| 摘要 |
PROBLEM TO BE SOLVED: To improve the efficiency of heat exchanging, in a double-pipe heat exchanger having an inner pipe 1 and an outer pipe 2.SOLUTION: A first spiral protrusion 3 and a second spiral protrusion 4 are bent and formed on the inner pipe 1 and the outer pipe 2, respectively, and surface contact is provided between the first spiral protrusion 3 and the second spiral protrusion 4. |
