Design and Experimental Evaluation of Cavitation-Assisted Microbubble Generation Using a 3D-Printed Device

Abstract

Micro-nano bubble (MNB) generation in liquid flows is fundamentally limited by turbulent breakup, commonly characterised by the Hinze scale, beyond which surface tension forces inhibit further size reduction. Achieving smaller bubbles requires additional localised high-energy dissipation, like cavitation collapse. This study experimentally evaluates a hybrid MNB generator integrating swirl-based shear with controlled Venturi-induced cavitation. Utilising 3D-printed PLA+ components, a 6 mm throat Venturi (σ ≈ 0.44) was coupled downstream of a swirl chamber to preserve vortex structures under mild cavitation, while a standalone 4 mm throat self-aspirating Venturi (σ ≈ 0.18) was developed to evaluate cavitation-dominated breakup. All configurations were evaluated using high-speed imaging coupled with a Python-based OpenCV image processing solver. Results demonstrate that standalone swirl-induced turbulence produces a mean bubble diameter of 262.12 μm. In contrast, the intense localised pressure collapse within the standalone self-aspirating Venturi yields a significantly finer mean bubble diameter of 158.09 μm. The hybrid swirl–Venturi configuration achieves the most uniform population, reducing the mean bubble diameter to 155.12 μm, a 40.8% reduction compared to the standalone swirl configuration. These experimental mean values approach the theoretical Hinze scale bounds calculated for this flow regime (30–150 μm), validating that while shear-driven turbulent breakup sets the primary baseline, cavitation-induced energy bursts provide a crucial secondary refinement mechanism. The findings highlight the design requirement of balancing cavitation intensity with upstream vortex stability to optimise hybrid hydrodynamic aeration performance.