Abstract:
Heat exchanger assemblies of increased strength are provided having louvered fins that achieve both high thermal efficiency and high strength simultaneously. 
     By providing for a three-piece louvered fin, tube-fin heat exchangers having at least one three-piece single louver block, and, in particular, a streamlined inclined three-piece single louver block, exhibit fins with superior characteristics and overall strength for heat exchanger assembly of louvered fin design, with reduced areas or zones of boundary layer air.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to heat exchangers having tubes and fins, and, particularly, automotive heat exchangers with fins having louvers. 
       BACKGROUND OF THE INVENTION 
       [0002]    Automotive heat exchangers used is applications such as engine cooling, air conditioning and the like, are of various types. Examples of such heat exchangers are the so called plate-fin types and tube-fin types, depending on the conduits and principle heat exchanger areas of the exchangers. 
         [0003]    Tube-fin type heat exchangers are the most common. This is due mainly because of their relatively high thermal efficiency, and mass manufacturing friendly design. A tube-fin type heat exchanger, for example, uses a heat carrying liquid (water for radiator, and R 134   a  for condenser, CO 2  for gas cooler for example), which can transmit or transfer heat to the tubes, and the tubes, subsequently, can transmit or transfer such heat either by directly (rejecting or otherwise dispersing or dissipating) heat to air, or transferring heat to fins, and having the heat then dissipated into the air. 
         [0004]    Heat exchanger fins, and, particularly those used in automotive heat exchange applications, often have features, such as louvers, to increase thermal performance. Air has a low thermal conductivity, meaning that when fins are exposed to air, the air side of the fin has a thermal resistance which is a major contributor to the total thermal resistance of the heat exchanger. 
         [0005]    Air is presented to the heat exchanger, typically at a certain air speed, due to movement of the vehicle and/or fans that cause air to pass by or through the heat exchanger elements. A typical air speed range (1 m/s to 5 m/s) is often found at the areas of contact of air and heat exchanger in automotive engine cooling or air conditioning applications, especially when measured near the fin surface. At the fin surface a so called the air speed and/or air temperature “boundary layer, is formed close to the area of the fin louvers. This layer is a temperature and/or air speed area, due to “air temperature” and/or “air speed”, that results in a boundary layer of lower heat transfer at the area of the surface of the fin. Such a boundary layer of air, therefore, results in a low thermal efficiency overall for the heat exchanger due to this boundary layer effect. 
         [0006]    In order to attempt to overcome the boundary layer effect, a louvered fin design is widely used, as shown in the  FIG. 1 . Each louver tries to break-up the air boundary layer, and, thereby allow better heat exchanger with the moving air, and, thus, increase thermal efficiency. 
         [0007]    But louvered fins, (as opposed to “plain” or “unlouvered” fins), do present drawbacks. For example, the louver in the fin has led to lower strength in the fin column direction of the fin, particular in the louvered area. The column strength of the fin is the strength of the fin against compression in the fin height direction ( FIG. 3 ). This can be important because the column strength of the fin. A strong fin is important during the tube/fin assembly process. 
         [0008]    This drawback becomes even more important when the fin gauge is reduced. For example, in prior art fins the fin gauge was often greater than or equal to 0.16 mm. Fin gauge for present applications are often found in much lower ranges under 0.16 m, even under 0.12 mm. 
         [0009]    One solution to these problems has been to use special high-strength material in louvered fin design. 
       SUMMARY OF THE INVENTION 
       [0010]    A tube-fin automotive heat exchanger, in aspects of the present invention, have at least one first end tank and at least one second end tank opposite the at least one first end tank, wherein one end of the plurality of tubes is attached to and in fluid communication with the one first end tank and wherein the other end of the plurality of tubes is attached to and in fluid communication with the at least one second end tank. 
         [0011]    Various aspects of the present invention propose solutions for prior art problems which improve the strength of the heat exchanger assembly by providing for louvered fins that achieve both high thermal efficiency and high strength simultaneously. By providing for a louvered fin, tube-fin heat exchanger having at least one three-piece single louver, various aspects of the present invention provide for fins with superior characteristics of louvered fin, with reduced areas or zones of boundary layer air, than that of prior art fin designs. 
         [0012]    Various aspects of the present invention, therefore, provide advantages such as increased column strength of louvered fins under compression and design flexibility to put fin strength where it is needed, in spite of the use of louvers with little or no negative impact to the air flow that flows over and around the fin louvers. In addition, these advantages can be obtained at no additional cost of that of louvered fins without the three-piece single louver feature. 
