Gas Dispersion Research Articles

Physical properties of circumnuclear ionising clusters III. Kinematics of gas and stars in NGC,7742

For this third paper in the series, we studied the kinematics of the ionised gas and stars, and calculated the dynamical masses of the circumnuclear star-forming regions in the ring of the face-on spiral NGC 7742. We used high spectral resolution data from the MEGARA instrument mounted on the Gran Telescopio Canarias (GTC) to measure the kinematical components of the nebular emission lines of selected HII regions and the stellar velocity dispersions from the CaT absorption lines that allow the derivation of the associated cluster virialised masses. The emission line profiles show two different kinematical components: a narrow one with a velocity dispersion of ∼ 10 km/s and a broad one with a velocity dispersion similar to the values found for the stellar absorption lines. The derived star cluster dynamical masses range from 2.5 times 10^6 to 10.0 times 10^7 M_⊙. The comparison of gas and stellar velocity dispersions suggests a scenario where the clusters have formed simultaneously in a first star formation episode with a fraction of the stellar evolution feedback remaining trapped in the cluster, subject to the same gravitational potential as the cluster stars. Between 0.15 and 7.07 % of the total dynamical mass of the cluster would have cooled down and formed a new, younger, population of stars, responsible for the ionisation of the gas currently observed.

CFD-based simulation of flammable gas dispersion in a complex geometry

CFD-based simulation of flammable gas dispersion in a complex geometry

CFD-Based Determination of Optimal Design and Operating Conditions of a Fermentation Reactor Using Bayesian Optimization.

The efficiency of fermentation reactors is significantly impacted by gas dispersion and concentration distribution, which are influenced by the reactor's design and operating conditions. As the process scales up, optimizing these parameters becomes crucial due to the pronounced concentration gradients that can arise. This study integrates the kinetics of the fermentation process with hydrodynamic analysis using Bayesian optimization to efficiently determine the optimal reactor design and operating conditions. By utilizing computational fluid dynamics (CFD) simulations, the study provides a comprehensive assessment of distributions ranging from gas supply to cell growth. The results demonstrate that a combination of wide baffle width, narrow impeller gap, slow gas flow rate, and high agitation speed significantly enhances reactor performance by improving gas distribution and minimizing stagnant zones. These findings underscore the importance of considering both kinetic and hydrodynamic factors to achieve more precise and scalable fermentation processes, offering valuable insights for industrial applications.

Integrated portable gas dispersion device

ABSTRACT This paper proposes a new portable device for gas dispersion investigations based on the simultaneous measurements of gas holdup and bubble size in an integrated system. The aim of developing this device is to acquire a better understanding of the interdependence of flotation hydrodynamic parameters mainly: gas holdup (ϵg), bubble size, represented in this study as Sauter mean bubble diameter (D32), superficial gas velocity (Jg), frother type and frother concentration. Utilisation of the device can extend from laboratory to plant processes for investigating the effect of naturally occurring and residual surfactants as well as salts in process water on bubble size and gas holdup using dilution and frother equivalent techniques. Additionally, conventional methods of frother classification such as critical coalescence concentration determination of frothers can be determined as well. Lastly, a preliminary investigation into the use of bubble size and gas holdup for frother classification is explored. Experiments were performed in two-phase batch tests at varying superficial gas velocities of 0.5 cm s−1 and 1 cm s−1 and the frothers used were MIBC (methyl isobutyl carbinol), Flottec F140 (commercial frother blend of aldehydes and ketones) and Flottec F150 (polypropylene glycol). The results show the practicality and versatility of the device.

