Abstract:
A method of forming tubing with integral fins oriented parallel to its length, and to a heat exchanger tube produced by such a method. The invention involves extruding a tube so that the tube has at least one internal longitudinal passage, an external surface having a cross-sectional shape in a plane transverse to the extrusion direction, and at least one integral fin parallel to the extrusion direction and extending in a direction away from the external surface of the tube. The tube may be one of a plurality of tubes assembled in parallel to a pair of manifolds, and such tubes are preferably oriented so that their integral fins are substantially parallel, with the fin(s) of a given tube extending toward an adjacent one of the tubes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a division patent application of co-pending U.S. patent application Ser. No. 10/604,143, filed Jun. 27, 2003, whose contents are incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention generally relates to heat exchangers, such as those of the type used in air-conditioning systems. More particularly, this invention relates to a heat exchanger tube configuration that incorporates integral fins for transferring heat to and from the tube.  
         [0004]     Heat exchangers are employed within the automotive industry as condensers and evaporators for use in air conditioning systems, radiators for cooling engine coolant, heater cores for internal climate control, etc. One type of heat exchanger construction used in the automotive industry for condensers and evaporators comprises a number of parallel tubes that are joined to and between a pair of manifolds, creating a parallel flow arrangement. The ends of the tubes are typically metallurgically joined (brazed, soldered or welded) to tube ports, generally in the form of holes or slots formed in a wall of each manifold. In order to maximize the amount of surface area available for transferring heat between the environment and a fluid flowing through the heat exchanger, automotive heat exchangers often have a tube-and-fin construction in which numerous tubes thermally communicate with high surface area fins. The fins are typically in the form of flat panels having apertures through which tubes with circular cross-sections are inserted, or in the form of sinusoidal centers that are positioned between adjacent pairs of “flat” tubes with oblong cross-sections. In either case, the resulting tube-and-fin assembly is oriented so that the edges of the fins face the fluid (e.g., air) flowing between the tubes, i.e., the fins are normal to the plane defined by the tubes of the heat exchanger.  
         [0005]     Alternative forms of fins have been suggested, examples of which include U.S. Pat. No. 4,546,819 to O° Connor, U.S. Pat. No. 4,951,742 to Keyes, and U.S. Pat. No. 5,353,868 to Abbott. Each of these patents discloses a cooling tube whose outer surface undergoes a second forming operation to have integral fins. Abbott discloses fin strips formed by lancing a conduit, while O&#39;Connor and Keyes disclose integral fins formed by rolling the exterior of a tube. An approach to forming integral fins on round plastic tubing is taught in U.S. Pat. No. 4,926,933 to Gray, in which integral helical fins are defined on the exterior of a round plastic tube during injection molding or extrusion of the tube.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The present invention provides a method for forming tubing with integral fins, and to a heat exchanger tube produced by such a method. The method generally involves extruding the tube through a die so that the tube has at least one internal passage extending in a longitudinal direction parallel to the longitudinal direction in which the tube was extruded, an external surface having a cross-sectional shape in a plane transverse to the extrusion direction, and at least one integral fin parallel to the extrusion direction and extending in a direction away from the external surface of the tube. As such, the one or more fins are parallel to the longitudinal axis of the tube. The tube can be one of a plurality of identical tubes assembled in parallel to a pair of manifolds, and such tubes are preferably oriented so that their integral fins are substantially parallel, with the fin(s) of a given tube extending toward an adjacent one of the tubes. In this arrangement, the fins are oriented substantially parallel to the plane in which the tubes lie, contrary to conventional practice.  
         [0007]     Significant advantages of the integral tube-and-fin construction of this invention include the elimination of separate fin stock and the costly manufacturing equipment associated with producing and brazing fins for heat exchanger tubing. Another feature of the invention is the potential for reducing the size of a heat exchanger for a given application as a result of the ability to more densely pack the tubes. Heat exchangers incorporating the integral tube-and-fin construction of this invention can find use in a variety of applications, including automotive and beverage cooling applications. For example, the integral tube-and-fin construction of this invention is suitable for use in conventional automotive cooling and air-conditioning units, as well as condensers and evaporators for CO 2 -based air-conditioning systems. For beverage cooling applications, the integral tube-and-fin construction has the potential to exhibit improved water shedding characteristics and greater resistance to clogging by dirt, dust and other debris commonly encountered by beverage coolers.  
