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.
Abstract The ability to trap and deposit particles from flowing suspensions onto solid substrates underpins a wide range of technological applications, from coatings and sensors to biomedical devices and filtration systems. Entrapping particles from non-colloidal suspensions onto cylindrical substrates is governed by a competition between transport/impaction and adhesion/retention. We quantify “dispersion energy” (agitation intensity) via a normalized parameter and evaluate its effect on microparticle capture for low (Al) and high (Ni) density non-Brownian polydisperse particle suspensions. Image-based metrics (surface coverage, particle-transfer efficiency, size distributions) and spatial statistics (SOM, Voronoi tessellation and Delaunay triangulation) reveal a non-monotonic response: capture is maximized at intermediate dispersion energy where Stokes-number driven transport is sufficient for impaction, but impact energy and shear remain low enough for binder-mediated adhesion to arrest particles. At the range between Ψ ≈ 0.04 ×10-6-0.15×10-6 m5kg-1s-2, Al (lower specific density) reaches coverage 17.82 ± 17.40, while Ni (higher specific density) attains coverage 11.29 ±3.77. Size distributions are lognormal, narrowing with increasing as large-particle capture is suppressed. Spatial descriptors corroborate the mechanistic picture: near-optimal Ψ yields the most isotropic local packing; at higher Ψ, rebound and shear-induced sliding/rolling reduce adhesion; at lower Ψ, insufficient impaction limits capture. The framework-linking Ψ, impaction (via Stokes number), and adhesion thresholds-provides actionable guidance for tuning agitation to maximize entrapment in binder-assisted coatings, filtration preforms, and surface functionalization.
Abstract Chip evacuation is a critical aspect of the micro-drilling process, as the confined nature of the chips between the hole wall and flute can lead to clogging, increased thrust and torque, tool wear, and potential failure. This paper presents a physics-based analytical model for predicting chip evacuation force using principles of granular chip particle kinetics and energy transfer. The model incorporates material properties, tool geometry, and cutting conditions, while also accounting for the adhesion and drag effects due to scaling of drilling process geometry. Validation through micro-drilling experiments on hardened steel demonstrates strong agreement between predicted and measured chip evacuation forces. The model offers a generalized approach applicable to various work materials eliminating the need for costly calibration experiments.
A geometry-based chip thickness model is proposed to enhance the understanding of chip behavior in the microdrilling of Stavax hardened steel under dry condition. Chip formation at specific cutting regions, including the primary cutting blade, secondary cutting blade, and chisel indentation zone, is evaluated in the model. The cutting size effect is incorporated into the model to address the unique plowing and shearing phenomena. The model is experimentally validated over a range of chiploads. The progression of chip morphology is observed. Overall chip thickness is shown to be thicker as compared to the theoretical chip thickness. Both experimental and analytical models show a strong dependence of chip thickness, chip thickening rate, and morphology on the size effect that dictates the effectiveness of the chip removal process.
