Abstract:
A water heater includes a water tank, a combustion chamber below the tank and communicating with the flue tube, and a flue system. The flue system includes a flue tube, and V-shaped fins that are metallurgically bonded to the flue tube wall to divide the flue tube into four flue chambers extending substantially parallel to the longitudinal axis of the flue tube. The V-shaped fins include radially extending apertures that reduce the thermal expansion of the V-shaped fins with respect to the flue tube to reduce stress at the joint between the fins and the flue tube. The flue system also includes a removable baffle hanging in each flue chamber. The baffles include adjustable turbulation surfaces to control the quality of combustion in the water heater.  
     This is a continuation-in-part of application Ser. No.  09/561,126  filed Apr.  28, 2000,  the entire contents of which are herein incorporated by reference.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to flue systems for gas-fired water heaters.  
         BACKGROUND  
         [0002]    It is known to weld or otherwise metallurgically bond fins inside a water heater flue tube to enhance heat conduction through the walls of the flue tube. It is also known to hang removable baffles in a flue tube to turbulate the exhaust gases flowing through the flue tube.  
           [0003]    However, known systems often do not meet the current gas-fired water heater regulations relating to efficiency and construction for facilitating cleaning, and many of those water heaters that do meet the current regulations will not meet the next, more strict regulations to be enacted. For example, under today&#39;s regulations, the flue of a water heater has to be cleanable to remove soot and other buildup that may be hazardous. Many known flue systems were not designed to be easily cleaned, and therefore may not meet this regulation.  
           [0004]    For example, one known flue tube fin arrangement includes a plurality of small fins extending radially inwardly into the flue tube from the flue tube wall. Soot can collect on these small fins, and the small fins are not easily cleaned with a brush. Another example is a twisted fin positioned within the flue tube. A twisted fin is not easily cleaned because a cleaning brush would have to be twisted to follow the contour of the fin.  
         SUMMARY  
         [0005]    The present invention provides a flue system for a water heater. The flue system permits the combustion characteristics of the water heater to be tuned or adjusted. The system also permits relatively easy cleaning of the flue. The flue system includes a fin that is metallurgically bonded to the flue tube, and a removable baffle having at least one turbulation surface. The combustion quality of the water heater is adjusted by adding or removing baffles and by adjusting the turbulation surfaces of the baffles. The fin may be a cruciform-shaped fin, a pair of V-shaped fins, or a plurality of straight fins. Preferably, the fins divide the flue tube into flue chambers extending substantially parallel to the longitudinal axis of the flue tube, and the removable baffles are hung in selected flue chambers.  
           [0006]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a perspective, partially cut-away view of a water heater embodying the present invention.  
         [0008]    [0008]FIG. 2 is an enlarged exploded view of part of the flue system of FIG. 1.  
         [0009]    [0009]FIG. 3 is an end view of a flue tube including a first fin construction.  
         [0010]    [0010]FIG. 4 is an end view of a flue tube including a second fin construction.  
         [0011]    [0011]FIG. 5 is an end view of a flue tube including a third fin construction.  
         [0012]    [0012]FIG. 6 is an end view of a flue tube including a fourth fin construction.  
         [0013]    [0013]FIG. 7 is an end view of a flue tube including a first baffle orientation.  
         [0014]    [0014]FIG. 8 is an end view of a flue tube including a second baffle orientation.  
         [0015]    [0015]FIG. 9 is an enlarged view of the top portion of the water heater of FIG. 1, illustrating the removal of a baffle under low-clearance circumstances.  
         [0016]    [0016]FIG. 10 is a perspective view of an alternative construction of the lower end of the fin structure.  
         [0017]    [0017]FIG. 11 is a perspective view of an alternative construction of the fin structure.  
         [0018]    [0018]FIG. 12 is a perspective view of an alternative construction of the fin structure. 
     
    
       [0019]    Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of “consisting of” and variations thereof herein is meant to encompass only the items listed thereafter. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order.  
       DETAILED DESCRIPTION  
       [0020]    [0020]FIG. 1 illustrates a water heater  10  that includes a base pan  14 , a tank  18  supported by the base pan  14  and containing water, an insulating jacket  22  surrounding the tank  18 , a control system  26 , a burner  30  disposed in a combustion chamber  34  beneath the tank  18 , a water inlet pipe  38 , a water outlet pipe  42 , and a flue system  50  including a flue tube  52 . In operation, gas fuel is provided to the burner  30  through a conduit  54 . The gas is released by the burner  30  in a controlled fashion, and the gas is lit by a pilot light  58  that continually burns within the combustion chamber  34 . Products of combustion from the burner  30  heat the water in the tank  18  through the tank bottom wall  62 , which is dome-shaped. The products of combustion also flow up through the flue tube  52  and heat the water through the wall of the flue tube  52 .  
