Patent Publication Number: US-2017363361-A1

Title: Header for a heat exchanger

Description:
BACKGROUND 
     The present disclosure relates to heat exchangers and more particularly, to headers for conveying fluid into and out of heat exchangers. 
     Conventional plate fin heat exchangers are multilayer sandwich layers/cores constructed out of flat sheet metal dividing plates, spacing bars, and two dimensional thin corrugated fins brazed together. The fabrication process is well established and relatively simple. However, the manufacturing simplicity has a negative impact on performance of the heat exchanger (i.e., how well the heat exchanger cools a high-temperature fluid). The integrity of the structure is limited by the strength and quality of the braze joints which may be subject to stress concentration since there is no mechanism to control the size of the corner fillets. Flat geometry of the dividing plates exposed to high pressure causes bending, so thicker plates are used to reduce the stress level, which increase the weight of the heat exchanger. Headers are required to convey hot and cool fluid into and out of the layers of the heat exchangers, but conventional headers add to the pressure drop and may induce large transient thermal stress (due to differences between the heating rate of the headers and the heating rate of the heat exchanger). Further, conventional headers do not increase heat transfer between the hot and the cool fluid. Such conventional systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved heat exchangers and for improved headers for conveying hot and cool fluids to those heat exchangers. 
     SUMMARY 
     A heat exchanger includes a first core with a first end and a second end and having a first plurality of hot flow channels fluidly isolated from a first plurality of cool flow channels with the first plurality of hot flow channels and the first plurality of cool flow channels being arranged in a first checkerboard pattern. The heat exchanger also includes a first header connected to the first end of the first core. The first header includes a first hot flow inlet section and a first cool flow outlet section. The first hot inlet section is connected to the first plurality of hot flow channels and has a first curved portion with a first inner hot flow route that is longer than a first outer hot flow route. The first cool flow outlet section is connected to the first plurality of cool flow channels and is fluidly isolated from the hot flow inlet section. 
     Another embodiment of a heat exchanger includes a core with hot flow channels and cool flow channels with the core having a center and outer edges and a first header connected to a first end of the core. The first header includes a hot flow inlet, first hot flow routes, two cool flow outlets distant from one another, and first cool flow routes. The first hot flow routes connect the hot flow channels to the hot flow inlet, with a first plurality of the first hot flow routes connecting the hot flow channels nearer the outer edges of the core to the hot flow inlet and being longer in length than a second plurality of the first hot flow routes that connect the hot flow channels nearer the center of the core to the hot flow inlet. The first cool flow routes connect the cool flow channels to one of the two cool flow outlets, with a first plurality of the first cool flow routes connecting the cool flow channels nearer the outer edges of the core to one of the two cool flow outlets and being shorter in length than a second plurality of the first cool flow routes that connect the cool flow channels nearer the center of the core to one of the two cool flow outlets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic of a heat exchanger. 
         FIG. 1B  is a first cross-sectional schematic of the heat exchanger of  FIG. 1A  taken along line  1 B- 1 B. 
         FIG. 1C  is a second cross-sectional schematic of the heat exchanger of  FIG. 1A  taken along line  1 C- 1 C. 
         FIG. 1D  is a third cross-sectional schematic of the heat exchanger of  FIG. 1A  taken along line  1 D- 1 D. 
         FIG. 1E  is a fourth cross-sectional schematic of the heat exchanger of  FIG. 1A  taken along line  1 E- 1 E. 
         FIG. 1F  is a fifth cross-sectional schematic of the heat exchanger of  FIG. 1A  taken along line  1 F- 1 F. 
         FIG. 2A  is a perspective view of the heat exchanger. 
         FIG. 2B  is a first cross-sectional perspective view of the heat exchanger. 
         FIG. 2C  is a second cross-sectional perspective view of the heat exchanger. 
         FIG. 2D  is a third cross-sectional perspective view of the heat exchanger. 
         FIG. 2E  is a fourth cross-sectional perspective view of the heat exchanger. 
         FIG. 2F  is a fifth cross-sectional perspective view of the heat exchanger. 
         FIG. 2G  is a sixth cross-sectional perspective view of the heat exchanger. 
         FIG. 2H  is a seventh cross-sectional perspective view of the heat exchanger. 
         FIG. 2I  is an eighth cross-sectional perspective view of the heat exchanger. 
         FIG. 2J  is a ninth cross-sectional perspective view of the heat exchanger. 
         FIG. 2K  is a tenth cross-sectional perspective view of the heat exchanger. 
         FIG. 2L  is an eleventh cross-sectional perspective view of the heat exchanger. 
         FIG. 3A  is a schematic of a heat exchanger pair. 
         FIG. 3B  is a first cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 B- 3 B. 
         FIG. 3C  is a second cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 C- 3 C. 
         FIG. 3D  is a third cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 D- 3 D. 
         FIG. 3E  is a fourth cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 E- 3 E. 
         FIG. 3F  is a fifth cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 F- 3 F. 
         FIG. 4  is a schematic of a heat exchanger system with four heat exchangers. 
         FIG. 5  is a schematic of another embodiment of a heat exchanger. 
     
    
    
     DETAILED DESCRIPTION 
     A heat exchanger with headers is disclosed herein that includes a core, which has a plurality of hot flow channels and a plurality of cool flow channels, and a header, which has either a hot flow inlet section with a cool flow outlet section or a hot flow outlet section with a cool flow inlet section. The heat exchanger can include a second header (opposite the first header) having either a hot flow outlet section with a cool flow inlet section or a hot flow inlet section with a cool flow outlet section. The core of the heat exchanger is configured to promote heat transfer between a hot fluid and a cool fluid by having the plurality of hot flow channels and the plurality of cool flow channels arranged in a checkboard pattern with each of the plurality of hot flow channels being surrounded by some of the plurality of cool flow channels. The plurality of hot flow channels and the plurality of cool flow channels can each have varying cross-sectional flow areas to promote heat transfer. The first header connects the hot flow inlet to the core and the cool flow outlet to the core, and the second header connects the cool flow inlet to the core and hot flow outlet to the core. Each header is arranged in an alternating hot-cool flow path orientation (that transitions the flow from a singular channel inlet or outlet to the checkerboard pattern of the core) so the change in temperature of the headers along a hot/cool flow path is gradual, reducing thermal expansion issues that can be caused by a sudden increase (or decrease) in temperature along a flow path. Further, the headers have a curved portion along each of the hot flow paths and the cool flow paths and the longer inlet flow paths connect to the shorter outlet flow paths such that the total flow path and the pressure drop between each inlet and outlet is nearly equal. 
     Other embodiments of the heat exchanger can include multiple cores and multiple headers arranged in parallel with one hot flow inlet providing hot fluid to two different headers that each have curved portions (that, in turn, provide hot fluid to two cores), with one cool flow inlet providing cool flow to two different headers that each have curved portions, with one hot flow outlet connected to two different headers that each have curved portions, and with one cool flow outlet connected to two different headers that each have curved portions. 
     The heat exchanger disclosed herein has numerous benefits. The core having a checkerboard pattern with varying cross-sectional flow areas can be arranged in a counter-flow configuration (i.e., the cool flow is in an opposite direction than the hot flow) that improves heat transfer across the entire length of the core, which increases the heat exchanger effectiveness for a given overall heat transfer area. The counter-flow configuration reduces the temperature differential across the heat exchanger because the cool flow outlet is aligned with the hot flow inlet in the first header (and vice versa in the second header). Further, the checkboard pattern increases the heat transfer surface area in the heat exchanger, which increases the efficiency and limits the need to use fins or other projections into the flow path. The checkerboard pattern enables optimization of high pressure channel shape (e.g., circular instead of rectangular) such that the stress from the pressure of the hot or cool fluid is minimized. The alternating hot-cool flow orientation created by the headers gradually integrates the counter-flow hot and cool routes such that the increase in temperature of the header is gradual, reducing thermal expansion issues and stresses that can result from a sudden increase (or decrease) in temperature along a flow path. The orientation of the curved headers balances out the flow length of each of the hot and cool flow paths so that the pressure drop across the heat exchanger is the same in all flow paths. After reviewing the description and corresponding figures below, these and other benefits will be realized. 
       FIG. 1A  is a schematic of a heat exchanger,  FIG. 1B  is a first cross-sectional schematic of the heat exchanger taken along line  1 B- 1 B,  FIG. 1C  is a second cross-sectional schematic of the heat exchanger taken along line  1 C- 1 C,  FIG. 1D  is a third cross-sectional schematic of the heat exchanger taken along line  1 D- 1 D,  FIG. 1E  is a fourth cross-sectional schematic of the heat exchanger taken along line  1 E- 1 E, and  FIG. 1F  is a fifth cross-sectional schematic of the heat exchanger taken along line  1 F- 1 F. 
     Heat exchanger  20  includes core  22 , first header  24 , second header  26 , hot flow inlet  28 , hot flow outlet  30 , cool flow inlet  32 , and cool flow outlet  34 . Core  22  includes first end  40 , second end  42 , center  44 , outer edges  46 , a plurality of hot flow channels  48 , a plurality of cool flow channels  50 , and checkerboard pattern  52 . First header  24  includes first hot flow inlet section  60 , first curved portion  62 , first inner hot flow route  64 , first outer hot flow route  66 , and first hot flow inlet section layers  68 . First header  24  also includes first cool flow outlet section  70 , second curved portion  72 , first inner cool flow route  74 , first outer cool flow route  76 , and first cool flow outlet section layers  78 . Second header  26  includes first hot flow outlet section  80 , third curved portion  82 , second inner hot flow route  84 , second outer hot flow route  86 , and first hot flow outlet section layers  88 . Second header  26  also includes first cool flow inlet section  90 , fourth curved portion  92 , second inner cool flow route  94 , second outer cool flow route  96 , and first cool flow inlet section layers  98 . Between hot flow inlet  28  and hot flow outlet  30  are a plurality of hot flow paths  100 , and between cool flow inlet  32  and cool flow outlet  34  are a plurality of cool flow paths  102 . 
