Mass transfer enhancement produced by laser induced cavitation

A microelectrode is used to measure the mass transfer perturbation and characteristics during the growth and subsequent collapse of a single bubble (which, following its initial expansion, achieved a maximum radius, Rm, of not, vert, similar500–1000 ?m). This mass transfer enhancement was associated with the forced convection, driven by bubble motion, as the result of a single cavitation event generated by a laser pulse beneath a 25 ?m diameter Au microelectrode. Evidence for bubble growth and rebound is gained from the electrochemical and acoustic measurements. This is supported with high-speed video footage of the events generated. A threshold for the formation of large cavitation bubbles in electrolyte solutions is suggested

An electrochemical study of laser induced cavitation

A dual microelectrode is employed to study the electrochemical effects of optical cavitation on erosion of a solid surface (using a passivated 125 &#956;;m diameter Pb electrode or 250/500 &#956;;m diameter Aluminium electrode) and mass transfer (using a soluble redox species and a 25/50 &#956;;m diameter Pt or 25 &#956;;m diameter Au electrode) to the solid surface. These electrodes were set into a solid surface in closed proximity (e.g. &lt;100 &#956;;m separation) to the laser generated cavitation bubble. The use of these dual microelectrodes has a number of important advantages over previous studies. First, they are small in size compared to the bubbles produced. Second, these electrodes allow the detection of cavitation effects at different locations with respect to the bubble centre. Third, the response time of the electrochemical systems employed allows high temporal definition of the processes occurring during the growth and collapse phases of the cavitation cycle. The experimental set up is optimised and improved throughout the project. It is shown that electrochemical means are well suited for studying laser generated cavitation. On the erosion sensor, current-time transients are recorded when the laser fires and also when the bubble collapses. New mechanisms to explain how erosion occurs when a surface is exposed to laser-induced cavitation are proposed. On the mass transfer sensor, the bubble growth and collapse are recorded along with secondary collapses.</p