Patent Publication Number: US-2023160647-A1

Title: Variable core heat exchanger with flow control

Description:
BACKGROUND 
     The present disclosure relates to heat exchangers, and in particular to headers for heat exchangers. 
     Heat exchangers are often used to transfer heat between two fluids. For example, on aircraft, heat exchangers are used to transfer heat between a relatively hot air source, e.g., bleed air from a gas turbine engine, and a relatively cool air source, e.g., ram air. 
     SUMMARY 
     In one example, a heat exchanger includes a core. The core includes a first side, a second side opposite the first side, a third side extending from the first side to the second side, a fourth side opposite the third side and extending from the first side to the second side. The core also includes a first layer and a second layer. The first layer includes a first plurality of primary fluid inlets on the first side of the core and a first plurality of primary fluid outlets on the second side of the core. A first plurality of primary fluid passages extends from the first plurality of primary fluid inlets to the first plurality of primary fluid outlets. A first plurality of secondary fluid inlets on the third side of the core and a first plurality of secondary fluid outlets on the fourth side of the core. A first plurality of secondary fluid passages extends from the first plurality of secondary fluid inlets to the first plurality of secondary fluid outlets. The second layer includes a second plurality of primary fluid inlets on the first side of the core and a second plurality of primary fluid outlets on the second side of the core. A second plurality of primary fluid passages extends from the second plurality of primary fluid inlets to the second plurality of primary fluid outlets. The second layer also includes a second plurality of secondary fluid inlets on the third side of the core and a second plurality of secondary fluid outlets on the fourth side of the core. A second plurality of secondary fluid passages extends from the second plurality of secondary fluid inlets to the second plurality of secondary fluid outlets. The heat exchanger also includes a primary fluid header attached to the first side of the core. The primary fluid header includes an inlet, a plenum, and a flow control mechanism within the plenum. The flow control mechanism selectively directs fluid through the first layer, through the second layer, or through both the first layer and the second layer. 
     In another example, a heat exchanger includes a core. The core includes a first layer and a second layer. The first layer includes a first plurality of primary fluid inlets, a first plurality of primary fluid outlets, and a first plurality of primary fluid passages extending from the first plurality of primary fluid inlets to the first plurality of primary fluid outlets. The first layer also includes a first plurality of secondary fluid inlets, a first plurality of secondary fluid outlets, and a first plurality of secondary fluid passages extending from the first plurality of secondary fluid inlets to the first plurality of secondary fluid outlets. The first plurality of secondary fluid passages extends transverse the first plurality of primary fluid passages. The second layer includes a second plurality of primary fluid inlets, a second plurality of primary fluid outlets, and a second plurality of primary fluid passages extending from the second plurality of primary fluid inlets to the second plurality of primary fluid outlets. The second plurality of primary fluid passages extends adjacent the first plurality of primary fluid passages. The second layer also includes a second plurality of secondary fluid inlets, a second plurality of secondary fluid outlets, and a second plurality of secondary fluid passages extending from the second plurality of secondary fluid inlets to the second plurality of secondary fluid outlets. The second plurality of secondary fluid passages extends transverse the second plurality of primary fluid passages. The heat exchanger also includes a primary fluid header attached to the core adjacent the first plurality of primary fluid inlets and the second plurality of primary fluid inlets. The primary fluid header includes an inlet, an outlet, a plenum between the inlet and the outlet, and a flow control mechanism within the plenum. The flow control mechanism selectively directs fluid through the first plurality of primary fluid inlets, through the second plurality of primary fluid inlets, or through both the first plurality of primary fluid inlets and the second plurality of primary fluid inlets. 
     Persons of ordinary skill in the art will recognize that other aspects and embodiments of the present invention are possible in view of the entirety of the present disclosure, including the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic of a perspective view of a heat exchanger. 
         FIG.  2 A  is a schematic diagram of a three-way valve in a first position inside a plenum of a header of the heat exchanger of  FIG.  1   . 
         FIG.  2 B  is a schematic diagram of the three-way valve in a second position inside the plenum of the header of the heat exchanger of  FIG.  1   . 
         FIG.  2 C  is a schematic diagram of the three-way valve in a third position inside the plenum of the header of the heat exchanger in  FIG.  1   . 
         FIG.  3 A  is a schematic diagram of a baffle assembly in a first position inside the plenum of the header of the heat exchanger in  FIG.  1   . 
         FIG.  3 B  is a schematic diagram of the baffle assembly in a second position inside the plenum of the header of the heat exchanger in  FIG.  1   . 
         FIG.  3 C  is a schematic diagram of the baffle assembly in a third position inside the plenum of the header of the heat exchanger in  FIG.  1   . 
