Search Results (749)

Deepwater oil–gas–water three-phase flow is widely regarded as a multiphase system. Intense interfacial interactions cause significant nonuniform fluid distributions in the wellbore, giving rise to complex nonlinear dynamics. In this study, a distributed conductance sensor (DCS) was developed to capture local flow information from a horizontal oil–gas–water simulation well. To quantify the complexity of nonlinear time series, phase permutation entropy (PPE) was first validated using artificial data, including the Tent map, Hénon map, and Lorenz system. PPE demonstrates superior capability in detecting abnormal dynamical changes compared with permutation entropy (PE). Subsequently, PPE is combined with the multiscale approach, i.e., multiscale phase permutation entropy (MPPE), to analyze the DCS signals and uncover the complexity of horizontal oil–gas–water flows. The results show that the MPPE analysis can reveal the spatial distribution characteristics of elongated gas bubbles, gas paths, dispersed bubbles and oil droplets. Full article

To address the fluctuation and instability of renewable power generation and the steady-state demands of chemical processes, a single-channel, non-isothermal computational fluid dynamics 3D model was developed. This model explicitly incorporates the coupling effects of electrochemical reactions, two-phase flow, and heat transfer. Subsequently, the influence of key operating parameters on proton exchange membrane water electrolyzer (PEMWE) system performance was investigated. The model accurately predicts the current–voltage polarization curve and has been validated against experimental data. Furthermore, the CFD model was employed to investigate the coupled effects of several key parameters—including operating temperature, cathode pressure, membrane thickness, porosity of the porous transport layer, and water inlet rate—on the overall electrolysis performance. Based on the numerical simulation results, the evolution of the ohmic polarization curve under temperature gradient, the block effect of bubble transport under high pressure, and the influence mechanism of the microstructure of the multi-space transport layer on gas–liquid, two-phase flow distribution are mainly discussed. Operational strategy analysis indicates that the high-efficiency mode (4.3–4.5 kWh/Nm³) is suitable for renewable energy consumption scenarios, while the economy mode (4.7 kWh/Nm³) reduces compression energy consumption by 23% through pressure–temperature synergistic optimization, achieving energy consumption alignment with green ammonia synthesis processes. This provides theoretical support for the optimization design and dynamic regulation of proton exchange membrane water electrolyzers. Full article

Intrusive phase-detection probes remain a standard tool for local characterization of gas–liquid bubbly flows, but their accuracy is strongly affected by probe geometry and bubble–probe interaction kinematics. This work presents a Monte Carlo-based framework to evaluate four-sensor intrusive probes in bubbly flow, relaxing the classical assumptions of spherical bubbles and purely axial trajectories. Bubbles are represented as spheres or ellipsoids, a broad range of non-dimensional probe geometries are explored, and local quantities such as interfacial area concentration, bubble and flux velocities, and chord lengths are recovered from synthetic four-sensor signals. The purpose of the framework is threefold: (i) it treats four-sensor probes in a unified way for interfacial area, velocity, and chord length estimation; (ii) it includes ellipsoidal bubbles and statistically distributed incidence angles; and (iii) it yields compact correction laws and design maps expressed in terms of the spacing-to-diameter ratio $a_p/D$, the dimensionless probe radius $r_p/D$, and the missing ratio $m_r$ (defined as the fraction of bubbles that cross the probe footprint without being detected), which can be applied to different intrusive four-sensor probes. The numerical results show that, within a recommended geometric range $0.5\le a_p/D\le 2$ and $r_p/D\le 0.25$ and for missing ratios $m_r\le 0.7$, the axial velocity $V_z$ estimates the bubble centroid velocity and its projection with typical errors within $\pm 10\%$, while a chord length correction $C{L}_{corr}\left(m_r\right)$ recovers the underlying chord length distribution with a residual bias of only a few percent. The proposed interfacial area correction, written solely in terms of $m_r$, remains accurate in polydisperse bubbly flows. Outside the recommended $(a_p/D,r_p/D)$ range, large probe radius or extreme tip spacing lead to velocity and chord length errors that can exceed 20–30%. Overall, the framework provides quantitative guidelines for designing and using four-sensor intrusive probes in bubbly flows and for interpreting their measurements through geometry-aware correction factors. Full article