Hazard Identification of Ammonia FSS for Ammonia Fuelled Ammonia Carrier

Ammonia is a zero-carbon fuel that has attracted considerable interest. The compound has high volumetric energy density and is easy to store and transport. Despite this, a proper study is necessary to ensure safety because ammonia fuel will likely be applied first to ammonia carriers. In this study, hazard identification (HAZID) was performed to identify the risk of the ammonia fuel supply system and preventive/mitigation measures were suggested to minimize the risk. The analyzed system scope was the ammonia fuel supply system from a fuel service tank on the deck to the front of the engine. The nodes with the most scenarios were the fuel service tank and the fuel supply line. The main factors included internal factors, such as design defects, malfunctions, and operational errors, and external factors, such as impact, thermal stress, hogging, and sagging. Recommendations are provided to reduce the risk of accident scenarios, including safety devices/alarm devices in process systems, system layout configurations, and heat and gas dispersion analysis. The results are expected to help predict/minimize damage regarding ammonia fuel supply system design, operational safety, and potential risks.

High-resolution observations of 12CO and 13CO J = 3 → 2 towards the NGC 6334 extended filament

NGC 6334 is a giant molecular cloud (GMC) complex that exhibits elongated filamentary structure and harbours numerous OB-stars, H II regions, and star-forming clumps. To study the emission morphology and velocity structure of the gas in the extended NGC 6334 region using high-resolution molecular line data, we made observations of the 12CO and 13CO J = 3 → 2 lines with the LAsMA instrument at the APEX telescope. The LAsMA data provided a spatial resolution of 20″ (~0.16 pc) and sensitivity of 0.4 K at a spectral resolution of 0.25 km s−1. Our observations revealed that gas in the extended NGC 6334 region exhibits connected velocity coherent structure over ~80 pc parallel to the Galactic plane. The NGC 6334 complex has its main velocity component at approximately −3.9 km s−1 with two connected velocity structures at velocities approximately −9.2 km s−1 (the ‘bridge’ features) and −20 km s−1 (the northern filament, NGC 6334-NF). We observed local velocity fluctuations at smaller spatial scales along the filament that are likely tracing local density enhancement and infall, while the broader V-shaped velocity fluctuations observed towards the NGC 6334 central ridge and G352.1 region located in the eastern filament EF1 indicate globally collapsing gas onto the filament. We investigated the 13CO emission and velocity structure around 42 WISE H II regions located in the extended NGC 6334 region and found that most H II regions show signs of molecular gas dispersal from the centre (36 of 42) and intensity enhancement at their outer radii (34 of 42). Furthermore most H II regions (26 of 42) are associated with least one ATLASGAL clump within or just outside of their radii, the formation of which may have been triggered by H II bubble expansion. Typically towards larger H II regions we found visually clear signatures of bubble shells emanating from the filamentary structure. Overall the NGC 6334 filamentary complex exhibits sequential star formation from west to east. Located in the west, the GM-24 region exhibits bubbles within bubbles and is at a relatively evolved stage of star formation. The NGC 6334 central ridge is undergoing global gas infall and exhibits two gas bridge features possibly connected to the cloud-cloud collision scenario of the NGC 6334-NF and the NGC 6334 main gas component. The relatively quiescent eastern filament (EF1 - G352.1) is a hub-filament in formation, which shows the kinematic signature of global gas infall onto the filament. Our observations highlight the important role of H II regions in shaping the molecular gas emission and velocity structure as well as the overall evolution of the molecular filaments in the NGC 6334 complex.

Biofabrication of polyhydroxybutyrate (PHB) in engineered Cupriavidus necator H16 from waste molasses

BackgroundCupriavidus necator H16, a native polyhydroxybutyrate (PHB) producer, has emerged as a promising candidate for sustainable bioproduction to replace conventional plastics. However, most fermentation processes still rely on expensive substrates. Therefore, developing an eco-friendly bioprocess for PHB using waste materials is urgent and essential. MethodAn engineered strain Lgg-H16, incorporating galactose permease (galP) and glucokinase (glk), was employed to boost glucose uptake and phosphorylation. Then, biomass and PHB production were improved by fine-tuning the carbon, nitrogen, and phosphorus ratios. Yeast extract was supplemented as an additional nutrient, and a tailored feeding strategy was applied to maximize PHB output. To lower the manufacturing costs, waste molasses from the sugar industry, was utilized for fed-batch fermentation. The physical properties of the PHB, such as molecular weight and crystallinity, were analyzed using differential scanning calorimeter (DSC) and gel permeation chromatography (GPC), respectively. Significant resultsEngineered Lgg-H16 strain exhibited a 2.15-fold increase in specific growth rate compared to the wild type with a C:N:P ratio of 20:1:18, as well as supplemented 2 g/L yeast extract in the medium. PHB yield reached 17.4 g/L with 70 % content from waste molasses in fed-batch fermentation with an atomizer to increase gas dispersion, costing only 1 % of pharmaceutical-grade glucose. All physical properties of the PHB produced by Lgg-H16 were comparable to commercial product, supporting this promising bioprocess by using the low-cost feedstocks for high-value bioplastic PHB.

