Gas Transport Characteristics Research Articles

Gas mass transfer characteristics in shales: Insights from multiple flow mechanisms, effective viscosity, and poromechanics

Accurate characterization of gas transport behavior is indispensable for successful shale gas reservoir development. In this study, a fractal-theory-based apparent permeability (AP) model is developed to better characterize real gas mass transfer in shales. The proposed model involves multi-scale organic matter (OM) and inorganic matter (IOM) flow channels and incorporates poromechanics-related dynamic pore size, multiple gas transport mechanisms, and dynamic viscosity. The discrete integration method (DIM) is employed to address viscosity changes during fractal scaling up. Experimental data, molecular dynamics simulations, and published theoretical models were used to verify the proposed model and reasonable agreements have been achieved. Results indicate that as the pore pressure and size increase, dominant mechanisms for gas transport change from surface diffusion at low pressure (lower than switch pressure) to viscous flow at higher pressure and larger pore sizes. Furthermore, higher organic matter content makes the permeability curve more similar to OM type. Ignoring effective viscosity results in underestimation of permeability, which is more noticeable when pressure rises and pore shrinks. Poromechanical properties primarily affect pore size, larger elastic modulus and smaller Poisson's ratio leads to significantly lower permeability. The real gas effect on AP reduction cannot be ignored, especially at high pressure. This work provides insights into the gas transport characteristics in shales, which have practical implications for shale gas reservoir simulation and development.

Preparation and characterisation of heat‐resistant fluorinated co‐polyimides and their gas transport characteristics

A series of fluorinated co-polyimide films based on the 6FDA-FTPPA/BAFL backbone were prepared from 4-(3-fluoro-4-(trifluoromethyl)phenyl)-2,6-bis(4-aminophenyl)pyridine (FTPPA),commercial 9,9-bis(4-aminophenyl)fluorene (BAFL), and 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), with varying ratios of FTPPA:BAFL units (3:1, 2:1, 1:1, 1:2, and 1:3). Co-polyimides not only exhibit high thermal stability ( Tg > 357°C), good optical properties (λcutoff > 327 nm) and hydrophobicity (contact angle >91.4°), but also favorable solubility properties in both high and low boiling organic solvents. The fractional free volume of the polymers was simulated using molecular mechanics and molecular dynamics and correlated with experimental gas separation data. The presence of bulky groups led to high FFVs (>17.8%) and the formation of large microcavities with diameters ranging from 5.48 to 5.72 Å, which efficiently increased gas permeability. In pure gas permeation experiments, the permeability coefficients of CO2 and He for the 6FDA-FTPPA/BAFL (3:1) film were 41.48 and 79.38 bar, respectively, which were superior to those of commercial Matrimid and Kapton in terms of gas permeability. In especial, the 6FDA-FTPPA/BAFL (1:2) and 6FDA-FTPPA/BAFL (1:3) in co-polyimide membranes exhibited the most attractive separation performance for O2/N2 gas pairs, approaching the 1991 Roberson upper limit.

Analysis of mass transfer characteristics in a planar solid oxide fuel cell with a chaotic flow channel

The flow channel design is crucial for the heat and mass transfer of reactants in a solid oxide fuel cell (SOFC), which ultimately affects the overall performance of the cell. To improve the gas transport characteristics and temperature uniformity, a chaotic flow channel with orthogonal corrugation is adopted for the design of a planar SOFC stack, and the influence of different wave parameters is evaluated. The results show that the chaotic flow channel induces secondary flow through the superposition of orthogonal waves, which reduces the low-oxygen region and enhances the local electrochemical reaction. The output power is improved in the chaotic flow channel by increasing the amplitude or decreasing the wavelength. The output power density with amplitude of 0.3 mm and wavelength of 1.2 mm at 0.5 V is increased by about 25.16 %. Meanwhile, the effective mass transfer coefficient and mass transfer efficiency is enhanced by 148 % and 378 %, respectively. Additionally, the chaotic structure improves the uniformity of oxygen and temperature. This study helps to improve the understanding of the gas transport processes within the flow channel and provides a basis for the design and optimization of SOFC flow channels.

