Gas Diffusion Coefficient Research Articles

Measurements of Drying and Wetting Gas Diffusion Coefficients and Gas Permeability of Unsaturated Soils Using a New Flexible-Wall Device

Measurements of Drying and Wetting Gas Diffusion Coefficients and Gas Permeability of Unsaturated Soils Using a New Flexible-Wall Device

Prediction and Simulation of Biodiesel Combustion in Diesel Engines: Evaluating Physicochemical Properties, Performance, and Emissions

Environmental and energy sustainability concerns have catalyzed a global transition toward renewable biofuel alternatives. Among these, biodiesel stands out as a promising substitute for conventional diesel in compression-ignition engines, providing compatibility without requiring modifications to engine design. A comprehensive understanding of biodiesel’s physical properties is crucial for accurately modeling fuel spray, atomization, combustion, and emissions in diesel engines. This study focuses on predicting the physical properties of PODL20 and EB100, including liquid viscosity, density, vapor pressure, latent heat of vaporization, thermal conductivity, gas diffusion coefficients, and surface tension, all integrated into the CONVERGE CFD fuel library for improved combustion simulations. Subsequently, numerical simulations were conducted using the predicted properties of the biodiesels, validated by experimental in-cylinder pressure data. The prediction models demonstrated excellent alignment with the experimental results, confirming their accuracy in simulating spray dynamics, combustion processes, turbulence, ignition, and emissions. Notably, significant improvements in key combustion parameters, such as cylinder pressure and heat release rate, were recorded with the use of biodiesels. Specifically, the heat release rates for PODL20 and EB100 reached 165.74 J/CA and 140.08 J/CA, respectively, compared to 60.2 J/CA for conventional diesel fuel. Furthermore, when evaluating both soot and NOx emissions, EB100 displayed a more balanced performance, achieving a significant reduction in soot emissions of 34.21% alongside a moderate increase in NOx emissions of 45.5% compared to diesel fuel. In comparison to PODL20, reductions of 20.4% in soot emissions and 3% in NOx emissions were also noted.

Estimation of gas diffusion coefficient for gas/oil-saturated porous media systems by use of early-time pressure-decay data: An experimental/numerical approach

This paper presented a novel numerical method for estimating the gas diffusion coefficient based on the early-time pressure-decay data. Experimentally, “flooding–soaking” procedures were developed to perform the gas diffusion in an oil-saturated tight core under different gas phase volume conditions. After flooding, the capillary bundle model was used to calculate the oil–gas contact area. The early-time pressure-decay data of the gas phase were monitored and recorded during the soaking process. Theoretically, a non-equilibrium inner boundary condition coupled with the characteristics of experimental early-time pressure had been incorporated to develop a diffusion model for a gas/oil-saturated tight core system. Based on gas-phase mass balance equations and gas equation of state, the diffusion coefficients were optimized once the discrepancy between experimental data and numerical solutions was minimized. According to the estimated results in this study, the CH4 diffusion coefficients were 3.74 × 10−11 and 3.86 × 10−11 m2/s in tight core saturated with crude oil, respectively. Moreover, the oil–gas contact area significantly impacts the diffusion flux in oil-saturated porous media. Specifically, an additional 10% contact area results in a 75% increase in CH4 diffusion mass. In addition, with the application of our proposed model to CH4/bitumen and CO2/bitumen systems, the diffusion coefficients were in close agreement with the results reported in previous literature, indicating that the proposed model was applicable to both gas/liquid and gas/liquid-saturated porous media systems.

