The Experts below are selected from a list of 3549 Experts worldwide ranked by ideXlab platform
Abbas Firoozabadi - One of the best experts on this subject based on the ideXlab platform.
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phase behavior and flow in shale nanopores from molecular simulations
Fluid Phase Equilibria, 2016Co-Authors: Zhehui Jin, Abbas FiroozabadiAbstract:Abstract Phase behavior and flow in shale nanopores, due to fluid heterogeneity, cannot be described by bulk and continuum-based formulations. The interactions between fluid and rock molecules are important in both phase behavior and flow. As a result, frameworks from bulk Equations of state in phase behavior, and continuum mechanisms and Klinkenberg slippage in flow may become inapplicable. Recently, we have studied both phase behavior and flow in nanopores using density functional theory and various molecular simulations. This work addresses a number of issues related to the adsorption of mixtures of hydrocarbons, carbon dioxide and water as well as methane flow at different pressure conditions in nanopores. For flow, we use the dual control volume-grand canonical molecular dynamics (DCV-GCMD) simulation as in our previous work. We use a smaller pressure difference between high and low pressure reservoirs connected to the nanopores. We find that similar to our past work, the flux of methane in the slit pores can be two orders of magnitude higher than the results from the Hagen-Poiseuille Equation.
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Flow of methane in shale nanopores at low and high pressure by molecular dynamics simulations
The Journal of chemical physics, 2015Co-Authors: Zhehui Jin, Abbas FiroozabadiAbstract:Flow in shale nanopores may be vastly different from that in the conventional permeable media. In large pores and fractures, flow is governed by viscosity and pressure-driven. Convection describes the process. Pores in some shale media are in nanometer range. At this scale, continuum flow mechanism may not apply. Knudsen diffusion and hydrodynamic expressions such as the Hagen-Poiseuille Equation and their modifications have been used to compute flow in nanopores. Both approaches may have drawbacks and can significantly underestimate molecular flux in nanopores. In this work, we use the dual control volume-grand canonical molecular dynamics simulations to investigate methane flow in carbon nanopores at low and high pressure conditions. Our simulations reveal that methane flow in a slit pore width of 1–4 nm can be more than one order of magnitude greater than that from Knudsen diffusion at low pressure and the Hagen-Poiseuille Equation at high pressure. Knudsen diffusion and Hagen-Poiseuille Equations do not account for surface adsorption and mobility of the adsorbed molecules, and inhomogeneous fluid density distributions. Mobility of molecules in the adsorbed layers significantly increases molecular flux. Molecular velocity profiles in nanopores deviate significantly from the Navier-Stokes hydrodynamic predictions. Our molecular simulation results are in agreement with the enhanced flow measurements in carbon nanotubes.
Lei Chen - One of the best experts on this subject based on the ideXlab platform.
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a model for predicting the hydraulic conductivity of warm saturated frozen soil
Building and Environment, 2020Co-Authors: Lei Chen, Xiyan ZhangAbstract:Abstract Buildings built in the permafrost regions are always subjected to frost heave and thawing settlement deformation, which is mainly attributed to changes in foundation soil properties with environmental temperature, especially the hydraulic conductivity of warm frozen soil. To investigate the influence of the temperature on hydraulic conductivity, this study presented a model for predicting the hydraulic conductivity of warm frozen soil. Based on the discontinuous noncircular capillary bundle model, the expression of the hydraulic conductivity of the unsaturated soil was derived with the modified Hagen- Poiseuille Equation, the Kelvin Equation, the Campbell model for the matric potential and the Darcy's law. Then, based on the assumption that water transport in saturated frozen soil behaves with the same process as that in unsaturated unfrozen soil, the hydraulic conductivity model for warm frozen soil was proposed. To assess the predictive power of the proposed model, the predicted and tested hydraulic conductivities of eight different sets of soil were compared. The comparison results suggest that the proposed model performs well for the tested data. The results suggest that the hydraulic conductivity of warm frozen soil is mainly determined by the unfrozen water content, which is controlled by the temperature and soil particle size distribution. The proposed model is simple in the mathematical formula and readily integrated into frost heave and thawing settlement models. In addition, the model shows the relationship of hydraulic conductivity between saturated frozen soil and unsaturated unfrozen soil.
