path through the cooler.
The present invention also provides an exhaust recirculation cooler including a housing having a first end and a second end spaced from the first end and at least partially enclosing a heat transfer region, and a primary exhaust flow path including two passes extending through the housing between the first and second ends in counter flow directions. At least a portion of the primary exhaust flow path can have heat-transfer augmentations and can extend through the heat transfer region wherein heat is transferred from exhaust traveling through the primary exhaust flow path to a coolant flow path. The cooler can also include a secondary exhaust flow path extending through the housing between the first end and the second end and being substantially free from heat transfer augmentations.
In addition, the present invention provides a method of operating an exhaust recirculation cooler including a housing at least partially defining a heat transfer region. The method can include the act of directing engine exhaust through the housing between first and second ends of the housing around the heat transfer region and back through the heat transfer region.
The present invention also provides a method of operating an exhaust recirculation cooler including a housing having a first end and a second end and at least partially defining a heat transfer region. The method can include the acts of directing engine exhaust along two passes through the heat transfer region in counter flow directions, transferring heat from the engine exhaust traveling through the heat transfer region to coolant traveling through the heat transfer region, and directing engine exhaust from the first end of the housing toward the second end of the housing through an internal bypass in the housing and around the heat transfer region.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger according to some embodiments of the present invention.

FIG. 2 is another perspective view of the heat exchanger shown in FIG. 1 with a collection tank removed.

FIG. 3 is an exploded perspective view of the heat exchanger shown in FIG. 1.

FIG. 4 is an end view of the heat exchanger shown in FIG. 1 with a collection tank removed.

FIG. 5 is a cross-sectional view of the heat exchanger shown in FIG. 1.

FIG. 6 is another cross-sectional view of the heat exchanger shown in FIG. 1.

FIG. 7 is yet another cross-sectional view of the heat exchanger shown in FIG. 1.

FIG. 8 is a perspective end view of the heat exchanger shown in FIG. 1 with a valve in a second position.

FIG. 9 is a perspective end view of the heat exchanger shown in FIG. 1 with the valve in a first position.

FIG. 10 is an end view of a portion of a heat exchanger according to an alternative embodiment of the present invention.

FIG. 11 is an exploded perspective view of the heat exchanger shown in FIG. 10.

FIG. 12 is a cross-sectional view of the heat exchanger shown in FIG. 10.

FIG. 13 is another cross-sectional view of the heat exchanger shown in FIG. 10.

FIG. 14 is yet another cross-sectional view of the heat exchanger shown in FIG. 10.