     Heat exchanger  20  can be as large or small as necessary, depending on the thermal exchange needs and the environment in which heat exchanger  20  is present (i.e., what type of engine/machine heat exchanger  20  is a part of, such as a gas turbine engine, electronics, etc.). Further, heat exchanger  20  can be configured to transfer as much or as little thermal energy as desired. While heat exchanger  20  is described as utilizing hot and cool fluid flowing through the plurality of hot flow paths  100  (the entire flow paths between hot flow inlet  28  and hot flow outlet  30 ) and the plurality of cool flow paths  102  (the entire flow paths between cool flow inlet  32  and cool flow outlet  34 ), respectively, the fluids can be air, another type of gas, or a liquid, such as cooling lubricant or water. Also, while heat exchanger  20  is described with regards to two different flow paths (the plurality of hot flow paths  100  between hot flow inlet  28  and hot flow outlet  30  and the plurality of cool flow paths  102  between cool flow inlet  32  and cool flow outlet  34 ), the temperature of the fluid flowing through heat exchanger  20  is arbitrary in that the temperature of the fluid flowing through heat exchanger  20  can be any temperature. For example, the fluid flowing into hot flow inlet  28  can be at a cooler temperature than the fluid flowing into cool flow inlet  32 . 
     As described below, multiple heat exchangers  20  can be utilized in parallel, and multiple heat exchangers  20  can be incorporated into one another such that hot flow inlet  28 , hot flow outlet  30 , cool flow inlet  32 , and cool flow outlet  34  provide hot and cool flow to multiple heat exchangers  20 . Heat exchanger  20  can be one continuous and monolithic piece, or each component of heat exchanger  20  can be multiple pieces fastened to one another. Heat exchanger  20  can be formed through a variety of manufacturing processes, such as forming pieces separately and fastening those pieces together or constructing all or parts of heat exchanger  20  through additive manufacturing. Heat exchanger  20  can be constructed from a variety of materials, including plastic, metal, an alloy, or another material. However, constructing heat exchanger  20  from a thermally conductive material may be beneficial to promote the transfer of thermal energy from the hot fluid to the cool fluid. In one embodiment, the disclosed heat exchanger  20  is constructed from a nickel-based alloy. 
     Core  22  of heat exchanger  20  has checkerboard pattern  52  made up of the plurality of hot flow channels  48  and the plurality of cool flow channels  50 . Core  22  can be any size and shape, but core  22  in the disclosure is approximately a rectangular cuboid between first end  40  and second end  42 . Core  22  has outer edges  46  and center  44  (shown in  FIG. 1C ), with outer edges  46  being outer walls when viewed perpendicular to the plurality of hot flow channels  48  and the plurality of cool flow channels  50  and center  44  being at an internal location when viewed perpendicular to the plurality of hot flow channels  48  and the plurality of cool flow channels  50 . The hot flow channels near center  44  are adjacent cool flow channels, while the hot flow channels near outer edges  46  are along outer walls and are only adjacent cool flow channels on two sides (when near a corner) or three sides. Core  22  is the primary thermal exchange portion of heat exchanger  20 , and the plurality of hot flow channels  48  and the plurality of cool flow channels  50  can have any configuration in relation to each other. Though, as shown in  FIG. 1D , each of the plurality of hot flow channels  48  is adjacent to and surrounded by some of the plurality of cool flow channels  50  (i.e., alternating hot-cool flow channels) with the flow of hot and cool fluid going in an opposite direction. For example, hot fluid flowing through the plurality of hot flow channels  48  flows from first end  40  to second end  42 , while cool fluid flowing through the plurality of cool flow channels  50  flows from second end  42  to first end  40 . Further, the plurality of hot flow channels  48  and the plurality of cool flow channels  50  within core  22  can be configured such that some of the plurality of cool flow channels  50  are along outer edges  46 , as shown in  FIG. 2L , with the plurality of hot flow channels  48  being closer to center  44 . 
     The plurality of hot flow channels  48  and the plurality of cool flow channels  50  can have a constant and unvaried cross-sectional shape/configuration throughout the length of core  22  between first end  40  and second end  42 . Alternatively, the cross-sectional shape/configuration can be varied, such as a change in the shape of each flow channel (e.g., a flow channel transitioning from a rectangular cross section to a circular cross section), the merging of flow channels (e.g., two flow channels of the plurality of hot flow channels  48  merge to create one flow channel), or another configuration. As shown in  FIGS. 2A-2L , the cross sections of each flow channel of the plurality of hot flow channels  48  and the plurality of cool flow channels  50  of core  22  can vary to transition the plurality of hot flow channels  48  and the plurality of cool flow channels  50  through core  22  from layers at first end  40  connected to first header  24  and at second end  42  connected to second header  26  to checkerboard pattern  52  near a middle of core  22 . The configuration of core  22  can be designed depending on the thermal exchange needs of heat exchanger  20  and the apparatus in which heat exchanger  20  is utilized. 
     Core  22  can be one continuous and monolithic piece, or core  22  can be multiple pieces fastened together, such as each of the plurality of hot flow channels  48  and the plurality of cool flow channels  50  being formed separately and fastened to one another to create checkerboard pattern  52 . Further, core  22  can be integrated into heat exchanger  20  such that heat exchanger  20  is one continuous and monolithic piece. Additive manufacturing may be used to minimize manufacturing tolerances and to ensure walls forming the plurality of hot flow channels  48  and the plurality of cool flow channels  50  are relatively thin, promoting heat transfer. Core  22  can be constructed from the same material as that used in the other components of heat exchanger  20 , or core  22  can be constructed from another material, such as those materials discussed above. 
     First header  24  is connected to first end  40  of core  22  at one end and to hot flow inlet  28  and cool flow outlet  34  at another end. First hot flow inlet section  60  extends between hot flow inlet  28  and the plurality of hot flow channels  48  of core  22  (to form a portion of the plurality of hot flow paths  100  shown in  FIG. 1A ), and first cool flow outlet section  70  extends between the plurality of cool flow channels  50  and cool flow outlet  34  (to form a portion of the plurality of cool flow paths  102  shown in  FIG. 1A ). First header  24  can be one continuous and monolithic piece, or first header  24  can be multiple pieces fastened together, such as first hot flow inlet section  60  and first cool flow outlet section  70  being formed separately and fastened together during the manufacturing process. Further, first header  24  can be integrated into heat exchanger  20  such that heat exchanger  20  is one continuous and monolithic piece. All or part of first header  24  can be constructed using additive manufacturing. 
     First hot flow inlet section  60  is integrated with first cool flow outlet section  70  such that flow routes of each section alternate with each other (i.e., a hot flow route is adjacent to a cool flow route). As shown in  FIGS. 1B and 1C , the flow routes in first hot flow inlet section  60  transition from an open, hot flow inlet  28  to first hot flow inlet section layers  68  (that alternate with first cool flow outlet section layers  78 ), and then to the plurality of hot flow channels  48  that make up checkerboard pattern  52  of core  22 . Similarly, the flow routes in first cool flow outlet section  70  transition from the plurality of cool flow channels  50  that make up checkerboard pattern  52  of core  22  to first cool flow outlet section layers  78  (that alternate with first hot flow inlet section layers  68 ), and then to an open, cool flow outlet  34 . While hot flow inlet  28  and cool flow outlet  34  can be positioned anywhere adjacent to first header  24 ,  FIGS. 1A-1F  show hot flow inlet  28  and cool flow outlet  34  on opposite sides of first header  24 . With such a configuration, multiple heat exchangers  20  can be configured in parallel with adjacent heat exchangers  20  sharing a hot flow inlet  28  and a cool flow outlet  34  (as will be discussed with regards to  FIGS. 3A-3F and 4 ). 
     First hot flow inlet section  60  includes first curved portion  62  that directs hot fluid from hot flow inlet  28  to core  22 . First curved portion  62  is divided into flow routes, with first inner hot flow route  64  being a hot flow route that has the greatest curve (the longest flow route between hot flow inlet  28  and core  22 ) and first outer hot flow route  66  being a hot flow route that does not have a curve or has only a mild curve (the shortest flow route between hot flow inlet  28  and core  22 ). Between first inner hot flow route  64  and first outer hot flow route  66  are other flow routes having lengths that are between a length of the first inner hot flow route  64  and a length of the first outer hot flow route  66 . All of the flow routes through first curved portion  62  of first hot flow inlet section  60  convey hot fluid from hot flow inlet  28  to core  22 . First inner hot flow route  64  is nearest a side opposite hot flow inlet  28 , while first outer hot flow route  66  is the flow route of first curved portion  62  closest to a side nearest hot flow inlet  28 . Along the flow route, first inner hot flow route  64  transitions from the open, hot flow inlet  28  ( FIG. 1B ) to separate layers making up first hot flow inlet section layers  68  ( FIG. 1C ), then to some of the plurality of hot flow channels  48  closest the side opposite hot flow inlet  28  ( FIG. 1D ). Similarly, along the flow route, first outer hot flow route  66  transitions from the open, hot flow inlet  28  ( FIG. 1B ) to separate layers making up first hot flow inlet section layers  68  ( FIG. 1C ), then to some of the plurality of hot flow channels  48  closest to the side nearest hot flow inlet  28  (different flow channels than those which first inner hot flow route  64  transitions to) ( FIG. 1D ). The flow routes between first inner hot flow route  64  and first outer hot flow route  66  make a similar transition, culminating in the plurality of hot flow channels  48  between the two sides of core  22 . 
