SUBCOOLED BOILING HEAT TRANSFER FOR TURBULENT FLOW OF WATER IN A SHORT VERTICAL TUBE

摘要

The subcooled boiling heat transfer for Platinum test tube divided into three sections (upper, mid and lower positions) for the flow velocities (u=4.0 to 13.3 m/s), the inlet liquid temperatures (T_(in)=295.26 to 305.25 K), the inlet pressures (P_(in)=739.26 to 1064.48 kPa) and the exponentially increasing heat input with various periods (Q=Q_0exp(t/τ), τ=22.52 ms to 26.31 s) was systematically measured by an experimental water loop comprised of a pressurizer. The Platinum test tube of inner diameter (d=2 mm), heated length (L=66.5 mm), L/d (=22.17) and wall thickness (δ=0.5 mm) with a commercial finish of inner surface (average roughness, Ra=0.40 μm) is used in this work. The outer surface temperature of the test tube was observed by an infrared thermal imaging camera. The axial variations of the inner surface temperature, the heat flux and the heat transfer coefficient from non-boiling to CHF were clarified. The subcooled boiling heat transfer for Platinum test tube with a commercial finish of inner surface was compared with the values calculated by other workers' correlations for the subcooled boiling heat transfer. The influence of exponential period (τ) and flow velocity (u) on the subcooled boiling heat transfer is investigated into details and the predictable correlation of the subcooled boiling heat transfer for turbulent flow of water in a short vertical tube is derived based on the experimental data for Platinum test tube with a commercial finish of inner surface. The correlation can describe the subcooled boiling heat transfer coefficients obtained in this work within 15 % difference.