Abstract:
A method of installing a baffle ( 46 ) in a tubular header ( 10 ), ( 12 ) for a heat exchanger includes the steps of a) providing a concavo-convex baffle ( 60 ) with a periphery smaller than the internal periphery of the header ( 10 ), ( 12 ); b) locating the baffle ( 60 ) at a desired location within the header ( 10 ), ( 12 ); and c) applying a compressive force ( 102 ), ( 110 ) to the baffle ( 60 ) to compress the baffle toward a planar shape.

Description:
This is a division of application Ser. No. 08/503,989 filed Jul. 19, 1995, now U.S. Pat. No. 5,799,396. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to heat exchangers, and more particularly, to baffles employed in heat exchangers. 
     BACKGROUND OF THE INVENTION 
     Recent years have seen an explosion in the popularity of so-called “parallel flow” heat exchangers. One typical construction is illustrated in U.S. Pat. No. 4,688,311 issued Aug. 25, 1987 to Saperstein, et al. 
     Heat exchangers of this sort have been employed in a variety of applications including condensers and evaporators in air conditioning and refrigerating systems and in oil coolers which are employed to cool lubricating oil or hydraulic fluid, particularly in vehicular applications. Indeed, there is suggestion in the prior art that parallel flow heat exchangers even be employed as radiators for cooling engine coolant in vehicles. 
     Modern day parallel flow heat exchangers are typically made of aluminum and employ two spaced tubular headers. Flattened tubes extend between and are in fluid communication with the interiors of the headers. Serpentine fins are located between the flattened tubes. 
     Conventionally, aluminum is the material of choice and the result is a compact, lightweight heat exchanger which operates with exceptional efficiency particularly when the hydraulic diameter of the fluid passageways within the flattened tubes is 0.070″ or less. 
     In many applications, it is desired that the fluid contained within the heat exchanger make more than one pass through the heat exchanger across the cooling air path in which the heat exchanger is disposed. To achieve this, it is conventional to locate one or more baffles in one or both of the headers to achieve as many passes as is desired. 
     Typically, the baffles have been plate-like inserts that are disposed in slits in the headers. To seal the slits as well as the point of contact of the baffle with the interior of the header, when the materials employed are aluminum reliance is made on the flow of braze alloy to seal any voids. The use of slits in the headers may tend to weaken the headers and, in some instances, may result in a significant number of leaky headers being formed as a result of fluid pressure within the headers that result from the application of heat to the heat exchanger during the brazing process. 
     In other cases, cap-like baffles have been inserted endwise into the headers to the desired location and then brazed in place. While such baffles usually are quite leak free, this method of installation does not lend itself to use with a header whose interior cross section may vary. 
     U.S. Pat. No. 4,615,385 issued Oct. 7, 1986 to Saperstein, et al., there is disclosed a unique header for heat exchangers of this type. To provide improved strength in the resulting heat exchanger, each header is formed of a generally cylindrical tube with a series of tube slots formed in one side thereof. Between each tube slot, a dome is formed, which dome is in the shape of a compound curve. Because of the use of the domes between adjacent tube slots, stresses at the tube to header joints in the resulting heat exchangers are considerably reduced and a much stronger heat exchanger results. 
     However, because of the use of the domes, the cross section of the header is relatively large where each dome is formed and is relatively smaller where each tube slot is formed. As a consequence, it has heretofore been impossible to provide such headers with baffles that are inserted endwise into the headers. 
     The present invention is directed to overcoming one or more of the above problems. 
     SUMMARY OF THE INVENTION 
     It is the principal object of the invention to provide a new and improved method of providing a header with an interior baffle. More specifically, it is an object of the invention to provide a new and improved method of installing a baffle in a tubular header. 
     It is also an object of the invention to provide a heat exchanger that includes a header provided with a baffle in accordance with the process or method of the invention. 
     Still another object of the invention is to provide a novel baffle preform that may be used in practicing the method of the invention. 
     An exemplary embodiment of a method of installing a baffle in a tubular header for a heat exchanger includes the steps of: (a) providing a baffle with a concave side periphery smaller than the internal periphery of the header; (b) locating the baffle at a desired location within the header; and (c) applying a compressive force to the baffle to compress the baffle toward a planar shape. 
     As a result of the foregoing, the baffle expands peripherally within the header to engage the interior of the header whereat it may be secured and sealed as, for example, but not necessarily, by brazing. 
     In one embodiment of the method, the baffle is concavo-convex has a generally circular periphery and includes a generally central convex dome surrounded by a peripheral, radially outward directed skirt. 
