Search Results (174)

It is well known that aqueous solutions can emit electromagnetic waves in the radio frequency range. However, the physical nature of this process is not yet fully understood. In this work, the possible role of gas nanobubbles formed in the bulk liquid is considered. We develop a theoretical model based on the concept of gas bubbles stabilized by ions, or “bubstons”. The role of bicarbonate and hydronium ions in the formation and stabilization of bubstons is explained through the use of quantum chemical simulations. A new model of oscillating bubstons, which takes into account the double electric layer formed around their gas core, is proposed. Theoretical estimates of the frequencies and intensities of oscillations of such compound species are obtained. It was determined that oscillations of negatively charged bubstons can occur in the GHz frequency range, and should be accompanied by the emission of electromagnetic waves. To validate the theoretical assumptions, we used dynamic light scattering (DLS) and showed that, after subjecting aqueous solutions to vigorous shaking with a force of 4 or 8 N (kg·m/s²) and a frequency of 4–5 Hz, the volume number density of bubstons increased by about two orders of magnitude. Radiometric measurements in the frequency range of 50 MHz to 3.5 GHz revealed an increase in the intensity of radiation emitted by water samples upon the vibrational treatment. It is argued that, according to our new theoretical model, this radiation can be caused by oscillating bubstons. Full article

The decommissioning and dismantling of nuclear research reactors can lead to a large amount of low- and intermediate-level radioactive waste. For repositories, the materials must be kept confined and safety must be ensured for extended time spans. Waste is encapsulated in concrete, which leads to alkaline conditions with pH values of 12 and higher. This can be advantageous for some radionuclides due to their precipitation at high pH. For other materials, such as reactive metals, however, it can be disadvantageous because it might foster their corrosion. The Studsvik R2 research reactor contained an AlMg3.5 alloy with a composition close to that of commercial Al5154 for its core internals and the reactor tank. Aluminum corrosion is known to start rapidly due to the formation of an oxidation layer, which later functions as natural protection for the surface. The corrosion can lead to pressure build-up through the accompanied production of hydrogen gas. This can lead to cracks in the concrete, which can be pathways for radioactive nuclides to migrate and must therefore be prevented. In this study, unirradiated rod-shaped samples were cut from the same material as the original reactor tank manufacture. They were embedded in concrete with elevated water–cement ratios of 0.7 compared to regular commercial concrete (ca. 0.45) to ensure water availability throughout all of the experiments. The sample containers were stored in pressure vessels with attached high-definition pressure gauges to read the hydrogen-induced pressure build-up. A second set of samples were exposed in simplified artificial cement–water to study similarities in corrosion characteristics between concrete and cement–water. Additionally, the samples were exposed to concrete and cement–water in free-standing sample containers for deconstructive examinations. In concrete, the corrosion rates started extremely high, with values of more than 10,000 µm/y, and slowed down to less than 500 µm/y after 2000 h, which resulted in visible channels inside the concrete. In the cement–water, the samples showed similar behavior after early fluctuations, most likely caused by the surface coverage of hydrogen bubbles. These trends were further supported by mass loss evaluations. Full article

The volatile organic compounds (VOCs) produced by K. cowanii Ch1 play a significant role in the inhibition of the mycelial growth of phytopathogen strains. As a continuation of our previous studies, we aim to elucidate the mechanisms of the responses of K. cowanii Ch1 against S. rolfsii during a colonization competence interaction in the presence and absence of a mixture of bacterial VOCs under in vitro conditions. The results of this study showed that, in the absence of bacterial VOCs, K. cowanii Ch1 cannot compete against S. rolfsii, and the RNA-Seq analysis revealed the differential expression of genes related to the oxidative stress response in K. cowanii Ch1 for survival. However, in the presence of bacterial VOCs, an interesting phenotypical response was observed in K. cowanii Ch1, resulting in the mycelial growth inhibition of S. rolfsii. The upregulated genes were related to the siderophore-mediated iron transport system, zinc ion transport system, antibiotic biosynthesis monooxygenase, carbohydrate metabolism, polyketide synthase modules, and related proteins, and katG was probably related to the phenotype resulting in the formation of gas bubbles by K. cowanii. In addition, the VOC profile analyzed at 36 h for bacterial growth revealed a cocktail with an ability to increase the competence of K. cowanii Ch1 against S. rolfsii in vitro and in vivo. This study provides evidence regarding the key role that VOCs play during the colonization competition involving K. cowanii Ch1, the comprehension of which may enable the development of new biocontrol strategies. Full article

