{"id":12819,"date":"2020-11-07T16:07:23","date_gmt":"2020-11-07T15:07:23","guid":{"rendered":"https:\/\/navier-lab.fr\/transport-in-porous-media\/"},"modified":"2024-08-01T15:47:10","modified_gmt":"2024-08-01T13:47:10","slug":"transport-in-porous-media","status":"publish","type":"page","link":"https:\/\/navier-lab.fr\/en\/research\/rheophysics-porous-media\/transport-in-porous-media\/","title":{"rendered":"Transport in Porous Media"},"content":{"rendered":"

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Researchers at RMP investigate transport phenomena (liquid, fluid, humidity, heat, acoustic waves) and how these phenomena are affected by the geometrical constraints present in porous materials, e.g. fibre stacks, solid foams with open \/ closed porosity and bio-based materials …<\/p>\n

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Hygrothermal properties of bio-based materials<\/h2>Read More<\/a><\/div>\n <\/article><\/div><\/div>
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NMR relaxometry for porous materials<\/h2>Read More<\/a><\/div>\n <\/article><\/div><\/div>
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Permeability and acoustic properties of solid foams<\/h2>Read More<\/a><\/div>\n <\/article><\/div><\/div>
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Liquid foams in porous media<\/h2>Read More<\/a><\/div>\n <\/article><\/div><\/div><\/div><\/div><\/section>
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Hygrothermal properties of bio-based materials<\/h3>\n

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Philippe Coussot, R. Sidi-Boulenouar, B. Maillet, Kang Hu (Postdoc), Yuliang Zou (Postdoc), Nicolas Daunais (PhD), Van-Truong Nguyen (PhD), Luoyi Yan (PhD), Karen Mourda (PhD),<\/h5>\n
Collaborations : S. Car\u00e9 (MSA), L. Brochard (ME)<\/h5>\n

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\nHow does water enter wood and induce swelling ? Why are we more comfortable wearing cotton, flax linen or hemp clothes ? Why does it take so long to dry wood or paper ? Why is it healthier to live in a house made of bio-based materials ? At the heart of these questions, we find the remarkable capacity of these materials to absorb liquid water or water vapour from the environment through hydrogen bonds, which create water nano-sized water inclusions between the cellulose microfibrils. This “bound\" water can make up to 30% of the dry mass of the material. It evaporates under a dry ambient atmosphere, hence regulating the ambient humidity. Bound water also induces the swelling or the retractation of their matrices proportionally to the amount of bound water. Bound water can also diffuse strikingly fast through the cellulose fibres. Bound water transport and its exchange with the liquid and vapour (standard) lead to complex and original transport properties in cellulose-based\u00a0 or plant-fibre-based materials.<\/p>\n

For instance, spontaneous water imbibition in wood is not governed by capillary effects but rather by diffusion of bound water ahead of the liquid front, which slows down the imbibition dynamics by several orders of magnitude. Conversely, wood drying is controlled by bound water diffusion which extracts the free water stored deep inside the sample, leading to a slow, two-step diffusion process. We observe and quantify these phenomena with specific scientific tools, among which NMR and MRI are particularly efficient as they access very low water content in solids and allows us to separate the signals from bound and free water. We have determined the transport and diffusion coefficient of bound water in wood samples, in a fibre network (bound water jumping from one fibre to another when they are in contact) and even along a single cellulose fibre.<\/p>\n

These studies will carry on in the framework of the PHYSBIOMAT ERC Advanced Grant, which aims to predict the hygrothermal behabiour of bio-based construction materials. We will characterise the elementary transport phenomena on model and real materials, along with a detailed modelling of the coupling between heat and humidity transfers. The first articles published on this topic underline how one must perform sorption dynamic measurements in a controlled fashio. They also show how it is possible to separately determine the diffusion coefficients of water vapour and bound water in a cellulose fibre structure; and to then deduce a global transport model from these coefficients, taking into account exchanges between the two phases.<\/p>\n

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Dynamical drying of a cellulose slurry under an air flux. Water content is measured by MRI. From Ben Abdelouahab, Cellulose 28<\/span>, <\/strong>28, 5321\u20135334, (2021)
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One-dimensional profiles of a cellulose slurry drying under a (vertical) air flux. We notice that drying is a two-step process. From Ben Abdelouahab, Cellulose 28<\/span>, <\/strong>28, 5321\u20135334, (2021)
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References<\/h4>\n