Tube bundle for shell-and-tube heat exchanger and method of constructing same

Abstract

A tube bundle is provided for a shell-and-tube heat exchanger. The tube bundle includes a plurality of elongated tubes, each of which has an intermediate portion that has a cross section in the form of a flattened circle with at least one axis of symmetry. The ends of the tubes may have a circular cross section, with the diameter of one of the circular ends being less than the other end and also less than the length of a shorter axis of symmetry of the intermediate portion of the tube. This tube construction allows the tube bundle to be assembled by inserting the smaller-diameter end of the tube through the aligned openings in the spaced-apart baffles in the tube bundle. The non-circular cross section of the intermediate portion of the tubes increases the tube-side and shell-side heat transfer coefficients.

What is claimed is: 
     
         1 . A tube bundle for a shell-and-tube heat exchanger, said tube bundle comprising:
 a plurality of hollow, elongated tubes extending in parallel and spaced-apart relationship to each other in a preselected pattern, each of said tubes having a first end for entry of a first fluid for flow within the tube along a longitudinal length of the tube and an opposite second end for the first fluid to exit the tube and an intermediate portion between the first and second ends, said intermediate portion of the tube having a cross section in the form of a flattened circle with at least one axis of symmetry;   a first tube sheet having holes into which the first ends of the tubes extend and are secured; and   a plurality of baffles positioned at spaced apart positions along the longitudinal length of the tubes for supporting the tubes and guiding flow of a second fluid exteriorly of said tubes, each of said baffles having a cutout for passage of fluid and a plurality of openings through which at least some of said tubes are inserted, wherein said cutouts of adjacent ones of said baffles are rotationally offset around a center longitudinal axis of said tube bundle.   
     
     
         2 . The tube bundle of  claim 1 , wherein said intermediate portion of the tube with said cross section in the form of a flattened circle is a majority of the longitudinal length of each tube. 
     
     
         3 . The tube bundle of  claim 1 , wherein said intermediate portion of the tube with said cross section in the form of a flattened circle is at least 75% of the longitudinal length of each tube. 
     
     
         4 . The tube bundle of  claim 1 , wherein said intermediate portion of the tube with said cross section in the form of a flattened circle is at least 90% of the longitudinal length of each tube. 
     
     
         5 . The tube bundle of  claim 1 , wherein said intermediate portion of the tube with said cross section in the form of a flattened circle is at least 95% of the longitudinal length of each tube. 
     
     
         6 . The tube bundle of  claim 1 , wherein each of said baffles is positioned in a plane generally perpendicular to the center longitudinal axis of said tube bundle. 
     
     
         7 . The tube bundle of  claim 1 , wherein each of said baffles is a partial disc and said cutout intersects a periphery of the disc. 
     
     
         8 . The tube bundle of  claim 1 , wherein said first tube sheet has additional openings into which the second ends of the tubes extend and are secured. 
     
     
         9 . The tube bundle of  claim 1 , including a second tube sheet having openings into which the second ends of the tubes extend and are secured. 
     
     
         10 . The tube bundle of  claim 1 , wherein said openings in said baffles are shaped to conform to the cross section of the intermediate portions of the tubes. 
     
     
         11 . The tube bundle of  claim 1 , wherein said cutout is a sector or segment of the baffle. 
     
     
         12 . The tube bundle of  claim 1 , wherein said preselected pattern is a square or triangular pitch. 
     
     
         13 . The tube bundle of  claim 1 , wherein said preselected pattern is a series of concentric circles. 
     
     
         14 . The tube bundle of  claim 13 , wherein in each tube the at least one axis of symmetry of the intermediate portion of the tube lies along a tangent of one of said concentric circles. 
     
     
         15 . The tube bundle of  claim 1 , wherein the cross section of the intermediate portion of each tube has two axes of symmetry with one axis being shorter than the other and wherein said first and second ends of the tubes are circular in cross section and one of said first and second ends has a diameter that is less than the length of said shorter axis of symmetry. 
     
     
         16 . The tube bundle of  claim 1 , wherein each of said tubes has said cross section in the form of a flattened circle along its entire longitudinal length. 
     
     
         17 . The tube bundle of  claim 1 , wherein said flattened circle is in the form of an elliptical or obround geometric shape. 
     
     
         18 . The tube bundle of  claim 1 , wherein said flattened circle is in the form of an oval or egg-shaped geometric shape. 
     
     
         19 . A shell-and-tube heat exchanger comprising:
 a shell having an interior volume in which a tube sheet in accordance with  claim 1  is positioned;   an inlet nozzle extending from said shell for introducing a shell-side fluid into the interior volume of the shell;   an outlet nozzle extending from the shell for removing a shell-side fluid from the interior volume of the shell;   another inlet nozzle for introducing a tube-side fluid into the first ends of the tubes within the tube bundle; and   another outlet nozzle for removing the tube-side fluid from the second ends of the tubes within the tube bundle.   
     
     
         20 . A method of assembling a tube bundle of  claim 1 , said method comprising the steps of:
 providing said first and second ends of the tubes with a circular cross section and providing said second end with a diameter that is less than the length of said at least one axis of symmetry of the intermediate portion of the tube;   spacing the baffles apart from each other a desired preselected distance with their openings in alignment;   fixing tie-rods to the baffles to secure the baffles in their spaced-apart and rotational relationship to each other;   inserting said second end of each tube through the aligned openings in each of the baffles;   fixing the first ends of each tube in holes in the first tube sheet; and   fixing the second ends of each tube in other holes in the first tube sheet or a second tube sheet.