     First curved portion  62  results in a varied length of the flow routes between hot flow inlet  28  and core  22 . However, as will be described below, the flow routes of third curved portion  82  of first hot flow outlet section  80  of second header  26  also have a varied length, but those lengths balance out the varied lengths of the flow routes of first curved portion  62  such that all of the plurality of hot flow paths  100  are approximately equal in length. The balancing out of the lengths of each of the plurality of hot flow paths  100  is accomplished by third curved portion  82  having flow routes that are the inverse of those in first curved portion  62  (i.e., hot fluid that flows through the longer first outer hot flow route  66  of first curved portion  62  will then flow through the shorter second inner hot flow route  84  (after flowing through core  22 ), and hot fluid that flows through the shorter first inner hot flow route  64  will then flow through the longer second outer hot flow route  86  (after flowing through core  22 )). 
     First cool flow outlet section  70  has a very similar configuration to first hot flow inlet section  60 , except that first cool flow outlet section  70  is mirrored to first hot flow inlet section  60  (i.e., because cool flow outlet  34  (to which first cool flow outlet section  70  is connected) is on an opposite side from hot flow inlet  28 ). First cool flow outlet section  70  is integrated with first hot flow inlet section  60  such that flow routes of each section alternate with each other (i.e., a cool flow route is adjacent to a hot flow route). 
     First cool flow outlet section  70  includes second curved portion  72  that directs cool fluid from core  22  to cool flow outlet  34 . Second curved portion  72  has a similar configuration to first curved portion  62  of first hot flow inlet section  60 , except that second curved portion  72  is mirrored to first curved portion  62 . Second curved portion  72  is divided into flow routes, with first inner cool flow route  74  being a cool flow route that has the greatest curve (the longest flow route between core  22  and cool flow outlet  34 ) and first outer cool flow route  76  being a cool flow route that does not have a curve or has a mild curve (the shortest flow route between core  22  and cool flow outlet  34 ). Between first inner cool flow route  74  and first outer cool flow route  76  are flow routes having lengths that are between a length of the first inner cool flow route  74  and a length of the first outer cool flow route  76 . All of the flow routes through second curved portion  72  of first cool flow outlet section  70  convey cool fluid from core  22  to cool flow outlet  34  because cool fluid in first header  24  flows in an opposite direction than hot fluid. First inner cool flow route  74  is nearest a side opposite cool flow outlet  34 , while first outer cool flow route  76  is the flow route of second curved portion  72  closest to a side nearest cool flow outlet  34 . Along the flow route, first inner cool flow route  74  transitions some of the plurality of cool flow channels  50  closest the side opposite cool flow outlet  34  ( FIG. 1D ) to separate layers making up first cool flow outlet section layers  78  ( FIG. 1C ), then to the open, cool flow outlet  34  ( FIG. 1B ). Similarly, along the flow route, first outer cool flow route  76  transitions from some of the plurality of cool flow channels  50  closest to the side nearest cool flow outlet  34  (different flow channels than those which first inner cool flow route  74  transitioned from) ( FIG. 1C ) to separate layers making up first cool flow outlet section layers  78  ( FIG. 1B ), then to the open, cool flow outlet  34  ( FIG. 1B ). The flow routes between first inner cool flow route  74  and first outer cool flow route  76  make a similar transition from the plurality of cool flow channels  50  between the two ends of core  22  to cool flow outlet  34 . 
     Similarly to first curved portion  62  of first hot flow inlet section  60 , second curved portion  72  of first cool flow outlet section  70  results in a varied length of the flow routes between core  22  and cool flow outlet  34 . However, the flow routes of fourth curved portion  92  of first cool flow inlet section  90  of second header  26  also have a varied length, but those lengths balance out the varied lengths of the flow routes of second curved portion  72  such that all of the plurality of cool flow paths  102  are approximately equal in length. The balancing out of the lengths of each of the plurality of cool flow paths  102  is accomplished by fourth curved portion  92  having flow routes that are the inverse of those in second curved portion  72  (i.e., cool fluid that flows through the shorter first outer cool flow route  76  of second curved portion  72  will have previously flowed through the longer second inner cool flow route  94  (after flowing through core  22 ), and cool fluid that flows through the longer first inner cool flow route  74  will have previously flowed through the shorter second outer cool flow route  96  (after flowing through core  22 )). 
     For at least a portion of first header  24 , first hot flow inlet section layers  68  are alternating with first cool flow outlet section layers  78  ( FIG. 1C ) between core  22  and hot flow inlet  28  and cool flow outlet  34  to provide a gradual heat transfer zone. The alternating hot-cool layers create a decrease in temperature of hot fluid within first hot flow inlet section  60  and the increase in temperature of cool fluid within first cool flow outlet section  70  that is gradual, reducing thermal expansion issues and stresses within first header  24  that can result from a sudden increase or decrease in temperature along the flow paths (which could be present between a nonintegrated header and core  22 ). Further, first hot flow inlet section layers  68  and first cool flow outlet section layers  78  provide a smooth transition from hot flow inlet  28  and core  22  and core  22  and cool flow outlet  34 , respectively, so that the pressure drop across heat exchanger  20  is reduced. 
     Second header  26  has the same configuration as first header  24 , except that the flow of hot fluid is out of core  22  to hot flow outlet  30  and the flow of cool fluid is into core  22  from cool flow inlet  32 . Second header  26  is connected to second end  42  of core  22  at one end and to hot flow outlet  30  and cool flow inlet  32  at another end. First hot flow outlet section  80  extends between the plurality of hot flow channels  48  of core  22  and hot flow outlet  30  (forming a portion of the plurality of hot flow paths  100 ), and first cool flow inlet section  90  extends between cool flow outlet  34  and the plurality of cool flow channels  50  (forming a portion of the plurality of cool flow paths  102 ). Second header  26  can be one continuous and monolithic piece, or second header  26  can be multiple pieces fastened together, such as first hot flow outlet section  80  and first cool flow inlet section  90  being formed separately and fastened together during the manufacturing process. Further, second header  26  can be integrated into heat exchanger  20  such that heat exchanger  20  is one continuous and monolithic piece. All or part of second header  26  can be constructed using additive manufacturing. 
     First hot flow outlet section  80  is similar in configuration to first hot flow inlet section  60 , with first hot flow outlet section  80  conveying hot fluid (which is cooler than when the hot fluid is flowing through first hot flow inlet section  60 ) from the plurality of hot flow channels  48  of core  22  to hot flow outlet  30 . First hot flow outlet section  80  is integrated with first cool flow inlet section  90  such that flow routes of each section alternate with each other (i.e., a hot flow route is adjacent to a cool flow route). As shown in  FIGS. 1D, 1E, and 1F , the flow routes in first hot flow outlet section  80  transition from the plurality of hot flow channels  48  that make up checkerboard pattern  52  of core  22  ( FIG. 1D ) to first hot flow outlet section layers  88  (that alternate with first cool flow inlet section layers  98 ) ( FIG. 1E ), and then to an open, hot flow outlet  30  ( FIG. 1F ). Similarly, the flow routes in first cool flow inlet section  90  transition from an open, cool flow outlet  34  ( FIG. 1F ) to first cool flow inlet section layers  98  (that alternate with first hot flow outlet section layers  88 ) ( FIG. 1E ), and then to the plurality of cool flow channels  50  that make up checkerboard pattern  52  of core  22  ( FIG. 1D ). While cool flow inlet  32  and hot flow outlet  30  can be positioned anywhere adjacent to second header  26 ,  FIGS. 1A-1F  show cool flow inlet  32  on an opposite side of second header  26  than hot flow inlet  30 . With such a configuration, multiple heat exchangers  20  can be configured in parallel with adjacent heat exchangers  20  sharing a hot flow outlet  32  and a cool flow inlet  32  (as will be discussed with regards to  FIGS. 3A-3F and 4 ). 
     First hot flow outlet section  80  includes third curved portion  82  divided into flow routes (that correspond to the flow routes of first curved portion  62 ), with second inner hot flow route  84  being a hot flow route that has the greatest curve (the longest flow route between core  22  and hot flow outlet  30 ) and second outer hot flow route  86  being a hot flow route that does not have a curve or has a mild curve (the shortest flow route between core  22  and hot flow outlet  30 ). Between second inner hot flow route  84  and second outer hot flow route  86  are other flow routes having lengths that are between a length of the second inner hot flow route  84  and a length of the second outer hot flow route  86 . All of the flow routes through third curved portion  82  of first hot flow outlet section  80  convey hot fluid from core  22  to hot flow outlet  30 . 
