Search Results (422)

Bubble columns are widely used in gas–liquid processes, yet predicting bubble hydrodynamics remains challenging because of the coupled effects of operating conditions and wall confinement. This study experimentally investigates the influence of confinement, gas flow rate, axial position, and liquid flow configuration on bubble size, rise velocity, and shape in rectangular bubble columns using high-speed visualization and shadowgraphy measurements. Experiments are performed at three confinement ratios, $\lambda =3.7$, $\lambda =11$, and $\lambda =18.5$. The results show that confinement strongly modifies bubble formation, growth, velocity, and shape. Under strong confinement, larger bubbles, higher aspect ratios, and significant axial increases in bubble size are observed, indicating continued bubble enlargement along the column height. Bubble rise velocity and dimensionless velocity are also strongly affected by confinement, whereas liquid flow configuration mainly influences bubble velocity under weak confinement. Furthermore, visual observations reveal the onset of transient heterogeneous flow structures under strong confinement despite conventional flow-regime maps predicting homogeneous flow. Existing aspect-ratio correlations reproduce the general trend but do not fully account for confinement effects. These findings demonstrate that confinement is a governing parameter in rectangular bubble columns and should be explicitly considered in future hydrodynamic and mass transfer models for confined gas–liquid systems. Full article

Electro-catalytic ozonation (ECO) achieves exceptional pollutant removal, yet the mass transfer limitations governing ozone delivery remain poorly characterized. This study presents the first systematic evaluation of ozone mass transfer in a bench-scale ECO reactor, using a 3 × 3 × 3 factorial design across pH (3.5, 6, 9), ozone dose, and applied current (0, 125, 175 mA), with clean-water baselines and synthetic phenolic wastewater under ECO conditions. Plain-ozonation established the bubble column’s intrinsic transfer capacity, with $k_{L}a$ of 1.05–1.21 min⁻¹ at pH 3.5 and dissolved ozone inventory fraction (DOIF) of 1.76–2.73%, consistent with this contactor class. Applying current reduced DOIF to 0.48–2.66%, from negligible at pH 3.5 and 125 mA to approximately fourfold at higher current and pH. This suppression is consistent with an increased reactive ozone sink rather than impaired gas–liquid transfer, since the contactor hardware was unchanged; the ECO arms carry combined demand from Fe²⁺-mediated reactions and phenol oxidation, which cannot be separated without a 0-mA phenolic control. The apparent coefficient ${k_{L}a}_{APP}$ therefore behaves as a lumped supply–consumption term rather than a physical transfer parameter. A two-stage saturator design is proposed to decouple ozone dissolution from the reactive environment. Full article

Power-to-Methane (PtM) offers a promising route for storing surplus renewable electricity by converting H₂ and CO₂ into CH₄. However, the performance and optimization of CO₂ biomethanation under low organic concentrations are unexplored—a scenario common in areas with abundant curtailed wind/solar power but limited organic waste. To address this gap, this study systematically optimized three key process parameters in a continuous stirred-tank reactor (CSTR). Increasing agitation intensity from 80 to 160 rpm raised the volumetric methane production rate (VMP) by 13.8% and the gas–liquid mass transfer coefficients ($k_{l}a$) by 53.8%, achieving a peak CH₄ content of 94%. A VMP of 1.07 L CH₄·L⁻¹·d⁻¹ was obtained when the gas recirculation rate was raised to 1200 mL·min⁻¹. The optimal H₂/CO₂ ratio was 4:1, maintaining stable pH (7.31–7.51) and low volatile fatty acids (VFAs). Microbial analysis revealed that enhanced mass transfer was strongly associated with the enrichment of hydrogenotrophic methanogens (especially Methanobacterium, up to 74.8% relative abundance) and a reduced relative abundance of acetoclastic methanogens (Methanosaeta < 2%), and hydrolytic/acidogenic bacteria (e.g., Firmicutes, Bacteroidota, Cloacimonadota), suggesting a potential trade-off between the dominance of the hydrogenotrophic pathway and overall microbial functional diversity. Overall, this study demonstrates that a CSTR can achieve efficient CO₂ biomethanation under low organic concentrations through integrated optimization of agitation, gas recirculation, and feed ratio. The results provide critical data support for PtM deployment in regions with high renewable energy surplus but limited organic waste, enabling grid-to-gas energy storage, industrial CO₂ utilization, and carbon emission reduction. Full article