         [0013]    As described herein, the at least one three-piece single louver has a flat area that increases column strength of fins under compression. Looking at the fin height from the fin top to fin bottom, it appears to have a continuous structure in the flat area. In aspects of the present invention, three-piece single louvers with flat areas reduce the total space available for non three-piece louvers. It is therefore clear that location of the three-piece single louver or louvers in the appropriate plane leads to a level of optimization of both fin strength and effectiveness, especially when the flat area of the three-piece single louver is 2 mm or less in width. 
         [0014]    As used herein, ‘half louver section’ and ‘half louver’, as they relate to the three-piece single louver, are used interchangeably. Likewise, as it relates to the three-piece single louver, ‘flat area’ or ‘flat area section’ or ‘flat area louver’ may be used interchangeably. 
         [0015]    In various aspects of the present invention, the at least one three-piece single louver is present on a fin, along with at least one non three-piece louver. The three-piece single piece and non three-piece louver or louvers form part of a block of louvers. At least two blocks of louvers form a part of the set of louvers that are present as a fin system in the heat exchanger. Preferably, the two blocks of louvers are symmetric, as shown in  FIG. 3  (A - - - A is center line of symmetry). 
         [0016]    The ratio of the average flat area length of the three-piece single louver(s) to the average width of the non three-piece louvers is between about 0.10 and 0.90. Particularly increased strength has been found when the ratio is between about 0.30 and 0.70; and highly increased strength when the ratio is between 0.40 and 0.60. In various aspects of the present invention, at least one block of louvers has a plurality of three-piece single louvers and non three-piece louvers along the fin, wherein the flat area sections of the three-piece single louvers have an average ratio of width of flat area sections to width of non three-piece louvers of between about 0.10 and 0.90. 
         [0017]    The flat area section is in the same plane as fin central plan. The inclination of the two half louver sections is usually identical on opposite sides of the ends of the flat area. 
         [0018]    In various aspects of the present invention, the angle off from the plane of the flat area of the three-piece single louver of the half louver (the inclination) is of a specific orientation. For example, inclination of the two half louver sections within the three-piece single louver is or can be at the same or at a similar angle as non three-piece louvers to a plane. In various aspects, the inclination of the two half louver sections are such that they are at angles similar to at least one, and preferably, to a plurality of non three-piece single louvers within the same louver set. By same louver set it is meant several louvers having almost the same louver angle/inclination. Also, by symmetrical louver block it is meant a group of two or more louvers sets having inclinations in opposing direction to one another (for example, the reverse louvers as in  FIG. 1 , louvers angles in the left block of the fin (see left area left of A - - - A) are almost opposite to those in the right block on the fin (area right of A - - - A)). In various aspects of the present invention, the at least two blocks of louvers are symmetrics, the blocks are symmetric around an axis (perpendicular) to the width of the fin. 
         [0019]    The average width of the two half louver sections of the three-piece single louver is ½ of the average width of the non three-piece louvers. 
         [0020]    This fin louver design can be applicable for wide range of fin width (or core depth), for example, ranging from 8 mm to 70 mm as shown by w in  FIG. 1 . 
         [0021]    The inclination of the two half louver sections within the three-piece single louver can be slightly different from the inclination of other non three-piece louvers. In this case, the relative difference should be less than ⅓. More specifically, the inclination of the two half louver sections should be within the range of a α±⅓α, where α (alpha) is the average inclination of non-three piece louvers (see  FIG. 4 ). 
         [0022]    The width of the two half louver could be slightly different from ½ of width of a non three-piece louver. However, their relative difference is normally less than about ⅓. 
         [0023]    In various aspects of the present invention, a plurality of the louvers in at least one block of louvers have an angle (alpha) with a center plane axis of the length of the fin that is similar or identical with each other within that block. 
         [0024]    In various aspects, all or essentially all of the louvers in each block have angles (alpha) with the center plane axis of the length of the fin that are similar or identical with each other within each respective block. 
         [0025]    The gauge of material used as fin stock, and, eventually provided for in the fins, various. Various aspects of the present invention provide for use of fins and/or use of fin stock in gauges of less than 0.10 mm (thin gauge fin). Other aspects of the present invention provide for fin stock and fins in ranges from about 0.05 mm-0.10 mm, other aspects in ranges of from about 0.07 mm-0.10 mm. 
