Patent Publication Number: US-2023144708-A1

Title: Circular crossflow heat exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 16/804,538 filed Feb. 28, 2020, which is a non-provisional application and is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     The present subject matter relates generally to heat exchangers, and more particularly, to a compact heat exchanger with improved heat transfer capability and structural rigidity. 
     BACKGROUND 
     Heat exchangers may be employed in conjunction with thermal management systems for transferring heat between one or more fluids. For example, a first fluid at a relatively high temperature may be passed through a first passageway, while a second fluid at a relatively low temperature may be passed through a second passageway. The first and second passageways may be in thermal contact or close proximity, allowing heat from the first fluid to be passed to the second fluid. Thus, the temperature of the first fluid may be decreased and the temperature of the second fluid may be increased. 
     Conventional heat exchangers include a large number of fluid passageways, each fluid passageway being formed using some combination of plates, bars, foils, fins, manifolds, support structures, mounting flanges, etc. Each of these parts must be individually positioned, oriented, and connected to the supporting structure, e.g., via brazing, welding, or another joining method. The manufacturing time and costs associated with the assembly of such a heat exchanger are very high and the likelihood of fluid leaks between the fluid passageways or from the heat exchanger in general is increased due to the number of joints formed. In addition, manufacturing restrictions limit the number, size, and configuration of heat exchanger features and structural components that may be included in the heat exchanger, e.g., within the fluid passageways. 
     Accordingly, a thermal management system with an improved heat exchanger would be useful. More specifically, a heat exchanger for a thermal management system that is easier to manufacture, is compact and includes features for improved thermal and structural performance would be particularly beneficial. 
     BRIEF DESCRIPTION 
     Aspects and advantages of the disclosure will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the disclosure. 
     In one exemplary embodiment of the present disclosure, a heat exchange module is provided. The heat exchange module includes a first heat exchanging fluid inlet, a first heat exchanging fluid outlet, and a plurality of heat exchange tubes fluidly coupling the first heat exchanging fluid inlet and the first heat exchanging fluid outlet. The plurality of heat exchange tubes defining a plurality of first heat exchanging fluid flow passages of equal length and a plurality of second heat exchanging fluid flow passages of equal hydraulic diameter. The heat exchange module defines a curved closed geometry defining a central axis that extends along the axial direction. 
     In another exemplary aspect of the present disclosure, a heat exchanger defining an axial direction, a radial direction, and a circumferential direction is provided. The heat exchanger includes a plurality of heat exchange modules stacked along the axial direction to define a flow passageway. Each of the plurality of heat exchange modules has a substantially curved closed geometry defining a central axis that extends along the axial direction. Each of the plurality of heat exchange modules includes a first heat exchanging fluid inlet, a first heat exchanging fluid outlet, and a plurality of heat exchange tubes fluidly coupling the first heat exchanging fluid inlet and the first heat exchanging fluid outlet. The plurality of heat exchange tubes define a plurality of first heat exchanging fluid flow passages of equal length and a plurality of second heat exchanging fluid flow passages of equal hydraulic diameter. 
     In still another exemplary aspect of the present disclosure, a method of manufacturing a heat exchanger is provided. The method includes depositing a layer of additive material on a bed of an additive manufacturing machine and selectively directing energy from an energy source onto the layer of additive material to fuse a portion of the additive material and form the heat exchanger defining an axial direction, a radial direction, and a circumferential direction. The heat exchanger including a plurality of heat exchange modules stacked along the axial direction to define a flow passageway. Each of the plurality of heat exchange modules has a substantially curved closed geometry defining a central axis that extends along the axial direction. Each of the plurality of heat exchange modules includes a first heat exchanging fluid inlet, a first heat exchanging fluid outlet, and a plurality of heat exchange tubes fluidly coupling the first heat exchanging fluid inlet and the first heat exchanging fluid outlet. The plurality of heat exchange tubes defining a plurality of first heat exchanging fluid flow passages of equal length and a plurality of second heat exchanging fluid flow passages of equal hydraulic diameter. 
     These and other features, aspects and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures. 
         FIG.  1    provides a top view of a heat exchange module, in accordance with one embodiment of the present disclosure; 
         FIG.  2    provides an isometric view of a plurality of heat exchange modules of  FIG.  1   , in a stacked configuration to form a heat exchanger, in accordance with one embodiment of the present disclosure; 
         FIG.  3    illustrates an enlarged and partial, cross-sectional view of the heat exchanger of  FIG.  2   , in accordance with one embodiment of the present disclosure; 
         FIG.  4    illustrates an enlarged and partial, cross-sectional view of a fluid flow in another embodiment of a heat exchanger, in accordance with one embodiment of the present disclosure; 
         FIG.  5    provides a top view of another embodiment of heat exchange module, in accordance with one embodiment of the present disclosure; 
         FIG.  6    provides a side view of the heat exchange module of  FIG.  5   , in accordance with one embodiment of the present disclosure; 
         FIG.  7    provides an isometric view of a plurality of heat exchange modules of  FIG.  5   , in a stacked configuration to form a heat exchanger, in accordance with one embodiment of the present disclosure; 
         FIG.  8    illustrates an enlarged and partial, cross-sectional view of the heat exchanger of  FIG.  7   , in accordance with one embodiment of the present disclosure; 
         FIG.  9    illustrates an enlarged and partial, cross-sectional view of a fluid flow in another embodiment of a heat exchanger, in accordance with one embodiment of the present disclosure; and 
         FIG.  10    is a method of manufacturing a heat exchanger, in accordance with one embodiment of the present disclosure. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to present embodiments of the disclosure, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the disclosure. As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The terms “forward” and “aft” refer to relative positions within a thermal management system, with forward referring to a position closer to component inlet and aft referring to a position closer to a component exhaust. The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows. Furthermore, as used herein, terms of approximation, such as “approximately,” “substantially,” or “about,” refer to being within a ten percent margin of error. 
