Abstract:
A new type of segmented fin  12  for use on a finned tube  18,  the unique type of finned tube  18  that is created with the new type of segmented fin  12,  specialized serrating wheels  14  and  16  for creating the new type of segmented fin  12,  and the process  10  for employing the specialized serrating wheels  14  and  16  to create the new type of segmented fin  12.  Each of the segments  26  of the new type of segmented fin  12  is permanently curved, and the segments  26  are coined to increase surface area of the segments  26  and to further shape the sheared edges  42  and  44  of the segments  26  into a more pointed configuration in order to make them more aerodynamic.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a new type of segmented fin for use on a finned tube, specialized serrating wheels for creating the new type of segmented fin, and the process for employing the specialized serrating wheels to create the new type of segmented fin. 
     The new type of segmented fin is unique because it is provided with individual segments that are curved in order to increase the heat transfer rate of the finned tube that is created when the fin is welded onto a heat exchanger tube. In addition, the segments are coined by the specialized serrating wheels, thus increasing the surface area of the segments and further shaping the sheared edges of each of the segments to result in segments with less air drag. 
     2. Description of the Related Art 
     Adding fins to the external surface of a heat exchange tube is an old and well-known way to increase the heat transfer rate between the exterior of the tube and the interior of the tube. Increased heat transfer rate is desirable because the purpose of the heat exchange tubes is to transfer heat between a liquid or gas located within the tube and a liquid or gas located outside the tube. Fins are normally attached to the external surface of the finned tube by employing a long, continuous fin that is wound in helical fashion around the tube so that the fin extends approximately perpendicular to the tube&#39;s longitudinal axis. 
     The practice of serrating the outward extending side of the fin to create segments in the fin prior to winding the flat, non-serrated inwardly extending side or base of the fin to the tube is also a commonly employed way of further increasing the heat transfer rate of the finned tube. 
     In addition, a variety of surface enhancements to the serrated portion of the fin have been proposed as means for further increasing the surface area of the segments and thus increase the heat transfer rate of the finned tube. One of the disadvantages of creating most of these types of surface enhancements in the segments is that the enhancements increase drag on the outside of the finned tube, either by the gas or liquid flowing past the fins external to the tube. 
     The present invention further increases the heat transfer rate of serrated finned tubes by creating a serrated fin that has curved segments. Each of these curved segments is concave on one side of the segment and is convex on the opposite side of the segment. This curvature of the segments results in better attachment of the external gas or liquid to the surfaces of the segments, resulting in a higher heat transfer rate. The curvature of the segments also makes them stronger. In addition, the segments are coined or pressed between the serrating wheels to further increase the surface area of the segments and to shape the edges of the segments. Increasing the surface area of the segments allows them to be more efficient at transferring heat and shaping the edges of the segments allows them to be more aerodynamic so that there is decreased drag on the fin when the finned tube is in service. 
     Finally, after serrating and coining the segments, the segments are passed between a final set of wheels in order to precisely align the segments relative to their base, making the fin ready for winding onto the tube to create a finned tube. 
     SUMMARY OF THE INVENTION 
     The present invention consists of a process for creating a new type of segmented fin, specially designed serrating wheels for creating the new type of segmented fin, the new type of segmented fin thus produced, and the unique type of finned tube that is created with the new type of segmented fin. 
     The method involves first passing a flat metal fin strip between two specially designed serrating wheels. Each of the specially designed serrating wheels is provided with a series of cutting edges around the wheel&#39;s perimeter. One of the wheels is provided around its perimeter with a series of concave surfaces, with one such concave surface being located between each adjacent pair of cutting edges provided on that first wheel. The other wheel is provided at its perimeter with a series of convex surfaces, with one such convex surface being located between each adjacent pair of cutting edges provided on that second wheel. The cutting edges of the two wheels are aligned with each other in cooperating fashion so that when the flat fin strip is passed between the wheels, the outward extending side of the fin is serrated by the cooperating cutting edges of the wheels, but the base of the fin strip remains unserrated. 
     The convex and concave surfaces of the two wheels are engaged and mated so that as the serrated portion of the fin completes its travel between the wheels, the segments are pressed or coined between the opposing convex and concave surfaces. This coining causes each of the segments to be stressed beyond the yield point of the metal and thereby causes each of the segments to be permanently bent into a curved configuration corresponding to the curvature of the mating concave and convex surfaces of the first set of wheels. 
