Patent Publication Number: US-2011048688-A1

Title: Heat Exchanger Assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     A heat exchanger assembly for transferring heat between a coolant and a flow of air, and specifically to an improved air fin design. 
     2. Description of the Prior Art 
     Japanese Patent Application No. 10365226, issued to Hiroshi et al., shows a heat exchanger assembly for transferring heat between a coolant and a flow of air. The &#39;388 application includes a first manifold and a second manifold, and a plurality of tubes extending in spaced and parallel relationship with one another between the first and second manifolds for conveying the coolant between the first and second manifolds. Adjacent tubes are spaced from one another by a fin space, and a plurality of air fins are disposed in the fin spaces. Each of the air fins has a cross-section presenting a plurality of legs and a plurality of bases interconnecting alternate ends of adjacent legs and engaging the adjacent tubes to present a serpentine pattern. Each of the bases extends through an arc between the ends of the adjacent legs and defines a lead-in radius interconnecting each base with one of the legs and an exit radius interconnecting each base with the other of the adjacent legs. A middle radius extends between the lead-in and exit radii. 
     U.S. Pat. No. 6,439,300, issued to Falta et al. on Aug. 27, 2002, shows a heat exchanger assembly including a plurality of air fins having a cross-section presenting a plurality of legs extending at equal and opposing angles to one another. 
     SUMMARY OF THE INVENTION 
     The invention is for such a heat exchanger assembly wherein the equal and opposing angles of the legs of the air fins are in the range of 1 to 4 degrees, the lead-in radius is in the range of 0.05 to 0.15 mm, the exit radius is in the range of 0.05 to 0.15 mm, and the middle radius is in the range of 0.5 to 1.5 mm. 
     The legs of the air fins are angled to maintain the structural integrity of the heat exchanger, i.e. to prevent the legs from collapsing during the manufacturing or use of the heat exchanger. However, the maximum angle is set at 4 degrees to maximize the length of the louvers on the legs of the air fin, and thereby avoid a pressure drop penalty, which results from having shorter louvers. Such a pressure drop negatively impacts the performance of the heat exchanger. Additionally, the angled legs improve the ability of the heat exchanger to shed water. 
     The lead-in and exit radii are minimized in order to maximize the length of the louvers, and thereby limit the pressure drop penalty explained above. However, the lead-in and exit radii must be large enough to allow the forming tool to release from the air fin at production speeds. 
     Finally, during the brazing process of joining the manifolds, tubes, and air fins together, because the areas of contact between the air fins and the flat sides of the tubes is not flat, but instead has a middle radius, capillary action by the brazing material occurs during the brazing process. In other words, a portion of the liquefied brazing material is pulled along the middle radius of the air fin. Upon cooling, the brazing material solidifies to form a strong fillet bonding the tubes to the air fins. This fillet is not only structurally strong, but it is also thermally conductive, thereby improving heat conduction from the coolant in the tubes to the air fins. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a perspective and partially exploded view of the heat exchanger assembly of the subject invention; 
         FIG. 2  is a perspective and fragmentary view of the air fins and tubes of the subject invention; and 
         FIG. 3  is a front view of one of the air fins extending between adjacent tubes. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a heat exchanger assembly  20  for transferring heat between a coolant and a flow of air is generally shown in  FIG. 1 . The heat exchanger assembly  20  has a number of uses, including but not limited to use as a: radiator, condenser, heater, evaporator, chiller or cooler. 
     The assembly includes a first manifold  22  and a second manifold  24  in spaced and parallel relationship with one another. A plurality of tubes  26 , generally indicated in  FIGS. 2 and 3 , extend in spaced and parallel relationship with one another between the first and second manifolds  22 ,  24  for conveying the coolant between the first and second manifolds  22 ,  24 . Each of the tubes  26  has a cross-section presenting flat sides  28  extending in a transverse direction interconnected by round ends  30 . The flat sides  28  of adjacent tubes  26  are spaced from one another by a fin space  32 . 