         [0008]     Other objects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective end view of an as-extruded tube with multiple integral fins in accordance with this invention.  
         [0010]      FIG. 2  is a perspective end view of the tube of  FIG. 1  following a secondary operation in which portions of each fin are removed in accordance with an embodiment of the invention.  
         [0011]      FIG. 3  is a perspective view of an alternative fin configuration formed by bending portions of each fin in a secondary operation.  
         [0012]      FIG. 4  schematically represents a process for forming the tube of  FIG. 2 .  
         [0013]      FIGS. 5 and 6  schematically represent individual steps of the forming process of  FIG. 4 .  
         [0014]      FIG. 7  is a perspective end view of a two-piece manifold for assembly with the tubes of  FIGS. 1 through 3 .  
         [0015]      FIG. 8  is a frontal view of a heat exchanger comprising multiple tubes of the type shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  represents a segment of an as-extruded heat exchanger tube  10  configured in accordance with this invention. The tube  10  is represented as a flat (oblong cross-section) tube portion  12  with multiple internal passages  14  that extend in a longitudinal direction of the tube portion  12 . According to a preferred aspect of the invention, the tube  10  is extruded and the passages  14  are formed during the extrusion process so as to be parallel to the extrusion direction of the tube  10 . The external surface of the tube portion  12  is defined by oppositely-disposed flat surfaces  16  and two oppositely-disposed lateral surfaces  18 . Multiple fins  22  extend from each of the flat surfaces  16  in a direction normal to the flat surfaces  16  and parallel to the extrusion direction. The fins  22  on one of the surfaces  16  are shown as being staggered relative to the fins  22  on the opposite surface  16 , though such a configuration is not required.  
         [0017]     As disclosed and defined herein, the fins  22  are “integral fins” with the tube portion  12  in that they are features formed of material continuous with the material that forms the tube portion  12 , and not formed of material subsequently attached or otherwise added to the tube portion  12 . In a preferred embodiment, the fins  22  are formed simultaneously with the tube portion  12 , i.e., during the extrusion process, though integral fins  22  could also be defined following the operation by which the tube portion  12  is formed by deforming the surface of the tube portion  12  to create the fins  22 .  
         [0018]      FIGS. 2 and 3  depict, respectively, a tube  20  and a portion of a tube  20  formed by performing secondary operations on the tube  10  of  FIG. 1 . The tube  20  in  FIG. 2  is depicted as having a relatively short length, though any length of tube is within the scope of this invention. In each case, the secondary operation has resulted in each fin  22  having alternating edge portions  24  and  26  along its length and terminal portions  28  spaced a longitudinal distance from each end of the tube portion  12 . As depicted in  FIGS. 2 and 3 , the edge portions  24  extend a greater distance from the surfaces  16  of the tube portion  12  than the edge portions  26 . In  FIG. 1 , the edge portions  26  are defined by the removal of rectangular sections from the edges of the fins  22 , while in  FIG. 2  the edge portions  26  are defined by bending over rectangular sections along the edges of the fins  22 . In either case, the edge portions  26  define a longitudinal gap between adjacent edge portions  24 , creating a profile similar to a square sawtooth. While the sections removed and bent in  FIGS. 2 and 3 , respectively, are rectangular in shape, various other shapes are possible.  