Fast search for toxic gas leakage on offshore platforms based on deep learning methods

In the context of addressing dangerous gas leakage on offshore platforms, the prompt identification of leakage sources is paramount for implementing targeted emergency measures. This paper introduces a rapid leakage source location method leveraging a preexisting database on gas leakage and dispersion consequences, coupled with a deep learning approach. Initially, latin hypercube sampling (LHS) and computational fluid dynamics (CFD) are employed to simulate the consequences of gas leakage and dispersion on offshore platforms. Subsequently, a neural network model, specifically a long short-term memory (LSTM) model, is trained using concentration data. This trained model facilitates the rapid localization of the leakage source based on real-time detector data. Furthermore, optimization of the model is conducted through an analysis of various hyperparameters. Finally, the efficacy of the proposed methodology is demonstrated through a comparison between predicted results and actual operating conditions. This approach enables swift and precise identification of leakage sources during incidents, thereby facilitating a more efficient emergency response.

Triggered and dispersed under feedback of super H ii region W4

The W3/4 Giant Molecular Cloud (GMC) was an ideal target to study the impact of H ii regions onto the surrounding molecular gas and star formation. We utilized PMO CO (1--0) data from the Milky Way Imaging Scroll Painting (MWISP) survey to analyze the cloud structure and the feedback effect from the W4 H ii region. Our observations showed that cold gas, traced by CO, mainly resided in the W3 GMC, with C18O concentrated in dense regions, while gas around W4 was dispersed. The 13CO position-position-velocity (PPV) distributions revealed a "C" shaped structure in the W3 cloud with more redshifted gas at higher galactic longitudes. A high density layer (HDL) region on the eastern side of the W3 region exhibited a flattened structure facing W4. Subdividing the area into sixteen subregions, we found that regions 6--9 on the HDL layer exhibited the strongest radiation, while clouds at the W4 bubble boundary not facing W3 exhibited weak signals, possibly due to star formation triggering and subsequent molecular gas dispersal by the H ii region. Analysis along four paths from the W4 H ii region to the far side showed a consistent trend of sharply increasing intensity followed by a slow decrease, indicating the gas was effectively eroded and heated by the photon dominated region (PDR) near the boundary of the H ii region. Clump identification based on 13CO emission revealed 288 structures categorized as "bubble," "HDL," and "quiescent" clumps. Analysis of mass-radius and Virial-mass relationships showed a potential for high-mass star formation in 29.5$<!PCT!>$ (85/288) of the clumps, with 39.2$<!PCT!>$ (113/288) being gravitationally bound. HDL clumps exhibited distinct $L/M$ and velocity dispersion, suggesting an earlier evolutionary stage and gravitational instability compared to quiescent and bubble clumps. Clump parameter differences provided evidence for triggered and dispersed effects of the W4 H ii region on the HDL and bubble regions, respectively.

