| Heater assembly for deicing and/or anti-icing a component -> Monitor Keywords |
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Heater assembly for deicing and/or anti-icing a componentRelated Patent Categories: Electric Heating, Heating Devices, Combined With Diverse-type Art Device, Vehicle Or Vehicle ComponentHeater assembly for deicing and/or anti-icing a component description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070187381, Heater assembly for deicing and/or anti-icing a component. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0002] The present invention relates to a heater assembly. More particularly, the present invention relates to an electrothermal heater assembly that is suitable for removing and/or preventing ice accumulation on a gas turbine engine component. [0003] It is desirable to minimize or prevent the formation of ice on certain components of a gas turbine engine in order to avoid problems attributable to ice accumulation. For example, if ice forms on air intake components, the flow of air into the gas turbine engine compressor may become obstructed, which then adversely affects engine operation and efficiency. Furthermore, chunks of ice that break loose from a gas turbine engine component during operation can damage other parts of the engine. [0004] There are many existing methods of removing or preventing the formation of ice on gas turbine engine components. Among these methods is the incorporation (or embedding) of an electrothermal heating element into a gas turbine engine component that is susceptible to ice formation. The heating element may also be applied to a surface of the component. The heating element heats the susceptible areas of the component in order to help prevent ice from forming. The heating element may be a metallic heating element (e.g., a foil element) formed of stainless steel, copper, wire cloth, etc., which typically converts electrical energy into heat energy. [0005] The metallic heating element is typically a part of a heater assembly that also includes a thermally conductive fabric layer attached to and supporting the heating element. For example, the heater assembly may be formed of a metallic heating element embedded into an epoxy fiber reinforced composite structure. In some cases, the fabric layer also electrically insulates an electrically conductive component from the heating element. Typically, multiple plies of fabric are required for sufficient electrical isolation of the metallic heater element. [0006] When the heater assembly is embedded in a composite structure of some gas turbine engine components, the heater assembly replaces some structural elements of the composite in order to maintain the dimensions of the component. In those cases, the heating element accounts for a percentage of the composite structure that forms the component. This may affect the strength and the structural characteristics, such as the transfer of structural loads, of the component. The larger the percentage the heater assembly constitutes, the larger the reduction in composite strength of the gas turbine engine component. [0007] In order to increase the strength of the component that includes the heater assembly, it is desirable to reduce the amount of space the heater assembly takes up in the component. One way of achieving the reduction in space is by reducing the thickness of the heater assembly. BRIEF SUMMARY [0008] The present invention is a heater assembly suitable for deicing and/or anti-icing a gas turbine engine component. The heater assembly includes a metallic heating element and a densely woven fabric layer impregnated with a high-temperature resin capable of withstanding temperatures of up to 550.degree. F. (288.degree. C.). BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1A is a schematic cross-sectional view of a heater assembly in accordance with a first embodiment of the present invention. [0010] FIG. 1B is a schematic cross-sectional view of a heater assembly in accordance with a second embodiment of the present invention. [0011] FIG. 1C is a schematic cross-sectional view of a heater assembly in accordance with a third embodiment of the present invention. [0012] FIG. 2 is a perspective view of an airfoil, which is cut-away to show a heater assembly that is embedded along a leading edge of the airfoil. [0013] It should be understood that the figures are not drawn to scale. DETAILED DESCRIPTION [0014] The present invention is an electrothermal heater assembly that includes a metallic heating element and a densely woven fabric layer impregnated with a high temperature resin that is capable of withstanding operating temperatures of up to 550.degree. F. (288.degree. C.). The resin reinforces the fabric layer. The metallic heating element is attached to the fabric layer using a thermoset adhesive and is electrically connected to a source of electrical power using any suitable conductor, such as a wire or flexible circuit. In one embodiment, the resin that is introduced into the fabric layer is also the thermoset adhesive that adheres the metallic heating element to the fabric layer. [0015] The heater assembly of the present invention is suitable for incorporating (or embedding) into a composite structure of a component (i.e., an internal application), including a gas turbine engine component, or for attaching to a surface of a component (i.e., an