| 1. |
- Alexandersson, Marcus, et al.
(författare)
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Triphasic Model of Heat and Moisture Transport with Internal Mass Exchange in Paperboard
- 2016
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 112:2, s. 381-408
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Tidskriftsartikel (refereegranskat)abstract
- Mixture theory is used to derive a triphasic model to describe processes in paperboard consisting of solid fiber, bound water and gas. The gas is viewed as a miscible mix of the two constituents dry air and water vapor. The governing equations are mass conservation laws for bound water, dry air, water vapor, and mixture energy balance. Constitutive relations are found by exploiting the macroscale dissipation inequality. Resulting constitutive equations include Fickian diffusion of water vapor and dry air, Darcian flow for gas and Fourier heat conduction for the mixture. Mass exchange between bound water, and water vapor due to adsorption/desorption is driven by the difference in chemical potential. The interaction function is based on equilibrium considerations for the bound water–water vapor system. From the description of the sorption isotherm, expressions for net isosteric heat and free energy related to water–fiber interaction are derived. The resulting thermodynamically consistent model is used to simulate moisture and heat dynamics for paperboard rolls. Simulation results are presented for a paperboard roll with anisotropic material properties subjected to a change in ambient relative humidity from 50 to 80 %.
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| 2. |
- ALI, ABDALLAH SHOKRY MAHMOUD, et al.
(författare)
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A Superposition Procedure for Calculation of Effective Diffusion and Elastic Parameters of Sparsely Porous Materials
- 2017
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 118:3, s. 473-494
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Tidskriftsartikel (refereegranskat)abstract
- Effective material parameters for diffusion and elastic deformation are calculatedfor porous materials using a continuum theory-based superposition procedure. The theory that is limited to two-dimensional cases, requires that the pores are sufficiently sparse. The methodleads to simple manual calculations that can be performed by, e.g. hospital staff at clinicaldiagnoses of bone deceases that involve increasing levels of porosity. An advantage is that theresult relates to the bone material permeability and stiffness instead of merely pore densities.The procedure uses precalculated pore shape factors and exact size scaling. The remainingcalculations do not require any knowledge of the underlying field methods that are used tocompute the shape factors. The paper establishes the upper limit for the pore densities that aresufficiently sparse. A cross section of bovine bone is taken as an example. The superpositionprocedure is evaluated against a full scale finite element calculation. The study compares thepore induced change of the diffusion coefficient and elastic modulus. The predictions differbetween superposition and full scale calculations with 0.3% points when pore contributionto the diffusion constant is 3–7%, and 0.7% points when the pore contribution to the modulusof elasticity is 4.5–5%. It is uncertain if the error is in the superposition method, which isexact for small pore densities, while the full scale finite model is not.
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| 3. |
- Billstein, Mats, et al.
(författare)
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Development and Validation of a Numerical Model of Flow Through Embankment Dams – Comparisons with Experimental Data and Analytical Solutions
- 1999
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Ingår i: Transport in Porous Media. - 0169-3913 .- 1573-1634. ; 35:3, s. 395-406
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Tidskriftsartikel (refereegranskat)abstract
- The development and validation of a numerical simulation model of the flow through embankment dams is described. The paper focuses on basic verification studies, that is, comparisons with analytical solutions and data from laboratory experiments. Two experimental studies, one dealing with the flow in a Hele-Shaw cell and the other with the flow through a bed of packed glass beads, are also described. Comparisons are carried out with respect to the phreatic surfaces, pressure profiles, seepage levels and discharges. It is concluded that the agreement between experimental, analytical and numerical results is generally satisfactory.
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| 4. |
- Bringedal, Carina, et al.
(författare)
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Effective Behavior Near Clogging in Upscaled Equations for Non-isothermal Reactive Porous Media Flow
- 2017
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 120:3, s. 553-577
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Tidskriftsartikel (refereegranskat)abstract
- For a non-isothermal reactive flow process, effective properties such as permeability and heat conductivity change as the underlying pore structure evolves. We investigate changes of the effective properties for a two-dimensional periodic porous medium as the grain geometry changes. We consider specific grain shapes and study the evolution by solving the cell problems numerically for an upscaled model derived in Bringedal et al. (Transp Porous Media 114(2):371-393, 2016. doi 10.1007/s11242-015-0530-9). In particular, we focus on the limit behavior near clogging. The effective heat conductivities are compared to common porosity-weighted volume averaging approximations, and we find that geometric averages perform better than arithmetic and harmonic for isotropic media, while the optimal choice for anisotropic media depends on the degree and direction of the anisotropy. An approximate analytical expression is found to perform well for the isotropic effective heat conductivity. The permeability is compared to some commonly used approaches focusing on the limiting behavior near clogging, where a fitted power law is found to behave reasonably well. The resulting macroscale equations are tested on a case where the geochemical reactions cause pore clogging and a corresponding change in the flow and transport behavior at Darcy scale. As pores clog the flow paths shift away, while heat conduction increases in regions with lower porosity.
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| 5. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete
- 2019
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Ingår i: Transport in Porous Media. - Netherlands : Springer. - 0169-3913 .- 1573-1634. ; 127:1, s. 113-141
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Tidskriftsartikel (refereegranskat)abstract
- Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water into the concrete, and it may take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of filling of air pores with water is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the thermodynamically constrained averaging theory as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete and yields results that comply with laboratory and in situ measurements.
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| 6. |
- Fabricius, John, et al.
(författare)
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Darcy's law for flow in a periodic thin porous medium confined between two parallel plates
- 2016
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 115:3, s. 473-493
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Tidskriftsartikel (refereegranskat)abstract
- We study stationary incompressible fluid flow in a thin periodic porous medium. The medium under consideration is a bounded perforated 3D-domain confined between two parallel plates. The distance between the plates is \(\delta \), and the perforation consists of \(\varepsilon \)-periodically distributed solid cylinders which connect the plates in perpendicular direction. Both parameters \(\varepsilon \), \(\delta \) are assumed to be small in comparison with the planar dimensions of the plates. By constructing asymptotic expansions, three cases are analysed: (1) \(\varepsilon \ll \delta \), (2) \(\delta /\varepsilon \sim \text {constant}\) and (3) \(\varepsilon \gg \delta \). For each case, a permeability tensor is obtained by solving local problems. In the intermediate case, the cell problems are 3D, whereas they are 2D in the other cases, which is a considerable simplification. The dimensional reduction can be used for a wide range of \(\varepsilon \) and \(\delta \) with maintained accuracy. This is illustrated by some numerical examples.
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| 7. |
- Fallahjoybari, Nima, et al.
