Duct section, system and method for constructing same
A duct section and system, including a laminated shroud, acting as a secondary duct, for aerospace and other applications, and a method for constructing same. The duct structure incorporates a metallic primary duct tube, with a laminated shroud surrounding the primary duct tube and separated therefrom by an annular gap. The laminated shroud includes a metallic inner layer and a polymeric outer layer. Preferably, the thin metallic layer is a corrosion resistant material such as corrosion resistant stainless steel or titanium. In one embodiment of the invention, the outer polymeric layer is a polyimide material, such as polyimide resin-impregnated fiberglass cloth.
1. A duct section, for conducting gaseous fluid from a first location to a second location, the duct section comprising:
a primary duct member, having a first end and a second end;
a multilayer shroud, having a first end and a second end, the multilayer shroud being positioned radially outwardly from and circumferentially surrounding at least a portion of the primary duct member, the primary duct member and the multilayer shroud defining an axially extending annular space therebetween;
a first closeout collar, permanently and sealingly affixed to the first end of the multilayer shroud and further permanently and sealingly affixed, at least indirectly, to the first end of the primary duct member, at a position proximate the first end of the primary duct member;
a second closeout collar, permanently and sealingly affixed to the second end of the multilayer shroud and further permanently and sealingly affixed, at least indirectly, to the second end of the primary duct member, at a position proximate the second end of the primary duct member;
the first and second closeout collars closing off opposite ends of the axially extending annular space defined by the primary duct member and the multilayer shroud, to preclude the flow of gases therefrom said space, and to prevent rotation of the multilayer shroud relative to the primary duct member;
the shroud having an inner surface and an outer surface, with a metallic inner layer positioned at the inner surface; and
a polymeric outer layer, bonded to the outer surface of the metallic inner layer.
2. The duct section according to claim 1 , further comprising first and second duct end flanges affixed to the first and second ends of the primary duct member.
3. The duct section according to claim 1 , wherein the primary duct member is fabricated from at least one of the following materials: corrosion resistant steel; and titanium.
4. The duct section according to claim 1 , wherein the metallic inner layer of the shroud is fabricated from one of the following materials: corrosion resistant steel; and titanium.
5. The duct section according to claim 1 , wherein the polymeric outer layer of the shroud is fabricated from polyimide.
6. The duct section according to claim 5 , wherein the polymeric outer layer comprises at least one ply of polyimide resin impregnated fiberglass cloth.
7. A duct system for conveying gaseous fluid from a first location to a second location, comprising:
at least two duct sections, each duct section having
a primary duct member, having a first end and a second end;
a multilayer shroud, having a first end and a second end, the multilayer shroud being positioned radially outwardly from and circumferentially surrounding at least a portion of the primary duct member, the primary duct member and the multilayer shroud defining an axially extending annular space therebetween;
a first closeout collar, permanently and sealingly affixed to the first end of the multilayer shroud and further permanently and sealingly affixed, at least indirectly, to the first end of the primary duct member, at a position proximate the first end of the primary duct member;
a second closeout collar, permanently and sealingly affixed to the second end of the multilayer shroud and further permanently and sealingly affixed, at least indirectly, to the second end of the primary duct member, at a position proximate the second end of the primary duct member;
the first and second closeout collars closing off opposite ends of the axially extending annular space defined by the primary duct member and the multilayer shroud, to preclude the flow of gases therefrom said space, and to prevent rotation of the multilayer shroud relative to the primary duct member;
the shroud having an inner surface and an outer surface, with a metallic inner layer positioned at the inner surface; and
a polymeric outer layer, bonded to the outer surface of the metallic inner layer; and
first and second duct end flanges affixed to the first and second ends of the primary duct member;
the first and second duct sections being disposed in abutting relationship to one another with a duct end flange of one of the at least two duct sections abutting a duct end flange of another of the at least two duct sections;
a clamp, engaging the abutting duct end flanges, and affixed thereto, to form a coupling between the one and the another of the at least two duct sections.
8. The duct system according to claim 7 , further comprising:
a coupling cover positioned around the coupling between the one and the another of the at least two duct sections, and affixed to outer surfaces of the shrouds of the one and the another of the at least two duct sections.
9. The duct section according to claim 1 , further comprising:
at least one standoff member disposed between the inner surface of the shroud and the primary duct member, and affixed to the shroud member and the primary duct member, at a position between the first and second ends of each of the primary duct member and the shroud.
10. The duct section according to claim 9 , wherein the at least one standoff member circumferentially encircles the primary duct member.
11. The duct section according to claim 9 , wherein the at least one standoff member has an aperture disposed therein to enable the passage of gaseous fluid therethrough.