Patent Publication Number: US-2018038654-A1

Title: System for fault tolerant passage arrangements for heat exchanger applications

Description:
BACKGROUND 
     The field of the disclosure relates generally to gas turbine engines and, more particularly, to a system for heat exchangers for use in a gas turbine engine. 
     At least some known gas turbine engines include one or more heat exchangers configured to cool and heat fluids within the gas turbine engine. Some heat exchangers include air-oil heat exchangers, fuel-oil heat exchangers, and air-air heat exchangers. To prevent leakage from one fluid stream within a heat exchanger to another fluid stream within the same heat exchanger, a double wall or redundant wall construction may be used. Double wall or redundant wall constructions add weight to the gas turbine engine and reduce the fuel efficiency of the gas turbine engine. 
     BRIEF DESCRIPTION 
     In one aspect, a heat exchanger assembly configured to transfer heat between a first fluid and a second fluid is provided. The heat exchanger assembly includes a heat exchanger body and a plurality of columns of fluid passages arranged in a first direction within the heat exchanger body. The plurality of columns of fluid passages includes at least one first fluid column of fluid passages and at least two second fluid columns of fluid passages. The first fluid column is interspersed between two second fluid columns. The first fluid column includes a plurality of first fluid passages configured to channel a first fluid through the heat exchanger body. The plurality of first fluid passages each includes an elliptical cross-section fluid passage. The at least two second fluid columns includes a plurality of second fluid passages configured to channel a second fluid through the heat exchanger body. The pluralities of second fluid passages each include an elliptical cross-section fluid passage. The plurality of first fluid passages is offset with respect to the plurality of second fluid passages. 
     In another aspect, a gas turbine engine is provided. The gas turbine engine includes a core engine including a high pressure compressor, a combustor, and a high pressure turbine in a serial flow arrangement. The gas turbine engine also includes a low pressure compressor and a low pressure turbine drivingly coupled to the low pressure compressor through a shaft and a power gear box. The gas turbine engine further includes a heat exchanger assembly coupled to the power gear box. The heat exchanger assembly includes a heat exchanger body and a plurality of columns of fluid passages arranged in a first direction within the heat exchanger body. The plurality of columns of fluid passages includes at least one first fluid column of fluid passages and at least two second fluid columns of fluid passages. The first fluid column is interspersed between two second fluid columns. The first fluid column includes a plurality of first fluid passages configured to channel a first fluid through the heat exchanger body. The plurality of first fluid passages each includes an elliptical cross-section fluid passage. The at least two second fluid columns includes a plurality of second fluid passages configured to channel a second fluid through the heat exchanger body. The pluralities of second fluid passages each include an elliptical cross-section fluid passage. The plurality of first fluid passages is offset with respect to the plurality of second fluid passages. 
     In yet another aspect, a gas turbine engine is provided. The gas turbine engine includes a core engine including a high pressure compressor, a combustor, and a high pressure turbine in a serial flow arrangement. The gas turbine engine also includes an inner casing circumscribing the core engine and an outer casing circumscribing the inner casing. The inner and outer casings define an undercowl space therebetween. The gas turbine engine also includes a heat exchanger assembly disposed within the undercowl space. The heat exchanger assembly includes a heat exchanger body and a plurality of columns of fluid passages arranged in a first direction within the heat exchanger body. The plurality of columns of fluid passages includes at least one first fluid column of fluid passages and at least two second fluid columns of fluid passages. The first fluid column is interspersed between two second fluid columns. The first fluid column includes a plurality of first fluid passages configured to channel a first fluid through the heat exchanger body. The plurality of first fluid passages each includes an elliptical cross-section fluid passage. The at least two second fluid columns includes a plurality of second fluid passages configured to channel a second fluid through the heat exchanger body. The pluralities of second fluid passages each include an elliptical cross-section fluid passage. The plurality of first fluid passages is offset with respect to the plurality of second fluid passages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIGS. 1-9  show example embodiments of the method and apparatus described herein. 
         FIG. 1  is a perspective view of an aircraft. 
         FIG. 2  is a schematic cross-sectional view of a gas turbine engine in accordance with an exemplary embodiment of the present disclosure that may be used with the aircraft shown in  FIG. 1 . 
         FIG. 3  is a schematic diagram of a heat exchanger. 
         FIG. 4  is a force diagram depicting forces on elliptical fluid passages within the heat exchanger shown in  FIG. 3 . 
