Shell and tube heat exchanger with welds joining the tubes to tube sheet

DETAILED DESCRIPTION According to one aspect of the invention, there is provided a falling film heat exchanger comprising a shell connected to vertically spaced apart horizontally arranged upper and lower tubesheets; a plurality of tubes vertically positioned and parallel to one another extending through holes in the tubesheets in fluid-tight sealing engagement therewith achieved by roll expansion of the tubes against the walls of the holes; and a continuous weld circumferentially joining each tube to the top of at least the upper tubesheet.
Although the tops of the tubes can be flush with the top surface of the upper tubesheet, the invention is more suitably used when the tops of the tubes extend uniformly above the top surface of the upper tubesheet.
However, when the tubes are close together, the tops of the tubes will generally be less than two inches above the tubesheet, unless the tubes are subsequently extended, because it is not feasible at present to manually or machine deposit the circumferential welds when the tubes are taller and close together because there is insufficient working room in which to weld.
According to a second aspect of the invention there is provided a falling film heat exchanger comprising a shell connected to vertically spaced apart horizontally arranged upper and lower tubesheets; a plurality of primary tubes vertically positioned close together and parallel to one another extending through holes in the tubesheets in fluid-tight sealing engagement therewith; the upper ends of the tubes projecting above the top surface of the upper tubesheet a short distance no greater than that which permits circumferential welding of the tube wall to the tubesheet by a fillet weld; a continuous fillet weld circumferentially joining each tube wall to the top of the upper tubesheet; and an extension tube axially positioned on, and welded to, the top ends of the primary tubes.
The top of the primary tubes will usually be less than two inches above the top surface of the upper tubesheet