Mouvements capillaires durant le séchage d'une pâte granulaire

Coussot, Philippe; Gauthier, Claude; Nadji, Djaouida; Borgotti, Jean-Claude; Vié, Philippe; Bertrand, François

doi:10.1016/s1287-4620(00)87024-6

Cited by 2 publications

(5 citation statements)

References 5 publications

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“…Then, under the action of capillary forces resulting from evaporation and slight air-liquid interface withdrawal inside the medium around the free surface, they can rearrange in a more compact way along the sample axis During a second period (regime A), the paste keeps a constant uniform water amount, but the water amount in the grain packing decreases homogeneously (see Fig.5). Such an extraction of water, and its replacement with air, from below the saturated paste, has already been observed in layered porous media (small pore over large pore regions) [11,[44][45][46]. The same effect occurs here as soon as the shrunk paste has become able to resist capillary forces.…”

Section: Drying Of Composite Systemssupporting

confidence: 61%

“…In this regime capillary equilibration processes allow for water redistribution throughout the medium so that the saturation (i.e. liquid to void volume ratio) decreases uniformly [4,[11][12][13][14]. This is generally followed by a falling-rate period (FRP) associated with the development of a heterogeneous profile of saturation [4,[11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

“…liquid to void volume ratio) decreases uniformly [4,[11][12][13][14]. This is generally followed by a falling-rate period (FRP) associated with the development of a heterogeneous profile of saturation [4,[11][12][13][14]. It is considered that the onset of this effect results from a demand of liquid, through the imposed evaporation rate at the free surface, larger than the liquid transport induced by a gradient of capillary pressure within the porous system [7,9,15].…”

Section: Introductionmentioning

confidence: 99%

“…We can certainly expect that a major role will be played by capillary effects which will tend to impose some specific distribution of liquid according to the different pore sizes in the different parts of the system [23]. This effect was for example observed during drying of systems made of two or three layers of bead packings with different bead sizes [11] and submitted to an air flux along the top surface: the water is removed from the layer made of the largest beads, whatever its position with regards to the sample free surface. Direct observations by MRI (Magnetic Resonance Imaging) [24] of the liquid distributions were also carried out with systems closer to real ones, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Convective drying of a porous medium with a paste cover

et al. 2019

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The convective drying of a composite system made of a porous medium covered with a paste is a situation often encountered with soils, roads, building and cultural heritage materials. Here we discuss the basic mechanisms at work during the drying of model composite system made of a homogeneous paste covering a simple granular packing. We start by reviewing the rather well-known case of the convective drying of a simple granular packing (i.e. without paste cover), which serves as a reference for physical interpretations. We show that a simple model assuming homogeneous desaturation then progressive development of a dry front from the sample free surface is in agreement with observations of the internal liquid distribution variations in time. In particular, this model is able to reproduce the saturation vs time curves of various simple granular systems, which supports our understanding of physical mechanisms at work. Then we show the detailed characteristics of drying of initially saturated model composite systems (with kaolin or cellulose paste) with the help of MRI measurements providing the liquid distribution in the sample at different times during the process up to the very last stages of drying. It appears that the granular medium is unaffected (i.e. remains saturated) during an initial period during which the paste shrinks and finally forms a sufficiently rigid porous structure which will not any more shrink later on. Then the drying process is governed by capillary effects down to very low saturation. Over a wide range of saturations both media desaturate homogeneously (within each medium) at different rates which depend on the specific porous structure of the media, so as to maintain capillary equilibrium throughout the sample. During these different stages the drying rate of the whole system remains constant. For sufficiently low saturation in the paste a dry front can develop, both in the paste and the porous medium below, and the drying rate now decreases. These results show that in a drying composite system liquid extraction can occur more or less simultaneously in the different parts of the material up to the very last stages of drying. The corresponding evolution of the distributions of liquid in the different parts of the sample also provides key information for the prediction of ion or particle transport and accumulation in the different parts of a composite system.

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Section: Drying Of Composite Systemssupporting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Convective drying of a porous medium with a paste cover

et al. 2019

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“…Basic scaling arguments [10] and more sophisticated descriptions [11] were provided for these different regimes. Direct visualizations from dye transport and deposition [12], neutron radiography [13], Gamma Ray densimetry [14], X-Ray tomography [15], Magnetic Resonance Imaging [16], or confocal microscopy [17], with samples of controlled wetting characteristics or controlled pore size provided an insight in different local characteristics and finally confirmed the different physical arguments of the above global scheme. In addition various studies with simplified porous structures [18][19][20][21][22] provided valuable information concerning the exact physical processes occurring at a local scale such as the influence of film shapes, pore shapes and wetting characteristics.…”

Section: Introductionmentioning

confidence: 86%

Drying of a model soil

Faure

Coussot

2010

Phys. Rev. E

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Drying experiments have been carried out with model soils made of different pastes filling granular packings. A detailed information concerning the time evolution of the water saturation distribution inside the sample was obtained from magnetic resonance imaging measurements. This study makes it possible to understand the physical origin of the drying characteristics of these materials. The drying curves exhibit a constant-rate period (CRP) and a falling-rate period (FRP) but the relative durations of these periods depend on the paste structure. With a kaolin suspension the CRP lasts down to very low water densities and is associated with a homogeneous drying of the paste throughout the sample. With a bentonite suspension the CRP is shorter and the drying in the FRP results from a complex process involving fractures progressing downward through the pasty matrix. With a gel the CRP period is even shorter and the drying in the FRP results from the progression of a dry front through the packing as a result of the shrinkage of the gel matrix. This provides an overview of the main possible processes at work when drying a soil as a function of its components along with some practical means for slowing down drying from soils.

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Mouvements capillaires durant le séchage d'une pâte granulaire

Cited by 2 publications

References 5 publications

Convective drying of a porous medium with a paste cover

Convective drying of a porous medium with a paste cover

Drying of a model soil

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