         FIG. 5  is a perspective view of the heat exchanger shown in  FIG. 3  with elliptical fluid passages. 
         FIG. 6  is a force diagram depicting forces on circular fluid passages within the heat exchanger shown in  FIG. 3 . 
         FIG. 7  is a perspective view of the heat exchanger shown in  FIG. 3  with circular fluid passages. 
         FIG. 8  is a force diagram depicting forces on racetrack fluid passages within the heat exchanger shown in  FIG. 3 . 
         FIG. 9  is a perspective view of the heat exchanger shown in  FIG. 3  with racetrack fluid passages. 
     
    
    
     Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. Any feature of any drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of the disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of the disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
     DETAILED DESCRIPTION 
     In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. 
     The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     The following detailed description illustrates embodiments of the disclosure by way of example and not by way of limitation. It is contemplated that the disclosure has general application to a system for cooling fluids in an aircraft engine. 
     Embodiments of the heat exchanger assembly described herein exchange heat between separate fluids in a gas turbine engine assembly. The heat exchanger assembly includes a plurality of columns of fluid passages. Each column of fluid passages includes a plurality of fluid passages arranged vertically in the column and each passage within the column of fluid passages is configured to channel the same fluid. In various embodiments, each passage includes an oblong or elliptical shaped cross-section. The columns of fluid passages are arranged horizontally within the heat exchanger assembly in an alternating pattern. That is, a heating fluid is channeled in a first column of fluid passages and the two adjacent columns of fluid passages channel cooling fluids. The fluid passages within a column are offset with respect to the fluid passages within the two adjacent columns. The heat exchanger assembly is a monolithic construction formed by milling a single solid block or by additive manufacturing methods. 
     The heat exchanger assemblies described herein offer advantages over known methods of exchanging heat between fluids in a gas turbine engine. More specifically, arranging the passages in the columns in an offset pattern minimizes the stress field between dissimilar fluids. Additionally, the elliptical shape of the passages combined with the arrangement of the fluid passages also minimizes the stress field between dissimilar fluids. The arrangement of the fluid passages ensures that, if a passage were to leak, the passage would leak into a passage which channels the same fluid rather than a passage which channels a different fluid, ensuring that a failure in one passage does not cause the entire heat exchanger to fail. Finally, the shape and arrangement of fluid passages improves the reliability of the heat exchanger assembly, eliminating the need for double wall or redundant wall construction, reducing the weight and cost of the gas turbine engine. 
       FIG. 1  is a perspective view of an aircraft  100 . In the example embodiment, aircraft  100  includes a fuselage  102  that includes a nose  104 , a tail  106 , and a hollow, elongate body  108  extending therebetween. Aircraft  100  also includes a wing  110  extending away from fuselage  102  in a lateral direction  112 . Wing  110  includes a forward leading edge  114  in a direction  116  of motion of aircraft  100  during normal flight and an aft trailing edge  118  on an opposing edge of wing  110 . Aircraft  100  further includes at least one engine  120  configured to drive a bladed rotatable member or fan to generate thrust. Engine  120  is coupled to at least one of wing  110  and fuselage  102 , for example, in a pusher configuration (not shown) proximate tail  106 . 
       FIG. 2  is a schematic cross-sectional view of gas turbine engine  120  in accordance with an exemplary embodiment of the present disclosure. In the example embodiment, gas turbine engine  120  is embodied in a high bypass turbofan jet engine. As shown in  FIG. 2 , turbofan engine  120  defines an axial direction A (extending parallel to a longitudinal axis  202  provided for reference) and a radial direction R. In general, turbofan  120  includes a fan assembly  204  and a core turbine engine  206  disposed downstream from fan assembly  204 . 
     In the example embodiment, core turbine engine  206  includes an approximately tubular outer casing  208  that defines an annular inlet  220  and a tubular inner casing  210  circumscribed by outer casing  208 . Outer casing  208  and inner casing  210  encase, in serial flow relationship, a compressor section including a booster or low pressure (LP) compressor  222  and a high pressure (HP) compressor  224 ; a combustion section  226 ; a turbine section including a high pressure (HP) turbine  228  and a low pressure (LP) turbine  230 ; and a jet exhaust nozzle section  232 . Outer casing  208  also includes an outer radial surface  209 . A high pressure (HP) shaft or spool  234  drivingly connects HP turbine  228  to HP compressor  224 . A low pressure (LP) shaft or spool  236  drivingly connects LP turbine  230  to LP compressor  222 . The compressor section, combustion section  226 , turbine section, and nozzle section  232  together define a core air flowpath  237 . An undercowl space  214  is defined by the volume between inner casing  210  and outer casing  208 . 
