The Experts below are selected from a list of 2826 Experts worldwide ranked by ideXlab platform
Tatiana Budtova - One of the best experts on this subject based on the ideXlab platform.
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Thermal conductivity/structure correlations in thermal super-insulating pectin aerogels.
Carbohydrate polymers, 2018Co-Authors: Sophie Groult, Tatiana BudtovaAbstract:Pectin aerogels were synthesized via dissolution-solvent exchange-drying with supercritical CO2. The goal was to correlate thermal conductivity with aerogel morphology and properties in order to understand how to obtain a thermal super-insulating material with the lowest possible conductivity. Polymer concentration, solution pH and presence of bivalent ions were varied to tune pectin gelation mechanism and the state of matter, solution or gel. For the first time for bio-aerogels, a U-shape curve of thermal conductivity as a function of aerogel density was obtained. It shows that to reach the lowest conductivity values, a compromise between density and pore sizes is needed to optimize the inputs from the conduction of solid and gaseous phases. The lowest value of conductivity, 0.015 W/m K, was for aerogels from non-gelled pectin solutions. Calcium-induced gelation leads to pectin aerogels with very low density, around 0.05 g/cm3, but with many macropores, thus reducing the contribution of Knudsen Effect.
Sophie Groult - One of the best experts on this subject based on the ideXlab platform.
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Thermal conductivity/structure correlations in thermal super-insulating pectin aerogels.
Carbohydrate polymers, 2018Co-Authors: Sophie Groult, Tatiana BudtovaAbstract:Pectin aerogels were synthesized via dissolution-solvent exchange-drying with supercritical CO2. The goal was to correlate thermal conductivity with aerogel morphology and properties in order to understand how to obtain a thermal super-insulating material with the lowest possible conductivity. Polymer concentration, solution pH and presence of bivalent ions were varied to tune pectin gelation mechanism and the state of matter, solution or gel. For the first time for bio-aerogels, a U-shape curve of thermal conductivity as a function of aerogel density was obtained. It shows that to reach the lowest conductivity values, a compromise between density and pore sizes is needed to optimize the inputs from the conduction of solid and gaseous phases. The lowest value of conductivity, 0.015 W/m K, was for aerogels from non-gelled pectin solutions. Calcium-induced gelation leads to pectin aerogels with very low density, around 0.05 g/cm3, but with many macropores, thus reducing the contribution of Knudsen Effect.
Moran Wang - One of the best experts on this subject based on the ideXlab platform.
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Characterization of nanopore morphology of shale and its Effects on gas permeability
Journal of Natural Gas Science and Engineering, 2017Co-Authors: Jiangtao Zheng, Ziyan Wang, Wenbo Gong, Moran WangAbstract:Abstract From a microscopic point of view, nano-scale pores are dominant in shale matrix, which provide transport space for natural gas. Accordingly, a pore-scale modeling, which can accurately capture the complex pore morphology and its Effects on gas flow behavior, is crucial for understanding the gas transport mechanisms in shale matrix. In this study, the focused ion beam-scanning electron microscope (FIB-SEM) technique was employed to observe and characterize the morphology of the nanopores in shale. Based on the morphology characterizations, three representative porous models (i.e. intergranular pore model, micro-crack model and “honeycomb” pore model) were proposed and generated by numerical methods. The high-Knudsen gas flows in these generated structures were simulated by the lattice Boltzmann method (LBM). A comparison of the simulation results among these three porous models suggests that the nano-scale pore morphology plays an important role in the gas transport properties. Moreover, the high-Knudsen Effect leads to a larger apparent permeability for each nano-scale porous model. Our work indicates the importance of the nano-scale pore morphology and the high-Knudsen Effect on gas transport properties of shale matrix.