     As mentioned previously, first hot flow outlet section  80  and third curve portion  82  have a configuration similar to first hot flow inlet section  60  and first curved portion  62 , including the configuration of second inner hot flow route  84  (similar to first inner hot flow route  64 ), second outer hot flow route  86  (similar to first outer hot flow route  86 ), and first hot flow outlet section layers  88  (similar to first hot flow inlet section layers  68 ). However, hot flow outlet  30  of second header  26  is located on the opposite side from hot flow inlet  28  of first header  24 , so second inner hot flow route  84  corresponds to first outer hot flow route  66  (i.e., fluid flowing through one will flow through the other) and second outer hot flow route  86  corresponds to first inner hot flow route  64  (i.e., fluid flowing through one will flow through the other). Thus, first outer hot flow route  66  is along the same flow path of the plurality of hot flow paths  100  as second inner hot flow route  84 , and first inner hot flow route  64  is along the same flow path of the plurality of hot flow paths  100  as second outer hot flow route  86  (but a different flow path than first outer hot flow route  66  and second inner hot flow route  84 ). A similar configuration is present for those flow paths therebetween (e.g., a flow route in first hot flow inlet section  60  closer to first outer hot flow route  66  will correspond to a flow route in first hot flow outlet section  80  closer to second inner hot flow route  84 , and similarly for other flow paths). With such a configuration, each flow path of the plurality of hot flow paths  100  will have an approximately equal length between hot flow inlet  28  and hot flow outlet  30 . The curved orientation of first curved portion  62  and third curved portion  82  balance out the length of each flow path of the plurality of hot flow paths  100  so that that the pressure drop across each of the plurality of hot flow paths  100  is approximately equal. 
     First cool flow inlet section  90  is similar in configuration to first cool flow outlet section  70 , with first cool flow inlet section  90  conveying cool fluid (which is cooler than when the cool fluid is flowing through first cool flow outlet section  70 ) from cool flow inlet  32  to the plurality of cool flow channels  50  of core  22 . As shown in  FIGS. 1D, 1E, and 1F , the flow routes in first cool flow inlet section  90  transition from an open, cool flow inlet  32  ( FIG. 1F ) to first cool flow inlet section layers  98  (that alternate with first hot flow outlet section layers  88 ) ( FIG. 1E ), and then to the plurality of cool flow channels  50  that make up checkerboard pattern  52  of core  22  ( FIG. 1D ). 
     First cool flow inlet section  90  includes fourth curved portion  92  divided into flow routes (that correspond to the flow routes of second curved portion  72 ), with second inner cool flow route  94  being a cool flow route that has the greatest curve (the longest flow route between cool flow inlet  32  and core  22 ) and second outer cool flow route  96  being a cool flow route that does not have a curve or has a mild curve (the shortest flow route between cool flow inlet  32  and core  22 ). Between second inner cool flow route  94  and second outer cool flow route  96  are other flow routes having lengths that are between a length of the second inner cool flow route  94  and a length of the second outer cool flow route  96 . All of the flow routes through fourth curved portion  92  of first cool flow inlet section  90  convey cool fluid from cool flow inlet  32  to core  22 . 
     As mentioned previously, first cool flow inlet section  80  and fourth curve portion  92  have a configuration similar to first cool flow outlet section  70  and second curved portion  72 , including the configuration of second inner cool flow route  94  (similar to first inner cool flow route  74 ), second outer cool flow route  96  (similar to first outer cool flow route  76 ), and first cool flow inlet section layers  98  (similar to first cool flow outlet section layers  78 ). However, cool flow inlet  32  of second header  26  is located on the opposite side from cool flow outlet  34  of first header  26 , so second inner cool flow route  94  corresponds to first outer cool flow route  76  (i.e., fluid flowing through one will flow through the other) and second outer cool flow route  96  corresponds to first inner cool flow route  74  (i.e., fluid flowing through one will flow through the other). Thus, first outer cool flow route  76  is along the same flow path of the plurality of cool flow paths  102  as second inner cool flow route  94 , and first inner cool flow route  74  is along the same flow path of the plurality of cool flow paths  102  as second outer cool flow route  96  (but a different flow path than first outer cool flow route  76  and second inner cool flow route  94 ). A similar configuration is present for those flow paths therebetween (e.g., a flow route in first cool flow outlet section  70  closer to first outer cool flow route  76  will correspond to a flow route in first cool flow inlet section  90  closer to second inner cool flow route  94 , and similarly for other flow paths). With such a configuration, each flow path of the plurality of cool flow paths  102  will have an approximately equal length between cool flow inlet  32  and cool flow outlet  34 . The curved orientation of second curved portion  72  and fourth curved portion  92  balance out the length of each flow path of the plurality of cool flow paths  102  so that that the pressure drop across each of the plurality of cool flow paths  102  is approximately equal, minimizing thermal energy transfer issues and increasing the predictability of heat exchanger  20 . Depending on the configuration of heat exchanger  20  and design considerations, the plurality of hot flow paths  100  can have an approximately equal length as the plurality of cool flow paths  102 , or the plurality of hot flow paths  100  can be shorter or longer than the plurality of cool flow paths  102 . 
     Core  22 , first header  24 , and second header  26  of heat exchanger  20  work together to promote thermal energy transfer between the hot fluid and the cool fluid by conveying hot fluid between hot flow inlet  28  and hot flow outlet  30  and cool fluid between cool flow inlet  32  and cool flow outlet  34 . The curved orientation of the plurality of hot flow paths  100  and the plurality of cool flow paths  102  through heat exchanger  20  provides numerous benefits. Each of the plurality of hot flow paths  100  have a length that is approximately equal, resulting in a similar pressure drop across all flow paths of the plurality of hot flow paths  100 . Similarly, each of the plurality of cool flow paths  102  have a length that is approximately equal, resulting in a similar pressure drop across all flow paths of the plurality of cool flow paths  100 . Further, the curved and alternating flow configuration (i.e., the flow of cool fluid through the plurality of cool flow paths  102  is in an opposite direction to the flow of hot fluid through the plurality of hot flow paths  100 ) gradually integrate the plurality of hot flow paths  100  and the plurality of cool flow paths  102  such that the increase in temperature in first header  24  and second header  26  is gradual, reducing thermal expansion issues and stresses that could result throughout heat exchanger  20 . 
     For some applications heat exchanger  20  would be installed entirely within a cool flow duct or flow stream. In that case, first header  24  and second header  26  can be configured such that first cool flow outlet section  70  and first cool flow inlet section  90  do not have second curved portion  72  and fourth curved portion  92 , respectively, such that the flow of cooling fluid through heat exchanger  20  is relatively straight with no curves (as will be described in greater detail in  FIG. 5 ). When heat exchanger  20  has relatively straight cool flow paths of the plurality of cool flow paths  102 , first header  24  could still include first curved portion  62  and second header  26  could still include third curved portion  82 . 
       FIG. 2A-2L  is a series of cross-sectional perspective views of heat exchanger  20  showing the transition of the plurality of hot flow paths  100  and the plurality of cool flow paths  102  from hot flow inlet  28  and cool flow outlet  34 , respectively, to core  22 . 
       FIG. 2A  is a perspective view of heat exchanger  20 . As described above with regards to the schematic of heat exchanger  20 , heat exchanger  20  includes core  22  between first header  24  and second header  26 , with first header  24  connected to hot flow inlet  28  and cool flow outlet  34 , and second header  26  connected to hot flow outlet  30  and cool flow inlet  32 . First header  24  includes first hot flow inlet section  60  with first curved portion  62  (not shown) and first cool flow outlet section  70  with second curved portion  72  (not shown). Second header  26  includes first hot flow outlet section  80  with third curved portion  82  (not shown) and first cool flow inlet section  90  with second curved portion  92  (not shown). Hot flow inlet  28  in  FIG. 2A  is a circular opening that is not yet divided into multiple flow paths of the plurality of hot flow paths  100 . Similarly, cool flow outlet  34  in  FIG. 2A  is a circular opening where the plurality of cool flow paths  102  have converged to form one circular flow path. While heat exchanger  20  of  FIG. 2A-2L  shows hot flow inlet  28  and hot flow outlet  30  having a smaller diameter than cool flow inlet  32  and cool flow outlet  34 , the inlets and outlets can have other sizes and shapes, such as inlets that are larger or smaller than the outlets, inlets and outlets that are noncircular, or other configurations. 
       FIG. 2B  is a first cross-sectional perspective view of heat exchanger  20  showing first cold flow outlet section  70  divided into a number of discrete vertical flow routes. First inner cool flow route  74  is on a side closest to hot flow inlet  28 , while first outer cool flow route  76  is on another side distant from hot flow inlet  28 . Between first inner cool flow route  74  and first outer cool flow route  76  are other cool flow routes. While  FIGS. 2A-2L  show the flow routes of first hot flow inlet section  60  and first cool flow outlet section  70  being divided by walls into separate and discrete paths (e.g., first cool flow outlet section  70  is shown with four flow routes in  FIG. 2B , first hot flow inlet section  60  is shown with three flow routes in  FIG. 2C , etc.), the flow routes of hot flow inlet section  60  and the flow routes of cool flow outlet section  70  do not need to be divided into discrete flow routes by walls. Rather, the flow routes can be connected across the cross section (i.e., no walls between flow routes) and only become discrete flow paths when each flow route transitions to checkerboard pattern  52 . For example, the flow routes of first hot flow inlet section  60  can be connected to one another until the cross section shown in  FIG. 2J  when each of the plurality of hot flow channels  48  become separated by adjacent flow channels of the plurality of cool flow channels  50 . Similarly, the flow routes of first cool flow outlet  70  do not need to be divided into discrete flow routes by walls and can be connected across the cross section (i.e., no walls between flow routes). 
