New insights on the cavitation development and the role of bubbles in Micro-Venturi channels.

This study investigates hydrodynamic cavitation (HC) inception and development in micro-Venturi channels, focusing on the mechanism that drives spatially irregular cavitation events. The study reveals that cavitation regeneration is primarily governed by the interaction between residual cavitation nuclei and low-pressure vortices. Using ultra-high-speed imaging and advanced bubble dynamics analysis, it was revealed that the residual nuclei trapped in the boundary layer or reverse flow near the sidewall of the microscale reactor are the key to cavitation regeneration. Their interaction with vortices shed from the shear layer, triggering spatially distributed inception events throughout the channel. Bubble velocity analysis showed a size-dependent pattern: smaller residual bubbles migrate upstream (negative velocities) before growing and being advected downstream (positive velocities), directly linking their motion dynamics to cavitation inception. Spectral analysis of the bubble populations demonstrated two frequency components: low-frequency signals in the transient regime, reflecting slow periodic replenishment of residual nuclei and high-frequency fluctuations driven by vortex activity. With increasing upstream pressure, the system shifted to periodic attached cavitation, characterized by regular shedding-driven fluctuations in bubble content. At even higher pressures, fully developed cavitation emerged, marked by intense shear-layer activity, sporadic downstream variations, and shear-induced bubble breakup that sustained mainstream cavitation. The findings of this study illustrate how residual nuclei and their interaction with transient vortices play a pivotal role in microscale cavitation inception, thereby offering critical insights on controlling cavitation in microfluidic systems such as "HC on a chip" reactors, where stochastic nucleation and bubble transport significantly influence performance.