         FIG.  4 A  is a schematic diagram of a plate assembly in a first position inside the plenum of the header of the heat exchanger in  FIG.  1   . 
         FIG.  4 B  is a schematic diagram of the plate assembly in a second position inside the plenum of the header of the heat exchanger in  FIG.  1   . 
         FIG.  4 C  is a schematic diagram of the plate assembly in a third position inside the plenum of the header of the heat exchanger in  FIG.  1   . 
     
    
    
     While the above-identified drawing figures set forth one or more embodiments of the invention, other embodiments are also contemplated. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings. Like reference numerals identify similar structural elements. 
     DETAILED DESCRIPTION 
     This disclosure relates to a heat exchanger with a first layer, a second layer, and a header. The first layer is configured to have a higher heat transfer rate than the second layer. The second layer is configured to have less pressure loss and greater efficiency than the first layer. The header includes a flow control mechanism that directs the fluid within the header to the first layer, the second layer, or both the first and second layer. The flow control mechanism enables the heat exchanger to provide a higher rate of heat exchange by directing the flow through the first layer during modes of operation that require high rates of heat exchange, i.e., during the take-off of an aircraft. The flow control mechanism also enables the heat exchanger to provide a higher efficiency heat exchanger by directing the fluid through the second layer during modes of operation that do not require as much heat exchange, i.e., during cruising speeds of an aircraft. The heat exchanger with the flow control mechanism within the header will be discussed with reference to  FIGS.  1 - 4 C  below. 
       FIG.  1    is a schematic of a perspective view of heat exchanger  10 . Heat exchanger  10  includes core  12 , primary fluid header  60  (shown in phantom), and secondary fluid header  80  (shown in phantom). Core  12  includes first side  14 , second side  16 , third side  18 , fourth side  20 , first layer  22 , and second layer  42 . First layer  22  includes first plurality of primary fluid inlets  24  (hereinafter “primary fluid inlets  24 ”), first plurality of primary fluid outlets  26  (hereinafter “primary fluid outlets  26 ”), first plurality of primary fluid passages  28  (hereinafter “primary fluid passages  28 ”), first plurality of secondary fluid inlets  30  (hereinafter “secondary fluid inlets  30 ”), first plurality of secondary fluid outlets  32  (hereinafter “secondary fluid outlets  32 ”), and first plurality of secondary fluid passages  34  (hereinafter “secondary fluid passages  34 ”). Primary fluid passages  28  (shown in phantom) and secondary fluid passages  34  (shown in phantom) can include flow restriction elements  36 . 
     Second layer  42  includes second plurality of primary fluid inlets  44  (hereinafter “primary fluid inlets  44 ”), second plurality of primary fluid outlets  46  (hereinafter “primary fluid outlets  46 ”), second plurality of primary fluid passages  48  (hereinafter “primary fluid passages  48 ”), second plurality of secondary fluid inlets  50  (hereinafter “secondary fluid inlets  50 ”), second plurality of secondary fluid outlets  52  (hereinafter “secondary fluid outlets  52 ”), and second plurality of secondary fluid passages  54  (shown in phantom and hereinafter “secondary fluid passages  54 ”). Primary fluid header  60  includes inlet  62 , plenum  64 , outlet  66 , and flow control mechanism  68 . Secondary fluid header  80  includes inlet  82 , plenum  84 , outlet  86 , and flow control mechanism  68 . 
     Second side  16  is opposite of first side  14 . Third side  18  extends from first side  14  to second side  16 . Fourth side  20  is opposite of third side  18  and extends from first side  14  to second side  16 . Primary fluid inlets  24  are on first side  14  and primary fluid outlets  26  are on second side  16 . Primary fluid passages  28  extend from primary fluid inlets  24  to primary fluid outlets  26 . Secondary fluid inlets  30  are on third side  18  and secondary fluid outlets  32  are on fourth side  20 . Secondary fluid passages  34  extend from secondary fluid inlets  30  to secondary fluid outlets  32 . 
     Primary fluid inlets  44  are on first side  14  in second layer  42  and primary fluid outlets  46  are on second side  16  in second layer  42 . Primary fluid passages  48  extend from primary fluid inlets  44  to primary fluid outlets  46 . Secondary fluid inlets  50  are on third side  18  and secondary fluid outlets  52  are on fourth side  20 . Secondary fluid passages  54  extend from secondary fluid inlets  50  to secondary fluid outlets  52 . 
