WO2006055916A2

WO2006055916A2 - Heat exchanger tube and method of making

Info

Publication number: WO2006055916A2
Application number: PCT/US2005/042183
Authority: WO
Inventors: Allan Stikeleather; Edward R. Stikeleather
Original assignee: Allan Stikeleather; Stikeleather Edward R
Priority date: 2004-11-18
Filing date: 2005-11-18
Publication date: 2006-05-26
Also published as: WO2006055916A3

Abstract

A heat exchanger assembly includes a tube configured to carry a first heat exchange medium and a fin coupled to at least a portion of the tube. The fin includes at least one vane formed therein. The vane is configured to direct the flow of a second heat transfer medium against the tube.

Description

HEAT EXCHANGER TUBE AND METHOD OF FORMING A HEAT EXCHANGER TUBE

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. provisional patent application Serial No.

60/629,476, filed November 18, 2004, and claims the benefit of U.S. provisional patent application Serial No. 60/630,406, filed November 23, 2004, and also claims the benefit of U.S. provisional patent application Serial No. 60/646,134, filed January 21, 2005, the entire disclosure of all of which applications is incorporated herein by reference.

FIELD

The present disclosure relates to heat exchanger tubes, and, in particular to heat exchanger tube having a fin or fins disposed on a surface thereof.

BACKGROUND

Heat exchanger tubes may include a metallic tube with a fin wound helically around an exterior surface thereof. In known constructions, the tube may have a circular cross- section and the fin may be a solid construction and integral with, or secured to, the outer surface of the tube. In some applications, however, heat applied to a bottom half of a tube may more directly heat the bottom of the tube than the top of the tube. This results in inefficient heat transfer for the tube and a heat exchanger including the tube.

There is therefore a need for a heat exchanger tube configuration, and a fin construction for the same, that directs heat onto a heat exchanger tube in an efficient manner.

BRIEF DESCRIPTION OF DRAWINGS

Features and advantages of the present invention are set forth by way of description of specific embodiments, which description should be considered in conjunction with the accompanying drawings, wherein:

FIG. 1 is radial cross-section of an embodiment of a heat exchanger tube including a fin consistent with the present invention;

FIG. 2 is an axial (lengthwise) cross-sectional view an embodiment of a heat exchanger tube consistent with the present invention showing a fin disposed on a. top exterior surface thereof; FIG. 3 is radial cross-section of an embodiment of a heat exchanger tube consistent with and embodiment of the present invention;

FIG. 4 is a perspective view of an embodiment of an initial heat exchanger tube assembly; FIG. 5 is a radial cross-section of another embodiment of a heat exchanger tube assembly consistent with the present invention;

FIG. 6 is a representational illustration of a shape alteration operation consistent with the present invention;

FIG. 7 representationally depicts the regions of induced stress in an embodiment of a heat exchanger tube assembly consistent with the present invention; and

FIG. 8 illustrates relief cuts which may be made in the fins of an initial heat exchanger tube assembly to mitigate buckling of the fins.