DETAILED DESCRIPTION

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 following 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.
Also, it is to be understood that phraseology and terminology used herein with reference to device or element orientation (such as, for example, terms like “central,” “upper,” “lower,” “front,” “rear,” and the like) are only used to simplify description of the present invention, and do not alone indicate or imply that the device or element referred to must have a particular orientation. In addition, terms such as “first,” “second,” and “third” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance.
FIGS. 1-9 illustrate a heat exchanger 10 according to some embodiments of the present invention. In some embodiments, including the illustrated embodiment of FIGS. 1-9, the heat exchanger 10 can operate as an exhaust gas recirculation cooler (EGRC) and can be operated with the exhaust system of a vehicle. In other embodiments, the heat exchanger 10 can be used in other (e.g., non-vehicular) applications, such as, for example, in electronics cooling, industrial equipment, building heating and air-conditioning, and the like. In addition, it should be appreciated that the heat exchanger 10 of the present invention can take many forms, utilize a wide range of materials, and can be incorporated into various other systems.
As shown in FIGS. 1-3 and 5-9, the heat exchanger 10 can include a housing 12 having a first end 14 and a second end 16. The housing 12 can also include an inlet 20 for receiving a first working fluid (e.g., water, engine coolant, CO₂, an organic refrigerant, R12, R245fa, air, and the like) and an outlet 22 for dispensing the first working fluid. In the illustrated embodiment of FIGS. 1-9, the inlet 20 can be positioned adjacent to the second end 16 of the housing 12 and the outlet 22 can be positioned adjacent to the first end 14 of the housing 12 such that the first working fluid travels along a flow path (represented by arrows 24 in FIGS. 1-7) through the length of the housing 12 between the first and second ends 14, 16 or through substantially the entire length of the housing 12. In other embodiments the inlet 20 and outlet 22 can have other locations along the housing 12 and the flow path 24 of the first working fluid can extend through other portions of the housing 12, or alternatively, through the housing 12 in a different manner.
In some embodiments such as the illustrated embodiment of FIGS. 1-9, the heat exchanger 10 can include a first collection tank 28 secured to the first end 14 of the housing 12 and a second collection tank 30 secured to the second end 16 of the housing 12. As shown in FIG. 3, the first collection tank 20 can include an inlet opening 32 and the second collection tank 30 can include first and second outlet openings 34, 36.
The heat exchanger 10 can also or alternatively include a first header 40 positioned between the first end 14 of the housing 12 and the first collection tank 28 and a second header 42 positioned between the second end 16 of the housing 12 and the second collection tank 30. In some such embodiments, the first header 40 can at least partially enclose a fluid reservoir of the first collection tank 28 and the second header 42 can at least partially enclose a fluid reservoir of the second collection tank 30. In other embodiments, the heat exchanger 10 can include a single header 40 and/or a single collection tank 28 located at one of the first and second ends 14, 16 or at another location on the heat exchanger 10.
In some embodiments, the first and second headers 40, 42 can be substantially similarly configured and can be substantially similarly sized. For example, in the illustrated embodiment of FIGS. 1-9, the first and second headers 40, 42 are substantially interchangeable. In other embodiments, the first and second headers 40, 42 can be differently sized and/or differently configured.
As shown in FIGS. 2-9, the heat exchanger 10 can also include a heat exchanger core 52 including a stack of tubes 56. In the illustrated embodiment, the heat exchanger core 52 includes two rows of seven tubes 56. In other embodiments, the heat exchanger core 52 can include two, three, four, five, six, or more tubes 56 arranged in one, two, three, or more adjacent rows. In still other embodiments, the heat exchanger core 52 can include a bundle of tubes 56, or alternatively, a ring or spiral arrangement of substantially parallel tubes 56. As shown in FIGS. 2-9, opposite ends of the tubes 56 are secured to the first and second headers 40, 42.
The heat exchanger core 54 can also include a number of baffles 58 (e.g., six in the illustrated embodiment of FIGS. 1-9) spaced between the first and second ends 44, 46 of the housing 12 for supporting the tubes 56 and for maintaining a desired spacing between each of the tubes 56. The baffles 58 can also or alternatively define or partially define the flow path 24 of the first working fluid. For example, in the illustrated embodiment of FIGS. 5-7, the flow path 24 of the first working fluid can extend between the inlet and outlet 20, 22 and between the baffles 58 such that the flow path 24 for the first working fluid follows a serpentine path through the heat exchanger core 54 and such that the first working fluid travels across and between the exterior surfaces of all or substantially all of the tubes 56 of the heat exchanger core 54. The flow path 24 for the first working fluid can also or alternatively extend across and between the exterior surfaces of the tubes 56 of the internal bypass 66 so that all or substantially all of the tubes 56 of the heat exchanger core 54 experience the same or similar temperature fluctuations and so that the thermal expansion of each of the tubes 56 is substantially the same as the adjacent tubes 56.
