Water droplet motion under the influence of Surface Acoustic Waves (SAW)

Abstract

The water droplet motion processes actuated by applying surface acoustic waves at various RF powers and frequencies were investigated by numerically modelling and compared with experiment. A three-dimensional computational model of a free water droplet streaming on the surface of the substrate have been developed using Finite Element Method (FEM) with Laminar Two-Phase Flow Moving Mesh approach for Navier–Stokes equations which were coupled with Convection Wave equation (CWE) module of the COMSOL Multiphysics. Water droplet motion speeds were experimentally measured and confirmed for water droplets with the volumes of 2 and 5 μl, at SAW frequencies 34 and 58 MHz, and power range 0.1–1.23 W. The effect of frequency on microfluidic performance such as streaming flows and droplet motion has been studied both numerically and experimentally toward developing MEMS devices for future energy sources, e.g., for direct methanol fuel cells, hydrogen energy, as well as for use in a wide variety of chemical, water desalination and purification of other fluids from salts, germs, bacteria, and viruses based on perspective multiphysical effects.

Droplet motion on sonically excited hydrophobic meshes

“…In some modes, droplet jumping and breaking into newborn small droplets become unavoidable. Although droplet behavior on hydrophilic and hydrophobic surfaces under acoustic excitations has been studied 6 , 21 – 23 , the sonic wave direct interaction with a droplet fluid and resulting droplet motion on hydrophobic mesh surfaces were left for future study. As a liquid droplet is dispensed over the mesh surface, the interfacial area of the droplet over the mesh reduces significantly because of the open screen area of the meshes.…”

Droplet Motion on Sonically Excited Hydrophobic Meshes

“…In some modes, droplet jumping and breaking into newborn small droplets become unavoidable. Although droplet behavior on hydrophilic and hydrophobic surfaces under acoustic excitations has been studied, 6,[21][22][23] the sonic wave direct interaction with a droplet fluid and resulting droplet motion on hydrophobic mesh surfaces were left for future study. As a liquid droplet is dispensed over the mesh surface, the interfacial area of the droplet over the mesh reduces significantly because of the open screen area of the meshes.…”