Search Results (132)

Hydrogen production by alkaline water electrolysis is a promising pathway for sustainable energy systems; however, conventional electrolyzers rely on membranes or diaphragms that increase cost, electrical resistance, and maintenance requirements. This study reports the development and experimental evaluation of a low-cost, membrane-less, flow-by tubular alkaline electrolyzer integrated with a dedicated gas–liquid separation and volumetric gas-measurement system. The electrolyzer was designed, constructed, experimentally validated, and electrochemically characterized using polarization curves. The effects of KOH concentration (0.50–2.00 mol L⁻¹), electrolyte flow rate (1.00–4.00 L min⁻¹), and applied voltage (2.20–3.20 V) on hydrogen production were investigated through a full factorial 3³ experimental design combined with analysis of variance, response surface methodology, and numerical optimization using the desirability function. The applied voltage was identified as the dominant operating variable, followed by KOH concentration and electrolyte flow rate, while significant interactions involving voltage were also observed. The quadratic regression model showed excellent predictive performance (R² = 0.9614), and within the investigated operating domain, the highest hydrogen production rate was obtained at 2.00 mol L⁻¹ KOH, 1.00 L min⁻¹ electrolyte flow rate, and 3.20 V, resulting in an experimental hydrogen production rate of 0.4395 mL s⁻¹. These findings demonstrate the potential of the proposed membrane-less flow-by electrolyzer as a simplified, low-cost, and experimentally validated platform for investigating and optimizing membrane-less alkaline water electrolysis under the evaluated operating conditions. Full article

Conventional parametric optimization of groove geometries for mechanical face seals is inherently constrained by predefined groove configurations, offering limited design flexibility, especially under complex gas–liquid two-phase lubrication conditions. To overcome this limitation, this study proposes a topology optimization framework specifically developed for gas–liquid two-phase lubricated turbopump mechanical face seals using liquid oxygen (LOX) as the working fluid. A finite element-based topology optimization model is established to systematically design hydrodynamic grooves under various geometric parameters and operating conditions. Numerical results demonstrate that the proposed framework exhibits strong robustness, with the optimized groove topologies being largely insensitive to the initial design guess. The final groove morphology and resulting sealing performance are governed by five key factors: groove-to-dam ratio, groove depth ratio, circumferential angle of the design domain, sealing pressure, and rotational speed. Parametric analysis indicates that the optimal groove-to-dam ratio lies in the range of 0.7–0.8, while the favorable groove depth ratio falls between 3.0 and 3.5. Compared with conventional spiral grooves having identical circumferential angles and depth ratios, the topology-optimized grooves yield significantly improved overall sealing performance, with the average liquid film opening force increased by 17.80–20.67%. The findings provide reliable theoretical foundations and practical parametric design guidelines for high-performance face seals operating under gas–liquid two-phase lubrication. Full article

To investigate the coupled evolution of cavity morphology, hydrodynamic characteristics, and motion behavior during the wide-speed-range acceleration of an underwater hypervelocity vehicle, a numerical framework for supercavitating multiphase flow was established by coupling the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model, the Schnerr–Sauer cavitation model, and the Volume of Fluid (VOF) method. Combined with the overset mesh technique and the DFBI six-degree-of-freedom model, the multiphase flow and motion characteristics during acceleration were systematically studied. The results show that the ventilated cavity strongly compresses the natural cavity, leading to a complex gas–vapor–liquid three-phase coexistence structure in the mid-body conical section and stern region, with the ventilated cavity eventually becoming dominant. The drag coefficient exhibits a three-stage evolution associated with cavity development over the conical section, cylindrical section, and the final formation of a supercavity. Once the vehicle is enveloped by the supercavity, pressure drag becomes dominant. Ventilation timing significantly affects supercavity formation and flow stability. Low-speed ventilation reduces drag earlier but prolongs the three-phase coexistence period and cavity formation process, whereas high-speed ventilation promotes the rapid formation of a stable supercavity. The supercavity formation time reaches 0.5 s under ventilation at 30 m/s, which is more than twice the value for ventilation at 70 m/s. Full article

