Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H1: Porous Media Flows: Wicking, Imbibition and Swelling |
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Chair: Chris MacMinn, University of Oxford Room: Auditorium |
Monday, November 23, 2015 10:35AM - 10:48AM |
H1.00001: Uniaxial deformation of a soft porous material Chris MacMinn, Eric Dufresne, John Wettlaufer Compressing a porous material will decrease the volume of pore space, driving fluid out. Similarly, injecting fluid into a porous material will drive mechanical deformation, distorting the solid skeleton. This poromechanical coupling has applications ranging from cell and tissue mechanics to geomechanics and hydrogeology. The classical theory of linear poroelasticity captures this coupling by combining Darcy's law with linear elasticity and then further linearizing in the strain. This is a good model for very small deformations, but it becomes increasingly inappropriate as deformations grow larger, and moderate to large deformations are common in the context of phenomena such as swelling, damage, and extreme softness. Here, we compare the predictions of linear poroelasticity with those of a rigorous large-deformation framework in the context of two uniaxial model problems. We explore the error associated with the linear model in both steady and dynamic situations, as well as the impact of allowing the permeability to vary with the deformation. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H1.00002: Dynamics of swelling and drying in a spherical gel Thibault Bertrand, Christopher W. MacMinn, Shomeek Mukhopadhyay, Jorge Peixinho Swelling is a fundamental process in biology, engineering, and the earth sciences. Macroscopically, swelling is a volumetric-growth process in which a porous material expands due to the spontaneous imbibition of additional pore fluid. However, swelling is distinct from other growth processes because it is inherently poromechanical: Local expansion of the pore structure requires that additional fluid be drawn from elsewhere in the material, or into the material from across the boundaries. Here, we study the swelling and subsequent drying of a sphere of hydrogel. Despite the apparent simplicity of this problem, no model has yet shown satisfying quantitative agreement with experiments in terms of the dynamics of swelling and drying. We develop a dynamic model based on large-deformation poromechanics and we compare the predictions of the model with a series of experiments performed with polyacrylamide spheres. We use the model and the experiments to study the dynamics of swelling and drying, and to highlight the fundamental differences between these two processes. Although we assume spherical symmetry, the model also provides insight into the transient patterns that form and then vanish during swelling, as well as the tendency of large spheres to fracture during drying. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H1.00003: Boundary conditions between poro-elastic medium and pure fluid in multi-scale modelling. Ugis Lacis, Shervin Bagheri Accurate modelling of porous and poro-elastic media has been a long standing issue in geophysics, fluid mechanics, and biology. There has been a notable development of continuous models for both porous and poro-elastic materials, nevertheless there is still an on-going debate about the modelling of effective boundary conditions between different types of media, such as, poro-elastic medium and free fluid, porous medium and solid wall. Some recent works have rigorously treated interface between porous medium and free fluid, however, there have been no detailed investigation regarding the interface between poro-elastic medium and free fluid. We use the multi-scale modelling to arrive with averaged, effective macroscopic equations for description of a poro-elastic medium. Then we investigate the interface in detail and arrive with effective boundary conditions. To validate our model, we construct direct numerical simulations using an immersed boundary (IB) method. The IB method is beforehand validated with respect to theoretical predictions for Darcy's flow in porous materials with a given pore structure. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H1.00004: Capillary rise and swelling in cellulose sponges Jonghyun Ha, Jungchul Kim, Ho-Young Kim A cellulose sponge, which is a mundane example of a porous hydrophilic structure, can absorb and hold a significant amount of liquid. We present the results of experimental and theoretical investigation of the dynamics of the capillary imbibition of various aqueous solutions in the sponge that swells at the same time. We find that the rate of water rise against the resistance caused by gravitational and viscous effects deviates from Washburn’s rule beyond a certain threshold height. We rationalize the novel power law of the rise height versus time by combining Darcy’s law with hygroscopic swelling equation and also predict the threshold height. The scaling law constructed through this work agrees well with the experimental results, shedding light on the physics of capillary flow in deforming porous media. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H1.00005: Capillary displacement of viscous liquids Peter Walls, Gregoire Dequidt, James Bird When a capillary tube is brought into contact with a wetting liquid, surface tension forces overcome gravity and the liquid spontaneously rises into the tube until an equilibrium height is reached. The early viscous dynamics of the rise typically follow the well-known Lucas-Washburn law, which is independent of gravity and neglects the displaced fluid. Here we explore the early viscous dynamics when the properties of displaced fluid are significant. Using a combination of experiments and theory, we show how the characteristic behavior of the Lucas-Washburn law is modified when the viscosity of the displaced fluid is comparable to or exceeds the wetting fluid. Additionally, we find that the effects of gravity reshape the dynamics of the capillary rise, not only in the late viscous regime, but also in the early viscous regime. