ID 23

Shear Driven Wetting Patterns on a Solid Substrate

 

Abstract:

A shear driven two-phase flow on a solid substrate creates various wetting patterns, which include motion of single drops, rivulets and thin liquid films. The flow is governed by viscous and inertial stresses, surface tension, aerodynamic pressure and shear from the airflow. The wetting patterns are also influenced significantly by microscopic factors like contamination of the liquid, substrate roughness and wettability.

In this study, a set of experiments of a shear driven liquid flow on a flat substrate is carried out in a wind tunnel. Wetting patterns on a flat plate are observed using a high-speed video system. The liquid flow rate, the surface properties and the outer airspeed are varied in the experiments. Among the observed phenomena are (i) film flow, (ii) film breakup, leading to generation of a number of meandering rivulets, (iii) rivulet propagation and breakup which leads to the creation of single drops, (iv) aerodynamic flow breakup which generates a number of secondary drops, etc. The main parameters of the liquid flow, like local rivulet width or rivulet angle, film breakup position, etc., have been determined using an automated image analysis algorithm.

Finally, a theoretical model for the shear driven flow on a solid substrate has been developed, which is able to predict the main flow patterns and their parameters, and the threshold conditions for transition.