     First layer  22  has a higher heat transfer rate than second layer  42 . As shown in the example in  FIG.  1   , primary fluid passages  28  of first layer  22  includes a sinusoidal profile as primary fluid passages  28  extend from primary fluid inlets  24  to primary fluid outlets  26 . Additionally, secondary fluid passages  34  include a sinusoidal profile as secondary fluid passages  34  extend from secondary fluid inlets  30  to secondary fluid outlets  32 . The sinusoidal profiles of primary fluid passages  28  and secondary fluid passages  34  increase the surface area between primary fluid passages  28  and secondary fluid passages  34 . The increased surface area between primary fluid passages  28  and secondary fluid passages  34  increases the heat transfer between the fluid within primary fluid passages  28  and the fluid within secondary fluid passages  34 . 
     As shown in  FIG.  1   , primary fluid passages  28  and secondary fluid passages  34  of first layer  42  include flow restriction elements  36  which add resistance to flow through primary fluid passages  28  and secondary fluid passages  34  to increase turbulent flow within primary fluid passages  28  and secondary fluid passages  34 . As shown in  FIG.  1   , flow restriction elements  36  can be protrusions that increase the surface area and increase the restriction to flow through primary fluid passages  28  and secondary fluid passages  34 . In another example, flow restriction elements  36  can be fins, airfoils, columns, or any other shape that increases the surface area and restricts flow through primary fluid passages  28  and secondary fluid passages  34 , and/or a combination thereof any of the suggested shapes. 
     In the example of  FIG.  1   , primary fluid passages  48  in second layer  42  are rectangular as primary fluid passages  48  extend from primary fluid inlets  44  to primary fluid outlets  46  and secondary fluid passages  54  are tubes that extend from secondary fluid inlets  50  to secondary fluid outlets  52  through primary fluid passages  48 . The design of primary fluid passages  48  and secondary fluid passages  54  in second layer  42  minimizes pressure loss within second layer  42  while exchanging heat between the fluid within primary fluid passages  48  and secondary fluid passages  54 . Therefore, first layer  22  has a higher heat transfer rate than second layer  42  while second layer  42  has a lower pressure loss than first layer  22 . 
     Primary fluid header  60  is attached to first side  14  of core  12 . Plenum  64  is between inlet  62  and first side  14  of core  12 . Plenum  64  includes flow control mechanism  68  to direct primary fluid PF through first layer  22 , through second layer  42 , or through both first layer  22  and second layer  42 . Secondary fluid header  80  is attached to third side  18  of core  12 . Plenum  84  is between inlet  82  and third side  18  of core  12 . Plenum  84  also includes flow control mechanism  68  to direct secondary fluid SF through first layer  22 , second layer  42 , and through both first layer  22  and second layer  42 . Primary fluid PF enters primary fluid header  60  at a first temperature and secondary fluid SF enters secondary fluid header  80  at a second temperature higher or lower than the first temperature. 
       FIGS.  2 A- 2 C  will be discussed concurrently.  FIGS.  2 A- 2 C  show a schematic diagram of primary fluid header  60 , plenum  64 , flow control mechanism  68 , first layer  22 , and second layer  42 . In the embodiment of  FIGS.  2 A- 2 C , flow control mechanism  68  comprises three-way valve  90 .  FIG.  2 A  shows three-way valve  90  in a first position.  FIG.  2 B  shows three-way valve  90  in a second position.  FIG.  2 C  shows three-way valve  90  in a third position. Three-way valve  90  includes plate  92 , torsional actuator  100 , and flow separator  102 . Plate  92  includes first side  94 , second side  96 , and window  98 . 
     In the example of  FIGS.  2 A- 2 C , three-way valve  90  is located within plenum  64  between inlet  62  of primary fluid header  60  and first side  14  of core  12  and controls the flow of primary fluid PF through primary fluid header  60 . First side  94  of plate  92  faces inlet  62  of primary fluid header  60  and second side  96  of plate  92  faces first side  14  of core  12 . Window  98  extends through first side  94  and through second side  96 . In the example of  FIGS.  2 A- 2 C , plate  92  is circular and window  98  is a hole through plate  92  that is non-concentric with plate  92 . 
     Torsional actuator  100  is attached to second side  96  of plate  92  and is integrated into flow separator  102 . Torsional actuator  100  rotates plate  92  of flow control mechanism  68  between the first position, the second position, and the third position. Flow separator  102  extends from second side  96  of plate  92  to first side  14  of core  12  between first layer  22  and second layer  42 . Flow separator  102  forms a first channel and a second channel inside primary fluid header  60  downstream from plate  92 . The first channel extends from plate  92  to primary fluid inlets  24  of first layer  22 . The second channel extends from plate  92  to primary fluid inlets  44  of second layer  42 . 