         [0021]    [0021]FIG. 2 illustrates the flue system  50 , which includes the flue tube  52  (FIG. 1), a fin structure  66 , and four removable baffles  70 . With additional reference to FIG. 3, the illustrated fin structure  66  is a cross-shaped or cruciform fin structure having four arms or fin portions  74  of substantially equal length joined along a central line that is substantially coincident with the longitudinal axis  78  of the flue tube  52 .  
         [0022]    The outer edges of the fin portions  74  are metallurgically bonded to the inner surface of the flue tube wall as shown in FIG. 3. As used herein, “metallurgically bonded” means welded, brazed, or otherwise joined or fused together to facilitate heat conduction between two members. Preferably, the fin portions  74  are welded to the flue wall from the outside by penetration, laser, arc, or electron beam welding. Alternatively, the fin portions  74  may be welded from inside the tube  52  with a torch. A continuous weld along the entire length of the edge of the fin portions  74  is not necessary. Rather, the fin portions  74  may be welded along only a portion of each edge, either in a continuous weld or in several segmented welds. In this regard, the fin portions  74  may be welded along 100% or less of the length of the edges. Preferably, the fin portions  74  are welded between about 75% and 100% of the length of the edges to provide the desired heat transfer efficiency. Preferably, the flue system  50  is made of mild (i.e., low carbon) steel. In high efficiency models where corrosion caused by condensation is a concern, the flue system  50  may be constructed of an alloy such as stainless steel, Inconel, or an alloy of nickel. Alternatively, any suitable material may be used to construct the flue system  50 .  
         [0023]    The cruciform fin structure  66  provides several advantages. First, the cruciform fin structure  66  provides structural stability to the flue tube  52 , which aids in the manufacture of the flue system  50 . The structural stability permits the flue tube  52  to resist distortion during the glass-firing process and during insertion of the flue tube  52  into heads during assembly.  
         [0024]    The cruciform fin structure  66  also substantially equally divides the inner volume of the flue tube  52  into four flue chambers  82  that extend substantially parallel to the longitudinal axis  78  of the flue tube  52 . The four flue chambers  82  act as four flue tubes of relatively small cross-sectional area. The hottest gas within each flue chamber  82  is geometrically centered in the cross-sectional area of the flue chamber  82 . If there were no fin structure  66  in the flue tube  52 , the hottest gas would be centered with respect to the cross-sectional area of the flue tube  52 . A second advantage of the cruciform fin structure  66 , therefore, is that the hottest gas is closer to the flue wall than if the fin structure  66  were not present or if the fin structure  66  did not divide the flue tube into separate flue chambers  82 .  
         [0025]    A third advantage of the cruciform fin structure  66  is that it facilitates cleaning the flue tube  52 . A cleaning brush may be easily inserted into the four flue chambers  82 , and no twisting of the brush is required.  
         [0026]    Another advantage lies in the fact that the four fin portions  74  of the fin structure  66  are connected at the center of the fin structure  66 . In this regard, if one of the welds along one of the edges were to fail, the fin structure  66  would still be supported by the welds on the other fin portion  74  edges.  
         [0027]    As shown in FIG. 1, the fin structure  66  is positioned within the flue tube  52  to leave a space  86  between the ends of the fin structure  66  and the ends of the tube  52 . The space  86  facilitates mounting the flue tube  52  and fin structure  66  assembly on a glass coating machine that coats the inside and outside of the flue tube  52  and the fin structure  66  with a protective glass coating to resist degradation of the fin structure  66  and flue tube wall. Additionally, because the fin structure  66  is recessed with respect to the lower end of the flue tube  52 , the fin structure  66  is less likely to be overheated by the extreme temperatures in the combustion chamber  34 . The space  86  may be, for example, about three inches, but may be more or less depending on the circumstances.  
         [0028]    To further facilitate the glass-coating process, one or more fin portions  74  may include a hole  90 . The hole  90  may be engaged with a hook to suspend the fin structure  66  and flue tube  52  during the heating procedure of glass coating. This is an advantage over providing a hole in the flue tube  52 . Holes in the flue tube  52  can interfere with welding the flue tube  52  to the head of the tank  18  if the hole is located too far from the end of the flue tube  52 . On the other hand, if the hole is positioned too close to the end of the tube  52 , the hook may tear through the flue tube wall at the elevated temperatures of the heating procedure. Additionally, a hole in the flue tube  52  would have to be patched or otherwise closed, while the hole in the fin portion  74  would not interfere with the operation of the water heater  10 .  