Effect of the Approach to Membrane Gas Transport Characteristics Determination on Gas Separation Process Simulation Results

Effect of the Approach to Membrane Gas Transport Characteristics Determination on Gas Separation Process Simulation Results

A pore network-based multiscale coupled model for rapid permeability prediction of tight sandstone gas

Tight sandstone has multiscale pore structures. Gas transport in tight sandstones involves several length scales and the complicated physics. Gas transport characteristics in tight sandstone can be represented by apparent gas permeability. Microstructure-based accurate and efficient calculation of gas permeability is challenging. By combining CT and SEM images along with statistical analysis, we present a novel pore network-based multiscale coupled model (MCPNM) to rapidly predict the apparent gas permeability. CT images are adopted to extract the large-scale pore network (LPNM) and the clay component, and SEM image is used to get the properties of small-scale pores. Upscaled model (UM) of small-scale pores is built via statistical analysis and then assigned to the clay domains. The LPNM and UM are coupled as MCPNM by the cross-scale connection structure with variable diameter. The pore spaces at several length scales and the flow characteristics in them are included in the MCPNM. We validate the MCPNM by comparing the calculated apparent gas permeability to the results of available multiscale pore network models and the experimental data. Compared with the available multiscale pore network models, MCPNM solves the accuracy/efficiency trade-off of tight gas permeability prediction. The effects of pressure, temperature, and gas type on gas permeability are studied. The MCPNM simplifies the permeability calculation process and can accurately and rapidly predict tight sandstone gas permeability.

Influence of the Approach to Membrane Mass Transfer Characteristics Determination on the Process Simulation Results

In this work, the dependence of the output characteristics determined in the simulation of the gas separation membrane process on the gas transport characteristics of the membrane specified as parameters of the membrane module model has been investigated. The study was carried out on a laboratory setup containing polyphenylene oxide hollow fibres. As a result of this integrated study, including theoretical and experimental approaches, it has been determined that when using the ideal gas transport characteristics obtained for pure gases to simulate the process, the error expressed in achievable concentration of the target component in the product stream ranges from 1.5 to 8.8% compared to the experimentally obtained values for the same module geometry and the same membrane area. This discrepancy can lead both to unattainable targets for the technological line and to an incorrect technical and economic evaluation of the process. Thus, the design of technological lines using mathematical modelling tools should be based on the “effective” gas transport characteristics of the material and/or product obtained for the components of real gas mixtures or simulating real gas mixtures.

Experimental Determination of the Gas Transport Characteristics of Polysulfone and Poly(phenylene oxide) Hollow Fiber Membranes in Relation to Noble Gases

Experimental Determination of the Gas Transport Characteristics of Polysulfone and Poly(phenylene oxide) Hollow Fiber Membranes in Relation to Noble Gases

Gas transport law in inorganic nanopores considering the influence of cross section shape and roughness

To study the gas transport characteristics in rough inorganic nanopores, the effective pore size models of circular and rectangular nanopores are established, considering the influence of the adsorption water film, rock surface roughness, effective stress and the shape of the nanopore section. On this basis, the gas flow patterns are coupled, and the gas transport models in circular and rectangular rough nanopore are established respectively. The effectiveness of this model is verified by comparing it with experimental data and other scholars' models. At the same time, the effects of roughness, cross-sectional shape, cross-sectional aspect ratio, and humidity on gas migration are analyzed. The results indicate that regardless of the cross-sectional shape, an increase in roughness will lead to varying degrees of reduction in the apparent permeability of micro and nano pores. When the pressure is small, the influence of roughness on the gas permeability of rectangular cross-section nanopores is greater than that of circular cross-section nanopores. As the pressure increases, the influence of roughness on the gas permeability of rectangular and circular cross-section nanopores tends to be the same. The influence of roughness on the water saturation of rectangular cross-section nanopores is less than that on circular cross-section nanopores.