DESCRIPTION FIG L is a cross-sectional view of one exemplary embodiment 100 of a heat exchanger consistent with the present invention. The illustrated exemplary embodiment includes a tube 102 and a fin 104. As shown, the fin 104 may be attached to an exterior surface 106 of the tube 102 and may be wound helically thereon. The heat exchanger 100 may advantageously be used in connection with a heat exchange system to provide heat transfer between a first heat transfer medium disposed within and/or circulating within the tube 102 and a second heat transfer medium moving or flowing over and/or around the heat exchanger 100. The flow of the second heat transfer medium over and/or around the heat exchanger 100 is indicated by arrows 114. For example, convective heat transfer may occur between the first heat transfer medium within the tube 102 and the second heat transfer medium moving or flowing over and/or around the heat exchanger 100. The first heat transfer medium and the second heat transfer medium may be fluid heat transfer mediums, such as gasses, liquids, etc. Furthermore, the first heat transfer medium within the tube may be different than the second heat transfer medium moving or flowing over and/or around the heat exchanger 100. In the illustrated exemplary embodiment, a bottom portion 108 of the fin 104, i.e., a portion of the fin 104 in an upstream position relative to the second heat transfer medium, is of solid construction, i.e. with no openings, serrations or vanes between an interior edge of the fin and an exterior edge of the fin. A top portion 110 of the fin 104, i.e., a portion of the fin 104 in a downstream position relative to the flow 114 of the second heat transfer medium, however, may include a one or more vanes 112 extending from a surface thereof for directing the second heat transfer medium flowing around and/or over the heat exchanger 100. The second heat transfer medium may be directed by the vanes 112 to flow along the exterior surface of the tube. As shown, the second heat transfer medium may have an upstream flow 114a that may be generally perpendicular to the axis of the tube 102. The upstream flow 114a may be incident on the bottom portion 108 of the fin 104 and of the tube 102. The downstream flow 114b of the second heat transfer medium may be directed around the tube 102 and the upper portion 110 of the fin 104 by the vanes 112. In this manner, the vanes 112 may increase and/or prolong the effective interaction between the tube 102, fin 104, and second heat transfer medium flowing around the heat exchanger 100. In one example, the vanes may direct the flow of heat transfer medium, e.g., a heated gas emanating from the bottom of the tube, against the top portion of the exterior tube surface 106, as indicated by arrows 114b. By directing the flow of the second heat transfer medium against the top portion of the tube exterior surface, the second heat transfer medium may be applied more evenly to the top and bottom portions of the tube and the fin, thereby increasing efficiency heat transfer. For example, directing the flow of the second heat transfer medium across the top portion of the tube and fin may increase the surface area of the fin and tube contacted by a flow the second heat transfer media effective for transferring heat between the first and second heat transfer mediums.

A variety of methods for forming the vanes 112 in the fin 104 will be known to those of ordinary skill in the art. For example, referring to FIG. 2, an axial sectional view of a portion of a heat exchanger tube consistent with the present invention is shown. As depicted, the vane 112 on the top portion of the fin 110 may be formed as a flap 116 extending outwardly from the body 11 S of the fin 104. Vanes 112 of such a configuration may be formed by stamping, die forming, etc. Other suitable configurations and forming techniques may also be employed herein, hi various embodiments the fin may be integrally formed with the tube and/or may be a separate component which may be coupled to the tube, e.g., by brazing, welding, swaging, interference fit, etc., The vanes may be formed in the fin before, during, or after the fin is coupled to the tube.

The vanes may be provided in a variety of configurations depending on the requirements of the application. For example, as shown in the embodiments depicted in FIGS. 1 and 2, the vanes 112 may be provided solely on the top half of the fin 104, or may extend at least partially into the bottom half of the tube. Also the vanes 112 may be provided in a variety of patterns for directing flow of gas against the tube. The illustrated exemplary embodiments are, therefore, provided by way of example, not of limitation.

FIG. 3 illustrates another exemplary embodiment of a heat exchanger tube assembly 300 consistent with the present invention. As shown, the tube 302 has a generally triangular or trapezoidal cross-section with fins 304 disposed on the side surfaces thereof. In one embodiment, the fins may extend about 0.5 inches from the exterior surface of the tube, and the inside diameter of the tube may be about 1 inch. Of course, the dimensions of the tube and the fins may be freely varied to accommodate various different applications. A first heat transfer medium may be disposed within and/or circulate or pass though the tube 302. A second heat transfer medium may surround and/or flow over or around the heat exchanger tube assembly 300 for transferring heat between the first and second heat transfer medium. The first and second heat transfer mediums may include fluid heat transfer mediums, such as liquids and/or gasses, etc.