A study was conducted to characterize the performance of a HydroFloat^® coarse particle flotation (CPF) cell using rougher tailings samples from an industrial copper mining operation. The work involved measuring internal hydrodynamic variables under a wide range of operating conditions. The effect of different operational and hydrodynamic conditions on the metallurgical performance of the HydroFloat^® cell was also evaluated. Gas dispersion measurements, such as bubble size distribution, superficial gas velocity (J_g), superficial area flux (Sb), and residence time distribution (RTD), were recorded, enabling a detailed analysis of the cell’s operation. Results show that copper recovery is strongly influenced by the superficial gas velocity (J_g) and the superficial liquid velocity (J_l). It was observed that the bubble diameter (d₃₂) remained relatively constant at 0.5 mm across all operating conditions, which is well below typical bubble sizes for conventional flotation cells. This suggests that contrary to what may be expected, in this kind of machine, small bubbles are able to float coarse particles. Bubble image inspection suggests that the HydroFloat^® cell creates conditions conducive to bubble–particle aggregates, which would explain how small bubbles can float coarse particles. This study contributes to the understanding of CPF and establishes a framework for optimization in copper concentrators. Full article

Nanobubbles have attracted increasing interest in food systems because they can modify gas dispersion, interfacial transport, washing performance, preservation processes, and the structures of dispersed matrices. However, their behavior cannot be interpreted based on bubble size alone. Proteins, polysaccharides, lipids, salts, colloidal particles, gas composition, and processing conditions can alter interfacial adsorption, gas transfer, bubble persistence, and matrix organization in food systems. This review examines the physicochemical mechanisms proposed to explain nanobubble persistence and functionality, with an emphasis on surface charge, interfacial adsorption, gas supersaturation, confinement, and interactions with food biopolymers. A central distinction is made between passive nanobubble-containing systems and externally activated systems involving hydrodynamic cavitation, ultrasound, plasma, pressure fluctuations, and reactive gases. Under passive conditions, nanobubbles mainly act as gas–liquid interfaces that influence local transport and adsorption. In activated systems, microbial inactivation, reactive oxygen species formation, and apparent mass-transfer enhancement often arise from external energy input, gas chemistry, turbulence, and transient supersaturation rather than from nanobubbles alone. Interfacial stability is used here as an organizing concept to connect nanobubble persistence, food-matrix interactions, generation methods, characterization limitations, and interpretation of reported technological effects. Current methods, such as dynamic light scattering and nanoparticle tracking analysis, provide useful size and concentration estimates but cannot unambiguously distinguish nanobubbles from protein aggregates, fat droplets, micelles, polysaccharide assemblies, and other colloidal structures in complex matrices. Therefore, reliable interpretation requires complementary methods, appropriate controls, and standardized reporting of gas composition, generation method, energy input, matrix properties, and processing conditions. Thus, nanobubble-containing technologies show promise for food processing; however, their value depends on the separation of nanoscale interfacial effects from concurrent hydrodynamic, chemical, and matrix-dependent phenomena. Full article

This study presents a transient computational fluid dynamics (CFD) analysis of dielectric flow behaviour and debris transport in micro-EDM milling, considering the effects of dielectric properties, inter-electrode gap (IEG) size (20–30 µm), and tool rotational speed (400–850 rpm). Four dielectric media, nitrogen gas, deionized water, HEDMA111 EDM oil, and sunflower seed oil, were investigated using a two-dimensional FEM-based model coupled with particle tracking simulations to evaluate debris mobility within the machining region. The results demonstrate that dielectric properties, particularly viscosity, strongly influence hydrodynamic behaviour and particle transport within the IEG. Under the adopted equal mass flow rate condition, nitrogen gas exhibited the highest flow velocities and the fastest debris evacuation due to the combined effects of its low viscosity and the resulting higher inlet velocity. Deionized water and HEDMA111 oil exhibit comparable intermediate behaviour, indicating that moderate viscosity variations within liquid dielectrics do not significantly alter the overall flow regime. In contrast, sunflower seed oil generates the most damped flow conditions, with reduced velocities and prolonged particle residence due to increased viscous resistance. Variations in IEG size produce only minor changes in evacuation efficiency compared with the dominant influence of dielectric properties, while tool rotational speed primarily affects velocity magnitude without altering qualitative transport behaviour. Full article

