Study on interfacial friction in the inverted annular film boiling regime

Abstract

The interfacial friction factor is an important closure model in the two-fluid model for the inverted annular film boiling (IAFB) regime. Almost all the interfacial friction factor correlations used in IAFB modeling were obtained based on experimental data from annular two-phase flows. This paper first reviews the interfacial friction factor models/correlations used in IAFB modeling. A laminar vapor film model is then derived for the smooth IAFB region based on a laminar flow assumption. Experimental data obtained from subcooled and low-quality film boiling experiments in the literature are reduced to calculate the interfacial friction factor by solving one-dimensional two-fluid momentum equations for the liquid and vapor phases. The trend of the interfacial friction factor indicates that the transition from the smooth to wavy IAFB regions occurs at a void fraction range of 0.2 to 0.4. Comparisons between the laminar vapor film model and corresponding experimental data and nine correlations in the literature indicate that the laminar vapor film model appears to provide the lower bound of the interfacial friction factor in the smooth IAFB region. Two interfacial friction factor correlations from the literature are recommended for the smooth and wavy IAFB regions based on the analysis. It can be concluded that the interfacial friction factor in the smooth IAFB region is dependent on the gas Reynolds number and vapor film thickness, while in the wavy IAFB region, it is primarily dependent on the amplitude of the interfacial waves.