Three-dimensional Gas Research Articles

Hierarchical Fibrous Metal-Organic Framework/Ionic Liquid Membranes for Efficient CO2/N2 Separation.

The structural diversity and chemical functionality of metal-organic frameworks (MOFs) render them promising candidates for CO2 adsorption and separation. However, their applications are often restricted by their intrinsic fragility and decreased processability. Herein, a hierarchical fibrous MOF/ionic liquid (IL) membrane was constructed by assembling well-ordered ZIF-8 nanounits with an encapsulated IL along the polyimide (PI) fibers. This design promotes the formation of an efficient three-dimensional gas transfer network and generates an abundance of nanopores decorated with CO2-philic units, thereby enhancing the separation of CO2 from N2. The hierarchical fibrous PI/ZIF-8/IL membranes exhibit remarkable structural features, including a large specific surface area of 79.89 m2 g-1, a high porosity of 93.28%, and excellent mechanical stability. Moreover, the PI/ZIF-8/IL membranes demonstrate an enhanced CO2 adsorption capacity of 3.32 mmol/g at 298 K and 1 bar, an excellent CO2/N2 selectivity of 28, and a stable recyclable regeneration capability. The integrated hierarchical pore structure proposed in this study provides a practical direction for the rational design of MOF/IL membranes for targeted gas separation applications.

Mass transfer behavior and desulfurization characteristics in the three-dimensional wet flue gas desulfurization tower

Mass transfer behavior and desulfurization characteristics in the three-dimensional wet flue gas desulfurization tower

Multi-scale Poincaré analysis of three-dimensional gas bubble trajectories in liquid

Multi-scale Poincaré analysis of three-dimensional gas bubble trajectories in liquid

Modeling the working process of a gas-diesel engine running on ammonia with the addition of hydrogen

BACKGROUND: Ammonia, as a carbon-free fuel, has attracted much attention from researchers in different countries and is considered one of the promising alternative fuels that reduce greenhouse gas emissions. Despite the fact that the properties of ammonia have been widely studied, the practical application of this type of fuel remains difficult. Additional research is needed to overcome problems, including low combustion rate, high emissions of nitrogen oxides and unburned ammonia. To stimulate the combustion process in the cylinder, it is possible to use hydrogen additive as an activator of the combustion of the ammonia-air mixture. This article is aimed at a computational study of the effect of replacing diesel fuel with ammonia on the characteristics and harmful emissions of an internal combustion engine. AIM: Computational study of the working process and harmful emissions from exhaust gases of a motor-tractor dual-fuel engine when operating on ammonia with the addition of hydrogen. METHODS: The object of the study was a modern automobile and tractor diesel engine YaMZ-53415. The calculations were carried out for the nominal operating mode of the engine. For three-dimensional modeling of the working process of a gas-diesel engine running on ammonia with the addition of hydrogen, the Ansys Forte software package was used, which was developed based on modern theoretical concepts of the physics of three-dimensional gas and liquid flows, fuel spray dynamics and combustion processes. RESULTS: Calculation of the working process of a dual-fuel engine running on ammonia with different ignition doses of diesel fuel showed that when the dose of diesel fuel is reduced from 100% to 5%, the engine power and efficiency are maintained, the maximum pressure in the cylinder is reduced by 26%, nitrogen oxide emissions and the amount of unburned ammonia increase. Calculation of the working process of a dual-fuel engine running on ammonia with hydrogen additive allowed us to determine the minimum hydrogen additive that ensures complete combustion of ammonia. CONCLUSIONS: Running a dual-fuel engine on ammonia results in a significant reduction in carbon dioxide emissions, more than an order of magnitude, i.e. ammonia can become an alternative to hydrocarbon fuel to achieve carbon neutrality. The use of a small hydrogen additive — 0.4% allows to significantly increase the combustion rate of the ammonia-air mixture and ensures almost complete combustion of ammonia. Nitrogen oxide emissions when replacing diesel fuel with ammonia increase more than twice. To reduce them, it is necessary to use known methods - exhaust gas recirculation, SCR-neutralizer.

Impact of Gas Diffusion Layer Compression on Electrochemical Performance in Proton Exchange Membrane Fuel Cells: A Three-Dimensional Lattice Boltzmann Pore-Scale Analysis.

