Patent Publication Number: US-2017363369-A1

Title: Reduced thermal expansion closure bars for a heat exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a divisional of U.S. patent application Ser. No. 13/963,435 filed Aug. 9, 2013 for “REDUCED THERMAL EXPANSION CLOSURE BARS FOR A HEAT EXCHANGER” by Michael Zager, Donald E. Army, George Kan, Charles J. McColgan, and Nigel Palmer. 
    
    
     BACKGROUND 
     The present disclosure relates to heat exchangers, and in particular to closure bars for plate fin heat exchangers. 
     Heat exchangers are often used to transfer heat between two fluids. For example, in aircraft environmental control systems, heat exchangers may be used to transfer heat between a relatively hot air source (e.g., bleed air from a gas turbine engine) and a relatively cool air source (e.g., ram air). Some heat exchangers, often referred to as plate fin heat exchangers, include a plate fin core having multiple heat transfer sheets arranged in layers to define air passages therebetween. Closure bars seal alternating inlets of hot air and cool air inlet sides of the core. Accordingly, hot air and cool air are directed through alternating passages to form alternating layers of hot and cool air within the core. Heat is transferred between the hot and cool air via the heat transfer sheets that separate the layers. In addition, to facilitate heat transfer between the layers, each of the passages can include heat transfer fins, often formed of corrugated material (e.g., aluminum), that are oriented in a direction of the flow within the passage. The heat transfer fins increase turbulence and a surface area that is exposed to the airflow, thereby enhancing heat transfer between the layers. 
     Typically, to further facilitate heat transfer within the core, components of a plate fin heat exchanger are formed of a material, such as aluminum, that has a relatively high heat transfer coefficient. However, as hot air passes over the closure bars (e.g., closure bars at the hot air inlet), a combination of a high velocity of hot air at the inlet and a relatively high coefficient of thermal expansion of aluminum can cause rapid physical expansion of the closure bars. Accordingly, because corners of the heat exchanger restrain overall expansion of the core, such rapid expansion of the closure bars can result in physical damage to components of the core (e.g., crushing of the heat transfer fins). 
     SUMMARY 
     In one example, a plate fin heat exchanger is configured to receive hot flow from a hot source and to receive cool flow from a cool source. The plate fin heat exchanger includes a plurality of plates arranged in parallel to define a plurality of flow passages therebetween. The plate fin heat exchanger further includes a first set of closure bars arranged at a first side of the plurality of plates to seal a first set of the plurality of flow passages against ingress of the hot flow, thereby directing the hot flow into a second set of the plurality of flow passages. Each respective closure bar of the set of closure bars includes an inner core formed of a first material having a first coefficient of thermal expansion, and an outer cladding arranged about the inner core. The outer cladding is formed of a second material having a second coefficient of thermal expansion. The first coefficient of thermal expansion is less than the second coefficient of thermal expansion. 
     In another example, a closure bar for a plate fin heat exchanger includes a first length defining a major axis of the closure bar extending from a first end of the closure bar to a second end of the closure bar, a first width defining a first minor axis of the closure bar extending from a first minor face of the closure bar to a second minor face of the closure bar, and a first thickness defining a second minor axis of the closure bar extending from a first major face of the closure bar to a second major face of the closure bar. The closure bar further includes an inner core formed of a first material having a first coefficient of thermal expansion. The inner core has a second length, less than the first length of the closure bar, extending from a first end of the inner core proximate the first end of the closure bar to a second end of the inner core proximate the second end of the closure bar. The closure bar further includes an outer cladding formed of a second material having a second coefficient of thermal expansion and arranged about the inner core to circumscribe the inner core about the major axis of the closure bar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a plate fin heat exchanger. 
         FIG. 2  is an exploded view of a portion of the core of the plate fin heat exchanger of  FIG. 1 . 
         FIG. 3  is a side view of a closure bar. 