Quantification of volcanic degassing and analysis of uncertainties using numerical modeling: the case of Stephanos crater (Nisyros Island, Greece)

Nisyros Island (Greece) is affected by widespread gas emissions from fumarolic fields located at the bottom of hydrothermal craters in the southern part of its caldera. This morphology and the current low gas fluxes make Nisyros an ideal site for testing the limits of physics-based gas dispersal models in confined and low-emission conditions. Here, we focused our attention on the local scale volcanic gas dispersion from the Stephanos hydrothermal crater. In April 2023, a 1-week survey was carried out to measure weather data, CO2 and H2S gas fluxes, air concentrations from portable gas stations, and chemical composition of fumarolic gases and to acquire thermal images of the crater floor. These data were used as inputs and boundary conditions for numerical simulations using a DISGAS-2.6.0 model in order to quantify the present-day volcanic degassing and its associated uncertainties, accounting for the meteorological variability. Model results are provided in terms of H2S probabilistic exceedance and persistence maps, showing gas concentrations within the crater that fall below the thresholds indicated for the occurrence of serious respiratory problems. Since DISGAS-2.6.0 does not account for chemical reactions, this study represents a good opportunity to discuss the methodological limits of simulating the dispersion of H2S which is challenging due to its rapid degradation and dilution in the atmosphere. In this regard, we also provided an empirical law of the H2S depletion in low-emission conditions that takes into account the uncertainties related to the field measurements.

An Inexpensive Adaptation of a Commercial Microwave Reactor for Solid Phase Peptide Synthesis.

A home-built apparatus to perform solid phase peptide synthesis (SPPS), assisted by microwave irradiation and heating, is presented. In contrast to conventional SPPS reaction vessels, which drain solvent and byproducts via a frit located at the bottom of the vessel, the presented apparatus employs a gas dispersion tube under vacuum to remove solvent, byproducts, and excess reagents. The same gas dispersion tube supplies nitrogen gas agitation of the SPPS beads during the reaction steps of coupling and deprotection. Microwave heating is beneficial for SPPS couplings of sterically hindered residues, such as alpha-aminoisobutyric acid (Aib), an alpha,alpha-dialkylated amino acid residue. This home-built apparatus has been used to prepare, via manual Fmoc SPPS methods, heptameric and octameric peptides dominated by the Aib residue, which is notoriously difficult to couple under standard room temperature conditions and reagents. Further, typical commercial microwave SPPS reactors are dedicated exclusively to SPPS synthesis rendering them inaccessible to non-SPPS users. In contrast, the presented apparatus preserves the versatility of the microwave reactor for conventional microwave acceleration of chemical reactions, as the apparatus is trivially removed from the commercial microwave reactor.

Comparative Study of CALPUFF and CFD Modeling of Toxic Gas Dispersion in Mountainous Environments

Comparative Study of CALPUFF and CFD Modeling of Toxic Gas Dispersion in Mountainous Environments

Experimental investigation of natural gas leakage and dispersion characteristics in utility tunnels under the effects of real facility layout and forced ventilation

Natural gas leakage occurring in underground utility tunnels usually poses a significant threat to public safety. In order to prevent unexpected fires and explosions, the evolution mechanism of natural gas leakage and dispersion in utility tunnels is urgently needed. In this study, an experimental apparatus was built to facilitate the understanding of leakage and dispersion dynamics in utility tunnels. Methane with a purity of 99.9% is used as a surrogate for natural gas. A schlieren imaging system with a Z-shaped optical path was designed to visualize the high-speed gas jet. The concentration distribution, alarm time, dilution efficiency, and gas jet image were analyzed under the effect of various facility layouts, ventilation, and leakage rates. The results show that the gas leakage and dispersion process can be divided into three zones: upwind zone, leak zone, and downwind zone, characterized by complicated airflow collision, high-speed get jets, and stable dilution dispersion respectively. Scenario analysis highlights the significance of key facilities, such as cable brackets, in experimental and numerical modeling due to their impact on dispersion trajectories. Higher ventilation rates prove beneficial in reducing peak concentration, hazardous areas, and enhancing purge efficiency. Conversely, higher leakage rates exacerbate the likelihood and severity of gas explosions. Alarm time exhibits a V-shaped distribution relative to the leak point, while purge time correlates positively with sensor positions. These findings are of practical importance in enhancing quantitative risk assessment and designing mitigation strategies for gas leakage accidents, which helps to improve the safety-risk-control capabilities of utility tunnels.

