Small Gas Research Articles

Small gas adsorption on metal clusters on trimer form of graphyne: First-principles density functional theory study

Small gas adsorption on metal clusters on trimer form of graphyne: First-principles density functional theory study

Intrinsically Microporous Polyimides Based on a Rigid-Soft Structure for Hydrogen Separation.

Polyimide (PI)-based gas separation membranes are of great interest in the field of H2 purification owing to their good thermal stability, chemical stability, and mechanical properties. Among polyimide-based membranes, intrinsically microporous polyimides are easily soluble in common organic solvents, showing great potential for fabricating hollow fiber gas separation membranes. However, based on the solution-diffusion model, improving the free volume or the movability of polymer chains can improve gas permeability, but would result in poor thermal stability. Herein, we develop a carbazole-alkyl-based diamine monomer that endows PI chains with a "rigid-soft" structure to balance the trade-off between them. Soft units enhance the movability of polymer chains during the film-forming process, ensuring that rigid units achieve tight chain packing and strong intermolecular interactions. Meanwhile, bulky carbazole groups could further restrict the motion of soft units in the solid state. On the one hand, it restricts the movability of the polymer chains below Tg, enhancing the small gas selectivity for H2 and He. On the other hand, it ensures good thermal stability. Moreover, extending the length of the alkyl chains helps improve the free volume and intermolecular interactions simultaneously, thereby further optimizing the gas permeability/selectivity trade-off. As a result, the as-prepared PI shows H2 permeability of 89.61 Barrer, H2/CH4 selectivity of 87.85, and H2/N2 selectivity of 45.03 in contrast to the reference FPI TFMB-6FDA exhibiting H2 permeability of 92.95 Barrer, H2/CH4 selectivity of 72.62, and H2/N2 selectivity of 38.57. Meanwhile, a high Tg value of 334 °C is also achieved.

Tunable Gas Permeation Behavior through Robust, Freestanding Self-Assembled Metal Nanoparticle Membranes.

Membrane-based gas separation offers a promising alternative route to energy-intensive industrial gas separation processes. Conventional microporous membranes often exhibit low gas selectivities for gases with similar kinetic diameters, primarily due to large pore sizes and reliance on Knudsen selectivity. In this study, we present self-assembled gold nanoparticle (Au NP) membranes that enable molecular gas separation within the kinetic diameter range of small gases such as H2, CO2, and O2. By grafting silane molecules of varying sizes onto NP ligands, the gas selectivity of these membranes becomes tunable. This strategy achieves remarkably high gas selectivities of 192 and 35 for H2/CO2 and CO2/O2 gas pairs. Moreover, the Au NP membrane demonstrates a mixed gas selectivity of up to 30 for H2/CO2 even at room temperature, establishing its potential as a novel class of gas separation membranes with high and tunable selectivity.

Comparative Assessment of Hydrogen and Methanol-Derived Fuel Co-Combustion for Improved Natural Gas Boiler Performance and Sustainability

Faced with a global consensus on net-zero emissions, the use of clean fuels to entirely or substantially replace traditional fuels has emerged as the industry’s primary development direction. Alcohol–hydrogen fuels, primarily based on methanol, are a renewable and sustainable energy source. This research focuses on energy sustainability and presents a boiler fuel blending system that uses methanol–hydrogen combinations. This system uses the boiler’s waste heat to catalytically decompose methanol into a gas mostly consisting of H2 and CO, which is then co-combusted with the original fuel to improve thermal efficiency and lower emissions. A comparative experimental study considering natural gas (NG) blending with hydrogen and dissociated methanol gas (DMG) was carried out in a small natural gas boiler. The results indicate that, with a controlled mixed fuel flow of 10 m3/h and an excess air coefficient of 1.2, a 10% hydrogen blending ratio maximizes the boiler’s thermal efficiency (ηt), resulting in a 3.5% increase. This ratio also results in a 1% increase in NOx emissions, a 25% decrease in HC emissions, and a 5.66% improvement in the equivalent economics (es). Meanwhile, blending DMG at 15% increases the boiler’s ηt by 3%, reduces NOx emissions by 13.8% and HC emissions by 20%, and improves the es by 8.63%. DMG, as a partial substitute for natural gas, outperforms hydrogen in various aspects. If this technology can be successfully applied and promoted, it could pave a new path for the sustainable development of energy in the boiler sector.

