Abstract:
A combustion gas furnace includes a plurality of primary heat exchangers for passage of combustion gases therethrough. A plurality of secondary heat exchangers receive the combustion gases from the primary heat exchanger. Each of the secondary heat exchangers includes a heat conductive element defining a plurality of elongate passageways for the flow of combustion gas therethrough. The passageways include aligned ports at either end thereof. The passageways are generally aligned and separated by longitudinal walls extending between the ends. The walls are positioned for heat conductive contact with the combustion gases flowing through passageways.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/902,763, filed on Feb. 22, 2007, herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to a furnace heat exchanger. More particularly, the present invention is directed to a multi-channel heat exchanger for combustion gases. 
       BACKGROUND OF THE INVENTION 
       [0003]    Heat exchangers are commonly used in gas fired hot air furnaces in both residential and commercial settings. Heat exchangers are generally divided into two types. The first includes tubular heat exchangers where a tube is formed in a serpentine configuration and hot combustion gases are allowed to propagate through the tube. The second type of heat exchanger includes a compact design which may have a clam shell construction. 
         [0004]    In typical use in a furnace, a series of heat exchangers are provided in which hot combustion gases pass through the exchangers transferring heat to the surfaces of the heat exchanger. Forced air passed externally over the heated surfaces of heat exchangers is warmed and circulated into a room which is to be heated. The efficiency of the heat exchanger is dictated by the effectiveness of the transfer of heat from the hot combustion gases within a heat exchanger to the external surfaces of the heat exchanger itself. 
         [0005]    Also, many furnaces employ secondary heat exchangers which are used to extract added heat from the combustion gas exiting the primary heat exchangers. 
         [0006]    As may be appreciated, it is desirable to increase the heat transfer between the combustion gases and the walls of the primary and secondary heat exchangers. 
         [0007]    One such example is shown in U.S. Pat. No. 6,938,688 which employs a clam shell design for primary heat exchangers where turbulent flow of the combustion gases is caused. This results in more efficient heat transfer. 
         [0008]    However, as may be appreciated, such techniques may increase the size of the heat exchanger. Thus, additionally employing such a design for secondary heat exchangers would increase both the size and cost of the furnace. 
         [0009]    It is, therefore, desirable to provide an increase in the heat transfer surface area of a heat exchanger that is exposed to the combustion gases without increasing the external size of the heat exchanger itself. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a heat exchanger which includes a heat conductive element defining a plurality of elongate passageways for the flow of combustion gases therethrough. The passageway includes aligned inlet ends and opposed aligned exhaust ends. The passageways are generally longitudinally aligned and separated by longitudinal wall extending between the ends. The walls are positioned for heat conductive transfer with the combustion gases flowing through the passageways. 
         [0011]    The present invention also provides a combustion gas furnace including a heat exchanger support having means for accommodating a burner. A plurality of multi-channel heat exchangers are arranged in spaced apart succession along the support. Each heat exchanger includes a plurality of side-by-side channels. Each channel includes an inlet port at one end and an outlet port at the other. The channels are separated by integrally formed channel walls extending therealong. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is an exploded perspective view of a furnace employing the heat exchangers of the present invention. 
           [0013]      FIGS. 2 and 3  are front and rear a perspective showings respectively of the heat exchangers of the furnace of  FIG. 1 . 
           [0014]      FIG. 4  is a cross sectional showing of one heat exchanger shown in  FIG. 3 . 
           [0015]      FIG. 5  is a schematic representation of the travel of the combustion gases through the heat exchangers of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    The present invention provides a novel heat exchanger construction which may be used preferably as a secondary heat exchanger. While in the present illustrative embodiment, the novel heat exchangers are shown as secondary heat exchangers, it is contemplated that they also may be employed in certain situations as primary heat exchangers. 
         [0017]    Referring now to  FIG. 1 , a furnace  10  employing the heat exchanger of the present invention is shown. Furnace  10  includes a pair of spaced apart supporting walls  12  and  14  which support therebetween primary heat exchangers  16  and secondary heat exchangers  18 . Each of the primary and secondary heat exchangers are formed of a heat conducting metal, preferably aluminum. The primary heat exchangers  16  may be of the type shown and described in commonly assigned U.S. Pat. No. 6,938,688, issued Sep. 6, 2005, and entitled “Compact High Efficiency Clam Shell Heat Exchanger”. This patent is incorporated herein for all purposes. 
         [0018]    Primary heat exchangers  16  may be aligned in vertically spaced succession and may be of the clam shell variety having an inlet port  16   a  at wall  12 , a serpentine passageway  17 , and an exhaust port  16   b  at the other end of the serpentine passageway  17  opening to wall  12 . Combustion gases from a burner (not shown) enter the primary heat exchanger  16  through port  16   a  travel through the serpentine passageway  17  and exit exhaust ports  16   b . In order to increase the efficiency of the furnace, secondary heat exchangers  18  are employed. Secondary heat exchangers  18  are designed to take the exhaust exiting outlet ports  16   b  and move the gases through the secondary heat exchangers so that the heat from the exhaust can be employed. 
         [0019]    As is well known, a fan (not shown) may be supported by the furnace  10  to move air across the primary and secondary heat exchangers to provide warm air to the space to be heated. 
         [0020]    The wall  12  of furnace  10  supports an exhaust chamber  20  which is disposed over the exhaust ports  16   b  and the ends of the secondary heat exchanger  18  to direct exhaust gases from the primary heat exchangers through the secondary heat exchangers in a manner which will be described in further detail hereinbelow. A fan or other similar device may be used to draw the exhaust gas through the primary and secondary heat exchangers. 
