Microbubble production in a confined cavitating radial jet

Microbubble populations generated via rapid depressurization of supersaturated water in a confined radial jet are characterized using shadowgraphy measurements. An experimental apparatus has been utilized enabling independent control of the two main parameters controlling the flow: cavitation number (𝜎_inj) and Reynolds number (Re). Saturated water was supplied at pressures between 200 and 1600 kPa, and outlet pressures were varied between 10 and 300 kPa, resulting in 𝜎_inj range 0.05 < 𝜎_inj < 0.6 and 𝑅e range 10000 < Re < 25000. Microbubbles form through turbulent break-up and gaseous diffusion in the cavity closure region. Generated populations have a ploy-disperse size distribution with a dominant bubble size of about 5-10 μm with the majority of bubbles smaller than 20 μm. Total production frequencies of up to 50 MHz are observed. The influence of Re on generated microbubble populations is found to be more pronounced than that of 𝜎_inj