| 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
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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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