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To solve the cryogenic temperature problems faced by all-concrete liquefied natural gas (ACLNG) storage tanks during servicing, a low temperature resistant and high strength concrete (LHC) was designed from the perspectives of reducing water-binder ratio, removing coarse aggregates, optimizing composite mineral admixture and utilizing steel fibers. The variation laws of compressive and tensile strength, elastic modulus and Poisson's ratio for C60 concrete and LHC were compared and analyzed under the temperatures from 10 to −165 °C through uniaxial compression and tensile tests. The rapid freezing method was adopted to analyze the evolution process of mass and relative dynamic elastic modulus loss rates for C60 and LHC in 0–300 freeze-thaw cycles. The gas permeability test was carried out, and the laws of gas permeability coefficient varied with temperature and cryogenic freeze-thaw cycles were obtained. Then, the grey dynamic model GM (1,1) was used to predict the variation laws of physical and mechanical parameters on the basis of the test data. The test results demonstrate that the compressive strength, elastic modulus and Poisson's ratio for both C60 and LHC increase significantly from 10 to −165 °C, but the specific variation laws are different, and there is a phenomenon that some parameters decrease after reaching a critical temperature range for C60. The uniaxial tensile strength increases first and then decreases as temperature decreases, and finally increases slightly at −165 °C for both C60 and LHC. The mass and relative dynamic elastic modulus loss rates of LHC are much lower than that of C60 under different freeze-thaw cycles. The gas permeability coefficient of C60 declines gradually with the drop of temperature, and increases gradually with the number of freeze-thaw cycles while the gas permeability coefficient of LHC basically remains stable and is much lower than that of C60. Therefore, such a conclusion can be drawn that LHC has better properties at cryogenic temperature. On the premise of providing consistent functional mode, GM (1,1) can predict the test data with high accuracy, which well reflects the variation laws of relevant parameters. [ABSTRACT FROM AUTHOR]

Landfill gas generated by municipal solid waste (MSW) landfills is the world's third largest source of greenhouse gas emissions. Additionally, the accumulation of landfill gas in waste piles can trigger instability in landfill piles. Based on the exponential distribution pattern of the variation of gas permeability coefficients with burial depth measured in situ, this paper presents an analytical solution for landfill gas-pressure distribution that is more in line with on-site conditions and has been verified by numerical calculations. Compared with cases where the gas permeability coefficient of landfill piles remains constant, the consideration that the gas permeability coefficient of MSW decreases exponentially with increasing burial depth is more likely to cause the accumulation of landfill gas at the landfill bottom, leading to higher gas pressure that can be more than five times higher than that in the former case. Based on a numerical analysis of gas extraction simulations, constant pressure gas extraction is relatively more effective in that a relative pressure of −0.1 kPa can lower the gas pressure in almost the entire pile, while bottom drainage fails to completely collect landfill gas even using a flux of 10–30 times ML. [ABSTRACT FROM AUTHOR]

Landfill gas generated by municipal solid waste (MSW) landfills is the world’s third largest source of greenhouse gas emissions. Additionally, the accumulation of landfill gas in waste piles can trigger instability in landfill piles. Based on the exponential distribution pattern of the variation of gas permeability coefficients with burial depth measured in situ, this paper presents an analytical solution for landfill gas-pressure distribution that is more in line with on-site conditions and has been verified by numerical calculations. Compared with cases where the gas permeability coefficient of landfill piles remains constant, the consideration that the gas permeability coefficient of MSW decreases exponentially with increasing burial depth is more likely to cause the accumulation of landfill gas at the landfill bottom, leading to higher gas pressure that can be more than five times higher than that in the former case. Based on a numerical analysis of gas extraction simulations, constant pressure gas extraction is relatively more effective in that a relative pressure of −0.1 kPa can lower the gas pressure in almost the entire pile, while bottom drainage fails to completely collect landfill gas even using a flux of 10–30 times ML.

