A physical model for huge wave movement in gas-liquid churn flow

A complete knowledge of the huge wave in churn flow is of great importance for the characterization of its entrainment. Huge wave in churn flow is experimentally identified as a highly disturbed wave; however, no specific model is available for this particular wave. Based on the force balance over the wave, we established an analytical model to study its growth and levitation and analyzed the effects of the parameters (including gravity, pressure force of gas and liquid, wall shear stress and interfacial shear stress) on the wave and the gas and liquid flow field. We proposed that the boundary layer in liquid film is more likely to be turbulent rather than laminar and the gas pressure force is the most influential factor. The proposed model was verified qualitatively and quantitatively. We hence theoretically concluded that the churn flow is characterized by the flooding of the film, the flow reversal is attributed to the transition to the annular flow and the pressure gradient decreases with the increase of the gas flow rate. These findings provided insight into the distinction between the churn flow and the annular flow. The wave properties (amplitude and velocity) were analyzed in detail and the churn/annular transition occurred at U ^*=1.12. The model helps understand the droplet entrainment in churn flow which is essential for the development of mechanistic models to predict the dryout condition.