The safety and stability of onboard Liquid Hydrogen (LH₂) storage systems depend strongly on gas–liquid two-phase flow, heat transfer, and phase change under sloshing; however, the coupled influence of filling ratio and sloshing on thermo-hydrodynamic behavior remains underexplored. We develop a Volume of Fluid (VOF)-based two-phase Computational Fluid Dynamics (CFD) model in ANSYS Fluent to quantify interfacial dynamics, pressure response, and temperature-field evolution in LH₂ tanks subjected to sinusoidal acceleration for filling ratios from 10% to 90%. Increasing the filling ratio strengthens net condensation in the ullage and thus intensifies depressurization. As the filling ratio increases from 10% to 90%, the pressure reduction over the 2.0 s sloshing process increases from 0.418 kPa to 2.410 kPa, and the corresponding initial depressurization rate rises from 0.209 to 1.205 kPa s⁻¹. Free-surface motion decreases with filling ratio: at 10%, large interface excursions can induce gas-cavity formation and splashing, increasing the risk of intermittent propellant supply, whereas at 90% the interface is constrained and oscillations are suppressed. Higher filling ratios lead to faster ullage cooling and larger temperature oscillations. The liquid warms modestly, and its warming rate decreases nonlinearly with filling ratio, consistent with the larger effective thermal mass at higher fillings. Overall, the obtained mechanistic understanding can support the engineering design of onboard LH₂ tanks, including filling-ratio selection and thermal-management optimization under sloshing conditions. Full article

Persistent organic contaminants and complex wastewater matrices challenge conventional treatment because parent-compound removal does not necessarily imply mineralization, detoxification, or improved environmental safety. Advanced oxidation processes can address these limitations, but practical effectiveness is often constrained by oxidant activation, gas–liquid mass transfer, reagent distribution, light penetration, catalyst contact, energy demand, and matrix scavenging. This work critically examines hydrodynamic cavitation-assisted advanced oxidation processes for water and wastewater treatment, including systems based on hydrogen peroxide, ozone, Fenton and Fenton-like reactions, persulfate, peroxydisulfate, peroxymonosulfate, UV irradiation, photocatalysis, cold plasma, multi-hybrid configurations, and emerging reduction-oriented approaches. The discussion covers reactor configurations, target contaminants, real matrices, and sustainability-related performance metrics. The central argument is that hydrodynamic cavitation is not automatically sustainable as a stand-alone treatment. It becomes relevant as a sustainable intensification module only when measurable improvements are demonstrated in oxidant activation, mass transfer, treatment depth, biodegradability, toxicity reduction, process integration, or scale-up at acceptable energy and chemical cost. A reporting framework is proposed based on mineralization, COD/TOC reduction, by-products, toxicity, biodegradability, normalized energy consumption, chemical efficiency, real-matrix validation, reproducibility, and cost-relevant indicators. Future progress should move from isolated degradation tests to integrated, controllable, and scalable treatment frameworks. Full article

This study utilizes a large-scale numerical simulation model to investigate the hydrodynamic behavior and particle transport characteristics of gas–liquid–solid three-phase flow in vertical wellbores featuring multi-source confluence and curved geometries. Simulation results indicate that increasing flow velocity shifts the dominant control mechanism from surface tension to inertial forces, transitioning the flow pattern from slug flow to churn flow. In curved pipe sections, centrifugal phase separation and geometric shielding effects cause significant flow asymmetry and maintain large bubble stability at the inner wall. Additionally, the multi-inlet structure induces shear rate gradients that result in the spatial coexistence of two distinct bubble scales. Furthermore, localized gas concentrations exceeding 70% at the upper inlet can trigger severe gas-locking phenomena and intense pressure pulsations. Full article

Space constraints in shipboard carbon capture require compact absorbers with high gas–liquid mass-transfer efficiency. However, the performance of emerging packing geometries cannot be inferred reliably from bed-scale correlations alone because liquid distribution and interfacial transport depend on unit-cell flow organization. This study aims to compare the micro-scale hydrodynamics and CO₂ mass-transfer behavior of the Kelvin cell and a Mellapak 250Y corrugated sheet unit using three-dimensional CFD simulations over liquid loads of 10 to 100 m³/(m²·h). The corrugated sheet guides liquid mainly along corrugation crimps, whereas the Kelvin cell redistributes liquid through its strut network and node intersections. For the M250Y unit, the periodic dripping cycle shortens as liquid load increases, and liquid holdup reaches only about 8% at 100 m³/(m²·h). In contrast, the Kelvin cell evolves from discrete dripping to liquid bridging and secondary breakup, maintains a liquid holdup about 3 to 6 times that of the corrugated sheet and delivers 2 to 3 percentage points higher mass-transfer efficiency. These results suggest a local hydrodynamic and mass-transfer advantage of the Kelvin cell over the M250Y benchmark under the present REU-scale conditions. Full article