(författare)
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A Subgrid-Scale Model for Turbulent Flow in Porous Media
- 2019
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Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 129:3, s. 619-632
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Tidskriftsartikel (refereegranskat)abstract
- Given the analogy between the filtered equations of large eddy simulation and volume-averaged Navier–Stokes equations in porous media, a subgrid-scale model is presented to account for the residual stresses within the porous medium. The proposed model is based on the kinetic energy balance of the filtered velocity field within a pore; hence, when using the model, numerical simulations of the turbulent flow in the pores are not required. The accuracy of the model is validated with available data in the literature on turbulent flow through packed beds and staggered arrangement of square cylinders. The validation yields that the model successfully captures the effect of the pore-scale turbulent motion. The model is then used to study turbulent flow in a wall-bounded porous media to assess its accuracy.
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| 8. |
- Farzaneh Kaloorazi, Meisam, 1982, et al.
(författare)
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Pore-Scale Transport and Two-Phase Fluid Structures in Fibrous Porous Layers: Application to Fuel Cells and Beyond
- 2021
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 1573-1634 .- 0169-3913. ; 136:1, s. 245-270
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Tidskriftsartikel (refereegranskat)abstract
- We present pore-scale simulations of two-phase flows in a reconstructed fibrous porous layer. The three-dimensional microstructure of the material, a fuel cell gas diffusion layer, is acquired via X-ray computed tomography and used as input for lattice Boltzmann simulations. We perform a quantitative analysis of the multiphase pore-scale dynamics, and we identify the dominant fluid structures governing mass transport. The results show the existence of three different regimes of transport: a fast inertial dynamics at short times, characterised by a compact uniform front, a viscous-capillary regime at intermediate times, where liquid is transported along a gradually increasing number of preferential flow paths of the size of one–two pores, and a third regime at longer times, where liquid, after having reached the outlet, is exclusively flowing along such flow paths and the two-phase fluid structures are stabilised. We observe that the fibrous layer presents significant variations in its microscopic morphology, which have an important effect on the pore invasion dynamics, and counteract the stabilising viscous force. Liquid transport is indeed affected by the presence of microstructure-induced capillary pressures acting adversely to the flow, leading to capillary fingering transport mechanism and unstable front displacement, even in the absence of hydrophobic treatments of the porous material. We propose a macroscopic model based on an effective contact angle that mimics the effects of the such a dynamic capillary pressure. Finally, we underline the significance of the results for the optimal design of face masks in an effort to mitigate the current COVID-19 pandemic.
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| 9. |
- Ferdos, Farzad, et al.
(författare)
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Hydraulic Conductivity of Coarse Rockfill used in Hydraulic Structures
- 2015
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 108:2, s. 367-391
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Tidskriftsartikel (refereegranskat)abstract
- Internal erosion is a major cause of embankment dam failure. Unravelling and instability of the downstream slope, initiated by internal erosion and leakage through the dam core, is one of the most likely breach mechanisms for large, zoned embankment dams. To be able to model this mechanism, the relationship between the hydraulic gradient and the flow velocity for the coarse rockfill material must be understood. Because most studies of this topic have focused on the flow parameters in gravel-size materials with Reynolds (Re) numbers lower than 25,000, permeability measurements are needed coarser rockfill material under heavily turbulent flow regimes prevailing in rockfill material under certain design flow scenarios. This paper presents the set-up and results of a series of field and laboratory experimental studies and the subsequent data interpretation, from which relevant hydraulic conductivity parameters, defined in applicable flow laws, were extracted. This study demonstrates that the exponent of a power flow law relating the hydraulic gradient and the flow velocity is Re number dependent for pore Re numbers 60,000. The power remains constant (Re number independent) above this Re number threshold for the fully developed turbulent regime. This validity threshold as well as the constant behaviour also applies if the flow law is written in a quadratic form. The aforementioned threshold lies beyond the ranges investigated experimentally by previous researchers. The experiments in this study examined Re numbers as large as 220,000 for grain-diameter distributions in the range 100-160 mm and as large as 320,000 in the range 160-240 mm.
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| 10. |
- Forslund, Tobias O.M. 1992-, et al.
(författare)
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Steady-State Transitions in Ordered Porous Media
- 2023
-
Ingår i: Transport in Porous Media. - : Springer Nature. - 0169-3913 .- 1573-1634. ; 149:2, s. 551-577
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Tidskriftsartikel (refereegranskat)abstract
- Previously performed experiments on flow through an ordered porous media cell with tomographic particle image velocimetry reveal a complex three-dimensional steady-state flow pattern. This flow pattern emerge in the region where inertial structures have been previously reported for a wide range of packings. The onset of these steady-state inertial flow structures is here scrutinized for three different types of packing using a finite difference method. It is concluded that the onset of the flow structure coincides with a symmetry break in the flow field and discontinuities in the pressure drop, volume averaged body forces and heat transfer. A quantity for identifying the transition is proposed, namely the pressure integral across the solid surfaces. It is also shown that the transition can both increase and decrease the heat transfer dependent on the actual geometry of the porous medium.
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| 11. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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The Effects of Periodicity Assumptions in Porous Media Modelling
- 2021
-
Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 137:3, s. 769-797
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Tidskriftsartikel (refereegranskat)abstract
- The effects of periodicity assumptions on the macroscopic properties of packed porous beds are evaluated using a cascaded Lattice-Boltzmann method model. The porous bed is modelled as cubic and staggered packings of mono-radii circular obstructions where the bed porosity is varied by altering the circle radii. The results for the macroscopic properties are validated using previously published results. For unsteady flows, it is found that one unit cell is not enough to represent all structures of the fluid flow which substantially impacts the permeability and dispersive properties of the porous bed. In the steady region, a single unit cell is shown to accurately represent the fluid flow across all cases studied
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| 12. |
- Frishfelds, Vilnis, et al.
(författare)
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Flow-induced deformations within random packed beds of spheres
- 2014
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 104:1, s. 43-56
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Tidskriftsartikel (refereegranskat)abstract
- Low Reynolds number flow-induced alterations of permeability of random packing of mono-sized spheres is studied. The number of spheres is several thousands and the porosities ranges between 0.4 and 0.6. The change of permeability is obtained for elastic deformations of the positions of the spheres using either of two methods. Each sphere is elastically attached to single points or the spheres that are connected via an elastic porous network. The system of spheres is divided into smaller volumes with Voronoi diagrams and the flow is derived by usage of a dual stream function. The local saturated flow fields are approximated as for close packed spheres and the overall flow pattern is obtained by minimising the dissipation rate of energy. The results show that the permeability for large random systems increases as a function of velocity and thus the deformation. The alteration is, however, much less than for two-dimensional cases like parallel cylinders. The relative increase in permeability becomes larger as the porosity increases from 0.4 to 0.6.
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| 13. |
- Frishfelds, Vilnis, et al.