     In the first position, as shown in  FIG.  2 A , window  98  is positioned over the first channel such that plate  92  and window  98  of flow control mechanism  68  fluidically connect inlet  62  of primary fluid header  60  and primary fluid inlets  24  of first layer  22  while closing the second channel and thereby blocking fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  44  of second layer  42 . In the second position, as shown in  FIG.  2 B , window  98  is positioned over the second channel such that plate  92  and window  98  of flow control mechanism  68  fluidically connect inlet  62  of primary fluid header  60  and primary fluid inlets  44  of second layer  42  while blocking fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  24  of first layer  22 . In the third position, as shown in  FIG.  2 C , window  98  is positioned partially over the first channel and partially over the second channel such that plate  92  and window  98  of flow control mechanism  68  fluidically connect inlet  62  of primary fluid header  60  to both primary fluid inlets  24  of first layer  22  and primary fluid inlets  44  of second layer  42 . 
     Flow control mechanism  68  in secondary fluid header  80  can have a configuration similar to primary fluid header  60 . For example, flow control mechanism  68  of secondary fluid header  80  includes three-way valve  90  within plenum  84  between inlet  82  and third side  18  of core  12  to control secondary fluid SF. First side  94  of plate  92  faces inlet  82  of secondary fluid header  80  and second side  96  of plate  92  faces third side  18  of core  12 . Window  98  extends through first side  94  and through second side  96 . In the example of  FIGS.  2 A- 2 C , plate  92  is circular and window  98  is a hole through plate  92  that is non-concentric with plate  92 . 
     Torsional actuator  100  is attached to second side  96  of plate  92  and is integrated into flow separator  102 . Torsional actuator  100  rotates plate  92  of flow control mechanism  68  between the first position, the second position, and the third position. Flow separator  102  extends from second side  96  of plate  92  to third side  18  of core  12  between first layer  22  and second layer  42 . Flow separator  102  forms a first channel and a second channel inside secondary fluid header  80  downstream from plate  92 . The first channel extends from plate  92  to secondary fluid inlets  30  of first layer  22 . The second channel extends from plate  92  to secondary fluid inlets  50  of second layer  42 . 
     In the first position, as shown in  FIG.  2 A , window  98  is positioned over the first channel such that plate  92  and window  98  of three-way valve  90  fluidically connect inlet  82  of secondary fluid header  80  and secondary fluid inlets  30  of first layer  22  while closing the second channel and thereby blocking fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  50  of second layer  42 . In the second position, as shown in  FIG.  2 B , window  98  is positioned over the second channel such that plate  92  and window  98  of three-way valve  90  fluidically connect inlet  82  of secondary fluid header  80  and secondary fluid inlets  50  of second layer  42  while blocking fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  30  of first layer  22 . In the third position, as shown in  FIG.  2 C , window  98  is positioned partially over the first channel and partially over the second channel such that plate  92  and window  98  of three-way valve  90  fluidically connect inlet  82  of secondary fluid header  80  to both secondary fluid inlets  30  of first layer  22  and secondary fluid inlets  50  of second layer  42 . 
       FIGS.  3 A- 3 C  will be discussed concurrently.  FIGS.  3 A- 3 C  show a schematic diagram of primary fluid header  60 , plenum  64 , flow control mechanism  68 , first layer  22 , and second layer  42 . In the embodiment of  FIGS.  3 A- 3 C , flow control mechanism  68  comprises baffle assembly  110 .  FIG.  3 A  shows baffle assembly  110  in a first position.  FIG.  3 B  shows baffle assembly  110  in a second position.  FIG.  3 C  shows baffle assembly  110  in a third position. Baffle assembly  110  includes plate  112 , linear actuator  120 , and hinge  130 . Plate  112  includes base end  114  and distal end  116 . Linear actuator  120  includes rod  122  and linkage arm  124 . 
     In the example of  FIGS.  3 A- 3 C , baffle assembly is located within plenum  64  between inlet  62  of primary fluid header  60  and first side  14  of core  12  and controls the flow of primary fluid PF through primary fluid header  60 . Plate  112  extends from base end  114  to distal end  116 . Base end  114  of plate  112  is connected to first side  14  of core  12  such that plate  112  extends inside plenum  64  from first side  14  of core  12  toward inlet  62  of primary fluid header  60 . Base end  114  of plate  112  is attached to first side  14  of core  12  between first layer  22  and second layer  42  by hinge  130 . Rod  122  is connected to linear actuator  120  and is driven linearly by linear actuator  120 . Linkage arm  124  is attached to rod  122  of linear actuator  120  by a first joint and is attached to distal end  116  of plate  112  by a second joint. As rod  122  of linear actuator  120  extends and retracts within linear actuator  120 , linkage arm  124  rotates plate  112  about hinge  130  to position baffle assembly  110  into the first position, the second position, or the third position. 