Enhancing the accuracy of XPS calculations: Exploring hybrid basis set schemes for CVS-EOMIP-CCSD calculations.

Reliable computational methodologies and basis sets for modeling x-ray spectra are essential for extracting and interpreting electronic and structural information from experimental x-ray spectra. In particular, the trade-off between numerical accuracy and computational cost due to the size of the basis set is a major challenge, since molecular orbitals undergo extreme relaxation in the core-hole state. To gain clarity on the changes in electronic structure induced by the formation of a core-hole, the use of sufficiently flexible basis for expanding the orbitals, particularly for the core region, has been shown to be essential. This work focuses on the refinement of core-hole ionized state calculations using the equation-of-motion coupled cluster family of methods through an extensive analysis on the effectiveness of "hybrid" and mixed basis sets. In this investigation, we utilize the CVS-EOMIP-CCSD method in combination and construct hybrid basis sets piecewise from readily available Dunning's correlation consistent basis sets in order to calculate x-ray ionization energies (IEs) for a set of small gas phase molecules. Our results provide insights into the impact of basis sets on the CVS-EOMIP-CCSD calculations of K-edge IEs of first-row p-block elements. These insights enable us to understand more about the basis set dependence of the core IEs computed and allow us to establish a protocol for deriving reliable and cost-effective theoretical estimates for computing IEs of small molecules containing such elements.

Permanent Nanobubbles in Water: Liquefied Hollow Carbon Spheres Break the Limiting Diffusion Current of Oxygen Reduction Reaction.

Porous liquids have traditionally been designed with sterically hindered solvents. Alternatively, recent efforts rely on dispersing microporous frameworks in simpler solvents like water. Here we report a unique strategy to construct macroporous water by selectively incorporating hydrophilicity on the surfaces of hydrophobic hollow carbon spheres (HCS). Specifically, we show that the stable dispersion surface ionized HCS in water while retaining the inherent porosity. The electrocatalytic conversion of small gas molecules in aqueous electrolytes is limited by the concentration and diffusion rates of gas molecules in water. In this case, macroporous water exhibited 6 times gas uptake compared to nonporous (pure) water. By leveraging the high gas capacity and enhanced diffusion kinetics, the limiting diffusion current of oxygen reduction reaction (ORR) in macroporous water is 2 times that in nonporous water, offering promising prospects for sustainable energy conversion technologies.

Fullerene-Doped Poly(ionic liquids) as Small Molecular Gas Sensors-Control of Intermolecular Interactions.

Here, we investigate the interactions between five representative gaseous analytes and two poly(ionic liquids) (PILs) based on the sulfopropyl acrylate polyanion in combination with the alkylphosphonium cations, P4,4,4,4 and P4,4,4,8, and their nanocomposites with fullerenes (C60, C70) to reveal the potential of PILs as sensitive layers for gas sensors. The gaseous analytes were chosen based on their molecular size (all of them containing two carbon atoms) and variation of functional groups: alcohol (ethanol), nitrile (acetonitrile), aldehyde (acetaldehyde), halogenated alkane (bromoethane), and carboxylic acid (acetic acid). The six variations of PILs-P4,4,4,4SPA (1), P4,4,4,4SPA + C60 (1 + C60), P4,4,4,4SPA + C70 (1 + C70), and P4,4,4,8SPA (2), P4,4,4,8SPA + C60 (2 + C60), P4,4,4,8SPA + C70 (2 + C70)-were characterized by UV-vis and Raman spectroscopy, and their interactions with each gaseous analyte were studied using electrochemical impedance spectroscopy. Exposure of all PIL samples to acetaldehyde, bromoethane, and ethanol leads to a decrease in the diffusion coefficient, while exposure to acetic acid reveals an increase. Fullerene-doping significantly enhances the response to the analyte. Semiempirical quantum mechanical xTB-GFN2 calculations revealed that hydrogen bonding and proton transfer events play an important role during the detection process.