According to one aspect, a heat exchanger tube assembly 300 consistent with the illustrated embodiment may present a portion of an exterior surface 305 exposed directly to a flow of the second heat transfer medium, indicated by arrows 306. The portion of the exterior surface 305 exposed directly to the flow of the second heat transfer medium 306 may be directly impinged by the flow of the second heat transfer medium. Additionally, the second heat transfer medium impinging an upstream portion of the exterior surface 305 of the tube 302 may flow downstream along and/or in contact with the portion of exterior surface 305 of the tube 302 which is exposed directly to the flow 306 of the second heat transfer medium. Impingement and/or flow of the second heat transfer medium along the exterior surface 305 and/or across the fins 304 may affect heat transfer between the first and second heat transfer mediums. A heat exchanger tube assembly 300 herein may exhibit improved heat transfer efficiency, relative to, for example, a tube having a circular cross-section. The increased heat transfer efficiency may, at least in part, be achieved by presenting a longer exterior surface exposed directly to the flow 306 of the second heat transfer medium, e.g., as compared to a tube of circular cross-section having a similar cross-sectional area. In the illustrated embodiment, only the top portion of the illustrated tube 302 may generally be not exposed directly to the flow 306 of the second heat transfer medium, as compared with nearly half of a circular cross-section tube which may not be directly exposed, i.e., the downstream half of the circular cross-section tube. In addition, to increasing the heat transfer efficiency, the generally flat exterior surfaces of the tube 302 facilitate attachment of the fins 304 to the tube 302.

The tube 302 and fins 304 may be constructed using equipment and techniques known in the art. For example, the fins 304 may be formed from a sheet or strip material. The fins 304 may be affixed to the generally flat exterior surfaces of the tube 302 by welding, brazing, or other suitable methods. In other embodiments, the fins may be integrally formed with the tube. The fins may be secured to the exterior surface of the tube either perpendicularly to the major axis of the tube, or at an angle, e.g. 45 degrees, thereto. In addition, the fins 304 on one or both sides of the tube may include one or more vanes disposed thereon, e.g., as described above with reference to FIGS. 1 and 2. Such vanes may further direct and/or encourage the flow of the second heat transfer medium against or along the exterior surface of the tube. Additionally, vanes may, at least to some degree, promote and/or increase flow of the second heat transfer medium along at least a portion of the exterior surface of the tube which is not exposed directly to the flow of the second heat transfer medium. Referring to FIGS. 4 through 8, an exemplary method of forming a heat exchanger tube assembly consistent with one aspect of the present invention is illustrated. In general, heat transfer between a first heat transfer medium within and/or flowing through a heat exchanger tube and a second heat transfer media surrounding and/or flowing over or around the heat exchanger tube may be improved by altering the shape of the heat exchanger tube to increase the exterior surface of the tube exposed directly to the flow of the second heat transfer media.

Referring to FIG. 4, an initial heat exchanger tube assembly 400 may generally include a tube 402 including a helically arranged fin 404 coupled to the exterior surface 406 of the tube 402. The fin 404 may be a separate component which may be attached to the exterior surface 406 of the tube 402, e.g., by welding, brazing, swaging into a groove in the tube, etc. Alternatively, the fin may be integrally formed with the tube. As shown, the flow, indicated by arrows 408, of the second heat transfer medium may generally directly contact only about one half of the exterior surface 406 of the tube. The downstream portion of the tube 402 may be shielded, to varying degrees, from the direct flow 408 of the second heat transfer medium, thus reducing the heat transfer in the shielded region of the tube.

