On Water Transfer and Hydraulic Connection Layer During the Convective Drying of Rigid Porous Material

Prime, Noémie; Housni, Z; Fraikin, Laurent; Léonard, Angélique; Charlier, Robert; Levasseur, Séverine

doi:10.1007/s11242-014-0390-8

Cited by 16 publications

(11 citation statements)

References 34 publications

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“…The basic phenomenological mechanisms of drying in simple systems initially filled with pure liquid have been identified [1][2][3][4][5][6][7]. After a short induction period of variable duration, a Constant drying Rate Period (CRP), associated with a homogeneous desaturation of the medium usually occurs.…”

Section: Introductionmentioning

confidence: 99%

“…It is generally considered that the onset of this second regime results from a demand of liquid, through the imposed evaporation rate, larger than the liquid flux towards the free surface and resulting from capillary effects. Such a situation would lead the inward growth of a dry region from the sample free surface [1,4,7]. In detail, it was also suggested that two FRP should be considered [4,[17][18][19], associated with the continuous and the discontinuous states of the liquid network.…”

Section: Introductionmentioning

confidence: 99%

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Drying regimes in homogeneous porous media from macro- to nanoscale

et al. 2017

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MRI visualization down to nanometric liquid films in model porous media with pore size from micro-to nano-meter enables to fully characterize the physical mechanisms of drying. In larger pores, we identify an initial constant drying rate period, probing homogeneous desaturation, followed by a falling drying rate period. This second period is associated with the development of a gradient in saturation underneath the sample free surface that initiates the inward recession of the contact line. During this latter stage, the drying rate varies in accordance with vapor diffusion through the dry porous region; possibly affected by Knudsen effect for small pore size. However, we show that for sufficiently small pore size and/or saturation the drying rate is increasingly reduced by the Kelvin effect. Subsequently, we demonstrate that this effect governs the kinetics of evaporation in nanopores as a homogeneous desaturation occurs. Eventually, under our experimental conditions, we show that the saturation unceasingly decreases in a homogeneous manner throughout the wet regions of the medium regardless of pore size or drying regime considered. This finding suggests the existence of continuous liquid flow towards the interface of higher evaporation, down to very low saturation or very small pore size. Paradoxically, even if this net flow is unidirectional and capillary driven, it corresponds to a series of diffused local capillary equilibrations over the full height of the sample, which might explain that a simple Darcy's law model does not predict the scaling of the net flow rate on the pore size observed in our tests.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Drying regimes in homogeneous porous media from macro- to nanoscale

et al. 2017

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“…The drying rate calculated based on equation (2) is filtrated using Lanczos method [13] to reduce noise generated by the subtraction between two mass measurements that only differ from an order of magnitude slightly larger than the weighing measurement error. The obtained curve highlights the two classical distinct drying stages [14,15].…”

Section: Data Treatmentmentioning

confidence: 99%

“…Stage II of drying starts when the internal conductive properties of the soil (permeability, diffusivity) do no longer allow a sufficient water flow to the soil surface to maintain the maximal evaporation rate. Therefore, the transition between the two periods, around the critical water content, expresses the progressive development of an internal mass transfer resistance in series to the previously limiting external mass transfer resistance [13,16]. From the Krischer curves obtained, the maximal drying rates and the critical water contents w crit are deduced.…”

Section: Data Treatmentmentioning

confidence: 99%

On the mechanisms and kinetics of evaporation of a compacted silt

et al. 2016

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Abstract. In order to define a convective evaporation model able to reproduce the evaporation rates according to the atmospheric conditions, drying tests have been performed on cylindrical samples of a compacted silt in a closed chamber where the relative humidity of the air is controlled by means of saturated saline solutions. Calibrating such models using experimental results from small sample sizes can indeed be an interesting alternative to simplify the experimental procedures and to reduce the test duration in comparison with the standard in-situ tests (e.g. lysimeter). However the influence of the size of the samples on the kinetics of evaporation has to be investigated. Samples with different diameters and heights are therefore tested. The results show that the observed mechanisms of drying are similar to those at the scale of the geostructure if the dimensions of the sample are higher than a critical height and a critical diameter. We show then that the experimental critical height is consistent with the concept of critical length proposed by Lehman et al. (2008), who expresses analytically when the hydraulic connection between the sample surface and the drying front is upset. Finally the kinetics of evaporation recorded under different relative humidities highlight that the mass transfer coefficient defined in the convective evaporation model does not depend on the relative humidity.

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“…In the latter case, the most frequently adopted work‐around consists in using a water‐based salt solution, containing elements with high Z , instead of distilled water. For example, concerning visualization of drying in porous media, water‐based solutions of CaI (Shokri et al ., ; Shokri & Sahimi, ) and a suspension of limestone powder in water (Prime et al ., ) have been used. Salt precipitation during drying of porous media has been successfully imaged with XACI for NaCl solutions (Norouzi Rad et al ., ; Norouzi Rad & Shokri, ).…”

Section: Introductionmentioning

confidence: 99%

Visualization of water drying in porous materials by X‐ray phase contrast imaging

Yang

Griffa

Bonnin

et al. 2016

Journal of Microscopy

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We present in this study results from X-ray tomographic microscopy with synchrotron radiation performed both in attenuation and phase contrast modes on a limestone sample during two stages of water drying. No contrast agent was used in order to increase the X-ray attenuation by water. We show that only by using the phase contrast mode it is possible to achieve enough water content change resolution to investigate the drying process at the pore-scale. We performed 3D image analysis of the time-differential phase contrast tomogram. We show by the results of such analysis that it is possible to obtain a reliable characterization of the spatial redistribution of water in the resolved pore system in agreement with what expected from the theory of drying in porous media and from measurements performed with other approaches. We thus show the potential of X-ray phase contrast imaging for pore-scale investigations of reactive water transport processes which cannot be imaged by adding a contrast agent for exploiting the standard attenuation contrast imaging mode.

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On Water Transfer and Hydraulic Connection Layer During the Convective Drying of Rigid Porous Material

Cited by 16 publications

References 34 publications

Drying regimes in homogeneous porous media from macro- to nanoscale

Drying regimes in homogeneous porous media from macro- to nanoscale

On the mechanisms and kinetics of evaporation of a compacted silt

Visualization of water drying in porous materials by X‐ray phase contrast imaging

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