Direct numerical simulation of electroconvective chaos near an ion-selective membrane
Abstract/Contents
- Abstract
- Electrokinetic transport plays an essential role in mature industrial applications and emerging technology such as: electrochemical devices, microfluidic chips, and electrodialysis used for water purification and chemical production. These systems use ion-selective surfaces and applied electric fields to manipulate aqueous electrolytes. In this dissertation we investigate a model system comprised of an ion-selective surface and a liquid electrolyte subject to an applied electric field. The applied field creates steep gradients in concentration and charge density which lead to an electrohydrodynamic instability referred to as electroconvection. At voltages of O(1)V, this instability can lead to chaotic dynamics. We investigate the onset of the instability and transport in the chaotic regime by formulating a specialized parallel numerical algorithm to solve the coupled Poisson-Nernst-Planck and Navier-Stokes equations. We developed a direct numerical simulation code called EKaos that can simulate chaotic electrokinetic phenomena in three dimensions with high resolution. The EKaos code was developed using numerical algorithms designed to efficiently solve the governing equations on parallel platforms. The equations are spatially discretized using a second order central finite difference scheme on a structured, staggered mesh. Time integration is performed with a specialised iterative procedure that uses physical and analytical insights to develop discrete operators that are easily invertible and converge quickly to second order temporal accuracy. EKaos efficiently solves 2D and 3D systems using non-dissipative algorithms that capture the high wavenumber physics critical to accurately simulating chaotic phenomena. 2D and 3D simulations from EKaos reveal interesting similarities between electroconvective chaos and turbulent flows such as: energy spectra with a wide range of spatiotemporal scales, vortices that interact with each other in an irregular manner, and substantial enhancement of transport and mixing. Quantitative analysis of statistics shows that although 2D and 3D simulations of electroconvective chaos are qualitatively very similar, inclusion of the third dimension is important for the prediction of mean quantities such as concentration, charge density, and current density. We assess the impact of electroconvection on the mean current density and appearance of instantaneous high current density hotspots on the membrane surface. Finally, we introduce ensemble averaged equations and discuss the relative importance of closed and unclosed terms for reduced order modeling.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Druzgalski, Clara |
|---|---|
| Associated with | Stanford University, Department of Mechanical Engineering. |
| Primary advisor | Mani, Ali, (Professor of mechanical engineering) |
| Thesis advisor | Mani, Ali, (Professor of mechanical engineering) |
| Thesis advisor | Iaccarino, Gianluca |
| Thesis advisor | Santiago, Juan G |
| Advisor | Iaccarino, Gianluca |
| Advisor | Santiago, Juan G |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Clara Druzgalski. |
|---|---|
| Note | Submitted to the Department of Mechanical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Clara Letitia Druzgalski
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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