With reference to FIG. 5, according to one aspect of the invention, the shape of the heat exchanger tube assembly 400 may be altered to provide a modified heat exchanger tube assembly 400. As shown, the round tube 402 with fins 404 may be modified to provide a tube 402a having different, unequal length cross-sectional axes AB, CD. In the illustrated embodiment, the modified tube 402 a may have a generally triangular or trapezoidal cross- sectional shape. The modified tube 402a, may, as such, exhibit an increased tube exterior surface 406a more directly exposed to the flow 408 of the second heat transfer media in a direction generally parallel to the longer altered tube axis AB. Heat transfer may be increased as a result of the additional tube exterior surface being more directly exposed to the flow 408 of the second heat transfer media generally parallel to this altered, longer tube/fin axes AB. Modified cross-sectional shapes, other than the generally triangular or trapezoidal cross-sectional shape, may also suitably provide an increased exterior surface that is more directly exposed to the flow of the second heat transfer medium. As illustrated in FIG. 6, one method of altering a round helically finned tube 402 may involve exerting a pressure on each of generally opposed sides of the tube 402. The pressure may compress, or otherwise deform, the tube 402, and/or the fins 404, to increase one cross- sectional axis and/or decrease the other cross-sectional axis of the tube 402. Consistent with the illustrated embodiment, the pressure to deform the tube 402 may be applied to the tube 402 via members configured to contact the tube 402 in between adjacent turns of the helically disposed fin 404. For example, appropriate edgewise pressure may be applied through a plurality of appropriately configured strips 410, 412. The strips 410, 412 maybe generally aligned at right angles to the main axis of the tube 402 and may be of appropriate strength material, and dimensions to allow the strips 410, 412 to be fitted and properly aligned with each other in the space between adjacent helical fin 404 prior to applying pressure on opposite sides of the finned portion of the tube 402 areas requiring alteration. In an alternative embodiment, instead of individual strips, forming blocks may be employed. The forming block may extend along at least a portion of the length of the tube and may include slots configured to at least partially receive respective portions of the helically wound fin. With the strips 410, 412 appropriately positioned relative to the tube 402, pressure may be applied by the strips 410, 412, to compress the round finned tube 402 to a desired exterior shape. In this manner the length of the exterior tube surfaces 406a exposed on opposite sides of the tube 402a to flow 408 of the second heat transfer medium, generally parallel to the longer axis of the finned tube, may be increased. Herein above the relative orientation of the strips 410, 412 has been described as generally opposed. With reference to FIG. 6 it will be understood that generally opposed may include converging and/or diverging angled orientations, as well as a parallel orientations of the strips 410, 412. Similarly, the planes of stress applied to the tube in order to bring about the desired deformation may include converging and diverging angled planes, as well as parallel planes of stress. In addition to applying pressure to the tube 402, the strips 410, 412 may in some embodiments, at least in part, control the changing geometry of the helical fin 404 resulting from the altered geometry of the tube compressing operation. With reference to FIG. 7, compressing the walls of the round helically finned tube 402 to achieve the desired altered shape may produce corresponding deformation of the fins 404, if they are securely attached to the tube 402 and must, therefore, move to conform to the altered geometry of the tube 402a. The movement of the fins to conform to the altered geometry of the tube 402a may induce stresses in the fins 404a. Tensile stresses may be induced in the fins at around each end of the longer axis of the alter shape, as designated by T in FIG. 7, due to the changed radius relative to the original tube geometry. Conversely, tensile compressive stresses may be induced in the fins 404a along the opposing flattened tube wall portions, designated by C in FIG. 7, due to the flattening of the tube wall under the fins 404a.

Compressive stresses induced in the fins 404a along the opposing flattened tube wall portions 405 may cause buckling of the fins 404a in these regions. Buckling of the fins 404a may reduce the openings between adjacent fins, which may result in an undesirable increase in the pressure drop of the second heat transfer medium flowing across the heat exchanger assembly 400a. According to one embodiment, the strips 410, 412 which apply pressure to alter the geometry of the tube 402, may also apply a compressive force to the fins 404 to control buckling of the fins 404a after deformation of the tube. Additionally, the strips 410, 412 may apply a force to the fins to stabilize the position of the fins to maintain the fin alignment during the tube shape alteration.

