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Investigation of the interface behavior of a viscous fluid under free surface shear flow using an eccentric transparent Couette cell

Abstract In the present work, a prototype was developed to observe the flow behavior of viscous fluids under free surface shear and determine an adhesion energy in this flow geometry. The geometry consists of an eccentric Couette cell (outer cylinder radius of 89.5 mm, inner cylinder radius of 43.75 mm and minimal gap of 3 mm) that can be used in two modes, where both cylinders can respectively rotate in the same or opposite directions. Cylinders are horizontal and short relatively to their diameters (30 mm long). Transparent windows allow in-situ flow observations. The design, development, and testing of the prototype with a model viscous fluid (silicone fluid with a 2.2 104 Pa.s Newtonian viscosity) are reported in this paper. The flow behavior of small fluid volumes (fill factor smaller than 15%) was investigated under co- and counter-rotating configurations to determine steady-state flow conditions. Stationary conditions were identified in the counter-rotating mode. The velocity conditions and resulting observations are studied and analysed. However, for the used silicone fluid, the bulk dissipative energy is much larger than the work of adhesive forces in the investigated regimes. The adhesion energy contribution could not be detected for this fluid.