Influence of Rayleigh-Bénard convection on electrokinetic instability in overlimiting current conditions

Valença, Joeri C. de; Kurniawan, Aziz; Wagterveld, R.M.; Wood, Jeffery A.; Lammertink, Rob G.H.

doi:10.1103/physrevfluids.2.033701

Cited by 28 publications

(32 citation statements)

References 41 publications

(68 reference statements)

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“…Near the flat membrane, the first particle motion (around τ EC ) occurs at random locations [see Supporting Information Movie S1 , as well as the supporting movies in de Valença et al (2015) and de Valença et al (2017) 25 , 29 ]. The particle pathlines reveal small vortices that grow and merge with other vortices while moving laterally along the surface.…”

Section: Resultsmentioning

confidence: 99%

“…The particles are illuminated with a thin (≈0.2 mm) laser sheet (808 nm, Firefly, Oxford Lasers), see Figure 2 , and the reflected light is captured through a long-distance magnifying lens (2–7×, Navitar) on a camera at 10 frames/s. From the recorded particle displacements, the vector field is determined using particle image velocimetry (μPIV) analysis (DaVis, LaVision) following the same algorithms as described in our previous paper, 25 see for example Figure 4 . The coordinate system is taken such that x represents the direction perpendicular to the membrane, y the direction along the membrane and in the plane of the illuminating laser sheet, and z the depth into the cell, as denoted by the axes in Figure 2 .…”

Section: Methodsmentioning

confidence: 99%

“…Concentration fields are measured using fluorescence lifetime image microscopy (FLIM), (LIFA, Lambert Instruments) by adding 2.5 μM green-fluorescent dye (Alexa Fluor 488 Cadaverine, Life Technologies) to the solution. The fluorescence decay of the dye is indicative of the CuSO 4 concentration in the range between 1 and 100 mM (see the supporting information of ref ( 25 ) for the calibration curve and error estimation). A modulated blue light emitting diode (LED) light is sent through a 5× magnifying objective (Zeiss), and the fluorescence is captured on a 696 × 520 pixels CCD camera, with each pixel representing an area of 4.17 × 4.17 μm 2 .…”

Section: Methodsmentioning

confidence: 99%

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Confined Electroconvective Vortices at Structured Ion Exchange Membranes

Valença

Jõgi²,

Wagterveld³

et al. 2018

Langmuir

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In this paper, we investigate electroconvective ion transport at cation exchange membranes with different geometry square-wave structures (line undulations) experimentally and numerically. Electroconvective microvortices are induced by strong concentration polarization once a threshold potential difference is applied. The applied potential required to start and sustain electroconvection is strongly affected by the geometry of the membrane. A reduction in the resistance of approximately 50% can be obtained when the structure size is similar to the mixing layer (ML) thickness, resulting in confined vortices with less lateral motion compared to the case of flat membranes. From electrical, flow, and concentration measurements, ion migration, advection, and diffusion are quantified, respectively. Advection and migration are dominant in the vortex ML, whereas diffusion and migration are dominant in the stagnant diffusion layer. Numerical simulations, based on Poisson–Nernst–Planck and Navier–Stokes equations, show similar ion transport and flow characteristics, highlighting the importance of membrane topology on the resulting electrokinetic and electrohydrodynamic behavior.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Confined Electroconvective Vortices at Structured Ion Exchange Membranes

Valença

Jõgi²,

Wagterveld³

et al. 2018

Langmuir

Self Cite

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“…The boundary of the vector field was defined using a geometrical mask to distinguish between regions were vector field should or should not be calculated. Following the vector field calculation, a post-processing algorithm was used to eliminate erroneous vectors and outlier detection was used based on the median value of the nearest neighbouring vectors 25 . If some vectors were rejected, they were interpolated or extrapolated from the accepted, neighbouring vectors.…”

Section: Methodsmentioning

confidence: 99%

Visualizing the hydrodynamics in sieve-based lateral displacement systems

Dijkshoorn

Valença²,

Wagterveld³

et al. 2018

Sci Rep

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Deterministic lateral displacement (DLD) systems structure suspension flow in so called flow lanes. The width of these flow lanes is crucial for separation of particles and determines whether particles with certain size are displaced or not. In previous research, separation was observed in simplified DLD systems that did not meet the established DLD geometric design criteria, by adjusting the outflow conditions. We here investigated why these simplified DLD systems are able to displace particles, by experimentally investigating the hydrodynamics in the device. Flow lanes were visualized and the local flow velocities were measured using µPIV and compared with 2D fluid dynamics simulations. The size of the flow lanes strongly correlates with the local flow velocity (Vy and Vx), which depends on the hydrodynamics. Therefore, the geometric design criteria of DLD devices is in fact just one method to control the local hydrodynamics, which may also be influenced by other means. These findings give a new perspective on the separation principle, which makes the technique more flexible and easier to translate to industrial scale.

