3D computational investigation of plug motion and film deposition in straight and Y-shaped tubes with pre-wetted walls

Liquid plug flow through tubes and the associated liquid film deposition play an important role in several applications, including medical procedures (e.g., surfactant replacement therapy), coating industry, chemical processing, etc. Previous studies have developed empirical and theoretical correlations predicting the thickness of the film deposited by the plug for relatively small capillary numbers. We present 3D CFD simulations of plug motion in straight and Y-shaped tubes with pre-wetted walls for a range of capillary numbers. The pre-existing film is differentiated from the deposited film by using a passive scalar that tags the liquid plug allowing for accurate quantification of transient film deposition. We study the temporal and spatial variation of the deposited film thickness, and show its dependency on pre-existing film thickness and interplay between gravity and plug inertia. Additionally, we present 3D simulations of plug splitting in Y-shaped tubes at various roll angles, where one daughter tube is gravitationally favored. The plug splitting is quantified as a plug split ratio. We also discuss the 3D orientation of the liquid plug in the bifurcation zone.