     In the first position, as shown in  FIG.  3 A , plate  112  is rotated counterclockwise about hinge  130  until distal end  116  of plate  112  contacts the inside wall of primary fluid header  60  to block second layer  42  from inlet  62  of primary fluid header  60 . In this the first position, plate  112  leaves open primary fluid inlets  24  to fluidically connect inlet  62  of primary fluid header  60  and primary fluid inlets  24  of first layer  22  while plate  112  blocks fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  44  of second layer  42 . In the second position, as shown in  FIG.  3 B , plate  112  is rotated clockwise about hinge  130  until distal end  116  of plate  112  contacts the inside wall of primary fluid header  60  to block first layer  22  from inlet  62  of primary fluid header. In the second position, plate  112  leaves open primary fluid inlets  44  to fluidically connect inlet  62  of primary fluid header  60  and primary fluid inlets  44  of second layer  42  while plate  112  blocks fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  24  of first layer  22 . In the third position, as shown in  FIG.  3 C , plate  112  is rotated normal to first side  14  of core  12  to fluidically connect inlet  62  of primary fluid header  60  to primary fluid inlets  24  of first layer  22  and primary fluid inlets  44  of second layer  42 . 
     Flow control mechanism  68  in secondary fluid header  80  can have a configuration similar to the example of primary fluid header  60  in  FIGS.  3 A- 3 C . For example, flow control mechanism  68  of secondary fluid header  80  includes baffle assembly  110  within plenum  84  between inlet  82  and third side  18  of core  12  to control secondary fluid SF. Baffle assembly  110  includes plate  112 , linear actuator  120 , and hinge  130 . Plate  112  includes base end  114  and distal end  116 . Linear actuator  120  includes rod  122  and linkage arm  124 . Plate  112  extends from base end  114  to distal end  116 . Base end  114  of plate  112  is connected to third side  18  of core  12  such that plate  112  extends inside plenum  64  from third side  18  of core  12  toward inlet  82  of secondary fluid header  80 . Base end  114  of plate  112  is attached to third side  18  of core  12  between first layer  22  and second layer  42  by hinge  130 . Rod  122  is connected to linear actuator  120  and is driven linearly by linear actuator  120 . Linkage arm  124  is attached to rod  122  of linear actuator  120  by a first joint and is attached to distal end  116  of plate  112  by a second joint. As rod  122  of linear actuator  120  extends and retracts within linear actuator  120 , linkage arm  124  rotates plate  112  about hinge  130  to position baffle assembly  110  into the first position, the second position, or the third position. 
     In the first position, as shown in  FIG.  3 A , plate  112  is rotated counterclockwise about hinge  130  until distal end  116  of plate  112  contacts the inside wall of secondary fluid header  80  to block second layer  42  from inlet  82  of secondary fluid header  80 . In this the first position, plate  112  leaves open secondary fluid inlets  30  to fluidically connect inlet  82  of secondary fluid header  80  and secondary fluid inlets  30  of first layer  22  while plate  112  blocks fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  50  of second layer  42 . In the second position, as shown in  FIG.  3 B , plate  112  is rotated clockwise about hinge  130  until distal end  116  of plate  112  contacts the inside wall of secondary fluid header  80  to block first layer  22  from inlet  82  of secondary fluid header  80 . In the second position, plate  112  leaves open secondary fluid inlets  50  to fluidically connect inlet  82  of secondary fluid header  80  and secondary fluid inlets  50  of second layer  42  while plate  112  blocks fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  30  of first layer  22 . In the third position, as shown in  FIG.  3 C , plate  112  is rotated normal to third side  18  of core  12  to fluidically connect inlet  82  of secondary fluid header  80  to secondary fluid inlets  30  of first layer  22  and secondary fluid inlets  50  of second layer  42 . 
       FIGS.  4 A- 4 C  will be discussed concurrently.  FIGS.  4 A- 4 C  show a schematic diagram of primary fluid header  60 , plenum  64 , flow control mechanism  68 , first layer  22 , and second layer  42 . In the embodiment of  FIGS.  4 A- 4 C , flow control mechanism  68  comprises plate assembly  140 .  FIG.  4 A  shows plate assembly  140  in a first position.  FIG.  4 B  shows plate assembly  140  in a second position.  FIG.  4 C  shows plate assembly  140  in a third position. Plate assembly  140  includes plate  142  and linear actuator  144 . Linear actuator  144  includes rod  146 . 