We experimentally studied the effect of a surfactant on bubble formation on a superhydrophobic surface (SHS). The bubble was created by injecting gas through an orifice on the SHS at a constant flow rate in the quasi-static regime. The surfactant, 1-pentanol, was mixed with water at concentration C ranging from 0 to 0.08 mol/L, corresponding to surface tension σ ranging from 72 to 43 mN/m. We found that as C increased, the bubble detachment volume (V_d) and maximum bubble base radius (R_d^max) decreased. For a low surfactant concentration, the static contact angle θ₀ remained nearly constant, and V_d and R_d^max decreased due to lower surface tensions, following the scaling laws R_d^max~σ^1/2 and V_d~σ^3/2. The bubble shapes at different concentrations were self-similar. The bubble height, bubble base radius, radius at the bubble apex, and neck radius all scaled with the capillary length. For high surfactant concentrations, however, θ₀ was greatly reduced, and V_d and R_d^max decreased due to the combined effects of reduced θ₀ and smaller σ. Lastly, we found that the surfactant had a negligible impact on the forces acting on the bubble, except for reducing their magnitudes, and had little effect on the dynamics of bubble pinch-off, except for reducing the time and length scales. Overall, our results provide a better understanding of bubble formation on complex surfaces in complex liquids. Full article

Increased emissions of carbon dioxide (CO₂) from industrial activities are the main cause of the growing problem of global warming and climate change, highlighting the needs for efficient CO₂ capture and storage (CCS) techniques. The present work aims to investigate the possibility of CO₂ sequestration using sodium hydroxide (NaOH) in a semi-batch column with an integrated gas lift tower and an ultra-micro bubbles generator, a novel setup designed to enhance mass transfer rates and capture efficiency. Unlike the previously reported setups, our system achieves a 50% faster capture rate with improved mass transfer, enhanced gas-liquid interaction and higher removal efficiency due to finer bubble dispersion, as confirmed by experimental findings. Preliminary tests to ascertain the effectiveness of CO₂ removal were carried out across various CO₂ gas flow rates (3, 5, 7 L/min), NaOH volumes (2, 3, 4 L) and concentrations (0.1, 0.2, 0.3 M). The results indicated that both gas flow rate and NaOH concentration have profound impacts on the CO₂ capture rate. Increasing either of these parameters, or using low concentrations of NaOH, leads to a rapid drop in pH due to a faster rate of neutralization and the formation of carbonic acid (H₂CO₃), a weak acidic solution. For instance, with 0.1 M NaOH and 2 L volume, the pH decreased from 13.07 to 7.02 within 1.5 min at gas flow rate of 7 L/min, while with 0.3 M NaOH, pH reduced to 7.3 after 6 min. Higher volumes and concentrations of NaOH caused a decrease in the capture rate of CO₂ due to reversed reaction with formed sodium carbonate. For instance, with 0.3 M NaOH and 4 L volume, the pH reduced from 13.58 to 8 after 5 min at 7 L/min gas flow rate. Scaling up to a 100 L semi-batch column with an ultra-fine micro bubble generator, as a new approach, reduced the time taken by half in the capture of CO₂. Additionally, the study also investigated the comparison of tap versus deionized water in CO₂ capture reaction. The results demonstrated that dissolved minerals in tap water, particularly Ca²⁺ and Mg²⁺ ions, affected precipitate formation and capture efficiency differently than deionized water, offering practical insights for CCS in varied water sources. Full article