     As used herein, a “fluid” may be a gas or a liquid. The present approach is not limited by the types of fluids that are used. In the preferred application, the cooling fluid is air, and the cooled fluid is oil. The present approach may be used for other types of liquid and gaseous fluids, where the cooled fluid and the cooling fluid are the same fluids or different fluids. Other examples of the cooled fluid and the cooling fluid include fuel, hydraulic fluid, combustion gas, refrigerant, refrigerant mixtures, dielectric fluid for cooling avionics or other aircraft electronic systems, water, water-based compounds, water mixed with antifreeze additives (e.g., alcohol or glycol compounds), and any other organic or inorganic heat transfer fluid or fluid blends capable of persistent heat transport at elevated or reduced temperature. 
     The present disclosure is generally directed to a heat exchanger comprised of a plurality of heat exchange modules and a method for additively manufacturing the heat exchanger. The heat exchanger includes one or more heat exchange modules having a substantially curved closed geometry, forming a heat exchanger. The heat exchanger includes a plurality of heat exchange modules, they are configured in a stacked formation. The heat exchanger provides a constant flow path and hydraulic diameter of the flow passages for each of the two fluids, and more particularly the cooled fluid and the cooling fluid, passing therethrough. The design as disclosed provides a more compact and efficient heat exchanger capable of being disposed within a conduit or pipe. 
     Each heat exchange module includes a plurality of heat exchange tubes that form a flow path for a flow of the cooled fluid (high density fluid) that extends from a fluid inlet to a fluid outlet and defines a flow path for the cooling fluid in a cross-flow configuration. The cooled fluid inlet and outlet fluidly couple the heat exchange tubes of adjacent heat exchange modules in a manner to form a flow path for the flow of the cooled fluid and a flow path for the cross-flow fluid flow. 
     Disclosed is an additively manufactured heat exchange module described according to exemplary embodiments of the present subject matter. The heat exchange modules may be used to transfer heat between two or more fluids in any suitable application. For example, the heat exchange modules may be configured for transferring heat from oil to air or between two streams of air within a gas turbine engine. However, it should be appreciated that the heat exchange modules can be configured for receiving any suitable number and type of fluids for use in the heat transfer process, examples of which are described herein. In addition, the concepts and heat exchanging structures disclosed herein could be similarly used in automotive, aviation, maritime, and other industries to assist in heat transfer between fluids. Moreover, the figures illustrate embodiments of the heat exchange module for the purpose of explaining its general operation, but the size, shape, and configuration of the heat exchange modules is not intended to limit the scope of the present subject matter. For example, the size, shape, number, and configuration of fluid passageways may be varied in a manner that maintains the described hydraulic diameter and constant flow path, while remaining within the scope of the present subject matter. 
     In general, the exemplary embodiments of the heat exchange modules and heat exchanger described herein may be manufactured or formed using any suitable process. However, in accordance with several aspects of the present subject matter, the heat exchange modules may be formed using an additive-manufacturing process, such as a 3-D printing process. The use of such a process may allow the heat exchange modules to be formed integrally, as a single monolithic component, or as any suitable number of sub-components or modules to form the heat exchanger. In particular, the manufacturing process may allow the heat exchange modules to be integrally formed and include a variety of features not possible when using prior manufacturing methods. For example, the additive manufacturing methods described herein enable the manufacture of heat exchangers having various features, configurations, thicknesses, materials, densities, fluid passageways, and mounting structures not possible using prior manufacturing methods. Some of these novel features are described herein. 
     As used herein, the terms “additively manufactured” or “additive manufacturing techniques or processes” refer generally to manufacturing processes wherein successive layers of material(s) are provided on each other to “build-up,” layer-by-layer, a three-dimensional component. The successive layers generally fuse together to form a monolithic component which may have a variety of integral sub-components. Although additive manufacturing technology is described herein as enabling fabrication of complex objects by building objects point-by-point, layer-by-layer, typically in a vertical direction, other methods of fabrication are possible and within the scope of the present subject matter. For example, although the discussion herein refers to the addition of material to form successive layers, one skilled in the art will appreciate that the methods and structures disclosed herein may be practiced with any additive manufacturing technique or manufacturing technology. For example, embodiments of the present disclosure may use layer-additive processes, layer-subtractive processes, or hybrid processes. 
     Suitable additive manufacturing techniques in accordance with the present disclosure include, for example, Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), 3D printing such as by inkjets and laserjets, Sterolithography (SLA), Direct Selective Laser Sintering (DSLS), Electron Beam Sintering (EBS), Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), Laser Net Shape Manufacturing (LNSM), Direct Metal Deposition (DMD), Digital Light Processing (DLP), Direct Selective Laser Melting (DSLM), Selective Laser Melting (SLM), Direct Metal Laser Melting (DMLM), and other known processes. 