       FIG. 2C  is a second cross-sectional perspective view of heat exchanger  20  showing first hot flow inlet section  60  divided into a number of flow routes. First inner hot flow route  64  is on a side closest to cool flow outlet  34 , while first outer hot flow route  66  is on another side distant from cool flow outlet  34 . Between first inner hot flow route  64  and first outer cool flow route  66  are other cool flow routes. The schematic of  FIG. 1  shows first outer hot flow path  66  and first outer cool flow path  76  as uncurved (i.e., a straight flow path) between hot flow inlet  28  and core  22  and between cool flow outlet  34  and core  22 , but, as shown in  FIGS. 2A-2L , first outer hot flow path  66  and first outer cool flow path  76  can have a slight curve due to hot flow inlet  28  being horizontally offset from core  22  and cool flow outlet  34  being offset from core  22 . A similar configuration can be present with hot flow outlet  30 , cool flow inlet  32 , and header  26 . While first outer hot flow route  66  and first outer cool flow route  76  may have a curve that makes each flow route slightly longer, each flow path of the plurality of hot flow paths  100  and each flow path of the plurality of cool flow paths  102  through heat exchanger  20  will still have approximately the same length as other hot or cool flow paths because second outer hot flow route  86  and second outer cool flow route  96  will also have a slight curve to balance out the lengths of each flow path of the plurality of hot flow paths  100  and each flow path of the plurality of cool flow paths  102 . Heat exchanger  20  can have other configurations, such as a configuration in which hot flow inlet  28  and hot flow outlet  30  are in another horizontal and/or vertical position in relation to core  22 , cool flow inlet  32  and cool flow outlet  34  are in another horizontal and/or vertical position in relation to core  22 , or another configuration. 
       FIG. 2D  is a third cross-sectional perspective view of heat exchanger  20  showing first inner hot flow route  64  and first inner cool flow route  74  beginning to divide into separate layers. First inner hot flow route  64  has a longer flow path than that of first outer hot flow route  66  because first inner hot flow route  64  must connect hot flow inlet  28  on one side to a portion of the plurality of hot flow channels  48  of core  22  that are located on a side of heat exchanger  20  opposite hot flow inlet  28 . Therefore, first inner hot flow route  64  must extend further across first header  24  than first outer hot flow route  66 , which connects hot flow inlet  28  to a portion of the plurality of hot flow channels  48  of core  22  that are located on the same side of heat exchanger  20  as hot flow inlet  28 . Similarly, first inner cool flow route  74  has a longer flow path than that of first outer cool flow route  76  because first inner cool flow route  74  must connect a portion of the plurality of cool flow channels  50  of core  22  that are located on a side of heat exchanger  20  opposite cool flow outlet  34  to cool flow outlet  34 . Therefore, first inner cool flow route  74  must extend further across first header  24  than first outer cool flow route  66 , which connect a portion of the plurality of cool flow channels  50  of core  22  that are located on the same side of heat exchanger  20  as cool flow outlet  34  to cool flow outlet  34 . 
       FIG. 2E  is a fourth cross-sectional perspective view of heat exchanger  20  showing first inner hot flow route  64  and first inner cool flow route  74  beginning to divide into first hot flow inlet section layers  68  and first cool flow outlet section layers  78 , respectively. 
       FIG. 2F  is a fifth cross-sectional perspective view of heat exchanger  20  showing the hot flow routes and the cool flow routes transitioning into first hot flow inlet section layers  68  and first cool flow outlet section layers  78 , respectively, in an alternating layer configuration. The alternating layer configuration of first hot flow inlet section  60  and first cool flow outlet section  70  of first header  24  has first cool flow outlet section layers  78  both on a top and a bottom with first hot flow inlet section layers  68  alternating with first cool flow outlet section layers  78  in a middle. Heat exchanger  20  can have other configurations of first hot flow inlet section layers  68  and first cool flow outlet section layers  78 , such as a configuration in which first hot flow inlet section layers  68  are on the top, on the bottom, or both the top and the bottom (i.e., the inverse of what is shown in  FIG. 2F-2L ) with first cool flow outlet section layers  78  alternating with first hot flow inlet section layers  68  in the middle. 
       FIG. 2G  is a sixth cross-sectional perspective view of heat exchanger  20  showing further developed first hot flow inlet section layers  68  and first cool flow outlet section layers  78 . With the gradual integration of first hot flow inlet section  60  and first cool flow outlet section  70  as shown in  FIGS. 2E-2G , the thermal energy transfer between the hot fluid flowing through first hot flow inlet section  60  and the cool fluid flowing through first cool flow outlet section  70  is gradual to reduce thermal expansion issues and stresses that result if such a gradual transition is not present. 
       FIG. 2H  is a seventh cross-sectional perspective view of heat exchanger  20  showing fully developed first hot flow inlet section layers  68  and first cool flow outlet section layers  78  at a transition point where first header  24  connects to first end  40  of core  22 . At this point, first hot flow inlet section layers  68  span across a total horizontal length of first header  24  and have a vertical height that is constant along the total horizontal length. Similarly, first cool flow outlet section layers  78  span across the total horizontal length of first header  24  and have a vertical height that is constant along the total horizontal length. While the hot flow routes and cool flow routes have only transitioned to first hot flow inlet section layers  68  and first cool flow outlet section layers  78  at the point where first header  24  connected to core  22  (as opposed to transitioning to checkerboard pattern  52 ), first header  24  can be configured such that first header  24  transitions from layers to a fully developed checkerboard pattern  52  (as shown in  FIG. 2I-2L ) entirely within first header  24  instead of partially within core  22 . Further, if desired, core  22  can include only layers instead of transitioning into checkerboard pattern  52 , or core  22  can have another configuration. 
       FIG. 2I  is an eighth cross-sectional perspective view of heat exchanger  20  showing first hot flow inlet section layers  68  beginning to transition from layers having a constant vertical height to discrete flow channels of the plurality of hot flow channels  48 . Such a transition may cause each flow channel of the plurality of hot flow channels  48  and each flow channel of the plurality of cool flow channels  50  to increase or decrease in cross-sectional area, depending on design and/or other considerations. 
       FIG. 2J  is a ninth cross-sectional perspective view of heat exchanger  20  showing the plurality of hot flow paths  100  that are almost transitioned to discrete flow channels of the plurality of hot flow channels  48  within core  22 . At this point, each of the plurality of hot flow channels  48  are adjacent to two hot flow channels of the plurality of hot flow channels  48  and two four cool flow channels of the plurality of cool flow channels  50  of core  22 . The plurality of hot flow channels  48  form an argyle pattern with each of the plurality of hot flow channels  48  having an approximately stretched-diamond (i.e., lozenge) shape. Cool flow channels of the plurality of cool flow channels  50  that are closer to center  44  of core  22  can have a hexagonal shape, while the cool flow channels of the plurality of cool flow channels  50  near outer edge  46  can have a variety of shapes, but may have a shape that ensures core  22  has an approximately rectangular cross section. 
       FIG. 2K  is a tenth cross-sectional perspective view of heat exchanger  20  showing the plurality of hot flow channels  48  of core  22  transitioning such that each has a diamond shape surrounded by the plurality of cool flow channels  50 , with some of the plurality of cool flow channels  50  near center  44  having an octagonal or hexagonal shape. 
       FIG. 2L  is an eleventh cross-sectional perspective view of heat exchanger  20  showing a fully developed checkerboard pattern  52  of core  22  with the plurality of hot flow channels  48  having a quasi-circular/square shape and the plurality of cool flow channels  50  surrounding the plurality of hot flow channels  50 . While  FIG. 2L  shows core  22  with a rectangular cross section, core  22  can have another configuration, such as a circular cross section, a square cross section, an oval cross section, or another shaped cross section. Further, while a portion of the plurality of cool flow channels  50  are on outer edges  46  with no plurality of hot flow channels  48  along outer edges  46 , core  22  can be configured so that some or all of the flow channels along outer edges  46  are hot flow channels. 
     While  FIGS. 2A-2L  show cross sections at various points along first header  24  and core  22 , cross sections at various points along second header  26  and core  22  would be similar with the plurality of hot flow paths  100  transitioning from the plurality of hot flow channels  48  of core  22  to first hot flow outlet section layers  88  of first hot outlet section  80 , and then to hot flow outlet  30 , and the plurality of cool flow paths  102  transitioning from cool flow inlet  32  to first cool flow inlet section layers  98  of first cool flow inlet section  90 , and then to the plurality of cool flow channels  50  of core  22 . Additionally, while heat exchanger  20  in  FIGS. 2A-2L  is shown as only one heat exchanger  20 , multiple heat exchangers can be arranged in parallel such that the cores of each of the multiple heat exchangers are adjacent to one another and adjacent heat exchangers share one hot flow inlet (i.e., one hot flow inlet provides hot fluid to two first headers), one hot flow outlet (i.e., two second headers convey hot fluid from two cores to one hot flow outlet), one cool flow inlet (i.e., one cool flow inlet provides cool fluid to two second headers), and one cool flow outlet (i.e., two first headers convey cool fluid from two cores to one cool flow outlet). A configuration including two heat exchangers in parallel is described with regards to  FIGS. 3A, 3B, 3C, 3D, 3E, and 3F , and a configuration including four heat exchangers in parallel is described with regards to  FIG. 4 . 
       FIG. 3A  is a schematic of a heat exchanger pair,  FIG. 3B  is a first cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 B- 3 B,  FIG. 3C  is a second cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 C- 3 C,  FIG. 3D  is a third cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 D- 3 D,  FIG. 3E  is a fourth cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 E- 3 E, and  FIG. 3F  is a fifth cross-sectional schematic of the heat exchanger pair of  FIG. 3A  taken along line  3 F- 3 F. 
