Abstract:
A flue-gas to air heat exchanger having a flue-gas containing shell with a heat exchange surface, flue-gas inlet and outlet sections, and at least one tubular clean-out fitting is provided with a removable plug having an outer peripheral portion resiliently engageable with a section of the inner peripheral portion of the fitting adjacent the shell. The plug periphery is expanded into gas-tight sealing contact with the fitting inner periphery by means affording installation and removal without tools.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to heat exchangers, and more particularly, the present invention relates to flue-gas to air heat exchangers having clean-out access openings.  
       BACKGROUND OF THE INVENTION  
       [0002]     Flue gas to air heat exchangers are used in hot air furnaces to transfer heat from a combustion chamber to air flowed across the heat exchanger surfaces for downstream distribution into an area to be heated. One example of such a heat exchanger is a shell having a hollow wall surrounding a combustion chamber to provide a substantial surface area for heat transfer. The shell is connected to the combustion chamber via a short pipe at one location, and the shell is connected to a flue ring at another location. Hot combustion, or flue, gases flow in a serpentine pattern through the shell between the combustion chamber outlet pipe and the flue ring. Over the course of time, soot from the combustion gases can form in the shell, thereby necessitating cleaning.  
         [0003]     In one model of such a furnace, a pair of access openings are provided in the shell at spaced locations near where the air is admitted to the heat exchanger. To afford access to the interior of the shell, the openings have tubular extensions, and caps are provided for the extensions remote from the heat exchanger shell. While this structure has certain advantages, it has certain limitations in that the extensions can accumulate soot and condensate, which, over time, may cause corrosion under certain conditions of use. Moreover, if the heat exchanger is not serviced regularly, even the extension caps can become difficult to remove and replace.  
       OBJECT OF THE INVENTION  
       [0004]     The present invention overcomes the aforementioned limitations by providing a shell heat exchanger access tube with a plug that is capable of being removed and reinstalled readily without tools to afford access to the heat exchanger shell interior for periodic cleaning.  
       SUMMARY OF THE INVENTION  
       [0005]     More specifically, a flue-gas to air heat exchanger having a flue-gas containing shell with a heat exchange surface, flue-gas inlet and outlet sections, and a tubular clean-out fitting having an inner peripheral portion of a predetermined length extending away from the shell to afford access to the interior of the shell for cleaning the shell interior is provided with a removable plug having an outer peripheral portion resiliently engageable with a section of the inner peripheral portion of the fitting adjacent the shell, and means for expanding the plug section into gas-tight sealing contact with the fitting inner periphery. Preferably, the plug includes a resiliently deformable tubular body having opposite end surfaces, a distal disc engaging one of the body end surfaces and extending transverse to the fitting, a proximal disc engaging the other of the body end surfaces and extending transverse to the fitting, and means for urging said the discs axially toward one another for peripherally expanding the tubular body into sealing engagement with the inner periphery of the fitting. More preferably, the proximal disc is larger than the distal disc and extends across the outer end of the fitting, and the tubular body is coextensive with a substantial portion of the predetermined length of the fitting.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The foregoing and other objects, features and advantages of the invention should become apparent from the following description when taken in conjunction with the accompanying drawings in which:  
         [0007]      FIG. 1  is a perspective view of a heat exchanger having a pair of clean-out plug assemblies embodying the present invention;  
         [0008]      FIG. 2  is a longitudinal cross-sectional view taken on line  2 - 2  of  FIG. 1  showing one of the plug assemblies in an installation/removal mode;  
         [0009]      FIG. 3  is a view similar to  FIG. 3 , but showing the plug in its operational mode;  
         [0010]      FIG. 4  is a transverse cross-sectional view taken on line  4 - 4  of  FIG. 2 ; and  
         [0011]      FIG. 5  is a transverse cross-sectional view taken on line  5 - 5  of  FIG. 3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring now to the drawings,  FIG. 1  illustrates a flue-gas to air heat exchanger  10  incorporating a pair of clean-out assemblies  12  and  14  embodying the invention. The heat exchanger  10  comprises an upright octagonal shell  16  adapted to be confined in an outer housing (not shown) to form a air plenum around the shell for enabling air to be heated as it flows upwardly in the direction of the solid line arrows in  FIG. 1  lengthwise of the shell  16  along an outer heat exchange surface  16   a  of the shell  16  and interiorly of the shell  16  along an inner heat exchange surface  16   b.  An upstanding cylindrical combustion chamber  18  is disposed centrally within the shell  16  and is connected as its lower end via an elbow (not shown) to a fuel burner, such as a oil burner, (not shown) having a nozzle section extending into an aperture  20  of a front, or proximal, burner mounting plate  22 . The shell  16  is hollow and contains flow directing baffles. The upper end of the combustion chamber  18  is connected by a short pipe  24  to the upper rear, or distal, end of the shell  16 . A flue ring  26  is connected to the upper front, or proximal, end of the shell  16 . Combustion or flue-gases are flowed in a serpentine path in the direction of the arrows shown in broken lines in  FIG. 1  to exit the flue ring  26 . As the flue-gases flow, they transfer heat to the heat exchange surfaces  16   a,    16   b,  and thus by convection to the air flowed upwardly along them, as shown in solid lines in  FIG. 1 .  