         FIG. 4  is a cross-sectional view along section A-A of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     According to techniques of this disclosure, a closure bar of a plate fin heat exchanger includes an inner core formed from a material (e.g., titanium) that has a lower coefficient of thermal expansion than a cladding (e.g., aluminum) arranged about the core. The inner core lowers the overall thermal expansion properties of the closure bar. The outer cladding can enable the closure bar to be more easily attached (e.g., welded) to other components of the heat exchanger (e.g., the heat exchanger housing) that may be formed of a similar material. Accordingly, a closure bar disclosed herein can help to prevent resulting stress and physical damage to components of the plate fin core, such as heat transfer fins of the core, which can result from rapid thermal expansion of the closure bar. In this way, the disclosed closure bar can increase reliability and longevity of components of a plate fin heat exchanger. 
       FIG. 1  is a schematic diagram of plate fin heat exchanger  10 , in accordance with one or more aspects of this disclosure. As illustrated, plate fin heat exchanger  10  includes hot air inlet  12 , hot air inlet manifold  13 , hot air outlet  14 , hot air outlet manifold  15 , and plate fin core  16 . Plate fin core  16  includes heat transfer plates  18 , cool air closure bars  20 , and hot air closure bars  22 . As illustrated, plate fin core  16  can further include a plurality of heat transfer structures disposed between heat transfer plates  18 , such as hot air fins  19  and cool air fins  21 . 
     Heat transfer plates  18  are arranged in parallel to define a plurality of flow passages therebetween. As illustrated, heat transfer plates  18  can be generally rectangular plates arranged in parallel layers to define flow passages (e.g., air flow passages) through gaps between the layers. As in the example of  FIG. 1 , heat transfer plates  18  can be arranged within plate fin core  16  to define a set of hot air flow passages  24  and a set of cool air flow passages  26 . Heat transfer plates  18  can be formed of one or more materials having a relatively high heat transfer coefficient, such as aluminum, copper, silver, gold, or other materials, thereby facilitating efficient heat transfer between air flows through alternating layers. Hot air fins  19  and cool air fins  21  can be disposed within hot air flow passages  24  and cool air flow passages  26 , respectively, and oriented in a direction of flow within a respective air flow passage, as is further described below. 
     Plate fin core  16  includes cladded cool air closure bars  20  disposed at hot air inlet side  28  and hot air outlet side  30  of plate fin core  16 . As illustrated, cool air closure bars  20  (i.e., a set of cool air closure bars  20 ) are arranged at hot air outlet side  30  in close physical proximity to the set of cool air flow passages  26  (e.g., by welding, brazing, or other attachment techniques) to seal the set of cool air flow passages  26  against ingress of hot air at hot air outlet side  30 . While illustrated as including cool air closure bars  20  arranged at hot air outlet side  30 , it should be understood that plate fin core  16  includes similar cool air closure bars  20  disposed at hot air inlet side  28  opposite hot air outlet side  30 . That is, each of cool air flow passages  26  is sealed against ingress of hot air at both hot air inlet side  28  and hot air outlet side  30  of plate fin core  16  by a set of cool air closure bars  20 . In this way, cool air closure bars  20  are configured to seal cool air flow passages  26  (i.e., a set of alternating flow passages of plate fin core  16 ) against ingress of hot air, thereby directing hot air received from a hot air source (e.g., engine bleed air from a gas turbine engine) into hot air flow passages  24 . 
