Experimental study of bubble growth by non-condensible disolved gas diffusion in super-saturated low-pressure water.

A recent study found that residual microbubbles that linger in locations of cavitation inception on curved surfaces act as nuclei for the re-inception of attached cavities. To better predict the re-inception process, this study experimentally measures the growth rate of a bubble by non-condensable gas diffusion in supersaturated low-pressure water, simulating the conditions close to regions of attached cavitation inception. Bubbles with an initial diameter of about 0.1 mm are released into a vertical 2 mm ×10 mm glass test section of a small-scale, pressure-controlled water tunnel. The flow in the test section is directed downwards with the speed required to counter the rising of the bubble. With this apparatus, the bubble remains stationary in the laboratory frame, and its growth process is filmed. The flow around the small bubbles is slow enough to keep it in the Stokes flow regime, which naturally allows for simplified analysis of the diffusive and convective contributions to the bubble growth. The experiments are performed using purified water while monitoring its temperature and dissolved gas level. The presentation will cover the experimental technique and present initial results showing the dependency of bubble growth rate on ambient pressures.