         [0019]      FIG. 4  schematically represents a process for forming the tube  10  of  FIG. 1  and performing a skiving operation to form the tube  20  depicted in  FIG. 2 . The tube  10  is shown as being extruded with a die  30  having an appropriate shape to produce the desired integral tube-and-fin form shown in  FIG. 1 . Following extrusion, the tube  10  is passed through a pair of sizing rollers  32  before entering a skiving die  34 , both of which are shown in more detail in  FIGS. 5 and 6  respectively. The sizing rollers  32  are intended to improve the form and finish of the tube  10  following extrusion, and for this purpose include individual rollers that travel the flat surfaces  16  of the tube portion  12  between fins  22 . The skiving die  34  is depicted as having multiple bores  36  into which skive punches  38  (only one of which is shown) are actuated to engage the fins  22  of the tube  10 , thereby removing the rectangular sections to define the alternating shorter and longer edge portions  24  and  26  along the edges of the fins  22 . To facilitate the skiving operation, the tube  10  is preferably fed from a separate source (e.g., a roll of the tube  10 ) instead of directly from the extrusion process, so that the tube  10  can be advanced into the skiving die  34  and then held stationary during the skiving operation. The skiving die  34  includes channels  40  that facilitate clearing of the rectangular sections removed from the fins  22 . As an alternative to material removal, the skive punches  38  can be configured to deform the rectangular sections to produce the tube configuration shown in  FIG. 3 . After the skiving operation, the tube  10  continues on to a die  42  where individual tubes  20  are cut from the tube  10 .  
         [0020]     The tube  10  (and therefore the tubes  20 ) is preferably formed from a suitable aluminum alloy, though other alloys could be used. The tubes  20  are attached, such as by brazing or soldering, to a pair of manifolds so that the tubes  20  are fluidically connected to the manifolds to allow fluid flow to and from the manifolds. The manifolds can be of any suitable configuration for the intended application.  FIG. 7  represents a particular embodiment for a manifold  50  suitable for assembly with the tubes  20  of this invention. The manifold  50  is shown to have a two-piece construction comprising a base profile  52  and a clad sheet  54 , the latter of which carries a brazing material and preferably a flux coating (not shown) for brazing the tubes  20  and the clad sheet  54  to the profile  52 . The base profile  52  is generally flat with a plurality of fluid passages  58 , and therefore has a configuration similar to a flat heat exchanger tube, e.g., the tube portion  12  of the tubes  10  and  20  in  FIGS. 1 through 3 . Transverse slots  60  are machined in one wall  56  of the profile  52  to permit assembly of the tubes  20  with the profile  52  by inserting the ends of the tubes  20  into the slots  60 . The base profile  52  includes oppositely-disposed tabs  62  for clinching the edges  64  of the sheet  54 , by which the clad sheet  54  can be mechanically secured to the profile  52 . The clad sheet  54  has openings  66  corresponding in size, shape and location to the slots  60  in the profile  52 . In this manner, the clad sheet  54  can be mechanically secured to the profile  52  with the tabs  60  so that the openings  66  are aligned with the slots  60 , and together the slots  60  and openings  66  define ports for the tubes  20 .  
         [0021]      FIG. 8  depicts a heat exchanger  70  in which a number of the tubes  20  are assembled with a pair of manifolds  50  of the type depicted in  FIG. 7 . The ends of the tubes  20  are received in ports  76  in walls  74  of the manifolds  50 . Based on the manifold construction of  FIG. 7 , the ports  76  are formed by the slots  60  and openings  66  in the profile  52  and cladding sheet  54 , respectively, and the walls  74  of the manifolds  50  are formed by the joining of the cladding sheets  54  to the walls  56  of the profiles  52 . As shown in  FIG. 8 , the terminal portions  28  of the fins  22  of each tube  20  abut the wall  74  of the manifolds  50 , such that the terminal portions  28  advantageously serve as tube stops during the assembly process. The tubes  20  are oriented so that their flat surfaces  16  are normal to the plane defined by the tubes  20 , with the result that the integral fins  22  of the tubes  20  are parallel to each other and to the plane defined by the tubes  20 , and extend toward an adjacent tube  20 . By spacing the longer portions  24  of each fin  22  a consistent distance apart, the longer and shorter portions  24  and  26  of the fins  22  can be aligned to create passages  72  within the heat exchanger  70  through which a fluid (e.g., air) flows for heat transfer with the tubes  20 .  
         [0022]     While the invention has been described in terms of particular embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the processing steps could be modified, and materials and tube and manifold configurations other than those noted above could be adopted in order to yield a heat exchanger suitable for a wide variety of applications. Accordingly, the scope of the invention is to be limited only by the following claims.