Abstract:
A header box for a heat exchanger assembly and the method of manufacture. The header box has a first header component and a second header component. The first header component has a first corner portion with a first wall and a second wall extending therefrom. The second header component has a second corner portion with a third wall and a fourth wall extending therefrom. Free ends of the first wall and the third wall cooperate to form a first seam which is welded to maintain the first wall in position relative to the second wall. The free ends of the second wall and the fourth wall cooperate to form a second seam which is welded to maintain the third wall in position relative to the fourth wall. The header box, with the first corner portion and the second corner portion, will withstand the stress concentrations associated with a flow of fluid in the header box.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to headers for air-cooled heat exchangers and, more specifically, to a header having a generally square or rectangular body which is reliable and reduces manufacturing costs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Air-cooled heat exchangers are frequently used in industrial applications. A fluid, either a gas or a liquid, is passed through a series of cooling tubes while air is mechanically passed over the exterior of the cooling tubes. The air absorbs heat from the cooling tubes, thereby lowering the temperature of the fluid within the tubes. The cooling tubes may include lateral or axial fins to aid in heat transfer. 
         [0003]    Heat exchangers typically include two header boxes having the cooling tubes extending therebetween. The header boxes are formed from a hollow body, each of which has a plurality of ports which allow fluid communication with the cooling tubes. One header box is connected to an inlet coupling and, typically, the other header box is connected to an outlet coupling. Within the body, pass plates may be disposed between groups of cooling tubes ports so that a fluid entering the first header through the inlet conduit must follow a serpentine path, back and forth through the cooling tubes between the headers, to reach the outlet coupling. 
         [0004]    Headers have many common cross-sectional shapes, for example, a quadrilateral, that is rectangular or square, round, oval or even obround. There are problems with header boxes of existing art. A quadrilateral header is typically formed by welding four individual flat plates together. Each of the seams between the plates must be welded. These long corner welds result in significant fabrication time and expense. In addition, these welds may fail, either in use or in testing prior to use. Because a quadrilateral header has generally right angle corners at the welds, the header is subject to stress concentrations which are localized along the welds. Thus, because stress concentrations contribute to potential failure of the header, it is preferable to reduce the number of welds and replace them with unwelded, curved surfaces in pressure vessels. 
         [0005]    A header having a circular, oval, or obround cross-section does not have large stress concentrations like those described with respect to the quadrilateral header. A circular or oval header does, however, have other problems. For example, the cooling tubes are typically parallel to each another. Thus, when drilling cooling tube openings in a circular or oval header, the drill bit must be maintained in single plane, regardless of where on the perimeter the drill is located. Maintaining the alignment of the drill makes drilling difficult at the top and bottom of a circular or oval header. Similarly, it is more difficult to attach cooling tubes to a curved surface than it is to attach the cooling tubes to a flat surface. 
         [0006]    Another problem in circular or oval headers is that, where threaded flat head shoulder plugs are used to plug access holes, the flat underside of the plug head does not fully engage the curved surface of the header. Thus, to provide an adequate sealing surface, the header may require spot face machining to provide flat surface for the plug to engage. Machining the header reduces the minimum thickness of the header wall in the area of the plug. Thus, the entire header may have to be manufactured with an additional material thickness to contain a specified pressure. 
         [0007]    The invention of the obround header solved some, but not all, of these problems and has its own disadvantages. An obround header has a unitary body with two flat opposing vertical sides which are connected by two curved opposing sides. The openings for the cooling tubes and plugs are located on the two flat sides. Thus, the drilling of the openings for the cooling tubes and the plug is simplified and the cooling tubes and plugs are more easily coupled to the header. Because the header is made from a unitary body, there are no weld seams except at the ends where end plates are attached. The inlet coupling and outlet coupling, however, must still be coupled to one of the curved sides. The coupling must be specially formed to match the curved sides, and attaching the coupling to the curved side is difficult. Additionally, the obround shape makes installation of the pass plates more difficult. Also, because the curved sides extend above and below the plane of the cooling tubes, the obround header requires more space than a traditional quadrilateral header. 
         [0008]    U.S. Pat. No. 6,523,260 discloses a header box with a hollow unitary body having four generally flat sides forming a generally quadrilateral cross-section. End plates are located at, and coupled to, each end of the unitary body. One generally flat side has a plurality of plug openings. The flat side opposite the one generally flat side with the plug openings includes a plurality of tube openings. Because the header is made from a unitary body, there are no weld seams except at the ends where end plates are attached. While this header box has no welds, the equipment needed to form the header box is specialized and not readily available, making the header box expensive and difficult to manufacture. 