The thermal development in heavy oil reservoirs with edge and bottom water is poor, while gas huff-n-puff development shows a high recovery and strong adaptability. The formation of foamy oil during gas huff-n-puff is one of the reasons for the high recovery. In order to determine the factors affecting the foamy oil flow during gas huff-n-puff, experiments using a one-dimensional sandpack were conducted. The influences of drawdown pressure and cycle number were analyzed. The formation conditions of foamy oil were preliminarily clarified, and the enhanced oil recovery (EOR) mechanism of foamy oil was revealed. The experimental results show that the drawdown pressure and cycle number are two important factors affecting the formation of foamy oil. Foamy oil flow is prone to forming under a moderate drawdown pressure of 0.5–0.75 MPa, and being too small or too large is unfavorable. Foamy oil is more likely to form in the first two cycles, and it becomes increasingly challenging with the increase in the cycle number. These two factors reflect two necessary conditions for the formation of foamy oil during gas huff-n-puff: one is allowing the oil and gas to flow adequately to provide the shear and mixing for the generation of micro-bubbles, and the other is that the oil content should not be too small to avoid the inability to disperse and stabilize bubbles. The formation of foamy oil, on the one hand, increases the volume of the oil phase, and on the other hand, it reduces the mobility of the gas phase and slows down the pressure decline rate in the core, thereby enhancing the driving force for oil displacement. So, under the influence of the foamy oil, the gas production volume in a cycle declined by about 26%, and the average oil recovery increased by 4.5–6.9%. Full article

The growth in public demand for clean water is increasing due to the development of the population, triggering the decline in clean water resources. Seawater provides an unrestricted, consistent supply of high-quantity water from the water cycle. It is a solution to the public issue of limited clean water, which can be processed with desalination technology to get fresh and clean water. Seawater desalination removes salt and other impurities from seawater to produce fresh, potable water. Furthermore, to produce freshwater using nanobubbles, seawater desalination and nanobubble flotation are interconnected through their roles in the water treatment and purification process. It is necessary to modify the nanobubble flotation, which has unique properties (minimal nano gas), to separate the salt ions and suspended solids from water to get freshwater. This paper has reviewed the water treatment that was conducted for the nanobubble flotation, especially ion flotation, which is a formation of positively buoyant bubble particles that agglomerate mixed with a recycling stream to saturate with air or carbon dioxide at high pressure to generate nanobubbles. This review investigates effective and efficient nanobubble flotation for the water treatment process in the seawater desalination issue to get pure water. The review highlights the mechanism of NB flotation that can effectively separate the dissolved ions and suspended solids in the flotation column, which contains seawater with different salt concentrations. This review focuses on ion flotation and investigates three mechanisms in the flotation process, which consist of collisions, attachment, and detachment. This process can enhance the flotation performance in the flotation separation process. As a result, it has produced fresh, potable water. Full article

This study explores the relation between catalyst research and chemical reaction engineering for developing ethanol to butadiene (ETB) technologies. An ETB process involves two distinct steps: ethanol dehydrogenation to acetaldehyde and butadiene synthesis. The catalyst functions can be tailored separately or imbedded in a single formulation, leading to two-stage and one-stage processes. The performance of selected ETB catalysts is confronted with predictions based on chemical equilibrium, considering the simultaneous formation of products, by-products and impurities. The analysis shows that, essentially, the performance of ETB catalysts is controlled by kinetic factors. A shortlist of relevant catalysts for industrial implementation is proposed. The analysis highlights two key issues for industrial reactor design: catalyst deactivation/regeneration and the use of inert gas as a major process cost. The first issue is addressed by developing a comprehensive fluidized bed reactor model operating in the bubbling regime, capable of handling complex reaction kinetics. Good performance close to plug flow is obtained with bubbles at a size of 4 to 8 cm and with intensive mass transfer. The simulation reveals an autocatalytic effect of acetaldehyde on the butadiene formation favored by a well-mixed dense phase. The second study investigates the optimization of the chemical reaction section in a reactor–separation–recycle system via economic potential. The costs associated with the catalytic reactor and the catalyst charge, including regeneration, along with the costs of recycling reactants and of an inert gas if used, are key factors in determining the optimal operation region. This approach, verified by simulation in Aspen Plus^TM, points out that better robustness and a limited use of an inert gas are necessary for developing industrial catalysts for the one-stage ETB process. Full article

