Heat exchanger with leak detecting double wall tubes

Claim 1

A heat exchanger for transferring heat from a primary fluid to a secondary fluid, said heat exchanger comprising a shell, a plurality of double wall tubes with at least one groove at the interface of the two walls, a single tubesheet having a plurality of holes for receiving one end of the tubes disposed at one end of the shell, a pair of generally parallel spaced apart tubesheets having holes for receiving the other end of the tubes disposed at the other end of the shell, the outer wall of each tube terminating adjacent the inner tubesheet of said pair, the inner wall of said tubes terminating adjacent the outer tubesheet of said pair, the inner and outer wall of the said other end of said tubes terminating adjacent the outer edge of said single tubesheet, said shell having enlarged bulbous portions disposed adjacent each end thereof, said shell extending into said bulbous portions forming a double wall which produces chambers between said bulbous portions and said shell, foraminous collars disposed between said chambers and the inner portion of said shell, each bulbous portions having a nozzle for said primary fluid, one of said primary fluid nozzles being an inlet nozzle, the other being an outlet nozzle, a head disposed on each end of said shell, said heads cooperating with the tubesheets on each end of said shell to form a header for said tubes, one of said heads having an inlet nozzle for said secondary fluid, and the other head having an outlet nozzle for said secondary fluid.