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Porosity variation within a porous bed composed of multisized grains

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Khalili,  Arzhang
Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Malekmohammadi,  Reza
Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Kuypers,  Marcel M.M.
Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Citation

Khalili, A., Matyka, M., Malekmohammadi, R., Weise, J., & Kuypers, M. M. (2018). Porosity variation within a porous bed composed of multisized grains. POWDER TECHNOLOGY, 338, 830-835. doi:10.1016/j.powtec.2018.07.039.


Cite as: https://hdl.handle.net/21.11116/0000-0003-B7C0-5
Abstract
We capture the interfacial region of randomly packed porous layers composed of multi-sized spherical or arbitrarily-shaped granules using X-ray computed tomography to explore the porosity-depth variation below a porous media interface. In the case of uni-sized spherical beads, we found in our previous study that the porosity varies from 1 to it's bulk value within a depth of the order of one grain diameter. In this study, we show that for the multi-sized spherical and randomly-shaped granules the porosity reaches it's bulk value within a depth equal to a multiple of the median diameter of the mixture. All multiplication factors for the samples examined here were between 2.6 and 3.8 and mimicked the experimental data with reasonable precision. A direct consequence of this observation is that the diffusion coefficient below the interface can not be considered as a constant. The effect of depth-dependent porosity on the the diffusion coefficient below the porous media interface was examined. It was found that the difference between a constant and a depth-dependent diffusion coefficient in the porous layer is significant and reaches up to 65% for sandy sediment (phi(b) = 0.35) and 20% for highly porous media (phi(b) = 0.90) immediately below the interface. This finding is of great significant when no experimental data of porosity as a function of depth is available. Such situations arise frequently in heat and mass transfer exchanges across fluid-porous or solid wall-porous boundaries. (C) 2018 Elsevier B.V. All rights reserved.