| 摘要 |
A firetube having an elongated cylindrical shell is characterized by a plurality of circular rows of elongated U-shaped fins, each having a bottom surface, preferably curved along a radius or flat, secured to the inner surface of the cylindrical shell and two flat, planar, preferably parallel sides extending upwardly from the bottom surface, with the fins in each row aligned substantially parallel along the axis of the cylindrical shell.
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