| 摘要 |
PROBLEM TO BE SOLVED: To obtain a high performance heating tube without increasing the weight per length by providing, on the outer surface thereof, with a plurality of grooves of specified depth, at a specified interval, in the direction of the tube axis and a large number of fins of specified height at a specified pitch and providing, on the inner surface thereof, with a plurality of protrusions extending spirally and intermittently in the direction of the tube axis. SOLUTION: Fins 1 are formed, at a fine pitch, on the outer surface of a copper tube being employed as the heating tube for a down-flow liquid film type heat exchanger and a large number of grooves 2 extending in the longitudinal direction to divide the fins 1 in the circumferential direction are formed, at a constant interval, in the circumferential direction. The grooves 2 are formed larger (deeper) than the height of the fin 1. Spiral protrusions are formed intermittently in the tube by pressing the tube with a protruding die spirally and intermittently from the outside thereby recessing the tube wall inwardly. The groove 2 has a depth of 0.5-2.0 mm and a circumferential interval of 0.3-4.0 mm and the fin 1 between the grooves has a height of 0.3-1.5 mm and a pitch of 0.4-1.5 mm.
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