Patent Publication Number: US-2020284531-A1

Title: Heat exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 62/815,835 filed Mar. 8, 2019 for “Heat Exchanger” by M. Maynard, A. Becene, M. Hu, F. Feng, M. Doe, G. Ruiz, and E. Joseph. 
    
    
     BACKGROUND 
     The present disclosure is related generally to heat exchangers and more particularly to heat exchanger core designs. 
     Heat exchangers can provide a compact, low-weight, and highly effective means of exchanging heat from a hot fluid to a cold fluid. Heat exchangers that operate at elevated temperatures, such as those used in modern aircraft engines, often have short service lifetimes due to thermal stresses, which can cause expansion and cracking of the fluid conduits. Thermal stresses can be caused by mismatched temperature distribution, component stiffness, geometry discontinuity, and material properties (e.g., thermal expansion coefficients and modulus), with regions of highest thermal stress generally located at the interface of the heat exchanger inlet/outlet and core. 
     A need exists for heat exchangers with improved performance under thermal stress. 
     SUMMARY 
     A heat exchanger includes a first flow circuit structure having at least a first portion defined by a plurality of conduits and a second flow circuit structure having at least a second portion disposed at the first portion such that walls of the second portion are disposed between the conduits and are free to move relative to the conduits. Fluid flowing through the first flow circuit structure is fluidically isolated from fluid flowing through the second flow circuit structure. 
     A method of making a heat exchanging arrangement includes forming a plurality of conduits defining at least a first portion of a first flow circuit structure, and forming a plurality of walls positioned between the conduits defining at least a second portion of a second flow circuit structure such that the second portion is free to move relative to the first portion. 
     The present summary is provided only by way of example, and not limitation. Other aspects of the present disclosure will be appreciated in view of the entirety of the present disclosure, including the entire text, claims and accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a heat exchanger according to an embodiment of the present disclosure. 
         FIG. 2  is a cut away view of the heat exchanger of  FIG. 1  taken perpendicular to a heat exchanger axis. 
         FIG. 3  is another cut away view of the heat exchanger of  FIG. 1  taken along the axis of the heat exchanger. 
     
    
    
     While the above-identified figures set forth embodiments of the present invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features, steps and/or components not specifically shown in the drawings. 
     DETAILED DESCRIPTION 
     Hot and cold passages are tied together in traditional heat exchanger designs. The present disclosure is directed to a heat exchanger in which hot and cold fluid passages are disconnected along the length of a heat exchanger core to provide improved performance under thermal stress. Cold passage walls or separating structures are arranged between hot flow conduits in a manner that allows cold passage structures to expand and contract independent of the hot flow conduits thereby reducing thermal stress within the heat exchanger. The heat exchanger of the present disclosure can be additively manufactured to achieve varied tubular dimensions (e.g., inner diameter, wall thicknesses, curvature, etc.) and to allow simultaneous and integral manufacture of hot and cold structures. 
       FIG. 1  shows a perspective view of heat exchanger  10 , hot flow circuit  12 , configured to direct a hot fluid F 1 , and a portion of cold flow structure  14 , disposed within and around hot flow circuit  12  to separate and direct flow of cooling fluid F 2 . Hot flow circuit  12  includes inlet header  16  (shown in  FIG. 3 ), outlet header  18 , and core  20  disposed there between. During operation of heat exchanger  10 , hot fluid F 1  is provided to inlet header  16 , flows through core  20 , and exits through outlet header  18 . Thermal energy is transferred from hot fluid F 1  to cooling fluid F 2  as hot fluid F 1  passes through core  20 . In one embodiment, illustrated in  FIG. 1 , core  20  can have a circular arrangement with a plurality of conduits  22  disposed in concentric rows around axis A, with axis A running through a center of inlet header  16  and outlet header  18 . Other core designs are contemplated, including but not limited to elliptical and rectangular designs. It will be understood by one of ordinary skill in the art that the disclosed independent cold flow structure can be tailored for use with a wide variety of core geometries and is not limited to the embodiments shown. The core geometry illustrated in  FIG. 1  is disclosed in the co-pending application, “CIRCULAR CORE FOR HEAT EXCHANGERS,” which is incorporated herein in full by reference. 
