A preliminary exploration of the micro-scale behaviour of capillary barrier effect using microfluidics

Capillary barrier effect (CBE) is employed in a large number of geotechnical applications to decrease deep percolation or increase slope stability. However, the micro-scale behaviour of CBE is rarely investigated, and thus hampers the scientific design of capillary barrier systems. This study uses microfluidics to explore the micro-scale behaviour of CBE. Capillarity-driven water flow processes from fine to coarse porous media with different pore topologies and sizes were performed and analysed. The experimental results demonstrate that the basic physics of CBE is the preferential water movement into the fine porous media due to the larger capillarity. The effects of CBE on water flow processes can be identified as delaying the occurrence of breakthrough into the coarse porous media and increasing the water storage of the fine porous media. The CBE can impede the increase of the normalized length and decrease the normalized width of the water front, suggesting that the two normalized parameters are potential indicators to assess the performance of CBE at micro scale. CBE can be formed in square and honeycomb networks with the ratio of coarse to fine pore throat width larger than 2.0 when gravity is neglected, and its performance can be affected by pore topology and size.

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Monitoring infiltration and subsurface stormflow in layered slope deposits with 3D ERT and hydrometric measurements – the capillary barrier effect as crucial factor

10.5194/hess-2017-144 ◽

2017 ◽

Author(s):

Rico Hübner ◽

Thomas Günther ◽

Katja Heller ◽

Ursula Noell ◽

Arno Kleber

Keyword(s):

Water Flow ◽

Water Movement ◽

Basal Layer ◽

Organic Layer ◽

Barrier Effect ◽

Capillary Barrier ◽

Shallow Subsurface ◽

Layered Slope ◽

Slope Deposits ◽

Flow Pathways

Abstract. Identifying principles of water movement in the shallow subsurface is crucial for adequate process-based hydrological models. Hillslopes are the essential interface for water movement in catchments. The shallow subsurface on slopes typically consist of different layers with varying characteristics. The aim of this study was to draw conclusion about the infiltration behaviour, to identify water flow pathways and derive general validity about the water movement on a hillslope with periglacial slope deposits (cover beds), where the layers differ in their sedimentological and hydrological properties. Especially the described varying influence of the basal layer (LB) as impeding layer on the one hand and as a remarkable pathway for rapid subsurface stormflow on the other. We used a time lapse 3D ERT approach combined with punctual hydrometric data to trace the spreading and the progression of an irrigation plume in layered slope deposits during two irrigation experiments. This multi-technical approach enables us to connect the high spatial resolution of the 3D ERT with the high temporal resolution of the hydrometric devices. Infiltration through the uppermost layer was dominated by preferential flow, whereas the water flow in the deeper layers was mainly matrix flow. Subsurface stormflow due to impeding characteristic of the underlying layer occurs in form of "organic layer interflow" and at the interface to the first basal layer (LB1). However, the main driving factor for subsurface stormflow is the formation of a capillary barrier at the interface to the second basal layer (LB2). The capillary barrier prevents water from entering the deeper layer under unsaturated conditions and diverts the seepage water according to the slope inclination. With higher saturation the capillary barrier breaks down and water reaches the highly conductive deeper layer. This highlights the importance of the capillary barrier effect for the prevention or activation of different flow pathways under variable hydrological conditions.

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Vadose Zone, Part I : Characterization and Flow Processes

Applied Stochastic Hydrogeology ◽

10.1093/oso/9780195138047.003.0016 ◽

2003 ◽

Author(s):

Yoram Rubin

Keyword(s):

Porous Media ◽

Water Flow ◽

Governing Equation ◽

Vadose Zone ◽

Stochastic Analysis ◽

Transport Processes ◽

Richards Equation ◽

Saturated Porous Media ◽

Flow And Transport ◽

Flow Processes

Many of the principles guiding stochastic analysis of flow and transport processes in the vadose zone are those which we also employ in the saturated zone, and which we have explored in earlier chapters. However, there are important considerations and simplifications to be made, given the nature of the flow and of the governing equations, which we explore here and in chapter 12. The governing equation for water flow in variably saturated porous media at the smallest scale where Darcy’s law is applicable (i.e., no need for upscaling of parameters) is Richards’ equation (cf. Yeh, 1998)

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Steam impinging and heat and water spreading in fabrics

Textile Research Journal ◽

10.1177/0040517518773373 ◽

2018 ◽

Vol 89 (8) ◽

pp. 1455-1471 ◽

Cited By ~ 2

Author(s):

Shuaitong Liang ◽

Ning Pan ◽

Yuexin Cui ◽

Xiongying Wu ◽

Xuemei Ding

Keyword(s):

Heat Transfer ◽

Water Flow ◽

Theoretical Approach ◽

Water Movement ◽

Heat And Mass Transport ◽

Inherent Anisotropy ◽

Flow Processes ◽

Theoretical Predictions ◽

The Mean ◽

Water Spreading

This study is about the heat and mass transport phenomena in a system with steam jet flow to eliminate/alleviate cloth wrinkles. We first adopted a theoretical approach to derive the mean capillary radii so that a fabric can be characterized as an assembly of capillary tubes with varying diameters. We then analyzed the processes as a heat transfer via the fibers and water via the pores in fabrics of different anisotropies. During water movement, the water weight actually intensifies the inherent anisotropy of the fabric in the water flow pattern. For heat transfer, the water weight becomes irrelevant and both convection and radiation are shown to be too trivial to include. Corresponding experiments are also conducted, using infrared and visible light cameras to record the heat and water flow processes, respectively. The results are compared with the theoretical predictions and the discrepancies are explored and explained.

