| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to eliminate a vibration at a twisted fin and to reduce the manufacturing cost with high durability by integrally molding the twisted fin in an inner tube at the time of extrusion molding the inner tube. SOLUTION: The twisted fin 11 of an inner tube 4 is molded integrally with the tube 4 at the time of extrusion molding to manufacture the tube 4. The twisting pitch of the fins 11 is decided from the heat transfer performance in the tube 4 and the diameter and length of the tube 4 and the easiness or difficulty at the time of molding. In this case, only one side edge of the fin 11 is integrally molded with the tube 4, and the other end may be slightly separated from the inner wall 4a of the tube 4. The fin 7 formed on the outer periphery of the tube 4 is integrally molded at the time of molding the tube 4. Thus, even if the boiling energy is operated at the time of vaporizing, the fin entirely has the integral structure with the inner tube, and hence no vibration is generated at the fin. Accordingly, the durability can be improved. |
