Power-law fluid micromixing enhancement using surface acoustic waves

Abstract

This study is aimed to numerically investigate the mixing efficiency of non-Newtonian fluid flow based on surface acoustic waves. The standing ultrasonic waves have been used to investigate their effect on the mixing efficiency of shear-thinning fluids, as well as shear-thickening ones that flow through a microchannel. Due to differences in time scales of acoustic physics and the mixing process and nonlinearity of the problem, the perturbation theory is employed. The fluid’s general motion is changed by the acoustic radiation force resulting from standing acoustic waves and the drag force resulting from acoustic streaming to overcome this challenge. The governing equations of fluid motion are divided into three categories: zeroth-order background flow, first-order acoustic field, and second-order acoustic streaming. In addition, power-law fluid with different indices is considered to investigate the impact of the shear-thinning, as well as the shear-thickening behavior on the mixing efficiency. Based on the obtained results, it is found that the acting fluid input velocity and power-law index significantly affect the efficiency of mixing. Moreover, it is revealed that although shear-thickening fluids experience a lower mixing efficiency at any given flow rate, the rate of increase in mixing efficiency at the pressure of acoustic field is much higher for highly shear-thickening fluids in comparison with shear-thickening fluids. The findings also show an increase of 71% in mixing efficiency for the shear-thickening fluid when the power-law index is 1.2, with an inlet velocity of 0.005 m/s and an actuation frequency of 1.97 MHz.