(författare)
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Fluid flow induced internal erosion within porous media : modelling of the no erosion filter test experiment
- 2011
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 89:3, s. 441-457
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of the potential to numerically model the no erosion filter test is performed here, where the flow through a large ensemble of particles is considered by applying minimisation of dissipation rate of energy on the ensemble that is discretised with modified Voronoi diagrams and Delaunay triangulation. Low-Reynolds number simulations are applied to each part of the Voronoi diagram using computational fluid dynamics. The mechanical friction between particles is modelled by increasing the effective viscosity for closely spaced particles. Microscopic mechanisms for successful and unsuccessful sealing of filters are obtained. The numerical results agree with previously presented experimental observations by Sherard and Dunnigan. A conformity is that the sealing starts from the end of the channel and continues outwards in the radial direction. The sealing implies that the permeability can be reduced several orders of magnitude during a test.
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| 14. |
- Frishfelds, Vilnis, et al.
(författare)
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Lattice gas analysis of liquid front in non-crimp fabrics
- 2010
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 84:1, s. 75-93
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Tidskriftsartikel (refereegranskat)abstract
- The liquid flow front during impregnation of non-crimp fabrics is considered. Irregularities in fibre bundle architecture lead to generation of bubbles at this front. The velocity of this interface is highly influenced by capillary forces mainly caused by the small fibres inside the bundles. In order to better understand which shapes the liquid front takes up at different conditions, a lattice gas model has been applied. First, the macroscopic properties of the solved gas in the liquid are discussed. Next, bubble inclusions are analyzed as to liquid-gas interface position and concentrations of minor component in each phase. The capillary effects at the fluid front are studied for systems both with and without gaps between the bundles. The flow in the interior of the fibre bundles is scrutinized, as well, by also considering the viscous stresses. The flow through unidirectional fabrics is considered by a one-dimensional model, which suggests that the liquid front inside bundles and gaps moves with the same speed when the liquid front inside the bundle has to catch up with the liquid front in the gap
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| 15. |
- Gebäck, Tobias, 1977, et al.
(författare)
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A Pore Scale Model for Osmotic Flow: Homogenization and Lattice Boltzmann Simulations
- 2019
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 126:1, s. 161-176
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Tidskriftsartikel (refereegranskat)abstract
- Osmosis is the phenomenon of spontaneous passage of solvents through a membrane that is permeable to the solvent but is completely or partially impermeable to solute particles. On a macroscopic scale, it is well understood how a difference in concentration of solute across a membrane gives rise to an osmotic pressure that may induce a flow through the membrane. On the pore scale inside the membrane, however, the ongoing processes are less well understood. In this paper, a model is presented for how osmotic effects on the pore scale are induced by forces acting on the solute from the membrane material. Furthermore, homogenization results rigorously derived elsewhere by one of the authors (Heintz and Piatnitski in Netw Heterog Media 11(3):585-610, 2016) are presented, and an implementation of the homogenized model using the lattice Boltzmann method is described. The homogenization results provide a means to compute macroscopic parameters determining the osmotic flow through a porous material, in particular the so called reflection coefficient. The numerical results show excellent agreement with theoretical results for straight cylindrical channels and also illustrate the applicability of the method to periodic porous media.
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| 16. |
- Icardi, M., et al.
(författare)
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Population Balance Models for Particulate Flows in Porous Media : Breakage and Shear-Induced Events
- 2023
-
Ingår i: Transport in Porous Media. - : Springer Nature. - 0169-3913 .- 1573-1634. ; 146:1-2, s. 197-222
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Tidskriftsartikel (refereegranskat)abstract
- Transport and particulate processes are ubiquitous in environmental, industrial and biological applications, often involving complex geometries and porous media. In this work we present a general population balance model for particle transport at the pore-scale, including aggregation, breakage and surface deposition. The various terms in the equations are analysed with a dimensional analysis, including a novel collision-induced breakage mechanism, and split into one- and two-particles processes. While the first are linear processes, they might both depend on local flow properties (e.g. shear). This means that the upscaling (via volume averaging and homogenisation) to a macroscopic (Darcy-scale) description requires closures assumptions. We discuss this problem and derive an effective macroscopic term for the shear-induced events, such as breakage caused by shear forces on the transported particles. We focus on breakage events as prototype for linear shear-induced events and derive upscaled breakage frequencies in periodic geometries, starting from nonlinear power-law dependence on the local fluid shear rate. Results are presented for a two-dimensional channel flow and a three dimensional regular arrangement of spheres, for arbitrarily fast (mixing-limited) events. Implications for linearised shear-induced collisions are also discussed. This work lays the foundations of a new general framework for multiscale modelling of particulate flows.
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| 17. |
- Jailin, C., et al.
(författare)
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Fast Tracking of Fluid Invasion Using Time-Resolved Neutron Tomography
- 2018
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 124:1, s. 117-135
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Tidskriftsartikel (refereegranskat)abstract
- Water flow in a sandstone sample is studied during an experiment in situ in a neutron tomography setup. In this paper, a projection-based methodology for fast tracking of the imbibition front in 3D is presented. The procedure exploits each individual neutron 2D radiograph, instead of the tomographic-reconstructed images, to identify the 4D (space and time) saturation field, offering a much higher time resolution than more standard reconstruction-based methods. Based on strong space and time regularizations of the fluid flow, with an a priori defined space and time shape functions, the front shape is identified at each projection time step. This procedure aiming at a fast tracking the fluid advance is explored through two examples. The first one shows that the fluid motion that occurs during one single 180(Formula presented.) scan can be resolved at 5 Hz with a sub-pixel accuracy whereas it cannot be unraveled with plain tomographic reconstruction. The second example is composed of 42 radiographs acquired all along a complete fluid invasion in the sample. This experiment uses the very same approach with the additional difficulty of large fluid displacement in between two projections. As compared to the classical approach based on full reconstructions at each invasion stage, the proposed methodology in the studied examples is roughly 300 times faster offering an enhanced time resolution.
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| 18. |
- Jensen, Mads Mønster, et al.
(författare)
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A Numerical Comparison of Ionic Multi-Species Diffusion with and without Sorption Hysteresis for Cement-Based Materials
- 2015
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 107:1, s. 27-47
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Tidskriftsartikel (refereegranskat)abstract
- A finite element solution for a mass transport model for porous materials accounting for sorption hysteresis is presented in this paper. The model is prepared for modeling of concrete durability, but the general presentation makes it suitable for other porous materials like soil and tissues. The model is an extended version of the Poisson–Nernst–Planck (PNP) system of equations. The PNP extension includes a two-phase vapor and liquid model coupled by a sorption hysteresis function and a chemical equilibrium term. The strong and weak solutions for the equation system are shown, and a finite element formulation is established by Galerkin’s method. A single-parameter implicit time integration scheme is used for solving the transient response, and the out-of-balance solution is minimized by using a modified Newton–Raphson scheme in which the tangential stiffness is not computed exactly. The sorption hysteresis is added to the solution procedure by a rate function. The hysteresis effect is described by scanning curves defined between two boundary sorption isotherms. A numerical example was constructed to show the applicability and compare a simple approach and a extended approach within the sorption hysteresis model. The examples illustrate the impact of changing relative humidity at the mass transport boundary on the adsorption and desorption stages of a cement-based material. Changes in the pore solution ion concentrations are a result of the changing moisture content, which are shown by the example. Comparing the two approaches showed significant deviations in the liquid content and ion concentrations, in parts of the domain considered.