         [0029]    Because the fin portions  74  are metallurgically bonded to the flue wall, heat transfer between the fin portions  74  and the flue wall is improved over fin portions that are not metallurgically bonded to the flue wall. The metallurgical bonding therefore results in more efficient transfer of heat from the products of combustion to the water in the tank  18 . The increased heat transfer of the cruciform fin structure  66  permits a water heater  10  to be made more compact than multiple flue designs. There is less welding, fewer components, lower cost, and less tooling involved in assembling a water heater  10  having the cruciform fin structure  66  when compared to a multiple flue design.  
         [0030]    As seen in FIG. 2, the baffles  70  are elongated and include hangers  94  and turbulation surfaces  98 . The baffles  70  may be constructed from, for example, strips of stainless steel having partially cut-out tabs that are bent to form the turbulation surfaces  98 . Preferably, the tabs  98  are bent in alternating directions along the length of the baffle  70  as illustrated. The tabs  98  may be semicircular in a shape as illustrated or any other suitable shape. The turbulation surfaces  98  cause turbulent flow in the products of combustion moving through the flue tube  52 . The turbulation surfaces  98  can be adjusted to provide more or less resistance to the flow of products of combustion. The turbulation surfaces  98  also resist downdrafts in the flue tube  52 .  
         [0031]    In this regard, the flue system  50  is adjustable, and the quality of combustion in the water heater  10  is able to be tuned to optimize combustion, residence time of the products of combustion within the flue tube  52 , and heat transfer to the water in the tank  18 . The baffles  70  may also be removed and replaced with baffles  70  having different arrangements of turbulation surfaces  98  to optimize these parameters and to accommodate different inputs to the burner  30 .  
         [0032]    As can be seen in FIGS. 7 and 8, the baffles  70  may be supported with the hangers  94  in a square or chord pattern (FIG. 7), in a radial pattern (FIG. 8), or in a combination of the chord and radial patterns. Thus, the orientation in which the baffles  70  are hung may be used to further tune the combustion quality of the water heater  10 . Also, one or more of the baffles  70  may be removed from the flue tube  52  to further customize the combustion quality.  
         [0033]    Referring now to FIG. 9, because the baffles  70  are made of relatively narrow strips of metal, they are more easily bent than traditional, larger baffles. As a result, the baffles  70  may be removed from a water heater  10  under low clearance conditions, where traditional, larger baffles could not be removed without first tipping or otherwise moving the water heater  10 . The flue  52  and fin structure  66  are easily cleaned by removing the baffles  70  from the flue tube  52  and scrubbing the flue wall and fin structure  66  with a brush.  
         [0034]    An alternative design for the lower end of the fin structure  66  is illustrated in FIG. 10. Here it is shown that the end  102  of the fin structure  66  may be shaped as a point (e.g., shaped as the end of a pointed stake). As condensation forms in the flue tube  52 , water runs down the fin structure  66 . In a flue system having a flat-bottom fin structure, some of the condensation may run along the domed bottom wall  62  of the tank  18  and drip onto the pilot light  58 , potentially extinguishing the pilot light  58 . With the pointed end  102  design shown in FIG. 10, substantially all of the condensation runs all the way down the fin structure  66  to the pointed end  102 , and falls on the burner  30 , where the condensation is evaporated. The pointed end  102  of the fin structure  66  may therefore help to keep the pilot light  58  from being inadvertently extinguished.  
         [0035]    [0035]FIG. 11 illustrates another alternative construction of the fin structure  66 . Here the fin structure  66  is provided with holes  106  to permit the cross-flow of the products of combustion through the fin structure  66 . The holes  106  do not significantly interfere with cleaning the flue tube  52  and fin structure  66 . The cross-flow holes  106  permit better mixing of the products of combustion.  
         [0036]    Additionally, the holes  106  in the fin structure  66  illustrated in FIG. 11 may be provided by shear-forming tabs in a similar fashion to the tabs  98  of the baffle  70  described above. The tabs may be bent in alternating directions. In such a construction, the hanging baffles  70  would not be necessary, as the bent tabs formed in the fin structure  66  would serve as turbulation surfaces. The tabs would provide a greater and more efficient heat transfer surface than the fin structure  66  illustrated in FIG. 11.  