     As illustrated in  FIG. 1 , heat exchanger  10  can be arranged as a counter-flow heat exchanger with cooling fluid F 2  flowing substantially parallel to and in the opposite direction of hot fluid F 1 . Cooling flow structure  14  has a plurality of walls  24 , which can be arranged in concentric cylinders to radially separate concentric sections of hot flow conduits  22 . Walls  24  can extend a full longitudinal length of core  20  or partial length depending on the hot flow circuit geometry (e.g., limited by branching in the geometry disclosed in  FIG. 1 ). In some embodiments, hot flow conduits  22  can extend from a branched inlet (not shown) to a branched outlet  25 . Walls  24  can extend between the branched inlet and the branched outlet  25 , as the point of branching would otherwise interrupt continuity of walls  24 . Cooling flow structure  14  can include a funnel-shaped inlet (not shown) to direct cooling fluid F 2  through cooling fluid passages formed between walls  24 . The funnel-shaped inlet can connect to the outermost wall  24  of cooling flow structure  14 . 
       FIG. 2  shows a cut away view of heat exchanger  10  taken in an axial plane of heat exchanger  10 . As illustrated, a singular cylinder-shaped cooling flow wall  24  can be disposed between each circular row of hot flow conduits  22  to improve heat transfer. It will be understood by one of ordinary skill in the art that the number of walls can be reduced (e.g., multiple rows of conduits  22  can be circumscribed by a single wall  24 ) for applications with lower heat transfer requirements. Walls  24  can be separate or unconnected from hot flow conduits  22  along the longitudinal length of hot flow conduits, such that walls  24  are free to move relative to hot flow conduits  22  during operation. The separation of walls  24  from conduits  22  allows for independent thermal expansion and contraction of each of the structures, which reduces thermal stress on core  20 . In some embodiments, cooling flow structure  14  can be designed with respect to hot flow structure  12  to provide space between walls  24  and conduits  22 , as illustrated in the expanded view of  FIG. 2 . In other embodiments, cooling flow structure  14  can be designed to allow walls  24  to come into contact with conduits  22 , while remaining detached along the longitudinal length of conduits  22  to provide axial compliance to cold flow structure  14 . During operation, walls  24  can slide on conduits  22  with thermal expansion and contraction. 
     In some embodiments, cylinder-shaped walls  24  can be tied together by one or more radially extending ribs  26 . Ribs  26  can improve heat transfer by increasing surface area inside cooling flow channels and can provide stiffness to cooling flow structure  14 . Increased stiffness can reduce vibrational response during operation but can also restrict thermal growth of cooling flow structure  14 . As such, the number and positioning of ribs  26  can be tailored to meet heat transfer, compliance, and stiffness requirements. For example, larger heat exchangers may require additional stiffness (i.e., more ribs  26 ), while smaller heat exchangers may not require any ribs  26 . Ribs  26  can extend radially from an innermost wall  24  to the outermost wall  24 . Rib  26  can extend a full longitudinal length of hot flow conduits  22  or a partial length depending on the geometry of hot flow circuit  12 . As described with respect to walls  24 , ribs  26  can extend between points of branching (e.g., between a branched inlet and a branched outlet of conduits  22 ). 
     In some embodiments, cooling flow structure  14  can include a central support structure  28 , which can tie together ribs  26  along axis A.  FIG. 3  shows a cut away view of heat exchanger  10  taken in a radial plane. As illustrated in  FIG. 3 , central support structure  28  can be tied to hot flow circuit  12  at a location point  29  on outlet header  18  to restrict axial, radial, and circumferential movement of cooling flow structure  14  during operation, while still retaining axial, radial, and transverse thermal compliance. Because walls  26  and ribs  28  remain unconnected from hot flow conduits  22 , walls  26  and ribs  28  are able to expand and contract relative to hot flow circuit  12  under varying thermal loads independent of conduits  22 . In alternative embodiments, cooling flow structure  14  can be tied to one or both inlet and outlet headers  16  and  18  by central support structure  28  at locations  29  and  30  or one or more walls  24  or ribs  26 , for example, at location  31 . It will be understood by one of ordinary skill in the art to maximize the distance between any two connection points to increase thermal compliance. 
     Although not illustrated, it will be understood by one of ordinary skill in the art that walls  24  can have any of a variety of geometries and connections to provide cooling flow channels around hot flow conduits of any of a variety of geometries. For example, a rectangular core can have a cooling flow structure arranged in a generally rectangular grid pattern. A support structure  28 , if used, can be positioned in a center of the core and can be connected to one or more of the walls  24  and one or both of inlet and outlet headers  16  and  18 . Alternatively, one or more walls  24 , such as an outermost wall, can be connected to one or both of inlet and outlet headers  16  and  18 . 
