Multi-pipe once-through type boiler

A multi-pipe once-through type boiler, comprising:

• a case having a substantially tubular shape with a longitudinal axis;
• at least one row of a plurality of circumferentially arranged piped around said longitudinal axis, each pipe extending substantially in parallel to along said axis so as to define one wall of an annular passage and to provide a pair of spaced ends;
• said row defining, at the inside thereof, a combustion chamber extending along said axis, said chamber being open at one end;
• means for generating the flow of a combustible mixture to be directed into the combustion chamber via said open end of said chamber;
• closure means for closing the other end of the combustion chamber facing the flow generating means;
• a combustion gas passageway through said annular passage, which extends along said axis and is formed around the combustion chamber and in contact with the at least one row of pipes;
• said combustion gas passageway having an inlet extending along substantially the entire length thereof along said axis for introduction of the combustion gas from the combustion chamber;
• said combustion gas passageway having an outlet extending along substantially the entire length thereof along said axis for removing the combustion gas from the passageway wherein the combustion gas travel an arcuate path through said annular passageway from said inlet to said outlet;
• flue means connected to the outlet for the removing of the combustion gas to the outside;
• a first header connected to the casing, the pipes being, at their first end, connected to the first header so that communication of fluid to be heated is attained therebetween;
• a second header axially spaced from the first header, the pipes being, at their second ends connected to the second header so that a communication of the fluid to be heated is attained therebetween;
• a plurality of fins each extending into said gas passageway radially in a cantilever fashion formed on substantially the entire length of the outer surfaces of the pipes in such a manner that said fins extend perpendicular to said pipe surfaces in contact with the flow of the combustion gas in the combustion passageway, each of said fins having a plate shape extending substantially parallel to the direction of the flow of the heating gas, each of said fins having a plate shape defining opposite parallel edges extending substantially transversely to the flow of the heating gas wherein a leading edge of said fins is substantially perpendicular to the flow and extends the entire perpendicular length of the fin from the surface of the pipe;
• and
• wherein each of said fins forms a plate shape extending substantially transverse to the axis of the corresponding pipes so as to define an outer edge, and each of said fins having at least one slit formed, each slit extending inwardly with respect to the outer edge so as to have two space apart slit edges of a single slit, which edges are substantially parallel with respect to the opposite side edges of the fin wherein said two space apart slit edges of said single slit are substantially parallel to the flow of said heating gas, so that a front edge effect is generated by the opposite side edges and said two spaced apart parallel edges of each of the slits to which the combustion gas is contacted thereby enhancing heat transfer efficiency.