Prediction of liquid film thickness in upward gas-liquid annular two-phase flows

In the past, the majority of one-dimensional models for predicting liquid film thickness in gas-liquid annular twophase flows have relied on various combinations of widely accepted dimensionless parameters. However, these combinations of commonly used dimensionless numbers mainly used gas and liquid Reynolds numbers and other dimensionless numbers introduced by simple models or data fitting. Because of this, though there are various forms of correlations or models for liquid film thickness in annular flows, their application ranges are limited. To broaden the applicable ranges, this study presents a novel model to predict liquid film thickness in vertical upward annular flow, derived from a one-dimensional force balance analysis. The model is derived from a first-principles force balance, linking film thickness to interfacial shear, wall shear, and gravitational forces. This mechanistic foundation enhances physical interpretability compared to purely empirical fits. In the proposed model, the influence of the interfacial inertia ratio on film thickness was found to be more pronounced compared to that of the Reynolds number ratio. Additionally, the impact of pipe diameter on film thickness was integrated into the model by validating its predictions against experimental data. The proposed model is capable of accurately predicting film thickness flows both in pipes and in rod bundles, which consist of an arrangement of rods.