The stable time for concrete permeability is of great significance to evaluate the permeability of concrete and predict the service life of actual engineering. Based on a test with an exposure time of more than 3 years in a natural tidal environment, the gas permeability and microstructure parameters of concrete with different water-binder ratios (w/b) and admixtures including fly ash (FA), slag (SG), silica fume (SF), and basalt fiber (BF) were tracked and tested. Then, the time-dependent gas permeability and main microstructure parameters and their stable time were investigated. Finally, the relationship between stable time for the gas permeability coefficient and microstructure parameters was studied. The results show that the apparent and intrinsic gas permeability coefficients of concrete both decrease with exposure time. For ordinary concrete, the gas permeability coefficient and the corresponding stable time increase with w/b. The stable time for gas permeability coefficients of SF concrete is the shortest among admixture concrete, while that of BF concrete is the longest. The timedependent gas permeability is in keeping with the change of total porosity and contributive porosity of large capillary pores (100 to 1000 nm) with exposure time. Moreover, the change trends of stable time for gas permeability, total porosity, and contributive porosity of large capillary pores with w/b and admixture type are consistent. The stable time for the intrinsic gas permeability coefficient has a better correlation with that for contributive porosity of large capillary pores than that for total porosity. The intrinsic gas permeability coefficient stabilizes first, followed by contributive porosity of large capillary pores, which is the most important factor influencing the stable time for the intrinsic gas permeability coefficient, and total porosity stabilizes last. [ABSTRACT FROM AUTHOR]

Abstract As an important indicator, permeability can predict the gas drainage yield and prevent the mine gas disasters. We first reviewed our previous inversion method to investigate permeability coefficient of gas in coal particles; however, the relationship between permeability and adsorption pressure had not been summarized and explained theoretically. Here, a permeability evolution model including two crucial parameters of initial permeability and deformation coefficient was developed. The inversion gas permeability coefficients were converted into permeability, and then, the permeability of the same coal sample was fitted according to the evolution model. The results show that (i) the modeled results are matched reasonably well with the inversion permeability data, and thus, this model has been validated; and (ii) as volatile matter content increases, the initial permeability decreases exponentially, but the deformation coefficient basically grows in a linear trend. These two parameters are coupling to lead to a negative exponential decrease in permeability as gas pressure rises.

As an important indicator, permeability can predict the gas drainage yield and prevent the mine gas disasters. We first reviewed our previous inversion method to investigate permeability coefficient of gas in coal particles; however, the relationship between permeability and adsorption pressure had not been summarized and explained theoretically. Here, a permeability evolution model including two crucial parameters of initial permeability and deformation coefficient was developed. The inversion gas permeability coefficients were converted into permeability, and then, the permeability of the same coal sample was fitted according to the evolution model. The results show that (i) the modeled results are matched reasonably well with the inversion permeability data, and thus, this model has been validated; and (ii) as volatile matter content increases, the initial permeability decreases exponentially, but the deformation coefficient basically grows in a linear trend. These two parameters are coupling to lead to a negative exponential decrease in permeability as gas pressure rises. [ABSTRACT FROM AUTHOR]

In order to reveal the influence of permeability and porosity structure on gas extraction in low permeability coal seam, theoretical analysis and experimental research methods were adopted to address the abnormal gas emission and excessive concentration of gas from the no.4 working faces in west no.2 mining area of no.9 coal seam in Jixian coal mine. On the basis of the analysis of gas source and the influence of syncline structure on gas occurrence in the working face, the permeability of coal samples in different directions was measured by a self-pressurized triaxial seepage testing device, the low field nuclear magnetic resonance test system was used to test the distribution law of the pore structure of the coal seam, and the permeability of the coal seam was measured by the radial flow method. The results show that the permeability of coal seam has significant influence on gas extraction and extraction rate, and the permeability decreases with the increase of gas pressure and shows anisotropy. The worse the porosity development of coal seam, the lower the permeability of coal seam, and the worse the gas permeability, the higher the adsorption gas content. It is revealed that permeability has a great influence on gas extraction and extraction rate in low permeability coal seam. The research conclusion has theoretical guiding significance to the selection of pressure relief and permeability improvement measures of low permeability coal seam and the parameters of gas extraction borehole. [ABSTRACT FROM AUTHOR]