Precise control of dissolved oxygen is essential for reproducing physiologically relevant conditions in microfluidic cell culture systems. Here, we present a standalone, polydimethylsiloxane-free gas exchange unit (GEU) which enables controlled oxygenation and deoxygenation of perfused liquids and is suitable for integration with existing microfluidic platforms. The GEU employs a flat-sheet membrane contactor design to achieve efficient gas–liquid mass transfer while remaining independent of the downstream device. Oxygen transfer was experimentally characterised using optical oxygen sensors under different liquid and gas flow conditions. Reoxygenation efficiency decreased with increasing liquid flow rate because of reduced residence time, whereas active airflow through the gas compartment enhanced oxygen transfer. Controlled deoxygenation was achieved by flowing nitrogen through the gas compartment, with higher nitrogen pressures producing progressively lower oxygen levels. Numerical flow simulations demonstrated uniform flow distribution within the device, and a simplified analytical diffusion model accurately predicted the observed oxygen transfer trends. The proposed GEU provides a simple, robust and modular strategy for regulating dissolved oxygen upstream of microfluidic devices without requiring device redesign or specialised fabrication. This approach offers a practical solution for incorporating physiologically relevant oxygen control into a wide range of microfluidic and cell culture applications. Full article

Natural wood possesses a hierarchically porous and anisotropic structure, which provides a foundation for functional utilization, but its flammability and hygroscopicity limit its applications. Conventional bulk impregnation modification involves introducing functional agents throughout the entire pore system. This approach can enhance performance, but inevitably leads to lumen occlusion and increased density. To address this trade-off, researchers have recently developed micronano coating strategies based on interfacial decoration rather than bulk deposition within the lumina. These strategies confine functional components to cell wall surfaces while preserving the natural porous scaffold. Two fabrication routes have been developed, namely liquid-phase methods and gas-phase methods, which differ in coating precision, penetration depth, and interfacial bonding. In flame retardancy, interfacial coatings act as physical barriers and promote chemical charring. Inorganic layers suppress oxygen diffusion and heat transfer, while phosphorus or nitrogen components catalyze cellulose dehydration. In acoustics, conformal coatings regulate pore wall roughness and acoustic impedance, enhancing viscous and thermal dissipation without blocking channels. Challenges for practical application include mass transfer limitations in large logs, conflicts between high-precision processes and industrial economics, and interfacial durability under service conditions. This narrative review summarizes fabrication strategies, flame-retardant mechanisms, and acoustic regulation principles, providing guidance for coating strategy selection and process optimization. It is noted that this review focuses on wood species with open, permeable pore structures suitable for functional modification, rather than species whose pores are occluded by heartwood extractives. Full article

