WO2009073638A1

WO2009073638A1 - Fin tube assembly for air cooled heat exchanger and method of manufacturing the same

Info

Publication number: WO2009073638A1
Application number: PCT/US2008/085208
Authority: WO
Inventors: Ranga Nadig
Original assignee: Holtec International, Inc.
Priority date: 2007-11-30
Filing date: 2008-12-01
Publication date: 2009-06-11
Also published as: CN101925791A; US20090173485A1; EP2225529A1

Abstract

A finned tube assembly for an air cooled condenser. The finned tube assembly comprises a non-circular core tube and at least one set of fins that are welded directly to the core tube. The core tube can be formed by a plurality of longitudinal transverse sections that are seam welded together. In another embodiment, the invention is a fined tube assembly having an outer surface that is made corrosion resistant by a surface conversion process, such as ferretic nitrocarburizafion.

Description

FIN TUBE ASSEMBLY FOR AIR COOLED HEAT EXCHANGER AND METHOD

OF MANUFACTURING THE SAME

Cross-Reference to Related Patent Applications

[0001] The present application claims the benefit of United States Provisional Application 60/991,322, filed November 30, 2007; United States Provisional Application 61/028,689, filed February 14, 2008; and United States Provisional Application 61/108,511, filed October 25, 2008, the entireties of which are hereby incorporated by reference.

Field of the Invention

[0002] The present invention relates generally to the field of air-cooled heat exchangers, and specifically to fin tube assemblies for air-cooled heat exchangers and methods of manufacturing the same.

Background of the Invention

[0003] Air-cooled heat exchangers are of use in a variety of industrial applications, particularly in applications where there is a scarcity of water for use as a cooling medium. Air-cooled steam condensers are a particular type of heat exchanger employed to condense steam. Condensers are widely used in the industrial, chemical, petrochemical and energy industries.

[0004] Air-cooled steam condensers typically include a number of fin tube assemblies connected in parallel. The fin tube assemblies typically comprise elongated core tubes of circular or non-circular cross-section and sets of fins attached to the outer surface of the core tubes to increase heat transfer from the fluid within the core tube to the surrounding air atmosphere by increasing the surface area The fins are typically crated of highly thermal conductive materials. In operation, steam (or other fluid) flows through the inside of the tubes while cooling air flows outside of the tube along the fins.

[0005] Typically, a finned tube assembly for air cooled condenser application in present day technology is formed by taking a rounded tube made of carbon steel, stainless steel and flattening the tube so that the vertical cross-section is noncircular. The tube is coated with aluminum and aluminum fins are then brazed to the tube. Brazing fins to core tubes is well known and the standard in the art.

[0006] Existing fin tube assemblies for air-cooled heat exchanger, and methods of manufacturing the same are disclosed in the following: (1) United States Patent No. 7,293,602, to Nadig et al., issued November 13, 2007; (2) United States Patent No.7,243,712, to Fay, issued July 17, 2007; (3) United States Patent No. 7,165,606, to Take, issued January 23, 2007; (4) United States Patent No. 6,332,494, to Bodas et al, issued December 25, 2001; (5) United States Patent No. 6,142,223, to Bodas et al, issued November 7, 2000; and (6) United States Patent No, 6,000,461, to Ross et al., issued December 14, 1999, the entireties of which are incorporated by reference.

[0007] While the aforementioned fin tube assemblies, and methods of manufacture, are suitable in many way, all of these suffer from one or more drawbacks, including complexity of manufacture, less than optimal heat transfer, use of expensive materials, and expensive manufacturing, which results in high end costs.

Disclosure of the Invention

[0008] It is an object of the present invention to provide a fin tube assembly for use in air cooled heat exchangers, and a method of manufacturing the same.

[0009] Another object of the present invention is to provide a fin tube assembly for use in air cooled heat exchangers, and method of manufacture, that is free of brazing.

[0010] Yet another object of the present invention is to provide a fin tube assembly for use in air cooled heat exchangers, and method of manufacture, that is easy, quick and cost effective to manufacture.

[0011] Still another object of the present invention is to provide a fin tube assembly for use in air cooled heat exchangers, and method of manufacture, having fins welded directly to the core tube without the use of a filler material.

[0012] A further object of the present invention is to provide a robust fin tube assembly for use in air cooled heat exchangers, and method of manufacture.

[0013] A yet further object of the present invention is to provide a fin tube assembly for use in air cooled heat exchangers, and method of manufacture, that utilizes a multi-part core tube.

[0014] A still further object of the present invention is to provide a fin tube assembly for use in air cooled heat exchangers, and method of manufacture, that is corrosion resistant.

[0015] These and other objects are met by the present invention which in one aspect can be a fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an internal passageway for carrying a fluid to be cooled, the core tube having a non-circular transverse cross-section; and at least one set of fins welded to an outside surface of the core tube. It is preferred, in some embodiments, that the at least one set of fins be welded directly to the outside surface of the core tube using a fusion welding technique that does not use a filler material. [0016] Preferably, the at least one set of fins can be a corrugated sheet having peaks terminating in ridges and valleys terminating in floors. More preferably, the floors of the valleys of the corrugated sheet can be contiguously laser welded to the outside surface of the core tube. Most preferably, the floors of the valleys comprise a substantially flat section that can be contiguously laser welded to the outside surface of the core tube. [0017] In another aspect, the invention can be a fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface forming a passageway for carrying a fluid to be cooled and an outsider surface having a first substantially flat face and a second substantially flat face opposite the first substantially flat face; the core tube constructed from a single flat plate structure bent into the shape of the core tube so that a longitudinal interface exists, the longitudinal interface being contiguously welded to form the core tube; and a set of fins connected to each of the first and second substantially flat faces. [0018] In yet another aspect, the invention can be a fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface forming a passageway for carrying a fluid to be cooled and an outsider surface having a first substantially flat face and a second substantially flat face opposite the first substantially flat face; the core tube constructed from a first flat plate structure bent into a first transverse section of the core tube and a second flat plate structure bent into a second transverse section of the core tube, the first and second transverse sections arranged in an adjacent manner so that first and second longitudinal interfaces exist, the first and second longitudinal interfaces being contiguously welded to form the core tube; at least one of the first or second longitudinal interfaces formed by either (1) contact between lateral edges of the first and second transverse sections, the lateral edges being butt welded together, or (2) contact between bottom surfaces of lateral flanges formed into the first transverse section and top surfaces of lateral flanges formed into the second transverse section, the lateral flanges being fusion welded together; and a set of fins connected to each of the first and second substantially flat faces.

[0019] In still another aspect, the invention can be a fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, the core tube having a non-circular transverse cross-section; at least one set of fins connected to an outside surface of the core tube; and a baked phenolic or zinc-based coating covering the at least one set of fins and the core tube. [0020] In a further aspect, the invention can be a method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, the core tube having a non-circular transverse cross-section; b) providing at least one set of fins; and c) welding the at least one set of fins to the outside surface of the core tube using a fusion welding technique that does not use a filler material.

[0021] In a yet further aspect, the invention can be a method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a substantially flat plat structure having a first lateral edge, a second lateral edge, a first end edge, a second end edge, a first major surface, and a second major surface, the first and second end edges defining a longitudinal length of the substantially flat plat structure; b) providing a first set of fins and a second set of fins; c) welding the first set of fins to a first portion of the first major surface of the substantially flat plat structure using a fusion welding technique that does not use a filler material, the first set of fins spaced from the first lateral edge so that the first major surface has a first perimeter portion extending longitudinally between the first set of fins and the first lateral edge that is free of fins; d) welding the second set of fins to a second portion of the first major surface of the substantially flat plat structure using the fusion welding technique, the second set of fins spaced from the first set of fins and the second lateral edge so that the first major surface has an elongated portion extending longitudinally between the first and second set of fins that is free of fins and a second perimeter portion extending longitudinally between the second set of fins and the second lateral edge that is free of fins; e) bending the first and second perimeter portions of the substantially flat plat structure to extend from a plane formed by the second major surface of the substantially fiat plat structure; f) bending the substantially flat plat structure being bent along the elongated portion so that the first and second portions of the first major surface are on opposite surfaces and the bent first and second perimeter portions contact one another forming a longitudinal interface; and g) contiguously welding the longitudinal interface to form a core tube wherein the second major surface forms an internal passageway of the core tube and the first major surface forms an outside surface of the core tube.

[0022] In a still further aspect, the invention can be a method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, the core tube having a non-circular transverse cross-section; b) providing at least one set of fins; c) connecting at least one set of fins to the outside surface of the core tube; and d) coating the at least one set of fins and the core tube with a baked phenolic coating or a zinc-based coating. [0023] In an even further aspect, the invention can be a method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a substantially fiat plat structure having a first lateral edge, a second lateral edge, a first end edge, a second end edge, a first major surface, and a second major surface, the first and second end edges defining a longitudinal length of the substantially flat plat structure; b) providing a first set of fins and a second set of fins; c) connecting the first set of fins to a first area of the first major surface of the substantially flat plat structure, the first set of fins spaced from the first lateral edge so that the substantially flat plat structure has a first portion extending longitudinally between the first set of fins and the first lateral edge that is free of fins; d) connecting the second set of fins to a second area of the first major surface of the substantially flat plat structure, the second set of fins spaced from the first set of fins and the second lateral edge so that the substantially flat plat structure has a second portion extending longitudinally between the first and second set of fins that is free of fins and a third portion extending longitudinally between the second set of fins and the second lateral edge that is free of fins; e) bending the first and third portions of the substantially flat plat structure to extend from a plane formed by the second major surface of the substantially flat plat structure; f) bending the substantially flat plat structure along the second portion so that the first and second areas of the first major surface are on opposite surfaces and the bent first and third portions contact one another forming a longitudinal interface; and g) contiguously welding the longitudinal interface to form a core tube wherein the second major surface forms an internal passageway of the core tube and the first major surface forms an outside surface of the core tube. [0024] In another aspect, the invention can be a method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a first substantially flat plate structure having a first lateral edge, a second later edge, a first major surface and a second major surface; b) providing a second substantially flat plate structure having a first lateral edge, a second later edge, a first major surface and a second major surface; c) connecting a first set of fins to the first major surface of the first substantially flat plate structure; d) connecting a second set of fins to the first major surface of the second substantially flat plate structure; e) bending the first substantially flat plate structure into a first transverse section of a core tube; f) bending the second substantially flat plate structure into a second transverse section of a core tube; g) arranging the first and second transverse sections in an adjacent manner so as to form first and second longitudinal interfaces; and h) contiguously welding the first and second longitudinal interfaces to form the core tube having a internal passageway formed by the second major surface of the first and second transverse sections. [0025] In even another aspect, the invention can be a method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a plurality of first substantially flat plate structures; b) connecting at least one set of fins to one of the plurality of substantially flat plate structures; c) bending the plurality of flat plate structures into transverse sections of a core tube; d) arranging the transverse sections in an adjacent manner so as to form a plurality of longitudinal interfaces; and e) contiguously welding the plurality of longitudinal interfaces to form the core tube having a internal passageway and an outer surface comprising the at least one set of fins.

In another aspect, the invention can be a fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled; at least one set of fins connected to an outside surface of the core tube; and wherein the outside surface of the core tube and the at least one set of fins is subjected to a ferretic nitrocarburization process.

In yet another aspect, the invention can be a method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, at least one set of fins connected to an outside surface of the core tube; and b) performing a surface conversion process to the at least one set of fins and the outside surface of the core tube that increases corrosion resistance. In one embodiment, it is preferred that the surface conversion process be a ferritic nitrocarburization process.

Brief Description of the Drawings

[0026] Figure 1 is a perspective view of a fin tube assembly for use in an air cooled heat exchanger according to one embodiment of the present invention.

[0027] Figure 2 is an exploded view of the fin tube assembly of FIG. l.ii

[0028] Figure 3 A is a transverse cross-sectional view of the fin tube assembly of FIG. 1.

[0029] Figure 3B is a longitudinal cross-sectional view of the fin tube assembly of FIG. 1 taken along a vertical plane passing through axis X-X of FIG. 3A.

[0030] Figure 3 C is atop view of a portion of the fin tube assembly of FIG. 1.

[0031] Figure 4A is a longitudinal cross-sectional view of a portion of a fin tube assembly that incorporates sets of fins according to a first alternative embodiment of the present invention.