     Plate fin core  16  further includes cladded hot air closure bars  22  disposed at cool air inlet side  32  and cool air outlet side  34  of plate fin core  16 . As illustrated, hot air closure bars  22  are arranged at cool air outlet side  34  in close physical proximity to the set of hot air flow passages  24  (e.g., by welding, brazing, or other attachment techniques) to seal the set of hot air flow passages  24  against ingress of cool air at cool air outlet side  34 . While illustrated as including hot air closure bars  22  arranged at cool air outlet side  34 , it should be understood that plate fin core  16  includes similar hot air closure bars  22  disposed at cool air inlet side  32  opposite cool air outlet side  34 . That is, each of hot air flow passages  24  is sealed against ingress of cool air at both cool air inlet side  32  and cool air outlet side  34  of plate fin core  16  by a set of hot air closure bars  22 . In this way, hot air closure bars  22  are configured to seal hot air flow passages  24  (i.e., a set of alternating flow passages of plate fin core  16 ) against ingress of cool air, thereby directing cool air received from a cool air source (e.g., ram air) into cool air flow passages  26 . 
     In some examples, as in the example of  FIG. 1 , each of hot air inlet side  28  and hot air outlet side  30  can be orthogonal to both of cool air inlet side  32  and cool air outlet side  34 . In such examples, plate fin core  16  includes hot air flow passages  24  that define a flow direction of hot air that is orthogonal a direction of a cool air flow defined by cool air flow passages  26 . In other examples, hot air inlet side  28  and hot air outlet side  30  need not be orthogonal to both of cool air inlet side  32  and cool air outlet side  34 . In general, plate fin core  16  can include any configuration of hot air flow passages and cool air flow passages such that hot air and cool air are directed through plate fin core  16  in alternating layers of hot and cool air. 
     According to techniques disclosed herein, cool air closure bars  20  and/or hot air closure bars  22  include an inner core formed of a first material having a first coefficient of thermal expansion and an outer cladding arranged about the inner core. The outer cladding can be formed of a second material having a second coefficient of thermal expansion. The first coefficient of thermal expansion can be less than the second coefficient of thermal expansion, thereby reducing the overall thermal expansion properties of the closure bar. 
     As an example operation of plate fin heat exchanger  10 , hot air is received by plate fin heat exchanger  10  via hot air inlet  12  from a hot air source, such as engine bleed air from a gas turbine engine. The hot air received via hot air inlet  12  is directed toward hot air inlet side  28  of plate fin core  16  by hot air inlet manifold  13 . Cool air closure bars  20 , arranged at hot air inlet side  28  of plate fin core  16 , seal cool air flow passages  26  from ingress of the hot air, thereby directing the hot air into hot air flow passages  24  (i.e., an alternating set of air passages of plate fin core  16 ). Accordingly, hot air flows through hot air flow passages  24  of plate fin core  16  along hot air flow path  36 . Hot air exiting hot air outlet side  30  is collected by hot air outlet manifold  15  and directed through hot air outlet  14 . Cool air is received by plate fin heat exchanger  10  via a cool air inlet (not illustrated) from a cool air source, such as ram air accumulated from an aircraft. The cool air is directed toward cool air inlet side  32  of plate fin core  16  by, for example, a cool air manifold. Hot air closure bars  22  seal hot air flow passages  24  from ingress of the cool air, thereby directing the cool air into cool air flow passages  26  (i.e., an alternating set of passages of plate fin core  16  that is complementary to the set of hot air flow passages  24 ). As such, cool air flows through cool air flow passages  26  of plate fin core  16  along cool air flow path  38  and exits plate fin core  16  at cool air outlet side  34 . 
     In operation, heat transfers between the alternating sets of hot air flow passages  24  and cool air flow passages  26  via heat transfer plates  18  that separate the layers. Hot air fins  19  disposed within hot air flow passages  24 , and cool air flow fins  21  disposed within cool air flow passages  26  enhance heat transfer between the layers. Cool air closure bars  20  and/or hot air closure bars  22  include an inner core formed of a material (e.g., titanium) that has a lower coefficient of thermal expansion than a material that forms an outer cladding arranged about the core (e.g., aluminum), as is further described below. Accordingly, the inner core lowers the overall thermal expansion properties of cool air closure bars  20  and/or hot air closure bars  22 , thereby decreasing a rate and/or amount of physical thermal expansion of cool air closure bars  20  and/or hot air closure bars  22 . In this way, cool air closure bars  20  and/or hot air closure bars  22  can reduce physical stress on components of plate fin heat exchanger  10  and/or damage to the components (e.g., crushing of heat transfer fins disposed between heat transfer plates  18 ) that can result from rapid expansion of cool air closure bars  20  and/or hot air closure bars  22 . 