This study systematically investigates the formation mechanism and development characteristics of the “foamy oil” phenomenon during pressure depletion development of high-viscosity crude oil through a combination of physical experiments and numerical simulations. Using Venezuelan foamy oil as the research subject, an innovative heterogeneous pore-etched glass model was constructed to simulate the pressure depletion process, revealing for the first time that bubble growth predominantly occurs during the migration stage. Experimental results demonstrate that heavy components significantly delay degassing by stabilizing gas–liquid interfaces, while the continuous gas–liquid diffusion effect explains the unique development characteristics of foamy oil—high oil recovery and delayed phase transition—from a microscopic perspective. A multi-scale coupling analysis method was established: molecular-scale simulations were employed to model component diffusion behavior. By improving the traditional Volume of Fluid (VOF) method and introducing diffusion coefficients, a synergistic model integrating a single momentum equation and fluid volume fraction was developed to quantitatively characterize the dynamic evolution of bubbles. Simulation results indicate significant differences in dominant controlling factors: oil phase viscosity has the greatest influence (accounting for ~50%), followed by gas component content (~35%), and interfacial tension the least (~15%). Based on multi-factor coupling analysis, an empirical formula for bubble growth incorporating diffusion coefficients was proposed, elucidating the intrinsic mechanism by which heavy components induce unique development effects through interfacial stabilization, viscous inhibition, and dynamic diffusion. This research breaks through the limitations of traditional production dynamic analysis, establishing a theoretical model for foamy oil development from the perspective of molecular-phase behavior combined with flow characteristics. It not only provides a rational explanation for the “high oil production, low gas production” phenomenon but also offers theoretical support for optimizing extraction processes (e.g., gas component regulation, viscosity control) through quantified parameter weightings. The findings hold significant scientific value for advancing heavy oil recovery theory and guiding efficient foamy oil development. Future work will extend to studying multiphase flow coupling mechanisms in porous media, laying a theoretical foundation for intelligent control technology development. Full article

China has abundant biomass and renewable energy resources suitable for producing green methanol via biomass thermochemical conversion. Given China’s increasing demand for sustainable fuel alternatives and the urgency to reduce carbon emissions, optimizing biomass utilization through gasification is critical. Research has highlighted the potential of integrating biomass gasification with water electrolysis to enhance efficiency in green methanol production, leveraging China’s vast biomass reserves to establish a cleaner energy pathway. Four main biomass gasification technologies—fixed-bed, fluidized-bed, pressurized fluidized-bed, and entrained-flow—have been investigated. Fixed-bed and bubbling fluidized-bed gasification face low gas yield and scaling issues; whereas, circulating fluidized-bed gasification (CFB) offers better gas yield, carbon efficiency, and scalability, though it exhibits high tar and methane in syngas. Pressurized fluidized-bed gasification improves gasification intensity, reaction rate, and equipment footprint, yet stable feedstock delivery under pressure remains challenging. Entrained-flow gasification achieves high carbon conversion and low tar but requires finely crushed biomass, restricted by biomass’ low combustion temperature and fibrous nature. Current industrially promising routes include oxygen-enriched and steam-based CFB gasification with tar cracking, which reduces tar but requires significant energy and investment; oxygen-enriched combustion to produce CO₂ for methanol synthesis, though oxygen in flue gas can poison catalysts; and a new high oxygen equivalence ratio CFB gasification technology proposed here, which lowers tar formation and effectively removes oxygen from syngas, thereby enabling efficient green methanol production. Overcoming feedstock challenges, optimizing operating conditions, and controlling tar and catalyst poisoning remain key hurdles for large-scale commercialization. Full article