Experimental Determination of the Gas Transport Characteristics of Polysuflone and Polyphenyleneoxide Hollow-Fiber Membranes in Relation to Noble Gases

This paper presents an an experimental study of commercially available hollow fiber membranes made of two polymers, polysulfone and polyphenylene oxide. The main objective is to determine the gas transport characteristics of these membranes with respect to air components and noble gases. Therefore, the permeabilities of the membranes for nitrogen, oxygen, helium, argon, xenon and krypton were determined as part of this study. Particular attention is paid to the xenon-containing air mixture, since the problem of capturing medical xenon seems to be an urgent chemical and technological problem due to the high cost of the process of obtaining this gas. In the course of the study, the values of the permeability of two membranes for pure gases were determined and the values of ideal selectivity were calculated. Thus, the membrane permeability values for argon, krypton, and xenon were 20.8, 8.4, and 6.8 GPU for the polysulfone membrane and 19.5, 6.2, and 4.8 GPU for the polyphenylene oxide membrane. It was found that the xenon permeability of these membranes decreases in the case of separation of a gas mixture consisting of oxygen nitrogen and xenon and is 5.9 and 4.1 GPU for polysulfone and polyphenylene oxide, respectively. The dependence of the performance of membrane modules based on polysulfone and polyphenylene oxide on the total area of the membrane has also been established.

Experimental Study on the Effect of CO2 Injection Pressure on the Migration Characteristics and Extraction Effects of Replacement CH4.

To study the effect of CO2 injection pressure on gas migration characteristics and coalbed methane (CBM) extraction, a platform for the experimental replacement of CH4 with CO2 was used to conduct experiments on the replacement of CH4 under different CO2 injection pressures and analyze the gas transport characteristics and CH4 extraction during the experiment. The results reveal that the rate of gas migration out of the coal seam accelerates with increasing gas injection pressure, as determined by comparisons of the migration rates between adjacent monitoring points. The change trend of the CH4 desorption rate under different gas injection pressures is divided into slow decline, sharp decline, and stability stages, and the maximum value of the effective diffusion coefficient increases from 2.3 × 10-5 to 3.4 × 10-5 and 4.6 × 10-5 cm2/s as the gas injection pressure increases from 0.6 to 0.8 and 1.0 MPa. Similarly, the change pattern of coal seam permeability can be divided into slow decline, sharp decline, and stability stages. After the gas injection pressure was increased from 0.6 to 0.8 and 1.0 MPa, the CH4 desorption volume increased from 90.2 to 94.1 and 97.8 L, whereas the coal seam CO2 sequestration volume increased from 269.2 to 274.2 and 322.8 L, respectively. In contrast, the CH4 extraction efficiency increased from 76.9 to 80.2 and 82.9%, respectively. The research results have important reference value and practical significance for optimizing the CO2 injection pressure and improving the CBM extraction.

Filling–adsorption mechanism and diffusive transport characteristics of N2/CO2 in coal: Experiment and molecular simulation

Enhanced coalbed methane (ECBM) is an effective development technology to improve energy utilisation and reduce greenhouse gas emissions by injecting N2/CO2 into coal seams. The process involves the adsorption, desorption, and diffusion of N2/CO2 in multi-scale coal pores. This results in gas storage and transport characteristics limited by the coal's structural distribution of nanoscale pores (≤100 nm). Thus, studying N2/CO2 storage and diffusive transport characteristics in pores at different scales is vital for efficiently implementing N2/CO2-ECBM. This paper performed low-pressure adsorption with N2/CO2 (LPA-N2/CO2) to evaluate coal samples' isothermal adsorption characteristics and pore structure, revealing the dual filling-adsorption mechanism of N2/CO2 in coal. A new coal pore classification method was proposed. Pores (≤50 nm) in coal-N2 or coal-CO2 adsorption systems were classified as inaccessible pores (<0.364 nm or < 0.33 nm), filling pores (0.364–1.65 nm or 0.33–1.36 nm), transition pores (1.65–2 nm or 1.36–1.60 nm), and adsorption pores (>2 nm or > 1.60 nm). Combining the experimental results to construct micropore and mesopore models, molecular dynamics were applied to simulate the loading and migration processes of N2/CO2 in the pore models. Filling, transition, and adsorption pores completed loading gas within 0.1–1 MPa, 1–5 MPa and 5–10 MPa in that order, visualising the gas filling-adsorption process in coal. Then, the adsorption capacity of N2 was controlled by the pore size and adsorption pressure, while CO2 was mainly influenced by adsorption pressure.