Upgrading biogas to pipeline-quality methane requires the efficient removal of CO₂, yet conventional physicochemical routes remain energy-intensive. Coupling a CO₂-selective membrane with microalgal photosynthetic fixation offers a green alternative, but is constrained by the low CO₂/CH₄ selectivity of common membranes and the poor adhesion of microalgae to hydrophobic membrane surfaces. Here, a dual-functional composite membrane was developed that simultaneously provides CO₂/CH₄ sieving and a biocompatible interface for microalgal attachment, and was integrated into a microalgae membrane bioreactor (MMBR). A cellulose acetate mixed-matrix membrane incorporating polyethyleneimine-grafted ZIF-8 (CA/PZIF-8(15)) achieved a mixed-gas CO₂ permeability of 122.3 Barrer and a CO₂/CH₄ selectivity of 41.17. An ionic-liquid-modified chitosan (CS/IL) coating, first optimized on a commercial flat-sheet polyethersulfone (PES) membrane used as a model surface for the adhesion study, reversed the surface charge from −30.8 to +3.75 mV, lowered the water contact angle to 51.2°, and increased the day-7 adhesion of Scenedesmus obliquus by ~108%. Transferring the coating onto CA/PZIF-8(15) further raised the permeability to 138 Barrer and the selectivity to 57.31, placing the composite above the 2008 Robeson upper bound. In the MMBR, CH₄ purity reached 95.13% after 48 h; a mass balance on the recirculating gas volume indicated that essentially all of the CO₂ removed from the gas phase permeated the membrane, of which an estimated 2% was fixed into microalgal biomass while the remainder was retained in the liquid phase. This work offers a membrane-design strategy that bridges gas-separation functionality and microalgal carbon fixation for sustainable biogas upgrading. Full article

Recovering nitrogen from wastewater is vital for a circular economy, yet conventional air stripping is limited by aerodynamic backpressure and CO₂-induced pH drops. This study evaluates a novel pilot-scale engineering approach for municipal reject water, integrating chemical phosphorus precipitation with a fundamentally redesigned ammonia stripping column. Upstream calcium hydroxide dosing achieved >99.9% phosphorus recovery and spontaneously alkalized the effluent (pH > 12.1), eliminating supplementary caustic addition. The downstream stripping column utilized negative-pressure (vacuum) operation and high-pressure liquid atomization to maximize mass transfer while preventing flooding and alkalinity neutralization. Comprehensive on-site testing established a clear mathematical relationship between aerodynamics and efficiency. Results demonstrate that high-efficiency recovery requires gas-to-liquid (G/L) ratios exceeding 70:1, a threshold uniquely unlocked by this negative-pressure design. Under optimal conditions, the continuous-flow system achieved 87.6% ammonia removal. A low-resistance acid scrubber captured ~100% of the volatilized ammonia (exhaust 0–1 ppm), producing a concentrated ammonium sulfate bio-fertilizer. This integrated technology provides a scalable, applied engineering blueprint for advancing sustainable Water Resource Recovery Facilities. Full article

Thermal runaway of lithium-ion batteries involves rapid heat release, gas generation, and multiphase transport, but their interaction inside a cell remains difficult to resolve. A multiscale computational fluid dynamics model was developed for a single 18650 cell by coupling microscale reaction kinetics, mesoscale interfacial heat transfer, and macroscale gas–liquid transport with a stationary porous-solid energy balance. The model describes internal temperature and the evolution of carbon dioxide, oxygen, water vapour, and hydrogen fluoride while examining the effects of porosity and the modelled dimethyl carbonate mass fraction. The medium-to-fine grid difference in carbon dioxide mass fraction was approximately 0.16%. Time steps of 0.01, 0.001, and 0.0001 s produced mass fractions of 0.0564, 0.0617, and 0.0618, respectively. Increasing the solvent mass fraction and porosity primarily shortened the induction period, while the peak temperature and terminal species levels remained similar. A quadratic response surface fitted to the simulation database was searched using grey wolf, genetic, and particle swarm methods. Grey wolf and particle swarm gave candidate times to peak temperature of about 238.8 s, whereas the genetic method gave 237.2 s, a difference of 1.6 s (0.67%). Particle swarm reached the high-response region within fewer iterations, while grey wolf maintained broader exploration. The proposed model connects reaction kinetics with macroscopic temperature and species evolution and clarifies how electrolyte composition and porous structure regulate the time scale of thermal runaway. Full article