With reference to FIG. 8, according to another embodiment, buckling of the fins may be, at least in part, controlled by selectively removing portions 414, 416, 418, 420 of the fins 404, e.g., by providing relief cuts, prior to alteration of the shape. The removed portions 414, 416, 418, 420 may allow the expansion of the regions of the fins 404a exhibiting induced compressive stress C without buckling. According to one embodiment, the size and placement of the removed portions 414, 416, 418, 420 of the helical fin 404 maybe coordinated such that the gaps may generally close-up when the shape of the tube is altered. Alteration of a finned tube shape as described herein may cause a corresponding reduction in the cross section area and/or hydraulic and/or equivalent diameter when a round tube is deformed in accordance with this invention. The reduction may increase the pressure drop through the tube. For this reason, conversion from a round helically finned tube to a shaped finned tube in order to increase the heat transfer may require larger starting round finned tube diameters to compensate for increased pressure drop resulting from the change in shape.

According to one aspect, a heat exchanger assembly is provided including a tube configured to carry a first heat exchange medium. A fin may be coupled to at least a portion of the tube. The fin may include at least one vane extending from a surface thereof. The vane may be configured to direct a flow of a second heat exchange medium against the tube.

According to another aspect, a heat exchanger assembly is provided including a tube having trapezoidal or triangular cross-sectional shape. The heat exchanger assembly may also include a fin attached to the tube. According to yet another aspect there is provided a method for forming a heat exchanger assembly. The method generally includes providing a tube and providing a helical fin coupled to the tube. The method may further include deforming the tube to provide a generally trapezoidal or triangular cross-sectional shape.

The invention herein has been set for the through the description of various embodiments consistent therewith. It should be recognized that any aspect or feature of any embodiment described herein may be used in combination with any other aspects or features of the various embodiments. The described embodiments are susceptible to numerous modifications and variations without departing from the invention herein, and should therefore not be construed as limiting the invention.

Claims

What is claimed is:

1. A heat exchanger comprising: a tube configured to carry a first heat exchange medium; and a fin coupled to at least a portion of the tube, the fin comprising at least one vane configured to direct a flow of a second heat exchange medium against the tube.

2. A heat exchanger according to claim 1, wherein the fin is helically disposed about the tube.

3. A heat exchanger according to claim 1 , wherein the fin is brazed or welded to the tube.

4. A heat exchanger according to claim 1 , wherein the fin is integrally formed with the tube.

5. A heat exchanger according to claim 1 , wherein the at least one vane is disposed only on a first portion of the fin relative to cross-section of the tube.

6. A heat exchanger according to claim 1, wherein the at least one vane comprises a flap protruding from the fin, the flap influencing a flow of the second heat exchange medium around the tube.

7. A heat exchanger comprising: a tube having a trapezoidal or triangular cross-sectional shape; and a fin attached to the tube.

8. A heat exchanger according to claim 7, wherein the fin is helically disposed around the tube.

9. A heat exchanger according to claim 7, wherein the tube has a first cross- sectional axis and a second cross-sectional axis, the first cross-sectional axis being longer than the second cross-sectional axis.

10. A heat exchanger according to claim 7, wherein the fin is brazed or welded to the tube.

11. A heat exchanger according to claim 7, wherein the fin only extends around a portion of the tube.

12. A method of forming a heat exchanger comprising: providing a tube; providing a helical fin coupled to the tube; and deforming the tube to provide a trapezoidal or triangular cross-sectional shape.

13. A method according to claim 12, wherein deforming the tube comprises applying a force to each of two generally opposed sides of the tube.

14. A method according to claim 13, wherein applying the force to each of two generally opposed sides of the tube comprises applying force along two intersecting planes.

15. A method according to claim 13, wherein the force is applied to each of two generally opposed sides of the tube by strips at least partially disposed between adjacent portions of the helical fin.

16. A method according to claim 12, further comprising providing at least one relief cut in the fin prior to deforming the tube.

17. A method according to claim 16, said method comprising providing a plurality of said relief cuts, and wherein said relief cuts are positioned according to regions of high induced stress by deforming the tube.