Experimental and Numerical Investigation of the Characteristics of Novel Disc Turbines in Aerated Stirred Tanks

In this work, the gas dispersion and transport characteristics of three different disc turbines, namely, parabolic disc turbine (PDT), novel swept-back parabolic disc turbine (SPDT), and staggered fan-shaped parabolic disc turbine (SFPDT), are characterized by experiments and two-fluid model/RANS simulations. The physical explanation of the superior power characteristics of SFPDT and SPDT is elaborated using the pressure distribution and drag force coefficient on a blade surface. Gas–liquid performance parameters such as critical dispersion speed, relative power demand (RPD), and volumetric mass transfer coefficient are assessed under different conditions. The results show that SFPDT and SPDT can produce smaller flow separation regions and trailing vortices, resulting in smaller gas cavities under aeration conditions. SFPDT has the lowest critical dispersion speed under a high flow rate, while SPDT consumes the least power. Both SFPDT and SPDT exert roughly 7% higher gassed power input than PDT under aeration conditions and have higher efficiency on gas–liquid mass transfer than PDT. Moreover, empirical correlations from experimental data for SFPDT and SPDT are presented to provide a reference to the design of industrial stirred tanks.

Investigation of DC and RF characteristics of spacer layer thickness engineered recessed gate and field‐plated III‐nitride nano‐HEMT on β‐Ga2O3 substrate

AbstractIn this work, a field plated recessed gate III‐nitride HEMT on β‐Ga2O3 substrate is proposed using AlN spacer between AlGaN and GaN layers. The two‐dimensional electron gas (2DEG) transport characteristics, input/output, and RF characteristics of the proposed HEMT with AlN spacer layer of different thickness (1, 2, 3, 4, and 5 nm) are numerically simulated and compared with HEMT without spacer layer. The 2DEG, which is created at the junction of AlGaN/GaN, plays a crucial role in the operation of GaN HEMTs. With the help of AlN as spacer layer between AlGaN and GaN, an augmented 2DEG concentration is accomplished owing to its large conduction band offset, high polarization effect, and higher barrier. Additionally, the inclusion of AlN spacer layer shifts the 2DEG density away from interface, resulting minimized interface scattering which results into greater mobility. The HEMT exhibited a mobility of 1261 cm2/Vs, threshold voltage of −0.45 V, drain current of 1.12 A/mm, breakdown voltage of 149 V, and excellent RF characteristics, that is, cut‐off frequency (maximum oscillation frequency) of 384 GHz (546 GHz) using 2‐nm AlN spacer layer. The proposed III‐nitride HEMT on β‐Ga2O3 substrate with 2‐nm AlN spacer can be used for RF/microwave and high‐power nanoelectronics applications.

Enhancing CO2 permeation features of PEBAX-based membrane via incorporating MgO nanoparticles in its polymeric matrix

Although polymeric membranes have been extremely applied in different gas separations, improving their permeability-selectivity data is still challenging. This goal encouraged the authors to fabricate a new nanocomposite membrane (NCM) composed of poly(ether-block-amide)− 1657 (PEBAX) and magnesium oxide (MgO) nanofillers for CO2/CH4 separation. The influence of various loadings of the nanoparticles (2, 4, 6, and 8 wt%) on gas (CO2 and CH4) transport characteristics of PEBAX-based nanocomposite membranes was investigated at pressure and temperature ranges of 3–15 bar and 25–55 °C, respectively. The pristine and NCMs were fabricated via solution casting, followed by the solvent evaporation method, and characterized by different analyses (FESEM, FT-IR, XRD, and TGA). The observed experimental outcomes showed that adding MgO nanofillers into the PEBAX polymeric structure improves the performance of the produced NCMs for the CO2/CH4 separation. The permeability of CO2 and the ideal selectivity of CO2/CH4 for 8 wt% of MgO-embedded NCM are 83.29 Barrer and 25.32, whereas those quantities, in the absence of nanoparticles, are 64.66 Barrer and 21.84.

