Search Results (46)

This study explores the visible-light-driven photolysis of Ferrioxalate complexes for the degradation of Toluidine Blue (TB), a persistent phenothiazine dye, using a 1 L recirculating batch-loop photoreactor. The reactor system incorporated two tubular photochemical units (35 cm × 3 cm each) in series: the first equipped with an immersed blue fluorescent lamp (12 W, 30 cm-tube), and the second with dual external blue LED lamps (18 W total, 30 cm) encasing a double-walled glass cell. Continuous flow between the units was maintained via a peristaltic pump. Experimental investigations were used to evaluate the effects of key parameters such as Fe(III) and oxalate concentrations, initial TB load, pH, light source, flow rate, ligand type, dissolved gas type, external H₂O₂ addition, and the presence of various inorganic ions. The results demonstrate efficient dye degradation, with ~75% TB removal within 1 h under combined fluorescent and LED irradiation, where each reactor contributing comparably. The optimal performance was achieved at pH 4, with a 10 oxalate-to-Fe(III) molar ratio (1 mM:0.1 mM) and a flow rate of 25 mL s⁻¹. Among various ligands tested (oxalate, acetate, citrate, EDTA), oxalate proved to be the most effective. The presence and type of anions significantly influenced degradation efficiency due to their potential scavenging effects. Although the process achieved high dye removal, TOC analysis indicated only moderate mineralization, suggesting the accumulation of non-colored intermediates. External H₂O₂ addition moderately improved TOC removal, likely due to enhanced hydroxyl radical generation via the Fenton mechanism. These findings highlight the promise of Ferrioxalate-based photochemical systems under visible light for dye removal, while also emphasizing the need for further research into by-product identification, mineralization enhancement, and toxicity reduction to ensure safe effluent discharge. 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

An exergy analysis of maize cob gasification in a concentric tube fixed-bed reactor was conducted to define the relationship between biomass in the combustion and gasification zones. Biomass exergy was estimated based on its elemental composition, and syngas was treated as an ideal gas. The results show a linear correlation between temperature and the mass ratio in both the combustion and gasification zones. The optimum exergy efficiency was 68.2% at a mass ratio of 2. Most irreversibilities were found in the combustion zone, with 42.9 kJ/kg destroyed, compared to 33.7 kJ/kg in the gasification zone. It is concluded that the allothermal gasification of biomass in two-zone gasifiers with concentric tubes improves the syngas LHV, demonstrating good reactor performance. Full article

This study evaluates the performance of continuous flow and drop-based microfluidic devices for the synthesis of silver nanoparticles (AgNPs) under identical hydrodynamic and chemical conditions. Flows at low values of Dean number (De < 1) were investigated, where the contribution of the vortices forming inside the drop to the additional mixing inside the reactor should be most noticeable. In the drop-based microfluidic device, discrete aqueous drops serving as reactors were generated by flow focusing using silicone oil as the continuous phase. Aqueous solutions of reagents were supplied through two different channels merging just before the drops were formed. In the continuous flow device, the reagents merged at a Tee junction, and the reaction was carried out in the outlet tube. Although continuous flow systems may face challenges such as particle concentration reduction due to deposition on the channel wall or fouling, they are often more practical for research due to their operational simplicity, primarily through the elimination of the need to separate the aqueous nanoparticle dispersion from the oil phase. The results demonstrate that both microfluidic approaches produced AgNPs of similar sizes when the hydrodynamic conditions defined by the values of De and the residence time within the reactor were similar. Full article

This study is focused on developing a machine learning (ML) meta-model to predict the progression of a multiple steam generator tube rupture (MSGTR) accident in the APR1400 reactor. The accident was simulated using the thermal–hydraulic code RELAP5/SCDAPSIM/MOD3.4. The model incorporates a mitigation strategy executed through operator interventions. Following this, uncertainty quantification employing the Best Estimate Plus Uncertainty (BEPU) methodology was undertaken by coupling RELAP5/SCDAPSIM/MOD3.4 with the statistical software, DAKOTA 6.14.0. The analysis concentrated on critical safety parameters, including Reactor Coolant System (RCS) pressure and temperature, as well as reactor vessel upper head (RVUH) void fraction. These simulations generated a comprehensive dataset, which served as the foundation for training three ML architectures: Gated Recurrent Unit (GRU), Long Short-Term Memory (LSTM), and Convolutional LSTM (CNN+LSTM). Among these models, the CNN+LSTM hybrid configuration demonstrated superior performance, excelling in both predictive accuracy and computational efficiency. To bolster the model’s transparency and interpretability, Integrated Gradients (IGs)—an advanced Explainable AI (XAI) technique—was applied, elucidating the contribution of input features to the model’s predictions and enhancing its trustworthiness. Full article