external application) in order to deice the component and/or prevent ice from forming thereon. The heater assembly may also be used in a hybrid configuration, which includes both internal and external applications. The component may be any component that is susceptible to ice formation. For example, the component may be an aircraft component or a gas turbine engine component such as, but not limited to, a vane, an airfoil leading edge, a front bearing of the engine, a structural strut that supports the front bearing, and a duct. The component may be formed of materials such as, but not limited to, fiberglass, metal, or carbon composite. [0016] FIG. 1A is a schematic cross-sectional view of electrothermal heater assembly 10 in accordance with the present invention. Heater assembly 10 includes densely woven fabric layer 12 and metallic heating elements 14, which are attached to densely woven fabric layer 12 with thermoset adhesive 16. Fabric layer 12 is impregnated with a high-temperature resin that is capable of withstanding temperatures of up to 550.degree. F. (288.degree. C.). Examples of suitable high-temperature resins that may be used in accordance with the present invention include, but are not limited to, bismaleimide, phthalonitrile, cyanate ester, polyimide adhesive, and polyimide resin. [0017] Fabric layer 12 includes about 45 to about 70 percent by volume of a fabric and about 30 to about 55 percent by volume of the high-temperature resin. In one embodiment, fabric layer 12 includes about 55 to about 60 percent by volume of the fabric and about 40 to about 45 percent by volume of the high-temperature resin. Suitable fabrics for including in fabric layer 12 include densely woven materials that have a continuous fiber. Preferably, the fabric is not easily distorted and maintains its weave pattern prior to and during the introduction of resin into the fabric during manufacture of heater assembly 10. Examples of suitable densely woven materials that may be used include a fiberglass fabric, such as Style 106, which is made commercially available by Clark Schwebel Tech-Fab Company of Anderson, S.C., and a polymer film, such as Kapton, which is made commercially available by DuPont High Performance Materials of Circleville, Ohio. [0018] Fabric layer 12 acts as a backing material to support heating elements 14, and in some embodiments, also acts as a structural element of a component (if heater assembly 10 is embedded in the component). Because fabric layer 12 supports heating elements 14, it may also be referred to as a "structural layer." Some heating elements 14 require a backing material because they are thin and fragile and, as a result, cannot be easily handled during the manufacturing process. For example, heater assembly 10 may be etched into a shape prior to application in or on a component. The shape typically depends upon the type of component and the area of the component that requires deicing and/or anti-icing. Some of these fragile heating elements 14 tend to break apart during the etching process without a backing material (i.e., fabric layer 12). Fabric layer 12 contributes to the mechanical integrity of heating elements 14. [0019] In comparison to many fabric layers in existing heating assemblies, fabric layer 12 of the present invention is load bearing and more stiff, due to the type of the fabric that is selected for including in fabric layer 12. As a result, if heater assembly lo is embedded into a component, fabric layer 12 contributes to the structural integrity of the component and can act as a structural element of the component, rather than merely taking up space in the component that could be occupied by a structural element. The fabric material included in fabric layer 12 may also constitute all or substantially all of the structural material in a composite component, such as a vane. [0020] In some embodiments, fabric layer 12 is also electrically insulating and configured to electrically insulate an electrically conductive component, such as one formed of a carbon composite or a metal alloy, from metallic heating elements 14, while at the same time, thermally conduct heat generated by heating elements 14. In situations where fabric layer 12 also electrically insulates heating elements 14, it is desirable for the fabric material forming fabric layer 12 to be woven tightly enough to be electrically insulating. Electrically insulating materials that may be used to form fabric layer 12 include fiberglass, Nextel or another suitable ceramic fiber fabric. [0021] A thickness of heater assembly 10 is minimized because fabric layer 12 is thinner than many existing heating assemblies, which include structural layers that are about 0.020 inches (0.0508 centimeters) thick. In contrast, heater assembly 10 of the present invention includes fabric layer 12 that is less than about 0.005 inches (0.0127 centimeters) thick. In one embodiment, fabric layer 12 is about 0.003 inches (0.00762 centimeters) to about 0.005 inches (0.0127 centimeters) thick. Given the increased structural integrity of fabric layer 12, and in some embodiments, its ability to electrically insulate heating elements 14, it has been found that only one layer of material is typically required to form fabric layer 12. Of course, fabric layer 12 may also be formed of multiple layers of material. 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