Advancing contact angles of Newtonian fluids during "high" velocity, transient, capillary-driven flow in a parallel plate geometry

Advancing contact angles in the order of 70degrees to 80degrees were measured for Newtonian fluids at relatively high capillary numbers using a system of parallel glass plates. The transient height attained by the fluids between the plates was fitted to an averaged-flow Navier-Stokes model in order to indirectly estimate the value of the dynamic advancing angle, Subsequently, using a highly nonlinear approximation for the contact angle, it was possible to describe the entire relaxation phenomena during the capillary rise at low meniscus rates (e.g., high viscosity fluids), as well as at front velocities on the order of a hundred millimeters per second (e.g., low viscosity fluids). Contact angles obtained by the parallel plates method agree well with experimental observations and phenomenological correlations put forward in recent literature, but cannot be explained in terms of the proportionalities between dynamic angle and velocity predicted by the classical hydrodynamic and molecular theories in the nonwetting case.