Critical conditions for the wetting of soils

[1] This study sheds light on the limitations of using [(cos ) 1 =2 ] to scale sorptivity by contact angle while reaffirming its scaling by geometrical Miller scaling factor ( 1 =2 ). The sorptivity for uniform and nonuniform (wavy) capillary tubes was determined by a mathematical model that includes the effect of inertia and dynamic contact angle. Given that real porous media are preferably represented by a bundle of nonuniform rather than uniform capillary tubes, the relationship between sorptivity and contact angle was examined for different combinations of contact angles and capillary tube degrees of waviness. A general relationship of S ¼ f [cos )] (with 1 = 2 ) was found. The deviation of from 1 = 2 (associated with uniform capillary tubes) increased with contact angle and capillary waviness increase. Zero sorptivity was obtained even for wettable capillaries, < 90 , a phenomenon that has been generally associated with hydrophobic capillaries ( ! 90 ). Contact angle and nonuniform pore structure had a synergistic effect on sorptivity. Capillary nonuniformity per se diminished sorptivity but its synergy with contact angle markedly magnified this reduction. Thus, following the sorptivity impact on finger width, it is rational to assume that larger-than-zero contact angles are involved in the formation of narrow fingers with an abrupt change between the inner wet and surrounding dry areas.

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“…, as was also noted by Ban et al [1987], Marmur [1989], Shirtcliffe et al [2006], and Czachor et al [2010].…”

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confidence: 63%

An extension of Miller scaling to scale sorptivity by contact angle

Wallach

Wang

2013

Water Resour. Res.

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“…The observed contact angle was measured using Krüss DSA software and the value just prior to the droplet's contact line moving was taken as the advancing contact angle. The surface tension of the ethanol solutions were consistent with those reported in the literature 16 and exhibit a range of advancing contact angles sufficient to investigate a range of r/R values of up to 1 (θ c =50.73°) 14,15 (Figure 2). Since an MED test uses a range of concentrations of ethanol to estimate the advancing contact angle at which an ethanol solution just penetrates a porous system it is useful to be able to transform numerically from ethanol concentration, c, to surface tension or advancing contact angle (on CTMS modified glass surfaces).…”

Section: Experimental Methodssupporting

confidence: 85%

Effect of Particle Size on Droplet Infiltration into Hydrophobic Porous Media As a Model of Water Repellent Soil

Hamlett

Shirtcliffe

McHale

et al. 2011

Environ. Sci. Technol.

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The wettability of soil is of great importance for plants and soil biota, and in determining the risk for preferential flow, surface runoff, flooding and soil erosion. The molarity of ethanol droplet (MED) test is widely used for quantifying the severity of water repellency in soils that show reduced wettability and is assumed to be independent of soil particle size. The minimum ethanol concentration at which droplet penetration occurs within a short time (≤ 10 s) provides an estimate of the initial advancing contact angle at which spontaneous wetting is expected. In this study, we test the assumption of particle size independence using a simple model of soil, represented by layers of small (∼0.2 to 2 mm) diameter beads that predict the effect of changing bead radius in the top layer on capillary driven imbibition. Experimental results using a three-layer bead system show broad agreement with the model and demonstrate a dependence of the MED test on particle size. The results show that the critical initial advancing contact angle for penetration can be considerably less than 90° and varies with particle size, demonstrating that a key assumption currently used in the MED testing of soil is not necessarily valid.

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“…for water on the carbon surfaces of GDL materials, so that water cannot spontaneously imbibe [12] into Toray090 (0% PTFE). This cannot be anticipated from a straight capillary tube model, which predicts spontaneous pore filling for any …”

Section: Discussionmentioning

confidence: 99%

Direct measurement of the capillary pressure characteristics of water–air–gas diffusion layer systems for PEM fuel cells

Gostick

Ioannidis

Fowler

et al. 2008

Electrochemistry Communications

115

114

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A method and apparatus for measuring the relationship between air-water capillary pressure and water saturation in PEMFC gas diffusion layers is described. Capillary pressure data for water injection and withdrawal from typical GDL materials are obtained, which demonstrate permanent hysteresis between water intrusion and water withdrawal. Capillary pressure, defined as the difference between the water and gas pressures at equilibrium, is positive during water injection and negative during water withdrawal. The results contribute to the understanding of liquid water behavior in GDL materials which is necessary for the development of effective PEMFC water management strategies.

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Critical conditions for the wetting of soils

Cited by 63 publications

References 15 publications

An extension of Miller scaling to scale sorptivity by contact angle

An extension of Miller scaling to scale sorptivity by contact angle

Effect of Particle Size on Droplet Infiltration into Hydrophobic Porous Media As a Model of Water Repellent Soil

Direct measurement of the capillary pressure characteristics of water–air–gas diffusion layer systems for PEM fuel cells

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