Gas turbine engine component with integrated heat pipe

The present invention relates to gas turbine engine components with integrated heat pipes.

The present invention generally relates to gas turbine engines and oil cooling methods in such engines.

Gas turbine engines are generally provided with a circulating oil system that lubricates and cools various engine components such as bearings, gearboxes, generators and the like. During operation, the oil absorbs a significant amount of heat that needs to be discharged to the external environment and keeps the oil at an acceptable temperature. As engine design advances, the amount of heat emitted is increasing.

Known oil cooling systems for gas turbine engines typically include one or more air-to-oil heat exchangers called "air-cooled oil coolers" or "ACOCs". These heat exchangers are heavy and can have high drag and may require special inlet and outlet ducts and large, heavy brackets. ACOC may also be used in series with fuel-to-oil heat exchangers and fuel tank return systems (FRTT) in complex cooling networks. However, the increasing heat load is expected to exceed the capacity of such systems.

In the prior art, it has been proposed to circulate the fluid directly inside a flow boundary structure such as an outlet guide vane (OGV). However, for flight essential fluids such as lubricants, damaged heat exchangers that can cause fires and significant oil losses are a problem.

Therefore, there is a need for a gas turbine engine heat exchanger with low drag that can physically separate the oil from the heat exchanger while maintaining a strong thermal connection throughout the cooling cycle.

<p num="0007"><patcit num="1"><text>U.S. Pat. No. 8,656,722</text></patcit></p>

This need is addressed by the present invention, which provides a flow boundary structure for a gas turbine engine with an integrated heat exchanger device.

According to one aspect of the present invention, the heat transfer device for a gas turbine engine has a component having a wall structure defining a flow boundary surface, a wicking structure formed in the component, a steam flow path, and the like. It comprises a chamber with a working fluid.

According to another aspect of the invention, the chamber is formed integrally with the wall structure.

According to another aspect of the invention, the wall structure transitions from a solid structure at the flow interface to a permeable structure on the inner surface.

According to another aspect of the invention, the wall structure comprises a collection of solids, the aggregate of solids having holes perpendicular to each other at intervals passing through it.

According to another aspect of the invention, the holes are arranged in two or more layers, and the holes in each layer have different diameters.

According to another aspect of the invention, the component comprises an airfoil portion having opposing positive and negative pressure side walls, a root portion, a tip, and spaced front and trailing edges.

According to another aspect of the invention, the chamber extends beyond the root or tip of the airfoil.

According to another aspect of the invention, the wicking structure straddles the space between the sidewalls, and a series of spanning vapor channels extend through the wicking structure.

According to another aspect of the invention, the wicking structure straddles the space between the sidewalls, and a wingspan vapor flow path with a blade-shaped cross section extends through the central portion of the wicking structure. To do.

According to another aspect of the invention, a plurality of struts extend laterally between the positive pressure side wall and the negative pressure side wall, and at least a part of one or more struts is a part of the wicking structure. Includes a clearing transparent material.

According to another aspect of the invention, a portion of the chamber extends beyond the rest of the components so that a sump surrounds the extending portion of the chamber and circulates fluid through it. Has been done.

According to another aspect of the invention, a portion of the chamber extends beyond the rest of the components and a fluid conduit is placed in contact with the extending portion of the chamber.

According to another aspect of the invention, the fluid conduit has an annular outer wall and the extending portion of the chamber has a concave saddle shape that contacts the outer wall of the fluid conduit.

According to another aspect of the invention, part of the chamber extends beyond the rest of the components and the stub portion of the fluid conduit is part of a single monolithic structure with an extending portion of the chamber. Is formed as.

According to another aspect of the present invention, the heat transfer device for a gas turbine engine is arranged in a ring shape around the engine and defines an inner end portion and an outer end portion which extend in a substantially radial direction and face each other. It comprises a plurality of components, each component having a wall structure defining a flow interface, a wicking structure formed within the components, a vapor flow path, and a chamber comprising a working fluid. The chamber comprises an evaporator end and an opposing condenser end, the evaporator end being located at the inner end of the corresponding component for a portion of the chamber and for another chamber. The evaporator end is located at the outer end of the corresponding component.

According to another aspect of the invention, the evaporator ends of each chamber are arranged such that gravity assists the flow of fluid from the condenser end to the evaporator end for a given orientation of the engine. Has been done.