Central versus Global Quenching Traced by the APEX-CALIFA Survey

Abstract The quest for the mechanisms that halt star formation in galaxies is essential to understand their evolution. Here, we use the APEX-CALIFA survey, which includes 560 galaxies (0.005 < z < 0.08), so far the largest sample of galaxies in the nearby universe with both Integral Field Spectroscopic, Calar Alto Legacy Integral Field Area (CALIFA) and single-aperture millimeter observations, as well as the extended CALIFA sample (823 targets). Using these observations we derive (i) the deficit or excess of star formation for a given stellar mass with respect to the star formation main sequence (ΔSFMS), (ii) the gas fraction, and (iii) the star formation efficiency (SFE) for two apertures (central and global apertures using the APEX-CALIFA and CALIFA samples, respectively). We confirm the so-called “inside-out” quenching, that is, for quiescent galaxies the central values of ΔSFMS are usually smaller than those values derived from global measurements. However, for a given ΔSFMS we find that for retired galaxies the central gas fraction is larger in comparison to global measurements. Furthermore, the central SFE is significantly smaller in comparison to global counterparts. In general, in comparison to the global measurements, the deficit of star formation at the center of retired galaxies is primarily caused by the inefficiency to form new stars rather than the lack of molecular gas. We suggest that even though at the center of retired galaxies the gas fraction is larger, morphological structures could prevent that the molecular gas is transformed into new stars. Even more so in the outskirts of some retired galaxies with small gas fractions, star formation activity is still occurring.

An Enhanced Gas Sensor Data Classification Method Using Principal Component Analysis and Synthetic Minority Over-Sampling Technique Algorithms.

This study addresses the challenge of multi-dimensional and small gas sensor data classification using a gelatin-carbon black (CB-GE) composite film sensor, achieving 91.7% accuracy in differentiating gas types (ethanol, acetone, and air). Key techniques include Principal Component Analysis (PCA) for dimensionality reduction, the Synthetic Minority Over-sampling Technique (SMOTE) for data augmentation, and the Support Vector Machine (SVM) and K-Nearest Neighbor (KNN) algorithms for classification. PCA improved KNN and SVM classification, boosting the Area Under the Curve (AUC) scores by 15.7% and 25.2%, respectively. SMOTE increased KNN's accuracy by 2.1%, preserving data structure better than polynomial fitting. The results demonstrate a scalable approach to enhancing classification accuracy under data constraints. This approach shows promise for expanding gas sensor applicability in fields where data limitations previously restricted reliability and effectiveness.

A Fluorine-Functionalized Tb(III)-Organic Framework for Ba2+ Detection.

The development of lanthanide-organic frameworks (Ln-MOFs) using for luminescence sensing and selective gas adsorption applications is of great significance from an energy and environmental perspective. This study reports the solvothermal synthesis of a fluorine-functionalized 3D microporous Tb-MOF with a face-centered cubic (fcu) topology constructed from hexanuclear clusters (Tb6O30) bridged by fdpdc ligands, formulated as {[Tb6(fdpdc)6(μ3-OH)8(H2O)6]·4DMF}n (1), (fdpdc = 3-fluorobiphenyl-4,4'-dicarboxylate). Complex 1 displays a 3D framework with the channel of 7.2 × 7.2 Å2 (measured between opposite atoms) perpendicular to the a-axis. With respect to Ba2+ cation, the framework of activated 1 (1a) exhibits high selectivity and reversibility in luminescence sensing function, with an LOD of 4.34665 mM. According to the results of simulations, compared to other small gas molecules (CO2, N2, H2, CO, and CH4), activated 1 (1a) shows a high adsorption selectivity for C2H2 at 298 K.

Performance and Emission Characteristics of a Small Gas Turbine Engine Using Hexanol as a Biomass-Derived Fuel.