     The additive manufacturing processes described herein may be used for forming components using any suitable material. For example, the material may be plastic, metal, concrete, ceramic, polymer, epoxy, photopolymer resin, or any other suitable material that may be in solid, liquid, powder, sheet material, wire, or any other suitable form. More specifically, according to exemplary embodiments of the present subject matter, the additively manufactured components described herein may be formed in part, in whole, or in some combination of materials including but not limited to pure metals, nickel alloys, chrome alloys, titanium, titanium alloys, magnesium, magnesium alloys, aluminum, aluminum alloys, and nickel or cobalt based superalloys (e.g., those available under the name Inconel® available from Special Metals Corporation). These materials are examples of materials suitable for use in the additive manufacturing processes described herein, and may be generally referred to as “additive materials.” 
     In addition, one skilled in the art will appreciate that a variety of materials and methods for bonding those materials may be used and are contemplated as within the scope of the present disclosure. As used herein, references to “fusing” may refer to any suitable process for creating a bonded layer of any of the above materials. For example, if an object is made from polymer, fusing may refer to creating a thermoset bond between polymer materials. If the object is epoxy, the bond may be formed by a crosslinking process. If the material is ceramic, the bond may be formed by a sintering process. If the material is powdered metal, the bond may be formed by a melting or sintering process. One skilled in the art will appreciate that other methods of fusing materials to make a component by additive manufacturing are possible, and the presently disclosed subject matter may be practiced with those methods. 
     In addition, the additive manufacturing process disclosed herein allows a single component to be formed from multiple materials. Thus, the components described herein may be formed from any suitable mixtures of the above materials. For example, a component may include multiple layers, segments, or parts that are formed using different materials, processes, and/or on different additive manufacturing machines. In this manner, components may be constructed which have different materials and material properties for meeting the demands of any particular application. In addition, although the components described herein are constructed entirely by additive manufacturing processes, it should be appreciated that in alternate embodiments, all or a portion of these components may be formed via casting, machining, and/or any other suitable manufacturing process. Indeed, any suitable combination of materials and manufacturing methods may be used to form these components. 
     An exemplary additive manufacturing process will now be described. Additive manufacturing processes fabricate components using three-dimensional (3D) information, for example a three-dimensional computer model, of the component. Accordingly, a three-dimensional design model of the component may be defined prior to manufacturing. In this regard, a model or prototype of the component may be scanned to determine the three-dimensional information of the component. As another example, a model of the component may be constructed using a suitable computer aided design (CAD) program to define the three-dimensional design model of the component. 
     The design model may include 3D numeric coordinates of the entire configuration of the component including both external and internal surfaces of the component. For example, the design model may define the body, the surface, and/or internal passageways such as openings, support structures, etc. In one exemplary embodiment, the three-dimensional design model is converted into a plurality of slices or segments, e.g., along a central (e.g., vertical) axis of the component or any other suitable axis. Each slice may define a thin cross section of the component for a predetermined height of the slice. The plurality of successive cross-sectional slices together form the 3D component. The component is then “built-up” slice-by-slice, or layer-by-layer, until finished. 
     In this manner, the components described herein may be fabricated using the additive process, or more specifically each layer is successively formed, e.g., by fusing or polymerizing a plastic using laser energy or heat or by sintering or melting metal powder. For example, a particular type of additive manufacturing process may use an energy beam, for example, an electron beam or electromagnetic radiation such as a laser beam, to sinter or melt a powder material. Any suitable laser and laser parameters may be used, including considerations with respect to power, laser beam spot size, and scanning velocity. The build material may be formed by any suitable powder or material selected for enhanced strength, durability, and useful life, particularly at high temperatures. 
     Each successive layer may be, for example, between about 10 μm and 200 μm, although the thickness may be selected based on any number of parameters and may be any suitable size according to alternative embodiments. Therefore, utilizing the additive formation methods described above, the components described herein may have cross sections as thin as one thickness of an associated powder layer, e.g., 10 μm, utilized during the additive formation process. 
     In addition, utilizing an additive process, the surface finish and features of the components may vary as need depending on the application. For example, the surface finish may be adjusted (e.g., made smoother or rougher) by selecting appropriate laser scan parameters (e.g., laser power, scan speed, laser focal spot size, etc.) during the additive process, especially in the periphery of a cross-sectional layer which corresponds to the part surface. For example, a rougher finish may be achieved by increasing laser scan speed or decreasing the size of the melt pool formed, and a smoother finish may be achieved by decreasing laser scan speed or increasing the size of the melt pool formed. The scanning pattern and/or laser power can also be changed to change the surface finish in a selected area. 
     Notably, in exemplary embodiments, several features of the components described herein were previously not possible due to manufacturing restraints. However, the present inventors have advantageously utilized current advances in additive manufacturing techniques to develop exemplary embodiments of such components generally in accordance with the present disclosure. While the present disclosure is not limited to the use of additive manufacturing to form these components generally, additive manufacturing does provide a variety of manufacturing advantages, including ease of manufacturing, reduced cost, greater accuracy, etc. 