As shown in FIGS. 2 and 4-9, the heat exchanger core 54 can also or alternatively include a heat transfer region 60. The heat transfer region 60 can include one or more of the tubes 56, and each of the tubes 56 in the heat transfer region 60 can include surface augmentations 62 for increasing heat transfer between the first working fluid traveling along the first flow path 24 and a second working fluid (e.g., exhaust gas, water, engine coolant, CO₂, an organic refrigerant, R12, R245fa, air, and the like) traveling along a second flow path (represented by arrows 64 in FIGS. 5-7). In the illustrated embodiment of FIGS. 2 and 4-9, the surface augmentations 62 are corrugated fins extending through the interior of each of the tubes 56 of the heat transfer region 60. In other embodiments, the tubes 56 of the heat transfer region 60 can also or alternatively include other surface augmentations, such as for example, protrusions, recesses, tubulators, etc. located along interior and/or exterior surfaces of the tubes 56 of the heat transfer region 60.
In some embodiments, such as the illustrated embodiments of FIGS. 1-9, the heat exchanger core 54 can also include an internal bypass 66 extending through at least one of the tubes 56 (e.g., three tubes 56 in the embodiment of FIGS. 1-9) and extending through the housing 12 between the first and second headers 40, 42 adjacent to the heat transfer region 60. As shown in FIGS. 2-6, the tubes 56 of the bypass 66 are substantially smooth and are free from heat transfer augmentations and provide a passthrough for the second working fluid such that the second working fluid can bypass the heat transfer region 60.
The tube or tubes 56 of the bypass 66 can also or alternatively be positioned along the flow path 24 of the first working fluid. In some embodiments, the tube or tubes 56 of the bypass 66 can be at least partially insulated and/or can have a thicker outer wall than the tube or tubes 56 of the heat exchange region 60 to prevent and/or reduce the transfer of heat between the first working fluid traveling along the first flow path 24 and the second working fluid traveling through the bypass 66 along the second flow path 64. Alternatively or in addition, the bypass 66 can be configured such that the second working fluid travels at a greater velocity through the tube or tubes 56 of the bypass 66 than the tubes 56 of the heat transfer region 60. For example, as shown in FIGS. 1-9, the bypass 66 includes three tubes 56 and the first pass through the heat transfer region 60 includes seven substantially similarly sized tubes 56. In this manner, while heat transfer can occur between the second working fluid traveling through the tubes 56 of the bypass 66 and the first working fluid traveling across the tubes 56 of the bypass 66, significantly more heat transfer can occur between the second working fluid traveling through the heat transfer region 60 and the first working fluid traveling across the tubes 56 of the heat transfer region 60.
The heat exchanger 10 can also include a valve 70 supported adjacent to a flow-directing wall 74 downstream from the second header 42 for controlling the flow of the second working fluid. In some embodiments such as the illustrated embodiment of FIGS. 1-9, the valve 70 can be supported in the second collection tank 30 along the flow path 64 for the second working fluid and can be moveable between a first position (shown in FIG. 9), in which the valve 70 directs the second working fluid from the bypass 66 along a first or primary pathway 64A of the second flow path 64 into the heat transfer region 60, and a second position (shown in FIG. 8), in which the valve 70 directs the second working fluid out of the second collection tank 30 and away from the heat exchanger 10 along a second or secondary pathway 64B of the second flow path 64.
During operation, the heat exchanger 10 can transfer heat from the second working fluid to the first working fluid. Alternatively, while reference is made herein to transferring heat between two working fluids, in some embodiments of the present invention, the heat exchanger 10 can operate to transfer heat between three or more fluids. In other embodiments, the heat exchanger 10 can operate as a recuperator and can transfer heat from a high temperature location of a heating circuit to a low temperature location of the same heating circuit. In some such embodiments, the heat exchanger 10 can transfer heat from a working fluid traveling through a first portion of the heat transfer circuit to the same working fluid traveling through a second portion of the heat transfer circuit.
With reference to FIG. 5, during normal operation, the second working fluid traveling along the second flow path 64 enters the first collection tank 28 through the inlet opening 32, travels through the first header 40, and through the bypass 66 around the heat transfer region 60 before entering the second collection tank 30 through the second header 42. In this manner, the second working fluid can travel in a first pass through the heat exchanger core 52 along the second flow path 64.
Once the second working fluid is downstream from the second header 42 and/or once the second working fluid enters the second collection tank 30, the valve 70 selectively directs the second working fluid into the heat transfer region 60 or away from the heat exchanger 10. More specifically, when the valve 70 is moved toward the second position (shown in FIG. 8), the valve 70 and the wall 74 prevent the second working fluid from entering the heat transfer region 60 through the second header 42 and direct the second working fluid outwardly through the first outlet opening 34 in the second collection tank 30 and along the secondary pathway 64B.
When the valve 70 is moved toward the first position (shown in FIG. 9), the valve 70 and the wall 74 prevent the second working fluid from exiting the heat exchanger 10 by sealing the first outlet opening 34 in the second collection tank 30 and direct the second working fluid back through the second header 42 and into the heat transfer region 60 along the primary pathway 64A. As shown in FIG. 6, the second working fluid then travels along a second pass through the heat exchanger core 52 along the flow path 64 before passing through the first header 40 and entering the first collection tank 28.