According to another aspect of the invention, the component is a guide vane.

The present invention can be best understood by reference to the following description in conjunction with the accompanying drawings.

<figref num="1">FIG. 5 is a schematic cross-sectional view of a gas turbine engine incorporating a heat exchanger system configured according to one aspect of the present invention.</figref><figref num="2">It is the schematic sectional drawing of the gas turbine engine which has an inverted fan.</figref><figref num="3">It is a perspective view of the outlet guide vane of the gas turbine engine of FIG.</figref><figref num="4">It is a schematic functional diagram of the outlet guide vane which shows the operation method of this invention.</figref><figref num="5">It is sectional drawing of the airfoil part which shows the 1st internal structure.</figref><figref num="6">It is sectional drawing of the airfoil part which shows another internal structure.</figref><figref num="7">It is sectional drawing of the airfoil part which shows another alternative internal structure.</figref><figref num="8">It is a schematic sectional view of the airfoil part which has an integrated heat pipe structure and a sump.</figref><figref num="9">It is the schematic sectional drawing of the airfoil part connected to the fluid conduit.</figref><figref num="10">It is the schematic which shows the airfoil part of an annular arrangement.</figref><figref num="11">It is a schematic front view of an exemplary heat pipe structure.</figref><figref num="12">FIG. 3 is a schematic cross-sectional view of a steam chamber integrally coupled to a fluid conduit stub.</figref><figref num="13">FIG. 2 is a schematic vertical cross-sectional view of the steam chamber and fluid conduit stub of FIG.</figref>

With reference to the drawings, the same reference numbers refer to the same elements throughout the various drawings, and FIG. 1 shows a gas turbine engine 10 incorporating a heat exchanger apparatus configured according to an aspect of the present invention. The illustrated example is a high bypass turbofan engine, but the principles of the invention are also applicable to other types of engines, such as low bypass turbojets. The engine 10 has a longitudinal centerline or axis A and an outer fixed annular casing 12 arranged concentrically around the axis A and coaxially along the axis A. The engine 10 has a fan 14, a booster 16, a compressor 18, a combustor 20, a high pressure turbine 22, and a low pressure turbine 24, which are arranged in a series flow relationship. During operation, the compressed air from the compressor 18 is mixed and ignited with the fuel in the combustor 20 to generate combustion gas. Some work is extracted from these gases by the high pressure turbine 22, which drives the compressor 18 via the outer shaft 26. The combustion gas then flows into the low pressure turbine 24, which drives the fan 14 and booster 16 via the inner shaft 28.

Engine 10 comprises a central hub 36 connected to the annular fan casing 38 by a fan outlet guide vane (OGV) 40 extending radially across the fan flow path. It is equipped with a fan frame 32. In this example, each of the OGV40s is both an air swirl element and a structural strut of the fan casing 38. In other configurations, separate members are provided for aerodynamic and structural functions.

The concepts of the present invention are described using the OGV40 as an example, but these concepts are configured to guide the airflow and / or to form all or part of the flow path of the airflow. It should be understood that it is applicable to any fixed structure within 10. Such a structure is generally referred to herein as a "flow boundary element" and includes a "flow boundary surface". As used herein, the term "boundary" is simply exposed to airflow during operation and therefore something, similar to the conventional concept of "flow guidance elements" such as airfoils that swirl airflow. Includes components such as parts of ducts or nacelles that guide or demarcate airflow in a manner. As an example, FIG. 2 shows a gas turbine engine 10'with an "underducted fan" having a row of external rotating fan blades 14'and a row downstream of the fixed guide vanes 40'. The principles of the present invention can be easily incorporated into the guide vanes 40'.

Some or all of the fans OGV40 in the engine 10 may include heat exchangers integrated within these structures. Figure 3 shows one of the fans OGV40 in more detail. The OGV includes an airfoil portion 42 having a front edge 44, a trailing edge 46, a tip 48, a root portion 50, a convex negative pressure side 52, and a concave positive pressure side 54. The bow-shaped inner platform 56 is located at the root 50 of the airfoil 42, and the outer platform 58 is located at the tip 48. Collectively, the negative pressure side 52, the positive pressure side 54, the inner platform 56 and the outer platform 58 define the "wall structure" of the OGV40, and collectively, the outer surface of the wall structure is the "flow interface". To define.

