Effect of Viscosity on Bouncing Dynamics of Elliptical Footprint Drops on Non-Wettable Ridged Surfaces.

Sungchan Yun

doi:10.3390/polym13244296

Abstract

An initial drop shape can alter the bouncing dynamics and significantly decrease the residence time on superhydrophobic surfaces. Elliptical footprint drops show asymmetric dynamics owing to a pronounced flow driven by the initial drop shape. However, the fundamental understanding of the effect of viscosity on the asymmetric dynamics has yet to be investigated, although viscous liquid drop impact on textured surfaces is of scientific and industrial importance. Here, the current study focuses on the impact of elliptical footprint drops with various liquid properties (density, surface tension, and viscosity), drop sizes, and impact velocities to study the bouncing dynamics and residence time on non-wettable ridged surfaces numerically by using a volume-of-fluid method. The underlying mechanism behind the variation in residence time is interpreted by analyzing the shape evolution, and the results are discussed in terms of the spreading, retraction, and bouncing. This study provides an insight on possible outcomes of viscous drops impinging on non-wettable surfaces and will help to design the desired spraying devices and macro-textured surfaces under different impact conditions, such as icephobic surfaces for freezing rain or viscous liquids.

Highlights

Drop impacting onto solid surfaces is a natural phenomenon [1,2] and essential for many engineering applications, such as spraying cooling [3], forensic application [4], pesticide deposition [5], inkjet printing [6], and impact erosion [7]
The impact dynamics can be determined by the following dimensionless numbers [1,2]: Weber number, We = ρDU2/σ, Reynolds number, Re = ρDU/μ, Ohnesorge number, Ohnesorge Number (Oh) = μ/(ρDσ)1/2, and capillary number, Ca = μU/σ, where U is the impact velocity and μ is the viscosity of liquid
Numerical simulations were carried out for the bouncing behavior and residence time of elliptical footprint drops on the ridged surface using the VOF method

Summary

Introduction

Drop impacting onto solid surfaces is a natural phenomenon [1,2] and essential for many engineering applications, such as spraying cooling [3], forensic application [4], pesticide deposition [5], inkjet printing [6], and impact erosion [7]. Yeong et al [17] demonstrated viscous liquid drop (μ~1–8 mPa s) impact on inclined SHSs and found that, as the viscosity of the fluid increased, the receding angle of the surfaces reduced significantly, thereby altering a drop’s rebound characteristics. Abolghasemibizaki et al [18] investigated liquid drops with various viscosities (μ~8–100 mPa s) and impact velocities They reported that the drop dynamics was related to residence time on non-wettable flat and textured surfaces, and the retraction velocity could be scaled as both inertial-capillary velocity (~(σ/ρD)1/2) and viscous-capillary velocity (~σ/μ). The current work focuses on studying the impact of ellipsoidal drops with various liquid properties (μ~1–100 mPa s) and drop sizes by predicting the bouncing behavior and residence time (tc) on ridged surfaces numerically, using the VOF method [26]. The results are discussed in terms of the spreading, retraction, and bouncing

Materials and Methods

Findings

Conclusions