     The components of heat exchanger  10  can be formed partially or entirely by additive manufacturing. For metal components (e.g., Inconel, aluminum, titanium, etc.), additive manufacturing processes include but are not limited to powder bed fusion techniques such as direct metal laser sintering (DMLS), laser net shape manufacturing (LNSM), electron beam manufacturing (EBM). For polymer or plastic components, stereolithography (SLA) can be used. Additive manufacturing is particularly useful in obtaining unique geometries (e.g., varied core tube radii, arcuate core tubes, branched inlet and outlet headers) and for reducing the need for welds or other attachments (e.g., between inlet header  16  and conduits  22 ). However, other suitable manufacturing process can be used. For example, header and core elements can in some embodiments be fabricated separately and joined via later manufacturing steps. Hot flow circuit  12  and cooling flow structure  14  can be formed simultaneously as an integral component thereby eliminating the need for subsequent assembly and allowing for increased complexity in design. 
     The disclosed core arrangement offers improved thermal and mechanical properties. By incorporating a cooling flow passages into the heat exchanger that are not connected to hot flow passages, cooling flow structures are allowed to expand and contract independent of the hot flow conduits thereby reducing thermal stress within the heat exchanger. 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A heat exchanger according to an embodiment of the present disclosure, among other things, a first flow circuit structure having at least a first portion defined by a plurality of conduits and a second flow circuit structure having at least a second portion disposed at the first portion such that walls of the second portion are disposed between the conduits and are free to move relative to the conduits. Fluid flowing through the first flow circuit structure is fluidically isolated from fluid flowing through the second flow circuit structure. 
     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 further embodiment of the heat exchanger of preceding paragraph, wherein the conduits can be separated from the walls by a gap. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein conduits can be arranged in a plurality of rows and the walls are arranged to separate the rows of conduits. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein conduits can be arranged around an axis in a plurality of concentric rows, and wherein the plurality of walls comprise cylinders that circumscribe the rows. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the plurality of walls can further include one or more ribs, wherein the one or more ribs extend radially and connect the cylinders. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the conduits can extend from a branched inlet to a branched outlet and wherein the cylinders can extend between the branched inlet and the branched outlet. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the ribs can extend between the branched inlet and the branched outlet. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the second flow circuit structure can be unconnected from the first flow circuit structure such that the second flow circuit structure is in a floating relationship flow circuit structure. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the second flow circuit structure can be connected to the first flow circuit structure at an axially remote location. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the first portion comprises a heat exchanger core, the core disposed between and in fluid connection with an inlet header and outlet header, and wherein the second flow circuit structure is connected to the inlet header or the outlet header. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the second flow circuit structure is connected to the inlet header or the outlet header by a support member disposed at the center of the core and connected to at least one wall of the plurality of walls. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the second flow circuit structure can be connected to an inlet header or an outlet header of the heat exchanger. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the second flow circuit structure can be connected to the inlet header or the outlet header by a support member disposed at the center of the core and connected to at least one wall of the plurality of walls. 
     A further embodiment of the heat exchanger of any of the preceding paragraphs, wherein the second flow circuit structure can be connected to the inlet header or the outlet header by an outermost wall of the second flow circuit structure, the outermost wall being disposed around the plurality of conduits. 
     A method of making a heat exchanging arrangement includes, among other possible steps, forming a plurality of conduits defining at least a first portion of a first flow circuit structure, and forming a plurality of walls positioned between the conduits defining at least a second portion of a second flow circuit structure such that the second portion is free to move relative to the first portion. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, additional components, and/or steps: 
     The method of the preceding paragraphs can further include forming the conduits in a plurality of rows and forming the walls to separate the rows of conduits. 
     The method of any of the preceding paragraphs can further include forming the conduits around an axis in a plurality of concentric rows and forming the walls to circumscribe the rows. 
     The method of any of the preceding paragraphs can further include forming one or more ribs to extend radially and connect the walls. 
     The method of any of the preceding paragraphs can further include forming a support member at a center of the walls and connecting the support member to one or more ribs. 
     The method of any of the preceding paragraphs can further include connecting the support member to an inlet header or an outlet header of the heat exchanger. 
     The method of any of the preceding paragraphs can further include connecting the second flow circuit structure to the first flow circuit structure at an axially remote location. 
     While the invention has been described with reference to particular 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.