Phenomenological Investigation of Drop Manipulation Using Surface Acoustic Waves

This paper aims at the investigation of acoustic streaming produced by surface acoustic waves (SAWs) in a drop. Computational simulation of acoustofluidic phenomenon, using lattice Boltzmann method (LBM), presenting acoustic applications in flow control, and a relatively complete parametric study are the motivations of this work. For this purpose, a computational fluid dynamics modeling based on multi-relaxation time multi-component multiphase color gradient lattice Boltzmann method was used. The simulations were carried out at wave frequencies ranging from 20 MHz to 271 MHz and wave amplitudes ranging from 0.5 nm to about 350 nm. First, the non-dimensional form of Navier-Stokes equations based on this phenomenon is presented in this work and the physics of flow is explained. Then, the consistency of the model and experimental observations is considered and our numerical results pass the physical reals. Based on our results, comparison between Lithium Niobate and Zinc Oxide Silicon devices shows that in the pumping mode, the wet length of drop on Zinc Oxide material is shorter about 10%. Also, drop moves faster on the Zinc Oxide Silicon device (about 20% in 64.5 MHz and 350 nm). Moreover, in the jetting mode, drop is detached, from Zinc Oxide Silicon device, in about 70% shorter time duration. The findings indicate that in the jetting mode a counter rotating vortex pair is formed near the drop, while the vortices are stronger for Zinc Oxide Silicon device. So, in the liquid transport applications, Zinc Oxide Silicon device is more suitable. Other important results which are presented in this work are about the non-dimensional parameters and their ranges in these phenomena. The most important non-dimensional parameters governing the physics of problem are identified. Additionally, the ranges of different physical modes (based on non-dimensional parameters) are determined, using numerical results and experimental data. The results show that in the pumping mode, Reynolds, Weber, and capillary numbers are between 3 and 1400, 10−5-0.02, and 4 × 10−5-2.5 × 10−3, respectively. Also, in the jetting mode, the mentioned parameters are between 757 and 4600, 0.008–0.3, and 0.001–0.006, respectively.