BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a prior art heat exchanger;
FIG. 2 is a schematic illustration of a tube with fins forming part of a prior art heat exchanger of FIG. 1;
FIG. 3 is a schematic illustration of an electric dual wire spray for spraying particulates onto the interior surfaces of the heat exchanger tube in accordance with another exemplary embodiment;
FIG. 4 is a simplified side elevation of conventional MIG welding apparatus that may be used in another exemplary embodiment of the invention; and
FIG. 5 is a perspective cut-away of a tube formed with an internal spiral groove, not necessarily to scale, using the apparatus of FIG. 4.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to the drawings, particularly to FIG. 1, there is illustrated a conventional heat exchanger generally designated 10. Heat exchanger 10 is comprised of a plurality of interconnected tubes 12 for carrying/circulating a fluid to be cooled. The hot fluid is typically conveyed back and forth in opposite directions (or in one way only) in tubes arranged in a large grid-like pattern. In the illustrated form, the tubes 12 extend from a hot fluid inlet 14, back and forth in the grid pattern and terminate at an outlet port 16. It will be understood that the tubes can be arranged in many different configurations, e.g., one above the other, in layers offset one above the other or in any other well-known and suitable configuration. It will be appreciated that, in use, the tubes 12 are in heat exchange relation with a cooling fluid e.g., air flowing across and through the grid-like pattern. It will also be appreciated that the tubes may carry a fluid to be heated by flowing a heated fluid across the tubes.
To facilitate the heat transfer, and using as an example heat exchange between tubes carrying a hot fluid and air passing over and about the tubes, a fan 18 with fan blades 20 is disposed, for example, below the tubes 12 for driving air through and across the grid. Thus, the air and the tubes 12 are in heat exchange relation one with the other such that the heated fluid passing through the tubes 12 is cooled and exits the heat exchanger at outlet port 16 at a lower temperature than fluid at the inlet 14. This invention also contemplates situations where only the latent heat is involved, such that the fluid will have energy removed, but will not actually be cooled.
An enlarged schematic illustration of a finned tube 12 is shown in FIG. 2. Thus, the tubes 12 in the heat exchanger may carry fins 22 which are attached to the tubes in a conventional manner. It will be appreciated that the fins increase the effective surface area of the interface between the cooling air and hot fluid enabling enhanced thermal cooling of the hot fluid as a result of the finned configuration.
Further enhancement of heat transfer in connection with fins is described in commonly owned co-pending application Ser. No. 11/493,022, filed Jul. 26, 2006.
As used in the description of various embodiments of this invention, the term “fluid” embraces liquids, gases, steam, two phase mixtures, and multi-component mixtures. Also, the heat exchanger may be of the type for condensing or evaporating fluid.
Referring now to FIG. 3, there is illustrated a dual wire spray head in which a random or patterned array of microturbulators may be applied and bonded to the interior surface 24 of a heat exchanger tube 26. Specifically, a moveable/retractable dual wire spraying mechanism 28 is utilized to controllably apply the metallic particles to the interior surface of the tube (of circular cross section). In this instance, the mechanism 28 includes an applicator head 30 having a pair of wires 32, 34 which are fed through electrical contact tubes 36, 38, respectively. The head 30 is also constructed to provide primary atomizing gas through a central aperture 40 and secondary atomizing gas through an annular secondary aperture 42. Any suitable gas may be employed, but air is less preferred since it may oxidize the metal particles preventing them from bonding to the tube. It will be appreciated that an electric arc between the wires 32, 34 vaporizes the wires, causing particulates 44 to mix with the atomizing gas and to be metalurgically bonded to the interior surface 24 of the tube 26, without having to apply an adhesive coat or layer.
Referring now to FIG. 4, a known MIG welding apparatus is illustrated that is available from Bore Repair Systems, Inc. of Alstead, N.H. The apparatus is also shown and described in U.S. Pat. No. 6,137,076. The apparatus includes a weld torch assembly 46 that incorporates a first hollow arm 48 and a second hollow arm 50 with a clutch control mechanism 52 in a housing 54 between the hollow arms. A nozzle 56 at the distal end of arm 50 is arranged to apply weld material to the interior surface of a round tube 58, with clamping means 60, adjustable support bracket 62 and mounting rod 64 enabling positioning of the nozzle. At the same time, a threaded guide 66, spindle 68 and clutch control mechanism 52 control axial movement of the torch through the tube.
In an exemplary but non-limiting embodiment, the weld torch 46 is rotated as it moves axially through an elongated heat exchange tube 58 (FIG. 5) located in the position of tube 58 in FIG. 4.
As the torch rotates and moves axially, the welding ingredients (welding current, welding wire and welding gas) are supplied through the arms 48 and 50 to the nozzle 56, depositing welding material 72 on the inner diameter surface of the heat exchanger tube 58, as a continuous spiral rib 74 (thus creating a spiral rib/groove configuration) extending substantially the entire length of the tube, as best seen in FIG. 5. Note in FIG. 5, a portion 76 of the tube has yet not been altered, or will remain in its original configuration and serve, for example, as a tube-end connector. Alternatively, weld material may be added to roughen the interior surface of the tube, the roughness achieved by depositing the weld material in a random or patterned array.
In each case, the interior surface area of the tube is increased to thereby enhance the heat transfer characteristics of the tube.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Patent Application
20080078535