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| 19. |
- Johannesson, Björn, et al.
(författare)
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A Numerical Approach for Non-Linear Moisture Flow in Porous Materials with Account to Sorption Hysteresis
- 2010
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 84:3, s. 735-754
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Tidskriftsartikel (refereegranskat)abstract
- A numerical approach for moisture transport in porous materials like concrete is presented. The model considers mass balance equations for the vapour phase and the water phase in the material together with constitutive equations for the mass flows and for the exchange of mass between the two phases. History-dependent sorption behaviour is introduced by considering scanning curves between the bounding desorption and absorption curves. The method, therefore, makes it possible to calculate equilibrium water contents for arbitrary relative humidity variations at every material point considered. The scanning curves for different wetting and drying conditions are constructed by using third degree polynomial expressions. The three coefficients describing the scanning curves is determined for each wetting and drying case by assuming a relation between the slope of boundary sorption curve and the scanning curve at the point where the moisture response enters the scanning domain. Furthermore, assuming that the slope of the scanning curve is the same as the boundary curve at the junction point, that is, at the point where the scanning curve hits the boundary curve once leaving the scanning domain, a complete cyclic behaviour can be considered. A finite element approach is described, which is capable of solving the non-linear coupled equation system. The numerical calculation is based on a Taylor expansion of the residual of the stated problem together with the establishment of a Newton-Raphson equilibrium iteration scheme within the time steps. Examples are presented illustrating the performance and potential of the model. Two different types of measurements on moisture content profiles in concrete are used to verify the relevance of the novel proposed model for moisture transport and sorption. It is shown that a good match between experimental results and model predictions can be obtained by fitting the included material constants and parameters.
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| 20. |
- Johannesson, Björn
(författare)
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Development of a Generalized Version of the Poisson-Nernst-Planck Equations Using the Hybrid Mixture Theory : Presentation of 2D Numerical Examples
- 2010
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 85:2, s. 565-592
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Tidskriftsartikel (refereegranskat)abstract
- A numerical scheme for the transient solution of generalized version of the Poisson-Nernst-Planck equations is presented. The finite element method is used to establish the coupled non-linear matrix system of equations capable of solving the present problem iteratively. The Poisson-Nernst-Planck equations represent a set of diffusion equations for charged species, i.e. dissolved ions. These equations are coupled to the ‘internally’ induced electrical field and to the velocity field of the fluid. The Nernst-Planck equations describing the diffusion of the ionic species and the Gauss’ law in used are, however, coupled in both directions. The governed set of equations is derived from a simplified version of the so-called hybrid mixture theory (HMT). This theory is a special version of the more ‘classical’ continuum mixture theories in the sense that it works with averaged equations at macro-scale and that it includes the volume fractions of phases in its structure. The background to the Poisson-Nernst-Planck equations can by the HMT approach be described by using the postulates of mass conservation of constituents together with the Gauss’ law used together with consistent constitutive laws. The HMT theory includes the constituent forms of the quasi-static version of Maxwell’s equations making it suitable for analyzes of the kind addressed in this work. Within the framework of HTM constitutive equations has been derived using the postulate of entropy inequality together with the technique of identifying properties by Lagrange multipliers. These results will be used in obtaining a closed set of equations for the present problem.
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| 21. |
- Jourak, Amir, et al.
(författare)
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Longitudinal dispersion coefficient : effects of particle-size distribution
- 2013
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 99:1, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- The effects of particle-size distribution on the longitudinal dispersion coefficient (DL) in packed beds of spherical particles are studied by simulating a tracer column experiment. The packed-bed models consist of uniform and different-sized spherical particles with a ratio of maximum to minimum particle diameter in the range of 1–4. The modified version of Euclidian Voronoi diagrams is used to discretize the system of particles into cells that each contains one sphere. The local flow distribution is derived with the use of Laurent series. The flow pattern at low particle Reynolds number is then obtained by minimization of dissipation rate of energy for the dual stream function. The value of DL is obtained by comparing the effluent curve from large discrete systems of spherical particles to the solution of the one-dimensional advection-dispersion equation. Main results are that at Peclet numbers above 1, increasing the width of the particle-size distribution increases the values of DL in the packed bed. At Peclet numbers below 1, increasing the width of the particle-size distribution slightly lowers DL.
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| 22. |
- Jouybari, Nima Fallah, et al.
(författare)
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Investigation of Hydrodynamic Dispersion and Intra-pore Turbulence Effects in Porous Media
- 2020
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Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 131:2, s. 739-765
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present paper is to evaluate and compare the pore level hydrodynamic dispersion and effects of turbulence during flow in porous media. In order to compute these quantities, large eddy simulations of turbulent flow in five unit cells comprised of spherical particles are performed and the results are averaged over the cells. Visualizations of vortical structures reveal that the size of the turbulence structures is of the size of the pores. Investigations furthermore yield that volume-averaged values of the hydrodynamic dispersion are of the same order as the Reynolds stress within the pores. It is also shown that the effect of intra-pore turbulence and hydrodynamic dispersion on the redistribution of macroscopic momentum within the porous medium is negligible compared to Forchheimer term. A discussion is provided on the accuracy of the eddy viscosity hypothesis in the modeling of the volume-averaged intra-pore Reynolds stresses. Finally, the effect of variation in the pore-scale geometry on the turbulence structures and averaged values of hydrodynamic dispersion and Reynolds stress is investigated.
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| 23. |
- Jouybari, Nima Fallah, et al.
(författare)
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Investigation of Post-Darcy Flow in Thin Porous Media
- 2021
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Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 138:1, s. 157-184
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Tidskriftsartikel (refereegranskat)abstract
- We present numerical simulations of post-Darcy flow in thin porous medium: one consisting of staggered arrangements of circular cylinders and one random distribution of cylinders bounded between walls. The simulations span a range of Reynolds numbers, 40 to 4000, where the pressure drop varies nonlinearly with the average velocity, covering nonlinear laminar flow to the fully turbulent regime. The results are compared to those obtained by replacing the bounding walls with symmetric boundaries with the aim to reveal the effect of bounding walls on microscopic characteristics and macroscopic measures, i.e., pressure drop, hydrodynamic dispersion and Reynolds stresses. We use large eddy simulation to directly calculate the Reynolds stresses and turbulent intensity. The simulations show that vortical structures emerge at the boundary between the cylinders and the bounding walls causing a difference between the microscopic flow in the confined and non-confined porous media. This affects the averaged values of pressure drop, the hydrodynamic dispersion and the Reynolds stresses. Finally, the distance between the bounding walls is altered with the particle Reynolds number kept constant. It is observed that the difference between results calculated in confined and non-confined cases increases when the bounding walls are narrower.
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| 24. |
- Khayamyan, Shervin, et al.