     Heat exchanger pair  110  includes heat exchanger  20  (as discussed with regards to  FIGS. 1A-1F  and  FIGS. 2A-2L ) and heat exchanger  120 . Heat exchanger  20  has the same configuration and includes the same components as those discussed in the previous paragraphs. Similar to heat exchanger  20 , heat exchanger  120  includes core  122 , third header  124 , fourth header  126 , second hot flow inlet  128 , and second cool flow inlet  132 . Heat exchanger  120  shares hot flow outlet  30  and cool flow outlet  34  with heat exchanger  20  such that first header  24  and third header  124  both connect to cool flow outlet  34 , and second header  26  and fourth header  126  both connect to hot flow outlet  30 . Core  122  includes first end  140 , second end  142 , center  144 , outer edges  146 , a plurality of hot flow channels  148 , a plurality of cool flow channels  150 , and checkerboard pattern  152 . Third header  124  includes second hot flow inlet section  160 , fifth curved portion  162 , third inner hot flow route  164 , third outer hot flow route  166 , and second hot flow inlet section layers  168 . Third header  124  also includes second cool flow outlet section  170 , sixth curved portion  172 , third inner cool flow route  174 , third outer cool flow route  176 , and second cool flow outlet section layers  178 . Fourth header  126  includes second hot flow outlet section  180 , seventh curved portion  182 , fourth inner hot flow route  184 , fourth outer hot flow route  186 , and second hot flow outlet section layers  188 . Fourth header  126  also includes second cool flow inlet section  190 , eighth curved portion  192 , fourth inner cool flow route  194 , fourth outer cool flow route  196 , and second cool flow inlet section layers  198 . Between second hot flow inlet  128  and hot flow outlet  30  are a second plurality of hot flow paths  200 , and between second cool flow inlet  132  and cool flow outlet  34  are a second plurality of cool flow paths  202 . 
     The configuration and functionality of heat exchanger  120  is the same as heat exchanger  20 , except that the orientation of heat exchanger  120  mirrors heat exchanger  20  about centerline C (such that first header  24  and third header  124  both connect to cool flow outlet  34  and second header  26  and fourth header  126  both connect to hot flow outlet  28 ). Heat exchanger pair  110  can be separate pieces fastened together, or heat exchanger pair  110  can be one continuous and monolithic piece. Heat exchanger pair  110  can be formed through a variety of manufacturing processes, such as forming pieces separately and fastening those pieces together or constructing all or parts of heat exchanger pair  110  through additive manufacturing. Heat exchanger pair  110  can be constructed from a variety of materials, including plastic, metal, an alloy, or another material. However, it may be beneficial to construct heat exchanger pair  110  from a thermally conductive material to promote the transfer of thermal energy from the hot fluid to the cool fluid. In one embodiment, the disclosed heat exchanger pair  110  is constructed from a nickel-based alloy. The flow of cool fluid through heat exchanger  20  and heat exchanger  120  can be the same (i.e., the same volume, flow rate, etc.) or different depending on the cooling needs and design considerations. 
     With heat exchanger  120  having fifth curved portion  162  (similar to first curve portion  62 ) and seventh curved portion  182  (similar to third curved portion  82 ), the second plurality of hot flow paths  200  through heat exchanger  120  are approximately the same length as the plurality of hot flow paths  100  through heat exchanger  20 , resulting in approximately the same drop in pressure across all hot flow paths of heat exchanger pair  110 . With heat exchanger  120  having sixth curved portion  172  (similar to second curved portion  72 ) and eighth curved portion  192  (similar to fourth curved portion  92 ), the second plurality of cool flow paths  202  through heat exchanger  120  are approximately the same length as the plurality of cool flow paths  102  through heat exchanger  20 , resulting in approximately the same drop in pressure across all cool flow paths of heat exchanger pair  110 . 
     Core  122  is adjacent to core  22  with the second plurality of hot flow channels  148  of core  122  flowing in the same direction as the plurality of hot flow channels  48  of core  22 , and the second plurality of cool flow channels  150  of core  122  flowing in the same direction as the plurality of cool flow channels  50  of core  22 . As shown in  FIG. 3D , core  22  and core  122  can be integrated such that checkerboard pattern  52  and checkerboard pattern  152  are continuous with one another with no dividing characteristics between them, such as having the plurality of cool flow channels  50  of core  22  being adjacent to the second plurality of cool flow channels  150  of core  122 . Rather, a portion of the plurality of hot flow channels  48  are adjacent to a portion of the second plurality of cool flow channels  150  in an alternating pattern, and a portion of the second plurality of hot flow channels  148  are adjacent to a portion of the plurality of hot flow channels  48  in an alternating pattern. 
     Third header  124  of heat exchanger  120  has the same configuration and functionality as first header  24  of heat exchanger  20 , except that the orientation of third header  124  mirrors that of first header  24  about centerline C so that second cool flow outlet section  170  of third header  124  connects core  122  to cool flow outlet  34 . As shown in  FIG. 3B , in heat exchanger pair  110 , both first cool flow outlet section  70  of first header  24  and second cool flow outlet section  170  of third header  124  connect to and convey cool fluid to cool flow outlet  34 . With heat exchanger pair  110  providing cool fluid to cool flow outlet  34 , cool flow outlet  34  can have a larger cross-sectional area (i.e., opening) than if only heat exchanger  20  was conveying cool fluid to cool flow outlet  34 . Further, cool flow outlet  34  can have another configuration/shape, such as a rectangular shape, an oval shape, or another shape. 
     Third header  124  includes second hot flow inlet  128 , which provides hot fluid that needs to be cooled by heat exchanger  120 . As shown in  FIG. 3B , second hot flow inlet  128  is on a side opposite that of hot flow inlet  28  of heat exchanger  20 , but can have the same configuration as hot flow inlet  28 . The hot fluid flowing into heat exchanger  120  from second hot flow inlet  128  can be the same hot fluid as that flowing into heat exchanger  20  from hot flow inlet  28 , or the hot fluid can be a different hot fluid and/or from a different hot fluid source (i.e., a different medium from a different machine or different part of a machine in which heat exchanger pair  110  is located). However, the medium of hot fluid (whether the fluid is a gas or liquid and whether the fluid is the same gas or the same liquid) may need to be the same in both heat exchanger  20  and heat exchanger  120  if both are designed to flow into hot flow outlet  30 . 
     As shown in  FIG. 3C , first hot flow inlet section layers  68  of heat exchanger  20  and second hot flow inlet section layers  168  can be integrated to form continuous layers across the total cross section of heat exchanger pair  110 , and first cool flow outlet section layers  78  of heat exchanger  20  and second cool flow outlet section layers  178  can also be integrated to form continuous layers across the total cross section of heat exchanger pair  110  (continuously across first header  24  and third header  124 ). 
     Fourth header  126  of heat exchanger  120  has the same configuration and functionality as second header  26  of heat exchanger  20 , except that the orientation of fourth header  126  mirrors that of second header  26  about centerline C so that second hot flow outlet section  180  of fourth header  126  connects core  122  to hot flow outlet  30 . In heat exchanger pair  110 , both first hot flow outlet section  80  of second header  26  and second hot flow outlet section  180  of fourth header  126  connect to and convey hot fluid to hot fluid outlet  30 . With heat exchanger pair  110  providing hot fluid to hot fluid outlet  30 , hot fluid outlet  30  can have a larger cross-sectional area (i.e., opening) than if only heat exchanger  20  was conveying hot fluid to hot fluid outlet  30 . Further, hot fluid outlet  30  can have another configuration/shape, such as a rectangular shape, an oval shape, or another shape. 
     Fourth header  126  includes second cool flow inlet  132 , which provides cool fluid that is used to cool the hot fluid flowing through heat exchanger  120 . As shown in  FIG. 3F , second cool flow inlet  132  is on a side opposite that of cool flow inlet  32  of heat exchanger  20 , but can have the same configuration as cool flow inlet  32 . The cool fluid flowing into heat exchanger  120  from second cool flow inlet  132  can be the same cool fluid as that flowing into heat exchanger  20  from cool flow inlet  32 , or the cool fluid can be a different cool fluid and/or from a different cool fluid source (i.e., a different medium from a different machine or different part of a machine in which heat exchanger pair  110  is located). However, the medium of cool fluid (whether the fluid is a gas or liquid and whether the fluid is the same gas or the same liquid) may need to be the same in both heat exchanger  20  and heat exchanger  120  if both are designed to flow into cool flow outlet  34 . 
     As shown in  FIG. 3E  (and similar to  FIG. 3C ), first hot flow outlet section layers  88  of heat exchanger  20  and second hot flow outlet section layers  188  of heat exchanger  120  can be integrated to form continuous layers across the total cross section of heat exchanger pair  110 , and first cool flow inlet section layers  98  of heat exchanger  20  and second cool flow inlet section layers  198  of heat exchanger  120  can also be integrated to form continuous layers across the total cross section of heat exchanger pair  110  (continuously across second header  26  and fourth header  126 ). 
     Heat exchanger  20  and heat exchanger  120  can be configured such that the hot fluid flowing through heat exchanger  20  is kept separate from and does not mix with the hot fluid flowing through heat exchanger  120 . Similarly the cool fluid in heat exchanger  20  and the cool fluid in heat exchanger  120  can be kept separate. Heat exchanger pair  110  can be configured with two hot flow outlets and two cool flow outlets (one for each heat exchanger) and have a wall between heat exchanger  20  and heat exchanger  120 . Further, heat exchanger pair  110  can be configured such that heat exchanger  20  and heat exchanger  120  share a hot flow inlet and a cool flow inlet while each having separate hot flow outlets and cool flow outlets (a configuration that is the inverse of that shown in  FIGS. 3A-3F ). Also, heat exchanger pair  110  can be incorporated into a larger heat exchanging system that includes more than two heat exchangers, as shown in  FIG. 4 . 
