Influence of Dissolved Gas Concentration on Subcooled Flow Boiling Critical Heat Flux in Short Vertical Tube

The subcooled flow boiling critical heat fluxes (CHFs) are systematically measured by using the water loop installed the pressurizer to investigate the pressurization gas effect for the flow velocities (u = 4.0 to 13.3 m/s), the inlet subcoolings (ΔT_sub,in = 70.08 to 145.57 K) and the inlet pressure (P_in = 740.67 to 975.43 kPa). The SUS304 tube of the inner diameter (d = 3 mm), the heated length (L = 66.5 mm) and L/d = 22.17 with the inner surface of rough finished was used. The CHF data under the pressurization by saturated vapor in a pressurizer were compared with the values calculated from the CHF correlations against outlet and inlet subcoolings based on the experimental data under the nitrogen (N₂) gas pressure previously obtained. The CHFs for the dissolved oxygen concentration of 6.59, 4, 2, 1, 0.5, 0.0496 and 0.0265 ppm were systematically measured for the flow velocities (u = 4.0 to 13.3 m/s), the inlet subcoolings (ΔT_sub,in = 137.49 to 153.87 K) and the inlet pressure (P_in = 762.97 to 975.78 kPa). And the CHFs for the test tube with the smooth finished inner surface were measured at the dissolved oxygen concentration of 0.1004 and 0.0413 ppm for the same experimental conditions. Influence of the inner surfaces of rough and smooth finished on the CHFs was clarified for low dissolved gas concentration.