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 G13: Electrokinetics: Porous Media and Related PhenomenaElectro
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Chair: Jarrod Schiffbauer, Colorado Mesa University Room: 506 |
Monday, November 20, 2017 10:35AM - 10:48AM |
G13.00001: Numerical analyses on the effect of capillary condensation on gas diffusivities in porous media Yuta Yoshimoto, Takuma Hori, Ikuya Kinefuchi, Shu Takagi We investigate the effect of capillary condensation on gas diffusivities in porous media composed of randomly packed spheres with moderate wettability. Lattice density functional theory simulations successfully reproduce realistic adsorption/desorption isotherms and provide fluid density distributions inside the porous media. We find that capillary condensations lead to the occlusion of narrow pores because they preferentially occur at confined spaces surrounded by the solid walls. Consequently, the characteristic lengths of the partially wet structures are larger than those of the corresponding dry structures with the same porosities. Subsequent gas diffusion simulations exploiting the mean-square displacement method indicate that while effective diffusion coefficients significantly decrease in the presence of partially condensed liquids, they are larger than those in the dry structures with the same porosities. Most importantly, we find that the porosity-to-tortuosity ratio, which is a crucial parameter that determines the effective diffusion coefficient, can be reasonably related to the porosity even for the partially wet porous media. [Preview Abstract] |
Monday, November 20, 2017 10:48AM - 11:01AM |
G13.00002: Salinity effects during immiscible displacement in porous media: electrokinetic stabilization of viscous fingering Mohammad Mirzadeh, Martin Bazant Interfacial instabilities are ubiquitous in Fluid Mechanics and have been one of the main the subjects of pattern formation. However, these instabilities could lead to inefficiencies which are undesired in many applications. For instance, viscous fingering results in residual trapping of oil during secondary recovery when a low-viscosity fluid, e.g. water, is used for injection. In their seminal work, Saffman and Taylor showed that the onset of this instability is controlled by the viscosity ratio of the two fluids. However, other physiochemical processes could enhance or suppress viscous fingering. Here we consider the role of salinity effects on the front stability. Our recent theory suggests that viscous fingering could be controlled, and even suppressed, by appropriately injecting electric currents. However, even in the absence of any external currents, strong electrokinetic coupling (present in small pores when the electric double layers overlap) can reduce viscous fingering by increasing the ``effective viscosity'' of the injected fluid. These findings suggest that it might be possible to improve extraction efficiencies by appropriately controlling the salt concentration of the injected fluid. [Preview Abstract] |
Monday, November 20, 2017 11:01AM - 11:14AM |
G13.00003: Kinetic energy budget for electroconvective flows near ion selective membranes Karen Wang, Ali Mani Electroconvection occurs when ions are driven from a bulk fluid through an ion-selective surface. When the driving voltage is beyond a threshold, this process undergoes a hydrodynamic instability called electroconvection, which can become chaotic due to nonlinear coupling between ion-transport, fluid flow, and electrostatic forces. Electroconvection significantly enhances ion transport and plays an important role in a wide range of electrochemical applications. We investigate this phenomenon by considering a canonical geometry consisting of a symmetric binary electrolyte between an ion-selective membrane and a reservoir using 2D direct numerical simulation (DNS). Our simulations reveal that for most practical regimes, DNS of electroconvection is expensive. Thus, a plan towards development of reduced-order models is necessary to facilitate the adoption of analysis of this phenomenon in industry. Here we use DNS to analyze the kinetic energy budget to shed light into the mechanisms sustaining flow and mixing in electroconvective flows. Our analysis reveals the relative dominance of kinetic energy sources, dissipation, and transport mechanisms sustaining electroconvection at different distances from the interface and over a wide range of input parameters. [Preview Abstract] |
Monday, November 20, 2017 11:14AM - 11:27AM |