In simulations of elastic flow using the lattice Boltzmann method (LBM), the steady-state behavior of the flow at low capillary numbers is typically poor and prone to the formation of bubbles with inhomogeneous lengths. This phenomenon undermines the precise control of heat transfer, mass transfer, and reactions within microchannels and microreactors. This paper establishes an LBM multiphase flow model enhanced by machine learning. The hyperparameters of the machine learning model are optimized using the particle swarm algorithm. In contrast, the non-dominated sorting genetic algorithm (NSGA-II) is incorporated to optimize bubble lengths and stability. This results in a coupled multiphase flow numerical simulation model that integrates LBM, machine learning, and the particle swarm algorithm. Using this model, we investigate the influence of elastic flow parameters on bubble length and stability in a T-shaped microchannel. The simulation results demonstrate that the proposed LBM multiphase flow model can effectively predict bubble elongation rates under complex conditions. Furthermore, multi-objective optimization determines the optimal gas–liquid two-phase inlet flow rate relationship, significantly mitigating elastic flow instability at low capillary numbers. This approach enhances the controllability of the elastic flow process and improves the efficiency of mass and heat transfer. Full article

Fluidized bed reactors (FBRs) are integral to various industries due to their exceptional capability in facilitating efficient gas–solid interactions, resulting in superior mixing and heat and mass transfer. This research delves into the impact of temperature on fluidization dynamics, particularly focusing on the collisional properties of particles within the bed. The investigation builds upon foundational research, notably Geldart’s classification of fluidization regimes and recent advancements in high-temperature experimental techniques, such as High-Temperature Endoscopic-Laser particle image velocimetry/digital image analysis. To explore these temperature effects, a coupled Discrete Element Method and Computational Fluid Dynamics (cfd–dem) model was employed. This approach enables a detailed examination of gas–particle and particle–particle interactions under varying temperature conditions. The simulations in this study explore the friction coefficient, as well as changes in both tangential and normal restitution coefficients, which affect the fluidization behavior. These changes were systematically analyzed to determine their influence on minimum fluidization velocity and bubble formation. The numerical results are compared with experimental data from high-temperature fluidization studies, highlighting the necessity of incorporating inter-particle forces to fully capture the observed phenomena. The findings underscore the critical role of particle collisional properties in high-temperature fluidization and suggest the potential increasing role of inter-particle forces. Overall, this paper provides new insights into the complex dynamics of fluidized beds at elevated temperatures, emphasizing the need for further experimental–numerical research to enhance the reliability and understanding of these systems in industrial applications. Full article

Gas embolism is a rare but life-threatening process characterized by the presence of gas bubbles in the venous or arterial systems. These bubbles, if sufficiently large or numerous, can block the delivery of oxygen to critical organs, in particular the brain, and subsequently they can trigger a cascade of adverse biochemical reactions with severe medical outcomes. Despite its critical nature, gas embolism remains poorly understood, necessitating extensive investigation, particularly regarding its manifestations in the human body and its modulation by various biological conditions. However, given its elusive nature, as well as potential lethality, gas embolism is extremely difficult to study in vivo, and nearly impossible to be the subject of clinical trials. To this end, we developed a microfluidic device designed to study in vitro the impact of blood properties and vascular geometries on the formation and evolution of gas bubbles. The system features a biomimetic vascular channel surrounded by two pressure chambers, which induce the genesis of bubbles under varying circumstances. The bubble parameters were correlated with different input parameters, i.e., channel widths, wall thicknesses, viscosities of the artificial blood, and pressure levels. Smaller channel widths and higher equivalent hematocrit concentrations in synthetic blood solutions increased the nucleation density and bubble generation frequencies. Small channel widths were also more prone to bubble formation, with implications for the vulnerability of vascular walls, leading to increased risks of damage or compromise to the integrity of the blood vessels. Larger channel widths, along with higher equivalent hematocrit concentrations, translated into larger bubble volumes and decreased bubble velocities, leading to an increased risk of bubble immobilization within the blood vessels. This biomimetic approach provides insights into the impact of patient history and biological factors on the incidence and progression of gas embolism. Medical conditions, such as anemia, along with anatomical features related to age and sex—such as smaller blood vessels in women and children or larger vascular widths in adult men—affect the susceptibility to the initiation and progression of gas embolism, explored here in vitro through the development of a controlled, physiological-like environment. The analysis of the videos that recorded gas embolism events in vitro for systems where pressure is applied laterally on the microvasculature with thin walls, i.e., 50 μm or less, suggests that the mechanism of gas transfer for the pressure area to the blood is based on percolation, rather than diffusion. These findings highlight the importance of personalized approaches in the management and prevention of gas embolism. Full article