The airfoil portion 42 is made of a material having strength and weight properties suitable for the intended application. One non-limiting example of a suitable alloy is the 7000 series aluminum alloy, especially the 7075 aluminum alloy.

The inside of the OGV40 is configured to function as a heat pipe. As used herein, the term "heat pipe" means any structure that acts as a heat pipe by transferring heat from one position to another using a phase-changing fluid. .. This structure does not necessarily have to be a conventional pipe shape or tube shape. Generally, as seen in FIG. 4, the OGV 40 includes a closed chamber 60 defining an internal cavity 62. As described in more detail below, some or all of the chamber 60 can be formed as an integral part of the OGV40 or other flow boundary element.

The internal cavities 62 are aligned with a capillary structure having a large number of small channels, cavities, or pores sized according to known principles that produce a capillary transport effect. This structure, together with one or more vapor channels 66 herein, is referred to as the "wick" or "wicking structure" 64 and holds the working fluid. Various working fluids such as water, ammonia, glycols, alcohols, organic substances and low melting point metals are known to be used in heat pipes. The working fluid can be non-flammable, thereby avoiding the risk of fire in the event of leakage or breakage within the chamber 60.

One end of the chamber 60 is configured to be placed in contact with a hot fluid (eg, engine lubricant) during operation. This portion is referred to as the "high temperature" or "evaporator" end, indicated by an "H". The opposite end of chamber 60, referred to as the "cold" or "condenser" end, indicated by "C", is the flow "F" of a relatively cold fluid, such as fan bypass air, during engine operation. Be exposed to. The terms "high temperature", "evaporator", "low temperature", and "condenser" as used in connection with chamber 60 describe the placement of chamber 60 within a relatively hot or cold region. It should be noted that it is not related to any particular aspect of the structure of the chamber 60 itself.

During operation, the oil that absorbs heat from various parts of the engine circulates in the OGV40 and heats the high temperature of the OGV40 or the evaporator end H. The removal of heat cools the oil to the permissible operating temperature, which allows the oil to then recirculate the engine 10. The removed heat is discharged to the external fluid flow F by convection. Considering the series of heat transfer processes from the oil to the external fluid flow, the heat transfer through the wall structure of the OGV contributes to a very small percentage of the total thermal resistance of the device (eg less than 10%). Please note. Therefore, the effectiveness of OGV40 as a heat exchanger does not strongly depend on the choice of material for the wall structure. This allows the use of materials with good mechanical performance, such as titanium, while maintaining acceptable heat transfer performance.

Specifically, the working fluid in the chamber 60 absorbs its heat and evaporates. The generated steam then travels through the steam flow path 66 and condenses at the cold end C of chamber 60, thereby transferring heat to the cold end C. The wick 64 completes circulation by returning the condensed liquid working fluid to the hot end H by capillary action. Capillary structure is not always necessary, depending on the orientation of the chamber 60.

The heat pipe structure described herein can also be used in other situations where an air-to-liquid heat transfer process is required. For example, in cold climates, the heat pipe structure can consist of a hot end H located in the air stream and a cold end C located in contact with the engine oil. The heat absorbed from the air stream can be used to heat the oil and dissolve the viscous oil at very low temperatures. As another alternative, the heat pipe structure can be used to cool another engine fluid such as fuel. Further, it should be noted that the heat pipe structures described herein do not necessarily require in-flight conditions as long as the air temperature and flow conditions provide a suitable sink for the heat emitted.

The wick 64 and steam flow path 66 can be incorporated into the chamber 60 in a variety of ways for the purpose of optimizing structural, thermal, and weight issues. Figures 5-7 show examples of some possible physical configurations.

FIG. 5 shows an airfoil 142 similar to the OGV 40, having a positive pressure side wall 154 and a negative pressure side wall 152 collectively forming a chamber 160 having a cavity 162 inside. The wicking structure 164 straddles the space between the side walls 154 and 152. A series of spanning vapor channels 166 extend through the wicking structure 164. In the illustrated example, the steam flow path 166 has a circular cross-sectional shape and is located approximately intermediate between the positive pressure side wall 154 and the negative pressure side wall 152.

FIG. 6 shows an airfoil portion 242 having a positive pressure side wall 254 and a negative pressure side wall 252 that collectively form a chamber 260 having a cavity 262 inside. The wicking structure 264 straddles the space between the side walls 254 and 252. The central steam flow path 266, which has a wing-shaped cross section, extends through the central portion of the wicking structure 264.