G13.00004: Electrical characteristics in reverse electrodialysis using nanoporous membranes Sourayon Chanda, Peichun Amy Tsai We experimentally and numerically investigate the effects of concentration difference and flow velocity on sustainable electricity generation and associated fluid dynamics using a single reverse electrodialysis (RED) cell. By exploiting the charge-selective nature of nanoporous interfaces, electrical energy is generated by reverse electrodialysis harnessing chemical Gibbs energy via a salinity gradient. Experimentally, a RED cell was designed with two reservoirs, which are separated by a nanoporous, cation-selective membrane. We injected deionized water through one reservoir, whereas a solution of high salt concentration through the other. The gradient of salt concentration primarily drives the flow in the charged nano-pores, due to the interplay between charge selectivity, diffusion processes, and electro-migration. The current-voltage characteristics of the single RED cell shows a linear current-voltage relationship, similar to an electrochemical cell. The membrane resistance is increased with increasing salt concentration difference and external flow rate. The present experimental work was further analyzed numerically to better understand the detailed electrical and flow fields under different concentration gradients and external flows. [Preview Abstract] |
Monday, November 20, 2017 11:27AM - 11:40AM |
G13.00005: Electrokinetic Response of Charge-Selective Nanostructured Polymeric Membranes Jarrod Schiffbauer, Diya Li, Feng Gao, William Phillip, Hsueh-Chia Chang Nanostructured polymeric membranes, with a tunable pore size and ease of surface molecular functionalization, are a promising material for separations, filtration, and sensing applications. Recently, such membranes have been fabricated wherein the ion selectivity is imparted by self-assembled functional groups through a two-step process. Amine groups are used to provide a positive surface charge and acid groups are used to yield a negative charge. The membranes can be fabricated as either singly-charged or patterned/mosaic membranes, where there are alternating regions of amine- lined or acid-lined pores. We demonstrate that such membranes, in addition to having many features in common with other charge selective membranes (i.e. AMX or Nafion), display a unique single-membrane rectification behavior. This is due to the asymmetric distribution of charged functional groups during the fabrication process. We demonstrate this rectification effect using both dc current-voltage characteristics as well as dc-biased electrical impedance spectroscopy. Furthermore, surface charge changes due to dc concentration polarization and generation of localized pH shifts are monitored using electrical impedance spectroscopy. [Preview Abstract] |
Monday, November 20, 2017 11:40AM - 11:53AM |
G13.00006: Surface functional groups in capacitive deionization with porous carbon electrodes Ali Hemmatifar, Diego I. Oyarzun, James W. Palko, Steven A. Hawks, Michael Stadermann, Juan G. Santiago Capacitive deionization (CDI) is a promising technology for removal of toxic ions and salt from water. In CDI, an applied potential of about 1 V to pairs of porous electrodes (e.g. activated carbon) induces ion electromigration and electrostatic adsorption at electrode surfaces. Immobile surface functional groups play a critical role in the type and capacity of ion adsorption, and this can dramatically change desalination performance. We here use models and experiments to study weak electrolyte surface groups which protonate and/or depropotante based on their acid/base dissociation constants and local pore pH. Net chemical surface charge and differential capacitance can thus vary during CDI operation. In this work, we present a CDI model based on weak electrolyte acid/base equilibria theory. Our model incorporates preferential cation (anion) adsorption for activated carbon with acidic (basic) surface groups. We validated our model with experiments on custom built CDI cells with a variety of functionalizations. To this end, we varied electrolyte pH and measured adsorption of individual anionic and cationic ions using inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography (IC) techniques. Our model shows good agreement with experiments and provides a framework useful in the design of CDI control schemes. [Preview Abstract] |
Monday, November 20, 2017 11:53AM - 12:06PM |