Simulation method of heat-mass transfer between hot wind and wet coating in the manufacturing process of pole piece

In order to improve the complex numerical calculation process for wet coating of pole piece, a three-dimensional numerical model of heat-mass transfer characteristics is established between hot wind and wet coating based on multi-field coupling theory of porous media and meshless parallel method, and its reliability is verified through literature data. Meanwhile, the difference calculation method and evaluation process are proposed for heat-mass transfer characteristics to solve this numerical model. The results show that the maximum errors are less than 14.7 % for this model. In addition, a scale modeling method is proposed to improve computational efficiency based on similarity theory. Meanwhile, the influences of different scale factors on temperature and humidity parameters are analyzed for wet coating. The results show that this method is accurate and reliable because the determination coefficient R2 of all parameters is more than 0.99. Meanwhile, compared with the calculation time of original model, the calculation efficiency increases by 44.6 % for the model with scale factor selected as 800. Finally, the variation and distribution of internal parameters are analyzed for wet coating during pore emptying process based on above simulation method. The results show that the variation trends of liquid film thickness, pore emptying rate, water saturation, gas saturation and effective gas diffusion coefficient are corresponding with the accelerated, uniform and decelerated drying processes of porous media. Meanwhile, the location of four-corner edges for wet coating is the weak link in heat-mass transfer process. Therefore, the heat-mass transfer characteristics for wet coating can be improved by increasing its initial thickness or adjust reasonable drying position in engineering.

A root mucilage analogue from chia seeds reduces soil gas diffusivity

AbstractGas exchange in the soil is determined by the size and connectivity of air‐filled pores. Root mucilage reduces air‐filled pore connectivity and thus gas diffusivity. It is unclear to what extent mucilage affects soil pore connectivity and tortuosity. The aim of this study was to gain a better understanding of gas diffusion processes in the rhizosphere by explaining the geometric alterations of the soil pore space induced by mucilage. We quantified the effect of a root mucilage analogue collected from chia seeds without intrinsic respiratory activity on oxygen diffusion at different water contents during drying–rewetting cycles in a diffusion chamber experiment. Quantification of oxygen diffusion showed that mucilage decreased the gas diffusion coefficient in dry soil without affecting air‐filled porosity. Without mucilage, a hysteresis in gas diffusion coefficient during a drying–rewetting cycle was observed. The effect depended on particle size and diminished with increasing mucilage content. X‐ray computed tomography imaging indicated a hysteresis in the connectivity of the gas phase during a drying–rewetting cycle for samples without mucilage. This effect was attenuated with increasing mucilage content. Furthermore, electron microscopy showed that mucilage structures formed in drying soil increase with mucilage content, thereby progressively reducing the connectivity of the gas phase. In conclusion, the effect of mucilage on soil gas diffusion highly depends on soil texture and mucilage content. The diminishing hysteresis with the addition of mucilage suggests that plant roots secrete mucilage to balance oxygen availability and water content, even under fluctuating moisture conditions.

Huge improved gas separation performance of carbon molecular sieve membrane by forming a double crosslinked polyimide precursor

A vital issue in searching for advanced gas separation membranes is understanding the precursor structure-gas separation properties of carbon molecular sieve (CMS) membranes. Here, we reported two crosslinked polyimides and used as CMS precursors, in which, the DCPI-4 is a double cross-linkable polyimide with 4 % triptycene triamine as a crosslinker (Type I) and COOH group that can be crosslinked at 350 °C by decarboxylation (Type II), whereas the DCPI-0 with COOH (Type II). After pyrolysis at 550 °C, the DCPI-4-CMS showed a higher SBET (812 vs 713 m2g-1), larger ultra-microporosity ratio (26.6 % vs 17.8 %), larger d-spacing (4.08 vs 3.94 Å), less graphitization (sp3/sp2 of 0.156 vs 0.118), 5.5 times higher CO2 permeability (7573 vs 1391 Barrer) and same CO2/CH4 selectivity (∼62) than DCPI-0-CMS. We consider this is due to the type I crosslinking enhances the rigidity of the polyimide backbone, and inhibits the collapse of micropores during the carbonization, which causes improved ultra-microporosity and ultra-micropore ratio that both enhances the gas diffusion and solubility coefficient as well activation energy difference of gas pairs. Conclusively, this double crosslinking method provides a good perspective for achieving CMS membranes with excellent gas separation performance.