     In a highly preferred embodiment of the invention, both the header and the baffle are aluminum and the baffle is braze clad on both sides thereof. 
     In one embodiment of the invention, step (b) is performed by placing the header over a spindle and abutting it against a stop and then placing the baffle within the header in abutment with the spindle. 
     In one embodiment of the invention, step (c) is performed by placing a second spindle within the header after the performance of step (b) and moving the second spindle against the baffle and towards the first-named spindle. 
     In one embodiment of the invention, step (b) is preceded by the step of sizing the interior of the header at the desired location of the baffle. 
     Preferably, the step of sizing is performed by locating an expandable mandrel within the header at the desired location and expanding the mandrel into the header at the desired location. 
     In a highly preferred embodiment of the invention, the expandable mandrel is a split mandrel and the step of expanding the expandable mandrel is performed by moving a wedge into the split mandrel. 
     In one embodiment of the invention, there is provided a heat exchanger that includes a header with a baffle therein and which is made according to the process described above. 
     According to another facet of the invention, a baffle preform is provided for use in the manufacture of a heat exchanger with a baffled, tubular header. The baffle preform comprises a metallic slug having a convex side and an opposite concave side. The slug is circular and has a generally semi-spherical dome of smaller diameter than the slug on one side thereof and a radially outward directed skirt extending from the base of the dome to the periphery of the slug. 
     Preferably, the skirt is frustoconical. 
     In a highly preferred embodiment, the minor base of the skirt merges into the base of the dome and the skirt also extends axially away from the dome. 
     Preferably, the slug is formed of aluminum sheet and is braze clad on both sides thereof. 
     The invention also contemplates a method of making a heat exchanger header with an internal baffle which comprises the steps of (a) providing a tubular header of generally cylindrical shape and having a series of tube receiving slots at one side thereof which are separated by domes shaped as compound curves, the cross section of the header being relatively larger at the domes and relatively smaller at the tube slots; (b) providing a concave baffle of a generally circular periphery, and of a diameter sufficiently small so as to be received in the header and located therein generally transverse thereto at the relatively larger cross section and of a diameter larger than the relatively small cross section; (c) locating the baffle within the header at a desired one of the domes; (d) causing the baffle to be generally transverse to the header; and (e) collapsing the baffle to a generally planar configuration at the desired one of the domes. 
     Preferably, step (e) is performed by relatively moving mandrels on opposite sides of the baffle towards each other. 
     Preferably, step (b) is performed by providing a baffle of sheet-like material having a dome surrounded by a generally radially outward directed skirt. 
     In this embodiment, the dome is generally semispherical and preferably, the skirt is generally frustoconical. 
     Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially exploded view of a heat exchanger, specifically, a condenser, made according to the invention, that may embody a header with an internal baffle made according to the invention; 
     FIG. 2 is an enlarged, fragmentary, sectional view of a header with a baffle installed therein and made according to the invention; 
     FIG. 3 is a side elevation of a baffle preform used in the invention; 
     FIG. 4 is a plan view of the baffle preform; 
     FIG. 5 is a block diagram of a method of manufacturing a heat exchanger, including a header with an internal baffle, according to the invention; 
     FIG. 6 is a fragmentary sectional view of an optional step performed in the method of the invention; 
     FIG. 7 is a view similar to FIG. 6 but illustrating another step in the performance of the invention; and 
     FIG. 8 illustrates the cross section of a spindle used in performing the step illustrated in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary embodiment of the invention is illustrated in the drawings in connection with a heat exchanger that will be recognized to be a condenser by those skilled in the art. However, it is to be expressly understood that the invention&#39;s applicability extends beyond condensers and may be employed in any type of heat exchanger utilizing tubular headers, including but not limited to, evaporators and oil coolers. 
     Referring to FIG. 1, a parallel flow condenser with which the invention may be used is seen to include spaced, generally parallel headers  10  and  12 . The headers  10  and  12  are preferably made up from generally cylindrical tubing. On their facing sides, they are provided with a series of generally parallel slots or openings  14  for the receipt of corresponding ends  16  and  18  of flattened condenser tubes  20 . The header tubes  10  and  12  are preferably welded and thus include a weld seam as shown at  19  in connection with the header tube  12 . 
     The slots  14  are punched on the facing sides of the headers  10  and  12 . The slots  14  are, of course, elongated and their direction of elongation is transverse to the direction of elongation of the headers  10  and  12 . 
