Abstract:
In accordance with certain embodiments, a cooler for multiple tube banks features a series of parallel and planar fins that have upstream louvers to direct incoming air through a fin near a first row of tubes and a downstream set of louvers near an adjacent tube row to direct air back through the same fin before the air exits. By way of example, the upstream louvers have the negative slope of the downstream louvers and a constant angle from louver to louver within a bank. A constant length in a section view may be provided.

Description:
BACKGROUND  
       [0001]     The subject invention relates to heat exchangers of the fin-and-tube type with an improved louver configuration.  
         [0002]     Fin-and-tube type heat exchangers are well known in the art. These heat exchangers include a number of fins with heat transfer tubes passing therethrough. The fins typically incorporate a number of louvers to redirect and mix the air flow across the fins to increase the heat transfer between the surfaces of the heat exchanger, which include the surfaces of the fins and the outside surfaces of the tubes, and the air flow. One issue that arises when disrupting the air flow is a pressure drop across the fins. A significant increase in the pressure drop across the fins is the penalty paid for the increased heat transfer.  
         [0003]     Therefore, there is a need for improved louvered fin designs for fin and tube heat exchangers that improve heat dissipation characteristics while reducing pressure drop in fluid flowing across the fin. Those skilled in the art will better understand the present invention from a review of the preferred embodiment and drawings that appear below and the claims that determine the full scope of the invention.  
       SUMMARY OF THE INVENTION  
       [0004]     In accordance with certain embodiments, a cooler for multiple tube banks features a series of parallel and planar fins that have upstream louvers to direct incoming air through a fin near a first row of tubes and a downstream set of louvers near an adjacent tube row to direct air back through the same fin before the air exits. The upstream louvers can have the negative slopes of the downstream louvers, and a constant angle from louver to louver within a bank can be provided. Moreover, a constant length in a section view is also contemplated.  
     
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0005]     These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:  
         [0006]      FIG. 1  is a plan view of a single, exemplary fin showing the louver layout and the tube openings;  
         [0007]      FIG. 2  is a section through the louvers in  FIG. 1 ;  
         [0008]      FIG. 3  is an alternative, exemplary embodiment to  FIG. 1  using louvers of shorter widths and gaps between them in a given bank of tubes;  
         [0009]      FIG. 4  is a section view through the louvers of  FIG. 3 ;  
         [0010]      FIG. 5  is a detail around an opening for a tube; and  
         [0011]      FIG. 6  is an alternative, exemplary embodiment to  FIG. 3  showing a different gap layout in the louvers. 
     