[0032] Figure 4B is a longitudinal cross-sectional view of a portion of a fin tube assembly of that incorporates sets of fins according to a second alternative embodiment of the present invention. [0033] Figure 5 A is a transverse cross-sectional view of a fin tube assembly that incorporates a multi-part core tube according to a first alternative embodiment of the present invention. [0034] Figure 5B is a transverse cross-sectional view of a fin tube assembly that incorporates a multi-part core tube according to a second alternative embodiment of the present invention. [0035] Figure 5 C is a transverse cross-sectional view of a fin tube assembly that incorporates a multi-part core tube according to a third alternative embodiment of the present invention. [0036] Figure 6A is a transverse cross-sectional view of a fin tube assembly that incorporates a single-part core tube according to a fourth alternative embodiment of the present invention. [0037] Figure 6B is a transverse cross-sectional view of a fin tube assembly that incorporates a single-part core tube according to a fifth alternative embodiment of the present invention. [0038] Figure 6C is a transverse cross-sectional view of a fin tube assembly that incorporates a single-part core tube according to a sixth alternative embodiment of the present invention. [0039] Figure 6D is a transverse cross-sectional view of a fin tube assembly that incorporates a single-part core tube according to a fifth alternative embodiment of the present invention. [0040] Figure 7 is a transverse cross-section of a multi-layer core tube that can be used in a fin tube assembly according to one embodiment of the present invention. [0041] Figure 8 is a cross-section of a portion of multi -layer fin set that can be used in a fin tube assembly according to one embodiment of the present invention. [0042] Figure 9A-9E illustrate a method of manufacture of a fin tube assembly utilizing a single plate structure core tube according to one embodiment of the present invention. [0043] Figure 1 OA-I OE illustrate a method of manufacture of a fin tube assembly utilizing a multi-part core tube according to one embodiment of the present invention. [0044] Figure 11 is a schematic of a power plant according to one embodiment of the present invention.

Detailed Description of the Drawings

[0045] Referring first to FIG.1, a section of a fin tube assembly 100 according to one embodiment of the present invention is illustrated. The fin tube assembly 100 is especially useful for incorporation into air-cooled condenser systems for power plants in dry climates. The invention, however, is not so limited, and the fin tube assembly 100 may be used in other heat transfer equipment and in any industrial, commercial or residential environment. [0046] Generally, the fin tube assembly 100 comprises an elongated core tube 10 and two sets of cooling fins 20A-B. The core tube 10 has an inner surface 11 that forms a longitudinal internal passageway 40 and an outer surface 12 to which the two sets of fins 20A-B are connected. The internal passageway 40 is a extends from an opening at a proximal end 13 of the fin tube assembly 100 to an opening at a distal end 14 of the fin tube assembly 100. The internal passageway 40 is a hermetically sealed fluid conduit for transporting fluids, such as steam and other vapors, therethrough to facilitate the removal of heat from the fluid while keeping the fluid isolated from the surrounding atmosphere. [0047] The core tube 10 (and the resulting internal passageway 40) has a transverse cross- section that is non-circular. In the illustrated embodiment, the core tube 10 generally comprises two opposing substantially flat sections 15, 16 that are connected by lateral sections (which, in this embodiment, are formed by lateral flanges 114-115 and 122-123). Of course, the invention is not so limited and the core tube can take on a wide variety of transverse cross-sectional shapes that are non-circular.

[0048] The core tube 10 extends a longitudinal length L_L. In some embodiments, the longitudinal length LL may be between 20 to 60 feet. The width (not marked in the figures) of the core tube 10 is preferably in a range between 4 to 18 inches. The thickness of the core tube 10 can be, in some embodiments, 0.035 to 0.12 inches. Of course, the invention is not so limited and the longitudinal length L_L, width and thickness can be any desired measurement. Moreover, while the core tube 10 is exemplified as extending along a linear longitudinal axis, the core tube 10, in other embodiments, can include curves, bends and/or angles.

[0049] The core tube 10 is preferably constructed of a metal or other material that effectively conducts heat. For example, and without limitation, the core tube 10 can be constructed of copper, aluminum, carbon, stainless steel, or combination thereof. Of course, other materials can be used.

[0050] The sets of fins 20A-B are preferably connected to the outside surface 12 of the substantially flat portions 15, 16 on opposite sides of the fin tube assembly 100. Preferably, in some embodiments of the invention, the sets of fins 20A-B will be connected directly to the core tube via a fusion welding technique that does not use a filler materials, such as a laser welding technique. The details of the connection of the sets of fins 20A-B to the core tube 10 will be described in greater detail below with respect to FIGS. 3A-3B. The sets of fins 20A-B extend along the entire longitudinal length L_L of the fin tube assembly 100. However, if desired, the sets of fins 20 A-B can extend only a portion of the longitudinal length L_L in some embodiments. Moreover, any number of sets of fins can be used and can be located in various positions and/or orientations on the fin tube assembly 100. [0051] Referring now to FIG. 2, the fin tube assembly 100 of FIG. 1 is illustrated in an exploded state. As can be seen, the core tube 10 is constructed of a top plate structure 10A and a bottom plate structure 10B, each of which forms a transverse section of the core tube 10. As used herein, the term "plate" is not intended to be limited by an specific thickness, rigidity or shape, and is intended to include both thin and thick sheets of material that are either rigid or flexible. For example, the plates can be formed by section of metal that come in coils, such as rolled sheet metal. In one example, the plate structures 10A, 10B can be formed from a stock metal coil having a thickness in the range of 1.0 to 2.0 millimeters. In other embodiments, the plate structures 10A, 10B can be formed from a stock metal coil having a thickness in the range of 10 to 20 millimeters. The invention however is not limited to any specific dimensions unless specifically stated in the claims. [0052] The top plate structure 10A comprises a first lateral edge 110, a second lateral edge 111, a proximal end edge 112 and a distal end edge 113. The top plate structure 10A comprises the flat portion 15 and first and second lateral flanges 114, 115 that extend downward and laterally outward from the flat portion 15. The lateral flanges 114, 115 have bottom surfaces 116, 117 respectively, and terminate in the lateral edges UO, 111. [0053] Similarly, the bottom plate structure 10B comprises a first lateral edge 118, a second lateral edge 119, a proximal end edge 120 and a distal end edge 121. The bottom plate structure 10B comprises the flat portion 16 and first and second lateral flanges 122, 123 that extend upward and laterally outward from the flat portion 16. The lateral flanges 122, 123 have top surfaces 124, 125 respectively, and terminate in the lateral edges 118, 119. [0054] The first set of fins 20A is connected to the substantially flat top surface of the flat portion 15 of the top plate structure 10A while the second set of fins 20B is connected to the substantially flat bottom surface of the flat portion 16 of the bottom plate structure 10B. [0055] Each set of the fins 20A, 20B is preferably a corrugated sheet of material having a high coefficient of thermal conductivity, such as aluminum, carbon steel, stainless steel, copper or combinations thereof. The corrugated sheets 20A, 20B can be of any length. Either a single or a plurality of the corrugated sheets can be used to cover the entire longitudinal length LL of a single face of the fin tube assembly 100. The dimensional and structural details of the corrugated sheets will be described below in greater detail with respect to FIGS. 3B-3C.

[0056] Referring now to FIGS. 3A-3B concurrently, the general structural cooperation of components of the fin tube assembly 100 will be described in greater detail. Beginning with the formation of the core tube 10, the top and bottom plate structures 10- 10B are arranged in an adjacent manner as illustrated. More specifically, the top and bottom plate structures 10A, 10B are arranged in an aligned manner so that the bottom surfaces 116-117 of the lateral flanges 114-115 of the top plate structure 10A come into surface contact with the top surfaces 124-125 of the lateral flanges 122-123 of the bottom plate structure 10B, thereby forming two longitudinal interfaces 126- 127. Respectively, the first longitudinal interface 126 is formed by the contact between the bottom and surfaces 116, 124 of the first lateral flanges 114, 122 while the second longitudinal interface 127 is formed by the contact between the bottom and top surfaces 117, 125 of the second lateral flanges 115, 123.

[0057] The combination of the first lateral flanges 114, 122 form a first longitudinal ridge 30 that protrudes from the outside surface 12 of a first side of the core tube 10 along the length L_L of the fin tube assembly 100. Similarly, the combination of the second lateral flanges 115, 123 form a second longitudinal ridge 31 that protrudes from the outside surface 12 of a second side of the core tube 10 along the length LL of the fin tube assembly 100. The first and second longitudinal ridges 30, 31 (and the interfaces 126, 127) are opposite one another and 180 degrees apart about a central longitudinal axis X-X (visible only as point X in FIG. 3A) of the fin tube assembly 100. The invention, however, is not so limited and the longitudinal ridges can be located at other transverse locations. Moreover, as will become apparent from the discussion below, any number of longitudinal ridges can exist, including none. The exact number is determined by the geometric configuration in which the lateral edge portions of the plate structures are bent and the number of plate structures used to create a complete desired transverse cross-section of the core tube 10.

[0058] In the illustrated embodiment of FIGS. 3A-3B, the fin tube assembly 100 has two longitudinal interfaces 126, 127 because the top and bottom plate structures 10A, 10B each form a transverse semi-section of the core tube 10. Thus, arranging the top and bottom plate structures 10-lOB in the adjacent and aligned orientation results in the formation of the complete transverse cross-section of the core tube 10 forming internal passageway 40. The invention, however, is not so limited and, as will become apparent from the discussion below, any number of longitudinal interfaces can exist, including one. The exact number is determined by the number of plate structures used to create a complete desired transverse cross-section of the core tube 10. Furthermore, it is not necessary for any longitudinal interface to be a linear interface (as exemplified). In alternative embodiments, the longitudinal interface may take on a step-like shape or a helical and/or twisting shape. [0059] In order to make the internal passageway 40 a fluid-tight conduit for carrying a fluid to be cooled, the first flanges 114, 122 of the top and bottom plate structures 10A, 10B are contiguously welded together, thereby connecting the top and bottom plate structures 10A, 10B together on one side and hermetically sealing the first longitudinal interface 126. Similarly, the second flanges 115, 123 of the top and bottom plate structures 10A, 10B are also contiguously welded together, thereby connecting the top and bottom plate structures 10A, 10B together on the other side and hermetically sealing the second longitudinal interface 127. The contiguous welding of the first flanges 114, 122 and/or the second flanges 115, 123 can be accomplished using any suitable welding technique that uses or does not use a filler material, including without limitation resistance seam welding, manual metal arc welding, metal inert gas welding, tungsten inert gas welding, submerged arc welding, plasma arc welding, gas welding, electroslag welding, electron beam welding, laser welding, thermit welding, resistance spot welding and/or combinations thereof. Most preferably, a resistance seam welding process is used.

[0060] Referring now to FIGS. 3B-3C concurrently, the sets of fins 20A, 20B will be discussed in greater detail. As discussed above, each of the sets of fins 20A, 20B are a corrugated sheet of material comprising a plurality of undulating and alternating peaks 21 A, 21B and valleys 22A, 22B (only some of which are numerically indicated to avoid clutter in the drawings). The peaks 21A, 21B respectively terminate in apex ridges 23A, 23B while the valleys 22A, 22B terminate in floors 24A, 24B. The connection of the first set of fins 20A to the top plate structure 10A will now be described with the understanding that the same is applicable to the connection of the second set of fins 20B to the bottom plate structure 10B. [0061] The first set of fins 20A is connected to the substantially flat upper/outer surface of the flat portion 15 of the top plate structure 10A by welding. More specifically, all of the floors 24A of the first set of fins 20A are directly welded to the top plate structure 10A by using a fusion welding technique that does not utilize a filler material so as to ensure adequate thermal conduction between the first set of fins 20A and the core tube 10. One such suitable fusion welding technique is laser welding.

[0062] In one embodiment, all of the floors 24A of the first set of fins 20A are fusion welded in a stitched manner to the top plate structure 10A along the entire fin width WF. In another embodiment, all of the floors 24A of the first set of fins 20A are contiguously fusion welded to the top plate structure 10A along the entire fin width WF. Of course, a combination of both contiguous fusion welding and stitch fusion welding techniques can be used for different floors 24A of fins 20A for the same fin tube assembly 100 if desired. In FIG. 3C, the stitch fusion welding is schematically illustrated as stitch line LWs and the contiguous fusion welding is schematically illustrated as contiguous line LWc. Most preferably, all of the floors 24A of the set of fins 20A are fusion welded directly to the top plate structure 10A of the core tube 10 for structural integrity and thermal conductivity purposes. Of course, this is not required in all cases.

