Influence of boiling initiation surface superheat on subcooled water flow boiling critical heat flux in a SUS304 circular tube at high liquid Reynolds number

Abstract

The subcooled boiling heat transfer and the steady-state critical heat flux (CHF) in a vertical circular tube for the liquid Reynolds numbers (Red=3.65×104–3.08×105) and the flow velocities (u=3.95–30.80m/s) were systematically measured by the experimental water loop comprised of a multistage canned-type circulation pump with high pump head. The SUS304 test tube of inner diameter (d=6mm) and heated length (L=59.5mm) was used in this work. The boiling initiation noise of outer surface of the test tube in the open air was simultaneously measured up to CHF point by the sound level meter (SLM) and the microphone of a video camera (MP). The outer surface temperatures of the SUS304 test tube with heating were also observed by an infrared thermal imaging camera (ITIC) and the color temperatures of outer surface of the test tube in the open air were observed by a video camera (VC). The subcooled boiling heat transfer and CHF for SUS304 circular tube were compared with the values calculated by authors’ and other researchers’ correlations for the subcooled flow boiling heat transfer. The influences of flow velocity on the boiling initiation surface heat flux, the boiling initiation surface superheat, the subcooled boiling heat transfer and the CHF were investigated into details based on the experimental data. At the flow velocities higher than 13.3m/s, boiling initiation surface heat fluxes were close to the CHFs and surface superheats at the CHF were over to the homogeneous spontaneous nucleation temperature as well as the lower limit of the heterogeneous spontaneous nucleation temperature. The dominant mechanism of the subcooled water flow boiling CHF on the SUS304 circular tube was discussed at high liquid Reynolds number.