     In the example embodiment, fan assembly  204  includes a variable pitch fan  238  having a plurality of fan blades  240  coupled to a disk  242  in a spaced apart relationship. Although fan assembly  204  is described as including a variable pitch fan  238 , fan assembly  204  could include a conventional fixed pitch fan. Fan blades  240  extend radially outwardly from disk  242 . Each fan blade  240  is rotatable relative to disk  242  about a pitch axis P by virtue of fan blades  240  being operatively coupled to a suitable pitch change mechanism (PCM)  244  configured to vary the pitch of fan blades  240 . In other embodiments, PCM  244  is configured to collectively vary the pitch of fan blades  240  in unison. Fan blades  240 , disk  242 , PCM  244 , and LP compressor  222  are together rotatable about longitudinal axis  202  by LP shaft  236  across a power gear box  246 . 
     Disk  242  is covered by rotatable front hub  248  aerodynamically contoured to promote an airflow through the plurality of fan blades  240 . Additionally, fan assembly  204  includes an annular fan casing or outer nacelle  250  that circumferentially surrounds fan  238  and/or at least a portion of core turbine engine  206 . In the example embodiment, nacelle  250  is configured to be supported relative to core turbine engine  206  by a plurality of circumferentially-spaced outlet guide vanes  252 . Moreover, a downstream section  254  of nacelle  250  may extend over an outer portion of core turbine engine  206  so as to define a bypass airflow passage  256  therebetween. 
     During operation of turbofan engine  120 , a volume of air  258  enters turbofan  120  through an associated inlet  260  of nacelle  250  and/or fan assembly  204 . As volume of air  258  passes across fan blades  240 , a first portion  262  of volume of air  258  is directed or routed into bypass airflow passage  256  and a second portion  264  of volume of air  258  is directed or routed into core air flowpath  237 , or more specifically into LP compressor  222 . A ratio between first portion  262  and second portion  264  is commonly referred to as a bypass ratio. The pressure of second portion  264  is then increased as it is routed through HP compressor  224  and into combustion section  226 , where it is mixed with fuel and burned to provide combustion gases  266 . 
     Combustion gases  266  are routed through HP turbine  228  where a portion of thermal and/or kinetic energy from combustion gases  266  is extracted via sequential stages of HP turbine stator vanes  268  that are coupled to outer casing  208  and HP turbine rotor blades  270  that are coupled to HP shaft or spool  234 , thus causing HP shaft or spool  234  to rotate, which then drives a rotation of HP compressor  224 . Combustion gases  266  are then routed through LP turbine  230  where a second portion of thermal and kinetic energy is extracted from combustion gases  266  via sequential stages of LP turbine stator vanes  272  that are coupled to outer casing  208  and LP turbine rotor blades  274  that are coupled to LP shaft or spool  236 , which drives a rotation of LP shaft or spool  236 , LP compressor  222 , and rotation of fan  238  across power gear box  246 . 
     Combustion gases  266  are subsequently routed through jet exhaust nozzle section  232  of core turbine engine  206  to provide propulsive thrust. Simultaneously, the pressure of first portion  262  is substantially increased as first portion  262  is routed through bypass airflow passage  256  before it is exhausted from a fan nozzle exhaust section  276  of turbofan  120 , also providing propulsive thrust. HP turbine  228 , LP turbine  230 , and jet exhaust nozzle section  232  at least partially define a hot gas path  278  for routing combustion gases  266  through core turbine engine  206 . 
     Exemplary embodiments of heat exchanger  300  (shown in  FIG. 3 ) may be located in various locations within gas turbine engine  120 . A heat exchanger  280  is coupled to power gear box  246  and exchanges heat between a lubricant stream (oil) from core turbine engine  206  and fuel. Heat exchanger  280  may also exchange heat between two streams of oil. In another embodiment, heat exchanger  280  may be formed integral to power gear box  246  rather than being a separate component coupled to power gear box  246 . A heat exchanger  282  is disposed within undercowl space  214  and exchanges heat between two streams of air, for example, air from undercowl space  214  and bleed air from LP compressor  222  and HP compressor  224 . Another air-air heat exchanger  284  is coupled to nacelle  250  and exchanges heat between two streams of air. Heat exchangers  280 ,  282 , and  284  may be located in any location within gas turbine engine  120  which enables heat exchangers  280 ,  282 , and  284  to operate as described herein. Other applications for heat exchangers  280 ,  282 , and  284  include exchanging heat between a stream of fuel and a stream of air, a stream of lubricant (oil) and a stream of air, and a stream of refrigerant and a stream of air. Heat exchangers  280 ,  282 , and  284  may be formed integral to pumps, controllers, valves, or any other components of gas turbine engine  120 . 