Fine-bubble aeration is a core process in wastewater treatment plants (WWTPs). However, the physical mechanisms linking bubble plume hydrodynamics to oxygen transfer performance remain insufficiently quantified under configurations representative of full-scale installations. This study presents a local multi-sensor experimental characterization of a multiple bubble plume system using a 4 × 4 array of commercial membrane diffusers in a pilot-scale aeration tank (2 m³), emulating WWTP diffuser density and geometry. Airflow rate was varied to analyze its effects on mixing and oxygen transfer efficiency. The experimental methodology combines three complementary measurement approaches. Oxygen transfer performance is quantified using a dissolved oxygen probe. Liquid-phase velocity fields are then mapped using Acoustic Doppler Velocimetry (ADV). Finally, local two-phase measurements are obtained using dual-tip Conductivity Probe (CP) arrays, which provide bubble size, bubble velocity, void fraction, and Interfacial Area Concentration (IAC). Based on these observations, a zonal hydrodynamic model is proposed to describe plume interaction, wall-driven recirculation, and the formation of a collective plume core at higher airflows. Quantitatively, the results reveal a 29% reduction in Standard Oxygen Transfer Efficiency (SOTE) between 10 and 40 m³/h, driven by a 41% increase in bubble size and an 18% rise in bubble velocity. Bubble chord length also increased with height, by 33%, 19%, and 15% over 0.8 m for 10, 20, and 40 m³/h, respectively. These trends indicate that increasing airflow enhances turbulent mixing but simultaneously enlarges bubbles and accelerates their ascent, thereby reducing residence time and negatively affecting oxygen transfer. Overall, the validated multiphase datasets and mechanistic insights demonstrate the dominant role of diffuser interaction in dense layouts, supporting improved parameterization and experimental benchmarking of fine-bubble aeration systems in WWTPs. Full article

Smoothed particle hydrodynamics (SPHs) is a Lagrangian meshless method with distinct strengths in managing unstable and complex interface behaviors. This study develops an integrated multiphase SPH framework by merging multiple algorithms and techniques to enhance stability and accuracy. The multiphase model is validated by several benchmark examples, including square droplet deformation, single bubble rising, and two bubbles rising. The selection of numerical parameters for multiphase simulations is also discussed. The validated model is then applied to simulate oil–water–gas bubbly flows. Interface behaviors, such as coalescence, fragmentation, deformation, etc., are reproduced, which helps to take into account multiphysics interactions in industrial processes. The rising processes of many oil droplets for oil–water separation are first simulated, showing the advantages and stability of the SPH model in dealing with complex interface behaviors. To fully explore the potential of the model, the model is further extended to the field of wax removal. The melting process of the wax layer due to heat conduction is simulated by coupling the thermodynamic model and the phase change model. Interesting behaviors such as wax layer cracking, droplet detachment, and thermally driven flow instabilities are captured, providing insights into wax deposition mitigation strategies. This study provides an effective numerical model for bubbly flows in petroleum engineering and lays a research foundation for extending the application of the SPH method in other engineering fields, such as multiphase reactor design and environmental fluid dynamics. Full article