[0063] In embodiments where a stitch fusion welding is used to connect the sets of fins 20A, 20B to the core tube 10, it may be preferable to coat the entire fin tube assembly 100 with a metal-based coating after the welding to achieve intimate contact between the entireties of the floors 24A, 24B so as to facilitate thermal conduction between the core tube 10 and the fins 20A, 20B. In one such specific application, the fin tube assembly 100 (i.e., the assembly of the fins 20A, 20B stitch fusion welded to the assembled core tube10) is dipped into a zinc or aluminum based liquid bath. As a result, the metal-based liquid enters and fills any gaps that may exists between the floors 24A, 24B of the fins 20A, 20B and the core tube 10. The fin- tube assembly is 100 then is allowed to cool. Of course, other metal-based coating can be used.

[0064] Finally, irrespective of whether a stitch or contiguous welding technique is used, the assembled fin tube assembly 100 can be coated with a corrosive resistant material so as to withstand operating and environmental conditions without substantial degradation. Suitable coatings include, without limitation, a metal-based coating or a baked phenol coating. Suitable metal-based coatings include without limitation zinc-based coatings and aluminum- based coatings. In order to minimize impedance of thermal transfer, the coating is less than 100 microns in some embodiments. As discussed, below, in other embodiments the fin tube assembly 100 can be made corrosion resistant by subjecting the assembly to a surface conversion process, such as ferritic nitrocarburization.

[0065] In one embodiment, the sets of fins will have a thickness between 0.005 to 0.015 inches and a height between 0.25 and 1.0 inches. The invention how ever is not limited to any specific dimensions. It is to be understood that the sets of fins 20A, 20B can take on a wide variety of shapes, sizes, thicknesses, structural arrangements and orientations on the core tube 10. None of which are limiting of the present invention unless specifically stated in the claims.

Additional Fin Embodiments

[0066] In FIGS. 4 A and 4B, two additional embodiments of fin sets for use in the present invention are illustrated. It is to be understood that additional embodiments are disclosed merely for additional illustration and contemplation of what may become the best mode of the invention. Those skilled in the art understand that many equivalent fin set structures exist and that the principles disclosed below can be applied in a wide variety of embodiments. [0067] Referring now to FIG. 4 A, a second embodiment of sets of fins 20A¹, 20B' that can be used with the fin tube assembly 100 (or any embodiments thereof) is illustrated. The sets of fins 20A', 20B* can replace and/or supplement one or more of the sets of fins 20A, 20B in the fin tube assembly 100 (or any embodiments thereof) of the present invention. The sets of fins 20A', 20B' are similar to the sets of fins 20A, 20B discussed above in relation to FIGS. 1-3C in many basic structural aspects, functioning and connection to the core tube 10. Thus the same reference characters will be used to identify like components of the sets of fins 20A', 20B' with the addition of a single prime suffix " ' ." In order to avoid redundancy, only those aspects of the sets of fins 20A', 20B' that differ from the sets of fins 20A, 20B will be discussed in detail below. Furthermore, the pertinent details of the sets of fins 20A', 20B' will now be described solely in relation to the first set of fins 20A' with the understanding that the same is applicable to the second set of fins 20B'.

[0068] The first set of fins 20A' is a orthogonally corrugated sheet of material, such as a metal or other thermally conductive material. The first set of fins 20A' comprises a plurality of orthogonally undulating and alternating peaks 21A' and valleys 22A* (only some of which are numerically indicated to avoid clutter in the drawings). The peaks 21A' respectively terminate in apex surfaces 23A' while the valleys 22 A' terminate in flat floor surfaces 24A*. [0069] For mass production of the fin tube assembly 100, the orthogonally corrugated shape of the fin set 20A' may be preferable in some regards to the fin set 20A because of the flat floor surfaces 24A'. Creating the fin set 20A' so that its floor surfaces 24A' have a substantially flat portion increases the surface area which is in direct contact with the outside surface of the core tube during the direct fusion welding connection process (discussed above). As a result, adequate laser welding of the fin set 20A' to the core tube 10 can be more easily and more reliably achieved without the need for extreme tolerances and precision in moving the laser torch across the fin width WF (same as that shown in FIG. 3C). Moreover, having the substantially flat floor surfaces 24A' increases the amount of intimate surface contact between the core tube and the fin set 20A' so as to increase thermal conduction between the two, which is needed for cooling the fluid. [0070] It should be noted that in some embodiments of the invention, the benefits of the flat floor surface 24A' can be achieved without having the fin set 20A' being of a purely orthogonal shape. In such embodiments, the walls and peaks may be angled and/or curved. [0071] Referring now to FIG. 4B, a third embodiment of sets of fins 20A", 20B" that can be used with the fin tube assembly 100 (or any embodiments thereof) is illustrated. The sets of fins 20A", 20B" can replace and/or supplement one or more of the sets of fins 20A, 20B or fins 20A', 20B* in the fin tube assembly 100 (or any embodiments thereof) of the present invention. The sets of fins 20A", 20B" are similar to the sets of fins 20A, 20B and fins 20A', 20B* discussed above in relation to FIGS. 1-4A in many basic structural aspects, functioning and connection to the core tube 10. Thus the same reference characters will be used to identify like components of the sets of fins 20A", 20B" with the addition of a double prime suffix " " ." In order to avoid redundancy, only those aspects of the sets of fins 20A", 20B" that differ from the sets of fins 20A, 20B and fins 20A', 20B* will be discussed in detail below. Furthermore, the pertinent details of the sets of fins 20A", 20B" will now be described solely in relation to the first set of fins 20A" with the understanding that the same is applicable to the second set of fins 20B".

[0072] The first set of fins 20A" comprise a plurality of separate L-shaped fins 28A" that are individually laser welded to the core tube 10. While the individual fins 28A" are orthogonal shaped, they can be curved or bent in other shapes if desired. Stated simply, it is to be understood that the sets of fins in the present invention do not have to formed out of a single piece of material but can be individually formed and welded to the core tube.

Additional Multi-Part Core Tube Embodiments

[0073] In FIGS. 5A-5C, three additional embodiments of multi-part core tubes for use in the fin tube assembly 100 of present invention are illustrated. It is to be understood that these additional embodiments are disclosed merely for additional illustration and contemplation of what may become the best mode of the invention. Those skilled in the art understand that many equivalent multi-part core tube arrangements exist and that the principles disclosed below can be applied in a wide variety of embodiments. Moreover, the invention is not limited to two-part core tube assemblies. It is to be understood that the concepts disclosed herein can be applied to multi-part core tubes having any number of transverse sections and that any one of the plate structures discussed herein can be created in multiple sections if desired.

[0074] Referring now to FIG. SA, a second embodiment of a core tube 10' that can be used with the fin tube assembly 100 (or any embodiment thereof) is illustrated. The core tube 10' can replace and/or supplement the entirety or a section of the core tube 10 disclosed in FIGS. 1-4B. The core tube 10' is similar to the core tube 10 discussed above in relation to FIGS. 1- 4B in many basic structural aspects, functioning and connection to the fin sets 20A, 20B. Thus the same reference characters will be used to identify like components of the core tube 10' with the addition of a single prime suffix " ' ." In order to avoid redundancy, only those aspects of the core tube 10' that differ from the core tube 10 will be discussed in detail below. [0075] The main difference between the core tube 10* and the core tube 10 is the shape of the lateral flanges 114'-11S', 122'-123' of the top and bottom plate structures 10A', 10B'. In this embodiment, the lateral flanges 114', 115' of the top plate structure 10A' extend downward and inward from the flat portion 15' of the top plate structure 10A*. Conversely, the lateral flanges 122', 123' of the bottom plate structure 10B' extend upward and inward from the flat portion 16' of the bottom plate structure 10B'.

[0076] As a result, when arranging the top and bottom plate structures 10A', 10B' in an adjacent and aligned orientation the bottom surfaces 116', 117' of the lateral flanges 114', 115' of the top plate structure 10A* (which are now formed by the outer surface 12' of the core tube) come into surface contact with the top surfaces 124', 125' of the lateral flanges 122', 123' of the bottom plate structure 10B' (which are also formed by the outer surface 12'), thereby forming the two longitudinal interfaces 126', 127'.

[0077] The combination of the first lateral flanges 114', 122' form a first longitudinal ridge 30' that protrudes into the internal passageway 40* from a first side of the core tube 10* along the length L_L of the fin tube assembly 100'. Similarly, the combination of the second lateral flanges 115', 123' form a second longitudinal ridge 31' that also protrudes into the internal passageway 40' from a second side of the core tube 10' along the length L_L of the fin tube assembly 100'.

[0078] As above, in order to make the internal passageway 40' a fluid-tight conduit for carrying a fluid to be cooled, the first flanges 114', 122* of the top and bottom plate structures 10A', 10B' are contiguously welded together along the first and second longitudinal interfaces 126', 127', thereby connecting the top and bottom plate structures 10A', 10B*. The contiguous welding of the first flanges 114', 122' and/or the second flanges 115', 123' can be accomplished using any suitable welding technique that uses or does not use a filler material, including without limitation resistance seam welding, manual metal arc welding, metal inert gas welding, tungsten inert gas welding, submerged arc welding, plasma arc welding, gas welding, electroslag welding, electron beam welding, laser welding, thermit welding, resistance spot welding and/or combinations thereof. Most preferably, a resistance seam welding process is used.

[0079] Referring now to FIG. 5B, a second embodiment of a core tube 10" that can be used with the fin tube assembly 100 (or any embodiment thereof) is illustrated. The core tube 10" can replace and/or supplement the entirety or a section of the core tube 10 disclosed in FIGS. 1-5 A. The core tube 10" is similar to the core tube 10 discussed above in relation to FIGS. 1- 4B in many basic structural aspects, functioning and connection to the fin sets 20A, 20B. Thus the same reference characters will be used to identify like components of the core tube 10" with the addition of a double prime suffix " " ." In order to avoid redundancy, only those aspects of the core tube 10" that differ from the core tube 10 will be discussed in detail below.

[0080] The main difference between the core tube 10" and the core tube 10 is the shape of the lateral flanges 114"-115", 122"-123" of the top and bottom plate structures 10A", 10B". In this embodiment, the lateral flanges 114", 115" of the top plate structure 10A" extend only downward from the flat portion 15" of the top plate structure 10A". Conversely, the lateral flanges 122", 123" of the bottom plate structure 10B" extend only upward from the flat portion 16" of the bottom plate structure 10B". More specifically, the lateral flanges 114"-115", 122"-123" are bent into generally 90 degree curved sections. Of course, in alternative embodiments the lateral flanges 114"-115", 122"-123" can merely extend at a right angle to the flat portions 15", 16".

[0081] When the top and bottom plate structures 10A", 10B" are arranged in the adjacent and aligned orientation illustrated, the lateral edges 110", 111" of the top plate structure 10A" come into contact and abut the lateral edges 118", 119" of the bottom plate structure 10B", thereby forming the two longitudinal interfaces 126", 127". [0082] As above, in order to make the internal passageway 40" a fluid-tight conduit for carrying a fluid to be cooled, the top and bottom plate structures 10A", 10B" are contiguously welded together along the first and second longitudinal interfaces 126", 127", thereby connecting the top and bottom plate structures 10A", 10B". A butt welding technique is preferably used in this embodiment that does or does not use a filler material. Suitable welding techniques include without limitation resistance seam welding, manual metal arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, gas welding, electron beam welding, laser welding, induction welding, high frequency welding and/or combinations thereof.

[0083] Referring now to FIG. 5C, a third embodiment of a core tube 10"' that can be used with the fin tube assembly 100 (or any embodiment thereof) is illustrated. The core tube 10"' can replace and/or supplement the entirety or a section of the core tube 10 disclosed in FIGS. 1-5B. The core tube 10'" is similar to the core tube 10 discussed above in relation to FIGS. 1-4B in many basic structural aspects, functioning and connection to the fin sets 20A, 20B. Thus the same reference characters will be used to identify like components of the core tube 10'" with the addition of a triple prime suffix " '" ." In order to avoid redundancy, only those aspects of the core tube 10'" that differ from the core tubes discussed above will be discussed in detail below.