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“…Experimental observations [212,[220][221][222][223][224][225][226][227][228][229] as well as theoretical evidences [216,230,231] show the dominant role of electroconvection in salt counterion overlimiting transfer in dilute solutions. Vortices, which appear under the action of electric field on the space charge, can increase the useful transfer of salt counterions in several times by mixing depleted solution [217,230,232,233].…”

Section: Current-induced Concentration Gradientsmentioning

confidence: 84%

Modelling of Ion Transport in Electromembrane Systems: Impacts of Membrane Bulk and Surface Heterogeneity

et al. 2018

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Artificial charged membranes, similar to the biological membranes, are self-assembled nanostructured materials constructed from macromolecules. The mutual interactions of parts of macromolecules leads to phase separation and appearance of microheterogeneities within the membrane bulk. On the other hand, these interactions also cause spontaneous microheterogeneity on the membrane surface, to which macroheterogeneous structures can be added at the stage of membrane fabrication. Membrane bulk and surface heterogeneity affect essentially the properties and membrane performance in the applications in the field of separation (water desalination, salt concentration, food processing and other), energy production (fuel cells, reverse electrodialysis), chlorine-alkaline electrolysis, medicine and other. We review the models describing ion transport in ion-exchange membranes and electromembrane systems with an emphasis on the role of micro-and macroheterogeneities in and on the membranes. Irreversible thermodynamics approach, "solution-diffusion" and "pore-flow" models, the multiphase models built within the effective-medium approach are examined as the tools for describing ion transport in the membranes. 2D and 3D models involving or not convective transport in electrodialysis cells are presented and analysed. Some examples are given when specially designed surface heterogeneity on the membrane surface results in enhancement of ion transport in intensive current electrodialysis.Recently, Svoboda et al. [13] developed a specific scanning cell for the analysis of heterogeneous IEM structure by micro-computed tomography, which provides volume reconstruction of the studied material. The unique working principle of the cell allows one to scan membranes not only in their dry state but also in fully swollen state. The micro-computed tomography showed that there are profound changes in the structure of the IEM associated with their transition from the dry state into the swollen one. This study applied to the heterogeneous cation-exchange membrane (CEM) coming from Mega a.s., Czech Republic showed that swelling of the membrane is caused by the swelling of the ion-exchange resin. Its volume increased nearly three times after exposure to deionized water, while the overall membrane volume increased by 50%. If the membrane contained approximately 28%vol. of the resin in the dry state, this content increased to 52%vol. after swelling.Micro-computed tomography not only allows one to analyse volumetric composition of the membrane bulk but also to quantify the composition of the surface. By using two different methods, Vobecka et al. [14] evaluated the fraction of the conductive area (e.g., the ion-exchange resin) on the surface of an AEM and CEM in the swollen state. The obtained results showed that the volume fraction of the conductive domains does not correspond to the surface fraction of these domains and thus the volume composition is not reflected on their surface. For example, the volume fraction of the conductive domains for the st...

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Influence of Rayleigh-Bénard convection on electrokinetic instability in overlimiting current conditions

Abstract: Image data and MATLAB models belonging to the publication: Influence of Rayleigh-Bénard convection on electrokinetic instability in overlimiting current conditions, Physical Review Fluids 2, 033701 (2017

Cited by 28 publications

References 41 publications

Confined Electroconvective Vortices at Structured Ion Exchange Membranes

Confined Electroconvective Vortices at Structured Ion Exchange Membranes

Visualizing the hydrodynamics in sieve-based lateral displacement systems

Modelling of Ion Transport in Electromembrane Systems: Impacts of Membrane Bulk and Surface Heterogeneity

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