Background/Objectives: Mesoporous silica nanoparticles (MSNs) are widely investigated as nanocarriers for drug delivery, gene transfer, and bioimaging. However, the mechanisms underlying their size-dependent cytotoxicity at the metabolic level remain incompletely understood. This study aimed to determine whether different-sized MSNs induce distinct patterns of subcellular injury and metabolic reprogramming in lung epithelial cells. Methods: A549 cells were exposed to 80 nm and 600 nm MSNs at 50 and 200 μg/mL for 24 h. Ultrastructural changes were examined by transmission electron microscopy (TEM). Intracellular reactive oxygen species (ROS) and Ca²⁺ were measured by 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA) and Fluo-4 AM fluorescence, respectively. Inflammatory gene expression (IL1B, IL6, TNFA, HIF1A) was quantified by reverse transcription quantitative polymerase chain reaction (RT-qPCR). Untargeted metabolomics were performed using combined gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–mass spectrometry (LC-MS) platforms, followed by principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and MetaboAnalyst-based pathway enrichment. Results: TEM revealed distinct size-dependent subcellular distributions: 80 nm MSNs were predominantly associated with mitochondrial abnormalities, including cristae disruption, swelling, and mitophagy-like features, whereas 600 nm MSNs accumulated in endocytic vesicles with membrane disruption. Metabolomic profiling showed that 80 nm MSNs were associated with TCA cycle blockade—characterized by the accumulation of early intermediates (citrate, oxaloacetate) and the depletion of distal intermediates (fumarate, malate)—with compensatory glycolytic activation (increased glyceraldehyde-3-phosphate and pyruvate) and reduced deoxynucleotide pools (dCDP, dUMP). By contrast, 600 nm MSNs triggered broad nucleotide triphosphate accumulation (ATP, CTP, dGTP, dCTP), amino acid depletion, and robust inflammatory activation, including a ~136-fold increase in IL1B expression and HIF1A transcriptional upregulation. PCA and PLS-DA confirmed distinct size-dependent metabolic phenotypes. Conclusions: MSN size strongly influences subcellular targeting—80 nm particles were predominantly associated with mitochondrial injury while 600 nm particles disrupted endocytic vesicles—driving qualitatively distinct patterns of metabolic reprogramming and inflammatory signaling. These findings establish a correlative mechanistic framework linking particle size to organelle-specific injury and provide candidate metabolic markers for nanotoxicological evaluation. Full article

Natural gas hydrates, with their vast reserves and high gas storage density, have emerged as a highly promising alternative energy source and technology for gas storage and transportation. Wettability, as a core surface property of porous media, directly influences hydrate nucleation, growth, occurrence morphology, and flow behavior. In this study, quartz sand with varying surface properties was prepared with the octyltrimethoxysilane (OTMS) silane coupling agent via surface chemical reactions. The methane hydrate (MH) equilibrium conditions as well as the formation kinetics in silica sand were measured, and the mechanism and potential of the surface modification for enhancing methane hydrate storage capacity were analyzed. The experimental results indicate that surface modification of quartz sand has no significant effect on the MH equilibrium condition. Hydrophobic modification of quartz sand provides more gas–liquid interfaces, increases the contact area, and thereby significantly enhances mass transfer under high-water-saturation conditions and accelerates the MH formation rate. However, excessively high surface hydrophobicity may reduce the effective gas–liquid interfacial area and limit the overall hydrate formation rate. Due to the influences of the hydrate distribution and aggregation, as well as gas diffusion on hydrate formation, the effect of the initial formation pressure on MH formation is only observed during the early stages of MH formation, while the temperature effect is less pronounced than that of formation pressure. It is suggested to further consider combining stirring with continuous gas injection to enhance gas–liquid flow and improve gas–liquid contact, thereby increasing the formation rate of hydrates. Full article