       FIG. 4  is a schematic of a heat exchanger system with four heat exchangers. Heat exchanger system  210  includes first heat exchanger  220 , second heat exchanger  320 , third heat exchanger  420 , and fourth heat exchanger  520 . First heat exchanger  220  is similar to heat exchanger  20  described previously, with first heat exchanger  220  having core  222 , first header  224 , and second header  226 . Second heat exchanger  320  is similar to heat exchanger  120  described in regards to  FIGS. 3A-3F , with second heat exchanger  320  having core  322 , first header  324 , and second header  326 . Third heat exchanger  420  is similar to heat exchanger  20  described previously, with third heat exchanger  420  having core  422 , first header  424 , and second header  426 . Fourth heat exchanger  520  is similar to heat exchanger  120  described in regards to  FIGS. 3A-3F , with fourth heat exchanger  520  having core  522 , first header  524 , and second header  526 . 
     On a first end, heat exchanger system  210  has first hot flow inlet  328  (providing hot fluid to first heat exchanger  220 ), second hot flow inlet  428  (providing hot fluid to second heat exchanger  320  and third heat exchanger  420 ), and third hot flow inlet  528  (providing hot fluid to fourth heat exchanger  520 ). Hot flow inlets  328 ,  428 , and  528  provide hot fluid to heat exchanger system  210  in a similar configuration and functionality than those hot flow inlets described previously. Second hot flow inlet  428  can provide an equal amount of hot fluid to each of second heat exchanger  320  and third heat exchanger  420 , or second hot flow inlet  428  can be configured to provide more hot fluid to one than the other. Similarly, on a second end, heat exchanger system  210  has first hot flow outlet  330  (providing an outlet for hot fluid from first heat exchanger  220  and second heat exchanger  320 ) and second hot flow outlet  430  (providing an outlet for hot fluid from third heat exchanger  420  and fourth heat exchanger  420 ). 
     On the second end, heat exchanger  210  has first cool flow inlet  332  (providing cool fluid to first heat exchanger  220 ), second cool flow inlet  432  (providing cool fluid to second heat exchanger  320  and third heat exchanger  420 ), and third cool flow inlet  532  (providing cool fluid to fourth heat exchanger  520 ). Cool flow inlets  332 ,  432 , and  532  provide cool fluid to heat exchanger system  210  in a similar configuration and functionality than those cool flow inlets described previously. Second cool flow inlet  432  can provide an equal amount of cool fluid to each of second heat exchanger  320  and third heat exchanger  420 , or second cool flow inlet  432  can be configured to provide more cool fluid to one than the other. Similarly, on the first end, heat exchanger system  210  has first cool flow outlet  334  (providing an outlet for cool fluid from first heat exchanger  220  and second heat exchanger  320 ) and second cool flow outlet  434  (providing an outlet for cool fluid from third heat exchanger  420  and fourth heat exchanger  420 ). 
     Cores  222 ,  322 ,  422 , and  522  of heat exchanger system  210  can be discrete such that each does not interact with an adjacent core. Alternatively, cores  222 ,  322 ,  422 , and  522  can be integrated such that a checkerboard pattern is continuous along an entire width of heat exchanger system  210  (similar to heat exchanger pair  110 ). Further, cores  222  and  322  can be integrated with one another and cores  422  and  522  can be integrated with one another, or cores  322  and  422  can be integrated with one another while cores  222  and  522  are discrete and do not interact with adjacent cores. 
     The flow paths through each heat exchanger  220 ,  320 ,  420 , and  520  are similar to the flow paths through heat exchanger  20  and heat exchanger  120  described previously, with each of the flow paths having an approximately equal length. Further, the flow layers in first headers  224 ,  324 ,  424 , and  524  can be integrated to form continuous layers across the total cross section of heat exchanger system  210  (continuously across first headers  224 ,  324 ,  424 , and  524 ). Similarly, the flow layers in second headers  226 ,  326 ,  426 , and  526  can be integrated to form continuous layers across the total cross section of heat exchanger system  210  (continuously across second headers  226 ,  326 ,  426 , and  526 ). 
     As with heat exchanger pair  110 , the hot flow paths through heat exchanger system  210  (whether the flow paths are through first heat exchanger  220 , second heat exchanger  320 , third heat exchanger  420 , or fourth heat exchanger  52 ) are approximately equal in length because each heat exchanger includes a curved configuration (with multiple curved portions) similar to first curved portion  62 , second curved portion  72 , third curved portion  82 , and fourth curved portion  92  of heat exchanger  20  (for first heat exchanger  220  and third heat exchanger  420 ) or fifth curved portion  162 , sixth curved portion  172 , seventh curved portion  182 , and eighth curved portion  192  of heat exchanger  120  (for second heat exchanger  320  and fourth heat exchanger  520 ). 
     While heat exchanger system  210  is shown with four heat exchangers  220 ,  320 ,  420 , and  520  in parallel, heat exchanger  210  can be configured to have any number of heat exchangers in parallel with additional heat exchangers similar to heat exchanger  20  and heat exchanger  120  described above being adjacent to either first heat exchanger  220  or fourth heat exchanger  520 . 
       FIG. 5  is a schematic of another embodiment of a heat exchanger pair. Heat exchanger pair  610  is similar to heat exchanger pair  110  of  FIGS. 3A-3F , except that heat exchanger pair  610  has first header  624  and second header  626  with first cool flow outlet section  670  and first cool flow inlet section  690  that do not have curves or a curved portion and allow cool fluid to flow in relatively straight cool flow paths of a plurality of cool flow paths  602  through heat exchanger pair  610 . Heat exchanger pair  610  with straight cool flow paths of the plurality of cool flow paths  602  may be installed entirely within a cool flow duct or flow stream, limiting the need for a smaller, focused cool flow inlet and cool flow outlet. Instead, cool flow inlet  632  and cool flow outlet  634  span the entire width and height of heat exchanger pair  620  (i.e., cool flow inlet  632  and cool flow outlet  634  have the same or a larger cross-sectional area than core  622  of first heat exchanger  620  and core  122  of second heat exchanger  720 ). 
     Heat exchanger pair  610  includes first heat exchanger  620  having first hot flow inlet  628  adjacent first hot flow inlet section  660  with first curved portion  662 , core  622 , and hot flow outlet  630  adjacent first hot flow outlet section  680  with third curved portion  682  (similar to those components of heat exchanger  20  of heat exchanger pair  110  in  FIGS. 3A-3F ). Heat exchanger pair  610  also includes second heat exchanger  720  having second hot flow inlet  728  adjacent second hot flow inlet section  760  with fifth curved portion  762 , core  722 , and hot flow outlet  630  adjacent second hot flow outlet section  780  with seventh curved portion  782  (similar to those components of heat exchanger  120  of heat exchanger pair  110  in  FIGS. 3A-3F ). Core  622 , core  722 , first hot flow inlet  628 , second hot flow inlet  728 , hot flow outlet  630 , first hot flow inlet section  660 , first hot flow outlet section  680 , second hot flow inlet section  760 , and second hot flow outlet section  780  have the same configuration as that of heat exchanger pair  110  in  FIGS. 3A-3F  and convey hot fluid through heat exchanger pair  610  to cool the hot fluid. 
     As mentioned above, first cool flow outlet section  670  and first cool flow inlet section  690  do not have curved portions and allow cool fluid to flow in relatively straight cool flow paths of the plurality of cool flow paths  602  through heat exchanger pair  610 . The cool fluid can be a gas or a liquid depending on the location and cooling requirements of heat exchanger pair  610 . As with other embodiments, heat exchanger pair  610  can include multiple heat exchangers in series or parallel to one another. 
     Heat exchanger  20  (and other embodiments) having first header  24  and second header  26  includes core  22 , which has a plurality of hot flow channels  48  and a plurality of cool flow channels  50 . First header  24  and second header  26  have either a hot flow inlet section  60  with a cool flow outlet section  70  or a hot flow outlet section  80  with a cool flow inlet section  90 . Heat exchanger  20  can include second header  26  (opposite first header  24 ) having either a hot flow outlet section  80  with a cool flow inlet section  90  or a hot flow inlet section  60  with a cool flow outlet section  70 . Core  22  of heat exchanger  20  is configured to promote heat transfer between the hot fluid and the cool fluid by having the plurality of hot flow channels  48  and the plurality of cool flow channels  50  arranged in checkerboard pattern  52  with each of the plurality of hot flow channels  48  being surrounded by cooling flow channels  50 . The plurality of hot flow channels  48  and the plurality of cool flow channels  50  can each have varying cross-sectional flow areas to promote heat transfer. First header  24  connects hot flow inlet  28  to core  22  and cool flow outlet  34  to core  22 . Second header  26  connects cool flow inlet  32  to core  22  and hot flow outlet  30  to the core  22 . Each header is arranged in an alternating hot-cool flow path orientation that transitions the flow from a singular channel inlet or outlet to checkerboard pattern  52  of core  22  so the change in temperature of the headers along a hot-cool flow path  100  and  102  is gradual, reducing thermal expansion issues that can be caused by a sudden increase (or decrease) in temperature along the plurality of flow paths  100  and  102 . Further, first header  24  and second header  26  have curved portion  62 ,  72 ,  82 , and  92  along each of the plurality of hot flow paths  100  and the plurality of cool flow paths  102 , respectively, to make a length of flow equal along each of the plurality of hot flow paths  100  and the plurality of cool flow paths  102  so that the pressure drop across heat exchanger  20  is the same in all flow paths  100  and  102 . 