The generation and stability of foam are critical attributes influencing the perceived efficacy and sensory experience of cleansing products like face cleansers and hair shampoos. This study rigorously investigated the influence of water hardness on the foam characteristics of a face cleanser and hair shampoo through integrated macroscopic, microscopic, and rheological analyses. Hard water consistently induced severe foam destabilization, evidenced by significantly increased foam decay and shortened drainage half-lives. Microstructural analysis revealed pronounced bubble coalescence, manifested as reduced bubble counts and elevated mean bubble areas. Rheologically, hard water compromised foam viscoelasticity, leading to diminished complex moduli (G*), earlier G″/G′ crossovers, and heightened phase angles (δ), signifying a rapid transition to a predominantly viscous, unstable state. Conversely, soft water consistently yielded highly elastic foams with robust G* values, maintained G′ dominance, and low δ, indicative of superior structural integrity and temporal stability. Notably, controlled rate viscosity profiles remained unaffected by water hardness. These findings collectively demonstrate that divalent cations fundamentally undermine foam lamellar film stability, inducing profound structural and mechanical degradation. Concurrently, tribological measurements revealed that the face cleanser consistently exhibited higher coefficients of friction in hard water across varying sliding speeds, whereas the hair shampoo displayed a more complex, speed-dependent frictional profile that was comparatively less sensitive to water hardness. This underscores the critical necessity for formulation chemists to mitigate water hardness effects to ensure consistent product performance and sensory attributes. Full article

Air flotation separation technology has emerged as one of the core techniques for oily wastewater treatment in oilfields, owing to its advantages of high throughput, high separation efficiency, and short retention time. Originally applied in mineral processing, this technology was first introduced to oilfield produced water treatment by Shell in 1960. With the optimization of microbubble generators, advances in microbubble generation technology—characterized by small size, high stability, and uniformity—have further expanded its applications across various wastewater treatment scenarios. To optimize the separation performance of a horizontal compact closed-loop cyclonic air flotation unit, this study employs CFD numerical simulation to investigate two key aspects: First, for the flotation zone, the effects of structural parameters (deflector height, inclination angle) and operational parameters (gas–oil ratio, bubble size, inlet velocity) on flow patterns and gas distribution were systematically examined. Device performance was evaluated using metrics such as gas–oil ratio distribution curves and flow field characteristics, enabling the identification of operating conditions for stratified flow formation and the determination of optimal deflector structural parameters. Second, based on the Eulerian multiphase flow model and RSM turbulence model, a numerical simulation model for the oil–gas–water three-phase flow field was established. The influences of key parameters (bubble size, throughput, gas–oil ratio) on oil–water separation efficiency were investigated, and the optimal operating conditions for the unit were determined by integrating oil-phase/gas-phase distribution characteristics with oil removal rate data. This research provides theoretical support for the structural optimization and engineering application of horizontal compact closed-loop cyclonic flotation units. Full article

Oil film cavitation in the friction pairs of wet clutches significantly compromises transmission stability and component durability. This study investigates the cavitation evolution across three microtexture types—hexahedral, cylindrical, and hemispherical—with texture ratios ranging from 3.205% to 12.917% and a constant depth of 0.0564 mm, under a 6000 rpm operating condition. A finite element model of the oil film was established to analyze the cavitation volume fraction, pressure field, and gas-phase mass transfer rate. The numerical simulations were complemented by visualization experiments, where high-speed imaging (550–1050 rpm) captured the cavitation bubble dynamics, and the transmitted torque was measured. The results indicate that microtexture parameters profoundly influence cavitation intensity. Hemispherical textures with a 6.41% texture ratio yielded the highest cavitation volume fraction (0.020215), substantially exceeding that of hexahedral textures (0.0015197). Cavitation initiates within the texture dimples, with hemispherical geometries facilitating its diffusion into non-textured regions. A threshold effect of the texture ratio was identified, where cavitation intensity peaks at 6.41% but diminishes at 12.917%, attributable to flow homogenization. Optimized designs can effectively suppress cavitation: either increasing the texture depth or adopting a high texture ratio (>45%) with hexahedral or cylindrical geometries reduces the pressure drop in low-pressure zones by over 30%. Experimental validation confirmed that an increased texture ratio reduces torque by 20%, correlating with the shrinkage of the oil film at the outer diameter. High-speed imaging revealed a periodic cavitation evolution, with the collapse of sheet-to-cloud cavitation occupying 15.2% of the cycle, which aligns with the simulated peak in mass transfer at t = 0.003 s. In conclusion, cavitation can be effectively controlled by optimizing the texture ratio, depth, and geometry to maintain a stable oil film pressure gradient. This study provides a theoretical foundation for the microtexture design of wet clutches, thereby enhancing their reliability in power-shift applications. Full article

