Search Results (506)

Modern aircraft fuel tank explosion protection relies critically on inerting efficiency. This study presents and investigates a novel scrubbing deoxygenation strategy utilizing mixed inert gas (MIG) generated by oxygen-consuming inerting systems for high-vapor-pressure RP5 aviation fuel. A high-fidelity computational fluid dynamics (CFD) numerical framework was established using the Eulerian–Eulerian two-fluid model coupled with Higbie’s penetration theory, with experimental validation ensuring computational accuracy (maximum errors for ullage oxygen concentration and dissolved oxygen in fuel controlled within 4.11% and 5.23%, respectively). The research systematically elucidates the influence mechanisms of bubble diameter, MIG temperature, and superficial gas velocity on mass transfer characteristics (oxygen mass transfer coefficient and volumetric mass transfer coefficient). Key findings reveal that reducing bubble diameter achieves localized polarization of mass transfer intensity in the central plume region through an “area-velocity” synergistic effect, with the oxygen volumetric mass transfer coefficient at 1.0 mm diameter increasing by 51.3% compared to 2.5 mm. The performance enhancement from superficial gas velocity primarily stems from the “area multiplication effect” triggered by surging gas holdup. Notably, MIG temperature exhibits a unique three-stage reversal characteristic of “kinetically dominated early stage, thermodynamically controlled late stage” on deoxygenation performance. These results provide critical physical foundations for the forward design of next-generation multifunctional onboard inerting systems. Full article

There are four types of bubble ascent paths: rectilinear, zigzag, spiral, and chaotic, but fewer quantitative studies on the dynamics of bubble spiral motion. In this paper, the spiral path dynamics of a single bubble with an initial diameter of 1.75–3.86 mm in still water is investigated. The bubble position on the spiral trajectory was quantitatively characterized as a function of time using the three-dimensional shadow imaging technique combined with image digitization processing. The additional forces that induce spiral motion were derived using Newton’s second law and subsequently integrated into the Lagrangian framework through Fluent User-Defined Functions (UDFs) to reproduce the spiral trajectory of the single bubble. The simulation results for bubble velocity and trajectory closely matched the experimental data. The forces, accelerations, velocities, trajectories, and swept volumes of the bubbles are discussed. Compared to the rectilinear motion, the swept volumes of the bubbles obtained after considering the spiral paths were increased by 29.5%, 34.4%, 38.2%, 40.6%, and 37.1% for 1.75, 1.83, 1.93, 2.05, and 3.86 mm, respectively. These results will contribute to a better understanding of the dynamic behavior of the bubble spiral motion. Full article

Protrusions on the flow-passing surfaces of hydraulic machinery readily induce localized cavitation and exacerbate cavitation erosion damage. This study investigates the influence of a spherical cap protrusion on a flat wall on the collapse dynamics of cavitation bubbles. By integrating high-speed photography experiments with Kelvin impulse theory, an impulse model is constructed based on boundary treatment and potential flow superposition. The dynamic evolution characteristics of cavitation bubbles at both symmetric and asymmetric positions are systematically analyzed, with emphasis on the effects of the spherical cap angle and bubble azimuthal angle on bubble morphology evolution, bubble wall collapse velocity, and the magnitude and direction of the Kelvin impulse. The results indicate that as the spherical cap angle increases, the non-spherical collapse of bubbles at symmetric positions becomes substantially more pronounced, and the collapse mode transitions from flat wall-dominated to protrusion-dominated behavior. At asymmetric positions, a larger spherical cap angle intensifies the non-uniformity of the bubble wall collapse velocity: the minimum velocity continues to decrease, and the location of this extremum shifts toward the side adjacent to the protrusion. Meanwhile, the Kelvin impulse magnitude exhibits accelerating growth, and its direction reorients from perpendicular to the wall toward the protrusion structure. Full article

To achieve efficient bubble refinement under high gas–liquid ratio (GLR) conditions in industrial applications, this study investigates the effects of Venturi geometry parameters and operating conditions on bubble size distribution under high GLR conditions. Experiments were conducted with throat velocities ranging from 4.34 to 13.02 m/s and GLRs from 10% to 60%, examining the effects of throat diameters (4 mm and 8 mm) and divergent angles (7.5°, 10°, and 12.5°). A novel baffled Venturi bubble generator was designed by maintaining constant throat flow area and principal parameters. Results showed that Venturi tubes with an 8 mm throat diameter produced smaller bubble sizes at higher liquid flow rates. In contrast, excessively large divergent angles produced unfavorable larger bubble sizes due to higher GLR and flow separation. Based on experimental data (Reynolds number range: 12,163–106,084), a comprehensive bubble size prediction model was established, which simultaneously considers the effects of throat diameter and divergent angle. Increasing the liquid flow rate and reducing the GLR effectively minimize bubble size, while the newly developed bubble generator demonstrates superior performance compared to conventional Venturi designs. These findings provide practical references for the design and industrial application of Venturi bubble generators under high GLR conditions. Full article