Research on the Calculation Method and Diffusion Pattern of VCE Injury Probability in Oil Tank Group Based on SLAB-TNO Method

Accidental leakage from oil–gas storage tanks can lead to the formation of liquid pools. These pools can result in vapor cloud explosions (VCEs) if combustible vapors encounter ignition energy. Conducting accurate and comprehensive consequence analyses of such explosions is crucial for quantitative risk assessments (QRAs) in industrial safety. In this study, a methodology based on the SLAB-TNO model to calculate the overpressure resulting from a VCE is presented. Based on this method, the consequences of the VCE accident considering the gas cloud concentration diffusion are studied. The probit model is employed to evaluate casualty probabilities under varying environmental and operational conditions. The effects of key parameters, including gas diffusion time, wind speed, lower flammability limit (LFL), and environment temperature, on casualty diffusion are systematically investigated. The results indicate that when the diffusion time is less than 100 s, the VCE consequences are significantly more severe due to the rapid spread of the gas cloud. Furthermore, increasing wind speed accelerates gas dispersion, reducing the spatial extent of casualty isopleths. The LFL is shown to have a direct impact on both the mass and diffusion of the flammable gas cloud, with higher LFL values shifting the explosion’s epicenter upward. The environmental temperature promotes gas diffusion in the core area and increases the mass of the combustible gas cloud. These findings provide critical insights for improving the safety protocols in oil and gas storage facilities and can serve as a valuable reference for consequence assessment and emergency response planning in similar industrial scenarios.

Comprehensive investigation of gas hold-up in a double coaxial mixer with shear-thinning fluids exhibiting yield stress: Experimental, numerical, and artificial neural network approaches

This study addresses the challenge of uneven gas dispersion in yield-stress, non-Newtonian fluids, commonly encountered in industries such as biopharmaceuticals, cosmetics, and food processing. While previous research demonstrated the advantages of dual coaxial mixers for pseudoplastic fluids, limited attention has been given to aerating yield-pseudoplastic fluids with higher aspect ratios. This study bridges that gap by investigating both local and global gas hold-up under various conditions, utilizing electrical resistance tomography and computational fluid dynamics. Key findings showed that increasing the anchor speed from stationary to 30 rpm significantly enhanced aeration efficiency (gas hold-up per specific power consumption), with improvements of 78 % in UP-CO mode and 25 % in UP-COUNTER mode at Nc = 350 rpm and Qg = 20 L/min. These results underscore enhanced gas dispersion under specific operating conditions, driving overall process intensification. To ensure accurate prediction of gas hold-up, both dimensional and dimensionless empirical correlations, along with an artificial neural networks (ANNs) model, were developed. The ANNs model exhibited superior accuracy, achieving R² values of 0.99 for both rotation modes, outperforming empirical models, which achieved R² values of 0.90 and 0.89 for UP-CO and UP-COUNTER modes, respectively.

Intense Star Cluster Formation: Stellar Masses, the Mass Function, and the Fundamental Mass Scale

Within the birth environment of a massive globular cluster, the combination of a luminous young stellar population and a high column density induces a state in which the thermal optical depth and radiation pressure are both appreciable. In this state, the sonic mass scale, which influences the peak of the stellar mass function, is tied to a fundamental scale composed of the Planck mass and the mass per particle. Thermal feedback also affects the opacity-limited minimum mass and how protostellar outflows and binary fragmentation modify stellar masses. Considering the regions that collapse to form massive stars, we argue that thermal stabilization is likely to flatten the high-mass slope of the initial mass function. Among regions that are optically thick to thermal radiation, we expect the stellar population to become increasingly top-heavy at higher column densities, although this effect can be offset by lowering the metallicity. A toy model is presented that demonstrates these effects and in which radiation pressure leads to gas dispersal before all of the mass is converted into stars.