     Once the serrated and coined fin completes its travel through the wheels, the base of the fin is then engaged by a second set of wheels that serve to apply a pulling force on the fin in order to pull it clear of the first set of wheels with sufficient tension so as to elongate the base of the fin. It is important that the second set of wheels engage only the base of the fin so that the curvatures of the serrations are not disturbed by the gripping action of the second set of wheels. 
     Finally, after the serrated and coined fin passes between the second set of wheels, it passes between a third set of wheels. The wheels comprising the third set of wheels are precisely spaced apart from each other so that as the segments pass between the third set of wheels, the segments are realigned with the longitudinal axis of the base without disturbing the curvature of the segments. 
     The final result of this process is a serrated fin having curved segments. Each segment is curved in a plane approximately parallel to the longitudinal axis of the fin&#39;s base so that each segment is provided with a concave side and an opposite convex side, with the two sides meeting at the serrated edges. 
     Also because of the coining process that the segments undergo as they pass between the serrating first set of wheels, the surface area of the segment is slightly increased and the edges of the segments are slightly pointed. 
     One of the added benefits of producing a fin with curved segments is that the segments, by virtue of their curved configuration, are inherently stronger. A segment will resist deflection by an amount that is proportional to the moment of inertia, and the moment of inertia is proportional to the cube of the thickness of the fin, including its curvature. Thus, by creating a curvature in the segments, the fin&#39;s apparent thickness is increased and also the strength of the segment is increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram illustrating the specialized serrating wheels and the process for creating from a flat fin strip a new type of aerodynamically curved segmented fin that is the subject of the present invention. 
     FIG. 2 is an enlarged view of a flat fin strip as it enters and is being serrated by the serrating first set of wheels in FIG.  1 . 
     FIG. 3 is an enlarged view of the fin strip of FIG. 1 that has been serrated and is being coined by the first set of wheels in FIG.  1 . 
     FIG. 4 is an enlarged view of the serrated and coined fin strip as it exits the first set of wheels in FIG.  1 . 
     FIG. 5 is an enlarged view of the new type of aerodynamically curved segmented fin as it exits the final set of wheels in FIG.  1 . 
     FIG. 6 is a side view of a heat exchange tube to which the fin of FIG. 5 is being attached. 
     FIG. 7 is an end view of the tube and fin of FIG.  6 . 
     FIG. 8 is an enlarged view of a couple of segments from FIG.  6 . 
     FIG. 9 is an enlarged view of one of the segments from FIG.  8 . 
     FIG. 10 is an end view of a finned tube constructed with the fin and tube of FIGS. 6 and 7. 
     FIG. 11 is a cut away perspective view of a portion of the finned tube of FIG. 10 with the finned tube cut in half along its longitudinal axis for ease in viewing. 
     FIG. 12 is a side view of the finned tube of FIG.  11 . 
     FIG. 13 is a side view of the new type of aerodynamically curved, segmented fin as it exits the final set of wheels in FIG.  1 . 
     FIG. 14 is a graph showing test results from a comparison of a first finned tube constructed in accordance with the present invention and a prior art finned tube. 
     FIG. 15 is a graph showing test results from a comparison of a second finned tube constructed in accordance with the present invention and a prior art finned tube. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Invention 
     Referring now to the drawings, and initially to FIG. 1, there is illustrated a method or process  10  in accordance with a preferred embodiment of the present invention for creating a new type of segmented fin  12 . Referring also to FIGS. 2-4, there is illustrated specially designed serrating wheels  14  and  16  constructed in accordance with a preferred embodiment of the present invention for creating the new type of segmented fin  12 . Referring to FIGS. 4-7, there is illustrate the new type of segmented fin  12  that is produced by employing the specially designed serrating wheels  14  and  16  and the process  10  illustrated in FIG.  1 . Finally, referring to FIGS. 10-12, there is illustrated a unique type of finned tube  18  constructed in accordance with a preferred embodiment of the present invention from a heat exchange tube  20  and the new type of segmented fin  12 . 