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estimation of hydraulic conductivity of saturated frozen soil from the soil freezing characteristic curve
Science of The Total Environment, 2020Co-Authors: Feng Ming, Lei Chen, Dongqing LiAbstract:Abstract Knowledge of hydraulic conductivity is crucial for determining water movement in frozen soil, and the objective of this study is to introduce the soil freezing characteristic curve to estimate the hydraulic conductivity of saturated frozen soil. Based on the non-uniform tortuous capillary bundle model and the assumption that the ice was first formed in the pores with largest size, a physical infiltration model of saturated frozen soil was developed. On the basis of this physical infiltration model, a new approach for estimating the hydraulic conductivity of saturated frozen soil was developed by using the Hagen-Poiseuille Equation and Darcy's law. To verify the validity of this approach, five soil data sets, including 29 data points with hydraulic conductivity between 10−6 cm/s and 10−11 cm/s, were used to compare the predicted results and experimental data. The results show that the new approach fits the experimental data well. This approach is more convenient than the soil water characteristic curve in numerical modeling, and it can be used to describe the relationship between hydraulic conductivity and minus temperature. Moreover, the new approach and the results in this study maybe also can provide a reference for the research on water flow and the related numerical modeling in cold regions environmental engineering.
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A Fractal Model of Hydraulic Conductivity for Saturated Frozen Soil
MDPI AG, 2019Co-Authors: Lei Chen, Feng Ming, Xiangyang Shi, Xin ChenAbstract:In cold regions, hydraulic conductivity is a critical parameter for determining the water flow in frozen soil. Previous studies have shown that hydraulic conductivity hinges on the pore structure, which is often depicted as the pore size and porosity. However, these two parameters do not sufficiently represent the pore structure. To enhance the characterization ability of the pore structure, this study introduced fractal theory to investigate the influence of pore structure on hydraulic conductivity. In this study, the pores were conceptualized as a bundle of tortuous capillaries with different radii and the cumulative pore size distribution of the capillaries was considered to satisfy the fractal law. Using the Hagen-Poiseuille Equation, a fractal capillary bundle model of hydraulic conductivity for saturated frozen soil was developed. The model validity was evaluated using experimental data and by comparison with previous models. The results showed that the model performed well for frozen soil. The model showed that hydraulic conductivity was related to the maximum pore size, pore size dimension, porosity and tortuosity. Of all these parameters, pore size played a key role in affecting hydraulic conductivity. The pore size dimension was found to decrease linearly with temperature, the maximum pore size decreased with temperature and the tortuosity increased with temperature. The model could be used to predict the hydraulic conductivity of frozen soil, revealing the mechanism of change in hydraulic conductivity with temperature. In addition, the pore size distribution was approximately estimated using the soil freezing curve, making this method could be an alternative to the mercury intrusion test, which has difficult maneuverability and high costs. Darcy’s law is valid in saturated frozen silt, clayed silt and clay, but may not be valid in saturated frozen sand and unsaturated frozen soil
Zhehui Jin - One of the best experts on this subject based on the ideXlab platform.
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phase behavior and flow in shale nanopores from molecular simulations
Fluid Phase Equilibria, 2016Co-Authors: Zhehui Jin, Abbas FiroozabadiAbstract:Abstract Phase behavior and flow in shale nanopores, due to fluid heterogeneity, cannot be described by bulk and continuum-based formulations. The interactions between fluid and rock molecules are important in both phase behavior and flow. As a result, frameworks from bulk Equations of state in phase behavior, and continuum mechanisms and Klinkenberg slippage in flow may become inapplicable. Recently, we have studied both phase behavior and flow in nanopores using density functional theory and various molecular simulations. This work addresses a number of issues related to the adsorption of mixtures of hydrocarbons, carbon dioxide and water as well as methane flow at different pressure conditions in nanopores. For flow, we use the dual control volume-grand canonical molecular dynamics (DCV-GCMD) simulation as in our previous work. We use a smaller pressure difference between high and low pressure reservoirs connected to the nanopores. We find that similar to our past work, the flux of methane in the slit pores can be two orders of magnitude higher than the results from the Hagen-Poiseuille Equation.
