Droplet retention on an incline

Abstract

The present study seeks to understand and predict droplet retention on smooth hydrophobic surfaces. The droplet shape and the advancing and receding contact angles are experimentally measured as a function of droplet size under the action of a gravitational force at different inclination angles. The advancing and receding contact angles are correlated with static contact angle and Bond number. A Volume of Fluid -Continuous Surface Force model with varying contact angles along the triple contact line is developed to predict droplet shape. The model is first verified against a twodimensional analytical solution. It is then used to simulate the shape of a sessile droplet on an incline at various angles of inclination and to determine the critical angle of inclination as a function of droplet size. Good agreement is found between experimental measurements and predictions. The contact line profile and contact area are also predicted. The contact area predictions based on a spherical-cap assumption are compared to the numerical predictions and are found to underpredict the droplet contact area.

Prediction of droplet dynamics on an incline

“…The test surfaces used in the experiments are identical to those described in Annapragada et al [24]. The experimental setup consists of a movable tilt stage for mounting the test surfaces, along with a high-speed camera for imaging from the side.…”

“…A pseudo-Lagrangian methodology, described below, is developed to reduce the domain size and hence the computational time. The VOF-CSF method itself is described in detail in Annapragada et al [24]. In the current model, volume fraction smoothing is used to reduce the spurious velocities at the interface associated with the VOF method [27,28].…”

“…To the authors' knowledge, experimentally validated simulations of droplets sliding on hydrophobic surfaces do not appear to be available in the literature. In related work by the authors, VOF simulations of sessile, static droplets on an incline were compared to experimental measurements [24]. Droplet shape and critical sliding angle were predicted for different sizes of water droplets resting on a smooth PTFE (polytetrafluoroethylene) surface.…”

Vapor bubble approaching a superheated wall

“…The mass source is then calculated from the energy source and the latent heat on a per volume basis (Eqs. (5) and (6)) and stored in a memory location for each cell. This approach of calculating mass source has been validated in the test cases studied by Akhtar and Kleis [1] and other works including that of Welch and Wilson [37].…”

Splat formation during plasma spraying for 8mol% yttria-stabilized zirconia droplets impacting on stainless steel substrate

“…Splashing of the splats has a decisive effect on final shape of splats. Usually, increasing the substrate temperature [16,17] and thermal contact resistance [21][22][23][24][25] will suppress the splashing. Other studies also confirmed that increasing the Reynolds number and Weber number could promote splashing [4,[18][19][20]31].…”