     In the example of  FIGS.  4 A- 4 C , plate assembly  140  is located within plenum  64  between inlet  62  of primary fluid header  60  and first side  14  of core  12  and controls the flow of primary fluid PF through primary fluid header  60 . Plate  142  extends perpendicular first side  14  of core  12 . Linear actuator  144  extends and retracts rod  146 . Rod  146  is attached to plate  142  and connects plate  142  to linear actuator  144  to move plate  142  and put plate assembly  140  in the first position, the second position, or the third position. 
     In the first position, as shown in  FIG.  4 A , linear actuator  144  retracts rod  146  to position plate  142  in front of primary fluid inlets  44  of second layer  42  and block fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  44  while allowing fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  24  of first layer  22 . In second position, as shown in  FIG.  4 B , linear actuator  144  extends rod  146  to position plate  142  in front of primary fluid inlets  24  of first layer  22  and block fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  24  while allowing fluidic communication between inlet  62  of primary fluid header  60  and primary fluid inlets  44  of second layer  42 . In third position, as shown in  FIG.  4 C , linear actuator  144  moves rod  146  to position plate  142  between first layer  22  and second layer  42 . With plate  142  positioned between first layer  22  and second layer  42 , inlet  62  of primary fluid header  60  can fluidically communicate with both primary fluid inlets  24  of first layer  22  and primary fluid inlets  44  of second layer  42 . 
     Flow control mechanism  68  in secondary fluid header  80  can have a configuration similar to primary fluid header  60 . For example, flow control mechanism  68  of secondary fluid header  80  includes plate assembly  140  located within plenum  84  between inlet  82  and third side  18  of core  12  to control secondary fluid SF. Plate assembly  140  includes plate  142  and linear actuator  144 . Linear actuator  144  includes rod  146 . Plate  142  extends perpendicular third side  18  of core  12 . 
     In the first position, as shown in  FIG.  4 A , linear actuator  144  retracts rod  146  to position plate  142  in front of secondary fluid inlets  50  of second layer  42  to block fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  50  of second layer  42  while allowing fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  30  of first layer  22 . In second position, as shown in  FIG.  4 B , linear actuator  144  extends rod  146  to position plate  142  in front of secondary fluid inlets  30  of first layer  22  and block fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  30  of first layer  22  while allowing fluidic communication between inlet  82  of secondary fluid header  80  and secondary fluid inlets  50  of second layer  42 . In third position, as shown in  FIG.  4 C , linear actuator  144  moves rod  146  to position plate  142  between first layer  22  and second layer  42 . With plate  142  positioned between first layer  22  and second layer  42 , inlet  82  of secondary fluid header  80  can fluidically communicate with both secondary fluid inlets  30  of first layer  22  and secondary fluid inlets  50  of second layer  42 . 
     In another example, flow control mechanism  68  within primary fluid header  60  can be three-way valve  90  and flow control mechanism  68  within secondary fluid header  80  can be baffle assembly  110  or plate assembly  140 . Similarly, flow control mechanism  68  within primary fluid header  60  and flow control mechanism  68  within secondary fluid header  80  can be any combination of three-way valve  90 , baffle assembly  110 , and/or plate assembly  140 . In yet another example, heat exchanger  10  can include flow control mechanism  68  within only within primary fluid header  60 . In contrast, heat exchanger  10  can include flow control mechanism  68  within only secondary fluid header  80 . 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A heat exchanger includes a core. The core includes a first side, a second side opposite the first side, a third side extending from the first side to the second side, a fourth side opposite the third side and extending from the first side to the second side. The core also includes a first layer and a second layer. The first layer includes a first plurality of primary fluid inlets on the first side of the core and a first plurality of primary fluid outlets on the second side of the core. A first plurality of primary fluid passages extends from the first plurality of primary fluid inlets to the first plurality of primary fluid outlets. A first plurality of secondary fluid inlets on the third side of the core and a first plurality of secondary fluid outlets on the fourth side of the core. A first plurality of secondary fluid passages extends from the first plurality of secondary fluid inlets to the first plurality of secondary fluid outlets. The second layer includes a second plurality of primary fluid inlets on the first side of the core and a second plurality of primary fluid outlets on the second side of the core. A second plurality of primary fluid passages extends from the second plurality of primary fluid inlets to the second plurality of primary fluid outlets. The second layer also includes a second plurality of secondary fluid inlets on the third side of the core and a second plurality of secondary fluid outlets on the fourth side of the core. A second plurality of secondary fluid passages extends from the second plurality of secondary fluid inlets to the second plurality of secondary fluid outlets. The heat exchanger also includes a primary fluid header attached to the first side of the core. The primary fluid header includes an inlet, a plenum, and a flow control mechanism within the plenum. The flow control mechanism selectively directs fluid through the first layer, through the second layer, or through both the first layer and the second layer. 
