COMSOL Analysis of Acoustic Streaming and Microparticle Acoustophoresis
We have simulated the ultrasound-induced acoustophoretic motion of microparticles suspended in an aqueous solution. The full first-order thermoviscous acoustics equations have been implented on a rectangular microfluidic 2D domain excited with an ultrasound field tuned to resonance near 2 MHz. The micrometer-thin but crucial viscous boundary layers at the rigid walls have been fully resolved. The imposed first-order ultrasound field generates second-order fields that leads to streaming flows and radiation forces with a non-zero time-average, which act on the suspended microparticles. We have characterized the cross-over from streaming-dominated vortex motion of small particles (< 2 um) to radiation-dominated linear motion of larger particles (> 2 um).