     A plurality of air fins  34 , generally indicated in  FIGS. 2 and 3 , are disposed in the fin spaces  32  between the flat sides  28  of adjacent tubes  26 . Each of the air fins  34  has a cross-section presenting a plurality of legs  36  extending between the flat sides  28  of the adjacent tubes  26 . Each of the legs  36  of the air fins  34  presents a plurality of louvers  38  for conveying the flow of air through the legs  36  between adjacent fin spaces  32 . Heat exchangers having parallel legs have a tendency to collapse during the manufacturing or use. Therefore, in the subject invention, the legs  36  of the air fins  34  are disposed at equal and opposing angles Φ to one another to maintain the structural integrity of the heat exchanger assembly  20 . However, the angle Φ the fins are disposed at is preferably minimized to enhance the length of the louvers  38 , and thereby, improve the air flow between the adjacent fin spaces  32 . The larger the angle Φ, the greater the pressure drop created by the louvers  38 . Therefore, in the subject invention, the angle Φ of the opposing legs  36  is preferably in the range of 1 to 4 degrees and is most preferably 1.53 degrees. Another advantage to having the legs  36  of the air fins  34  disposed at an angle Φ is the improved ability to shed water when the heat exchanger assembly  20  is used as an evaporator. In other words, when water condenses on the legs  36  of the air fins  34 , gravity carries it down the slope of the angled legs  36 , and the liquid water eventually spills off the air fin  34 . In contradistinction, water tends to rest on the legs of parallel air fins. 
     A plurality of bases  40  interconnect alternate ends of adjacent legs  36  and engage the flat sides  28  of the adjacent tubes  26 . The bases  40  and legs  36  of the air fins  34  present a serpentine pattern extending between the first and second manifolds  22 ,  24 . Each of the legs  36  of the air fins  34  has a length L, preferably in the range of 5 to 6 mm. 
     Each of the bases  40  of the air fins  34  has a base width W b , and adjacent bases  40  are spaced from one another along the flat sides  28  of the tubes  26  by a span S. The ratio of the base width W b  to the span S is preferably in the range of 0.80 to 0.90 to maximize the length of the louvers  38 , and thereby, minimize the pressure drop penalty explained above. 
     Each of the bases  40  extends through an arc between the ends of the adjacent legs  36 . Each base  40  defines a lead-in radius R 1  integrally connected with one of the legs  36  and an exit radius R 2  integrally connected with the other of the adjacent legs  36 . The lead-in and exit radii R 1 , R 2  are minimized in order to maximize the length of the louvers  38 , and thereby limit the pressure drop penalty explained above. However, the lead-in and exit radii R 1 , R 2  must be large enough to allow the forming tool to release from the air fin  34  at production speeds. Additionally, the forming tool can overheat when making air fins  34  with small lead-in and exit radii R 1 , R 2 . The lead-in and exit radii R 1 , R 2  are preferably the same, and in the range of 0.05 to 0.15 mm. A middle radius R 3  extends between the lead-in and exit radii R 1 , R 2 . The middle radius R 3  is greater than the lead-in and exit radii R 1 , R 2 , and is preferably in the range of 0.5 to 1.5 mm. 
     The manifolds  22 ,  24 , tubes  26 , and air fins  34  are joined together using a brazing process. Because the area of each air fin  34  in contact with the flat sides  28  of the tubes  26  is not flat, but instead has a middle radius R 3 , capillary action by the brazing material occurs during the brazing process. In other words, a portion of the liquefied brazing material is pulled along the middle radius R 3  of the air fin  34 . Upon cooling, the brazing material solidifies to form a strong fillet bonding the tubes  26  to the air fins  34 . This fillet is not only structurally strong, but is also thermally conductive, thereby improving heat conduction from the coolant in the tubes  26  to the air fins  34 . 
     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.