Limiting Current Density in Water Vapor-Fed Polymer Electrolyte Membrane Electrolyzers

Polymer electrolyte membrane water electrolyzers (PEMWE) are a critical technology in development for addressing the need for efficient hydrogen production. In order to make hydrogen a cost-effective fuel or industrial feedstock, the overpotentials across the cell needs to be decreased and platinum-group metal loading reduced. Devising novel electrode structures that enable ultra-high current densities at low oxygen evolution reaction (OER) catalyst (e.g. Iridium oxide) loadings is one approach to achieving efficiency and cost targets. One of the overpotentials that needs to be addressed is due to mass transport limitations within the porous transport layer (PTL) and anode catalyst layer, which could be a limiting factor at ultra-high current densities. When operating at ultra-high current densities, the rate of the OER may reach a point at which oxygen gas bubbles fill the pores of the anode catalyst layer PTL, blocking access of liquid water to the anode catalyst layer. Because of this, there is a possibility that the cell will rely on water vapor diffusion through the evolving oxygen gas to deliver the water reactant to the OER catalyst. To assess the limitation of a PEMWE while relying on water vapor diffusion, a commercially manufactured membrane electrode assembly (MEA) was tested by flowing water vapor into the anode as the reactant. With the aim of identifying a limiting current density (LCD) of the electrolyzer under these conditions, potentiostatic polarization curves were obtained for a range of relative humidities (RH) and back pressures. The RH was varied to assess the impact of reactant concentration on the LCD, while the back pressure was varied to identify the impact of the molecular gas diffusion coefficient on the LCD. In this presentation, we will present our analysis of the significance of the water vapor diffusion transport resistance through the pressure-dependent resistance evaluation. Furthermore, we will discuss application of this approach to evaluating the impact of vapor operation on membrane water transport and OER reaction kinetics.

Molecular Dynamics Simulations of Gas Transport Properties in Cross-Linked Polyamide Membranes: Tracing the Morphology and Addition of Silicate Nanotubes.

This study employs molecular dynamics (MD) simulations to fundamentally provide insight into the role of cross-link density in the CO2 separation properties of interfacially polymerized polyamide (PA) membranes. For this purpose, two atomistic models of pure polyamide membranes with different cross-link densities are constructed by MD simulations to conceptually determine how the fractional free volume of polyamide affects the gas separation performance of the membrane. The PA membrane with a lower cross-link density (LCPA) shows a higher gas diffusion coefficient, a lower gas solubility coefficient, and a higher gas permeability than the PA membrane with a higher cross-link density (HCPA). Moreover, the pristine and modified silicate nanotubes (SNTs) as the fast gas transport channels are incorporated into the polyamide membranes to assess the effect of the SNT/PA interface chemistry on the CO2 separation properties of the membranes. SNTs are systematically modified by three modifying agents with different CO2-philic groups and different interfacial interaction energies with the polyamide matrix. The results of MD simulations demonstrate that the incorporation of silicate nanotubes into the PA matrix increases the gas diffusivity and permeability and decreases the CO2/gas selectivity. Moreover, the membranes containing modified SNTs possessing high CO2-philicity and high SNTs/PA interfacial interactions show a high CO2 separation performance.

Investigating hydrodynamics and gas diffusion coefficient in CFB of binary particles with significant differences in particle properties

A composite fluidized bed (SCFB), which integrated the bubbling fluidization and circulating fluidization into one bed, was developed in this work. Wavelet transform was employed to analyze time-series signals of the pressure fluctuations and the steady-state tracer injection technique was used to study the gas diffusion coefficient in SCFB. The energy contribution in BFB and CFB mainly concentrated on the macrostructures, while that in SCFB was caused principally by the mesostructures as gas velocity was high. The circulating particles could effectively reduce particle aggregates and promoted a uniform distribution of heavy particles in the bottom region. Radial dispersion coefficients in SCFB were greater than that in BFB and CFB, demonstrating that the circulating particles enhanced gas mixing in SCFB. The ratio of Da/Dr in SCFB was less than that in BFB, indicating that gas-solid flow in SCFB was more closely to the mixed-type flow compared to the BFB.