This paper presents a comprehensive review of mixed convective heat transfer phenomena involving fluids with varying Prandtl numbers, specifically focusing on their behavior in different geometries and orientations. This study systematically explores heat transfer characteristics for fluids with low, medium, and high Prandtl numbers across a range of tube geometries, including circular, rectangular, triangular, and elliptical cross-sections, and examines their effects in both horizontal and vertical tube orientations. By consolidating existing research findings and analyzing various experimental and numerical studies, this review elucidates the complex interactions between fluid properties, tube geometry, and flow orientation that influence mixed convection heat transfer. Key insights are provided into the mechanisms driving heat transfer enhancements or degradations in different scenarios. In view of the findings from this paper, more than 84% of studies were conducted in a horizontal orientation and circular cross-section with a tendency to use medium-to-high Prandtl numbers as the working fluid for the past 10 years. This paper also identifies critical gaps in current knowledge and suggests future research directions to advance the understanding and application of mixed convective heat transfer in diverse engineering systems. Furthermore, apart from having different geometries applied in industrial applications, there is still room for improvement through the addition of passive methods to the heat transfer system, including helical coils, corrugations, swirl generators, and ribs. Overall, from the literature review, it is found that there are few relevant numerical simulations and experimental studies concentrating on middle Prandtl number fluids. Hence, it is recommended to perform more research on medium Prandtl number fluids that can be used as energy storage systems (ESS) in concentrating solar power plants, nuclear reactors, and geothermal systems. Full article

N₂ oxidation to NO_x is a challenging reaction, and alternative routes to the industrial Ostwald process are of interest. A perovskite under flowing O₂-N₂ mixtures at atmospheric pressure in a quartz tube reactor was irradiated by microwaves (MW), leading to the formation of hot spots and plasmas within the catalyst bed. NO_x concentrations up to 2.5 vol.% in one pass were obtained at 600 W. Using a lower MW power of 100 W led to a pulsed mode yielding lower NO_x concentrations and no noticeable damage to the quartz reactor. The formation of plasma was strongly dependent on the perovskite bed packing. The perovskite acted primarily as a susceptor and likely also as a catalyst, although the proportion of heterogeneous and homogenous reactions could not be determined in the present study. The simple reactor layout allowing operation at atmospheric pressure is promising for the development of practical MW-assisted N₂ fixation technologies. Full article

The adsorption properties of microporous carbon materials modified with iron citrate were investigated. The carbon materials were produced based on resorcinol-formaldehyde resin, treated in a microwave assisted solvothermal reactor, and next carbonized in the tube furnace at a temperature of 700 °C under argon atmosphere. Iron citrate was applied as a modifier, added to the material precursor before the synthesis in the reactor, in the quantity enabling to obtain the nanocomposites with C:Fe mass ratio equal to 10:1. Some samples were additionally activated using potassium oxalate or potassium hydroxide. The phase composition of the produced nanocomposites was determined using the X-ray diffraction method. Scanning and transmission electron microscopy was applied to characterize the changes in samples’ morphology resulting from the activation process and/or the introduction of iron into the carbon matrix. The adsorption of nitrogen from gas phase and dyes (methylene blue and congo red) from water solution on the obtained materials was investigated. In the case of methylene blue, the adsorption equilibrium isotherms followed the Langmuir isotherm model. However, in the case of congo red, a linear dependency of adsorption and concentration in a broad equilibrium concentration range was found and well-described using the Henry equation. The most efficient adsorption of methylene blue was noticed for the sample activated with potassium hydroxide and modified with iron citrate, and a maximum adsorption capacity of 696 mg/g was achieved. The highest congo red adsorption was noticed for the non-activated sample modified with iron citrate, and the partition coefficient for this material equaled 171 dm³/g. Full article