(författare)
-
Experimental investigation of transitional flow in porous media with usage of a pore doublet model
- 2014
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 101:2, s. 333-348
-
Tidskriftsartikel (refereegranskat)abstract
- The transition from laminar to turbulent flow in porous media is studied with a new method. To mimic inter-connected pores, a simplified geometry is studied consisting of a pipe with a relatively large diameter that is split into two parallel pipes with different diameters. This is a pore-doublet set-up and the pressure drops over the parallel pipes are recorded by pressure transducers for different flow rates. Results show that the flow in the parallel pipes is redistributed when turbulent slugs pass through one of them. The presence of the slugs is revealed by positive skewness in the pressure signals as well as an increase of the standard deviation of the pressure drops and correlation between the pressure drops of the pipes. A frequency analysis of the pressure drops show that lower band frequency pressure variations in one pipe are communicated to the other pipe while higher band frequencies are filtered out.
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| 25. |
- Khayamyan, Shervin, et al.
(författare)
-
Measurements of Transitional and Turbulent Flow in a Randomly Packed Bed of Spheres with Particle Image Velocimetry
- 2017
-
Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 116:1, s. 413-431
-
Tidskriftsartikel (refereegranskat)abstract
- Particle image velocimetry (PIV) has been used to investigate transitional and turbulent flow in a randomly packed bed of mono-sized transparent spheres at particle Reynolds number, (Formula presented.). The refractive index of the liquid is matched with the spheres to provide optical access to the flow within the bed without distortions. Integrated pressure drop data yield that Darcy law is valid at (Formula presented.). The PIV measurements show that the velocity fluctuations increase and that the time-averaged velocity distribution start to change at lower (Formula presented.). The probability for relatively low and high velocities decreases with (Formula presented.) and recirculation zones that appear in inertia dominated flows are suppressed by the turbulent flow at higher (Formula presented.). Hence there is a maximum of recirculation at about (Formula presented.). Finally, statistical analysis of the spatial distribution of time-averaged velocities shows that the velocity distribution is clearly and weakly self-similar with respect to (Formula presented.) for turbulent and laminar flow, respectively
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| 26. |
- Khayamyan, Shervin, et al.
(författare)
-
Transitional and Turbulent Flow in a Bed of Spheres as Measured with Stereoscopic Particle Image Velocimetry
- 2017
-
Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 117:1, s. 45-67
-
Tidskriftsartikel (refereegranskat)abstract
- Stereoscopic particle image velocimetry has been used to investigate inertia dominated, transitional and turbulent flow in a randomly packed bed of monosized PMMA spheres. By using an index-matched fluid, the bed is optically transparent and measurements can be performed in an arbitrary position within the porous bed. The velocity field observations are carried out for particle Reynolds numbers, (Formula presented.), between 20 and 3220, and the sampling is done at a frequency of 75 Hz. Results show that, in porous media, the dynamics of the flow can vary significantly from pore to pore. At (Formula presented.) around 400 the spatially averaged time fluctuations of total velocity reach a maximum and the spatial variation of the time-averaged total velocity, (Formula presented.) increases up to about the same (Formula presented.) and then it decreases. Also in the studied planes, a considerable amount of the fluid moves in the perpendicular directions to the main flow direction and the time-averaged magnitude of the velocity in the main direction, (Formula presented.), has an averaged minimum of 40% of the magnitude of (Formula presented.) at (Formula presented.) about 400. For (Formula presented.), this ratio is nearly constant and (Formula presented.) is on average a little bit less than 50% of (Formula presented.). The importance of the results for longitudinal and transverse dispersion is discussed.
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| 27. |
- Lal, Sreeyuth, et al.
(författare)
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Investigation of Water Uptake in Porous Asphalt Concrete Using Neutron Radiography
- 2014
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 105:2, s. 431-450
-
Tidskriftsartikel (refereegranskat)abstract
- Porous asphalt (PA), a highly porous hydrophobic composite material, is subjected to water uptake and the process is documented with neutron radiography (NR). While the un-aged laboratory-prepared PA specimens do not show any water uptake, we observe uptake in aged PA even though the bitumen binder is a hydrophobic material. The moisture content distribution plots derived from the NR images clearly identify regions in the aged specimens where water uptake is active. Two-dimensional degree of saturation (DoS) distribution images, which are obtained by combining micro-computer tomography and NR images, identify those pores where saturated flow is certainly active. However, to clearly distinguish between saturated and unsaturated flows in the remaining wet pores, the DoS distribution images are read together with the three-dimensional PA microstructure obtained by micro-CT. It is observed that uptake begins mainly as unsaturated film/corner flow at large well-defined pores. As this uptaken water travels further into the material, the flow transforms into a combination of saturated flow and unsaturated film/corner flow. Saturated flow is seen to be mostly active in the small pores within the mastic. From the observed succession of unsaturated and saturated flows in an aged PA specimen, it can be concluded that years of environmental and mechanical loading has resulted in the stripping of binder from the aggregate surfaces and has consequently exposed patches of hydrophilic aggregate to water, which enables the capillary uptake of water. We also simulate an absolute permeability experiment and observe that relatively less tortuous and more connected paths play an important role in determining the preferential path of the uptaken water.
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| 28. |
- Landa-Marban, David, et al.
(författare)
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An Upscaled Model for Permeable Biofilm in a Thin Channel and Tube
- 2020
-
Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 132:1, s. 83-112
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we derive upscaled equations for modeling biofilm growth in porous media. The resulting macroscale mathematical models consider permeable multi-species biofilm including water flow, transport, detachment and reactions. The biofilm is composed of extracellular polymeric substances (EPS), water, active bacteria and dead bacteria. The free flow is described by the Stokes and continuity equations, and the water flux inside the biofilm by the Brinkman and continuity equations. The nutrients are transported in the water phase by convection and diffusion. This pore-scale model includes variations in the biofilm composition and size due to reproduction of bacteria, production of EPS, death of bacteria and shear forces. The model includes a water-biofilm interface between the free flow and the biofilm. Homogenization techniques are applied to obtain upscaled models in a thin channel and a tube, by investigating the limit as the ratio of the aperture to the length epsilon of both geometries approaches to zero. As epsilon gets smaller, we obtain that the percentage of biofilm coverage area over time predicted by the pore-scale model approaches the one obtained using the effective equations, which shows a correspondence between both models. The two derived porosity-permeability relations are compared to two empirical relations from the literature. The resulting numerical computations are presented to compare the outcome of the effective (upscaled) models for the two mentioned geometries.
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| 29. |
- Lehoux, A. P., et al.