     The method  10  involves first passing a flat metal fin strip  22  between the rotating two specially designed serrating wheels  14  and  16 . Each of the specially designed serrating wheels  14  and  16  is provided with a plurality of cutting edges,  14 A and  16 A respectively, provided around a perimeter,  14 P and  16 P respectively, provided on the wheels  14  and  16 . One of the wheels  14  is provided with a plurality of concave surfaces  14 B, with one such concave surface  14 B being located between each adjacent pair of cutting edges  14 A provided on the perimeter  14 P of that first wheel  14 . The other wheel  16  is provided with a plurality of convex surfaces  16 B, with one such convex surface  16 B being located between each adjacent pair of cutting edges  16 A provided on the perimeter  16 P of that second wheel  16 . The cutting edges  14 A and  16 A of the two wheels  14  and  16  are aligned with each other in cooperating fashion. When the flat metal fin strip  22  is passed between the wheels  14  and  16 , a first longitudinal edge of the flat metal fin strip  22 , that will eventually become an outwardly extending side or serrated portion  24  of the segmented fin  12 , is serrated by the cooperating cutting edges  14 A and  16 A of the wheels  14  and  16 , forming a plurality of segments  26  in the serrated portion  24 . This serration process is shown in FIG.  2 . The flat metal fin strip  22  is provided with an opposite second longitudinal edge that will remain unserrated and will form an inwardly extending side or base  28  of the segmented fin  12 . 
     As illustrated in FIGS. 1-3, the convex surfaces  16 B and concave surfaces  14 B of the two wheels  14  and  16  mate together so that as segments  26  in the serrated portion  24  of the segmented fin  12  complete their travel between the wheels  14  and  16 , the segments  26  are cold worked by being pressed or coined between the opposing convex and concave surfaces,  16 B and  14 B. This causes each of the segments  26  to be stressed beyond the metallurgical yield point of the steel metal from which it is formed, and thereby causing each of the segments  26  to be permanently bent into a curved configuration corresponding to the curvature of the mating concave and convex surfaces  16 B and  14 B. As illustrated in FIG. 13, the longitudinal axis  30  of each of the segments  26  is approximately perpendicular to the longitudinal axis  32  of the base  28  of the segmented fin  12 . In addition, the segments  26  are curved in a plane so that a cross section of each of the segments  26  along the longitudinal axis  30  of that segment  26  would cut through the segment  26  in a straight line, forming two mirror image halves of the segment  26 . The curvature or arc of each segment  26  is defined by the curvature of the mating concave and convex surfaces  16 B AND  14 B provided on the specially designed serrating wheels  14  and  16 . This curvature is at a radius range of 0.20 inches to 0.30 inches. 
     Once the serrated and coined fin  12  completes its travel through the first set of wheels  14  and  16 , the base  28  of the fin  12  is then engaged by a second set of rotating wheels  34  and  36 . The wheels  34  and  36  have a slightly higher surface speed than the first set of wheels  14  and  16  so the second set of wheels  34  and  36  serve to apply a pulling force on the fin  12  in order to pull it clear of the first set of wheels  14  and  16 . This pulling force is set large enough to elongate the base  28  of the fin  12  approximately 1-6%, thereby facilitating the subsequent segment realignment. It is important that the second set of wheels  34  and  36  engage only the base  28  of the fin  12  so that the curvatures of the segments  26  are not disturbed. 
     Finally, after the base  28  of the serrated and coined fin  12  passes between the second set of wheels  14  and  16 , the serrated portion  24  of the fin  12  passes through a third set of rotating wheels  38  and  40 . The wheels  38  and  40  are precisely positioned relative to each other so that as the segments  26  pass between the wheels  38  and  40 , the wheels  38  and  40  push against the segments  26 , causing the segments  26  to twist slightly and be pushed back into approximate alignment with the longitudinal axis of the base  28  of the fin  12 . However, it is important that during this operation, that the wheels  38  and  40  are spaced apart a sufficient distance so that this operation does not squeeze the segments  26  too tightly and thus does not disturbed the curvature of the segments  26 . 
     The product of this cold working process is the serrated fin  12  that is provided with curved segments  26 . Also because of the coining process that the segments  26  undergo as they pass between the serrating first set of wheels  14  and  16 , edges  42  and  44 , that are provided on each of the segments  26  at the serrations, are slightly pointed. This is illustrated in FIG. 8 which shows the left and right edges  42  and  44  of each segment  26  being pointed by an angle of, “X” and “Y” respectively, from the normal perpendicular cut  46  that would exist except for the effect of coining on the segment  26 . The angles “X” and “Y” will preferably be between 10 and 20 degrees, depending on the force exerting on the segments  26  by the first set of wheels  14  and  16  during the coining process. 
