Droplet impact on a wettability-patterned woven mesh

Droplet impact and breakup on meshes are relevant to a number of applications involving filters,textiles,and other spatially inhomogeneous media encountering gasdispersed liquids.This study presents high-resolution simulation results of mm-size droplets striking wettability-patterned meshes with the goal of(a)replicating prior physical experiments,(b)identifying sensitivities to the initial conditions and wettability of the mesh wires,and(c)studying the fluid-field dynamics when droplets strike such meshes.The insights from the present model may help to advance understanding of droplet atomization on meshes,which depends on a number of parameters that are nontrivial to control in an experimental setting.The analysis is carried out by benchmarking the numerical methods used in a commercial software package for orthogonal droplet impact on a flat smooth surface,followed by a convergence analysis,and finally,simulation of specific experiments and case studies involving wettability-patterned mesh targets.We show that the wettability contrast between the hydrophilic and hydrophobic domains on the mesh as well as the contact angle hysteresis on each side play a critical role in determining whether liquid pinchoff occurs.The three-dimensional computational framework constructed in this work is a step toward predicting the postimpact behavior of droplets that strike woven meshes and other porous inhomogeneous media consisting of materials with different wetting properties.

Droplet orthogonal impact on nonuniform wettability surfaces

The vast majority of prior studies on droplet impact have focused on collisions of liquid droplets with spatially homogeneous(i.e.,uniform-wettability)surfaces.But in recent years,there has been growing interest on droplet impact on nonuniform wettability surfaces,which are more relevant in practice.This paper presents first an experimental study of axisymmetric droplet impact on wettability-patterned surfaces.The experiments feature millimeter-sized water droplets impacting centrally with We<100 on a flat surface that has a circular region of wettabilityθ_(1)(Area 1)surrounded by a region of wettabilityθ_(2)(Area 2),whereθ_(1)<θ_(2)(i.e.,outer domain is less wettable than the inner one).Depending upon the droplet momentum at impact,the experiments reveal the existence of three possible regimes of axisymmetric spreading,namely(I)interior(only within Area 1)spreading,(II)contact-line entrapment at the periphery of Area 1,and(III)exterior(extending into Area 2)spreading.We present an analysis based on energetic principles forθ_(1)<θ_(2),and further extend it for cases whereθ_(1)>θ_(2)(i.e.,the outer domain is more wettable than the inner one).The experimental observations are consistent with the scaling and predictions of the analytical model,thus outlining a strategy for predicting droplet impact behavior for more complex wettability patterns.