(författare)
-
Transport and Adsorption of Nano-Colloids in Porous Media Observed by Magnetic Resonance Imaging
- 2017
-
Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 119:2, s. 403-423
-
Tidskriftsartikel (refereegranskat)abstract
- We use magnetic resonance imaging to follow the adsorption of colloids during their transport through a porous medium (grain packing). We injected successive pulses of a suspension of nanoparticles able to adsorb onto the grains. To get quantitative information we carry out 2D imaging and 1D measurements of the evolution in time of the distribution profile of all particles (suspended or adsorbed) in cross-sectional layers along the sample axis during the flow. For the first injections we observe the 1D profile amplitude progressively damping as particles advance through the sample, due to their adsorption. 2D imaging shows that successive injections finally result in a coverage of grains by adsorbed particles regularly progressing along the sample. The analysis of the results makes it possible to get a clear description of the adsorption process. In our specific case (particle charged oppositely to the adsorption sites) it appears that the particles rapidly explore the pores and adsorb as soon as they encounter available sites on grains, and the surplus of particles goes on advancing in the sample. A further analysis of the profiles makes it possible to distinguish the respective concentration distribution of suspended and adsorbed particles over time at each step of the process.
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| 30. |
- Lewis, Helen, et al.
(författare)
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Interactions Between Imbibition and Pressure-Driven Flow in a Microporous Deformed Limestone
- 2023
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 146:3, s. 559-585
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron imaging is used for direct observation of evolving water–air and deuterated water–normal water exchanges in flow experiments performed on a laboratory-deformed, microporous laminated limestone, an extremely fine-textured rock altered by arrays of superposed fractures generated in a rock mechanics apparatus. The neutron images document significant, evolving, water speed and flow direction variability at the deci-micron scale and spatially complex patterns of both increasing and decreasing water saturation. We infer that capillarity-driven and pressure-driven water movement occurs concurrently, in close proximity and in competition, and that as local and global water saturations evolve these two drivers can change their dominance in both matrix and deformed elements. Thin sections are used to obtain sub-micron resolution SEM images that provide multi-scale information on the textural features’ spatial arrangements. The textural characteristics are consistent with the inferences made from the coarser flow imaging. Alternating lamina types provide the primary lithological heterogeneity, while the experimentally created deformations lead to quasi-planar zones of highly comminuted matrix and fracture-like voids, each with lengths ranging from sub-mm to cm. Together deformation features delineate a partially connected array. The interplay between fluid movement through deformation features, and flow into (and out of) the laminae, implies near-equivalence of local driving pressure- and capillary-related energies, with subtle shifts in this balance as water saturation increases. The insights gained invite a re-examination of common rules-of-thumb for multi-phase fluid flow often adopted in fractured, low-permeability microporous rocks.
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| 31. |
- Li, Liangxing, et al.
(författare)
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Experimental Study on the Effective Particle Diameter of a Packed Bed with Non-Spherical Particles
- 2011
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 89:1, s. 35-48
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study is conducted to determine the characteristics of frictional pressure drops of fluid flow in porous beds packed with non-spherical particles. The objective is to examine the applicability of the Ergun equation to flow resistance assessment for packed beds with non-spherical particles. The experiments are carried out on the POMECOFL facility at KTH. Hollow spheres and cylinders are used to pack the beds. Either water or air is chosen as the working fluid. The experimental data show that the Ergun equation is applicable to all the test beds if the effective particle diameter used in the equation is chosen as the equivalent diameter of the particles, which is the product of Sauter mean diameter and shape factor of the particles in each bed.
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| 32. |
- Lundström, Staffan, et al.
(författare)
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Measurement of the permeability tensor of compressed fibre beds
- 2002
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Ingår i: Transport in Porous Media. - 0169-3913 .- 1573-1634. ; 47:3, s. 363-380
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Tidskriftsartikel (refereegranskat)abstract
- A new method to measure the permeability tensor of highly compressed fibre beds is developed. The method is based on saturated parallel flow and is evaluated through experiments with various textile materials: press fabrics used in papermaking and fibre reinforcements designed for composites. Since the materials are in the form of sheets, two measuring cells are used, one for the principal in-plane permeabilities and the other for the out-of-plane permeability. A unique feature is that the edge and the bulk flow are measured separately, so that any influence from enhanced or suppressed edge flow may be eliminated. The technique is evaluated with good results in terms of scatter in the measured permeability and the influence of test geometry, pressure, and liquid properties.
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| 33. |
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| 34. |
- Nordlund, Markus, et al.
(författare)
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Effect of multi-scale porosity in local permeability modelling of non-crimp fabrics
- 2008
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 73:1, s. 109-124
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Tidskriftsartikel (refereegranskat)abstract
- The influence of multi-scale porosity of fibre reinforcements on local permeability is investigated, in order to determine the possibility of simplifying permeability models for more efficient permeability calculations. Unit cell models of a biaxial Non-Crimp Fabric are developed and used to investigate, whether or not the porous bundles can be excluded, when modelling the local permeability. Numerical accuracy of calculations is controlled to guarantee the quality of the results and the conclusions drawn from them. It is found that fibre bundles with high fibre density can be excluded from permeability models, while bundles with low fibre volume fractions need to be included. A new method to model the local permeability of multi-scale reinforcements is developed and verified for low fibre density in the bundles. In this method, the effects of the flow inside the fibre bundles are included through modifications of the boundary conditions of a single-scale model representing the interbundle regions. The local permeability of multi-scale reinforcements can, therefore, be calculated by models with simplified fluid domains for all fibre bundle porosities, instead of being calculated by models consisting of the entire multi-scale geometry.
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| 35. |
- Pérez-Ràfols, Francesc, 1990-, et al.
(författare)
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A Stochastic Two-Scale Model for Rarefied Gas Flow in Highly Heterogeneous Porous Media
- 2020
-
Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 135:1, s. 219-242
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the development of a model enabling the analysis of rarefied gas flow through highly heterogeneous porous media. To capture the characteristics associated with the global- and the local-scale topology of the permeable phase in a typical porous medium, the heterogeneous multi-scale method, which is a flexible framework for constructing two-scale models, was employed. The rapid spatial variations associated with the local-scale topology are accounted for stochastically, by treating the permeability of different local-scale domains as a random variable. The results obtained with the present model show that an increase in the spatial variability in the heterogeneous topology of the porous medium significantly reduces the relevance of rarefaction effects. This clearly shows the necessity of considering a realistic description of the pore topology and questions the applicability of the results obtained for topologies exhibiting regular pore patterns. Although the present model is developed to study low Knudsen number flows, i.e. the slip-flow regime, the same development procedure could be readily adapted for other regimes as well.
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| 36. |
- Qin, Menghao, et al.
(författare)
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Nonisothermal moisture transport in hygroscopic building materials: modeling for the determination of moisture transport coefficients
- 2008
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 72:2, s. 255-271
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Tidskriftsartikel (refereegranskat)abstract
- A mathematical model for calculating the nonisothermal moisture transfer in building materials is presented in the article. The coupled heat and moisture transfer problem was modeled. Vapor content and temperature were chosen as principal driving potentials. The coupled equations were solved by an analytical method, which consists of applying the Laplace transform technique and the Transfer Function Method. A new experimental methodology for determining the temperature gradient coefficient for building materials was also proposed. Both the moisture diffusion coefficient and the temperature gradient coefficient for building material were experimentally evaluated. Using the measured moisture transport coefficients, the temperature and vapor content distribution inside building materials were predicted by the new model. The results were compared with experimental data. A good agreement was obtained.