     The heat exchanger of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     the first layer has a higher heat transfer rate than the second layer; 
     the flow control mechanism is a three-way valve operating between a first position, a second position, and a third position; 
     the three-way valve in the first position fluidically connects the inlet of the primary fluid header to the first plurality of primary fluid inlets while blocking fluidic communication between the inlet of the primary fluid header and the second plurality of primary fluid inlets, the three-way valve in the second position fluidically connects the inlet of the primary fluid header to the second plurality of primary fluid inlets while blocking fluidic communication between the inlet of the primary fluid header and the first plurality of primary fluid inlets, and the three-way valve in the third position fluidically connects the inlet of the primary fluid header to the first plurality of primary fluid inlets of the first layer and the second plurality of primary fluid inlets; 
     the three-way valve further comprises: a plate, wherein the plate comprises: a first side facing the inlet of the primary fluid header; a second side facing the outlet of the primary fluid header; and a window, wherein the window extends through the first side and the second side of the plate; and a torsional actuator mechanically coupled to the second side of the plate, wherein the torsional actuator rotates the plate to place the three-way valve in the first position, the second position, and the third position, and wherein the window enables fluidic communication between the inlet of the primary fluid header and the first plurality of primary fluid inlets and/or the second plurality of primary fluid inlets; 
     a flow separator within the plenum of the primary fluid header extending between the second side of the flow control mechanism and the core, wherein the flow separator forms a first channel and a second channel inside the primary fluid header downstream from the plate, wherein the first channel extends from the plate to the first plurality of primary fluid inlets, and wherein the second channel extends from the plate to the second plurality of primary fluid inlets; 
     the flow control mechanism is a baffle assembly, and wherein the baffle assembly comprises: a baffle extending from the first side of the core between the first layer and the second layer toward the inlet of the primary fluid header; and an actuator mechanically attached to the baffle to operate the baffle between a first position, a second position, and a third position; 
     the baffle comprises: a base end; and a distal end opposite the base end, wherein a hinge attaches the base end of the baffle to the first side of the core; 
     the actuator comprises: a rod; at least one linkage arm attached to the rod by a first joint and attached to the distal end of the baffle by a second joint; 
     the baffle in the first position fluidically connects the inlet of the primary fluid header to the first plurality of primary fluid inlets while blocking fluidic communication between the inlet of the primary fluid header and the second plurality of primary fluid inlets, the baffle in the second position fluidically connects the inlet of the primary fluid header to the second plurality of primary fluid inlets while blocking fluidic communication between the inlet of the primary fluid header and the first plurality of primary fluid inlets, and the baffle in the third position fluidically connects the inlet of the primary fluid header to the first plurality of primary fluid inlets of the first layer and the second plurality of primary fluid inlets; 
     the flow control mechanism is a plate assembly, and wherein the plate assembly comprises: a plate located between the inlet of the primary fluid header and the first side of the core and extending perpendicular the first plurality of primary fluid inlets and the second plurality of primary fluid inlets; and a linear actuator that moves the plate between a first position, a second position, and a third position; 
     the plate in the first position blocks fluidic communication between the inlet of the primary fluid header and the second plurality of primary fluid inlets while allowing fluid communication between the inlet of the primary fluid header and the first plurality of primary fluid inlets, the plate in the second position blocks fluidic communication between the inlet of the primary fluid header and the first plurality of primary fluid inlets while allowing fluid communication between the inlet of the primary fluid header and the second plurality of primary fluid inlets, and the plate in the third position allows the first plurality of primary fluid inlets and the second plurality of primary fluid inlets to fluidically communicate with the inlet of the primary fluid header; 
     a secondary fluid header attached to the third side of the core, wherein the secondary fluid header comprises: an inlet; a plenum; and a flow control mechanism within the plenum, wherein the flow control mechanism of the secondary fluid header selectively directs fluid through the first layer, through the second layer, or through both the first layer and second layer; 
     the flow control mechanism of the secondary fluid header comprises one of: a three-way valve comprising: a plate, wherein the plate comprises: a first side facing the inlet of the secondary fluid header; a second side facing the third side of the core; and a window extending through the first side and the second side of the plate; and a torsional actuator mechanically coupled to the second side of the plate, wherein the torsional actuator rotates the plate to change the orientation of the window, and wherein the window enables fluidic communication between the inlet of the secondary fluid header and the first plurality of secondary fluid inlets and/or the second plurality of secondary fluid inlets; a baffle assembly comprising: a baffle extending from the third side of the core between the first layer and the second layer toward the inlet of the secondary fluid header and an actuator mechanically attached to the baffle to actuate the baffle, wherein baffle comprises a base end opposite a distal end, wherein a hinge attaches the base end of the baffle to the first side of the core, and wherein the actuator comprises at least one linkage arm attached to the distal end of the baffle; and a plate assembly comprising: a plate located between the inlet of the secondary fluid header and the third side of the core extending perpendicular third side of the core and an actuator that moves the plate, wherein the flow control mechanism of the secondary fluid header operates between a first position, a second position, and a third position; and/or 
     the flow control mechanism of the secondary fluid header in the first position fluidically connects the inlet of the secondary fluid header to the first plurality of secondary fluid inlets while blocking fluidic communication between the inlet of the secondary fluid header and the second plurality of secondary fluid inlets, the flow control mechanism in the second position fluidically connects the inlet of the secondary fluid header to the second plurality of secondary fluid inlets and blocks fluidic communication between the inlet of the secondary fluid header and the first plurality of secondary fluid inlets, and second control mechanism in the third position fluidically connects the inlet of the primary fluid header to the first plurality of secondary fluid inlets and the second plurality of secondary fluid inlets. 