The global transition to renewable energy has amplified the need for sustainable aviation fuels. This study investigates hexanol, a biomass-derived alcohol, as an alternative fuel for small-scale gas turbines. Experimental trials were conducted on a JETPOL GTM-160 turbine, assessing blends of 25% (He25) and 50% (He50) hexanol with kerosene (JET A) under rotational velocities ranging from 40,000 to 110,000 RPM. The parameters measured included thrust-specific fuel consumption (TSFC), turbine inlet and outlet velocities, and the emission indices of NOx and CO. The results demonstrated that the He25 and He50 blends achieved comparable thermal efficiency to pure JET A at high rotational velocities, despite requiring higher fuel flows due to hexanol's lower heating value. CO emissions decreased significantly at higher velocities, reflecting improved combustion efficiency with hexanol blends, while NOx emissions exhibited a slight increase, attributed to the oxygen content of the fuel. This study contributes a novel analysis of hexanol-kerosene blends in gas turbines, offering insights into their operational and emission characteristics. These findings underscore hexanol's potential as an environmentally friendly alternative fuel, aligning with global efforts to reduce fossil fuel dependency and carbon emissions.

Coordinated intelligent control strategy and power management for marine gas turbine under pulsed load using optimized neural network

Faced with the challenges of potentially irreversible damage due to instantaneous large pulsed power loads onboard, considering all-electric ship's small power grid capacity and complex gas turbine system, this study proposes a coordinated intelligent control strategy. It utilizes multi-objective optimization neural network to control a validated 20MW ship three-shaft gas turbine, ensuring global optimization tailored to pulsed load variations. Research findings reveal that the gas turbine efficiency at the design point is 32.3%, with a steady-state error within 2.8% and a maximum steady time error of 3.4 seconds, demonstrating acceptable accuracy. Under slope-type pulsed load of 20MW change in 5s, the proposed control strategy effectively manages speed while utilizing the energy storage system to smooth load inputs. It is worth noting that, increasing the fuel flow rate to 1.28 kg/s and inlet guide vane to 5.8 degrees reduces overshoot by 0.7% and rotor steady time by 15.4 seconds. Under transient-type pulsed load of 10MW back and forth change in 5s, the coordinated inlet guide vane control strategy mitigates surge margin and exhaust temperature issues. Adjusting the fuel flow to 1.17 kg/s and inlet guide vane to 9.96 degrees enables the gas turbine to operate within safety boundaries, reducing rotor speed overshoot by 0.4% and steady time by 6.1 seconds. Importantly, the optimized control strategy without energy storage system provides faster and safer dynamic regulation and power transmission for ship acceleration processes under radar load. However, considering only the coordinated strategy of the fuel sub-control loop, it is advisable to avoid compressor surge and over-temperature protection for electromagnetic ejection load scenarios. The research results will lay a valuable technical foundation for the intelligent control and smooth power transfer of the all-electric ship gas turbine power system with pulse loads in the extreme missions of ships in the future.

Micro/Nanobubble-Assisted Lipotransfer: In Vivo Evidence of Improved Graft Outcomes.

Retention rates of lipotransfer remain variable, with the underlying cause associated with tissue oxygenation and blood supply barriers. One promising new method of improving tissue oxygenation is micro/nanobubbles (MNBs), which are small gas bubbles (<100 μm) generated within a saline solution. MNBs are stable and carry a significant amount of oxygen, and because of their negatively charged surface characteristics, they are an ideal oxygen-delivery solution. Thus, we hypothesize that washing/oxygenating lipoaspirate tissue prior to transplantation in a micro/nanobubble saline solution will improve graft survival and quality compared to a saline control. Human lipoaspirate samples obtained from healthy donors were washed with an oxygenated MNB or saline wash. These samples were then injected into the dorsum of sixteen 6-week-old male BALB/c mice, where each mouse received one saline and one MNB-washed graft. At 2-, 4-, 8-, and 12-week time points, the explants were harvested and weighed, and gas pycnometry was performed to assess graft volume. The tissues were also subjected to hematoxylin and eosin (HE) staining and immunohistochemistry to detect perilipin and blood vessels (CD31). These stains, as well as adipocyte count and area quantifications, were analyzed using ImageJ. HE staining revealed that the control group demonstrated notable adipocyte hypertrophy, while MNB-washed samples had evident adipocyte hyperplasia. This observation was confirmed by an analysis of variance (ANOVA), which showed that the control group had a larger average graft mass and volume (P < 0.01). MNB-washed grafts also exhibited significantly greater adipocyte counts and smaller adipocytes (P < 0.001). Perilipin staining was also greater in the MNB group at the 2- and 4-week time point indicating improved de novo adipogenesis following implantation. Lastly, CD31 staining revealed a significantly greater core vessel density and angiogenesis at the 4-week and 12-week time points (P < 0.01). Our study demonstrates that MNBs enhance tissue quality as indicated by a significant increase in de novo adipogenesis, higher vessel density, and decreased adipocyte hypertrophy. Additional studies are needed to evaluate the clinical effectiveness. Nevertheless, incorporating MNBs into procedures holds great promise in tackling the ongoing challenge of inconsistent outcomes in lipotransfer.