With reference to FIG. 7, from the first collection tank 28, the second working fluid travels around a flow-directing wall 76 before passing back through the first header 40, reentering the heat transfer region 60, and traveling along a third pass through the heat exchanger core 52. As the second working fluid travels along both passes of the flow path 64 through the heat transfer region 60, heat is transferred from the second working fluid to the first working fluid traveling along the flow path 24 through the housing 12. The cooled second working fluid then continues along the second flow path 64 through the second header 42 and out of the second collection tank 30 through the second outlet opening 36.
In the illustrated embodiment of FIGS. 1-9, the heat transfer region 60 has a U-shape such that the second working fluid travels through the heat exchange region 60 along two substantially parallel counter-flow passes (i.e., through a first pass between the second header 42 and the first header 40 and back through a second pass between the first header 40 and the second header 42). In addition, the heat exchange core 52 of the illustrated embodiment of FIGS. 1-9 is configured such that the second working fluid traveling along the flow path 64 travels through the heat exchanger core 52 along a first pass (i.e., through the bypass 66) before traveling along the two additional passes (i.e., through the two passes of the heat exchange region 60) of the heat exchange core 52. In other embodiments, the heat transfer region 60 and the heat exchange core 52 can have other shapes and configurations.
FIGS. 10-14 illustrate an alternate embodiment of a heat exchanger 110 according to the present invention. The heat exchanger 110 shown in FIGS. 10-14 is similar in many ways to the illustrated embodiments of FIGS. 1-9 described above. Accordingly, with the exception of mutually inconsistent features and elements between the embodiment of FIGS. 10-14 and the embodiments of FIGS. 1-9, reference is hereby made to the description above accompanying the embodiments of FIGS. 1-9 for a more complete description of the features and elements (and the alternatives to the features and elements) of the embodiment of FIGS. 10-14. Features and elements in the embodiment of FIGS. 10-14 corresponding to features and elements in the embodiments of FIGS. 1-9 are numbered in the 100 series.
In the illustrated embodiment of FIGS. 10-14, the heat exchanger 110 includes an inlet 120 positioned adjacent to the second end 116 of the housing 112 for receiving a first working fluid and an outlet 122 positioned adjacent to the first end 114 of the housing 112 for dispensing the first working fluid. During operation, the first working fluid travels along a flow path (represented by arrows 124 in FIGS. 11-14) through the length of the housing 112 between the first and second ends 114, 116 and between the baffles 158.
As shown in FIGS. 10-14, the heat exchanger 110 can include a collection tank 128 secured to the first end 114 of the housing 112 and a mounting flange 143 secured to the second end 116 of the housing 112. The heat exchanger 110 can also or alternatively include a first header 140 positioned between the first end 114 of the housing 112 and the collection tank 128 and a second header 142 positioned between the second end 116 of the housing 112 and the mounting flange 143. As shown in FIGS. 10-14, the mounting flange 143 can define first, second, and third openings 144, 146, 148.
While reference is made herein to an embodiment in which a collection tank 128 is secured to one end (i.e., the first end 114) of the housing 112 and a mounting flange 143 is secured to an opposite end (i.e., the second end 116) of the housing 112, in other embodiments, mounting flanges 143 can be secured to both the first and second ends 114, 116 of the housing 112, or alternatively, a collection tank 128 can be secured to the second end 116 of the housing 112 and a mounting flange 143 can be secured to the first end 114 of the housing 112. As shown in FIGS. 10 and 12-14, a valve 170 can be supported adjacent to a flow-directing wall 174 downstream from the mounting flange 143 for controlling the flow of the second working fluid.
With reference to FIG. 12, during normal operation, the second working fluid traveling along the second flow path 164 enters the collection tank 128 through the inlet opening 132, and travels through the first header 140 and through the bypass 166 around the heat transfer region 160 before passing through the first opening 144 in the mounting flange 143. In this manner, the second working fluid can travel in a first pass through the heat exchanger core 152 along the second flow path 164.
Once the second working fluid is downstream from the second header 142 and/or the mounting flange 143, the valve 170 selectively directs the second working fluid into the heat transfer region 160 or away from the heat exchanger 110. More specifically, when the valve 170 is moved toward a second position, the valve 170 and the wall 174 prevent the second working fluid from entering the heat transfer region 160 through the second opening 146 in the mounting flange 143 and direct the second working fluid outwardly away from the heat exchanger 110 and along the secondary pathway (not shown).
When the valve 170 is moved toward the first position, the valve 170 and the wall 174 prevent the second working fluid from exiting the heat exchanger 110 and direct the second working fluid toward the second opening 146 in the mounting flange 143 and into the heat transfer region 160 along the primary pathway 164A. As shown in FIG. 13, the second working fluid then travels along a second pass through the heat exchanger core 152 along the flow path 164 before entering the collection tank 128.
With reference to FIGS. 13 and 14, from the collection tank 128, the second working fluid travels around a flow-directing wall 176 before reentering the heat transfer region 160 and traveling along a third pass through the heat exchanger core 152. As the second working fluid travels through both passes along the flow path 164 through the heat transfer region 160, heat is transferred from the second working fluid to the first working fluid traveling through the housing 112 along the first flow path 124. The second working fluid then continues along the second flow path 164 through the third opening 148 in the second header 142 and away from the heat exchanger 110.
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 are possible.