FIG. 7 shows an airfoil portion 342 having a positive pressure side wall 354 and a negative pressure side wall 352 collectively forming a chamber 360 having a cavity 362 inside. The wicking structure 364 straddles the space between the side walls 354 and 352. The steam flow path 366 extends through the central portion of the wicking structure 364. The strut 368 extends laterally between the positive pressure side wall 354 and the negative pressure side wall 352. The stanchion 368 may be a continuous lateral bulkhead that effectively divides the vapor flow path 366 into smaller portions, or may be individual pins or stanchions. Each of the struts 368 can include a solid material, a capillary structure, or any combination of the two. In addition, each of the struts 368 has various shapes, such as a prism shape or an hourglass shape.

All or part of the OGV40 or a portion thereof may be part of a single, integral or monolithic component, or a manufacturing process involving layer-by-layer construction or additional manufacturing (conventional machining). It may be manufactured using (as opposed to material removal) as in the process. Such processes can be referred to as "fast manufacturing processes" and / or "additional manufacturing processes", and the term "additional manufacturing process" as used herein generally refers to such processes. Additional manufacturing processes include, but are not limited to, direct metal laser sintering (DMLS), direct metal laser melting (DMLM), laser net shape manufacturing (LNSM), electron beam sintering, selective laser sintering (SLS), Includes 3D printing such as by inkjet and laser jet, stereolithography (SLS), electron beam melting (EBM), laser processing net shaping (LENS), and direct metal deposition (DMD).

The OGV40 can often have a high aspect ratio, a significant amount of twist over the wingspan, and a small wall thickness. These properties tend to make manufacturing using conventional methods difficult or impossible. Therefore, additive manufacturing can be a technique that enables the manufacture of the OGVS40 and other components described herein.

The wicking structure 64 can incorporate a gentle transition over its thickness. The first portion of the wall thickness of the OGV40 or other flow boundary element from the outer surface may be solid. It can then migrate inward and become a permeable surface configured to eject the liquid by capillary force. Finally, there may be open void regions to which the fluid vapors move. The wicking structure can also be varied in a direction perpendicular to the wall surface. For example, a microstructure with small pores may be used in a high temperature region (evaporator) to provide a large discharge force. However, it is effective to have a rough structure in the transition portion where the condensate flows back into the evaporator region, whereby the flow resistance of the fluid can be lowered.

FIG. 11 shows an example of one possible configuration of the wicking structure 464. This is generally a collection of solids, which have holes 466A, 466B perpendicular to each other at intervals of 3D arrays passing through it. In this example, the first group of holes 466A have a first diameter and are located in a layer adjacent to the metal side 468 of structure 464. The holes 466B in the second group have a second diameter smaller than the first diameter and are located adjacent to the first layer. Multiple layers of holes of different sizes can be used. This structure 464 is particularly suitable for being formed as an integral or single part of the wall of the flow boundary element, for example using an additional manufacturing process as described above.

In use, the OGV40 or other flow boundary structure will be placed in thermal contact with the oil or other fluid to be cooled. FIG. 8 shows one possible device that couples the chamber 60 of the OGV40 to the fluid to be cooled. The sump 400 is formed around the base of chamber 60, which extends beyond the root 50 of the OGV 40. The fluid "L" to be cooled (oil in this example) flows through the inlet tube 402 into the sump 400, where it flows around the chamber 60 and transfers heat there. The fluid then flows through the outlet pipe 404. The fluid can then be sent to the adjacent OGV40 or another part of the engine oil system.

FIG. 9 shows another possible device that couples the chamber 60 of the OGV40 to the fluid to be cooled. The fluid conduit 406 is positioned near the root 50 of the OGV40. The protruding end of the chamber 60 is formed in a concave saddle shape 408 that is placed in direct contact with the fluid conduit 406. If desired, the protruding end of the chamber 60 may be joined to the fluid conduit 406, for example by brazing, welding, gluing, etc. In use, heat is transferred directly to chamber 60 through the walls of fluid conduit 406. Alternatively, the stub portion of the fluid conduit may be formed in part of the chamber as part of an integral, single or monolithic whole. For example, FIGS. 12 and 13 show a chamber 60'with a wall that is integral with the wall of fluid conduit portion 406'. This configuration maximizes the heat transfer capacity and allows the chamber 60'to be connected to the piping system (not shown) using the type of fitting known at 410 as shown in FIG.