Unified mixed conductivity model

Matter conductivities are crucial physical properties that directly determine the engineering application value of materials. In reality, the majority of materials are multiphase composites. However, there is currently a lack of theoretical models to accurately predict the conductivities of composite materials. In this study, we develop a unified mixed conductivity (UMC) model, achieving unity in three aspects: (1) a unified description and prediction for different conductivities, including elastic modulus, thermal conductivity, electrical conductivity, magnetic permeability, liquid permeability coefficient, and gas diffusion coefficient; (2) a unified-form governing equation for mixed conductivities of various composite structures, conforming to the Riccati equation; (3) a unified-form composite structure, i.e., a three-dimensional multiphase interpenetrating cuboid structure, encompassing over a dozen of typical composite structures as its specific cases. The UMC model is applicable for predicting the conductivity across six different types of physical fields and over a dozen different composite structures, providing a broad range of applications. Therefore, the current study deepens our understanding of the conduction phenomena and offers a powerful theoretical tool for predicting the conductivities of composite materials and optimizing their structures, which holds significant scientific and engineering implications.

Investigating temperature-dependent gas permeation in PIM-1: Hysteresis, annealing effects, and thermal history impact

This study investigates the gas permeability, diffusion coefficients, and solubility coefficients of CO2 and N2 in PIM-1 over the temperature range of 35 °C–135 °C. During the first heating-cooling cycle, both gases' permeability exhibited hysteresis, which diminished during the second cycle. Thermal mechanical analysis confirmed volume relaxation occurring at temperatures above 95 °C, indicating physical aging. By calculating the relaxation time associated with volume relaxation, the influence of physical aging was minimized through measurements on samples annealed at 135 °C for 15 h. This approach enabled a successful evaluation of the temperature dependence of gas permeability under conditions where the impact of physical aging could be disregarded. The results revealed that the permeability of CO2 decreased, and that of N2 increased with increasing temperature. The diffusion coefficients showed positive temperature dependence, while the solubility coefficients decreased. Physical aging significantly affected the diffusion coefficients but had minimal impact on the solubility coefficients. Heat of sorption and activation energies for gas permeability and diffusion estimated, and it was found that the decrease in CO2 permeability with temperature was mainly attributed to the large heat of sorption for CO2.

Simulation and experimental study of gas-phase diffusion coefficient of selenium dioxide

Improving the removal effect of selenium in wet flue gas desulfurization system is a key way to reduce the emission of selenium pollutants from coal-fired power plants. In order to clarify the removal mechanism of selenium pollutants in the desulfurization tower, it is necessary to obtain accurate selenium gas-phase diffusion coefficient. In this paper, molecular dynamics simulations were used to carry out theoretical calculations of gas-phase diffusion coefficients of SeO2 (the main form of selenium in coal combustion flue gas). The gas-phase diffusion coefficients of SeO2 in the range of 393 K–433 K were measured by a self-developed heavy metal gas diffusion coefficient testing device to verify the accuracy of the molecular dynamics calculations. Furthermore, the calculated gas-phase diffusion coefficients of SeO2 under typical binary and ternary components were obtained by correcting on the basis of Fuller's formula. Finally, a single-droplet absorption model for SeO2 was constructed and experiments were carried out to compare the effect of the gas-phase diffusion coefficient on the accuracy of the model calculations. The error of the model calculations was reduced from 8.09 % to 1.96 % after the correction. In this study, the gas-phase diffusion coefficient of SeO2 in the low-temperature range of coal-fired flue gas was obtained. This study can provide basic data for the development of selenium migration mechanism and control technology.