Review of Shale Gas Transport Prediction: Basic Theory, Numerical Simulation, Application of AI Methods, and Perspectives

The gas transport mechanism in shale reservoirs is extremely complex and is a typical multiscale and multiphysics coupled transport process, considering the complex shale rock structure, wide distribution of micropores and nanopores in shale gas reservoirs, diverse gas occurrence forms, and large pore size spans. An accurate understanding of the shale gas transport process and mechanism is important for effective exploration of shale gas reservoirs. In this work, a review of the recent progress in the prediction of shale gas transport in porous media is presented. The basic theory of gas transport in nanopores is discussed. The gas transport in organic and inorganic matter and the gas adsorption effect are covered. Then, gas transport simulations with conventional multiscale numerical methods, including molecular dynamics and lattice Boltzmann simulations, are reviewed, and the multiscale modeling methods are discussed. Furthermore, the application of artificial intelligence (AI) methods in shale gas transport research is discussed. The focus is on the characterization of the shale porous geometry, including porosity, tortuosity, pore size distribution, and reconstruction of the shale porous medium. The application of AI-based methods such as neural networks and machine learning for the prediction of porous flow properties is discussed. This study intends to provide a comprehensive review of shale gas transport characteristics and to enable the accessibility of AI tools in the research of shale gas.

Numerical Study of High-Temperature Gas Transport Characteristics During the Continuous Welding Process

Numerical Study of High-Temperature Gas Transport Characteristics During the Continuous Welding Process

Practical Manufacturing of Asymmetric Hollow Fiber Membranes for Gas Separation Made of Poly(2,6-dimethylphenylenoxide-1,4)

The regularities of manufacturing of hollow fiber membranes made of poly(2,6-dimethylphenylene oxide-1,4) for gas separation were studied. The phase inversion method was used to manufacture the membranes. The dependence of the separation characteristics of the membrane on such spinning parameters as the type of solvent, the exposure time of the polymer solution in the “air” gap, and the type of non-solvents (coagulants) has been studied. The characteristics of the membrane were obtained by determining their gas permeability. It is shown that higher separation and gas transport characteristics of the PPO membrane are obtained using the wet spinning method. An intrinsic selectivity of 4.8 ± 0.4 was obtained at a specific oxygen permeability (20°C) – (P/l) 790 ± 82 [m3 (s.t.p.) m–2 s–1 kPa] for oxygen–nitrogen system. The developed membranes are promising for use in case for producing nitrogen and oxygen-enriched air.

Performance of amine‐functionalized MIL‐53 incorporated thin‐film nanocomposite Pebax membranes for CO2/CH4 mixed gas separation

AbstractIn the present paper, the gas transport characteristics of amine‐functionalized MIL‐53 metal–organic frameworks (MOFs) integrated thin‐film nanocomposite (TFN) Pebax 2533 membranes dip‐coated over a polysulfone (PSF) layer were studied. Various characterization methods were used to investigate the impact of ligand functionalization by NH2 on the characteristics of the generated TFN membranes and their gas transport properties, including TGA, FESEM, BET, gas adsorption tests, and a series of CO2/CH4 mixed gas separation tests. According to the FESEM pictures, the NH2‐MIL 53(Al) particles were well distributed in the TFN membranes, with no apparent agglomeration, The gas adsorption experiment of NH2‐MIL 53(Al) particles showed that they adsorb CO2 selectively. The incorporation of NH2‐MIL 53(Al) into TFN membranes led to improved CO2/CH4 selectivity and increased gas permeability. In addition, CO2/CH4 selectivity and CO2 permeability of the CO2/CH4 mixed gas were enhanced from 11.05 to 26.55 and from 111.6 to 260.2 Barrer, respectively, when NH2‐MIL 53(Al) 20 wt% was added to the TFN membrane. In the CO2/CH4 mixed gas experiment, increasing the temperature from 30 to 50°C increased the permeability of both CH4 and CO2 while decreasing the CO2/CH4 selectivity. Furthermore, the performance of the prepared membranes was assessed at different feed pressures ranging from 4 to 8 bar. As the feed pressure increased, the CO2/CH4 separation improved. Also, with pure gas, the increase in NH2‐MIL53(Al) loading resulted in lower diffusivity selectivity amounts for the TFN membrane than for the pristine TFN, and solubility selectivity was enhanced from 5 to 20 wt% and was reduced to 25 and 30 wt% in the TFN, respectively. In the present study, the best results were obtained at 6 bar pressure, 30°C temperature, and 20 wt% loading of NH2‐MIL53(Al).