FIG. 10 is a diagram showing an annular arrangement, that is, a ring-shaped OGV40 installed in the engine 10. For reference, the ring is shown at the clock position, i.e. 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock. During normal engine operation, the OGV 40 at 12 o'clock is oriented to extend "up" vertically from the engine center line, i.e. away from the ground, and the OGV at 6 o'clock is vertical from the engine center line. Extends "down", that is, toward the ground.

The balance of forces acting on the working fluid in each OGV40 changes depending on its position in the ring. While the gravitational force acting on the working fluid is always downward, the desired return direction may be upward or downward, which means that the gravitational force can act in opposition to the capillary force. For example, if the hot end H described above is placed inside, gravity will condense to the OGV40 at the top of the ring, for example from just above 9 o'clock to just below 3 o'clock through 12 o'clock. It tends to assist the return of steam. When the hot end H is placed inside, gravity acts toward the lower side of the 3 o'clock position through 6 o'clock with respect to the return of the condensed steam on the lower side of 9 o'clock, so the hot end H Can be alternated outside the OGV 40, which is located relative to the OGV, which is located slightly below the 9 o'clock, towards the slightly lower side at 3 o'clock through 6 o'clock. Therefore, the designs described herein allow the hot end H to be located at the root or tip of the OGV40, allowing one of ordinary skill in the art to adapt the cooling structure to increase heat dissipation capacity.

The present invention described herein has several advantages over prior art. Flow boundary elements with integrated heat pipes can conduct large heat loads. This configuration can prevent the oil from being damaged by foreign matter (FOD). Compared to the prior art ACOC, heat pipes are two deficient before oil discharge can occur (ie, the wall that separates the evaporator and oil reservoir of the heat pipe, and the heat pipe that separates the steam chamber and airflow. Condenser wall) is required, while current prior art ACOCs can fail after a single wall has been dehiscenced, so the present invention is configured to provoke resistance to the fan stream. Eliminates the introduction of elements and brings high reliability. The present invention combines structural, thermal, and aerodynamic functions into a single component. This allows for further heat dissipation with minimal drag. This has the potential to maintain the temperature of the components within acceptable limits for cheap aluminum alloys, such as about 150 ° C (300 ° F), even when the fluid to be cooled is hot. Reducing weight and drag can result in lower fuel consumption rates (SFC).

In the above, the flow boundary element having an integrated heat pipe structure has been described. All of the features disclosed herein (including any accompanying claims, abstracts and drawings) and / or all of the steps of any method or process disclosed are such features and /. Alternatively, any combination can be combined, except for combinations in which at least some of the steps are mutually exclusive.

Each feature disclosed herein (including any accompanying claims, abstracts and drawings) shall be exchanged for the same, equal or similar purpose-appropriate alternative features unless otherwise stated. can do. Therefore, unless otherwise stated, each disclosed feature is merely an example of an inclusive series of equal or similar features.

