| 摘要 |
The present invention relates to a various kinds of boilers including a steam boiler, a hot water boiler, a waste-heat boiler and an exhaust gas boiler. Projections are provided on a heat-transfer tube which connects an upper header and a lower header with each other such that a heat-transfer area pet unit length of the heat-transfer tube becomes smaller in an upstream region than that in a downstream region of combustion gas. It is preferable that installation pitches between adjacent upper and lower projections and/or projecting lengths of the projections from the heat-transfer tube are changed such that the heat-transfer area per unit length of the heat-transfer tube becomes smaller in the upstream region than those in the downstream region of the combustion gas.
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