Proton exchange membrane fuel cells (PEMFCs) are being pursued for applications in the maritime industry to meet stringent ship emissions regulations. Further basic research is needed to improve the performance of PEMFCs in marine environments. Assembly stress compresses the gas diffusion layer (GDL) beneath the ribs, significantly altering its pore structure and internal transport properties. Accurate evaluation of the PEMFC cathode's electrochemical performance at the pore scale is critical. This study employs a three-dimensional multicomponent gas transport and electrochemical reaction lattice Boltzmann model to explore the complex interplay between GDL compression and factors such as overpotential, pressure differential, porosity, and porosity gradient on PEMFC performance. The findings indicate that compression accentuates the reduction in oxygen concentration along the flow path and diminishes the minimum current density. Furthermore, compression exacerbates the reduction in current density under varying pressure conditions. Increased local porosity near the catalyst layer (CL) enhances oxygen accessibility and water vapor exclusion, thereby elevating the mean current density. Sensitivity analysis reveals a hierarchy of impact on mean current density, ranked from most to least significant: overpotential, porosity, compression, porosity gradient, and pressure difference. These insights into the multicomponent gas transfer dynamics within compressed GDLs inform strategic structural design enhancements for optimized performance.

3D Gap opening in non-ideal MHD protoplanetary disks: Asymmetric accretion, meridional vortices, and observational signatures

Abstract Recent high-angular resolution ALMA observations have revealed rich information about protoplanetary disks, including ubiquitous substructures and three-dimensional gas kinematics at different emission layers. One interpretation of these observations is embedded planets. Previous 3-D planet-disk interaction studies are either based on viscous simulations, or non-ideal magnetohydrodynamics (MHD) simulations with simple prescribed magnetic diffusivities. This study investigates the dynamics of gap formation in 3-D non-ideal MHD disks using non-ideal MHD coefficients from the look-up table that is self-consistently calculated based on the thermo-chemical code. We find a concentration of the poloidal magnetic flux in the planet-opened gap (in agreement with previous work) and enhanced field-matter coupling due to gas depletion, which together enable efficient magnetic braking of the gap material, driving a fast accretion layer significantly displaced from the disk midplane. The fast accretion helps deplete the gap further and is expected to negatively impact the planet growth. It also affects the corotation torque by shrinking the region of horseshoe orbits on the trailing side of the planet. Together with the magnetically driven disk wind, the fast accretion layer generates a large, persistent meridional vortex in the gap, which breaks the mirror symmetry of gas kinematics between the top and bottom disk surfaces. Finally, by studying the kinematics at the emission surfaces, we discuss the implications of planets in realistic non-ideal MHD disks on kinematics observations.

Neural operators for hydrodynamic modeling of underground gas storage facilities

Objectives. Much of the research in deep learning has focused on studying mappings between finite-dimensional spaces. While hydrodynamic processes of gas filtration in underground storage facilities can be described by partial differential equations (PDE), the requirement to study the mappings between functional spaces of infinite dimension distinguishes this problem from those solved using traditional mapping approaches. One of the most promising approaches involves the construction of neural operators, i.e., a generalization of neural networks to approximate mappings between functional spaces. The purpose of the work is to develop a neural operator to speed up calculations involved in hydrodynamic modeling of underground gas storages (UGS) to an acceptable degree of accuracy.Methods. In this work, a modified Fourier neural operator was built and trained for hydrodynamic modeling of gas filtration processes in underground gas storages.Results. The described method is shown to be capable of successful application to problems of three-dimensional gas filtration in a Cartesian coordinate system at objects with many wells. Despite the use of the fast Fourier transform algorithm in the architecture, the developed model is also effective for modeling objects having a nonuniform grid and complex geometry. As demonstrated not only on the test set, but also on artificially generated scenarios with significant changes made to the structure of the modeled object, the neural operator does not require a large training dataset size to achieve high accuracy of approximation of PDE solutions. A trained neural operator can simulate a given scenario in a fraction of a second, which is at least 106 times faster than a traditional numerical simulator.Conclusions. The constructed and trained neural operator demonstrated efficient hydrodynamic modeling of underground gas storages. The resulting algorithm reproduces adequate solutions even in the case of significant changes in the modeled object that had not occurred during the training process. The model can be recommended for use in planning and decision-making purposes regarding various aspects of UGS operation, such as optimal control of gas wells, pressure control, and management of gas reserves.