         [0021]    Referring now to  FIGS. 2-4 , the secondary heat exchangers  18  of the present invention are shown. Each secondary heat exchanger  18  is an elongate integrally formed heat conductive metal member having a plurality of aligned channels therethrough. 
         [0022]    Referring specifically to  FIG. 4 , each heat exchanger  18  includes a top wall  22 , a bottom wall  24  and a plurality of integrally formed dividing walls  26  forming individual elongate channels  25 . The number of such channels may be selected based upon space and heat efficiency needs. The centrally located walls  26   a  are generally planar and parallel to one another while the end walls  26   b  may include a curved configuration. The walls  26  divide the heat exchanger into smaller parallel channels which result in higher heat transfer efficiency while maintaining a compact overall configuration. Such an arrangement assures more wall contact between the surface of the heat exchanger and the gases passing therethrough. Moreover, the open area of the secondary heat exchanger is significantly less than the open area of the primary area heater and there is a relatively large pressure drop loss as the gases flow through the secondary heat exchanger tubes. The flow resistance through the secondary tubes causes a “balanced” flow through the tube. The gases “look” for the flow path of least resistance thus balancing the flow. Maintaining a high flow velocity significantly improves heat transfer. By increasing the number of passes without any increase in the size of the heat exchanger heat transfer is improved. 
         [0023]    As shown in  FIGS. 2 and 3 , a plurality of such heat exchangers, in the present example 12, are arranged in a vertically stacked arrangement between support elements  30  and  32  supporting opposite ends of the heat exchangers  18 . The support members are in turn supported by walls  12  and  14  of furnace  10  ( FIG. 1 ). Each of the heat exchangers  18  is preferably formed of identical construction. The ends of the channels supported by the support members define ports  34  which provide for inlet or outlet of exhaust gases flowing within the channels  25 . As shown in  FIG. 4 , the channels  25 , being bounded by top and bottom walls  22  and  24 , and dividing walls  26 , effectively transfer the heat of the exhaust gases flowing therethrough to the walls. Also, by increasing the number of walls in contact with the exhaust gases, additional heat transfer to the surface of the heat exchanger is provided. Due to the compact size of the heat exchanger  18  and the effective transfer of heat to the walls thereof, an over all increase in heat transfer efficiency is achieved. 
         [0024]    As noted above, the heat exchangers  18  are supported between support elements  30  and  32 . Support element  30  supports one end of the heat exchangers with the ports  34  at that end being exteriorly accessible through the wall of the support  30 . An exhaust gas chamber  40  is positioned on support wall  30  so as to overlie the ports of all but the upper three of the heat exchangers. The chamber has an interior  42  which is in fluid communication with the ports of the covered heat exchangers. The chamber  40  includes a lower exhaust opening  44  which will be described in further detail herein below. 
         [0025]    The opposite ends of the heat exchangers are supported in support element  32 . Support element  32  individually accommodates each end of all of the heat exchangers and defines a fluid chamber, the interior  33  of which is in communication with each of the ends of the heat exchanger ports supported therein. Thus, chamber  40  as well as the chamber defined by support  32  are in fluid communication through the heat exchangers supported therebetween. 
         [0026]    Turning additionally again to  FIG. 1 , exhaust chamber  20  is positioned to overlie exhaust ports  16   b  as well as support  30  and the chamber  40  positioned thereover. Exhaust chamber  20  places each of the exhaust ports  16   b  and the heat exchanger ports  34  which are not covered by chamber  40 , in fluid communication. Exhaust chamber  20  includes an exhaust opening  22  aligned with opening  44  of chamber  40 . The exhaust chamber  20  allows exhaust gas exiting through ports  16   b  to be received within the ports  34  of the exposed heat exchangers  18  so that the exhaust gases traveling through heat exchangers  16  may be recaptured and used through secondary heat exchangers  18 . This allows the furnace  10  of the present invention to extract additional energy from the flue gas exiting the primary heat exchangers  16 . 
         [0027]    The flow of the exhaust gases through the secondary heat exchanger is shown schematically in  FIG. 5 . The exhaust gases which exit ports  16   b  ( FIG. 1 ) from the primary heat exchangers  16  are directed to ports  34  of the upper three of the secondary heat exchangers  18 . As noted above, a fan maybe used to directionally pull the exhaust gases. As shown by the arrows, the exhaust gases travel through the individual channels  25  ( FIG. 4 ) of heat exchangers  18  transferring the heat of the exhaust gases to the walls of the secondary heat exchangers  18 . The exhaust gases exit the opposite end of the heat exchangers  18  through ports  34  and are directed towards the next three heat exchangers immediately below. The exhaust gases thereupon enter ports  34  supported within support member  32  and travel along channels  25  again heating the walls therebetween. This travel of the exhaust gases continues in a serpentine fashion until finally the exhaust gases exit opening  44  in chamber  40  and are vented. 
         [0028]    Thus, the present invention employs the exhaust gas exiting primary heat exchangers  16  to heat the secondary heat exchangers  18  to extract additional heat from the exhaust gas. Moreover, as the secondary heat exchangers place the exhaust gases in direct contact with multiple wall surfaces of the heat exchangers  18 , the heat from the exhaust gas which would normally be directly vented may be efficiently employed in the furnace  10 . 
         [0029]    While the invention has been described in related to the preferred embodiments with several examples, it will be understood by those skilled in the art that various changes may be made without deviating from the fundamental nature and scope of the invention as defined in the appended claims.