Abstract:
A compact heat exchanger for providing coolant gas flow through a part is provided. The compact heat exchanger reduces internal pressure losses through the compact heat exchanger. The compact heat exchanger has at least one inlet through which a coolant gas may enter, a circuit channel in fluid communication with the at least one inlet, and at least one outlet in fluid communication with the circuit channel through which the coolant gas may exit the circuit channel. The circuit channel is formed from superimposition of a plurality of alternating serpentine circuits, where at least one crossover of the circuit channel has a flow stabilizer that is formed in the channel and reduces internal pressure losses in the circuit channel.

Description:
GOVERNMENT RIGHTS IN THE INVENTION  
       [0001]     The invention was made by or under contract with the Air Force of the United States Government under contract number F33615-03-D-2354. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a compact heat exchanger or microcircuit for providing heat dissipation and film protection. More specifically, the invention relates to a linked compact heat exchanger or microcircuit with low levels of internal pressure loss.  
         [0004]     2. Description of the Related Art  
         [0005]     As a result of moving at high speeds through gas or having high-speed gas passing over static parts, parts such as turbines employ various techniques to dissipate internal heat, as well as provide a protective cooling film over the surface of the part. One such technique involves the integration of cooling channels into the part through which cool gas can flow, absorbing heat energy, and exiting so as to form a protective film.  
         [0006]     With reference to  FIG. 1 , there is illustrated a cooling channel fabricated as a linked microcircuit. This linked microcircuit is the subject of U.S. Pat. No. 6,705,831 to Draper, which is commonly owned with the present application and the disclosure of which is incorporated herein by reference. The linked microcircuit provides coolant gas flow through a part, such as, for example, combustor liners, turbine vanes, turbine blades, turbine BOAS, vane endwalls, and/or airfoil edges. The exemplary embodiment of the Draper linked microcircuit comprises an inlet through which a coolant gas may enter, a circuit channel extending from the inlet through which the coolant gas may flow and an outlet appended to the circuit channel through which the coolant gas may exit the circuit channel (as depicted in the two sets of arrows). The circuit channel is formed from the superimposition of a plurality of alternating serpentine circuits.  
         [0007]     The linked microcircuit of Draper provides improved thermal coverage while reducing the incongruity of coolant gas properties present at the junctions or crossover points of the component serpentine microcircuits. This is due at least in part to the property that similar points along the circuit channel of the Draper linked microchannel would end up coincident, and the properties of the coolant gases present at any one such point joining after traveling through adjacent circuit channels would be nearly identical. The resulting mixing of gases in the Draper microchannel occurs with a reduction of incongruities in gas temperature or pressure.  
         [0008]     However, the use of serpentine circuit channels having an abrupt 180° turn therein (e.g., adjacent 90° turns), creates internal pressure losses. Thus, there is a need for a microcircuit that reduces internal pressure losses while maintaining the efficiency of heat exchange.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide an improved system and method for heat dissipation and film protection.  
         [0010]     It is a further object of the present invention to provide such a system and method that reduces internal pressure losses.  
         [0011]     It is another object of the present invention to provide such a system and method that improves thermal coverage, while reducing the incongruity of coolant gas properties flowing therein.  
         [0012]     A compact heat exchanger for providing coolant gas flow through a part is provided. The compact heat exchanger comprises at least one inlet through which a coolant gas may enter; a circuit channel in fluid communication with the at least one inlet, wherein the circuit channel is formed from superimposition of a plurality of alternating serpentine circuits; and at least one outlet in fluid communication with the circuit channel through which the coolant gas may exit the circuit channel. The at least one crossover of the circuit channel has a flow stabilizer that is formed in the circuit channel. The flow stabilizer reduces internal pressure losses in the circuit channel.  
         [0013]     In another aspect, a method of dispensing heat in a part is provided. The method comprises providing a compact heat exchanger in thermal communication with the part, with the microcircuit being formed from superimposition of a plurality of alternating serpentine circuits that provide adjacent flow paths that converge and/or diverge at crossovers; and directing at least two of the adjacent flow paths to converge or diverge at an angle with respect to each other at one or more of the crossovers.  
         [0014]     The flow stabilizer may direct the flow along a non-orthogonal path. The at least one crossover can be adjacent to the at least one inlet. The flow stabilizer may be positioned along a downstream portion of the at least one crossover. The flow stabilizer can reduce a cross-sectional area of the at least one crossover. The at least one crossover may be positioned along a portion of the part that is in proximity to a low-pressure ratio area.  