Time-dependent gas dynamic diffusion process in shale matrix: model development and numerical analysis

Gas diffusion is a pivotal process during shale gas recovery, which is determined by diffusion coefficient to a large extent. In previous studies, the gas diffusion coefficient is generally assumed as a constant. However, increasing experiments prove that the diffusion coefficient of shale gas is strongly time-dependent. Therefore, to perfect the theory of shale gas diffusion, this paper proposes a time-dependent diffusion model for shale gas, which incorporates time-dependent gas diffusion coefficient, composing of the bulk diffusion coefficient for free gas in organic and inorganic pores, as well as the surface diffusion coefficient for adsorbed gas in organic pores. To validate the accuracy of the new theory, we calibrate the theoretical results against experimental data, and the results show that they have strong correlation, and the time-dependent diffusion model is superior to classical model. Finally, the numerical analysis of gas dynamic diffusion process in shale matrix is conducted. The results show that at the end of diffusion, a large amounts of shale gas remain trapped in the matrix core due to the attenuation of gas diffusion coefficient. In addition, neglecting the time-dependent nature of gas diffusion in shale matrix leads to a significant overestimation of gas production.

Characteristics of the gas diffusion in water-bearing coal with different damage degree and its influence mechanism

The moisture content and degree of damage in water-bearing coal affect the gas diffusion characteristics in coal, which limits the effect of gas extraction. The experiments were carried out on water-bearing coal with different damage degrees using a self-built coal and gas adsorption–desorption system to study the gas diffusion characteristics of water-bearing coal with varying degrees of damage. The results show that the pore volume of tectonic coal is positively correlated with the degree of damage. The increased moisture content in coal decreases gas desorption performance, embodied in the simultaneous reduction of desorption amount, desorption speed, and diffusion coefficient. Under the same water content condition, the gas desorption amount, gas desorption rate, and gas diffusion coefficient of coal with different damage degrees all show a downward trend, and the decline range is positively correlated with the water content. The relation between the amount of gas desorption, the time, and the moisture content of the water-bearing coal with different damage degrees has been set up. The study results provide a solid theoretical foundation for evaluating and predicting the gas extraction characteristics of coal seams with varying degrees of damage.

The trade-off effects of water flow velocity on denitrification rates in open channel waterways

Ditches and river networks play crucial roles in nitrogen (N) removal within aquatic ecosystems, and their effectiveness depends on various biogeochemical and hydraulic factors. Among these, water flow velocity, as a hydraulic factor, has been relatively underexplored due to the limited N removal quantifying method in flowing open channel waterway. In this study, we used argon as a tracer to calibrate the diffusion coefficient of N2. We then applied the gas diffusion coefficient method to assess how water flow velocity affects denitrification rates. Our results provide new insights into the trade-off role of water flow velocity in N removal through denitrification across a range of flow velocities (0, 1, 4, 6, 10 cm s−1) in open channel waterway. This trade-off effect arises from the interplay between increased NO3− transfer and rising dissolved oxygen levels as water flow velocity increases, resulting in an initially increased and subsequently declined denitrification rate with increased water flow velocities. The denitrification rates reached maximum and minimum values at the water flow velocity of 4 cm s−1 and 0 cm s−1, respectively, regardless of the presence of vegetation. Average denitrification rates ranged from 36.8 to 358.8 µmol N2 m−2h−1 in unvegetated sediments and from 133.0 to 383.5 µmol N2 m−2h−1 in vegetated sediments within the spectrum of water flow velocities. In addition, we observed significantly higher denitrification rates at night than during the day, likely due to the photosynthesis and respiration processes associated with plant metabolism. These findings of this study contribute to the understanding of how water flow velocity affects denitrification rates and provide valuable information for the simulation and restoration efforts aimed at enhancing the N removal capacity of river networks.

