Characterisation of flow behaviour and velocity induced by ultrasound using particle image velocimetry (PIV): Effect of fluid rheology, acoustic intensity and transducer tip size

Acoustic streaming phenomena of ultrasound propagation through liquid media was investigated experimentally employing particle image velocimetry (PIV). Parameters associated with the ultrasonic processor of ultrasonic amplitude (i.e., acoustic power) and transducer tip diameter (i.e., surface area), as well as, fluid rheology (i.e., water, glycerol solution and CMC solution), were studied for their effects on overall flow behaviour and fluid velocity. PIV yielded velocity gradient maps, demonstrating the acoustic streaming phenomena of ultrasound and its associated flow behaviour as a function of ultrasonic amplitude and fluid rheology, whereby increasing amplitude allowed for greater penetration of the acoustic-beam through the bulk of the fluid, and increasing fluid rheology yielded the converse effect. Moreover, upon impingement of the acoustic-beam with the base of vessel, vortex formation occurred, yielding a recirculation pattern. The maximum observed fluid velocities for water, glycerol solution and CMC solution were 0.329 m s−1, 0.423 m s−1, and 0.304 m s−1, respectively (large diameter sonotrode tip for an ultrasonic amplitude of 80%). Furthermore, shear rates were attained (maximum values of 24.25 s−1), and Reynolds numbers were determined in order to assess the degree of turbulence as a function of investigated parameters.