Enhanced tubular heat exchanger

Abstract

The present invention is an enhanced tubular heat exchanger for a furnace with the heat tubes of the heat exchanger having two straight sections connected by a bend. The tubes of the heat exchanger include an enhanced portion which has a smaller cross-sectional area than the flue portion, in the form of an elliptically shaped tube. The enhanced portion further includes turbulators to promote the heat exchange from the heated flue gases. Circulation of air around the exterior of the tubes is also facilitated because the enhanced portion is disposed at a small angle relative to the flue portion. A plurality of tubes are disposed within the heat exchanger so that the circulation air first flows over the enhanced portions then over and around the generally cylindrical portions. This lowers the initial pressure drop in the circulation air flow and thereby facilitates the circulation of and heat transfer to the air being heated.

What is claimed is:  
     
       1. A heat exchanger element for use in a furnace including a burner, an exhaust system, and a heat exchanger having at least one heat exchanger element, said heat exchanger element comprising; : an elongated tube having an inlet adapted to be operably connected to the burner, an outlet adapted to be operably connected to the exhaust system, a flue portion located adjacent to said inlet and adapted to receive heated flue gases, and an enhanced portion defined by a substantial axial portion of said elongated tube, said enhanced portion located adjacent to said outlet and adapted to expel said heated flue gases, said enhanced portion being generally flattened and thereby having a smaller cross-sectional area than the cross-sectional area of said flue portion  a circular cross- section, said tube having first and second straight sections connected by a bend, said tube having an inlet adapted to be operably connected to the burner, an outlet adapted to be operably connected to the exhaust system, a flue portion including said first straight section and located adjacent to said inlet and adapted to receive said heated flue gases, and an enhanced portion including said second straight section and located adjacent to said outlet and adapted to expel said heated flue gases, said enhanced portion being generally flattened along a majority of its length and thereby having a smaller cross - sectional area than the cross - sectional area of said flue portion.   
     
     
       2. The heat exchanger element according to claim  1  wherein said enhanced portion comprises a generally straight portion of the length of said heat exchanger element, which is connected to the remainder of the heat exchanger by a bend portion. 
     
     
       3. The heat exchanger element according to claim  1  wherein said enhanced portion includes a turbulating means for disrupting and radially mixing said heated flue gases to increase the heat transfer from heated flue gases within said enhanced portion. 
     
     
       4. The heat exchanger element according to claim  1  further comprising an inlet turbulator for quenching the flames of a burner, said inlet turbulator including a body extending within said flue portion and a plurality of tabs angularly extending from said body. 
     
     
       5. The heat exchanger element of claim  4  wherein said body has a spiral shape. 
     
     
       6. The heat exchanger element of claim  1  wherein said enhanced portion and said flue portion are connected by a bend portion, said bend portion including a transition portion which gradually decreases in cross-sectional area from said flue portion to said enhanced portion. 
     
     
       7. A furnace comprising: 
       a burner;  
       a casing defining a plenum;  
       a fan operably connected to said plenum; and  
       at least one elongated tube disposed in said plenum, said tube including a flue portion, an enhanced portion, an inlet operably connected to said burner, and an outlet, said flue and enhanced portions defining a passageway for a flow of heated flue gases from said inlet to said outlet, said tube being in fluid flow communication with said fan, said flue portion located adjacent to said inlet and adapted to receive said heated flue gases, said enhanced portion comprising a substantial axial portion of said elongated tube, said enhanced portion located adjacent to said outlet, said enhanced portion being generally flattened relative to said flue portion and having a smaller cross-sectional area than the cross-sectional area of said flue portion  having first and second straight sections connected by a bend, and including a flue portion including said first straight section, and enhanced portion including said second straight section, an inlet operably connected to said burner, and an outlet, said flue portion and enhanced portion defining a passageway for a flow of heater flue gases from said inlet to said outlet, said tube being in fluid flow communication with said fan, said flue portion having a circular cross- section, said flue portion located adjacent to said inlet and adapted to receive said heated flue gases, said enhanced portion being generally flattened relative to said flue portion throughout its length, and having a smaller cross - sectional area than the cross - sectional area of said flue portion.   
     
     
       8. The furnace of claim  7  further comprising an inlet turbulator for quenching the flames of said burner, said inlet turbulator including a body extending within said flue portion and a plurality of tabs angularly extending from said body. 
     