Feasibility of compacted attapulgite/diatomite amended clayey soils as gas barrier materials

Compacted clay liners are extensively used as barriers to control the upward diffusion of vapors of volatile or semi-volatile organic contaminants released from unsaturated contaminated soils at industry-contaminated sites. This study aimed to investigate the gas diffusion barrier performance of compacted clayey soils amended with three agents including attapulgite and diatomite individually, and attapulgite/diatomite mixture. The properties including water retention, volumetric shrinkage, gas diffusion, and unconfined compressive strength were evaluated through a series of laboratory tests of amended compacted clayey soils. The results demonstrate that the decrease in volume proportions of inter-aggregate pores leads to an increase in unconfined compressive strength (qu). Both hydrophilic groups and microstructures of attapulgite and diatomite result in an increase in water retention percent (Wt) of compacted clayey soil specimens after amendment regardless of the type of agent or initial water content (w0). Furthermore, the ratio of the gas diffusion coefficient (De) to the gas diffusion coefficient in the air (Da) was significantly reduced owing to a decrease in volume proportions of inter-aggregate pores, hydrophilic group, and microstructures of attapulgite and diatomite. Scanning electron microscope analyses revealed that rod-shaped attapulgite filled the inter-aggregate pores formed by clay particles, whereas the disc-shaped diatomite particles, characterized by micropores, failed to obstruct the inter-aggregate pores due to their larger particle size. Mercury intrusion porosimetry (MIP) analyses showed a reduction in pore volume in the inter-aggregate pores, leading to a reduction in the total pore volume for both the attapulgite and attapulgite/diatomite mixture amended clays, which is in accordance with the scanning electron microscope (SEM) results. The findings are pertinent to the practical application of compacted clay liners as gas barriers against the upward migration of volatile or semi-volatile organic contaminants at contaminated sites.

Study of CO Gas Dilution in Forcing Ventilation System at Ramp Down KKRB 4 Utama, Pongkor, West Java

CO is a hazardous gas formed from the reaction of explosives that lack oxygen balance. These explosives have the potential to generate toxic gases, including CO. It is crucial to minimize CO concentration at the work site by ensuring proper air circulation. This study aims to examine the impact of varying ducting distances on CO gas dilution, using the gas diffusion coefficient value as a basis. The research method employed is observational, involving the assessment of CO gas dilution in the tested tunnel at varying distances from the working front to the sensor. The research was conducted on the Ramp Down KKRB 4 Utama. Result of the research is the most ideal carbon monoxide reduction time at RD KKRB 4 Utama is shown at sensor placement distance 1 using the blow system, where A Sensor takes 2.21 hours and B Sensor takes 1.06 hours to reach a concentration level below the TLV (Threshold Limit Value) 50 ppm.

Enhancing CO2/N2 and CO2/CH4 separation in mixed matrix membrane: A comprehensive study on Pebax®1657 with SSMMP/IL for improved efficiency

AbstractMixed matrix membranes (MMMs) have been proposed as a solution to surmount Robeson's trade‐off curves and have demonstrated efficacy in gas separation processes, particularly for CO2 capture. In this study, MMMs based on Pebax®1657 were obtained utilizing synthetic silico‐metallic mineral particles (SSMMP) functionalized with ionic liquids (ILs). The objective was to attain enhanced CO2 separation performance, thereby showcasing the potential to mitigate the environmental repercussions of industrial processes that entail greenhouse gas emissions. For membrane production, an ethanol/water mixture was used as solvent, with the SSMMP/IL content varying from 0.5 to 20% by weight of the polymer. The primary aim of this study was to assess the effect of filler addition on permeability and selectivity for CO2, CH4, and N2. Comprehensive analyses, including SEM, FTIR, TGA, DSC, and DMA were conducted to evaluate the properties of the produced membranes. Gas permeability and ideal selectivity were measured at 25°C and different pressures, ranging from 1 to 7 bar. Characterization results demonstrate that the glass transition temperature (Tg) of MMMs increased compared to pure Pebax®1657, indicating that the addition of SSMMP/IL reduces the flexibility of the PEO chains, forming a rigid interface at the polymer/filler, which may enhance selectivity. This effect, corroborated by gas permeation, was observed for both CO2/N2 and CO2/CH4. For CO2/N2, the highest selectivity was achieved at lower filler concentrations, gradually decreasing as the filler load increased. MMM‐0.5 wt% achieved the highest selectivity of 91.96. The membrane CO2 permeability rose with an elevated filler content, rising from 84.21 for pure Pebax®1657 to 192.17 Barrer for MMM‐20 wt% at 4 bar. The permeability results were influenced by the gas diffusion coefficients of the MMMs, which increased with increasing SSMMP/IL content. The effect of feed pressure on MMM‐5 wt% was also assessed, revealing that CO2 permeability increased with increasing pressure, from 126.72 Barrer at 1 bar to 165.56 Barrer at 7 bar. This work showcased the viability of MMMs incorporating SSMMP/IL for industrial use, as they displayed separation capabilities that exceeded the 2008 Robeson upper bound.Highlights Mixed matrix membranes based on Pebax®1657 and SSMMP‐20%‐[bmim][Tf2N] were prepared. CO2 permeability of the MMMs was increased by 128% and CO2/N2 selectivity by 83%. Higher CO2 pressures increase MMMs permeability. The obtained MMMs have separation performances above the Robeson upper Bound.