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Numerical Evaluation of Fractional Vertical Soil Water Flow Equations

Water ◽

10.3390/w13040511 ◽

2021 ◽

Vol 13 (4) ◽

pp. 511

Author(s):

Ali Ercan ◽

M. Levent Kavvas

Keyword(s):

Porous Media ◽

Soil Water ◽

Water Flow ◽

Water Movement ◽

Least Square ◽

Flow In Porous Media ◽

Fickian Diffusion ◽

Richards Equation ◽

Governing Equations ◽

Soil Water Flow

Significant deviations from standard Boltzmann scaling, which corresponds to normal or Fickian diffusion, have been observed in the literature for water movement in porous media. However, as demonstrated by various researchers, the widely used conventional Richards equation cannot mimic anomalous diffusion and ignores the features of natural soils which are heterogeneous. Within this framework, governing equations of transient water flow in porous media in fractional time and multi-dimensional fractional soil space in anisotropic media were recently introduced by the authors by coupling Brooks–Corey constitutive relationships with the fractional continuity and motion equations. In this study, instead of utilizing Brooks–Corey relationships, empirical expressions, obtained by least square fits through hydraulic measurements, were utilized to show the suitability of the proposed fractional approach with other constitutive hydraulic relations in the literature. Next, a finite difference numerical method was proposed to solve the fractional governing equations. The applicability of the proposed fractional governing equations was investigated numerically in comparison to their conventional counterparts. In practice, cumulative infiltration values are observed to deviate from conventional infiltration approximation, or the wetting front through time may not be consistent with the traditional estimates of Richards equation. In such cases, fractional governing equations may be a better alternative for mimicking the physical process as they can capture sub-, super-, and normal-diffusive soil water flow processes during infiltration.

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Unsaturated flow in coarse porous media

Canadian Geotechnical Journal ◽

10.1139/t04-070 ◽

2005 ◽

Vol 42 (1) ◽

pp. 252-262 ◽

Cited By ~ 16

Author(s):

Jeff R Reinson ◽

Delwyn G Fredlund ◽

G Ward Wilson

Keyword(s):

Porous Media ◽

Hydraulic Conductivity ◽

Soil Water ◽

Unsaturated Soils ◽

Unsaturated Flow ◽

Characteristic Curve ◽

Matric Suction ◽

Coarse Grained ◽

Capillary Barrier ◽

Coarse Porous Media

Design of effective capillary barrier systems requires a thorough understanding of the soilwater interactions that take place in both coarse- and fine-grained unsaturated soils. Experimental observations of water flow through coarse porous media are presented to gain greater understanding of the processes and mechanisms that contribute to the movement and retention of water in coarse-grained unsaturated soils. The use of pendular ring theory to describe how water is held within a porous material with relatively low volumetric water contents is explored. Experimental measurements of seepage velocity and volumetric water content were obtained for columns of 12 mm glass beads using digital videography to capture the movement of a dye tracer front at several infiltration rates. An estimated curve for hydraulic conductivity versus matric suction is shown and compared to a theoretical curve. The method is shown to provide a reasonable predictive tool.Key words: soil-water characteristic curve, hydraulic conductivity curve, water permeability function, capillary barrier, matric suction.

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Impacts of a capillary barrier on infiltration and subsurface stormflow in layered slope deposits monitored with 3-D ERT and hydrometric measurements

Hydrology and Earth System Sciences ◽

10.5194/hess-21-5181-2017 ◽

2017 ◽

Vol 21 (10) ◽

pp. 5181-5199 ◽

Cited By ~ 8

Author(s):

Rico Hübner ◽

Thomas Günther ◽

Katja Heller ◽

Ursula Noell ◽

Arno Kleber

Keyword(s):

Water Flow ◽

Water Movement ◽

Basal Layer ◽

Organic Layer ◽

Seepage Water ◽

Capillary Barrier ◽

Shallow Subsurface ◽

Layered Slope ◽

Slope Deposits ◽

Flow Pathways

Abstract. Identifying principles of water movement in the shallow subsurface is crucial for adequate process-based hydrological models. Hillslopes are the essential interface for water movement in catchments. The shallow subsurface on slopes typically consists of different layers with varying characteristics. The aim of this study was to draw conclusions about the infiltration behaviour, to identify water flow pathways and derive some general interpretations for the validity of the water movement on a hillslope with periglacial slope deposits (cover beds), where the layers differ in their sedimentological and hydrological properties. Especially the described varying influence of the basal layer (LB) as an impeding layer on the one hand and as a remarkable pathway for rapid subsurface stormflow on the other. We used a time lapse 3-D electrical resistivity tomography (ERT) approach combined with punctual hydrometric data to trace the spreading and the progression of an irrigation plume in layered slope deposits during two irrigation experiments. This multi-technical approach enables us to connect the high spatial resolution of the 3-D ERT with the high temporal resolution of the hydrometric devices. Infiltration through the uppermost layer was dominated by preferential flow, whereas the water flow in the deeper layers was mainly matrix flow. Subsurface stormflow due to impeding characteristic of the underlying layer occurs in form of organic layer interflow and at the interface to the first basal layer (LB1). However, the main driving factor for subsurface stormflow is the formation of a capillary barrier at the interface to the second basal layer (LB2). The capillary barrier prevents water from entering the deeper layer under unsaturated conditions and diverts the seepage water according to the slope inclination. With higher saturation, the capillary barrier breaks down and water reaches the highly conductive deeper layer. This highlights the importance of the capillary barrier effect for the prevention or activation of different flow pathways under variable hydrological conditions.

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