| 摘要 |
PROBLEM TO BE SOLVED: To provide an internally grooved heating tube excellent in evaporation and condensation heat transfer characteristics and having optimal structure in which the helix angle of fin having effect on the performance is also taken into account as one factor by finding out the relationship between the performance and the ratio of fin pitch to the outer circumferential length of heating tube. SOLUTION: The internally grooved heating tube is provided with a plurality of fins formed on the inner wall face having outside diameter less than 10 mm along a line making a specified angle against the axis of tube. Assuming the outside diameter of the heating tube is D, the thickness on the bottom is Tw, the number of fins is N and the angle (helix angle) between the axis of tube and the fin isβ, the ratio (Pf/πD) between a pitch Pf determined according to a formula Pf=(D-2.Tw)π/N.cosβand the outer circumferential length of the internally grooved tube is set in the range of 0.0135-0.018.
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