The foaming of hydrogels presents a promising strategy for tailoring mechanical and radiological properties to replicate biological soft tissues for biomedical phantom applications. A computational fluid dynamics (CFD) framework is developed to predict void fraction distribution in alginate hydrogel precursor solutions aerated by air injection through a bottom nozzle. The objective is to use the framework for the design of the foaming system to match the desired gas-fraction distribution and radiological property. Seven parametric cases are investigated, varying inlet air velocity, alginate concentration, and surface tension. Results show that higher inlet velocities promote stronger jet penetration and greater gas accumulation, while increasing alginate concentration confines the bubble plume, with quasi-steady gas fractions displaying a non-monotonic trend with concentration. Elevated surface tension yields broader plume coverage and improved gas distribution uniformity at the expense of peak void fraction. The predicted void fractions map to Hounsfield Unit (HU) values of −34 to −103, corresponding to adipose and fatty breast tissue attenuation (−50 to −150 HU). The peak gas fraction at 5.0 wt% alginate yields −307 HU, approaching published experimental CT measurements for the same formulation (−460 to −233 HU). Full article

This study examines the electrohydrodynamic (EHD) behavior of air bubbles rising in deionized water under a non-uniform electric field, with particular emphasis on the influence of applied voltage (0.5–3.0 kV) and gas flow rates of 30 and 40 mL ${\min }^{-1}$ (corresponding to Reynolds numbers of $R{e}_g=107$–142) on bubble dynamics. High-speed imaging reveals bubbles with equivalent diameters in the range of $d_{eq}\approx 0.8$–3.5 mm, enabling a detailed characterization of their deformation, trajectory, and interfacial response under coupled hydrodynamic and electric stresses. At $R{e}_g=107$, bubbles exhibited stable vertical trajectories with negligible lateral displacement, whereas at $R{e}_g=142$, inertial and wake effects induced deviations. Increasing $B{o}_E$ reduced lateral displacement, restoring alignment with the electric field. Bubble rise velocities increased by ∼20–30% with applied voltage due to polarization-driven EHD forces. A transition from hydrodynamically dominated to EHD-dominated regimes was identified. While polarization forces govern the initial bubble motion under a strong electric field, bubbles progressively transition downstream to a hydrodynamic regime as the electric field weakens, reducing the influence of polarization effects. These findings provide quantitative insight into coupled hydrodynamic–electrohydrodynamic interactions and support the development of predictive models for controlling bubble trajectories, with implications for electrically tunable multiphase and microfluidic systems. Full article

This study experimentally investigates the dynamics of air bubble plumes in water under varying thermal and hydrodynamic conditions using a two-dimensional Particle Image Velocimetry (PIV) system. The experimental setup consists of a transparent acrylic tank equipped with a bubble generator, a controlled heating system, and a synchronized PIV arrangement to capture both bubble motion and the induced liquid flow field. Experiments were conducted over a range of water temperatures (21–60 °C), air flow rates, and water depths (200–600 mm) to systematically quantify their coupled influence on bubble plume behavior. The results demonstrate that bubble rising velocity (defined here as the mean vertical, buoyancy-driven component of bubble motion measured in the fully developed plume region) increases with water temperature, gas flow rate, and water depth. For a fixed gas flow rate and water depth, increasing the water temperature from 40 °C to 60 °C resulted in an approximately twofold increase in bubble rising velocity, primarily due to reduced liquid viscosity and enhanced buoyancy forces. Bubble velocity also increased with gas flow rate and water depth, reflecting stronger momentum input and extended acceleration distances within taller water columns. PIV-resolved velocity fields further reveal that the surrounding fluid velocity increases proportionally with bubble rising velocity and temperature, confirming a strong coupling between bubble motion and plume-induced circulation. The surrounding liquid velocity reached approximately 30–60% of the corresponding bubble rising velocity, depending on operating conditions. These findings provide quantitative experimental insight into the coupled effects of thermal conditions, gas injection rate, and liquid depth on bubble–liquid interactions. The results contribute valuable validation data for multiphase flow modeling and offer practical relevance for thermal–hydraulic, chemical, and environmental engineering applications involving bubble-driven transport processes. Full article