         [0026]    In various aspects of the present invention, a three-piece single louver is provided as part of a thin gauge fin. The three-piece single louver comprises two half louver sections, connected by a central flat area section. Various aspects of the present invention have two half louver sections with orientations relative to the plane of the flat area that are in opposite, that is to say, pointing upward or downward at approximately the same α, in the orientation of the plane B - - - B streamlined inclined three-piece single louver SITSL (see  FIG. 4 ). In particular, various aspects of the present invention provide for a “streamlined inclined three-piece single louver”, wherein the louver comprises two half louver section that are at approximately or at the same angle, but on opposite sides, of the plane of the flat area of the louver, i.e. allows air flow to continue in the same general direction (streamlined with air stream) in that block. 
         [0027]    As described herein in various aspects of the present invention, folded tubes and fins are present. In various aspects having a plurality of tubes, at least two of the plurality of tubes are folded tubes in a row that have a joint at the fold area and the at least one block of louvers is located adjacent to or immediately across from, the area of the joint location of the folded tube. Also, in various aspects of the present invention having a plurality of tubes, at least two of the plurality of tubes are folded tubes in a row that have a joint at the fold area and the at least one block of louvers is located adjacent to or immediately across from, the area of the joint location of the folded tube. 
         [0028]    Various aspects of the present invention provide for a fin system for a heat exchanger having louvers to enhance transfer of heat from a first medium to a second medium, comprising at least two blocks of louvers, each block having at least one set of louvers per block, and each block having at least one set of louvers having at least one three piece single louver and at least one non three-piece louver. In other aspects, at least one block of louvers comprises a plurality of non three-piece louvers and a plurality of three-piece single louvers, and wherein the average length of the non-three piece louvers is approximately equal to the average length of the three-piece single louvers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a schematic representation of a prior art louvered fin design used in automotive heat exchangers. 
           [0030]      FIG. 2  is a schematic representation of an automotive louvered fin design wherein boundary layer air formation is broken up in four directions by louver using a non-streamlined inclined louver. 
           [0031]      FIG. 3  is a schematic representation as seen from above showing a prior art louvered fin design under compression during tube fin assembly, and used in automotive heat exchanger applications. 
           [0032]      FIGS. 4   a  and  4   b  are schematic representations of a fin having streamlined inclined three-piece single louver design, showing louver angle a, in accordance with an aspect of the present invention. 
           [0033]      FIG. 5  is a schematic cross sectional representation from above of a fin and tube arrangement having an automotive louvered fin and two rows of folded tube, with three-piece louver block facing a joint of the folded tube, in accordance with an aspect of the present invention. 
           [0034]      FIG. 6  shows an automotive tube-fin heat exchanger, having fins with louvers, in accordance with an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]      FIG. 1  illustrates a prior art fin ( 11 ) having louvers ( 12 ,  14 ) in a pattern symmetrical around line A - - - A and oriented in a column Axis (A - - - A) represents fin length direction. M represents air flow through one block of non three-piece louver. N represents air flow through another block of non three-piece louver. Q represents air flow at reversal louver. Breaking louver ( 14 ), non three-piece louver ( 12 ) and reversal louver wings ( 13 ) are shown. 
         [0036]      FIG. 2  shows a fin design in which a non-streamlined inclined three-piece single louver ( 25 ) is a reversal louver and has two half louvers ( 24 ) and connected by a flat area. In this design, the two downward facing half louvers are along/with similar angles (α), having two opposite directions, therefore forcing air (F) to change flow directions, resulting in additional air side pressure drop. 
         [0037]      FIG. 3  illustrates a second louvered fin ( 31 ) having louver blocks ( 32   a ) ( 32   b ) arranged around a central axis (A - - - A), B - - - B being the line of fin length direction. Arrows (X and Y) illustrates force of compression from tubes on fin end radius area, with louvers breaking structure integrity causing reduced fin column strength in the X-Y orientation. Blocks of louvers ( 32   a ) ( 32   b ) of fin ( 31 ) could be weakened by compression. 
         [0038]    In various aspects of the present invention, a tube-fin automotive heat exchanger comprising: a plurality of tubes running basically parallel to one another; a plurality of fins having at least one block of louvers, the plurality of fins running between the tubes and being basically coplanar relative to the tubes; at least one end tank connected to the tubes is provided. 
         [0039]    In various aspects of the present invention, the block of louvers comprises a set of louvers having at least one three-piece single louver having two half louver sections and one flat area louver section. 
