| 摘要 |
PROBLEM TO BE SOLVED: To provide an internally grooved heat transfer pipe excellent in the property of contact between the outer surface of the pipe and fins and in heat- transfer performance, and also to provide a manufacturing apparatus for the pipe. SOLUTION: The internally grooved heat transfer pipe has spiral grooves and/or crossing grooves formed on its inner surface. Sinusoidal, periodical projecting and recessed parts formed on the outer surface of the pipe have an average interval of 0.8 mm or more as measured over 5 mm in the direction of the pipe axis and have a height difference of not more than 5μm between the apex of the highest projecting part and the bottom of the lowest recessed part. The average surface roughness Ra of the pipe outer surface measured in the direction of the pipe axis is not more than 0.4μm, with the maximum surface roughness Rmax being 4μm or less. Further, when grooves are transferred onto the inner surface of the heat transfer pipe by means of drum-shaped rolling rolls, the surface roughness Ra of the rolling roll in its circumferential direction and in the direction of the roll axis is 0.2μm or less, with its maximum surface roughness Rmax being 1.5μm or less. COPYRIGHT: (C)2004,JPO
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