Heat exchanger

Abstract

A condensing heat exchanger of the kind having a primary heat exchanger and a secondary heat exchanger connected downstream of and in series with the primary heat exchanger. The secondary heat exchanger is arranged to at least partially condense combustion gases discharged from the primary heat exchanger. The primary heat exchanger comprising a drum having a longitudinal axis and the secondary heat exchanger comprising a plurality of small diameter tubes arranged by the side of the drum and extending parallel with the longitudinal axis of the drum.

1 . A condensing heat exchanger of the kind having a primary heat exchanger and a secondary heat exchanger connected downstream of and in series with the primary heat exchanger, in which the secondary heat exchanger is arranged to at least partially condense combustion gases discharged from the primary heat exchanger,
 wherein the primary heat exchanger comprises a drum having a longitudinal axis and the secondary heat exchanger comprises a plurality of tubes,   wherein each tube has a longitudinal axis and an outer surface which includes a spiral formation concentric with the longitudinal axis of the tube, and   wherein the tubes are arranged to extend parallel with the longitudinal axis of the drum.   
     
     
         2 . (canceled) 
     
     
         3 . A condensing heat exchanger according to  claim 1  wherein the spiral formation begins at a predetermined distance from one end of the tube and stops at a predetermined distance from the opposite end of the tube, so that the ends of the tube are plain. 
     
     
         4 . A condensing heat exchanger according to  claim 1  wherein the tubes have a diameter in the range of approximately 4 mm to 8 mm. 
     
     
         5 . (canceled) 
     
     
         6 . A condensing heat exchanger according to  claim 1  wherein the tubes are provided between inlet and outlet plates, as a subassembly of the heat exchanger. 
     
     
         7 . A condensing heat exchanger according to  claim 6  wherein the inlet plate and outlet plate are preformed with tube apertures for receiving the ends of the tubes in a pre-defined array. 
     
     
         8 . A condensing heat exchanger according to  claim 7  wherein each tube aperture has a peripheral flange to provide a sleeve for receiving part of the length of a respective tube. 
     
     
         9 . A condensing heat exchanger according to  claim 1  wherein the primary heat exchanger comprises a subassembly including a cylindrical drum sealingly attached to an outlet plate; wherein the secondary heat exchanger comprises a subassembly including said plurality of tubes sealing attached to an inlet plate; and wherein the two subassemblies are united with one another by attachment between the outlet plate and inlet plate. 
     
     
         10 . A condensing heat exchanger according to  claim 9 , further including a closure for connecting the two subassemblies and defining a passageway for combustion gases to be channelled from the primary heat exchanger to the secondary heat exchanger. 
     
     
         11 . A condensing heat exchanger according to  claim 10  wherein the closure has a box-type configuration with four side walls and a base wall, wherein the base wall has a pressed configuration in which an outer surface of the base wall extends outwardly. 
     
     
         12 . A condensing heat exchanger according to  claim 10 , further including an array of concentric circles press-formed into a major surface of the closure. 
     
     
         13 . A method of assembling a condensing heat exchanger of the kind having a primary heat exchanger and a secondary heat exchanger connected downstream of and in series with the primary heat exchanger, and in which the secondary heat exchanger is arranged to at least partially condense combustion gases discharged from the primary heat exchanger, comprising the steps of:
 providing the primary heat exchanger in the form of a drum having a longitudinal axis,   providing the secondary heat exchanger in the form of a plurality of tubes, and   providing an inlet plate and an outlet plate for the tubes, the inlet and outlet plates being preformed with tube apertures for receiving the ends of the tubes in a pre-defined array,   wherein the method further includes the steps of
 arranging the plates in a spaced array with said tubes arranged between the plates with the tubes in alignment with the tube apertures, and 
 forcing the ends of the tubes into the respective tube apertures by driving the plates in the direction of one another, and then 
 arranging the tubes to extend parallel with the longitudinal axis of the drum. 
   
     
     
         14 . (canceled) 
     
     
         15 . A method according to  claim 14  wherein each tube aperture is provided with a peripheral flange projecting from the associated plate to provide a sleeve for part of the length of a respective tube. 
     
     
         16 . A method according to  claim 15  wherein the peripheral flange is swaged to fixedly couple the flange to the tubes. 
     
     
         17 . A method according to  claim 13  wherein a spiral thread is formed in the outer surface of each tube prior to incorporation in the assembly. 
     
     
         18 . A method according to  claim 17  wherein each tube is drawn and then the spiral thread is formed on the drawn tube, prior to a second drawing operation, to remove any significant deformations generated when the thread is formed. 
     
     
         19 . A method according to  claim 13  wherein: the primary heat exchanger is formed as a subassembly including a cylindrical drum sealingly attached to an outlet plate; the secondary heat exchanger is formed as a separate subassembly including said plurality of tubes sealing attached to an inlet plate; and the two subassemblies are united with one another by attachment between the outlet plate and inlet plate. 
     
     
         20 . A method according to  claim 19  wherein a closure is attached to the united subassemblies to define a passageway for combustion gases to be channelled from the primary heat exchanger to the secondary heat exchanger. 
     
     
         21 . A method according to  claim 20  wherein an array of concentric circles is pressed into a surface of the closure to reduce noise during flexure of the closure under thermal expansion. 
     
     
         22 . A method according to  claim 20  wherein the closure is of pre-formed box-type configuration having four side walls and a base wall, wherein the base wall is pressed outwards, to reduce noise during flexure of the closure under thermal expansion.