Dynamic Behavior of Droplet Impact on Inclined Surfaces with Acoustic Waves.

Mehdi H. Biroun,Mohammad Rahmati,Ran Tao,Yongqing Fu,Mehdi Jangi,Hamdi Torun

doi:10.1021/acs.langmuir.0c01628

Abstract

Droplet impact on arbitrary inclined surfaces is of great interest for applications such as antifreezing, self-cleaning, and anti-infection. Research has been focused on texturing the surfaces to alter the contact time and rebouncing angle upon droplet impact. In this paper, using propagating surface acoustic waves (SAWs) along the inclined surfaces, we present a novel technique to modify and control key droplet impact parameters, such as impact regime, contact time, and rebouncing direction. A high-fidelity finite volume method was developed to explore the mechanisms of droplet impact on the inclined surfaces assisted by SAWs. Numerical results revealed that applying SAWs modifies the energy budget inside the liquid medium, leading to different impact behaviors. We then systematically investigated the effects of inclination angle, droplet impact velocity, SAW propagation direction, and applied SAW power on the impact dynamics and showed that by using SAWs, droplet impact on the nontextured hydrophobic and inclined surface is effectively changed from deposition to complete rebound. Moreover, the maximum contact time reduction up to ∼50% can be achieved, along with an alteration of droplet spreading and movement along the inclined surfaces. Finally, we showed that the rebouncing angle along the inclined surface could be adjusted within a wide range.

Highlights

Our results showed that the transferred surface acoustic waves (SAWs) energy into the liquid medium during the impingement can alter the internal recirculation field of the droplet, which leads to a faster detachment of droplet from the surface
A good agreement between the experimental and numerical results can be found, proving that simulation results can be precisely used to analyze the effect of the SAW on droplet impact
The potential of applying SAWs to modify the droplet impact dynamics on inclined surfaces is investigated in this paper

Summary

Introduction

Liquid droplet impact on solid surfaces, on either flat, inclined, or complex-shaped surfaces, has been extensively studied because of its significance in scientific understanding and industrial applications, including antifogging,[1] antiacing,[2−4] inkjet printing,[5−8] agriculture,[9,10] spray cooling,[11,12] self-cleaning,[13−15] anticorrosion,[16−18] internal combustion engines,[19,20] optical devices,[21] anti-infection surfaces,[22] water collection systems,[23,24] and liquid material transportation and distribution.[25,26]After the droplet impact on solid surfaces (either horizontal or inclined surfaces) and in the absence of splashing, the droplet spreads on the solid surface to a maximum spreading diameter, and depending on the surface and liquid physiochemical properties and impact velocity, the droplet can retract or permanently remain spread on the surface.[27]. Šikalo et al investigated the effects of surface roughness and liquid viscosity on the dynamics of the droplet impact on inclined surfaces. They reported the observation of asymmetry in the front and back sides of the droplet after the impact.[31] A few studies have attempted to explain the main contributing parameters in the droplet impact regime on the inclined surfaces. Bird et al reported that the tangential velocity vector plays a major role in the droplet splash dynamics on inclined surfaces.[32] Chiarot and Jones[33] and Zheng et al.[34] showed that the rebouncing regime of the high-velocity impact of continuous droplet stream on inclined superhydrophobic surfaces is functions of droplet ejection rate and impact velocity

Methods

Results

Conclusion