       FIG. 2  is an exploded view of a portion of plate fin core  16  of  FIG. 1 . As illustrated in  FIG. 2 , plate fin core  16  includes heat transfer plates  18 , cool air closure bars  20 , and hot air closure bars  22 . As further illustrated, plate fin core  16  can include hot air flow fins  19  and cool air flow fins  21  disposed between heat transfer plates  18 . Heat transfer plates  18  are arranged in parallel to define a plurality of air passages therebetween, such as hot air flow passages  24  and cool air flow passages  26 . Cool air closure bars  20  are configured to be mounted (e.g., welded, brazed, and the like) adjacent cool air flow passages  26  at the hot air inlet side and hot air outlet side of plate fin core  16  to seal cool air flow passages  26  from ingress of hot air, thereby directing hot air received from a hot air source through hot air flow passages  24 . Hot air closure bars  22  are configured to be mounted (e.g., welded, brazed, and the like) adjacent hot air flow passages  24  at the cool air inlet side and cool air outlet side of plate fin core  16  to seal hot air flow passages  24  from ingress of cool air, thereby directing cool air received from a cool air source through cool air flow passages  26 . While the example illustration of  FIG. 2  includes one cool air closure bar  20  and one hot air closure bar  22 , it should be understood that plate fin core  16  can include multiple such cool air closure bars  20  and hot air closure bars  22 . For instance, as illustrated in  FIG. 1 , plate fin core  16  can include multiple cool air closure bars  20  disposed at alternating air flow passages of both a hot air inlet side (e.g., hot air inlet side  28  of  FIG. 1 ) and a hot air outlet side (e.g., hot air outlet side  30  of  FIG. 1 ) of plate fin core  16 . Similarly, plate fin core  16  can include multiple hot air closure bars  22  disposed at alternating flow passages of both a cool air inlet side (e.g., cool air inlet side  32  of  FIG. 1 ) and a cool air outlet side (e.g., cool air outlet side  34  of  FIG. 1 ) of plate fin core  16 . 
     As illustrated, hot air flow fins  19  and cool air flow fins  21  can each be formed of a corrugated sheet of material and oriented in a direction of flow within a respective air flow passage. For instance, hot air flow fins  19  can be oriented within hot air flow passages  24  such that folds in the corrugation are oriented in a direction of hot air flow through hot air flow passages  24 . Cool air flow fins  21  can be oriented within cool air flow passages  26  such that folds in the corrugation are orientated in a direction of cool air flow through cool air flow passages  26 . 
     As further described below, cool air closure bars  20  and/or hot air closure bars  22  can include an inner core formed of a first material (e.g., titanium) that has a lower coefficient of thermal expansion than a material that forms a cladding (e.g., aluminum) arranged about the inner core. The inner core can reduce the rate and/or amount of thermal expansion (e.g., volumetric and/or linear expansion) of cool air closure bars  20  and/or hot air closure bars  22  when subjected to hot air flow, thereby reducing stress and/or damage to components of plate fin core  16  resulting from such expansion of the closure bars (e.g., crushing of hot air flow fins  19  and/or cool air flow fins  21 ). 