This review paper investigates the use of air lubrication to reduce ship hull skin frictional drag, a technology whose fundamental drag-reduction mechanisms and impact on seakeeping are increasingly being studied through Computational Fluid Dynamics (CFD). Simulating this process is challenging, as the air phase often manifests as dispersed bubbles rather than a continuous film, necessitating high-fidelity models. Traditional simulations treating air and water as distinct phases fall short, and while Direct Numerical Simulation (DNS) captures bubble behaviour, its computational cost is prohibitive for practical application. This paper, therefore, reviews numerical simulation methods for air lubrication systems, evaluating their capabilities and limitations in capturing the system’s hydrodynamics and structural interaction, in contrast to traditional towing tank testing. The evaluation reveals a critical trade-off: methods with high computational feasibility (e.g., standard LES with VOF) provide an adequate estimation of overall drag reduction but consistently fail to accurately model the detailed bubble breakup and coalescence dynamics crucial for predicting system performance across different vessel speeds and pressures. Specifically, the review establishes that current mainstream CFD approaches underestimate the pressure-induced stability effects on bubbles. The paper concludes that accurate and practical simulation requires the integration of advanced techniques, such as Population Balance Models or Lagrangian Particle Tracking, to account for these distinct, flow-dependent phenomena, thereby highlighting the path forward for validated numerical models in marine air lubrication. Full article

Africa hosts numerous emerald deposits, among which Sumbawanga, located at the junction of Tanzania, Zambia, Congo, and Malawi, stands out as one of the significant localities. This study presents a comprehensive analysis of the gemological, spectroscopic, and inclusion characteristics of Sumbawanga (Tanzania) emerald samples utilizing techniques such as gem microscopy, UV-Vis-NIR spectroscopy, Raman spectroscopy, GEM-3000, and EPMA, etc. These emerald crystals look like rolled pebbles and display a bluish-green coloration. They contain fingerprint-like fluid inclusions, which occasionally encompass a circular bubble (the gas phase is CO₂). Sumbawanga emeralds are characterized by abundant mineral inclusions, including quartz, apatite, anhydrite, diaspore, chrysoberyl, rutile, hematite, and magnetite. Particularly diagnostic are the mineral inclusion of chrysoberyl twins and the assemblages of quartz and diaspore. Full article

The risk of environmental accumulation of aluminum ash and red mud is increasing, emphasizing the demand for high-value utilization. In this study, the conversion of aluminum ash and red mud into porous refractory materials with good thermal insulation performance is successfully demonstrated, demonstrating that both residues can be recovered as a resource and their environmental impact can be reduced in a sustainable manner. The phase composition and microstructure of the waste are evaluated by XRD and SEM/EDS, respectively, while their high-temperature behavior and performance were assessed through visual high-temperature furnace testing. The influence of the aluminum ash-red mud ratio on the rheological behavior of slurries containing surfactants at a constant alkaline pH was highlighted. A slurry composition of 40% red mud and 30% aluminum ash exhibited the lowest shear stress and viscosity values, required to facilitate bubble growth. Building on this formulation, foaming with 2% (mass fraction) H₂O₂ at 80 °C and sintering at 1250 °C produces a material with the optimum performance: a compressive strength of 1.03 MPa, a porosity of 58.55%, and thermal conductivity of 0.19 W/(m·K). The material exhibits long-lasting stability at temperatures ≤ 1100 °C. Thus, complementary compositions of aluminum ash and red mud show potential for practical application and value addition in the preparation of porous refractory materials with thermal insulation properties. Full article