Desorption Characteristics of CH4-C2H6 Mixed Gas in Heavy Hydrocarbon-Rich Coal Seams.

The gas desorption characteristics of coal are closely related to the gas content of the coal seam. The gas in heavy hydrocarbon-rich coal seams contains CH4 and C2H6 heavy hydrocarbons. However, most current research on the gas desorption characteristics of coal seams focuses on CH4 analysis, ignoring the influence of the C2H6 heavy hydrocarbon gas. To accurately determine the gas content of a heavy hydrocarbon-rich coal seam, methods based on CH4 analysis are inadequate and the desorption characteristics of CH4-C2H6 mixed gas must be clarified. This work experimentally and theoretically studies the desorption characteristics of single-component gas and CH4-C2H6 mixed gas from coal samples. The results show that increasing the adsorption-equilibrium pressure was found to increase the desorption quantity and desorption speed of single-component gas and increase the desorption quantity, desorption ratio, and diffusion coefficient of mixed gas. Under the same adsorption-equilibrium pressure, the desorption quantity and rate of single-component CH4 gas exceeded those of C2H6. The quantity and speed of mixed gas desorption increased with rising CH4 concentration and decreased with rising C2H6 concentration. The change in the mixed gas concentration during desorption reflects the distribution characteristics of light hydrocarbon components on the outer surface and heavy hydrocarbon components on the inner surface of coal. From the desorption characteristics of mixed gas, desorption models of mixed gas were obtained at different concentrations, laying a theoretical foundation for accurate determinations of gas contents in heavy hydrocarbon-rich coal seams.

Experimental and Numerical Simulation Study of Oxygen Transport in Proton Exchange Membrane Fuel Cells at Intermediate Temperatures (80 °C-120 °C).

Investigating the oxygen transport law within the Membrane Electrode Assembly at intermediate temperatures (80-120 °C) is crucial for enhancing fuel cell efficiency. This study analyzed the resistance to oxygen transport within the Membrane Electrode Assembly at intermediate temperatures using limiting current density and electrochemical impedance spectroscopy. The study findings reveal that, as temperature progressively increases, the Ostwald ripening effect leads to a 34% rise in the local oxygen transport resistance (Rlocal) in relation to the pressure-independent resistance (Rnp) within the cathode catalytic layer. Concurrently, the total transport resistance (Rtotal) decreases from 27.8% to 37.5% due to an increase in the gas diffusion coefficient and molecular reactivity; additionally, there is a decrease in the amount of liquid water inside the membrane electrode. A three-dimensional multiphysics field steady-state model was also established. The model demonstrates that the decrease in oxygen partial pressure can be mitigated effectively by increasing the back pressure at intermediate temperatures to ensure the cell's performance.