Driven by the large-scale deployment of renewable electricity, water electrolysis has emerged as a leading pathway for high-efficiency hydrogen production. Under practical operating conditions, gas evolution and gas–liquid two-phase flow inside electrolyzers substantially reshape electrode interfacial states and the in-cell mass transfer environment and have been reported to cause performance losses on the order of 10–30% under unfavorable conditions. This review summarizes the evolution of electrode-generated bubbles during nucleation, growth, detachment, and coalescence, and consolidates the fundamental features of two-phase hydrodynamics and phase-distribution patterns in electrolyzer channels. Progress and limitations of major two-phase modeling approaches are then assessed with respect to their capability to resolve the relevant interfacial and transport processes. The impacts of gas evolution and two-phase flow on electrochemical performance, stability, and durability are subsequently discussed. Finally, recent advances in two-phase-flow management—through flow-field organization and structural design, as well as the introduction of external physical fields—are reviewed, together with experimental and diagnostic methods used to quantify bubble behavior and phase distributions. This review aims to provide a coherent understanding of the governing behaviors, research tools, and performance implications of gas evolution and two-phase flow in water electrolysis, and to inform electrode/transport-layer design, flow-field management, and the development of predictive numerical models. 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

Natural gas streams extracted from production wells often contain undesirable components such as water vapor, gas condensate, and solid particulates. These impurities reduce fuel quality and damage downstream equipment through corrosion, fouling, and foaming. This study presents the development and field-scale evaluation of a high-performance gas–liquid separator designed for the deep decontamination of natural gas. The proposed separator incorporates 30 suspended baffles arranged in three rows and an anti-foaming mesh to enhance phase separation and prevent liquid re-entrainment. Field experiments were conducted at the Somontepa gas field in Uzbekistan. Compared to the baseline industrial unit, the upgraded separator reduced gas condensate from 16.58 g/m³ to 0.725 g/m³, water from 4.84 g/m³ to 0.10 g/m³, and solid impurities from 1.20 g/m³ to 0.0058 g/m³. The foam height was lowered from 96.4 mm to 10.2 mm, and the average bubble diameter was reduced by over 60%. The design maintained low pressure drops and demonstrated stable operation under varying flow rates. Fractional analysis confirmed the quality of a recovered condensate suitable for downstream utilization. The proposed configuration offers substantial improvements in gas purification performance and economic efficiency. These results support the application of this separator design for high-contaminant natural gas streams in industrial gas processing facilities. Full article

Liquefied natural gas (LNG) sloshing occurs during marine transportation and storage due to vessel motion or external disturbances, leading to complex fluid–structure interactions within the containment system. This study employs OpenFOAM to develop a numerical model of LNG sloshing. The model solves the incompressible multiphase Navier–Stokes equations and utilizes the Volume of Fluid (VOF) method to capture the dynamic behavior of gas–liquid interface. The numerical model was validated against experimental data. Based on this model, the key hydrodynamic characteristics are investigated for LNG sloshing, including nonlinear free surface, transient pressure distribution on the tank walls due to liquid impact, and energy dissipation mechanisms. By varying excitation frequencies, amplitudes, and the configuration of internal components such as baffles or anti-sloshing devices, the study explores the sloshing response and effective control strategies. The results indicate that appropriately designed baffles can significantly mitigate sloshing-induced impact pressures on tank walls and enhance system stability. In the future, this study could extend to multi-layer fluids, multi-degree-of-freedom motions, and simulations under more complex real-world conditions. Full article

Non-thermal plasma-driven advanced oxidation is a promising method for treating organic wastewater, which exhibits rapid reaction kinetics and high pollutant removal and does not need chemical reagents. However, its practical application is often limited by high specific energy consumption and the inefficient mass transfer of short-lived reactive species across the gas–liquid interface. This review summarizes the fundamentals of non-thermal plasma chemistry and the process intensification of plasma multiphase reactors by mass transfer enhancement and waste energy-driven conversion. This review focus on four coupling approaches: microbubble-assisted plasma to expand the reactive interfacial area; plasma coupled with hydraulic cavitation to enhance convection and radical formation; plasma–piezoelectric catalysis coupling to harvest hydraulic energy and promote charge-driven reactions; and plasma-assisted Fenton oxidation to improve the utilization of weakly oxidizing species (H₂O₂). The energy efficiency of various plasma-based oxidation systems is compared and discussed clearly. Key remaining challenges are also discussed, including standardized energy efficiency assessment, scale-up and hydrodynamic control, catalyst stability and fouling, by-product formation and toxicity, and long-term operational reliability. Overall, this review aims to provide guidance for developing efficient plasma-based wastewater treatment systems for large-scale applications. Full article