Mechanical Engineering - Theses
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ItemAcoustic microstreaming in the vicinity of oscillating microbubbles( 2012)Acoustic microstreaming has gained increased interest in the past few years due to innovative medical treatments such as sonoporation and sonothrombolysis [1-4]; however, few flow visualizations or measurements of velocity fields and other significant metrics havebeen conducted. In this study, work first conducted by Tho et al. [2] has been further explored. Micro-PIV (Particle Image Velocimetry) measurements and streak photography were used to study the flow field around single bubbles, ranging in diameters of 30-300 um, oscillating in various fluid mediums. The bubbles were attached onto the lower surface of a microchamber (pendant), and held in place via capillary forces. Previous studies have focused on the visible secondary flow of acoustic microstreaming, not the potentially more significant primary flow within the Stokes boundary layer. Since primary-flow velocities are much higher, they may exert stresses on nearby surfaces and be of much greater biological significance. In this study, whilst the key focus has still been at studying the secondary flow fields, a novel approach was used to capture and quantify the velocity/speed of the primary vortices, which were observed to be twice an order of magnitude stronger than the secondary vortices. Surfactants have been introduced into the fluid medium to study the possible effects on microstreaming and if there was a correlation to observed increases in rates of rectified diffusion. The addition of surfactants lead to an increase in the streaming metrics, however the results did not fully correlate with those of observed increased rates of rectified diffusion. This would suggest that the increase in streaming velocity due to the introduction of surfactants is not the primary driver for the increase in rectified diffusion rates.