         [0009]    There is, therefore, a need for a header for a heat exchanger which has a quadrilateral cross-sectional profile and which has one set of opposing, flat sides having openings therethrough which are structured to be coupled to either cooling tubes or plugs, and a second set of opposing, flat sides having openings therethrough that are structured to be coupled to an inlet coupling or an outlet coupling. There is a further need for the header to be stable and easily manufacturable to facilitate connection to the other components of the heat exchanger. 
       SUMMARY OF THE INVENTION 
       [0010]    These needs, and others, are satisfied by the invention, which provides a method of making a header box for a heat exchanger assembly. The method includes the steps of: forming a first header component with a first integral corner; forming a second header component with a second integral corner; positioning the first header component proximate the second header component such that both ends of the first header component are positioned proximate respective ends of the second header component; and welding the ends of the first header component to the ends of the second header component to form a header box. The header box, with the first integral corner and the second integral corner, will withstand the stress concentrations associated with a flow of fluid in the header box. 
         [0011]    The method may include the additional steps of: determining the position of the first integral corner and the second integral corner; and positioning the first integral corner and the second integral corner in a location in which maximum corner stress concentrations associated with the flow of fluid in the header box will occur. This reduces stresses associated with the ends of the first header component which are welded to the ends of the second header component. 
         [0012]    Another aspect of the invention is directed to method of making a header box for a heat exchanger assembly. The method includes forming a pair of identical header components, with each of the first and second header components being formed into an L-shape. Each of the first and second headers also has a bent corner positioned between two sidewalls, with the sidewalls having free ends which extend away from the bent corner. The method also includes positioning the first header component proximate the second header component, with the second header component rotated approximately 180 degrees relative to the first header component. The free ends of the first header component are positioned proximate the free ends of the second header component. The method includes the additional step of welding the free ends of the first header component to the free ends of the second header component to form a header box. The header box, with the first integral corner and the second integral corner, will withstand the stress concentrations associated with a flow of fluid in the header box. 
         [0013]    Another aspect of the invention is directed to a header box for a heat exchanger assembly. The header box has a first header component and a second header component. The first header component has a first corner portion with a first wall and a second wall extending therefrom. The first and second walls have free ends which extend away from the first corner portion. The first wall extends in a direction which is essentially perpendicular to the second wall. The second header component has a second corner portion with a third wall and a fourth wall extending therefrom. The third and fourth walls have free ends which extend away from the second corner portion. The third wall extends in a direction which is essentially perpendicular to the fourth wall. The first corner and the second corner are positioned in opposed corners of the header box. The free ends of the first wall and the third wall cooperate to form a first seam which is welded to maintain the first wall in position relative to the second wall. The free ends of the second wall and the fourth wall cooperate to form a second seam which is welded to maintain the third wall in position relative to the fourth wall. The header box, with the first corner portion and the second corner portion, will withstand the stress concentrations associated with a flow of fluid in the header box. 
         [0014]    The header box and the method of manufacture of the header components reduce the labor and cost associated with the manufacture of the header assemblies when compared to the prior art. In addition, the bent, rounded corners of the header components provide strength in areas of high stress concentrations, increasing the stability and reliability of the header assembly. 
         [0015]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an isometric view of a heat exchanger assembly with two header boxes. 
           [0017]      FIG. 2  is a cross-sectional view of a respective header box of the heat exchanger assembly of  FIG. 1 . 
           [0018]      FIG. 3  is a side view of the respective header box of  FIG. 2 . 
           [0019]      FIG. 4  is a schematic diagram of the manufacturing steps for assembling the header boxes of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    As shown in  FIG. 1 , a heat exchanger assembly  1  includes two quadrilateral header assemblies or header boxes  10 , that is, a first header box  12  and a second header box  14 . The header boxes  12 ,  14  are held in a spaced relation. The heat exchanger assembly  1  further includes a plurality of tubes  16  and two couplings  18 ,  20 . The header boxes  12 ,  14  are generally symmetrical and, as such, only one header box will be described. The header box  12  includes a hollow body  22  having a generally quadrilateral cross section. The body  22  has a first generally flat side  24  spaced from and generally parallel to a generally flat second side  26 . As shown in  FIGS. 1 and 2 , the first and second sides  24 ,  26  are generally horizontal. The body  22  also has a third generally flat side  28  spaced from and generally parallel to a generally flat fourth side  30 . The third and fourth sides  28 ,  30  extend generally perpendicular to the first and second sides  24 ,  26 . The third side  28  is integrally coupled to the front side  24  by a rounded corner  40  to form a first header component  27 . The fourth side  30  is integrally coupled to the second side  26  by a second rounded corner  40  to form a second header component  29 . The first and second sides  24 ,  26  may be described as a first set of spaced, horizontal sides where one side is an upper side  24  and one side is a lower side  26 . The third and fourth sides  28 ,  30  may be described as a second set of spaced, vertical sides. In the embodiment shown, the horizontal sides  24 ,  26  are, preferably, between about six and twelve inches in width, and more preferably, about 8 inches in width. The vertical sides  28 ,  30  are, preferably, between about six and twelve inches in width, and more preferably, about 8 inches in width. However, the sizes of the horizontal sides and vertical sides are not required to be equal and are not required to be in the recited ranges in order to be included within the scope of the invention. The body  22  is formed with two seams  31  as shown in  FIG. 2 . The seams  31  are welded to join the first header component  27  to the second header component to form the body  22 . 
