Patent Publication Number: US-2019170445-A1

Title: High temperature plate fin heat exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This disclosure claims priority to U.S. Provisional Patent Application No. 62/593,379 filed Dec. 1, 2017. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under contract number FA8626-16-C-2139 awarded by the United States Air Force. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     A plate fin heat exchanger includes adjacent flow paths that transfer heat from a hot flow to a cooling flow. The flow paths are defined by a combination of plates and fins that are arranged to transfer heat from one flow to another flow. The plates and fins are created from sheet metal material brazed together to define the different flow paths. Thermal gradients present in the sheet material create stresses that can be very high in certain locations. The stresses are typically largest in one corner where the hot side flow first meets the coldest portion of the cooling flow. In an opposite corner where the coldest hot side flow meets the hottest cold side flow, the temperature difference is much less resulting in unbalanced stresses across the heat exchanger structure. Increasing temperatures and pressures can result in stresses on the structure that can exceed material and assembly capabilities. 
     Turbine engine manufactures utilize heat exchangers throughout the engine to cool and condition airflow for cooling and other operational needs. Improvements to turbine engines have enabled increases in operational temperatures and pressures. The increases in temperatures and pressures improve engine efficiency but also increase demands on all engine components including heat exchangers. 
     Turbine engine manufacturers continue to seek further improvements to engine performance including improvements to thermal, transfer and propulsive efficiencies. 
     SUMMARY 
     In a featured embodiment, a heat exchanger includes at least one plate including a first end portion. A second end portion is spaced apart from the first end portion. A cavity is disposed between the first end portion and the second end portion. The cavity defines a first flow path. An outer surface portion defines a second flow path. The at least one plate includes a single unitary part without a joint between any two portions. A first end cap defines an inlet disposed at the first end portion. A second end cap defines an outlet at the second end portion. 
     In another embodiment according to the previous embodiment, the first end portion and the second end portion include an upper support surface portion within a common upper plane and a lower support surface portion within a common lower plane. 
     In another embodiment according to any of the previous embodiments, fin portions extend outward from the outer surface portion. 
     In another embodiment according to any of the previous embodiments, the outer surface portion includes a first side and a second side and the fin portions extend from both the first side and the second side. 
     In another embodiment according to any of the previous embodiments, the fin portions include a tip portion that extends past either of the upper common plane and the lower common plane. 
     In another embodiment according to any of the previous embodiments, the cavity includes at least one tabulator extending into the first flow path. 
     In another embodiment according to any of the previous embodiments, the at least one plate includes a first plate, stacked on a second plate such that the lower support surface portion of the first plate abuts the upper support surface portion of the second plate and the second flow path is defined within a space between the first plate and the second plate. 
     In another embodiment according to any of the previous embodiments, additional plates stacked against one of the first plate and the second plate and aligned such that a lower support surface portion of one plate abuts an upper support surface portion of another plate, wherein each of the plates defines a first flow path through the plate and the second flow path is defined in spaced between the stacked plates. 
     In another embodiment according to any of the previous embodiments, the heat exchanger is an air to air heat exchanger and the first flow path through the at least one plate is configured for an airflow that is to be cooled and the second flow path is for a cooling airflow. 
     In another featured embodiment, a plate for a heat exchanger, the plate includes a first end portion spaced apart from a second end portion. A cavity defines a first flow path between the first end portion and the second end portion. An outer surface portion defines a second flow path. The plate includes a single unitary part without a joint between any two portions. 
     In another embodiment according to any of the previous embodiments, the first end portion and the second end portion include an upper support surface portion within a common upper plane and a lower support surface portion within a common lower plane. 
     In another embodiment according to any of the previous embodiments, the outer surface portion includes a first side and a second side and the fin portions extend from both the first side and the second side. 
     In another embodiment according to any of the previous embodiments, the fin portions include a top portion that extends past either of the upper common plane and the lower common plane. 
     In another embodiment according to any of the previous embodiments, the cavity includes a means for disrupting flow. 
     In another featured embodiment, a method of building a heat exchanger includes creating a core defining internal features including an inner cavity of a completed plate. The core is inserted within a mold cavity that defines outer surfaces of a completed plate. The plate is molded to include the outer surfaces defined by the mold cavity an inner surfaces defined by the core. The completed plate defines a first flow path through the inner cavity and an outer surface defining a second flow path. At least one completed plate is assembled to a first end cap at a first end portion of a completed plate and a second end cap to a second end portion of the completed plate. 