     In this regard, utilizing additive manufacturing methods, even multi-part components may be formed as a single piece of continuous metal, and may thus include fewer sub-components and/or joints compared to prior designs. The integral formation of these multi-part components through additive manufacturing may advantageously improve the overall assembly process. For example, the integral formation reduces the number of separate parts that must be assembled, thus reducing associated time and overall assembly costs. Additionally, existing issues with, for example, leakage, joint quality between separate parts, and overall performance may advantageously be reduced. 
     Also, the additive manufacturing methods described above enable much more complex and intricate shapes and contours of the components described herein. For example, such components may include thin additively manufactured layers and unique fluid passageways with integral collector manifolds. In addition, the additive manufacturing process enables the manufacture of a single component having different materials such that different portions of the component may exhibit different performance characteristics. The successive, additive nature of the manufacturing process enables the construction of these novel features. As a result, the components described herein may exhibit improved heat transfer efficiency and reliability. 
     Referring to  FIGS.  1 - 4   , a heat exchange module  100  will be described according to a first embodiment of the present subject matter. In this regard,  FIG.  1    provides a front view of the heat exchange module  100 .  FIG.  2    illustrates a plurality of the heat exchange modules  100  of  FIG.  1   , assembled in stacked configuration to form a heat exchanger  150 .  FIG.  3    illustrates an enlarged cross-sectional view of the heat exchanger of  FIG.  2   , taken through line  3 - 3  of  FIG.  2   .  FIG.  4    illustrates a fluid flow in a sectional view of an alternate embodiment of the heat exchanger. As illustrated, the heat exchange module  100  generally defines an axial direction A, a radial direction R, and a circumferential direction C. Likewise, the heat exchanger  150  generally defines an axial direction A, a radial direction R, and a circumferential direction C. According to the illustrated embodiment, the heat exchange module  100  and the heat exchanger  150 , generally define a flow passageway  154 , as best illustrated in  FIGS.  2  and  3   , extending along the axial direction A. According to the illustrated embodiment, each of the one or more heat exchange modules  100  defines a substantially curved closed geometry, and more particularly, a circular cross-section defining a central axis  106  ( FIG.  2   ) that extends along the axial direction A. In this manner, the flow passageway  154  is an elongated cylinder and provides the heat exchanger  150  to fit, for example, within or replace and existing pipe or circular conduit to facilitate a heat exchange process. However, it should be appreciated that according to alternative embodiments, the heat exchange module  100  may have any substantially curved closed geometry such as an ellipse, oval, Reuleaux or other curve-linear triangle, etc. For example, the heat exchange module  100  may have a non-circular cross section and may have a curved central axis  106  such that the heat exchange module  100  can fit in non-linear flow paths or conduits. 
     Heat exchanger  150  includes a plurality of heat exchange modules  100  in a stacked configuration to define the flow passageway  154  along the central axis  106 , i.e., the axial direction A in the illustrated embodiment. Each heat exchange module  100  includes a first heat exchanging fluid inlet  110 , that when in a stacked formation to form the heat exchanger  150 , is in fluid communication with an adjacent upstream heat exchange module  100  or a source of heat exchanging fluid (not shown). In addition, each heat exchange module  100  includes a first heat exchanging fluid outlet  112 , that when in a stacked formation to form the heat exchanger  150 , is in fluid communication with an adjacent downstream heat exchange module  100  or serves as a discharge. Each first heat exchanging fluid inlet  110  is in fluid communication with an inlet manifold  114 , having a generally arc-shape of a circle. Similarly, each first heat exchanging fluid outlet  112  is in fluid communication with an outlet manifold  116 , having a generally arc-shape of a circle. A plurality of heat exchange tubes  120  extend between the inlet manifold  114  and the outlet manifold  116 . In this particular embodiment, each of the plurality of heat exchange tubes  120  is generally “S” shaped such that the length of each of the plurality of heat exchange tubes  120  in a single heat exchange module  100  are equal. 
     During operation, a first heat exchanging fluid flow  118  enters the inlet manifold  114  in an arc shape and is distributed to the plurality of heat exchange tubes  120 . The plurality of heat exchange tubes  120  are fluidly coupled to the arc shaped outlet manifold  116  that is on the opposite side of the circular shaped heat exchange module  100 . In an embodiment, a first heat exchanging fluid flow passage  122  defined within each of the plurality of heat exchange tubes  120  can be configured as a single flow passage, or include multiple flow passages or other shapes internal to the “S” shape. A plurality of extended surface fins  124  may be included in the design, spanning between the plurality of “S” shaped heat exchange tubes  120 , and defining a plurality of second heat exchanging fluid flow passages  128  for passage therethrough of a second heat exchanging fluid flow  126 . The spacing and shape of the plurality of extended surface fins  124  are such that the second heat exchanging fluid flow  126 , such as air, passing through the heat exchange module  100  in a cross-flow direction to the first heat exchanging fluid flow  118 , has the same hydraulic diameter in each of the plurality of second heat exchanging fluid flow passages  128  defined by the fins  124 . 
     To increase the surface area of the plurality of extended surface fins  124  and thereby increase the thermal transfer capability, each of the plurality of extended surface fins  124  may be angled or curved with respect to the plurality of heat exchange tubes  120 . The plurality of extended surface fins  124  which define the plurality of second heat exchanging fluid flow passages  128  for the second heat exchanging fluid flow  126  may be curved so that they comprise a variable angle with a curved surface or they can be configured to be straight and formed at an acute or obtuse angle to the heat exchange tubes  120 . In selecting any single fin  124 , it will be seen that on one side of the fin an acute angle is formed with the heat exchange tubes  120  and the supplementary angle (on the opposing side) is an obtuse angle. Fin configurations as shown in  FIG.  1    increase the length (and surface area) of the fins, and the fins may be angled/curved in opposing directions as well, and in a manner that provide for equal hydraulic diameter in each second heat exchanging fluid flow passage  128  defined by the plurality of extended surface fins  124 . 