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H1.00006: Liquid spreading on ceramic-coated carbon nanotube films and patterned microstructures Hangbo Zhao, A. John Hart We study the capillary-driven liquid spreading behavior on films and microstructures of ceramic-coated vertically aligned carbon nanotubes (CNTs) fabricated on quartz substrates. The nanoscale porosity and micro-scale dimensions of the CNT structures, which can be precisely varied by the fabrication process, enable quantitative measurements that can be related to analytical models of the spreading behavior. Moreover, the conformal alumina coating by atomic layer deposition (ALD) prevents capillary-induced deformation of the CNTs upon meniscus recession, which has complicated previous studies of this topic. Washburn-like liquid spreading behavior is observed on non-patterned CNT surfaces, and is explained using a scaling model based on the balance of capillary driving force and the viscous drag force. Using these insights, we design patterned surfaces with controllable spreading rates and study the contact line pinning-depinning behavior. The nanoscale porosity, controllable surface chemistry, and mechanical stability of coated CNTs provide significantly enhanced liquid-solid interfacial area compared to solid microstructures. As a result, these surface designs may be useful for applications such as phase-change heat transfer and electrochemical energy storage. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H1.00007: Switchable imbibition in nanoporous gold Patrick Huber, Juergen Markmann, Huiling Duan, Joerg Weissmueller, Yahui Xue Spontaneous imbibition enables the elegant propelling of nano-flows because of the dominance of capillarity at small length scales. The imbibition kinetics are, however, solely determined by the static host geometry, the capillarity, and the fluidity of the imbibed liquid. This makes active control particularly challenging. Here we show for aqueous electrolyte imbibition in nanoporous gold that the fluid flow can be reversibly switched on and off through electric potential control of the solid–liquid interfacial tension, that is, we can accelerate the imbibition front, stop it, and have it proceed at will. Simultaneous measurements of the mass flux and the electrical current allow us to document simple scaling laws for the imbibition kinetics, and to explore the charge transport in the metallic nanopores. Our findings demonstrate that the high electric conductivity along with the pathways for fluid/ionic transport render nanoporous gold a versatile, accurately controllable electrocapillary pump and flow sensor for minute amounts of liquids with exceptionally low operating voltages. (1) Yahui Xue, Juergen Markmann, Huiling Duan, Joerg Weissmueller, Patrick Huber, Nature Communications 5, 4237 (2014). [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H1.00008: Wettability control on fluid-fluid displacements in patterned microfluidics Benzhong Zhao, Christopher MacMinn, Ruben Juanes Two-phase flow in porous media is important in many natural and industrial processes. While it is well known the wetting properties of porous media can vary drastically depending on the media and the pore fluids, their effect continues to challenge our microscopic and macroscopic descriptions. We conduct experiments via radial displacement of silicone oil by water in microfluidic devices patterned with vertical posts. These devices allow for flow visualization in a complex but well-defined microstructure. Additionally, the surface energy of the devices can be tuned over a wide range of contact angles. We perform injection experiments with highly unfavorable mobility contrast at rates over four orders of magnitude. We focus on three wetting conditions: drainage $\theta =$120$^{\circ}$, weak imbibition $\theta =$60$^{\circ}$, and strong imbibition $\theta =$7$^{\circ}$. In drainage, we see a transition from viscous fingering at high capillary numbers to a morphology that differs from capillary fingering. In weak imbibition, we observe stabilization of flow due to cooperative invasion at the pore scale. In strong imbibition, we find the flow is heavily influenced by a precursor front that emanates from the main imbibition front. Our work shows the important, yet intricate, impact of wettability on immiscible flow in porous media. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H1.00009: What controls the wettability of bidisperse sphere packings? Robabeh Moosavi, Julie Murison, Thomas Hiller, Martin Brinkmann, Matthias Schr\"oter We report experiments on liquid two-phase flow in bidisperse sphere packings. The bidisperse bead pack consists of small and large beads which are either oil wetting or water wetting. Aim of our work is to understand what determines the average wettability of the sample and what affects the amount of remaining oil trapped in the bead pack invaded by water. The method is to measure the capillary pressure saturation curves (CPSC). The data indicates that segregation plays a role. Moreover, we compare the experimental results obtained using x-ray tomography and CPSC measurement with the multi-particle collision dynamics numerical results. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H1.00010: Convective drying of a macroporous medium: a comparison of original porous asphalt geometry with randomized Kelvin cells Sreeyuth Lal, Francesco Lucci, Thijs Defraeye, Lily Poulikakos, Manfred Partl, Dominique Derome, Jan Carmeliet Forced convective drying of a macroporous medium is a complex interplay of enhanced air-vapor mixing due to turbulent airflow at the air-solid interface and the momentum transfer resulting from air infiltration into the material. Such air infiltration is expected to have a non-trivial effect on the drying rate of a material like porous asphalt (PA), which is characterized by large, interconnected pores open to the surface. Through a series of CFD simulations performed on an original PA geometry extracted from CT scans, we quantify the relative impacts of interior material resistance and boundary layer resistance on moisture transport in PA. At wind speeds below 1 m/s, the effect of material resistance on the total moisture transfer is found to be high due to low air infiltration. At higher wind speeds, air infiltration increases by which the material resistance decreases. Similar simulations are performed on an idealized PA geometry made from randomized Kelvin cells (KC) since they are computationally less expensive, and thus ideal for parametric studies. However, in KC cells, drying from air infiltration is stronger than diffusive drying even at low wind speeds. This shows the need to fine-tune the pore connectivity of KC to better match the air infiltration observed in PA. [Preview Abstract] |
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