Slag splashing protection is the dominant technology for extending refractory lining service life and enhancing production efficiency in basic oxygen furnace (BOF) steelmaking. However, the intrinsic mechanism of gas-slag-steel multiphase coupled splashing remains poorly understood, and existing numerical methods suffer from prohibitive computational costs and inaccurate characterization of interfacial momentum transfer and multiphase interactions. This study establishes a fully coupled three-dimensional numerical model integrating Volume of Fluid (VOF)–Discrete Particle Method (DPM) bidirectional phase transition, adaptive mesh refinement (AMR), and Eulerian Wall Film Model (EWFM), and the multiphase flow simulation in this study adopts constant thermophysical parameters of molten steel and slag at the industrial splashing temperature of 1650 °C. Taking the Blowing Number (N_B) as the core similarity criterion, a 1:10 scaled geometric model of a 50-ton industrial BOF is employed to systematically investigate the regulatory effects of top-blowing flow rate, lance height, and N_B on droplet splashing behavior and wall liquid film evolution. The model is validated against mercury-glycerol cold model experimental data, with a relative error of less than 3% in total splashing mass prediction. Results demonstrate that increasing N_B significantly enhances splashing intensity. Under optimal conditions (200 mm lance height, 11.76 Nm³/h flow rate, N_B = 9.30), the wall liquid film fully covers the middle-upper furnace wall with a uniform thickness of 0.8–1.2 mm. N_B dominates jet momentum distribution: high N_B forms a deep-penetrating four-lobed impact cavity, remarkably improving droplet axial momentum and residence time. Molten steel droplets concentrate at 3–4 mm, while slag droplets shift to 2–4 mm at high flow rates of 11.76 Nm³/h, with maximum slag droplet production at N_B = 6.99. This work provides reliable theoretical support for industrial BOF slag-splashing process optimization. Full article

Hydrothermal carbonization (HTC) of digested dairy manure produces hydrochar and a nitrogen-rich post-liquid. This study evaluated a submerged tubular expanded polytetrafluoroethylene (ePTFE) gas-permeable membrane (GPM) system for ammonia recovery from post-HTC liquid derived from digested dairy manure, focusing on the effects of feed temperature, acid circulation rate, and feed volume-to-membrane surface area ratio (FV/MS). Compared with filtered digested manure, the post-HTC liquid had a similar total ammoniacal nitrogen (TAN) concentration (1151 vs. 1164 mg N L⁻¹) but a slightly higher pH (8.38 vs. 7.94), which favored ammonia transfer. Increasing feed temperature from 20 to 60 °C raised 24 h TAN recovery from 63.5% to 99.6% and average TAN transfer flux from 11.1 to 17.7 g m⁻² d⁻¹, although it also increased water vapor crossover and diluted the acid trapping solution. Increasing acid circulation from 10 to 30 mL min⁻¹ improved 48 h TAN recovery from 85.2% to 94.0%, while a further increase to 50 mL min⁻¹ produced only a small additional gain. In contrast, elevating FV/MS from 0.015 to 0.045 m³ m⁻² reduced 48 h TAN recovery from 94.0% to 59.6% while increasing average TAN transfer flux from 8.2 to 16.2 g m⁻² d⁻¹ because larger feed volumes sustained the concentration driving force for a longer period. Nitrogen mass balance showed that more than 94–99% of the initial TAN was accounted under most conditions, with only a small fraction lost to volatilization. Full article

This study develops a 3D computational fluid dynamics model of a polymer electrolyte fuel cell cathode gas channel with seven discrete liquid breakthrough inlets, one gas inlet, and a two-phase outlet. Two-phase flow and droplet evolution on the gas diffusion layer are simulated using the volume-of-fluid method in OpenFOAM. The model agrees well with reported experimental and numerical data in terms of droplet size, morphology, and detachment behavior. Results show that breakthrough geometry governs droplet dynamics: circular openings promote stronger aerodynamic loading and earlier detachment, while sharp-cornered geometries (e.g., triangular and polygonal) stabilize droplets and prolong residence time. Among all investigated geometries, the circular breakthrough exhibits the highest drainage efficiency, in agreement with recent experimental studies demonstrating that laser-drilled circular pores facilitate water removal and reduce oxygen mass-transfer resistance in polymer electrolyte fuel cells. Complex interactions with the gas diffusion layer surface, gas channel walls, and corners lead to coalescence, sliding, and rivulet formation. Force decomposition reveals the competition among aerodynamic, capillary, adhesion, and shear forces. The study provides a mechanistic basis for geometry-controlled water transport and guidance for gas diffusion layer design and water management. Full article

