AN EXPERIMENTAL STUDY OF THERMOCAVITATION IN SMALL LIQUID GAPS

This study investigates the behavior of cavitation bubbles generated by a continuous wave (CW) laser in confined environments. Using a 1940 nm, 3W CW laser, cavitation bubbles are induced in water contained within a glass cuvette with a secondary boundary (glass slide) positioned at varying distances from the bubble nucleation site. The experiment aims to understand how confinement alters bubble growth dynamics, maximum bubble diameter, and collapse patterns. These characteristics have significant implications for applications in medical ultrasonics and microfluidics. The bubble diameter is found to be independent of boundary-boundary gap distance for the range explored. However, the bubble growth and collapse shape were observed to be impacted significantly by the gap distance. A dimensionless ratio of bubble maximum diameter to gap distance is defined to quantify the threshold of when these shapes and outcomes occur. When this dimensionless ratio is greater than or equal to 2.05, separation is observed. At values greater than or equal to 1.16, necking occurs during the bubble’s collapse phase. A scale analysis applied to the Navier-Stokes equation is conducted to ascertain what fluid factors may influence bubble behavior. Additionally, a means to quantify the pressure differential between the inside and outside of the bubble during expansion and collapse is obtained. The results of this experimental study provide a foundation to verify future computational exploration of these dynamics.