We have developed a convenient route to transform biomass power plant ashes (BPPA) into porous sponge-like fertilizer composites. The absence of water prevents the chemical reaction and carbon dioxide formation when concentrated sulfuric acid is mixed with BPPA and CaCO₃. Adding water, however, initiates the protonation reaction of carbonate ion content and starts CO₂ evolution. The key element of the method was that the BPPA and, optionally, CaCO₃ and/or CaSO₄·0.5H₂O were mixed with concentrated sulfuric acid to make a paste-like consistency. No gas evolution occurred at this stage; however, with the subsequent and controlled addition of water, CO₂ gas evolved and was released through the channels developed in the pastry-like material due to the internal gas pressure, but without foaming. Using a screw-containing tube reactor, the water can be introduced under pressure. Due to the pressure, the pores in the pastry-like material became smaller, and consequently, the mechanical strength of the granulated and solidified mixture became higher than that of the reaction products prepared under atmospheric pressure. The main reaction products were syngenite (K₂Ca(SO₄)₂·H₂O) and polyhalite (K₂Ca₂Mg(SO₄)₄·2H₂O). These compounds are valuable fertilizer components in themselves, but the material’s porous nature helps absorb solutions of microelement fertilizers. Surprisingly, concentrated ammonium nitrate solutions transform the syngenite content of the porous fertilizer into ammonium calcium sulfate ((NH₄)₂Ca(SO₄)₂·2H₂O, koktaite). Koktaite is slightly soluble in water, thus the amount of ammonium ion released on the dissolution of koktaite depends on the amount of available water. Accordingly, ammonium ion release for plants can be increased with rain or irrigation, and koktaite is undissolved and does not decompose in drought situations. The pores (holes) of this sponge-like fertilizer product can be filled with different solutions containing other fertilizer components (phosphates, zinc, etc.) to adjust the composition of the requested fertilizer compositions for particular soils and plant production. The method allows the preparation of ammonium nitrate composite fertilizers containing metallic microelements, and various solid sponge-like composite materials with adjusted amounts of slowly releasing fertilizer components like syngenite and koktaite. Full article

Compound parabolic concentrator (CPC) photocatalytic reactors are commonly used for photocatalytic water splitting in hydrogen production. This study aimed to gain a better understanding of the physical processes in CPC photocatalytic reactors and provide theoretical support for their design, optimization, and operation. The analysis involved the ray tracing approach, Euler–Euler two-fluid model, and discrete ordinates method (DOM) to study solar radiation transfer and particle flow in the reactor. The distribution of solar radiation on the receiving tube’s surface after CPC concentration was obtained by conducting the ray tracing approach. This solar radiation distribution was then coupled into the Euler–Euler two-fluid model to solve for the natural convection flow field, the temperature field, and particle phase volume fraction distribution inside the receiving tube over a period of 120 s. Lastly, the discrete ordinates method (DOM) was used to analyze the transfer of radiation inside the receiving tube at different times, obtaining the distribution of local volume radiative power absorption (LVRPA) and the total radiative power absorption (TRPA) inside the tube. The results showed that the TRPA reached its maximum at 120 s, accounting for 66.61% of the incident solar UV radiation. According to the above results, it could be suggested that adopting an intermittent operation mode in CPC photocatalytic reactors is reasonable and efficient. Full article

In this study, several adsorption models were studied to predict the adsorption kinetics of turbidity on an electro-generated adsorbent throughout the electrocoagulation remediation of real groundwater. A new design for an electrocoagulation reactor consisting of a finned anode positioned concentrically in a tube-shaped cathode was fabricated, providing a significant active area compared to its immersed volume. This work completed a previous electrochemical study through a deep investigation of adsorption technology that proceeded throughout the electrocoagulation reactor under optimal operating conditions, namely a treatment period of 2–30 min, a 2.3-Ampere current, and a stirring speed of 50 rpm. The one-, two-, and three-parameter adsorption models investigated in this study possess significant regression coefficients: Henry (R² = 1.000), Langmuir (R² = 0.9991), Freundlich (R² = 0.9979), Temkin (R² = 0.9990), Kiselev (R² = 0.8029), Harkins–Jura (R² = 0.9943), Halsey (R² = 0.9979), Elovich (R² = 0.9997), Jovanovic (R² = 0.9998), Hill–de Boer (R² = 0.8346), Fowler–Guggenheim (R² = 0.8834), Dubinin–Radushkevich (R² = 0.9907), Sips (R² = 0.9834), Toth (R² = 0.9962), Jossens (R² = 0.9998), Redlich–Peterson (R² = 0.9991), Koble–Carrigan (R² = 0.9929), and Radke–Prausnitz (R² = 0.9965). The current behavior of the adsorption–electrocoagulation system follows pseudo-first-order kinetics (R² = 0.8824) and the Bangham and Burt mass transfer model (R² = 0.9735). The core findings proved that an adsorption-method-based electrochemical cell has significant outcomes, and all the adsorption models could be taken into consideration, along with other kinetic and thermodynamics investigations as well. Full article