A molecular simulation study on amine-functionalized silica/polysulfone mixed matrix membrane for mixed gas separation

Polysulfone (PSF) based mixed matrix membranes (MMMs) are one of the most broadly studied polymeric materials used for CO2/CH4 separation. The performance of existing PSF membranes encounters a bottleneck for widespread expansion in industrial applications due to the trade-off amongst permeability and selectivity. Membrane performance has been postulated to be enhanced via functionalization of filler at different weight percentages. Nonetheless, the preparation of functionalized MMMs without defects and its empirical study that exhibits improved CO2/CH4 separation performance is challenging at an experimental scale that needs prior knowledge of the compatibility between the filler and polymer. Molecular simulation approaches can be used to explore the effect of functionalization on MMM's gas transport properties at an atomic level without the challenges in the experimental study, however, they have received less scrutiny to date. In addition, most of the research has focused on pure gas studies while mixed gas transport properties that reflect real separation in functionalized silica/PSF MMMs are scarcely available. In this work, a molecular simulation computational framework has been developed to investigate the structural, physical properties and gas transport behavior of amine-functionalized silica/PSF-based MMMs. The effect of varying weight percentages (i.e., 15–30 wt.%) of amine-functionalized silica and gas concentrations (i.e., 30% CH4/CO2, 50% CH4/CO2, and 70% CH4/CO2) on physical and gas transport characteristics in amine-functionalized silica/PSF MMMs at 308.15 K and 1 atm has been investigated. Functionalization of silica nanoparticles was found to increase the diffusion and solubility coefficients, leading to an increase in the percentage enhancement of permeability and selectivity for amine-functionalized silica/PSF MMM by 566% and 56%, respectively, compared to silica/PSF-based MMMs at optimal weight percentage of 20 wt.%. The model's permeability differed by 7.1% under mixed gas conditions. The findings of this study could help to improve real CO2/CH4 separation in the future design and concept of functionalized MMMs using molecular simulation and empirical modeling strategies.

Sorption and Gas Transport Characteristics of Polyimides Based on a Mixture of Diethyl Toluene Diamine Isomers

The transport of oxygen, nitrogen, and hydrocarbons C1–C4 in polyimides based on 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and biphenyl-3,3',4,4'-tetracarboxylic acid dianhydride (BPDA) and diethyl toluene diamine (DETDA) has been studied. The dependences of the diffusion coefficient on the diffusant effective diameter and the solubility coefficients on the Lennard–Jones potential of pair interaction have been considered. It is shown that the diffusion coefficients of butane are out of the linear dependence of the logarithm of the diffusion coefficient on the square of the effective diameter of the diffusant, which may indicate the plasticization of polymers with butane at a pressure of 1 atm. The permeability of mixtures of gases O2–N2 (29 : 71 v/v) and CO2–CH4 (62 : 38 v/v) has been studied. There are no significant differences in the gas separation parameters in comparison with the experiment for individual gases; however, for a mixture of CO2–CH4, a slight increase in the separation factor has been found as compared to the ideal selectivity. The data on the measurement of sorption isotherms and solubility coefficients O2, N2, and CH4 are also presented in the article. Gas solubility coefficients have been found to be close to the values obtained indirectly as P/D.