Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session D15: Microscale Flows: Porous and Structured MediaMicro
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Chair: Amir Gat, Technion - Israel Institute of Technology Room: 601 |
Sunday, November 19, 2017 2:15PM - 2:28PM |
D15.00001: A multiscale analysis of electrokinetic transport in porous media Shima Alizadeh, Martin Z. Bazant, Ali Mani A wide range of applications, including electrochemical energy conversion, deionization, and lab-on-a-chip devices involve transport phenomena in porous media or networks of microchannels. Transport in such systems is governed by electrokinetic phenomena describing the coupling between fluid flow, ion transport, and electrostatic effects. In these systems, surface conduction through electric double layers (EDLs) can lead to nonlinear dynamics such as deionization shocks. Additionally, when pore size varies randomly in space, electrokinetic effects can generate internally induced flow loops, leading to enhanced mixing and increased effective diffusivity. We have developed an efficient computational model that can accurately capture the aforementioned nonlinearities inside porous media by modeling a porous medium as a network of pores each governed by one-dimensional partial differential equations. Using this model, we demonstrate simulations of massive networks of pores, and discuss the impact of pore size variability and random connectivity on macroscopic behavior and transport rates in porous media. [Preview Abstract] |
Sunday, November 19, 2017 2:28PM - 2:41PM |
D15.00002: Design of Microporosity in Membrane Distillation Tom Zhao, Neelesh Patankar Membrane Distillation (MD) is a desalination method where only vapor can pass through pores in a hydrophobic membrane. Unlike reverse osmosis, MD is insensitive to feed salinity (osmotic pressure) and demonstrates near 100{\%} salt rejection in processing wastewater with a high concentration of nonvolatile impurities. To maximize vapor flux and maintain salt rejection, we demonstrate using molecular dynamics the critical pore radius below which the liquid feed will not intrude or nucleate inside the pores for cylindrical, re-entrant and conical pore geometries. We note that re-entrant structures not only can process low surface-tension wastewater due to its inherent oleophobicity, but can also be optimized to achieve maximum vapor transport compared to all other pore geometries as a function of the material hydrophobicity. [Preview Abstract] |
Sunday, November 19, 2017 2:41PM - 2:54PM |
D15.00003: Membrane morphology and topology for fouling control in Reverse Osmosis filtration systems Bowen Ling, Ilenia Battiato Reverse Osmosis Membrane (ROM) filtration systems are widely utilized in waste-water recovery, seawater desalination, landfill water treatment, etc. During filtration, the system performance is dramatically affected by membrane fouling which causes a significant decrease in permeate flux as well as an increase in the energy input required to operate the system. Design and optimization of ROM filtration systems aim at reducing membrane fouling by studying the coupling between membrane structure, local flow field and foulant adsorption patterns. Yet, current studies focus exclusively on oversimplified steady-state models that ignore any dynamic coupling between fluid flow and transport through the membrane. In this work, we develop a customized solver (SUMembraneFoam) under OpenFOAM to solve the transient equations. The simulation results not only predict macroscopic quantities (e.g. permeate flux, pressure drop, etc.) but also show an excellent agreement with the fouling patterns observed in experiments. It is observed that foulant deposition is strongly controlled by the local shear stress on the membrane, and channel morphology or membrane topology can be modified to control the shear stress distribution and reduce fouling. Finally, we identify optimal regimes for design. [Preview Abstract] |
Sunday, November 19, 2017 2:54PM - 3:07PM |
D15.00004: Simulating single-phase and two-phase non-Newtonian fluid flow of a digital rock scanned at high resolution Moussa Tembely, Ali M. AlSumaiti, Mohamed S. Jouini, Khurshed Rahimov, Ali Dolatabadi Most of the digital rock physics (DRP) simulations focus on Newtonian fluids and overlook the detailed description of rock-fluid interaction. A better understanding of multiphase non-Newtonian fluid flow at pore-scale is crucial for optimizing enhanced oil recovery (EOR). The Darcy scale properties of reservoir rocks such as the capillary pressure curves and the relative permeability are controlled by the pore-scale behavior of the multiphase flow. In the present work, a volume of fluid (VOF) method coupled with an adaptive meshing technique is used to perform the pore-scale simulation on a 3D X-ray micro-tomography (CT) images of rock samples. The numerical model is based on the resolution of the Navier-Stokes equations along with a phase fraction equation incorporating the dynamics contact model. The simulations of a single phase flow for the absolute permeability showed a good agreement with the literature benchmark. Subsequently, the code is used to simulate a two-phase flow consisting of a polymer solution, displaying a shear-thinning power law viscosity. The simulations enable to access the impact of the consistency factor (K), the behavior index (n), along with the two contact angles (advancing and receding) on the relative permeability. [Preview Abstract] |
Sunday, November 19, 2017 3:07PM - 3:20PM |