       FIG. 3  is a side view of a closure bar for a plate fin heat exchanger, in accordance with one or more aspects of this disclosure. As illustrated in  FIG. 3 , closure bar  44  includes inner core  46  and outer cladding  48 . Inner core  46  can be formed of a first material having a first coefficient of thermal expansion. Examples of the first material of the inner core can include titanium, nickel, platinum, or other materials. Outer cladding  48  can be formed of a second material, different than the first material of inner core  46 . Examples of the second material of the outer cladding can include aluminum, stainless steel, or other materials. The second material can have a second coefficient of thermal expansion. The first coefficient of thermal expansion of inner core  46  can be less than the second coefficient of thermal expansion of outer cladding  48 . In certain examples, the second material that forms outer cladding  48  can be the same material as a material that forms a housing of the plate fin core. In some examples, the second material that forms outer cladding  48  can be a material that has a melting point that is within a threshold temperature range of a melting point of the material that forms a housing of the plate fin core (e.g., ten degrees Celsius, twenty degrees Celsius, fifty degrees Celsius, or other threshold amounts), thereby enabling attachment of closure bar  44  via attachment techniques such as welding, brazing, or other such techniques. In general, inner core  46  can be formed of any material that has a lower coefficient of thermal expansion than the material that forms outer cladding  48 . In this way, inner core  46  can lower the overall thermal expansion properties of closure bar  44 , thereby reducing the volumetric and/or linear physical thermal expansion of closure bar  44  when closure bar  44  is subjected to hot flow. 
     As illustrated in  FIG. 3 , closure bar  44  has closure bar length  50  extending from first closure bar end  52  to second closure bar end  54  and defining a major axis (i.e., an axis having greatest length) of closure bar  44 . Inner core  46  has inner core length  56  extending from first inner core end  58 , proximate first closure bar end  52 , to second inner core end  60 , proximate second closure bar end  54 . As illustrated, inner core length  56  can be less than closure bar length  50 , such that outer cladding  48  is arranged about inner core  46  and circumscribes inner core  46  along the major axis from first closure bar end  52  to second closure bar end  54 . 
     In some examples, inner core  46  can taper from a maximum width toward at least one of first inner core end  58  and second inner core end  60 . For example, as illustrated in  FIG. 3 , inner core  46  can taper along taper length  62  to a point. In other examples, inner core  46  can taper from a maximum width to a non-zero minimum width. The taper from the maximum width toward at least one of first inner core end  58  and second inner core end  60  can help to smooth a transition of thermal expansion properties of closure bar  44 , such that reduced thermal expansion properties of closure bar  44  provided by inner core  46  do not abruptly change within closure bar  44 . 
       FIG. 4  is a cross-sectional view along section A-A of  FIG. 3 . As illustrated in  FIG. 4 , closure bar  44  includes inner core  46  and outer cladding  48 . Closure bar  44  has closure bar width  64  extending from first closure bar minor face  66  to second closure bar minor face  68  (i.e., minor faces having less area than an area of a major face of closure bar  44 ) and defining a first minor axis of closure bar  44  (i.e., an axis having less than the greatest length of the axes of closure bar  44 ). Closure bar  44  has thickness  70  extending from first closure bar major face  72  to second closure bar major face  74  and defining a second minor axis of the closure bar. Inner core  46  has inner core width  76  extending from first inner core minor face  78  to second inner core minor face  80 . 
     In some examples, such as the illustrated example of  FIG. 4 , inner core width  76  can be greater than half of closure bar width  64 , such that inner core  46  forms greater than half of a width and/or volume of closure bar  44 . In other examples, inner core width  76  can be less than half of closure bar width  64 . In certain examples, as illustrated in  FIG. 4 , a thickness of inner core  46  can extend from first closure bar major face  72  to second closure bar major face  74 , such that a thickness of inner core  46  is the same as (e.g., equal to) thickness  70  of closure bar  44 . In this way, outer cladding  48  can be arranged about inner core  46  to circumscribe inner core  46  along a major axis of closure bar  44  (e.g., a length of closure bar  44 ) and not to circumscribe inner core  46  about the major faces of closure bar  44 . In other examples, outer cladding  48  can be arranged about inner core  46  to surround inner core  46  about each of the faces of inner core  46 , thereby enclosing inner core  46  within outer cladding  48  (not illustrated). 