         [0040]      FIG. 4  illustrates a fin ( 40 ) having a louvers ( 46 - 49 ), oriented in a pattern. The streamlined inclined three-piece single louver ( 44 ) is found in a zig-zag shape oriented such that two half louvers ( 48   a ,  48   b ) have almost the same inclination as other louvers ( 46 ,  49 ). Fin ( 40 ) has two symmetric blocks of louvers, only one is shown on the left of A - - - A in this figure. Each block has breaking louvers ( 46 ), streamlined inclined three-piece single louvers ( 44 ), regular louvers ( 49 ) and reversal louvers may be present. The “streamlined inclined” three-piece louver ( 44 ) has at least one flat area ( 47 ).  FIG. 4   b  illustrates angle a of one of the louvers of  FIG. 4   a.    
         [0041]    As also illustrated on  FIGS. 4 and 5 , the streamlined inclined three-piece single louver ( 44 ,  57 ), therefore, consists of three parts: two half louvers ( 48   a ,  48   b ) ( 58   a ,  58   b ) connected by a flat area ( 47 ) ( 57 ). The two half louvers ( 48   a ,  489   b ) ( 58   a ,  58   b ) incline in the same direction. That is to say that the two half louver sections (sometime referred to as ‘half louvers’) exist relative to plane B - - - B, such that half louver ( 48   a ) ( 58   a ) is on one side of the plane B and half louver ( 48   b ) ( 58   b ) is on the other side of plane B - - - B. The two half louvers are connected to or touching or integral to each other via a flat connecting area, and particularly, the two half louvers are found, one on each flat area end section. 
         [0042]    Preferably, the three parts of the “streamlined inclined” single louvers (two half louvers or louvers pieces and flat area louver or louver piece) are structurally integral or form one unity. In various aspects of the present invention, the α of the half louver at the end of the flat areas is between about 5° to 48 degrees, as measured from the plane of the flat area louver section. The width of the flat area louver section is greater than zero. The ratio of flat louver piece width to width of the half louver in various aspects of the present invention is approximately between 0.2 to 1.8. 
         [0043]    The streamlined inclined three-piece single louver comprises, therefore, two non-flat or half louvers and at least one flat area section The flat area (louver) section lies in a plane that follows B - - - B. By having a flat area between two half louvers, the column strength of fin is significantly increased, particularly under compression, and in particular if the compression is mainly concentrated near the flat area louver section. 
         [0044]      FIG. 5  illustrates a portion of a tube fin heat exchanger ( 55 ) comprising two rows of folded tube ( 56   a ) ( 56   b ), and tube joint areas (J) and (J′). Tube joint areas are typically highly compressed in order to obtain good braze of folded tube joint. Streamlined inclined integral three-piece single louver in block ( 54 ) is formed or placed such that flat area ( 57 ) of the streamlined inclined three-piece single louver faces folded tube joint (J, J′), enhancing the resistance of the tube joint to compression. 
         [0045]    Fins comprising at least one “streamlined inclined” three-piece single louver, in various aspects of the present invention, are designed such that the fin height at location of the streamlined inclined three-piece single louver or louvers is higher than other parts of the fin in order to ensure the streamlined inclined three-piece single louver portion bears the compression force during the tube/fin assembly. 
         [0046]    The streamlined inclined three-piece single louver found in various aspects of the present invention, comprises two half louvers having the same or almost identical inclination, relative to the plane of the flat area louver (see B - - - B of figures). Due to this orientation, air can flow through the three-piece single louver with little or no disturbance on its air flow. Therefore, the boundary layer, normally present at the area of the louvers, is reduced and, in general, at start of each louver, the thickness of boundary layer restarts from zero. 
         [0047]      FIG. 6   a  shows a heat exchanger ( 60 ) comprising tubes ( 66 ) and louvered fins ( 61 ).  FIG. 6   s  shows tubes ( 66 ) and the louvered fins ( 61 ) comprising a group of non three-piece (not shown) and integral “streamlined inclined” three-piece louver fins ( 62 ). The “streamlined inclined” three-piece louver ( 62 ) faces the folded tube joint (J), leading to increased column compression strength of fins. First and second tanks ( 69 ,  70 ) and connected to and in fluid communication with a plurality of tubes ( 66 ). 
         [0048]    Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. Plural structural components can be provided by a single integrated structure. Alternatively, a single integrated structure might be divided into separate plural components. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. 
         [0049]    The preferred embodiment of the present invention has been disclosed. A person of ordinary skills in the art would realize, however, that certain modifications will come within the teachings of this invention. Therefore, the following claims should be studied to determine the true scope and content of the invention