Phase diagrams for two-phase flow in circular capillary tubes under the influence of a dynamic contact angle

• We develop phase diagrams for capillary flow according to the Lucas–Washburn theory.
• The nonequilibrium Young force depends monotonically on the capillary number.
• Ten flow scenarios (liquid infiltration or withdrawal) and three equilibria may occur.
• The phase diagrams are two-dimensional.

We analyze theoretically gas–liquid flow in a circular capillary tube, the inlet of which is connected to a constant-pressure liquid reservoir. Based on previously derived analytical solutions, we present for the first time comprehensive, two-dimensional phase diagrams, which predict the flow scenario from only two nondimensional numbers: a nondimensional pressure and a nondimensional gravity parameter. Diagrams are developed for both a constant and a dynamic contact angle where in the latter case the nonequilibrium Young force depends monotonically on the capillary number. The diagrams subdivide the entire parameter space into regions that are associated with either liquid withdrawal, liquid infiltration, or metastable and stable equilibrium states.