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| 37. |
- Sudhakar, Yogaraj, et al.
(författare)
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Higher-Order Homogenized Boundary Conditions for Flows Over Rough and Porous Surfaces
- 2021
-
Ingår i: Transport in Porous Media. - : Springer Nature. - 0169-3913 .- 1573-1634. ; 136:1, s. 1-42
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Tidskriftsartikel (refereegranskat)abstract
- We derive a homogenized macroscopic model for fluid flows over ordered homogeneous porous surfaces. The unconfined free flow is described by the Navier-Stokes equation, and the Darcy equation governs the seepage flow within the porous domain. Boundary conditions that accurately capture mass and momentum transport at the contact surface between these two domains are derived using the multiscale homogenization technique. In addition to obtaining the generalized version of the widely used Beavers-Joseph slip condition for tangential velocities, the present work provides an accurate formulation for the transpiration velocity and pressure jump at fluid-porous interfaces; these two conditions are essential for handling two- and three-dimensional flows over porous media. All the constitutive parameters appearing in the interface conditions are computed by solving a set of Stokes problems on a much smaller computational domain, making the formulations free of empirical parameters. The tensorial form of the proposed interface conditions makes it possible to handle flows over isotropic, orthotropic, and anisotropic media. A subset of interface conditions, derived for porous media, can be used to model flows over rough walls. The accuracy of the proposed macroscopic model is numerically quantified for flows over porous and rough walls by comparing the results from our homogenized model with those obtained from geometry-resolved microscopic simulations.
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| 38. |
- Tavassoli, Z., et al.
(författare)
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Analytic analysis for oil recovery during counter-current imbibition in strongly water-wet systems
- 2005
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Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 58:1-2, s. 173-189
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Tidskriftsartikel (refereegranskat)abstract
- We study counter-current imbibition, where a strongly wetting phase ( water) displaces non-wetting phase spontaneously under the influence of capillary forces such that the non-wetting phase moves in the opposite direction to the water. We use an approximate analytical approach to derive an expression for saturation profile when the viscosity of the non-wetting phase is non-negligible. This makes the approach applicable to water flooding in hydrocarbon reservoirs, or the displacement of non-aqueous phase liquid (NAPL) by water. We find the recovery of non-wetting phase as a function of time for one-dimensional flow. We compare our predictions with experimental results in the literature. Our formulation reproduces experimental data accurately and is superior to previously proposed empirical models.
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| 39. |
- Tong, Fuguo, et al.
(författare)
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A Numerical Model of Tracer Transport in a Non-isothermal Two-Phase Flow System for Geological Storage Characterization
- 2013
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 98:1, s. 173-192
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Tidskriftsartikel (refereegranskat)abstract
- For the purpose of characterizing geologically stored including its phase partitioning and migration in deep saline formations, different types of tracers are being developed. Such tracers can be injected with or water, and their partitioning and/or reactive transfer from one phase to another can give information on the interactions between the two fluid phases and the development of their interfacial area. Kinetic rock-water interactions and geochemical reactions during two-phase flow of and brine have been incorporated in numerical simulators (e.g., Xu et al., TOUGHREACT User's Guide: A Simulation Program for Non-isothermal Multiphase Reactive Geochemical Transport in Variably Saturated Geologic Media. LBNL Report 55460, V.1.2., Berkeley, CA, 2004). However, chemical equilibrium between the fluid phases is typically assumed, and multi-component, multiphase, non-isothermal codes for -brine systems that incorporate kinetic mass transfer of tracers between the two fluid phases are not readily available. New models or further developments of existing models are therefore needed to provide the capability for interpreting the signals of novel tracers, including tracers with kinetic/time-dependent interface transfer. This paper presents such new numerical model of tracer transport in a non-isothermal two-phase flow system. The model consists of five different governing equations describing liquid phase (aqueous) flow, gas ( flow, heat transport and the movement of the tracers within the two phases, as well as allowing kinetic transport of the tracers between the two phases. A finite element method is adopted for the spatial discretization and a finite difference approach is used for temporal discretization. Some special technologies and solution strategies are adopted for increasing the convergence, ensuring the numerical stability and eliminating non-physical oscillations. The new numerical model is validated against the code TOUGH2/ECO2N as well as some analytical/semi-analytical solutions. Good agreement between the simulated and analytical results indicates that the model has capability to simulate two-phase flow and tracer transport in a non-isothermal two-phase flow system with high confidence. Finally, the capability to model transport and kinetic mass transfer of tracers between the two fluid phases is demonstrated through examples.
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| 40. |
- Tong, Fuguo, et al.
(författare)
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A Water Retention Curve Model for the Simulation of Coupled Thermo-Hydro-Mechanical Processes in Geological Porous Media
- 2012
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 91:2, s. 509-530
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new water retention curve (WRC) model for the simulation of coupled thermo-hydro-mechanical processes in geological porous media. The model simultaneously considers the impact of porosity and temperature on suction, for both wetting processes and drying processes. The model is based on an idealization of porous geological media as having an isotropic and homogeneous microscopic pore structure. Suction is expressed as a function of degree of saturation, porosity, surface tension of the water-air interface, and the length of air bubble perimeter of the pores per unit area on a random 2D cross-section of the medium. The tension of water-air interface is written as a function of temperature, and the length of perimeter of the water-air interface of the pores becomes a function of porosity and degree of saturation. The final equation of the new WRC is a function of suction, effective degree of saturation, temperature, porosity, pore-gas pressure, and the rate of degree of saturation change with time for both wetting and drying processes. The model was used to fit experimental data of the FEBEX bentonite, with good agreements between measured and calculated results.
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| 41. |
- Vasilyev, Leonid, et al.
(författare)
-
On the Properties of the Parameter Space of the Generalized Continuum Transport Model for Description of Fluid Flow in Porous Networks
- 2017
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 119:3, s. 673-688
-
Tidskriftsartikel (refereegranskat)abstract
- Generalized transport models, such as Dual and Multiple Continua Models, Global Random Walk, Multirate Mass Transfer and Continuous Time Random Walk are widely used for description of anomalous transport in fractured and porous media. For these models the form of the parameter space is crucial for the most accurate description of anomalous effects as well as the mean transport phenomenon. Constraining of the parameter space is required for the proper interpretation of the physical properties taking place. In this study the Generalized Continuum Transport model is considered as a versatile tool for the parameter space selection as well as better quantification of anomalous (non-Fickian) transport. Different variants of the parameter space are applied to the GCT model and the breakthrough curves obtained from the pore-network models with strong anomalities are fitted. Flexibility of the model is demonstrated through its static and dynamic adaptivity to network structure and transport complexity. The beneficial results of the curve fitting are also compared with the classical models. It is thus demonstrated that the complexity of the model as well as the model parameters can be directly determined based on fine-scale simulations.