     The plurality of extended surface fins  124  may be about 0.006 inches thick or less. The plurality of extended surface fins  124  can be thinner because they do not have to be leak free. The fluid on the other side of the fin surface will be from the same fluid stream (second heat exchanging fluid flow  126 ), as it will be approximately the same temperature and pressure, thus there will be no driving force to move the fluid between fins. 
     In combination, the equal length of the plurality of “S” shaped heat exchange tubes  120  and spacing and shape of the plurality of extended surface fins  124  provide for the maintenance of a constant flow path and hydraulic diameter for each of the first heat exchanging fluid flow  118  and the second heat exchanging fluid flow  126 . This enables a more compact and efficient design. 
     Referring briefly to  FIGS.  2  and  3   , as shown, the heat exchanger  150  comprises a plurality of heat exchange modules  100  stacked adjacent each other. In addition, the heat exchanger  150  defines a plurality of outer manifolds  156 , with each outer manifold  156  coupling adjacent heat exchange modules  100 , e.g., to steer the first heat exchanging fluid flow  118  back into the plurality of heat exchange tubes  120 . More specifically, each of the plurality of outer manifolds  156  is configured to bridge two adjacent heat exchange modules  100 , via fluidic coupling to the first heat exchanging fluid inlet  110  and the first heat exchanging fluid outlet  112  of the two adjacent heat exchange modules  100 , respectively, to provide fluid communication between the two adjacent heat exchange modules  100 . 
     As illustrated, the heat exchange modules  100  extend through flow passageway  154  substantially along the radial direction R and axial direction A, when stacked adjacent to each other and fluidly coupled using the plurality of outer manifolds  156 . In this manner, the first heat exchanging fluid flow  118  within each of the heat exchange modules  100  will flow through the plurality of heat exchange tubes  120  of each heat exchange module  100  in the heat exchanger  150 . 
     The heat exchange modules  100  are positioned within the flow passageway  154  such that they are fluidly isolated from the flow passageway  154  but in thermal communication with the second heat exchanging fluid flow  126  flowing therein. The upstream-most, or the first heat exchange module  100  of the heat exchanger  150 , is referred to herein as an inlet heat exchange module, and the downstream-most heat exchange module  100  of the heat exchanger  150  is referred to herein as a discharge heat exchange module. The first heat exchanging fluid flow  118  may flow through the first heat exchanging fluid inlet  110  of the inlet heat exchange module  100  and pass through the heat exchange modules  100  along the axial direction A until passing through the first heat exchanging fluid outlet  112  of the discharge heat exchange module. 
     In addition, according to an exemplary embodiment, the heat exchanger  150 , and more particularly the heat exchange modules  100 , define a second heat exchanging fluid inlet  130  and a second heat exchanging fluid outlet  132 . As illustrated, the second heat exchanging fluid inlet  130  provides for the second heat exchanging fluid flow  126  to the inlet heat exchange module  100 . The second heat exchanging fluid flow  126  passes through the heat exchange modules  100  before exiting the heat exchanger  150  through the discharge heat exchange module  100  and the second heat exchanging fluid outlet  132 . Any suitable number of heat exchange modules  100  may be stacked along the central axis  106  and the second heat exchanging fluid inlet  130  and the second heat exchanging fluid outlet  132  may be spaced apart along the axial direction A to supply and receive the second heat exchanging fluid flow  126 . 
     The heat exchange module  100  is described herein as passing the first heat exchanging fluid flow  118  substantially along the radial direction R and the second heat exchanging fluid flow  126  substantially along the axial direction A (i.e., perpendicular to the radial direction R). In this manner, the heat exchange module  100  is configured such that the flows are perpendicular to each other and in a cross-flow heat exchange arrangement. As described in detail above, any suitable alternative heat exchanging fluids may be used. 
     Additionally, each successive heat exchange module  100  may be clocked to steer and/or provide interruption of the second heat exchanging fluid flow  126  along the axial direction A through the flow passageway  154 . Such a configuration might improve heat transfer at the cost of sink-side pressure drop. By contrast, according to still another embodiment, the heat exchange modules  100  may be uniformly oriented along the axial direction A, e.g., to reduce flow losses and pressure drop within flow passageway  154 . 
     In an alternate embodiment of the heat exchanger, generally referenced  160 , as illustrated in  FIG.  4   , one of the relative fluid directions of the first heat exchanging fluid flow  118  or the second heat exchanging fluid flow  126  can be reversed from that illustrated in  FIG.  3   , resulting in a different flow configuration that is of use. This type of flow configuration results in a co-flow heat exchanger as illustrated in  FIG.  4   , wherein the first heat exchanging fluid flow  118  or the second heat exchanging fluid flow  126  flow in generally the same axial direction. 