Elucidating 3D Water Distributions in PEM Water Electrolyzers Via Neutron Imaging

A key challenge in polymer electrolyte membrane (PEM) water electrolysis stems from product oxygen bubble accumulation in the titanium (Ti) porous transport layer (PTL), which limits hydrogen production at high current densities. To design the next generation of PTLs with efficient porous structures that enhance bubble removal, obtaining three-dimensional (3D) water and gas distributions in an operating electrolyzer is critical. Previous works have demonstrated that neutron [1,2] and X-ray [3] imaging techniques can be used to quantify gas and water content, but capturing these phenomena with 3D imaging remains a challenge due to low transmission through metallic cell hardware, limitations in spatial and temporal resolutions, and low contrast between reactant water and product gas bubbles.In this work, we used the high flux neutron beam at the NeXT instrument of the Institut Laue-Langevin to perform operando radiography during electrolysis and to acquire tomography scans of the steady-state water and gas distributions. We designed a custom PEM electrolysis cell with a Ti PTL and serpentine flow field design for neutron radiography and tomography to reveal the water distribution and its evolution in the PTL. To correlate electrochemical losses to reactant distributions, polarization curves and EIS measurements were acquired. Operando radiography was employed to reveal changes in water distributions over time with increasing current density. Additionally, to elucidate the steady-state water and gas distributions at a variety of current densities, neutron tomography was utilized. Within our analysis, we reveal the impact of water and bubble distributions through the PTL on activation, ohmic, and mass transport overpotentials, particularly at the PTL and catalyst layer interface. The insights provided will aid in identifying performance degradation mechanisms and desirable reactant distributions for the next generation of PTL design. References J. K. Lee et al., Energy Convers Manag, 226, 113545 (2020)CH. Lee et al., J Power Sources, 446, 227312 (2020)S. De Angelis et al., J Mater Chem A Mater, 9, 22102–22113 (2021)

Spatio-temporal and multi-mode prediction for blast furnace gas flow

Spatio-temporal and multi-mode prediction for blast furnace gas flow

Compressed sensing reconstruction for high-SNR, rapid dissolved 129Xe gas exchange MRI.

Three-dimensional hyperpolarized 129Xe gas exchange imaging suffers from low SNR and long breath-holds, which could be improved using compressed sensing (CS). The purpose of this work was to assess whether gas exchange ratio maps are quantitatively preserved in CS-accelerated dissolved-phase 129Xe imaging and to investigate the feasibility of CS-dissolved 129Xe imaging with reduced-cost natural abundance (NA) xenon. 129Xe gas exchange imaging was performed at 1.5 T with a multi-echo spectroscopic imaging sequence. A CS reconstruction with an acceleration factor of 2 was compared retrospectively with conventional gridding reconstruction in a cohort of 16 healthy volunteers, 5 chronic obstructive pulmonary disease patients, and 23 patients who were hospitalized following COVID-19 infection. Metrics of comparison included normalized mean absolute error, mean gas exchange ratio, and red blood cell (RBC) image SNR. Dissolved 129Xe CS imaging with NA xenon was assessed in 4 healthy volunteers. CS reconstruction enabled acquisition time to be halved, and it reduced background noise. Median RBC SNR increased from 6 (2-18) to 11 (2-100) with CS, and there was strong agreement between CS and gridding mean ratio map values (R2 = 0.99). Image fidelity was maintained for gridding RBC SNR > 5, but below this, normalized mean absolute error increased nonlinearly with decreasing SNR. CS increased the mean SNR of NA 129Xe images 3-fold. CS reconstruction of dissolved 129Xe imaging improved image quality with decreased scan time, while preserving key gas exchange metrics. This will benefit patients with breathlessness and/or low gas transfer and shows promise for NA-dissolved 129Xe imaging.

Three-dimensional numerical simulations and experimental studies on the viscoelastic rheological and deformation behavior of polymer catheter in gas-assisted extrusion processing

Gas-assisted extrusion is an effective method for improving the deformation behavior of polymer catheters during extrusion. However, the underlying mechanisms that dictate how geometrical and constitutive models influence the complex rheological behavior of the melt are not yet fully understood, which hinders further utilization and optimization. In this study, the three-dimensional (3D) gas–liquid–gas model for catheter gas-assisted extrusion was constructed. Subsequently, the Bird–Carreau model and the Phan–Thien–Tanner (PTT) model were employed in finite element numerical simulations to analyze the complex behavior. For comparative analysis, simplified two-dimensional (2D) model numerical simulations were also conducted. Additionally, experiments on catheter gas-assisted extrusion and parameterization studies of key constitutive model parameters were performed. The findings indicate that the 3D model, when integrated with the PTT constitutive model, demonstrates superior predictability and aligns more closely with experimental results. Furthermore, as the flow rate increases, discrepancies among different models diminish, and the distance required for the melt and gas to achieve motion equilibrium decreases. The internal mechanisms behind these phenomena are elucidated through the analysis of velocity and stress field distributions. This research enhances our understanding of the complex rheological behavior in polymer catheter gas-assisted extrusion, providing valuable insights for both academic research and industrial production in this field.