     Exemplary turbofan engine  120  depicted in  FIG. 2  is by way of example only, and in other embodiments, turbofan engine  120  may have any other suitable configuration. It should also be appreciated, that in still other embodiments, aspects of the present disclosure may be incorporated into any other suitable gas turbine engine. For example, in other embodiments, aspects of the present disclosure may be incorporated into, e.g., a turboprop engine. 
       FIG. 3  is a cross-section of a heat exchanger  300 . Heat exchanger  300  includes a heat exchanger body  302 . In the exemplary embodiment, heat exchanger body  302  is a matrix style heat exchanger of unitary construction manufactured by printing a single block by additive manufacturing methods or by milling a single block of material. Heat exchanger body  302  includes a plurality of first columns  304  and a plurality of second columns  306  interdigitated with plurality of first columns  304 . Each column  304  of plurality of first columns  304  includes a plurality of first flow passages  307  that extend into and out of the page as shown in  FIG. 3 . Each column  306  of plurality of second columns  306  includes a plurality of second flow passages  308  that also extend into and out of the page parallel with respect to each other of the plurality of first flow passages  307  and plurality of second flow passages  308 . In one embodiment, shown in  FIGS. 3-5 , flow passages  307  and  308  include an elliptical or oblong cross-section having a centroid  309 . In another embodiment, shown in  FIGS. 6-7 , flow passages  307  and  308  include a circular cross-section having a centroid  309 . In yet another embodiment, shown in  FIGS. 8-9 , flow passages  307  and  308  include a racetrack cross-section having a centroid  309 . First flow passages  307  are offset by a predetermined distance or pitch  310  (see  FIG. 3 ) with respect to second flow passages  308 . 
       FIGS. 3-9  show flow passages  307  and  308  with uniform cross-sectional areas. However, flow passages  307  and  308  may include varying cross-sectional areas or may include different cross-sections. For example, first columns  304  may include first flow passages  307  with circular cross-sections and second columns  306  may include second flow passages  308  with elliptical cross-sections. Additionally, the cross-sectional area of each first flow passage  307  of the plurality of first flow passages  307  may be distinct from the cross-sectional areas of the other first flow passages  307  within the plurality of first flow passages  307 . The cross-section and cross-sectional areas of first and second flow passages  307  and  308  may be varied to achieve a required heat transfer rate or a required pressure drop through heat exchanger  300 . 
     During operation, heat exchanger  300  is configured to transfer heat between a first fluid flowing in first flow passages  307  and a second fluid in second flow passages  308 . First fluid and second fluid could include air, fuel, and oil. First passages  304  and second passages  306  may be configured in a counter-current flow arrangement or a parallel flow arrangement. 
     In the example embodiment, heat exchanger  300  is formed unitarily of a sintered metal material, using for example, an additive manufacturing process. In one embodiment, heat exchanger  300  is formed by an additive manufacturing process. The sintered metal material comprises a superalloy material, such as, but not limited to cobalt chrome, aluminum alloys, titanium alloys, and austenite nickel-chromium-based superalloys, and the like. As used herein, “additive manufacturing” refers to any process which results in a three-dimensional object and includes a step of sequentially forming the shape of the object one layer at a time. Additive manufacturing processes include, for example, three dimensional printing, laser-net-shape manufacturing, direct metal laser sintering (DMLS), direct metal laser melting (DMLM), selective laser sintering (SLS), plasma transferred arc, freeform fabrication, and the like. One exemplary type of additive manufacturing process uses a laser beam to sinter or melt a powder material. Additive manufacturing processes can employ powder materials or wire as a raw material. Moreover, additive manufacturing processes can generally relate to a rapid way to manufacture an object (article, component, part, product, etc.) where a plurality of thin unit layers are sequentially formed to produce the object. For example, layers of a powder material may be provided (e.g., laid down) and irradiated with an energy beam (e.g., laser beam) so that the particles of the powder material within each layer are sequentially sintered (fused) or melted to solidify the layer. 