[0084] The main difference between the core tube 10'" and the core tube 10 is the shape of the lateral flanges 114"'-115'", 122"'-123'" of the top and bottom plate structures 10A'", 10B'". In this embodiment, the lateral flanges 114'", 115'" of the top plate structure 10A" extend only downward from the flat portion 15"' of the top plate structure 10A"'. Conversely, the lateral flanges 122'", 123'" of the bottom plate structure 10B"' extend only upward from the flat portion 16'" of the bottom plate structure 10B'". More specifically, the lateral flanges 114"'-115"\ 122"'-123'" are bent into generally 90 degree curved sections. Of course, in alternative embodiments the lateral flanges 114'"-115"\ 122"'-123"' can merely extend at a right angle to the flat portions 15'", 16'".

[0085] The top plate structure 10B'"is wider than the top plate structure 10A'". When the top and bottom plate structures 10A'", 10B'" are in the adjacent and aligned orientation, a portion of the top plate structure 10A'" nests within the bottom plate structure 10B"¹. As a result, the bottom surfaces 116'", 117'" of the lateral flanges 114'", 115'" of the top plate structure 10A'" (which are now formed by the outer surface 12"') come into surface contact with the top surfaces 124"', 125'" of the lateral flanges 122'", 123"' of the bottom plate structure 10B'" (which are now formed by the inner surface 11'"), thereby forming the two longitudinal interfaces 126"', 127"'.

[0086] As above, in order to make the internal passageway 40'" a fluid-tight conduit for carrying a fluid to be cooled, the first and second longitudinal interfaces 126'", 127'" are contiguously welded shut, thereby connecting the top and bottom plate structures 10A'", 10B'". This contiguous welding can be accomplished using any suitable welding technique that uses or does not use a filler material. Suitable welding techniques include without limitation resistance seam welding, manual metal arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, gas welding, electron beam welding, laser welding, induction welding, high frequency welding and/or combinations thereof.

Single-Plate Core Tube Construction Embodiments

[0087] In FIGS. 6A-6D, four embodiments of core tubes whose transverse cross-section is formed by a single-plate core tubes for use in the fin tube assembly 100 of present invention are illustrated. It is to be understood that these single-plate core tube embodiments are disclosed merely for additional illustration and contemplation of what may become the best mode of the invention. Those skilled in the art understand that many equivalent single-plate core tube arrangements exist and that the principles disclosed below can be applied in a wide variety of embodiments.

[0088] Referring first to FIG. 6A, an embodiment of a fin tube assembly 1100 having a core tube 1010 constructed of a single-plate is illustrated. The core tube 1010 can replace and/or supplement the entirety or a section of any of the core tubes disclosed in FIGS. 1-5C. The fin tube assembly 1100 is similar to the fin tube assembly 100 discussed above in relation to FIGS. 1-4B in many of the structural aspects, functioning and cooperation of components. Thus the same reference characters will be used to identify like components of the fin tube assembly 1100 with the addition of one-thousand ("1000"). In order to avoid redundancy, only those aspects of the fin tube assembly 1100 that differ from the fin tube assembly 100 will be discussed in detail below.

[0089] The main difference between the fin tube assembly 1100 and fin tube assembly 100 is the construction of the core tube 1010 out of a single plate structure 1010 rather than a multipart assembly of transverse sections. In this embodiment, a single plate structure IOIOA forms the entirety of the transverse cross-section of the core tube 1010. As will be discussed in greater detail below, the single plate structure IOIOA begins the manufacturing process as a substantially flat plate structure and is bent, rolled and otherwise formed into the transverse shape shown in FIG. 6A.

[0090] The plate structure IOIOA comprises an outer surface 1012, an inner surface 1011, a first lateral edge 1110, and a second lateral edge 1111. A first lateral flange 1114 is formed into the plate structure IOIOA near the first lateral edge 1110 while a second lateral flange 1115 is formed into the plate structure IOIOA near the second lateral edge 1111. The plate structure IOIOA is bent in an approximately 180 degree curved bend between the top flat portion 1015 and the bottom flat portion 1016 until the bottom surface 1116 of the first lateral flange 1114 comes into surface contact with the top surface 1117 of the second lateral flange 1115, thereby forming the first (and only) longitudinal interface 1126. As a result, the one lateral side 1070 of the core tube 1010 is unitary and free of a longitudinal interface, thus eliminating the need for a weld. The sole longitudinal interface 1126 is located on the opposite lateral side 1071 of the core tube 1010.

[0091] The first lateral flange 1114 and the second lateral flange 1115 form a single longitudinal ridge 1030 extending and protruding outward from the outside surface 1012 of the core tube 1010. As with the other embodiments of this kind, in order to make the internal passageway 1040 a fluid-tight conduit for carrying a fluid to be cooled, the longitudinal interface 1126 is contiguously welded shut, thereby connecting the first lateral flange 1114 and the second lateral flange 1115. This contiguous welding can be accomplished using any suitable welding technique that uses or does not use a filler material. Suitable welding techniques include without limitation resistance seam welding, manual metal arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, gas welding, electron beam welding, laser welding, induction welding, high frequency welding and/or combinations thereof. Most preferably, a resistance seam welding process is used. [0092] Referring now to FIG. 6B, a second embodiment of a fin tube assembly 2100 having a core tube 2010 constructed of a single-plate is illustrated. The core tube 2010 can replace and/or supplement the entirety or a section of any of the core tubes disclosed in FIGS. 1-6A. The fin tube assembly 2100 is similar to the fin tube assembly 100 discussed above in relation to FIGS. 1-4B in many of the structural aspects, functioning and cooperation of components. Thus the same reference characters will be used to identify like components of the fin tube assembly 2100 with the addition of two-thousand ("2000"). In order to avoid redundancy, only those aspects of the fin tube assembly 2100 that differ from the fin tube assembly 100 will be discussed in detail below.

[0093] The main difference between the fin tube assembly 2100 and fin tube assembly 100 is the construction of the core tube 2010 out of a single plate structure 2010 rather than a multipart assembly of transverse sections. In this embodiment, a single plate structure 2010A forms the entirety of the transverse cross-section of the core tube 2010. As will be discussed in greater detail below, the single plate structure 2010A begins the manufacturing process as a substantially flat plate structure and is bent, rolled and otherwise formed into the transverse shape shown in FIG. 6B.

[0094] The plate structure 2010A comprises an outer surface 2012, an inner surface 2011, a first lateral edge 2110, and a second lateral edge 2111. A first lateral flange 2114 is formed into the plate structure 2010A near the first lateral edge 2110 while a second lateral flange 2115 is formed into the plate structure 2010A near the second lateral edge 2111. The plate structure 2010A is bent in an approximately 180 degree curved bend between the top flat portion 2015 and the bottom flat portion 2016 until the bottom surface 2116 of the first lateral flange 2114 comes into surface contact with the top surface 2117 of the second lateral flange 2115, thereby forming the first (and only) longitudinal interface 2126. As a result, the one lateral side 2070 of the core tube 2010 is unitary and free of a longitudinal interface, thus eliminating the need for a weld. The sole longitudinal interface 2126 is located on the opposite lateral side 2071 of the core tube 1010. [0095] The first lateral flange 2114 and the second lateral flange 2115 form a single longitudinal ridge 2030 extending inward into the internal passageway 2040 of the core tube 2010. As with the other embodiments of this kind, in order to make the internal passageway 2040 a fluid-tight conduit for carrying a fluid to be cooled, the longitudinal interface 2126 is contiguously welded shut, thereby hermetically connecting the first lateral flange 2114 and the second lateral flange 2115. This contiguous welding can be accomplished using any suitable welding technique that uses or does not use a filler material. Suitable welding techniques include without limitation resistance seam welding, manual metal arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, gas welding, electron beam welding, laser welding, induction welding, high frequency welding and/or combinations thereof. Most preferably, a resistance seam welding process is used. [0096] Referring now to FIG. 6C, a third embodiment of a fin tube assembly 3100 having a core tube 3010 constructed of a single-plate is illustrated. The core tube 3010 can replace and/or supplement the entirety or a section of any of the core tubes disclosed in FIGS. 1-6B. The fin tube assembly 3100 is similar to the fin tube assembly 100 discussed above in relation to FIGS. 1-4B in many of the structural aspects, functioning and cooperation of components. Thus the same reference characters will be used to identify like components of the fin tube assembly 3100 with the addition of three-thousand ("3000"). In order to avoid redundancy, only those aspects of the fin tube assembly 3100 that differ from the fin tube assembly 100 will be discussed in detail below.

[0097] The main difference between the fin tube assembly 3100 and fin tube assembly 100 is the construction of the core tube 3010 out of a single plate structure 3010 rather than a multipart assembly of transverse sections. In this embodiment, a single plate structure 3010A forms the entirety of the transverse cross-section of the core tube 3010. As will be discussed in greater detail below, the single plate structure 3010A begins the manufacturing process as a substantially flat plate structure and is bent, rolled and otherwise formed into the transverse shape shown in FIG. 6C.

[0098] The plate structure 3010A comprises an outer surface 3012, an inner surface 3011, a first lateral edge 3110, and a second lateral edge 3111. A first lateral flange 3114 is formed into the plate structure 3010A near the first lateral edge 3110 while a second lateral flange 3115 is formed into the plate structure 3010A near the second lateral edge 3111. The first and second lateral flanges 3114, 3115 are formed as 90 degree bends. The plate structure 3010A is bent in an approximately 180 degree curved bend between the top flat portion 3015 and the bottom flat portion 3016 until the first lateral edge 3110 comes into contact with the second lateral edge 3111, thereby forming the first (and only) longitudinal interface 3126. As a result, the one lateral side 3070 of the core tube 3010 is unitary and free of a longitudinal interface, thus eliminating the need for a weld. The sole longitudinal interface 3126 is located on the opposite lateral side 3071 of the core tube 3010.

[0099] As with the other embodiments of this kind, in order to make the internal passageway 3040 a fluid-tight conduit for carrying a fluid to be cooled, the longitudinal interface 3126 is contiguously welded shut, thereby hermetically connecting the first lateral edge 3110 and the second lateral edge 3111. A butt welding technique is preferably used in this embodiment that does or does not use a filler material. Suitable welding techniques include without limitation resistance seam welding, manual metal arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, gas welding, electron beam welding, laser welding, induction welding, high frequency welding and/or combinations thereof. [0100] Referring now to FIG. 6D, a fourth embodiment of a fin tube assembly 4100 having a core tube 4010 constructed of a single-plate is illustrated. The core tube 4010 can replace and/or supplement the entirety or a section of any of the core tubes disclosed in FIGS. 1 -6A. The fin tube assembly 4100 is similar to the fin tube assembly 100 discussed above in relation to FIGS. 1-4B in many of the structural aspects, functioning and cooperation of components. Thus the same reference characters will be used to identify like components of the fin tube assembly 4100 with the addition of four-thousand ("4000"). In order to avoid redundancy, only those aspects of the fin tube assembly 4100 that differ from the fin tube assembly 100 will be discussed in detail below.

[0101] The main difference between the fin tube assembly 4100 and fin tube assembly 100 is the construction of the core tube 4010 out of a single plate structure 4010 rather than a multipart assembly of transverse sections. In this embodiment, a single plate structure 4010A forms the entirety of the transverse cross-section of the core tube 4010. As will be discussed in greater detail below, the single plate structure 4010A begins the manufacturing process as a substantially flat plate structure and is bent, rolled and otherwise formed into the transverse shape shown in FIG. 6D.

[0102] The plate structure 4010A comprises an outer surface 4012, an inner surface 4011, a first lateral edge 4110, and a second lateral edge 4111. A first lateral flange 4114 is formed into the plate structure 4010A near the first lateral edge 4110 while a second lateral flange 4115 is formed into the plate structure 4010A near the second lateral edge 4111. The first and second lateral flanges 4114, 4115 are formed as 90 degree bends. The plate structure 4010A is bent in an approximately 180 degree curved bend between the top flat portion 4015 and the bottom flat portion 4016 until the bottom surface 4116 (formed in this embodiment by the outside surface 4012) of the first lateral flange 4114 comes into surface contact with the top surface 4117 (formed in this embodiment by the inner surface 4011) of the second lateral flange 4115, thereby forming the first (and only) longitudinal interface 4126. The bottom flat portion 4016 is wider than the top flat portion 4015 so as to create the offset during the bending.