     A heat exchanger includes a core. The core includes a first layer and a second layer. The first layer includes a first plurality of primary fluid inlets, a first plurality of primary fluid outlets, and a first plurality of primary fluid passages extending from the first plurality of primary fluid inlets to the first plurality of primary fluid outlets. The first layer also includes a first plurality of secondary fluid inlets, a first plurality of secondary fluid outlets, and a first plurality of secondary fluid passages extending from the first plurality of secondary fluid inlets to the first plurality of secondary fluid outlets. The first plurality of secondary fluid passages extends transverse the first plurality of primary fluid passages. The second layer includes a second plurality of primary fluid inlets, a second plurality of primary fluid outlets, and a second plurality of primary fluid passages extending from the second plurality of primary fluid inlets to the second plurality of primary fluid outlets. The second plurality of primary fluid passages extends adjacent the first plurality of primary fluid passages. The second layer also includes a second plurality of secondary fluid inlets, a second plurality of secondary fluid outlets, and a second plurality of secondary fluid passages extending from the second plurality of secondary fluid inlets to the second plurality of secondary fluid outlets. The second plurality of secondary fluid passages extends transverse the second plurality of primary fluid passages. The heat exchanger also includes a primary fluid header attached to the core adjacent the first plurality of primary fluid inlets and the second plurality of primary fluid inlets. The primary fluid header includes an inlet, an outlet, a plenum between the inlet and the outlet, and a flow control mechanism within the plenum. The flow control mechanism selectively directs fluid through the first plurality of primary fluid inlets, through the second plurality of primary fluid inlets, or through both the first plurality of primary fluid inlets and the second plurality of primary fluid inlets. 
     The heat exchanger of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     the first layer has a greater heat transfer rate than the second layer; 
     the first primary fluid passages and the first secondary fluid passages are sinusoidal, and wherein the first primary fluid passages and the first secondary fluid passages comprise flow restriction elements that increase the heat transfer rate between the first primary fluid passages and the first secondary fluid passages; 
     the flow control mechanism of the primary fluid header comprises one of the following: a three-way valve comprising: a plate, wherein the plate comprises: a first side facing the inlet of the primary fluid header; a second side facing the outlet of the primary fluid header; and a window, wherein the window extends through the first side and the second side of the plate; and a torsional actuator mechanically coupled to the plate, wherein the torsional actuator rotates the plate to change the orientation of the window, and wherein the window enables fluidic communication between the inlet of the primary fluid header and the first primary fluid inlets and/or the second primary fluid inlets; a baffle assembly comprising: a baffle extending from the core between the first layer and the second layer toward the inlet of the primary fluid header and an actuator mechanically attached to the baffle to actuate the baffle, wherein the baffle comprises a base end opposite a distal end, wherein a hinge attaches the base end of the baffle to the core, and wherein the actuator comprises at least one linkage arm attached to the distal end of the baffle; and a plate assembly comprising: a plate located between the inlet of the primary header and the core extending perpendicular the first plurality of primary fluid inlets and the second plurality of primary fluid inlets; and an actuator that moves the plate, wherein the flow control mechanism of the primary fluid header operates between a first position, a second position, and a third position; and/or 
     the flow control mechanism in the first position fluidically connects the inlet of the primary fluid header to the first primary fluid inlets while blocking fluidic communication between the inlet of the primary fluid header and the second primary fluid inlets, the flow control mechanism in the second position fluidically connects the inlet of the primary fluid header to the second primary fluid inlets while blocking fluidic communication between the inlet of the primary fluid header and the first primary fluid inlets, and flow control mechanism in the third position fluidically connects the inlet of the primary fluid header to the first primary fluid inlets and the second primary fluid inlets. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.