     Referring now to  FIGS.  5 - 9   , a heat exchange module  200  will be described according to additional embodiments of the present subject matter. In this regard,  FIG.  5    provides a front view of the heat exchange module  200 .  FIG.  6    illustrates a side view of the heat exchange module  200  of  FIG.  5   .  FIG.  7    illustrates a plurality of the heat exchange modules  200  of  FIG.  5   , assembled in stacked configuration to form a heat exchanger  250 .  FIG.  8    illustrates a sectional view of the heat exchanger of  FIG.  7    taken through line  8 - 8  of  FIG.  7   .  FIG.  9    illustrates fluid flow in a sectional view of an alternate embodiment of the heat exchanger. As illustrated, the heat exchange module  200  generally defines an axial direction A, a radial direction R, and a circumferential direction C. Likewise, the heat exchanger  250  generally defines an axial direction A, a radial direction R, and a circumferential direction C. According to the illustrated embodiment, heat exchange module  200 , and when in a stacked configuration, the heat exchanger  250 , generally define a flow passageway  154 , as best illustrated in  FIG.  7   , extending along the axial direction A. According to the illustrated embodiment, each of the one or more heat exchange modules  200  defines a circular cross section defining a central axis  106  that extends along the axial direction A. In this manner, the flow passageway  154  is an elongated cylinder and, similar to the previous embodiment, may be used to fit within or replace and existing pipe or circular conduit to facilitate a heat exchange process. However, it should be appreciated that according to alternative embodiments, the heat exchange module  100  may have any substantially curved closed geometry such as an ellipse, oval, Reuleaux or other curve-linear triangle, etc. For example, the heat exchange module  100  may have a non-circular cross section and may have a curved central axis  106  such that the heat exchange module  100  can fit in non-linear flow paths or conduits. 
     Heat exchanger  250  includes a plurality of heat exchange modules  200  in a stacked configuration to define the flow passageway  154  along the central axis  106 , i.e., the axial direction A in the illustrated embodiment. Each heat exchange module  200  includes a first heat exchanging fluid inlet  110  in fluid communication with an adjacent upstream module  100  or a source of fluid (not shown). In addition, each heat exchange module  200  includes a first heat exchanging fluid outlet  112  in fluid communication with an adjacent downstream heat exchange module  100 , or to discharge the first heat exchanging fluid flow  118  from the heat exchanger  250 . 
     In this particular embodiment, the first heat exchanging fluid flow  118 , such as high density fluid (e.g. oil), is routed from an outer radius of the heat exchange module  200  to an inner radius of the heat exchange module  200  through a plurality of equidistant heat exchange tubes  202  that are spaced such that a second heat exchanging fluid flow  126 , such as a low density fluid (e.g. air) passes in a cross-flow direction to the first heat exchanging fluid flow  118  within the plurality of equidistant heat exchange tubes  202 . The plurality of equidistant heat exchange tubes  202  define therein multiple spiral first heat exchanging fluid flow passages  208 , such that a length of each spiral first heat exchanging fluid flow passages  208  is the same. 
     The first heat exchanging fluid flow  118  enters the heat exchange module  200  via the first heat exchanging fluid inlet  110  into a circular outer manifold  204  and is distributed to the plurality of spiral first heat exchanging fluid flow passages  208 . The specific shape of each of the plurality of equidistant heat exchange tubes  202 , and thus the multiple spiral first heat exchanging fluid flow passages  208 , is an involute of a circle. The spiral first heat exchanging fluid flow passages  208  are in fluid communication with an internal tube or annulus, that acts as the outlet  112 , in the form of a central manifold  206 . The plurality of spiral first heat exchanging fluid flow passages  208  can be configured as a single flow passage through each of the plurality of equidistant heat exchange tubes  202 , or multiple passages or other shapes internal to the plurality of equidistant heat exchange tubes  202 . The plurality of equidistant heat exchange tubes  202  are spaced such that the hydraulic diameter of the second heat exchanging fluid flow  126  is the same at all locations in the fluid path  154 . In an embodiment, a plurality of extended surface fins  124  may be included between the plurality of equidistant heat exchange tubes  202 . The spacing and shape of the plurality of extended surface fins  124  are such that the second heat exchanging fluid flow  126 , such as air, passing through the heat exchange module  200  in a cross-flow direction to the first heat exchanging fluid flow  118 , has the same hydraulic diameter in each flow passage defined by the plurality of extended surface fins  124 . 
     In combination, the plurality of equidistant heat exchange tubes  202  and spacing and shape of the plurality of extended surface fins  124  provide for the maintenance of a constant flow path and hydraulic diameter for each of the first heat exchanging fluid flow  118  and the second heat exchanging fluid flow  126 . As previously stated with regard to the first disclosed embodiment, this enables a more compact and efficient design. 
     Referring more specifically to  FIG.  5   , as shown, each of the plurality of spiral first heat exchanging fluid flow passages  208  extends between the first heat exchanging fluid inlet  110 , and more particularly the circular outer manifold  204 , inward substantially along the radial direction R toward a central aperture or the outlet  112 , and more particularly the central manifold  206 . 
     Referring briefly to  FIGS.  7  and  8   , as shown, heat exchanger  250  comprises a plurality of heat exchange modules  200  stacked adjacent each other. In addition, heat exchanger  250  defines a plurality of bulkheads  210  defined between the central manifolds  206  of the heat exchange modules  200 , e.g., to steer the first heat exchanging fluid flow  118  back into the plurality of equidistant heat exchange tubes  202 . In this manner, the central manifolds  206  of the heat exchange modules  200  extend along the central axis  106  and are alternately separated by the plurality of bulkheads  210  along the axial direction A. 