[0103] The one lateral side 4070 of the core tube 4010 is unitary and free of a longitudinal interface, thus eliminating the need for a weld. The sole longitudinal interface 4126 is located on the opposite lateral side 4071 of the core tube 4010. As with the other embodiments of this kind, in order to make the internal passageway 4040 a fluid-tight conduit for carrying a fluid to be cooled, the longitudinal interface 4126 is contiguously welded shut, thereby hermetically connecting the first lateral flange 4114 and the second lateral flange 4115. This contiguous welding can be accomplished using any suitable welding technique that uses or does not use a filler material. Suitable welding techniques include without limitation resistance seam welding, manual metal arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, gas welding, electron beam welding, laser welding, induction welding, high frequency welding and/or combinations thereof. Most preferably, a resistance seam welding process is used.

Single-Layer and Multi-Layer Embodiments

[0104] In all of the embodiments illustrated in FIGS. 1-6D, the core tube and the sets of fins are constructed as single-layer structures. In other words, the core tube and the sets of fins are constructed of a single layer of the desired metal material, such as a layer of copper, a layer of aluminum, a layer of stainless steel, a layer of carbon steel, etc. The invention however, is not so limited, and in any of the embodiments disclosed herein, the core tube and/or the sets of fins can be constructed as multi-layer structures. [0105] Referring now to FIG. 7, a multi-layer core tube 5010 is illustrated. The core tube 5010 comprises a first material layer 5080 and a second material layer 5090. An inner surface 5011 of the first material layer 5080 forms the internal passageway 5040 of the core tube 5010. The second material layer 5090 surrounds the first material layer 5080. The outside surface 5012 forms the outside surface of the core tube 5010. [0106] The outside surface 5081 of the first material layer 5080 is in substantially intimate surface contact with the inner surface 5091 of the second material layer 5090 so as to not negatively impact thermal conduction between the two layers 5080, 5090 in a significant manner. The connection of the layers 5080, 5090 can be accomplished via a cladding or compression rolling process.

[0107] The first and second layers 5080, 5090 can be constructed of the same or different materials. Suitable materials include without limitation copper, aluminum, carbon steel and stainless steel. It may be preferred that the first/inner layer 5080 be constructed of a material having a higher coefficient of thermal expansion than the second/outer layer 5090 so as to ensure intimate surface contact under elevated thermal conditions. [0108] While two-layers of material are exemplified in the multi-layer core tube 5010, any number of layers can be used as desired. Moreover, while the core tube 5010 is of the single- plate structure type, it is to be understood that the multi-layer concept can be applied, without limitation, to any of the multi-part core-tube configurations disclosed above in FIGS. 1-5C. [0109] Referring now to FIG. 8, a portion of a multi-layer fin set 5020 is illustrated. The fin set 5020 comprises a first material layer 5025 and a second material layer 5026. The lower surface 5027 of the first material layer 5025 is in substantially intimate surface contact with the upper surface 5028 of the second material layer 5026 so as to not negatively impact thermal conduction between the layers 5025, 5026 in a significant manner. The connection of the layers 5025, 5026 can be accomplished via a cladding or compression rolling process. [0110] The first and second layers 5025, 5026 can be constructed of the same or different materials. Suitable materials include without limitation copper, aluminum, carbon steel, and stainless steel. When connected to a core tube, the bottom surface 5029 of the second layer 5026 contacts the outer surface of the core tube. In an embodiment where a multi-layer fin set 5020 is to be welded directly to the core tube using a fusion welding technique that does not use a filler material, the first material layer 5025 should be constructed of a material that metallurgically compatible with the material of the core tube for welding purposes. [0111] While two-layers of material are exemplified in the multi-layer fin set 5020, any number of layers can be used as desired. Moreover, the multi-layer fin concept can be applied to any of the fin types discussed above in FIGS. 1-4B.

[0112] It should finally be noted that any of the structural alternative discussed above with respect to FIG. 1-8 can be combined in any manner as desired to create the desire fin tube assembly.

Examples of Methods of Manufacturing.

[0113] Two examples of method of manufacturing fin tube assemblies in accordance with the present invention are described in greater detail below. It is to be understood that the general principles of manufacture discussed below can be utilized to create any of the fin tube assembly embodiments discussed above in FIGS. 1-8 in addition to derivations thereof. Moreover, it is to be understood that any of the techniques and structural aspects discussed are applicable to structures and techniques discussed below.

[0114] FIGS. 9A-E illustrate the major steps of creating the single plate structure fin tube assembly 3100 of FIG. 6C. Of course, a similar manufacturing technique can be used for any of the single-plate structures discussed above in FIGS. 6A-6D. [0115] Beginning with FIG. 9 A, a single-layer substantially flat plate structure 3010A is provided. The flat plate structure 3010A has an upper major surface 3012 and a bottom major surface 3011, which are also substantially flat and free of any significant curvature. The top and bottom major surfaces 3012, 3011 are laterally delimited by a right lateral edge 3110 and a left lateral edge 3111. The top and bottom major surfaces 3012, 3011 are longitudinally delimited by two end edges (not numerically indicated). The flat plate structure 3010A is a rectangular shape and can be cut to the desired size from a roll of sheet metal on the site of manufacture if desired or formed in any other suitable manner. Preferably, the flat plate structure 3010A is constructed of carbon steel. However, as discussed above, the invention is not so limited.

[0116] Referring now to FIG. 9B, once the flat plate structure 3010A is created in the desired size and shape (or otherwise obtained), the first and second sets of fins 3020A, 3020B are created. In this embodiment, each of the first and second set of fins 3020A, 3020B are formed from a single sheet of metal by bending the sheet of metal into the desired corrugated configuration having peaks terminating in ridges 3023A, 3023B and valleys terminating in floors 3024A, 3024B. It is preferred that the first and second set of fins 3020A, 3020B be formed from sheets of carbon steel. However, as discussed above, the invention is not so limited. Moreover, if desired, the sets of fins 3020A, 3020B can be created into any of the alternative configurations disclosed above and other derivatives. [0117] Once the first and second set of fins 3020A, 3020B are created (or otherwise obtained), the first set of fins 3020A are positioned atop the top surface 3012 of the flat plate structure 3010A extending longitudinally between the end edges. Similarly, the second set of fins 3020B are also positioned atop the top major surface 3012 of the flat plate structure 3010A extending longitudinally between the end edges. Of course, the first and second sets of fins 3020A, 3020B do not have to extend the entire longitudinal length of the plate 3010A. [0118] The first set of fins 3020A are positioned atop the top major surface 3012 of the flat plate structure 3010A spaced from and near the right lateral edge 3110. The second set of fins 3020B are also positioned atop the top major surface 3012 of the flat plate structure 3010A but are spaced from and near the left lateral edge 3111 of the flat plate structure 3010A. The first and second set of fins 3020A, 3020B are also spaced from one another. [0119] As a result of the above positioning of the fin sets 3020A, 3020B, a first longitudinal strip area 3012A exists between the first set of fins 3020A and the right lateral edge 3110 that is substantially free of fins. A second longitudinal strip area 3012B also exists between the second set of fins 3020B and the left lateral edge 3110 that is substantially free of fins. Finally, a third longitudinal strip area3012C also exists between the first set of fins 3020A and the second set of fins 3020B that is substantially free of fins. [0120] The first and second set of fins 3020A, 3020B are then welded directly to the flat plate structure 3010A via a fusion welding process that does not use a filler material, such as a laser weld. Most preferably, the floors 3024A, 3024B of the first and second set of fins 3020A, 3020B are contiguously laser welded to the flat plate structure 3010A. The laser welding process is achieved by creating relative motion between the laser torch and the assembly 3900 (i.e., the flat plate structure 3010A and the first and second set of fins 3020A, 3020B). In the illustration the relative movement would be left to right or vice-versa along the floors 3024A, 3024B. In one embodiment, it may be preferred to move the assembly 3900 in an assembly line style arrangement and keep the laser torch stationary so as to avoid undesired directional movements of the laser torch.

[0121] In order to keep the floors 3024A, 3024B of the first and second set of fins 3020A, 3020B in contact with the upper surface 3012 of the plate structure 3010A during laser welding, a wheel or other member that compresses the floors 3024A, 3024B against the flat plate structure 3010A may be adjacent to and/or lead the laser torch. Of course, other compression techniques can be used if desired, such as clamping, vacuum force, etc. [0122] Once the first and second set of fins 3020A, 3020B are welded to the flat plate structure 3010A, the first and second strip areas 3012 A, 3012B are bent along arrows B to form the lateral flanges 3114, 3115 respectively (shown in FIG. 9C). More specifically, the first and second strip areas 3012 A, 3012B are bent downward so as to extend from an imaginary plane formed by the remaining flat portion of the bottom major surface 3011. [0123] Referring now to FIG. 9C, the lateral flanges 3114, 3115 are approximately 90 degree bends. However, the lateral flanges 3114, 3115 can be formed in any of the shapes described above or derivatives thereof. The bending can be achieved using a suitable brake press or similar machine. [0124] While the bending/formation of the lateral flanges 3114, 3115 may be accomplished before or after the fin sets 3020A, 3020B are welded to the plate structure 3010A, it may be preferred to perform the fin connection first as the fins sets 3020A, 3020B will provided rigidity to the plate structure 3010A during flange formation, thereby eliminating unwanted curvature in certain portions of the plate 3010A. Additionally, bending the lateral flanges 3114, 3115 prior to connecting the fin sets 3020A, 3020B may result in the flat portions to which the fin sets 3020A, 3020B are to be welded to become bent due to residual stresses. This is undesirable because laser welding can be performed with a higher integrity when the surfaces are flat.

[0125] Referring now to FIG. 9D, once the lateral flanges 3114, 3115 are formed into the plate structure 3010A, the flat plat structure 3010A is then bent along the third strip area 3012C as indicated by arrow C. The bending can be achieved using a suitable brake press or similar machine. The bending along arrow C continues for about 180 degrees until the right lateral edge 3110 (which is part of the lateral flange 3114) comes into contact with the left lateral edge 3111 (which is part of the lateral flange 3115), illustrated in FIG. 9E. [0126] Referring now to FIG. 9E, the plate structure IOIOA is illustrated fully bent along strip area 1012C so that the right lateral edge 3110 of the lateral flange 3114 is in contact with the left lateral edge 3111 of the lateral flange 3115, thereby forming the first longitudinal interface 3126. At this point, the right lateral edge 3110 is contiguously welded to the left lateral edge 3111 along the longitudinal interface 3126 so as to form the hermetic internal passageway 3040 and the core tube 3010. The contiguous weld may be achieved using a butt welding technique describe above.

[0127] As is apparent, the fin tube assembly 3100 (along with any of the other embodiments described above) can be completely manufactured without brazing. [0128] FIGS. 10A-E illustrate the major steps of creating a fin tube assembly having a multi- plate core tube, and specifically fin tube assembly 100 of FIGS. 1-3C. Of course, a similar manufacturing technique can be used for any of the fin tube assemblies having multi-plate core tubes discussed above.

[0129] Beginning with FIG. 10A, a first flat plate structure 10A and a second flat plate structure 10B are provided. The flat plate structures 10A, 10B have upper major surfaces 12A, 12B and bottom major surface HA, HB, all of which are also substantially flat and free of any significant curvature. The top and bottom major surfaces 12A, HA of the first plate structure 10A are laterally delimited by a right lateral edge HO and a left lateral edge 111. The top and bottom major surfaces 12A, HA of the first plate structure 10A are longitudinally delimited by two end edges (not numerically indicated). Similarly, the top and bottom major surfaces 12B, HB of the second plate structure 10B are laterally delimited by a right lateral edge 119 and a left lateral edge 118. The top and bottom major surfaces 12B, HB of the second plate structure 10B are longitudinally delimited by two end edges (not numerically indicated).

