Critical Heat Fluxes of Subcooled Water Flow Boiling in Short Vertical Tubes (Part 8. Transient CHF Correlation)

摘要

The transient critical heat fluxes (CHFs) of the subcooled water flow boiling for the flow velocities (u=4.0 to 13.3 m/s), the inlet subcoolings (ΔT{sub}(sub,in)=68.1 to 161.1 K), the inlet pressure (P{sub}(in)=718.3 to 1314.6 kPa), the dissolved oxygen concentration (O{sub}2=2.94 ppm to Saturated one) and the exponentially increasing heat input (Q{sub}0 exp(t/τ), τ=16.8 ms to 15.5 s) are systematically measured with the experimental water loop comprised of the pressurizer. The SUS304 tubes of the inner diameters, (d=3, 6, 9 and 12 mm), heated lengths, (L=33.15 to 132.9 mm), L/d=5.48 to 11.08 and wall thickness (δ=0.3 and 0.5 mm) with the rough finished inner surface (Surface roughness, Ra=3.18 μm) are used in this work. The transient CHF data are compared with the steady state ones previously obtained and with the values calculated by the transient CHF correlation against inlet subcooling and the steady state CHF correlation against outlet subcooling. The transient CHF correlation against outlet subcooling is also derived based on the experimental data. The transient CHF is investigated into details for the exponentially increasing heat input (Q{sub}0 exp(t/τ), τ=16.8 ms to 15.5 s) and the dominant mechanism of the subcooled flow boiling critical heat flux for high heating rate is discussed.