Secondary air induced flow structures and their interplay with the temperature field in fixed bed combustors

Air staging in solid fuel combustion features widely in small scale domestic boilers to large scale moving grate combustors. Whilst the effects of air staging on the combustion characteristics of these systems are generally known, there is very little insight available into the role of secondary air on the flow and temperature field in the freeboard of batch-type fixed bed biomass combustors. Three-dimensional gas phase simulations using the Transition 𝑘kl-𝜔 and Finite Rate/Eddy Dissipation models were validated against freeboard temperatures and emissions (CO2 and O2) measured on the same set-up. Results show that secondary air at Qs/Qt ≥0.25 induces two recirculation zones, upstream and downstream of its injection point with maximum freeboard temperatures generally observed around these recirculation zones, if Qs/Qt drops to 0.12-0.18 only an upstream recirculation zone is observed until it diminishes by Qs/Qt = 0.06. However, there is a trade-off caused by what appears to be a cooling effect if Qs/Qt is increased between 0.25 and 0.71. Modelling results show that in reacting cases, unlike non-reacting modelling on the same geometry, the strength of the secondary air induced upstream recirculation zone appears significantly stronger.

Three-dimensional vortex and gas entrainment analysis in rotating liquid flow with a free surface

Three-dimensional vortex and gas entrainment analysis in rotating liquid flow with a free surface

Three-dimensional particle-scale investigation of transient gas–solid flow characteristics in the propulsion system with a complex charge structure

This work is focused on researching the particle behavior of the transient gas–solid flow in the propulsion system with the modular charge structure, which has a great effect on the temporal-spatial distribution of energy release. Based on the coupling method of computational fluid dynamics and the discrete element method, an efficient three-dimensional unsteady gas–solid model is developed to provide a detailed means of capturing particle behavior in the propulsion system with a complex structure. Comparisons of the particle distribution of simulation results are done with experimental research, and a reasonable match has been obtained. Furthermore, the particle behavior characteristics can be divided into three stages. In the first stage, the particle behavior is dominated by the high-pressure, high-speed gas from the igniter. In the other two stages, the particle behavior is dominated by the complex gas flow generated by the opening of the module and the groove structure of the vehicle. The results show that the distribution of particles consists of slope accumulation and horizontal accumulation. The slope accumulation with a large gradient contains 84% of the total particles, and the height of the slope accumulation is increased exponentially along the axis.

Impurity in a zero-temperature three-dimensional Fermi gas

Impurity in a zero-temperature three-dimensional Fermi gas

Analysis of the effect of probe structure on sampling accuracy in supersonic airflow

The accuracy of the sampling of the gas components has a significant impact on the measurement of various performance parameters in the combustion chamber of an aero-engine. This paper examines the accuracy of a six-point gas sampling probe when used in supersonic airflow. A numerical simulation method of component transport and fluid-solid coupling is employed to construct a three-dimensional probe multi-component gas flow characteristic solution model. Three kinds of probes with 28°, 30° and 32° angles and structure-modified conical probes were established, and the influence law of probe structure on gas sampling accuracy was analyzed. The results of the study demonstrate that the 28° and structurally modified conical probes yield a more effective improvement in sampling accuracy in comparison to the original 30° structure. The test data of the test bench are in good agreement with the simulation results, thereby demonstrating the reliability and accuracy of the sampling probe following structural modification.

Analysis of the Effect of Sampling Probe Geometry on Measurement Accuracy in Supersonic Gas Flow

The accuracy of sampling of gas components has a significant impact on the measurement of various performance parameters in the combustion chamber of an aero-engine. In order to investigate the effect of the probe geometry of a six-point gas sampling probe on sampling accuracy in supersonic gas flow, a three-dimensional probe gas flow characteristic solution model is established through numerical simulation methods of components of transport and fluid–solid coupling. Probes with three angles of 28°, 30°, and 32° and an optimized conical probe are constructed. The sampling accuracy of the probes with different geometries is compared and evaluated by the deviation of the component volume fraction before and after sampling and the resulting combustion efficiency error. This paper presents a set of calculation methods for solving the relative deviation of volume fraction by an iterative method based on the ideal gas law and the Redlich–Kwong equation (R-K equation). The method is designed to solve the exact component volume fraction problem in the simulation calculation. The study results demonstrate that the 28° and optimized conical probes improve sampling accuracy more effectively than the original 30° structure. The deviation of the volume fractions of the two structures is less than 1.7%, and the combustion efficiency error is less than 0.09%. The developed iterative calculation method can significantly reduce the theoretical calculation error to less than 0.06%. The experimental data of the test bench are in good agreement with the simulation results, thereby demonstrating the reliability and accuracy of the sampling probe following structural optimization.