In order to improve the gas extraction rate and reduce the attenuation speed of extraction concentration, the influence of pumping hole leakage on gas extraction concentration under different conditions of pumping negative pressure, different coal seam initial pressure and different coal seam permeability coefficient is studied by using the pressure relief and gas leakage experimental platform and the method of combining theoretical analysis with experimental research. The results show that the extraction concentration first increases and then decreases with the increase of negative extraction pressure. The optimal negative extraction pressure is between 30KPa and 40 kPa, and the highest extraction concentration is at 35 kPa. With the increase of permeability coefficient of coal seam and initial pressure of coal seam, the decline rate of mining concentration slows down and is stable at a higher gas extraction concentration. The variation curve of extraction concentration with extraction time accords with the exponential decay fitting equation. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the influence of introducing calcium sulfate whiskers (CSW) and basalt fiber (BF) on the gas permeability coefficients of concrete. Employing the Cembureau method, the research quantifies gas permeability while utilizing Nuclear Magnetic Resonance (NMR) to precisely measure pore structure parameters. The results highlight that the incorporation of CSW leads to a substantial reduction in gas permeability, exhibiting a remarkable 57.6% decrease when utilized at a dosage of 3.0 kg/m³ compared to the standard concrete. In contrast, the introduction of BF at the same dosage does not yield a commensurate reduction in permeability. Notably, the combined application of CSW and BF at 3.0 kg/m³ each yields the most effective mitigation of gas permeability. Furthermore, the judicious addition of either CSW or BF demonstrates the capacity to diminish the overall porosity of concrete, alongside a reduction in the proportion of harmful pores (R 100 , featuring diameters larger than 100 nm). Optimal outcomes manifest when both CSW and BF are introduced at the 3.0 kg/m³ dosage, effectively minimizing R 100 and the gas permeability coefficient. It is interesting to find that in comparison to the correlation observed between the total porosity and gas permeability of concrete, the relationship between the proportion of R 100 and gas permeability emerges as more statistically significant (R 2 approximately 0.800), especially for CSW concrete. This can reveal the interconnection between the concrete's pore structure and its gas permeability characteristics more appropriately. • Optimal gas impermeability achieved with 3.0 kg/m3 of CSW and BF in concrete. • Optimal CSW and BF dosage mitigates total porosity and reduces harmful pores (R100). • Gas permeability coefficient has a strong correlation with R 100 proportion. [ABSTRACT FROM AUTHOR]

Compressive stress and tensile stress were applied to concrete specimens using test rigs designed by RILEM TC 246-TDC. Ultrasonic wave velocity and autoclam permeability system were used to characterize the damage variable and gas permeability coefficient of concrete, respectively. The experimental results show that the strain value of concrete increases with the increasing of stress level and loading time. The damage variable and gas permeability coefficient of concrete under compressive stress decrease at first and increase after a threshold value between 0 and 0.6. When the concrete is under tensile load, the damage variable and gas permeability coefficient increase with tensile stress, with a significant increase from 0.3 to 0.6 tensile stress. There is a strong linear relationship between the damage variable and the gas permeability coefficient, suggesting both as good indicators to characterize the damage of concrete under stress. [ABSTRACT FROM AUTHOR]

Permeability is an important indicator for predicting gas drainage yield and preventing mine gas disasters. Gas permeability coefficient derived from the permeability is introduced in this work to develop a model of methane adsorption of coal particle based on Darcy's permeation, which is solved by our self-developed software, and then the methane isothermal adsorption of six granular coal samples are measured by quasi-constant pressure adsorption experiments. A new inversion approach for gas permeability coefficient of coal particle is performed by matching simulation results with experiment data. Meanwhile, the impacts of adsorption pressure and coal rank on gas permeability coefficient are also analyzed quantitatively. The results show that (i) a suitable gas permeability coefficient of coal particle can be determined by adjusting simulated curve to match with experimental data, which verifies the feasibility and effectiveness of the inversions; (ii) the gas permeability coefficient of coal particle decreases exponentially as the adsorption pressure or volatile matter content grows. This research provides an alternative approach to determine the permeability of granular coal samples and we hope it will bring some references to researchers. [ABSTRACT FROM AUTHOR]

