Search Results (239)

Helium (He) accumulation in tungsten—widely used as a plasma-facing material in fusion reactors—can lead to clustering, trap mutation, and eventual formation of helium bubbles, critically impacting material performance. To clarify the atomic-scale mechanisms governing this process, we conducted systematic molecular statics and molecular dynamics simulations across a wide range of vacancy cluster sizes (n = 1–27) and temperatures (500–2000 K). We identified the onset of trap mutation through abrupt increases in tungsten atomic displacement. At 0 K, the critical helium-to-vacancy (He/V) ratio required to trigger mutation was found to scale inversely with cluster size, converging to ~5.6 for large clusters. At elevated temperatures, thermal activation lowered the mutation threshold and introduced a distinct He/V stability window. Below this window, clusters tend to dissociate; above it, trap mutation occurs with near certainty. This critical He/V ratio exhibits a linear dependence on temperature and can be described by a size- and temperature-dependent empirical relation. Our results provide a quantitative framework for predicting trap mutation behavior in tungsten, offering key input for multiscale models and informing the design of radiation-resistant materials for fusion applications. Full article

Reactive oxygen–nitrogen species (RONS) production in a Peltier-cooled hybrid dielectric barrier discharge (HDBD) reactor operated with humid air is characterized. Fourier-transform infrared spectroscopy (FTIR) is used to determine the RONS in the HDBD-produced gases. The presence of molecules ${\mathrm{O}}_3$, ${\mathrm{NO}}_2$, ${\mathrm{N}}_2$O, ${\mathrm{N}}_2{\mathrm{O}}_5$, and ${\mathrm{HNO}}_3$ is evaluated. The influence of HDBD reactor operation parameters on the FTIR result is discussed. The strongest influence of Peltier cooling on RONS chemistry is reached at conditions related to a high specific energy input (SEI): high voltage and duty cycle of plasma width modulation (PWM), and low gas flow. Both PWM and Peltier cooling can achieve a change in the chemistry from oxygen-based to nitrogen-based. ${\mathrm{N}}_2{\mathrm{O}}_5$ and ${\mathrm{HNO}}_3$ are detected at a low humidity of 7% in the reactor input air but not at humidity exceeding 90%. In addition to the FTIR analysis, the plasma-activated water (PAW) is investigated. PAW is produced by bubbling the HDBD plasma gas through 12.5 mL of distilled water in a closed-loop circulation at a high SEI. Despite the absence of ${\mathrm{N}}_2{\mathrm{O}}_5$ and ${\mathrm{HNO}}_3$ in the gas phase, the acidity of the PAW is increased. The pH value decreases on average by 0.12 per minute. Full article

The conventional spent lithium-ion batteries (LIBs) recycling method suffers from complex processes and excessive chemical consumption. Hence, this study proposes an electrochemical strategy for achieving reductant-free leaching of high-valence transition metals and efficient separation of valuable components from spent cathode sheets (CSs). An innovatively designed sandwich-structured electrochemical reactor achieved efficient reductive dissolution of cathode materials (CMs) while maintaining the structural integrity of aluminum (Al) foils in a dilute sulfuric acid system. Optimized current enabled leaching efficiencies exceeding 93% for lithium (Li), cobalt (Co), manganese (Mn), and nickel (Ni), with 88% metallic Al foil recovery via cathodic protection. Multi-scale characterization systematically elucidated metal valence evolution and interfacial reaction mechanisms, validating the technology’s tripartite innovation: simultaneous high metal extraction efficiency, high value-added Al foil recovery, and organic removal through single-step electrochemical treatment. The process synergized the dissolution of CM particles and hydrogen bubble-induced physical liberation to achieve clean separation of polyvinylidene difluoride (PVDF) and carbon black (CB) layers from Al foil substrates. This method eliminates crushing pretreatment, high-temperature reduction, and any other reductant consumption, establishing an environmentally friendly and efficient method of comprehensive recycling of battery materials. 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

Biomass fluidized bed gasification technology has attracted significant attention due to its high efficiency and clean energy conversion capabilities. However, its industrial application has been limited by insufficient technological maturity. This paper systematically reviews the research progress on biomass fluidized bed gasification characteristics; compares the applicability of bubbling fluidized beds (BFBs), circulating fluidized beds (CFBs), and dual fluidized beds (DFBs); and highlights the comprehensive advantages of CFBs in large-scale production and tar control. The gas–solid flow characteristics within CFB reactors are highly complex, with factors such as fluidization velocity, gas–solid mixing homogeneity, gas residence time, and particle size distribution directly affecting syngas composition. However, experimental studies have predominantly focused on small-scale setups, failing to characterize the impact of flow dynamics on gasification reactions. Therefore, numerical simulation has become essential for in-depth exploration. Additionally, this study analyzes the influence of different gasification agents (air, oxygen-enriched, oxygen–steam, etc.) on syngas quality. The results demonstrate that oxygen–steam gasification eliminates nitrogen dilution, optimizes reaction kinetics, and significantly enhances syngas quality and hydrogen yield, providing favorable conditions for downstream processes such as green methanol synthesis. Based on the current research landscape, this paper employs numerical simulation to investigate oxygen–steam CFB gasification at a pilot scale (500 kg/h biomass throughput). The results reveal that under conditions of O₂/H₂O = 0.25 and 800 °C, the syngas H₂ volume fraction reaches 43.7%, with a carbon conversion rate exceeding 90%. These findings provide theoretical support for the industrial application of oxygen–steam CFB gasification technology. Full article