Study on the Application of Comprehensive Gas Control Technology for Source-Separated Three-Dimensional Gas Extraction in Large Mining Faces.

In order to address the challenges of high gas outburst in both the adjacent layers and the coal seam itself faced by large mining faces, a study on the three-dimensional extraction of gas from different sources at a large mining face was conducted. Based on the research on the instability and failure characteristics of the overlying strata during mining and the gas outburst characteristics at the large mining face, a source-separated three-dimensional gas extraction system was established. A comprehensive gas management model for the large mining face, involving the extraction of gas from different sources, has been proposed. This model is suitable for gas management at large mining faces where there is a high gas emission in the adjacent layers and a complex structure of the coal seam. Through numerical simulations using FLAC3D, the height of the "three zones" of the overlying strata and the range of the floor fracture zone at the large mining face were obtained, providing guidance for the layout of high-level drainage roadway, low-level drainage roadway, and floor drainage roadways. Following the coordinated layout of high-level drainage roadway, inclined high-level drainage roadway, and low-level drainage roadway, the reasonable optimization of gas extraction techniques in the coal seam, and the reasonable arrangement of floor rock predrainage roadways, the methane capture efficiency of the large 15115 mining face reached 87.5%. The methane concentrations at the upper corner and in the return airflow being below 0.8%. The methane concentration extracted from the coal seam boreholes is 2.9 times higher than that from the ordinary mining face after adopting "ordinary boreholes + large-diameter boreholes". This gas management model effectively addresses the gas-related challenges of the large mining face and improves the gas extraction rate, achieving harmonious mining and extraction of coal and methane.

Investigation on the pressure pulsation characteristics in a twin-screw multiphase pump

A three-dimensional gas–liquid two-phase transient numerical model for a twin-screw multiphase pump based on dynamic grid technology was established and validated with experiments. The pump's simulated pressure distributions, velocity fields, and pressure pulsations were analyzed to reveal the mechanisms of pressure transmission and pressure pulsation characteristics. The results indicated that the flow rate of the pump fluctuated twice due to the discharge of the male and female rotors in one cycle. As the inlet gas volume fractions increased, the flow rate decreased, but the pressure pulsations increased. At the engaging positions of the two rotor tips, a sudden pressure drop happened due to the combined effect of both tooth-tip and tooth-flank leakage. When the discharge port opened, the backflow happened; the flow rate and the pressure in the discharge chamber decreased, but the pressure in the working and suction chambers increased. When the suction port closed, a slight compression of the fluid in the low-pressure working chamber occurred, causing a pressure increase in the working chamber. The working chambers inhaled and discharged once in one cycle, so the first harmonic of pressure pulsations at the suction and discharge chamber was two times the running speed. The transient flow due to the simultaneous closing and opening of the suction and discharge ports at both sides of the male and female rotors generated a harmonic of four times the running speed. This study would help to improve the operational stability of twin-screw multiphase pumps.

GaN-based E-mode p-FETs with polarization-doped p-type graded AlGaN channels

Herein, a novel enhancement-mode (E-mode) GaN-based p-channel FETs (p-FETs) with a linearly graded AlGaN (LGA) p-channel is proposed and numerically studied by Silvaco TCAD. Thanks to strong polarization-induced doping, three-dimensional hole gas (3DHG) can be uniformly generated in LGA to form a continuous p-channel with a hole concentration over 1018 cm–3. Combined with an optimized recessed gate structure, the LGA p-FET can simultaneously achieve a large threshold voltage (|V TH|) > 2 V and a high current density (|J DS|) of ∼10 mA mm−1 at V DS = −10 V. Additionally, two critical parameters of the LGA p-FETs, i.e. the depth of recessed gate and initial Al composition of LGA, are specifically studied to reveal the unique carrier behavior of 3DHG in the devices. Importantly, the LGA structure is further optimized and implemented as the p-type cap layer to construct an E-mode GaN n-FET. Thereby, based on the same LGA configuration, a GaN-based inverter with the matched complementary n- and p-FETs is monolithically constructed, showing sharp voltage transition. The reported novel LGA structure and its availability in both GaN-based E-mode n- and p-FETs provides valuable insights and guidance to construct highly efficient GaN p-type devices and All-GaN-based integrated circuits for compact power electronic systems.