     Similarly, as best illustrated in  FIG.  8   , the circular outer manifolds  204  are configured to bridge two adjacent heat exchange modules  200  to provide fluid communication between the two adjacent heat exchange modules  200 . As illustrated, the heat exchange modules  200  extend through flow passageway  154  substantially along the radial direction R. When stacked adjacent to each other and coupled using the circular outer manifolds  204  and the plurality of bulkheads  210  as described herein, the first heat exchanging fluid flow  118  within each of the heat exchange modules  200  will flow through the plurality of equidistant heat exchange tubes  202 . 
     The heat exchange modules  200  are positioned within the flow passageway  154  such that they are fluidly isolated from the flow passageway  154  but in thermal communication with the second heat exchanging fluid flow  126  flowing therein. An optional housing  102  may define the first heat exchanging fluid inlet  110  positioned upstream of the first heat exchange module  200 , or inlet heat exchange module, and the first heat exchanging fluid outlet  112  positioned downstream of a last heat exchange module  200 , or discharge heat exchange module. The first heat exchanging fluid flow  118  may flow through the first heat exchanging fluid inlet  110  of the inlet heat exchange module  200  and pass through the heat exchange modules  200  along the axial direction A until passing through the first heat exchanging fluid outlet  112  of the discharge module. 
     In addition, according to an exemplary embodiment, the heat exchanger  250 , and more particularly the heat exchange modules  200 , define a second heat exchanging fluid inlet  130  and a second heat exchanging fluid outlet  132 . As illustrated, the second heat exchanging fluid inlet  130  is in fluid communication with the inlet heat exchange module  200  for providing the second heat exchanging fluid flow  126  to the inlet heat exchange module  200 . The second heat exchanging fluid flow  126  passes through the heat exchange modules  200  before exiting the heat exchanger  250  through the discharge heat exchange module  200  and the second heat exchanging fluid outlet  132 . Any suitable number of heat exchange modules  200  may be stacked along the central axis  106  and the second heat exchanging fluid inlet  130  and the second heat exchanging fluid outlet  132  may be spaced apart along the axial direction A to supply and receive the second heat exchanging fluid flow  126 . 
     The heat exchange module  200  is described herein as passing the first heat exchanging fluid flow  118  substantially along the radial direction R and the second heat exchanging fluid flow  126  substantially along the axial direction A (i.e., perpendicular to the radial direction R). In this manner, the heat exchange module  200  is configured such that the flows are perpendicular to each other and in a cross-flow heat exchange arrangement. However, it should be appreciated that the directional orientation of the plurality of equidistant heat exchange tubes  202  relative to housing  102  and flow passageway  154  may vary while remaining within the scope of the present disclosure. As described in detail above, any suitable alternative heat exchanging fluids may be used. 
     Additionally, similar to the first embodiment, each successive heat exchange module  200  may be clocked to steer and/or interrupt the second heat exchanging fluid flow  126  along the axial direction A through the flow passageway  154 . By contrast, according to still another embodiment, the heat exchange modules  200  may be uniformly oriented along the axial direction A, e.g., to reduce flow losses and pressure drop within flow passageway  154 . 
     In an alternate embodiment of the heat exchanger, generally referenced  160 , as illustrated in  FIG.  9   , one of the relative fluid directions of the first heat exchanging fluid flow  118  or the second heat exchanging fluid flow  126  can be reversed from that illustrated in  FIG.  7   , resulting in a different flow configuration that is of use. This type of flow configuration results in a co-flow heat exchanger as illustrated in  FIG.  9   , wherein the first heat exchanging fluid flow  118  or the second heat exchanging fluid flow  126  flow in generally the same axial direction. 
     In the previously disclosed embodiments, the heat exchange tubes  120 ,  202  may be formed of aluminum, titanium 6-4, Inconel 718, or a cobalt chrome alloy. Other materials may be used as well if they have similar and/or satisfactory performance attributes. In addition, the heat exchange tubes  120 ,  202  may be any suitable size and shape, within the parameters defined for obtaining constant flow pressures, for facilitating improved heat transfer while minimizing pressure losses within the first and second heat exchanging fluid flows  118 ,  126 . For example, according to the illustrated embodiments, the heat exchange tubes  120 ,  202  have a substantially circular cross sectional profile. However, according to alternative embodiments, any other suitable cross sectional shape may be used, such as an elliptical cross section or even a varying or undulating cross sectional shape. For example, the cross section could be airfoil-shaped (e.g., similar to the shape of a teardrop). The heat exchange tubes  120 ,  202  may be formed in any suitable size, number, spacing, and shape depending on the application and the type of heat exchanging fluid. These various configurations are enabled by the additive manufacturing processes disclosed herein and are considered to be within the scope of the present subject matter. 
     Although exemplary embodiments are described herein, it should be appreciated that heat exchange tubes  120 ,  202  may be configured in any suitable manner depending on the application, the types of heat exchanging fluids being used, space considerations, etc. In addition, each heat exchange module  100 ,  200  may include a slightly different structure or may include heat exchange tubes  120 ,  202  that are offset from each other along the axial direction A to maximize contact between heat exchange tubes  120 ,  202  and the second heat exchanging fluid flow  126 . 
