Falling liquid films in vertical pipes are found in a variety of different industrial applications and industrial equipment, such as downcomers, caisson separators and reactors. The hydrodynamics of the falling film in vertical two-phase pipe flow can affect droplet entrainment, gas entrainment, and pressure drop. Therefore, a mechanistic model for prediction of falling liquid film thickness, falling liquid film velocity and a correlation for liquid droplet entrainment fraction in vertical downward liquid-gas systems has been proposed.
The falling film model developed is based on applying momentum balance on the liquid film. The liquid film is assumed to be in steady-state, incompressible and free of entrained gas. The mechanistic model includes both the developing and the developed regions. The shear effect between the gas core and the falling liquid film is considered. The liquid droplet entrainment fraction traveling in the gas core is considered and a new correlation for its prediction is proposed. Detailed uncertainty analysis is performed for liquid film thickness and liquid film velocity model predictions, including Monte Carlo simulation. Predicted liquid film thickness, liquid film velocity and liquid droplet entrainment fraction are validated against experimental data for different liquid fluid properties, such as water, Conosol mineral oil (light oil) and Drake mineral oil (heavy oil).