Experimental investigation on transition mechanisms and modal decomposition analysis of gas–liquid flow patterns in horizontal–vertical elbow

A series of experiments are conducted to investigate the transition mechanisms and characteristics of six typical gas–liquid flow patterns in a horizontal–vertical elbow using electrical capacitance tomography and high-speed camera. The dominant modes and corresponding time coefficients are obtained by performing proper orthogonal decomposition on the pulsating gas holdup (GHU) distribution data to explore their physical mechanisms and correlations. Reduced-order descriptions for different flow patterns are discussed. The results show that after passing through the elbow, the horizontal slug or bubble flow turns into vertical bubble flow due to the small gas volume content and the mixing effect of secondary flow, accompanied by a swirl-switching phenomenon. A slug flow forms at the elbow outlet when there is a stratified flow comes from the horizontal pipe, and changes in flow conditions will affect the generation frequency and stability of Taylor bubbles. The horizontal annular or mist flow with high gas volume content will be transformed into churn flow in the vertical pipe. The modal decomposition analysis indicates that, for all the investigated conditions in the present study, mode 1 represents the mean distribution of GHU fluctuations, and there is a pair of modes representing the dominant swirling features. For the slug and churn flows, mode 2 characterizes the features of gas slug or large bubbles, the time coefficient of which is highly connected with that of mode 1. Meanwhile, it is also shown that the obtained low-dimensional descriptions of different flow patterns using the dominant modes are able to reconstruct most of the GHU distribution features in gas–liquid flows with the reconstructive loss less than 3%.

Design of a small gas flow calibration facility by piston prover method

Design of a small gas flow calibration facility by piston prover method

Impact of swirler sleeve length on outlet temperature distribution of a small gas turbine combustor

Small gas turbine engine combustors hold promising application prospects. Investigating the patterns and mechanisms of how design parameters influence outlet temperature distribution plays a pivotal role in the development of small gas turbine engines with high thrust-to-weight ratios and extended lifespans. Therefore, this study employs high-temperature thermocouple scanning thermometry, particle image velocimetry, planar Mie scattering, and OH* chemiluminescence to examine the impact of varying swirler sleeve lengths on the outlet temperature distribution of a small gas turbine combustor. Both the pilot and main stages of the combustor are fueled with kerosene. Thermocouple test results indicate that increasing the sleeve length leads to an elevation in hot spots at the combustor exit and an expansion of high-temperature regions. In conjunction with optical results, it is revealed that elongating the sleeve enhances and “protects” the fuel–air mixing process within the sleeve, facilitating the formation of high-concentration fuel–air mixtures. Additionally, a longer sleeve stabilizes the heat release zone and recirculation zone further downstream in the combustor, thereby shortening the mixing distance and, to some extent, weakening the heat exchange effects between the mixing/cooling gases and the high-temperature jet core.

Flow pattern formation due to the interdependency of multi-component interactions and their impact on the performance of turbine and exhaust duct of gas turbine

Abstract Drawing the inspiration from Full Engine Simulation performed by the scientific community, the methodology for performing an integration analysis of single stage turbine with convergent exhaust nozzle of a small gas turbine engine is developed in the present study. Initially, a numerical simulation on exhaust system supported with experimental validation has been discussed. A scope of improvement in the exhaust system study has been identified and these principles are applied to improve the accuracy of prediction of CFD analysis. By taking the confidence from the validation, a 3D steady pressure-based analysis is carried out to understand the flow patterns and aero-thermal properties of the single stage turbine with convergent type nozzle influenced by the integration. The integration resulted in increased specific work output of the turbine and increased the thrust coefficient of the nozzle. Further important outcomes of this study highlight the changes observed in the performance parameters with and without integration. The thermal pattern across the rotor blades from CFD analysis is observed to be in-line with the used blades of the gas turbine engine thereby reinforcing the accuracy of the methodology developed for the integration study.

