Patent ID: 7984752

Claim:
A double-pipe heat exchanger in which an outer tube is fitted over an outer circumference of an inner tube, a space between both end portions of both tubes is closed, a first inlet/outlet of a first fluid are opened in the outer circumference at both end portions of the outer tube to provide a first flow path in which said first fluid flows in an axial direction thereof between the outer circumferential side of the inner tube and the inner circumferential side of the outer tube, and a second inlet/outlet provides a second flow path in which a second fluid flows on the inner circumferential side of the inner tube, wherein said inner tube is so constructed that three or more swollen portions in a bladder-like shape in section protruded in a radial direction from the center are formed at equal intervals in a circumferential direction of the inner tube along an axis line, and each bladder-like shape portion has a closed mouth portion section toward the axis line preventing fluid from flowing through the mouth portion into an adjacent bladder-like shape portion, each of said three or more swollen portions having a distal portion away from the mouth portion, the distal portions of the swollen portions defining a wave shape along an axial direction with top portions of the waves being in contact with the inner circumferential side of the outer tube; wherein said inner tube is formed in a circular shape in section at both end portions thereof, with both end portions being connected to the outer tube; wherein both tubes are applied with an external force in a state that the outer tube is fitted over the outer circumference of the inner tube so that axis lines thereof are bent to deform plastically; and wherein said top portions of the wave in said swollen portions of the inner tube that are in contact with the outer tube are not fixed to said outer tube allowing relative movement between said outer tube and inner tube in an area of said contact during bending of said heat exchanger.