G13.00007: Selective passive adsorption of nitrate with surfactant treated porous electrode and electrostatic regeneration Diego I. Oyarzun, Ali Hemmatifar, James W. Palko, Michael Stadermann, Juan G. Santiago Nitrate is an important pollutant in drinking water worldwide, and a number of methods exist for the removal of nitrate from water including ion exchange and reverse osmosis. However, these approaches suffer from a variety of disadvantages including the need for a regenerating brine supply and disposal of used brine for ion exchange and low water recovery ratio for reverse osmosis. We are researching and developing a form of capacitive deionization (CDI) for energy efficient desalination and selective removal of ionic toxins from water. In CDI an electrode is used to electrostatically trap ions in a pair of porous electrodes. Here, we demonstrate the use of high surface area activated carbon electrodes functionalized with ion exchange moieties for adsorption of nitrate from aqueous solution. Unlike a traditional ion exchanger, the functionalized surfaces can be repeatedly regenerated by the application of an electrostatic potential which displaces the bound NO3- while leaving an excess of electronic charge on the electrode. Trimethylammonium has an intrinsic selectivity, we are using this moiety to selectively remove nitrate over chloride. We performed adsorption/desorption cycles under several desorption voltages and ratios of concentrations. [Preview Abstract] |
Monday, November 20, 2017 12:06PM - 12:19PM |
G13.00008: Comprehensive Study of Performance and Efficiency of Water Desalination with Capacitive Deionization For Various System Configurations Yasamin Salamat, Carlos Hidrovo Capacitive Deionization (CDI) is a novel desalination technology which uses an external electric field to remove ions from low salinity water streams. Its ability to recover a portion of the used energy during the desalination phase has distinguished CDI from other common water desalination techniques. CDI process includes different multiscale transport phenomena with associated timescales. In this work, we have studied effects of these time constants on the overall behavior of a CDI system by taking the desalination performance, water recovery ratio and energy efficiency into account. Additionally, we have investigated different regeneration strategies aiming at improving the desalination and energy efficiency of cyclic CDI systems. To obtain comprehensive comparison between different CDI configurations, a new metric has been introduced which encompasses desalination performance and recovery ratio of water and energy. [Preview Abstract] |
Monday, November 20, 2017 12:19PM - 12:32PM |
G13.00009: Systematic and reliable multiscale modelling of lithium batteries Selcuk Atalay, Markus Schmuck Motivated by the increasing interest in lithium batteries as energy storage devices (e.g. cars/bycicles/public transport, social robot companions, mobile phones, and tablets), we investigate three basic cells: (i) a single intercalation host; (ii) a periodic arrangement of intercalation hosts; and (iii) a rigorously upscaled formulation of (ii) as initiated in [1,2,3]. By systematically accounting for Li transport and interfacial reactions in (i)--(iii), we compute the associated chracteristic current-voltage curves and power densities. Finally, we discuss the influence of how the intercalation particles are arranged. Our findings are expected to improve the understanding of how microscopic properties affect the battery behaviour observed on the macroscale and at the same time, the upscaled formulation (iii) serves as an efficient computational tool [4]. [1] M. Schmuck, Appl. Math. Res. eXpr. doi:10.1093/amrx/abx003 (2017). [2] M. Schmuck $\&$ M.Z. Bazant, SIAM J. Appl. Math. 75(3):1369-1401 (2015). [3] M. Schmuck $\&$ P. Berg, J. Electrochem. Soc. 161(8):E3323-E3327 (2014). [4] A. Ververis $\&$ M. Schmuck, J. Comp. Phys. 344:485-498 (2017). [Preview Abstract] |
Monday, November 20, 2017 12:32PM - 12:45PM |
G13.00010: Theoretical analysis of non-linear Joule heating effects over an electro-thermal patterned flow Salvador Sanchez, Gabriel Ascanio, Federico Mendez, Oscar Bautista In this work, non-linear Joule heating effects for electro-thermal patterned flows driven inside of a slit microchannel are analyzed. Here, the movement of fluids is controlled by placing electro-thermal forces, which are generated through an imposed longitudinal electric field, $E_{0}$, and the wall electric potential produced by electrodes inserted along the surface of the microchannel wall, $\zeta$. For this analysis, viscosity and electrical conductivity of fluids are included as known functions, which depend on the temperature; therefore, in order to determine the flow, temperature and electric potential fields together with its simultaneous interactions, the equations of continuity, momentum, energy, charges distribution and electrical current have to be solved in a coupled manner. The main results obtained in the study reveal that with the presence of thermal gradients along of the microchannel, local electro-thermal forces, $\bar{F}_{\chi}$, are affected in a sensible manner, and consequently, the flow field is modified substantially, causing the interruption or intensification of recirculations along of the microchannel. [Preview Abstract] |
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