Double-tube heat exchanger and manufacturing method therefor

A manufacturing method for a double-tube heat exchanger, the doble-tube heat exchanger including:

• an outer tube;
• and
• an inner tube inserted into the outer tube,
• the double-tube heat exchanger being provided with an inside channel inside the inner tube and provided with an outside channel between the inner tube and the outer tube, and the double-tube heat exchanger being configured to exchange heat between a fluid flowing through the inside channel and a fluid flowing through the outside channel,
• wherein according to an insertion direction front side being a front side and an insertion direction rear side being a rear side, when the inner tube is inserted into the outer tube,
• the inner tube includes an inner tube large-diameter portion, an inner tube first small-diameter portion, an uneven portion arranged between the inner tube large-diameter portion and the inner tube first small-diameter portion, and an inner tube second small-diameter portion that has a same outer diameter as the inner tube first small-diameter portion, wherein the uneven portion comprises a concave portion and a convex portion, a rear end of the uneven portion is connected to the inner tube large-diameter portion by the convex portion, a front end of the uneven portion is connected to the inner tube first small-diameter portion by the concave portion, and the inner tube second small-diameter portion and the inner tube first small diameter portion are at opposite axial end sides of the inner tube large-diameter portion,
• a large-diameter sealing portion is interposed between a rear end portion of the outer tube and the inner tube, a small-diameter sealing portion having a smaller diameter than the large-diameter sealing portion is interposed between a front end portion of the outer tube and the inner tube, and
• the outside channel and the uneven portion are arranged by using a difference in axial position and a difference in diameter between the large-diameter sealing portion and the small-diameter sealing portion,
• the manufacturing method comprising:
• inserting a front end of the inner tube into a rear end of the outer tube;
• positioning the inner tube and the outer tube by moving the inner tube forward relative to the outer tube after insertion;
• and
• forming the large-diameter sealing portion by connecting the rear end portion of the outer tube and the inner tube after positioning, and forming the small-diameter sealing portion by connecting the front end portion of the outer tube and the inner tube after positioning.