         [0015]     The downstream portion of the at least one crossover can be substantially convex. The upstream portion of the at least one crossover may be substantially convex. The upstream and downstream portions of the at least one crossover can be substantially symmetrical. The circuit channel can have a first-cross-sectional area, and the at least one crossover can have a second cross-sectional area that is twice as large as the first cross-sectional area.  
         [0016]     The circuit channel can have a third cross-sectional area, and the first cross-sectional area can be twice as large as the third cross-sectional area. The inner geometry of the first crossover can direct flow in a non-orthogonal path. The downstream portion of the first crossover may be convex. The downstream portion of the second crossover can be planar. The method may further comprise directing one or more of the flow paths to eliminate 90° turns along a portion of the compact heat exchanger that is subject to a low-pressure ratio. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Other uses and advantages of the present invention will become apparent to those skilled in the art upon reference to the specification and the drawings, in which:  
         [0018]      FIG. 1  is a schematic view of a linked microcircuit as depicted in U.S. Pat. No. 6,705,831.  
         [0019]      FIG. 2  is a cross-sectional view of a gas turbine engine that may employ a compact heat exchanger in accordance with the present invention;  
         [0020]      FIG. 3  is a schematic view of an exemplary embodiment of the compact heat exchanger of the present invention; and  
         [0021]      FIG. 4  is a schematic view of another exemplary embodiment of a compact heat exchanger of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 2  shows a portion of a gas turbine engine  1  that may employ a compact heat exchanger or linked microcircuit of the present invention. The gas turbine has numerous components known in the art including, but not limited to, a blade  2  and a blade outer air seal  3  with a gas flow path shown by arrow  5  and cooling path or supply shown by arrows  6 .  FIG. 3  provides a schematic view of an exemplary embodiment of a microcircuit heat exchanger of the present invention generally represented by reference numeral  10 . The microcircuit  10  is usable with various parts or components moving at high speeds through gas or having high-speed gas passing thereover to dissipate internal heat, as well as provide a protective cooling film over the surface of the part. Such parts or components can be, but are not limited to, components of the gas turbine of  FIG. 2 .  
         [0023]     Microcircuit  10  is a compact heat exchanger, which is a superimposition of alternating serpentine microcircuits or heat exchangers, where the pitch of the alternating serpentine microcircuits has been reduced such that adjacent alternating serpentine microcircuits touch. The pitch is the distance between each of the parallel paths of the circuit channel  20  of the alternating serpentine microcircuits. The degree to which the pitch may be reduced to cause superimposition of the alternating serpentine microcircuits when creating compact heat exchanger  10  is variable, and depends upon the desired coolant gas flow characteristics.  
         [0024]     The circuit channels  20  are in communication with one or more inlets  30  and one or more outlets  40  for the flow of a cooling medium or fluid therethrough along the flow path indicated by arrows  25 . In a gas turbine engine, the cooling fluid is typically compressed ambient air. However, the present disclosure contemplates the use of other cooling fluids such as, for example, ethylene glycol, propylene glycol, steam or the like that are used in the cooling of parts or components such as, for example, internal combustion engines, steam turbines and/or heat exchanger applications.  
         [0025]     Referring to  FIG. 4 , the circuit channels  120  converge and/or diverge at crossover points  150 . In the exemplary embodiment of compact heat exchanger  100 , the microcircuit is used within a component or part that is subjected to a pressure differential. In  FIG. 2 , the cooling passages of the blade outer air seal  3  are supplied from a single supply chamber. Region  60  has a higher pressure than does region  70 . From the supply chamber, coolant flow  6 , which exits to the region upstream of the blade  2 , is at a lower pressure ratio than that of flow  6  which exits to the downstream region  70 . The use of a compact heat exchanger  100  would require a lower supply pressure to drive cooling flow than would the configuration described in the prior art. At locations where pressure ratio is limited, it is preferred to have internal cooling features with lower pressure losses. This minimizes the supply pressure needed and reduces leakage resulting in a more efficient system.  
         [0026]     Referring back to  FIG. 3 , to reduce the internal pressure losses along the microcircuit  10 , the crossovers  50  in the low-pressure ratio area  60  are provided with flow stabilizers  80 . The flow stabilizers  80  provide a change of geometry to the turn in the circuit channel  20  to reduce the internal pressure loss. The flow stabilizers  80  preferably have a concave shape. In the exemplary embodiment of microcircuit  10 , the flow stabilizers are positioned along a downstream portion of the crossover  50  and are adjacent to each of the inlets  30 . The flow stabilizers  80  eliminate the 90° turns that the cooling fluid must accomplish to pass through these crossovers  50  by deflecting or directing the flow along a substantially non-orthogonal and/or curved path.  