         [0021]    The header box  12  also has two ends and a first end plate  42  ( FIG. 1 ) and a second end plate  44  ( FIG. 2 ). The end plates  42 ,  44  are sized to fit snugly within the perimeter at either end of the body  22 . The end plates  42 ,  44  are coupled to the body  22 , preferably by welding. When the end plates  42 ,  44  are coupled to the body  22 , a fluid chamber  45  is formed. 
         [0022]    The header box  12  also includes a plurality of plug openings  46  on the third side  28  and tube openings  48  on the fourth side  30 . To facilitate use of an expander tool (not shown) for attaching tubes  16  to the tube openings  48  each plug opening  46  is created directly opposite a tube opening  48 , and a centerline  50  passing through each plug opening  46  is also a centerline of an opposed tube opening  48 . The tubes  16  may also be attached to the tube openings  48  by welding the tube  16  to the header box body  22 . In this case, openings  46  may also be created in the header box  22  to facilitate the welding process, but direct alignment of openings  46  and  48  is not necessary. 
         [0023]    Each header assembly tube  16  may have one or more fins  17  attached thereto. The fins  17  aid in heat exchange between the fluid within the tubes  16  and the fluid outside the tubes  16 . The tubes  16  may also have interior fins (not shown) to assist in heat transfer. Each tube  16  is coupled to both box headers  12 ,  14  at the location of a tube opening  48 . Preferably, each tube  16  is expanded to the box headers  12 ,  14 . Each tube  16  is in fluid communication with the fluid chamber  45 . As such, a fluid in the first header fluid chamber  45  may pass through the tubes  16  to the second header fluid chamber (not shown). 
         [0024]    As shown in  FIG. 3 , pass plates  60  may be disposed within fluid chamber  45 . Each pass plate includes a generally planar body. The pass plates  60  divide the fluid chamber  45  into two or more sub-chambers  62 ,  64 . The pass plates  60  are disposed at an angle relative to the vertical axis of the header box  12 ,  14 . Each pass plate  60  passes between, but does not overlap or cover, the tube openings. The pass plates  60  may be welded to the body  22 , thereby sealing the first sub-chamber  62  from the second sub-chamber  64 . 
         [0025]    The header assembly  10  also includes an inlet coupling  18  and an outlet coupling  20 . Both the inlet coupling  18  and the outlet coupling  20  are in fluid communication with a header box fluid chamber  45 . Depending on the number of pass plates  60  disposed in the fluid chamber  45  of each header box  12 ,  14 , the inlet coupling  18  and the outlet coupling  20  may be disposed on the same header box  12 , as shown in  FIG. 3 , or on different header boxes  12 ,  14 , as shown on  FIG. 1 . 
         [0026]    For example, in operation, describing the header assembly  10  shown in  FIG. 1 , a hot fluid enters the header assembly  10  through inlet coupling  18 , and travels into the first sub-chamber  62  of the fluid chamber  45  of header box  12  located on a first side of the first header box pass plate  60 A. The hot fluid then travels through a first portion of the tubes  16 A to the second header box  14 . As the hot fluid travels through the tubes  16 , the fluid is cooled by transferring heat to the air outside of the tubes  16 . The second header box pass plate  60 B prevents the hot fluid from traveling directly to the outlet coupling  20 . Instead, the hot fluid travels through a second portion of the tubes  16 B back to the first header box  12  into the second sub-chamber  64  ( FIG. 3 ) of the fluid chamber  45  of first header box  12 , located on a second side of the first header box pass plate  60 A. Again, as the hot fluid travels through the tubes  16 , the fluid is cooled by transferring heat to the air outside of the tubes  16 . The fluid then travels through a third portion of the tubes  16 C back to the second header box  14 , being cooled further by traveling through the tubes  16 . The cooled fluid then exits the header assembly  10  through outlet coupling  20 . 