D15.00005: Wicking in hierarchical surfaces: Micropattern governs the enhancement. Arif Rokoni, Dong-ook Kim, Min Pack, Ying Sun Wicking in hierarchical surfaces has gained significant attention due to its potential applications in thermal management. Hierarchical surfaces have shown to enhance wicking over microstructured surfaces by some researchers, while others found very limited improvement. In this work, we demonstrate the importance of the micropatterns on wicking enhancement of hierarchical surfaces using ZnO nanorods grown on circular silicon micropillars of varying spacings and heights. The wicking front over hierarchical surfaces is found to follow a two-tiered motion, where wicking is faster while crossing the micropillars but slower while moving between micropillars. The former is driven by a stronger capillary force around the pillar perimeters and the latter by a weaker capillary force between pillars. The added capillary action due to nanorods is not significant when the wicking front moves across the pillars but plays an important role by altering the meniscus shape when wicking is between pillars. The competition between the added capillary action and viscous dissipation results in a critical micropillar diameter-to-spacing ratio, below which wicking enhancement due to nanostructures is more substantial. This new finding sheds light on more effective design of hierarchical surfaces for wicking enhancement. [Preview Abstract] |
Sunday, November 19, 2017 3:20PM - 3:33PM |
D15.00006: Engineering Surfaces for Enhanced Nucleation and Droplet Removal During Dropwise Condensation. Sanmitra Dutta, Sameera khan, Sushant Anand Condensation plays critical role in numerous industrial applications, such as condensers, HVAC,etc In the most applications,fast formation (i.e. high nucleation) and subsequent removal of water droplets is critical for enhancing the efficiencies of their associated systems. Significant focus has been placed on the aspect of droplet removal from surfaces.This has led to, development of superhydrophobic surfaces with special textures on which droplets are self-removed after coalescence. However,because of their inherent low surface energy, nucleation energy barriers are also high on such surfaces. In contrast to conventional superhydrophobic surfaces, here we show that surfaces can be engineered such that the simultaneous benefits of high nucleation rates and fast droplet removal can be obtained during the condensation process.These benefits are obtained by impregnating a superhydrophobic surface with an oil that despite its defect-free interface provides low nucleation energy barrier during condensation.At the same time,the oil facilitates high droplet shedding rates by providing a lubricating layer below the droplets due to which droplets have negligible contact angle hysteresis. We provide a guide to choose oils that lead to enhanced nucleation, and provide experimental evidence supporting the proposed guide. We discuss the importance of different oil properties in affecting the droplet growth and subsequent removal of water droplets. [Preview Abstract] |
Sunday, November 19, 2017 3:33PM - 3:46PM |
D15.00007: Dynamics of poroelastocapillary rise Babak Nasouri, Gwynn Elfring The surface-tension-driven rise of a liquid between two elastic sheets can result in their deformation or coalescence depending on their flexibility. When the sheets are poroelastic, the flexibility of the immersed parts of the sheets can change considerably thereby altering the dynamical behavior of the system. To better understand this phenomenon, we study the poroelastocapillary rise of a wetting liquid between poroelastic sheets. Using the lubrication theory and linear elasticity, we quantify the effects of the change in material properties of the wet sheets on the capillary rise and the equilibrium state of the system. [Preview Abstract] |
Sunday, November 19, 2017 3:46PM - 3:59PM |
D15.00008: Rigorous derivation of porous-media phase-field equations Markus Schmuck, Serafim Kalliadasis The evolution of interfaces in Complex heterogeneous Multiphase Systems (CheMSs) plays a fundamental role in a wide range of scientific fields such as thermodynamic modelling of phase transitions, materials science, or as a computational tool for interfacial flow studies or material design. Here, we focus on phase-field equations in CheMSs such as porous media [1,2]. To the best of our knowledge, we present the first rigorous derivation of error estimates for fourth order, upscaled, and nonlinear evolution equations. For CheMs with heterogeneity $\epsilon$, we obtain the convergence rate $\epsilon^{1/4}$ , which governs the error between the solution of the new upscaled formulation and the solution of the microscopic phase-field problem [1,2]. This error behaviour has recently been validated computationally in [3]. Due to the wide range of application of phase-field equations, we expect this upscaled formulation to allow for new modelling, analytic, and computational perspectives for interfacial transport and phase transformations in CheMSs. [1] M. Schmuck $\&$ S. Kalliadasis, SIAM J. Appl. Math, accepted (2017). [2] M. Schmuck et al., Nonlinearity, 26(12):3259-3277 (2013). [3] A. Ververis $\&$ M. Schmuck, J. Comp. Phys., 344:485-498 (2017). [Preview Abstract] |
Sunday, November 19, 2017 3:59PM - 4:12PM |
D15.00009: Continuous Purification of Colloidal Quantum Dots in Large-Scale Using Porous Electrodes in Flow Channel Hosub Lim, Ju Young Woo, Doh Chang Lee, Jinkee Lee, Sohee Jeong, Duckjong Kim Colloidal Quantum dots (QDs) afford huge potential in numerous applications owing to their excellent optical and electronic properties. After the synthesis of QDs, separating QDs from unreacted impurities in large scale is one of the biggest issues to achieve scalable and high performance optoelectronic applications. Thus far, however, continuous purification method, which is essential for mass production, has rarely been reported. In this study, we developed a new continuous purification process that is suitable to the mass production of high-quality QDs. As-synthesized QDs are driven by electrophoresis in a flow channel and captured by porous electrodes and finally separated from the unreacted impurities. Nuclear magnetic resonance and ultraviolet/visible/near-infrared absorption spectroscopic data clearly showed that the impurities were efficiently removed from QDs with the purification yield, defined as the ratio of the mass of purified QDs to that of QDs in the crude solution, up to 87\%. Also, we could successfully predict the purification yield depending on purification conditions with a simple theoretical model. The proposed large-scale purification process could be an important cornerstone for the mass production and industrial use of high-quality QDs. [Preview Abstract] |
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