    
     DETAILED DESCRIPTION  
       [0012]     Air coolers are generally known to those skilled in the art. They comprise cooling tubes disposed parallel to each other in rows and the rows being parallel to each other. A collection of fins are generally stacked parallel to each other with a typical, exemplary fin  10  shown in  FIG. 1 . Again,  FIG. 1  is but a partial view of an exemplary fin for illustrative purposes to show a row of holes  12 ,  14 ,  16  and  18  for receiving tubes therethrough. A second parallel row of holes  20 ,  22 ,  24  and  26  for receiving tubes is also shown. Edge  30  is the upstream or air inlet edge and edge  32  is the downstream or air outlet side. Advantageously, each illustrated edge has a series of bent triangular shapes  34  to add to the rigidity of the edges.  
         [0013]     The upstream louvers are generally  36  and the downstream louvers are generally  38 . These two louver banks  36 ,  38  align generally with a row of tubes. This forces air that comes in between openings  24  and  26  to work its way around opening  16  since the tubes (not shown) that go in their respective holes are offset from one row to the next. The louvers can be punched out of the fin  10 . As illustrated, they all extend above and below a fin but variations can be used where some or all louvers in the upstream bank  36  extend only from the top and some up to all louvers in bank  38  extend only from the bottom.  
         [0014]     Now looking at  FIG. 2 , the orientation of the upstream louvers  36  and the downstream louvers  38  can more clearly be seen. As illustrated, both banks are at a common angle  40 , such as 25°, with respect to fin  10  but in mirror image. As a result, the slope of the louvers in bank  36  is the negative of the louver slope in bank  38 . The louvers in bank  36  extend above and below the planar surface of the fin  10 , although some to all of the louvers could extend toward the region marked top in  FIG. 2 . In bank  38  the louvers extend above and below the planar surface of fin  10  but optionally some to all the louvers there could extend only in the region marked bottom in  FIG. 2 . As illustrated, the angle of inclination of each louver in a bank such as  36  or  38  is the same or close to the same as an adjacent louver in that bank. However, this inclination angle of the louvers within each bank may vary with respect to one another, if desired. The total dimension of the louver in a bank, as seen in  FIG. 2 , is the same or nearly the same, and this dimensioning may carry forward as being the same or nearly the same as between different banks that have negative slopes with respect to one another. However, it is worth noting that banks having varying dimensioning, with respect the banks and within the banks, are envisaged.  
         [0015]     The desired effect at a single fin  10  is in part illustrated in  FIG. 2 . Air that comes in over edge  30  is shown entering in part by arrow  42 . After engaging the louvers, it flows through them and toward the region labeled bottom where it can mix with entering air (arrow  44 ) coming in below fin  10 . Some of the air stream  42  continues parallel to fin  10  as indicated by arrow  46 . Eventually a portion of stream  44  that originated below fin  10  and parts of stream  42  directed below fin  10  engage the louvers in bank  38  and go back up above fin  10  (as indicated by arrow  48 ) now in general alignment with the cooling tubes (not shown) in openings  12 - 18 . While flow around a single fin  10  is illustrated, those skilled in the art will appreciate that there are a plurality of fins like  10  above and below it whose spacing can be optimized to alter the tip to tip gap of louvers of adjacent fins thus regulating how big a portion of the incoming stream to a particular fin can pass straight through in the direction of arrow  44 . Moreover, the width of the aperture defined by each louver or the width of each louver itself may be varied or maintained constant. Additionally, flow through the louvers from above represented by arrow  42  goes below the fin to make turbulent flow with the stream trying to get past under the louvers in bank  36 . Similarly, any flow represented by arrow  46  has to mix with flow passing down through louvers in the next fin above fin  10 . Thereafter as zone  50  is crossed, stream  46  encounters stream  48  coming up from below fin  10  for further mixing. These effects are repeated as between the pairs of adjacent fins  10 . Spacers  5 , which extend from the fin  10  surface to facilitate spacing of adjacent fins, can be optionally used in zone  50 , for example. (See  FIG. 1 .) With respect to the orientation of  FIG. 2 , the first bank of louvers  36  are said to have a positive slope, while the second bank of louvers  38  have a negative slope, with the fin  10  defining the X-axis and with the Y-axis extending through a location between the first and second banks of louvers.  
         [0016]      FIGS. 3 and 4  represent an alternative embodiment that in most ways is the same as  FIGS. 1 and 2 . One difference can be seen in banks  36 ′ and  38 ′. Starting from edge  30 ′, breaks  52  and  54  are illustrated as converging away from edge  30 ′, in effect creating shorter louvers measured in a direction perpendicular to the incoming air as indicated by arrow  42 ′. In the same bank  36 ′ two more breaks  56  and  58  diverge in the direction of incoming air shown by arrow  42 ′. Bank  38 ′ can have the same treatment but offset from bank  36 ′ due to the layout of the cooling tubes. Using shorter widths of leading and trailing louvers in a given bank tends to make such louvers stiffer and distort less when subjected to air flow conditions. An alternative is shown in  FIG. 6  where a break  59  is aligned with the direction of air flow and with the tube in the bank behind it passing through, for example opening  16 . Bank  38  can also have such breaks such as  61  that align with an opening such as  22  that is in front of it. Indeed, a variety of configurations for the breaks, such as convergence and divergence and angles therefor, are envisaged. Furthermore, FIG.  4  shows that openings such as  12 ′ and  20 ′ have raised flanges  60  and  62 . Flanges  60  and  62  also act to maintain a predetermined distance between parallel fins. Optionally, spacers  64  shown in  FIG. 3  and disposed between rows of holes can also be used to maintain the separation distance between fins  10 . Referring to  FIG. 5 , a section through raised opening  66  is shown. It has a flange  68  spaced from and generally parallel to the plane of fin  10 . A protrusion  70  is in or near the plane of the fin  10  and prevents warping of the fin  10  when a tube (not shown) is expanded into sealing contact with an opening such as  12 .  
         [0017]     Those skilled in the art will appreciate that changes can be made in the optimization process. What is optimized is a collection of variables that relate to cost, pressure drop, overall size and thermal performance. Commonality of patterns such as louver dimensions and angles saves cost; hence the preferred embodiment emphasizes such patterns. In the present invention the mixing of the air stream in an over, under and back to over pattern helps the thermal performance. Using planar fins saves cost. Spreading out the over, under and over pattern through two or more rows of tubes also promotes thermal performance and saves cost. The  FIG. 3  and  6  designs add strength to some of the louvers and reduce distortion from flexing or vibration from air flow and to some extent reduces pressure drop of the air.  
         [0018]     Again, the above description is illustrative of exemplary embodiments, and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.