         [0013]     Over the course of time, soot can accumulate inside the hollow shell  16 , thereby necessitating cleaning to maintain the thermal efficiency of the heat exchanger  10 . To this end, a pair of tubular clean out fittings  30 ,  32  are provided in the shell outer wall adjacent its lower end outer wall  18   a.  Each fitting, such as the fitting  30 , is tubular and extends horizontally outward from the heat exchanger shell wall  16   a  a predetermined distance determined by the location of a front furnace housing wall (not shown). Thus, the elongate fitting  30  facilitates access by a maintenance technician to the interior of the shell from a proximal location adjacent the fuel burner in the front of the furnace without having to remove the furnace housing. Heretofore, the open ends of the fittings were simply capped.  
         [0014]     To overcome the limitations noted, supra, the present invention provides a plug assembly which is readily removable and reinstallable without the need for tools, and which keeps soot and potential corrosion from forming in the clean-out fittings.  
         [0015]     As best seen in  FIG. 2 , the plug assembly  34  preferably extends from a location adjacent to the shell wall  16   a  to the open front end  30   a  of the fitting  30 . The plug assembly includes a distal disc  36 , a proximal disc  38  of larger diameter than the distal disc  36  for engaging the front end edge  30   a  of the fitting  30 , and a resilient tubular body  40  extending axially of the fitting  30  between and engaging at its opposite end faces  40   a  and  40   b,  the discs  36  and  38 , respectively. When the discs are urged axially toward one another, they expand the resilient body  40  into gas-tight sealing engagement with the inner periphery of the fitting  30  as shown in  FIG. 3 .  
         [0016]     In order to expand the tubular body  40 , a means is provided to urge the discs  36  and  38  toward one another. For this purpose, a machine bolt  42  extends axially between the discs  36  and  38  with its head  42   a  engaging the distal side of the distal disc  36  and with its threaded section  42   b  extending through the proximal disc  38 . A nut  46  is molded into a hand grip  48  having finger lugs  48   a,    48   b  for engaging the threads of the bolt  42 .  
         [0017]     When the hand grip  48  is rotated clockwise (facing the handle  FIG. 1 ) the axial end surface  46   a  of the nut engages the proximal side of the proximal disc and tensions the bolt axially. This causes the body  40  to undergo a peripheral expansion from the position shown in  FIG. 2  to the position shown in  FIG. 3 . When the hand grip  48  is thus fully tightened it remains in place until again removed for cleaning the shell in a known manner. Removal for cleaning is effected by reversely rotating the hand grip  48  to allow the body  40  to return to its relaxed state shown in  FIG. 2 , and then pulling on the hand grip  48  axially to disengage the plug assembly  34  from the fitting  30 .  
         [0018]     Preferably, the resilient body  40  is about three (3) inches long and is fabricated of heat resistant elastomeric material such as neoprene rubber reinforced with polyester cord and is capable of withstanding temperatures in excess of 180° F. Preferably, the outside diameter of the tubular body is slightly less than the inside diameter of the fitting. By way of example, for a fitting having a nominal inside diameter of 2.0 inches, the tubular body has an outside diameter of 1.93 inches in its relaxed state before being compressed axially between the discs. This dimensional relation provides satisfactory insertion and removal and controlled expansion with minimal turning of the hand grip.  
         [0019]     While a preferred embodiment of the present invention has been described in detail, various modifications, alterations and changes may be made without departing from the spirit and scope of the present invention as defined in the appended claims.