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Flow of methane in shale nanopores at low and high pressure by molecular dynamics simulations
The Journal of chemical physics, 2015Co-Authors: Zhehui Jin, Abbas FiroozabadiAbstract:Flow in shale nanopores may be vastly different from that in the conventional permeable media. In large pores and fractures, flow is governed by viscosity and pressure-driven. Convection describes the process. Pores in some shale media are in nanometer range. At this scale, continuum flow mechanism may not apply. Knudsen diffusion and hydrodynamic expressions such as the Hagen-Poiseuille Equation and their modifications have been used to compute flow in nanopores. Both approaches may have drawbacks and can significantly underestimate molecular flux in nanopores. In this work, we use the dual control volume-grand canonical molecular dynamics simulations to investigate methane flow in carbon nanopores at low and high pressure conditions. Our simulations reveal that methane flow in a slit pore width of 1–4 nm can be more than one order of magnitude greater than that from Knudsen diffusion at low pressure and the Hagen-Poiseuille Equation at high pressure. Knudsen diffusion and Hagen-Poiseuille Equations do not account for surface adsorption and mobility of the adsorbed molecules, and inhomogeneous fluid density distributions. Mobility of molecules in the adsorbed layers significantly increases molecular flux. Molecular velocity profiles in nanopores deviate significantly from the Navier-Stokes hydrodynamic predictions. Our molecular simulation results are in agreement with the enhanced flow measurements in carbon nanotubes.
Xiyan Zhang - One of the best experts on this subject based on the ideXlab platform.
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a model for predicting the hydraulic conductivity of warm saturated frozen soil
Building and Environment, 2020Co-Authors: Lei Chen, Xiyan ZhangAbstract:Abstract Buildings built in the permafrost regions are always subjected to frost heave and thawing settlement deformation, which is mainly attributed to changes in foundation soil properties with environmental temperature, especially the hydraulic conductivity of warm frozen soil. To investigate the influence of the temperature on hydraulic conductivity, this study presented a model for predicting the hydraulic conductivity of warm frozen soil. Based on the discontinuous noncircular capillary bundle model, the expression of the hydraulic conductivity of the unsaturated soil was derived with the modified Hagen- Poiseuille Equation, the Kelvin Equation, the Campbell model for the matric potential and the Darcy's law. Then, based on the assumption that water transport in saturated frozen soil behaves with the same process as that in unsaturated unfrozen soil, the hydraulic conductivity model for warm frozen soil was proposed. To assess the predictive power of the proposed model, the predicted and tested hydraulic conductivities of eight different sets of soil were compared. The comparison results suggest that the proposed model performs well for the tested data. The results suggest that the hydraulic conductivity of warm frozen soil is mainly determined by the unfrozen water content, which is controlled by the temperature and soil particle size distribution. The proposed model is simple in the mathematical formula and readily integrated into frost heave and thawing settlement models. In addition, the model shows the relationship of hydraulic conductivity between saturated frozen soil and unsaturated unfrozen soil.
Dongqing Li - One of the best experts on this subject based on the ideXlab platform.
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estimation of hydraulic conductivity of saturated frozen soil from the soil freezing characteristic curve
Science of The Total Environment, 2020Co-Authors: Feng Ming, Lei Chen, Dongqing LiAbstract:Abstract Knowledge of hydraulic conductivity is crucial for determining water movement in frozen soil, and the objective of this study is to introduce the soil freezing characteristic curve to estimate the hydraulic conductivity of saturated frozen soil. Based on the non-uniform tortuous capillary bundle model and the assumption that the ice was first formed in the pores with largest size, a physical infiltration model of saturated frozen soil was developed. On the basis of this physical infiltration model, a new approach for estimating the hydraulic conductivity of saturated frozen soil was developed by using the Hagen-Poiseuille Equation and Darcy's law. To verify the validity of this approach, five soil data sets, including 29 data points with hydraulic conductivity between 10−6 cm/s and 10−11 cm/s, were used to compare the predicted results and experimental data. The results show that the new approach fits the experimental data well. This approach is more convenient than the soil water characteristic curve in numerical modeling, and it can be used to describe the relationship between hydraulic conductivity and minus temperature. Moreover, the new approach and the results in this study maybe also can provide a reference for the research on water flow and the related numerical modeling in cold regions environmental engineering.