Generalization of disturbance wave velocity of vertical annular flow considering entrained droplets effect

Abstract

A full knowledge of the interfacial effect on disturbance wave is vital for accurately predicting disturbance wave velocity in annular flow. However, almost all of the existing disturbance wave velocity models do not ponder the droplet-film mass transfer, which largely limits the applicable scope and prediction accuracy of the model. This article leads into the entrained droplets effect to the interfacial shear modeling, proposing a new disturbance wave velocity model with a widely applied range. The effects of entrainment and liquid film thickness on the characteristics of the gas core mixture (bulk density and velocity) were included, and the mean velocity of the liquid film surface was introduced in the modelling. For the verifying experiments, an annular flow loop with film metering device and electrode sensor was developed, and the entrainment and liquid film thickness were also modelled for the convenience of usage in cases without raw measured data. The new developed disturbance wave velocity model collapses the experiments corresponding to all entrained conditions well within ± 5.0% deviation for an 85.2% confidence interval. The comparative analysis with the existing empirical correlations confirms the critical role of entrained droplets on the disturbance wave velocity. The scalability and wide scope of application were further validated by the open data in the literature, and finally, practical suggestions were given for the disturbance wave velocity prediction on various pressure and pipe diameter conditions.