This study investigates the synergistic effects of pulsed heat load and helium plasma irradiation on the surface damage evolution of high-purity tungsten, a candidate plasma-facing material (PFM) for future fusion reactors. Using a self-developed linear plasma device, tungsten samples were exposed to controlled single-pulse heat loads (32–124 MW·m⁻²) and helium plasma fluxes (7.76 × 10²²–2.40 × 10²³ ions·m⁻²·s⁻¹). SEM and XRD analyses revealed a progressive damage mechanism involving helium bubble formation, pit collapse, coral-like nanostructure evolution, and melting-induced restructuring. These surface changes were accompanied by grain refinement, lattice contraction, and peak shifts in the (110) diffraction plane. Mechanical testing showed a flux-dependent variation in hardness, with initial hardening followed by softening due to crack propagation. Surface reflectivity significantly declined with increasing load, indicating severe optical degradation. This work demonstrates the nonlinear coupling between thermal and irradiation effects in tungsten, offering new insights into damage accumulation under realistic reactor conditions. The findings highlight the dominant role of transient heat loads in driving structural and property changes and emphasize the importance of accounting for synergistic effects in material design. These results provide essential experimental data for optimizing PFMs in divertor and first-wall applications and suggest directions for future research into cyclic loading, long-term exposure, and microstructural recovery mechanisms. Full article

To enhance contact time between microalgae and nutrients in reactors, thereby improving the growth rate of microalgae and increasing pollutant removal efficiency, two funnel-shaped spoilers were added inside a traditional column photobioreactor. Compared to conventional column photobioreactors, the addition of these spoilers resulted in increased updraft, which improved horizontal flow. This change led to a greater shear force near the spoilers and a reduction in bubble diameter. As a result, the mass transfer coefficient and gas content increased by 12.17% and 7.71%, respectively, while the mixing time decreased by 30.57%. These improvements resulted in an 18.18% increase in microalgal biomass, a 13.95% increase in the CO₂ fixation rate, and increases of 4.48%, 7.5%, and 4.7% in the removal of COD, TP, and NH₄⁺-N, respectively, in the column photobioreactor with funnel-shaped spoilers. This was achieved when CO₂ was introduced at a concentration of 10%, compared to a conventional column photobioreactor. This innovative design enhances the growth efficiency of microalgae, offering a new solution for reducing carbon emissions, promoting recycling of water resources, and advancing sustainable development. Full article

In this study, through RH water model simulation experiments, the effects of precipitation bubbles on the two-phase flow pattern, liquid steel flow behavior, and flow characteristics in an RH reactor during the whole decarburization process were comparatively investigated and analyzed by using quasi-counts that reflected the similarity of the precipitation bubble phenomenon. The experimental results show that an increase in precipitation bubbles is positively related to an increase in circulating flow rate, a reduction in mixing time, and an increase in gas content and negatively related to the residence time of liquid steel in the vacuum chamber. The two-phase flow pattern of the rising tube under the influence of precipitation bubbles includes bubble flow, slug flow, mixing flow, and churn flow. Under the influence of precipitation bubbles, the liquid surface spattering inside the vacuum chamber is reduced, the fluctuation amplitude is reduced, the efficiency of liquid steel processing is improved, it is not easy for cold steel to form, and the fluctuation frequency is increased, which is conducive to increasing the surface area of the vacuum chamber; the bubbles’ rising, aggregating, and crushing behavior increases the stirring effect inside the vacuum chamber, which is conducive to improving the decarburization and mass transfer rate. Under the influence of the precipitated bubbles, the concentration gradient between the ladle and the vacuum chamber is increased, which accelerates the mixing speed of the liquid steel in the ladle, and the volume of the dead zone is reduced by 50%. The lifting gas flow rate can be appropriately reduced in the plant. Full article

Helium (He) accumulation, a byproduct of nuclear transmutation, poses a significant reliability challenge for the materials used in nuclear reactors. Nanomaterials, with their high density of interfaces, offer superior He tolerance by absorbing He atoms and suppressing bubble growth. However, the long-term stability of these materials under continuous He accumulation remains a concern. This study investigated the microstructural and mechanical property responses of ZrN nanofilms to excessive He accumulation. Different doses of He atoms were introduced via magnetron sputtering. The results indicate that increasing the He dose induced a nanocrystalline-to-amorphous transition and instability in the mechanical properties. The structural and mechanical instability, characterized by surface blistering, softening, abnormal lattice shrinkage, and amorphization, was primarily triggered by the degradation of the grain boundaries with He accumulation, and an amorphization model of nanomaterials is proposed. Full article