Severe fracturing-fluid retention and low post-fracturing flowback efficiency are common in the Lianggaoshan shale reservoirs of the Sichuan Basin. Liquid loading may also occur during late production. To address these problems, this study investigates a synergistic flowback technology that combines natural fracturing-fluid flowback with CO₂ gas lift. First, based on the complex fracture network characteristics of the Lianggaoshan shale reservoir, the interaction mechanisms between hydraulic fractures and natural fractures were investigated. An energy model for fracturing-fluid flowback under natural flowback conditions was established, revealing that reservoir gas expansion energy, hydromechanical energy, and rock elastic energy are the primary driving forces for fracturing-fluid flowback. Furthermore, considering fracture closure behavior, fluid leakoff, and wellbore flow dynamics, a calculation model for the natural flowback of fracturing fluid was developed, and a staged pressure-controlled flowback strategy was proposed. Subsequently, to address the decline in liquid unloading capacity caused by formation-energy depletion during the late stage of natural flowback, a gas-lift-assisted flowback multiphase flow model for the wellbore was established. The effects of the gas injection pressure, gas injection rate, and wellhead pressure on liquid unloading efficiency were systematically investigated. The results indicate that the liquid unloading rate increases with an increasing gas injection pressure and gas injection rate; however, a pronounced diminishing marginal effect is observed. For the Well H1 reference case, the central recommended gas injection pressure was 12 MPa, the gas injection rate was 8 × 10⁴–10 × 10⁴ m³/d, and the wellhead backpressure was maintained below 0.5 MPa. Furthermore, the CO₂-assisted flowback mechanisms were evaluated by distinguishing between the effects explicitly represented in the model and the potential reservoir-scale physicochemical effects. The reduction in wellbore mixture density and bottomhole flowing pressure was simulated directly, whereas CO₂–oil mass transfer, viscosity reduction, mineral dissolution, and changes in water-blocking behavior were interpreted with reference to published experimental studies. Based on these mechanisms, a three-stage synergistic optimized flowback scheme, consisting of “CO₂ soaking–natural flowback–CO₂ gas lift,” was established. A sequence of stagewise quasi-steady PIPESIM calculations was subsequently performed over the 30-day operating schedule. Under the adopted simulation conditions, the recommended soaking period is 5–7 days. The operation should be switched to gas lift when the wellhead pressure falls below 1.5 MPa or when daily liquid production declines continuously by more than 20%. Under the synergistic scheme, the 30-day cumulative flowback volume was predicted to reach 3492 m³. This value was substantially higher than those obtained by conventional natural flowback and standalone gas-lift processes. Moreover, the flowback curve exhibits a distinct “secondary surge” characteristic. These findings provide a theoretical basis and technical support for efficient fracturing-fluid flowback and stable long-term production in the Lianggaoshan Formation. They may also be applicable to other shale oil reservoirs with low porosity and ultra-low permeability. Full article

Liquid hydrogen (LH2) is a promising energy carrier for maritime transportation owing to its high storage density and carbon-free utilization. However, its cryogenic storage temperature inevitably causes boil-off gas (BOG) generation, even with advanced insulation, and ship-induced sloshing can further disturb interfacial heat and mass transfer. This study numerically investigates BOG generation in a Type-C LH2 tank under sloshing conditions. A transient two-phase CFD model was developed using the volume of fluid method to track the liquid–vapor interface and the Lee phase-change model to calculate evaporation and condensation. Sloshing excitation was imposed through mesh motion, and parametric simulations were performed for different filling ratios, frequencies, amplitudes, and baffle configurations. The results show that the 50% filling condition produced the lowest boil-off rate, while amplitude had a stronger influence than frequency by increasing free-surface deformation, internal velocity, and convective heat transfer. Baffles reduced liquid motion but could increase BOG through additional conductive heat-transfer paths. These findings support BOG prediction and baffle design for Type-C LH2 tanks. Full article