       FIG. 4  is force diagram depicting forces acting on a fluid passage  402  with elliptical cross-sections, such as first flow passages  307  or second flow passages  308  (both shown in  FIG. 3 ).  FIG. 5  is a perspective view of heat exchanger  300  with fluid passage  402  with elliptical cross-sections.  FIG. 6  is force diagram depicting forces acting on a fluid passage  602  with circular cross-sections.  FIG. 7  is a perspective view of heat exchanger  300  with fluid passage  602  with circular cross-sections.  FIG. 8  is force diagram depicting forces acting on a fluid passage  802  with racetrack cross-sections.  FIG. 9  is a perspective view of heat exchanger  300  with fluid passage  802  with racetrack cross-sections. Fluid passages  402 ,  602 , and  802  are fluid passages within first flow passages  307  and fluid passages  404 ,  604 , and  804  are fluid passages within second flow passages  308 . The forces acting on fluid passages  402 ,  602 , and  802  are similar to each other. Fluid passages  402 ,  602 , and  802  receive two horizontal forces  406  on either side of fluid passages  402 ,  602 , and  802 , two vertical forces  408  on top and on bottom of fluid passages  402 ,  602 , and  802 , and four diagonal forces  410  during operation of heat exchanger  300 . Horizontal forces  406  act in a horizontal direction  407  and vertical forces act in a vertical direction  409 . Horizontal forces  406  include compressive forces and vertical forces  408  include tensile forces. Horizontal forces  406 , vertical forces  408 , and diagonal forces  410  are created primarily by differential thermal expansion of first flow passages  307  relative to second flow passages  308  or by mechanical (pressure) loading of first flow passages  307  and second flow passages  308 . 
     Diagonal forces  410  result in zero or near zero stress between fluid passages which channel dissimilar fluids. The highest stress due to forces between fluid passages originates from horizontal forces  406  and vertical forces  408 . Horizontal forces  406  and vertical forces  408  result in stresses between fluid passages which channel the same fluids. Thus, the most likely failure mode for heat exchanger  300  is between fluid passages with similar fluids, which would not cause heat exchanger  300  to fail in operation because the flow in each passage is flowing in parallel already. 
     The offset arrangement described above orients fluid passages  308  such that horizontal forces  406  and vertical forces  408  act between fluid passages with like fluids. That is, if a failure were to occur due to either horizontal forces  406  or vertical forces  408 , the fluid within fluid passage  402  would leak into a fluid passage channeling the same fluid as fluid passage  402 . The only forces acting between fluid passages which channel dissimilar forces are diagonal forces  410 . Thus, heat exchanger  300  is configured to fail, if at all, between two fluid passages with similar fluids that are always in the same fluid circuit. A failure between two fluid passages with dissimilar fluids is unlikely because diagonal forces  410  are significantly lower than horizontal forces  406  and vertical forces  408 . 
     The above-described heat exchange assembly provides an efficient method for exchanging heat between fluids in a gas turbine engine. Specifically, arranging the passages in an offset pattern minimizes the stress field between passages carrying dissimilar fluids. More specifically, the shape of the passages combined with the arrangement of the fluid passages, minimizes the stress field between passages carrying dissimilar fluids. Additionally, the arrangement of the fluid passages ensures that, if a passage were to leak, the passage would leak into a passage which channels the same fluid rather than a passage which channels a different fluid, ensuring that a failure in one passage does not cause the entire heat exchanger to fail. Finally, the shape and arrangement of fluid passages improves the reliability of the heat exchanger assembly, eliminating the need for double wall or redundant wall construction, reducing the weight and cost of the gas turbine engine. 
     Exemplary embodiments of the heat exchanger assembly are described above in detail. The heat exchanger assembly, and methods of operating such systems and devices are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may also be used in combination with other systems requiring heat exchange between fluids, and are not limited to practice with only the systems and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other machinery applications that are currently configured to receive and accept heat exchanger assemblies. 
     Example methods and apparatus for exchanging heat between fluids are described above in detail. The apparatus illustrated is not limited to the specific embodiments described herein, but rather, components of each may be utilized independently and separately from other components described herein. Each system component can also be used in combination with other system components. 
     This written description uses examples to describe 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 have 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.