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Permeability of high-Kn real gas flow in shale and production prediction by pore-scale modeling
Journal of Natural Gas Science and Engineering, 2016Co-Authors: Ziyan Wang, Yangyu Guo, Moran WangAbstract:Abstract Although shale gas has been commercially exploited, the gas transport mechanism in shale is still unclear. Because nanoscale pores are dominant in shale, the Knudsen number of the flow is relatively high so that the conventional Darcy's law fails. What is more, the shale gas in situ is under high pressure and high temperature so that the real gas (or non-ideal gas) Effect is significant. Aiming at these two challenges, we did a pore-scale modeling by using lattice Boltzmann method in this work. We developed a pore-field-iteration (PFI) method to bridge up the pore-scale modeling results with the field-scale concerns, such as inflow performance relationship and decline curve analysis. Our results show that the high Knudsen Effect leads to a higher gas flow rate, while the real gas Effect causes lower gas flow rate. The gas production may be overestimated at early stage due to the real gas Effect, while underestimated at late stage because of the high Knudsen number Effect. These results may be very helpful for better understanding of gas transport mechanism in shale and for possible process optimization of shale gas developments in future.
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Pore-scale geometry Effects on gas permeability in shale
Journal of Natural Gas Science and Engineering, 2016Co-Authors: Ziyan Wang, Xu Jin, Xiaoqi Wang, Liang Sun, Moran WangAbstract:Abstract One main challenge for prediction of gas permeability in shale is the geometrical complexity at pore scale of shale. Shale structure is highly anisotropic and heterogeneous, which cannot be well described by packing of spheres or bundle of tubes. Besides, there are abundant nanoscale pores in shale so that the Knudsen number of gas flow is high, leading to failure of the conventional Darcy's law. Aiming at these challenges, we have studied the influences from pore-scale anisotropy and heterogeneity of shale microstructures on gas permeability including the high Knudsen number Effect (or Klinkenberg Effect for Darcy scale). First, a geometry-based method is proposed to quantify the pore-scale anisotropy and heterogeneity of shale. Then we reconstruct three-dimensional shale structures by the random generation-growth algorithm and use the lattice Boltzmann method to predict its permeability. To reveal the high Knudsen number Effect, both intrinsic permeability and apparent permeability are evaluated. Our results suggest that the intrinsic permeability increases with the anisotropy of pore geometry in parallel direction to the bed, while decreases in perpendicular direction. The slip factor for Klinkenberg correction also exhibits anisotropy when high Knudsen Effect is considered. On the other hand, the heterogeneity of pore distribution may have positive influences on intrinsic permeability for given porosities.
Sohrab Alex Mofid - One of the best experts on this subject based on the ideXlab platform.
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Nano Insulation Materials Exploiting the Knudsen Effect
IOP Conference Series: Materials Science and Engineering, 2019Co-Authors: Bjørn Petter Jelle, Sohrab Alex Mofid, Tao Gao, Mathieu Grandcolas, Malin Sletnes, Espen SagvoldenAbstract:As the world's focus is turned even stronger toward miscellaneous energy efficiency and saving aspects, the development of new high-performance thermal insulation materials for building applications will play an important role in this regard. The aim of the presented study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen Effect in nanoporous insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major goal. NIMs based on hollow silica nanospheres (HSNS) have been synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen Effect. HSNS with reduced thermal conductivity compared to their solid counterparts have been prepared where the hollow sphere cavities and voids between the spheres are filled with air at atmospheric pressure, i.e. eliminating the need for various measures like e.g. protective metallized foils to maintain a vacuum or expensive low-conducting gases in the cavities and voids. Hence, HSNS represent a promising stepping-stone toward the future high-performance thermal insulation materials.
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Hollow silica nanospheres as thermal insulation materials for construction: Impact of their morphologies as a function of synthesis pathways and starting materials
Construction and Building Materials, 2018Co-Authors: Bjørn Petter Jelle, Tao Gao, Linn Ingunn Christie Sandberg, Sohrab Alex MofidAbstract:Abstract Hollow silica nanospheres (HSNS) show a promising potential to become good thermal insulators with low thermal conductivity values for construction purposes. The thermal conductivity of HSNSs is dependent on their structural features such as sizes (inner diameter and shell thickness) and shell structures (porous or dense), which are affected by the synthetic methods and procedures including reaction medium, polystyrene template, and silica precursor. Formation of thermally insulating HSNS was favoured by alkaline reaction, whereby highly porous silica shells were formed, promoting less silica per volume of material, thus a lower solid state thermal conductivity. The Knudsen Effect is in general reducing the gas thermal conductivity including the gas and pore wall interaction for materials with pore diameters in the nanometer range, which is also valid for our HSNS reported here. Further decreasing the pore sizes would invoke a higher impact from the Knudsen Effect. The additional insulating Effect of the inter-silica voids (median diameter D50 ≈ 15 nm) within the shell coating contributed also to the insulating properties of HSNS. The synthesis route with tetraethyl orthosilicate (TEOS) was more robust and produced more porous silica shells than the one with water glass (Na2SiO3, WG), although the latter might represent a greener synthetic method.