The present invention is not limited to the details of the above embodiments. The present invention relates to any novel feature or any combination of features disclosed herein (including any accompanying claims, abstracts and drawings), or any method or process step disclosed. It extends to any new feature or any combination of. [Phase 1] A heat transfer device for gas turbine engines (10,10') Components with wall structures that define the flow boundary, A chamber (60,160,260,360) formed within the components and comprising a wicking structure (64,164,264,364,464), a vapor flow path (66,166,266,366) and a working fluid. Heat transfer device for gas turbine engine (10,10') equipped with. [Phase 2] The device according to embodiment 1, wherein the chamber (60,160,260,360) is formed integrally with the wall structure. [Phase 3] The device according to embodiment 2, wherein the wall structure shifts from a solid structure at the flow interface to a permeable structure on the inner surface. [Phase 4] The apparatus according to embodiment 1, wherein the wall structure comprises a three-dimensional aggregate, the three-dimensional aggregate having holes (466A, 466B) perpendicular to each other at a series of intervals passing through the three-dimensional aggregate. [Embodiment 5] The device according to embodiment 4, wherein the holes (466A, 466B) are arranged in two or more layers, and the holes (466A, 466B) in each layer have different diameters. [Embodiment 6] The components are the opposing positive pressure side walls (54,154,254,354) and negative pressure side walls (52,152,252,352), the root (50), the tip (48), and the spaced front and trailing edges (44). The apparatus according to the first embodiment, comprising a wing-shaped portion (42,142,242,342) having the [Phase 7] The device of embodiment 6, wherein the chamber (60,160,260,360) extends beyond the root (50) or tip (48) of the airfoil (42,142,242,342). [Embodiment 8] A wicking structure (64,164,264,364,464) straddles the space between the side walls (154,152), The apparatus according to embodiment 6, wherein a series of spanning vapor channels (166) extend through a wicking structure (64,164,264,364,464). [Embodiment 9] A wicking structure (64,164,264,364,464) straddles the space between the side walls (154,152), The apparatus according to embodiment 6, wherein a spanning vapor flow path (266) having a blade-shaped cross section extends through a central portion of a wicking structure (64,164,264,364,464). [Embodiment 10] A plurality of struts (368) extend laterally between the positive pressure side wall (354) and the negative pressure side wall (352). The apparatus of embodiment 6, wherein at least one or more of the stanchions (368) comprises a permeable material that defines a portion of the wicking structure (64,164,264,364,464). [Embodiment 11] Part of the chamber (60,160,260,360) extends beyond the rest of the components, A device comprising the device according to embodiment 1, wherein the sump (400) surrounds an extending portion of the chamber (60,160,260,360) and is configured to circulate fluid through it. [Embodiment 12] Part of the chamber (60,160,260,360) extends beyond the rest of the components, The device according to embodiment 1, wherein the fluid conduit (406) is arranged in contact with the extending portion of the chamber (60,160,260,360). [Embodiment 13] Fluid conduit (406) has an annular outer wall12. The device of embodiment 12, wherein the extending portion of the chamber (60,160,260,360) has a concave saddle shape (408) that contacts the outer wall of the fluid conduit (406). [Phase 14] Part of the chamber (60,160,260,360) extends beyond the rest of the components, and the stub portion of the fluid conduit (406) is part of a single monolithic structure with an extension of the chamber (60,160,260,360). The device according to embodiment 1 which is formed. [Embodiment 15] A heat transfer device for gas turbine engines (10,10') Arranged in a ring around the engine (10,10'), it has multiple components that extend approximately radially and define the opposing inner and outer ends, each component The wall structure that defines the flow boundary surface, Formed within the component, it has a wicking structure (64,164,264,364,464), a vapor flow path (66,166,266,366) and a chamber (60,160,260,360) with working fluid, the chamber (60,160,260,360) facing the evaporator end. Equipped with a condenser end For some chambers (60,160,260,360), the evaporator end is located at the inner end of the corresponding component, and for the other chamber (60,160,260,360), the evaporator end is located at the outer end of the corresponding component. Heat transfer device for gas turbine engine (10,10') located in the section. [Embodiment 16] The evaporator ends of each chamber (60,160,260,360) are arranged so that gravity assists the flow of fluid from the condenser end to the evaporator end for a given orientation of the engine (10,10'). The apparatus according to the fifteenth embodiment. [Phase 17] The device according to embodiment 15, wherein the component is a guide vane (40,40').

10 gas turbine engine 10'gas turbine engine 12 casing 14 fans 14'Rotating fan blade 16 Booster 18 compressor 20 Combustor 22 High pressure turbine 24 low pressure turbine 26 outer shaft 28 Inner shaft 32 fan frame 36 Central hub 38 fan casing 40 Exit Guide Vane 40 fan OGV 40'guide vane 42 Airfoil 44 Front edge 46 trailing edge 48 tip 50 root 52 Negative pressure side 54 Positive pressure side 56 Inner platform 58 outer platform 60 Closed chamber 60'chamber 62 Internal cavity 64 wicking structure, wick 66 Steam flow path 142 Airfoil 152 Negative pressure side wall 154 Positive pressure side wall 160 chamber 162 Cavity 164 Wicking structure 166 Steam flow path 242 Airfoil 252 Negative pressure side wall 254 Positive pressure side wall 260 chamber 262 cavity 264 wicking structure 266 Steam flow path 342 Airfoil 352 Negative pressure side wall 354 Positive pressure side wall 360 chamber 362 Cavity 364 Wicking structure 366 Steam flow path 368 stanchions 400 sumps 402 Entrance pipe 404 exit pipe 406 Fluid conduit 408 saddle shape 410 fittings 464 Wicking structure 466A hole 466B hole 468 Metal side A axis C cold end H evaporator end, high temperature end