| 1. |
- 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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| 2. |
- Jansson, Anton, 1986-, et al.
(författare)
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Multi-material gap measurements using dual-energy computed tomography
- 2018
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Ingår i: Precision engineering. - : Elsevier. - 0141-6359 .- 1873-2372. ; 54, s. 420-426
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Tidskriftsartikel (refereegranskat)abstract
- X-ray computed tomography is a highly versatile investigation method with applications in a wide range ofareas. One of the areas where the technique has seen an increased usage, and an increased interest from industry,is in dimensional metrology. X-ray computed tomography enables the measurement of features and dimensionsthat are difficult to inspect using other methods. However, there are issues with the method when it comes tomeasurements of objects that consist of several materials. In particular, it is difficult to obtain accurate computedtomography results for all materials when the attenuation of materials differs significantly. The aim of this workwas to measure small air gaps between different materials using dual-energy X-ray computed tomography. Thedual-energy method employed in this work uses two energy spectra and fuses the data in the projections spaceusing non-linear fusion. The results from this study show that the dual-energy method used in this work was ableto capture more measurements than regular absorption computed tomography in the case of specimens withhighly different attenuation, enabling, in particular, the measurement of smaller gaps. The contrast-to-noise ratiowas also increased significantly with the use of dual-energy.
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| 3. |
- Maggiolo, Dario, 1985, et al.
(författare)
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Characterization of fluid-mechanic efficiency of porous electrodes using X-ray computed tomography and Lattice-Boltzmann simulations
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Flow batteries are a promising solution for storing the energy produced by carbon-free intermittent renewable sources. They are constituted by liquid electrolytes flowing and reacting into carbon felt porous electrodes. In order to enhance their performances it is necessary to maximise electrolyte dispersion and reaction together and to minimize the flow resistance through the porous media [1]. It is well reported in the literature how peculiar and anomalous can be the dispersion behaviour in natural porous media [2] and in fibrous materials [3]; however, it is still badly known how much it affects the performances of real electrodes of flow batteries. To clarify this issue, real carbon felt electrodes have been reconstructed by means of X-ray computed tomography (CT). In particular, a metrological micro-CT system has been used to obtain accurate three-dimensional reconstructions, which have then been used as input for Lattice-Boltzmann flow simulations coupled with a Lagrangian Particle Tracking algorithm, in order to investigate the dispersion and reaction behaviour of tracers through the medium microstructures, see e.g. Fig.1. For each material, macroscopic dispersion, reaction efficiencies and flow resistance have been evaluated from the underlying microscopic statistics of flow and tracer trajectories. From these analyses, the overall fluid-mechanic efficiency of each material has been evaluated and compared allowing the identification of the optimal porous microstructure for flow battery applications, which shows the highest dispersion and reaction rate together with the lowest pressure drop. [1] Wang B., Kuo J., Bae S.C. and Granick S., 2012. Nature Materials, 11(6): 481-5. [2] Alotto P., Guarnieri M. and Moro F., 2014. Renewable and Sustainable Energy Reviews, 29, pp.325-335. [3] Maggiolo D., Picano F. and Guarnieri M., 2016. Physics of Fluids, 28(10), p.102001.
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| 4. |
- Maggiolo, Dario, 1985, et al.
(författare)
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Particle based method and X-ray computed tomography for pore-scale flow characterization in VRFB electrodes
- 2019
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Ingår i: Energy Storage Materials. - : Elsevier BV. - 2405-8297. ; 16, s. 91-96
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Tidskriftsartikel (refereegranskat)abstract
- Porous electrodes are pivotal components of Vanadium Redox Flow Batteries, which influence the power density, pressure drop losses, activation overpotentials, limit current density, bulk and contact resistance, and ohmic losses. The quantification of the fluid-mechanic efficiency of porous electrodes based on their real geometry is a useful measure, as it primarily affects the mass transport losses and the overall battery performances. Although several studies, both numerical and experimental, have been devoted to the electrode enhancement, most analyses are carried out under the simplifying assumption of linear, macrohomogeneous and isotropic behavior of the fluid mechanics in the porous material. We present an original approach built on the Lattice-Boltzmann Method and Lagrange Particle Tracking that makes use of pore-scale accurate geometrical data provided by X-ray computed tomography with the aim of studying the dispersion and reaction rates of liquid electrolyte reactants in the flow battery porous electrode. Following this methodology, we compare the fluid-dynamic performances provided by a commonly used carbon felt and an unconventional material, that is, a carbon vitrified foam. Surprisingly, results unveil the possibility of achieving higher fluid-mechanic efficiencies with the foam electrode, whose intrinsic microstructure promotes higher reaction rate.
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| 5. |
- Maggiolo, Dario, 1985, et al.
(författare)
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Solute transport and reaction in porous electrodes at high Schmidt numbers
- 2020
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 896:A13
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Tidskriftsartikel (refereegranskat)abstract
- We present lattice Boltzmann pore-scale numerical simulations of solute transport and reaction in porous electrodes at a high Schmidt number, Sc=10^2. The three-dimensional geometry of real materials is reconstructed via X-ray computed tomography. We apply a volume-averaging upscaling procedure to characterise the microstructural terms contributing to the homogenised description of the macroscopic advection–reaction–dispersion equation. We firstly focus our analysis on its asymptotic solution, while varying the rate of reaction. The results confirm the presence of two working states of the electrodes: a reaction-limited regime, governed by advective transport, and a mass-transfer-limited regime, where dispersive mechanisms play a pivotal role. For all materials, these regimes depend on a single parameter, the product of the Damköhler number and a microstructural aspect ratio. The macroscopic dispersion is determined by the spatial correlation between solute concentration and flow velocity at the pore scale. This mechanism sustains reaction in the mass-transfer-limited regime due to the spatial rearrangement of the solute transport from low-velocity to high-velocity pores. We then compare the results of pre-asymptotic transport with a macroscopic model based on effective dispersion parameters. Interestingly, the model correctly represents the transport at short characteristic times. At longer times, high reaction rates mitigate the mechanisms of heterogeneous solute transport. In the mass-transfer-limited regime, the significant yet homogeneous dispersion can thus be modelled via an effective dispersion. Finally, we formulate guidelines for the design of porous electrodes based on the microstructural aspect ratio.
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| 6. |
- Pejryd, Lars, 1955-, et al.
(författare)
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Computed Tomography as a Tool for Examining Surface Integrity in Drilled Holes in CFRP Composites
- 2014
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271 .- 2212-8271. ; 13, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- In light weight structures the joining of composite materials and of composites to metals are key technologies. A manufacturing method associated with joining is the drilling of holes. The hole creation in CRFP through drilling is associated with several defects related to the process, both on the entry and exit sides of the hole and also with dimensional and surface roughness issues of the hole wall. The detection of damage due to the process is not trivial. Especially interesting is non-destructive methods. In this work X-ray computed tomography is used to determine defects due to drilling of holes in a CFRP composite using twist drills with different geometrical features at different drilling parameters. The results can be used to establish relationship between different geometrical features of drills in combination with cutting parameters and resulting surface integrity of holes. © 2014 The Authors. Published by Elsevier B.V.
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