Dense twisted bundle heat exchanger

Abstract

A shell and tube heat exchanger is disclosed that is comprised of a dense hexagonal bundle of tubes with tube spacing maintained by spacers on the individual tubes. Exchanger performance is enhanced by any or all of three types of bends of the tubes: bundle twisting; bundle enlargement at the tubesheets; and shell bending. Referring to FIG. 7, the spacing enlargement bending is illustrated.

1 . A heat exchanger comprised of:
 a. a hexagonal bundle of tubes in triangular pitch configuration;   b. helically wound spacers on some of the tubes;   c. a closely conforming shell containing the bundle; and   d. a tubesheet at each end of the shell plus bundle;   e. wherein at least some of the tubes are bent.   
     
     
         2 . The heat exchanger according to  claim 1  wherein the spacers maintain tube-to-tube spacing of less than 1.25 tube diameters along most of the bundle, and wherein the tubes are bent at each end of the bundle to increase the tube-to-tube spacing to the tubesheet spacing which is no less than 1.25 tube diameters. 
     
     
         3 . The heat exchanger according to  claim 1  wherein at least some of said tube bends are due to the bundle being twisted inside said shell, whereby individual tubes assume a helicoidal shape. 
     
     
         4 . The heat exchanger according to  claim 2  wherein at least some of said tube bends are from bending the shell plus bundle. 
     
     
         5 . The heat exchanger according to  claim 1  wherein the tube bends are due to a combination of bundle twisting and shell bending. 
     
     
         6 . The heat exchanger according to  claim 1  wherein said spacers are sparsely distributed on approximately every third tube, and wherein the hexagonal bundle has an odd number of rings of tubes, and wherein the center tube of the hexagonal bundle has a spacer. 
     
     
         7 . The heat exchanger according to  claim 1  wherein said spacers are sparsely distributed on approximately every third tube, and wherein the hexagonal bundle has an even number of rings of tubes, and wherein the center tube of the hexagon does not have a spacer. 
     
     
         8 . A heat exchanger comprised of a circular shell that contains a twisted bundle of heat exchange tubes, plus a tubesheet for each end of the bundle. 
     
     
         9 . The heat exchanger according to  claim 8  additionally comprised of spacers around some of the tubes, and wherein the bundle of tubes is twisted at least one revolution 
     
     
         10 . The heat exchanger according to  claim 9  wherein the spacers are helically wrapped around some of the tubes, wherein for any adjoining tubes with spacers the spacers are wound in opposite direction, and wherein the bundle of tubes is hexagonal with triangular pitch. 
     
     
         11 . The heat exchanger according to  claim 10  wherein the shell plus bundle is bent into a helical coil. 
     
     
         12 . The heat exchanger according to  claim 10  wherein the shell plus bundle has at least one bend and at least two straight sections. 
     
     
         13 . The heat exchanger according to  claim 10  wherein the bundle and the tubesheets have the same tube-to-tube spacing, and that spacing is at least 1.25 tube diameters. 
     
     
         14 . The heat exchanger according to  claim 10  wherein the tube-to-tube spacing of the bundle is less than the tube-to-tube spacing of the tubesheets, and additionally comprised of tube bends at each end of the bundle to transition from the one spacing to the other. 
     
     
         15 . A process for manufacturing a heat exchanger comprising:
 a. assembling a hexagonal bundle of parallel tubes;   b. inserting said bundle into a circular shell;   c. loosely inserting the tubes into tubesheets at each end of the bundle;   d. twisting one of the tubesheets at least one revolution relative to the other tubesheet;   e. attaching the tubesheets to the shell; and   f. attaching the tubes to the tubesheets.   
     
     
         16 . The process according to  claim 15  additionally comprising placing helically wrapped spacers on some of the tubes before step a. 
     
     
         17 . The process according to  claim 15  additionally comprising bending the shell between steps e. and f. 
     
     
         18 . The process according to  claim 15  additionally comprising bending the tubes at each end of the bundle to match tubesheet spacing, between steps b. and c. 
     
     
         19 . The heat exchanger according to  claim 2  wherein at least some of said tube bends are due to the bundle being twisted inside said shell, whereby individual tubes assume a helicoidal shape, and wherein said heat exchanger has no baffles for the tubes. 
     
     
         20 . The heat exchanger according to  claim 1  wherein at least some of said tube bends are from bending the shell plus bundle, and wherein said heat exchanger has no baffles for the tubes.