Histopathology of the small airways: Similarities and differences between ageing and COPD.

Age-related lung function decline is associated with small airway closure and gas trapping. The mechanisms which cause these changes are not fully understood. It has been suggested that COPD is caused by accelerated ageing. We have investigated pathological changes in the small airways during ageing, and evaluated whether the same or different processes exist in COPD. Histopathology and immunohistochemistry were used to examine small airway remodelling in healthy ageing, and then compare to age matched COPD patients. Ageing was associated with reduced alveolar attachment numbers (rho= -0.4 p = 0.049), increased epithelial area (rho = 0.5 p = 0.01), greater luminal narrowing due to epithelial expansion (rho = 0.5 p = 0.04) and increased alveolar septal neutrophils (rho = 0.6 p = 0.005). Compared to age matched controls, COPD small airways had 31% less alveolar attachments per airway (p = 0.02) and significantly more alveoalr septal neutrophils (p = 0.0007). Increased airway wall thickness was a feature of COPD but was not related to ageing in non-smokers. Alveolar attachment loss, accompanied by alveolar septum neutrophilic inflammation, and increased luminal narrowing due to epithelial expansion are major features of small airway remodelling during ageing. These features can explain the increased small airway narrowing and closure during ageing. Alveolar attachment loss is accelerated in COPD, likely due to increased neutrophilic inflammation.

Assessment of simulated and observed cavitation-induced erosion damage in spallation neutron source target vessels

Cavitation-induced erosion damage in different Spallation Neutron Source (SNS) target designs are simulated using explicit finite element–based techniques and compared with observations of erosion in targets after operation. The efficacy of the previously developed method, called saturation time, was evaluated using erosion-damaged samples from new target designs. A new metric called maximum bubble size was implemented under the rationale that larger cavitation bubbles will collapse more intensely. The maximum cavitation bubble size over 1 ms of simulated time was calculated based on the Rayleigh–Plesset equation for each element integration point and presented as a contour map at the vessel surface for assessing with erosion observations. SNS targets are now operated with helium gas injection to reduce cavitation damage. A simulation method using a material model for the mixture of mercury and gas bubbles was recently developed and used to account for the effect of small gas bubbles on the structural response of the target vessel. This work compares the new method's results with observed cavitation damage. Maps of the calculated maximum bubble size for targets operated with and without gas injection were compared with photographs of erosion damage observed in SNS targets. The patterns in maximum bubble size maps correlated well with observations of erosion patterns in target vessels after service. Advantages and challenges of the maximum bubble size simulation technique are provided, and differences between results from the previous and the newly proposed metric are discussed.

Study on the aging behavior and mechanism of nitrile rubber composites in combined radiation-thermal environments

This contribution investigates the aging property changes and mechanism of nitrile rubber (NBR) under the combined radiation-thermal environments in the N2 atmosphere. Aging resulted in a decrease in elongation at break from 309.01 % to 64.74 %, an increase in modulus of elasticity from 3.84 MPa to 9.09 MPa, and a slight increase in thermal stability. The crosslink density increases and the mass loss of the sample is reduced, while the chemical structure of the sample surface is almost intact. By gas-phase infrared spectroscopy, the irradiation aging-induced gases from NBR were also analyzed, including CO2, CO, and alkanes (CH4, C2H6, C3H8). This indicates that chain scission and pendant group removal also take place, whereas chain breaking primarily occurs at the macromolecular chain end. The above degradation reactions and the decomposed additives account for the generated trace amount of small molecule gas products. These findings suggest that the primary aging mechanisms of NBR are the cross-linking of macromolecular chains and additive loss. Furthermore, radiation and thermal have a synergistic effect on NBR aging, and this effect has a threshold temperature that is clearly between 50 °C and 70 °C. The synergistic effect of additive cleavage is only apparent at temperatures above 65 °C under radiation-thermal conditions.