The subcooled flow boiling CHF and the heat transfer characteristics for the flow velocities (u=4.0 to 13.3 m/s), the inlet subcoolings (ΔTsub,in=137.49 to 153.87 K), the inlet pressure (Pin=740.67 to 975.78 kPa) and the dissolved oxygen concentration (O=8.63 to 0.0288 ppm) are systematically measured by the experimental water loop installed the pressurizer. The SUS304 tubes of d=3 mm and L=66.5 mm (L/d=22.17) with the inner surfaces of smooth and mirror finished are mainly used in this work. Heat transfer characteristics and CHF data are compared with those for the rough finished inner surface (RF) previously obtained and the CHFs are compared with the values calculated by the CHF correlations against outlet and inlet subcoolings based on the experimental data for the rough finished inner surface under the N2 gas pressure. The influence of inner surface roughness on the heat transfer characteristics and the CHFs for wide range of dissolved gas concentration are investigated in detail.

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