         [0037]    Alternative fin structure  66  configurations are illustrated in FIGS.  4 - 6 . Each alternative fin structure  66  configuration includes a plurality of fin portions  74 . In each configuration, however, the fin portions  74  substantially divide the flue tube  52  into four flue chambers  82 . In each configuration, the fin portions  74  may be sized so that they abut each other near the center of the flue tube  52 , or the fin portions  74  may be intentionally sized to not quite touch each other. If the fin portions  74  do not touch each other, the space between the inner edges of the fin portions  74  acts as a buffer, absorbing any distortion of the flue tube  52 , and permitting the flue tube  52  to be radially compressed before the fin portions  74  touch each other and provide support for the flue wall.  
         [0038]    In FIG. 4, the outer edge of each of four fin portions  74  is metallurgically bonded to the flue wall. The inner edge of each fin portion  74  is positioned near the longitudinal axis  78  of the flue tube  52 .  
         [0039]    In FIG. 5, three fin portions  74  are provided, one of which is metallurgically bonded to the flue wall along both edges, and two that each have one edge metallurgically bonded to the flue wall. The two fin portions  74  that have free ends may or may not touch the fin portion  74  that is metallurgically bonded at both ends.  
         [0040]    [0040]FIG. 6 illustrates a configuration with two fin portions  74 , in which the fin portions  74  are V-shaped in cross-section. The V-shaped fin portions  74  each include a longitudinally extending point, or base  76  and two legs  80  that extend away from the base  76 . The base  76  defines a substantially vertical line that is substantially parallel to the longitudinal axis  78  of the flue tube  52 . Each leg  80  is substantially planar and includes an edge that is metallurgically bonded to the inner surface of the flue tube  52 . The V-shaped fin portion  74  is preferably welded to the inner surface on one side of each leg  80 , but may alternatively be welded on both sides of each leg  80 . The bases  76  of the V-shaped fin portions  74  are positioned near each other substantially along the longitudinal axis  78  of the flue tube  52  and preferably within approximately 0.030 inches from each other. The lines defined by the bases  76  of the two fin portions  74  may define a plane that includes the longitudinal axis  78 . The V-shaped fin portions  74  may alternatively be welded along the longitudinal axis  78  at their respective bases  76 .  
         [0041]    [0041]FIG. 12 illustrates another fin structure  66  that includes V-shaped fin portions  74  having at least one slot  92  to reduce cracking effects caused by the thermal expansion of the fin structure  66 . The fin structure  66  is welded or otherwise metallurgically bonded to the inside surface of the flue tube  52 . Differences between the thermal expansion of the flue tube  52  and that of the fin structure  66  may develop thermal stresses at the weld joint between the V-shaped fin portion  74  and the flue tube wall. The number and the location of the slots  92  can be varied to reduce the thermal stress on the fin portions  74  at the joints while accommodating the actual thermal growth in the V-shaped fin portions  74 .  
         [0042]    As shown in FIG. 12, the six slots  92  are preferably cut horizontally across each V-shaped fin portion  74 . The ends of the slots  92  are rounded to avoid high stress concentrations that could lead to crack propagation. The slots  92  project an equal distance from the base  76  of the fin portion  74  along each leg  80  to within ⅜ of an inch from the edge of each leg  80 . The slots  92  may alternatively be asymmetrical with respect to the base  76 , and extend further along one leg  80  than the other leg  80 . The slots  92  may also alternatively be angled with respect to horizontal and may be longer, shorter, wider, or narrower than illustrated to optimize heat transfer while still minimizing the stresses due to thermal expansion. It should also be noted that the baffles  70  illustrated in FIGS. 1, 2, and  7 - 9  and described above may be used with the fin structure  66  illustrated in FIG. 12 (one baffle  70  is partially shown in FIG. 12).  
         [0043]    In an alternative embodiment, the total length of the V-shaped fin portion  74  is 39⅝ inches. The lowest slot  92  is preferably 4{fraction (13/16)} inches away from the bottom end of the fin portion  74  and all of the slots  92  are equally spaced approximately 6 inches apart from each other such that the top slot is also 4{fraction (13/16)} inches away from the top end of the fin portion  74 . By way of this configuration, the V-shaped fin portion can be oriented in either direction before being inserted into the flue tube  52  during assembly.  
         [0044]    Although all of the fin structure  66  configurations illustrated herein substantially divide the flue tube  52  into four flue chambers  82 , other fin structure configurations are contemplated. For example, a fin structure configuration could be provided in which the flue tube is divided into less than or more than four flue chambers  82  (e.g., with only one V-shaped fin portion or with more than two V-shaped fin portions).