         [0027]    The quadrilateral header box  10  of  FIG. 1  may be constructed using two L-shaped header components  27 ,  29  which are welded together, as shown in  FIG. 4 . The method of constructing the quadrilateral header assembly  10  begins with forming the header components  27 ,  29  from flat plates  100 . The plates  100  may be mounted on one or more dies (not shown) structured to pass through a forming machine. The plates  100  are then passed through a hydraulic forming machine (not shown), of the type known in the metal forming industry. The forming machine engages and bends the flat plates  100 , deforming the flat plates  100  to have an L-shaped configuration. The method used to create the L-shaped header components  27 ,  29  may be either a cold forming process or a hot forming process. 
         [0028]    Once the L-shaped header components  27 ,  29  are formed, the components are taken off of the dies. The header components  27 ,  29  have exactly the same profile and are made using the same process and the same forming machine. When assembling the header box  10 , two header components are used with one header component  27  rotated 180 degrees from the other header component  29 . The header components may then be heat treated to remove any internal stress caused by the forming machine. Mill scale from the heat treating process can be removed by shot blasting the components or by using other commonly known methods of removing mill scale such as buffing or grinding. Thus, what remains are seamless L-shaped header components  27 ,  29 . The sides of the header component have a thickness which is generally between about 0.5 and 1.25 inches, but may be outside the range without departing from the scope of the invention. 
         [0029]    The header components  27 ,  29  may then be cut to the appropriate size for the respective box headers  12 ,  14 . The first and second header components  27 ,  29  are then welded along seams  31  to form the body  22  of the partially assembled header box  10 . In the embodiment shown, the plug openings  46  and a coupling opening are then drilled and/or cut in the header component  27 , and the tube openings  48  are then drilled and/or cut in the header component  29 . Alternatively, the plug openings  46 , tube openings  48  and coupling opening may be drilled prior to the header components  27 ,  29  being welded along the seams  31 . The positioning of the openings on either of the respective header components  27 ,  29  and respective sides  24 ,  26 ,  28 , is determined by the desired positioning of the rounded corners  40  when the header box or assembly  10  is assembled. The rounded corners  40  are positioned such that the maximum stress concentrations exerted on the corners of the header assembly  10  by the flow of the fluid in the heat exchanger system are applied to the rounded corners  40  and not to the welded seams  31 . 
         [0030]    The end plates  42 ,  44  and any pass plates  60  are welded to the assembled header components  27 ,  29 . The plug openings  46  are then tapped and couplings  18 ,  20  are then attached, preferably by welding. The partially complete assembly  10  may be heated to relieve any stress caused by the assembly process. The tubes  16  are then attached to two header boxes  12 ,  14 , extending therebetween, at the tube openings  48  by known methods, such as an expansion tool or seal welding. The header assembly  10  is completed by installing plugs  120 , preferably a bolt  122  and a gasket  124 , in the tapped plug openings  46 . 
         [0031]    The header assemblies or header boxes  10  shown and described herein have many advantages over the prior art header boxes which are assembled from four individual plates or which are formed from a cylindrical tube. Each header component  27 ,  29  is made from a metal plate which is easily obtainable. As the header components  27 ,  29  are made from the same stock material, the amount of different items which must be stored in inventory is reduced. As the plate material is readily available and is often used for other items, the cost of the plate material is relatively low and controlled. In addition, as the machinery needed to bend the header components  27 ,  29  is known in the industry and is commonly available, the cost of processing the header components is significantly reduced when compared to the cost of process and forming cylindrical tubes into quadrilateral headers. 
         [0032]    The use of the header components  27 ,  29  reduces the labor and cost associated with the manufacture of the header assemblies when compared to the prior art method of welding four individual plates to form the header assembly. By reducing the number of welds from four to two, the labor, fabrication time and expense associated with the assembly of the header assembly are greatly reduced. In addition, long corner welds may fail, either in use or in testing prior to use. In the present invention, as some of the welded corners are replaced by stronger bent or rounded corners  40 , the header assemblies  10  can be positioned such that the bent rounded corners  40  are positioned in the corners with the highest stress concentrations, thereby preventing failure of the header assembly  10 . 
         [0033]    While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. For example, the inlet and outlet couplings  18 ,  20  are typically on the lower of the two horizontal sides  26 . The inlet and outlet couplings  18 ,  20  may, however, be on any side  24 ,  26 ,  28 ,  30 . 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. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.