Neutrons interact with the magnetic moment of the atomic shell of an atom, as is common for X-rays, but mainly they interact directly with the nucleus. Therefore, the atomic number and the related number of electrons does not play a role in the strength of an interaction. Instead, hydrogen that is nearly invisible for X-rays has a higher attenuation for neutrons than most of the metals, e.g., zirconium, and thus would be visible through dark contrast in neutron images. Consequently, neutron imaging is a precise, non-destructive method to quantify the amount of hydrogen in materials with low attenuation. Because nuclear fuel cladding tubes of light water reactors are made of zirconium (98%), the hydrogen amount and distribution in metallic claddings can be investigated. Even hydrogen concentrations smaller than 10 wt.ppm can be determined locally with a spatial resolution of less than 10 μm (with a high-resolution neutron microscope). All in all, neutron imaging is a very fast and precise method for several applications. This article explains the basics of neutron imaging and provides samples of investigation possibilities, e.g., for hydrogen in zirconium alloy cladding tubes or in situ investigations of hydrogen diffusion in metals. Full article

Vegetative cells of Listeria monocytogenes and Escherichia coli and spores of Bacillus subtilis and Aspergillus niger were inoculated in soy milk at an initial concentration of ≈5 log CFU/mL. Inoculated and control (non-inoculated) soy milk samples were submitted to three types of treatments using a tubular annular thin film short-wave ultraviolet (UV-C) reactor with 1 mm of layer thickness. Treatments applied depended on the flow rate and the number of entries to the reactor, with UV-C doses ranging from 20 to 160 J/mL. The number of entries into the reactor tube (NET) was established as the most determining parameter for the efficiency of the UV-C treatments. Conidiospores of A. niger were reported as the most resistant, followed by B. subtilis spores, while vegetative cells were the most sensible to UV-C, with Listeria monocytogenes being more sensible than Escherichia coli. Treatments of just 80 J/mL were needed to achieve a 5 log CFU/mL reduction of L. monocytogenes while 160 J/mL was necessary to achieve a similar reduction for A. niger spores. Full article

Methanol is expected to be a possible solution for reducing global greenhouse gas emissions and minimizing the dependency on fossil fuels. This paper presents a systematic approach of methanol (MeOH) production from industrial waste gases including flue gas (FG) and coke oven gas (COG) that are considered an important threat to the environment. The impact of process parameters, including dimensional parameters (length, diameter, and number of tubes) and operational parameters (reactor temperature, pressure, and thermal fluid temperature) over the MeOH synthesis, are investigated by Aspen Plus. Firstly, the synthesis process is designed and optimized using syngas (SG) as a feed material. Secondly, by replacing the feed material with FG and COG, methanol production variability is investigated and demonstrated for the same optimized process. Afterward, an efficient heat exchange network system is developed for all three different processes using Aspen Energy Analyzer. The optimized dimensional parameters of the MeOH synthesis reactor are determined to be a length of 12 m, a diameter of 0.06 m, and 5000 tubes for achieving a conversion rate of 75%. Meanwhile, the optimized operational parameters are identified as a reactor temperature of $209 °\mathrm{C}$, reactor pressure of 70 bar, and thermal fluid temperature of $196 °\mathrm{C}$. Furthermore, the influence of the stoichiometric number (SN) on the process was observed with higher SN values resulting in increased hydrogen (H₂) concentration and an improved forward reaction of MeOH synthesis, leading to higher conversion rates. The findings and insights gained from this study can serve further improvements and advancements in MeOH synthesis processes. Full article

A proof of concept of a novel parallel-flow solid–solid heat exchanger consisting of two L-Valves with concentric vertical tubes, named as Double L-Valve, is presented for the case of the Carbonate Looping process, as a CO₂ capture technology. The operational objective of the solid–solid heat exchanger is to heat up the relatively cold solid stream coming from the carbonator reactor by absorbing heat from the hotter stream coming from the calciner. This novel solid–solid heat exchanger concept has been constructed on a small scale to study the hydrodynamic response of the system experimentally at different designs and airflow rates in its cold state. Based on the experimental data from the small prototype, a scaled-up hydrodynamic model is proposed that provides estimations for the operational requirements at an industrial scale. Apart from the cold flow pilot model, the heat exchanger is being assessed in the current work for an industrial case study in terms of the following: (a) the heat transfer via rigorous one-dimensional thermal modelling, (b) the structural integrity of the design through Finite Element Method (FEM) analysis, and (c) a parametric study for its expected cost. The purpose of this work is to provide a holistic approach of this novel solid–solid heat exchanger concept, the main advantage of which is its simple design and relatively low cost. Full article