     Other embodiments of the heat exchanger (heat exchanger pair  110  and heat exchanger system  210 ) can include multiple cores and multiple headers arranged in parallel with one hot flow inlet providing hot fluid to two different headers (that, in turn, provide hot fluid to two cores), with one cool flow inlet providing cool flow to two different headers, with one hot flow outlet connected to two different headers, and with one cool flow outlet connected to two different headers. 
     The heat exchanger disclosed herein has numerous benefits. Core  22  having checkerboard pattern  52  with varying cross-sectional flow areas can be arranged in a counter-flow configuration (i.e., the cool flow is in an opposite direction than the hot flow) that improves heat transfer across the entire length of heat exchanger  20 , which increases the effectiveness of heat exchanger  20  for a given overall heat transfer area. The counter-flow configuration reduces the temperature differential across heat exchanger  20  because cool flow outlet  34  is aligned with hot flow inlet  28  in first header  24  (and vice versa in second header  26 ). Further, checkerboard pattern  52  increases the heat transfer surface area in heat exchanger  20 , which increases the efficiency and limits the need to use fins or other projections into the plurality of hot flow paths  100  and the plurality of cool flow paths  102 . Checkerboard pattern  52  enables optimization of high pressure channel shape (e.g., circular instead of rectangular) such that the stress from the pressure of the hot or cool fluid is minimized. The curved and alternating hot-cool flow orientation created by first header  24  and second header  26  gradually integrate the counter-flow hot and cool routes such that the increase in temperature of first header  24  and second header  26  is gradual, reducing thermal expansion issues and stresses that can result from a sudden increase (or decrease) in temperature along the plurality of hot flow paths  100  and the plurality of cool flow paths  102 . The curved orientation of first header  24  and second header  26  balance out the flow length of each of the plurality of hot flow paths  100  and each of the plurality of cool flow paths  102  so that the pressure drop across heat exchanger  20  is constant along all flow paths. 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A heat exchanger includes a first core with a first end and a second end having a first plurality of hot flow channels fluidly isolated from a first plurality of cool flow channels with the first plurality of hot flow channels and the first plurality of cool flow channels being arranged in a first checkerboard pattern. The heat exchanger also includes a first header connected to the first end of the first core. The first header includes a first hot flow inlet section and a first cool flow outlet section. The first hot inlet section is connected to the first plurality of hot flow channels and has a first curved portion with a first inner hot flow route that is longer than a first outer hot flow route. The first cool flow outlet section is connected to the first plurality of cool flow channels and is fluidly isolated from the hot flow inlet section. 
     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 cool flow outlet section of the first header includes a second curved portion with a first inner cool flow route that is longer than a first outer cool flow route. 
     The first cool flow outlet section of the first header includes a first straight flow portion having a first plurality of cool flow routes. 
     A second header connected to the second end of the first core that includes a first hot flow outlet section connected to the first plurality of hot flow channels with the first hot flow outlet section having a third curved portion with a second inner hot flow route that is longer than a second outer hot flow route, and a first cool flow inlet section connected to the first plurality of cool flow channels with the first cool flow inlet section being fluidly isolated from the first hot flow outlet section. 
     The first cool flow inlet section of the second header includes a fourth curved portion with a second inner cool flow route that is longer than a second outer cool flow route. 
     Each of the hot flow paths is configured so that a pressure drop of a fluid flowing through each of the hot flow paths is equal to one another. 
     The first cool flow inlet section of the second header includes a second straight flow portion having a second plurality of cool flow routes. 
     The first hot flow inlet section, the first plurality of hot flow channels, and the first hot flow outlet section form a plurality of hot flow paths between a hot flow inlet and a hot flow outlet with a length of each of the plurality of hot flow paths being substantially equal to one another. 
     The first hot flow outlet section of the second header is divided into first hot flow outlet section layers and the first cool flow outlet section of the second header is divided into first cool flow inlet section layers, wherein the first hot flow outlet section layers are each adjacent to a corresponding first cool flow inlet section layer within the second header. 
     The first hot flow inlet section has multiple first hot flow inlet section layers and the first cool flow outlet section has multiple first cool flow outlet section layers, wherein the first hot flow inlet section layers are each adjacent to a corresponding first cool flow outlet section layer. 
     A second core adjacent to the first core with the second core having a first end and a second end and a second plurality of hot flow channels fluidly isolated from a second plurality of cool flow channels and the second plurality of hot flow channels and the second plurality of cool flow channels being arranged in a second checkerboard pattern, and a third header connected to the first end of the second core with the first end of the second core being adjacent to the first end of the first core with the third header including a second hot flow inlet section adjacent to the first hot flow inlet section of the first header and the second hot flow inlet section connected to the second plurality of hot flow channels. The second hot flow inlet section also having a fifth curved portion with a third inner hot flow route that is longer than a third outer hot flow route with the third outer hot flow route being adjacent to the first outer hot flow route of the first header. The second header also including a second cool flow outlet section distant from the first cool flow outlet section of the first header, connected to the second plurality of cool flow channels, and being fluidly isolated from the second hot flow inlet section. The second cool flow outlet section also having a sixth curved portion with a third inner cool flow route that is longer than a third outer cool flow route with the third inner cool flow route being adjacent to the first inner cool flow route of the first header. 
     A first hot flow inlet with a first end connected to both of the first hot flow inlet section and the second hot flow inlet section. 
     A fourth header connected to the second end of the second core with the second end of the second core being adjacent to the second end of the first core. The fourth header includes a second hot flow outlet section distant from the first hot flow outlet section of the second header, connected to the second plurality of hot flow channels, and having a seventh curved portion with a fourth inner hot flow route that is longer than a fourth outer hot flow route with the fourth inner hot flow route being adjacent to the second inner hot flow route of the second header. The fourth header also includes a second cool flow inlet section adjacent to the first cool flow inlet section of the second header, connected to the second plurality of cool flow channels, being fluidly isolated from the second hot flow outlet section, and having an eighth curved portion with a fourth inner cool flow route that is longer than a fourth outer cool flow route with the fourth inner cool flow route being adjacent to the second inner cool flow route of the second header. 
     A first cool flow inlet with a first end connected to both the first cool flow inlet section and the second cool flow inlet section. 
     The first checkerboard pattern of the first core and the second checkerboard pattern of the second core are integrated with one another so that a hot flow channel of the first plurality of hot flow channels of the first core is adjacent to a cool flow channel of the second plurality of cool flow channels of the second core. 
     Another embodiment of a heat exchanger includes a core with hot flow channels and cool flow channels with the core having a center and outer edges and a first header connected to a first end of the core. The first header includes a hot flow inlet, first hot flow routes, two cool flow outlets distant from one another, and first cool flow routes. The first hot flow routes connect the hot flow channels to the hot flow inlet, with a first plurality of the first hot flow routes connecting the hot flow channels nearer the outer edges of the core to the hot flow inlet and being longer in length than a second plurality of the first hot flow routes that connect the hot flow channels nearer the center of the core to the hot flow inlet. The first cool flow routes connect the cool flow channels to one of the two cool flow outlets, with a first plurality of the first cool flow routes connecting the cool flow channels nearer the outer edges of the core to one of the two cool flow outlets and being shorter in length than a second plurality of the first cool flow routes that connect the cool flow channels nearer the center of the core to one of the two cool flow outlets. 
     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: 
     A second header connected to a second end of the core. The second header includes two hot flow outlets distant from one another, second hot flow routes connecting the hot flow channels to one of the two hot flow outlets with a first plurality of the second hot flow routes connecting the hot flow channels nearer the outer edges of the core to one of the two hot flow outlets and being shorter in length than a second plurality of the second hot flow routes that connect the hot flow channels nearer the center of the core to one of the two hot flow outlets, a cool flow inlet, and second cool flow routes connecting the cool flow channels to the cool flow inlet with a first plurality of the second cool flow routes connecting the cool flow channels nearer the outer edges of the core to the hot flow inlet and being longer in length than a second plurality of the second cool flow routes that connect the cool flow channels nearer the center of the core to the cool flow inlet. 
     The first hot flow routes, the hot flow channels, and the second hot flow routes form multiple hot flow paths between the hot flow inlet and the two hot flow outlets with a length of each of the multiple hot flow paths being substantially equal to one another. 
     The first cool flow routes, the cool flow channels, and the second cool flow routes form multiple cool flow paths between the two cool flow inlets and the cool flow outlet with a length of each of the multiple cool flow paths being substantially equal to one another. 
     Each of the first hot flow routes of the first header are adjacent to at least one of the first cool flow routes of the first header and each of the second hot flow routes of the second header are adjacent to at least one of the second cool flow routes of the second header. 
     Any relative terms or terms of degree used herein, such as “substantially,” “essentially,” “generally,” “approximately,” and the like should be interpreted in accordance with and subject to any applicable definitions or limits expressly stated herein. In all instances, any relative terms or terms of degree used herein should be interpreted to broadly encompass any relevant disclosed embodiments as well as such ranges or variations as would be understood by a person of ordinary skill in the art in view of the entirety of the present disclosure, such as to encompass ordinary manufacturing tolerance variations; incidental alignment variations; alignment or shape variations induced by thermal, rotational, or vibrational operational conditions; and the like. 
     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.