Heat exchanger and method

Abstract

A shell and tube heat exchanger includes a plurality of tubes having non-circular cross sectional shapes to improve heat transfer. The tubes may have central portions having an oblong cross-sectional shape with generally flat opposite side faces. The side faces may include raised portions to increase heat transfer. Alternatively, the tubes may have a C-shape in cross section. The shape of the tubes promotes thin film boiling of the fluid in the tubes to improve heat transfer.

The invention claimed is: 
     
         1 . A heat exchanger, comprising:
 a shell defining a cavity and including fluid inlets and outlets to permit flow of a first fluid through the cavity;   an inner tube assembly comprising at least one elongated tube and fluid conduits connected to opposite ends of the tube, the fluid conduits extending outside the shell to permit flow of a second fluid through the inner tube assembly; and wherein:   the at least one tube includes an elongated internal passageway, wherein at least a portion of the elongated internal passageway of the tube has an oblong shape in cross section to promote thin film boiling of fluid flowing through the elongated internal passageway to thereby provide increased heat transfer from the first fluid to the second fluid.   
     
     
         2 . The heat exchanger of  claim 1 , wherein:
 the tube comprises a plurality of tubes having elongated internal passageways, wherein at least a portion of the elongated passageways have oblong shapes in cross section.   
     
     
         3 . The heat exchanger of  claim 2 , wherein:
 each tube has opposite ends, each opposite end defining a substantially circular opening.   
     
     
         4 . The heat exchanger of  claim 3 , wherein:
 each tube includes transition sections extending between the substantially circular openings and the portion of each tube having an oblong shape in cross section.   
     
     
         5 . The heat exchanger of  claim 4 , wherein:
 each tube includes an elongated central portion having an oblong cross sectional shape.   
     
     
         6 . The heat exchanger of  claim 5 , wherein:
 the elongated central portion of each tube includes a pair of generally planar side wall portions that are spaced apart, and a pair of curved sidewall end portions interconnecting the generally planar side wall portions.   
     
     
         7 . The heat exchanger of  claim 6 , wherein:
 the generally planar side wall portions have a substantially uniform thickness.   
     
     
         8 . The heat exchanger of  claim 7 , wherein:
 at least a portion of each generally planar side wall portion includes a plurality of raised portions forming protrusions on outer surfaces of each generally planar side wall portion.   
     
     
         9 . The heat exchanger of  claim 8 , wherein:
 the protrusions comprise elongated ridges extending along the tubes.   
     
     
         10 . The heat exchanger of  claim 8 , wherein:
 the protrusions comprise a plurality of generally circular bulges.   
     
     
         11 . The heat exchanger of  claim 1 , wherein:
 the at least one tube comprises sheet metal having a substantially uniform thickness.   
     
     
         12 . A tube assembly for a shell and tube heat exchanger, the tube assembly comprising:
 first and second end plates having a plurality of generally circular openings therethrough;   a plurality of tubes extending between the first and second end plates, each tube having opposite end portions with outer surfaces that have a generally circular cross sectional shape, wherein the opposite end portions are received in the openings of the first and second end plates and being connected thereto; and wherein:   the tubes have flattened central portions forming fluid passageways having oblong cross sectional shapes to thereby provide improved heat transfer.   
     
     
         13 . The tube assembly of  claim 12 , wherein:
 the flattened central portions of each tube includes a pair of spaced apart side wall portions that are generally planar.   
     
     
         14 . The tube assembly of  claim 13 , wherein:
 each tube includes curved side wall portions extending between and interconnecting the generally planar side wall portions.   
     
     
         15 . The tube assembly of  claim 13 , wherein:
 the generally planar side wall portions include a plurality of raised portions forming protrusions on outer surfaces of each generally planar side wall portion.   
     
     
         16 . The heat exchanger of  claim 15 , wherein:
 the protrusions comprise elongated ridges extending along the tubes.   
     
     
         17 . The heat exchanger of  claim 15 , wherein:
 the protrusions comprise a plurality of generally circular bulges.   
     
     
         18 . A tube for shell and tube heat exchangers, the tube comprising:
 an elongated tubular structure having spaced apart inner and outer side walls that are generally C-shaped in cross section, wherein the inner and outer side walls are interconnected by transverse end wall portions to form an internal passageway that is generally C-shaped.   
     
     
         19 . The tube of  claim 18 , wherein:
 the inner and outer side walls define outer surfaces that are generally cylindrical in shape.   
     
     
         20 . The tube of  claim 18 , wherein:
 the tube comprises sheet metal having elongated opposite edge portions that are interconnected to form a tube.   
     
     
         21 . The tube of  claim 20 , wherein:
 the opposite edge portions are interconnected by folds to form a first transverse end wall portion.   
     
     
         22 . The tube of  claim 21 , wherein:
 the tube comprises a single piece of sheet metal that is deformed to define a second transverse end wall portion.