     In another embodiment according to any of the previous embodiments, the mold cavity includes features for defining fin portions that extend outward from an outer surface of a completed plate. 
     In another embodiment according to any of the previous embodiments, the core includes portion for defining flow disrupting features within the inner cavity of the completed plate. 
     In another embodiment according to any of the previous embodiments, each plate includes a single unitary part without a joint between any two portions. 
     Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
     These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an example heat exchanger embodiment. 
         FIG. 2  is a perspective sectional view of the example heat exchanger. 
         FIG. 3  is a perspective view of an example plate for the heat exchanger. 
         FIG. 4  is a side view of the example plate. 
         FIG. 5  is a partial cross-sectional view of the example heat exchanger. 
         FIG. 6  is a partial top view of the example plate. 
         FIG. 7  is a partial cross-sectional view of the example plate. 
         FIG. 8  is a sectional view illustrating a cavity of the plate. 
         FIG. 9  is an enlarged view of an inlet for the example plate. 
         FIG. 10  is a schematic representation of a method for fabricating the example plate. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a heat exchanger  10  that includes a first end cap  14  and a second end cap  16  disposed on either end of the plurality of stacked plates  12 . The first end cap  14  includes an inlet  22  for a first airflow  18 . The second end cap  16  includes an outlet  24  for the first airflow  18 . The first airflow  18  in this example embodiment is a hot airflow that is cooled by a cooling airflow  20  that flows through passages between the pluralities of stacked plates  12 . The example heat exchanger  10  is an air to air heat exchanger which cools hot air  18  that flows through cavities within the plurality of plates  12 . 
     The plurality of plates  12  are integrally formed separate individual parts that are stacked upon each other and then placed in communication with the end caps  14  and  16 . Cooling airflow  20  flows through the passages created between stacked plates  12  to cool the airflow  18  that is flowing through cavities defined within the plates  12 . 
     Referring to  FIG. 2  with continued reference to  FIG. 1 , the example heat exchanger  10  includes the end caps  14 ,  16  that define a flow path from the inlet  22  to inlets for each of the plurality of stacked plates  12 . In this example, the stacked plates  12  define a first flow path  32  for the hotter airflow  18  and also define the second flow path  34  in spaces defined between the plates  12  for the cooling airflow  20 . Airflow  18  flows into the inlet  22  of the first end cap  14  through a cavity defined within each of the plates  12  and exits through the second end cap  16 . 
     Referring to  FIGS. 3 and 4  with continued reference to  FIGS. 1 and 2 , the example plate  12  is a single unitary part without any joints between any portions of the plate. The plate  12  includes a first end portion  28  and a second end portion  30 . The cavity  26 , (Shown in  FIG. 5 ), extends between the first end portion  28  and the second end portion  30 . The first end portion  28  includes an upper support surface  40  and a lower support surface  42 . The second end portion  30  also includes an upper support surface  40  and a lower support surface  42 . 
     The upper and lower support surfaces  40 ,  42  are disposed within common planes across the first and second end portions  28 ,  30 . In this example, the upper support surfaces  40  are disposed within a common upper plane  44  and the lower support surfaces  42  are disposed within a common lower plane  46 . The plate  12  includes an outer top surface  36  in an outer bottom surface  38 . From each of the outer surfaces  36 ,  38  extend a plurality of fins  48 . The fins  48  are an integral part of the outer surfaces  36 ,  38 . The fins  48  define the second flow path  34  there between. In other words, each of the plurality of fins  48  extends upward and across the plate  12  perpendicular to the flow paths  32  defined within each of the plates  12 . 
     Each of the fins  48  include a tip portion  50 . In this example, the tip portion  50  is disposed above the respective ones of the common upper plane  44  and the common lower plane  42 . In other words, each of the fins  48  extends past corresponding upper and lower support surfaces  40 ,  42 . The fins  48  are offset between the upper and lower surfaces  36 ,  38  such that fins  48  extending downward from the lower surface  38  fit between fins  48  extending upward from an upper surface  36  of another plate  12 . This inter-fit configuration enables the plates  12  to be stacked one on top of the other to define a plurality of second flow paths  34 . The stacked plates  12  define a plurality of first flow paths  32  that go through the plates  12  and the plurality of second flow paths  34  that flows through the spaces defined between fins  48  of plates in the stacked configuration. 