Characterizing instability in gas–liquid flows is difficult because flow dynamics interact across multiple scales. In this work, we develop an integrated framework that combines multi-resolution analysis with composite multiscale equiprobable symbolic sample entropy (MRA-CMESSE). This combination enables us to examine flow instability from a multistructural and multiscale perspective. A comprehensive evaluation across four distinct metrics shows that our method is more robust to changes in data length than multiscale sample entropy and composite multiscale sample entropy approaches. Furthermore, MRA-CMESSE is applied to analyze differential pressure time series from vertical air–water two-phase flow, providing a quantitative characterization of the instability of three flow patterns. Among these, bubble flow is the most unstable, with energy spread out and high complexity at small scales; slug flow is the most stable, with its energy focused at larger scales with low complexity, and churn flow falls in between. A central finding is that as superficial gas velocity increases, energy and complexity shift to the meso-scale and micro-scale. This quantitative analysis identifies increased agitation at the meso-scale and micro-scale as the primary driver of enhanced overall flow instability. This framework offers a new quantitative basis for analyzing gas–liquid two-phase flows and strengthens the physical foundation for the monitoring and control of related industrial systems. Full article

This work investigated the influence of thickness-direction boundary conditions on the flow characteristics of granular material in a quasi-two-dimensional silo using the discrete element method (DEM). Two types of boundary conditions were considered in the thickness direction: wall conditions and periodic boundary conditions. The simulation results indicate that under wall conditions, velocity waves propagate upward, manifested by the formation of bubble-like sub-flow zones in the velocity field, and the particle motion in the upper bed region exhibits a clear stick–slip feature. In contrast, under periodic boundary conditions, particle motion displays a resonant mode. Further statistical analysis reveals that, despite the distinct macroscopic motion mode under the two boundary conditions, the probability distributions of particle vertical fluctuating velocities share similar characteristics: both exhibit fat-tailed and asymmetric features and deviate from Gaussian distribution. Additionally, under wall conditions, the horizontal distributions of particle vertical velocity conform to the kinematic model throughout the bed, whereas under periodic boundary conditions, the horizontal distributions in the upper bed region display plug flow characteristics. In summary, the results of this work demonstrate that thickness-direction boundary conditions play a crucial role in determining the flow characteristics of granular assembly in silos. Full article

In engineering flow systems such as hydraulic machinery and marine propulsion, interactions among cavitation bubbles can significantly influence collapse dynamics. This study investigates the collapse behavior of unequal-sized dual cavitation bubbles in a free field, focusing on jet formation modes, morphological evolution, and the characteristics of the Bjerknes force and Kelvin impulse. Particular emphasis is placed on the effect of the bubble radius ratio on the collapse dynamics. The results indicate that: (1) as the radius ratio decreases, the counter-directed jets formed during the collapse of dual cavitation bubbles gradually disappear; (2) with a decreasing radius ratio, the amplitude of the bubble wall velocity first decreases and then increases; and (3) both the Bjerknes force and the Kelvin impulse decrease as the radius ratio decreases. Full article

This study employs high-speed photography to investigate the collapse dynamics of laser-induced bubbles inside a pendant droplet, focusing on the effects of bubble-to-droplet radius ratio (λ) and eccentricity (ε). Additionally, a theoretical model describing the Kelvin impulse of the bubble is derived using the image method. Both the flow field and Kelvin impulse distributions are examined. The conclusions are given as follows: (1) Four jet patterns are identified with varying radius ratios: no jet, weak jet, strong jet, and complex jet. (2) The dominant role of radius ratio and eccentricity in the inhomogeneity and anisotropies of the velocity field is clarified. It manifests as a significant increase in the velocity difference between the bubble wall and the droplet surface along the bubble-droplet centerline. (3) Both the bubble migration velocity and Kelvin impulse intensity increase significantly with rising radius ratio and eccentricity. Larger bubbles closer to the droplet surface exhibit more intense interactions. Furthermore, the Kelvin impulse remains oriented toward the droplet center. As λ increases, the migration velocity of the bubble center can exceed 40 m/s, and the Kelvin impulse intensity can exceed 10⁻³ kg·m/s. Full article

In complex-composition fluid environments, fine solid particles exacerbate cavitation on equipment surfaces, accelerating surface erosion and damage. This study employs high-speed photography and Kelvin impulse theory to investigate bubble collapse dynamics near triple unequally sized particles, mainly focused on the particle size ratio effect and associated symmetry-breaking behavior. Key findings include: (1) The size ratio of the particles has a significant influence on the bubble collapse morphology, and an increase in the size ratio exacerbates the asymmetric deformation of bubbles. (2) The size ratio of the particles has a pronounced effect on the velocity field of the ambient flow field surrounding the bubble, and an increase in the size ratio aggravates the inhomogeneity of the liquid velocity distribution. (3) The increase in the size ratio of the particles leads to a decrease in the number of zero-Kelvin impulse points and changes in their positions. Full article

