Aerosol flow-driven instability and droplet-interfacial stabilization of mRNA lipid nanoparticles during mesh nebulization.

Coupled dynamics of droplet formation and breakup in symmetric and asymmetric T-junction microchannels

We report the breakup dynamics of shear-thinning droplets in microfluidic environment through a comprehensive integration of experiments, numerical simulations, and machine learning (ML). Particularly, we investigate the breakup of droplets interacting with a ribbed structure within a microfluidic conduit. Our findings reveal an on-demand, obstacle-driven breakup under varying orientations and rheological conditions. Based on experimental results, and supported by three-dimensional numerical simulations, we reveal that the underlying breakup dynamics depend on the intricate balance between the pressure differential and the shear-stress distribution along the droplet interface, which governs the change in the advancing curvature of the shear-thinning droplet. In addition, we developed a specialized artificial neural network (ANN) that incorporates six key input variables: the capillary and Reynolds numbers for both continuous and dispersed phases, the mother droplet length, and the obstacle aspect ratio, to predict the breakup volume of the daughter droplets. Using SHapley Additive exPlanation (SHAP) applied to our machine learning model, we quantified the relative importance of these parameters in controlling droplet breakup dynamics. We found that the obstacle aspect ratio plays the dominant role (∼70%), followed by the mother droplet length (∼10%), where these percentage contributions correspond to the mean absolute SHAP values. We believe that the development of the ANN model for the breakup of non-Newtonian droplets offers significant insights for researchers in point-of-care diagnostics, where shear-thinning fluids, such as blood, are routinely encountered.

Droplet breakup regimes and critical conditions in two-inlet T-junction microchannels

ABSTRACT Solvent extraction involves coupled phenomena that strongly affect the performance at large scale. Given the urgent need to reduce process development costs and time in the hypercompetitive context of recycling, it is essential to adapt our R&D methodology, historically based on large-scale pilot tests. In this context, we have proposed to predict the drop size distribution in liquid-liquid contactors based on small-scale instrumented experiments, and proper numerical simulations. This method was tested on a case of industrial interest, the recovery of copper, considering the actual process fluids (although mass transfer was not considered) and a scale jump of 40 in volume. Tests carried out in a semi-industrial mixer-settler at Umicore’s facilities in Olen revealed a quite satisfactory agreement between measurements and predictions, hence validating the relevance of the proposed approach in order to guide industrial transposition and provide early stage-evaluation of relevant performance criteria such as interfacial area and phase entrainment due to tiny droplets. The benchmark also highlighted the need to reduce the empiricism of the models used in population balance equations to describe droplet breakup and coalescence under real conditions, in order to facilitate the transposition from one chemical system to another.

High-speed visualization of ultrasonic emulsification in microgravity: interactions between cavitation dynamics and liquid\u2013liquid interface topology

Droplet deformation and breakup in 3D-printed millichannels featuring arrays of rectangular obstacles with different configurations

Investigation of droplet deformation and breakup dynamics in porous media using machine learning-assisted computer vision

For a thin liquid film around a vertical solid cylinder, this study aims to understand the flow phenomenon while it falls down the cylinder assisted by gravity, using a three-dimensional finite volume scheme. The problem is described broadly in three stages of development, i.e., film dynamics, convergence of film into a jet, and jet behavior. The interplay between inertia, gravity, and surface tension dictates these evolutions: gravity promotes vertical drainage, inertia stabilizes the jet, and surface tension minimizes the interface area, leading to Rayleigh–Plateau instability, which ultimately produces droplet breakup. The film flow is described with a self-similar scaling. Pressure distributions and velocity vectors are employed to understand convergence. Correlations are developed for the dripping/jet responses to the globally defined parameters. The jet formation is represented as a direct consequence of the propagation of wave patterns on the film, highlighting that the spatial and temporal evolution of film disturbances sets the parameters for the jet's velocity profile, diameter, and breakup phenomenon, summarized in a parametric regime map. Finally, a Lagrangian analogy is constructed between interwoven beads falling down a vertical pole and the draining liquid moieties, where the attractive inter-bead forces, mimicking surface tension, overcome the inertial resistance to effectively pinch the layer to capillary length scale.