[0130] The flat plate structures 10A, 10B are rectangular in shape and can be cut to the desired size from a roll of sheet metal on the site of manufacture if desired or formed in any other suitable manner. Preferably, the flat plate structures 10A, 10B are constructed of carbon steel. However, as discussed above, the invention is not so limited. [0131] Referring now to FIG. 10B, once the flat plate structures 10A, 10B are created in the desired size and shape (or otherwise obtained), the first and second sets of fins 20A, 20B are created. In this embodiment, each of the first and second set of fins 20A, 20B are formed from a single sheet of metal by bending the sheet of metal into the desired corrugated configuration having peaks terminating in ridges 23A, 23B and valleys terminating in floors 24A, 24B. It is preferred that the first and second set of fins 20A, 20B be formed from sheets of carbon steel. However, as discussed above, the invention is not so limited. Moreover, if desired, the sets of fins 20A, 20B can be created into any of the alternative configurations disclosed above and other derivatives.

[0132] Once the first and second set of fins 20A, 20B are created (or otherwise obtained), the first set of fins 20A are positioned atop the top surface 12A of the first flat plate structure 10A extending longitudinally between its end edges. Similarly, the second set of fins 20B are positioned atop the top major surface 12B of the second flat plate structure 10B extending longitudinally between its end edges. Of course, the first and second sets of fins 20A, 20B do not have to extend the entire longitudinal lengths of the plates 10A, 10B. [0133] Specifically, the first set of fins 20A are positioned atop the top major surface 12A of the first flat plate structure 10A spaced from both the right lateral edge 110 and the left lateral edge 111. As a result of this positioning of the fin set 20A, a first longitudinal strip area 12C exists between the first set of fins 20A and the right lateral edge 110 that is substantially free of fins while a second longitudinal strip area 12D also exists between the set of fins 20A and the left lateral edge HO that is substantially free of fins.

[0134] Similarly, the second set of fins 20B are positioned atop the top major surface 12B of the second flat plate structure lOBspaced from both the right lateral edge 119 and the left lateral edge 118. As a result of this positioning of the fin set 20B, a first longitudinal strip area 12E exists between the second set of fins 20B and the right lateral edge 119 that is substantially free of fins while a second longitudinal strip area 12F also exists between the set of fins 20B and the left lateral edge 118 that is substantially free of fins [0135] The first and second set of fins 20A, 20B are then welded directly to the flat plate structure 10A, 10B respectively via a fusion welding process that does not use a filler material, such as a laser weld. Most preferably, the floors 24A, 24B of the first and second set of fins 20A, 20B are contiguously laser welded to the flat plate structures 10A, 10B. The laser welding process is achieved by creating relative motion between the laser torch and the assemblies 900A, 900B. In the illustration the relative movement would be left to right or vice-versa along the floors 24A, 24B. In one embodiment, it may be preferred to move the assemblies 900A, 900B in an assembly line style arrangement and keep the laser torch stationary so as to avoid undesired directional movements of the laser torch. [0136] In order to keep the floors 24A, 24B of the first and second set of fins 20A, 20B in contact with the upper surfaces 12A, 12B of the plate structures 10A, 10B respectively during laser welding, a wheel or other member that compresses the floors 24A, 24B against the flat plate structures 10A, 10B may be adjacent to and/or lead the laser torch. Of course, other compression techniques can be used if desired, such as clamping, vacuum force, etc. [0137] While it is illustrated that the fin sets 20, 20B are welded to separate plate structures 10A, 10B, in some embodiments one or more fin sets may be welded to a single plate structure that is then cut into multiple plate structures.

[0138] Once the first set of fins 20A are welded to the flat plate structure 10A the first and second strip areas 12C, 12D are bent along arrows D to form the lateral flanges 114, 115 respectively (shown in FIG. 10C). More specifically, the first and second strip areas 12C, 12D are bent downward and outward so as to extend from an imaginary plane formed by the remaining flat portion of the bottom major surface HA. Similarly, once the second set of fins 20B are welded to the flat plate structure 10B the first and second strip areas 12E, 12F are bent along arrows E to form the lateral flanges 123, 122 respectively (shown in FIG. 10C). More specifically, the first and second strip areas 12E, 12F are bent downward and outward so as to extend from an imaginary plane formed by the remaining flat portion of the bottom major surface HB.

[0139] Referring now to FIG. 10C, the lateral flanges 114-115, 122-123 bend downward and outward. However, the lateral flanges can be formed in any of the shapes described above or derivatives thereof. The bending can be achieved using a suitable brake press or similar machine. [0140] While the bending/formation of the lateral flanges 114-115, 122-123 may be accomplished before or after the fin sets 20A, 20B are welded to the plate structures 10A, 10B, it may be preferred to perform the fin connection first as the fins sets 20A, 20B will provided rigidity to the plate structures 10A, 10B during flange formation, thereby eliminating unwanted curvature in certain portions of the plates 10A, 10B. Additionally, bending the lateral flanges 114-115, 122-123 prior to connecting the fin sets 20A, 20B may result in the flat portions to which the fin sets 20A, 20B are to be welded to become bent due to residual stresses. This is undesirable because laser welding can be performed with a higher integrity when the surfaces are flat.

[0141] Referring now to FIG. 10D, once the lateral flanges 114-115, 122-123 are formed into the plate structures 10A, 10B, the first plat structure 10A and second plate structure 10B are arranged so that their lower surfaces 11,A, HB oppose one another and the lateral flanges 114-115, 122-123 are aligned. The plate structures 10A, 10B, are then moved into an adjacent and abutting relationship (discussed above with respect to FIG. 3A), as shown in FIG. 10E.

[0142] Referring to FIG. 10E, the plate structures 10A, 10B are illustrated in their adjacent arrangement wherein the bottom surfaces of the lateral flanges 114, 115 of the first plate structure 10A are in surface contact with the top surfaces of the lateral flanges 122, 123 of the second plate structure 10B, thereby forming the first and second longitudinal interfaces 126, 127. At this point, the lateral edges are contiguously welded together as discussed above along the longitudinal interfaces 126, 127 so as to form the hermetic internal passageway 40 and the core tube 10. The contiguous weld may be achieved using a seam welding technique describe above.

[0143] As is apparent, the fin tube assembly 100 (along with any of the other embodiments described above) can be completely manufactured without brazing.

Power Plant

[0144] Referring now to FIG. 11, a power plant 6000 according to the present invention is illustrated. Generally, the power plant 600 is Rankine cycle power plant and comprises a boiler 6100, a turbine 6200, and air-cooled condenser 6300 and a pump 6400. The air cooled condenser 6300 incorporates one or more of the fin tube assemblies described above. [0145] In another embodiment, the invention can be an air-cooled condenser incorporating one or more of the fin tube assemblies described above.

Additional Embodiment Havine Ferritic Nitrocarburization (FNCi Coatins [0146] In one specific embodiment, the inventive air cooled condenser utilizes a carbon steel

(Al 008/1010) fin and tube assembly having a surface conversion process in lieu of a coating for external corrosion protection. In one embodiment, the process is a ferritic nitrocarburization process

[0147] In this embodiment, the internal surface of the tube will be exposed to steam under a vacuum in an oxygen deficient environment. As the internal surface of the carbon steel tube corrodes, a layer of magnetite is formed which protects the carbon steel surface from further corrosion. Therefore, no supplemental treatment for the prevention of corrosion is required for the internal surface of the finned tube. However, the external surface of the carbon steel finned tube does require corrosion protection.

[0148] As mentioned above, a surface conversion process can be used in lieu of a coating for external corrosion protection. The process is a ferritic nitrocarburization process as outlined below.

[0149] First the finned tube is pre-heated to ~ 750⁰F in an air environment. The finned tube bundle is then immersed in a molten salt bath which is between 900 and 1165⁰F. The primary constituents of the molten salt are alkali cyanate and alkali carbonate which are actively aerated. The nitrocarburizing process occurs within the molten salt bath. The active constituent of the bath is the alkali cyanate. At elevated temperatures, the alkali cyanate causes a reaction to occur with the carbon steel surface. A nitrocarburized layer is formed which consists of an outer compound layer (iron-nitride) and a diffusion layer beneath. This reaction also causes the formation of alkali carbonate which is regenerated. The duration of this process is 60 to 120 minutes.

[0150] The bundle is removed from the molten salt bath and then placed in an oxidation cooling bath having a temperature maintained between 750 and 850⁰F. The oxidation bath causes an iron oxide layer (magnetite) to be formed on the surface. The bundle is then removed from the oxidation bath and cooled down to ambient temperature and cleaned by quenching the bundle in a water bath.

[0151] The last stage of the FNC process is to dip the bundle in a sealant bath. This bath contains emulsified oil. The bundle is dipped into the bath long enough to allow the emulsified oil to penetrate the pores of the compound layer. The bundle is then removed from the sealant bath and cleaned.

[0152] While the invention has been described and illustrated in sufficient detail that those skilled in this art can readily make and use it, various alternatives, modifications, and improvements should become readily apparent without departing from the spirit and scope of the invention.

Claims

ClaimsWhat is claimed is:

1. A fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an internal passageway for carrying a fluid to be cooled, the core tube having a non-circular transverse cross-section; and at least one set of fins welded to an outside surface of the core tube.

2. The fin tube assembly of claim 1 wherein the at least one set of fins is a corrugated sheet having peaks terminating in ridges and valleys terminating in floors.

3. The fin tube assembly of claim 2 wherein the floors of the valleys of the corrugated sheet are contiguously laser welded to the outside surface of the core tube.

4. The fin tube assembly of claim 3 wherein the floors of the valleys comprise a substantially flat section that is contiguously laser welded to the outside surface of the core tube.

5. The fin tube assembly of claim 2 wherein the floors of the valleys of the corrugated sheet are laser welded in a stitched manner to the outside surface of the core tube.

6. The fin tube assembly of claim 5 further comprising a metal-based coating covering exposed areas of the at least one set of fins and the core tube.

7. The fin tube assembly of claim 6 wherein the metal is zinc.

8. The fin tube assembly of claim 1 wherein the at least one set of fins is a corrugated sheet having peaks terminating in ridges and valleys terminating in floors, the peaks and valleys being orthogonally shaped.

9. The fin tube assembly of claim 1 wherein the core tube is a single-layer tube and the at least one set of fins is a single layer material.

10. The fin tube assembly of claim 6 wherein the core tube is made of carbon steel, stainless steel, aluminum or copper and the at least one set of fins is made of carbon steel, stainless steel, aluminum or copper, the materials of the core tube and the at least one set of fins being metallurgically compatible for welding.

11. The fin tube assembly of claim 1 wherein the core tube is a multi-layer tube and the at least one set of fins is a multi-layer material.

12. The fin tube assembly of claim 1 further comprising: the outside surface of the core tube comprising opposite substantially flat faces; and a set of fins welded to each of the substantially flat faces.

13. The fin tube assembly of claim 1 further comprising a coating of a corrosion resistant material covering exposed areas of the at least one set of fins and the core tube.

14. The fin tube assembly of claim 13 wherein the coating is a baked phenolic coating or a zinc-based coating or an aluminum-based coating.

15. The fin tube of claim 14 wherein the coating is less than 100 microns thick.

16. The fin tube assembly of claim 1 wherein the at least one set of fins is welded to the outside surface of the core tube using a fusion welding technique that does not use a filler material.

17. The fin tube assembly of claim 1 wherein the at least one set of fins comprises a plurality of separate fins individually welded to the outside surface of the core tube.

18. The fin tube assembly of claim 1 further comprising: the outside surface of the core tube comprising opposite substantially flat faces; a set of fins welded to each of the substantially fiat faces; the sets of fins being corrugated sheets having peaks terminating in ridges and valleys terminating in floors having a substantially flat section; the floors of the valleys of the corrugated sheets being welded along the substantially flat sections of the floors to the substantially flat faces of the core tube; a coating of a corrosion resistant material covering exposed areas of the at least one set of fins and the core tube; and the sets of fins welded to the outside surface of the core tube using a fusion welding technique that does not use a filler material.

19. The fin tube assembly of claim 1 wherein the core tube is constructed of a single plate structure bent into the shape of the core tube so that a longitudinal interface exists, the longitudinal interface being contiguously welded to form the core tube.

20. The fin tube assembly of claim 19 wherein the longitudinal interface is formed by contact between a first lateral edge of the plate structure and a second lateral edge of the plate structure, the first and second lateral edges being butt welded together.

