A self-consistent three-field constitutive model set for predicting co-current annular flow

Abstract Three-field analysis tools require interfacial and interfield models to describe the interaction of the vapor, liquid film and droplets. This work develops and assesses a physically based and self-consistent model set for co-current annular flow that: (1) applies an interfacial shear model that explicitly accounts for the presence of interfacial waves, (2) idealizes the structure of the interface in a manner that is consistent with both the interfacial shear model and visual observations, (3) includes three mechanistically based entrainment rate models (roll wave stripping, Kelvin–Helmholtz lifting, and liquid bridge breakup) that calculate a theoretical entrainment rate based on the governing phenomena as they are currently understood, and (4) provides a functional relationship between the actual and theoretical entrainment rates based on comparisons to experimental data. The self-consistent nature of the modeling package references the consistent use of parameters between the interfacial drag model, entrainment rate models, and flow regime map. For example, the disturbance wave height, velocity, and interfacial shear stress calculated by the two-zone model are used as input to the entrainment rate models. The inclusion of this package in an in-house version of COBRA-TF reduced the mean relative error in entrained fraction from 20.2% (underprediction) to 4.5% (overprediction) and in axial pressure gradient from 108.2% to 7.6% (both overprediction). Also, this work is one of the few that examined the predictive capabilities of transient analysis codes within the developing annular flow region.