We investigate droplet deformation following laser-pulse impact at low Weber numbers ( ${\textit{We}}\sim 0.1{-}100$ ). Droplet dynamics can be characterised by two key parameters: the impact Weber number and the width, W , of the distribution of the impact force over the droplet surface. By varying laser-pulse energy, our experiments traverse a phase space comprising (i) droplet oscillation, (ii) breakup or (iii) sheet formation. Numerical simulations complement the experiments by determining the pressure width and by allowing We and W to be varied independently, despite their correlation in the experiments. A single phase diagram, integrating observations from both experiments and simulations, demonstrates that all phenomena can be explained by a single parameter: the deformation Weber number ${\textit{We}}_{{d}}=f({\textit{We}},{W})$ that is based on the initial radial expansion speed of the droplet, following impact. The resulting phase diagram separates (i) droplet oscillation for ${\textit{We}}_{{d}}\lt 5$ , from (ii) breakup for $5\lt {\textit{We}}_{{d}}\lt 60$ and (iii) sheet formation for ${\textit{We}}_{{d}}\gt 60$ .

In the context of clean energy transition, colloidal fuel droplets have attracted significant attention, owing to their high energy density and better combustion performance. Yet, considerable uncertainty remains regarding the dynamics and evaporation of colloidal droplets under the influence of an acoustic field. Among other methods, acoustic levitation provides a contactless platform for investigating droplet dynamics in the absence of solid interfaces. This Review presents a complete exploration of droplet dynamics in acoustically levitated colloidal droplets, from fundamentals to advanced applications. First, the fundamentals of acoustic levitation, including ultrasonic standing-wave generation and acoustic radiation forces that enable the stable, contact-free levitation of droplets, are outlined. The influence of acoustic levitation on the adjacent flow and thermal fields is considered, with an emphasis on acoustic streaming and other transport phenomena that substantially thin boundary layers and promote heat and mass transfers along levitated droplets. Subsequently, the influence of the acoustic field on droplet oscillations, droplet breakup and coalescence, and droplet evaporation behavior is discussed in detail. Across these aspects, recent studies have shown that the dynamics of colloidal droplets differ from those of pure fluids. Finally, current limitations and future research directions that could yield further insights into droplet dynamics are highlighted, as colloidal droplets have wide-ranging interdisciplinary applications.

This study employs numerical simulation to investigate the mechanisms through which centrifugal nozzle structural parameters and superheated steam velocity influence steam desuperheating performance. The model accuracy was validated against factory measurement data, demonstrating a maximum deviation of only 1.07% (specifically for the outlet steam temperature in Case 2, comparing the simulated 696.65 K against the measured 704.21 K). Results indicate that the spray cone angle is the primary factor governing desuperheating efficiency, exerting a stronger influence than the droplet Sauter Mean Diameter (SMD). Specifically, the simulations identified that optimal atomization and heat transfer occur at a nozzle stem angle of 30° and a swirl hole angle of 67.5°. Furthermore, increasing the swirl chamber angle and steam velocity (> 45 m/s) markedly enhances heat exchange by promoting droplet breakup and dispersion. Based on these findings, an L9(34) orthogonal experiment was conducted to determine the optimal configuration. The resulting parameter combination – a 67.5° swirl hole, 120° swirl chamber, 30° nozzle stem, and 75 m/s steam velocity – exhibited superior performance. Compared with the original model, the optimized design reduced the droplet SMD by 22.2%, increased the spray cone angle by 3%, and improved the steam temperature reduction rate by 6.6 percentage points. This study provides a theoretical foundation for the structural optimization of high-efficiency centrifugal adjustable nozzles.