21. The fin tube assembly of claim 19 wherein the longitudinal interface is formed by contact between a bottom surface of a first lateral flange formed into the plate structure and a top surface of a second lateral flange formed into the plate structure, the first and second lateral flanges being seam welded together.

22. The fin tube assembly of claim 1 wherein the core tube is constructed of a plurality of plate structures bent into a transverse section of the core tube, the transverse sections arranged in an adjacent manner so that a plurality of longitudinal interfaces exist, the longitudinal interfaces being contiguously welded to form the core tube.

23. The fin tube assembly of claim 22 comprising a first plate structure bent into a first transverse section of the core tube and a second plate structure bent into a second transverse section of the core tube, the first and second transverse sections arranged in the adjacent manner so that first and second longitudinal interfaces exist, the first and second longitudinal interfaces being contiguously welded to form the core tube.

24. The fin tube assembly of claim 23 wherein the first and second longitudinal interfaces are formed by contact between lateral edges of the first and second transverse sections, the lateral edges being butt welded together.

25. The fin tube assembly of claim 23 wherein the first and second longitudinal interfaces are formed by contact between bottom surfaces of lateral flanges formed into the first transverse section and top surfaces of lateral flanges formed into the second transverse section, the lateral flanges being seam welded together.

26. A fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface forming a passageway for carrying a fluid to be cooled and an outsider surface having a first substantially flat face and a second substantially flat face opposite the first substantially flat face; the core tube constructed from a single flat plate structure bent into the shape of the core tube so that a longitudinal interface exists, the longitudinal interface being contiguously welded to form the core tube; and a set of fins connected to each of the first and second substantially flat faces.

27. The fin tube assembly of claim 26 wherein the longitudinal interface is formed by contact between a first lateral edge of the flat plate structure and a second lateral edge of the flat plate structure, the first and second lateral edges being butt welded together.

28. The fin tube assembly of claim 26 wherein the longitudinal interface is formed by contact between a bottom surface of a first lateral flange formed into the plate structure and a top surface of a second lateral flange formed into the plate structure.

29. The fin tube assembly of claim 28 wherein the first lateral flange and the second lateral flange extend outward from the outside surface of the core tube, the first and second lateral flanges being seam welded together.

30. The fin tube assembly of claim 28 wherein the first lateral flange and the second lateral flange extend inward toward the passageway, the first and second lateral flanges being welded together by a fusion welding technique.

31. The fin tube assembly of claim 26 wherein the longitudinal interface is formed by contact between a bottom surface of a first lateral flange formed into the flat plate structure and a top surface of a second lateral flange formed into the flat plate structure, the first and second lateral flanges being welded together by a fusion welding technique that does not use a filler material.

32. The fin tube assembly of claim 26 further comprising: the sets of fins being corrugated sheets having peaks terminating in ridges and valleys terminating in floors having a substantially flat section; and the sets of fins welded to the first and second substantially flat faces along the substantially flat sections of the floors using a fusion welding technique that does not use a filler material.

33. The fin tube assembly of claim 32 further comprising a coating of a corrosion resistant material covering the sets of fins and the core tube.

34. The fin tube assembly of claim 33 wherein the coating is a baked phenolic coating or a zinc-based coating or an aluminum-based coating.

35. The fin tube assembly of claim 32 wherein the sets of fins are either stitch laser welded or contiguously laser welded to the first and second substantially flat faces along the substantially flat sections of the floors.

36. The fin tube assembly of claim 26 wherein the flat plate structure is a single-layer material.

37. The fin tube assembly of claim 26 wherein the flat plate structure is a multi-layer material.

38. A fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface forming a passageway for carrying a fluid to be cooled and an outsider surface having a first substantially flat face and a second substantially flat face opposite the first substantially flat face; the core tube constructed from a first flat plate structure bent into a first transverse section of the core tube and a second flat plate structure bent into a second transverse section of the core tube, the first and second transverse sections arranged in an adjacent manner so that first and second longitudinal interfaces exist, the first and second longitudinal interfaces being contiguously welded to form the core tube; at least one of the first or second longitudinal interfaces formed by either (1) contact between lateral edges of the first and second transverse sections, the lateral edges being butt welded together, or (2) contact between bottom surfaces of lateral flanges formed into the first transverse section and top surfaces of lateral flanges formed into the second transverse section, the lateral flanges being fusion welded together; and a set of fins connected to each of the first and second substantially flat faces.

39. The fin tube assembly of claim 38 wherein both the first or second longitudinal interfaces are formed by contact between the bottom surfaces of lateral flanges formed into the first transverse section and the top surfaces of lateral flanges formed into the second transverse section.

40. The fin tube assembly of claim 39 wherein the lateral flanges of the first and second transverse sections extend outward from the outside surface of the core tube, the first and second lateral flanges being seam welded together.

41. The fin tube assembly of claim 39 wherein the lateral flanges of the first and second transverse sections extend inward toward the passageway, the first and second lateral flanges being seam welded together.

42. The fin tube assembly of claim 38 wherein both the first or second longitudinal interfaces are formed by contact between lateral edges of the first and second transverse sections.

43. The fin tube assembly of claim 38 further comprising: the sets of fins being corrugated sheets having peaks terminating in ridges and valleys terminating in floors; and the sets of fins welded to the first and second substantially flat faces along the floors using a fusion welding technique that does not use a filler material.

44. A fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, the core tube having anon-circular transverse cross-section; at least one set of fins connected to an outside surface of the core tube; and a baked phenolic coating covering the at least one set of fins and the core tube.

45. A method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, the core tube having a non-circular transverse cross-section; b) providing at least one set of fins; and c) welding the at least one set of fins to the outside surface of the core tube using a fusion welding technique that does not use a filler material.

46. The method of claim 45 further comprising: step b) comprising corrugating a metal sheet to form the at least one set of fins, the corrugated metal sheet having peaks terminating in ridges and valleys terminating in floors; and step c) comprising welding the floors of the corrugated metal sheet to the outside surface of the core tube using the fusion welding technique that does not use the filler material.

47. The method of claim 46 further comprising step c) comprising stitch welding the floors of the corrugated metal sheet to the outside surface of the core tube using the fusion welding technique that does not use the filler material; and d) coating the at least one set of fins and the core tube with a metal-based coating.

48. The method of claim 47 wherein the metal is zinc

49. The method of claim 46 further comprising step c) comprising contiguously welding the floors of the corrugated metal sheet to the outside surface of the core tube using the fusion welding technique that does not use the filler material.

50. The method of claim 45 further comprising: d) coating the at least one set of fins and the core tube with a corrosion resistant material; and wherein the coating is a baked phenolic coating or a zinc-based coating or an aluminum-based coating.

51. The method of claim 45 further comprising: step b) comprising corrugating a metal sheet to form the at least one set of fins, the corrugated metal sheet having peaks terminating in ridges and valleys terminating in floors having a substantially flat portion; and step c) comprising laser welding the substantially flat portions of the floors of the corrugated metal sheet to the outside surface of the core tube.

52. The method of claim 45 further comprising: step b) comprising corrugating a metal sheet to form the at least one set of fins, the corrugated metal sheet having peaks terminating in ridges and valleys terminating in floors; and step c) comprising compressing the floors of the corrugated metal sheet against the outside surface of the core tube with a compression member, the compression member leading a laser torch as it laser welds the floors of the corrugated metal sheet to the outside surface of the core tube.

53. The method of claim 45 wherein the core tube is a single-layer material and the at least one set of fins is a single layer material.

54. The method of claim 53 wherein the core tube is made of carbon steel, stainless steel, aluminum or copper and the at least one set of fins is made of carbon steel, stainless steel, aluminum or copper, the materials of the core tube and the at least one set of fins being metallurgical Iy compatible for welding.

55. The method of claim 45 wherein the outside surface of the core tube comprises opposite substantially flat faces, and step c) further comprises welding a set of the fins to each of the substantially flat faces using the fusion welding technique that does not use a filler material.

56. The method of claim 45 wherein step a) comprises) providing a substantially flat plate structure; bending the substantially flat plate structure into the shape of the core tube so that a longitudinal interface exists; and contiguously welding the longitudinal interface to form the core tube.

57. The method of claim 56 wherein the longitudinal interface is formed by contact between a first lateral edge of the flat plate structure and a second lateral edge of the flat plate structure, the first and second lateral edges being butt welded together.

58. The method of claim 56 wherein the longitudinal interface is formed by contact between a bottom surface of a first lateral flange bent into the flat plate structure and a top surface of a second lateral flange bent into the flat plate structure, the first and second lateral flanges being seam welded together.

59. The method of claim 58 wherein the first and second lateral flanges extend outward from the outside surface of the core tube forming a longitudinal ridge protruding from the outside surface of the core tube, the first and second lateral flanges being seam welded together.

60. The method of claim 58 wherein the first and second lateral flanges extend inward toward the passageway.

61. The method of claim 56 wherein the at least on set fins is welded to a section of the flat plate structure prior to bending.

62. The method of claim 61 wherein the section of the flat plate structure remains substantially flat after bending.

63. The method of claim 43 wherein step a) comprises) providing a first substantially flat plate structure; providing a second substantially flat plate structure; bending the first substantially flat plate structure into a first transverse section of the core tube; bending the second substantially flat plate structure into a second transverse section of the core tube; arranging the first and second transverse sections in an adjacent manner so as to form first and second longitudinal interfaces; and contiguously welding the first and second longitudinal interfaces to form the core tube.

64. The method of claim 63 wherein the first substantially flat plate structure is bent so that the first transverse section comprises a first substantially flat face and the second substantially flat plat structure is bent so that the second transverse section comprises a second substantially flat face, and wherein step c) comprises welding at least one set of the fins to each of the first and second substantially flat faces.

65. The method of claim 64 wherein the sets of fins are welded to the first and second substantially flat plate structures prior to bending.

66. The method of claim 63 wherein the first and second longitudinal interfaces are formed by contact between lateral edges of the first and second transverse sections, the first and second lateral edges being butt welded together.

67. The method of claim 63 wherein the first and second longitudinal interfaces are formed by contact between bottom surfaces of lateral flanges bent into the first flat plate structure and top surfaces of lateral flange bent into the second flat plate structure.

68. The method of claim 67 wherein the lateral flanges extend outward from the outside surface of the core tube forming a longitudinal ridge protruding from the outside surface of the core tube, the first and second lateral flanges being seam welded together.

69. The method of claim 67 wherein the first and second lateral flanges extend inward toward the passageway.

70. The method of claim 45 wherein step a) comprises) providing a plurality of substantially flat plate structures; bending the plurality of substantially flat plate structures into transverse sections of the core tube; arranging the transverse sections in an adjacent manner so as to form a plurality of longitudinal interfaces; and contiguously welding the plurality of longitudinal interfaces to form the core tube.

71. A method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a substantially flat plat structure having a first lateral edge, a second lateral edge, a first end edge, a second end edge, a first major surface, and a second major surface, the first and second end edges defining a longitudinal length of the substantially flat plat structure; b) providing a first set of fins and a second set of fins; c) welding the first set of fins to a first portion of the first major surface of the substantially flat plat structure using a fusion welding technique that does not use a filler material, the first set of fins spaced from the first lateral edge so that the first major surface has a first perimeter portion extending longitudinally between the first set of fins and the first lateral edge that is free of fins; d) welding the second set of fins to a second portion of the first major surface of the substantially flat plat structure using the fusion welding technique, the second set of fins spaced from the first set of fins and the second lateral edge so that the first major surface has an elongated portion extending longitudinally between the first and second set of fins that is free of fins and a second perimeter portion extending longitudinally between the second set of fins and the second lateral edge that is free of fins; and e) bending the first and second perimeter portions of the substantially flat plat structure to extend from a plane formed by the second major surface of the substantially flat plat structure; and f) bending the substantially flat plat structure being bent along the elongated portion so that the first and second portions of the first major surface are on opposite surfaces and the bent first and second perimeter portions contact one another forming a longitudinal interface; and g) contiguously welding the longitudinal interface to form a core tube wherein the second major surface forms an internal passageway of the core tube and the first major surface forms an outside surface of the core tube.

72. The method of claim 71 further comprising: step b) comprising corrugating a first metal sheet to form the first set of fins and corrugating a second metal sheet to form the second set of fins, the first and second corrugated metal sheet having peaks terminating in ridges and valleys terminating in floors; and steps c) and d) comprising welding the floors of the first and second corrugated metal sheet to the first major surface of the substantially flat plat structure using the fusion welding technique.