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| 42. |
- Vilarrasa, Victor, et al.
(författare)
-
Shear-Induced Flow Channels in a Single Rock Fracture and Their Effect on Solute Transport
- 2011
-
Ingår i: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 87:2, s. 503-523
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of mechanical shearing on fluid flow anisotropy and solute transport in rough rock fractures was investigated by numerical modeling. Two facing surfaces of a rock fracture of 194 mm x 194 mm in size were laser scanned to generate their respective digital profiles. Fluid flow through the fracture was simulated using a finite element code that solves the Reynolds equation, while incremental relative movement of the upper surface was maintained numerically to simulate a shearing process without normal loading. The motion of solute particles in a rough fracture undergoing shear was studied using a particle tracking code. We found that shearing introduces anisotropy in fracture transmissivity, with a greatly increased flow rate and particle travel velocity in the direction perpendicular to the shearing direction. Shear-induced channels yield a transport behavior in which advection dominates in the direction parallel with shear and dispersion dominates in the direction perpendicular to shear. The shear-induced flow channels not only increase the flow connectivity, but also the transport connectivity in the direction perpendicular to shear. This finding has an important impact on the interpretation of the results of coupled hydromechanical and tracer transport experiments for measurements of hydraulic and transport properties of rock fractures.
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| 43. |
- Zou, Liangchao, et al.
(författare)
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Modeling of Solute Transport in a 3D Rough-Walled Fracture-Matrix System
- 2017
-
Ingår i: Transport in Porous Media. - : SPRINGER. - 0169-3913 .- 1573-1634. ; 116:3, s. 1005-1029
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Tidskriftsartikel (refereegranskat)abstract
- Fluid flow and solute transport in a 3D rough-walled fracture-matrix system were simulated by directly solving the Navier-Stokes equations for fracture flow and solving the transport equation for the whole domain of fracture and matrix with considering matrix diffusion. The rough-walled fracture-matrix model was built from laser-scanned surface tomography of a real rock sample, by considering realistic features of surfaces roughness and asperity contacts. The numerical modeling results were compared with both analytical solutions based on simplified fracture surface geometry and numerical results by particle tracking based on the Reynolds equation. The aim is to investigate impacts of surface roughness on solute transport in natural fracture-matrix systems and to quantify the uncertainties in application of simplified models. The results show that fracture surface roughness significantly increases heterogeneity of velocity field in the rough-walled fractures, which consequently cause complex transport behavior, especially the dispersive distributions of solute concentration in the fracture and complex concentration profiles in the matrix. Such complex transport behaviors caused by surface roughness are important sources of uncertainty that needs to be considered for modeling of solute transport processes in fractured rocks. The presented direct numerical simulations of fluid flow and solute transport serve as efficient numerical experiments that provide reliable results for the analysis of effective transmissivity as well as effective dispersion coefficient in rough-walled fracture-matrix systems. Such analysis is helpful in model verifications, uncertainty quantifications and design of laboratorial experiments.
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| 44. |
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| 45. |
- Hager, Jörgen, et al.
(författare)
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The thermodynamic significance of the local volume averaged temperature
- 2002
-
Ingår i: Transport in Porous Media. - 0169-3913. ; 46:1, s. 19-35
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Tidskriftsartikel (refereegranskat)abstract
- Since the temperature is not an additive function, the traditional thermodynamic point of view suggests that the volume integral of the temperature has no precise physical meaning. This observation conflicts with the customary analysis of non-isothermal catalytic reactors, heat pipes, driers, geothermal processes, etc., in which the volume averaged temperature plays a crucial role. In this paper we identify the thermodynamic significance of the volume averaged temperature in terms of a simple two-phase heat transfer process. Given the internal energy as a function of the point temperature and the density e(beta) = F (T-beta, rho(beta)), we show that the volume averaged internal energy is represented by [e(beta)](beta) = F([T-beta](beta), [rho(beta)](beta)), when e(beta) is a linear function of T-beta and rho(beta), or when the traditional length-scale constraints associated with the method of volume averaging are satisfied. When these conditions are not met, higher order terms involving the temperature gradient and the density gradient appear in the representation for [e(beta)](beta).
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| 46. |
- Kvashchuk, Anna, et al.
(författare)
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A Second‑Order Finite Volume Method for Field‑Scale Reservoir Simulation
- 2023
-
Ingår i: Transport in Porous Media. - 0169-3913. ; 150, s. 109-129
-
Tidskriftsartikel (refereegranskat)abstract
- Subsurface reservoirs are large complex systems. Reservoir flow models are defined on complex grids that follow geology with relatively large block sizes to make consistent simulations feasible. Reservoir engineers rely on established reservoir simulation software to model fluid flow. Nevertheless, fluid front position inaccuracies and front smearing on large grids may cause significant errors and make it hard to predict hydrocarbon production efficiency. We investigate higher-order methods that reduce these undesired effects without refining the grid, thus making reservoir simulation more accurate and robust. For this paper, we implemented a second-order finite volume method with linear programming (LP) reconstruction in the open-source industry-grade reservoir simulator OPM Flow (part of the open porous media initiative, OPM). We benchmark it against the first-order method on full-scale cases with standard coarse and refined grids. We prepared open refined-grid models of a synthetic reservoir with an unstructured grid and refined Norne field example. Our results confirm that the LP method predicts front positions as accurately as the first-order method on the refined grid for problems dominated by transport. These include the water alternating gas scenario on the synthetic reservoir and piston-type injection on the Norne field. Moreover, we study the gains from the LP method for CO2 injection problems on the Norne field with full multi-phase complexity beyond transport. We observe the relevant difference between the first- and the second-order methods in these cases. However, in some configurations, the reservoir complexity overshadows the gains from the second-order methods.
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| 47. |
- Nilsson, Lars, et al.
(författare)
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Effects of serial and parallel pore nonuniformities: Results from two models of the porous structure
- 1996
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Ingår i: Transport in Porous Media. - 0169-3913. ; 25:3, s. 335-350
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Tidskriftsartikel (refereegranskat)abstract
- The effects of parallel-type and serial-type pore nonuniformities on the effective diffusivity and the permeability of a porous material were evaluated, constant porosity and constant specific surface area being assumed. Two structural models were considered. In the first model, the porous structure was described as a bundle of cylindrical capillaries penetrating the whole thickness of the material and in the other it was described instead as a collection of randomly distributed obstacles hindering transport. Both models predicted that parallel-type pore nonuniformities produce an increase in permeability compared with uniform structures having the same porosity and specific surface area. Both models also predicted that the increase in permeability due to parallel-type pore nonuniformities would be larger than the increase in effective diffusivity. Regarding serial-type pore nonuniformities, both models predicted a decrease in permeability and that this decrease would be greater than the decrease in effective diffusivity. The predicted changes in effective diffusivity due to nonuniformities of the sample differed for the two structural models.
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