Circumferential incoherent distribution of film thickness for multi-dimensional two-phase annular flow

Abstract

Annular flow in rod bundle geometry is characterized by multi-dimensional properties in terms of two distinct length scales, rendering no consensus yet on an available model for predicting the circumferential incoherent distribution of film thickness. Current paper presents a semi-empirical but original correlation based on pertinent underlying physics. Gas phase Reynolds number is used to illustrate the gas–liquid interfacial shear-off mechanism. Liquid source term is scaled by the combination of void fraction and liquid volumetric flux. Circumferential shear stress produced by secondary flow is employed to denote mass transport in subchannel. Four available datasets including 189 data points are collected to develop and validate the proposed correlation from both cross-sectional and subchannel local regions perspectives. The majority of data can be correlated with the maximum relative error of ± 20.0%. Based upon the heuristic correlation, the circumferential incoherent distribution of film thickness is analyzed. The average film thickness on center rod increases slightly as the liquid velocity increased, since most of liquid phase migrates to corner region leading to a dramatically increase in film thickness on rod nearby duct wall. Two dependent factors are mainly responsible for the rod peripheral distribution of liquid thickness, in which the hydrodynamic effect dominates over the secondary flow factor, but the secondary flow makes the peripheral distribution of film thickness more uniform. Among the hydrodynamic parameters, both void fraction and gas velocity contribute to the thinning of the liquid film, but the increasing of liquid thickness along with rod periphery is attributed to the variation of subchannel characteristic length.