     Preferably, between the slots  14 , in the area shown at  22 , each of the headers  10  and  12  is provided with a somewhat spherical dome to improve resistance to pressure as is more fully described in commonly assigned U.S. Pat. No. 4,615,385 mentioned previously. 
     The header  10  has one end closed by a cap  24  brazed or welded thereto. In the preferred embodiment of the invention, the various components are all formed of aluminum and are all brazed together and accordingly, in the usual case, brazing will be the means employed to fasten the cap  24  to the header  10 . Similarly, fittings such as the fitting  26  are brazed to other components and a tube  28  may be connected to the fitting  26  to define an outlet for the condenser. 
     The lower end of the header  12  is closed by a cap  30 , preferably brazed in place similarly to the cap  24 , while the upper end of the welder  12  is provided with a welded or brazed in place fitting  32 . Typically, the fitting  32  will serve as an inlet although flow direction may be reversed in some instances. 
     A plurality of the tubes  20  extend between the headers  10  and  12  and are in fluid communication therewith. The tubes are geometrically in parallel with each other and hydraulically in parallel as well. Disposed between adjacent ones of the tubes  20  are serpentine fins  34  although plate fins could be used if desired. Upper and lower side channels  36  and  38  extend between the headers  10  and  12  to provide rigidity to the system. Each end of each of the channels  36  and  38  include an outturned flange  39  of which is adapted to be bonded to the adjacent header  10  or  12 . 
     As can be seen in FIG. 1, each of the tube  20  is a flattened tube and within its interior includes an undulating spacer or insert of elongate construction. In cross-section, the insert appears as more fully disclosed in previously identified U.S. Pat. No. 4,688,311. However, it should be understood that multi-passage, extruded tubes may be used as well. 
     Those skilled in the art will appreciated from the foregoing description that a single pass parallel flow heat exchanger has been described. As noted previously, however, in some instances, it is desirable that there be multiple passes. In such a case, one or more baffles are placed in one or the other or both of the header tubes  10  and  12 . 
     Turning to FIG. 2, the header  10  is illustrated although it should be understood that what is there illustrated is equally applicable to the header  12 . 
     More specifically, the tube slots  20  are illustrated as receiving the ends  16  of the tubes  14 . The domes  22  between each of the flattened tubes  14  are illustrated and it will be appreciated that in a section taken parallel to the direction of elongation of the header  10 , the domes  22  are curved. 
     It will be appreciated that because the headers  10  are generally cylindrical, the domes  22  will also have a curved appearance in a section taken through anyone of the domes  22  transverse to the header  10 . Thus, the domes  22  are formed of compound curves and as can be seen in FIG. 2, this results in the header having a relatively larger cross-section  42  at each of the domes  22  and a relatively smaller cross-section  44  at each of the tube slots  20 . 
     It will also be appreciated that since the tube slots  20  and the domes  22  are located on only one side of each header, that at least a part of the header will retain an interior cylindrical shape over an arc length in excess of 180°. 
     A baffle  46  is disposed within the header  10  at a desired location at the center of a desired one of the domes  22  and is oriented so as to be transverse to the direction of elongation of the header  10 . The same is brazed in place during the assembly of the heat exchanger. 
     As illustrated in FIG. 2, the baffle  46  is generally planar although the same will typically have a small shallow recess  48  on one side thereof and a relatively larger, shallow raised area  50  oppositely of the shallow recess  48 . In many instances, adjacent the dome  22 , the baffle  46  will have a slight angular offset as shown at  52 . 
     The baffle  46  is formed of a preform such as that illustrated in FIGS. 3 and 4. The preform is basically a circular slug  60  having a semispherical dome  62  at one side thereof. The base  64  of the dome  62  merges with the minor base of a frustoconical skirt  66 . The arrangement is such that the preform slug  60  is convex on its left side as illustrated in FIG.  3  and concave on its right side, i.e., concavo-convex. 
     The slug  60  may be formed by taking a circular piece of sheet aluminum braze clad on both sides, and pressing the same down on a ball bearing whose diameter is equal to that of the semi-spherical dome  62  on the interior surface  68  thereof. 
     The height of the slug is designated “H” as seen in FIG. 3 while the diameter is shown as “D”, also in FIG.  3 . In general, the ratio of “D” to “H” will be 2:1 or greater. 
     The following table illustrates parameters that may be used in forming baffles for use in standard aluminum tubing employed as headers in heat exchangers. One material that may be used in making the baffles is Number  12  braze sheet 0.062″ thick 3003-0 aluminum sheet clad with 4343 on both sides. All dimensions are given in inches unless otherwise indicated. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 BAFFLE 
                   