Ziyan Wang - One of the best experts on this subject based on the ideXlab platform.
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Characterization of nanopore morphology of shale and its Effects on gas permeability
Journal of Natural Gas Science and Engineering, 2017Co-Authors: Jiangtao Zheng, Ziyan Wang, Wenbo Gong, Moran WangAbstract:Abstract From a microscopic point of view, nano-scale pores are dominant in shale matrix, which provide transport space for natural gas. Accordingly, a pore-scale modeling, which can accurately capture the complex pore morphology and its Effects on gas flow behavior, is crucial for understanding the gas transport mechanisms in shale matrix. In this study, the focused ion beam-scanning electron microscope (FIB-SEM) technique was employed to observe and characterize the morphology of the nanopores in shale. Based on the morphology characterizations, three representative porous models (i.e. intergranular pore model, micro-crack model and “honeycomb” pore model) were proposed and generated by numerical methods. The high-Knudsen gas flows in these generated structures were simulated by the lattice Boltzmann method (LBM). A comparison of the simulation results among these three porous models suggests that the nano-scale pore morphology plays an important role in the gas transport properties. Moreover, the high-Knudsen Effect leads to a larger apparent permeability for each nano-scale porous model. Our work indicates the importance of the nano-scale pore morphology and the high-Knudsen Effect on gas transport properties of shale matrix.
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Permeability of high-Kn real gas flow in shale and production prediction by pore-scale modeling
Journal of Natural Gas Science and Engineering, 2016Co-Authors: Ziyan Wang, Yangyu Guo, Moran WangAbstract:Abstract Although shale gas has been commercially exploited, the gas transport mechanism in shale is still unclear. Because nanoscale pores are dominant in shale, the Knudsen number of the flow is relatively high so that the conventional Darcy's law fails. What is more, the shale gas in situ is under high pressure and high temperature so that the real gas (or non-ideal gas) Effect is significant. Aiming at these two challenges, we did a pore-scale modeling by using lattice Boltzmann method in this work. We developed a pore-field-iteration (PFI) method to bridge up the pore-scale modeling results with the field-scale concerns, such as inflow performance relationship and decline curve analysis. Our results show that the high Knudsen Effect leads to a higher gas flow rate, while the real gas Effect causes lower gas flow rate. The gas production may be overestimated at early stage due to the real gas Effect, while underestimated at late stage because of the high Knudsen number Effect. These results may be very helpful for better understanding of gas transport mechanism in shale and for possible process optimization of shale gas developments in future.
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Pore-scale geometry Effects on gas permeability in shale
Journal of Natural Gas Science and Engineering, 2016Co-Authors: Ziyan Wang, Xu Jin, Xiaoqi Wang, Liang Sun, Moran WangAbstract:Abstract One main challenge for prediction of gas permeability in shale is the geometrical complexity at pore scale of shale. Shale structure is highly anisotropic and heterogeneous, which cannot be well described by packing of spheres or bundle of tubes. Besides, there are abundant nanoscale pores in shale so that the Knudsen number of gas flow is high, leading to failure of the conventional Darcy's law. Aiming at these challenges, we have studied the influences from pore-scale anisotropy and heterogeneity of shale microstructures on gas permeability including the high Knudsen number Effect (or Klinkenberg Effect for Darcy scale). First, a geometry-based method is proposed to quantify the pore-scale anisotropy and heterogeneity of shale. Then we reconstruct three-dimensional shale structures by the random generation-growth algorithm and use the lattice Boltzmann method to predict its permeability. To reveal the high Knudsen number Effect, both intrinsic permeability and apparent permeability are evaluated. Our results suggest that the intrinsic permeability increases with the anisotropy of pore geometry in parallel direction to the bed, while decreases in perpendicular direction. The slip factor for Klinkenberg correction also exhibits anisotropy when high Knudsen Effect is considered. On the other hand, the heterogeneity of pore distribution may have positive influences on intrinsic permeability for given porosities.