Laser-driven control of droplets is important in microfluidics, targeted delivery, and droplet-based laser-matter interactions, yet propulsion direction and breakup remain difficult to predict. Here, we demonstrate that an acoustically levitated droplet's propulsion polarity and breakup morphology can be selected by controlling axial placement relative to the external (no-droplet) optical focus together with incident pulse energy. We combine time-resolved shadowgraphy with aberration-aware optical simulations that locate the prebreakdown irradiance maxima, and we connect these linear field calculations to laser-induced breakdown using experimentally calibrated thresholds in the liquid and in near-field air. Expressing irradiance in threshold-referenced form yields a first-crossing rule that identifies whether breakdown initiates at the illumination surface, in the interior, at the shadow surface, or in wake-side near-field air. The resulting placement-energy maps anticipate forward, backward, and near-radial droplet responses. A polarity index and a reliability metric quantify directionality and highlight narrow transition corridors in parameter space where competing initiation sites are nearly tied under experimental jitter. The predicted landscapes agree with experiments, and multiphase simulations reproduce the early-time shock-driven deformation. Because the regime structure is set by caustic geometry together with breakdown thresholds, the framework transfers across transparent liquids after threshold calibration and reduces to a surface-trigger condition in the strongly absorbing limit.

Continuous emulsification is a desirable alternative to batch processing, especially in sectors such as food and beverage, cosmetics, and pharmaceuticals, where large volumes of consistent emulsions are required. Vortex-based hydrodynamic cavitation (VD) devices have emerged as efficient and scalable options using cavitation-induced local energy dissipation to promote droplet breakup. However, practical guidance for device design and pathways for scale-up and scale-out remains limited. This study investigates the influence of the outlet configuration, chamber geometry, number of inlets, and scale-up or scale-out on the performance of VD for continuous production of liquid-liquid emulsions. The results indicate that including a vortex stabilizer in the chamber and using a multiple-inlet device improved the cavitation activity. Geometrically similar scale-up (1-5 LPM) resulted in a slight increase in the Sauter mean diameter and lower energy efficiency, which confirmed the flow characteristics related to the distribution of turbulence dissipation rates becoming attenuated at larger scales. The scale-out options were investigated considering two and four 1 LPM nominal flow rate devices operated in parallel to increase the nominal flow rate to 5 LPM for the four devices. The results confirm that while scale-up and scale-out have limited impact on final droplet size distribution, they influence energy effectiveness. Multi-inlet designs were seen to enhance emulsification efficiency and reduce droplet size, especially when operating at low pressure drop values. Overall, this study provides practical guidelines for designing and deploying vortex-based HC devices for continuous emulsification applications.

Confinement effects on droplet deformation and breakup in cross-junction flows

Metal droplet breakup and rapid solidification behavior under multi-stage-controlled atomization process: NiTi alloys 3D printing special powder preparation

Submarine pipeline leaks in offshore oil and gas production release gas–oil mixtures that rapidly ascend to the ocean surface, posing significant environmental threats. Mechanical dispersion through imposed shear flows effectively fragments large bubbles into smaller droplets, decelerating their rise and promoting enhanced natural biodegradation. Optimizing such dispersion techniques demands a detailed quantitative analysis of bubble deformation and breakup under various shear conditions. This study employs a multicomponent Shan–Chen pseudopotential lattice Boltzmann method (LBM) combined with a single relaxation time Bhatnagar-Gross-Krook (BGK) collision operator to simulate air-water bubble behavior under controlled shear and extensional stresses, representative of water-jet dispersion scenarios. To maintain thermodynamic consistency, the Guo forcing scheme will be implemented within the LBM framework. Simulations will be carried out in two dimensions using a D2Q9 lattice configuration, systematically exploring a parameter space characterized by varying shear rates and Reynolds numbers. Key simulation outputs include the temporal evolution of droplet shapes and breakup time scales, validated against experimental correlations and existing numerical benchmarks. The investigation of bubble dynamics in controlled shear conditions provides a robust framework for understanding bubble behaviors across different flow regimes. These insights are critical for optimizing mechanical dispersion systems, ultimately enhancing droplet suspension times and biodegradation rates, thereby significantly contributing to effective environmental protection strategies in offshore petroleum operations.