Kojic acid (KA) is an economically important molecule, due to its functions as an anti-inflammatory, antifungal, and facial skin-lightening agent. Considering the wide application of this metabolite, it is essential to study processes that increase or improve its production. The objective of this study was to evaluate the effect of agitation on fungal KA production. To evaluate the effect of agitation on fungal KA production, liquid medium fermentation was carried out using batch bioreactors with a capacity of one liter. The Aspergillus oryzae strain was used, with glucose as the sole carbon source. Three experimental factors were evaluated: illumination (light or darkness), agitation type (no agitation, bubbling, and tangential), and time (0, 24, 48, 72, 96, 120, 144, 168 h). The evaluated variables included pH, product-to-biomass yield, protein content, reducing sugar consumption, and KA concentration. The bubbling level with light for 144 h showed the highest efficiency by producing 7.86 ± 2.21 g KA/L. The production of KA in liquid medium with the fungus A. oryzae requires bubbling conditions with light to achieve the best yields and production. The findings in this study provide insights into the influence of agitation conditions on KA biosynthesis and its potential for scaling up industrial fermentation. However, future work could investigate the metabolic and genetic mechanisms of this enhanced production to generate more efficient biotechnological applications for KA production. 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

Carbonation precipitation processes have been widely used due to their numerous applications in a wide range of fields. The complexity of these processes lies within the interplay of transport phenomena, multiphase flows, chemical reactions, and solid precipitation, deeming the experimental analysis and in-depth mechanistic understanding of the process dynamics a rather challenging task. In this work, a three-dimensional CFD model is developed, focusing on the carbonation step of the carbonation precipitation process, taking into account the flow dynamics of the liquid solution in the stirred tank, the CO₂ bubble flow, and the dissolution in the liquid solution, as well as its dissociation in water. The model is validated with experimental measurements, and a very good agreement is achieved. Additionally, a parametric analysis is conducted to study the effect of different process parameters, such as temperature, CO₂ flow rate, and rotational speed. The analysis of the different phenomena and their interplay reveals the key mechanisms that dictate the carbonation step, resulting in an in-depth understanding of the process. The presented computational approach can potentially pave the way towards a knowledge-based process and reactor design; thus, assisting the scale-up of such processes in stirred tank reactors. Full article

Bubbly flow is a flow regime common in many industrial applications involving heat and mass transfer, such as reactors, cooling systems, and separation units. Accurate knowledge of bubble velocity, shape, and volume is crucial as these parameters directly influence the efficiency of phase interaction and the mixing process performance. Over the past few decades, numerous techniques have been developed to measure the velocity, shape, and volume of bubbles. Most efforts have focused on non-intrusive methods to minimize disturbance to the flow. However, a technique capable of simultaneously measuring these bubble characteristics across a dense spatial domain remains elusive. In this research, an image-based technique that enables simultaneous measurement of bubble velocity, shape, and volume in bubbly flows over a densely sampled linear domain is presented. A high-speed camera captures the variation in light intensity as bubbles pass in front of a collimated laser sheet, providing real-time, high-resolution data. The accuracy of the proposed methodology is evaluated and the uncertainties associated with the velocity and volume measurements are quantified. Given the promising results and the simplicity of the hardware and setup, this study represents an important step toward developing a technique for online monitoring of industrial processes involving bubbly flows. Full article

The tubular flocculation reactor is a new and efficient device for treating algae-containing wastewater. The introduction of bubbles during the reaction process can effectively shorten the time required for floc separation. However, the impact of bubbles on floc formation and removal in the tubular flocculation reactor is not well understood. To further clarify the effect of bubbles on the reactor’s operation, this study employed a uniform experimental design, varying the flow rate, chemical dosage, bubble reaction distance, and bubble injection rate in the reactor to examine the influence of bubbles under different operating conditions. The results indicated that as the bubble reaction distance increased from 0 m to 7.6 m, the removal efficiency increased from 60% to 70%, the floc size increased from 160 μm to 165 μm, and the fractal dimension decreased from 2.1 to 1.9. When the bubble volume increased from 5% to 30%, the removal efficiency increased from 50% to 80%. Under constant bubble conditions, the rising speed of the flocs increased from 0.4 mm·s⁻¹ to 1.2 mm·s⁻¹, while the removal efficiency increased from 30% to 90%. A logarithmic correlation was observed between the rising speed and removal efficiency. A linear relationship was found between the floc rising speed and the floc size, with floc size increasing from 200 μm to 800 μm and the rising speed increasing from 0.4 mm·s⁻¹ to 2.3 mm·s⁻¹. An exponential relationship was found between the fractal dimension and the rising speed, with the rising speed decreasing from 2.3 mm·s⁻¹ to 0.4 mm·s⁻¹, while the fractal dimension increased from 1.93 to 2.02. 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