This study employs a Computational Fluid Dynamics (CFD) approach based on the Two-Fluid Model (TFM) to investigate the CO₂ capture characteristics in a bubbling fluidized bed reactor using potassium carbonate (K₂CO₃) as the sorbent. The simulations are conducted at five superficial gas velocities ranging from 1.5 to 3.5 times the minimum bubbling velocity (u_mb = 0.26 m/s), with a particle diameter of 0.4 mm, particle density of 2300 kg/m³, and an initial solid volume fraction of 0.55. The gas mixture consists of CO₂, H₂O, and N₂ at a molar ratio of 0.1:0.1:0.8 and a temperature of 343 K. First, the numerical simulation was validated against experimental data reported in the literature, confirming its accuracy in quantitatively describing the adsorption process. Subsequently, the distributions of CO₂ concentration and adsorption reaction rate in both the bubble phase and the emulsion phase were analyzed under different superficial gas velocities. The simulation results indicate that CO₂ concentration and adsorption reaction rate in both phases decrease along the bed height. Compared to the emulsion phase, the bubble phase exhibits higher CO₂ concentration and gas temperature but a lower adsorption reaction rate. As the gas velocity increases, CO₂ concentration rises in both the bubble and emulsion phases, accompanied by an increase in the proportion of the bubble phase, and a higher CO₂ concentration at the reactor outlet. Further comparison of CO₂ concentrations in the bubble and emulsion phases at the upper part of the bed with the outlet concentration reveals that the outlet CO₂ primarily originates from the unadsorbed portion within the bubble phase, while the contribution from unadsorbed CO₂ in the emulsion phase is almost negligible. Full article

The foundry industry produces over 66 million tons of mixed casting waste sand, containing toxic and harmful substances such as phenols and aldehydes, every year, which has caused serious soil pollution, water source pollution, and large amounts of CO₂ emissions. Green resource recycling and utilization are urgently needed. The hot method circulating fluidized bed furnace is currently the mainstream technology for the regeneration of casting waste sand. However, traditional equipment has a series of key technical bottlenecks, such as VOC (volatile organic compound) emissions, low yield of fine sand, poor stability of phase change sand, and uneven fluidization, which directly limit the effectiveness, large-scale promotion, and application of waste sand regeneration. This study, based on a self-designed experimental prototype, constructed models with different hood densities and inlet air velocity parameters. A CFD-DEM coupled model, combined with two turbulence models, was used for numerical simulations and experimental validation, and the optimal combination of fluidization parameters was determined. The study confirmed that the k–ω SST model is more suitable for precise simulation of such gas–solid two-phase flows. The research revealed quantitative relationships between key parameters and sand particle fluidization states, addressing the core problem of uneven fluidization in conventional bubbling furnaces and providing important guidance for the optimized design of new thermal cycle bubbling furnaces. It has significant engineering value for promoting the efficient resource utilization of foundry waste sand and the green and sustainable development of the industry. Full article

Dissolved-air flotation (DAF) is widely used for surface-water pretreatment but remains insufficiently explored for chemically complex groundwater. This study develops a thermodynamic and bubble-dynamics modeling framework to evaluate the feasibility of DAF pretreatment for groundwater containing elevated arsenic, natural organic matter (NOM), and color. The study is theoretical and model-based; no experimental dissolved-air flotation tests were performed. Air solubility was calculated at pressures of 4–6 bar and temperatures of 13–17 °C, while microbubble size, rise velocity, and bubble–floc interaction efficiencies were estimated using established physical models. Laboratory coagulation–flocculation jar tests with FeCl₃ and FeCl₃/PAC were used to define realistic floc properties prior to flotation modeling. No experimental dissolved-air flotation tests were conducted; all flotation-related results presented in this study are derived from thermodynamic and hydrodynamic modeling. Results show that a temperature decrease from 17 to 13 °C increases effective gas supersaturation by ~15% and shifts predicted microbubble diameters from ~60–90 µm to ~35–60 µm under identical operating conditions. The qualitative consistency between modeled flotation-relevant parameters and previously observed coagulation–flocculation trends for color, total organic carbon, and arsenic removal supports the proposed mechanistic framework. The study demonstrates how coupling coagulation chemistry with thermodynamically optimized air dissolution can enhance DAF applicability for arsenic- and NOM-rich groundwater. Full article