| 摘要 |
PROBLEM TO BE SOLVED: To provide a once-through boiler the output of which can be controlled easily in variable pressure operation and which can be cooled highly efficiently and can reduce the mass flow rate in a tube. SOLUTION: The furnace wall of a once-through boiler is formed of a ribbed tube provided with a spiral rib on its internal surface and the ribbed tube is inclined by 45 deg.-90 deg. from the vertical direction. In addition, the equivalent inside diameter (d), height (h), and lead angleθof the ribbed tube are selected so that a dimensionless amount F (F=d/(hcosθ) is may be positioned in the area between the curves (c) and (b), preferably, between the curves (a) and (b) against the mass flow rate M of a fluid flowing through the ribbed tube when the steam output is 100%. When the swirling force of the internal fluid along the wall of the ribbed tube is increased by selecting the winding direction of the rib in accordance with the flowing direction of the fluid on the front side when viewed from the inside of the furnace of the boiler, a more satisfactory result can be obtained.
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