Gas transport properties of PIM-1 films treated by elemental fluorine in a liquid perfluorodecalin were investigated. The investigation included an estimation of fluorine content in a fluorinated layer, pure and mixed gas permeability, diffusion and solubility coefficients measurement, ideal selectivity assessment and analysis of fluorination time effect on gas transport properties. An increase of treatment duration resulted in an increase of concentration of fluorine in the fluorinated layer as well as a depth of fluorination. The depths of fluorination linearly increased with square of fluorination time indicating a diffusion of fluorine in the fluorinated layer to be a restrictive stage of kinetics of fluorination. The effect of the drop in gas permeability was demonstrated to be dependent on the kinetic size of the penetrant. The comparison of liquid-phase and gas-phase regimes was performed, and it was shown that sharp decrease in gas permeability is observed for gas-phase regime at short times of fluorination already, whereas this decrease is more gradual for liquid-phase fluorination. According to a Barrie method, the gas transport parameters of the fluorinated layer of the modified PIM-1 films were calculated, which turned out to be much lower than those for the virgin PIM-1 polymer and slightly lower than the gas transport parameters for dry Nafion. The reduction of the gas permeability coefficients is mostly induced by a sharp decrease in the gas diffusion coefficients. According to combination of permeability and selectivity, the fluorinated PIM-1 samples show excellent results exceeding the 2008 Robeson upper bounds for H 2 /CH 4 , H 2 /CO 2 , H 2 /N 2 , He/CH 4 and others gas pairs. Mixed gas experiments were also conducted for hydrogen-containing mixtures and fluorinated PIM-1 samples have demonstrated good separation characteristics for the model binary mixtures attaining separation factors as high as 115–143 (H 2 /CH 4), 4.4–6.7 (H 2 /CO 2) and 49–146 (He/CH 4), which makes these materials promising for helium recovery from natural gas and hydrogen recovery from various catalytic and biohydrogen production mixtures. Ten-months aging of the PIM-1 sample fluorinated during 30 min showed a decline of permeability by 25 and 40%, respectively and a slight decrease of ideal selectivity. [Display omitted] • Exponential decrease of F content along the thickness of the fluorinated samples. • Sharp increase of selectivity for fluorinated PIM-1 samples. • 25–40% decrease of permeability for aged fluorinated samples. • The fluorinated PIM-1 samples can be applied for H2-CH4, H2-CO2, H2-N2 separation. [ABSTRACT FROM AUTHOR]

By using the theories and basic formula of pressure build-up curves in petroleum and gas exploitation, and combining the occurrence features of coal seams, the theories and methods of pressure build-up curves to determine the gas occurrence parameters of coal seams were constructed, which could determine the parameters quickly-such as gas pressure in coal seam and gas permeability coefficient, and guide gas drainage and coal and gas outburst prevention and efficient extraction of coalbed methane in coal mines. By comparing it with the test results of Hudi Coal Mine, the methods of pressure build-up curve were proved viable. [ABSTRACT FROM AUTHOR]

Filler surfaces in elastomers influence mobility of rubber matrix molecules. Mobility of rubber matrix molecules then determines elastomer properties and behaviour of rubber products in applications. Effect of filler in elastomer-filler system is usually characterized by different properties: Modulus seem to depend mainly on filler cluster size and filler network behaviour but effect of mobility of rubber matrix molecules is also evident. Bound rubber characterize fraction of rubber immobilized on filler particle surfaces, however, can be obtained only for uncured rubber-filler compounds. As it is shown in this paper, the permeability coefficient of permanent gas in rubber-filler system could characterize mobility of rubber matrix molecules around the filler particles and the activation energy of its permeation could characterize strength of physical bonds between the rubber matrix molecules and surface of filler particles. [ABSTRACT FROM AUTHOR]