| 摘要 |
<p>According to the present invention, a first tube (2) is constructed by connecting a plate material (21, 22) into a tubular shape. In the manufacturing process, after an inner fin (5) is disposed around an outer wall of a second tube (3), the first tube (2) is disposed around the second tube (3), and the first tube (2) and the second tube (3) are fixed by connecting the plate material (21, 22) in such a manner that the inner fin (5) is in contact with the both tubes (2, 3). In this way, the inner fin (5) and both tubes (2, 3) are certainly contacted closely to each other without enlarging the second tube (3). <IMAGE></p> |