Claims

1. An exhaust recirculation cooler for transferring heat between engine exhaust and a coolant, the heat exchanger comprising:

a housing having a first end and a second end spaced from the first end;

a heat transfer region extending through the housing and including a plurality of tubes positioned along a flow path for the coolant; and

an internal bypass extending through the housing between the first end and the second end adjacent to the heat transfer region, together, at least one of the plurality of tubes and the internal bypass providing an exhaust flow path through the cooler.

2. The exhaust recirculation cooler of claim 1, wherein the coolant is directed across a wall of the bypass.

3. The exhaust recirculation cooler of claim 1, wherein the exhaust flow path is a first exhaust flow path, and further comprising a second exhaust flow path extending through an other of the plurality of tubes, and a valve located adjacent to the second end of the housing and being moveable relative to the housing to selectively direct the exhaust through the first and second exhaust flow paths.

4. The exhaust recirculation cooler of claim 1, further comprising a header secured to an end of the plurality of tubes and defining an inlet to the heat transfer region, an outlet to the heat transfer region and one of an inlet and an outlet to the bypass.

5. The exhaust recirculation cooler of claim 1, wherein the exhaust flow path includes two passes extending through the housing between the first and second ends in counter flow directions.

6. The exhaust recirculation cooler of claim 1, wherein the exhaust flow path is a first exhaust flow path, and further comprising a second exhaust flow path extending through an other of the plurality of tubes, and a valve located adjacent to an outlet of the bypass and being moveable relative to the housing to selectively direct the exhaust from the first exhaust flow path through the second exhaust flow path and away from the cooler.

7. An exhaust recirculation cooler comprising:

a housing having a first end and a second end spaced from the first end and at least partially enclosing a heat transfer region;

a primary exhaust flow path including two passes extending through the housing between the first and second ends in counter flow directions, at least a portion of the primary exhaust flow path having heat-transfer augmentations and extending through the heat transfer region wherein heat is transferred from exhaust traveling through the primary exhaust flow path to a coolant flow path; and

a secondary exhaust flow path extending through the housing between the first end and the second end and being substantially free from heat transfer augmentations.