In recent years, liquid–solid triboelectric nanogenerators (L-S TENGs) have been rapidly developed in the field of liquid energy harvesting and self-powered sensing. This is due to a number of advantages inherent in the technology, including the low cost of fabricated materials, structural diversity, high charge-energy conversion efficiency, environmental friendliness, and a wide range of applications. As liquid phase dielectric materials typically used in L-S TENG, a variety of organic and inorganic single-phase liquids, including distilled water, acidic solutions, sodium chloride solutions, acetone, dimethyl sulfoxide, and acetonitrile, as well as paraffinic oils, have been used in experiments. However, it is noteworthy that the function of multiphase liquids as dielectric materials is still understudied. The “Multiphase Liquid Triboelectric Nanogenerator Prototype (ML-TENG Pro)” presented in this paper takes a single-electrode solid–liquid triboelectric nanogenerator as the basic model and uses lubricating oil and deionized water as dielectric materials. After verifying the stability of single-phase liquid materials (e.g., DI water, seawater, ethanol, etc.) for power generation, the power generation performances of oil–water two-phase, gas–oil–water three-phase (with a small number of bubbles), and gas–oil–water three-phase (with many bubbles) in open space are further investigated. COMSOL Multiphysics 6.0 software was used to investigate the material transport mechanism and formation of oil–water two-phase and gas–oil–water three-phase. Finally, this study presents the power generation performance of ML-TENG Pro in the extreme state of gas–oil–water three-phase “emulsification”. This paper outlines the limitations of the ML-TENG, named PRO, and suggests avenues for future improvement. The research presented in this paper provides a theoretical basis for evaluating the quality of lubricants for mechanical power equipment. Full article

The productivity prediction of weakly volatile fractured reservoirs is influenced by reservoir parameters and fluid characteristics. To address the computational challenges posed by complex fractures, an equivalent fracture element method is proposed to calculate equivalent permeability in fractured zones. A three-phase seepage model based on material balance is developed, using the Baker linear model to determine the relative permeabilities of oil, gas, and water while accounting for bound water saturation. Dynamic drainage distance and conductivity coefficients are introduced to calculate production at each stage, with the semi-analytical model solved iteratively for pressure and saturation. Validation against commercial simulation software confirms the model’s accuracy, enabling the construction of productivity curves and analysis of reservoir characteristics and injection scenarios. Results showed that the equivalent fracture element method effectively handled multiphase nonlinear seepage and predicted productivity during water flooding. Productivity was more sensitive to through-fracture models, with production increasing as the fracture extent expanded. Optimal water injection occurred when the formation pressure dropped to 80% of the bubble point pressure, and the recovery efficiency improved with periodic-injection strategies compared to conventional methods. These findings have significant implications for improving oil recovery, optimizing injection strategies, and advancing the design of efficient reservoir management techniques across scientific, practical, and technological domains. Full article