     The following are non-exclusive descriptions of embodiments of the present disclosure. 
     A plate fin heat exchanger is configured to receive hot flow from a hot source and to receive cool flow from a cool source. The plate fin heat exchanger includes a plurality of plates arranged in parallel to define a plurality of flow passages therebetween. The plate fin heat exchanger further includes a first set of closure bars arranged at a first side of the plurality of plates to seal a first set of the plurality of flow passages against ingress of the hot flow, thereby directing the hot flow into a second set of the plurality of flow passages. Each respective closure bar of the first set of closure bars includes an inner core formed of a first material having a first coefficient of thermal expansion, and an outer cladding arranged about the inner core. The outer cladding is formed of a second material having a second coefficient of thermal expansion. The first coefficient of thermal expansion is less than the second coefficient of thermal expansion. 
     The plate fin heat exchanger of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components: 
     The plate fin heat exchanger may further include a second set of closure bars arranged at a second side of the plurality of plates to seal the second set of the plurality of flow passages against ingress of the cool flow, thereby directing the cool flow into the first set of the plurality of flow passages. 
     Each respective closure bar of the second set of closure bars may comprise an inner core formed of the first material having the first coefficient of thermal expansion and an outer cladding arranged about the inner core, the outer cladding formed of the second material having the second coefficient of thermal expansion. 
     The first set of the plurality of flow passages and the second set of the plurality of flow passages may comprise alternating sets of the plurality of flow passages. 
     The plate fin heat exchanger may further include a plurality of heat transfer structures disposed between each of the plurality of plates and within each of the plurality of defined flow passages. Each of the plurality of heat transfer structures may be oriented in a flow direction of the respective flow passage. 
     Each of the plurality of heat transfer structures may comprise a plurality of heat transfer fins. 
     Each of the plurality of heat transfer fins may be formed of a corrugated sheet of the second material. 
     The first side of the plurality of plates may be orthogonal to the second side of the plurality of plates. 
     The first material may comprise titanium. 
     The second material may comprise aluminum. 
     A maximum width of the inner core of each respective closure bar of the first set of closure bars may be greater than half of a width of the respective closure bar. 
     The inner core of each respective closure bar of the first set of closure bars may taper from a maximum width of the inner core toward at least one of a first and second end of the inner core. 
     A length of each respective closure bar of the first set of closure bars may be greater than a length of the inner core of the respective closure bar. 
     A thickness of the outer cladding of each respective closure bar of the first set of closure bars may be equal to a thickness of the inner core of the respective closure bar. 
     The plate fin heat exchanger may further include an outer housing that encloses the plurality of plates. The outer housing may be formed of the second material. 
     A closure bar for a plate fin heat exchanger includes a first length defining a major axis of the closure bar extending from a first end of the closure bar to a second end of the closure bar, a first width defining a first minor axis of the closure bar extending from a first minor face of the closure bar to a second minor face of the closure bar, and a first thickness defining a second minor axis of the closure bar extending from a first major face of the closure bar to a second major face of the closure bar. The closure bar further includes an inner core formed of a first material having a first coefficient of thermal expansion. The inner core has a second length, less than the first length of the closure bar, extending from a first end of the inner core proximate the first end of the closure bar to a second end of the inner core proximate the second end of the closure bar. The closure bar further includes an outer cladding formed of a second material having a second coefficient of thermal expansion and arranged about the inner core to circumscribe the inner core about the major axis of the closure bar. 
     The closure bar for the plate fin heat exchanger of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components: 
     The first material may comprise titanium. The second material may comprise aluminum. 
     The inner core may have a second thickness equal to the first thickness of the closure bar and extending from the first major face of the closure bar to the second major face of the closure bar along the second minor axis of the closure bar. 
     A maximum width of the inner core extending along the first minor axis of the closure bar may be greater than half of the first width of the closure bar. 
     The inner core may taper from a maximum width of the inner core toward each of the first and second ends of the closure bar. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.