8. The exhaust recirculation cooler of claim 7, wherein the heat transfer region includes a plurality of tubes, and further comprising an internal bypass extending through the housing between the first end and the second end adjacent to the heat transfer region.

9. The exhaust recirculation cooler of claim 8, wherein the primary exhaust flow path extends through at least one of the plurality of tubes.

10. The exhaust recirculation cooler of claim 8, wherein the coolant flow path is directed across a wall of the bypass.

11. The heat exhaust recirculation cooler of claim 7, further comprising a heat exchanger core including a plurality of tubes supported in the housing and extending through the heat transfer region, the primary exhaust flow path extending through at least one of the plurality of tubes, and wherein the secondary exhaust flow path extends through an other of the plurality of tubes.

12. The heat exhaust recirculation cooler of claim 7, further comprising a header supported at one end of the housing and at least partially defining an inlet to each of the primary and secondary exhaust flow paths.

13. The exhaust recirculation cooler of claim 7, further comprising a valve located adjacent to the second end of the housing and being moveable relative to the housing to selectively direct the exhaust through the primary and secondary exhaust flow paths.

14. The exhaust recirculation cooler of claim 7, further comprising a header secured to one of the first end and the second end of the housing and defining an inlet to the primary exhaust flow path, an outlet to the primary exhaust flow path, and one of an inlet and an outlet to the secondary exhaust flow path.

15. A method of operating an exhaust recirculation cooler including a housing at least partially defining a heat transfer region, the method comprising the act of:

directing engine exhaust through the housing between first and second ends of the housing around the heat transfer region and back through the heat transfer region.

16. The method of claim 15, further comprising moving a valve relative to the housing to adjust the exhaust flow through the housing.

17. The method of claim 16, wherein moving the valve includes moving the valve from a first position, in which the valve directs the engine exhaust from a bypass extending through the housing between the second end and the first end into the heat transfer region, and a second position, in which the valve directs the engine exhaust from the bypass away from the heat transfer region.

18. The method of claim 15, wherein the heat exchanger includes a header supported in the housing, and wherein directing the engine exhaust through the housing includes directing the exhaust through an inlet of an exhaust flow path defined in the header and directing the engine exhaust through an outlet of the exhaust flow path defined in the header.

19. The method of claim 15, wherein directing the engine exhaust around the heat transfer region includes directing the exhaust through an internal bypass extending through the housing.

20. The method of claim 19, wherein the heat exchanger includes a header supported in the housing, and wherein directing the engine exhaust through the internal bypass includes directing the engine exhaust through an outlet of the internal bypass defined in the header and through an inlet of an exhaust flow path defined in the header.

21. The method of claim 15, wherein directing the engine exhaust through the housing includes directing the engine through two passes extending through the housing between the first and second ends in counter flow directions.

22. A method of operating an exhaust recirculation cooler including a housing having a first end and a second end and at least partially defining a heat transfer region, the method comprising the acts of:

directing engine exhaust along two passes through the heat transfer region in counter flow directions;

transferring heat from the engine exhaust traveling through the heat transfer region to coolant traveling through the heat transfer region; and

directing engine exhaust from the first end of the housing toward the second end of the housing through an internal bypass in the housing and around the heat transfer region.

23. The method of claim 22, further comprising moving a valve relative to the housing to adjust the flow of engine exhaust through the housing.

24. The method of claim 23, wherein moving the valve includes moving the valve from a first position, in which the valve directs the engine exhaust from the bypass into the heat transfer region, and a second position, in which the valve directs the engine exhaust from the bypass away from the heat transfer region.

25. The method of claim 24, wherein the heat exchanger includes a header supported in the housing, and wherein directing the engine exhaust through the internal bypass includes directing the engine exhaust through an outlet of the internal bypass defined in the header and through an inlet of an exhaust flow path defined in the header.