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COMSOL Analysis of Acoustic Streaming and Microparticle Acoustophoresis

H. Bruus[1], P.B. Muller[1], R. Barnkob[1], M.J.H. Jensen[2]
[1]Technical University of Denmark, Kongens Lyngby, Denmark
[2]COMSOL, Kongens Lyngby, Denmark

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).