     Also because of the coining process, surface area of each of the segments  26  is slightly increased over the normal surface area that would have resulted from serrating alone. The surface area is increase by approximately 26% due to the coining. 
     One of the added benefits of producing the fin  12  with its curved segments  26  is that the segments  26 , are inherently stronger than flat or non-curved segments. Increased strength will result in less damage to fin surfaces during manufacturing assembly operations. 
     The normally weak fin segment has undergone a substantial improvement in resistance to deflection because of two features of the aero curved fin  12 . The coining process increases the minimum yield stress by approximately one-third (⅓). In carbon steel fin material, for example, the minimum yield stress changes from approximately 30,000 p.s.i to approximately 40,000 p.s.i. The second improvement comes from the curved shape itself. With dimensions described herein, this improvement can be approximately a 30% increase in resistance to deflection. 
     Referring to FIG. 9, a curved fin segment  26  of a height “H” and a base “B” is illustrated. The actual metal thickness of the fin segment  26 , not accounting for the curvature of the fin segment  26 , is represented in FIG. 9 by the numeral  48 . The actual segment metal thickness  48  is less that the height “H” by the amount of the sweep or depth “D” of the curvature of the segment  26 . 
     Referring now to FIG. 5, it is readily apparent that the realignment of the segments  26  by the third set of wheels  38  and  40  does not accomplish a perfect realignment of the segments  26 . If the segments  26  were perfectly realigned, then the segments  26  would align so that the multiple fin segment thickness  50  of a row of multiple segments  26  provided on the fin  12 , and illustrated in FIG. 5, would be the same as the single fin thickness or height “H”, as illustrated in FIG.  9 . Instead, the multiple fin segment thickness  50  is greater that the single fin thickness “H” because, as can be seen from FIGS. 5 and 6, the segments  26  are offset somewhat from a perfectly straight alignment with each other, with this offset being a maximum of 0.025 inches. Also, as can be seen from FIG. 5, the fact that the segments  26  are somewhat offset from each other, causes a more aerodynamically desirable orientation of the leading right edge  44  of the segments  26 , causing the somewhat pointed edge  44  to face into the oncoming flow of outside gas or liquid, as denoted by arrow “A” in FIGS. 5 and 6. Also, this offset alignment works in conjunction with the curvature of the segments to cause better attachment of the external gas or liquid with the segments  26 , resulting in better heat transfer between the segments  26  and the gas or liquid that is flowing over the exterior of the finned tube  18 . 
     Test Results 
     Referring now to FIGS. 14 and 15, there are presented charts that show actual test runs that have been conducted by Applicant on finned tubes  18  constructed in accordance with a preferred embodiment of the present invention. 
     Referring first to FIG. 14, the chart shows a graphical comparison of the heat transfer performance (shown on the vertical axis of the chart in units of BTU/Hour/Square Foot/Degree Fahrenheit) for various gas mass velocities (shown on the horizontal axis of the chart in units of Pounds/Square Foot/Hour) between a finned tube  18  constructed in accordance with the present invention, as indicated by numeral  52 , and a standard prior art finned heat exchange tube, as indicated by numeral  54 . 
     Each tube represented in FIG. 14 is one and a half (1½) inch in diameter, each tube is provided with 0.75 inch high serrated fins, and each tube has six (6) fins per inch. Also, both tubes were employed in a staggered tube layout for testing. As the chart clearly shows, the finned tube  18  constructed according to the present invention consistently outperformed a comparable conventional prior art finned heat exchange tube. 
     Referring next to FIG. 15, this chart also shows a graphical comparison of the heat transfer performance (also shown on the vertical axis of the chart in units of BTU/Hour/Square Foot/Degree Fahrenheit) for various gas mass velocities (also shown on the horizontal axis of the chart in units of Pounds/Square Foot/Hour) between another finned tube  18  constructed in accordance with the present invention, as indicated by numeral  56 , and a standard prior art finned heat exchange tube, as indicated by numeral  58 . 
     Each tube represented in FIG. 15 is two (2) inches in diameter, each tube is provided with 1.0 inch high serrated fins, and each tube has six (6) fins per inch. Also, both tubes were employed in a staggered tube layout for testing. As this chart also clearly shows, the finned tube  18  constructed according to the present invention consistently outperformed a comparable conventional prior art finned heat exchange tube. 
     While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for the purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.