Ammonia (NH3) has emerged as a promising carbon-free fuel for next-generation green energy systems due to its high hydrogen density, ease of storage and transport, and compatibility with existing infrastructure. These attributes contrast with hydrogen, which presents major challenges related to storage, safety, and high-pressure handling. Thus, ammonia offers a more practical alternative for combustion-based applications. However, its low reactivity and complex vaporization behavior, particularly under flash-boiling conditions, pose challenges for accurate modeling. This study presents a comprehensive numerical investigation of liquid-ammonia spray behavior under a range of ambient pressures, encompassing both flash-boiling and non-flashing conditions. Simulations were conducted using the Lagrangian particle tracking method, coupled with various turbulence models (the renormalization group (RNG) family, k-ω family, ς − f, V2F models) to evaluate their predictive performance. Validation against experimental data for liquid and vapor penetration demonstrated that the V2F model achieved the best overall balance between accuracy and computational efficiency. Under strong flash-boiling conditions (2 bar), rapid droplet breakup and notable cooling were observed, with droplet temperatures decreasing to approximately 235 K within a few millimeters of the nozzle. In contrast, the cooling effect was more moderate under non-flashing conditions at higher ambient pressures (10–15 bar). Although the current findings were based on numerical simulations, experimental studies are ongoing to validate and refine the modeling framework further. This work provided valuable insights into the coupled effects of turbulence, phase change, and thermal transport in superheated ammonia sprays. Future research will build upon these results by extending the model to NH3/H2 dual-fuel systems, refining turbulence-phase interaction models, and exploring the potential application of ammonia-based flash-boiling cooling systems for electric vehicle (EV) battery thermal management.

This study numerically investigates the flow field characteristics and oil droplet behavior in a cylindrical oil–water hydrocyclone under high-Reynolds-number turbulent swirling flow conditions. An Eulerian multiphase model combined with the Reynolds Stress Model (RSM) is employed to resolve the anisotropic turbulence, while the Population Balance Model (PBM) is used to describe the coalescence and breakup of dispersed oil droplets. The simulated flow corresponds to Reynolds numbers on the order of 104–105, representative of practical oil–water separation operations. The results show that the tangential velocity is directly related to the swirl intensity and gradually attenuates along the axial direction. The axial velocity distribution clearly exhibits the characteristic dual-vortex structure, while the radial velocity governs the convergence rate of the oil phase toward the swirl center. The pressure field presents a typical radial distribution with low pressure at the core and high pressure near the wall, and an axial trend characterized by a sharp pressure drop near the inlet followed by gradual stabilization. The oil phase is preferentially concentrated in the central region of the hydrocyclone, with the separation degree decreasing rapidly near the inlet and becoming stable downstream. Quantitatively, increasing the inlet oil volume fraction from 0.1 to 1% leads to a pronounced increase in oil droplet size and oil phase aggregation, although the growth rate gradually diminishes. Larger initial droplet size distributions result in stronger oil phase concentration, whereas the droplet size distribution has a negligible influence on the velocity field.

The dynamics of an impacting droplet can be controlled by microstructuring the surface. This work presents a numerical investigation of droplet impact characteristics on a hydrophobic surface microstructured with sinusoidal wavy patterns. The effects of amplitude and wavelength of the wavy surfaces on droplet deformation are analyzed for different impact velocities. A dynamic contact angle model is incorporated into the numerical method to track the three-phase contact line accurately. The influence of the Weber number on the wettability transition is analyzed, and the flow characteristics inside the droplet at different flow regimes are explained. A regime map is prepared to show the transition between different regimes for different surface attributes and Weber numbers. The initial contact of the impacting droplet with the surface is influenced by the amplitude and wavelength of the roughness element, leading to different wettability states. The Wenzel (wetting), Cassie (non-wetting), and mixed wetting states affect the droplet's spreading, recoiling, and rebound characteristics. The Cassie state of a plane surface is transformed into the Wenzel state due to microstructuring the surface with small amplitude and wavelength. A further increase in amplitude and wavelength leads to a transition from the Wenzel state to a mixed state, and finally from the mixed state to the Cassie state. The amplitude-controlled mixed state results in partial rebound of the droplet, whereas the wavelength-controlled state results in partial rebound and rebound with droplet breakup. The study may aid in designing droplet retention surfaces required for practical applications.