73. The method of claim 72 further comprising step c) and d) comprising stitch welding the floors of the first and second corrugated metal sheet to the first major surface of the substantially fiat plat structure using the fusion welding technique; and d) coating the core tube and the first and second set of with a metal-based coating.

74. The method of claim 72 further comprising steps c) and d) comprising contiguously laser welding the floors of the corrugated metal sheet to the outside surface of the core tube.

75. The method of claim 71 further comprising: h) coating the first and second set of fins and the core tube with a corrosion resistant material; and wherein the coating is a baked phenolic coating or a zinc-based coating or an aluminum-based coating.

76. The method of claim 71 further comprising: step b) comprising corrugating a first metal sheet to form the first set of fins and corrugating a second metal sheet to form the second set of fins, the first and second corrugated metal sheet having peaks terminating in ridges and valleys terminating in floors having a substantially flat portion; and steps c) and d) comprising laser welding the substantially flat portions of the floors of the first and second corrugated metal sheet to the first major surface of the substantially flat plat structure.

77. The method of claim 71 wherein the longitudinal interface is formed by contact between the first lateral edge and the second lateral edge, the first and second lateral edges being butt welded together.

78. The method of claim 71 further comprising: step e) comprising bending a first lateral flange into the first perimeter portion of the substantially flat plat structure and a second lateral flange into the second perimeter portion of the substantially flat plat structure, the first and second lateral flanges extend from the plane formed by the second major surface of the substantially fiat plat structure; and wherein the longitudinal interface is formed by contact between a bottom surface of the first lateral flange and a top surface of the second lateral flange.

79. The method of claim 78 wherein the first and second lateral flanges extend outward from the outside surface of the core tube forming a longitudinal ridge protruding from the outside surface of the core tube, the first and second lateral flanges being seam welded together.

80. The method of claim 78 wherein the first and second lateral flanges extend inward toward the passageway.

81. The method of claim 71 wherein the first and second set of fins are welded to the substantially flat plate structure prior to bending.

82. The method of claim 71 wherein the first and second portions of the substantially flat plate structure remains substantially flat after all bending is completed.

83. A method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, the core tube having a non-circular transverse cross-section; b) providing at least one set of fins; and c) connecting at least one set of fins to the outside surface of the core tube; and d) coating the at least one set of fins and the core tube with a baked phenolic coating or a zinc-based coating or an aluminum-based coating.

84. A method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising:

a) providing a substantially flat plat structure having a first lateral edge, a second lateral edge, a first end edge, a second end edge, a first major surface, and a second major surface, the first and second end edges defining a longitudinal length of the substantially flat plat structure; b) providing a first set of fins and a second set of fins; c) connecting the first set of fins to a first area of the first major surface of the substantially flat plat structure, the first set of fins spaced from the first lateral edge so that the substantially flat plat structure has a first portion extending longitudinally between the first set of fins and the first lateral edge that is free of fins; d) connecting the second set of fins to a second area of the first major surface of the substantially flat plat structure, the second set of fins spaced from the first set of fins and the second lateral edge so that the substantially flat plat structure has a second portion extending longitudinally between the first and second set of fins that is free of fins and a third portion extending longitudinally between the second set of fins and the second lateral edge that is free of fins; and e) bending the first and third portions of the substantially flat plat structure to extend from a plane formed by the second major surface of the substantially flat plat structure; and f) bending the substantially flat plat structure along the second portion so that the first and second areas of the first major surface are on opposite surfaces and the bent first and third portions contact one another forming a longitudinal interface; and g) contiguously welding the longitudinal interface to form a core tube wherein the second major surface forms an internal passageway of the core tube and the first major surface forms an outside surface of the core tube.

85. The method of claim 84 wherein steps c) and/or d) are performed subsequent to steps e) and/or f).

86. A method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a first substantially flat plate structure having a first lateral edge, a second later edge, a first major surface and a second major surface; b) providing a second substantially flat plate structure having a first lateral edge, a second later edge, a first major surface and a second major surface; c) connecting a first set of fins to the first major surface of the first substantially flat plate structure; d) connecting a second set of fins to the first major surface of the second substantially flat plate structure; e) bending the first substantially flat plate structure into a first transverse section of a core tube; f) bending the second substantially flat plate structure into a second transverse section of a core tube; g) arranging the first and second transverse sections in an adjacent manner so as to form first and second longitudinal interfaces; and h) contiguously welding the first and second longitudinal interfaces to form the core tube having a internal passageway formed by the second major surface of the first and second transverse sections .

87. The method of claim 86 further comprising: step c) comprising connecting the first set of fins to the first major surface of the first substantially flat plate structure so as to be spaced from both the first and second lateral edges of the first substantially flat plate structure, thereby forming fin-free portions along the first and second lateral edges of the first substantially flat plate structure; step d) comprising connecting the second set of fins to the first major surface of the second substantially flat plate structure so as to be spaced from the first and second lateral edges of the second substantially flat plate structure, thereby forming fin-free portions along the first and second lateral edges of the second substantially flat plate structure; step e) comprising bending the fin-free portions of the first substantially flat plate structure toward the second major surface of the first substantially flat plate structure; step f) comprising bending the fin-free portions of the second substantially flat plate structure toward the second major surface of the second substantially flat plate structure; and step g) comprising arranging the first and second transverse sections in an adjacent manner so that the fin-free portions of the first and second substantially flat plate structures come into contact and form the first and second longitudinal interfaces.

88. The method of claim 87 further comprising: step e) comprising bending the fin-free portions of the first substantially flat plate structure into first and second lateral flanges; step f) comprising bending the fin-free portions of the second substantially flat plate structure into first and second lateral flanges; and step g) comprising arranging the first and second transverse sections in an adjacent manner so that bottom surfaces of the first and second lateral flanges of the first substantially flat plate structure contact top surface of the first and second lateral flanges of the second substantially flat plate structure, thereby forming the first and second longitudinal interfaces.

89. The method of claim 88 wherein the lateral flanges of the first and second substantially flat plate structures extend outward from an outside surface of the core tube forming longitudinal ridges protruding from the outside surface of the core tube, and step h) comprises seam welding the lateral flanges.

90. The method of claim 88 wherein the lateral flanges of the first and second substantially flat plate structures extend inward toward the internal passageway.

91. A method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a plurality of first substantially flat plate structures; b) connecting at least one set of fins to one of the plurality of substantially flat plate structures; c) bending the plurality of flat plate structures into transverse sections of a core tube; d) arranging the transverse sections in an adjacent manner so as to form a plurality of longitudinal interfaces; and e) contiguously welding the plurality of longitudinal interfaces to form the core tube having a internal passageway and an outer surface comprising the at least one set of fins.

92. A fin tube assembly for an air-cooled heat exchanger comprising: a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled; at least one set of fins connected to an outside surface of the core tube; and wherein the outside surface of the core tube and the at least one set of fins is subjected to a ferretic nitrocarburization process.

93. The fin tube assembly of claim 92 wherein the inner surface of the core tube comprises a layer of magnetite.

94. The fin tube assembly of claim 92 wherein the core tube and the at least one set of fins are constructed of steel.

95. The fin tube assembly of claim 92 wherein the at least one set of fins is laser welded to the core tube.

96. The fin tube assembly of claim 92 wherein the at least one set of fins and the outer surface of the core tube comprises a nitrocarburized layer.

97. The fin tube assembly of claim 92 further: wherein the outsider surface of the core tube has a first substantially flat face and a second substantially flat face opposite the first substantially flat face; the core tube constructed from a first flat plate structure bent into a first transverse section of the core tube and a second flat plate structure bent into a second transverse section of the core tube, the first and second transverse sections arranged in an adjacent manner so that first and second longitudinal interfaces exist, the first and second longitudinal interfaces being contiguously welded to form the core tube; the first and second longitudinal interfaces formed by contact between bottom surfaces of lateral flanges formed into the first transverse section and top surfaces of lateral flanges formed into the second transverse section; and wherein the lateral flanges of the first and second transverse sections extend inward toward the passageway, the first and second lateral flanges are seam welded together along the first and second longitudinal interfaces.

98. The fin tube assembly of claim 97 wherein the first and second lateral flanges are seam welded together along the first and second longitudinal interfaces using a fusion welding technique that uses a filler material.

99. The fin tube assembly of claim 98 wherein the at least one set of fins is fusion laser welded to the core tube.

100. The fin tube assembly of claim 92 wherein the at least one set of fins is a corrugated sheet having peaks terminating in ridges and valleys terminating in floors.

101. The fin tube assembly of claim 100 wherein the valleys comprise a substantially flat section.

102. The fin tube assembly of claim 101 wherein the peaks comprise a curved section.

103. The fin tube assembly of claim 92 wherein the core tube has a non-circular transverse cross-section.

104. A method of manufacturing a fin tube assembly for an air-cooled heat exchanger comprising: a) providing a core tube having an inner surface that forms an internal passageway for carrying a fluid to be cooled, at least one set of fins connected to an outside surface of the core tube; and b) performing a surface conversion process to the at least one set of fins and the outside surface of the core tube that increases corrosion resistance.

105. The method of claim 104 wherein the surface conversion process is a ferritic nitrocarburization process.

106. The method of claim 105 wherein the at least one set of fins and the core tube are constructed of steel.

107. The method of claim 105 wherein the ferritic nitrocarburization process comprises: heating the core tube and the at least one set of fins; immersing the core tube and the at least one set of fins in a molten salt bath; and immersing the core tube and the at least one set of fins to an oxidation cooling bath.

108. The method of claim 105 wherein the ferritic nitrocarburization process comprises immersing the core tube and the at least one set of fins in a molten salt bath.

109. The method of claim 108 wherein the molten salt bath comprises alkali cyanate and alkali carbonate which are actively aerated.

110. The method of claim 105 further comprising subjecting the core tube and the at least one sets of fins to water.

111. The method of claim 105 further comprising sealing the core tube and the at least one sets of fins.

112. The method of claim 111 wherein the sealing comprises immersing the core tube and the at least one sets of fins in an emulsified oil bath.

113. The method of claim 104 further comprising subjecting the inner surface of the core tube to steam in a sub-atmospheric and oxygen deficient environment prior to step b).

114. The method of claim 104 wherein step a) comprises: providing a first substantially flat plate structure having a first lateral edge, a second later edge, a first major surface and a second major surface; providing a second substantially flat plate structure having a first lateral edge, a second later edge, a first major surface and a second major surface; connecting a first set of fins to the first major surface of the first substantially flat plate structure; connecting a second set of fins to the first major surface of the second substantially flat plate structure; bending the first substantially flat plate structure into a first transverse section of a core tube; bending the second substantially flat plate structure into a second transverse section of a core tube; arranging the first and second transverse sections in an adjacent manner so as to form first and second longitudinal interfaces; and contiguously welding the first and second longitudinal interfaces.

115. The method of claim 114 further comprising: connecting the first set of fins to the first major surface of the first substantially flat plate structure so as to be spaced from both the first and second lateral edges of the first substantially flat plate structure, thereby forming fin-free portions along the first and second lateral edges of the first substantially flat plate structure; connecting the second set of fins to the first major surface of the second substantially flat plate structure so as to be spaced from the first and second lateral edges of the second substantially flat plate structure, thereby forming fin-free portions along the first and second lateral edges of the second substantially flat plate structure; bending the fin-free portions of the first substantially flat plate structure toward the second major surface of the first substantially flat plate structure; bending the fin-free portions of the second substantially flat plate structure toward the second major surface of the second substantially flat plate structure; and arranging the first and second transverse sections in an adjacent manner so that the fin-free portions of the first and second substantially flat plate structures come into contact and form the first and second longitudinal interfaces.

116. The method of claim 115 further comprising: bending the fin-free portions of the first substantially flat plate structure into first and second lateral flanges; bending the fin-free portions of the second substantially flat plate structure into first and second lateral flanges; and arranging the first and second transverse sections in an adjacent manner so that bottom surfaces of the first and second lateral flanges of the first substantially flat plate structure contact top surface of the first and second lateral flanges of the second substantially flat plate structure, thereby forming the first and second longitudinal interfaces.

117. The method of claim 116 wherein the lateral flanges of the first and second substantially flat plate structures extend inward toward the internal passageway.