| 摘要 |
A boiler has a plurality of inner heat-transfer tubes which makes up an inner heat-transfer tube row, and a plurality of outer heat-transfer tubes which makes up an outer heat-transfer tube row. Inner fins project from each of the inner heat-transfer tubes on an outer circumferential side of the inner heat-transfer tube row. Outer fins project from each of the outer heat-transfer tubes on an inner circumferential side of the outer heat-transfer tube row. An inner row communicating portion is provided in a lower end portion of the inner heat-transfer tube row. An outer row communicating portion is provided in an upper end portion of the outer heat-transfer tube row. An inner-fin absent region is provided in a lower end portion of each of the inner heat-transfer tubes. An outer-fin absent region is provided in a longitudinally middle portion of each of the outer heat-transfer tubes.
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