                   
               
               
                   
                 HEADER 
                 DIAMETER 
                 BALL FORMING 
                 DOME HEIGHT 
               
               
                   
                 SIZE 
                 (D) 
                 DIAMETER 
                 (H) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 .688 
                 .562 
                 .250 
                 .222 
               
               
                 2. 
                 .875 
                 .750 
                 .312 
                 .290 
               
               
                 3. 
                 25 mm 
                 .875 
                 .375 
                 .318 
               
               
                 4. 
                 1.25 
                 1.125 
                 .500 
                 .325 
               
               
                   
               
             
          
         
       
     
     Turning now to FIG. 5, the steps in the method of manufacture of a heat exchanger are shown. A first step is the formation of a header with tube slots and domes and is shown at block  70 . This step amounts to making the headers  10  and  12  as disclosed in the previously identified U.S. Pat. No. 4,615,385. 
     After the header is formed, it is optionally placed on an expanding mandrel as shown at block  71  and the mandrel expanded to size the header as shown at block  72 . The steps shown at block  71  and  72  are optional and depend upon the ability to hold tolerances in formation of the header. The manner in which the step shown at block  71  and  72  is accomplished is illustrated in FIG.  6 . As seen, a mandrel  80  is located on a stop surface  82 . A formed header such as the header  10  is located over the mandrel  80 . 
     At its upper end, the mandrel  80  has a split shown at  84  and is formed of relatively resilient material. A generally circular bead  86  is formed on one leg  88  of the split mandrel while a similar bead  90  is formed on the other leg  92  of the split mandrel  80 . The beads have nominally the same radius as the inside diameter of the header  10  but when the same come together, they are sufficiently close to one another so that they may readily pass into the header  10  in spite of the presence of the relatively smaller cross-sectional sections  44  (FIG.  2 ). 
     The length of the mandrel  80  in relation to the stop surface  82  is such that the beads  86  and  90  will be positioned at the center point of a selected dome  22  where the baffle is to eventually be located. A wedge-like element  94  is moved from the opposite end of the header  10  between the legs  88  and  92  of the split mandrel  80  to drive the beads  86  and  90  into engagement with the dome  22  and the opposite part of the wall of the header  10 . The resulting sizing of the interior of the selected dome  22  is dependent upon the degree of incursion of the wedge-like element  94  into the mandrel  80  which, in turn, is chosen to obtain the desired, cross-sectional shape at the location, which cross-sectional shape is made uniform from one header  10  to the next as a result of the sizing operation. 
     It will of course be appreciated that if tolerances can be held during the manufacture of the headers  10 , then there is no need to perform the steps shown at block  70  and  72  in FIG.  5 . In such a case, the method may proceed directly to a block  100  which represents the step of placing the header  10  on a fixed mandrel or spindle  102  against step surface  103 . As shown in FIG. 7, the fixed mandrel  102  has an upper surface  104  that is located 0.031″ (half the thickness of the sheet of which the preform  60  is made) below the mid-point of the selected dome  22  in relation to the stop surface  103 . This distance is chosen for an aluminum sheet thickness of 0.062″ that is used in making the preform  60  as mentioned previously. 
     The preform  60  may be introduced sidewise into the header and then turned to be transverse to the direction of elongation of the header  10 , resting upon the upper surface  104  with the dome  62  uppermost. 
     This step is shown at block  102  in FIG.  5  and the resulting orientation of the components is apparent in FIG.  7 . 
     The baffle is then expanded by compressing the same towards a planar configuration. That is to say, the preform  60  is collapsed and this is accomplished through the application of a compressive force by a movable spindle or mandrel  110  which is moved downwardly within the header  10  into engagement with the dome  62 . Once this step is finished, the preform  60  will appear as the baffle  46  shown in FIG.  2 . 
     To facilitate the compressive process, the spindles and/or mandrels  102 ,  110  are generally cylindrical, having a shape that is closely approximate to the inner peripheral configuration of the header  10  or  12 . The same is also provided with a flat  112  (FIG. 8) on one surface thereof so as to allow for clearance at the relatively smaller cross-sections adjacent the tube slots  20 . 
     The step of expanding the baffle is shown in FIG. 5 at the block  114  and following the performance of that step, the header  10  is removed from the mandrel as shown at a block  116 . 
     The header  10  is then moved to a sensing station where a determination is made as to whether the baffle is in fact in place. This is shown at a block  118  and can simply be as simple as placing a light source at one end of the header  10  and a photosensitive device at the opposite end. 
     Assuming that the presence of a baffle has been sensed at the step represented by the block  118 , an identifying mark is placed on the header as shown at step  120  to facilitate subsequent inspection. Following the marking of the header, brazing flux, such as a potassium fluoaluminate flux used in the so-called Nocolok™ brazing process, is introduced to the side of the baffle  46  that originally was the dome side. This is shown at a block  122 . 
     The components are then assembled to the configuration generally illustrated in FIG.  1  and held in place by a suitable fixture as is well known. This is represented by the block  124 . The fixture is then placed in a brazing furnace and the components brazed together as shown by a block  126 . 
     The resulting assembly may then be tested, packaged and shipped. 
     From the foregoing, it will be appreciated that the method of the present invention does not involve weakening the headers as by slitting the same and does away with the cost of such a forming operation. Leaks associated with baffles introduced through slits are avoided and the relatively better sealing obtained through endwise insertion of baffles can be achieved, not withstanding the fact that the headers, in a preferred embodiment, are of the type having domes located between tube slots and therefore have an irregular interior. Of course, the method can be used with headers that have perfectly cylindrical interiors, i.e., without the domes  22 , if desired.