Direct methanol fuel cells (DMFCs) offer advantages such as high energy density and ease of storage and transportation. However, carbon dioxide bubbles generated in the anode flow channels are one factor affecting cell performance. To investigate the multi-bubble coalescence phenomenon of CO₂ bubbles in DMFC flow channels, a three-dimensional anode channel dual-pore model of DMFC is established using the software COMSOL Multiphysics. Through numerical simulation, a systematic study is conducted on the kinetic mechanisms governing the growth, detachment, and coalescence behavior of CO₂ bubbles in the DMFC anode flow channel. The study reveals that bubbles readily coalesce to form large-scale plug flow with low-methanol velocity, whereas high-flow velocity inhibits coalescence and promotes rapid bubble discharge. Pore size significantly influences the aggregation and detachment of CO₂ bubbles, due to the increase in surface tension with the increasing pore diameter, which prevents bubbles from detaching and makes neighboring bubbles more prone to coalescence. Pore spacing directly influences the frequency and intensity of aggregation behavior; increasing pore spacing helps suppress bubble aggregation. The contact angle indirectly affects bubble coalescence and distribution uniformity by regulating bubble detachment rates, and hydrophilic wall surfaces inhibit bubble coalescence. Full article

Predicting phase-change heat transfer in two-phase closed thermosyphons (TPCTs) represents a significant challenge owing to the complex interaction of boiling, condensation, and conjugate heat transfer (CHT) mechanisms. This study presents a numerical investigation of a TPCT using the Combined Boiling Model (CBM) within a conjugate heat transfer (CHT) framework. Unlike prior TPCT studies, the CBM integrates an improved RPI-based wall boiling model with sliding bubble dynamics, a laminar film condensation closure, and Lee-type bulk phase change in a single, energy-consistent formulation suited for engineering-scale meshes and time-steps. Building on these extensions, we demonstrate the approach on a vertical TPCT with full CHT and validate it against experiments and a VOF–Lee reference. Simulations for heat loads ranging from 173 to 376 W capture key flow features, including vapour generation, vapour-pocket dynamics, and thin-film condensation, while reducing temperature deviations typically below 3% in the evaporator and adiabatic sections and about 2 to 5% in the condenser. The results confirm that the CBM provides a physically consistent and computationally efficient approach for predicting evaporation–condensation phenomena in TPCTs. Full article

The classic second-order Rayleigh equation governs the linear stability of single-phase inviscid plane flows, and its extension to two-phase inviscid plane flows with a crossflow of another fluid remains to be investigated. The present work studies the linear stability of steady uniform inviscid two-phase flow in a horizontal channel with gas bubbles injected from the lower wall and removed from the upper wall. An extended fourth-order Rayleigh equation with constant coefficients is derived for the linear stability of the two-phase uniform inviscid plane flow with the bubble crossflow injected at the bubble terminal velocity. Our analytical results show that the uniform inviscid plane flow driven by the bubble crossflow is linearly unstable with rapidly growing disturbances in the absence of the lift force. On the other hand, when the positive lift force coefficient is nearly equal to the added mass coefficient, the uniform inviscid plane flow driven by the bubble crossflow is linearly stable to the admissible disturbances consistent with the bubble-injection boundary conditions. These analytical results reveal the destabilizing effect of the bubble crossflow and confirm the stabilizing effect of the positive lift force on the inviscid plane flows, which could stimulate further research interest in the qualitatively different roles of the bubble crossflow and the lift force in the stability of inviscid plane flows as compared to viscous plane flows. Full article

Methane pyrolysis for turquoise hydrogen production faces dual challenges of reactor clogging and carbon contamination, particularly the difficulty in extracting high-purity carbon from molten media. While most existing studies focus on two-phase systems, carbon products are inevitably contaminated by the medium. This work presents a novel dual-layer bubble column reactor (Cu₀.₄₅Bi₀.₅₅ alloy/NaCl salt) operating at 900–1100 °C. The system achieved continuous operation for over 72 h without clogging. Crucially, the selected NaCl salt offers distinct advantages: its low cost, non-toxicity and high water solubility facilitate effective carbon separation strategies. This configuration reduced metal contamination in carbon from 52.4 wt% to below 4.0 wt%, with post-treatment achieving ultralow metal content below 1.5 wt%. Moreover, the molten salt environment induced valuable structural modifications in the carbon. This work provides an economically viable process for co-producing clean hydrogen and high-value carbon, addressing key technical barriers in molten media reactors. Full article