     The various portions of heat exchange modules  100 ,  200  may be constructed using any suitable material, in any suitable geometry, density, and thickness, as needed to provide necessary structural support to the heat exchanger  150 ,  160 ,  250 ,  260 . For example, the optional housing  102  of the heat exchange module  200  may be formed from a rigid, thermally insulating material. In addition, the housing  102  may be thicker and denser to provide structural support for loads experienced by heat exchange modules  200  during mounting, assembly, and operation. In addition, heat exchange module  100  may include a housing as described with reference to heat exchange module  200 . By contrast, heat exchange tubes  120 ,  202  may be thinner and constructed of a more thermally conductive material in order to enhance heat transfer. For example, heat exchange tubes  120 ,  202  may have a wall thickness of 20 μm or any other suitable thickness. 
     Now that the construction and configuration of heat exchange modules  100 ,  200  according to the exemplary embodiments of the present subject matter have been presented, an exemplary method  300  for forming a heat exchanger according to an exemplary embodiment of the present subject matter is provided. Method  300  can be used by a manufacturer to form heat exchanger  150 ,  160 ,  250 ,  260 , or any other suitable heat exchanger. It should be appreciated that the exemplary method  300  is discussed herein only to describe exemplary aspects of the present subject matter, and is not intended to be limiting. 
     Referring now to  FIG.  10   , method  300  includes, at step  302 , depositing a layer of additive material on a bed of an additive manufacturing machine. Method  300  further includes, at step  304 , selectively directing energy from an energy source onto the layer of additive material to fuse a portion of the additive material and form the heat exchange module  100 ,  200  defining a flow passageway and a plurality of heat exchange tubes extending between an inlet and an outlet. For example, using the example from above, heat exchange module  100 ,  200  may be formed for transferring heat between to streams of air, between streams of air and oil, or any other suitable heat exchanger may be formed. The method further includes, at step  306 , stacking a plurality of the heat exchange modules  100 ,  200  to form a heat exchanger  150 ,  160 ,  250 ,  260 , including an inlet in fluid communication with the inlet of a first inlet heat exchange module and an outlet in fluid communication with a discharge heat exchange module. 
     According to exemplary embodiments, method  300  may further include using the additive manufacturing methods described herein to form an integral inlet manifold and an integral outlet manifold. Notably, according to an exemplary embodiment, the plurality of heat exchange modules, the inlet manifolds, the outlet manifolds, the heat exchange tubes, and other parts of the heat exchanger such as described above are integrally formed as a single monolithic component. Accordingly, in an alternate method, the complete heat exchanger  150 ,  160 ,  250 ,  260  is formed, at step  308 , by selectively directing energy from an energy source onto the layer of additive material, deposited in step  302 , to fuse a portion of the additive material and form a complete heat exchanger  150 ,  160 ,  250 ,  260  defining a flow passageway and a plurality of heat exchange tubes extending between an inlet and an outlet as a monolithic component. 
       FIG.  10    depicts steps performed in a particular order for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that the steps of any of the methods discussed herein can be adapted, rearranged, expanded, omitted, or modified in various ways without deviating from the scope of the present disclosure. Moreover, although aspects of method  300  are explained using heat exchange module  100  and heat exchanger  150 , as an example, it should be appreciated that these methods may be applied to manufacture heat exchange module  200 , heat exchanger  160 ,  250 ,  260  and any suitable heat exchanger. 
     It should be appreciated that heat exchange modules  100 ,  200  and the heat exchangers  150 ,  160 ,  250 ,  260  are described herein only for the purpose of explaining aspects of the present subject matter. For example, the heat exchange modules  100 ,  200  will be used herein to describe exemplary configurations, constructions, and methods of manufacturing the heat exchangers  150 ,  160 ,  250 ,  260 . It should be appreciated that the additive manufacturing techniques discussed herein may be used to manufacture other heat exchangers for use in any suitable device, for any suitable purpose, and in any suitable industry. Thus, the exemplary components and methods described herein are used only to illustrate exemplary aspects of the present subject matter and are not intended to limit the scope of the present disclosure in any manner. 
     An additively manufactured heat exchanger and a method for manufacturing that heat exchanger are described above. Notably, the heat exchange module  100 ,  200  may generally be intended to fit within or replace an existing pipe or conduit to facilitate a heat exchange process. The heat exchange module  100 ,  200  may include performance-enhancing geometries and heat exchanging features whose practical implementations are facilitated by an additive manufacturing process, as described below. For example, using the additive manufacturing methods described herein, the heat exchanger may include heat exchange modules defining first and second heat exchange flow passages for transferring thermal energy between two streams of fluid, wherein the defined flow passages provide a constant flow path and hydraulic diameter for each of the two fluids, thereby reducing flow losses and pressure drops within the flow passageways. In addition, the additive manufacturing techniques described herein enable the formation of a heat exchanger with integral inlet and outlet manifolds and heat exchange tubes designed to improve the thermal efficiency of the heat exchanger. These features may be introduced during the design of the heat exchanger, such that they may be easily integrated into heat exchanger during the build process at little or no additional cost. Moreover, the entire heat exchanger, including the heat exchange modules, and all other features can be formed integrally as a single monolithic component. 
     This written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.