     
       9. The furnace of claim  8  wherein said body has a spiral shape. 
     
     
       10. The furnace of claim  7  wherein said elongated tube includes a bend portion connecting said enhanced portion and said flue portion, said bend portion having a shape which gradually decreases in cross-sectional area from said flue portion to said enhanced portion. 
     
     
       11. The furnace of claim  7  further comprising a circulation fan disposed adjacent said plenum and arranged to blow air sequentially over said enhanced portion and said flue portion, said enhanced portion having a cross-sectional elliptical shape which is disposed with the major axis defining a line which is generally parallel with the direction of air blown by said exhaust fan whereby said blown air experiences a relatively low pressure drop while passing over said enhanced portion and thereby does not shield said flue portion from said blown air. 
     
     
       12. The furnace of claim  7  further comprising an air conditioner unit mounted adjacent said casing. 
     
     
       13. The furnace according to claim  7  wherein said enhanced portion includes turbulating means for disrupting and radially mixing heated flue gases to increase heat transfer from said heated flue gases in said enhanced portion. 
     
     
       14. The furnace according to claim  7  wherein said enhanced portion comprises a generally straight portion of the length of said elongated tube, which is separated from the remainder of said elongated tube by a bend portion. 
     
     
       15. The furnace of claim  14  wherein said turbulating means includes a plurality of ribbed indentations formed in said enhanced portion to cause the flow of said heated flue gases through said enhanced portion to be nonlaminar. 
     
     
       16. The furnace of claim  14  wherein said turbulating means includes an insert positioned within the interior of said enhanced portion, said insert having an elongate body and a plurality of tab portions which extend at angles from said insert body, said tab portions causing the flow of heated flue gases through said enhanced portion to be nonlaminar. 
     
     
       17. The furnace of claim  13  wherein said turbulating means includes a plurality of indentations formed in said enhanced portion for causing the flow of said heated flue gases in said enhanced portion to be nonlaminar. 
     
     
       18. The furnace of claim  13  wherein said turbulating means includes an insert positioned within the interior of said enhanced portion, said insert having an elongate body and a plurality of tab portions which extend at angles from said insert body whereby said tab portions cause the flow of said heated flue gases in said enhanced portion to be nonlaminar. 
     
     
       19. A furnace comprising: 
       a burner;  
       a casing defining a plenum;  
       an exhaust fan operatively associated with said plenum;  
       a plurality of elongated tubes disposed in said plenum, each said tube including an inlet operably connected to said burner, an outlet operably connected to said exhaust fan, a flue portion located adjacent to said inlet and adapted to receive heated flue gases from said burner, and an enhanced portion located adjacent to said outlet for expelling said heated flue gases, said enhanced portion comprising a substantial axial portion of said elongated tube  having first and second straight sections connected by a bend, including an inlet operably connected to said burner, an outlet operably connected to said exhaust fan, a flue portion of circular cross- section, said flue portion including said first straight section and located adjacent to said inlet and adapted to receive heated flue gases from said burner, and an enhanced portion including said second straight section and located adjacent to said outlet for expelling said heated flue gases , said enhanced portion being narrowed and having a smaller cross-sectional area than the cross-sectional area of said flue portion, said flue portion and enhanced portion of each of said tubes defining a communication passage for the flow of heated flue gases from said inlet to said outlet; and  
       a circulation fan in communication with said plenum and arranged to cause a flow of air over said tubes in a first direction;  
       at least one said enhanced portion having a cross-sectional elliptical shape which is disposed with the major axis defining a line which is generally parallel with said first direction.  
     
     
       20. The furnace of claim  19  wherein the major axis of said at least one enhanced portion is disposed at about an 11.5° angle with respect to a plane which is defined by the axial center of said inlet and the axial center of said outlet. 
     
     
       21. The furnace of claim  19  wherein said tubes are spaced apart by approximately the sum of the diameter of said flue portion and the length of the minor axis of said at least one enhanced portion, and said plurality of tubes blocks direct flow of said air flow through said plenum. 
     
     
       22. The furnace of claim  19  further comprising an air conditioner unit mounted adjacently to said casing. 
     
     
       23. The furnace according to claim  19  wherein said enhanced portion comprises a generally straight portion of the length of each of said elongated tubes, each said enhanced portion being separated from the remainder of each said elongated tube by a bend portion.