         [0027]     In the exemplary embodiment of microcircuit  100  of  FIG. 4 , the crossovers  150  in the low-pressure ratio area  60  are reduced in cross-sectional area by the flow stabilizers  180  so as to maintain a substantially uniform total cross-sectional area through which the cooling fluid flows. This is more evident by comparing the crossovers  150  of the low-pressure ratio areas  60  of the exemplary embodiment, with the expanded crossover points of  FIG. 1 . Maintaining a substantially uniform total cross-sectional area along the flow path  125 , eliminates any region for expansion of the fluid as it passes through the crossover  150 . The cross-sectional area of the crossover  150  is preferably substantially equal to twice the cross-sectional area of the circuit channel  120 . This reduces internal pressure loss by maintaining a uniform volume through which the cooling fluid is flowing.  
         [0028]     In contrast, the crossovers of the prior art of  FIG. 1 , which do not have flow stabilizers  180 , are larger in cross-sectional area than cross-overs  150 . Use of this geometry in locations with high pressure ratios  70  compensates for the higher internal pressure losses.  
         [0029]     In the alternative exemplary embodiment of  FIG. 4 , microcircuit  100  has a circuit channel  120  with one or more inlets  130  and one or more outlets  140  for the flow of a cooling medium or fluid therethrough along the flow path indicated by arrows  125 . Flow stabilizers  180  are positioned at substantially each of the crossovers  150 , where the adjacent flow paths  125  converge and/or diverge. The number of flow stabilizers  180  that are used in the circuit channel  120 , and how far along the microcircuit  100  that the flow stabilizers are positioned, depends upon the pressure ratios to which the microcircuit  180 , and its component, are subjected.  
         [0030]     The flow stabilizers  180  are concave at the upstream and downstream portions of the crossovers  150 . In this embodiment, the flow stabilizers  180  are symmetrical. However, the present disclosure also contemplates the use of non-symmetrical flow stabilizers  180 . The crossovers  150  are reduced in cross-sectional area by the flow stabilizers  180  so as to maintain a substantially uniform total cross-sectional area through which the cooling fluid flows. Maintaining a substantially uniform total cross-sectional area along the flow path  125 , eliminates any region for expansion of the fluid as it passes through the crossover  150 . The cross-sectional area of the crossover  150  is preferably substantially equal to twice the cross-sectional area of the circuit channel  120 . This reduces internal pressure loss by maintaining a uniform volume through which the cooling fluid is flowing.  
         [0031]     The flow stabilizers  180  also eliminate the 90° turns that the cooling fluid must accomplish to pass through these crossovers  50  by deflecting or directing the flow along a substantially non-orthogonal and/or curved path. Also, the flow stabilizers  180  direct adjacent flow paths  125  so that when they converge at the crossovers  150 , they are not moving in directly opposite directions to each other. The flow stabilizers  180  converge and diverge the adjacent flow paths  125  at an angle to each other, which reduces the internal pressure loss at the crossover  150 .  
         [0032]     The microcircuit  100  was subjected to testing with respect to the internal pressure loss. It was determined from this testing that the flow stabilizers  80  and  180  reduce internal pressure losses at the crossovers  50  and  150 , respectively. The prior art crossovers having adjacent 90° turns and expanded crossover regions, provided inherent instability where the adjacent flow paths were converging and/or diverging, including increased pressure loss and a higher heat transfer coefficient. It has been determined that the changing of the geometry of the crossovers  50  and  150 , including eliminating adjacent 90° turns, utilizing a substantially uniform cross-sectional area (approximately twice the cross-sectional area of the circuit channels  20  and  120 ), and eliminating directly opposite convergence of adjacent flow paths, has reduced internal pressure losses for the compact heat exchangers.  
         [0033]     Compact heat exchangers  10  and  100  may be placed in thermal communication with a part, such as a turbine or airfoil, utilizing an array of small channels. The microcircuits  10  and  100  and their corresponding circuit channels  20  and  120  can be tailored for the local heat load and geometry requirements of the part. Compact heat exchangers  10  and  100  offer advantages during fabrication. Because the linked serpentine circuit channels  20  or  120  are linked, the core body used to create them will also be linked. This linking will make a more rigid structure for the casting process greatly increasing the chances of casting success.  
         [0034]     While the instant disclosure has been described with reference to one or more exemplary embodiments, 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 thereof. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.