Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A35: Electrokinetic Flows: General |
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Chair: Michael Booty, NJIT Room: 617 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A35.00001: CO$_2$-driven diffusiophoresis: motion of charged particles near CO$_2$ dissolving boundaries Suin Shim, Orest Shardt, Sepideh Khodaparast, Ching-Yao Lai, Jesse T. Ault, Bhargav Rallabandi, Howard A. Stone We present experimental and theoretical investigations for CO$_2$-driven diffusiophoresis of charged particles. An aqueous suspension of charged particles initially in contact with a CO$_2$ dissolving interface shows directional migration either up or down the concentration gradient, depending on the particle charges. We use a cylindrical CO$_2$ bubble in a circular Hele-Shaw cell to study the behavior of polystyrene particles. By experiments and numerical model calculations considering multicomponent gas dissolution, we prove the diffusiophoretic accumulation and exclusion of particles near the bubble interface. Then using two geometrical conditions with moving and fixed boundaries, we show diffusiophoresis of bacterial cells driven by dissolution of CO$_2$. \textit{Vibrio Cholerae}, a Gram-negative bacteria, has a negative surface charge and thus migrates away from a CO$_2$ source. Using PIV we show behaviors of wild type cells and a mutant lacking flagella, suggesting that CO$_2$-driven diffusiophoresis may prevent biofilm formation by reducing the population of cells approaching an interface. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A35.00002: AC Electrokinetics in the Limits of Extremely High Voltage and Ion-Asymmetry Arunraj Balaji, Shahab Mirjalili, Ali Mani The aim of this study is to extend understanding of AC electrokinetics to regimes involving Dielectric Barrier Discharge (DBD) plasmas. To this end, we consider a simple model utilizing the Poisson-Nernst-Planck and Navier-Stokes equations, as commonly used in analysis of electrokinetic phenomena. To study the specific regimes relevant to plasmas, we consider the limits of extremely high AC voltage ($V=O(10^4 V_T)$) and extremely high ion-asymmetry ($\frac{D^-}{D^+}=O(10^4)$). Direct numerical simulation (DNS) of the governing equations is performed in one- and two-dimensional spatial domains, and different regimes of response are identified in terms of input voltage and diffusion asymmetry parameters. In addition to the results of DNS, this work also focuses on modeling considerations for the plasma regime and steps toward a more complete simulation of DBD: one that includes the effects of thermal-nonequilibrium and reactions. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A35.00003: A model for electrokinetic flow with deformable interfaces Michael Booty, Manman Ma, Michael Siegel A hybrid or multiscale model is introduced to describe the evolution of a drop in the two-phase flow of immiscible, ionic fluid electrolytes that are driven by an electric field. It is formed from the PNP equations in the Stokes flow regime in the limit when the Debye layers are thin relative to the undeformed drop size. For arbitrary deformation, the model consists of boundary integral equations for the electrostatic potential and the interface fluid velocity together with relations that contain the coupling between the electrostatic and fluid fields within the thin Debye layers. The results of sample numerical simulations are presented, together with comparison to a small-deformation analysis in the limit of a weak applied field; further generalizations of the model are also discussed. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A35.00004: Characterization of surface-solute interactions by diffusioosmosis Jesse Ault, Sangwoo Shin, Howard Stone The measurement of wall zeta potentials and solute-surface interaction length scales for electrolyte and non-electrolyte solutes, respectively, is critical to the design of biomedical and microfluidic applications. We present a microfluidic approach using diffusioosmosis for measuring either the zeta potentials or characteristic interaction length scales for surfaces exposed to, respectively, electrolyte or non-electrolyte solutes. When flows containing different solute concentrations merge in a junction, local solute concentration gradients can drive diffusioosmosis due to interactions between the solute molecules and solid surfaces. We demonstrate a microfluidic system in which solute concentration gradients drive diffusioosmosis within a pore, resulting in predictable fluid and solute profiles. Furthermore, we present analytical results and a methodology to determine the zeta potential or interaction length scale for the pore surfaces in the system. We apply this method to the experimental data of Lee et al., and we use 3D numerical simulations to validate the theory. To the best of our knowledge this is the first flow-based approach to characterize surface/solute interactions with non-electrolyte solutes. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A35.00005: ABSTRACT WITHDRAWN |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A35.00006: Microscale Electrodeionization: in situ Concentration Profiling and Flow Visualization Sudong Park, Rhokyun Kwak Electrodeionization (EDI) is a membrane-based desalination system utilizing ion exchange membranes and resins. By combining electrodialysis and ion exchanger, EDI can produce ultrapure water in continuous-flow manner. Although its theoretical mechanisms are well documented, there is no experimental platform which can provide microscopic details inside the system. In this paper, we present microscale EDI that visualizes in situ ion concentration, pH, and fluid flow. The platform was fabricated by filling ion exchange resins as a monolayer in a transparent polydimethylsiloxane channel between cation/anion exchange membranes. According to operating voltages (0-15V), distinct behaviors of ion concentration profile, pH shift, and fluid flow were observed in ohmic, limiting, and overlimiting regimes. It is noteworthy that overlimiting regimes can be sub-categorized as water-splitting regime and electroconvection regime. In early stage (4-6V), water-splitting is dominant with pH change near the membranes and resins; under higher voltage (8-15V), electroconvection start to occur even water-splitting tries to suppress the development of the electroconvective instability on the resins. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A35.00007: Non-isothermal electrokinetic effects in an electro-osmotic flow Edgar Ramos, Federico Mendez, Jose Lizardi In this work, we study numerically the combined influence of some non-isothermal electrokinetics effects derived from a Debye length versus the fluid viscosity, when both depend on the temperature for an electroosmotic laminar flow circulating in a slit microchannel. Considering then that the Debye length depends on temperature T, together with the fluid viscosity, we obtain additional temperature gradients along the microchannel and the isothermal hypothesis is no longer valid. Therefore, the Navier-Stokes equations together with the energy, Poisson and Ohmic current conservation equations are solved by using a routine finite element method. For this purpose, the governing equations are written in a dimensionless format and we introduce a dimensionless thermal parameter $\alpha $ that measures the temperature deviations of a reference temperature and a dimensionless parameter $\gamma $, which defines the effects of the variable viscosity. The numerical predictions show that the influence of these parameters yields different regimes for the behavior of the volumetric flow rate in comparison with a uniform Debye length and strong induced pressure gradients are sensibly altered by the existence of these dimensionless parameters. [Preview Abstract] |
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