High-Speed Cavitation Nozzle Flow Visualization of Liquid Jets

Cavitation or cold boiling is a rupture in liquid continuum due to excessive stress, it occurs when the local pressure drops below the vapor pressure leading to a two-phase mixture of liquid and vapor/gas. Cavitation is recognized to play an important role in the process of liquid fuel atomization and spray formation but the mechanism is not well understood. This has limited its applicability due to a lack of control of spray characteristics. In this study, a review of the state of knowledge of cavitating nozzles is presented along with motivation for continuing research. Ongoing work is also described in which cavitation phenomena through the nozzle were observed using transparent Plexiglas nozzles. A plunger pump was used to continuously drive filtered purified water through the nozzle prior to release to the atmosphere. High-resolution still images of the nozzle internal flow regimes starting from incipient cavitation to supercavitation, and their resulting external spray using visible light source are obtained. Results revealed the cavitation bubble growth, collapse, and bursting processes are the main mechanisms responsible of the enhancements of liquid jet disintegration. At supercavitation regime, bubbles are swept outside the nozzle exit where they burst and promote more efficient atomization. However, the effect of developing cavitation to enhance the jet is smaller due to the collapse of bubbles within the nozzle.