Heat exchanger with double wall tubes and three tube sheets

Claim 1

A heat exchanger comprising a shell, a plurality of generally straight double wall tubes each tube having an inner wall portion and an outer wall portion which are contiguous, and at least one groove at the interface of the wall portions, said groove generally extending the length of the tube, a single tube sheet adjacent one end of the tubes and a pair of tube sheets adjacent the other end of the tubes, said pair of tube sheets being disposed in a spaced relationship to form an enclosed space, the inner wall portion of one end of the tubes terminating adjacent one of said pair of tube sheets and the outer wall portion of said tubes terminating adjacent the other of said pair of tube sheets and the groove being in fluid communication with the enclosed space, the outer wall portions of the tubes being sealed at the junctions between the outer wall portions and both side of the single tube sheet, and a segment of the outer wall portion within the single tube sheet having at least one opening extending therethrough and disposed in communication with the groove, whereby leak detection can be made in the enclosed space regardless of whether a leak occurs in either wall of the tube or at any weld between the tube and the tube sheet.