     Referring to  FIG. 5  with continued reference to  FIGS. 2-4 , the heat exchange  10  utilizes a plurality of plates  12 . In this example, a first plate  12   a,  a second plate  12   b,  and a third plate  12   c  are illustrated by way of example. Each of the plates  12   a,    12   b  and  12   c  are abutted at the first end portion  28  and the second end portion  30 . The second end portion  30  is not shown in this example but is identical to the abutting assembly indicated with regard to the first end portions  25  shown in  FIG. 5 . In this configuration, the plates  12  are stacked atop each other such that the support surface  40  of a plate  12   c  abuts a lower support surface  42  of the plate  12   b.  Similarly, the upper support surface  40  of the plate  12   b  abuts a lower support surface  42  of the plate  12   a.  As appreciated, although only three plates  12  are shown by way of example, any number of plates  12  could be utilized to define the first flow path  32  and second flow paths  34 . 
     Referring to  FIG. 6  with continued reference to  FIG. 5 , the second flow path  34  is shown where each of the fins  48  define channels  54  between the fins  48 . The second cooling flow  20  therefore flows through the second flow passages  34  between the fins  48  and through the channels  54 . 
     Referring to  FIGS. 7 and 8 , the example plate  12  is shown in partial cross-section and includes an inlet  60  at each of the first and second end portions  28 . In this example, only the first end portion  28  is disclosed however, the second end portion would be substantially identical to the first end portion  28 . The plate cavity  26  extends from the first end portion  28  to the second end portion  30 . The plate cavity  26  may be a smooth cavity to provide a smooth uninterrupted passage for airflow with the first flow  18 . The cavity  26  may also include a rib  56  to subdivide the channel and also flow disrupting features  52 . The flow disrupting features can include tabulators, pins, trip strips, chevrons, raised features, riblets, dimples, bumps, and local surface roughness that may disrupt and create a turbulent flow and improve thermal transfer through the plate  12  as are shown in  FIG. 8 . 
     Referring to  FIG. 9  with continued reference to  FIGS. 7 and 8 , the example inlet  60  may include inlet ribs  58  that may be utilized to divide and direct flow through the cavity  26 . 
     Referring to  FIG. 10  the example plate  12  is fabricated as a single unitary one piece part. Because the plate  12  is fabricated as a single unitary piece, there are no brazed joints, seems or other potential welds that may create potential weak spots due to thermal gradients and difference throughout the plate  12  caused by the different temperatures in the hot and cooling airflows. Additionally, the single unitary plate  12  does not have mechanical strength debits or potential geometric and/or material discontinuities inherent in brazed joints. 
     A method of fabricating the plate  12  is generally indicated at  62  and schematically illustrated in  FIG. 10  and includes the generation of a core  68 . In this example, the core  68  is fabricated from a ceramic material and defines the internal features of the cavity  26  of the plate  12 . Those internal features may be defined by space  70  for the rib  56  or spaces  72  to define the flow disrupting features  52 . It should be understood that although a single rib  70  is illustrated along with schematic illustrations of flow disrupting features  72 , other features within the cavity  26  that may improve the transfer of thermal energy from the hot air flow  18  may also be utilized and fabricated and defined by the core assembly  68 . 
     The core assembly  68  is inserted into a mold  64  for formation of a completed part as part of known over-molding processes. The mold  64  defines a cavity  66  that defines the outer features of the plate  12 . Typical insert molding operations utilize the core  68  that is inserted and held within the mold in a specific orientation to define the interior features of a completed product. 
     Molding operations are performed by injecting material into the mold and holding the material under pressure until cured sufficiently to allow removal of the part. In this example the material comprise a metal alloy material capable of performing at elevated temperatures as are encountered during operation of a gas turbine engine. The core  68  is then removed through a heating step or other processes as are known. The completed plate  12  is a single unitary structure and is combined with other separate plates to assemble and configure a heat exchanger with the desired thermal transfer capacity. 
     The example heat exchanger is fabricated utilizing a plurality of single unitary plate structures. A single plate structure may operate as a heat exchanger or may be combined with a plurality of other plate structures to increase the flow of capacities. Because a single plate structure is utilized instead of a brazed or welded multi-piece structure, thermal gradients do not generate stresses at joints that could result in failure of the heat exchanger. Accordingly, the example plate structure provides a robust system for assembling a heat exchanger that resists mechanical fatigue and failures that are present in multi-piece heat exchanger assemblies. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.