Numerical simulation of microfluidic mixing by ultrasonic-induced acoustic streaming

Abstract

Laminar flow is dominant in the microfluidic device, and hence it is difficult to improve the mixing performance efficiently. To solve this problem, a fast and homogenized mixing application through microstreaming generated by ultrasonic resonance in fluid has been proposed. In this article, the acoustic streaming patterns in two-dimensional microchannel are investigated based on the Reynolds stress method (RSM) and limiting velocity method (LVM). It is found that the classical Rayleigh streaming pattern can be well described by both methods, but the LVM adopts uniform meshes with fewer elements for more efficient computation. Therefore, the LVM is more suitable to explore acoustic streaming and microfluidic mixing performance in three-dimensional models. Results also show that the similar sound pressure distribution and different acoustic streaming patterns are found in microchannels with different aspect ratio. Four symmetric vortices are formed in transducer-plane streaming model driven by ultrasonic standing waves at h/w = 1/20, while eight symmetrical acoustic vortices in Rayleigh-like acoustic streaming model at h/w = 1/3. When the inlet velocity is large, the mixing effect of the fluids is not significant. With the decrease of inlet velocity, the mixing efficiency is increased gradually. In addition, the mixing performance of the two models is close to each other at the same inlet velocity. The solution flow rate in the Rayleigh-like microchannel is seven times larger than that of the transducer-plane streaming model. Therefore, the disturbance intensity in the Rayleigh-like acoustic streaming model is stronger.