Gas Leakage Risk Management Of Biogas Powerplant Using Aloha Gas Dispersion Modelling And Bowtie Analysis

Biogas, a fuel derived from organic waste, has gained popularity as a sustainable energy source. The adaptability of biogas allows its utilization for electricity and heating. This study aims to evaluate the risk of biogas leakage using ALOHA gas dispersion modeling and Bowtie analysis to identify hazard zones and evaluate the effectiveness of preventive and mitigation measures. The research method using Gas dispersion modeling in ALOHA software can simulate the spread of leaked biogas, identify potential hazard zones, and inform emergency response planning. The results show that gas dispersion reaches up to 296 meters from the leak source in a worst-case scenario without ignition, with significant implications for safety. The ignition scenario produces high thermal radiation, further exacerbating the risk. In conclusion, these findings highlight the intolerable risk of biogas leakage, requiring comprehensive risk mitigation measures. This study recommends the implementation of a robust control system, routine maintenance, and emergency response plan to ensure the safety and sustainability of biogas facility operations

An efficient dimensionality reduction approach for modelling cryogenic hydrogen release

This study develops a precise and cost-effective method for reducing the complexity of cryogenic hydrogen unintended release. For this purpose, the dominant modes of a well-characterised cryogenic hydrogen jet (Sandia National Laboratories), with stagnation pressure and temperature fixed at 5 bar and 50 K, are extracted using the proper orthogonal decomposition (POD) method. Building on validating the large eddy simulation (LES) against experimental measurements, the velocity field within the LES results is analysed near the release point. The mass fraction half-width of cryogenic hydrogen jets grows linearly with a slope of 0.1115 against the downstream distances, resembling room-temperature jets. The first 10 extracted modes from 500 LES snapshots demonstrate dominance over the remaining modes. In addition, this study evaluates the flammable gas dispersion using LES and 10-mode POD, showing POD effectively identifies high-risk areas within hydrogen's flammability range. Minor deviations (2.1–3.3%) confirm POD's reliability for hazard assessment compared with LES. Furthermore, an in-depth analysis is performed on the radial distributions of hydrogen mass fraction and centreline hydrogen mole fraction.

Numerical investigation of the leakage and diffusion characteristics of hydrogen-blended natural gas in long-distance pipelines

This paper uses Fluent software to create a 3D leakage model for hydrogen-blended natural gas pipelines and analyzes how hydrogen blending ratio (HBR), soil type, and leakage hole shape affect gas dispersion. Results show that hydrogen and methane have different concentration distributions in soil: hydrogen forms an ‘n' shaped distribution while methane forms an ‘M' shaped distribution, with higher hydrogen concentrations observed further from leakage holes. HBR has a minimal effect on diffusion; higher HBR leads to lower concentrations at saturation. Soil type significantly impacts diffusion, with sandy soils showing higher gas concentrations than clay. Slit-type holes result in faster concentration saturation compared to square-type holes. Increasing the number of leakage holes from two to four enhances concentration differences and accelerates diffusion. The optimal axial spacing for fast diffusion is 200 mm. These findings support monitoring and risk assessment for hydrogen-blended natural gas pipelines.

Can the infection risk in elevators be negligible? A comparative study of airborne infection probability in elevators and conference rooms

People in crowded and poorly ventilated elevators are at risk of respiratory infection. However, due to the short duration of the elevator ride, the transmission of respiratory diseases in elevators does not get enough attention. To evaluate the infection risk, this study investigated the airborne transmission of respiratory diseases in the hospital elevator by comparison to the conference room. A validated computational fluid dynamics (CFD) model was adopted to simulate airflow, temperature and tracer gas dispersion in the elevator and conference room. We used Wells-Riley model to evaluate the infection probability of the susceptible persons. In addition, the influences of source patient posture and ventilation strategy on the transmission of tracer gas were analyzed. The results showed that the infection probability in the elevator with 5 min (average 2.70%) was higher than that in the conference room with 50 min (average 1.77%). The effects of source patient posture and ventilation strategy on the infection probability in the elevator were more significant than those in the conference room. Local air circulation could gather the tracer gas inside a confined space in the elevator and led to a high infection probability. The infection risk of respiratory diseases in the elevator was non-negligible.